JP6030045B2 - Ceramic heater and manufacturing method thereof - Google Patents

Description

  The present invention relates to a ceramic heater and a manufacturing method thereof.

  In a semiconductor manufacturing apparatus, a ceramic heater for heating a wafer is employed. As such a ceramic heater, a heater electrode is known by printing a metal paste on one surface of a ceramic sintered body and firing it (see, for example, Patent Document 1).

Japanese Patent No. 4529690 (for example, paragraph 0017)

  However, when a metal paste is printed on one surface of the ceramic sintered body and fired, a temperature difference occurs between the central portion and the outer periphery of the ceramic sintered body during firing, that is, the ceramic sintered body has a temperature difference. Unevenness sometimes occurred. The metal paste becomes a heater electrode after firing, but when such temperature unevenness occurs, the sintered state of the heater electrode differs between the central portion and the outer peripheral portion of the ceramic sintered body. As a result, the heater electrode has different resistance values at the central portion and the outer peripheral portion of the ceramic sintered body, and there is a problem that the thermal uniformity of the ceramic heater deteriorates.

  The present invention has been made in order to solve such problems, and a main object of the present invention is to increase heat uniformity in a ceramic heater having a heater electrode on one surface of a ceramic sintered body.

The method for producing the ceramic heater of the present invention is as follows:
A metal bonding material containing Al and Mg is stretched around one surface of the ceramic sintered body, and the metal bonding material is heated to a temperature below the liquidus temperature of the metal bonding material and applied to the ceramic sintered body. It includes an electrode forming step of forming a heater electrode by pressure bonding.

  In this method of manufacturing a ceramic heater, a heater electrode is formed by pressure-bonding a metal bonding material to a ceramic sintered body in a state where the metal bonding material is heated to a temperature below the liquidus temperature of the metal bonding material. When a heater electrode is formed by sintering a metal paste as in the prior art, temperature unevenness may occur between the central portion and the outer peripheral portion of the ceramic sintered body during sintering. If it does so, a difference will arise in the sintered part of a heater electrode, and resistance value of a heater electrode by the center part and outer peripheral part of a ceramic sintered compact, and soaking property will worsen. However, in the method of manufacturing a ceramic heater according to the present invention, the metal bonding material to be a heater electrode remains in a solid phase before and after bonding, so the resistance value of the heater electrode is the same as that of the ceramic sintered body. There is no difference between the outer periphery. In addition, the heater electrode in which the metal bonding material is bonded in the solid phase has a higher bonding strength between the heater electrode and the ceramic sintered body than the heater electrode in which the metal paste is sintered. Even after a repeated cycle test, it is difficult to peel from the ceramic sintered body. For these reasons, the ceramic heater manufactured by the manufacturing method of the present invention has high thermal uniformity. Further, since the oxide layer present on the surface of the ceramic sintered body is removed by the highly active Mg contained in the metal bonding material, the bonding strength between the ceramic sintered body and the metal bonding material is increased.

  The temperature at which the metal bonding material is pressure bonded to the ceramic sintered body in a heated state may be, for example, a temperature equal to or lower than the liquidus temperature of the metal bonding material and equal to or higher than the solidus temperature. Although it is good also as temperature below temperature, it is preferable that it is the vicinity of solidus temperature (for example, solidus temperature +/- 10 degreeC). This is because the solid phase remains almost before and after the metal bonding material is bonded.

  Moreover, as a metal bonding material, for example, an Al—Si—Mg bonding material or an Al—Mg bonding material is preferable.

  The manufacturing method of the ceramic heater of the present invention may include a grinding step of grinding the heater electrode until the thickness becomes 10 to 50 μm after the electrode forming step. In this way, even when the conductivity of the metal bonding material is high, the cross-sectional area of the metal bonding material is small, so that the electrical resistance increases and heat is easily generated. In this case, after the grinding step, a cooling plate joining step of joining a metal cooling plate to a surface of the ceramic sintered body on which the heater electrode is formed via a resin adhesive layer may be included. Since the thickness of the heater electrode is as thin as 10 to 50 μm, a gap is hardly generated between the ceramic sintered body and the adhesive layer, and hot spots are not easily generated.

The ceramic heater of the present invention is
A ceramic sintered body having a wafer mounting surface;
A heater electrode stretched around a surface of the ceramic sintered body opposite to the wafer mounting surface;
With
The heater electrode contains Al and MgO is present at the bonding interface.

  This ceramic heater can be obtained, for example, by the above-described ceramic heater manufacturing method.

  In the ceramic heater of the present invention, the heater electrode preferably has a thickness of 10 to 50 μm. In this way, even when the conductivity of the metal bonding material is high, the cross-sectional area of the metal bonding material is small, so that the electrical resistance increases and heat is easily generated.

  Such a ceramic heater may have a metal cooling plate bonded to a surface of the ceramic sintered body on which the heater electrode is formed via a resin adhesive layer. Since the thickness of the heater electrode is as thin as 10 to 50 μm, a gap is hardly generated between the ceramic sintered body and the bonding layer. When a gap is generated between the ceramic sintered body and the adhesive layer, the portion where the gap is generated is likely to become a hot spot because heat from the ceramic sintered body is difficult to escape to the metal cooling plate. However, here, since a gap is hardly generated between the ceramic sintered body and the adhesive layer, such a hot spot is hardly generated.

FIG. 4 is a cross-sectional view of the electrostatic chuck heater 20. FIG. 6 is a manufacturing process diagram of the electrostatic chuck heater 20. The top view of the metal joining material 126. FIG. The graph which shows the relationship between the frequency | count of the cycle test which repeats low temperature control and high temperature control, and temperature difference (DELTA) T of an Example and a comparative example. The graph which shows the relationship between heater electrode thickness and temperature difference (DELTA) T of an Example and a comparative example.

  Next, an electrostatic chuck heater 20 which is a preferred embodiment of the ceramic heater of the present invention will be described below. FIG. 1 is a cross-sectional view of the electrostatic chuck heater 20.

  The electrostatic chuck heater 20 includes a ceramic sintered body 22 capable of adsorbing a wafer W to be plasma-treated to the wafer mounting surface 22a, a cooling plate 30 disposed on the back surface of the ceramic sintered body 22, and a ceramic sintered body. 22 and an adhesive layer 40 that bonds the cooling plate 30 to each other.

  The ceramic sintered body 22 is a disk-shaped plate made of ceramic (for example, made of alumina or aluminum nitride) whose outer diameter is smaller than the outer diameter of the wafer W.

  An electrostatic electrode 24 is embedded in the ceramic sintered body 22. The electrostatic electrode 24 is a planar electrode to which a DC voltage can be applied by a power supply device (not shown). When a DC voltage is applied to the electrostatic electrode 24, the wafer W is attracted and fixed to the wafer mounting surface 22a by a Coulomb force or a Johnson-Rahbek force. The suction fixation of is released.

A heater electrode 26 is stretched around a surface 22b of the ceramic sintered body 22 opposite to the wafer mounting surface 22a. The heater electrode 26 is a resistance wire patterned in the manner of one stroke over the entire surface 22b, and is formed in a spiral shape from one end portion 26a disposed at the center to an end portion 26b disposed near the outer periphery. Has been. Power supply terminals 28a and 28b are joined to both ends 26a and 26b by solder or Al-Cu, respectively. The heater electrode 26 is obtained by pressure-bonding a metal bonding material containing Al and Mg to the ceramic sintered body 22 in a state where the metal bonding material is heated to a temperature equal to or lower than the solidus temperature of the metal bonding material. Such a bonding method is referred to as TCB bonding (Thermal compression bonding). The highly active Mg contained in the metal bonding material removes the oxide layer present on the surface 22b of the ceramic sintered body 22 and increases the bonding strength between the ceramic sintered body 22 and the metal bonding material. Further, MgO is present at the bonding interface of the heater electrode 26. As a metal bonding material containing Al and Mg, an Al—Si—Mg bonding material, an Al—Mg bonding material, or the like is preferable. For example, the Al—Si—Mg based bonding material contains 88.5 wt% Al, 10 wt% Si, 1.5 wt% Mg, the solid phase temperature is about 560 ° C., and the liquid phase temperature is about When a 590 ° C. bonding material is used, the TCB bonding is performed at a pressure of ^{20 to} 140 kg / mm ² , preferably 30 to 60 kg / mm ² in a state heated to about 520 to 580 ° C. which is lower than the liquidus temperature. Pressurized for ~ 6 hours. The TCB bonding is preferably performed in a vacuum atmosphere or an inert gas atmosphere. The heater electrode 26 is ground to a thickness of 10 to 50 μm (preferably 10 to 20 μm) after TCB bonding of a metal bonding material having a thickness of several hundreds of μm. By doing so, even if the conductivity of the metal bonding material is high, the cross-sectional area of the metal bonding material is reduced, so that the electrical resistance is increased and heat is easily generated.

  The cooling plate 30 is a disk made of metal (for example, aluminum or aluminum alloy). The cooling plate 30 is bonded to a surface 22b of the ceramic sintered body 22 opposite to the wafer mounting surface 22a via an adhesive layer 40 made of an insulating resin. The cooling plate 30 has a refrigerant passage 32 through which the refrigerant cooled by an external cooling device (not shown) circulates. The cooling plate 30 includes through holes 34 a and 34 b for inserting a pair of power supply terminals 28 a and 28 b attached to the heater electrode 26. The inner surfaces of the through holes 34a and 34b are covered with a ceramic insulating layer. In addition, the cooling plate 30 also has a through hole (not shown) for inserting a power supply terminal (not shown) that supplies power to the electrostatic electrode 24.

  The adhesive layer 40 is a solidified epoxy, silicon or acrylic adhesive sheet. The thickness of the adhesive layer 40 is 100 to 300 μm. A pair of power supply terminals 28 a and 28 b penetrates the adhesive layer 40. When the thickness of the heater electrode 26 is 10 to 50 μm, the step between the surface 22 b of the ceramic sintered body 22 and the heater electrode 26 is very small, so that a gap is hardly generated between the surface 22 b and the adhesive layer 40. When a gap is generated between the surface 22b and the adhesive layer 40, the portion where the gap is generated is likely to be a hot spot because the heat of the ceramic sintered body 22 is difficult to escape to the cooling plate 30. However, in the present embodiment, since a gap is hardly generated between the ceramic sintered body 22 and the adhesive layer 40, such a hot spot is hardly generated. In addition, in order to acquire such an effect reliably, it is more preferable that the thickness of the heater electrode 26 shall be 10-20 micrometers.

  Next, a usage example of the electrostatic chuck heater 20 will be described. First, the wafer W is placed on the wafer placement surface 22 a of the ceramic sintered body 22 with the electrostatic chuck heater 20 installed in a vacuum chamber (not shown). Then, the inside of the vacuum chamber is reduced by a vacuum pump so as to have a predetermined degree of vacuum, and a DC voltage is applied to the electrostatic electrode 24 of the ceramic sintered body 22 to generate a Coulomb force or a Johnson Rabeck force, The wafer W is sucked and fixed to the wafer mounting surface 22a of the ceramic sintered body 22. Next, the inside of the vacuum chamber is set to a reactive gas atmosphere at a predetermined pressure (for example, several tens to several hundreds Pa), and plasma is generated in this state. Then, the surface of the wafer W is etched by the generated plasma. A controller (not shown) controls the power supplied to the heater electrode 26 so that the temperature of the wafer W becomes a preset target temperature.

  Next, a manufacturing example of the electrostatic chuck heater 20 will be described. FIG. 2 is a manufacturing process diagram of the electrostatic chuck heater 20, and FIG. 3 is a plan view of the metal bonding material 126. First, a ceramic sintered body 22 in which the electrostatic electrode 24 is embedded is prepared (see FIG. 2A). Such a ceramic sintered body 22 can be prepared, for example, according to the description in JP-A-2005-343733. Subsequently, as shown in FIG. 3, a metal bonding material 126 having a thickness of several hundreds μm previously formed in a predetermined pattern (here, spiral) is prepared, and the metal bonding material 126 is opposite to the wafer mounting surface 22a. It is mounted on the side surface 22b (see FIG. 2B). The diameter of the vortex at the outermost periphery of the spiral formed by the metal bonding material 126 is slightly smaller than the diameter of the surface 22 b of the ceramic sintered body 22. Subsequently, the ceramic sintered body 22 on which the metal bonding material 126 is placed is put into a carbon mold 50. At this time, a graphite sheet 52 (for example, a product name Grafoil manufactured by Graftech) is interposed between the metal bonding material 126 and the mold 50 (see FIG. 2C). Then, in a state where the metal bonding material 126 is heated to a temperature equal to or lower than the liquidus temperature of the metal bonding material 126, the ceramic sintered body 22 on which the metal bonding material 126 is placed is moved by the upper mold and the lower mold of the mold 50. Pressurize from above and below. Thereby, the metal bonding material 126 is bonded to the ceramic sintered body 22. After joining, the ceramic sintered body 22 is taken out from the mold 50. The metal bonding material 126 is bonded to the ceramic sintered body 22 but is not bonded to the graphite sheet 52. Therefore, the ceramic sintered body 22 can be easily taken out from the mold 50. Then, it cuts until the thickness of the metal joining material 126 becomes 10-50 micrometers, and is set as the heater electrode 26 (refer FIG.2 (d)). Then, power supply terminals 28a and 28b are joined to both ends 26a and 26b of the heater electrode 26 by solder or Al—Cu brazing material (see FIG. 2E).

  On the other hand, a cooling plate 30 having a refrigerant passage 32 formed therein is prepared. Then, the surface 30a of the cooling plate 30 and the surface 22b of the ceramic sintered body 22 face each other, and the power supply terminal 28a is inserted into the through holes 34a and 34b of the cooling plate 30 with the adhesive sheet sandwiched between both surfaces 30a and 22b. , 28b is inserted, and the ceramic sintered body 22 is pressed against the cooling plate 30. Thereby, the surface 22b of the ceramic sintered body 22 and the surface 30a of the cooling plate 30 are joined via the adhesive layer 40, and the electrostatic chuck heater 20 is obtained (refer FIG.2 (f)).

  According to the electrostatic chuck heater 20 of the present embodiment described in detail above, the thermal uniformity becomes high. When a heater electrode is formed by sintering a metal paste as in the prior art, temperature unevenness may occur between the central portion and the outer peripheral portion of the ceramic sintered body during sintering. If it does so, a difference will arise in the sintered part of a heater electrode, and resistance value of a heater electrode by the center part and outer peripheral part of a ceramic sintered compact, and soaking property will worsen. However, in the electrostatic chuck heater 20 of the present embodiment, most of the metal bonding material to be the heater electrode 26 remains in a solid phase before and after bonding, so the resistance value of the heater electrode 26 is a ceramic sintered body. There is no difference between the central portion of 22 and the outer peripheral portion. In addition, the heater electrode 26 in which the metal bonding material is bonded in the solid phase has a higher bonding strength between the heater electrode 26 and the ceramic sintered body 22 than the heater electrode in which the metal paste is sintered. It is difficult to peel from the ceramic sintered body 22. For these reasons, the electrostatic chuck heater 20 of the present embodiment has high thermal uniformity.

  It should be noted that the present invention is not limited to the above-described embodiment, and it goes without saying that the present invention can be implemented in various modes as long as it belongs to the technical scope of the present invention.

  For example, in the above-described embodiment, the heater electrode 26 is formed in a spiral shape over the entire surface of the electrostatic chuck heater 20, but is not particularly limited to a spiral shape, and may have any shape. Further, the electrostatic chuck heater 20 may be divided into a plurality of zones, and heater electrodes may be formed in a manner of one stroke writing for each zone. The plurality of zones may be, for example, two zones, an inner zone (circular) and an outer zone (doughnut shape), or two zones, a left zone (semicircle) and a right zone (semicircle). Also good.

  In the above-described embodiment, the electrostatic chuck heater 20 is exemplified as the ceramic heater of the present invention. However, the electrostatic electrode 24 of the electrostatic chuck heater 20 may be omitted, or the ceramic heater may be used. A high frequency electrode for generating plasma may be further embedded in the ceramic sintered body 22.

[Example 1]
The electrostatic chuck heater 20 was manufactured according to the above-described manufacturing example (see FIG. 2). Note that the ceramic sintered body 22 in which the electrostatic electrode 24 was embedded was a ceramic sintered body having a diameter of 297 mm and a thickness of 4 mm. The metal bonding material 126 contains 88.5 wt% Al, 10 wt% Si, 1.5 wt% Mg, Al—Si having a solid phase temperature of about 560 ° C. and a liquid phase temperature of about 590 ° C. -Mg based bonding material was used. TCB bonding was performed at a pressure of 30 kg / mm ² for 5 hours in a vacuum atmosphere heated to 560 ° C. The metal bonding material 126 was ground until the thickness of the metal bonding material 126 after TCB bonding became 20 μm, and the heater electrode 26 was obtained. When the cross section of the heater electrode 26 was observed with SEM / EPMA, it was confirmed that MgO was present at the bonding interface. As the bonding sheet, an epoxy resin sheet having a thickness of 300 μm was used. The cooling plate 30 was made of aluminum and had a diameter of 300 mm and a thickness of 25 mm.

[Comparative Example 1]
In Comparative Example 1, Example 1 was used except that instead of forming the heater electrode 26 by TCB joining the metal bonding material 126 to the ceramic sintered body 22 in Example 1, the heater electrode was formed using a metal paste. In the same manner, an electrostatic chuck heater was manufactured. Specifically, a metal paste kneaded with tungsten powder and a firing aid in an ethyl cellulose binder is printed on the surface of the ceramic sintered body so as to form a spiral pattern, and degreased at 800 ° C. in nitrogen gas, The heater electrode was formed by firing at 1600 ° C. in nitrogen gas and grinding to a predetermined thickness (here, 50 μm).

[Soaking evaluation test-Part 1]
An electrostatic chuck heater was placed in a vacuum chamber (not shown), and a temperature measurement wafer was placed on the wafer placement surface. As the temperature measurement wafer, a silicon wafer having a diameter of 300 mm, 12 points on the circumference of 145 mm in diameter, and 12 points on the circumference of 290 mm in diameter were each embedded with a thermocouple. A plurality of measurement points on each circumference were arranged at equal intervals. The internal pressure of the vacuum chamber was set to less than 10 Pa, and the temperature of the refrigerant circulated in the refrigerant passage of the cooling plate was set to 10 ° C. The target temperature of the ceramic was set to 60 ° C. Temperature difference ΔT (° C.) obtained by subtracting the minimum value from the maximum value of the temperature of each point of the temperature measurement wafer when the power supplied to the heater electrode is controlled so that the ceramic temperature matches the target temperature by a controller (not shown). Was determined as a soaking index. Moreover, about the heater electrode, the inside resistivity (inside resistivity) of a circle with a diameter of 200 mm and the outside resistivity (outside resistivity) of a circle with a diameter of 200 mm were also measured. The results are shown in Table 1. As is apparent from Table 1, Example 1 had a smaller temperature difference ΔT than that of Comparative Example 1, and was excellent in heat uniformity. In addition, Example 1 had less variation in inner resistivity and outer resistivity than Comparative Example 1.

[Soaking evaluation test-2]
In Example 1 and Comparative Example 1, after setting the target temperature of the ceramic to 20 ° C. (1 minute) instead of setting the target temperature of the ceramic to 60 ° C. One cycle was set to 80 ° C. (1 minute), and this was carried out for 50,000 cycles. The temperature was measured with an IR camera every 10,000 cycles including the initial stage, and the temperature difference ΔT, which is a soaking index, was obtained. The result is shown in FIG. From FIG. 4, in Example 1, the temperature difference ΔT was constantly less than 3 ° C. from the initial stage until 50,000 cycles. In contrast, in Comparative Example 1, the temperature difference ΔT already exceeded 4 ° C. in the initial stage, and the temperature difference ΔT further increased as the number of cycles increased. In Comparative Example 1, the heater electrode peels from the ceramic sintered body as the number of cycles increases, and heat cannot be efficiently released from the ceramic sintered body to the cooling plate around the peeled portion. It is thought that the thermal properties deteriorated. On the other hand, in Example 1, it is considered that the heater electrode did not peel from the ceramic sintered body until 50,000 cycles. Thus, it can be seen that the bonding strength between the heater electrode and the ceramic sintered body is higher when the metal bonding material bonded with TCB is used as the heater electrode than when the sintered body of the metal paste is used.

[Examples 2 to 5]
In Example 1, the thickness of the heater electrode 26 was 20 μm by grinding, but in Example 2, it was 10 μm, Example 3 was 50 μm, Example 4 was 100 μm, and Example 5 was 200 μm (no grinding).

[Comparative Examples 2 to 5]
In Comparative Example 1, the thickness of the heater electrode was 50 μm by grinding. However, Comparative Example 2 was 10 μm, Comparative Example 3 was 20 μm, Comparative Example 4 was 100 μm, and Comparative Example 5 was 200 μm (no grinding).

[Soaking evaluation test-Part 3]
In accordance with the above-described [Soaking evaluation test-No. 1], the soaking properties of each example and each comparative example were determined. FIG. 5 shows the relationship between the thickness of the heater electrode and the thermal uniformity (ΔT). As shown in FIG. 5, the heater electrode with the most uniform heat uniformity among the comparative examples had a heater electrode thickness of 50 μm, and the heat uniformity deteriorated regardless of whether it was thicker or thinner. In the comparative example, when the thickness was 20 μm or less, the heater electrode was peeled off or chipped during grinding, so the resistivity became non-uniform and the thermal uniformity deteriorated. This is probably because the heater electrode of the comparative example is made by firing a metal paste, and bubbles are contained inside or become brittle, resulting in non-uniform resistivity. On the other hand, when Examples and Comparative Examples having the same heater electrode thickness were compared, the Examples were superior in heat uniformity. Further, in the examples, when the thickness of the heater electrode was 10 to 50 μm, the temperature uniformity was higher than that of the comparative example having the highest temperature uniformity (thickness of the heater electrode being 50 μm). Since the heater electrode of the example is a metal bonding material that remains mostly in a solid phase before and after TCB bonding, it is considered that no peeling or chipping occurs even when grinding, and the resistivity becomes uniform.

20 Electrostatic chuck heater, 22 Ceramic sintered body, 22a Wafer mounting surface, 22b surface, 24 Electrostatic electrode, 26 Heater electrode, 26a, 26b End, 28a, 28b Power supply terminal, 30 Cooling plate, 30a Surface, 32 Refrigerant passage, 34a, 34b through-hole, 40 adhesive layer, 50 mold, 52 graphite sheet, 126 metal joint, W wafer.

Claims (6)

A metal bonding material containing Al and Mg is stretched around one surface of the ceramic sintered body, and the metal bonding material is heated to a temperature below the liquidus temperature of the metal bonding material and applied to the ceramic sintered body. A method for producing a ceramic heater, comprising an electrode forming step of forming a heater electrode by pressure bonding. It is a manufacturing method of the ceramic heater of Claim 1, Comprising:
After the said electrode formation process, the grinding process of grinding the said heater electrode until it becomes thickness 10-50 micrometers, The manufacturing method of the ceramic heater. A method for producing a ceramic heater according to claim 2,
After the said grinding process, the manufacturing method of the ceramic heater including the cooling plate joining process of joining a metal cooling plate to the surface in which the said heater electrode was formed among the said ceramic sintered compact through the resin-made adhesive layer. A ceramic sintered body having a wafer mounting surface;
A heater electrode stretched around a surface of the ceramic sintered body opposite to the wafer mounting surface;
With
The heater electrode is an Al-Si-Mg-based bonding material or an Al-Mg-based bonding material, and MgO is present at the bonding interface.
Ceramic heater. The heater electrode has a thickness of 10 to 50 μm.
The ceramic heater according to claim 4. A ceramic heater according to claim 4 or 5,
The ceramic heater provided with the metal cooling plate joined to the surface in which the said heater electrode was formed among the said ceramic sintered compact through the resin-made adhesive layer.