WO2007091619A1

WO2007091619A1 - Electrostatic chuck

Info

Publication number: WO2007091619A1
Application number: PCT/JP2007/052175
Authority: WO
Inventors: Masami Ando; Jun Miyaji; Osamu Okamoto
Original assignee: Toto Ltd.
Priority date: 2006-02-08
Filing date: 2007-02-08
Publication date: 2007-08-16
Also published as: KR20080089444A; KR100989230B1; JP4244229B2; CN101379607A; CN101379607B; JP2007214287A; TWI342059B; TW200737398A

Abstract

[PROBLEMS] To provide an electrostatic chuck that, even after exposure to plasma, can maintain a smooth surface and consequently can suppress contamination of a material to be adsorbed, such as a silicon wafer, with particles, is excellent in adsorption and desorption properties of an adsorbent material, and can easily be prepared by low-temperature firing. [MEANS FOR SOLVING PROBLEMS] An electrostatic chuck comprising a dielectric material for an electrostatic chuck. The dielectric material comprises not less than 99.4% by weight of alumina, more than 0.2% by weight and not more than 0.6% by weight of titanium oxide, has a volume resistivity at room temperature of 108 to 1011 Ωcm, and has a structure in which titanium oxide is segregated at the boundary of alumina particles.

Description

Specification

Electrostatic chuck

Technical field

The present invention relates to an electrostatic chuck for adsorbing and fixing an object to be adsorbed such as a semiconductor wafer and a glass substrate for FPD with an electrostatic force.

Background art

Conventional electrostatic chuck ceramic dielectrics have been configured for the purpose of controlling their electrical characteristics (see, for example, Patent Document 1).

In such a case, when the ceramic structure is exposed to a plasma environment, the structure is eroded and the surface roughness is deteriorated. As a result, a change with time due to a change in the contact state between the electrostatic chuck surface and the wafer is caused. In some cases, this may cause the particles to fall out of the sintered body to generate particles and cause a short circuit between the LSI wires.

[0003] Further, there is an example in which an alumina ceramic material having a particle size of 2 m or less and a relative density of 99.9% and improved plasma resistance is applied to an electrostatic chuck (for example, see Patent Document 2). . However, even in this case, even though the plasma resistance is good, there is no description about the electrical physical properties, and the basic function of the so-called Johnsen Rahbek type electrostatic chuck that expresses a large adsorption force cannot be exhibited.

[0004] Further, an alumina ceramic containing 0.1 to 1% titanium oxide and having a volume resistivity of 10 ° to 10 ⁴⁰ «! 1 is disclosed (for example, see Patent Document 3). ) ₀ However, it is impossible to obtain electrical characteristics as to function as the case electrostatic chuck.

[0005] Further, an electrostatic chuck is disclosed in which the volume resistivity of the dielectric is lowered by adding 0.5 to 2 wt% of titanium oxide to alumina ceramic. (For example, refer to Patent Document 4.) In this case, it is disclosed that the resistance does not decrease when the content is lower than 0.5 wt%, and that the current flows too much when 2 wt% or more is added. Furthermore, it is disclosed that titanium oxide precipitates at the grain boundaries of alumina ceramics. In other words, an additive of at least 0.5% or more is required to lower the volume resistivity, and the amount of additive is large as an electrostatic chuck with severe restrictions on the mixing of impurities into the adsorbed substance. [0006] In addition, an electrostatic chuck in which alumina is 99% or more, an average particle diameter is 1 to 3 μm, and a volume resistivity is 10 ⁸ to: ίΟ ^ Ωcm at 300 to 500 ° C Is disclosed. (For example, Patent Document 5) However, there is no description regarding the physical properties of the dielectric necessary for the electrostatic chuck used at other temperatures, for example, at a relatively low temperature of 100 ° C or lower.

Patent Document 1: Japanese Patent No. 3084869

Patent Document 2: Japanese Patent Laid-Open No. 10-279349

Patent Document 3: Japanese Patent Laid-Open No. 2004-18296

Patent Document 4: Japanese Patent Publication No. 6-97675

Patent Document 5: Japanese Patent Laid-Open No. 11 312729

Disclosure of the invention

Problems to be solved by the invention

[0007] The present invention can maintain a smooth surface even after being exposed to plasma. As a result, it is possible to suppress particle contamination with respect to an adsorbent such as a silicon wafer and to have excellent adsorption and desorption characteristics of the adsorbent. An electrostatic chuck that can be easily manufactured by low-temperature firing is provided. Means for solving the problem

[0008] In the present invention in order to achieve the above object, alumina 99. 4 wt% or more, Sani匕titanium is greater than 0. 2wt% 0. 6wt% or less, lC lO ¹¹ Q volume resistivity at room temperature An electrostatic chuck comprising a dielectric for an electrostatic chuck having a structure in which titanium oxide is impregnated at the grain boundary of cm and alumina particles has been disclosed. As a result, it has become possible to improve the plasma resistance of the electrostatic chuck dielectric and the basic functions of the electrostatic chuck at a high level, and to be manufactured at low cost.

[0009] The reason why the volume resistivity needs to be 10 ⁸ ~: ΟΟ Ω cm is that the Johnsen-Rahbek effect is used as the attractive force of the electrostatic chuck. By using the Johnsen-Rahbek effect, a very large attracting force is generated, and as a result, the surface of the electrostatic chuck is provided with a convex portion so that the contact area with the object to be attracted is 1-10. % Can be reduced.

[0010] Further, by making the height of the convex portion provided on the surface 5 to 15 m, the attracting force can be exerted even in the contacted portion. As a result, the area of the convex part is 0.00 with respect to the area of the suction surface. It can be 1% or more and less than 0.5%. Since the temperature of the object to be adsorbed is transferred through the contact portion as the contact area of the convex portion becomes smaller, even if the texture of the convex portion is eroded by plasma, the influence is reduced. Therefore, an electrostatic chuck with little change with time can be realized as a result of increasing plasma resistance and minimizing contact with the object to be adsorbed.

[0011] Further, in order to improve the response characteristic of the above attractive force, it is necessary to reduce the value of the following equation.

ts = l. 731 X 10 "X p (ε r + d / h) (seconds)

Where ts is the time (seconds) until the initial attractive force is 100% and collapses to 2%, is the volume resistivity (Ωm) of the dielectric layer, εr is the relative dielectric constant of the dielectric layer, d Is the thickness (m) of the dielectric layer, and h is the height (m) of the protrusion. If the value of this formula is 0.001 force 0.6 and the height of the convex part is 5 to 15 / zm, the area of the convex part should be 0.001 to 0.5% with respect to the adsorption surface. It is possible to provide an electrostatic chuck that can respond to the voltage marking of the attractive force and has good response to unloading.

The above equation is obtained analytically from the equivalent circuit in Fig. 1 and derived from [Equation 1] to [Equation 4]. Where ql is the charge density, S is the electrode area, C is the capacitance, G is the conductance, V is the applied voltage, t is the time (variable), and T is the voltage application time.

[0012] [Equation 1]

q _l (t-T))

[0013] [Equation 2]

2 (C, + C,)

G ₂ [0014] [Equation 3]

^{2 0 r} h

-丄 R ₂ = 丄 pd

[0015] [Equation 4]

t> T

-V-exp (t-T)

c, + c, C, + C-,

[0016] Further, in another embodiment of the present invention, alumina 99. 4 wt% or more, significantly 0. 6 wt% of titanium oxide than 0. 2 wt% or less, Caゝbulk density is 3. 97 g / cm ³ or more An electrostatic chuck including a dielectric for electrostatic chuck having a structure in which volume resistivity is lC lO ¹¹ Ωcm at room temperature and titanium oxide is biased at the grain boundary of alumina particles is disclosed. As a result, this electrostatic chuck has a low porosity of the tissue, and further enables improvement in plasma resistance and a high degree of compatibility between the basic functions of the electrostatic chuck, and can be manufactured at low cost.

[0017] In a preferred embodiment of the present invention, the electrostatic chuck is used at a low temperature of 100 ° C or lower.

[0018] In a preferred embodiment of the present invention, a plurality of convex portions are formed and a dielectric having a smooth surface on which the object to be attracted is placed on the upper surface of the convex portions. The ratio of the total area and the area of the dielectric surface is 0.001% or more and less than 0.5%, and the height of the convex part is 5 to 15 m. An electrostatic chuck according to any one of the above has been disclosed. As a result, it is possible to minimize the influence of the change in the adsorption state on the adsorbent due to the influence of the surface roughness due to the plasma erosion at the contact portion with the adsorbent. At this time, if the ratio of the contact area is 0.001% or less, the size per convex portion becomes too fine, and processing becomes difficult. On the other hand, if it exceeds 1%, the influence of erosion on the plasma on the surface of the convex part that comes into contact with the adsorbent cannot be ignored.

The invention's effect [0019] According to the present invention, a smooth surface can be maintained even after being exposed to plasma. As a result, particle contamination of an adsorbed object such as a silicon wafer can be suppressed, and the adsorbed object can be adsorbed and separated. If an electrostatic chuck that can be easily manufactured by low-temperature firing can be manufactured, there is an effect.

Brief Description of Drawings

FIG. 1 is a diagram showing an electrostatic chuck of the present invention.

FIG. 2 is a diagram showing an equivalent circuit of the electrostatic chuck of the present invention.

FIG. 3 is an enlarged view of the surface pattern of the electrostatic chuck of the present invention.

FIG. 4 is an electron micrograph showing the structure of an electrostatic chuck dielectric according to the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

[0021] As raw materials, alumina, titanium oxide, and other transition metal oxides were granulated at a blending ratio shown in Table 1. Alumina having an average particle diameter of 0.1 l ^ m and a purity of 99.99% or more was prepared. Titanium oxide having a purity of 98% or more was used.

[0022] (Slurry adjustment, granulation, raw processing)

The above raw materials were mixed and pulverized at a blending ratio shown in Table 1, an acrylic binder was added, and after adjustment, the mixture was granulated with a spray dryer to produce granulated powder. The granulated powder was packed into a rubber mold, and then CIP (pressure ltonZcm ² ) was performed to produce an ingot, which was then processed into a predetermined shape to produce a formed shape. Ion exchange water etc. was used for mixing so that no impurities were mixed.

(Baking)

The raw processed body was fired in a nitrogen and hydrogen gas reducing atmosphere. The firing temperature was 1150 to 1350 ° C., the firing time was 1 to 8 hours, and the conditions with the highest bulk density were selected. At this time, use humidified gas for degreasing. The purpose of reducing firing is to adjust the volume resistivity in order to make the non-stoichiometric composition of titanium oxide.

(HIP processing)

Further HIP processing was performed. The HIP condition was Ar gas 1500 atm, and the temperature was the same as the firing temperature or 30 ° C lower.

(Physical property measurement) What was obtained by the above HIP treatment was subjected to firing force density density, average particle size measurement by SEM observation, volume resistivity measurement, friction force measurement in vacuum, and residual time measurement. For frictional force measurement and residual time measurement, the thickness of the ceramic dielectric layer was lmm. The adsorption voltage was 200V, and the remaining time was measured by turning off the power after applying the voltage for 1 minute and measuring the attenuation of the remaining frictional force. The object to be adsorbed was a silicon wafer mirror surface. The remaining time was defined as the time for the frictional force to decay to 2% after the power was turned off.

In addition, the surface roughness of the ceramics (centerline average roughness Ra) was measured by actually irradiating the plasma. In the initial state, the surface roughness was RaO. 05 m or less. Plasma is a reactive ion etching system, etching gas is CF +0, 1000W, plasma discharge for 5 hours

4 2

I let you.

In addition, as an evaluation of the practical chucking force of the electrostatic chuck for a part of the sample, the pressure (PO POFF Power) was recorded. The adsorption voltage at this time is 1000V.

(Comparative product)

For comparison, alumina ceramics produced by a conventional manufacturing method is illustrated. The compound 1 is 98 wt% alumina with an average particle size of 0. 0%, titanium oxide 2 wt%, comparative product 2 is alumina 99 wt%, titanium oxide 1 wt%, and the firing temperature is 1580 ° C. The surface roughness of Comparative Product 1 was RaO. 23 m in the initial state. The surface roughness of Comparative Product 2 was RaO. 2 μm in the initial state. The comparative product is not HIP treated.

The results of the above test are shown in Tables 1 and 2. It can be seen that by controlling the firing temperature, a volume resistivity that functions as an electrostatic chuck can be obtained with a force density of 3.97 gZcm ³ or more with an addition amount of titanium oxide greater than 0.2 wt% and less than 0.6 wt%. I helped. In the past, it was proved that the same effect can be obtained with a very small addition amount compared to the amount added conventionally when the particle size is 50 m or more. In the conventional manufacturing method, since the firing temperature is as high as 1580 ° C, titanium oxide added reacts with alumina to become a compound such as aluminum titanate (Al TiO).

twenty five

In contrast, in the present invention, the use of a high-purity, fine-grained alumina raw material having an average particle size of less than 0 and a purity of 99.9% or more lowers the firing temperature to 1300 ° C or lower. Titanium oxide titanium does not react with alumina and exists as titanium oxide. Was confirmed by X-ray diffraction. Aluminum titanate is known to have a relatively high volume resistivity, and in order to reduce the volume resistivity of alumina, the efficiency is worse than that of titanium oxide. Conceivable. Next, as a microstructure of the dielectric material for electrostatic chucks of the present invention, FIG. 4 shows a SEM photograph of a sample subjected to thermal etching at a temperature lower by about 80 to 150 ° C. than the firing temperature. It can be seen that the structure is such that the titanium oxide (white part of the photograph) is connected to the grain boundary of the alumina particles (black part of the photograph) with an average particle diameter of 2 μm or less and connected continuously. I helped. It is considered that the volume resistivity can be efficiently reduced by the network formed by this titanium oxide. From the above results, the dielectric resistivity for the electrostatic chuck of the present invention was able to lower the volume resistivity by adding a small amount of acid titanium as compared with the conventional one. This is because there is no reaction with alumina and it remains in the form of a titanium oxide, and the titanium oxide is prejudiced to the grain boundaries of the alumina particles to form a continuously connected structure. . Titanium oxide is considered to have further improved conductivity because it becomes non-stoichiometrically formed by reduction firing. Thus, it was thought that the volume resistivity could be controlled by a small amount of titanium oxide, and that chemical contamination of silicon wafers and the like could be remarkably suppressed compared to the conventional case.

[table 1]

NO. Alumina Titanium oxide Firing temperature Firing body bulk density

. C g / cm ³

1 100 t% 0wt% 1240 3.79

2 100wt% 0wt% 1270 3.88

3 99.9wt% 0.1 wt% 1300 378

4 99.9wt% 0.1 wt% 1240 3.89

5 99.8wt% 0.2wt% 1210 3.74

6 99.8wt% 0.2wt% 1240 3.89

7 99.7wt 0.3wt% 1180 3.23

8 99Jwt 0.3wt 1210 3.91

9 99.6wt% 0.4wt% 1180 3.60

1 0 99.6wt% 0.4wt 1210 3.92

1 1 99.5wt% 0.5wt% 1 150 3.60

1 2 99.5wt% 0.5wt% 1180 3.92

1 3 99.4wt 0.6wt% 1 150 3.92

1 4 99.4wt 0.6wt% 1 180 3.92 Comparative product 1 98wt% 2wt% 1580 3.75 Comparative product 2 99wt% 1 wt% 1580 3- 7 [ Table 2]

As a result of the evaluation of electrical characteristics, it was found that it can be controlled in a wide range from 10 ⁸ to: 10 ¹⁶ Q cm depending on the addition ratio of titanium oxide alone or titanium oxide + transition metal oxide.

When using resist, the electrostatic chuck is 100 considering its heat resistance temperature. It is desirable to use below C. The electrical characteristics required for the dielectric material for the electrostatic chuck are desired to be the temperature at which the electrostatic chuck is used, and the volume resistivity is ⁸ ) ¹¹ Ωcm. The 10 less than ⁸ Omega cm lower limit may cause damage to the device too excessive current flowing into © E c, the upper limit 10 ¹¹

If it is larger than Ωcm, the response to voltage application for wafer adsorption and desorption will decrease. For example, in processes such as process etching below 100 ° C, the lower limit is desired to be about Κ ^ ΙΟ ^ Ω cm.

[0027] If the amount of titanium oxide is more than 0.6 wt%, the volume resistivity becomes less than 10 ⁸ Ω «η, and the current flowing into the wafer becomes excessive, which may damage the device. On the other hand, if it is 0.2 wt% or less, the effect S of reducing the volume resistivity due to the titanium oxide additive S becomes small.

[0028] Plasma resistance was evaluated by the change in surface roughness because any substance is etched if the energy of ions in the plasma is excessive.

As a result, the ceramic dielectric according to the present invention has a significantly smaller change in surface roughness than the conventional one. This is presumed that the size of particles that generate dust is small!

[0029] Including a dielectric for an electrostatic chuck having a smooth surface on which a plurality of convex portions are formed and an object to be adsorbed is placed on the upper surface of the convex portion and having a volume resistivity of 10 ⁹ · ³ Ωcm An electrostatic chuck in which the ratio of the total area of the upper surfaces of the convex portions of the electrostatic chuck to the area of the dielectric surface was 0.089% was produced. At this time, a convex part of φ θ. 25 mm is continuously arranged on each surface of each apex of an equilateral triangle with a side of 8 mm. The height of the convex part is 10 m.

[0030] As a result, the change in the surface roughness after plasma irradiation and the fact that the contact area with the object to be adsorbed are extremely small are superimposed on each other. The change over time of the change could be extremely reduced.

[0031] The POPOFF adsorption force was recorded as lOOtorr or more in all samples. In other words, it was found that a practical force was sufficiently obtained to adsorb an adsorbent such as a silicon wafer.

Claims

The scope of the claims

[1] Alumina is more than 99.4 wt%, titanium oxide is more than 0.2 wt% and less than 0.6 wt%, and volume resistivity is at room temperature ^) ⁸ 〜 ^) ¹ ^ ^ !! An electrostatic chuck comprising a dielectric for an electrostatic chuck having a structure in which titanium oxide is biased at the grain boundary of alumina particles.

[2] alumina 99. 4 wt% or more, Sani匕titanium is greater than 0. 2wt% 0. 6wt% or less, the forceゝIs density is 3. 97 g / cm ³ or more, a volume resistivity of the room temperature Oi Te ^) ⁸ - ^) ¹ ^ ^ !!, and an electrostatic chuck, wherein the Sani匕titanium with an electrostatic chuck dielectric structure Hen'ino the grain boundary of alumina particles.

[3] No aluminum titanate (Al TiO) is present in the grain or boundary of the alumina particles.

twenty five

The electrostatic chuck according to claim 1 or 2, wherein

[4] The electrostatic chuck according to any one of claims 1 to 3, wherein the electrostatic chuck is used at a low temperature of 100 ° C or lower.

[5] It is composed of a dielectric having a smooth surface on which a plurality of convex portions are formed and an object to be adsorbed is placed on the upper surface of the convex portion, and the total area of the upper surfaces of the plurality of convex portions and the area of the dielectric surface 5. The electrostatic chuck according to claim 1, wherein the ratio of the height of the convex portion is 0.001% or more and less than 0.5%, and the height of the convex portion is 5 to 15 m.