JP2008044846A - Aluminum nitride sintered compact and electrostatic chuck using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an aluminum nitride sintered compact which is free from disadvantage such as occurrence of electric discharge when a voltage is impressed and which has low volume resistivity while maintaining high thermal conductivity, and to provide an electrostatic chuck using the same. <P>SOLUTION: The aluminum nitride sintered compact having volume resistivity at normal temperature of 1×10<SP>9</SP>to 1×10<SP>14</SP>Ω cm is obtained by incorporating an element of the lanthanide in an amount of 0.5 to 7 mass%, expressed in terms of its oxide, so as to form a compound oxide of the lanthanide element and aluminum on the grain boundary of aluminum nitride crystals. A body 10 to be attracted is attracted by using this aluminum nitride sintered compact as a dielectric layer 2 for attracting the body 10 to be attracted and impressing a voltage to an electrode 3 provided below the dielectric layer 2. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an aluminum nitride sintered body having a low volume resistivity, and an electrostatic chuck using the same.

  Ceramics are often used in harsh environments because they are superior in corrosion resistance such as chemical resistance and gas resistance compared to metals. Among them, semiconductor manufacturing equipment, flat panel display manufacturing equipment such as liquid crystal and plasma displays, and chemical processing equipment have processes of severe corrosive environment, and ceramics are used as parts of equipment used in such processes. It is used a lot. In particular, when heating a processed material in a corrosive environment, parts such as a ceramic heater in which electrodes are embedded in ceramics are used.

  In recent years, aluminum nitride parts that are excellent in thermal conductivity and corrosion resistance have attracted attention as ceramic parts used in such an environment. Particularly in semiconductor manufacturing equipment, electrodes are used in aluminum nitride sintered bodies. Electrostatic chucks, susceptors, and heaters with embedded electrodes have been used.

As such an aluminum nitride sintered body, it is common to use aluminum nitride using yttrium oxide as a sintering aid in order to improve thermal conductivity, or aluminum nitride without using a sintering aid. The volume resistivity at room temperature is known to be around 1 × 10 ¹⁵ Ω · cm.

  When the aluminum nitride sintered body having such a volume resistivity is applied to the dielectric layer of the electrostatic chuck, a high adsorption force can be obtained in a high temperature atmosphere of 300 ° C. or higher.

However, such as a film forming process performed in a temperature atmosphere near 200 ° C., an exposure process performed in a room temperature atmosphere (about 25 ° C.), or an etching process performed in a low temperature atmosphere of about −30 to 0 ° C. Furthermore, it is known that ceramics having a volume resistivity of 1 × 10 ⁹ to 1 × 10 ¹⁴ Ω · cm at room temperature are suitable as the dielectric layer in a temperature atmosphere of 200 ° C. or lower. When an aluminum nitride sintered body is applied to an electrostatic chuck used in an environment, there is a problem that the volume resistivity is too high to obtain a sufficient adsorption force.

  As a means for reducing the volume resistivity of aluminum nitride, it has been proposed to add a conductive substance to aluminum nitride (Patent Documents 1 to 3). However, in the sintered body to which the conductive material is added in this way, the distance between the conductive particles is shortened as the volume resistivity is lowered. When a voltage is applied to the electrode of the electrostatic chuck using the sintered body, nitriding is performed. There is a possibility that conductive substances in aluminum are easily discharged, resulting in local heat generation, causing a partial decrease in volume resistivity and an unstable adsorption force.

On the other hand, it has also been proposed to reduce the volume resistivity by dissolving a IIb, IVb, VIb group element or oxygen in an aluminum nitride crystal by chemical vapor synthesis (Patent Document 4). ~ 8). However, since this technique introduces defects and strains in the aluminum nitride crystal, a decrease in thermal conductivity cannot be avoided, and the meaning of using aluminum nitride is diminished.
JP-A-7-297265 JP-A-10-189698 Japanese Patent Laid-Open No. 11-354620 JP-A-7-326655 Japanese Patent Application Laid-Open No. 8-51001 JP-A-8-78202 JP-A-8-153603 JP-A-8-157263

  The present invention has been made in view of such circumstances, and does not cause inconvenience such as discharge when a voltage is applied, and has a low volume resistivity while maintaining high thermal conductivity. An object is to provide a sintered body and an electrostatic chuck using the same.

As a result of intensive studies to achieve the above object, the present inventors have obtained the following knowledge.
(1) By adding an appropriate amount of a lanthanoid element to aluminum nitride, the volume resistivity at room temperature becomes 1 × 10 ⁹ to 1 × 10 ¹⁴ Ω · cm without causing the above-mentioned disadvantages.
(2) By using at least one of Sm and La as the lanthanoid element and further containing an appropriate amount of titanium nitride, the volume resistivity at room temperature can be more stably achieved without causing the above-described disadvantages. 1 × 10 ⁹ to 1 × 10 ¹⁴ Ω · cm.

  The present invention has been completed based on such findings, and provides the following (1) to (4).

(1) The lanthanoid element is contained in an oxide equivalent content of 0.5% by mass or more and 7% by mass or less, and the balance is substantially made of aluminum nitride. An aluminum nitride sintered body in which a composite oxide is formed and a volume resistivity at room temperature is 1 × 10 ⁹ to 1 × 10 ¹⁴ Ω · cm.

  (2) The aluminum nitride sintered body according to (1), wherein the lanthanoid element is at least one of Sm and La.

(3) At least one of Sm and La is an oxide equivalent content of 0.5 mass% or more and 7 mass% or less, and further 28 mass% of titanium nitride in order to suppress discharge of liquid phase components. The volume resistivity at room temperature is 1 × 10 ⁹ to 1 × 10 ¹⁴ Ω · cm, and the discharge hardly occurs when a voltage is applied. Aluminum nitride sintered body.

  (4) An electrostatic chuck having an electrode and a dielectric layer that is provided on the electrode and adsorbs an object to be adsorbed by applying a voltage to the electrode. To an electrostatic chuck characterized by using the aluminum nitride sintered body according to any one of (3) to (3).

  As described above, according to the present invention, by adding an appropriate amount of lanthanoid element to aluminum nitride, by using at least one of Sm and La as the lanthanoid element, and further including an appropriate amount of titanium nitride. An aluminum nitride sintered body having a low volume resistivity can be obtained without causing inconveniences such as occurrence of discharge when a voltage is applied and maintaining a high thermal conductivity. In addition, an electrostatic chuck using the aluminum nitride sintered body of the present invention as a dielectric layer can obtain a good adsorption force in a lower temperature range than a conventional aluminum nitride electrostatic chuck.

Hereinafter, the present invention will be described in detail.
The aluminum nitride sintered body according to the first embodiment of the present invention contains a lanthanoid element in terms of oxide content of 0.5% by mass or more and 7% by mass or less, with the balance being substantially made of aluminum nitride. A composite oxide of a lanthanoid element and aluminum is formed at the grain boundary of the aluminum nitride crystal, and the volume resistivity at room temperature is 1 × 10 ⁹ to 1 × 10 ¹⁴ Ω · cm.

By adding the lanthanoid element in this manner, the lanthanoid element is present in the grain boundary phase of the aluminum nitride crystal, and the composite oxide of the lanthanoid element and aluminum is present in the grain boundary. This contributes to a decrease in the volume resistivity of the aluminum sintered body, and the volume resistivity at room temperature can be set to 1 × 10 ⁹ to 1 × 10 ¹⁴ Ω · cm.

When the crystal phase of the aluminum nitride sintered body sintered with the lanthanoid element added in this way was identified by X-ray diffraction, an aluminum nitride peak and a complex oxide peak of the lanthanoid element and aluminum were obtained. It was. That is, by adding a lanthanoid element to aluminum nitride, a composite oxide of the lanthanoid element and aluminum is formed in the grain boundary phase of the aluminum nitride sintered body, and the composite oxide is the volume resistivity of the aluminum nitride sintered body. It has been found that this contributes to a decrease in. A specific composition is represented by RAlO ₃ , R ₂ Al ₂₂ O ₃₆ , R ₄ Al ₂₂ O ₉ (R is a lanthanoid element).

Using the same raw material, the liquid phase component does not crystallize after the holding time of the firing temperature is completed (that is, peaks of RAlO ₃ , R ₂ Al ₂₂ O ₃₆ , R ₄ Al ₂₂ O ₉ are obtained by X-ray diffraction). No) When a sintered body cooled at a speed was produced, an aluminum nitride sintered body of 1 × 10 ¹⁵ Ω · cm was obtained. This also confirmed that the crystals of these composite oxides contributed to the reduction in resistance of the aluminum nitride sintered body.

  In the present invention, the high thermal conductivity of the aluminum nitride is maintained because the composite oxide of the lanthanoid element and aluminum is formed in the grain boundary phase of the aluminum nitride sintered body to reduce the volume resistivity. . In addition, it is difficult for a discharge to occur when a voltage is applied.

  The lanthanoid element has a function of reducing the volume resistivity as described above, and also functions as a sintering aid. Examples of such lanthanoid elements include lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium ( Any of Dy), holmium (Ho), thulium (Tm), ytterbium (Yb), and lutetium (Lu) may be used. Since the volume resistivity of the aluminum nitride sintered body varies depending on each lanthanoid element to be contained, a material exhibiting a desired volume resistivity may be used. Of these, La and Sm are preferred. In addition to being excellent in the effect as a sintering aid, Sm has the effect that the decrease in resistivity with temperature rise can be reduced. Therefore, it is preferable to use at least one of La and Sm as the lanthanoid element, and among them, the addition of Sm alone is particularly preferable.

The content of the lanthanoid element is 0.5% by mass or more and 7% by mass or less in terms of oxide. If it exceeds 7% by mass, the lanthanoid element becomes excessive, and the volume resistivity becomes about 1 × 10 ¹⁵ Ω · cm. On the other hand, when the content is less than 0.5% by mass, the volume resistivity is about 1 × 10 ¹⁵ Ω · cm because the amount of the lanthanoid element and aluminum composite oxide is too small.

Next, a method for producing the aluminum nitride sintered body will be described.
Since the aluminum nitride sintered body needs to contain a lanthanoid element, aluminum nitride powder and an oxide of the lanthanoid element are used as starting materials and mixed. In order to improve the moldability, an organic binder such as PVA (polyvinyl alcohol) may be added to the starting material. In this case, a degreasing step of the organic binder is necessary after the molding.

  The raw materials thus mixed are molded to produce a molded body, and the obtained molded body is fired in a non-oxidizing atmosphere at 1600 to 1950 ° C. to obtain an aluminum nitride sintered body having a desired volume resistivity. be able to. Of course, you may use the hot press baking method which sinters, adding further press on the same conditions.

  Aluminum nitride to which no sintering aid is added is difficult to sinter, but the oxide of the lanthanoid element or the composite oxide powder of the lanthanoid element and aluminum acts as a sintering aid for aluminum nitride (Yoneya et al. , Journal of the Ceramic Industry Association, 1981), it can be fired at 2000 ° C. or lower and without using a hot press firing method. In addition, oxygen and lanthanoid elements present on the surface of aluminum nitride particles react with aluminum to form a complex oxide of lanthanoid elements and aluminum, resulting in a liquid phase component. The effect of improving the rate is obtained.

  The aluminum nitride powder is produced by a reduction nitridation method or a direct nitridation method, but any of the production methods can be used. When the obtained aluminum nitride sintered body is used as a part of a semiconductor manufacturing apparatus such as an electrostatic chuck, a susceptor, or a heater, impurities are a cause of semiconductor contamination. Therefore, it is desirable that the aluminum nitride powder has a high purity. .

The firing temperature is desirably 1650 to 1950 ° C, and a firing temperature of 1650 to 1850 ° C is particularly preferable. When the temperature is lower than 1650 ° C., no liquid phase component is generated, so that densification is not promoted, and an insufficient sintered body density, specifically, an aluminum nitride sintered body having a relative density of 95% or less can be obtained. is there. Such a sintered body with insufficient sintering often has a volume resistivity of about 1 × 10 ¹⁵ Ω · cm and an insufficient strength. Conversely, when the temperature is higher than 1950 ° C., most of the complex oxide of lanthanoid element and aluminum, which is a liquid phase component, is discharged, which is not preferable.

  The range of 1650 ° C. to 1850 ° C. is particularly preferable. In this range, the densification is sufficiently promoted, and the lanthanoid element is hardly discharged from the aluminum nitride sintered body. This is because the content can be easily controlled because it is contained in the sintered body as it is.

When aluminum nitride powder added with yttrium oxide, which is often used as a sintering aid for aluminum nitride sintered bodies, is baked in such a temperature range, yttrium and aluminum form composite oxides as in the case of lanthanoid elements. However, this composite oxide is easily discharged from the aluminum nitride sintered body, and the amount of yttrium present in the sintered body is considerably less than the initial amount added. However, such a phenomenon is unlikely to occur when a lanthanoid element is added. This is because the melting point of RAlO ₃ , R ₂ Al ₂₂ O ₃₆ , and R ₄ Al ₂₂ O ₉ , which are complex oxides of lanthanoid elements and aluminum, is about 200 ° C. higher than the melting point of complex oxides of yttrium and aluminum. Because.

  When the firing temperature is 1850 to 1900 ° C., the lanthanoid element and aluminum complex oxide is slightly discharged, but in that case, it can be easily dealt with by adding a little more than the target content.

  Firing can be performed in a reducing atmosphere, for example, a nitrogen or argon atmosphere. In the present invention, an oxide of a lanthanoid element is added and this acts as a sintering aid, so that normal pressure firing is possible, but hot press firing can also be used. When hot press firing is used, firing can be performed at a lower temperature and in a shorter time compared to normal pressure firing.

  The average crystal grain size of the aluminum nitride sintered body is preferably about 2 to 10 μm. When the average crystal grain size is larger than 10 μm, the composite oxide of lanthanoid elements and aluminum existing in the grain boundary phase is unevenly distributed, and not only does the volume resistivity vary in the aluminum nitride sintered body, but also the sintered body. Manufacturing problems such as chipping and the like are likely to occur during processing. Conversely, it is difficult to make the average crystal grain size smaller than 2 μm.

The aluminum nitride sintered body according to the second embodiment of the present invention contains 0.5% by mass or more and 7% by mass or less of an oxide equivalent content of at least one of Sm and La, and further a liquid phase. In order to suppress the discharge of components, titanium nitride is contained in an amount of 28% by mass or less, and the balance is substantially made of aluminum nitride, and the volume resistivity at room temperature is 1 × 10 ⁹ to 1 × 10 ¹⁴ Ω · cm, When voltage is applied, it is difficult for discharge to occur.

  By including titanium nitride in the aluminum nitride sintered body in this manner, the discharge of the liquid phase component is suppressed, the control of the content of the lanthanoid element is facilitated, and since titanium nitride is a conductive particle, further volume is required. Contributes to a decrease in resistivity.

  The reason why the amount of titanium nitride added is 28% by mass or less is that when it exceeds 28% by mass, the titanium nitride particles present in the grain boundary phase are too close to each other. When an electrostatic chuck is produced using such an aluminum nitride sintered body, when a voltage is applied to the electrodes, a portion where the titanium nitride particles are discharged is generated, and heat generation further reduces the volume resistivity. The volume resistivity is not uniform in the sintered body, which is not preferable. Furthermore, when the addition amount is 30% by mass or more, titanium nitride in the grain boundary phase constitutes a three-dimensional network, so that the aluminum nitride sintered body becomes a conductor. The preferable addition amount of titanium nitride is 10% by mass or less. More preferably, it is 1-6 mass%.

  By using at least one of Sm and La as the lanthanoid element, a stable volume resistivity can be obtained even when titanium nitride is added, and discharge can be made difficult to occur when a voltage is applied.

  Since the aluminum nitride sintered body of the second embodiment needs to contain at least one of La and Sm, which are lanthanoid elements, and titanium nitride, aluminum nitride powder, oxide of lanthanoid element, and titanium nitride are used as starting materials. And mix them. The subsequent procedure is the same as in the first embodiment.

  By using the aluminum nitride sintered body of the present invention as described above for an electrostatic chuck, a good adsorption force can be obtained in a temperature range lower than that of a conventional aluminum nitride electrostatic chuck. In particular, when attention is focused on the adsorption characteristics near room temperature, not only the adsorption force is improved, but the adsorption and separation time of the silicon wafer is greatly shortened.

  Next, an example of an electrostatic chuck using the aluminum nitride sintered body will be described. 1 and 2 are sectional views showing an electrostatic chuck using the aluminum nitride sintered body of the present invention. FIG. 1 shows a monopolar type, and FIG. 2 shows a bipolar type.

  The monopolar electrostatic chuck 1 shown in FIG. 1 is fixedly provided on a base 5 made of aluminum or the like, has a suction surface, and is a dielectric composed of an aluminum nitride sintered body of the present invention. It has a body layer 2, an electrode 3 provided thereunder, and an insulating layer 4 provided between the electrode 3 and the base 5, and a DC power source 6 is connected to the electrode 3. By supplying power to the electrode 3 from the DC power source 6, the silicon wafer 10, which is an object to be adsorbed, placed on the dielectric layer 2 is electrostatically adsorbed.

  The bipolar electrostatic chuck 1 ′ shown in FIG. 2 includes a pair of electrodes 3a and 3b provided between a dielectric layer 2 and an insulating layer 4, and a DC power source 6 is connected to these electrodes. The silicon wafer 10 placed on the dielectric layer 2 is electrostatically attracted by supplying charges having opposite polarities from 6 to these electrodes.

  The structure of the electrostatic chuck is not particularly limited. In addition to the structure shown in FIGS. 1 and 2, a dielectric layer having an electrode formed on one surface is bonded to a ceramic plate or an aluminum pedestal with an adhesive. Various structures such as a pasted structure can be employed. The electrode structure is not particularly limited, and may be a monopolar electrode or a bipolar electrode as described above, and the shape thereof is not limited.

  The aluminum nitride sintered body of the present invention is suitable as a dielectric layer of an electrostatic chuck, but is not limited thereto, and there is no problem even if it is used for a susceptor or a heater.

Examples of the present invention will be described below.
As shown in Table 1, lanthanoid element oxides were added to aluminum nitride powder produced by the reduction nitriding method (Nos. 1 to 23). Some of the No. For 2, 6, 7, 8, 11, and 23, La or Sm was used as a lanthanoid element, and titanium nitride powder was further added. These raw material powders were mixed for 24 hours using resin balls as a mixing medium and an appropriate amount of IPA (isopropyl alcohol) as a solvent. The obtained slurry was dried and passed through a mesh to produce a raw material powder.

  The obtained raw material powder was hot-press fired at a firing temperature of 1800 ° C., a firing time of 3 hours, and a press pressure of 5 MPa to obtain a sintered body having a diameter of 50 × 10 mm. This sintered body was processed, and the resistivity was measured according to JIS C2141 “Ceramic material test method for electrical insulation”. The amount of lanthanoid element in the aluminum nitride sintered body was measured by ICP emission method. In addition, No. 1 to 20 are within the scope of the present invention. 21-23 are outside the scope of the present invention.

From Table 1, the lanthanoid element amount is 0.5 mass% or more and 7.0 mass% or less. Samples 1 to 20 became low-resistance aluminum nitride sintered bodies satisfying 1 × 10 ⁹ to 1 × 10 ¹⁴ Ω · cm. Among these, No. in which titanium nitride was added in the range of 28% by mass or less. 2, 6, 7, 8, and 11 were confirmed to have a tendency to become a sintered body having a lower resistance than those obtained by adding only the lanthanoid element. That is, No. with La and TiN added. No. 2 was obtained by adding only La. No. 1 in which volume resistivity is smaller than 1, and Sm and TiN are added. Nos. 6, 7, and 8 are No.s to which only Sm was added. The volume resistivity is smaller than 9, 10, and no. No. 11 was the same No. with only Sm added. The volume resistivity was less than 10. Further, they did not cause a significant decrease in thermal conductivity or discharge when a voltage was applied. On the other hand, the amount of lanthanoid element or titanium nitride is outside the scope of the present invention. In 21 to 23, the volume resistivity did not satisfy the above range.

1 is a cross-sectional view showing a monopolar electrostatic chuck to which the present invention is applied. 1 is a cross-sectional view showing a bipolar electrostatic chuck to which the present invention is applied.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 1 '... Electrostatic chuck 2 ... Dielectric layer 3, 3a, 3b ... Electrode 4 ... Insulating layer 5 ... Base 6 ... DC power supply 10 ... Silicon wafer (adsorbed body)

Claims (4)

A lanthanoid element content of 0.5 to 7% by mass in terms of oxide, the balance being substantially made of aluminum nitride, and a composite oxide of lanthanoid element and aluminum at the grain boundaries of the aluminum nitride crystal Is formed, and the volume resistivity at room temperature is 1 × 10 ⁹ to 1 × 10 ¹⁴ Ω · cm.   The aluminum nitride sintered body according to claim 1, wherein the lanthanoid element is at least one of Sm and La. Contains at least one of Sm and La in terms of oxide, 0.5% by mass or more and 7% by mass or less, and further contains 28% by mass or less of titanium nitride in order to suppress discharge of liquid phase components. The remaining portion is substantially made of aluminum nitride, and has a volume resistivity at room temperature of 1 × 10 ⁹ to 1 × 10 ¹⁴ Ω · cm, and discharge is difficult to occur when a voltage is applied. Union.   An electrostatic chuck having an electrode and a dielectric layer provided on the electrode and adsorbing an object to be adsorbed by applying a voltage to the electrode, wherein the dielectric layer is defined as claims 1 to 3. An electrostatic chuck comprising the aluminum nitride sintered body according to any one of the above.

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