JPH05243367A - Electrostatic chuck - Google Patents

Abstract

PURPOSE:To prevent that an electrostatic force is lowered by a method wherein the diffusion of impurities from an insulating layer for an electrostatic chuck to a wafer is suppressed. CONSTITUTION:In an electrostatic chuck, an insulating layer 2 is formed on a substrate 1, an electrode 3 is formed between the substrate 1 and the insulating layer 2, the electrode 3 is connected to a DC power supply 5 via a lead wire 4 and a protective film 6 is formed on the surface of the insulating layer 2. A material for the protective film 6 is selected from a ceramic material which contains Si such as Si3N4, SiC, SiO2 or the like or from a material whose heat conductivity is high such as AlN, BN, C (diamond) or the like with reference to a material for the insulating layer 2. Concretely, a material in which the volume electric resistivity value rho of the insulating layer 2 and the volume electric resistivity value rhov of the protective film 6 are at rhov/rho 10<-1> is selected.

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 attracting and fixing an object to be attracted such as a semiconductor wafer by electrostatic force.

[0002]

2. Description of the Related Art As a fixture for performing plasma etching, CVD, ion plating or the like on a semiconductor wafer in a reduced pressure atmosphere, an internal electrode is provided between a substrate and an insulating layer (dielectric layer) or inside the insulating layer An electrostatic chuck provided with is known as Japanese Patent Publication No. 60-59104.

In the general electrostatic chuck described above, the upper surface of the insulating layer serves as a suction surface, and the semiconductor wafer is mounted on the suction surface. However, with such a structure, since the semiconductor wafer and the insulating layer are in direct contact with each other, impurities may diffuse or mix into the semiconductor wafer from the insulating layer. Therefore, the applicant of the present application filed Japanese Patent Application No. 3-
The specification of 186854 proposes an electrostatic chuck in which a protective film for preventing diffusion of impurities is formed on the surface of an insulating layer.

[0004]

As described above, if a protective film is formed on the surface of the insulating layer, diffusion of impurities into the wafer can be prevented, but the wafer is adsorbed depending on the electrical characteristics of the protective film. It also affects the electrostatic force of the wafer and sometimes the wafer cannot be attracted.

[0005]

In order to solve the above problems, the present inventor has made the present invention by paying attention to an equivalent circuit of an electrostatic chuck, and the present invention is based on the volume characteristic of the insulating layer of the electrostatic chuck. The resistance value ρ and the volume specific resistance value ρ _{v of the} protective film are
ρ _v / ρ ≧ 10 ⁻¹ .

[0006]

According to the equivalent circuit of the electrostatic chuck, the volume resistivity values of the insulating layer and the protective film are constant, that is, ρ _v / ρ ≧ 10 ^-1.
In the case of, the electrostatic force sufficient to attract the wafer can be obtained.

[0007]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a sectional view of an electrostatic chuck according to the present invention,
FIG. 2 is a diagram showing an equivalent circuit of the electrostatic chuck. This electrostatic chuck forms an insulating layer 2 on a substrate 1, forms an electrode 3 between the substrate 1 and the insulating layer 2, and 3 is connected to a DC power source 5 via a lead wire 4, a protective film 6 is formed on the surface of the insulating layer 2, and the semiconductor wafer W placed on this protective film 6 is directly connected to ground. , Or electrical connection by plasma.

The substrate 1 is made of Al ₂ O ₃ , Si ₃ N ₄ and Al.
Insulating layer 2 is made of N, BN or SiC, and in consideration of erosion resistance, mechanical strength and electrical characteristics, Al ₂ O ₃ is the main component, and transition metal oxide such as TiO ₂ or Cr ₂ O ₃ is added to it. The material is added to adjust the insulation resistance value. Further, as the material of the insulating layer 2, in addition to the above, Si
_A ceramic sintered body made of ₃ N ₄ , SiC, AlN, ZrO ₂ , SiO ₂ .Al ₂ O ₃ or BN, or an organic substance such as chloroprene rubber or acrylic rubber may be used as the material.

Further, the material of the protective film 6 is Si ₃ N ₄ ,
A ceramic material containing Si such as SiC or SiO ₂ or a material having high thermal conductivity such as AlN, BN or C (diamond) is selected in relation to the material of the insulating layer 2. Specifically, the volume resistivity ρ of the insulating layer 2 and the volume resistivity ρ _{v of the} protective film 6 are selected so that ρ _v / ρ ≧ 10 ⁻¹ .

As described above, the volume resistivity value ρ of the insulating layer 2
The reason why the volume resistivity value ρ _{v of the} protective film 6 and the volume resistivity value ρ _v have a constant relationship will be described below. First, the capacitance C1, which is an element of the equivalent circuit of the electrostatic chuck shown in FIG.
C ₂ and conductances G ₁ and G ₂ are ρ (Ωm), the volume resistivity of the insulating layer 2, ε _r , the relative permittivity of the insulating layer 2, and the distance (thickness between the inner electrode 3 and the surface of the protective layer 6). ) Is d (m),
If the area S (m ² ) of the wafer W, the contact resistance between the wafer W and the surface of the protective layer 6 is R (Ω), and the gap between the wafer W and the surface of the protective layer 6 is δ (m), then Represented by 1).

[0011]

[Equation 1]

At this time, the gap δ can be approximately expressed by the following (Equation 2).

[Equation 2]

The electrostatic force F after the voltage application time has sufficiently passed is expressed by the following (Equation 3).

[0014]

[Equation 3]

From the above (Equation 3), the electrostatic force F is the contact resistance R
And the volume resistivity value ρ of the insulating layer 2 is determined by the ratio R / ρ. That is, when the contact resistance R becomes small, the voltage divided between the protective film 6 and the wafer W becomes small, and the amount of charge accumulated in the capacitor C ₁ formed at the interface decreases. Therefore, when the contact resistance R (the reciprocal of the conductance G ₁ ) is smaller than the volume specific resistance value ρ of the insulating layer 2, the electrostatic force F becomes small. The result of experimenting this is shown in FIG.

In order to positively control the contact resistance R, it is appropriate and convenient to use the volume specific resistance value ρ _v of the protective film described below. Therefore, the contact resistance R and the volume specific resistance value ρ of the protective film 6 are appropriate. Consider the relationship with _v . When the wafer W is adsorbed on the surface of the protective film 6, microscopically, the surface of the protective film 6 and the wafer W are in contact with each other at a plurality of points. The contact resistance r at each contact point can be approximated to only the concentrated resistance, and since the volume specific resistance ρ _plate of the wafer W is sufficiently smaller than the volume specific resistance value ρ _v of the protective film 6, it can be expressed as (Equation 4). it can.

[0017]

[Equation 4]

The contact resistance R can be considered as a plurality of resistances r at each contact point arranged in parallel. Then, assuming that the resistances r at the respective contact points are equal, the following (Equation 5) is derived, and from (Equation 5), the contact resistance R is the protective film 6
It can be seen that it is proportional to the volume resistivity ρ _v of.

[0019]

[Equation 5]

In summary, to summarize the above, in order to maintain a sufficient electrostatic force when the protective film is formed, a constant value is maintained between the volume specific resistance value ρ _v of the protective film 6 and the volume specific resistance value ρ of the insulating layer. It can be said that it is necessary to have a relationship. Therefore,
FIG. 4 shows the result of an experiment on the relationship between the electrostatic force F and the ratio of the volume resistivity ρv of the protective film 6 to the volume resistivity ρ of the insulating layer. From FIG. 4, it can be seen that if the ρ _v / ρ ratio is 10 ⁻² or less, sufficient electrostatic force for adsorbing the semiconductor wafer cannot be obtained. Also, to obtain a sufficient electrostatic force, ρ _v /
It can be said that it is sufficient to set the ρ ratio to 10 ^-1 or more. When it is difficult to measure the volume resistivity ρ _v of the protective film 6, the surface resistivity ρ _s hardly changes, so
The surface resistivity ρ _s may be used.

[0021]

As described above, according to the present invention, since the protective film is formed on the surface of the insulating layer, it is possible to prevent the impurities from diffusing or mixing from the insulating layer to the semiconductor wafer. Moreover, the volume resistivity value of the protective film ρ _v
And the volume resistivity ρ of the insulating layer, ρ _v / ρ ≧ 10
^Since it has a relationship of ^-1, it is possible to exert a sufficient electrostatic force.

[Brief description of drawings]

FIG. 1 is a sectional view of an electrostatic chuck according to the present invention.

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

FIG. 3 is a graph showing the relationship between the electrostatic resistance and the ratio of the contact resistance to the volume resistivity of the insulating layer.

FIG. 4 is a graph showing the relationship between the ratio of the volume specific resistance values of the protective film and the insulating layer and the electrostatic force.

[Explanation of symbols]

1 ... Substrate, 2 ... Insulating layer, 3 ... Internal electrode, 4 ... Lead wire,
5 ... Power source, 6 ... Protective film, W ... Semiconductor wafer.

Claims (1)

[Claims] 1. An electrostatic chuck in which an internal electrode is provided in an insulating layer or between an insulating layer and a substrate, and a protective film is formed on the surface of the insulating layer, the volume resistivity value ρ of the insulating layer.
And the volume specific resistance value ρ _{v of the} protective film have the following relationship.