JPH02199832A - Wafer polishing apparatus - Google Patents

Abstract

PURPOSE:To prevent a defective flatness caused by an uneven heat distribution on the surface of a polishing cloth and to process an extremely highly accurate flatness of a wafer by a method wherein the surface itself of the polishing cloth is cooled directly and, in addition, only a part where processing heat has been generated inside the surface of the polishing cloth is cooled locally. CONSTITUTION:An inside passage 6 used to circulate a cooling liquid 6a via introduced exists 12, 13 of the cooling liquid which have been installed at side parts of a shaft 11 is formed on the back side of a surface plate 8; heat is removed from the back side of the surface plate 8. In addition, the following are arranged, on the surface of a turntable 1, by using the shaft 11 of the surface plate 8 as the center in symmetrical positions in its peripheral direction; a polishing station 30 which holds a wafer 5; a cooling station 20 which removes processing heat generated when the wafer 5 is polished. Compressed air whole pressure has been adjusted in accordance with a polishing pressure and a speed of revolution and which has been cooled and controlled to a prescribed temperature is sprayed toward a face of a polishing cloth 2 from a air nozzle 21; the processing heat is removed.

Description

[Detailed Description of the Invention] "Industrial Application Field" The present invention realizes control of the temperature of the surface of the polishing cloth during polishing and uniformity of its distribution, thereby achieving mirror finishing of the semiconductor wafer surface with a high degree of flatness. The present invention relates to a polishing apparatus for polishing, and particularly to a polishing apparatus equipped with cooling means and/or heating means for cooling the surface of a polishing cloth that rubs the surface of the wafer through an abrasive.

"Conventional Technology" Traditionally, semiconductor wafers, which serve as the base for manufacturing semiconductor devices such as diodes, transistors, ICs (integrated circuits), and LSIs (large-scale integrated circuits), have been made of single crystal semiconductors such as silicon and germanium. After slicing the inbod F into wafers, it is further lapped and etched, and then at least one surface is subjected to a polishing method called mechanochemical boring (a polishing method that combines mechanical polishing and chemical polishing). It is formed by mirror polishing the base.

Such a polishing device is, for example, as shown in FIG. 1 (the device shown in FIG. 1 is an embodiment of the present invention, but is used for reference in order to explain the prior art). a turntable l which is attached with a turntable 1 and rotates by receiving a driving force from the outside; a plate 3 which is positioned on the table l via an abrasive cloth 2 and has one or more semiconductor wafers 5 fixed to its lower surface; It consists of a head part 4 that applies a pressing force from the upper surface side of the plate 3, and a slurry pipe 5 and a turntable l.
While dispersing the liquid chemical polishing agent 7 containing abrasive grains such as 5i02 onto the polishing cloth 2 using the centrifugal force generated by the rotation of the semiconductor wafer 5 and the polishing cloth 2 (abrasive agent 7). However, in order to accurately borize the wafer 5, it is necessary to perform processing that affects the flatness of the table 1, the quality of the wafer 5, the physical properties of the polishing process, etc. It is necessary to keep the temperature constant.

For this purpose, in a known device, an internal passage B is provided in the turntable l, and while a cooling liquid 6a whose flow rate and temperature are controlled is circulated in the passage, the abrasive 7 is dispersed on the surface of the polishing cloth. In order to suppress temperature fluctuations during the processing as much as possible using a wheel that controls the temperature of the table 1, and to further improve the flatness of the surface of the table 1 and facilitate the formation of the internal passage 6.

The table l is composed of a surface plate 8 having a high and flat upper surface bordering on the position where the internal passage 8 is formed, and a surface plate support 8 that rigidly supports the surface plate 8, and both are integrally connected by screws or the like. It is fixed to

The surface plate support 8 and the surface plate 8 are formed of materials having substantially the same coefficient of thermal expansion in order to prevent flatness defects due to thermal distortion as much as possible, and the upper surface shape of the surface plate 8 is adjusted to the temperature of the cooling liquid 8a. The top surface is configured to have a slightly convex or concave shape at room temperature, which is approximately equivalent to , and the top surface shape becomes flat when the temperature rises to approximately the processing temperature due to frictional heat caused by the rubbing of the wafer 5. There is.

"Problems to be Solved by the Invention" Now, the polishing cloth 2 is not rubbed uniformly over the entire surface by the wafer 5, but the polishing load is uneven, resulting in the amount of processing heat accumulated and the temperature distribution on the surface of the polishing cloth. becomes non-uniform, resulting in poor wafer flatness.

Therefore, miniaturization of semiconductor elements formed on chips,
In the current situation where surface finishing accuracy such as flatness and parallelism of the wafer 53 surface is being set to sub-micron or less due to higher integration, polishing equipment must be designed taking into account even the minute flatness defects as mentioned above. need to be done.

Conventionally, in order to remove machining heat, the constant 918 has been formed of a material with high thermal conductivity, and the amount of heat absorbed energy (flow rate or machining temperature) of the cooling liquid 6a flowing through the back side of the surface plate 8 has been conventionally used. Attempts have been made to eliminate the above-mentioned drawbacks by increasing the temperature difference, etc., but favorable results have not always been obtained for the following reasons.

That is, in the former method, the temperature of the surface plate 8 itself is equalized, but the polishing cloth 2 attached to the surface of the surface plate 8 is made of non-woven fabric or resin material, and the polishing cloth 2 has minute particles. Since many voids are built-in, the heat insulation effect is large, and the above-mentioned drawbacks cannot be solved.

Furthermore, there is also a device that removes heat from the back side of the plate 3 holding the wafer 3 using a cooling liquid 8a or the like, which locally cools only the area where processing heat is generated.
Even in such a device, the above-mentioned drawbacks cannot be solved.

In these conventional techniques, not only is the temperature distribution not uniform, but processing heat is removed by cooling the surface plate or the back of the plate, which causes a heat flow to flow through them, resulting in a temperature difference between the front and back surfaces. However, this temperature difference causes thermal distortion. Since the surface plate and the plate are the reference planes for obtaining flat wafers, if these reference planes are distorted, flat knees cannot be obtained.

In view of the drawbacks of the prior art, the present invention prevents flatness defects caused by uneven surface heat distribution on the surface of the surface plate and of the polishing cloth attached to the surface of the surface plate.

The purpose is to provide a polishing device that can achieve finishing accuracy on the submicron level.

Another object of the present invention is to provide a polishing apparatus capable of extremely highly accurate wafer flatness processing with a simple configuration.

"Means for Solving the Problem" The first invention as set forth in claim 1) removes the machining heat accumulated on the polishing cloth 2 from the back side of the surface plate 8 or plate 3, as in the prior art. It is not intended to be removed, and the surface plate B
The method described above does not attempt to cool or heat the entire surface of the polishing cloth, but directly cools the surface of the polishing cloth itself, and further locally cools only the portion of the surface of the polishing cloth where processing heat is generated. As shown in Fig. 1 and Fig. 3, wave distortion is shown in Fig. 3. Cooling means 21, 2 can be installed at predetermined locations on the polishing cloth.
5.28 is arranged, (2) This aims to remove the processing heat caused by the wafer rubbing on the polishing cloth and the rubbing from the cooling means 21, 25.28, and improves the temperature distribution on the polishing cloth surface. The structural requirement is to reduce non-uniformity as much as possible.

Such a configuration is placed on the polishing cloth, for example, when the polishing cloth is attached to a rotatable disc surface plate. This can be easily achieved by arranging the polishing station 30 that holds the wafer and the cooling station 20 that removes processing heat generated during polishing the wafer at symmetrical positions in the circumferential direction of the surface plate with the rotation axis of the surface plate as the center.

According to this configuration, since only the part 2A where machining heat is generated is directly cooled, the heat removal effect is high and the machining heat can be quickly removed. Since the temperature distribution on the surface of the polished polishing cloth becomes uniform, it is possible to prevent undulations caused by local differences in the heat distribution of the polishing cloth that hinder high flatness polishing, and it is possible to perform high flatness polishing. .

In this case, it is preferable that the heat removal effect imparted to the polishing cloth from the cooling station 20 is configured to be variable in response to variations in polishing pressure, rotation speed, and other polishing conditions, thereby further improving the effect. .

Furthermore, the cooling medium for the cooling 21, 25, and 28 includes a culture medium,
For example, when pressure gas is used as the cooling medium of the cooling means 21, the gas is injected onto the polishing body while the liquid polishing agent moistened in the polishing cloth is heated. The water is evaporated, and the latent heat of vaporization removed at this time is used to cool and control the temperature.

In addition, when the liquid abrasive 7 cooled to the processing temperature is used as the cooling medium of the cooling means 2B, the abrasive is blown onto the surface of the polishing cloth in the form of a jet, and the processing heat retained in the gaps of the polishing cloth lowers the temperature. This method, in which cooling is performed by replacing the abrasive that has become dry with a cooled abrasive, has the additional effect that wafers can always be polished with fresh abrasive.

Now, the first aspect of the invention is that in order to prevent the abrasive from being contaminated by impurities in the pressurized gas, the pressure gas must be purified, or the droplets generated when the liquid abrasive is sprayed onto the polishing cloth. There are disadvantages such as the need to prevent contamination of the working environment caused by.

In order to avoid such drawbacks and to achieve the same effect as the invention described above, that is, to eliminate unevenness in the temperature distribution on the surface of the polishing cloth due to processing heat generated during polishing, we have developed a vehicle that heats the low-temperature region of the surface of the polishing cloth by thermal radiation from a heating means. A characteristic polishing apparatus is proposed in claim 2). This is the second invention.

In this case, it is preferable that the heating means is configured to be able to adjust the heating area and amount of heat. For example, by configuring the heater to be able to irradiate the polishing cloth with radiant heat via a heating control plate, the difference in temperature distribution can be further improved. This enables highly accurate wafer flatness processing.

The invention described in claim 2 (3) is mainly a combination of the first invention and the second invention, and has the effects of both the inventions. In this case, (cold) thermal energy includes both cooling and heating energy.

"Embodiments" Hereinafter, preferred embodiments of the present invention will be described in detail by way of example with reference to the drawings. However, unless otherwise specified, the dimensions, materials, shapes, and relative positions of the components described in this example are not intended to limit the scope of this invention, but are merely illustrative. Just an example.

FIG. 1 is a front sectional view showing a polishing apparatus according to a first embodiment of the present invention.

As described above, the turntable l is constructed by integrally fixing the surface plate 8 with the polishing cloth 2 attached to the high and flat upper surface and the surface plate support 8 that rigidly supports the surface plate 8 with screws or the like. and a rotating shaft 11 provided on the lower axis of the surface plate support 9.
It is configured to be rotatable around the center by an external drive.

The constant ff18 and the surface plate support e are made of metal materials having good thermal conductivity and similar coefficients of thermal expansion, and a cooling liquid 8a is introduced on the back side of the constant g18 on the side of the rotating shaft 11. An internal passage B is formed in which the cooling liquid 6a circulates through the outlet 12, 13, and heat is removed from the back side of the surface plate 8.

Also said turntable! A slurry pipe 5 that opens on the surface of the polishing cloth 21 is installed on the axis of the polishing cloth 21, and liquid abrasive 7 introduced from the slurry pipe 5 can be dispersed onto the polishing cloth 2 by the action of centrifugal force due to the rotation of the table l. Configure. The polishing agent 7 used is a suspension of silica in an alkaline aqueous solution.

Meanwhile said turntable! On the top surface, a polishing station 30 that holds the wafer 5 and a cooling stage 20 that removes processing heat generated during polishing of the wafer 5 are arranged at symmetrical positions in the circumferential direction around the rotation axis 11 having a constant f118. are doing.

As described above, the polishing stage plate 30 consists of the plate 3 that holds the wafer 5 in a highly flat state and the mount head 4 attached to the back side of the plate 3, and the head salt applies a predetermined pressing force from above. The plate 3 is configured to be rotatable at the same rotation speed in synchronization with the surface plate 8 through the rotating shaft 11 while being rotated, and an internal gap 40 is provided on the back side of the plate 3 through which a cooling liquid circulates through one passage. It is configured to remove the heat generated during polishing.

The cooling stage weight 20 includes an air nozzle 21 located above the polishing cloth 2, a regulating valve 22 that adjusts the pressure of the pressurized air supplied to the nozzle 21, and a regulating valve 22 located downstream of the regulating valve 22 to maintain a predetermined pressure. A cooler 23 that controls cooling of the regulated pressure air to a predetermined temperature. To change the polishing pressure and rotation speed, a microprocessor controls the degree of opening and closing of the regulating valve 22 in accordance with the surface temperature of the polishing cloth after passing through the polishing station 30.
24 and a pressure source 28.

Then, from the air nozzle 21, pressurized air whose pressure is adjusted according to the polishing pressure and rotational speed and which is cooled and controlled to a predetermined temperature is injected toward the surface of the polishing cloth 2, and the pressure air cools the polishing cloth with sensible heat. The pressurized air evaporates moisture in the polishing agent moistened on the polishing cloth 2, and processing heat is removed by the latent heat of vaporization taken away at that time.

The inventor of the present invention conducted an uninvented confirmation experiment using the device with the above configuration, and found that the flatness was different when pressurized air was blown from the air nozzle 21 and when it was not blown. It was confirmed that there was a significant improvement.

In this example, the air blown onto the surface of the polishing cloth was at room temperature and had a flow rate of 1801/win. The nozzle position of the air nozzle 21 was placed at a height of 10 cm from the polishing cloth, and the shape of the nozzle was devised so that the jetted air spread uniformly over a range of 15 cm in diameter. It was found that the temperature distribution on the surface of the polishing cloth was significantly improved by air blowing. This effect of temperature distribution improvement, which is shown in the figure, is closely related to the above-mentioned significant improvement in the flatness of the polished wafer shown in FIG. 4.

In addition to the air nozzle 21, the cooling station 20 has a metal cylinder 25 in which a cooling liquid 25a circulates, as shown in FIG. 2, which is brought into direct contact with the surface of the polishing cloth 2. It may be configured to be cooled.

Furthermore, an infrared lamp may be placed above the polishing cloth 2 to apply heat to the low temperature region of the surface of the polishing cloth.

In this case, there is a heating area control that can arbitrarily adjust the heating area of the radiant heat from the infrared lamp 40 between the above-mentioned constant 518! By intervening t41 or electrically controlling the intensity of the infrared rays, the temperature distribution difference can be further alleviated, and thereby the flatness processing of the wafer 5 can be performed with higher precision.

FIG. 3 shows another embodiment in which the abrasive itself is used as a cooling medium.

In this embodiment, the slurry pipe 5 is not installed on the central axis of the surface plate 8, but an abrasive jet nozzle 28 is installed at a position above the surface plate 8 corresponding to the cooling station 2°. Abrasive 7 cooled to a predetermined temperature
It is constructed so that it is ejected directly onto the polishing cloth 2 and collides with it.

According to this embodiment, the abrasive whose temperature has increased due to processing heat held in the voids in the polishing cloth 2 due to the ejection pressure of the abrasive 7 itself is replaced by cooled fresh abrasive. Processing heat is removed. or,
In this embodiment, since the liquid abrasive 7 itself is used as the pressure fluid that functions as a cooling medium, the pressure fluid is directly applied to the polishing cloth 2.
Even when the abrasive is ejected upward, the composition ratio of the abrasive 7 does not change, which is preferable.

In order to facilitate the replacement of the abrasive, it is advantageous to use a porous sheet as the abrasive cloth 2, and such a abrasive cloth 2 is made mainly of non-woven fabric or polymer elastomer with micro open cells formed therein. It is possible to use a resin bat etc.

"Effects of the Invention" As described above, according to the present invention, by applying (cold) thermal energy directly to a predetermined location on the polishing cloth, it is possible to reduce as much as possible the non-uniformity of the temperature distribution on the surface of the polishing cloth. In particular, by directly cooling the polishing cloth itself, and by locally cooling only the part of the polishing cloth where processing heat is generated, the surface plate and the polishing material attached to the surface of the surface plate can be cooled. In order to prevent flatness defects caused by local heat distribution differences in the cloth and enable high-precision wafer flatness processing, it is possible to provide a polishing device that can achieve finishing accuracy on the submicron level. It has various effects such as:

[Brief explanation of the drawing]

FIGS. 1(A) and 2(B) are a schematic sectional view and a plan view showing a polishing apparatus according to an embodiment of the invention set forth in claim 2), and FIG. FIG. 2 is a schematic diagram showing a polishing apparatus according to an embodiment of the invention as set forth in claim 3). FIGS. 4(A) and 4(CB) are graphs for confirming the effects of the present invention, in which (A) shows the temperature distribution and CB) shows the flatness state of the wafer. Patent applicant: Shin-Etsu Semiconductor Co., Ltd.

Claims (1)

[Scope of Claims] 1) In a polishing apparatus that polishes a semiconductor wafer by the rubbing motion of a polishing cloth while periodically moving relative to the polishing cloth, heat can be removed from a portion of the polishing cloth where the wafer is rubbed. A polishing device 2 characterized in that a cooling means is disposed at a predetermined location on the polishing cloth, thereby directly absorbing heat from the high temperature region on the polishing cloth, and reducing non-uniformity of temperature distribution on the surface of the polishing cloth as much as possible. ) In a polishing apparatus that polishes a semiconductor wafer by the sliding movement of a polishing cloth while periodically moving the polishing cloth relative to the polishing cloth, a heating means is arranged at a predetermined location on the polishing cloth. A polishing device characterized by reducing the non-uniformity of the temperature distribution on the surface of the polishing cloth as much as possible while directly applying heat. 3) Polishing a semiconductor wafer by the sliding movement of the polishing cloth while periodically moving it relative to the polishing cloth. The polishing apparatus is characterized in that a cooling means and a heating means are arranged at predetermined locations on the polishing cloth, so that cooling or heating is possible at or near the portion of the polishing cloth where the wafer is rubbed. polishing equipment. 4) The amount of thermal energy applied to or removed from the polishing cloth by the cooling means and the heating means is configured to be variable in response to variations in polishing pressure, rotation speed, and other polishing conditions. ) or the polishing device described in 3). 5) Claim 1) characterized in that the cooling action of the cooling means is performed using a liquid abrasive, and the abrasive is ejected onto the polishing cloth to replace the abrasive retained in the abrasive cloth gap. Or the polishing device described in 3). 6) A claim characterized in that pressure gas is used as the cooling medium of the cooling means, and the gas is ejected onto the polishing cloth while cooling is performed by the latent heat of vaporization of the liquid polishing agent impregnated in the polishing cloth. The polishing device according to item 1) or 3). 7) The polishing apparatus according to claim 2) or 3), wherein a heater is used as the heating means, and the radiant heat of the heater is configured to be irradiated onto the polishing cloth via a heating area control plate.