Ceramic substrate, electrostatic chuck and substrate fixing device

Abstract

The invention provides a ceramic substrate, an electrostatic chuck and a substrate fixing device. The ceramic substrate comprises a first phase made of aluminum oxide and a second phase made of yttrium aluminum garnet containing silicon.

Description

Technical Field

[0001] The present invention relates to a ceramic substrate, an electrostatic chuck and a substrate fixing device. Background Art

[0002] A kind of material comprising aluminum oxide and yttrium aluminum garnet (Y3Al5O 12 :YAG) electrostatic chuck. According to this electrostatic chuck, high plasma resistance can be achieved by containing YAG. However, in order to manufacture an electrostatic chuck including alumina and YAG having a high theoretical density ratio without using a sintering additive, high temperature and long-term firing are required. In addition, an electrostatic chuck including alumina and YAG and added with cerium is proposed.

[0003] Citation List

[0004] Patent Literature

[0005] PTL1: JP2018-186209A

[0006] PTL2: JP2013-502721A Summary of the invention

[0007] However, when the green sheet used as the material of the electrostatic chuck includes cerium, the cerium may diffuse from the green sheet and adhere to the inside of the firing furnace during firing. Therefore, it is desired to achieve a high theoretical density ratio without using cerium.

[0008] The present invention provides a ceramic substrate, an electrostatic chuck, and a substrate fixing device capable of achieving a high theoretical density ratio.

[0009] According to one aspect of the present disclosure, a ceramic substrate comprises:

[0010] a first phase made of (formed from) aluminum oxide; and

[0011] The second phase is made of (formed from) yttrium aluminum garnet containing silicon.

[0012] According to the present disclosure, a high theoretical density ratio can be achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 is a plan view showing a substrate fixing device according to an embodiment.

[0014] Figure 2 is a cross-sectional view showing the substrate fixing device according to this embodiment.

[0015] Figure 3 is a cross-sectional view showing the structure of a ceramic substrate.

[0016] Figure 4A and Figure 4B is a cross-sectional view illustrating a method for manufacturing an electrostatic chuck.

[0017] FIG. 5A to FIG. 5C The figure shows a cross-sectional SEM image of a ceramic substrate.

[0018] FIG. 6A to FIG. 6D It is a figure which shows the result of SEM-EDX (Part 1).

[0019] FIG. 7A to FIG. 7D It is a figure which shows the result of SEM-EDX (part 2).

[0020] Figure 8 is a graph showing the relationship between temperature and volume resistivity.

[0021] Fig. 9 The boundary between the area where silicon is detected and the area where silicon is not detected is shown by a dotted line. Fig.6D A graph of the analysis results.

[0022] Fig.10 The boundary between the area where silicon is detected and the area where silicon is not detected is shown by a dotted line. Fig.7D A graph of the analysis results. DETAILED DESCRIPTION

[0023] Embodiments of the present disclosure will be described in detail below with reference to the accompanying drawings. It should be noted that in the specification and the drawings, constituent elements having substantially the same functional configuration are denoted by the same reference numerals, and redundant descriptions may be omitted.

[0024] [Structure of substrate fixing device]

[0025] First, the configuration of a substrate fixing device according to the embodiment will be described. Figure 1 is a plan view showing a substrate fixing device according to an embodiment. Figure 2 is a cross-sectional view showing the substrate fixing device according to this embodiment. Figure 2 Corresponding to the Figure 1 A cross-sectional view taken along line II-II.

[0026] like Figure 1 and Figure 2 As shown, the substrate fixing device 1 according to the present embodiment includes a base plate 10, an adhesive layer 20, and an electrostatic chuck 30 as main constituent elements. The substrate fixing device 1 is a device that adsorbs and holds an object such as a substrate (wafer, etc.) as a target object to be adsorbed by the electrostatic chuck 30 fixed to one surface 10a of the base plate 10.

[0027] It should be noted that in the present disclosure, it is assumed that the description “in a plan view (when looking down)” means viewing the target object from the normal direction of the surface 10a of the base plate 10, and the description “plane shape” means the shape of the target object viewed from the normal direction of the surface 10a of the base plate 10.

[0028] 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 or the like for controlling plasma. By supplying a predetermined high-frequency power to the base plate 10, the energy for causing ions or the like in the generated plasma state to collide with the substrate adsorbed on the electrostatic chuck 30 can be controlled, so that the etching process can be performed efficiently.

[0029] The electrostatic chuck 30 is a component that attracts and holds a wafer as a target object to be attracted. The planar shape of the electrostatic chuck 30 is, for example, circular. The diameter of the wafer as a target object to be attracted by the electrostatic chuck 30 is, for example, 8 inches, 12 inches, or 18 inches.

[0030] The electrostatic chuck 30 is provided on one surface 10a of the base plate 10 via the adhesive layer 20. The material of the adhesive layer 20 is, for example, a silicon-based 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 to the electrostatic chuck 30, and has the effect of reducing stress generated by the difference in thermal expansion coefficient between the electrostatic chuck 30 made of ceramic and the base plate 10 made of aluminum.

[0031] The electrostatic chuck 30 includes a ceramic substrate 31, a positive electrode 32P, and a negative electrode 32N. The upper surface of the ceramic substrate 31 is a placement surface 31a on which a target object to be adsorbed is placed. The electrostatic chuck 30 is, for example, a Coulomb force type electrostatic chuck. The electrostatic chuck 30 may also be a Johnson Rahbek type electrostatic chuck or a gradient type electrostatic chuck.

[0032] The thickness of the ceramic substrate 31 is, for example, approximately 1 mm to 6 mm, and the relative dielectric constant (kHz) of the ceramic substrate 31 is, for example, approximately 9 to 10. Figure 3 is a cross-sectional view showing the structure of a ceramic substrate.

[0033] like Figure 3As shown, the ceramic substrate 31 includes a first phase 41 made of aluminum oxide (Al2O3) and a second phase 42 made of yttrium aluminum garnet (YAG) containing silicon (Si). The first phase 41 includes Al2O3 crystals, and the second phase 42 includes Si-containing YAG crystals. The first phase 41 and the second phase 42 are mixed in the ceramic substrate 31. For example, the proportion of the first phase 41 is greater than the proportion 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 more than 1.2 times and less than 1.8 times the total area of ​​the second phase 42. The total area of ​​the first phase 41 may be more than 1.3 times and less than 1.7 times, or more than 1.4 times and less than 1.6 times the total area of ​​the second phase 42.

[0034] Although the ceramic substrate 31 may include pores (voids), 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 further more preferably 99.0% or more.

[0035] The proportion of silicon in the ceramic substrate 31 is, for example, 0.10 mass % to 0.50 mass % inclusive. The proportion of silicon in the ceramic substrate 31 is preferably 0.12 mass % to 0.45 mass % inclusive, and more preferably 0.14 mass % to 0.40 mass % inclusive.

[0036] In addition, the volume resistivity of the ceramic substrate 31 at 300°C is preferably 1.0×10 15 Ω·cm or more, more preferably 1.1×10 16 Ω·cm or more, and more preferably 1.2×10 17 Ω·cm or more.

[0037] The positive electrode 32P and the negative electrode 32N are bipolar electrostatic electrodes formed of a thin film and are buried in the ceramic substrate 31. The positive electrode 32P and the negative electrode 32N are formed, for example, into a comb-shaped electrode pattern, and the teeth of each electrode are alternately arranged side by side at a predetermined interval. The positive electrode 32P and the negative electrode 32N are connected to a power supply provided outside the substrate fixing device 1, and an adsorption force is generated by static electricity between the electrode and the wafer when a predetermined voltage is applied from the power supply. Thus, the wafer can be adsorbed and held on the placement surface 31a of the ceramic substrate 31 of the electrostatic chuck 30. When a higher voltage is applied between the positive electrode 32P and the negative electrode 32N, the adsorption force becomes stronger. As the material of the positive electrode 32P and the negative electrode 32N, for example, tungsten, molybdenum, etc. are used.

[0038] like Figure 2 As shown, the base plate 10 , the adhesive layer 20 , and the ceramic substrate 31 are provided with a voltage supply path for applying a positive (+) voltage to the positive electrode 32P and a negative (−) voltage to the negative electrode 32N.

[0039] In the ceramic substrate 31 , a heating element (heater) which generates heat when a voltage is applied from the outside of the substrate fixing device 1 and heats the placement surface 31 a of the ceramic substrate 31 to a predetermined temperature may also be provided.

[0040] [Method for manufacturing electrostatic chuck]

[0041] Next, a method for manufacturing the electrostatic chuck 30 will be described. Figure 4A and Figure 4B is a cross-sectional view illustrating a method for manufacturing the electrostatic chuck 30 .

[0042] First, if Figure 4A As shown, a plurality of green sheets 35 are stacked, each of which has a thickness of about 0.5 mm to 0.6 mm and includes powders of aluminum oxide (Al2O3), yttrium oxide (Y2O3) and silicon dioxide (SiO2). In the green sheet 35, the molar concentration of aluminum oxide is, for example, 80 mol% or more and 90 mol% or less, the molar concentration of yttrium oxide is, for example, 10 mol% or more and 20 mol% or less, and the molar concentration of silicon dioxide is, for example, 0.10 mol% or more and 0.70 mol% or less. The molar concentration of silicon dioxide is preferably 0.20 mol% or more and 0.60 mol% or less, and more preferably 0.30 mol% or more and 0.50 mol% or less. In addition, in the middle layer of the plurality of green sheets 35, a metal paste 32 such as tungsten for forming the positive electrode 32P and the negative electrode 32N is provided by printing or the like.

[0043] It should be noted that the number of stacked green sheets 35 is not particularly limited, and for example, several to several tens of green sheets 35 may be stacked.

[0044] Next, the plurality of green sheets 35 and the metal paste 32 are heated to about 1500° C. Then, by maintaining this state for several hours, each green sheet 35 and the metal paste 32 are sintered. Figure 4B As shown, ceramic substrate 31 is obtained from a plurality of green sheets 35, and positive electrode 32P and negative electrode 32N are obtained from metal paste 32. At this time, a portion of aluminum oxide and yttrium oxide react to produce YAG, and silicon in silicon dioxide is introduced into YAG, thereby producing first phase 41 and second phase 42.

[0045] In this way, the electrostatic chuck 30 can be manufactured.

[0046] When manufacturing the substrate fixing device 1, another base plate 10 is prepared, 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 way, the substrate fixing device 1 of this embodiment can be manufactured.

[0047] In the substrate fixing device 1, the ceramic substrate 31 has a first phase 41 made of (formed by) alumina and a second phase 42 made of (formed by) YAG containing silicon. By including YAG in the second phase 42, high plasma resistance can be obtained. In addition, in the manufacturing process of the ceramic substrate 31, silicon dioxide is used as a sintering aid. Therefore, a high theoretical density ratio can be achieved without a particularly high temperature or a long time during the firing process. In addition, in the firing of the green sheet 35, silicon is difficult to release to the outside and is likely to remain in the green sheet 35. Therefore, contamination of the firing furnace used during firing, etc., can be avoided.

[0048] Here, scanning electron microscope (SEM) images of cross sections of three types of ceramic substrate samples (Sample No. 1, Sample No. 2, and Sample No. 3) prepared by the inventors of the present application are described. FIG. 5A to FIG. 5C The figure shows a cross-sectional SEM image of a ceramic substrate. Figure 5A A cross-sectional SEM image of sample No. 1 to which no silica was added during the manufacturing process is shown. Figure 5B A cross-sectional SEM image of sample No. 2 to which 0.32 mol % of silica was added during the manufacturing process is shown. Figure 5C A cross-sectional SEM image of sample No. 3 to which 0.65 mol % of silica was added during the manufacturing process is shown.

[0049] Figure 5A The cross-sectional SEM image of sample No. 1 showed many pores (particularly dark black portions), and the theoretical density ratio of the ceramic substrate was 97.0%. Figure 5C The cross-sectional SEM image of sample No. 3 showed fewer pores, and the theoretical density ratio of the ceramic substrate was 98.5%. Figure 5B The cross-sectional SEM image of sample No. 2 shows particularly few pores, and the theoretical density ratio of the ceramic substrate is 99.2%. It should be noted that the theoretical density ratio is a value measured based on the Archimedean principle.

[0050] SEM-energy dispersive X-ray spectroscopy (EDX) analysis was also performed on sample No. 2 and sample No. 3. The results are as follows 6A to 7D shown. FIG. 6A to FIG. 6D is a diagram showing the results of SEM-EDX analysis of sample No. 2, and FIG. 7A to FIG. 7D 3 is a diagram showing the results of SEM-EDX analysis of sample No. 3. Fig. 6A and Fig. 7A The results of oxygen analysis are shown. Figure 6B and Figure 7B The analysis results of aluminum are shown. Figure 6C and Figure 7C The analysis results of yttrium are shown, and Fig.6D and Fig.7D The analysis results of silicon are shown. Fig. 9 The boundary between the region where silicon is detected and the region where silicon is not detected is indicated by a dotted line for easy understanding, thereby showing Fig.6D The analysis results. Fig.10 The boundary between the region where silicon is detected and the region where silicon is not detected is indicated by a dotted line for easy understanding, thereby showing Fig.7D The analysis results.

[0051] like FIG. 6A to FIG. 6D and FIG. 7A to FIG. 7D As shown in FIG. 1 , silicon was detected mainly in the region where yttrium was detected. This indicates that silicon is contained in YAG.

[0052] In addition, the inventors of the present invention conducted an X-ray diffraction (XRD) analysis. As a result, in any of Sample No. 1, Sample No. 2, and Sample No. 3, an amorphous phase derived from silicon dioxide was not detected.

[0053] Next, an experiment on the volume resistivity of a ceramic substrate conducted by the inventors of the present invention is described. In this experiment, three types of samples (sample No. 4, sample No. 5, and sample No. 6) were prepared. Sample No. 4 is a sample based on the above-described embodiment, and includes a first phase 41 and a second phase 42. The proportion of silicon in the ceramic substrate is 0.17 mass%. Sample No. 5 contains alumina with a purity of 99.9 mass%. Sample 6 includes alumina and YAG, and cerium is added. During the manufacturing process, 0.5 mol% of cerium dioxide (CeO2) is added to the raw sheet as a cerium source. Then, the change in volume resistivity with temperature is measured. The results are as follows. Figure 8 shown. Figure 8 is a graph showing the relationship between temperature and volume resistivity.

[0054] like Figure 8 As shown, in any of the samples No. 4, No. 5, and No. 6, 1×10 15 That is, in sample No. 4, the volume resistivity was equivalent to that of sample No. 5 and sample No. 6.

[0055] Although the preferred embodiments have been described in detail, the present disclosure is not limited to the above embodiments, and various changes and substitutions may be made to the above embodiments without departing from the scope defined in the claims.

Claims

1. A ceramic substrate, comprising: a first phase made of aluminum oxide; as well as The second phase is made of yttrium aluminum garnet containing silicon.

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

3. The ceramic substrate according to claim 1 or 2, wherein: The proportion of the first phase is greater than the proportion of the second phase.

4. The ceramic substrate according to claim 1 or 2, wherein: In the cross section, the total area of ​​the first phase is 1.2 times or more and 1.8 times or less of the total area of ​​the second phase.

5. An electrostatic chuck, comprising: The ceramic substrate according to claim 1 or 2; as well as An electrode is embedded in the ceramic substrate.

6. The electrostatic chuck according to claim 5, wherein: The proportion of the first phase is greater than the proportion of the second phase.

7. The electrostatic chuck according to claim 5, wherein: In the cross section, the total area of ​​the first phase is 1.2 times or more and 1.8 times or less of the total area of ​​the second phase.

8. A substrate fixing device, comprising: Base plate; as well as The electrostatic chuck according to claim 5, which is fixed to the base plate.

9. The substrate fixing device according to claim 8, wherein: The proportion of the first phase is greater than the proportion of the second phase.

10. The substrate fixing device according to claim 8, wherein: In the cross section, the total area of ​​the first phase is 1.2 times or more and 1.8 times or less of the total area of ​​the second phase.

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