JP2007283435A - Silicon-carbide-based polishing plate, manufacturing method, and polishing method for semiconductor wafer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a silicon-carbide-based polishing plate which improves a polishing accuracy of a wafer and improves a polishing efficiency. <P>SOLUTION: The silicon-carbide-based polishing plate has a thermal conductivity of 200 W/m×K or more and a Young's modulus of 450 GPa or more. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a silicon carbide-based polishing plate, a manufacturing method, and a method for polishing a semiconductor wafer, and more particularly to a silicon carbide-based polishing plate used for polishing a semiconductor wafer and characterized by characteristics such as thermal conductivity and Young's modulus. The present invention relates to a method for polishing a semiconductor wafer.

  In general, a semiconductor wafer is manufactured by being thinly sliced from a single crystal ingot and then mirror-polished by a lapping and polishing process.

  The basic configuration of a semiconductor wafer polishing apparatus used in these polishing processes is composed of a polishing head equipped with a polishing plate and a polishing surface plate with a polishing cloth attached thereto. By exchanging the polishing plate, the polishing apparatus is continuously operated. It is operating.

  The semiconductor wafer is fixed to the polishing plate with thermoplastic wax, and is pressed against the polishing platen while being supplied with a chemical polishing liquid between the polishing surface of the polishing cloth and the surface to be polished, and polished.

  In recent years, demands for polishing accuracy have become stricter as semiconductor wafers have shifted to larger diameters and have become finer.

  In order to polish a large-diameter semiconductor wafer with high accuracy, it is important to reduce the temperature distribution due to frictional heat during polishing and to reduce the variation in polishing pressure within the wafer surface.

  The frictional heat at the time of polishing is transmitted to the polishing plate through the semiconductor wafer. However, if the temperature distribution in the polishing plate becomes uneven, thermal deformation occurs, and the polishing accuracy of the semiconductor wafer is lowered. Therefore, in order to eliminate the uneven temperature distribution of the polishing plate, a material having high thermal conductivity and a low thermal expansion coefficient is required.

  On the other hand, in order to reduce the variation of the polishing pressure in the wafer surface, it is possible to increase the rigidity by design, but the polishing apparatus becomes large and the polishing plate becomes heavy. , Leading to increased costs and decreased productivity.

  Accordingly, the mechanical properties required for the polishing plate are low density, high strength, and high rigidity, and the thermal properties include high thermal conductivity and low thermal expansion.

  In order to meet these demands, in recent years, polishing plates using silicon carbide ceramics have increased.

  Silicon carbide-based ceramics have characteristics such as high thermal conductivity, rigidity, and low thermal expansion, and proposals have been made using this.

For example, it is proposed to use a dense body made of silicide ceramic or carbide ceramic having a density of 2.7 g / cm ³ or more for the polishing plate (Patent Document 1), and silicon carbide sintered body is impregnated with Si A polished polishing plate has been proposed (Patent Document 2).

  It is already known that silicon carbide ceramics including those described in Patent Document 1 are generally dense and have a high thermal conductivity when manufactured using a BC sintering aid. It has been.

  In general, a method for producing silicon carbide ceramics by atmospheric pressure sintering is performed as follows.

  An α- or β-type silicon carbide powder having an average particle size of sub-μm to several μm is used as a raw material, and a slurry is prepared by mixing required amounts of a BC sintering aid, a binder and a solvent. Next, granulated powder is produced using a spray dryer or the like, and the granulated powder is put into a mold and molded. As a forming method, CIP, uniaxial press or the like is generally used.

  The obtained molded body is fired at a temperature of 2000 ° C. or higher in a non-oxidizing atmosphere to obtain silicon carbide ceramics.

  Since the silicon carbide ceramic produced in this manner sinters the powder raw material, there are pores inside the material. For this reason, various attempts have been made to lower the porosity and increase the material bulk density, but it is very difficult to eliminate the pores.

The thermal conductivity of the sintered body has a correlation with the bulk density, and the higher the bulk density, the higher the tendency. It has a high density of 3.159 g / cm ³ and has a thermal conductivity of around 170 W / m · K, and it is very difficult to make a product having a density exceeding 200 W / m · K. There are methods such as hot pressing or HIP as a firing method for decreasing the porosity and increasing the bulk density, but large products cannot be stably supplied at low cost.

As for other properties, the three-point bending strength is about 450 MPa, the Young's modulus is about 350 GPa to 450 GPa, and the thermal expansion coefficient is about 4.5 × 10 ⁻⁶ / K (at room temperature to 1000 ° C.). is there.

Furthermore, there is a method using a Si—SiC composite material as in the polishing plate described in Patent Document 2, but since the pores are all filled with Si and structurally poreless, the thermal conductivity is generally Although it is higher than silicon carbide ceramics, it is difficult to produce a material having a Young's modulus of 350 GPa or more. As for other characteristics, the bulk density is around 3.1 g / cm ³ and the thermal expansion coefficient is around 4.3 × 10 ⁻⁶ / K.

  Patent Document 3 discloses a Si-impregnated silicon carbide vacuum chuck having a thermal conductivity of 200 W / m · K and a Young's modulus of 320 GPa.

However, a material having a high thermal conductivity and a high Young's modulus cannot be produced yet, and a silicon carbide polishing plate that improves the polishing accuracy of the wafer and improves the polishing efficiency has not been realized.
JP-A-11-320394 JP 2002-36102 A JP 2005-72039 A

  The present invention has been made in view of the above-described circumstances, and an object thereof is to provide a silicon carbide-based polishing plate that improves the polishing accuracy of a wafer and improves the polishing efficiency.

  It is another object of the present invention to provide a method for manufacturing a silicon carbide polishing plate capable of manufacturing a silicon carbide polishing plate that improves the polishing accuracy of the wafer and improves the polishing efficiency.

  It is another object of the present invention to provide a semiconductor wafer polishing method capable of polishing a semiconductor wafer with high accuracy and efficiency.

As a result of diligent research, the present inventors have found that the thermal conductivity and Young's modulus are in a contradictory relationship with the amount of Si to be impregnated, and based on this finding, the bulk density is 2.60 g / cm ³ to 2. The silicon carbide sintered body of .90 g / cm ³ was impregnated with molten Si, so that the bulk density was 3.05 g / cm ^{3 to} 3.15 g / cm ³ . Also, the three-point bending strength was found to have the highest bending strength within this range. The present invention has been made based on these findings.

  That is, in order to achieve the above-described object, the silicon carbide based polishing plate according to the present invention has a thermal conductivity of 200 W / m · K or more and a Young's modulus of 450 GPa or more.

Preferably impregnated with the melted Si silicon carbide sintered body having a bulk density of ^{2.60g / cm 3 ~2.90g / cm 3} , a bulk density of ^{3.05g / cm 3 ~3.15g / cm 3} , It is a Si-SiC composite material having a bending strength of 500 MPa or more.

The method for producing a silicon carbide polishing plate according to the present invention comprises blending a B-C sintering aid, a binder and a solvent with an α-type silicon carbide powder having an average particle size of 0.01 μm or more and less than 1 μm. A step of kneading to prepare a slurry, a step of producing a granulated powder having an average particle size of about 50 μm using a spray dryer, and filling the granulated powder into a predetermined rubber mold, followed by CIP molding A step of producing a body, a step of firing the molded body at 1900 ° C. to 2300 ° C. in an Ar atmosphere, and producing a silicon carbide sintered body having a bulk density of 2.60 g / cm ^{3 to} 2.90 g / cm ³ , Characterized in that it comprises a step of impregnating a silicon carbide sintered body with molten Si at 1450 ° C. under reduced pressure to produce a silicon carbide-based polishing plate having a thermal conductivity of 200 W / m · K or more and a Young's modulus of 450 GPa or more. To do.

  Further, in the method for polishing a semiconductor wafer according to the present invention, the silicon carbide polishing plate is attached to a polishing head of a semiconductor wafer polishing apparatus, and the semiconductor wafer attached to the silicon carbide polishing plate using wax is attached. It is attached to a rotating polishing surface plate and is pressed against a rotating polishing cloth for polishing.

  According to the silicon carbide based polishing plate of the present invention, it is possible to provide a silicon carbide based polishing plate that improves the polishing accuracy of the wafer and improves the polishing efficiency.

  According to the method for manufacturing a silicon carbide-based polishing plate according to the present invention, it is possible to manufacture a silicon carbide-based polishing plate that improves the polishing accuracy of the wafer and improves the polishing efficiency.

  According to the semiconductor wafer polishing method of the present invention, the semiconductor wafer can be polished with high accuracy and efficiency.

  A silicon carbide based polishing plate according to an embodiment of the present invention, a method for manufacturing the polishing plate, and a method for polishing a semiconductor wafer using the polishing plate will be described with reference to the accompanying drawings.

  FIG. 1 is a conceptual diagram showing a use state in which a silicon carbide polishing plate of the present invention is incorporated in a polishing apparatus.

  As shown in FIG. 1, the silicon carbide polishing plate 1 of the present invention is attached to a polishing head 3 of a semiconductor wafer polishing apparatus 2 and attached to the silicon carbide polishing plate 1 using wax 4. The semiconductor wafer 5 is polished by being pressed against a rotating polishing cloth 7 attached to a rotating polishing surface plate 6.

  Silicon carbide-based polishing plate 1 is made of silicon carbide and has a disk shape, a thermal conductivity of 200 W / m · K or more, and a Young's modulus of 450 GPa or more.

In addition, the thermal conductivity and Young's modulus are in a relationship opposite to the amount of Si to be impregnated, and the polishing plate 1 is a silicon carbide sintered body having a bulk density of 2.60 g / cm ^{3 to} 2.90 g / cm ³ . It is preferably an Si—SiC composite material that is impregnated with molten Si, has a bulk density of 3.05 g / cm ^{3 to} 3.15 g / cm ³ , and a bending strength of 500 MPa or more.

A material having high thermal conductivity has a great merit that thermal deformation of the polishing jig is suppressed because temperature distribution due to frictional heat generated during wafer polishing can be reduced. Since the thermal expansion coefficient of the silicon carbide-based material is approximately 4.3 × 10 ⁻⁶ / K, which is close to the wafer, the stress between the polishing jig and the wafer generated by the heat distribution can be reduced. This improves the polishing accuracy of the wafer. Further, since the Young's modulus exceeds 450 GPa, the deformation of the polishing jig due to the polishing pressure is reduced, and the in-plane variation is also reduced. Therefore, even when a large-diameter wafer is polished, it is possible to prevent a decrease in polishing accuracy.

  Furthermore, since the rigidity is high, it is possible to reduce the thickness of the polishing jig, and the specific heat capacity is also relatively lowered, so that the temperature distribution is also reduced. Similarly, since it leads to weight reduction, apparatus load and cost can be reduced.

Also, the bulk density of the silicon carbide sintered body 2.60 g / cm ³ less than the thermal conductivity is high, there is a tendency that the Young's modulus is reduced, conversely, when greater than 2.90 g / cm ³ Since the silicon carbide sintered body is being densified, the pores that were open pores become closed pores, which impedes Si impregnation. The characteristics approach that of a silicon carbide sintered body, and the thermal conductivity cannot be increased to 200 W / m · K or more.

Therefore, both the thermal conductivity and Young's modulus characteristics are in a sufficiently high range by impregnating molten silicon with a silicon carbide sintered body having a bulk density of 2.60 g / cm ^{3 to} 2.90 g / cm ³ , This is a case where the bulk density is 3.059 g / cm ^{3 to} 3.15 g / cm ³ .

A particularly preferred range, the sintered body bulk density is ^{2.70g / cm 3 ~2.85g / cm 3} .

  Also, the three-point bending strength is the highest at 500 MPa or more in this range. When affixing the wafer to the polishing plate, the polishing plate is heated and fixed wax is used. Regarding the stress caused by the thermal cycle and the ease of handling, the higher the three-point bending strength, It will be advantageous.

  According to the silicon carbide-based polishing plate of the present embodiment, a silicon carbide-based polishing plate that improves the polishing accuracy of the wafer and improves the polishing efficiency is realized.

  By using this silicon carbide based polishing plate, polishing of a semiconductor wafer with high accuracy and efficiency is realized.

  Next, a method for manufacturing a silicon carbide based polishing plate according to the present invention will be described.

  Α-type silicon carbide powder having an average particle size of 0.01 μm or more and less than 1 μm is used as a raw material, and necessary amounts of a B-C sintering aid, a binder and a solvent are mixed therein and mixed for 24 hours in a ball mill. A slurry was prepared.

  If the α-type silicon carbide powder has an average particle size of less than 0.01 μm, poor filling during molding tends to occur and molding becomes difficult. Further, since the density of the obtained molded body is low, cracks and cracks are likely to occur during handling of the molded body. When the average particle size is 1 μm or more, sintering failure tends to occur at the time of firing, and the sintered body density becomes low.

  Next, using a spray dryer, granulated powder having an average particle diameter of 50 μm was produced.

The granulated powder was filled into a predetermined rubber mold, and CIP molding was performed at 1.5 ton / cm ² to obtain a molded body.

  The formed body was fired at 1900 ° C. to 2300 ° C. in an Ar atmosphere to obtain a silicon carbide sintered body.

Here, when silicon carbide reaches a high temperature of 1800 ° C. or higher, sintering starts, and at this time, densification proceeds with volume shrinkage. Therefore, in order to obtain a silicon carbide sintered body having a bulk density of 2.60 g / cm ^{3 to} 2.90 g / cm ³ , the relationship between the heat treatment temperature and the density is investigated and controlled.

  Further, the addition amount of the sintering aid is also important because it affects the sintering shrinkage, and this enables control with higher accuracy.

  The silicon carbide sintered body was impregnated with molten Si at 1450 ° C. under reduced pressure. The reason why the pressure is reduced is that the pores of the silicon carbide sintered body are sufficiently impregnated with Si.

  Moreover, all the characteristics including the thermal conductivity shown in the present invention were measured in accordance with JIS.

  According to the method for manufacturing a silicon carbide based polishing plate of the present embodiment, it is possible to manufacture a silicon carbide based polishing plate that improves the polishing accuracy of the wafer and improves the polishing efficiency.

Example 1 A silicon carbide sintered body having a bulk density of 2.70 g / cm ³ was produced, and Si impregnation treatment was performed at 1450 ° C. to obtain a Si—SiC composite material. This Si—SiC composite material had a thermal conductivity of 235 W / m · K, a Young's modulus of 455 GPa, a bulk density of 3.09 g / cm ³ , and a three-point bending strength of 520 MPa.
Using this material, a polishing plate for φ12 inch wafer was manufactured and a polishing test was performed.
Since the frictional heat increases as the polishing pressure increases, the temperature distribution of the polishing plate also increases and the amount of deformation increases. Normally, polishing conditions are determined based on the wafer accuracy after polishing. However, a higher polishing pressure improves the polishing efficiency, and therefore a higher polishing pressure is advantageous.
After polishing, one point at the center and eight points on the outer periphery were measured to calculate the flatness of the wafer.
The point at which the flatness was greater than 0.5 μm was determined as a judgment point, and the polishing pressure was 300 gf / cm ² .

Example 2 A silicon carbide sintered body having a bulk density of 2.85 g / cm ³ was produced, and Si impregnation treatment was performed at 1450 ° C. to obtain a Si—SiC composite material. This Si-SiC composite material had a thermal conductivity of 220 W / m · K, a Young's modulus of 470 GPa, a bulk density of 3.12 g / cm ³ , and a three-point bending strength of 600 MPa.
As in Example 1, a polishing plate for φ12 inch wafer was manufactured using this material.
From the results obtained in Example 1, the same evaluation was performed at a polishing pressure of 300 gf / cm ^2. As a result, the flatness of the wafer was 0.3 μm.

Comparative Example 1 A silicon carbide sintered body having a bulk density of 2.50 g / cm ³ was produced, and Si impregnation treatment was performed at 1450 ° C. to obtain a Si—SiC composite material. This Si—SiC composite material had a thermal conductivity of 240 W / m · K, a Young's modulus of 340 GPa, a bulk density of 3.00 g / cm ³ , and a three-point bending strength of 280 MPa.
As in Example 1, a polishing plate for φ12 inch wafer was manufactured using this material.
As a result of performing the same evaluation as in Example 2, the flatness of the wafer was 1.2 μm.

(Comparative Example 2) A silicon carbide sintered body having a bulk density of 3.00 g / cm ³ was produced, and Si impregnation treatment was performed at 1450 ° C to obtain a Si-SiC composite material. This Si—SiC composite material had a thermal conductivity of 170 W / m · K, a Young's modulus of 400 GPa, a bulk density of 3.01 g / cm ³ , and a three-point bending strength of 410 MPa.
As in Example 1, a polishing plate for φ12 inch wafer was manufactured using this material.
As a result of performing the same evaluation as in Example 2, the flatness of the wafer was 2.0 μm.
With respect to this material, since almost no increase in bulk density was observed, the material was cut and the structure was observed. As a result, Si was not sufficiently impregnated and was not different from the silicon carbide sintered body structure.

The conceptual diagram which shows the use condition by incorporating the silicon carbide type polishing plate which concerns on this invention in a grinding | polishing apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Silicon carbide type polishing plate 2 Semiconductor wafer polishing apparatus 3 Polishing head 4 Wax 5 Semiconductor wafer 6 Polishing surface plate 7 Polishing cloth

Claims (4)

A silicon carbide based polishing plate having a thermal conductivity of 200 W / m · K or more and a Young's modulus of 450 GPa or more. In bulk density 2.60 g ^/ cm 3 impregnated with the melted Si silicon carbide sintered body ~2.90g / cm ^3, a bulk density of ^{3.05g / cm 3 ~3.15g / cm 3} , flexural strength The silicon carbide based polishing plate according to claim 1, wherein is a Si—SiC composite material of 500 MPa or more. A step of preparing a slurry by blending an α-type silicon carbide powder having an average particle size of 0.01 μm or more and less than 1 μm with a BC sintering additive, a binder and a solvent, and kneading the mixture;
Using a spray dryer to produce a granulated powder having an average particle size of approximately 50 μm;
Filling the granulated powder into a predetermined rubber mold and performing CIP molding to produce a molded body;
Firing the molded body at 1900 ° C. to 2300 ° C. in an Ar atmosphere to produce a silicon carbide sintered body having a bulk density of 2.60 g / cm ^{3 to} 2.90 g / cm ³ ;
Characterized in that it comprises a step of impregnating a silicon carbide sintered body with molten Si at 1450 ° C. under reduced pressure to produce a silicon carbide-based polishing plate having a thermal conductivity of 200 W / m · K or more and a Young's modulus of 450 GPa or more. A method for manufacturing a silicon carbide polishing plate. The silicon carbide polishing plate according to claim 1 or 2 is attached to a polishing head of a semiconductor wafer polishing apparatus, and the semiconductor wafer attached to the silicon carbide polishing plate using wax is used as a rotating polishing platen. A method of polishing a semiconductor wafer, wherein the polishing is performed by pressing against a polishing cloth attached and rotating.

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