JP7194306B1 - Alumina sintered body and electrostatic chuck - Google Patents

Abstract

Kind Code: A1 An alumina sintered body that can be fired in an air atmosphere, does not substantially contain elements that have a high impact on the living body and the environment, exhibits a black or dark gray color, and has low resistance, and a static ceramic body that uses the alumina sintered body. Provide electric chuck.
An alumina sintered body having an Al ₂ O ₃ content of 85% by mass or more, wherein Fe is 0.7% by mass or more and 6.6% by mass or less in terms of Fe ₂ O ₃ and Ti is TiO 1 mass % or more and 5 mass % or less in terms of ₂ , 1 mass % or more and 5 mass % or less of Si in terms of SiO ₂ , and 0.1 mass % or more and 9 mass % or less of Y in terms of Y ₂ O ₃ . This alumina sintered body is used for the mounting plate 1 in the electrostatic chuck.
[Selection drawing] Fig. 1

Description

The present invention relates to an alumina sintered body and an electrostatic chuck using the alumina sintered body.

For example, in semiconductor manufacturing equipment, in order to expose and form a film on a silicon wafer for the purpose of circuit formation, and to etch the silicon wafer, it is necessary to maintain the flatness of the target wafer and prevent the wafer from having a temperature distribution. , to hold the wafer. Mechanical methods, vacuum chucking methods, and electrostatic chucking methods have been proposed as such wafer holding means. Among these holding means, the electrostatic adsorption method is a method of holding a wafer with an electrostatic chuck, and is widely used because it can be used in a vacuum atmosphere.

Electrostatic chucks include a type that uses Coulomb force as an attraction force (Coulomb type) and a type that uses Johnsen-Rahbek force (Johnsen-Rahbek type). The latter Johnsen-Rahbek force is a force generated when a minute electric current flows through a small gap at the interface between the dielectric and the wafer, causing electrification polarization. In order to use the Johnsen-Rahbek force to secure the chucking force required for an electrostatic chuck, it is necessary that the volume resistivity of the dielectric be within the range of 10 ⁹ to 10 ¹² Ω·cm. Also, dielectrics for electrostatic chucks must be black or dark gray in order to allow optical recognition.

As a dielectric having such characteristics, Patent Document 1 discloses an alumina-based dielectric containing 0.8 to 3% by mass of titania and 0.2 to 1% by mass of boron carbide, and a method for producing the same. there is However, in the manufacturing method of Patent Document 1, firing is performed under pressurized conditions such as hot pressing, HIP, gas pressure firing, etc., and the firing atmosphere is a reducing atmosphere or in a vacuum, so expensive equipment is required. necessary. Dielectrics for electrostatic chucks are consumables, and users are demanding low-cost replacement materials.

On the other hand, a method of adding Cr, Mn, Co or Ni is mainly used for blackening the alumina sintered body in air atmosphere firing. For example, Patent Literature 2 discloses a method of blending three or four selected from Cr ₂ O ₃ , Mn ₂ O ₃ , Fe ₂ O ₃ and CoO and firing in an air atmosphere. Further, Patent Document 3 discloses a method of adding Mn or the like and firing in an air atmosphere. However, Cr, Mn, Co, and Ni are known to be expensive and have adverse effects on living organisms and the environment.
Therefore, in recent years, blackening methods that do not use these elements have been studied. For example, Patent Documents 4 and 5 disclose black alumina that can be fired in an air atmosphere by blending alumina with titania and iron oxide. A method of manufacture is disclosed. However, these methods do not reduce the volume resistivity to within the range of 10 ⁹ -10 ¹² Ω·cm, which is the dielectric requirement for Johnsen-Rahbek type electrostatic chucks.

Many production methods have been proposed so far for reducing the volume resistivity of alumina sintered bodies, but most of them are sintered in an inert atmosphere or a reducing atmosphere as in Patent Document 1 above. equipment is required. Although there are some examples of sintering in an air atmosphere, elements such as Cr, Mn, Co, and Ni, which have a high impact on the living body and the environment, are added as in Patent Documents 2 and 3 above.

Japanese Patent No. 6738505 JP-A-05-238810 Japanese Patent No. 4248833 Japanese Patent Application Laid-Open No. 2020-180020 Japanese Patent No. 4994092

In view of the above, the problem to be solved by the present invention is an alumina sintered body that can be fired in an air atmosphere, does not substantially contain elements that have a high burden on the living body and the environment, exhibits a black or dark gray color, and has a low resistance. and to provide an electrostatic chuck using the alumina sintered body.

The present inventors have found the above-mentioned problems in the alumina sintered body, namely (1) that it can be fired in an air atmosphere, (2) that it does not substantially contain elements that have a high biological and environmental load, and (3) As a result of repeated tests and research to simultaneously solve the four problems of exhibiting a black or dark gray color and (4) having a low resistance, specific amounts of Fe, Ti, Si and Y were obtained in terms of oxides. The inventors have found that it is effective to contain each of them separately, and have arrived at the present invention.

That is, according to one aspect of the present invention, the following alumina sintered body is provided.
An alumina sintered body having an Al ₂ O ₃ content of 85% by mass or more,
0.7 mass % or more and 6.6 mass % or less of Fe in terms of Fe ₂ O ₃ , 1 mass % or more and 5 mass % or less of Ti in terms of TiO ₂ , and 1 mass % or more and 5 mass % or less of Si in terms of SiO ₂ , contains 0.1% by mass or more and 9% by mass or less of Y in terms of Y ₂ O ₃ , and the total amount of Cr, Mn, Co and Ni in terms of oxides is 0.1% by mass or less. Sintered body.

According to another aspect of the present invention, there is provided an electrostatic chuck using the alumina sintered body of the present invention as a mounting plate.

According to the present invention, an alumina sintered body that can be fired in an air atmosphere, does not substantially contain elements that have a high biological and environmental load, exhibits a black or dark gray color, and has low resistance, and the alumina sintered body It is possible to provide the electrostatic chuck used.

1 is a schematic diagram showing a configuration example of an electrostatic chuck using an alumina sintered body as a mounting plate according to an embodiment of the present invention; FIG.

The alumina sintered body of the present invention contains 85% by mass or more of Al ₂ O ₃ as its main component. If the content of Al ₂ O ₃ is less than 85% by mass, the excellent properties originally possessed by the alumina sintered body, such as high hardness and strength, and excellent volumetric stability, are impaired. In particular, when the hardness is low, the plasma resistance required for use in electrostatic chucks is lowered, and as a result, sufficient durability cannot be obtained. The content of Al ₂ O ₃ is preferably 90% by mass or more.

In addition to Al ₂ O ₃ as a main component, the alumina sintered body of the present invention contains 0.7% by mass or more and 6.6% by mass or less of Fe in terms of Fe ₂ O ₃ and 1% by mass of Ti in terms of TiO ₂ 5 mass % or less, 1 mass % or more and 5 mass % or less of Si in terms of SiO ₂ , and 0.1 mass % or more and 9 mass % or less of Y in terms of Y ₂ O ₃ .

If the Fe content (meaning the Fe ₂ O ₃ equivalent value; the same applies hereinafter) is less than 0.7% by mass, black or dark gray (hereinafter collectively referred to as “black”) does not appear. That is, blackening becomes insufficient, and resistance reduction becomes insufficient. On the other hand, if the Fe content exceeds 6.6% by mass, the mechanical properties, particularly hardness, are degraded. The Fe content is preferably 1.9% by mass or more and 3.3% by mass or less.
If the Ti content (meaning a _TiO2 equivalent value; the same shall apply hereinafter) is less than 1% by mass, blackening will be insufficient and resistance will not be sufficiently lowered. On the other hand, if the Ti content exceeds 5% by mass, the mechanical properties, particularly hardness, are degraded. The Ti content is preferably 1.5% by mass or more and 3% by mass or less.
Although the details will be described later, in the alumina sintered body of the present invention, at least part of Fe and Ti is Fe ₂ TiO ₅ , and it is believed that this Fe ₂ TiO ₅ contributes to the blackening.

If the Si content (meaning a _SiO2 equivalent value; the same shall apply hereinafter) is less than 1% by mass, the reduction in resistance will be insufficient. On the other hand, if the Si content exceeds 5% by mass, the mechanical properties, particularly hardness, are degraded. The Si content is preferably 1.2% by mass or more and 3% by mass or less.
If the Y content (meaning Y ₂ O ₃ equivalent value; hereinafter the same) is less than 0.1% by mass, the reduction in resistance is insufficient. On the other hand, when the Y content exceeds 9% by mass, the blackening becomes insufficient and the mechanical properties, especially the hardness, deteriorate. The Y content is preferably 0.9% by mass or more and 4.5% by mass or less.

By containing Fe, Ti, Si, and Y in specific amounts in terms of oxides, the four problems described above can be solved simultaneously for the first time.

The alumina sintered body of the present invention can further contain Zr. By containing Zr, the above four problems can be solved at the same time while reducing the content of Ti and Y. Specifically, the sum of Zr converted to ZrO2 _, Ti converted to _TiO2 , and Y converted to _Y2O3 can be ₇ % by mass or less. As a result, excessive production of by-products such as aluminum titanate during firing can be suppressed, and mechanical properties can be improved. Also, by making the above total content 7% by mass or less, the content of Al ₂ O ₃ can be relatively increased, and from this point also, the mechanical properties can be improved.

The alumina sintered body of the present invention does not substantially contain Cr, Mn, Co, and Ni, which are elements that have a high impact on living bodies and the environment. Here, "substantially free" means that Cr, Mn, Co and Ni are not actively used for blackening, etc., and the content of these elements is 0. However, inclusion at the impurity level is allowed. In fact, the raw material used to produce the alumina sintered body may contain Cr, Mn, Co, or Ni as impurities, and in that case, the alumina sintered body will contain these elements at impurity levels. Become. Here, as a guideline for the "impurity level", "the total oxide conversion value of Cr, Mn, Co and Ni is 0.1% by mass or less".

The alumina sintered body of the present invention contains an alumina raw material, an iron oxide raw material, a titanium oxide raw material, a silica raw material, a yttria raw material, and, if necessary, a zirconia raw material. It can be obtained by mixing and molding the compound blended so as to obtain the composition, and then firing it in an air atmosphere. The firing temperature can be 1300° C. or higher and 1500° C. or lower. Specifically, the alumina sintered body of the present invention is obtained by firing until the relative density reaches 95% or more. Note that the Fe ₂ TiO ₅ described above is produced during the firing process in an air atmosphere.
Further, when a zirconia raw material is used, a general zirconia raw material contains a stabilizing component such as Y ₂ O ₃ . The content of stabilizing components such as ₂ O ₃ is also summed.

FIG. 1 schematically shows a configuration example of an electrostatic chuck using an alumina sintered body as a mounting plate, which is one embodiment of the present invention. The electrostatic chuck shown in the figure is a Johnsen-Rahbek type electrostatic chuck, and includes a mounting plate 1 for mounting a sample such as a wafer, a substrate 2 integrated with this mounting plate, and these mounting plates. 1 and a substrate 2, and a power supply portion 4 provided so as to penetrate the substrate 2 to supply power to the internal electrode 3. An alumina sintered body, which is one embodiment, is used.

As described above, when the alumina sintered body of the present invention is used as a mounting plate for a Johnsen-Rahbek type electrostatic chuck, the specific volume resistivity is within the range of 10 ⁹ to 10 ¹² Ω·cm as described above. There is a requirement. Therefore, when the alumina sintered body of the present invention is used as a mounting plate of a Johnsen-Rahbek type electrostatic chuck, the specific volume resistivity can be adjusted within the above range by adjusting the mixing ratio of the above ingredients. to When used as a mounting plate for a Johnsen-Rahbek type electrostatic chuck, the specific volume resistivity is preferably in the range of more than 1×10 ¹¹ Ω·cm and 1×10 ¹² Ω·cm or less. More preferably, it is in the range of more than 5×10 ⁹ Ω·cm and 1×10 ¹¹ Ω·cm or less.
On the other hand, the alumina sintered body of the present invention can also be used for applications other than the mounting plate of the Johnsen-Rahbek type electrostatic chuck, for example, as a member for removing static electricity in a semiconductor manufacturing apparatus. Also in such applications, it is necessary to reduce the resistance, and specifically, it is preferable that the specific volume resistivity is 10 ¹² Ω·cm or less. The lower limit of the specific volume resistivity is not particularly limited, but in the alumina sintered body of the present invention, the content of Al ₂ O ₃ is 85% by mass or more, and Fe, which contributes to lower resistance, Since the upper limits of the contents of Ti, Si and Y are also specified, the lower limit of the specific volume resistivity is naturally determined. Specifically, the lower limit is about 10 ⁶ Ω·cm.

An alumina raw material, an iron oxide raw material, a titanium oxide raw material, a silica raw material, a yttria raw material, a zirconia raw material and other raw materials were blended so as to have the oxide conversion value content of each example shown in Table 1 to obtain a blend. The compound of each example was mixed, molded and fired to obtain an alumina sintered body of each example. The presence or absence of Fe ₂ TiO ₅ , specific volume resistivity, color tone determination, and Vickers hardness were evaluated for the obtained alumina sintered body. Here, the above-mentioned "other raw materials" are raw materials containing at least one of Cr, Mn, Co and Ni, and were used only in Example 11. Further, the firing was performed in the temperature range of 1350 to 1450° C. in an air atmosphere.

The evaluation method for each evaluation item is as follows.
The presence or absence of Fe ₂ TiO ₅ was evaluated by confirming the peak of Fe ₂ TiO ₅ by powder X-ray diffraction using Cu—Kα rays.
The specific volume resistivity was measured by the three-probe method (applied voltage 1000 V, room temperature). The evaluation is as follows: ⊚ (excellent) when the specific volume resistivity is over 5× ^{10 9} Ω·cm and 1× ^{10 11} Ω·cm or less; ), and exceeding 1×10 ¹² Ω·cm was defined as × (defective).
The color tone was determined visually.
Vickers hardness was measured based on JIS Z2244 (applied pressure 1 kgf). Vickers hardness (HV) of 1350 or more was evaluated as ◯ (good), and less than 1350 as x (bad).

In Table 1, Examples 1 to 12 are all alumina sintered bodies within the scope of the present invention, and good evaluation results were obtained. Particularly good evaluation results were obtained in Examples 9 to 11, which are within the preferred range of the present invention. Although not shown in the evaluation in Table 1, among Examples 1 to 12, Examples 1, 3, and 9 to 11 in which the content of Al ₂ O ₃ is 90% by mass or more are other examples. Vickers hardness tended to be higher than that of

Comparative Example 1 is an example containing no Fe, and Fe ₂ TiO ₅ was not generated, the color tone remained white, and the resistance was insufficiently lowered. On the other hand, Comparative Example 2 is an example in which the Fe content exceeds the upper limit of the present invention, and sufficient hardness was not obtained.

Comparative Example 3 is an example containing no Ti, and Fe ₂ TiO ₅ was not generated, the color tone remained white, and the resistance was insufficiently lowered. On the other hand, Comparative Example 4 is an example in which the Ti content exceeds the upper limit of the present invention, and sufficient hardness was not obtained.

Comparative Example 5 is an example containing no Si, and the reduction in resistance was insufficient. On the other hand, Comparative Example 6 is an example in which the Si content exceeds the upper limit of the present invention, and sufficient hardness was not obtained.

Comparative Example 7 is an example in which Y is not contained, and the reduction in resistance was insufficient. On the other hand, Comparative Example 8 is an example in which the Y content exceeds the upper limit of the present invention, and blackening was insufficient and sufficient hardness was not obtained.

REFERENCE SIGNS LIST 1 mounting plate 2 substrate 3 internal electrode 4 feeding part

Claims (5)

An alumina sintered body having an Al ₂ O ₃ content of 85% by mass or more,
0.7 mass % or more and 6.6 mass % or less of Fe in terms of Fe ₂ O ₃ , 1 mass % or more and 5 mass % or less of Ti in terms of TiO ₂ , and 1 mass % or more and 5 mass % or less of Si in terms of SiO ₂ , contains 0.1% by mass or more and 9% by mass or less of Y in terms of Y ₂ O ₃ , and the total amount of Cr, Mn, Co and Ni in terms of oxides is 0.1% by mass or less. Sintered body. The alumina sintered body according to claim ₁ , wherein at least part of said Fe and said Ti is _Fe2TiO5 . The alumina firing according to claim ₁ , further containing Zr, wherein the sum of Zr converted to ZrO2 _, Ti converted to _TiO2 , and Y converted to _Y2O3 is 7% by mass or less. body. 2. The alumina sintered body according to claim 1, having a specific volume resistivity of 10< ¹² > [Omega].cm or less. An electrostatic chuck using the alumina sintered body according to any one of claims 1 to 4 as a mounting plate.

Images