JPH04367247A - Ceramic electrostatic chuck - Google Patents

Abstract

PURPOSE:To improve the strength and hardness of an electrostatic chuck itself by preventing the scattering of Ca, Ba, etc., contained in the ferroelectric ceramic substance used for forming the chuck so that contamination of silicon wafers can be prevented. CONSTITUTION:This electrostatic chuck is constituted by forming a coating layer 6 composed of the oxide or nitride of Al or Si or a compound of these elements on the surface of a ceramic plate-like body 1 which is provided with an internal electrode 2 and composed of a ferroelectric ceramic substance having a specific inductive capacity of >=50.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ceramic electrostatic chuck used for fixing, straightening, or transporting silicon wafers in semiconductor manufacturing equipment and the like.

0002

[Prior Art] The electrostatic chucks conventionally used have mainly had internal electrodes coated with insulating resin, but recently ceramic electrostatic chucks with excellent corrosion resistance and precision have been used. (For example, Japanese Patent Application Laid-Open No. 62-2646
(See Publication No. 38, etc.) Furthermore, the applicant has already proposed a ceramic using ferroelectric ceramics such as CaTiO3 and BaTiO3 (
(See Japanese Patent Application No. 2-339325).

[0003]Also, such electrostatic chucks are used to fix silicon wafers in the manufacturing process of semiconductor devices, but in particular, electrostatic chucks for etchers that perform dry etching processing on silicon wafers are used. The surface of the electrostatic chuck was easily damaged by the plasma used to process silicon wafers. Therefore,
In the electrostatic chuck using the above ferroelectric ceramics,
Since its components such as Ca and Ba contaminate the wafer, resins such as polyimide have generally been used in electrostatic chucks for etchers.

0004

[Problem to be solved by the invention] However, in recent years, the processing speed of silicon wafers has increased and more powerful etching has become necessary, so there is a problem that electrostatic chucks made of resin such as polyimide are severely damaged. There was a point. Furthermore, as described above, electrostatic chucks using ferroelectric ceramics may contaminate silicon wafers, so they could not be suitably used for etchers.

Furthermore, in the silicon wafer processing process, the electrostatic chuck and the wafer mechanically slide, but CaTiO3
, BaTiO3, and other ferroelectric ceramic materials generally have low mechanical strength, and repeated adsorption and separation can cause chipping, especially at the edges, and the resulting dust can damage the wafer. .

[0006]

[Means for Solving the Problems] Accordingly, the present invention provides a plate-shaped body made of ferroelectric ceramic having a dielectric constant of 50 or more, which is provided with internal electrodes, and a surface of the ceramic plate-shaped body is coated with oxides of Al and Si. The electrostatic chuck is constructed by forming a coating layer made of , nitride, or a composite compound thereof.

[0007]

[Operation] According to the present invention, since a coating layer is formed on the surface of the ceramic plate, scattering of Ca, Ba, etc. can be prevented, and contamination of the silicon wafer can be eliminated, and the electrostatic chuck itself can be can improve the strength and hardness of

[0008]

[Examples] Examples of the present invention will be described below.

As shown in FIGS. 1 and 2, the electrostatic chuck of the present invention includes a ceramic plate-like body 1 and an internal electrode 2, which is fixed to a base plate 4 with a bonding agent 3. Further, as shown in an enlarged cross-sectional view in FIG.
has been formed.

An electrode lead-out portion 4a for supplying current to the internal electrode 2 is formed on the base plate 4, and a voltage is applied from a power source 7 between the internal electrode 2 and the silicon wafer 6 through this electrode lead-out portion 4a. By doing so, the silicon wafer 6 can be attracted onto the attraction surface 1a. Although a monopolar electrostatic chuck is shown in this embodiment, a bipolar electrostatic chuck can also be obtained by forming a plurality of internal electrodes 2 and applying a voltage between these internal electrodes 2.

[0011] Furthermore, the ceramic plate-like body 1 is made of calcium titanate (CaTiO3), barium titanate (
A ferroelectric ceramic whose main component is BaTiO3 and has a dielectric constant of 50 or more is used. Then, this ceramic is molded into a sheet shape to form internal electrodes 2 made of Ag, Pd, etc., and then the sheet-like molded bodies are stacked and integrally fired to create a ceramic plate-like body 1 in which the internal electrodes 2 are embedded. can be obtained. However, this internal electrode 2 does not necessarily need to be embedded in the ceramic plate-like body 1. Although not shown, the internal electrode 2 is formed on the surface of the ceramic plate-like body 1 opposite to the adsorption surface 1a, and It is also possible to fix the base plate 4 thereon via the bonding agent 3.

Furthermore, as the bonding agent 3, an adhesive,
Glass, silicone resin, etc. are used. In addition, the base plate 4
A metal material such as aluminum or a ceramic material such as alumina or forsterite is used.

Furthermore, the covering layer 5 is made of a material that does not have a bad effect on the silicon wafer, specifically, Al, Si, etc.
oxides and nitrides of Al2O3, SiO2,
AlN, Si3 N4, or a composite compound thereof, mullite (3Al2 O3 .2SiO2), is used. By forming the covering layer 5 in this way, it is possible to prevent substances such as Ca and Ba from contaminating the silicon wafer 6 even when used as an electrostatic chuck for an etcher. Note that the thickness t of this coating layer 5 is 20
~200 μm is good, and if the film thickness t is smaller than 20 μm,
The coating layer 5 peels off during wafer adsorption and easily contaminates the wafer. On the other hand, if the film thickness t is greater than 200 μm, the internal electrode 2
The distance d between this and the suction surface 1a becomes too large, and the suction force becomes weak.

Furthermore, this coating layer 5 can be formed by a known thin film forming method such as a CVD method or an ion sputtering method. Furthermore, by forming this coating layer 5, the strength and hardness of the electrostatic chuck itself can be improved.

Experimental Example 1 As an electrostatic chuck of the present invention, the ceramic plate 1 was composed of ceramics containing calcium titanate as a main component (dielectric constant ε=100), had a diameter of 96 mm, and had an orientation flat. It has a shape. Also, Pd
An internal electrode 2 consisting of is embedded in a ceramic plate-like body 1,
Furthermore, on the surface of the ceramic plate 1 by CVD method,
A coating layer 5 made of SiO2 and having a thickness t of 50 μm was formed, and the distance d between the internal electrode 2 and the adsorption surface 1a was 400 μm.
The surface roughness (Rmax) of the suction surface 1a was set to 2S.

[0016] Furthermore, a coating layer 5 having the same shape and size as above is also provided.
We prepared electrostatic chucks that did not form any porosity as comparative examples, and conducted adsorption/detachment tests using these electrostatic chucks. The adsorption/detachment test was conducted at a vacuum degree of 10 −3 Torr, an electrostatic chuck surface temperature of 24° C., and an applied voltage of 100 to 1000 V. The results are as shown in FIG. 4, which shows the relationship between applied voltage and adsorption force, and FIG. 5, which shows the adsorption/detachment response curve.

From these results, it is clear that the electrostatic chuck of the example of the present invention was able to obtain a suction force of 80 g/cm 2 or more at an applied voltage of 600 V, which is sufficient for practical use. In addition, the adsorption and desorption response was able to perform the adsorption and desorption operations in 2 to 3 seconds, and although the reaction was about 1 second slower than in the comparative example, the reaction rate was sufficient for practical use.

Experimental Example 2 Next, using the electrostatic chuck of the present invention, the adsorption force and the silicon wafer 6 were measured when the thickness t of the coating layer 5 was varied.
The presence or absence of contamination was investigated. Regarding adsorption power, 60
Those with an adsorption force of 80 g/cm 2 or more when a voltage of 0 V was applied were rated as ○, and those with an adsorption force of less than 80 g/cm 2 were rated as ×. Regarding contamination of the silicon wafer 6, after adsorbing the silicon wafer 6 using each electrostatic chuck and performing a dry etching process, an EPMA analysis was performed on the silicon wafer 6, and Ca was not detected. Those detected were marked ○, and those detected were marked ×.

The results are shown in Table 1, where the thickness t of the coating layer 5
If the film thickness t is smaller than 20 μm, the silicon wafer 6 may be contaminated, while if the film thickness t is larger than 200 μm, a practically sufficient suction force cannot be obtained. Therefore, the thickness t of the coating layer 5 was preferably in the range of 20 to 200 μm.

[0020]

[Table 1]

Experimental Example 3 Next, as an example of the present invention, Al2O3, SiO2
, Si3 N4, and mullite (3Al2 O3
・2SiO2) was prepared with a coating layer 5 formed thereon, and as a comparative example, a ceramic plate 1 with no coating layer 5 formed thereon was prepared, and the bending strength (
JIS 3-point bending) and Vickers hardness (load: 500 g). As shown in Table 2, the results show that the examples of the present invention in which the coating layer 5 was formed have improved both strength and hardness compared to the comparative examples.

[0022]

[Table 2]

[0023]

Effects of the Invention As described above, according to the present invention, an oxide, nitride, or oxide of Al, Si, or By forming a coating layer made of these composite compounds, Ca and Ba contained in ferroelectric ceramics can be reduced.
Since it is possible to prevent the scattering of such substances, it is possible to eliminate contamination of silicon wafers, and it is possible to provide an electrostatic chuck particularly suitable for use in etchers. In addition, even if a covering layer is formed, if the film thickness is within a predetermined range, adsorption force that does not cause any practical problems can be obtained, and furthermore, by forming a covering layer, mechanical strength can be improved, etc. Can be done.

[Brief explanation of drawings]

FIG. 1 is a perspective view showing a ceramic electrostatic chuck of the present invention.

FIG. 2 is a sectional view taken along the line XX in FIG. 1;

FIG. 3 is an enlarged sectional view of section A in FIG. 2;

FIG. 4 is a graph showing the relationship between applied voltage and adsorption force by electrostatic chucks of the present invention and comparative examples.

FIG. 5 is a graph showing adsorption/detachment response curves by electrostatic chucks of the present invention and comparative examples.

[Explanation of symbols]

1... Ceramic plate-shaped body 2...Internal electrode 3...Joining material 4...Base board 5...Covering layer 6...Silicon wafer 7...Power supply

Claims (1)

[Claims] [Claim 1] A plate-like body made of ferroelectric ceramic having a dielectric constant of 50 or more and having internal electrodes is coated with Al, Si, etc. on the surface thereof.
Ceramic electrostatic chuck with a coating layer made of oxide, nitride, or a composite compound thereof.