JP2000286333A - Electrostatic chuck - Google Patents

Abstract

PROBLEM TO BE SOLVED: To display a stabilized electrostatic characteristic matching the temperature used. SOLUTION: The insulating layer of an electrostatic chuck consists of the solid solution particles 21 of alumina and a transition metal oxide and the glass 22, wherein the solid solution particles are present. As the transition metal oxide, whose substance forms a solid solution with alumina such as a chromium structure similar to alumina crystal structure, can be enumerated.

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 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). ), The volume resistivity of the insulating layer is set in a predetermined range (Japanese Patent Publication No. 61-14660,
22166) and the like, and as a means for easily removing the object to be adsorbed, helium gas is blown between the chuck surface and the object to be adsorbed (Japanese Utility Model Laid-Open No. 2-120831).
A voltage having a polarity opposite to that of the voltage at the time of adsorption is applied.
No. 63304).

Among the conventional methods described above, the means for increasing the attraction force focuses only on the insulating layer, and there is a tendency that even if the attraction force increases, the residual attraction force also increases. Also, it takes more than 60 seconds before the residual adsorbing force is reduced and the object to be adsorbed can be easily removed, and it is not possible to cope with a case where the object to be adsorbed is to be immediately removed after processing, and therefore, it is necessary to remove the object to be adsorbed. To make it easier, there is a disadvantage that a new operation must be added in addition to another device or a normal operation, and there is a problem particularly in use at a low temperature.

Therefore, as shown in FIG. 1, the present inventors formed an insulating layer 2 on a substrate 1, formed an electrode 3 between the substrate 1 and the insulating layer 2, and connected the electrode 3 to a lead wire 4. It is assumed that the semiconductor wafer W is connected to the DC power supply 5 via a direct connection, and the semiconductor wafer W is directly connected to the ground or electrically connected by plasma. From the equivalent circuit, the decay time t _s (the time required for the residual electrostatic force to attenuate 98% of the saturated electrostatic force)
And the volume resistivity ρ (Ωm) of the insulating layer at the operating temperature of the electrostatic chuck, the relative permittivity ε _{r 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 substance to be adsorbed and the surface of the insulating layer
(M) was clarified. This relationship is shown in the following (Equation 1).

[0007]

(Equation 1)

[0008]

From the above (Equation 1), it can be seen that the detachability of the object 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 irrespective of the use temperature, it is necessary that the volume resistivity of the insulating layer can be arbitrarily and widely adjusted when manufacturing the electrostatic chuck.

However, the material constituting the insulating layer (dielectric layer) of the conventional electrostatic chuck cannot adjust its volume resistivity arbitrarily and widely. For example, it has been proposed to add titania as a transition metal oxide to alumina.However, when the added amount of titania increases, the amount of composite oxide particles precipitated between alumina particles increases, and the electric conduction characteristics depend on the electric field strength. The nature becomes remarkable. That is, the volume specific resistance sharply decreases at a certain electric field intensity, and the predetermined electrostatic characteristics cannot be maintained.

[0010]

According to the present invention, there is provided an electrostatic chuck provided with an internal electrode in an insulating layer, wherein the insulating layer comprises alumina and chromia (Cr ₂ O ₃ ) having a corundum structure. And a transition metal oxide precipitated at the grain boundaries of the solid solution particles. With the above configuration, the volume resistivity of the electrostatic chuck is set to 10 ⁸ to 1
It can be set to 0 ¹² Ωcm. Further, as transition metal oxides precipitated at the grain boundaries of solid solution particles, titania (Ti
O ₂ ), and the ratio is suitably 2% by weight or less.

[0011]

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

[0012]

Embodiments of the present invention will be described below with reference to the accompanying drawings. Here, FIG. 1 is a diagram showing an equivalent circuit of the electrostatic chuck according to the present invention, and FIG. 2 is an enlarged schematic diagram of an insulating layer of the electrostatic chuck according to the present invention.

In the electrostatic chuck according to the present invention, as shown in FIG. 1, an insulating layer 2 is formed on a substrate 1.
An electrode 3 is formed between the semiconductor wafer W 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 by plasma. ing.

As is apparent from the enlarged schematic diagram of FIG. 2, the insulating layer 2 of the electrostatic chuck according to the present invention is made of solid solution particles 21 of alumina and transition metal oxide and solid solution particles of solid metal particles. Glass 22 present at grain boundaries and precipitate 2 of titania (transition metal oxide not having a corundum structure)
Consists of three. The glass 22 functions as a binder, does not affect the characteristics of the electrostatic chuck, and may be omitted if sintering can be performed without glass.

Here, as the transition metal oxide, one that forms a solid solution with alumina, specifically, chromia (Cr ₂ O ₃ ) having a corundum crystal structure similar to alumina is preferable. FIG. 3 shows alumina (Al ₂
FIG. _{3 is} a phase diagram of O ₃ ) and chromia (Cr ₂ O ₃ ), and it can be seen from FIG.

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

In the insulating layer having a structure as shown in the enlarged schematic diagram of FIG. 2, since the solid solution particles 21 have lower resistance than the glass 22 at the grain boundary, electric charges are conducted through the solid solution particles 21. It will be. In this case, as shown in FIG. 5, even when the electric field strength increases, the current follows Ohm's law. Therefore, there is no dielectric breakdown due to a sudden increase in current,
Damage to the silicon wafer can be prevented.

FIG. 6 is a graph showing the relationship between titania (TiO ₂ ) concentration and volume resistivity, and FIG. 7 is a graph showing titania (TiO ₂ ).
It is a graph which shows the relationship between a density | concentration, the volume resistivity of an insulator, and an electric field strength. When titania is added, unless it is 2 weight% or less, a volume resistivity will be 10%.
^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 increases, and dielectric breakdown due to a sudden increase in current is likely to occur.

Next, a method for manufacturing the electrostatic chuck according to the present invention will be described. First, alumina powder, a transition metal oxide having a corundum structure (chromia), titania, and a sintering aid are prepared as raw materials, weighed, mixed and pulverized with a ball mill, and a binder, toluene, butyl acetate, etc. are added thereto. After that, a green sheet is formed through defoaming and aging, and the green sheet is laminated on an unsintered supporting substrate on which an electrode layer is printed, and is heated to 1500 to 1650 ° C. in a reducing atmosphere.
(Normally 1600 ° C.) for 1 to 7 hours (normally 2 hours) to obtain an electrostatic chuck.

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 the addition is not exhibited, and if it exceeds 50% by weight, sufficient firing cannot be performed. In addition, as a kind of the sintering aid, silica sand, clay, glass frit, carbonate or nitrate of alkaline earth metal is used, and the addition ratio is 6 to
12% by weight. This is because if the amount is less than 6% by weight, the shrinkage of the ceramic decreases, causing a decrease in the withstand voltage.

[0021]

[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 attaching / detaching time, the leakage current (when a 6-inch wafer is sucked) and the electric field strength of 1 It is a value measured as .67 × 10 ⁶ V / m.
The electrostatic chuck used in the measurement was prepared by mixing and pulverizing alumina, chromia, titania and 9% by weight of a sintering aid in Table 1 by a ball mill with a binder and toluene.
After adding butyl acetate, etc., a green sheet is formed through defoaming and aging, and this green sheet is laminated on a supporting substrate which is similarly formed into a green sheet and has an electrode layer of tungsten, molybdenum, etc. printed on the upper surface. The mixture was obtained by baking at 1600 ° C. as a mixed gas of hydrogen and nitrogen as an atmosphere gas.

[0022]

[Table 1]

As is clear from Table 1, according to the present invention, the insulating layer of the electrostatic chuck is formed on the solid solution particles of alumina and chromia (Cr ₂ O ₃ ) having a corundum structure and the grain boundaries of the solid solution particles. Since the structure is made of the deposited transition metal oxide, the volume resistivity of the insulating layer can be arbitrarily and broadly adjusted at the time of manufacture, and an electrostatic chuck exhibiting stable electrostatic characteristics according to the use temperature can be obtained.

[Brief description of the drawings]

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

FIG. 2 is an enlarged schematic view of an insulating layer of the electrostatic chuck according to the present invention.

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 chromia addition ratio and the volume resistivity.

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

FIG. 6 is a graph showing the relationship between titania (TiO ₂ ) concentration and volume resistivity.

FIG. 7 is a graph showing a relationship between titania (TiO ₂ ) concentration, volume resistivity of an insulator, and electric field strength.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Substrate, 2 ... Insulating layer, 3 ... Electrode, 21 ... Solid solution particle,
22: glass, 23: precipitate.

Claims (4)

[Claims] In an electrostatic chuck having an internal electrode provided in an insulating layer, the insulating layer is formed of a solid solution particle of alumina and chromia (Cr ₂ O ₃ ) having a corundum structure and a transition metal deposited on a grain boundary of the solid solution particle. An electrostatic chuck comprising an oxide. 2. The electrostatic chuck according to claim 1, wherein said electrostatic chuck has a volume resistivity of 10 ⁸ to 10 ¹² Ω.
cm. 3. The electrostatic chuck according to claim 1, wherein a ratio of a transition metal oxide precipitated at a grain boundary of the solid solution particles is 2% by weight or less. 4. The electrostatic chuck according to claim 1, wherein the transition metal oxide deposited on the grain boundaries of the solid solution particles is titania (TiO ₂ ). Electric chuck.