JP3084869B2 - 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 an electrostatic chuck for attracting and fixing an object such as a semiconductor wafer by electrostatic force.

[0002]

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

[0003] The characteristics required of this electrostatic chuck are such that a large suction force is generated while a voltage is applied to prevent the object to be sucked from dropping, and the suction force is immediately reduced when the voltage application is released. 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).

[0005] Among the conventional methods described above, the means for increasing the attraction force focuses only on the insulating layer, and even if the attraction force increases, the residual attraction force tends to increase. 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. The nature becomes remarkable. That is, the volume specific resistance sharply decreases at a certain electric field strength, and the predetermined electrostatic characteristics cannot be maintained.

[0010]

In order to solve the above-mentioned problems, the present invention provides an electrostatic chuck having an internal electrode provided in an insulating layer.
The insulating layer is made of alumina and chromium having a corundum structure.
A ) Solid solution particles with (Cr ₂ O ₃ )
Transition metals precipitated at grain boundaries of existing glass and solid solution particles
It is made of an oxide and has a volume resistivity of 10 ⁸ to 10 ¹² Ωc
m. Precipitates at the grain boundaries of the solid solution particles
The proportion of the transition metal oxide is preferably 2% by weight or less.
New Also, a transition metal precipitated at a grain boundary of the solid solution particles.
As the oxide, titania (TiO ₂ ) can be used.

[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 shows an electrostatic chuck according to the present invention.
FIG. 2 shows an equivalent circuit, and FIG. 2 shows the insulation of the electrostatic chuck of the present invention.
It is an enlarged schematic diagram of a layer.

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 clear from the enlarged schematic diagram of FIG. 2, the insulating layer 2 is an insulating layer of the electrostatic chuck according to the present invention.
2 are solid solution particles 21 of alumina and a transition metal oxide.
And glass 22 at the grain boundaries of solid solution particles and titani
A (Transition metal oxide without corundum structure) precipitate 2
Consists of three.

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 its 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 of solid solution particles of alumina and a transition metal oxide having a corundum structure, and glass present at the grain boundaries of the solid solution particles. And precipitate at the grain boundaries of solid solution particles 2
Since it is composed of a transition metal oxide of not more than% by weight, the volume resistivity of the insulating layer can be adjusted arbitrarily and broadly at the time of manufacturing, so that 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 the relationship between volume resistivity and electric field strength.

FIG. 6 shows the relationship between titania (TiO ₂ ) concentration and volume resistivity.
Graph showing the person in charge

FIG. 7: Titania (TiO _Two ) Concentration and volume specific resistance of insulator
Graph showing the relationship between resistance 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.

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-62-94953 (JP, A) JP-A-2-22166 (JP, A) JP-A-62-286248 (JP, A) JP-A-2- 206147 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01L 21/68 B65G 49/07 B23Q 3/15 H02N 13/00

Claims (3)

(57) [Claims] 1. An electrostatic chuck having an internal electrode provided in an insulating layer, wherein the insulating layer has an alumina and corundum structure.
Solid solution particles with chromia (Cr ₂ O ₃ ) , glass existing at the interface between solid solution particles, and transition at the grain boundaries of solid solution particles
A metal oxide having a volume resistivity of 10 ⁸ to 10
An electrostatic chuck having a resistivity of ¹² Ωcm . 2. The electrostatic chuck according to claim 1, wherein
Of the transition metal oxide precipitated at the grain boundaries of the solid solution particles.
Characterized in that the proportion is not more than 2% by weight.
H. 3. The method according to claim 1, wherein
In the electrostatic chuck described above, the solid solution particles precipitate at the grain boundaries.
The transition metal oxide to be produced is titania (TiO 2). _Two )
An electrostatic chuck characterized by the above-mentioned.