JP2003017551A - Wafer support member - Google Patents

Abstract

(57) [PROBLEMS] To prevent breakage of an electrostatic chuck and peeling of a bonding layer due to thermal stress acting on a wafer support member that joins an electrostatic chuck and a metal pedestal. Kind Code: A1 Abstract: In a wafer support member 1 in which an electrostatic chuck 10 and a metal pedestal 13 are joined via a joining layer 14 made of indium or an indium alloy, the thickness T of the joining layer 14 is set to 50 μm or more, and During 14,
A spacer 2 made of a metal such as gold, silver, copper, aluminum, nickel, or tin or an alloy containing these as a main component is arranged so that the gap between the electrostatic chuck 10 and the metal pedestal 13 is maintained at equal intervals. .

Description

Description: BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] The present invention relates to a wafer support member used mainly for holding a wafer such as a semiconductor wafer or a liquid crystal substrate by electrostatic attraction. is there. 2. Description of the Related Art Conventionally, for example, in a process of manufacturing a semiconductor device, an etching process for performing fine processing on a semiconductor wafer such as a silicon wafer (hereinafter simply referred to as a wafer), a film forming process for forming a thin film on the wafer, Alternatively, a wafer supporting member using an electrostatic chuck has been used because it is necessary to hold the wafer with high accuracy in the transfer between various processing steps. The structure of such a wafer supporting member is shown in FIG.
As shown in FIG. 1, one main surface of the plate-shaped ceramic body 11 is
An electrostatic chuck 10 having a mounting surface 11a on which the wafer W is mounted and an electrostatic chucking electrode 12 built in the plate-shaped ceramic body 11, and the other of the plate-shaped ceramic body 11 forming the electrostatic chuck 10 The electrostatic chuck 10 and the metal pedestal 13 are joined together via a joining layer 14 made of a brazing material made of an aluminum alloy, an organic adhesive, glass, or the like. there were. In order to hold the wafer W using the wafer support member 20, a voltage is applied between the electrostatic attraction electrode 12 and the wafer W, so that an electrostatic attraction force is developed between the two. As a result, the wafer W is fixed by suction to the installation surface 11a. The metal pedestal 13 can be easily assembled to the apparatus, and a cooling mechanism such as a cooling water channel can be provided inside the metal pedestal 13 so that the electrostatic chuck 10 can be provided.
By cooling the wafer W sucked and held on the metal base or applying high-frequency power to the metal pedestal 13, plasma is generated between the wafer W and a separately provided plasma generating electrode, thereby increasing various processing speeds. . However, when the joining layer 14 is made of a brazing material made of an aluminum alloy, an organic adhesive, glass, or the like, when a temperature change occurs, the plate-like ceramic body that forms the metal pedestal 13 and the electrostatic chuck 10 is formed. There has been a problem that the electrostatic chuck 10 is cracked by the thermal stress generated in the joint due to the difference in thermal expansion from the joint 11 or the joint layer 14 is peeled off. Therefore, the electrostatic chuck 10 and the metal pedestal 13
It has been proposed to use a soft indium or an indium alloy having a layer thickness of 20 to 100 μm as the bonding layer 14 in order to absorb and alleviate the thermal stress caused by the difference in thermal expansion between the two. Gazette). However, even if soft indium or an indium alloy is used for the bonding layer 14, if the thickness of the layer is less than 50 μm, the electrostatic chuck 10 and the metal are not affected when a temperature change occurs. There is a problem that the thermal stress generated between the pedestal 13 and the pedestal 13 cannot be sufficiently absorbed and relaxed, and the electrostatic chuck 10 is still damaged or the bonding layer 14 is peeled off.
When the layer thickness of the electrostatic chuck 10 is 50 μm or more, the electrostatic chuck 10 is inclined and joined to the joining surface of the metal pedestal 13, and the mounting surface 11 of the electrostatic chuck 10 is joined to the joining surface of the metal pedestal 13.
There was a problem that the parallelism of a was impaired or the joint was performed in a state where the bias of the stress occurred, and the flatness of the installation surface 11a was impaired. That is, if the joining temperature at which the electrostatic chuck 10 and the metal pedestal 13 are joined by indium brazing or indium alloy brazing is high, the indium brazing or indium alloy brazing is a soft material, and the thickness of the bonding layer 14 is increased. Is thick, it is difficult to keep the distance between the electrostatic chuck 10 and the metal pedestal 13 constant, the inclination of the electrostatic chuck 10 is likely to occur, and the joining temperature is slightly lower than the softening point of the indium brazing or indium alloy brazing. When the bonding is performed while controlling the temperature to a high degree, the layer thickness of the bonding layer 14 is partially biased. When the electrostatic chuck 10 is bonded in this state, the electrostatic chuck 10 is warped or distorted. Therefore, the flatness of the installation surface 11a is impaired. SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object to enable an electrostatic chuck to be accurately bonded to a metal pedestal and to be peeled off even after repeated thermal cycling. It is an object of the present invention to provide a wafer supporting member that can be used for a long period of time without performing. In view of the above problems, the present invention has been made in view of the above-mentioned problems, and has one principal surface of a plate-shaped ceramic body as an installation surface on which a wafer is mounted, and is provided in the plate-shaped ceramic body. A wafer support member comprising: an electrostatic chuck having a built-in electrode for electro-adsorption, and a metal pedestal bonded to the other main surface of the plate-shaped ceramic body forming the electrostatic chuck via a bonding layer made of indium or an indium alloy. In the above, while the thickness of the bonding layer is 50 μm or more, in the bonding layer, a spacer made of a metal such as gold, silver, copper, aluminum, nickel, or tin or an alloy containing these as a main component is disposed, The distance between the electrostatic chuck and the metal pedestal is maintained at an equal distance. Embodiments of the present invention will be described below. FIG. 1 is a sectional view showing a wafer supporting member according to the present invention, and FIG. 2 is an enlarged sectional view of a portion A in FIG. The same parts as those in the conventional example are denoted by the same reference numerals. The wafer support member 1 is configured such that one main surface of a plate-like ceramic body 11 is placed on an installation surface 11a on which a wafer W is mounted.
And an electrostatic chuck 10 having an electrostatic chucking electrode 12 built in the plate-shaped ceramic body 11 and a metal bonded to the other main surface of the plate-shaped ceramic body 11 forming the electrostatic chuck 10. The electrostatic chuck 10 and the metal pedestal 13 are joined together via a joining layer 14 made of indium or an indium alloy. The electrostatic chuck 10 is formed as shown in FIG. The metallized layer 3 is formed on the other main surface of the plate-shaped ceramic body 11 to be
Are formed, and are bonded therebetween through a bonding layer 14 made of indium or an indium alloy. The metallization layer 3 and the plating layer 4 are made of a metal mainly composed of silver, copper, nickel or the like, which has good wettability with indium. The thickness T of the bonding layer 14 is 50 μm or more, and the bonding layer 14 is made of a metal such as gold, silver, copper, aluminum, nickel, tin or an alloy containing these as a main component. The spacers 2 are arranged so that the distance between the electrostatic chuck 10 and the metal pedestal 13 is maintained at equal intervals. In order to hold the wafer W using the wafer support member 1, the electrostatic chucking electrode 12 and the wafer W
By applying a voltage between the two, an electrostatic attraction force is developed between the two, and the wafer W is attracted and fixed to the installation surface 11a. Since a metal pedestal 13 is joined to the surface of the electrostatic chuck 10 opposite to the installation surface 11a,
In addition to being easy to assemble to various devices, if a cooling mechanism such as a cooling water channel is provided inside the metal pedestal 13, the wafer W sucked and held on the electrostatic chuck 10 can be efficiently cooled, If high-frequency power is applied to the metal pedestal 13, plasma can be generated between the metal pedestal 13 and a separately provided plasma generating electrode, and various processing speeds for the wafer W can be increased. Further, the wafer supporting member 1 of the present invention comprises a bonding layer 14 for bonding the electrostatic chuck 10 and the metal pedestal 13.
In addition, since soft indium or indium alloy is used and the thickness T of the bonding layer 14 has a sufficient thickness of 50 μm or more, heat between the electrostatic chuck 10 and the metal pedestal 13 due to a temperature change. Even if stress acts,
The thermal stress is absorbed and alleviated by the bonding layer 14, and the electrostatic chuck 10 can be effectively prevented from being damaged and the bonding layer 14 from peeling off. However, if soft indium or an indium alloy is used for the bonding layer 14 and the thickness T of the bonding layer 14 is increased to 50 μm or more, partial unevenness occurs in the bonding layer 14, causing a thickness variation. However, the parallelism of the installation surface 11a of the electrostatic chuck 10 with respect to the bonding surface of the electrostatic chuck 10 may be impaired, or the flatness of the installation surface 11a may be impaired. Since the spacers 2 are interposed in the bonding layer 14 so as to keep the space between the electrostatic chuck 10 and the metal pedestal 13 at equal intervals, the electrostatic chuck 10 is accurately held on the metal pedestal 13. While being able to
The flatness of the installation surface 11a is not impaired. That is, when the joining temperature at which the electrostatic chuck 10 and the metal pedestal 13 are joined by indium brazing or indium alloy brazing is controlled to a temperature slightly higher than the softening point of the indium brazing or indium alloy brazing, a partial Unevenness occurs in the layer thickness T of the bonding layer 14, and the installation surface 11
Although the flatness of a may be impaired, in the present invention, even if the bonding temperature is set higher than the softening point of indium brazing or indium alloy brazing, the space between the electrostatic chuck 10 and the metal pedestal 13 is increased by the interposition of the spacer 2. Because it can be kept constant, the thickness T of the bonding layer 14 varies,
There is no occurrence of bias. As a material for forming the spacer 2,
Gold, silver, copper, aluminum, nickel, and the like having good wettability with indium or an indium alloy forming the bonding layer 14
Since a metal such as tin or an alloy containing these as a main component is used, a reaction layer can be formed between indium and an indium alloy and can be firmly adhered to each other. Due to the thermal stress acting due to the difference in thermal expansion, peeling occurs at the bonding portion between the bonding layer 14 and the spacer 2, and this peeling progresses, and the space between the electrostatic chuck 10 and the bonding layer 14 or between the metal pedestal 13 and the bonding layer 14 can be effectively prevented from occurring. In addition, gold, silver,
Since metals such as copper, aluminum, nickel, and tin or alloys containing these as main components have excellent thermal conductivity similarly to indium or an indium alloy forming the bonding layer 14, the electrostatic chuck 10 and the metal pedestal Since the heat transfer performance between the metal base 13 and the metal base 13 is not hindered and the heat transfer can be performed uniformly over the entire joint, for example, a metal base 13 provided with a cooling mechanism such as a cooling water channel is provided. In this case, the wafer W sucked and held on the electrostatic chuck 10 can be efficiently cooled, and the wafer W
Can be made uniform. Therefore, various types of processing accuracy such as film formation and etching on the wafer W can be improved. The metal having good wettability with indium or an indium alloy is a metal capable of forming a reaction layer with indium or an indium alloy. For example, the material of the spacer 2 is W or Mo. In this case, the reactivity with indium or the indium alloy is low, and the spacer cannot be used because the spacer 2 is damaged. The plate-like ceramic body 11 forming the electrostatic chuck 11 of the wafer supporting member 1 is made of alumina (Al ₂ O ₃ ), aluminum nitride (Al
N), silicon nitride (Si ₃ N ₄ ), sialon, yttrium aluminum garnet (hereinafter referred to as YAG)
A ceramic sintered body mainly composed of aluminum nitride or the like can be used. Among them, when high uniformity is required when the wafer W is adsorbed, aluminum nitride having excellent thermal conductivity ( It is preferable to use a ceramic sintered body mainly composed of AlN), and when an inexpensive one is required, use a ceramic sintered body mainly composed of alumina (Al ₂ O ₃ ). Is preferred.
In addition, since the ceramic sintered body containing aluminum nitride (AlN) or alumina (Al ₂ O ₃ ) as a main component also has excellent corrosion resistance and plasma resistance, a halogen-based corrosive gas is used. It can be suitably used also in various film forming processes, etching processes, and the like. As a material for forming the electrostatic attraction electrode 12 embedded in the plate-shaped ceramic body 11, a metal such as tungsten (W) or molybdenum (Mo) may be used. Since the difference in thermal expansion from the binder is small, it can be embedded in the plate-shaped ceramic body 11 with good adhesion. Further, as a material for forming the metal pedestal 13, aluminum (Al) or copper (C) having a high thermal conductivity is used.
u) or an alloy containing these as a main component can be used. In the case of further exposure to a halogen-based gas, aluminum (Al) or an aluminum alloy having high corrosiveness to these gases should be used. The indium forming the bonding layer 14 has an indium content of 100% by weight, and the indium alloy has an indium content of 40 to 99% by weight.
In contrast to n), a material containing at least one kind of metal such as Sn, Ag, Pb, Ab, Zn, and Al is referred to. Softness means that among various metals, hardness is low and flexibility is excellent. Say that The shape of the spacer 2 is not particularly limited as long as the shape allows the electrostatic chuck 10 to be accurately joined to the metal pedestal 13. The spacer 2 has a ring shape or a plate shape. However, in this case, since it is difficult to finish the flatness on the upper and lower surfaces of the ring-shaped body or the plate-shaped body with high precision, the shape of the spacer 2 is a columnar body or a spherical body, and is supported at three or more points. It is preferable that
At this time, the center line of the electrostatic chuck 10 is set to the three spacers 2.
May be arranged so as to be positioned inside the triangle connecting. Next, a method for manufacturing the wafer support member 1 of the present invention will be described. First, in the electrostatic chuck 10, a plate-like ceramic body is manufactured by sandwiching and laminating an electrostatic attraction electrode 12 between a plurality of ceramic green sheets and integrally sintering the ceramic green sheet. To the wafer W
It is manufactured by forming the installation surface 11a. The mounting surface 1 of the electrostatic chuck 10
A metal paste mainly composed of silver, copper, nickel or the like is applied to the surface on the side opposite to 1a and baked to form a metallized layer 3. On the other hand, silver,
A plating layer 4 of a metal mainly composed of copper, nickel or the like is formed. Then, a paste obtained by dissolving indium or an indium alloy powder with alcohol is applied to the metallized layer 3 formed on the electrostatic chuck 10 and the plated layer 14 of the metal pedestal 13, respectively. As a coating method, a screen printing method may be used, and printing is performed so that the final thickness becomes a predetermined thickness. Thereafter, the alcohol is dried and evaporated. Next, the electrostatic chuck 10 and the metal pedestal 13 are bonded to each other. In the meantime, the spacer 2 made of a metal such as gold, silver, copper, aluminum, nickel, tin, or an alloy containing these as a main component is used. And heating to a temperature higher than the softening temperature (157 ° C.) of indium or an indium alloy to make the indium or indium alloy sufficiently coated with the metallized layer 3 or the plating layer 4, and then cooled and cured. Thus, the wafer support member 1 shown in FIG. 1 can be manufactured. In forming the bonding layer 14, an indium foil may be used. (Example 1) Here, a wafer support member using indium for a bonding layer for bonding an electrostatic chuck and a metal pedestal was manufactured, and bonding was performed when the thickness of the bonding layer was changed. The stress acting on the part was analyzed by the finite element method and verified by experiments. The measurement conditions were as follows. The plate-like ceramic body forming the electrostatic chuck was a disk-like body having a diameter of 200 mm and a thickness of 3 mm, and was made of an aluminum nitride sintered body and an alumina sintered body. The metal pedestal was a substantially disc-shaped body having a diameter of 200 mm, a thickness of 50 mm, and a flange of 300 mm in diameter, and aluminum was used as the material.
The coefficient of thermal expansion of aluminum is 15 × 10 ⁻⁶ / ° C.
The coefficient of thermal expansion of the alumina sintered body was 7 × 10 ⁻⁶ / ° C., and the coefficient of thermal expansion of the aluminum nitride sintered body was 5 × 10 ⁻⁶ / ° C. The thermal stress acting between the electrostatic chuck and the metal pedestal when a thermal cycle from room temperature (25 ° C.) to 100 ° C. was applied was calculated by the finite element method. The results are as shown in Table 1. [Table 1] As a result, as can be seen from Table 1, the stress can be reduced by increasing the thickness of the bonding layer. When the thickness of the bonding layer is 50 μm or more, the stress can be reduced to 60 MPa or less. When the thickness of the bonding layer is 100 μm or more, the stress can be reduced to 30 to 40 MPa. did it. Therefore, a wafer support member is actually manufactured,
An experiment was conducted to measure the flatness of the installation surface at that time and to examine the durability when a heat cycle was applied. In this experiment, a plate-shaped ceramic body forming an electrostatic chuck was a disk-shaped body having a diameter of 200 mm and a thickness of 3 mm, and was formed of an aluminum nitride sintered body. Further, the metal pedestal is a substantially disc-shaped body having a diameter of 200 mm, a thickness of 50 mm, and a diameter of 300 mm of a flange portion.
The one formed of aluminum was used. Then, indium was used as a bonding layer for bonding the electrostatic chuck and the metal pedestal, and one in which spacers of different materials were arranged in the bonding layer and one in which no spacer was interposed were prepared. In the case of using a spacer, the spacer has a diameter of 120 μm and a length of 10 m.
m, and three such spacers were equally arranged on the joint surface of the three metal pedestals. Then, after measuring the flatness of the installation surface of the obtained wafer support member with a three-dimensional measuring machine, as shown in FIG. 3, it is mounted in a vacuum processing chamber of a plasma etching apparatus used in a semiconductor manufacturing process. After adsorbing and holding the wafer on the wafer support member, high frequency power is applied between the plasma generating electrode installed in the vacuum processing chamber and the metal pedestal of the wafer support member to generate plasma, and as an etching gas. An etching process is performed by flowing a CF ₃ gas, and the number of processes until the electrostatic chuck of the wafer support member is damaged by the heat acting at the time of the etching process or the bonding layer is peeled off is examined to evaluate the durability. did. The plasma output in the etching process was 4 kW, and the etching time was 3 minutes per wafer. The results are as shown in Table 2. [Table 2] As a result, the sample No. in which the thickness of the bonding layer was 50 μm or less was obtained. In Nos. 1 and 2, although the flatness of the installation surface can be reduced to 5 μm or less, as shown in Table 1, since the thermal stress acting on the joint between the electrostatic chuck and the metal pedestal is large, the etching is performed about 1,000 times. Peeling of the bonding layer was observed by the treatment, and it became unusable. Sample No. 3 in which the thickness of the bonding layer was 50 μm or more and molybdenum or tungsten was used as the spacer material. In Nos. 6 and 7, the flatness of the installation surface was as poor as 30 μm. In addition, since the wettability of the bonding layer with indium was poor, the bonding layer was peeled off by about 1500 times of etching treatment, making the bonding layer unusable. On the other hand, the thickness of the bonding layer is set to 50 μm or more, and copper, nickel,
Sample No. using silver, gold, aluminum, and tin. 3-5
8 to 12, the flatness of the installation surface is 5 μm or less, and the electrostatic chuck and the metal pedestal can be accurately bonded to each other, and when the thickness of the bonding layer is 50 μm or more, as shown in Table 1, Since the thermal stress acting on the joint between the electrostatic chuck and the metal pedestal was small, it could withstand 5000 or more etching processes. As a result, the thickness of the joining layer between the electrostatic chuck and the metal pedestal is set to 50 μm or more, and a spacer made of copper, nickel, silver, gold, aluminum, and tin is interposed in the joining layer. It can be seen that the electrostatic chuck can be bonded to the metal pedestal with high precision and can be used for a long period of time even in an environment where a heat cycle is applied. As described above, according to the present invention, one main surface of the plate-shaped ceramic body is used as a mounting surface on which a wafer is mounted, and the main surface of the plate-shaped ceramic body is used for electrostatic attraction. In a wafer support member comprising an electrostatic chuck having a built-in electrode and a metal pedestal bonded to the other main surface of the plate-shaped ceramic body forming the electrostatic chuck via a bonding layer made of indium or an indium alloy, The thickness of the bonding layer is 50 μm or more, and gold,
Since a spacer made of a metal such as silver, copper, aluminum, nickel, or tin or an alloy containing these as a main component is arranged, and the gap between the electrostatic chuck and the metal pedestal is kept at equal intervals, It can be bonded to a metal pedestal accurately without deforming the electrostatic chuck, and prevents damage to the electrostatic chuck and peeling of the bonding layer even when used in an environment where thermal cycles are repeated. Can be used over a period of time.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view showing a wafer support member according to the present invention. FIG. 2 is an enlarged sectional view of a portion A in FIG. FIG. 3 is a cross-sectional view schematically showing an experimental device for examining durability. FIG. 4 is a cross-sectional view showing a conventional wafer support member. [Description of Signs] 1, 20: Wafer support member 2: Spacer 3: Metallized layer 4: Plating layer 10: Electrostatic chuck 11: Plate-shaped ceramic body 11
a: Installation surface 12: Electrostatic adsorption electrode 13: Metal pedestal W: Wafer

Claims (1)

Claims: 1. An electrostatic chuck in which one main surface of a plate-shaped ceramic body is an installation surface on which a wafer is mounted, and an electrostatic chuck electrode is built in the plate-shaped ceramic body. A wafer supporting member comprising a metal pedestal bonded to the other main surface of the plate-shaped ceramic body forming the electrostatic chuck through a bonding layer made of indium or an indium alloy, wherein the thickness of the bonding layer is 50 μm or more. And a spacer made of a metal such as gold, silver, copper, aluminum, nickel, tin or an alloy containing these as a main component is disposed in the bonding layer, and a space between the electrostatic chuck and the metal pedestal is provided. Are held at equal intervals.