Dielectric for an electrostatic chuck

Abstract

The present invention provides a dielectric for an electrostatic chuck, which can ensure sufficient hardness while ensuring basic properties such as the volume resistivity required for a Johnson-Rabeck type dielectric for an electrostatic chuck. The main crystal phase of the dielectric for an electrostatic chuck of the present invention is composed of corundum, contains Al5BO9 as another crystal phase, and the peak intensity I A of Al5BO9 (021 plane) based on powder X-ray diffraction B and the peak intensity I A of corundum (012 plane) B The ratio: I A / I B is 0.04 or more and 0.4 or less.

Description

Technical Field

[0001] The present invention relates to a dielectric used for an electrostatic chuck that highly accurately positions and fixes semiconductor wafers such as silicon wafers and various substrates such as LCD substrate glass. Background Art

[0002] For example, in a semiconductor manufacturing apparatus, in order to perform exposure, film formation, and etching of a silicon wafer for the purpose of forming a circuit, it is necessary to maintain the flatness of the wafer as an object and to maintain the wafer in such a manner that no temperature distribution occurs in the wafer. As means for holding such a wafer, a mechanical method, a vacuum adsorption method, and an electrostatic adsorption method have been proposed. Among these holding means, the electrostatic adsorption method is a method of holding a wafer using an electrostatic chuck, and since it can be used in a vacuum atmosphere, it is often used.

[0003] For an electrostatic chuck, there are a type that uses Coulomb force as an adsorption force (Coulomb type) and a type that uses Johnson-Rahbek force as an adsorption force (Johnson-Rahbek type). The latter Johnson-Rahbek force is a force generated by inducing a small current to flow through a small gap at the interface between the dielectric and the wafer and by band electrode polarization, and is generated when the volume resistivity of the dielectric is 10 12 ~10 13 Ω·cm or less. Moreover, in order to use the Johnson-Rahbek force to ensure the adsorption force required for an electrostatic chuck, it is a necessary condition that the volume resistivity of the dielectric is in the range of 10 9 ~10 13 Ω·cm.

[0004] Conventionally, as a dielectric for an electrostatic chuck of the Johnson-Rahbek type, a ceramic obtained by adding a transition metal element to alumina, such as an Al2O3-TiO2 system, etc. (for example, refer to Patent Document 1), has been known.

[0005] Prior Art Documents

[0006] Patent Documents

[0007] Patent Document 1: Japanese Patent No. 4354138 Gazette Summary of the Invention

[0008] Problems to be Solved by the Invention

[0009] When the present inventor used the Al2O3-TiO2-based dielectric of Patent Document 1 in the electrostatic chuck of an etching apparatus, it was found that the durability was insufficient. That is, it was found that when the electrostatic chuck was used in a plasma atmosphere in the etching apparatus, the hardness of the Al2O3-TiO2-based dielectric of Patent Document 1 was insufficient, and thus the plasma resistance was reduced. As a result, sufficient durability could not be obtained.

[0010] Accordingly, the problem to be solved by the present invention is to provide a dielectric for an electrostatic chuck that can ensure sufficient hardness while ensuring basic properties such as the volume resistivity required for a Johnson-Rabek type electrostatic chuck dielectric.

[0011] Means for Solving the Problem

[0012] To solve the above problems, the inventors of the present invention repeated experiments and research, and as a result, learned that by appropriately containing Al5BO9 as another crystal phase in a dielectric for an electrostatic chuck whose main crystal phase is composed of corundum, it is possible to ensure sufficient hardness while ensuring basic properties such as the volume resistivity required for a Johnson-Rabek type electrostatic chuck dielectric.

[0013] That is, according to the present invention, the following dielectrics 1 to 3 for an electrostatic chuck are provided.

[0014] 1. A dielectric for an electrostatic chuck, wherein the main crystal phase is composed of corundum, contains Al5BO9 as another crystal phase, and the peak intensity I of Al5BO9 (021 plane) A with respect to the peak intensity I of corundum (012 plane) B The ratio: I A / I B is 0.04 or more and 0.4 or less.

[0015] 2. The dielectric for an electrostatic chuck according to the above 1, wherein the Vickers hardness is 16 GPa or more.

[0016] 3. The dielectric for an electrostatic chuck according to the above 1 or 2, which is obtained by mixing, molding, and firing a blend containing 0.8% by mass or more and 3% by mass or less of titanium dioxide, 0.2% by mass or more and 1% by mass or less of boron carbide, and the balance mainly composed of an alumina raw material.

[0017] Advantages of the Invention

[0018] According to the present invention, it is possible to ensure sufficient hardness while ensuring basic properties such as the volume resistivity required for a Johnson-Rabek type electrostatic chuck dielectric. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 is the powder X-ray diffraction intensity data of Example 1 as an example of the present invention.

[0020] Figure 2 is a conceptual cross-sectional view of an example of a Johnson-Rabek type electrostatic chuck. DETAILED DESCRIPTION OF THE INVENTION

[0021] The main crystal phase of the dielectric for an electrostatic chuck of the present invention is composed of corundum, and as other crystal phases, it contains Al5BO9. Moreover, the peak intensity of Al5BO9 (021 plane) based on powder X-ray diffraction is set as I A , and the peak intensity of corundum (012 plane) based on powder X-ray diffraction is set as I B . When the peak intensity ratio (I A / I B ) is 0.04 or more and 0.4 or less.

[0022] If I A / I B is less than 0.04, sufficient hardness cannot be ensured.

[0023] On the other hand, if I A / I B exceeds 0.4, a large amount of Al5BO9 is generated at the grain boundaries. Therefore, the volume resistivity increases and the adsorption force decreases. That is, in the dielectric for an electrostatic chuck of the Johnson-Rabek type, by forming a low-resistance grain boundary phase at the grain boundaries, appropriate conductivity is ensured and the volume resistivity is reduced. However, if a large amount of Al5BO9 is generated at the grain boundaries, Al5BO9 hinders the conductivity of the low-resistance grain boundary phase. As a result, the volume resistivity increases.

[0024] Regarding the hardness of the dielectric for an electrostatic chuck of the present invention, the Vickers hardness can be 16 GPa or more. That is, "the Vickers hardness is 16 GPa or more" is an index to ensure sufficient hardness. From the aspect of ensuring more sufficient hardness, the hardness of the dielectric for an electrostatic chuck of the present invention can also make the Vickers hardness 18 GPa or more. In order to ensure that the Vickers hardness is 18 GPa or more, I A / I B is preferably 0.18 or more and 0.4 or less.

[0025] Such a dielectric for an electrostatic chuck of the present invention can be manufactured as follows: A mixture containing 0.8 mass% or more and 3 mass% or less of titanium dioxide, 0.2 mass% or more and 1 mass% or less of boron carbide, and the balance mainly composed of an alumina raw material is mixed, molded, and fired.

[0026] If the content rate of titanium dioxide in the mixture is less than 0.8 mass%, the generation amount of Ti 3+ decreases, the volume resistivity increases, and there is a concern that the adsorption force decreases. That is, titanium dioxide (TiO2) is dissolved in the grain boundary phase of alumina (Al2O3) raw material particles, reducing the volume resistivity. Specifically, during firing, a part of Ti 4+ of TiO2 is reduced to Ti 3+ , and this Ti 3+Replace Al dissolved in Al2O3 3+ sites, thereby forming a low-resistance grain boundary phase ((Al, Ti)2O3). Therefore, if the content rate of titanium dioxide in the blend is less than 0.8% by mass, the amount of Ti 3+ generated decreases, the volume resistivity increases, and there is a concern that the adsorption force decreases.

[0027] On the other hand, if the content rate of titanium dioxide in the blend exceeds 3% by mass, the volume resistivity decreases excessively and the leakage current becomes large, which may cause adverse effects on the circuit of the wafer and the like.

[0028] If the content rate of boron carbide (B4C) in the blend is less than 0.2% by mass, it may not be possible to ensure sufficient hardness. Especially when the electrostatic chuck is used in a plasma atmosphere, if sufficient hardness cannot be ensured, it may deteriorate quickly and the durability may decrease. In addition, if the content rate of boron carbide in the blend is less than 0.2% by mass, the blackening of the electrostatic chuck becomes insufficient, and there may be a concern that dirt becomes obvious.

[0029] On the other hand, if the content rate of boron carbide in the blend exceeds 1% by mass, a large amount of Al5BO9 is generated at the grain boundaries, so the volume resistivity increases, and there is a concern that the adsorption force decreases.

[0030] From the aspect of ensuring more sufficient hardness, the content rate of boron carbide in the blend is preferably 0.4% by mass or more and 1% by mass or less.

[0031] As described above, the dielectric for an electrostatic chuck of the present invention is obtained by mixing a specified amount of titanium dioxide, boron carbide, and alumina raw materials, molding them into a specified shape by pressing, CIP (cold isostatic pressing), doctor blading, etc., degreasing as needed, and then firing.

[0032] The firing can be carried out by ordinary atmospheric sintering, but it is likely to be relatively low density, so pressure sintering such as hot pressing, HIP, and gas pressure sintering is preferred. The firing atmosphere can be set to an inert gas atmosphere such as argon, a reducing gas atmosphere such as hydrogen (i.e., a non-oxidizing atmosphere), or a vacuum. The firing temperature can be set to 1200 °C or more and 1700 °C or less.

[0033] It should be noted that in the blend of the present invention, the balance other than titanium dioxide and boron carbide is mainly composed of alumina raw materials, but in addition to the alumina raw materials, magnesia (MgO), silica (SiO2), lanthanum oxide (La2O3), yttrium oxide (Y2O3), calcium oxide (CaO), cerium oxide (Ce2O3), etc. can be contained as sintering aids. However, their content rates are preferably set to 3% by mass or less (including 0) in total.

[0034] Example

[0035] Titanium dioxide, boron carbide, and alumina raw materials were blended so as to have the content ratios shown in each example of Table 1 to obtain a blend. The blends of each example were respectively mixed, formed, and fired to obtain dielectrics for an electrostatic chuck in each example.

[0036] For the dielectrics for an electrostatic chuck obtained in each example, the peak intensity I of the (021 plane) of Al5BO9 was evaluated by powder X-ray diffraction based on Cu-Kα rays. A And the peak intensity I of the (012 plane) of corundum B Ratio: I A / I B , and the Vickers hardness, volume resistivity, and adsorption force were evaluated, and the color tone was determined together.

[0037] [Table 1]

[0038]

[0039] In Figure 1 , as an example of powder X-ray diffraction, the powder X-ray diffraction intensity data of Example 1 as an example of the present invention are shown. Based on such powder X-ray diffraction intensity data, the peak intensity I of the (021 plane) of Al5BO9 was evaluated. A And the peak intensity I of the (012 plane) of corundum (Al2O3) B Ratio: I A / I B . It should be noted that the peak intensity ratio (I A / I B ) of each example was mainly adjusted by adjusting the content ratio of boron carbide in the blend.

[0040] The Vickers hardness was measured based on JIS Z2244 (applied pressure: 1 kgf). For the evaluation, a Vickers hardness of 18 GPa or more was evaluated as ◎ (excellent), 16 GPa or more and less than 18 GPa was evaluated as ○ (good), and less than 16 GPa was evaluated as × (poor).

[0041] The volume resistivity was measured by the three-terminal method (applied voltage: 500 V, room temperature). For the evaluation, a volume resistivity of 9.7×10 9 Ω·cm or more and 3.8×10 10 Ω·cm or less was set as ◎ (excellent), more than 3.8×10 10 Ω·cm and 1.3×10 11 Ω·cm or less, or 3.8×10 9 Ω·cm or more and less than 9.7×10 9Set Ω·cm as ○ (good), and set values exceeding 1.3×10 11 Ω·cm or less than 3.8×10 9 Ω·cm as × (bad).

[0042] It should be noted that in Table 1, among those marked as ○ (good), values exceeding 3.8×10 10 Ω·cm and 1.3×10 11 Ω·cm or less are marked as ○ (H), values of 3.8×10 9 Ω·cm or more and less than 9.7×10 9 Ω·cm are marked as ○ (L). Additionally, among those marked as × (bad), values exceeding 1.3×10 11 Ω·cm are marked as × (H), and values less than 3.8×10 9 Ω·cm are marked as × (L).

[0043] The adsorption force is measured by assembling the dielectric of each example into the Figure 2 shown Johnson-Rabek type electrostatic chuck. That is, as Figure 2 shown, Ti is sputtered on one surface of the dielectric 1 to impart an electrode as the conductor layer 3. The insulator substrate 2 (aluminum oxide) is bonded thereto using an epoxy-based adhesive 4 with the conductor layer 3 sandwiched in between. At this time, a hole is pre-opened at the center of the insulator substrate 2 for use as a lead electrode. Finally, the dielectric 1 is ground and polished to a thickness of 2 mm, and a lead electrode 5 is installed to fabricate the electrostatic chuck. Then, a DC voltage of 300 V is applied to this electrostatic chuck through a power supply 7 in a vacuum for 60 seconds, and the adsorption force when a silicon wafer 6 is adsorbed in the vacuum is measured. Regarding the evaluation, an adsorption force of 40 g / cm 2 or more is set as ◎ (excellent), 20 g / cm 2 or more and less than 40 g / cm 2 is set as ○ (good), and less than 20 g / cm 2 is set as × (bad).

[0044] The hue determination is carried out visually.

[0045] In Table 1, Examples 1 to 7 are dielectrics within the scope of the present invention, and each evaluation is ◎ (excellent) or ○ (good), which is good; the hue determination is also black or blue, which is good. Among them, for Examples 1, 3, 4, 6, and 7 where the peak intensity ratio (I A / I B ) is 0.18 or more and 0.4 or less, the Vickers hardness is 18 GPa or more (◎ (excellent)), which is particularly good, and the hue determination is also black, which is particularly good.

[0046] In contrast, Comparative Example 1 has a peak intensity ratio (I A / I B)Examples with too small values, where the Vickers hardness is less than 16 GPa (× (defective)), do not achieve sufficient hardness. Additionally, the color tone determination is cyan, which is defective.

[0047] On the other hand, Comparative Example 2 is an example where the peak intensity ratio (I A / I B ) is too large, and the volume resistivity rises to exceed 1.3 × 10 11 Ω·cm, resulting in a decrease in the adsorption force.

[0048] Description of the reference numerals

[0049] 1 Dielectric

[0050] 2 Insulator substrate

[0051] 3 Conductor layer (electrode)

[0052] 4 Epoxy-based adhesive

[0053] 5 Lead electrode

[0054] 6 Silicon wafer

[0055] 7 Power supply

Claims

1. Dielectric for an electrostatic chuck, wherein, The main crystal phase is composed of corundum, and contains Al5BO9 as other crystal phases. The peak intensity I of the (021 plane) of Al5BO9 based on powder X-ray diffraction A and the peak intensity I of the (012 plane) of corundum B The ratio: I A / I B is 0.04 or more and 0.4 or less.

2. The dielectric for an electrostatic chuck according to claim 1, wherein, The Vickers hardness is 16 GPa or more.

3. The dielectric for an electrostatic chuck according to claim 1 or 2, which is obtained by mixing, molding, and firing a blend, the blend containing 0.8% by mass or more and 3% by mass or less of titanium dioxide, 0.2% by mass or more and 1% by mass or less of boron carbide, and the balance including an alumina raw material.

4. The dielectric for an electrostatic chuck according to claim 3, wherein, The blend further contains a sintering aid.

5. The dielectric for an electrostatic chuck according to claim 4, wherein, The sintering aid is selected from magnesium oxide MgO, silicon dioxide SiO2, lanthanum oxide La2O3, yttrium oxide Y2O3, calcium oxide CaO, and cerium oxide Ce2O3.

Images