US20060199135A1

US20060199135A1 - Metal heater

Info

Publication number: US20060199135A1
Application number: US10/535,986
Authority: US
Inventors: Kazutaka Mashima
Original assignee: Ibiden Co Ltd
Current assignee: Ibiden Co Ltd
Priority date: 2002-11-25
Filing date: 2003-11-25
Publication date: 2006-09-07
Also published as: WO2004049762A1

Abstract

The present invention aims to provide a metal heater that hardly causes dispersion in the temperature of a semiconductor wafer or the like upon heating, and heats it quickly without causing warping and sagging in its metal plate. The present invention provides a metal heater which includes metal plates and a heating element, wherein the number of said metal plates is a plural number, the heating element is sandwiched between the metal plates, and the thickness of a metal plate on a heating face side is the same as or larger than the thickness of a metal plate on a side opposite to said heating face side.

Description

TECHNICAL FIELD

The present invention relates to a metal heater that is mainly used in the semiconductor industry and optical industry.

BACKGROUND ART

With respect to an etching device, and a semiconductor producing/examining device including a chemical vapor deposition device or the like, metal heaters having substrates of a metal material such as stainless steel have been used.
FIG. 4 is a cross-sectional view that schematically shows a metal heater having a structure that has been conventionally used.
In this metal heater 450, a heater 453 in which a nichrome wire 452 is sandwiched between silicon rubbers 461 is provided to an aluminum plate 451 having a thickness of 15 mm.

SUMMARY OF THE INVENTION

However, metal heaters with such structures have the following problems.
Metal plates to be used for the metal heaters are needed to have a thickness to a certain extent. It is because if the metal plates are thin, the rigidity are low and the metal plates are warped and sagged since the metal plates are pushed from the surrounding because of thermal expansion attributed to heating or there is a difference of thermal expansion coefficients between supporting cases and metal plates.
If such warping, sagging and the like occurs in the metal plates, a semiconductor wafer placed on the metal plates cannot be heated evenly, so that a dispersion of temperature or a damage in the semiconductor wafer is generated in some cases.
However, if the metal plates are made thick, the heat capacity of the metal plates is increased, and in the case of heating or cooling an object to be heated, the temperature of the heating faces of the metal plates cannot promptly follow the change of the voltage or the electric current applied to the heating elements, and there has been a problem that temperature control becomes difficult.
Further, there has been a problem that it takes a long time (a long recovery time) to recover the previous temperature of the heating face and productivity reduces in the case a semiconductor wafer is placed on the metal plate and the temperature of the heating face of the metal plate abruptly drops.
Further, such metal heaters may have, in the case temperature is increased, an overshoot phenomenon that the temperature temporarily goes over the set temperature. If the overshoot phenomenon occurs, it takes further longer time to bring the temperature of the heating faces of the metal plates to the set temperature.
Additionally, along with the recent tendency of enlargement of the diameter of semiconductor wafers and the like, and other reasons, metal heaters with a larger diameter are desired. With the enlargement of the diameter of the metal plates, the uneven temperature distribution in the metal plates themselves tends to occur, and accordingly, the above temperature evenness of the semiconductor wafer is further deteriorated.
In view of the above-mentioned problems, the present inventor has made extensive research efforts for the purpose of obtaining a metal heater which has a comparatively fast temperature-rising speed and a comparatively short recovery time, hardly causes temperature change in a semiconductor wafer and the like upon heating, and is free from warping and sagging in metal plates, and found that, by: sandwiching a heating element between a plurality of metal plates; and making the thickness of a metal plate on a heating face side larger than the thickness of a metal plate on the opposite side, it becomes possible to ensure the flatness of the heating face and consequently to maintain the temperature of the heating face in an even level; thus, a first aspect of the present invention has been completed.
In other words, a metal heater according to a first aspect of the present invention comprises a metal plate and a heating element. Herein, the number of the metal plates is a plural number, the heating element is sandwiched between the metal plates, and the thickness of a metal plate on a heating face side is the same as or larger than the thickness of a metal plate on a side opposite to said heating face side.
The metal heater according to the first aspect of the present invention comprises the plurality of metal plates, and the heater is sandwiched between the metal plates. The metal heater having this structure makes it possible to more quickly heat an object to be heated, such as a semiconductor wafer or the like, in comparison with a metal heater that is formed by a single metal plate with a heater placed on a side opposite to the heating face side of the metal plate, and also to shorten the recovery time.
Since the metal heater according to the first aspect of the present invention is designed so that the thickness of the metal plate on the heating face side is the same as or larger than the thickness of a metal plate on the side opposite to said heating face side, it becomes possible to improve the flatness of the heating face upon heating and, also, to evenly heat the entire semiconductor wafer.
The reason therefor will be briefly described below.
In the metal heater according to the first aspect of the present invention, since the thickness of the metal plate on the heating face side is made larger, the mechanical strength becomes higher, making the metal plate less likely to have warping and the like upon heating. Therefore, upon heating, the flatness of the heating face is improved.
Moreover, in the case where the thickness of the metal plate on the heating face side is made larger, the thermal capacity of the metal plate on the side opposite to said heating face side is made relatively smaller than the thermal capacity of the metal plate on the heating face side. For this reason, the metal plate on the side opposite to said heating face side is made less likely to have accumulation of heat in comparison with the metal plate on the heating face side. Therefore, even in the case where ordinary-temperature silicon wafers are successively placed on the heating face so as to carry out a continuous process, heat conduction hardly occurs from the metal plate on the side opposite to said heating face side to the metal plate on the heating face side. Of course, temperature change hardly occurs in the metal plate on the heating face side due to an overshoot phenomenon caused by the heat conduction from the metal plate on the side opposite to said heating face side to the metal plate on the heating face side. Therefore, it becomes possible to easily control the temperature of the metal plate on the heating face side, and consequently to maintain the heating treatment temperature at a constant level.
The metal heater according to the first aspect of the present invention may have a structure in which another metal plate is further attached to the heating element placed on the metal plate, that is, a structure in which a heating element is sandwiched between two metal plates or a structure in which heating elements are sandwiched among three or more metal plates.
In the case where the metal heater according to the first aspect of the present invention comprises three or more metal plates, the thickness of the metal plate on the heating face side refers to the thickness of metal plates located above the heater of the uppermost layer, and the thickness of the metal plate on the side opposite to said heating face side refers to the total thickness of the metal plates located below the heater on the uppermost layer.
FIG. 3 shows a structure of a metal heater comprising three metal plates. Herein, FIG. 3 shows only the metal plate and the heater.
In the case of the metal heater as shown in FIG. 3, the thickness of the metal plate on the heating face side refers to a thickness a of a metal plate A located above a heater A of the uppermost layer. Moreover, the thickness of the metal plate on the side opposite to the heating face side refers to a total thickness b+c of a metal plate B and a metal plate C located below the heater A on the uppermost layer.
In the following, a metal heater having a structure in which a heater is sandwiched between two metal plates will be mainly described according to the first aspect of the present invention. Here, in the case where the metal heater has the structure having two metal plates as described above, the metal plate on the heating face side is referred to as an upper metal plate, and the metal plate on the side opposite to said heating face side is referred to as a lower metal plate.
In the metal heater according to the first aspect of the present invention, the lower limit of the thickness of the upper metal plate is desirably 3 mm.
If the thickness of the upper metal plate is less than 3 mm, the distance between the heating element and the heating face becomes too short; thus, the pattern of the heating element is reflected to the temperature distribution of the heating face. As a result, it becomes difficult to evenly heat an object to be heated such as a semiconductor wafer or the like in some cases. In contrast, if the thickness of the upper metal plate is within the above-mentioned range, the pattern of the heating element is not reflected to the temperature distribution of the heating face so that it becomes possible to evenly heat the object to be heated.
Moreover, if the thickness of the substrate is within the above-mentioned range, the metal heater is allowed to have superior mechanical strength without occurrence of warping, sagging and the like, making it possible to positively ensure the flatness of the heating face.
Furthermore, the lower limit of the thickness of the upper metal plate is more desirably 5 mm.
The upper limit of the thickness of the upper metal plate is desirably 50 mm. The thickness of the upper metal plate exceeding 50 mm sometimes makes it difficult for the temperature of the heating face of the metal plate to follow change in a voltage and an amount of current to be applied to the heating element, failing to quickly heat the object to be heated, such as a semiconductor wafer or the like, and when the semiconductor wafer is placed on the heating face, time (recovery time) taken to bring the decreased temperature back to the previous temperature takes longer to cause a prolonged working time and the subsequent reduction in productivity.
The upper limit of the thickness of the upper metal plate is more desirably 30 mm.
Moreover, in the case of the above-mentioned structure, the upper limit of the thickness of the lower metal plate is desirably 50 mm, more desirably 30 mm, and the lower limit thereof is desirably 1 mm, more desirably 3 mm.
Furthermore, the ratio of the thickness of the upper metal plate and the thickness of the lower metal plate (thickness of upper metal plate/thickness of lower metal plate) is desirably 1 to 10. When the ratio exceeds 10, the thermal capacity of the upper metal plate becomes too high, sometimes failing to quickly heat the object to be heated. Moreover, when the thermal capacity of the upper metal plate becomes too high, the temperature difference between the outermost circumference of the heating face and the vicinity of the center portion becomes too large, sometimes causing reduction in the temperature evenness on the heating face.
The ratio of the thickness of the upper metal plate and the thickness of the lower metal plate is optimally larger than 1 and 10 or less. If the ratio of the thickness of the upper metal plate and the thickness of the lower metal plate is within the above-mentioned range, it becomes possible to provide superior temperature evenness on the heating face in a steady state.
In the metal heater according to the first aspect of the present invention, the heater is sandwiched between the upper metal plate and the lower metal plate, and the heating element is formed inside the heater. A circuit constituting the heating element is desirably divided into two or more portions.
In the case where the circuit constituting the heating element is divided into two or more portions, it becomes possible to carry out a precise temperature controlling operation on the outermost circumference of the metal heater, the part of which is more likely to have a temperature drop, and consequently to suppress dispersion in the temperature of the metal heater.
Moreover, in the metal heater according to the first aspect of the present invention, all the diameters of the metal plates and the heater are desirably the same. This arrangement makes it possible to evenly transmit heat from the heater to the heating face of the metal plate.
In the case where a heat insulating ring or the like is interposed between the metal plate and the supporting case, the diameters of the metal plates may be made different from one another.
In the metal heater according to the first aspect of the present invention, the diameter of the metal plates is desirably 200 mm or more. As the diameter of the metal heater becomes larger, the temperature of the semiconductor wafer tends to become uneven upon heating; therefore, in such a large diameter, the structure of the first aspect of the present invention is allowed to function more effectively. Moreover, a substrate having such a large diameter makes it possible to receive a semiconductor wafer having a large diameter.
In particular, the diameter of the metal plates is desirably 12 inches (300 mm) or more. This size is mainly used for semiconductor wafers in the next generation.
In the metal plates constituting the metal heater according to the first aspect of the present invention, flatness on the surface thereof is desirably 50 μm or less. In the case where a semiconductor wafer is heated by using the metal heater according to the first aspect of the present invention, since the distance between the semiconductor wafer and the metal plate is maintained at an almost constant level, the entire semiconductor wafer can be evenly heated. Here, the flatness on the surface of the metal plate is more desirably 30 μm or less.
In order to realize a metal heater that is superior in flatness, it is necessary to prevent the metal plate from curving due to pressure imposed from the side faces upon thermal expansion of the metal plate. For this reason, it is desirable to maintain a space between each of the side faces of the metal plate and the supporting case (bottom plate) so that each of the side faces is not made in contact with the metal plate.
The material of the above-mentioned metal plates desirably has superior thermal conductivity with high rigidity, and is less likely to be deformed even when thermally expanded so that, upon completion of the machining processes of the metal plate, the metal plate is desirably allowed to have a superior flatness.
With respect to the material of the metal plates constituting the metal heater according to the first aspect of the present invention, examples thereof include aluminum, an aluminum alloy, copper, a copper alloy, stainless, inconel, steel and the like. Among these, an aluminum alloy is desirably used, and an aluminum-copper alloy is more desirably used. Since the aluminum-copper alloy has high mechanical strength, neither warping nor distortion takes place due to applied heat even when the thickness of the metal plate is made thinner. For this reason, the metal plate can be made thinner and lighter. Moreover, since the aluminum-copper alloy is also superior in thermal conductivity, the temperature of the heating face is allowed to follow temperature change in the heating element when it is used as the metal plate. In other words, the temperature of the heating element is changed by varying the voltage and current value so that the heating face temperature of the upper metal plate can be controlled.
In the metal heater according to the first aspect of the present invention, the material of the upper metal plate and the material of the lower metal plate are desirably the same. This makes it possible to prevent occurrence of deformations such as warping, sagging and the like in the upper metal plate due to a difference in thermal expansion coefficients of the materials, and consequently to positively ensure the flatness of the heating face.
Moreover, with respect to the aluminum-copper alloy, other materials such as magnesium, manganese, silicon, zinc and the like may be added thereto in addition to aluminum and copper. This is because, it becomes possible to further improve various functions, such as workability, corrosion resistance and low expansion property.
In the case where aluminum, an aluminum alloy or the like is used as the material of the metal plate, the surface of the metal plate is desirably subjected to an alumite treatment.
This alumite treatment makes it possible to improve the corrosion resistance of the metal plate and, also, to harden the surface thereof; thus, the metal plate is made less likely to have scratches and the like. Moreover, even when used in actual semiconductor producing/examining processes, the metal plate is made less likely to have corrosion due to a resist solution, corrosive gases and the like.
Moreover, a hard alumite treatment can be carried out by performing an anodic oxide coating treatment at a lower temperature, a higher voltage, and a higher current density compared with a common alumite treatment. Such a hard alumite treatment enables to obtain a harder and thinner coating.
Here, the thickness of the coat film is desirably set to 1 μm or more. In the case of the hard alumite treatment, the thickness of the coat film can be set to 3 μm or more.
In the metal heater according to the first aspect of the present invention, the outer rim of an area on which the heating element is formed is desirably located at a position within 25% of the diameter of the metal plate from the circumference of the metal plate. Since heat radiation takes place from the peripheral edge of the metal plate, the circumferential portion of the metal plate normally has a temperature drop in comparison with the center portion of the metal plate; thus, the temperature of the heating face tends to become uneven. However, in the metal heater according to the first aspect of the present invention, since the heating element is also disposed at such a peripheral portion, a semiconductor wafer or the like, that is, the object to be heated can be evenly heated without dispersion in temperature.
Moreover, the heating element is desirably divided into two or more portions.
If the heating element is divided into two or more portions, the respective heating elements can be temperature-controlled in a separate manner so that the temperature of the heating face can be maintained at a more even level. More specifically, for example, by preparing the heating element pattern formed on the outermost circumference as a complex divided pattern, a precise temperature controlling operation can be carried out on the outermost circumference of the metal heater that tends to have a temperature drop; thus, it becomes possible to suppress dispersion in the temperature of the heating face.
In the metal heater according to the first aspect of the present invention, a wafer guide ring may be placed at a side face of the metal plate, or it may be placed at the peripheral edge or the surface of the heating face of the metal plate.
In the case where the metal heater is attached to a supporting case and used, a gas flow is generated from the metal plate side toward a semiconductor wafer placed on the metal heater; thus, this gas flow tends to make it difficult to maintain the evenness in temperature of the semiconductor wafer. However, the provision of the wafer guide ring can prevent the gas flow toward the semiconductor wafer; therefore, it becomes possible to further ensure the evenness in temperature of the semiconductor wafer.
In view of the above-mentioned problems, the present inventor has made extensive research efforts for the purpose of obtaining a metal heater which has a comparatively fast temperature-rising speed and a comparatively short recovery time, and can evenly heat an object to be heated such as a semiconductor wafer or the like, without causing warping and sagging in its metal plate, and found that, by: sandwiching a heating element between a plurality of metal plates; and forming these metal plates from the same material, it becomes possible to ensure the flatness of the heating face and consequently to maintain the temperature of the heating face at an even level; thus, a second aspect of the present invention has been completed.
That is, a metal heater according to a second aspect of the present invention comprises a plurality of metal plates and a heating element, with the heating element sandwiched between the metal plates. Herein, the plurality of metal plates are made of the same material.
The metal heater according to the second aspect of the present invention comprises the plurality of metal plates, and the heater is sandwiched between the metal plates. In comparison with a metal heater that is formed by a single metal plate with a heater provided on the face on the side opposite to the heating face side of the metal plate, since the metal heater having this structure makes the thickness of the metal plate located on the heating face side of the heater thinner than the above-mentioned single metal plate, it becomes possible to more quickly heat an object to be heated, such as a semiconductor wafer or the like, and also to shorten the recovery time.
In the metal heater according to the second aspect of the present invention, since the plurality of metal plates are made of the same material, even when the temperature of the metal heater is raised or lowered, the plurality of the metal plates are expanded or shrunk at the same ratio. Therefore, even when these metal plates are secured with securing screws, neither warping nor sagging occurs in the metal plate on the heating face side of the heater so that it becomes possible to maintain the flatness of the heating face upon heating and, also, to make the distance between the semiconductor wafer and the heating face constant; thus, the entire semiconductor wafer can be heated evenly.
In the metal heater according to the second aspect of the present invention, with respect to the plurality of metal plates, the thickness of the metal plate (upper metal plate) on the heating face side of the heater is desirably made larger than the thickness of the metal plate (lower metal plates) on the opposite side.
Moreover, in the case where the thickness of the metal plate on the heating face side is made larger, the thermal capacity of the metal plate on the side opposite to the heating face side is made relatively smaller than the thermal capacity of the metal plates on the heating face side. For this reason, the metal plate on the side opposite to the heating face side is made less likely to have accumulation of heat in comparison with the metal plate on the heating face side. Therefore, even in the case where ordinary-temperature silicon wafers are successively placed on the heating face so as to carry out a continuous process, heat conduction hardly occurs from the metal plate on the side opposite to the heating face side to the metal plate on the heating face side. Of course, temperature change hardly occurs in the metal plate on the heating face side due to an overshoot phenomenon caused by the heat conduction from the metal plate on the side opposite to the heating face side to the metal plate on the heating face side. Therefore, it becomes possible to easily control the temperature of the metal plate on the heating face side, and consequently to maintain the heating treatment temperature at a constant level.
The metal heater according to the second aspect of the present invention may have a structure in which another metal plate is further attached to the heating element placed on the metal plate, that is, a structure in which a heating element is sandwiched between two metal plates, or a structure in which heating elements are sandwiched among three or more metal plates. In the case where the metal heater according to the second aspect of the present invention has three or more metal plates, the thickness of the metal plate on the heating face side (upper metal plate) and the thickness of the metal plate on the side opposite to the heating face side (lower metal plate) are defined in the same manner as those of the first aspect of the present invention.
In the following, a metal heater having a structure in which a heater is sandwiched between two metal plates will be mainly described according to the second aspect of the present invention.
In metal heater according to the second aspect of the present invention, the lower limit of the thickness of the upper metal plate is desirably 3 mm. The reason therefor is the same as that described in the first aspect of the present invention. Moreover, the lower limit of the thickness of the upper metal plate is more desirably 5 mm.
The upper limit of the thickness of the upper metal plate is desirably 50 mm. The reason therefor is the same as that described in the first aspect of the present invention. The upper limit of the thickness of the upper metal plate is more desirably 30 mm.
Moreover, in the case of the above-mentioned structure, the upper limit of the thickness of the lower metal plate is desirably 50 mm, more desirably 30 mm, and the lower limit thereof is desirably 1 mm, more desirably 3 mm.
Furthermore, the ratio of the thickness of the upper metal plate and the thickness of the lower metal plate (thickness of upper metal plate/thickness of lower metal plate) is desirably 1 to 10. The reason therefor is the same as that described in the first aspect of the present invention. In particular, the ratio is optimal in a case exceeding 1. Thus, it becomes possible to provide superior temperature evenness on the heating face in a steady state.
In the metal heater according to the second aspect of the present invention, the heater is sandwiched between the upper metal plate and the lower metal plate, with the heating element formed inside the heater. In the same manner as the first aspect of the present invention, a circuit constituting the heating element is desirably divided into two or more portions, and all the diameters of the plurality of metal plates and the heater are desirably the same. In the case where a heat insulating ring or the like is interposed between the metal plate and the supporting case, the diameters of the metal plates may be made different from one another.
In the metal heater according to the second aspect of the present invention, the diameter of the metal plates is desirably 200 mm or more, more desirably 12 inches (300 mm) or more. The reason therefor is the same as that described in the first aspect of the present invention.
In the metal plates constituting the metal heater according to the second aspect of the present invention, the flatness on the surface thereof is desirably 50 μm or less, more desirably 30 μm or less. The reason therefor is the same as that described in the first aspect of the present invention.
In order to realize a metal heater that is superior in flatness, it is necessary to prevent the metal plate from curving due to pressure imposed from the side faces upon thermal expansion of the metal plate. For this reason, it is desirable to maintain a space between each of the side faces of the metal plate and the supporting case (bottom plate) so that each of the side faces is not made in contact with the metal plate.
In the second aspect of the present invention, the plurality of metal plates are made of the same material, and the material of the metal plates desirably has a superior thermal conductivity with high rigidity, and is less likely to be deformed even when thermally expanded so that, upon completion of the machining processes of the metal plates themselves, each metal plate is desirably allowed to have a superior flatness. With respect to the material of the metal plates, for example, the same materials and the like as in the first aspect of the present invention may be used.
With respect to the material of the metal plates constituting the metal heater according to the second aspect of the present invention, an aluminum alloy is desirably used, and an aluminum-copper alloy is more desirably used, for the same reason as that described in the first aspect of the present invention. In the same manner as the first aspect of the present invention, with respect to the aluminum-copper alloy, other materials such as magnesium, manganese, silicon, zinc and the like may be added thereto in addition to aluminum and copper.
In the case where aluminum, an aluminum alloy or the like is used as the material of the metal plate, the surface of the metal plate is desirably subjected to an alumite treatment as in the same manner described in the first aspect of the present invention.
Here, after the alumite treatment, the thickness of the coat film is desirably 1 μm or more, and in the case of the hard alumite treatment, the thickness of the coat film may be set to 3 μm or more.
In the metal heater according to the second aspect of the present invention, the peripheral edge of an area on which the heating element is formed is desirably located at a position within 25% of the diameter of the metal plate from the periphery of the metal plate.
Moreover, the heating element is desirably divided into two or more portions. In the metal heater according to the second aspect of the present invention, a wafer guide ring may be placed at a side face of the metal plate, or it may be placed at the peripheral edge or the surface of the heating face of the metal plate. The reason therefor is the same as that described in the first aspect of the present invention.
In the metal heater according to the second aspect of the present invention, a convex portion for supporting an object to be heated is desirably placed on the heating face opposing the object to be heated of the metal plate corresponding to an area on which a heating element is formed. Thus, it becomes possible to make a semiconductor wafer or the like, that is, the object to be heated, less likely to have sagging and, also, to make the distance between the semiconductor wafer or the like and the heating face of the metal plate constant so that the entire semiconductor wafer or the like can be heated evenly.
In the second aspect of the present invention, the terms “a convex portion for supporting an object to be heated is placed corresponding to an area on which a heating element is formed” and “an area on which a heating element is formed” are used under the same definitions as those of a third aspect of the present invention, which will be described later.
With respect to the number of the above-mentioned convex portions, if the diameter of the area on which a heating element is formed is 250 mm or more and less than 300 mm, the number is desirably 6 or more. If the diameter of the area on which a heating element is formed is 200 mm or more and less than 250 mm, the number is desirably 5 or more. If the diameter of the area on which a heating element is formed is 300 mm or more, the number is desirably 7 or more. The reason therefor is the same as that which will be described in the third aspect of the present invention.
With respect to the upper limit of the number of the convex portions formed on the heating face of the metal plate, although not particularly limited, if the diameter of the area on which a heating element is formed is 250 mm or more and less than 300 mm, the number is desirably 20 or less. If the diameter of the area on which a heating element is formed is 200 mm or more and less than 250 mm, the number is desirably 15 or less. The reason therefor is the same as that which will be described in the third aspect of the present invention.
Moreover, with respect to positions at which the convex portions are formed, for example, the same layout as that which will be described in the third aspect of the present invention later may be used.
The positions at which the convex portions are formed are desirably widely dispersed on the metal plate, with the positions being rotation-symmetrical with respect to the center. The reason therefor is the same as that which will be described in the third aspect of the present invention.
In the case where the convex portions are placed on the metal plate in a biased manner and/or the convex portions are placed with irregular intervals, a portion having a wide interval between the convex portions is formed, and in such a portion, the semiconductor wafer tends to have sagging; as a result, the distance between the semiconductor wafer and the metal plate tends to become uneven, making it difficult to evenly heat the semiconductor wafer.
With respect to a method for placing the convex portions on the heating face of the metal plate, the same method as that used for the following third aspect of the present invention may be used.
With respect to a method for securing supporting pins into the concave portions, the same method as that used for the following third aspect of the present invention may be used.
With respect to the metal heater according to the second aspect of the present invention, those metal heaters in which the diameter of the area on which the heating element is formed is 250 mm or more, with six or more supporting pins placed on the heating face of the metal plate may be optimally used. Moreover, at least one supporting pin is desirably placed in the center of the area in which the heating element is formed.
With respect to the shape of the supporting pin, for example, a pinnacle shape with a cone on the tip, a pinnacle shape with a pyramid on the tip, a semi-spherical shape or the like may be desirably used. Here, in the case where the shape of the supporting pin other than the tip is a cylindrical shape, the diameter thereof is desirably 1 to 10 mm. Moreover, the height of the cylindrical-shaped portion of the supporting pin is desirably 1 to 10 mm. The reason therefor is the same as that which will be described in the third aspect of the present invention.
In the case where the supporting pin has a head portion shaped like a nail, the head portion is desirably formed into a shape and a size that are suitably fitted to each concave portion. The reason therefor is the same as that which will be described in the third aspect of the present invention.
The supporting pins are desirably made of ceramics, and in consideration of abrasion resistance to silicon wafers with comparatively little thermal deformation, productivity, costs and the like, oxide ceramic materials such as alumina, silica and the like are desirably used.
In the above-mentioned metal heater, the supporting pins are desirably designed so as to protrude from the heating face of the metal plate with the same height. The reason therefor is the same as that which will be described in the third aspect of the present invention.
The height at which the supporting pin protrudes from the metal plate is desirably 5 to 5000 μm, that is, in a state where the object to be heated is held so as to be apart from the heating face of the metal plate by 5 to 5000 μm. The reason therefor is the same as that which will be described in the third aspect of the present invention.
The distance between the object to be heated and the heating face of the metal plate is desirably 5 to 500 μm, more desirably 20 to 200 μm.
The diameters of the concave portion in which the supporting pin is placed and the through hole used for the supporting pin are desirably 1 to 10 mm. Moreover, the depth of each concave portion is desirably 1 to 10 mm. The reason therefor is the same as that which will be described in the third aspect of the present invention.
In view of the above-mentioned problems, the present inventor has made extensive research efforts for the purpose of obtaining a metal heater which is superior in temperature evenness in surface in transition period, has a comparatively short recovery time, and can evenly heat an object to be heated such as a semiconductor wafer, without causing sagging in the object to be heated upon heating, and found that by: sandwiching a heating element between a plurality of metal plates; and providing convex portions on a heating face opposing the object to be heated of the metal plate corresponding to an area on which the heating element is formed, it becomes possible to evenly heat the object to be heated, without causing any sagging in the semiconductor wafer; thus, the third aspect of the present invention has been completed.
That is, a metal heater according to the third aspect of the present invention comprises a plurality of metal plates and a heating element, with the heating element sandwiched between the metal plates. Herein, a convex portion for supporting an object to be heated is placed on a heating face opposing the object to be heated of the metal plate corresponding to an area on which the heating element is formed.
The metal heater according to the third aspect of the present invention comprises the plurality of metal plates, and the heater is sandwiched between the metal plates. In comparison with a metal heater that is formed by a single metal plate with a heater provided on the face on the side opposite to the heating face side of the metal plate, since the metal heater having this structure makes the thickness of the metal plate located on the heating face side of the heater thinner than the above-mentioned single metal plate, it becomes possible to more quickly heat an object to be heated, such as a semiconductor wafer or the like, and also to shorten the recovery time.
In the metal heater according to the third aspect of the present invention, since convex portions for supporting an object to be heated are placed on the heating face opposing the object to be heated of the metal plate corresponding to the area in which the heating element is formed, it becomes possible to make the semiconductor wafer or the like, that is, the object to be heated, less likely to have sagging. Consequently, it is possible to make the distance between the semiconductor wafer or the like and the heating face of the metal plate constant; thus, the entire semiconductor wafer can be heated evenly.
In the third aspect of the present invention, the term, “a convex portion for supporting an object to be heated is placed corresponding to an area on which a heating element is formed”, refers to a structure in which an appropriate number of convex portions are placed at appropriate positions on the heating face of the metal plate corresponding to the size of the area on which the heating element of the metal plate is formed and the size of the semiconductor wafer to be heated.
Here, the term, “an area on which a heating element is formed”, is defined as follows: when the heating element pattern formed on the metal plate is perpendicularly shifted onto the heating face of the metal plate, the area corresponds to an inner area of the minimum circle that includes all of the heating element pattern.
With respect to the number of the convex portions, if the diameter of the area on which a heating element is formed is 250 mm or more and less than 300 mm, the number is desirably 6 or more. If the number of the convex portions is less than 6, the interval between the convex portions becomes too wide; as a result, the semiconductor wafer tends to have sagging to cause dispersion in the distance between the semiconductor wafer and the metal plate, and the subsequent difficulty in evenly heating the entire semiconductor wafer. If the diameter of the area on which a heating element is formed is 200 mm or more and less than 250 mm, the number of the convex portions is desirably 5 or more. If the diameter of the area on which a heating element is formed is 300 mm or more, the number thereof is desirably 7 or more.
With respect to the upper limit of the number of the convex portions formed on the heating face of the metal plate, although not particularly limited, if the diameter of the area on which a heating element is formed is 250 mm or more and less than 300 mm, the number is desirably 20 or less. This arrangement is prepared from the viewpoints of avoiding complex manufacturing processes, of cutting manufacturing costs, and of maintaining the temperature of the heating face in a more even level. In the case where the diameter of the area on which a heating element is 200 mm or more and less than 250 mm, the number of the convex portions is desirably set to 15 or less.
Moreover, with respect to positions at which the convex portions are formed, for example, a layout in which on an area forming a comparatively circumferential portion of the metal plate, a plurality of convex portions are placed on circumferences of concentric circles of the metal plate with equal intervals, with a single supporting pin attached to the center of the metal plate, may be used, or another layout in which on an area forming a comparatively circumferential portion of the metal plate, a plurality of supporting pins are respectively placed on circumferences of concentric circles of the protruding metal plate as well as on circumferences of concentric circles corresponding to the inner circumference thereof, with a single supporting pin attached to the center of the metal plate, may be used.
The positions at which the convex portions are formed are desirably widely dispersed on the metal plate, with the positions being rotation-symmetrical with respect to the center. The reason therefor is as follows. By providing the convex portions at the above-mentioned positions, upon heating a semiconductor wafer, the semiconductor wafer is made free from sagging, and the distance between the semiconductor wafer and the metal plate is made almost constant so that the heating process is carried out on the semiconductor wafer evenly.
In the case where the convex portions are placed on the metal plate in a biased manner and/or the convex portions are placed with irregular intervals, a portion having a wide interval between the convex portions is formed, and in such a portion, the semiconductor wafer tends to have sagging; as a result, the distance between the semiconductor wafer and the metal plate tends to become uneven, making it difficult to evenly heat the semiconductor wafer.
For example, each of the convex portions may be placed on the heating face of the metal plate by forming a concave portion on the heating face of the metal place and inserting a supporting pin in the concave portion so as to secure the convex portion therein, or may be attached onto the heating face by forming a through hole in the metal plate and inserting a supporting pin in the through hole so as to secure the convex portion therein. Here, the through hole for the supporting pin and the concave portion may be formed in combination.
By using these methods, the supporting pin can be secured onto the metal plate comparatively easily.
With respect to a method for fixedly securing the supporting pin in the concave portion, for example, a method in which a supporting pin having a head portion like a nail is inserted to a concave portion formed as a cylindrical-shaped hollow portion formed in the heating face of the metal plate with the head portion placed on the metal plate side, and a spring having a C-shape is fitted to the concave portion in a manner so as to surround the supporting pin so that the supporting pin is fixedly secured thereon by using the spring force, may be used.
By using such a method, the supporting pin is positively secured thereon without coming off from the metal plate.
With respect to the metal heater according to the third aspect of the present invention, those metal heaters in which the diameter of the area on which the heating element is formed is set to 250 mm or more, with six or more supporting pins being attached to the heating face of the metal plate may be optimally used. Moreover, at least one supporting pin is desirably placed in the center of the area on which the heating element is formed.
With respect to the shape of the supporting pin, for example, a pinnacle shape with a cone on the tip, a pinnacle shape with a pyramid on the tip, a semi-spherical shape or the like may be desirably used. When a semiconductor wafer is placed on the supporting pins having such a shape, the semiconductor wafer is supported through point contacts, making the semiconductor wafer free from formation of hot spots and the like.
Here, in the case where the shape of the supporting pin other than the tip is a cylindrical shape, the diameter thereof is desirably 1 to 10 mm. Upon placing the semiconductor wafer, the diameter of less than 1 mm tends to fail to provide a stable supporting function as the supporting pin, while the diameter exceeding 10 mm tends to cause hot spots and the like on the semiconductor wafer.
Moreover, the height of the cylindrical-shaped portion of the supporting pin is desirably 1 to 10 mm. The height of less than 1 mm tends to fail to positively secure the supporting pin onto the heating face of the metal plate, while the height exceeding 10 mm tends to fail to evenly heat the semiconductor wafer.
In the case where the supporting pin has a head portion shaped like a nail, the head portion is desirably formed into a shape and a size that are suitably fitted to each concave portion. When the head portion is too small in comparison with the size of the concave portion, the supporting pin becomes unstable.
The supporting pins are desirably made of ceramics, and in consideration of abrasion resistance to silicon wafers with comparatively little thermal deformation, productivity and costs, oxide ceramic materials such as alumina, silica and the like are desirably used.
In the above-mentioned metal heater, the supporting pins are desirably designed so as to protrude from the heating face of the metal plate with the same height. In the case where all the heights by which the supporting pins protrude are made the same, upon placing a semiconductor wafer, the semiconductor wafer is made in parallel with the heating face of the metal plate, and since all the supporting pins are allowed to support the semiconductor wafer, no sagging occurs. Consequently, the distance between the semiconductor wafer and the metal plate is maintained in an even level so that the semiconductor wafer can be evenly heated. In contrast, when the heights by which the supporting pins protrude are different from one another, the semiconductor wafer tends to tilt, or those supporting pins having short heights are not made in contact with the semiconductor wafer to cause sagging. Consequently, dispersion tend to occur in the distance between the semiconductor wafer and the metal plate, making it difficult to evenly heat the semiconductor wafer.
The height at which the supporting pin protrudes from the heating face of the metal plate is desirably 5 to 5000 μm, that is, in a state in which the object to be heated is apart from the heating face of the metal plate by 5 to 5000 μm. The height of less than 5 μm tends to make the temperature of the semiconductor wafer uneven due to influences from the temperature distribution of the metal plate, and might cause the wafer to come into contact with the metal plate. The height exceeding 5000 μm makes it difficult to raise the temperature of the semiconductor wafer to cause a temperature drop, in particular, on the peripheral portion of the semiconductor wafer.
The distance between the object to be heated and the heating face of the metal plate is desirably 5 to 500 μm, more desirably 20 to 200 μm.
The diameters of the concave portion in which the supporting pin is placed and the through hole for the supporting pin are desirably 1 to 10 mm. The diameter of less than 1 mm tends to fail to positively secure the supporting pin, while the diameter exceeding 10 mm tends to cause cooling spots.
Moreover, the depth of each concave portion is desirably 1 to 10 mm. The depth of less than 1 mm might cause the supporting pins to come off, while the depth exceeding 10 mm tends to cause cooling spots.
In the metal heater according to the third aspect of the present invention, with respect to the plurality of metal plates, the thickness of the metal plate (upper metal plate) on the heating face side of the heater is desirably made larger than the thickness of the metal plate (lower metal plates) on the opposite side. The reason therefor is the same as that in the metal heater according to the second aspect of the present invention.
The metal heater according to the third aspect of the present invention may have a structure in which another metal plate is further attached to the heating element placed on the metal plate, that is, a structure in which a heating element is sandwiched between two metal plates, or a structure in which heating elements are sandwiched among three or more metal plates. In the case where the metal heater according to the third aspect of the present invention has three or more metal plates, the thickness of the metal plate on the heating face side (upper metal plate) and the thickness of the metal plate on the side opposite to the heating face side (lower metal plate) are defined in the same manner as those of the first aspect of the present invention.
In the following, a metal heater in which a heater is sandwiched between two metal plates will be mainly described according to the third aspect of the present invention.
In metal heater according to the third aspect of the present invention, the lower limit of the thickness of the upper metal plate is desirably 1 mm. In the case where the thickness of the upper metal plate is less than 1 mm, the distance between the heating element and the heating face becomes too short; thus, the pattern of the heating element is reflected to the temperature distribution of the heating face. As a result, it becomes difficult to evenly heat an object to be heated such as a semiconductor wafer or the like in some cases. In contrast, when the thickness of the upper metal plate is within the above-mentioned range, the pattern of the heating element is not reflected to the temperature distribution of the heating face so that it becomes possible to evenly heat the object to be heated.
Moreover, when the thickness of the substrate is within the above-mentioned range, the metal heater is allowed to have superior mechanical strength without occurrence of warping, sagging and the like in the metal plate, making it possible to positively ensure the flatness of the heating face.
Furthermore, the lower limit of the thickness of the upper metal plate is more desirably 5 mm.
The upper limit of the thickness of the upper metal plate is desirably 50 mm. The thickness of the upper metal plate exceeding 50 mm sometimes makes it difficult for the temperature of the heating face of the metal plate to follow a voltage to be applied to the heating element and change in the amount of electric current, failing to quickly heat an object to be heated, such as a semiconductor wafer or the like, and when the semiconductor wafer is placed on the heating face, time (recovery time) taken to bring the decreased temperature back to the previous temperature takes longer to cause a prolonged working time and the subsequent reduction in productivity.
In the above-mentioned structure, the upper limit of the thickness of the lower metal plate is desirably set to 50 mm, more desirably 30 mm, and the lower limit thereof is desirably 1 mm, more desirably 3 mm.
Moreover, the ratio of the thickness of the upper metal plate and the thickness of the lower metal plate (thickness of upper metal plate/thickness of lower metal plate) is desirably 1 to 10. The reason therefor is the same as that described in the first aspect of the present invention. In particular, the ratio exceeding 1 is optimally used. Thus, it becomes possible to provide superior temperature evenness on the heating face in steady state.
In the metal heater according to the third aspect of the present invention, the heater is sandwiched between the upper metal plate and the lower metal plate, and the heating element is formed inside the heater. In the same manner as the first aspect of the present invention, a circuit constituting the heating element is desirably divided into two or more portions, and all the diameters of the plurality of metal plates and the heater are desirably the same. In the case where a heat insulating ring or the like is interposed between the metal plate and the supporting case, the diameters of the metal plates may be made different from one another.
In the metal heater according to the third aspect of the present invention, the diameter of the metal plates is desirably 200 mm or more, more desirably 12 inches (300 mm) or more. The reason therefor is the same as that described in the first aspect of the present invention.
In the metal plates constituting the metal heater according to the third aspect of the present invention, the flatness on the surface thereof is desirably 50 μm or less, more desirably 30 μm or less. The reason therefor is the same as that described in the first aspect of the present invention.
In order to realize a metal heater that is superior in its flatness, it is necessary to prevent the metal plate from curving due to pressure imposed from the side faces upon thermal expansion of the metal plate. For this reason, it is desirable to maintain a space between each of the side faces of the metal plate and the supporting case (bottom plate) so that the side faces is not made in contact with the metal plate.
In the third aspect of the present invention, the plurality of metal plates are desirably made of the same material. Moreover, the material of the metal plates desirably has a superior thermal conductivity with high rigidity, and is less likely to be deformed even when thermally expanded so that, upon completion of the machining processes of the metal plates themselves, the metal plates are desirably allowed to have a superior flatness. With respect to the material of the metal plates, for example, the same material as that used in the first aspect of the present invention, and the like are proposed.
Also in the third aspect of the present invention, an aluminum alloy is desirably used, and an aluminum-copper alloy is more desirably used in the same manner as the first aspect of the present invention. Moreover, with respect to the aluminum-copper alloy, other materials such as magnesium, manganese, silicon, zinc and the like may be added thereto.
In the case where aluminum, an aluminum alloy or the like is used as the material of the metal plate, the surface of the metal plate is desirably subjected to an alumite treatment in the same manner as the first aspect of the present invention.
In the case of the alumite treatment, the thickness of the coat film is desirably 1 μm or more, and in the case of a hard alumite treatment, the thickness of the coat film may be set to 3 μm or more.
In the metal heater according to the third aspect of the present invention, the peripheral edge of an area in which the heating element is formed is desirably located at a position within 25% of the diameter of the metal plate from the periphery of the metal plate.
Moreover, the heating element is desirably divided into two or more portions. In the metal heater according to the third aspect of the present invention, a wafer guide ring may be placed at a side face of the metal plate, or it may be placed at the peripheral edge or the surface of the heating face of the metal plate. The reason therefor is the same as that described in the first aspect of the present invention.
The metal heater according to the third aspect of the present invention may be used as a heater module or the like by fixedly securing an optical waveguide such as quartz or the like thereon. In this case, the optical waveguide may be supported by convex portions.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view that schematically shows one example of a metal heater according to a first aspect of the present invention.
FIG. 2 is a horizontal cross-sectional view of a heater that constitutes a part of the metal heater shown in FIG. 1.
FIG. 3 is a cross-sectional view that schematically shows a metal plate and the heater of the metal heater according to the first aspect of the present invention.
FIG. 4(a) is a cross-sectional view that schematically shows another example of a conventional metal heater, and FIG. 4(b) is a plan view of FIG. 4(a).
FIG. 5(a) is a cross-sectional view that schematically shows one example of a metal heater according to a second aspect of the present invention. FIG. 5(b) schematically shows a method by which a heating element and a conductive line are joined to each other by caulking using a joining foil in the metal heater shown in FIG. 5(a).
FIG. 6(a) is a cross-sectional view that schematically shows one example of a metal heater according to a third aspect of the present invention. FIG. 6(b) schematically shows a method by which a heating element and a conductive line are joined to each other by caulking using a joining foil in the metal heater shown in FIG. 6(a).
FIG. 7 is a plan view that shows the metal heater shown in FIG. 6(a).
FIG. 8 shows a three dimensional shape of a part of a metal heater heating face according to Example 1 at ordinary temperature.
FIG. 9 shows a three dimensional shape of a part of a metal heater heating face in according with Example 1 at 140° C.
FIG. 10 shows a three dimensional shape of a part of a metal heater heating face according to Test Example 1 at 140° C.
FIG. 11 shows a three dimensional shape of a part of a metal heater heating face according to Example 8 at ordinary temperature.
FIG. 12 shows a three dimensional shape of a part of a metal heater heating face in according with Example 8 at 140° C.
FIG. 13 shows a three dimensional shape of a part of a metal heater heating face according to Test Example 3 at 140° C.
FIG. 14 is a graph that shows a relationship between a wafer temperature and time in the vicinity of 100° C. when a metal heater according to Example 12 is used.
FIG. 15 is a graph that shows a relationship between a wafer temperature and time in the vicinity of 120 to 130° C. when the metal heater according to Example 12 is used.
FIG. 16 is a graph that shows a relationship between a wafer temperature and time in the vicinity of 140° C. when the metal heater according to Example 12 is used.
FIG. 17 is a graph that shows a relationship between a wafer temperature and time in the vicinity of 100° C. when the metal heater according to Example 16 is used.
FIG. 18 is a graph that shows a relationship between a wafer temperature and time in the vicinity of 120 to 130° C. when the metal heater according to Example 16 is used.
FIG. 19 is a graph that shows a relationship between a wafer temperature and time in the vicinity of 140° C. when the metal heater according to Example 16 is used.
FIG. 20 shows a three dimensional shape of a part of a metal heater heating face according to Example 12 at ordinary temperature.
FIG. 21 shows a three dimensional shape of a part of a metal heater heating face in according with Example 12 at 140° C.
FIG. 22 shows a three dimensional shape of a part of a metal heater heating face according to Comparative Example 2 at 140° C.

EXPLANATION OF SYMBOLS

410, 510, 610 Metal heater
411, 511, 611 Upper metal plate
411 a, 511 a, 611 a Heating face
412, 512, 612 Heater
414, 514, 614 Bottomed hole
415, 515, 615 Through hole
416, 516, 616 Temperature measuring element
417, 517, 617 Metal plate securing screw
418, 518, 618 Supporting pin
419, 519, 619 Semiconductor wafer
420, 520, 620 Supporting case
421, 521, 621 Lower metal plate
422, 522, 622 Pressing plate
423, 523, 623 Heat shielding plate
424, 524, 624 Conductive line
425 Heating element
525, 625 Supporting plate
426 Mica plate
627 Spring
628 Concave portion
529, 629 Stainless foil
530, 630 Stainless foil for connection
531, 631 Attaching member
532, 632 Barrier ring

DETAILED DISCLOSURE OF THE INVENTION

In the following, description will be given of metal heaters according to the first to third aspects of the present invention in succession.
First, an embodiment of the first aspect of the present invention will be described.
The metal heater according to the first aspect of the present invention is a metal heater comprising a metal plate and a heating element. Herein, the number of the metal plates is a plural number, the heating element is sandwiched between the metal plates, and the thickness of a metal plate on a heating face side is the same as or larger than the thickness of a metal plate on a side opposite to the heating face side.
Referring to the drawings, description will be given of a metal heater in which a heater is sandwiched between two metal plates as one example of the metal heater according to the first aspect of the present invention.
FIG. 1 is a cross-sectional view that schematically shows the metal heater of this type, and FIG. 2 is a horizontal cross-sectional view of a heater that constitutes a part of the metal heater shown in FIG. 1.
In this metal heater 410, a heater 412 is sandwiched between an upper metal plate 411 and a lower metal plate 421, each of which has a disk shape, and the upper metal plate 411, the heater 412 and the lower metal plate 421 are fixedly secured to, and tightly bound to one another through metal plate securing screws 417 so that heat from the heater 412 is suitably transmitted to the upper metal plate 411.
Moreover, the thickness of the upper metal plate 411 is made larger than the thickness of the lower metal plate 421. Therefore, as has been described already, the flatness of the heating face is maintained, and the temperature of the heating face is equalized so that the object to be heated can be evenly heated.
By securing the metal plate using the metal plate securing screws 417, the thickness of the metal plate becomes substantially large so that the flatness of the heating face is further improved.
The metal heater 410 according to the first aspect of the present invention makes it possible to realize a flatness of 50 μm or less on a heating face 411 a of the upper metal plate 411. By realizing such a flatness, upon heating a semiconductor wafer, the distance between the semiconductor wafer and the metal plate is made almost constant so that the heating process is carried out on the entire semiconductor wafer evenly.
In the metal heater 410 according to the first aspect of the present invention, the side faces of the upper metal plate 411, the heater 412 and the lower metal plate 421 are not made in tightly contact with a supporting case 420, and secured in a non-contact state. With this structure, the metal plate can be prevented from being curved due to pressure from the side faces when the upper metal plate 411 has been thermally expanded, and upon heating an object to be heated, heat released from the metal plate and the like is reduced so that an object to be heated can be heated more quickly in comparison with the case in which the side faces of the upper metal plate 411, the heater 412 and the lower metal plate 421 are made in tightly contact with the supporting case 420. In this case, an air layer is allowed to function as a heat insulating material.
Moreover, the metal heater 410 has a structure in which the metal plate securing screws 417 do not penetrate supporting case 420, and are only allowed to penetrate the upper metal plate 411, the heater 412 and the lower metal plate 421, and designed to secure these members. With this structure, it becomes possible to prevent deformation in the upper metal plate 411 due to a difference in thermal expansion coefficients between the upper metal plate 411 and the supporting case 420, and also to reduce heat released from the upper metal plate 411 and the like upon heating an object to be heated so that the object to be heated can be heated quickly.
A heat shielding plate 423 is placed on the bottom portion of the supporting case 420 so that it becomes possible to prevent heat, released from the upper metal plate 411 and the lower metal plate 421, from conducting to the device. Here, a barrier ring 428 is placed on the peripheral edge of the supporting case 420. The provision of the barrier ring 428 makes it possible to prevent outside gases from flowing therein to cause a temperature change in the heating face 411 a.
Moreover, a bottomed hole 414 is formed in the metal heater 410, and a temperature measuring element 416 configured to measure the temperature of the upper metal plate 411 is inserted into the bottomed hole 414, and sealed with an inorganic adhesive or the like (not shown) to be secured therein.
In the metal heater 410, supporting pins 418, each having a pinnacle-like tip, are placed on the heating face, and the semiconductor wafer 419 is supported through the supporting pins 418 so that the semiconductor wafer 419 can be heated with a fixed distance kept from the heating face of the upper metal plate 411.
In the metal heater according to the first aspect of the present invention, with respect to the number of the supporting pins, although not particularly limited, it is desirably set to six or more in the case where, for example, the diameter of the metal plate is 12 inches (300 mm) or more. When the number of the supporting pins is six or more, a clearance between the heating face and the semiconductor wafer is accurately maintained so that it becomes possible to easily maintain the evenness of temperature on the heating face in transition period.
Moreover, the metal heater 410 is also provided with through holes 415 each of which penetrates the upper metal plate 411, the heater 412, the lower metal plate 421 and the supporting case 420, and by inserting pillar-shaped lifter pins and the like through the through holes 415, a semiconductor wafer 419, that is, the object to be heated is supported with a fixed distance kept from the heating face 411 a of the upper metal plate 411 so that the semiconductor wafer 419 can be properly transported.
Here, the heater 412 is connected to a conductive line 424, and the conductive line 424 is led outside from a through hole formed in the supporting case 420 and the heat shielding plate 423, and connected to a power supply or the like (not shown).
In the metal heater 410 shown in FIG. 1, a part of the heating element 425 made of a metal foil such as stainless foil or the like is exposed down to the lower side of the through hole formed in the lower metal plate 421 so that one end of the conductive line 424 is wrapped with the exposed foil (hereinafter, referred to as foil for connection), and an attaching member 427 made of metal having a caulking portion (not shown) is then attached thereto; thus, the caulking portion of the attaching member 427 is caulked so that the heating element 425 and the conductive line 424 are connected to each other.
Alternatively, the conductive line 424 may be connected to a heating element placed inside the heater 412 on the side face of the heater 412.
Moreover, in the metal heater 410, the upper metal plate 411, the heater 412 and the lower metal plate 421 are secured through the metal plate fixing screws 417. Here, the metal plate fixing screws 417 are attached in a manner so as to penetrate the heater 412 and the lower metal plate 421 and so as not to penetrate the upper metal plate 411.
As described above, in the case where the upper metal plate 411 and the like are secured through the metal plate securing screws 417, the length of the portion of each metal plate securing screw 417 inserted into the upper metal plate 411 is desirably set to ¾ or less of the thickness of the upper metal plate.
When the length of the portion of each metal plate securing screw 417 inserted into the upper metal plate 411 is longer than ¾ of the thickness of the upper metal plate 411, the temperature of a portion right above each metal plate securing screw 417 of the heating face of the metal plate becomes higher in comparison with the temperature of its peripheral portion, failing to evenly heat an object to be heated.
Moreover, the metal heater 410 has a structure in which the screw head of each metal plate securing screw 417 is embedded in the lower metal plate 421. Therefore, the upper metal plate 411, the heater 412 and the lower metal plate 421 can be firmly secured inside the supporting case 420 more positively so that the upper metal plate 411 is allowed to have a structure that is less likely to result in a deformation such as warping, sagging and the like.
The heater 412 has a circular shape in its plan view in the same manner as the upper metal plate 411 and the lower metal plate 421, and the heating element 425, constituted by closed circuits, is arranged in the heater 412 so as to heat the entire heating face 411 a of the upper metal plate 411 to an even temperature. With respect to the heating element 425, as shown in FIG. 2, a heating element, of a pattern in which a winding line is repeatedly placed in a ring shape on the periphery of a heater to form a closed circuit, and a heating element, of a pattern in which a winding line is repeatedly placed inside thereof in a manner so as to form a part of a concentric circle to form a closed circuit, are arranged.
Moreover, although not shown in the figures, the heater 412 has a structure in which the heating element 425 is sandwiched by two mica plates and secured therein, and upon current application, the heating element 425 heats the mica plates so that an object to be heated is heated by secondary radiation from the mica plates.
In the metal heater 410 of the first aspect of the present invention, the peripheral edge of the heating element 425 formed inside the heater 412 is desirably located at a position within 25% of the diameter of the metal plate 411 from the periphery of the metal plate 411. Normally, the temperature on the peripheral portion of the metal plate 411 tends to become uneven due to heat radiation from the surface of the peripheral portion of the metal plate 411; however, in the metal heater 410 according to the first aspect of the present invention, since the heating element is also disposed at the peripheral portion, a semiconductor wafer or the like, that is, the object to be heated can be evenly heated without dispersion in temperature.
With respect to the material, shape and the like of the metal heater forming the first aspect of the present invention and the manufacturing method of the metal heater according to the first aspect of the present invention, detailed description will be given later.
In the following, description will be given of an embodiment according to the second aspect of the present invention.
The metal heater according to the second aspect of the present invention is a metal heater comprising a plurality of metal plates and a heating element, the heating element sandwiched between the metal plates. Herein, the plurality of metal plates are made of the same material. Referring to the drawings, description will be given of a metal heater in which a heater is sandwiched between two metal plates as one example of the metal heater according to the second aspect of the present invention.
FIG. 5(a) is a cross-sectional view that schematically shows such a metal heater, and FIG. 5(b) schematically shows a method by which a heating element and a conductive line are joined to each other by caulking using a joining foil in the metal heater shown in FIG. 5(a).
In this metal heater 510, a heater 512 is sandwiched between an upper metal plate 511 and a lower metal plate 521, each of which has a disk shape, and the upper metal plate 511, the heater 512 and the lower metal plate 521 are fixedly secured to, and tightly bound to one another through metal plate securing screws 517 so that heat from the heater 512 is suitably transmitted to the upper metal plate 511.
Moreover, the thickness of the upper metal plate 511 is made larger than the thickness of the lower metal plate 521. Therefore, as has been described already, the flatness of the heating face is maintained, and the temperature of the heating face is made even so that the object to be heated can be evenly heated.
By securing the metal plate using the metal plate securing screws 517, the thickness of the metal plate becomes substantially large so that the flatness of the heating face is further improved.
The upper metal plate 511, the heater 512 and the lower metal plate 521, fixedly secured to one another through the metal plate securing screws 517 are supported by a supporting plate 525 placed on the bottom face of a supporting case 520 having a cylinder shape with a bottom, and in this structure, portions other than the contact portion to the supporting plate 525 do not contact with the supporting case 520. Moreover, a heat shielding plate 523 for shielding heat is provided below the supporting case 520. Moreover, a barrier ring 532 is placed on the peripheral edge of the supporting case 520. By providing the barrier ring, it becomes possible to prevent outside gases from flowing therein, and consequently to prevent temperature change in the heating face 511 a.
With the above-mentioned structure, the metal heater 510 according to the second aspect of the present invention makes it possible to realize a flatness of 50 μm or less on the heating face 511 a of the upper metal plate 511. By realizing such a flatness, upon heating a semiconductor wafer, the distance between the semiconductor wafer and the metal plate can be made almost constant so that the entire semiconductor wafer can be heated to an even temperature.
The metal heater 510 according to the second aspect of the present invention may be provided with a wafer guide ring 526 on the peripheral edge portion of the heating face 511 a so as to prevent temperature change due to a gas flowing therein from outside.
In the metal heater 510 according to the second aspect of the present invention, the side faces of the upper metal plate 511, the heater 512 and the lower metal plate 521 are not made in tightly contact with the supporting case 520, and secured in a non-contact state, and the lower metal plate 521 also does not directly contact with the bottom face of the supporting case 520, and is supported by a supporting plate 525. With this arrangement in which the side faces of the upper metal plate 511, the heater 512 and the lower metal plate 521 are not made in contact with the supporting case 520, the upper metal plate 511 can be prevented from being curved due to pressure from the side faces when the upper metal plate 511 has been thermally expanded. Moreover, the upper metal plate 511, the heater 512 and the lower metal plate 521 are supported only through the supporting plate 525, without contacting with any other portions; thus, upon heating an object to be heated, heat released from the metal plate and the like is reduced so that an object to be heated can be heated more quickly in comparison with the case in which the side faces of the upper metal plate 511, the heater 512 and the lower metal plate 521 are made in tightly contact with the supporting case 520. In this case, an air layer is allowed to function as a heat insulating layer.
Here, the upper metal plate 511, the heater 512, the upper metal plate 521 and the like, as they are, may be placed on the bottom face of the supporting case 520, without providing the supporting member 525 on the bottom face of the supporting case 520.
After the heating process, the upper metal plate 511, the heater 512 and the lower metal plate 521 sometimes need to be cooled quickly, and in such a case, for example, a cooling pipe or the like is connected to the bottom plate of the supporting case 520, with cooled air or the like introduced into the supporting case 520, so that it becomes possible to carry out a quick cooling process.
Moreover, the metal heater 510 has a structure in which the metal plate securing screws 517 do not penetrate supporting case 520, and are allowed to penetrate only the upper metal plate 511, the heater 512 and the lower metal plate 521, and designed to secure these members. With this structure, it becomes possible to prevent deformation in the upper metal plate 511 due to a difference in thermal expansion coefficients between the upper metal plate 511 and the supporting case 520, and also to reduce heat released from the upper metal plate 511 and the like upon heating an object to be heated so that the object to be heated can be heated quickly.
A heat shielding plate 523 is placed on the bottom portion of the supporting case 520 so that it becomes possible to prevent heat, released from the upper metal plate 511 and the lower metal plate 521, from transferring to the device.
Moreover, a bottomed hole 514 is formed in the metal heater 510, and a temperature measuring element 516 used for measuring the temperature of the upper metal plate 511 is embedded in the bottomed hole 514.
Here, in the metal heater 510, supporting pins 518, each having a pinnacle-like tip, are placed on the heating face, and the semiconductor wafer 519 is supported through the supporting pins 518 so that the semiconductor wafer 519 can be supported with a fixed distance kept from the heating face of the upper metal plate 511, so as to be heated.
In the metal heater according to the second aspect of the present invention, with respect to the number of the supporting pins, although not particularly limited, it is desirably six or more in the case where, for example, the diameter of the metal plate is 12 inches (300 mm) or more. The reason therefor is the same as that described in the metal heater according to the first aspect of the present invention.
Moreover, the metal heater 510 is provided with through holes 515 each of which penetrates the upper metal plate 511, the heater 512, the lower metal plate 521 and the supporting case 520, and by inserting pillar-shaped lifter pins and the like through the through holes 515, a semiconductor wafer 519, that is, the object to be heated is supported with a fixed distance kept from the heating face 51 a of the upper metal plate 511 so that the semiconductor wafer 519 can be properly transported.
Here, the heater 512 is connected to a conductive line 524, and the conductive line 524 is led outside from a through hole formed in the supporting case 520 and the heat shielding plate 523, and connected to a power supply or the like (not shown).
In the metal heater 510 shown in FIG. 5, the through hole is formed in the lower metal plate 521, and the conductive line 524 is inserted into the through hole; however, the conductive line 524 may be connected to a heating element placed inside the heater on the side face of the heater 512.
Moreover, in the metal heater 510, the upper metal plate 511, the heater 512 and the lower metal plate 521 are fixedly secured by the metal plate securing screws 517. Here, the metal plate securing screws 517 are attached in a manner so as to penetrate the heater 512 and the lower metal plate 521, and so as not to penetrate the upper metal plate 511.
As described above, in the case where the upper metal plate 511 and the like are secured through the metal plate securing screws 517, the length of the portion of each metal plate securing screw 517 inserted into the upper metal plate 511 is desirably ¾ or less of the thickness of the upper metal plate.
When the length of the portion of each metal plate securing screw 517 inserted into the upper metal plate 511 is longer than ¾ of the thickness of the upper metal plate 511, the temperature of a portion right above each metal plate securing screw 517 of the heating face of the metal plate becomes higher than the temperature of its peripheral portion, failing to evenly heat an object to be heated.
The heater 512 has a circular shape in its plan view in the same manner as the upper metal plate 511 and the lower metal plate 521, and the heating element 525, constituted by closed circuits, is arranged in the heater 512 so as to heat the entire heating face 511 a of the upper metal plate 511 to an even temperature.
In the heater 512, as shown in FIG. 2, a heating element, of a pattern in which a winding line is repeatedly placed in a ring shape on the periphery of the heater 512 to form a closed circuit, and a heating element, of a pattern in which a winding line is repeatedly placed inside thereof in a manner so as to form a part of a concentric circle to form a closed circuit, are arranged.
Moreover, although not shown in the figures, the heater 512 has a structure in which the heating element is sandwiched between two mica plates and secured therein, and upon current application, the heating element heats the mica plates so that an object to be heated can be heated by secondary radiation from the mica plates. The heating element may be formed by a stainless foil.
In the metal heater 510 according to the second aspect of the present invention, the peripheral edge of the heating element formed inside the heater 512 is desirably located at a position within 25% of the diameter of the metal plate 511 from the periphery of the metal plate 511. Normally, the temperature on the peripheral portion of the metal plate 511 tends to become uneven due to heat radiation from the surface of the peripheral portion of the metal plate 511; however, in the metal heater 510 according to the second aspect of the present invention, since the heating element is also disposed at the peripheral portion, a semiconductor wafer or the like, that is, the object to be heated can be evenly heated without dispersion in temperature.
With respect to the material, shape and the like of the metal heater forming the second aspect of the present invention and the manufacturing method of the metal heater according to the second aspect of the present invention, detailed description will be given later.
In the following, description will be given of an embodiment according to the third aspect of the present invention.
The metal heater according to the third aspect of the present invention is a metal heater comprising a plurality of metal plates and a heating element, with the heating element sandwiched between the metal plates. Herein, a convex portion for supporting an object to be heated is placed on a heating face opposing the object to be heated of the metal plate corresponding to an area on which the heating element is formed.
Referring to the drawings, description will be given of a metal heater in which a heater is sandwiched between two metal plates as one example of the metal heater according to the third aspect of the present invention.
FIG. 6(a) is a cross-sectional view that schematically shows such a metal heater, and FIG. 6(b) schematically shows a method by which a heating element and a conductive line are joined to each other by caulking using a joining foil in the metal heater shown in FIG. 6(a). Moreover, FIG. 7 is a plan view that shows the metal heater of FIG. 6(a). Here, in FIG. 7, the heating element is indicated by a broken line.
In a metal heater 610, each of supporting pins 618 having a tip portion like a nail is inserted into each of concave portions 628 prepared as cylinder shaped hollow sections formed on the upper metal plate 611, and a C-shaped spring 627 is fitted to each concave portion 628 so as to contact therewith in a manner so as to enclose the supporting pin 618 so that the supporting pin 618 is fixedly secured to the heating face 611 a of the upper metal plate 611.
Here, in the present embodiment, the supporting pin is placed on the heating face of the metal plate by using a means shown in FIG. 6; however, with respect to the means for placing the supporting pin on the heating face of the metal plate, not limited to the means shown in FIG. 6, for example, a method in which a supporting pin having a screw portion is engaged with a concave portion in which thread grooves are formed.
Moreover, as shown in FIG. 2, on the heating face 611 a of the upper metal plate 611, eight supporting pins 618 are placed on circumferences of concentric circles of the upper metal plate 611 and one supporting pin 618 is placed on the center portion of the upper metal plate 611 at an area located on a comparatively peripheral portion of the upper metal plate 611; thus, the total nine supporting pins 618 are placed thereon. Here, the supporting pins located on the same circumference are placed so as to have the same interval, in order to prevent sagging in the semiconductor wafer 619.
Here, the other structures are the same as those of the metal heater 510 according to the second aspect of the present invention shown in FIG. 5; therefore, the description thereof is omitted.
The metal heater 610 according to the third aspect of the present invention, which has the above-mentioned structure, makes it possible to realize a flatness of 50 μm or less on the heating face 611 a of the upper metal plate 611. By realizing such a flatness, upon heating a semiconductor wafer, the distance between the semiconductor wafer and the metal plate is made almost constant so that the entire semiconductor wafer can be heated to have an even temperature.
The metal heater 610 according to the third aspect of the present invention may be provided with a wafer guide ring 626 on the peripheral edge portion of the heating face 611 a so as to prevent temperature changes due to a gas flowing therein from outside, or may be provided with a barrier ring 632 thereon.
The metal heater 610 according to the third aspect of the present invention is different from a conventional metal heater 450 shown in FIGS. 4(a) and 4(b) in the following points.
First, as described above, the metal heater 610 has the structure in which the total nine supporting pins 618 are placed on the heating face 611 a of the upper metal plate 611, while the metal heater 450 has a structure in which the total five supporting pins 458 are placed on the heating face 451 a of the metal plate 451; thus, the numbers of the supporting pins are different from each other. Therefore, since the metal heater 610 has a narrower gap between the supporting pins 618, it becomes possible to make the semiconductor wafer 619 less likely to sagging. For this reason, the distance between the semiconductor wafer 619 and the heating face 611 a of the upper metal plate 611 is made almost constant so that the heating process can be carried out on the entire semiconductor wafer 619 evenly.
Moreover, in the metal heater 610, the side faces of the upper metal plate 611, the heater 612 and the lower metal plate 621 are not made in tightly contact with the supporting case 620, and secured in a non-contact state, and the lower metal plate 621 is not made in direct contact with the bottom face of the supporting case 620 either, and supported by a supporting plate 625. With this structure in which the side faces of the upper metal plate 611, the heater 612 and the lower metal plate 621 are kept in a non-contact state with the supporting case 620, the upper metal plate 611 can be prevented from being curved due to pressure from the side faces when the upper metal plate 611 has been thermally expanded. In the case of the structure in which the upper metal plate 611, the heater 612 and the lower metal plate 621 are supported only through the supporting plate 625, with no other portions made in contact therewith, upon heating an object to be heated, heat released from the metal plate and the like is reduced so that an object to be heated can be heated more quickly in comparison with the case in which the side faces of the upper metal plate 611, the heater 612 and the lower metal plate 621 are made in tightly contact with the supporting case 620. In this case, an air layer is allowed to function as a heat insulating layer.
Here, the upper metal plate 611, the heater 612 and the lower metal plate 621, as they are, may be placed on the bottom face of the supporting case 620, without providing the supporting member 625 on the bottom face of the supporting case 620.
After the heating process, the upper metal plate 611, the heater 612 and the lower metal plate 621 sometimes need to be cooled quickly, and in such a case, for example, a cooling pipe or the like is connected to the bottom plate of the supporting case 620, with cooled air or the like introduced into the supporting case 620, so that it becomes possible to carry out a quick cooling process.
Moreover, the metal heater 610 has a structure in which the metal plate securing screws 617 do not penetrate the supporting case 620, and are allowed to penetrate only the upper metal plate 611, the heater 612 and the lower metal plate 621, and designed to secure these members. With this structure, it becomes possible to prevent deformation in the upper metal plate 611 due to a difference in thermal expansion coefficients between the upper metal plate 611 and the supporting case 620, and also to reduce heat released from the upper metal plate 611 and the like upon heating an object to be heated so that the object to be heated can be heated quickly.
In the metal heater 610 according to the third aspect of the present invention, the peripheral edge of the heating element 625 formed inside the heater 612 is desirably located at a position within 25% of the diameter of the metal plate 611 from the periphery of the metal plate 611. The reason therefor is the same as described in the first aspect of the present invention.
With respect to the material, shape and the like of the metal heater forming the third aspect of the present invention and the manufacturing method of the metal heater according to the third aspect of the present invention, detailed description will be given later.
In the following, description will be given of the materials, shapes and the like of the metal heaters according to the first to third aspects of the present invention. Here, since the materials, shapes and the like of the metal heaters according to the first to third aspects of the present invention are almost the same, the description thereof will be given all together.
With respect to each of the metal heaters according to the first to third aspects of the present invention, the metal plate is provided with bottomed holes formed on the side opposite to the heating face side on which an object to be heated is placed, toward the heating face, and the bottom of each bottomed hole is formed relatively closer to the heating face from the heating element, and a temperature measuring element (not shown), such as a thermocouple or the like is desirably provided on the bottomed hole.
Moreover, the distance between the bottom of the bottomed hole and the heating face is desirably between 0.1 mm and ½ of the thickness of the metal plate. Thus, the temperature measuring place is made closer to the heating face from the heating element so that it becomes possible to measure the temperature of the semiconductor wafer more accurately.
The distance between the bottom of the bottomed hole and the heating face of less than 0.1 mm causes heat radiation, resulting in a distribution of temperature on the heating face; in contrast, the distance exceeding ½ of the thickness makes the metal plate more likely to be influenced from the temperature of the heating element, resulting in a failure in temperature control, and the subsequent distribution of temperature on the heating face.
The diameter of the bottomed hole is desirably 0.3 to 5 mm. The reason therefor is because, when the diameter is too large, the heat radiating property becomes too high, while, when the diameter is too small, the machining property becomes too low; thus, it becomes impossible to evenly maintain the distance from the heating face.
With respect to the temperature measuring element, for example, a thermocouple, a platinum temperature measuring resistor, a thermistor and the like may be used. With respect to the thermocouple, for example, as listed in JIS-C-1602 (1980), K-type, R-type, B-type, S-type, E-type, J-type and T-type thermocouples may be used. Among these, the K-type thermocouples are more desirably used.
The size of the coupling portion of the thermocouple is set to the same as the diameter of an element wire, or greater than the diameter thereof, and is desirably 0.5 mm or less. The coupling portion that is greater than this tends to cause a great thermal capacity and the subsequent reduction in responsivity. Here, it is difficult to make the coupling portion smaller than the diameter of an element wire.
The temperature measuring element may be bonded to the bottom of the bottomed hole by using gold alloy, silver alloy or the like, or may be sealed with a heat resistant resin after having been inserted into the bottomed hole, or both of the above-mentioned methods may be used in combination.
With respect to the heat resistant resin, examples thereof include thermosetting resins, in particular, epoxy resin, polyimide resin, bismaleimide-triazine resin and the like. Each of these resins may be used alone, or two or more resins of these may be used in combination.
With respect to the gold alloy, at least one kind selected from the group consisting of Au (37 to 80.5% by weight)—Cu (63 to 19.5% by weight) alloy and Au (81.5 to 82.5% by weight)—Ni (18.5 to 17.5% by weight) alloy is desirably used. These alloys have melting temperatures of 900° C. or more, and hardly melt even at a high-temperature range.
With respect to the silver alloy, for example, Ag—Cu-based alloys may be used.
With respect to the heater, a mica heater as shown in FIG. 2, a silicon rubber heater or the like may be used. Moreover, a heater in which a heating element line is simply formed on an insulating seal may also be used.
With respect to the mica heater, a heater in which a heating element such as a nichrome wire or the like, formed into an optional pattern, is sandwiched by mica plates serving as insulating members may be used. Moreover, with respect to the silicon rubber heater, a heater in which a heating element such as a nichrome wire or the like, formed into an optional pattern, is sandwiched by silicon rubber plates serving as insulating members may be used.
With respect to the heating element to heat the heater, not limited by the above-mentioned nichrome wire, another metal line, such as a tungsten line, a molybdenum line and the like, and the like may be used as long as it generates heat upon applying a voltage.
Moreover, with respect to the heating element, in addition to the metal line, metal foil may be used. With respect to the metal foil, a heating element in which nickel foil, stainless foil or the like is etched into a pattern is desirably used. The patterned metal foils may be bonded to each other by using a resin film or the like.
With respect to the insulating member used for coating the heating element, not limited to the above-mentioned mica plate and silicon rubber, for example, a material, such as fluororesin, polyimide resin, polybenzoimidazole (PBI) or the like, may be used as long as it is capable of preventing short-circuiting and of withstanding high temperatures, and a material in which fibers made from ceramics or the like are formed into a mat shape may also be used.
In the case where the metal heater has a structure in which the heater is sandwiched between metal plates, a plurality of the heaters may be provided. In this case, with respect to the patterns of the respective layers, heating elements are desirably formed in any of the layers so as to compensate for one another, and the pattern is desirably formed in any of areas, when viewed from above the heating face. Examples of such a structure include a staggered structure.
Moreover, with respect to the pattern of the heating element in the metal heaters according to the first to third aspects of the present invention, not limited to the pattern as shown in FIG. 2 and the like, for example, patterns, such as a concentric circle pattern, a spiral pattern, an eccentric circular pattern and the like, maybe used. Moreover, a combined pattern of them may be used.
The heating element is desirably divided into two or more parts, as described above.
Moreover, the area resistivity of the heating element is desirably 0.1 to 10Ω/
. When the area resistivity exceeds 10Ω/
, the diameter of the heating element needs to be made extremely smaller in order to ensure a desired quantity of heat generation, and, for this reason, even a slight chip or the like tends to cause disconnection or dispersion in resistance value. Moreover, in the case where the area resistivity is less than 0.1Ω/
, the diameter of the heating element needs to be made larger so as to ensure a sufficient quantity of heat generation; thus, the degree of freedom in designing the pattern of the heating element is lowered, and it becomes difficult to evenly control the temperature of the heating face.
With respect to the means for connecting the heating element to a power supply, as shown in FIG. 1, a part of the heating element made of metal foil is exposed to form a connecting foil, and one end of the conductive line is wrapped with the connecting foil, with an attaching member having a caulking portion attached to this portion, so that the connection is made by caulking the caulking portion, or conductive lines may be attached to the both ends of the heating element through soldering or the like so that the connection to the power supply or the like may be made through these conductive lines, or terminals may be attached to the two ends of the heating element so that the connection to the power supply or the like may be made through these terminals.
Here, the terminals are desirably attached to the heating element through soldering, brazing, crimping, caulking or the like. The terminals are desirably attached through soldering because nickel prevents thermal diffusion of solder. With respect to the connecting terminals, for example, external terminals made of Kovar may be used.
With respect to the solder used for connecting the connecting terminals, an alloy, such as a silver-lead alloy, a lead-tin alloy, a bismuth-tin alloy and the like, may be used. The thickness of the solder layer is preferably 0.1 to 50 μm. This range makes it possible to sufficiently ensure connection through soldering.
Moreover, in the metal heater according to the first to third aspects of the present invention, an intermediate plate may be interposed between the metal plate and the heater. By interposing such an intermediate plate, heat generated by the heating element can be transmitted to the metal plate in a further even state.
With respect to the material of the intermediate plate, ametal having a superior thermal conductivity is desirably used, and, for example, copper, a copper alloy or the like may be used.
In the metal heater shown in FIG. 1, the side face of the metal plate and the supporting case are in a non-contact state; however, in the case where these members are made in contact with each other, a heat insulating ring is desirably interposed between the side face of the metal plate and the supporting case. Since heat is released from the peripheral portion of the metal plate, it becomes possible to prevent temperature dispersion from occurring on the heating face of the metal plate.
The supporting case and the heat shielding plate may be integrally formed, or the heat shielding plate may be coupled and secured to the supporting case. Desirably, the supporting case and the heat shielding plate are integrally formed. Thus, it becomes possible to ensure the strength of the entire metal heater.
The supporting case desirably has a cylinder shape, and the heat shielding plate desirably has a disk shape. Moreover, the thickness of the supporting case and that of the heat shielding plate are desirably 0.1 to 5 mm. The thickness of less than 0.1 mm causes insufficient strength, and the thickness exceeding 5 mm makes the thermal capacity greater.
The supporting case and the heat shielding plate are desirably made of a metal, such as SUS, aluminum, inconel (nickel-based alloy containing 16% of chrome and 7% of iron) or the like, so as to allow easy machining and superior mechanical properties and ensure sufficient strength in the entire metal heater.
In the case where the supporting case and the heat shielding plate are not prepared as an integral part, the heat shielding plate may be made of a material, such as a heat resistant resin, a ceramic plate, a composite plate formed by blending heat-resistant organic fibers and inorganic fibers into these materials, or the like, that has a thermal conductivity that is not so high, and is superior in heat resistance, so as to achieve a superior heat shielding property.
Moreover, a coolant introducing pipe may be attached to the supporting case or the heat shielding plate. By introducing a coolant or the like used for forcibly cooling the metal heater, the metal heater can be quickly cooled. Moreover, a through hole for discharging the introduced coolant or the like for forcible cooling may be formed in the supporting case or the heat shielding plate.
In the following, description will be given of a manufacturing method of the metal heaters according to the first to third aspects of the present invention.
(1) Manufacturing Processes of Metal Plate
A plate-shaped member, made of a material such as an aluminum-copper alloy or the like, is machined at outer diameter portion by using an NC lathe and formed into a disk shape, and this plate-shaped member is then subjected to an end-face machining process, a surface machining process and a rear-face machining process in succession.
In this case, the thickness of the plate-shaped member to form an upper metal plate is made larger than the thickness of a plate-shaped member to form a lower metal plate.
Next, each of parts to be through holes into which lifter pins for supporting a semiconductor wafer are inserted, each of concave portions on which supporting pins are placed and each of parts to be bottomed holes in which a temperature measuring element, such as a thermocouple, is embedded are formed by using a machining center (MC) or the like. Moreover, after bottomed holes have been formed at predetermined positions, thread grooves are formed in the bottomed holes so that screw holes through which metal plate securing screws are inserted are formed.
In particular, in the case where the metal heater according to the third aspect of the present invention is manufactured, the concave portions for placing the supporting pins are formed in a manner so as to widely spread the supporting pins on the metal plate as well as place them with equal intervals. With respect to the layout thereof, for example, as shown in FIG. 7, a plurality of supporting pins 618 are placed on circumferences of concentric circles of the metal plate at equal intervals, with a single supporting pin 618 placed in the center portion of the metal plate. With this arrangement, upon heating the semiconductor wafer, the semiconductor wafer is made free from sagging so that the distance of a semiconductor wafer and a metal plate is made even; thus, the semiconductor wafer can be evenly heated.
Moreover, the plate-shaped member to form the upper metal plate is subjected to a surface grinding process by using a rotary grinding machine so that the upper metal plate and the lower metal plate are manufactured. By carrying out this surface grinding process, the flatness of the surface of the metal plate can be set to about 20 to 30 μm.
Furthermore, a wafer guide ring for suppressing an ambient gas (for example, air or the like) flow may be formed on the upper metal plate, if necessary. The above-mentioned wafer guide ring maybe made of, for example, an aluminum-copper alloy, SUS or the like. Moreover, a barrier ring may be formed on the uppermost portion of the supporting case for the same purpose.
By providing the wafer guide ring and the barrier ring, the ambient gas flows inside and outside the heating area are intervened so that the object to be heated can be evenly heated.
Next, the upper metal plate and the lower metal plate are subjected to an alumite treatment so that oxide coat films are formed on the surfaces of the upper metal plate and the lower metal plate. By carrying out this treatment, the corrosion resistance of the metal plate is improved with a harder surface; therefore, the metal plate becomes less likely to have scratches or the like. Moreover, even when the metal plate is used during actual semiconductor producing and examining processes, the metal plate becomes less likely to receive corrosion due to a resist solution, corrosive gases and the like.
With respect to the alumite treatment (anode oxidation coating treatment), for example, a sulfate method, an oxalate method or the like may be used, and the oxalate method is desirably used. Thus, it becomes possible to prevent surface pinholes from occurring after the treatments.
(2) Placement of Heater
A heater, formed by sandwiching a heating element such as a nichrome wire processed into a predetermined pattern, a metal foil like a stainless foil, or the like between ceramic plates such as mica plates or the like, is placed between the upper metal plate and the lower metal plate, and after metal plate securing screws have been inserted through screw holes formed in the lower metal plate and the heater, the lower metal plate and the heater are fastened into an integral part by tightening the screws.
Here, since the entire heater needs to be set to an even temperature in the heating element, a pattern or the like which is basically formed by repeatedly placing a winding line in a ring shape or repeatedly drawing a winding line in a manner so as to form a part of each of concentric circles is preferably used.
Moreover, an intermediate plate, made of a material having superior thermal conductivity such as copper or the like, may be sandwiched between the metal plate and the heater. With this arrangement, heat radiated from the heater can be transmitted to the upper metal plate in a further even state.
(3) Attachment of Supporting Case
A device in which the metal plate and the heater are integrally formed in this manner is supported in a cylinder-shaped supporting case shown in FIG. 1 and secured therein.
A heat shielding plate, made from the same material as the supportin gcase, is placed on the bottom face of the supporting case, and through holes, which allow a temperature measuring element, a conductive line and the like to pass, are formed in the supporting case.
In the metal heaters according to the first to third aspects of the present invention, as shown in FIG. 1, the side faces of the metal plate and the heater are desirably supported and secured in the supporting case in a non-contact state therewith.
This structure is prepared because the peripheral portion of the heating face of the metal plate tends to have a low temperature due to released heat from the side faces of the metal plate and the heater.
In the case where the side faces of the metal plate and the heater are supported and secured in the supporting case in a contact state therewith, a heat insulating ring made of polyimide resin, fluororesin or the like is desirably interposed between the metal plate and the supporting case.
(4) Connection to Power Supply or the Like
Terminals (external terminals) for use in connection to a power supply are attached to both ends of the heating element provided in the heater through a brazing material or solder, or by using a mechanical attaching method (attaching means) such as crimp screwing, caulking or the like, so that the heater is connected to an external power supply or the like; thus, the manufacturing processes of the metal heater are completed. Here, in the case where the metal heater according to the third aspect of the present invention is manufactured, after supporting pins formed on the heating face of the metal plate have been inserted, the supporting pins are secured by using springs or the like to complete the manufacturing processes of the metal heater.

BEST MODE FOR CARRYING OUT THE INVENTION

In the following, description will be given of the first to third aspects of the present invention by way of examples in detail.
The following examples exemplify a case in which a metal heater for heating a semiconductor wafer is used; however, the first to third aspects of the present invention may be applied to a heater for temperature adjustment for an optical waveguide.

EXAMPLE 1

Manufacturing of metal heater (see FIGS. 1 and 2)
(1) A plate-shaped member, made of an aluminum-copper alloy (A2219 (JIS-H4000)), was machined at outer-diameter portion by using an NC lathe (manufactured by Washino Machinery Co., Ltd.) and formed into a disk shape, and this plate-shaped member was then subjected to an end-face machining process, a surface machining process and a rear-face machining process so that a disk-shaped member for an upper metal plate and a disk-shaped member for a lower metal plate were manufactured.
Next, each of parts to be through holes 415 to which lifter pins used for supporting a semiconductor wafer 419 are inserted, each of concave portions in which supporting pins 418 are placed and each of parts to be a bottomed hole 414 in which a temperature measuring element 416 is embedded were formed by using a machining center (Hitachi Seiki Co., Ltd.).
Here, the through holes 415 were formed at three positions, and the concave portions for placing the supporting pins 418 were formed at nine positions.
After the bottomed holes or the through holes had been formed at predetermined positions in the same manner, thread grooves were formed in the bottomed holes or the through holes so that screw holes through which metal plate securing screws 17 are inserted were formed in the disk shape.
Here, the screw holes were formed in the upper metal plate and the plate-shaped member with a depth of ¾ of the thickness thereof.
(2) Next, the disk member for the upper metal plate, manufactured through the processes of (1), was subjected to a surface grinding process on its surface on the heating face side by using a rotary grinding machine (manufactured by Okamoto Machine Tool Works, Ltd.) so that an upper metal plate 411 having a thickness of 15 mm and a diameter of 330 mm and a lower metal plate 421 having a thickness of 5 mm and a diameter of 330 mm were obtained.
Moreover, a barrier ring 428 for suppressing a gas flow toward a semiconductor wafer that is an object to be heated was placed on a side face of the upper metal plate 411 by using the above-mentioned method.
In other words, the peripheral edge portion of the supporting case was made higher than the upper face (heating face) of the upper metal plate so that the barrier ring was formed.
Here, in this example, the thickness of the upper metal plate 411 was made larger than the thickness of the lower metal plate 421.
(3) Next, the upper metal plate 411 and the lower metal plate 421 were subjected to an alumite treatment under conditions of 10% H₂SO₄electrolytic solution, a voltage of 10 V, a current density of 0.8 A/dm²and a liquid temperature of 20° C. so that an oxide coat film having a thickness of 15 μm was formed on each of the surfaces of the upper metal plate 411 and the lower metal plate 421.
(4) A heating element 425, made of a stainless foil having a thickness of 200 μm on which a winding wire shown in FIG. 2 is placed in a repeated pattern to form a ring shape and a winding wire is repeatedly placed in a pattern so as to form a part of each of concentric circles, was sandwiched between two mica plates 426 having a thickness of 0.3 mm to obtain a heater 412 having a diameter of 330 mm.
Here, in the heater 412, the heating element 425 was formed so that the outer rim of the heating element was placed at a position within 25% of the diameter of the upper metal plate 411 from the periphery of the upper metal plate 411, and the total number of the circuits of the heating element 425 was set to four.
Moreover, parts to be through holes 415, a part to be the bottomed hole 414 and parts to be screw holes through which metal plate securing screws 417 are inserted were preliminary formed in the mica plate 426.
Thereafter, the heater 12 was sandwiched between the upper metal plate 411 and the lower metal plate 421 manufactured through the processes of (1) to (3), and after the metal plate securing screws 417 had been inserted through the screw holes formed in the lower metal plate 421 and the heater 412, the securing screws were tightened so that the upper metal plate 411, the lower metal plate 421 and the heater 412 were combined into an integral part.
(5) Next, a supporting case 420 having a cylinder shape as shown in FIG. 1, made of SUS, was manufactured, and after parts to be the through holes 415, a part to be the bottomed hole 414 and a through hole through which the conductive wire 424 is inserted had been formed in the bottom face of the supporting case 420, a heat shielding plate 423 having a disk shape, made of SUS, was placed on the bottom portion of the supporting case 420.
Moreover, the upper metal plate 411 to which the heater 412 and the lower metal plate 421 had been attached, manufactured in the process (4), was placed inside the supporting case 420 in which the heat shielding plate 423 had been placed, and fixedly secured therein so that the side faces of the upper metal plate 411, the heater 412 and the lower metal plate 621 were kept in no-contact with the supporting case 420.
Here, in the metal heater in this example, the screw head of each metal plate securing screw 417 was designed to be embedded into the lower metal plate 421 so that the bottom face of the lower metal plate 421 was made in contact with the inner face of the supporting case 420.
(6) After a temperature measuring element 416 made of a platinum temperature measuring resistor for use in controlling temperatures had been inserted into the bottomed hole 414, the bottomed hole 414 was sealed by using an inorganic adhesive (Aron ceramic, made by Toagosei Co., Ltd.) . Moreover, supporting pins 418 were placed in the concave portions formed on the heating face of the upper metal plate 411.
(7) Next, the conductive wire 424 was wrapped by a connecting foil taken out of the stainless foil serving as the heating element provided in the heater 412, and a metallic attaching member was attached thereto, and this was then caulked so that the connecting foil and the conductive wire 424 were connected to each other and secured with each other. Thus, the heating element provided in the heater 412 was connected to an external power supply or the like so that a metal heater 410 was obtained.

EXAMPLE 2

Manufacturing of Metal Heater
The same processes as those of Example 1 were carried out except that the thickness of the upper metal plate 411 was set to 20 mm and that the thickness of the lower metal plate 421 was set to 5 mm so that a metal heater was manufactured.

EXAMPLE 3

Manufacturing of Metal Heater
The same processes as those of Example 1 were carried out except that the thickness of the upper metal plate 411 was set to 25 mm and that the thickness of the lower metal plate 421 was set to 10 mm so that a metal heater was manufactured.

EXAMPLE 4

Manufacturing of Metal Heater
The same processes as those of Example 1 were carried out except that the thickness of the upper metal plate 411 was set to 40 mm and that the thickness of the lower metal plate 421 was set to 5 mm so that a metal heater was manufactured.

EXAMPLE 5

The same processes as those of Example 1 were carried out except that the thickness of the upper metal plate 411 was set to 20 mm and that the thickness of the lower metal plate 421 was set to 20 mm so that a metal heater was manufactured.

EXAMPLE 6

The same processes as those of Example 1 were carried out except that the thickness of the upper metal plate 411 was set to 36 mm and that the thickness of the lower metal plate 421 was set to 3 mm so that a metal heater was manufactured.

EXAMPLE 7

The same processes as those of Example 1 were carried out except that the thickness of the upper metal plate 411 was set to 50 mm and that the thickness of the lower metal plate 421 was set to 5 mm so that a metal heater was manufactured.

TEST EXAMPLE 1

The same processes as those of Example 1 were carried out except that in the processes of (1) to (3) in Example 1, the thickness of the upper metal plate was set to 5 mm and that the thickness of the lower metal plate was set to 20 mm so that a metal heater was manufactured. In this test example, the thickness of the lower metal plate was made larger than the thickness of the upper metal plate.

TEST EXAMPLE 2

The same processes as those of Example 1 were carried out except that in the process of (5) of Example 1, the supporting case 420 was manufactured in such a manner that the inner diameter of the supporting case 420 was made almost the same as the diameter (330 mm) of the upper metal plate 411, the heater 412 and the lower metal plate 411 are placed and fixedly secured inside the supporting case 420 with the side faces thereof being made in tightly contact with the supporting case 420; thus, a metal heater was manufactured.

COMPARATIVE EXAMPLE 1

A metal heater in which an intermediate plate made of copper and a heater were placed on the bottom face of a metal plate was manufactured. The thickness of the metal plate was 55 mm, and the pattern of the heating element was the same as that of Example 1.
A current was applied to each of the metal heaters according to Examples 1 to 7, Test Examples 1 and 2 and Comparative Example 1 to raise the temperature; thus, evaluation was made on each of the following points: (1) temperature evenness in surface in steady state, (2) temperature evenness in surface in transition period, (3) measurements on flatness; (4) overshoot amount. The results thereof are shown in Table 1.
The respective evaluating processes were carried out by using the following methods.
(1) Temperature Evenness in Surface in Steady State
After the temperature of the metal heater had been raised to 140° C., a wafer with a temperature sensor equipped with a thermocouple was placed on the heating face of the metal heater so that the distribution of temperature on the heating face was measured. The distribution of temperature was indicated by a maximum value of a temperature difference between the highest temperature and the lowest temperature during the temperature rise.
(2) Temperature Evenness in Surface in Transition Period
The wafer with a temperature sensor was heated from ordinary temperature to 140° C. by the metal heater so that the distribution of temperature in surface of the wafer with a temperature sensor was measured. The distribution of temperature was measured at 100° C., 120° C. and 130° C. respectively, and indicated by a maximum value of a temperature difference between the highest temperature and the lowest temperature.
(3) Measurements on Flatness
The flatness on the heating face of the metal plate was measured at ordinary temperature as well as at 140° C. by a laser displacement gauge (made by Keyence Corporation).
(4) Overshoot Amount
The overshoot amount (the value obtained by subtracting the set temperature (140° C.) from the maximum temperature during the process) in the case where 20 silicon wafers were processed at 140° C. was measured.

Here, with respect to the evaluation of (3) measurements on flatness, a three-dimensional shape of a part of the heating face of the metal heater according to Example 1 at ordinary temperature is shown in FIG. 8; a three-dimensional shape of a part of the heating face of the metal heater according to Example 1 at 140° C. is shown in FIG. 9; and a three-dimensional shape of a part of the heating face of the metal heater according to Test Example 1 at 140° C. is shown in FIG. 10.

TABLE 1


Thickness of	Distribution of	Distribution of
metal plate	temperature in	temperature in		Overshoot amount
(mm)	surface in	surface in	Flatness (μm)	(° C.)

	Upper	Lower	steady state	transition period	At		after processing
	metal	metal	(° C.)	(° C.)	ordinary		20 wafers at

	plate	plate		140° C.	100° C.	120° C.	130° C.	temperature		140° C.	140° C.)

Example 1	15	5	0.17	5.37	2.38	2.01	29	30	0.30
Example 2	20	5	0.24	5.38	2.80	1.51	29	30	0.35
Example 3	25	10	0.19	5.45	2.22	1.76	29	29	0.33
Example 4	40	5	0.25	4.80	2.24	1.64	28	29	0.31
Example 5	20	20	0.31	4.16	2.53	1.96	28	35	0.35
Example 6	36	3	0.32	4.20	2.53	1.95	28	36	0.30
Example 7	50	5	0.27	4.98	2.62	1.97	28	29	0.30
Test	5	20	0.44	9.56	6.66	5.10	37	47	1.32
Example 1
Test	15	5	0.36	4.78	2.67	2.13	40	53	0.35
Example 2
Comparative	55	0	0.42	5.58	3.66	2.36	44	56	0.32
Example 1

As shown in Table 1, the metal heaters according to Examples 1 to 7 had an even temperature on the heating face of the upper metal plate in steady state as well as in transition period. This is presumably because the thickness of the metal plate on the heating face side is large so that heat transmitted to the metal plate is sufficiently dispersed to prevent the pattern of the heating element from being reflected to the heating face.

Moreover, as shown in Table 1 as well as in FIGS. 8 and 9, since the flatness in the metal heaters of Examples 1 to 4 is 50 μm or less, the distance between the upper metal plate and the sensor wafer becomes less likely to have dispersion to provide an even heating process.
This is presumably because, since the metal heaters according to Examples 1 to 4 have a structure in which the lower metal plate having a fixed thickness is placed on the bottom face of the heater, thermal radiation released from the heater is made even.
Furthermore, in the metal heaters of Examples 5 and 6, the temperature evenness of the heating face in steady state is inferior to that of the metal heaters of Examples 1 to 4; however, the temperature evenness of the heating face in transition period is superior to that of the metal heaters of Examples 1 to 4.
In contrast, in the case of the metal heaters according to Test Examples 1 and 2, the temperature of the heating face of the upper metal plate was uneven in steady state as well as in transition period. This is presumably because the thickness of the upper metal plate is thin; thus, warping and sagging occur in the metal plate due to thermal expansion during the heating process.
Moreover, in the metal heater according to Comparative Example 1, since the heater is placed on the bottom face of the metal plate without the lower metal plate, the flatness of the heating face becomes inferior; thus, the temperature on the heating face becomes uneven.
With respect to the overshoot amount, the measured results of the metal heater according to Test Example 1 gave values greater than those of the measured results of the other metal heaters. This is presumably because, since the thickness of the lower metal plate is larger than the thickness of the upper metal plate with the thermal capacity of the lower metal plate being relatively greater than the thermal capacity of the upper metal plate, heat is accumulated in the lower metal plate to cause heat conduction from the lower metal plate to the upper metal plate and the subsequent overshooting phenomenon due to the heat conduction.

EXAMPLE 8

Manufacturing of Metal Heater (see FIG. 5)
(1) A plate-shaped member, made of an aluminum-copper alloy (A2219 (JIS-H4000)), was machined at outer-diameter portion by using an NC lathe (made by Washino Machinery Co., Ltd.) and formed into a disk shape, and this disk-shaped member was then subjected to an end-face machining process, a surface machining process and a rear-face machining process so that a disk-shaped member for an upper metal plate and a disk-shaped member for a lower metal plate were manufactured.
Next, each of parts to be through holes 515 to which lifter pins for supporting a semiconductor wafer 519 are inserted, each of concave portions in which supporting pins 518 are placed and a part to be a bottomed hole 514 in which a temperature measuring element 516 is embedded were formed in these disk members by using a machining center (Hitachi Seiki Co., Ltd.).
Here, the through holes 515 were formed at three positions, and the concave portions used for placing the supporting pins 518 were formed at nine positions.
After the bottomed holes or the through holes had been formed at predetermined positions in the same manner, thread grooves were formed in the bottomed holes or the through holes so that screw holes through which metal plate securing screws 517 are inserted were formed in the disk members.
Here, the screw holes were formed in the upper metal plate and the plate-shaped member with a depth of ¾ of the thickness thereof.
(2) Next, the disk member for the upper metal plate, manufactured through the processes of (1), was subjected to a surface grinding process on its surface on the heating face side by using a rotary grinding machine (made by Okamoto Machine Tool Works, Ltd.) so that an upper metal plate 511 having a thickness of 15 mm and a diameter of 330 mm and a lower metal plate 521 having a thickness of 5 mm and a diameter of 330 mm were obtained.
Moreover, a barrier ring for a wafer that is an object to be heated was formed on the side face of the upper metal plate 511 by using the following method.
In other words, the outer rim portion of the supporting case was made higher than the upper face of the heating face of the upper metal plate so that the barrier ring 532 was formed.
Here, in this example, the thickness of the upper metal plate 511 was made larger than the thickness of the lower metal plate 521.
(3) Next, the upper metal plate 511 and the lower metal plate 521 were subjected to an alumite treatment under conditions of 10% H₂SO₄electrolytic solution, a voltage of 10 V, a current density of 0.8 A/dm²and a liquid temperature of 20° C. so that an oxide coat film having a thickness of 15 μm was formed on each of the surfaces of the upper metal plate 511 and the lower metal plate 521.
(4) A heating element, made of a stainless foil having a thickness of 200 μm on which a winding wire is placed in a repeated pattern to form a ring shape and a winding wire is repeatedly placed in a pattern so as to form a part of each of concentric circles as shown in FIG. 2, was sandwiched between two mica plates having a thickness of 0.3 mm to obtain a heater 512 having a diameter of 330 mm.
Here, in the heater 512, the heating element was formed so that the outer rim of the heating element was placed at a position within 25% of the diameter of the upper metal plate 511 from the periphery of the upper metal plate 511, and the total number of the circuits of the heating element was set to four.
Moreover, parts to be through holes 515, a part to be the bottomed hole 514 and parts to be screw holes through which metal plate securing screws 517 are inserted were preliminary formed in the mica plate 526.
Thereafter, the heater 512 was sandwiched between the upper metal plate 511 and the lower metal plate 521 manufactured through the processes of (1) to (3), and after the metal plate securing screws 517 had been inserted through the screw holes formed in the lower metal plate 521 and the heater 512, the securing screws were tightened so that the upper metal plate 511, the lower metal plate 521 and the heater 512 were combined into an integral part.
(5) Next, a supporting case 520 having a cylinder shape with a bottom as shown in FIG. 5, made of SUS, was manufactured, and a supporting plate 525 was placed on the bottom face of the supporting case 520 and parts to be the through holes 515, a part to be the bottomed hole 514 and a through hole through which the conductive wire 524 was inserted had been formed in the bottom face of the supporting case 520, a heat shielding plate 523 having a disk shape, made of SUS, was placed on the bottom portion of the supporting case 520.
Moreover, the upper metal plate 511 to which the heater 512 and the lower metal plate 521 had been attached, manufactured in the process (4), was placed inside the supporting case 520 on which the heat shielding plate 523 had been placed through the supporting plate 525, and fixedly secured therein.
(6) After a temperature measuring element 516 made of a platinum temperature measuring resistor for use in controlling temperatures had been inserted into the bottomed hole 514, the bottomed hole 514 was sealed by using an inorganic bonding agent (Aron ceramic, made by Toagosei Co., Ltd.) serving as a sealing material. Moreover, supporting pins 518 were placed in the concave portions formed on the heating face of the upper metal plate 511.
(7) Next, the conductive wire 524 was wrapped by a connecting stainless foil 530 taken out of the stainless foil 529 serving as the heating element attached to the heater 512, and this was then caulked with an attaching member 531 attached thereto so that the conductive wire 524 was attached to the connecting stainless foil 530, and connected to an external power supply or the like; thus, a metal heater 510 was obtained.

EXAMPLE 9

Manufacturing of Metal Heater
The same processes as those of Example 8 were carried out except that the thickness of the upper metal plate 511 was set to 20 mm and that the thickness of the lower metal plate 521 was set to 5 mm so that a metal heater was manufactured.

EXAMPLE 10

Manufacturing of Metal Heater
The same processes as those of Example 8 were carried out except that the thickness of the upper metal plate 511 was set to 25 mm and that the thickness of the lower metal plate 521 was set to 10 mm so that a metal heater was manufactured.

EXAMPLE 11

Manufacturing of Metal Heater
The same processes as those of Example 8 were carried out except that the thickness of the upper metal plate 511 was set to 40 mm and that the thickness of the lower metal plate 521 was set to 5 mm so that a metal heater was manufactured.

TEST EXAMPLE 3

The same processes as those of Example 8 were carried out except that the lower metal plate was made of copper so that a metal heater was manufactured. In this test example, the thickness of the upper metal plate was made larger than the thickness of the lower metal plate.
A current was applied to each of the metal heaters according to Examples 8 to 11 and Test Example 3 to raise the temperature; thus, evaluation was made on each of the following points: (1) temperature evenness in surface in steady state, (2) temperature evenness in surface in transition period, (3) measurements on flatness; (4) overshoot amount. The results thereof are shown in Table 2. Here, the same evaluation method as the method of Example 1 was used.

Moreover, in the evaluation of the measurements on the flatness (5), a three dimensional shape of a part of a metal heater heating face of Example 8 at ordinary temperature is shown in FIG. 11, a three dimensional shape of a part of a metal heater heating face of Example 8 at 140° C. is shown in FIG. 12, and a three dimensional shape of a part of a metal heater heating face of Test Example 3 at 140° C. is shown in FIG. 13.

TABLE 2


Thickness of	Distribution of	Distribution of
metal plate	temperature in	temperature in		Overshoot amount
(mm)	surface in	surface in	Flatness (μm)	(° C.)

	plate	plate		140° C.	100° C.	120° C.	130° C.	temperature		140° C.	140° C.)

Example 8	15	5	0.17	5.37	2.38	1.62	29	30	0.31
Example 9	20	5	0.24	5.38	2.80	1.51	29	30	0.34
Example 10	25	10	0.19	5.45	2.22	1.76	29	29	0.32
Example 11	40	5	0.25	4.80	2.24	1.64	28	29	0.35
Test	20	5	0.52	4.48	3.33	1.86	28	40	0.30
Example 3
Comparative	55	0	0.42	5.58	3.66	2.36	44	56	0.32
Example 1

As shown in Table 2, the metal heaters according to Examples 8 to 11 had an even temperature on the heating face of the upper metal plate in steady state as well as in transition period. This is presumably because, since the material of the metal plate on the heating face side as well as on the opposite side was the same, the thermal expansion coefficient was equal so that no warping occurs even upon a temperature rise; thus, no dispersion occurs in the distance between the wafer and the heating face, making it possible to carry out an even heating process.
In contrast, in the case of the metal heater according to Test Example 3, since the materials of the upper metal plate and the lower metal plate are different from each other, the thermal expansion coefficients are different from each other, with the result that a deformation occurs upon heating to cause dispersion in the temperature of the heating face.
Moreover, the metal heaters according to Examples 8 to 11 have superior temperature evenness on the heating face in steady state as well as in transition period, in comparison with the metal heater according to the above-mentioned Comparative Example 1.
With respect to the overshoot amount, all the metal heaters according to Examples 8 to 11, Test Example 3 and Comparative Example 1 had almost the same measured results.

EXAMPLE 12

Manufacturing of Metal Heater (see FIGS. 6(a) and 6(b), and FIG. 7)
(1) A plate-shaped member, made of an aluminum-copper alloy (A2219 (JIS-H4000)), was machined at outer diameter portion by using an NC lathe (made by Washino Machinery Co., Ltd.) and formed into a disk shape, and this disk-shaped member was then subjected to an end-face machining process, a surface machining process and a rear-face machining process so that a disk-shaped member for an upper metal plate and a disk-shaped member for a lower metal plate were manufactured.
Next, each of parts to be through holes 615 to which lifter pins used for supporting a semiconductor wafer 619 are inserted, each of parts to be concave portions 628 in which supporting pins 618 are placed and a part to be a bottomed hole 614 in which a temperature measuring element 616 is embedded were formed in this disk-shaped member by using a machining center (Hitachi Seiki Co., Ltd.).
Here, the through holes 615 were formed at three positions, and the concave portions used for placing the supporting pins 618 were formed at nine positions. With respect to the layout of the positions, as shown in FIG. 6(a), eight supporting pins were placed on circumferences of concentric circles of the upper metal plate with equal intervals, and a single supporting pin was placed in the center portion of the upper metal plate.
After the bottomed holes or the through holes had been formed at predetermined positions in the same manner, thread grooves were formed in the bottomed holes or the through holes so that screw holes through which metal plate securing screws 617 are inserted were formed in the disk member.
Here, the screw holes were formed in the upper metal plate and the plate-shaped member with a depth of ¾ of the thickness thereof.
(2) Next, the disk member for the upper metal plate, manufactured through the processes of (1), was subjected to a surface grinding process on its surface on the heating face side by using a rotary grinding machine (manufactured by Okamoto Machine Tool Works, Ltd.) so that an upper metal plate 611 having a thickness of 15 mm and a diameter of 330 mm and a lower metal plate 621 having a thickness of 5 mm and a diameter of 330 mm were obtained.
Moreover, a barrier ring for a wafer that is an object to be heated was formed on the side face of the upper metal plate 611 by using the following method. In other words, the outer rim portion of the supporting case was made higher than the upper face of the heating face of the upper metal plate so that the barrier ring 632 was formed.
Here, in this example, the thickness of the upper metal plate 611 was made larger than the thickness of the lower metal plate 621.
(3) Next, the upper metal plate 611 and the lower metal plate 621 were subjected to an alumite treatment under conditions of 10% H₂SO₄electrolytic solution, a voltage of 10 V, a current density of 0.8 A/dm²and a liquid temperature of 20° C. so that an oxide coat film having a thickness of 15 μm was formed on each of the surfaces of the upper metal plate 611 and the lower metal plate 621.
(4) A heating element, made of a stainless foil having a thickness of 200 μm on which, as shown in FIG. 7, a winding wire is repeatedly placed in a repeated pattern to form a ring shape and a winding wire is repeatedly placed in a pattern so as to form a part of each of concentric circles, was sandwiched between two mica plates having a thickness of 0.3 mm to obtain a heater 612 having a diameter of 330 mm.
Here, in the heater 612, the heating element was formed so that the area including the heating element had a diameter of 320 mm, and the total number of the circuits of the heating element was set to four.
Moreover, parts to be through holes 615, a part to be the bottomed hole 614 and parts to be screw holes through which metal plate securing screws 617 are inserted were preliminary formed in the mica plate 626.
Thereafter, the heater 612 was sandwiched between the upper metal plate 611 and the lower metal plate 621 manufactured through the processes of (1) to (3), and after the metal plate securing screws 617 had been inserted through the screw holes provided in the lower metal plate 621 and the heater 612, the securing screws were tightened so that the upper metal plate 611, the lower metal plate 621 and the heater 612 were combined into an integral part.
(5) Next, a supporting case 620 having a cylinder shape with a bottom as shown in FIG. 6(a), made of SUS, was manufactured, and a supporting plate 625 was placed on the bottom face of this supporting case 620; then, after parts to be the through holes 615, apart to be the bottomed hole 614 and a through hole through which the conductive wire 624 is inserted had been formed in the bottom face of the supporting case 620, a heat shielding plate 623 having a cylinder shape, made of SUS, was placed on the bottom portion of the supporting case 620.
Moreover, the upper metal plate 611 to which the heater 612 and the lower metal plate 621 had been attached, manufactured in (4), was placed inside the supporting case 620 in which the heat shielding plate 623 had been placed, and fixedly secured therein through the supporting plate 625.
(6) After a Pt temperature measuring element 616 made of a Pt temperature measuring resistor for use in controlling temperatures had been inserted into the bottomed hole 614, the bottomed hole 614 was sealed by using an inorganic bonding agent (Aron ceramic, made by Toagosei Co., Ltd.). Moreover, supporting pins 618 having a shape as shown in FIG. 6(a), made of alumina, were inserted into nine concave portions 628 formed on the heating face of the upper metal plate 611, and a spring 627 having a C-shape was fitted to each concave portion 628 in a manner so as to surround each supporting pin 618 so that the supporting pins were fixedly secured onto the heating face 611 a of the upper metal plate 611.
(7) Next, the conductive wire 624 was wrapped by a connecting stainless foil 630 taken out of a stainless foil 629 serving as the heating element provided in the heater 612, and an attaching member 631 was attached thereto, and this was then caulked so that the conductive wire 624 was attached to the connecting stainless foil 630, and connected to an external power supply or the like; thus, a metal heater 610 was obtained.

EXAMPLE 13

Manufacturing of Metal Heater
The same processes as those of Example 12 were carried out except that the thickness of the upper metal plate 611 was set to 20 mm and that the thickness of the lower metal plate 621 was set to 5 mm, with the number of pins set to six in total, one in the center and five on the same circumference on the periphery thereof, so that a metal heater was manufactured.

EXAMPLE 14

Manufacturing of Metal Heater
The same processes as those of Example 12 were carried out except that the thickness of the upper metal plate 611 was set to 25 mm and that the thickness of the lower metal plate 621 was set to 10 mm, with the number of pins set to nineteen in total, one in the center, six on the same circumference on the periphery thereof, and twelve on the same circumference located outside thereof, so that a metal heater was manufactured.

EXAMPLE 15

Manufacturing of Metal Heater
The same processes as those of Example 12 were carried out except that the thickness of the upper metal plate 611 was set to 40 mm and that the thickness of the lower metal plate 621 was set to 5 mm so that a metal heater was manufactured.

EXAMPLE 16

The same processes as those of Example 12 were carried out except that in the process (2) of Example 12, five concave portions for placing supporting pins were formed on the surface on the heating face side of the circular plate member for the upper metal plate and that in the process (6) thereof, supporting pins were placed in the five concave portions formed on the heating face of the upper metal plate so that a metal heater was manufactured. In Example 16, total five supporting pins were placed on the heating face of the upper metal plate with a layout in which four supporting pins were placed on circumferences of concentric circles of the upper metal plate with equal intervals, with a single supporting pin placed in the center of the upper metal plate.

EXAMPLE 17

In this example, the same processes as those of Example 12 were carried out except that the heater had a diameter of 220 mm, and that the number of pins was set to five in total, that is, one in the center and four on the same circumference on the periphery thereof; thus, a metal heater was manufactured.

EXAMPLE 18

In this example, the same processes as those of Example 12 were carried out except that the heater had a diameter of 220 mm, and that the number of pins was set to fifteen in total, that is, one in the center, four on the same circumference on the periphery thereof and ten on the same circumference outside thereof; thus, a metal heater was manufactured.

TEST EXAMPLE 4

In this test example, the same processes as those of Example 12 were carried out except that the number of pins was set to four in total, that is, one in the center and three on the same circumference on the periphery thereof so that a metal heater was manufactured.

TEST EXAMPLE 5

In this test example, the same processes as those of Example 17 were carried out except that three supporting pins were placed on circumferences of concentric circles of the upper metal plate with equal intervals so that a metal heater was manufactured.

COMPARATIVE EXAMPLE 2

A metal heater in which an intermediate plate made of copper and a heater were placed on the bottom face of a metal plate was manufactured. The thickness of the metal plate was 55 mm, and the pattern of the heating element was the same as that of Example 12, without any supporting pins.
A current was applied to each of the metal heaters according to Examples 12 to 18, Test Examples 4 and5and Comparative Example 2 to raise the temperature; thus, evaluation was made on each of the following points: (1) temperature evenness in surface in steady state, (2) temperature evenness in surface in transition period, (3) measurements on flatness; (4) overshoot amount. The results thereof are shown in Table 3. Here, the same evaluation method as that of Example 1 was used.
Here, with respect to the evaluation of (2) temperature evenness in surface in transition period, the relationship between the temperature and time at each of measuring points of the wafer with a temperature sensor, obtained when measurements are carried out by using the metal heater according to Example 12, is shown in each of FIGS. 14 to 16, and the relationship between the temperature and time at each of measuring points of the wafer with a temperature sensor, obtained when measurements are carried out by using the metal heater according to Example 16, is shown in each of FIGS. 17 to 19.
FIGS. 14 and 17 show the relationship between the temperature and time in the vicinity of 100° C.; FIGS. 15 and 18 show the relationship between the temperature and time in the vicinity of 120 to 130° C.; and FIGS. 16 and 19 show the relationship between the temperature and time in the vicinity of 140° C.

Moreover, with respect to (3) measurements on flatness, a three-dimensional shape of a part of the heating face of the metal heater according to Example 12 at ordinary temperature is shown in FIG. 20; a three-dimensional shape of a part of the heating face of the metal heater according to Example 12 at 140° C. is shown in FIG. 21; and a three-dimensional shape of a part of the heating face of the metal heater according to Comparative Example 2 at 140° C. is shown in FIG. 22.

TABLE 3


Thickness of	Distribution of	Distribution of
metal plate	temperature in	temperature in		Overshoot amount
(mm)	surface in	surface in	Flatness (μm)	(° C.)

	plate	plate		140° C.	100° C.	120° C.	130° C.	temperature		140° C.	140° C.

Example 12	15	5	0.17	5.37	2.38	2.01	29	30	0.30
Example 13	20	5	0.24	5.38	2.80	1.51	29	30	0.33
Example 14	25	10	0.19	5.45	2.22	1.76	29	29	0.32
Example 15	40	5	0.25	4.80	2.24	1.64	28	29	0.35
Example 16	15	5	0.38	17.30	12.19	7.53	29	30	0.31
Example 17	15	15	0.18	5.31	2.30	2.00	29	30	0.34
Example 18	15	15	0.19	5.20	2.75	1.86	29	30	0.33
Test	15	5	0.25	11.90	8.20	5.20	30	33	0.30
Example 4
Test	15	15	0.29	12.67	10.00	5.75	29	30	0.35
Example 5
Comparative	55	0	1.31	20.00	15.30	9.38	44	56	0.34
Example 2

As shown in Table 3 as well as in FIGS. 14 to 16, the metal heaters according to Examples 12 to 15 had an even temperature on the heating face of the upper metal plate in steady state as well as in transition period. This is presumably because, since the thickness of the metal plate on the heating face side is higher than a certain value, heat, transmitted through the metal plate, is sufficiently dispersed so that the pattern of the heating element is not reflected to the heating face.
Moreover, the fact that the temperature is maintained in an even level, in particular, in transition period is because, since the interval between the supporting pins is narrow, no sagging occurs in the sensor wafer so that no dispersion occurs in the distance between the heating face of the upper metal plate and the sensor wafer.
Since the metal heaters according to examples 12 to 15 are allowed to have a flatness of 50 μm or less, as shown in Table 3 as well as in FIGS. 20 and 21, no dispersion occurs in the distance between the upper metal plate and the sensor wafer, making it possible to carry out an even heating process.
Furthermore, in the metal heaters according to examples 12 to 15, since the lower metal plate having a certain thickness is placed on the bottom face of the heater, thermal radiation released from the heater is made even.
In contrast, in the case of the metal heater according to Example 16, in transition period, the temperature on the heating face of the upper metal plate became uneven as shown in Table 3 and FIGS. 17 to 19. The reason that dispersion occur in the temperature of the heating face is because, since the interval between the supporting pins is wider, slight sagging occurs in the sensor wafer, with the result that slight dispersion occur in the distance between the heating face of the upper metal plate and the sensor wafer. In this case, however, the temperature on the heating face of the upper metal plate is maintained in an almost even level in steady state, causing no serious problems in practical use.
Moreover, in the metal heaters according to Examples 17 and 18, as shown in Table 3, the temperature on the heating face of the upper metal plate is maintained in an even level in steady state as well as in transition period. This is presumably because, since a sufficient number of supporting pins are arranged on the heating face, the clearance between the heating face and the semiconductor wafer is precisely maintained without any sagging in the semiconductor wafer; thus, it becomes possible to easily ensure the evenness in the temperature of the heating face, in particular, the evenness in the temperature of the heating face in transition period.
As shown in Table 3, in the case of the metal heater according to Test Example 4, the temperature on the heating face of the upper metal plate becomes uneven in transition period, in comparison with the metal heater according to Example 12. Moreover, in the case of the metal heater according to Test Example 5, as shown in Table 3, the temperature on the heating face of the upper metal plate becomes uneven in transition period, in comparison with the metal heater according to Example 17. The reason that dispersion occur in the temperature on the heating face in transition period is because, since the interval between the supporting pins is wide, slight sagging occurs in the sensor wafer to cause slight dispersion in the distance between the heating face of the upper metal plate and the sensor wafer.
As shown in Table 3, in the case of the metal heater according to Comparative Example 2, the temperature on the heating face of the upper metal plate is uneven in steady state as well as in transition period. The reason that dispersion occur in the temperature on the heating face is presumably because big undulation occurs to cause dispersion in the distance between the metal plate and the sensor wafer.
With respect to the overshoot amount, all the measured results of the metal heaters according to Examples 8 to 11, Test Example 3 and Comparative Example 1 are almost the same.

INDUSTRIAL APPLICABILITY

As described above, the metal heater according to the first aspect of the present invention makes it possible to more quickly heat an object to be heated, such as a semiconductor wafer or the like, in comparison with a metal heater that is formed by a single metal plate with a heater placed on the side opposite to the heating face side of the metal plate.
Moreover, since the metal heater according to the first aspect of the present invention is designed so that the thickness of the metal plate on the heating face side is the same as, or larger than the thickness of a metal plate on the side opposite to the heating face side, the flatness of the heating face is improved at the time of heating, and the temperature evenness is also improved so that it becomes possible to evenly heat the entire semiconductor wafer.
As described above, the metal heater according to the second aspect of the present invention makes it possible to more quickly heat an object to be heated, such as a semiconductor wafer or the like, in comparison with a metal heater that is formed by a single metal plate with a heater placed on the side opposite to the heating face side of the metal plate.
Moreover, since the metal heater according to the second aspect of the present invention is designed so that a plurality of metal plates constituting the metal heater are made from the same material, the flatness of the heating face is improved at the time of heating, and the distance between the semiconductor wafer and the object to be heated can be made constant so that it becomes possible to heat the semiconductor wafer or the like evenly.
As described above, the metal heater according to the third aspect of the present invention makes it possible to more quickly heat an object to be heated, such as a semiconductor wafer or the like, in comparison with a metal heater that is formed by a single metal plate with a heater placed on the side opposite to the heating face side of the metal plate.
Moreover, since the metal heater according to the third aspect of the present invention is designed so that a convex portion for supporting an object to be heated is placed on the heating face opposing the object to be heated of the metal plate corresponding to an area on which a heating element is formed, it is possible to make a semiconductor wafer or the like, that is, the object to be heated, less likely to generate sagging; thus, the distance between the semiconductor wafer or the like and the heating face of the metal plate can be made constant so that it becomes possible to heat the semiconductor wafer or the like evenly.

Claims

1. A metal heater comprising a metal plate and a heating element,

wherein

the number of said metal plates is a plural number,

said heating element is sandwiched between said metal plates, and

the thickness of a metal plate on a heating face side is the same as or larger than the thickness of a metal plate on a side opposite to said heating face side.

2. The metal heater according to claim 1,

wherein

said heating element is divided into two or more portions.

3. A metal heater comprising a plurality of metal plates and a heating element, said heating element sandwiched between said metal plates,

wherein

said plurality of metal plates are made of the same material.

4. The metal heater according to claim 3,

wherein

said plurality of metal plates comprises a copper-aluminum alloy.

5. A metal heater comprising a plurality of metal plates and a heating element, with said heating element sandwiched between said metal plates,

wherein

a convex portion for supporting an object to be heated is placed on a heating face opposing the object to be heated, of said metal plate corresponding to an area on which said heating element is formed.

6. The metal heater according to claim 5,

wherein

the area on which said heating element is formed has a diameter of 250 mm or more, and the number of convex portions is 6 or more.

7. The metal heater according to claim 5,

wherein

the area on which said heating element is formed has a diameter of 200 to 250 mm, and the number of said convex portions is 5 or more.

8. The metal heater according to any of claims 5 to 7,

wherein

said heating element is divided into two or more portions.