JP4722463B2 - Dielectric ceramics for electrostatic chuck and manufacturing method thereof - Google Patents

Description

  The present invention relates to a dielectric ceramic for an electrostatic chuck suitable for an electrostatic chuck used for fixing, transporting, and flattening a silicon substrate, a compound semiconductor substrate, or a glass substrate in a semiconductor or liquid crystal manufacturing process.

  Conventionally, electrostatic chucks have been used to fix and transport silicon substrates, compound semiconductor substrates, and glass substrates in semiconductor and liquid crystal manufacturing processes. In particular, when a substrate is fixed and transported in a vacuum, such as an electron beam lithography apparatus, dry etching apparatus, CVD apparatus, and PVD apparatus, a vacuum chuck cannot be used, so that the substrate can be fixed and transported even if there is no gas pressure difference. The electrostatic chuck was effective. Furthermore, in recent years, with the miniaturization of devices, the flatness of wafers and glass substrates, which are substrates, has been increasingly emphasized, and electrostatic chucks are being used for correction.

In order to correct the flatness of such a substrate, an extremely large adsorption force is required. For this purpose, a transition metal oxide such as titania (TiO ₂ ) is mixed with an insulator such as alumina (Al ₂ O ₃ ). It has been proposed to reduce the volume resistivity of dielectric ceramics and improve electrostatic attraction (see Patent Document 1, Patent Document 2, Non-Patent Document 1, Patent Document 3, Patent Document 4, etc.). .

Japanese Patent Laid-Open No. 62-94953 JP-A-2-22166 JP-A-3-147784 JP 2003-188247 A JP 37-8579 A JP-A-11-176920 Jpn. J. et al. Appl. Phys. Vol. 32 (1993) p. 864-87

Hereinafter, although titanium (Ti) is demonstrated to an example as a transition metal, it is not restricted to this. When Al ₂ O ₃ is used a mixture of TiO _2, added was Ti is dissolved in the Al ₂ O ₃ within the particles, further, since the Ti in the grain boundary phase present between Al ₂ O ₃ particles are dissolved, The volume resistivity of the dielectric ceramic that is the parent phase is lowered. If this volume resistivity is in the range of 1 × 10 ⁹ to 1 × 10 ¹¹ Ωcm, a small current flows through a small gap at the interface between the dielectric ceramic and the object to be adsorbed, and the adsorption power is greatly increased by the Johnson Rabeck effect. To improve. However, when TiO ₂ is mixed and sintered, a composite oxide composed of aluminum (Al) and Ti, such as aluminum titanate (Al ₂ TiO ₅ ), is present between Al ₂ O ₃ particles constituting the dielectric ceramic. It is formed at the same time. This Al ₂ TiO ₅ is a high-resistance compound having a eutectoid decomposition temperature of 1150 to 1300 ° C. and a resistance of 10 ¹² Ωcm or more in an Al ₂ O ₃ —TiO ₂ binary system. In this way, when there are phases with different resistivity, the object to be adsorbed cannot be easily detached from the adsorption surface, and the response characteristics to voltage (adsorption force saturation time, residual adsorption force extinction time) are inferior. The inventors have found. This is because the charge movement easily occurs in the Al ₂ O ₃ matrix having a relatively low resistivity, but is blocked when it reaches the boundary with Al ₂ TiO ₅ .

In particular, the techniques disclosed in Patent Document 2 and Patent Document 4 include oxides of alkaline earth metals such as magnesium (Mg) and calcium (Ca) in addition to transition metal oxides such as TiO _2. Yes. Al ₂ TiO ₅ is relatively unstable and easily decomposed at low temperatures, but it has long been known that the addition of alkaline earth metal oxides such as magnesia (MgO) is effective in suppressing decomposition (patents). Reference 5). This is considered to be because the composite oxides (MgTi ₂ O ₅ ) composed of Al ₂ TiO ₅ , Ti, and Mg each form a full solid solution and lower the eutectoid decomposition temperature of Al ₂ TiO ₅ . For this reason, high resistance composite oxides (Al ₂ TiO ₅ , MgAl ₈ Ti ₆ O ₂₅ , Mg _0.3 Al _1.4 Ti _1.3 O ₅ , Mg _0.6 Al _0.8 Ti _0.6 O _5, etc.) are stable between the Al ₂ O ₃ particles. And the desorption response characteristics such as the residual adsorption disappearance time are deteriorated.

In Patent Document 2, the residual electrostatic attraction force is reduced by a decrease in the volume resistivity of the dielectric ceramic, and the disappearance rate of the remaining volume charge and surface charge is increased in inverse proportion to the volume resistivity. According to the present invention, in order to set the volume resistivity to, for example, 1 × 10 ⁸ Ωcm, it is necessary to mix about 25% by mass of TiO _2. You must avoid as much as possible. Further, if the volume resistivity is too low, a new problem arises that a large leak current flows from the adsorption device to the silicon substrate and the circuit of the wafer is destroyed.

  Particularly in recent years, there has been a strong demand for shortening the processing time in various processing steps for semiconductors and liquid crystals and improving productivity, and the deterioration of response characteristics is the time required to process one substrate (throughput). Is a big problem. For example, in the semiconductor manufacturing process, it is necessary that the residual adsorption power disappearance time is within 10 seconds, and preferably within 3 seconds.

A technique for solving the above problem is proposed in Patent Document 6. According to this, if a powder of titanium nitride (TiN) of _2.5 to 5 mass% and 5 mass% or less of TiO ₂ is added to Al ₂ O ₃ , the sintered body is kneaded, molded and fired. In addition, oxynitride formation occurs between TiO ₂ and TiN or Al ₂ O ₃ and TiN in the sintered body or at the grain boundary, and the charge transfer rate becomes faster than when only TiO ₂ is added, and the desorption response It is possible to form an electrostatic attraction portion having high properties. However, in the above-described invention, a high-resistance composite oxide such as Al ₂ TiO ₅ is also formed at the same time, so that the charge transfer speed is slow at the interface between Al ₂ O ₃ and the composite oxide, and as a result, There was a problem that the desorption responsiveness was not sufficiently improved.

  Therefore, the problem to be solved by the present invention is that dielectric ceramics for electrostatic chucks mainly composed of alumina have a high adsorption force without increasing the leakage current flowing from the adsorption device to the object to be adsorbed. The object is to greatly improve the desorption response while maintaining the same.

  The present invention has been made in view of such problems, and has a large adsorption force during application of a voltage, a small leakage current flowing from the adsorption device to the object to be adsorbed, and further, the voltage application is stopped. It is an object of the present invention to propose a dielectric ceramic for an electrostatic chuck and a method for manufacturing the same, in which an object to be adsorbed can be easily detached.

That is, the gist of the present invention is as follows.
(1) alumina, the transition metal oxide and the electrostatic chuck dielectric ceramics composed of unavoidable impurities, among the alumina grains forming the dielectric ceramics, the transition metal oxide grains 0.3 to 10 wt% ( However, 0.6 mass% or less is excluded.) A dielectric ceramic for an electrostatic chuck characterized in that the composite oxide crystal grain of alumina and transition metal oxide is 3 mass% or less.
(2) The dielectric ceramic for electrostatic chuck according to (1), wherein the transition metal is one or several selected from titanium, chromium, iron, nickel, niobium, and zirconium.
(3) The dielectric material for electrostatic chuck according to (1) or (2) above, wherein the dielectric ceramic has a volume resistivity at 25 ° C. of 1 × 10 ⁹ to 1 × 10 ¹³ Ωcm. Ceramics.
(4) Transition metal oxide raw material containing 0.3 to 10% by mass of transition metal oxide crystal grains between alumina particles, and 3% by mass or less of composite oxide crystal grains of alumina and transition metal oxide The method for producing a dielectric ceramic for an electrostatic chuck according to any one of the above (1) to (3), wherein the mixed powder to which is added is fired in a reducing atmosphere.
(5) The dielectric for electrostatic chuck according to the above (4), wherein the firing is any one of normal pressure firing, gas pressure firing, hot press firing, HIP firing, or a combination thereof. Manufacturing method of ceramics.

The present invention relates to dielectric ceramics for electrostatic chucks composed of Al ₂ O ₃ , transition metal oxides, and inevitable impurities , wherein transition metal oxide crystal grains are placed between Al ₂ O ₃ grains constituting the dielectric ceramics. .3-10% by mass, Al ₂ O ₃ and transition metal oxide compound oxide crystal grains contain 3% by mass or less, so when adsorbing a silicon substrate or glass substrate, the adsorption force is sufficiently strong and desorption Responsiveness is extremely excellent. Further, since it is a dense dielectric ceramic, generation of particles due to degranulation can be suppressed, and its utility value is extremely high in industry.

The present invention relates to dielectric ceramics for electrostatic chucks composed of Al ₂ O ₃ , transition metal oxides, and inevitable impurities , wherein transition metal oxide crystal grains are placed between Al ₂ O ₃ grains constituting the dielectric ceramics. .3-10% by mass, Al ₂ O ₃ and transition metal oxide composite oxide crystal grains (hereinafter simply referred to as “composite oxide”) are contained in an amount of 3% by mass or less. Is the gist.

Thus, if the dielectric ceramic for an electrostatic chuck containing 0.3 to 10% by mass of transition metal oxide crystal grains between Al ₂ O ₃ particles constituting the dielectric ceramic is used, the transition metal oxide itself is Many oxygen vacancies are generated by firing in a reducing atmosphere, and the volume resistivity decreases from 1 × 10 ⁰ to 1 × 10 ⁸ Ωcm. For this reason, the dielectric ceramic sintered body is in a state where low-resistance particles are dispersed in the Al ₂ O ₃ matrix, and the charge transfer speed is increased at the interface between the Al ₂ O ₃ and the transition metal oxide, resulting in a desorption response. It is possible to form a dielectric ceramic for an electrostatic chuck having excellent properties. However, since the transition metal oxide crystal grains are dispersed and contained in a small amount of 0.3 to 10% by mass, the volume resistivity of the dielectric ceramic itself is not greatly lowered. For this reason, it is possible to form the dielectric ceramic for an electrostatic chuck having excellent desorption response without increasing the leakage current flowing from the adsorption device to the object to be adsorbed. If the transition metal oxide is less than 0.3% by mass, the effect of improving desorption characteristics is reduced. Moreover, when there are more transition metal oxides than 10 mass%, the outstanding mechanical characteristic of the alumina sintered compact which is a main component will be degraded by the sintering inhibition. Moreover, when a large amount of transition metal oxide is added, the volume resistivity of the dielectric ceramic itself is greatly reduced, and a large leak current flows from the adsorption device to the object to be adsorbed, thereby destroying the wafer circuit. Will also occur.

Thus, the dielectric ceramic for an electrostatic chuck having excellent desorption responsiveness by including 0.3 to 10% by mass of transition metal oxide crystal grains between the Al ₂ O ₃ particles constituting the dielectric ceramic. Even if it is fabricated, if a large amount of high-resistance composite oxide is formed, the charge transfer speed at the interface between Al ₂ O ₃ and the composite oxide becomes slow, and the desorption response of the entire dielectric ceramic deteriorates. End up. In the present invention, since the formation of this complex oxide is suppressed to 3% by mass or less, such deterioration is small, and finally dielectric ceramics for an electrostatic chuck with good desorption response can be obtained.

Here, between the Al ₂ O ₃ particles constituting the dielectric ceramic, a sintering aid such as silica (SiO ₂ ), calcia (CaO), MgO or the like, or an amorphous phase caused by impurities contained in the ceramic raw material May be contained to such an extent that the desorption characteristics are not deteriorated.

  The transition metal may be one or several selected from Ti, chromium (Cr), iron (Fe), niobium (Nb), and zirconium (Zr), and Ti is particularly preferable.

The gist of the present invention is a dielectric ceramic for an electrostatic chuck, wherein the dielectric ceramic has a volume resistivity of 1 × 10 ⁹ to 1 × 10 ¹³ Ωcm. A volume resistivity of 1 × 10 ⁹ Ωcm or more is preferable because sufficient insulation can be obtained, and a leak current flowing through the substrate is small and does not damage the circuit on the substrate. For example, if the dielectric ceramic has a volume resistivity of 1 × 10 ⁹ Ωcm or more, an electrostatic chuck having a dielectric thickness of 3 mm and a diameter of 300 mm will have a leakage current of 1 μA / min when a voltage of 250 V is applied. It becomes less than cm ² and does not damage the circuit on the substrate. On the other hand, if the volume resistivity is 1 × 10 ¹³ Ωcm or less, it is preferable because a high adsorption force can be obtained by the Johnson Rabeck effect. In the prior art, when the volume resistivity of the dielectric ceramic is relatively high, 1 × 10 ¹² to 1 × 10 ¹³ Ωcm, the adsorption power is improved by the Johnson Rabeck effect, and the leakage current is suppressed to a low level. However, there was a problem that the desorption characteristics were greatly deteriorated. However, in the dielectric ceramic according to the present invention, even if the volume resistivity is relatively high, 1 × 10 ¹² to 1 × 10 ¹³ Ωcm, the transition occurs between the Al ₂ O ₃ particles constituting the dielectric ceramic. Since the metal oxide crystal grains are contained in an amount of 0.3 to 10% by mass, the charge transfer speed is faster than that of the case of Al ₂ O ₃ alone, and it is possible to achieve both an extremely small leakage current and excellent desorption characteristics. .

Further, the dielectric ceramic for electrostatic chuck of the present invention comprises Al ₂ O ₃ as a main component, and contains 0.3 to 10% by mass of transition metal oxide crystal grains between Al ₂ O ₃ particles. By firing the mixed powder to which the transition metal oxide raw material is added so as to contain 3% by mass or less of crystal grains in a reducing atmosphere, the adsorption power is sufficiently high, the leakage current flowing from the adsorption device to the adsorbent is small, and Thus, dielectric ceramics for electrostatic chucks excellent in desorption response can be obtained.

These starting materials include an Al ₂ O ₃ powder having a purity of 99% or more and an average particle size of 2.0 μm or less, preferably an average particle size of 1.0 μm or less, an average particle size of 5 μm or less, preferably an average particle size of 2 μm or less. It is preferable to use a transition metal oxide powder.

  Moreover, as a molding method of this starting material, a normal molding method such as a normal mold press, cold isostatic press (CIP), or sheet molding can be used.

Firing must be performed in a reducing atmosphere. As the reducing atmosphere, an atmosphere having a reducing source such as H ₂ , Ar, N ₂ , a carbon heater, a carbon container, or a combination thereof can be used. The sintering temperature is maintained at 1200 to 1700 ° C. for about 1 to 10 hours. As a firing method, any of normal pressure firing, gas pressure firing, hot press firing, HIP firing, or a combination thereof can be used.

The transition metal oxide present between the Al ₂ O ₃ particles causes many oxygen vacancies upon firing in the reducing atmosphere, and as a result, it is 1 × 10 ⁰ to 1 × 10 ⁸ Ωcm lower than the Al ₂ O ₃ matrix. Of the volume resistivity. For example, TiO ₂ is known to exhibit a low volume resistivity of 1 × 10 ⁰ to 1 × 10 ⁵ Ωcm in a non-stoichiometric composition of TiO _2−X (X ≧ 0.1). Yes. This oxygen deficiency X can be obtained by measuring the lattice constant of TiO ₂ using a normal X-ray diffractometer. This oxygen deficiency is not formed in a thermal equilibrium state, and the resistivity of the transition metal oxide is greatly reduced in a stronger reducing atmosphere. Therefore, firing is performed in a more non-equilibrium atmosphere such as gas pressure firing, hot press firing, and HIP firing. It is desirable. Furthermore, usually, if a large amount of transition metal oxide remains in the Al ₂ O ₃ grains and at the grain boundaries, sintering inhibition is caused and a dense sintered body cannot be obtained. Therefore, it is preferable to perform gas pressure firing, hot press firing, and HIP firing in order to obtain a dense dielectric ceramic.

Composite oxide of a transition metal oxide and Al ₂ O _3, for example in the Al ₂ O ₃ -TiO ₂ two-component system, eutectoid decomposition from Al ₂ TiO ₅ in the 1150 to 1300 ° C. to Al ₂ O ₃ and TiO ₂ There is a reaction. For this reason, at a firing temperature of 1300 ° C. or higher, Al ₂ O ₃ and TiO ₂ react to produce a composite oxide, Al ₂ TiO _5, but the firing conditions are optimal, such as slowing the cooling rate after firing. By reconstitution, it can be re-decomposed into Al ₂ O ₃ and TiO ₂ again. However, since the eutectoid decomposition reaction of Al ₂ TiO ₅ involves volume shrinkage, it is difficult to obtain a dense sintered body by normal pressure firing. To obtain a dense dielectric ceramic, gas pressure firing, hot press firing, It is preferable to perform HIP firing.

Further, if the firing is carried out at or below the eutectoid decomposition temperature, the formation of Al ₂ TiO ₅ can be suppressed, but at the above temperature, the sintering of Al ₂ O ₃ does not proceed and a dense sintered body cannot be obtained. Therefore, in order to obtain a dense dielectric ceramic, it is preferable to perform gas pressure firing, hot press firing, and HIP firing.

Examples of the present invention will be described in detail below, but the present invention is not limited thereto. In order to obtain dielectric ceramics for an electrostatic chuck having sufficiently strong adsorption power, little leakage current flowing from the adsorption device to the object to be adsorbed, and excellent desorption characteristics such as residual adsorption extinction time. Therefore, it is considered necessary to improve the material of the dielectric ceramic layer, and 0.3 to 10% by mass of a transition metal oxide crystal grain is combined between Al ₂ O ₃ particles constituting the dielectric ceramic. The inventors have found that a dielectric ceramic containing 3% by mass or less of oxide crystal grains can provide a desired dielectric ceramic for an electrostatic chuck, and have completed the present invention by examining various conditions.

As an example of dielectric ceramics for electrostatic chucks of the present invention, a predetermined amount of TiO ₂ powder was weighed into α-Al ₂ O ₃ powder, and distilled water, an organic binder for molding, and a dispersant were added and ball mill mixed. The obtained slurry was granulated with a spray dryer to obtain granulated powder. This was CIP-molded into a disk shape and then degreased at 500 ° C. in the atmosphere to obtain a molded body. This molded body was subjected to hot press firing at a pressure of 30 MPa for 2 hours at a temperature shown in Table 1 in an argon gas to obtain a sintered body. The obtained sintered body was processed into □ 40 mm and a thickness of 3 mm to obtain a dielectric . The sintered density of the dielectric was measured by the Archimedes method, and the volume resistivity was measured by the three-terminal method (applied voltage 250 V, room temperature). Moreover, the content was quantitatively analyzed from the identification of the constituent phase by X-ray diffraction and the obtained X-ray intensity ratio. Next, Ti was sputtered on the surface of one side of the dielectric to give an electrode as a conductor layer. An insulating substrate (alumina) was bonded to this with an epoxy adhesive so that the conductor layer was sandwiched between them. At this time, the dielectric was ground and lapped to a thickness of 2.5 mm, and a lead electrode was attached to produce an electrostatic chuck.

In Invention Examples 1 to 7 in Table 1, the contents of TiO ₂ and Al ₂ TiO ₅ are both within the appropriate range. In Comparative Examples 1 to ₅ , the content of TiO ₂ or Al ₂ TiO ₅ is outside the proper range of the present invention.

  For these electrostatic chucks, a silicon wafer was placed on the suction surface of the electrostatic chuck, and the electrostatic suction force and the leakage current after applying a voltage of 250 V from the lead electrode for 2 minutes were measured. Furthermore, the response characteristics of various electrostatic chucks were measured by applying a silicon wafer at a voltage of 250 V for 2 minutes, then stopping the voltage application, and measuring the time during which the suction force was 20 gf or less (residual suction time).

  Table 1 shows the results of adsorption force, leakage current, and residual adsorption time, together with the values of dielectric density and volume resistivity.

From Table 1, it can be seen that Examples 1 to 7 of the present invention have sufficiently high adsorption power and extremely short residual adsorption time. On the other hand, in Comparative Examples 1-4, it turns out that residual adsorption time is very long and adsorption power is also low. In Comparative Example 5, since the dielectric volume resistivity is low, the residual adsorption time is short, but it can be seen that the leakage current is very large.

When Example 1 of the present invention and Comparative Example 1 are compared, the volume resistivity of the dielectric is the same as 5 × 10 ⁹ Ωcm, but due to the difference in the contents of TiO ₂ and Al ₂ TiO ₅ , the present invention In Example 1, it can be seen that the adsorption force is sufficiently high and the desorption response is extremely excellent, whereas in Comparative Example 1, both the adsorption force and the desorption characteristic are greatly inferior.

This in Patent Document 2, Zanryu attracting force is contrary to be reduced by lowering the volume resistivity of the dielectric ceramics, the Ai configuration of dielectric ceramics is that it had a very Okina effect desorption characteristics It suggests. In the case of this material control method, there is an advantage that a dielectric ceramic having a very small residual adsorption force can be produced. The residual adsorption force is removed by applying a reverse voltage or an alternating current, or slit processing is performed to reduce the capacitance component. Thus, there is no need to perform characteristic processing such as reducing the residual adsorption force.

  In addition, since Examples 1 to 7 of the present invention have a very high density of sintered bodies and are dense, suppress the decrease in the degree of vacuum due to the separation of the adsorbed gas when used in a vacuum, and the generation of particles due to degranulation. Can do.

Claims (5)

In the dielectric ceramic for an electrostatic chuck composed of alumina, transition metal oxide, and unavoidable impurities, 0.3 to 10% by mass of transition metal oxide crystal grains are contained between the alumina particles constituting the dielectric ceramic . 6) The dielectric ceramic for electrostatic chuck, wherein the composite oxide crystal grains of alumina and transition metal oxide are 3% by mass or less.   The dielectric ceramic for an electrostatic chuck according to claim 1, wherein the transition metal is one or several selected from titanium, chromium, iron, nickel, niobium, and zirconium. 3. The dielectric ceramic for electrostatic chuck according to claim 1, wherein the dielectric ceramic has a volume specific resistivity at 25 ° C. of 1 × 10 ⁹ to 1 × 10 ¹³ Ωcm.   The transition metal oxide raw material was added so that the transition metal oxide crystal grains included 0.3 to 10% by mass between the alumina particles, and the composite oxide crystal grains of alumina and transition metal oxide were 3% by mass or less. 4. The method for producing a dielectric ceramic for an electrostatic chuck according to claim 1, wherein the mixed powder is fired in a reducing atmosphere.   5. The method for producing a dielectric ceramic for an electrostatic chuck according to claim 4, wherein the firing is one of normal pressure firing, gas pressure firing, hot press firing, HIP firing, or a combination thereof. .