JPH07221168A - Surface polishing method of electrostatic chuck - Google Patents

Abstract

PURPOSE:To enable the dielectric layer surface to be polished with high preci sion without being scratched by stone dust at all by a method wherein the dielectric layer surface is polished with stone dust softer than the dielectric layer itself to produce a reactant of both component materials of the dielectric layer and the stone dust to be mechanically removed later. CONSTITUTION:The surface of a dielectric layer 2 of an electrostatic chuck is polished with stone dust softer than the dielectric later 2 itself to create a locally high temperature and high pressure state so that a reactant of both component materials of the dielectric layer 2 and the stone dust may be chemically produced. Next, at least the reactant or the product produced after the decomposition of the reactant is mechanically removed out of the surface of the dielectric layer 2. For example, it is recommended that the dielectric layer 2 mainly comprises Al2O3 the stone dust comprises SiO2 and the reactant from the material comprising the dielectric layer 2 and the material comprising the stone dust mainly comprises kainite. Finally, the reactant is polished while feeding a polishing solution 6 containing SiO2 stone dust using a high rigid polisher 5.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for polishing the surface of a dielectric layer of an electrostatic chuck.

[0002]

2. Description of the Related Art Conventionally, a semiconductor wafer is subjected to a process such as plasma etching or plasma CVD under reduced pressure. A chuck utilizing electrostatic force is known as a chuck for holding a semiconductor wafer under such a reduced pressure, and this electrostatic chuck has an upper surface made of Al ₂
The dielectric layer is mainly O ₃ . Then, the surface of the dielectric layer is subjected to surface grinding with a diamond grindstone, polishing with diamond abrasive grains, SiC abrasive grains, Al ₂ O ₃ abrasive grains and the like having abrasive hardness equal to or higher than Al ₂ O _3. Has been done.

[0003]

As described above, with respect to the polishing of the surface of the dielectric layer on the upper surface of the electrostatic chuck, conventionally, hard abrasive grains such as diamond abrasive grains are used to improve the processing accuracy. However, scratches such as indentation and scratching due to hard abrasive grains occur on the surface of the dielectric layer. The scratches may damage the wafer when the semiconductor wafer is attached and detached, and particles may adhere to the semiconductor wafer. Furthermore, a mechanically polishing method using hard abrasive grains creates a work-affected layer on the surface of the dielectric layer. May adhere to.

Although chemical polishing and electrolytic polishing are known in place of the mechanical polishing as described above, they are inferior in processing accuracy and cannot be applied to an electrostatic chuck which requires high processing accuracy.

[0005]

In order to solve the above-mentioned problems, the present invention is to polish the surface of the dielectric layer with abrasives softer than the dielectric layer to form a dielectric layer on the surface of the dielectric layer and the abrasives. The reaction product with the substance constituting the is chemically generated, and at least the reaction product or the product obtained after decomposing the reaction product is mechanically removed from the surface of the dielectric layer.

[0006]

For example, Al ₂ O ₃ forming the dielectric layer and SiO ₂ forming the abrasive grains are reacted with each other to form sillimanite such as kyanite, and the formed kyanite is mullite. The surface of the electrostatic chuck is polished by mechanochemical polishing that has a mechanical surface of removing the material by making it amorphous or amorphous.

[0007]

Embodiments of the present invention will be described below with reference to the accompanying drawings. Here, FIG. 1 is a diagram showing a state in which the electrostatic chuck is being polished. The electrostatic chuck forms a dielectric layer 2 on a substrate 1, and an internal portion is provided between the substrate 1 and the dielectric layer 2. An electrode 3 is provided, and a power supply line 4 for supplying a high voltage is connected to the internal electrode 3.

The electrostatic chuck is prepared as a green sheet containing 75% by weight or more of Al ₂ O ₃ , less than 25% by weight of transition metal oxide, and 10% by weight or less of glass components such as SiO ₂ , MgO and CaO. Then, a tungsten or molybdenum paste serving as an internal electrode is printed on one surface of a predetermined green sheet, and the green sheets are laminated so as to sandwich the printed surface and fired.

In the electrostatic chuck obtained by firing, the dielectric layer 2 has a thickness of 250 to 500 by a surface grinder.
It is ground to about μm, and the average surface roughness (R
Rough polishing is performed until a) becomes about 0.25 μm, and then finish polishing is performed by the method of the present invention using the polishing disk 5.

In the finish polishing, the polishing plate 5 having high rigidity is provided with an abrasive grain softer than the material forming the dielectric layer 2, for example, Si.
Polishing is performed while supplying a polishing liquid 6 containing O ₂ abrasive grains. Then, a high temperature / high pressure state is locally generated, and Al ₂ O ₃ forming the dielectric layer reacts with SiO ₂ forming the abrasive grains to mainly produce kyanite. This Kyanite is mA
l ₂ O ₃ · nSiO ₂ (m: 62.9%, n: 37.1%)
, The oxygen ions take the closest packing, and in this, Si
It is a triclinic mineral in which the ions are tetrahedral and sometimes Al-ion hexahedrally bonded. In addition, Kyanite is 132
Above 5 ° C, it decomposes into mullite and silica, is subjected to polishing stress, and is mechanically and easily removed from the surface of the dielectric layer. As a result, the surface of the dielectric layer has an average surface roughness (Ra) of 0.15.
Finish polishing is performed so as to be less than μm. In addition to kyanite, andalusite (orthorhombic system with a true specific gravity of 3.1 ~
3.2) and sillimanite (orthorhombic and true specific gravity 3.23 to 3.25)
It is considered that some are also generated, but these are decomposed into mullite and silica at a higher temperature than kyanite.

The following (Table 1) shows the results of an experiment carried out by changing the conditions such as the polishing agent used.

[0012]

[Table 1]

The composition ratio of the dielectric layer of the chuck used in the experiment was 83 wt% Al ₂ O _{3 and} 1% transition metal oxide.
0.5 wt%, total of SiO ₂ , MgO, and CaO is 6.5 wt%
The diameter of the polishing machine used is 1000 mm.
The hard foam polyurethane polishing cloth of No. 1 was used, and the rotation speed of the polishing plate was 60 rpm and the load load was 0.2 kg / cm ² . Further, as abrasive grains, SiO ₂ (silicon oxide), CeO
₂ (cerium oxide) and TiO ₂ (titanium oxide) were used, but other than these, MgO (magnesium oxide), Y ₂ O
It is also possible to use relatively soft abrasive grains such as ₃ (yttrium oxide) and SnO ₂ (tin oxide). Further, the abrasive grains are used by being dispersed in a liquid, but the ratio of the abrasive grains to the liquid is 10 to 10.
The pH of the solution was 20%, the pH of the solution was 8 to 13, and the supply rate of the polishing solution was 20 cc / min.

The presence or absence of scratches in (Table 1) is SE.
The contamination level was evaluated by M observation, and a mirror surface of a silicon wafer was placed on the surface of the dielectric layer, and a voltage of 1 KV was set to 3
Apply for a minute to quantify the concentration of the element of the attached contaminant,
The surface roughness is measured according to JIS B06 using a stylus type surface roughness meter.
The average surface roughness (Ra) was measured according to No. 01, and the glossiness of the polished surface was measured according to JIS Z8741 as Gs (60 °).

2 (a), (b) and (c) show 5000 the particle structure of the surface of the dielectric layer polished by silicon oxide abrasive grains, cerium oxide abrasive grains and diamond abrasive grains, respectively.
3 (a), (b), and (c) show the measurement results of the surface roughness of the dielectric layer surface shown in FIGS. 2 (a), (b), and (c), respectively. It is a graph shown. As is clear from these figures and (Table 1), it is possible to form an extremely smooth surface by polishing the surface of the dielectric layer with abrasives softer than the dielectric layer as in the method of the present invention. I understand.

In this experiment, the one using the dielectric layer containing Al ₂ O ₃ as a main component was explained.
A dielectric material that can be used for an electrostatic chuck, such as 1N, SiC, or Si ₃ N _4, may be used. Even for these materials, by _{polishing, mAl 2 O 3 · nSiO 2} , SiO 2 ( amorphous) or the like can be generated by processing.

[0017]

As described above, according to the present invention, by polishing the surface of the dielectric layer of the electrostatic chuck with abrasive grains softer than the dielectric layer, the dielectric layer is locally brought to a high temperature / high pressure state. Since the reaction product of the substance that constitutes the abrasive grain and the substance that constitutes the abrasive grain is chemically generated, and then this reaction product and the product decomposed by it are mechanically removed from the surface of the dielectric layer, high precision is achieved. The surface of the dielectric layer can be polished and scratches on the surface of the dielectric layer due to abrasive grains (scratch)
Does not occur. Therefore, the surface of the semiconductor wafer is prevented from being contaminated by particles or heavy metal ions.

[Brief description of drawings]

FIG. 1 is a diagram showing a state in which an electrostatic chuck is being polished.

FIG. 2 (a) is a 5000 × photomicrograph showing the particle structure on the surface of a dielectric layer polished with silicon oxide abrasive grains. Double magnification micrograph (c) is a 5000 times micrograph showing the particle structure of the surface of the dielectric layer polished by diamond abrasive grains.

3A is a graph showing the measurement results of the surface roughness of the dielectric layer surface shown in FIG. 2A, and FIG. 3B is a surface roughness of the dielectric layer surface shown in FIG. 2B. (C) is a graph showing the measurement result of the surface roughness of the surface of the dielectric layer shown in FIG. 2 (c).

[Explanation of symbols]

1 ... Substrate, 2 ... Dielectric layer, 3 ... Internal electrode, 5 ... Polishing board,
6 ... Polishing liquid.

Continuation of front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location H02N 13/00 D

Claims (2)

[Claims] 1. A substance constituting the dielectric layer and a substance constituting the abrasive grain are locally brought to a high temperature and high pressure state by polishing the surface of the dielectric layer of the electrostatic chuck with abrasive grains softer than the dielectric layer. The surface of an electrostatic chuck characterized in that the above-mentioned reaction product is chemically generated, and at least this reaction product or a product obtained after decomposing this reaction product is mechanically removed from the surface of the dielectric layer. Polishing method. 2. The method of polishing a surface of an electrostatic chuck according to claim 1, wherein the dielectric layer is mainly composed of Al ₂ O _3, and the abrasive grains are composed of SiO ₂ , and the dielectric layer is composed. A method of polishing a surface of an electrostatic chuck, characterized in that a reaction product of a substance to be formed with a substance constituting an abrasive grain is mainly kyanite.