JPH05211228A - Electrostatic chuck - Google Patents

Abstract

PURPOSE:To obtain an electrostatic chuck displaying stable electro-static characteristics in conformity with a working temperature. CONSTITUTION:The insulating layer of an electrostatic chuck is composed of the solid solution particles of alumina and a transition metal oxide and glass existing on the grain boundaries of the solid solution particles. For the substance producing a solid solution between itself and alumina, concretely chromia (Cr2O3) having the crystal structure of corundum structure, crystal structure of which is similar to alumina, is cited as the transition metal oxide at that time.

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 jig for fixing a wafer when a semiconductor wafer is subjected to processes such as plasma etching, CVD, and ion plating in a reduced pressure atmosphere, an internal electrode is provided between the substrate and an insulating layer (dielectric layer). An electric chuck is used.

The characteristics required for this electrostatic chuck are that a large attracting force is generated while a voltage is applied to prevent the object to be attracted from falling and the like, and when the voltage application is released, the attracting force is immediately increased. The object is to make it small so that the object to be adsorbed can be easily removed.

As means for increasing the adsorption force, the relative dielectric constant of the insulating layer is increased (Japanese Patent Publication No. 60-59104 and Japanese Patent Publication No. 62-19060), and the thickness of the insulating layer is controlled (Japanese Patent Laid-Open No. 57-64950). The volume resistivity of the insulating layer is within a predetermined range (Japanese Patent Publication No. 61-14660, JP-A-2-
No. 22166) and the like, and as a means for facilitating the removal of the adsorbed material, helium gas is blown between the chuck surface and the adsorbed material (Actual No. 2-120831).
A voltage with the opposite polarity to the voltage at the time of adsorption is applied.
63304) and the like.

Of the above-mentioned conventional methods, the means for increasing the suction force focuses only on the insulating layer, and the residual suction force tends to increase even if the suction force increases. Further, the residual adsorption force is attenuated, and it takes more than 60 seconds before the adsorbent can be easily removed, and it is not possible to deal with the case where the adsorbent is to be immediately removed after processing. Therefore, the adsorbent must be removed. There is a disadvantage that a new operation must be added in addition to another device or a normal operation for facilitating the operation, and there is a problem particularly in use at a low temperature.

Therefore, as shown in FIG. 1, the present inventor forms an insulating layer 2 on a substrate 1, forms an electrode 3 between the substrate 1 and the insulating layer 2, and connects the electrode 3 to a lead wire 4. Assuming an electrostatic chuck which is connected to the DC power source 5 via the semiconductor wafer W and is directly connected to the ground or is electrically connected by plasma, focusing on the equivalent circuit of this electrostatic chuck, Decay time ts from equivalent circuit (time required for residual electrostatic force to decay 98% with respect to saturated electrostatic force)
And the volume specific resistance ρ (Ωm) of the insulating layer at the operating temperature of the electrostatic chuck, the relative dielectric constant εr of the insulating layer at the operating temperature of the electrostatic chuck, and the distance d (m) between the internal electrode and the surface of the insulating layer. And the gap δ between the object to be adsorbed and the surface of the insulating layer
The relationship with (m) was clarified. This relationship is shown in (Equation 1) below.

[0007]

[Equation 1]

[0008]

From the above (Formula 1), it can be seen that the detachability of the object to be adsorbed at the operating temperature of the electrostatic chuck largely depends on the volume resistivity of the insulating layer.
That is, in order to exhibit stable electrostatic characteristics regardless of the operating temperature, it is necessary to adjust the volume resistivity of the insulating layer to a wide range at the time of manufacturing the electrostatic chuck.

However, the material constituting the insulating layer (dielectric layer) of the conventional electrostatic chuck cannot adjust its volume resistivity to a wide range. For example, it has been proposed to add titania as a transition metal oxide to alumina, but as the amount of titania added increases, the number of complex oxide particles precipitated between alumina particles increases, and the electric conductivity depends on the electric field strength. Sex becomes remarkable. That is, the volume specific resistance sharply decreases at a certain electric field strength, and a predetermined electrostatic characteristic cannot be maintained.

[0010]

In order to solve the above-mentioned problems, an electrostatic chuck according to the present invention comprises an insulating layer of an electrostatic chuck,
The solid solution particles and the glass existing at the grain boundaries of the solid solution particles, or the solid solution particles, the glass existing at the grain boundaries of the solid solution particles and 2% by weight or less of the transition metal oxide precipitated at the grain boundaries of the solid solution particles, further comprising: The solid solution particles were composed of alumina and a transition metal oxide having a corundum structure.

[0011]

When the transition metal oxide has a corundum structure, the corundum structure is similar to the crystal structure of alumina, so that it easily forms a solid solution with alumina.

[0012]

Embodiments of the present invention will be described below with reference to the accompanying drawings. As shown in FIG. 1, the electrostatic chuck according to the present invention forms an insulating layer 2 on a substrate 1, forms an electrode 3 between the substrate 1 and the insulating layer 2, and connects the electrode 3 to a lead wire. The semiconductor wafer W is directly connected to ground or electrically connected to plasma by connecting to the DC power source 5 via 4.

As is apparent from the enlarged schematic view of FIG. 2, the insulating layer 2 has a solid solution particle 21 of alumina and a transition metal oxide and a glass 22 existing at the grain boundary of the solid solution particle.
Consists of. Here, the transition metal oxide is preferably one that forms a solid solution with alumina, specifically, chromia (Cr ₂ O ₃ ) having a crystal structure of a corundum structure similar to that of alumina. In addition, FIG. 3 shows alumina (Al
It is a phase diagram of ₂ O ₃ ) and chromia (Cr ₂ O ₃ ), and it is clear from this figure that complete solid solution is achieved.

By the way, the volume resistivity of alumina is 10
Above ¹⁴ Ωcm, the volume resistivity of chromia is 10 ⁶ Ωc
It is estimated that m, and as described above, alumina and chromia are completely dissolved, so that the volume resistivity of the insulating layer 2 can be adjusted by changing the addition ratio of chromia. FIG. 4 is a graph showing the relationship between the addition ratio of chromia and the volume resistivity. From this graph as well, it can be seen that the volume resistivity of the insulating layer 2 can be arbitrarily adjusted within a predetermined range.

Further, in the insulating layer having the structure shown in the enlarged schematic view of FIG. 2, the solid solution particles 21 have a lower resistance than the glass 22 at the grain boundaries, so that charges are conducted through the solid solution particles 21. It will be. In this case, as shown in FIG. 5, even if the electric field strength increases, the current follows Ohm's law. Therefore, there is no dielectric breakdown due to a sudden increase in current,
It is possible to prevent damage to the silicon wafer.

FIG. 6 is an enlarged schematic view of an insulating layer 2 according to another embodiment. In this embodiment, solid solution particles 2 of alumina and chromia (transition metal oxide of corundum structure) are formed.
1. Precipitate 2 of glass 22 and titania (transition metal oxide not having a corundum structure) existing at grain boundaries of solid solution particles
Insulating layer 2 is formed from 3.

FIG. 7 is a graph showing the relationship between titania (TiO ₂ ) concentration and volume resistivity, and FIG. 8 is titania (TiO ₂ ).
It is a graph showing the relationship between the concentration and the volume resistivity of the insulator and the electric field strength. From these graphs, when titania is added, the volume resistivity is 10% unless the content is 2% by weight or less.
^It is difficult to control in the range of ⁸ Ωcm to 10 ¹² Ωcm,
It can be seen that the electric field dependence of the volume resistivity becomes large and dielectric breakdown is likely to occur due to a rapid increase in current.

Next, a method of manufacturing the electrostatic chuck according to the present invention will be described. First, prepare alumina powder and corundum-structured transition metal oxide (chromia) as raw materials, titania and a sintering aid, add them to a binder, toluene, butyl acetate, etc. after weighing and mixing them with a ball mill. Then, after defoaming and aging, a green sheet is formed, and the green sheet is laminated on an unfired supporting substrate on which an electrode layer is printed, and the temperature is 1500 to 1650 ° C. in a reducing atmosphere.
By firing (usually 1600 ° C.) for 1 to 7 hours (usually 2 hours), an electrostatic chuck is obtained.

Here, the addition ratio of the transition metal oxide having a corundum structure is 1 to 50% by weight. This is because if it is less than 1% by weight, the effect of addition is not exhibited, and if it exceeds 50% by weight, sufficient firing cannot be performed. Further, as the type of the sintering aid, silica sand, clay, glass frit, alkaline earth metal carbonate or nitrate, etc. are used, and the addition ratio is 6 to
12% by weight. This is because if it is less than 6% by weight, the shrinkage of ceramics is lowered and the withstand voltage is lowered, and if it exceeds 12% by weight, a liquid layer is formed at a low temperature and sufficient firing cannot be performed.

[0020]

EFFECTS OF THE INVENTION (Table 1) shows the volume resistivity of the insulating layer of the electrostatic chuck according to the present invention and the conventional electrostatic chuck, the attachment / detachment time, the leakage current (when a 6-inch wafer is adsorbed), and the electric field strength. It is a value measured as 0.67 × 10 ⁶ V / m.
The electrostatic chuck used for the measurement was a mixture of alumina, chromia, titania of Table 1 and sintering aid of 9% by weight in a ball mill, which was crushed and mixed with a binder and toluene.
After adding butyl acetate, etc., it is defoamed and aged to form a green sheet, and this green sheet is laminated on a support substrate which is also made into a green sheet and has an electrode layer such as tungsten or molybdenum printed on its upper surface. It was obtained by firing at 1600 ° C. using an atmosphere gas as a mixed gas of hydrogen and nitrogen.

[0021]

[Table 1]

As is clear from Table 1, solid particles and solid solution particles of alumina and a transition metal oxide having a corundum structure and a transition metal oxide having a corundum structure are used as the insulating layer of the electrostatic chuck according to the present invention. Or a solid solution particle of alumina and a transition metal oxide having a corundum structure, glass existing in the grain boundary of the solid solution particle and 2% by weight or less precipitated in the grain boundary of the solid solution particle. Since it is made of a transition metal oxide, the volume resistivity of the insulating layer can be adjusted to a wide range at the time of manufacturing, so that an electrostatic chuck that exhibits stable electrostatic characteristics according to the operating temperature can be obtained.

[Brief description of drawings]

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

FIG. 2 is an enlarged schematic diagram of an insulating layer.

[Fig. 3] Phase diagram of alumina (Al ₂ O ₃ ) and chromia (Cr ₂ O ₃ ).

FIG. 4 is a graph showing the relationship between the addition ratio of chromia and the volume resistivity.

FIG. 5 is a graph showing the relationship between volume resistivity and electric field strength.

FIG. 6 is an enlarged schematic view of an insulating layer according to another embodiment.

FIG. 7 is a graph showing the relationship between titania (TiO ₂ ) concentration and volume resistivity.

FIG. 8 is a graph showing the relationship between the titania (TiO ₂ ) concentration and the volume resistivity of the insulator and the electric field strength.

[Explanation of symbols]

1 ... Substrate, 2 ... Insulating layer, 3 ... Electrode, 21 ... Solid solution particles,
22 ... Glass, 23 ... Precipitate.

Claims (5)

[Claims] 1. An electrostatic chuck in which an internal electrode is provided in an insulating layer, wherein the insulating layer is formed on a solid solution particle of alumina and a transition metal oxide of a corundum structure and a transition metal oxide of a corundum structure, and a grain boundary of the solid solution particle. An electrostatic chuck characterized by being made of existing glass. 2. An electrostatic chuck in which an internal electrode is provided in an insulating layer, wherein the insulating layer comprises solid solution particles of alumina and a transition metal oxide having a corundum structure, and glass and solid solution particles existing at a grain boundary of the solid solution particles. An electrostatic chuck comprising 2 weight or less of a transition metal oxide deposited on a grain boundary. 3. The electrostatic chuck according to claim 1, wherein the transition metal oxide forming the solid solution particles is chromia (Cr ₂ O ₃ ). 4. The transition metal oxide constituting the solid solution particles is chromia (Cr ₂ O ₃ ), and the transition metal oxide precipitated at the grain boundaries of the solid solution particles is titania (TiO ₂ ). The electrostatic chuck according to claim 2. 5. The volume resistivity of the insulating layer is 10 ¹³ Ω.
The electrostatic chuck according to any one of claims 1 to 4, wherein the electrostatic chuck has a size of cm or less.