JP3275901B2 - Design method of electrostatic chuck - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for designing an electrostatic chuck for adsorbing and fixing an object to be adsorbed such as a semiconductor wafer by electrostatic force.

[0002]

2. Description of the Related Art An internal electrode is provided between a substrate and an insulating layer (dielectric layer) as a jig for fixing a semiconductor wafer to a process such as plasma etching, CVD, or ion plating in a reduced pressure atmosphere. An electric chuck is used.

[0003] The characteristics required of this electrostatic chuck are that, while a voltage is applied, a large suction force is generated to prevent the object to be sucked from dropping, etc., and immediately after the voltage application is released, the suction force is reduced. The object is to reduce the size so that the object can be easily removed.

As means for increasing the attraction force, the relative dielectric constant of the insulating layer is increased (Japanese Patent Publication No. 60-59104, Japanese Patent Publication No. 62-19060), and the thickness of the insulating layer is controlled (Japanese Patent Laid-Open No. 57-64950). No. 1) and means for setting the volume resistivity of the insulating layer within a predetermined range (Japanese Patent Publication No. 61-14660). Helium gas is injected (Japanese Utility Model Laid-Open No. 2-120831), and a voltage having a polarity opposite to the voltage at the time of adsorption is applied (Japanese Patent Publication No. 2-63304).

[0005]

Among the conventional methods described above, the means for increasing the attraction force focuses only on the insulating layer, and the residual attraction force tends to increase even if the attraction force increases.
In addition, it takes more than 60 seconds until the residual adsorbing force is attenuated (98% or more) and the object to be removed can be easily removed. In order to facilitate removal of the adsorbate, there is a disadvantage that a new operation must be added in addition to a separate device or a normal operation, and there is a problem particularly in use at a low temperature.

[0006]

The present inventor has focused on the equivalent circuit of the electrostatic chuck in order to obtain a characteristic of the electrostatic chuck itself in which the residual electrostatic force attenuates in a short time even at a low temperature. What was done. That is, in the related art, the gap δ (m) between the object to be adsorbed and the surface of the insulating layer has not been considered as a component of the equivalent circuit, but the equivalent circuit is assumed in consideration of the gap δ (m). Accordingly, an object of the present invention is to make it possible to design an electrostatic chuck in which the residual electrostatic force is attenuated in a short time while increasing the electrostatic attraction force.

The volume resistivity of the insulating layer at the operating temperature of the electrostatic chuck is ρ (Ωm), the relative permittivity of the insulating layer at the operating temperature of the electrostatic chuck is ε _r , and the distance between the internal electrode and the surface of the insulating layer ( When the thickness is d (m) and the gap between the object to be adsorbed and the surface of the insulating layer is δ (m), they are designed to have the relationship shown in the following (Equation 5).

[0008]

(Equation 5)

The volume resistivity of the insulating layer at 25 ° C. is ρ ′ (Ωm), the relative permittivity of the insulating layer at 25 ° C. is ε _r ′, and the distance (thickness) between the internal electrode and the surface of the insulating layer is d.
(M), the gap between the object to be adsorbed and the surface of the insulating layer is δ (m)
In this case, they are designed so as to satisfy the relationship shown in the following (Equation 6).

[0010]

(Equation 6)

The volume resistivity of the insulating layer at the operating temperature of the electrostatic chuck is ρ (Ωm), the relative permittivity of the insulating layer at the operating temperature of the electrostatic chuck is ε _r , and the distance between the internal electrode and the insulating layer surface (thickness). Is d (m), the gap between the object to be adsorbed and the insulating layer surface is δ (m), the relative permittivity of the protective film formed on the chuck surface at the operating temperature of the electrostatic chuck is ε _rt , and the volume of the protective film. The specific resistance is ρ _t (Ωm), and the thickness of the protective film is _dt
In the case of (m), these are designed to have the relationship shown in the following (Equation 7).

[0012]

(Equation 7)

The volume resistivity of the insulating layer at the operating temperature of the electrostatic chuck is ρ (Ωm), the relative permittivity of the insulating layer at the operating temperature of the electrostatic chuck is ε _r , the distance between the internal electrode and the insulating layer surface (thickness). Is d (m), the surface roughness (maximum height) of the insulating layer is (Rmax) esc (m), and the surface roughness (maximum height) of the object is (Rmax) plate (m). In this case, they are designed so as to satisfy the relationship shown in the following (Equation 8).

[0014]

(Equation 8)

[0015]

[Effect] By associating the electrostatic force remaining time with the volume resistivity, the relative dielectric constant, the thickness of the insulating layer or the protective film, etc. from the equivalent circuit of the electrostatic chuck, the electrostatic force in which the electrostatic force attenuates in a short time even in a low temperature range. A chuck is obtained.

[0016]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a diagram showing an equivalent circuit of the electrostatic chuck. This electrostatic chuck forms an insulating layer 2 on a substrate 1,
An electrode 3 is formed between the substrate 1 and the insulating layer 2, and the electrode 3 is connected to a DC power supply 5 via a lead wire 4, and the semiconductor wafer W is directly connected to the ground or electrically connected to a plasma. Connecting.

The substrate 1 is made of Al ₂ O ₃ , Si ₃ N ₄ , Al
In consideration of erosion resistance, mechanical strength and electrical characteristics, the insulating layer 2 is mainly composed of Al ₂ O ₃ , and a transition metal oxide such as TiO ₂ or Cr ₂ O _{3 is} added thereto. The material added for adjusting the insulation resistance is used as the material.
The material of the insulating layer 2 may be Si ₃ N ₄ , Si
A ceramic sintered body made of C, 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.

In order to produce the substrate 1 and the insulating layer 2, the above-mentioned materials are kneaded with a solvent and formed into a sheet, and then the upper surface of the sheet serving as the substrate or the lower surface of the sheet serving as the insulating layer 2 is formed. A paste-like electrode material such as tungsten (W) is applied to one of them, and these sheets are stacked and fired.

By the way, capacitances C ₁ and C ₂ and conductances G ₁ and G ₂ , which are elements of an equivalent circuit of the electrostatic chuck, have a volume resistivity of the insulating layer ρ (Ωm) and a relative permittivity of the insulating layer ε. _r , the distance (thickness) between the internal electrode and the insulating layer surface is d (m), the area S (m ² ) of the wafer, the contact resistance between the object to be adsorbed and the insulating layer surface is R (Ω), Assuming that the gap between the adsorbate and the surface of the insulating layer is δ (m), it is represented by the following (Equation 9).

[0020]

(Equation 9)

The residual electrostatic force F when the application of the voltage to the electrostatic chuck is released is the following (Equation 10) when the voltage is V, the time is t, and the relative permittivity in vacuum is ε _0. ).

[0022]

(Equation 10)

The following equation (10) is derived. The electrostatic attraction force is represented by the following (Equation 11) from the charge Q ₁ (t) stored in the gap.

[0024]

[Equation 11]

[0025] Thus it is clear response characteristics of the electrostatic attraction force by calculating the transient characteristics for the voltage application and removal of Q _1. When a single rectangular wave (the applied voltage is V from time 0 to T, and 0 after T) is input to the power supply of the equivalent circuit in FIG.

[0026]

(Equation 12)

Solving this, the electric charge Q ₁ accumulated in the capacitance of the gap is expressed by the following (Equation 13) when 0 ≦ t ≦ T (voltage application time) and t> T (voltage application time). Then, the following (Equation 14) is obtained.

[0028]

(Equation 13)

[Equation 14]

When the equation (13) is substituted into the equation (11), a change in electrostatic force when a voltage is applied is calculated. When the surface roughness of the electrostatic chuck is small, C ₁ >> C _2. Therefore, (Equation 14) is substituted into (Equation 11), and t−T is the time when the application of the voltage is released again. (Equation 10) is derived when the origin is set to.

In the above (Equation 10), it is the value of 2 (G ₁ + G ₂ ) / (C ₁ + C ₂ ) that determines the decay speed of the residual electrostatic force, where the residual electrostatic force is the saturated electrostatic force. 98%
Assuming that the time required for attenuation is t _s , t _s is represented by the following (Equation 15).

[0031]

(Equation 15)

When the object to be adsorbed is a silicon wafer or the like, the contact resistance R is sufficiently large, so that t _s can be expressed by the following (Equation 16).

[0033]

(Equation 16)

As described above, to obtain an electrostatic chuck having a shorter residual time than the conventional electrostatic chuck, the following (Equation 1) is used.
The volume resistivity ρ and the like of the insulating layer may be set so as to satisfy the condition (7).

[0035]

[Equation 17]

In the above (Equation 17), the volume resistivity ρ and the relative permittivity ε _r of the insulating layer are values at the operating temperature of the electrostatic chuck. It is represented by (Equation 18).

[0037]

(Equation 18)

Here, A represents the slope of the common logarithm of the volume resistivity to the reciprocal of the absolute temperature (logρ = A · 1 /
T + B A and B are constants) and are values specific to the substance. For example, FIG. 4 shows the temperature change of the volume resistivity of the Al ₂ O ₃ —Cr ₂ O ₃ —TiO ₂ ceramic. In this graph, A is about 800 in the low temperature range and about 2 in the high temperature range.
A value of 500 is shown. When these values are applied to the above (Equation 18), the following (Equation 19), (Equation 20) and (Equation 2)
1).

[0039]

[Equation 19]

(Equation 20)

(Equation 21)

The gap can also be represented by surface roughness (maximum height). That is, when the surface roughness (maximum height) of the insulating layer is (Rmax) esc and the surface roughness (maximum height) of the object to be adsorbed is (Rmax) plate,
7) is represented by the following (Equation 22). Here, the measurement of the surface roughness is performed based on JIS (B0601). The gap can substitute the surface roughness with the maximum surface undulation.
Here, the measurement of the surface waviness may be performed based on JIS (B0610).

[0041]

(Equation 22)

FIG. 2 is a sectional view of an electrostatic chuck according to another embodiment. In this embodiment, impurities are diffused or mixed from the insulating layer 2 to the wafer W on the surface of the insulating layer 2 serving as a suction surface. A protective film 6 is formed to prevent the occurrence of the above. The protective film 6 is made of a ceramic material containing Si, such as Si ₃ N ₄ , SiC, or SiO ₂ , or a material having a high thermal conductivity, such as AlN or C (diamond).

The remaining time t when the protective film 6 is provided
_{In order} to reduce _s to 60 seconds or less, the volume resistivity ρ and the like of the insulating layer may be set so as to satisfy the following (Equation 23).

[0044]

(Equation 23)

Tables 1 to 4 show the volume resistivity ρ of the insulating layer and the distance (thickness) between the internal electrode and the surface of the insulating layer, respectively.
d, the gap between the object to be adsorbed and the surface of the insulating layer is δ (δ =
{(Rmax) esc + (Rmax) plate} / 2) and the values of the residual time calculated by the above equations and the measured values when the material of the insulating layer is changed are shown. From these (tables), it can be seen that the calculated values and the measured values agree well. Therefore, it is calculated from the volume resistivity of the insulating layer, the relative dielectric constant, the distance between the internal electrode and the adsorption surface, the surface roughness of the insulating layer, and the surface roughness of the object to be adsorbed, which satisfy the above (Equation 1) to (Equation 4). By setting an appropriate gap, an electrostatic chuck having a desired remaining time can be obtained. Table 5 shows that Si ₃ N ₄ was used as a protective film,
It shows the calculated value and the measured value of the residual value when using SiC and SiO ₂ .

[0046]

[Table 1]

[Table 2]

[Table 3]

[Table 4]

[Table 5]

In the embodiment, a single-electrode type is shown as the form of the electrode of the electrostatic chuck.
The bipolar type shown in FIG. The equivalent circuit in this case is as shown in FIG. Where C ₃ ,
C ₄ indicates capacitance, and G ₃ and G ₄ indicate conductance.

[0048]

As described above, according to the present invention, according to the present invention, a protective film is formed on the insulating layer constituting the electrostatic chuck, the volume resistivity, the relative permittivity, the distance between the internal electrode and the attraction surface, and furthermore, the attraction surface. When formed, the relative permittivity of the protective film, the thickness of the protective film, and the like are set to have a fixed relationship, so that the electrostatic force attenuates in a short time not only at a normal operating temperature but also in a low temperature region. An electric chuck is obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing an equivalent circuit of an electrostatic chuck.

FIG. 2 is a cross-sectional view of an electrostatic chuck according to another embodiment.

FIG. 3 is a diagram showing an equivalent circuit of an electrostatic chuck according to another embodiment.

FIG. 4 is a graph showing a temperature change of a volume resistivity of an Al ₂ O ₃ —Cr ₂ O ₃ —TiO ₂ ceramic.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... board | substrate, 2 ... insulating layer, 3, 3a, 3b ... electrode, 6 ... protective film.

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-2-22166 (JP, A) JP-A-62-286248 (JP, A) JP-A-3-188645 (JP, A) JP-A 62-286 2632 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01L 21/68 B23Q 3/15 H02N 13/00

Claims (4)

(57) [Claims] 1. A method for designing an electrostatic chuck provided with internal electrodes in an insulating layer, wherein the volume resistivity of the insulating layer at the operating temperature of the electrostatic chuck is ρ (Ωm), and the volume resistivity at the operating temperature of the electrostatic chuck is ρ (Ωm). When the relative permittivity of the insulating layer is ε _r , the distance (thickness) between the internal electrode and the surface of the insulating layer is d (m), and the gap between the object to be adsorbed and the surface of the insulating layer is δ (m),
These are in a relationship shown in the following (Equation 1). (Equation 1) 2. A method for designing an electrostatic chuck having an internal electrode provided in an insulating layer, wherein the volume resistivity of the insulating layer at 25 ° C. is ρ ′ (Ωm), and the relative permittivity of the insulating layer at 25 ° C. Assuming that εr ′, the distance (thickness) between the internal electrode and the insulating layer surface is d (m), and the gap between the object to be adsorbed and the insulating layer surface is δ (m), these are expressed by the following (Equation 2). A method for designing an electrostatic chuck, characterized by the following relationship: (Equation 2) 3. A method for designing an electrostatic chuck in which an internal electrode is provided in an insulating layer and a protective film is formed on a surface in contact with an object to be adsorbed, wherein the volume resistivity of the insulating layer at the operating temperature of the electrostatic chuck is determined. ρ (Ωm), the relative dielectric constant of the insulating layer at the operating temperature of the electrostatic chuck is εr, the distance (thickness) between the internal electrode and the insulating layer surface is d (m), and the distance between the object to be adsorbed and the insulating layer surface is The gap is δ (m), and the volume resistivity of the protective film at the operating temperature of the electrostatic chuck is ρt.
(Ωm), when the relative dielectric constant of the protective film is εrt, and the thickness of the protective film is dt (m), these have the relationship shown in the following (Formula 3). Design method. (Equation 3) 4. A method for designing an electrostatic chuck provided with an internal electrode in an insulating layer, wherein the volume resistivity of the insulating layer at the operating temperature of the electrostatic chuck is ρ (Ωm), The relative dielectric constant of the insulating layer is εr, the distance (thickness) between the internal electrode and the insulating layer surface is d (m), the surface roughness (maximum height) of the insulating layer is (Rmax) esc (m), When the surface roughness (maximum height) of the object is represented by (Rmax) plate (m), these have the relationship shown in the following (Equation 4). (Equation 4)