Ceramic substrate, electrostatic chuck and substrate fixing device

Abstract

To provide a ceramic substrate, an electrostatic chuck, and a substrate fixing device that can obtain a high theoretical density ratio.SOLUTION: A ceramic substrate has a first phase comprised of alumina and a second phase comprised of yttrium aluminum garnet containing silicon.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present disclosure relates to a ceramic substrate, an electrostatic chuck, and a substrate clamping device. [Background technology]

[0002] Alumina and yttrium aluminum garnet (Y 3 Al 5 O 12 An electrostatic chuck containing alumina and YAG (YAG) is known. The inclusion of YAG in this electrostatic chuck allows it to have high resistance to plasma. However, in order to manufacture an electrostatic chuck containing alumina and YAG with a high theoretical density ratio without using a sintering aid, high temperature and long sintering time are required. In addition, an electrostatic chuck made only of alumina and YAG with added cerium has been proposed. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2018-186209 A [Patent Document 2] Special Publication No. 2013-502721 Summary of the Invention [Problem to be solved by the invention]

[0004] However, when the green sheet used as the material for the electrostatic chuck contains cerium, the cerium may diffuse out of the green sheet during firing and adhere to the inside of the firing furnace. Therefore, it is desirable to obtain a high theoretical density ratio without using cerium.

[0005] An object of the present disclosure is to provide a ceramic substrate, an electrostatic chuck, and a substrate fixing device that are capable of achieving a high theoretical density ratio. [Means for solving the problem]

[0006] According to one aspect of the present disclosure, there is provided a ceramic substrate having a first phase made of alumina and a second phase made of yttrium aluminum garnet containing silicon. Effect of the Invention

[0007] According to the present disclosure, a high theoretical density ratio can be obtained. [Brief description of the drawings]

[0008] [Figure 1] 1 is a plan view illustrating a substrate fixing device according to an embodiment; [Diagram 2] 1 is a cross-sectional view illustrating a substrate fixing device according to an embodiment. [Diagram 3] 1 is a cross-sectional view illustrating a configuration of a ceramic substrate. [Figure 4] 1A to 1C are cross-sectional views illustrating a method for manufacturing an electrostatic chuck. [Diagram 5] FIG. 2 is a diagram illustrating a cross-sectional SEM image of a ceramic substrate. [Figure 6] FIG. 1 is a diagram illustrating the results of SEM-EDX (part 1). [Figure 7] FIG. 2 is a second diagram illustrating the results of SEM-EDX. [Figure 8] FIG. 4 is a diagram illustrating the relationship between temperature and volume resistivity. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. In this specification and the drawings, components having substantially the same functional configurations are denoted by the same reference numerals, and redundant description may be omitted.

[0010] [Configuration of the substrate fixing device] First, the configuration of the substrate fixing device according to the embodiment will be described. Fig. 1 is a plan view illustrating the substrate fixing device according to the embodiment. Fig. 2 is a cross-sectional view illustrating the substrate fixing device according to the embodiment. Fig. 2 corresponds to a cross-sectional view taken along line II-II in Fig. 1.

[0011] 1 and 2, a substrate fixing device 1 according to the embodiment mainly includes a base plate 10, an adhesive layer 20, and an electrostatic chuck 30. The substrate fixing device 1 is a device that adsorbs and holds an object such as a substrate (wafer, etc.) that is an object to be adsorbed, by the electrostatic chuck 30 fixed to one surface 10a of the base plate 10.

[0012] In this disclosure, a planar view refers to viewing an object from the normal direction of the surface 10a of the base plate 10, and a planar shape refers to the shape of an object viewed from the normal direction of the surface 10a of the base plate 10.

[0013] The base plate 10 is a member for mounting the electrostatic chuck 30. The thickness of the base plate 10 is, for example, about 20 mm to 40 mm. The base plate 10 is made of, for example, aluminum, and can be used as an electrode for controlling plasma. By supplying a predetermined high-frequency power to the base plate 10, it is possible to control the energy for causing ions in a generated plasma state to collide with the substrate attracted to the electrostatic chuck 30, thereby enabling an effective etching process.

[0014] The electrostatic chuck 30 is a part that attracts and holds a wafer, which is an object to be attracted. The planar shape of the electrostatic chuck 30 is, for example, circular. The diameter of the wafer, which is an object to be attracted to the electrostatic chuck 30, is, for example, 8 inches, 12 inches, or 18 inches.

[0015] The electrostatic chuck 30 is provided on one surface 10a of the base plate 10 via an adhesive layer 20. The material of the adhesive layer 20 is, for example, a silicone adhesive. The thickness of the adhesive layer 20 is, for example, about 0.1 mm to 1.5 mm. The adhesive layer 20 bonds the base plate 10 and the electrostatic chuck 30, and also has the effect of reducing stress caused by the difference in thermal expansion coefficient between the ceramic electrostatic chuck 30 and the aluminum base plate 10.

[0016] The electrostatic chuck 30 has a ceramic substrate 31, a positive electrode 32P, and a negative electrode 32N. The upper surface of the ceramic substrate 31 is a mounting surface 31a for mounting an object to be attracted. The electrostatic chuck 30 is, for example, a Coulomb force type electrostatic chuck. The electrostatic chuck 30 may be a Johnsen-Rahbek type electrostatic chuck or a gradient type electrostatic chuck.

[0017] The ceramic substrate 31 has a thickness of, for example, about 1 mm to 6 mm, and a relative dielectric constant (1 MHz) of the ceramic substrate 31 is, for example, about 9 to 10. Fig. 3 is a cross-sectional view illustrating the configuration of the ceramic substrate.

[0018] As shown in FIG. 3, the ceramic substrate 31 is made of alumina (Al 2 O 3 The first phase 41 is made of Al, and the second phase 42 is made of yttrium aluminum garnet (YAG) containing silicon (Si). 2 O 3 and the second phase 42 includes YAG crystals containing Si. The first phase 41 and the second phase 42 are mixed in the ceramic substrate 31. For example, the ratio of the first phase 41 is higher than the ratio of the second phase 42. In any cross section of the ceramic substrate 31, for example, the total area of ​​the first phase 41 is 1.2 to 1.8 times the total area of ​​the second phase 42. The total area of ​​the first phase 41 may be 1.3 to 1.7 times, or may be 1.4 to 1.6 times the total area of ​​the second phase 42.

[0019] The ceramic substrate 31 may contain pores, but the theoretical density ratio (ratio of actual density to theoretical density) of the ceramic substrate 31 is preferably 98.0% or more, more preferably 98.5% or more, and even more preferably 99.0% or more.

[0020] The proportion of silicon in the ceramic substrate 31 is, for example, 0.10 mass % or more and 0.50 mass % or less. The proportion of silicon in the ceramic substrate 31 is preferably 0.12 mass % or more and 0.45 mass % or less, and more preferably 0.14 mass % or more and 0.40 mass % or less.

[0021] The volume resistivity of the ceramic substrate 31 at 300° C. is preferably 1.0×10 15 Ω cm or more, and more preferably 1.1×10 16 Ω cm or more, and more preferably 1.2×10 17 Ω·cm or more.

[0022] The positive electrode 32P and the negative electrode 32N are bipolar electrostatic electrodes formed of thin films and are built into the ceramic substrate 31. The positive electrode 32P and the negative electrode 32N are formed, for example, in a comb-like electrode pattern, with the teeth of each electrode arranged alternately at a predetermined interval. The positive electrode 32P and the negative electrode 32N are connected to a power source provided outside the substrate fixing device 1, and when a predetermined voltage is applied from the power source, an electrostatic adsorption force is generated between the positive electrode 32P and the negative electrode 32N and the wafer. This allows the electrostatic chuck 30 to adsorb and hold the wafer on the mounting surface 31a of the ceramic substrate 31. The adsorption force becomes stronger as the voltage applied between the positive electrode 32P and the negative electrode 32N becomes higher. For example, tungsten, molybdenum, etc. are used as the material of the positive electrode 32P and the negative electrode 32N.

[0023] As shown in FIG. 2, the base plate 10, the adhesive layer 20, and the ceramic substrate 31 are provided with voltage supply paths for applying a positive (+) voltage to the positive electrode 32P and a negative (-) voltage to the negative electrode 32N.

[0024] A heating element (heater) may be provided inside the ceramic substrate 31, which generates heat when a voltage is applied from the outside of the substrate fixing device 1 so that the mounting surface 31a of the ceramic substrate 31 reaches a predetermined temperature.

[0025] [Electrostatic chuck manufacturing method] Next, a description will be given of a method for manufacturing the electrostatic chuck 30. FIG 4 is a cross-sectional view illustrating an example of the method for manufacturing the electrostatic chuck 30.

[0026] First, as shown in FIG. 4(a), alumina (Al 2 O 3 ), yttria (Y 2 O 3 ), and silicon dioxide (SiO 2 ) and a thickness of about 0.5 mm to 0.6 mm. The molar concentration of alumina in the green sheets 35 is, for example, 80 mol % to 90 mol %, the molar concentration of yttria is, for example, 10 mol % to 20 mol %, and the molar concentration of silicon dioxide is, for example, 0.10 mol % to 0.70 mol %. The molar concentration of silicon dioxide is preferably 0.20 mol % to 0.60 mol %, and more preferably 0.30 mol % to 0.50 mol %. In addition, a metal paste 32 such as tungsten for forming a positive electrode 32P and a negative electrode 32N is provided by printing or the like on the intermediate layers of the green sheets 35.

[0027] The number of layers of the green sheets 35 is not limited, and for example, several layers to several tens of layers of the green sheets 35 can be laminated.

[0028] Next, the green sheets 35 and the metal paste 32 are heated to a temperature of about 1500°C. This state is maintained for several hours to sinter the green sheets 35 and the metal paste 32. As a result, as shown in Fig. 4(b), a ceramic substrate 31 is obtained from the green sheets 35, and a positive electrode 32P and a negative electrode 32N are obtained from the metal paste 32. At this time, a part of the alumina reacts with the yttria to produce YAG, and silicon in the silicon dioxide is taken into the YAG, producing a first phase 41 and a second phase 42.

[0029] In this manner, the electrostatic chuck 30 can be manufactured.

[0030] When manufacturing the substrate fixing device 1, a base plate 10 is separately prepared, and the base plate 10 and the electrostatic chuck 30 are bonded together using an uncured adhesive, and the adhesive is cured to form the adhesive layer 20. In this manner, the substrate fixing device 1 according to the embodiment can be manufactured.

[0031] In the substrate fixing device 1, the ceramic substrate 31 has a first phase 41 made of alumina and a second phase 42 made of YAG containing silicon. The second phase 42 containing YAG can provide high plasma resistance. In addition, silicon dioxide is used as a sintering aid in the manufacturing process of the ceramic substrate 31. This allows a high theoretical density ratio to be obtained without using a particularly high temperature or long time during firing. Furthermore, silicon is not easily released to the outside during firing of the green sheet 35, and tends to remain within the green sheet 35. This allows contamination of the firing furnace and the like used for firing to be avoided.

[0032] Here, the scanning electron microscope (SEM) images of the cross-sections of three types of samples (Sample No. 1, Sample No. 2, and Sample No. 3) of the ceramic substrate fabricated by the inventor of the present application will be described. FIG. 5 is a diagram illustrating the cross-sectional SEM image of the ceramic substrate. FIG. 5(a) shows the cross-sectional SEM image of Sample No. 1 to which silicon dioxide was not added during the manufacturing process. FIG. 5(b) shows the cross-sectional SEM image of Sample No. 2 to which 0.32 mol% of silicon dioxide was added during the manufacturing process. FIG. 5(c) shows the cross-sectional SEM image of Sample No. 3 to which 0.65 mol% of silicon dioxide was added during the manufacturing process.

[0033] As shown in FIG. 5(a), many pores (especially the dark black portions) were present in the cross-sectional SEM image of Sample No. 1, and the theoretical density ratio of this ceramic substrate was 97.0%. As shown in FIG. 5(c), there were fewer pores in the cross-sectional SEM image of Sample No. 3, and the theoretical density ratio of this ceramic substrate was 98.5%. As shown in FIG. 5(b), there were particularly few pores in the cross-sectional SEM image of Sample No. 2, and the theoretical density ratio of this ceramic substrate was 99.2%. These theoretical density ratios are values measured based on Archimedes' principle.

[0034] For Sample No. 2 and Sample No. 3, SEM-energy dispersive X-ray spectroscopy (EDX) was also performed. The results are shown in FIGS. 6 and 7. FIG. 6 is a diagram illustrating the results of SEM-EDX of Sample No. 2, and FIG. 7 is a diagram illustrating the results of SEM-EDX of Sample No. 3. Also, FIGS. 6(a) and 7(a) show the analysis results of oxygen, FIGS. 6(b) and 7(b) show the analysis results of aluminum, FIGS. 6(c) and 7(c) show the analysis results of yttrium, and FIGS. 6(d) and 7(d) show the analysis results of silicon.

[0035] As shown in FIGS. 6 and 7, silicon was mainly detected in the region where yttrium was detected. This indicates that silicon is contained in YAG.

[0036] Furthermore, when the inventors of the present application performed X-ray diffraction (XRD) analysis, no amorphous phase resulting from silicon dioxide was detected in any of Sample No. 1, Sample No. 2, and Sample No. 3.

[0037] Next, an experiment on the volume resistivity of the ceramic substrate conducted by the inventor of the present application will be described. In this experiment, three types of samples (sample No. 4, sample No. 5, and sample No. 6) were produced. Sample No. 4 was made according to the above embodiment and was composed of a first phase 41 and a second phase 42. The percentage of silicon in the ceramic substrate was 0.17 mass%. Sample No. 5 was composed of alumina with a purity of 99.9 mass%. Sample No. 6 was composed only of alumina and YAG to which cerium was added. In the manufacturing process, 0.5 mol% of cerium dioxide (CeO2) was added to the green sheet as a cerium source. Then, the change in volume resistivity with respect to temperature was measured. The results are shown in FIG. 8. FIG. 8 is a diagram illustrating the relationship between temperature and volume resistivity.

[0038] As shown in FIG. 8, in all of Samples No. 4, 5, and 6, the melting point was 1×10 15 In other words, sample No. 4 had a volume resistivity that was comparable to those of sample No. 5 and sample No. 6.

[0039] Although the preferred embodiments have been described in detail above, the present disclosure is not limited to the above-described embodiments, and various modifications and substitutions can be made to the above-described embodiments without departing from the scope of the claims. [Explanation of symbols]

[0040] 1 Board fixing device 10 Base plate 20 Adhesive layer 30 Electrostatic Chuck 31 Ceramic Substrate 32N negative pole 32P positive electrode 35 Green Sheet 41 Phase 1 42 Phase 2

Claims

1. a first phase consisting of alumina; a second phase comprising silicon-containing yttrium aluminum garnet; A ceramic substrate having

2. 2. The ceramic substrate according to claim 1, wherein the content of silicon is 0.10 mass % or more and 0.50 mass % or less.

3. 3. The ceramic substrate according to claim 1, wherein the ratio of the first phase is higher than the ratio of the second phase.

4. 3. The ceramic substrate according to claim 1, wherein the total area of ​​the first phases is 1.2 to 1.8 times the total area of ​​the second phases in any cross section.

5. The ceramic substrate according to claim 1 or 2; An electrode embedded in the ceramic substrate; The electrostatic chuck has

6. 6. The electrostatic chuck of claim 5, wherein the percentage of the first phase is higher than the percentage of the second phase.

7. 6. The electrostatic chuck according to claim 5, wherein in any cross section, a total area of ​​the first phases is 1.2 times or more and 1.8 times or less than a total area of ​​the second phases.

8. A base plate; The electrostatic chuck according to claim 5 , which is fixed to the base plate; A substrate fixing device having a

9. The substrate fixing device according to claim 8 , wherein the ratio of the first phase is higher than the ratio of the second phase.

10. 9. The substrate fixing device according to claim 8, wherein in any cross section, the total area of ​​the first phases is 1.2 to 1.8 times the total area of ​​the second phases.

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