JPH11214493A - Electrostatic chuck - Google Patents

Abstract

(57) [Problem] To provide an aluminum nitride electrostatic chuck capable of obtaining a high adsorption force by Johnson-Rahbek force in a temperature range of 0 to 50 ° C. An object chucking surface (5) is an electrostatic chuck (1) made of a ceramic containing aluminum nitride as a main component, and the ceramic is made of at least cerium (C).
e) containing 5 to 20% by volume in terms of oxide, and C
By controlling the atomic ratio of e ³⁺ / Ce ⁴⁺ to a range of 1 to 3, the volume resistivity can be set to 10 ⁸ to 10 ¹² Ω-cm in a temperature range of 0 ° C. to 50 ° C. Thereby, a high adsorption force due to the Johnson-Rahbek force in a low temperature region can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrostatic chuck for adsorbing and holding an object to be fixed by an electrostatic attraction force, and is mainly used for manufacturing semiconductor devices, liquid crystal substrates and the like in the process of manufacturing semiconductor wafers and glass substrates. It is used to hold an object to be fixed.

[0002]

2. Description of the Related Art Conventionally, in a semiconductor manufacturing process, a semiconductor wafer is held in an etching process for performing fine processing on a semiconductor wafer, a film forming process for forming a thin film, or an exposure process for a photoresist. Therefore, an electrostatic chuck is used.

[0003] This type of electrostatic chuck has an electrode for electrostatic attraction between an insulating base and a dielectric layer, and has an upper surface of the dielectric layer as an attraction surface, and is fixed to the attraction surface. A semiconductor wafer, which is an object, is placed and a voltage is applied between the electrostatic chucking electrode and the semiconductor wafer to generate Coulomb force or Johnson-Rahbek force due to dielectric polarization to hold the wafer by suction. .

Further, a plurality of electrostatic chucking electrodes are provided between the insulating base and the dielectric layer, and a voltage is applied between these electrodes so that the wafer mounted on the chucking surface is held by suction. A bipolar type is also known.

[0005] The dielectric layer constituting these electrostatic chucks has little sliding wear due to the attachment and detachment of the wafer.
Further, it is required that the material is not easily corroded by corrosive gas used in various processing steps, and as a material satisfying such required characteristics, insulating ceramics such as alumina and silicon nitride having high wear resistance and corrosion resistance have been used. Was used.

However, in recent years, as the degree of integration of an integrated circuit has been improved, the dielectric layer constituting the suction surface has excellent plasma resistance in addition to abrasion resistance and corrosion resistance, and has a high thermal conductivity. And the use of aluminum nitride as such a material has been proposed (JP-A-62-286247).

[0007]

However, although aluminum nitride has a high attraction force in a high-temperature atmosphere of 300 ° C. or higher, aluminum nitride has a film-forming step performed in a lower-temperature atmosphere or a room-temperature atmosphere. Sufficient adsorbing power can be obtained in an atmosphere at a temperature of 200 ° C. or lower, particularly 0 to 50 ° C., such as an exposure processing step performed at about 25 ° C. or an etching step performed at a low temperature atmosphere of about 0 ° C. There was a problem that it could not be done.

That is, there are two types of electrostatic attraction force for attracting a wafer: a Cron force and a Johnson-Rahbek force. The Clone force depends on the dielectric constant of the material constituting the dielectric layer. It is known that it depends on the volume resistivity of the material constituting the dielectric layer.

More specifically, when the volume resistivity of the dielectric layer is greater than 10 ¹⁵ Ω-cm, the attraction force is governed by Coulomb force, and as the volume resistivity of the dielectric layer decreases, Johnson. When the Labech force is developed and the volume resistivity of the dielectric layer becomes less than 10 ¹¹ Ω-cm, the attraction force is controlled by the Johnson-Rahbek force, which provides a greater attraction force than the Coulomb force.

On the other hand, since the volume resistivity of ceramics decreases as the temperature rises, for example, in the case of aluminum nitride, the volume resistivity in a temperature atmosphere of 300 ° C. or more is about 10 ¹² Ω-cm. Although a high adsorption force due to the Johnson-Rahbek force can be obtained from this fact, the volume resistivity at room temperature (25 ° C.) is 1
0 ¹⁶ Ω-cm or higher, only an attractive force by Coulomb force is obtained, and the dielectric constant is not so high.
Under an atmosphere at a temperature of 00 ° C. or less, a sufficient adsorption force cannot be obtained.

Therefore, when a warped wafer is sucked, the entire surface of the wafer cannot be brought into contact with the suction surface, so that flattening and soaking of the wafer are impaired. Cannot form a thin film having a uniform thickness on the wafer, and cannot perform high-precision processing in the exposure process or the etching process, and can be used only in a limited temperature atmosphere. Was.

[0012]

In order to solve the above-mentioned problems, the present inventors have studied a ceramic resistor forming an object-to-be-fixed adsorbing surface of an electrostatic chuck, particularly from the viewpoint of a material constituting the electrostatic chuck. As a result of stacking, at least cerium (C
e) and by controlling the ratio of trivalent to tetravalent valence by Ce to a specific range, to obtain a resistance characteristic with small temperature dependence even in a temperature range of at least 0 to 50 ° C. Was found, and as a result, a stable adsorption force was obtained even in a low temperature range.

That is, in the electrostatic chuck according to the present invention, the object-adsorbing surface is made of a ceramic containing aluminum nitride as a main component, and the ceramic contains at least cerium (Ce) and Ce ³ (Ce ^{3). +} / Ce ⁴⁺
Is controlled in the range of 1 to 3.

[0014]

1 (a) and 1 (b) are a perspective view showing an electrostatic chuck 1 according to the present invention and a sectional view taken along the line XX of FIG. 1, showing a surface of a ceramic substrate 2 having an insulating property. An electrode 4 for electrostatic attraction is provided, and a dielectric layer 3 is provided on the surface of the ceramic substrate 2 so as to cover the electrode 4 for electrostatic attraction. Surface 5 is formed.

According to the present invention, the dielectric layer 3 is formed of a ceramic containing aluminum nitride as a main component. In this aluminum nitride ceramic, at least cerium (Ce) is used as a sintering aid. Alternatively, it is contained as a resistance adjuster.

Usually, when Ce oxide is contained in aluminum nitride, Ce compounds such as CeAlO ₃ and CeO ₂ are formed at the grain boundaries of the main crystal phase of aluminum nitride. It is considered that conductivity is exhibited by the formation of these Ce compounds.

According to the present invention, the Ce valence of these Ce compounds is trivalent or tetravalent, and the Ce ³⁺ / C
The volume resistivity of the aluminum nitride sintered body is controlled by controlling the ratio of e ⁴⁺ , and from such a viewpoint, the ratio of Ce ³⁺ / Ce ⁴⁺ is set to 1 to 3, especially 1.2 to 2 It is important to control in the range of 0.5.

That is, the resistance value depends on the ratio of Ce ³⁺ / Ce ⁴⁺ , and if the ratio of Ce ³⁺ / Ce ⁴⁺ exceeds 3, the effect of reducing the resistance is small, and it is difficult to obtain the desired resistance. Also, Ce ³⁺ / C
If the ratio of e ⁴⁺ is less than 1, the resistance is too low and the leakage current at the time of adsorption increases, which is inappropriate.

In the present invention, the content of Ce in the aluminum nitride ceramics is 5 in terms of oxide.
It is desirable that the content be 20 to 20% by volume, particularly 7 to 15% by volume.

When the amount of Ce is less than 5% by volume in terms of oxide, the effect of reducing the resistance is small, and the desired resistance is hardly obtained. When the amount exceeds 20% by volume, the control of the ratio of Ce ³⁺ / Ce ⁴⁺ is performed. Is difficult, and the resistance value tends to be too low. As a result, there is a large possibility that a leakage current is generated at the time of adsorption.

In the present invention, in order to prepare an aluminum nitride ceramic having the above-mentioned characteristics for forming a dielectric layer having an object-adsorbing surface, a Ce compound such as CeO ₂ or CeAlO _{3 is} added to aluminum nitride powder. After mixing at a ratio of 5 to 20% by volume, especially 7 to 15% by volume in terms of oxide, the mixture is formed into a predetermined shape by a known molding means, for example, a die press, a cold isostatic press, an extrusion molding or the like. Form into shape. Thereafter, the molded body is placed in a non-oxidizing atmosphere such as nitrogen at a temperature of 1750 to 2100 ° C. for 0.5 to 5 ° C.
It is manufactured by firing for about an hour to densify to a relative density of 95% or more.

In the present invention, the above ceramics Ce ³⁺
The ratio of / Ce ⁴⁺ can be easily controlled by controlling the oxidation / reduction atmosphere by controlling the oxygen partial pressure in the firing atmosphere. That is, when the ratio of Ce ³⁺ / Ce ⁴⁺ is controlled to 2 or more, a nitrogen / hydrogen mixed gas containing 0 to 30% of hydrogen is used, and the ratio of Ce ³⁺ / Ce ⁴⁺ is 1.5 or less. in the case of control, put CeO ₂ powder during firing case for containing the molded body may be controlled CeO ₂ cases units in volume. Further, when the ratio of Ce ³⁺ / Ce ⁴⁺ is controlled to 1.5 to 2, it can be controlled by appropriately using the above two methods.

Further, the resistance value of the dielectric layer 3 forming the suction surface is closely related to the suction force, and it is desired that the resistance value of the dielectric layer 3 has a small change with respect to temperature. From this viewpoint, according to the electrostatic chuck of the present invention, the temperature of the aluminum nitride ceramic forming the dielectric layer 3 is reduced from 0 ° C. to 50 ° C.
It is desirable that the volume resistivity at 10 ° C. is 10 ⁸ to 10 ¹² Ω-cm.

This aluminum nitride sintered body has a resistance of 10 ⁸ to 10 ¹² in a temperature range of 0 ° C. to 50 ° C.
Since it can be appropriately adjusted so as to be in the range of Ω-cm, by applying a voltage between the electrostatic chucking electrode 4 of the electrostatic chuck 1 and the fixed object 10 placed on the suction surface 5, ,
Since a very small leakage current flows between the fixed object 10 and the electrostatic chucking electrode 4, the chucking force due to the Johnson-Rahbek force can be developed, and the fixed object 10 is moved to the suction surface 5.
Can be firmly absorbed and held.

Further, according to the present invention, the electrostatic chuck 1
It is desirable that the ceramic substrate 2 and the dielectric layer 3 are integrally formed by sintering.
The electrostatic chuck 1 can be used in a temperature atmosphere of 0 ° C., and furthermore, the entire electrostatic chuck 1 is made of ceramics resistant to plasma and corrosive gas, so that it can be suitably used in a film forming step, an etching step, and the like.

The ceramic substrate 2 may be formed of an insulating ceramic such as alumina, silicon nitride, or aluminum nitride. In particular, if the ceramic substrate 2 is formed of an aluminum nitride ceramic, the aluminum nitride constituting the dielectric layer 3 may be formed. Since the difference in thermal expansion from the porous ceramics can be eliminated, a highly reliable electrostatic chuck can be obtained without warping or distortion during firing.

In this embodiment, an example of a monopolar electrostatic chuck has been described. However, it is needless to say that the present invention can be applied to a bipolar electrostatic chuck.

[0028]

EXAMPLE 1 Next, an electrostatic chuck 1 shown in FIG. 1 suitable for use in an atmosphere at room temperature (25 ° C.) was prototyped.
The adsorption characteristics were measured. First, purity 99
%, An organic binder and a solvent are added to AlN powder having an average particle size of 1.2 μm to form a slurry, and a plurality of green sheets having a thickness of about 0.5 mm are formed by a doctor blade method, and the green sheets are laminated to form a ceramic. A molded body for forming the substrate 2 was obtained. Then, on one main surface thereof, a tungsten paste in which 5% by volume of AlN powder was mixed with tungsten powder was printed and applied by a screen printing method to form a metal film forming the electrode 4 for electrostatic attraction.

On the other hand, for 93% by volume of AlN powder having a purity of 99% and an average particle size of 1.2 μm, 7% by volume of CeO ₂ having an average particle size of 0.9 μm was added. Then, a green sheet having a thickness of about 0.5 mm is formed by a doctor blade method.
Molded article was obtained.

The dielectric layer 3 is formed on the surface of the formed body for the ceramic substrate 2 provided with the metal film forming the electrode 4 for electrostatic attraction.
And a thermocompression bonding at 80 ° C. under a pressure of 50 kg / cm ² . Thereafter, the laminate is subjected to a cutting process to form a disc, and the disc-shaped laminate is vacuum degreased. Then, at a firing temperature of about 1900 ° C., 10% by volume of hydrogen (H
By baking for 3 hours in a hydrogen / nitrogen mixed atmosphere containing ₂ ), the ceramic substrate and the dielectric layer are both electrostatically adsorbed with a relative density of 99% or more, having an outer diameter of 200 mm, a thickness of 8 mm, and a thickness of 15 μm inside. The plate-shaped body provided with the electrode 4 was formed. Then, the surface of the aluminum nitride ceramics forming the dielectric layer 3 was polished to form the suction surface 5 to form an electrostatic chuck.

The ratio of Ce ³⁺ / Ce ⁴⁺ of the dielectric layer in the manufactured electrostatic chuck was ^measured by using an X-ray photoelectron spectrometer (XPS).
The state of Ce was analyzed by (QUANTUM2000 manufactured by ULVAC-PHI) and Ce ³⁺ in the narrow band spectrum was analyzed.
After separation of the peaks of Ce ⁴⁺ and Ce ^4+, the ratio of Ce ³⁺ / Ce ⁴⁺ was calculated from the respective area ratios. As a result, it was 2.3.

At room temperature (2
5 ° C.), an 8-inch diameter silicon wafer is placed on the suction surface 5, and a voltage of 300 V is applied between the silicon wafer and the electrostatic suction electrode 4 to cause the wafer 10 to be suction-held on the suction surface 5, In this state, when a force required to peel the silicon wafer was measured as a suction force, a suction force of 520 g / cm ² was obtained.

Comparative Example On the other hand, for comparison, an electrostatic chuck (Comparative Example 1) using a high-purity aluminum nitride ceramic made of the same material as the ceramic substrate 2 as a dielectric layer (Comparative Example 1) and Ce ³⁺ /
Electrostatic chucks each having a dielectric layer of aluminum nitride ceramics having a Ce ⁴⁺ ratio of 0.5 (Comparative Example 2) or 4 (Comparative Example 3) were manufactured under the same conditions as in Example 1. Force required to peel off silicon wafer (adsorption force)
Was measured.

As a result, Comparative Example 1 in which the dielectric layer was made of high-purity aluminum nitride ceramics
° C) is 10 ¹⁶ Ω-cm or more, so that only an adsorption force of 10 g / cm ² was obtained.

Further, the ratio of Ce ³⁺ / Ce ⁴⁺ of the dielectric layer is 4
Comparative Example 3 of Aluminum Nitride Ceramics
Has a volume resistivity of 10 ¹⁴ Ω at room temperature (25 ° C.)
Since the pressure was about −cm, the adsorption power was as low as 150 g / cm ² , but there was residual adsorption, and there was a problem in practical use.

In Comparative Example 2 in which the dielectric layer was made of an aluminum nitride ceramic having a Ce ³⁺ / Ce ⁴⁺ ratio of 0.5, the adsorptive power was almost the same as in Example 1 according to the present invention. However, since the volume resistivity at room temperature (25 ° C.) is about 10 ⁵ Ω-cm and less than 10 ⁸ Ω-cm, the amount of leakage current is large, which may adversely affect the wafer.

Further, the high-purity aluminum nitride ceramic of Comparative Example 1 has a volume resistivity of 1 × 10 3 at 300 ° C.
¹² Ω-cm, 5 × 10 ⁹ Ω-cm at 500 ° C., and the aluminum nitride ceramics of Comparative Example 3 having a dielectric layer ratio of Ce ³⁺ / Ce ⁴⁺ of 4 was 1 × 10 ¹⁴ at 25 ° C. Ω-cm,
At 50 ° C., 5 × 10 ¹¹ Ω-cm, all of which had a large rate of change in resistance value and could be used only in a narrow temperature range.

(Example 2) Next, aluminum nitride ceramics (diameter 6) in which the content of cerium (Ce) (in terms of oxide) and the ratio of Ce ³⁺ / Ce ⁴⁺ were respectively changed were used.
A disk having a thickness of 0 mm and a thickness of 2 mm) was prepared in the same manner as in Example 1, and the volume resistivity at 25 ° C. and 0 to 50 ° C. was 3
It was measured by the terminal method. The ratio of Ce ³⁺ / Ce ⁴⁺ was controlled by changing the amount of hydrogen gas in the atmosphere at the time of firing, or by arranging a predetermined amount of CeO ₂ powder in a sagger containing a compact. Each result is as shown in Table 1.

[0039]

[Table 1]

As a result, as can be seen from Table 1, Ce ³⁺ /
Samples Nos. ⁴ and 13 in which the ratio of Ce ⁴⁺ was less than 0.5 and 1 had a volume resistivity at 50 ° C. of 1 × 10 ⁵ Ω-cm or less and a large leakage current. On the other hand, Ce ³⁺ / Ce
Samples Nos. 2 and 9 having a ⁴⁺ ratio of more than 4 were 0 to 50 ° C.
Within the temperature range of 1 × 10 ⁸ to 1 × 10
¹² Ω-cm could not be achieved.

On the other hand, when the ratio of Ce ³⁺ / Ce ⁴⁺ is 1 to 3,
Samples Nos. 3, 5 to ^{8 and} 10 to 12 have a volume resistivity value of 1 × 10 ⁸ to 1 × in a temperature atmosphere of 0 to 50 ° C.
It could be set in the range of 10 ¹² Ω-cm.

From this, when the electrostatic chuck according to the present invention is used, in various processing steps performed at a temperature of 0 to 50 ° C., an attractive force by Johnson-Rahbek force can be obtained, and the object to be fixed can be highly absorbed. It turns out that it can be held with force.

[0043]

As described above, according to the present invention, the adsorption surface for adsorbing and holding an object to be fixed is formed of aluminum nitride ceramic containing Ce, and the Ce ³⁺ / Ce ⁴⁺ ratio is set to a specific range. By controlling the temperature to 50 ° C. or less, it is possible to express the adsorption force by the Johnson-Rahbek force in an atmosphere at a temperature of 50 ° C. or less, and to hold the fixed object with a high adsorption force. Since the change in the resistance value is small, it is possible to provide an electrostatic chuck that can cover a wide temperature range.

Therefore, for example, when the electrostatic chuck of the present invention is used in a film forming process, a thin film having a uniform thickness can be coated on an object to be fixed. If used, the object to be fixed can be subjected to accurate exposure and processing.

[Brief description of the drawings]

FIG. 1A is a perspective view showing an electrostatic chuck according to the present invention, and FIG. 1B is a sectional view taken along line XX of FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Electrostatic chuck 2 ... Ceramic substrate 3 ... Dielectric layer 4 ... Electrostatic adsorption electrode 5 ... Suction surface 10 ... Fixed object

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Yumiko Ito 1-4-4 Yamashita-cho, Kokubu-shi, Kagoshima Inside the Kyocera Research Institute

Claims (3)

[Claims] An object to be fixed is an electrostatic chuck made of a ceramic containing aluminum nitride as a main component, wherein the ceramic is made of at least cerium (Ce).
And an atomic ratio of Ce ³⁺ / Ce ⁴⁺ is 1 to 3. 2. The electrostatic chuck according to claim 1, wherein the ceramic contains 5 to 20% by volume of cerium (Ce) in terms of oxide. 3. The electrostatic chuck according to claim 1, wherein the ceramic has a volume resistivity at 0 ° C. to 50 ° C. of 10 ⁸ to 10 ¹² Ω-cm.