KR20080089444A - Electrostatic chuck - Google Patents

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 7cm, and has a structure in which titanium oxide is segregated at the boundary of alumina particles.

Description

Electrostatic chuck

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrostatic chuck for adsorption and fixing of adsorbed materials such as semiconductor wafers and glass substrates for FPD with electrostatic force.

The conventional electrostatic chuck ceramic dielectric is configured for the purpose of controlling its electrical characteristics (see Patent Document 1, for example).

In such a case, when the ceramic structure is exposed in the plasma environment, the structure is eroded and the surface roughness becomes poor, and as a result, changes over time due to a change in the contact state between the surface of the electrostatic chuck and the wafer, or particles from the sintered body The particles may be detached and oscillated as particles to cause short circuits between the LSIs and the like.

In addition, there is an example in which an alumina ceramic material having a particle diameter of 2 µm or less and a relative density of 99.9% has been improved in plasma resistance and applied to an electrostatic chuck (see Patent Document 2, for example). However, even in this case, even if the plasma resistance is good, there is no description on the electrical properties, and thus the basic function of the so-called Johnsen-Rahbeck electrostatic chuck, which exhibits a large adsorption force, cannot be exhibited.

Moreover, the alumina ceramic which contains 0.1-1 weight% of titanium oxide and shows a volume resistivity of 10 <^0> -10 <^4> ohm-cm is disclosed (for example, refer patent document 3). In this case, however, it is impossible to obtain an electrical characteristic that serves as an electrostatic chuck.

Moreover, the electrostatic chuck which lowered the volume resistivity of a dielectric by adding 0.5-2 weight% of titanium oxide to an alumina ceramic is disclosed (for example, refer patent document 4). In this case, when it is lower than 0.5 weight%, resistance does not fall, but when 2 weight% or more is added, it turns out that an electric current flows too much. In addition, it is disclosed that titanium oxide is precipitated at grain boundaries of alumina ceramics. That is, at least 0.5 wt% or more of additives are required to lower the volume resistivity, and the amount of the additives is large as an electrostatic chuck having strict restrictions on the incorporation of impurities into the substance to be adsorbed.

Moreover, the electrostatic chuck which has 99% or more of alumina, an average particle diameter of 1-3 micrometers, and whose volume resistivity becomes 10 ^{8-10 11} ohm-cm at 300-500 degreeC is disclosed (for example, patent document 5). . However, there is no description regarding the physical properties of the dielectric required for the electrostatic chuck used at other temperatures, for example, at relatively low temperatures of 100 ° C or lower.

Patent Document 1: Japanese Patent No. 3084869

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

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

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

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

Disclosure of the Invention

Problems to be Solved by the Invention

The present invention can maintain a smooth surface even after being exposed to plasma, and as a result, it is possible to suppress particle contamination on adsorbed materials such as silicon wafers, and also has excellent adsorption and desorption characteristics of the adsorbed materials. An object of the present invention is to provide an electrostatic chuck that is easy to do.

Means to solve the problem

In order to achieve the above object, in the present invention, alumina is 99.4% by weight or more, titanium oxide is greater than 0.2% by weight and 0.6% by weight or less, and the volume resistivity is 10 ⁸ to 10 ¹¹ Ωcm at room temperature, and also oxidized to grain boundaries of the alumina particles. An electrostatic chuck having an electrostatic chuck dielectric having a structure in which titanium is segregated is disclosed. As a result, the plasma resistance of the electrostatic chuck dielectric can be improved and the basic functions of the electrostatic chuck can be achieved at the same time.

The volume resistivity needs to be 10 ⁸ to 10 ¹¹ Ωcm because the Johnsen Lavec effect is used as the adsorption force of the electrostatic chuck. By using the Johnsen Lavec effect, a very large adsorption force is generated, and consequently, convex portions are provided on the surface of the electrostatic chuck, so that the contact area with the adsorbed material can be reduced to 1 to 10% of the area of the adsorption surface.

Moreover, by making the height of the convex part provided in the surface into 5-15 micrometers, adsorption force can be made to work also in a to-be-contacted part. As a result, the area of the convex portion can be made 0.001% or more and less than 0.5% with respect to the area of the adsorption surface. Since the temperature of the object to be adsorbed is heat-transferred through the contact portion as the contact area of the convex portion becomes smaller, even if the structure of the convex portion is subjected to erosion by plasma, the effect is reduced. Therefore, the electrostatic chuck with little change over time can be realized by increasing plasma resistance and making contact with the to-be-adsorbed object as possible as possible.

In addition, in order to improve the response characteristic of the said adsorption force, it is necessary to make the value of the following formula small.

ts = 1.731 × 10 ^-11 × ρ (εr + d / h) (sec)

Where ts is the initial adsorption force at 100% and time until it collapses to 2%, ρ is the volume resistivity of the dielectric layer (Ωm), εr is the dielectric constant of the dielectric layer, d is the thickness of the dielectric layer (m), h is the height m of the convex part. If the value of this equation is 0.001 to 0.6 and the height of the convex part is 5 to 15 µm, the area of the convex part can be made to 0.001 to 0.5% with respect to the adsorption surface, and the voltage of the adsorption force can be reduced or removed. It can be made into electrostatic chuck with good response.

The above equation is obtained by analytically calculating from the equivalent circuit of FIG. 1 to derive [Equation 1] to [Equation 4]. Where q1 is charge density, S is electrode area, C is capacitance, G is conductance, V is applied voltage, t is time (variable), and T is voltage application time.

In another embodiment of the present invention, alumina is at least 99.4% by weight, titanium oxide is greater than 0.2% by weight, 0.6% by weight or less, bulk density is at least 3.97 g / cm 3, and the volume resistivity is 10 ⁸ to 10 ¹¹ Ω at room temperature. An electrostatic chuck having an electrostatic chuck dielectric having a structure in which titanium oxide is segregated at grain boundaries of alumina particles is disclosed. As a result, the electrostatic chuck has a low porosity of the tissue, enables improved plasma resistance, high compatibility of the basic functions of the electrostatic chuck, and can be manufactured at low cost.

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

In a preferred embodiment of the present invention, a plurality of convex portions are formed and are composed of a dielectric having a smooth surface on which the adsorbed body is placed on the upper surface of the convex portion, and the ratio of the total area of the upper surfaces of the plurality of convex portions to the dielectric surface area is The electrostatic chuck in any one of Claims 1-4 characterized by the above-mentioned being 0.001% or more and less than 0.5%, and the height of a convex part is 5-15 micrometers. As a result, the influence of the change of the adsorption state to the to-be-adsorbed object by the influence of the roughness of the surface by the erosion by the plasma of the contact part with a to-be-adsorbed object can be minimized. At this time, when the ratio of the contact area becomes 0.001% or less, the dimension per one convex part becomes too fine and processing becomes difficult. Also, if it is greater than 1%, the influence of erosion on the plasma of the convex surface in contact with the adsorbed body cannot be ignored.

Effects of the Invention

According to the present invention, a smooth surface can be maintained even after being exposed to plasma, and as a result, particle contamination on adsorbed substances such as silicon wafers can be suppressed, and adsorption and detachment characteristics of the adsorbed substance are excellent, and There is an effect that an electrostatic chuck which can be easily manufactured by firing can be manufactured.

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

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

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

Figure 4 is an electron micrograph showing the structure of the dielectric for electrostatic chuck of the present invention.

Implement the invention  Best form for

Alumina, titanium oxide, and other transition metal oxides were granulated at the blending ratios shown in Table 1 as raw materials. The alumina prepared the thing of average particle diameter 0.1 micrometer, purity 99.99% or more. As the titanium oxide, a purity of 98% or more was used.

(Slurry adjustment, assembly, raw processing)

The raw materials were mixed and pulverized at the compounding ratio shown in Table 1, an acrylic binder was added and adjusted, and then granulated powder was prepared by granulating with a spray dryer. The granulated powder was filled in a rubber mold, and then subjected to CIP (pressure 1 ton / cm 2) to produce an ingot, and then processed into a predetermined shape to produce a product body. In the mixing, ion exchange water or the like was used to prevent possible impurities from mixing.

(Firing)

The raw green body was calcined under nitrogen and hydrogen gas reducing atmosphere. The baking temperature was 1150-1350 degreeC, and the baking time was 1-8 hours, and the conditions with the highest bulk density were selected. At this time, humidifying gas is used for degreasing. Reducing firing is aimed at controlling the volume resistivity of a non-stoichiometric composition of titanium oxide.

(HIP processing)

Further HIP treatment was performed. The HIP conditions were set to 1500 atm of Ar gas, and the temperature was the same as the firing temperature or lowered by 30 ° C.

(Property measurement)

The thing obtained by the said HIP process performed the measurement of the bulk volume density, the average particle diameter by SEM observation, the volume resistivity measurement, the frictional force measurement in vacuum, and the residence time measurement. In the friction force measurement and the residence time measurement, the thickness of the ceramic dielectric layer was 1 mm. The adsorption voltage was set at 200 V, and the residual time was measured, and the power was turned off after 1 minute of contact pressure was applied to measure the attenuation of the remaining frictional force. The object to be adsorbed was a silicon wafer mirror surface. As the residence time, the time during which the frictional force attenuates to 2% after the power-off is taken as the residence time.

In addition, the change of the surface roughness (center line average roughness Ra) of the ceramic which actually irradiated the plasma was measured. In the initial state, surface roughness was Ra 0.05 micrometer or less. The plasma was a reactive ion etching apparatus, and the etching gas was plasma discharged at 1000 W for 5 hours with CF ₄ + O ₂ .

Moreover, the pressure (POPOFF adsorption force) when the to-be-adsorbed body peeled was recorded by loading the pressure of He gas with the to-be-adsorbed body adsorb | sucked to a part of sample as a practical evaluation of the adsorption force of an electrostatic chuck. At this time, the adsorption voltage is 1000V.

(Comparative goods)

Moreover, the alumina ceramic by a conventional manufacturing method was illustrated for comparison. In the formulation, Comparative Product 1 was 98% by weight of alumina having an average particle diameter of 0.5 µm, 2% by weight of titanium oxide, Comparative Product 2 was 99% by weight of alumina, 1% by weight of titanium oxide, and the firing temperature was 1580 ° C. In addition, the surface roughness of the comparative product 1 was Ra 0.23 µm in the initial state. The surface roughness of Comparative Product 2 was Ra 0.2 μm in the initial state. The comparative product was not HIP treated.

The results of the test are shown in Table 1 and Table 2. When the firing temperature was adjusted, it was found that a volume resistivity functioning as an electrostatic chuck at a bulk density of 3.97 g / cm 3 or more was obtained with an added amount of more than 0.2 wt% of titanium oxide and 0.6 wt% or less. Conventionally, it turned out that the equivalent effect is acquired by the addition amount very small compared with the quantity added when the particle diameter becomes 50 micrometers or more. In the conventional manufacturing method, since the firing temperature is high at 1580 ° C., the added titanium oxide reacts with alumina to form a compound such as aluminum titanate (Al ₂ TiO ₅ ). Since the firing temperature was lowered to 1300 ° C. or lower by using fine alumina raw materials with high purity of 99.9% or more, it was confirmed from X-ray diffraction that the added titanium oxide remained as titanium oxide without reacting with alumina. . It is known that aluminum titanate has a relatively high volume resistivity, and in order to lower the volume resistivity of alumina, efficiency is worse than that of titanium oxide, and it is considered that a larger amount of addition is required. Next, as a microstructure of the dielectric for electrostatic chuck of the present invention, an SEM photograph of a sample subjected to thermal etching at a temperature as low as 80 to 150 ° C with respect to the firing temperature is shown in FIG. 4. It was found that titanium oxide (white portion in the photo) segregated to the grain boundaries of the alumina particles (black portion in the photo) having an average particle diameter of 2 µm or less, and thus had a continuous structure. It is thought that the volume resistivity could be reduced efficiently by the network which this titanium oxide forms. The above results indicate that the volume resistivity of the electrostatic chuck dielectric of the present invention can be lowered by adding a small amount of titanium oxide as compared with the conventional one, in which the added titanium oxide exists as titanium oxide without reacting with alumina. And titanium oxide segregate at the grain boundaries of the alumina particles to form a continuously connected structure. In addition, since titanium oxide becomes nonstoichiometric composition by reducing baking, it is thought that electroconductivity improved further. Thus, it was thought that the trace amount of titanium oxide can be controlled by the small amount of titanium oxide, and chemical contamination on silicon wafers and the like can be significantly suppressed as compared with the prior art.

As a result of the evaluation of the electrical properties, it was found that control was possible over a wide range of 10 ⁸ to 10 ¹⁶ Ωcm depending on the addition ratio of titanium oxide alone or titanium oxide + transition metal oxide.

In the case of using a resist, considering the heat resistance temperature, the electrostatic chuck is preferably used at 100 ° C or lower.

The electrical characteristics required for the electrostatic chuck dielectric are preferably 10 ⁸ to 10 ¹¹ Ωcm in volume resistivity at the temperature using the electrostatic chuck. If the lower limit is less than 10 ⁸ Ωcm, the current flowing into the wafer may be excessively excessive, resulting in damage to the device. If the upper limit is greater than 10 ¹¹ Ωcm, the response to the application of the wafers to the adsorption and release of the wafer is reduced. For example, in a process such as process etching at 100 ° C or lower, the lower limit is preferably about 10 ⁹ to 10 ¹¹ Ωcm.

If the titanium oxide is more than 0.6% by weight, the volume resistivity is less than 10 ⁸ Ωcm, and the current flowing into the wafer becomes excessively excessive, which may cause device damage. Moreover, when it is 0.2 weight% or less, the fall effect of the volume resistivity by addition of a titanium oxide will become small.

Plasma resistance was evaluated as a change in surface roughness because any substance was etched when the energy of ions in the plasma was excessive.

As a result, the change in surface roughness of the ceramic dielectric material according to the present invention was remarkably small compared with the conventional one. This fact was assumed to be small in size.

A plurality of convex portions are formed to have a smooth surface on which the adsorbed body is placed on the upper surface of the convex portion, and the total area of the upper surface of the convex portion of the electrostatic chuck comprising an electrostatic chuck dielectric having a volume resistivity of 10 ^9.3 Ωcm An electrostatic chuck having a ratio of 0.089% was produced. At this time, the convex part of ø0.25 mm is arrange | positioned on the surface continuously in each vertex of the equilateral triangle whose one side is 8 mm. The height of the convex part is 10 micrometers.

As a result, the change of the surface roughness after plasma irradiation and the thing with very small contact area with the to-be-adsorbed object overlapped, and the time-dependent change of the temperature change at the time of the process of the silicon wafer which is an to-be-adsorbed material was very small.

POPOFF adsorption force recorded more than 100 torr for the whole sample. That is, it turned out that sufficient practical force is acquired in order to adsorb | suck adsorption bodies, such as a silicon wafer.

Claims (5)

An electrostatic chuck dielectric with alumina of at least 99.4% by weight, titanium oxide at greater than 0.2% by weight and below 0.6% by weight, volume resistivity of 10 ⁸ to 10 ¹¹ Ωcm at room temperature, and titanium oxide segregated at the grain boundaries of the alumina particles. Electrostatic chuck characterized in that provided. Alumina is not less than 99.4% by weight, titanium oxide is greater than 0.2% by weight and not more than 0.6% by weight, bulk density is not less than 3.97 g / cm 3, volume resistivity is 10 ⁸ to 10 ¹¹ Ωcm at room temperature, and titanium oxide at grain boundaries of alumina particles An electrostatic chuck comprising the dielectric for electrostatic chuck of this segregated structure. The method according to claim 1 or 2, Electrostatic chuck characterized in that the aluminum titanate (Al ₂ TiO ₅ ) is not present in the grains and grain boundaries of the alumina particles. As the electrostatic chuck of any one of claims 1 to 3, Electrostatic chuck, characterized in that used at low temperatures below 100 ℃. The method according to any one of claims 1 to 4, A plurality of convex portions are formed, and a dielectric having a smooth surface on which the adsorbed body is placed on the upper surface of the convex portion, and the ratio of the total area of the upper surfaces of the plurality of convex portions to the dielectric surface area is not less than 0.001% and less than 0.5%. In addition, the height of the convex portion of the electrostatic chuck, characterized in that 5 ~ 15 ㎛.

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