JP2008127276A - Aluminum nitride sintered compact for electrostatic chuck and method of forming the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an aluminum nitride compact for an electrostatic chuck which has volume resistivity in a prescribed range to applied voltage. <P>SOLUTION: The aluminum nitride sintered compact for an electrostatic chuck comprises a composition prepared by adding 0.1-1.0 wt.% chromium oxide, 1.0-3.0 wt.% yttrium oxide and the aluminum nitride as the remainder to make 100 wt.% in total. The aluminum nitride sintered compact for an electrostatic chuck has 1×10<SP>13</SP>-1×10<SP>15</SP>volume resistivity at a normal temperature and small change of the volume resistivity to the applied voltage and the rate of the change of the volume resistivity in a 3000 V/mm electric field to that in a 100 V/mm electric field is ≤5%. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an aluminum nitride sintered body for an electrostatic chuck and a method for forming the same. More specifically, the present invention relates to an aluminum nitride sintered body used for an electrostatic chuck that supports a semiconductor wafer and a method for forming the same.

  An electrostatic chuck that supports a semiconductor substrate or a glass substrate in a semiconductor manufacturing process or a liquid crystal manufacturing process is used. Electrostatic chucks can be broadly classified into methods that use Coulomb force and methods that use Johnson-Rahbek's force.

In the electrostatic chuck using the Coulomb force, the wafer is fixed using electrostatic attraction between particles having different charges existing on the upper and lower surfaces of the dielectric. In this case, the dielectric is preferably 1 × 10 ¹⁵ Ωcm or more. However, when the semiconductor substrate or the glass substrate is enlarged, there is a problem that a sufficiently large electrostatic adsorption force is not uniformly formed on the entire wafer contact surface.

The electrostatic chuck using the Johnson rabek force has a sufficiently low attracting force by using a dielectric having a relatively low volume resistivity, for example, a volume resistivity of 1 × 10 ⁸ to 1 × 10 ¹⁵ Ωcm. Can be provided. However, when the volume resistivity of the dielectric is 1 × 10 ⁸ Ωcm or less, leakage current may occur, and the volume resistivity of the dielectric is maintained in the range of 1 × 10 ¹¹ to 1 × 10 ¹⁵ Ωcm. It is necessary to

There have been many proposals for an electrostatic chuck so far. For example, as an electrostatic chuck using a Coulomb force, a sufficient attracting force can be obtained, and an electrostatic chuck that does not crack during processing [ [Patent Document 1], there is an electrostatic chuck [refer to Patent Document 2] in which particles adhering to the substrate are reduced while maintaining the attractive force, and a ceramic layer as an electrostatic chuck using a Johnson-Rahbek force. And dielectric layer of resin layer, and electrodes that generate electrostatic adsorption force, suppress the generation of excessive leakage current, maintain the adsorption characteristics for a long time, and improve the desorption response of the substrate Chuck (refer to Patent Document 3), an aluminum nitride electrostatic chuck that can obtain a high adsorption force in a high temperature atmosphere of usually 250 ° C. or higher. When other yttrium oxide, erbium oxide, there is an electrostatic chuck which is adapted sufficient suction force can be obtained even at a temperature atmosphere of 200 ° C. or less contain a like ytterbium oxide [Patent Document 4].
Further, as an aluminum nitride sintered body having a small volume resistivity change with temperature change, an aluminum nitride sintered body containing at least one of samarium and lanthanum, iron and nickel (see Patent Document 5), and a nitride containing a rare earth element There is a proposal of an aluminum sintered body (see Patent Document 6).

JP 2007-214288 A JP 2007-173596 A JP 2006-287210 A JP 2002-324832 A Japanese Patent Laid-Open No. 2006-045000 Japanese Patent Laid-Open No. 11-100300

Further, when a predetermined voltage is applied to the electrostatic chuck, the leakage current increases nonlinearly. The leakage current (I) and the applied voltage (V) at this time are represented by the following formula 1 (where I is the leakage current, V is the applied voltage, a is a nonlinear coefficient, and k is a proportional constant).

  In Formula 1, it is preferable that the value of the nonlinear coefficient a which is an increase coefficient of the leakage current I with respect to the applied voltage V has a value of 1.0 or less.

  Accordingly, an object of the present invention is to solve the problems in the prior art, and an aluminum nitride sintered body for an electrostatic chuck that can have a volume resistivity within a certain range with respect to an applied voltage, and the aluminum nitride. It is providing the formation method of a sintered compact.

In order to achieve the above object, the aluminum nitride sintered body for an electrostatic chuck according to the present invention has a composition in which the chromium oxide is 0.1 to 1.0% by weight, the balance is aluminum nitride and the whole is 100% by weight. Yes.
This aluminum nitride sintered body for electrostatic chucks has a volume resistivity of 1 × 10 ¹³ to 1 × 10 ¹⁵ Ωcm at room temperature, a small change in volume resistivity with respect to an applied voltage, and an electric field of 100 V / mm. The volume resistivity change rate in an electric field of 3000 V / mm is within 5% of the volume resistivity at.

Moreover, the aluminum nitride sintered body of the present invention comprises 0.1 to 1.0% by weight of chromic acid, 1.0 to 3.0% by weight of yttrium oxide, the balance being aluminum nitride and 100% by weight as a whole. The composition can also be made. Also in this case, the volume resistivity is 1 × 10 ¹³ to 1 × 10 ¹⁵ Ωcm at room temperature, the change in volume resistivity is small with respect to the applied voltage, and 3000 V with respect to the volume resistivity in an electric field of 100 V / mm. The rate of change of volume resistivity in an electric field of / mm is within 5%.

  The aluminum nitride sintered body for an electrostatic chuck of the present invention is a step of preparing an aluminum nitride powder as a main raw material, and 0.1 to 1.0% by weight of chromic acid is added thereto to make 100% by weight as a whole. The method includes forming a raw material powder having a composition and firing the raw material powder.

  In addition, in the composition in which yttrium oxide is added, the whole powder is obtained by adding 1.0 to 3.0% by weight of yttrium oxide together with 0.1 to 1.0% by weight of chromic acid to the aluminum nitride powder at the stage of forming the raw material powder. The composition is adjusted to 100% by weight.

The aluminum nitride sintered body for an electrostatic chuck according to the present invention is composed of aluminum nitride as a main component, and 0.1 to 1.0% by weight of chromium oxide and 100% by weight as a whole, The volume resistivity of the aluminum nitride sintered body is 1 × 10 ¹³ Ωcm to 1 × 10 ¹⁵ Ωcm at room temperature.

In the composition of the aluminum nitride sintered body, when the chromium oxide is less than 0.1% by weight, the volume resistivity of the aluminum nitride sintered body at a high applied voltage is reduced to 1 × 10 ¹³ Ωcm or less. Even when the content exceeds 0% by weight, the volume resistivity decreases to 1 × 10 ¹³ Ωcm or less at a high applied voltage even when the sintered aluminum nitride is used. In addition, in the aluminum nitride sintered body containing less than 0.1 wt% or more than 1.0 wt% chromium oxide, the volume resistivity at an electric field of 3000 V / mm is compared with the volume resistivity at an electric field of 100 V / mm. The rate of change increases.

  In addition, the aluminum nitride sintered body for electrostatic chucks according to the present invention is further added with yttrium oxide in order to improve the sinterability, and contains aluminum nitride as a main component, and chromium oxide 0.1 to It is also possible to obtain a composition that is 100% by weight by adding 1.0% by weight and 1.0 to 3.0% by weight of yttrium oxide.

  With this composition, when the yttrium oxide is less than 1.0% by weight, the sinterability of the aluminum nitride sintered body is deteriorated, and the relative density may be lowered. When the yttrium oxide exceeds 3.0% by weight Although the volume resistivity of the aluminum nitride sintered body increases, the rate of change in volume resistivity at an electric field of 3000 V / mm may be larger than the volume resistivity at an electric field of 100 V / mm.

  Next, a method for forming an aluminum nitride sintered body will be described. First, after mixing aluminum nitride powder and chromium oxide powder in a composition ratio of 0.1 to 1.0% by weight of chromic acid and the balance being aluminum nitride and the whole being 100% by weight, and further mixed in a solvent , Dry and pulverize. An example of the solvent is absolute ethanol.

  In another embodiment, the composition ratio is 0.1 to 1.0% by weight of chromic acid, 1.0 to 3.0% by weight of yttrium oxide, the balance being aluminum nitride and the whole being 100% by weight. The aluminum nitride powder, the chromium oxide powder, and the yttrium oxide powder are mixed with each other, and further mixed in a solvent, followed by drying and pulverizing.

  Next, a powder mixture obtained by adding chromium oxide powder to the aluminum nitride powder and further adding yttrium oxide powder in the second embodiment is sintered to obtain an aluminum nitride sintered body.

  The sintering temperature in the sintering step is preferably 1700 to 1850 ° C., more preferably 1750 to 1800 ° C., preferably 1 to 10 hours, more preferably 2 to 5 hours. If the sintering maintenance time is less than 1 hour, the relative density of the aluminum nitride sintered body may decrease. In addition, if the sintering time exceeds 10 hours, the properties of the sintered body are not substantially detrimental, but there is no advantage of performing for a long time, which is economically disadvantageous.

The aluminum nitride sintered body according to the present invention thus manufactured has a volume resistivity in the range of 1 × 10 ¹³ Ωcm to 1 × 10 ¹⁵ Ωcm at room temperature. Further, this sintered body has a feature that a change in volume resistivity at a high electric field is small as compared with a low electric field. That is, it was confirmed that the ratio (A / B) of the volume resistivity (A) in the electric field of 100 V / mm and the volume resistivity (B) in the electric field of 3000 V / mm is small, and the influence of the voltage is small.

1. Manufacture of sintered aluminum nitride Aluminum nitride:
High purity reduced aluminum nitride powder having an average particle size of 1.29 μm was used except for 99.9% or more of oxygen. The main impurities in this high-purity reduced aluminum nitride are oxygen; 0.84 wt%, carbon; 31.0 × 10 ⁻³ wt%, potassium; 0.8 × 10 ⁻³ wt%, silicon; 0.9 It confirmed that it was * 10 <^-3> weight% and iron; 0.4 * 10 <^-3> weight%.

Preparation of powder for sintered aluminum nitride:
Mixing aluminum nitride powder with 0.1% by weight of chromium oxide (Cr ₂ O ₃ ) and 1.0% by weight of yttrium oxide (Y ₂ O ₃ ) to obtain a raw material powder mixture with a total of 100% by weight. In a nylon container, absolute ethanol was added and wet mixed using an alumina ball for 20 hours. After mixing, after removing the solvent, the mixture was dried at 80 ° C. and then ground using an alumina mortar. A powder for an aluminum nitride sintered body was obtained through an 80-mesh sieve.

Production of sintered aluminum nitride:
Example 1 After the powder for aluminum nitride sintered body was placed in a graphite mold having a diameter of 210 mm and fired at a sintering temperature of 1750 ° C. under a press pressure of 0.1 MPa for 3 hours in a high-temperature pressure sintering furnace, It was naturally cooled to obtain an aluminum nitride sintered body.

  Examples 2 and 3 An aluminum nitride sintered body was produced in the same manner as in Example 1 except for the chromium oxide content. The composition according to each example is shown in Table 1.

  Comparative Examples 1 and 2 Aluminum sintered bodies were produced in the same manner as in Example 1 except for the content of chromium oxide. The composition according to each comparative example is shown in Table 1.

  Examples 4 to 6: Aluminum nitride sintered bodies were produced in the same manner as in Example 1 except for the contents of chromium oxide and yttrium oxide. The composition according to each example is shown in Table 2.

  Comparative Examples 3 to 8: An aluminum nitride sintered body was produced in the same manner as in Example 1 except for the chromium oxide and yttrium oxide contents. The composition according to each comparative example is shown in Table 2.

2. Volume resistivity measurement method of aluminum nitride sintered body: A disk-shaped test piece having a diameter of 210 mm and a thickness of 0.5 mm was manufactured from the aluminum nitride sintered body, and the electrode shape was set to a main electrode diameter of 26 mm and a protective electrode diameter of 38 mm. An electric field was applied. In this case, the electric field was set to 100, 250, 500, 1000, 2000, and 3000 V / mm, and the volume resistivity was measured based on the voltage application time of 60 seconds. Further, after measuring the leakage current value due to the applied voltage, the nonlinear coefficient (a) was obtained by the slope of the linear function obtained by using the least square method for the log value with respect to the leakage current value.
Results: The results of measuring the volume resistivity of the aluminum nitride sintered bodies for electrostatic chucks using the aluminum nitride sintered bodies produced in the examples and comparative examples are shown in Table 3 and FIGS.

  Referring to Table 3 and FIGS. 1 to 5, in Comparative Examples 1 and 2 where the chromium oxide is less than 0.1 wt% or more than 1.0 wt% with respect to 100 wt% of the total composition, the chromium oxide is 0.1 wt%. It can be confirmed that the volume resistivity is remarkably reduced at a high applied electric field as compared with the example of the aluminum nitride sintered body containing ˜1.0% by weight. In particular, in Comparative Examples 1 and 2, when an electric field of 3000 V / mm is applied to a specimen of an aluminum nitride sintered body, the volume resistivity is remarkably reduced as compared with the case of an electric field of 100 V / mm. It can be confirmed.

Specifically, the volume resistivity is 2.93 × 10 ¹⁴ Ωcm when an electric field of 100 V / mm is applied to the aluminum nitride sintered body according to Comparative Example 1, while the volume is when an electric field of 3000 V / mm is applied. The resistivity is 8.95 × 10 ¹² Ωcm. Therefore, the ratio (A / B) of the volume resistivity (A) with respect to the electric field of 100 V / mm and the volume resistivity (B) with respect to the electric field of 3000 V / mm is 32.7, and when the high electric field is applied It can be confirmed that the volume resistivity is remarkably reduced.

When an electric field of 100 V / mm is applied to the aluminum nitride sintered body according to Comparative Example 2, the volume resistivity is 7.43 × 10 ¹⁴ Ωcm, while it is 3.73 × 10 when an electric field of 3000 V / mm is applied. ¹² Ωcm. Therefore, the volume resistivity ratio (A / B) is 199. It can be confirmed that the volume resistivity is remarkably reduced when a high electric field is applied to the aluminum nitride sintered body according to Comparative Example 2.

  On the other hand, in Comparative Examples 3 to 5 and Comparative Examples 6 to 8 of less than 1.0% by weight or more than 3.0% by weight of yttrium oxide, nitriding containing 1.0 to 3.0% by weight of yttrium oxide according to the present invention It can be confirmed that the volume resistivity is reduced as compared with the aluminum sintered body. In particular, when an electric field of 3000 V / mm is applied to a specimen of an aluminum nitride sintered body, the volume resistivity is reduced as compared to the case of an electric field of 100 V / mm.

When an electric field of 100 V / mm is applied to the aluminum nitride sintered body of Comparative Example 3, while the volume resistivity is 2.01 × 10 ¹⁴ Ωcm, the volume resistivity when an electric field of 3000 V / mm is applied. Is 8.91 × 10 ¹³ Ωcm. Therefore, the ratio (A / B) of the volume resistivity (A) at an electric field of 100 V / mm to the volume resistivity (B) at an electric field of 3000 V / mm is 2.26. When a high electric field is applied to the aluminum nitride sintered body of Comparative Example 3, it can be confirmed that the volume resistivity decreases. In Comparative Example 4, the volume resistivity is 2.13 × 10 ¹⁴ Ωcm when an electric field of 100 V / mm is applied, and 9.26 × 10 ¹³ Ωcm when an electric field of 3000 V / mm is applied, The volume resistivity ratio (A / B) is 2.30.

In Comparative Example 5, the volume resistivity is 2.18 × 10 ¹⁴ Ωcm when an electric field of 100 V / mm is applied, and 9.56 × 10 ¹³ Ωcm when an electric field of 3000 V / mm is applied. The volume resistivity ratio (A / B) is 2.28.

In the case of an aluminum nitride sintered body in which the yttrium oxide exceeds 3.0 wt%, the volume resistivity is 2.31 × 10 ¹⁵ when an electric field of 100 V / mm is applied to the aluminum nitride sintered body of Comparative Example 6. It is 9.70 × 10 ¹⁴ Ωcm when an electric field of 3000 V / mm is applied. Therefore, the ratio (A / B) of the volume resistivity (A) at an electric field of 100 V / mm to the volume resistivity (B) at an electric field of 3000 V / mm is 2.38.

When a high electric field is applied to the aluminum nitride sintered body according to Comparative Example 6, it can be confirmed that the volume resistivity is remarkably reduced.
In Comparative Example 7, the volume resistivity was 2.35 × 10 ¹⁵ Ωcm at an electric field of 100 V / mm, and 9.90 × 10 ¹⁴ Ωcm at an electric field of 3000 V / mm, and the volume resistivity ratio (A / B ) Is 2.37. When a high electric field is applied to the aluminum nitride sintered body according to Comparative Example 7, it can be confirmed that the volume resistivity is remarkably reduced.

In Comparative Example 8, the volume resistivity at an electric field of 100 V / mm is 2.65 × 10 ¹⁵ Ωcm, and at an electric field of 3000 V / mm, it is 8.38 × 10 ¹⁴ Ωcm, and the volume resistivity ratio (A / B ) Is 3.16. When a high electric field is applied to the aluminum nitride sintered body according to Comparative Example 8, it can be confirmed that the volume resistivity is remarkably reduced.

  On the other hand, in the aluminum nitride sintered bodies according to the present invention (Examples 1 to 6), the rate of change between the volume resistivity in an electric field of 100 V / mm and the volume resistivity in an electric field of 3000 V / mm, that is, 100 V / mm. The ratio (A / B) of the volume resistivity (A) in the electric field to the volume resistivity (B) in the electric field of 3000 V / mm is 1.5 or less, the change due to the applied voltage field is small, and the nonlinear coefficient is 0.1. It is as follows. Therefore, even when the applied voltage increases, the increase in leakage current can be relatively reduced.

As described above, the aluminum nitride sintered body according to the present invention has a volume resistivity of 1 × 10 ¹³ to 1 × 10 ¹⁵ Ωcm at room temperature, and the applied voltage is increased from 100 V / mm to 3000 V / mm. Also, the aluminum nitride sintered body has a small volume resistivity change and a relatively low volume resistivity change rate.
This aluminum nitride sintered body for electrostatic chucks has excellent leakage current characteristics.

  As described above, the embodiments of the present invention have been described in detail. However, the present invention is not limited to the embodiments, and as long as it has ordinary knowledge in the technical field to which the present invention belongs, without departing from the spirit and spirit of the present invention, The present invention can be modified or changed.

It is a graph which shows the volume resistivity with respect to an applied electric field in Examples 1-3 of this invention. It is a graph which shows the volume resistivity with respect to an applied electric field in Examples 4-6 of this invention. It is a graph which shows the volume resistivity with respect to the applied electric field in the comparative examples 1 and 2. It is a graph which shows the volume resistivity with respect to an applied electric field in Comparative Examples 3-5. It is a graph which shows the volume resistivity with respect to an applied electric field in Comparative Examples 6-8.

Claims (8)

  An aluminum nitride sintered body for an electrostatic chuck, comprising 0.1 to 1.0% by weight of chromium oxide and a balance of 100% by weight of aluminum nitride as a whole.   2. The aluminum nitride sintered body for electrostatic chuck according to claim 1, wherein the volume resistivity change rate in an electric field of 3000 V / mm is within 5% with respect to the volume resistivity in an electric field of 100 V / mm. . 2. The aluminum nitride sintered body for an electrostatic chuck according to claim 1, wherein the volume resistivity is 1 × 10 ¹³ to 1 × 10 ¹⁵ Ωcm at room temperature.   An electrostatic chuck characterized by comprising 0.1 to 1.0% by weight of chromic acid, 1.0 to 3.0% by weight of yttrium oxide, and the balance being aluminum nitride with the whole being 100% by weight. Aluminum nitride sintered body.   5. The aluminum nitride sintered body for electrostatic chuck according to claim 4, wherein the rate of change in volume resistivity at an electric field of 3000 V / mm is within 5% of the volume resistivity at an electric field of 100 V / mm. . The volume resistivity is 1 × 10 ¹³ to 1 × 10 ¹⁵ Ωm at normal temperature, and the aluminum nitride sintered body for electrostatic chuck according to claim 4. Preparing an aluminum nitride powder;
Molding a raw material powder having a composition of 100 wt% of the whole by adding 0.1 to 1.0 wt% of chromic acid to the aluminum nitride powder;
Firing the raw material powder, and a method of forming an aluminum nitride sintered body for an electrostatic chuck. Preparing an aluminum nitride powder;
Molding a raw material powder having a composition of 100 wt% in total by adding 0.1 to 1.0 wt% chromic acid and 1.0 to 3.0 wt% yttrium oxide to the aluminum nitride powder;
Firing the raw material powder, and a method of forming an aluminum nitride sintered body for an electrostatic chuck.

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