JP2000006012A - Polishing surface plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polishing surface plate having a high hardness and an even hardness distribution. SOLUTION: In a polishing surface plate made of a nodular graphite cast iron which includes C: 2.0 to 3.5%, Si: 2.0 to 2.7%, Mn: 0.5 to 1.0%, and Ni: 0.2 to 0.6%, in the weight ratio, and the remaining part consisting of Fe and an additional impurity, 0.05 to 0.3 wt.% of Sn is included to the nodular graphite cast iron, and the formation is heat processed by the quenching and tempering to make into a tempered martensite formation, with Vickers hardness >=390 and hardness dispersion between +20 and -20. By including the Sn, the time difference of the starting and the finishing to make the surface plate into the martensite formation by quenching can be reduced, the transformation by the heat treatment can be minimized, and the hardness of the surface plate can be made even.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polishing table used for lapping a silicon wafer or the like.

[0002]

2. Description of the Related Art Generally, in the lapping polishing of silicon wafers or the like, slurry-like abrasive grains are supplied between a pair of upper and lower polishing platens and a workpiece, and the rotating motion of the platen is applied while applying a processing pressure. Then, a required amount is removed from the workpiece with a cutting blade of the abrasive, and thereby the flatness of the surface plate is transferred to the workpiece. Such polishing is often used not only for silicon wafers but also for flattening the surface of workpieces such as glass, jewelry, metal, ceramics, etc. In recent years, silicon wafers are particularly related to the development of electronics. Demand is increasing year by year.

[0003]

The polishing platen is manufactured by using a graphite mold as a lower mold, and casting and solidifying an upper mold with a general sand mold. In this case, unidirectional solidification is performed from the graphite mold surface toward the upper mold, and the solidified structure is likely to be coarse and has an uneven hardness distribution.

Conventionally, the material used for the polishing platen is spheroidal graphite cast iron, and heat treatment such as oil quenching and tempering is generally performed to obtain high hardness of the platen. In this conventional polishing platen, the hardness of the platen becomes uneven due to the thickness of the platen, and there is a time difference between the start and end of the martensitic transformation during oil quenching, and the time difference deforms the platen. When this is machined to make it a fixed surface plate, a difference occurs in the processing dimensions, and the unbalance of the processing allowance causes a variation in hardness in the surface plate. When a silicon wafer is polished with such a surface plate, uneven wear of the surface plate itself and deterioration of flatness are caused due to unevenness of hardness of the surface plate, and the yield of the silicon wafer is significantly reduced. In particular, recently, the surface plate has been increased in size, and improvement has been desired. The present invention has been made in view of the above circumstances, and has as its object to provide a polishing surface plate having high hardness and a uniform hardness distribution.

[0005]

The polishing platen according to the present invention has a weight ratio of C: 2.0 to 3.5% and Si: 2.0 to 2.0%.
2.7%, Mn: 0.5 to 1.0%, Ni: 0.2 to
In a polishing platen made of spheroidal graphite cast iron containing 0.6% with the balance being iron and incidental impurities, tin is added to the spheroidal graphite cast iron in a weight ratio of 0.05 to 0.3%, and quenching / tempering is performed. The tempered martensitic structure was obtained by the heat treatment described above, and the Vickers hardness was 390 or more and the hardness variation was within ± 20. By containing tin, the time difference between the start and end of martensitic transformation of the platen by quenching can be reduced, the deformation due to heat treatment can be minimized, and the hardness of the platen can be made uniform. did.

[0006]

Embodiments of the present invention will be described below.
First, the material components (% by weight) of the polishing platen of the example and the results of the measurement of the amount of warpage and hardness of the platen material after the heat treatment are compared with those of a conventional spheroidal graphite cast iron polishing platen, and are shown in Table 1. In addition, the sample No. in the table. Sample Nos. 1 and 2 are conventional comparative examples. 3 ~
6 is an embodiment of the present invention.

[0007]

[Table 1]

Hereinafter, the purpose of addition of each composition component and the reason for limiting the composition range will be described. Si is added to improve the spheroidization ratio and castability. However, when Si exceeds 2.7%, ferrite is present even by heat treatment, and the hardness tends to decrease, and it is difficult to increase the Hv to 200 or more.
If the content of Si is less than 2.0%, castability is particularly deteriorated, and shrinkage cavities which are not desirable as a surface plate are likely to occur.

When the Mn is 0.5% or less, the surface plate (thickness of 40 to
(60 mm), the ferrite is likely to be generated during air cooling toward the center of a thick casting, and the wear resistance is deteriorated. On the other hand, if it exceeds 1%, the hardened phase tends to be deflected easily in the grains, which is undesirable.

P and S are preferably reduced as much as possible in order to reduce the generation of inclusions. The inclusions are hard and irregular, and thus easily damage the silicon wafer. For this reason, the content is preferably 0.03% or less. 0.
When the content exceeds 03%, inclusions (Fe ³ ,
MnS, MgS, etc.) are not desirable.

Mg is an alloying element necessary for spheroidizing graphite. When the spheroidization ratio is 0.03% or less, the spheroidization ratio hardly falls within a preferable range (for example, 80% or more).
%, It is not desirable because irregular shaped carbides are easily formed.

Ni and Cu are used to make the structure uniform.
For example, the structure is made uniform in the depth direction from the surface to eliminate variations in hardness, and particularly, in a region 20 mm from the surface, H
V is an element effective for maintaining 30 to 50. Ni has the effect of preventing oxide formation during heat treatment. If the content of Ni is 0.2% or less, these effects are small, and if 0.6% or more is added, these effects are not so effective and are not economical. On the other hand, Cu, like Ni, has a.
If it is 3% or less, the effect on uniformity is small. Conversely, if 0.7% or more of Cu is added, there is a tendency that a Cu phase is precipitated on the matrix, the structure becomes nonuniform, and the wear resistance deteriorates.

When Sn is added in an amount of 0.04 to 0.24%,
The time difference between the start and end of martensitic transformation can be reduced, and deformation of the surface plate due to heat treatment can be minimized.

Mo enhances the strength of the alloy matrix by imparting toughness to an alloy which becomes brittle due to the addition of Si.
When Mo is 0.3% or less, the toughness provided is small,
If the content is 2.0% or more, the toughness is reduced due to generation of a Mo compound.

Next, Table 1 shows the results of comparison of the amount of warpage and the hardness between the present embodiment using a polishing platen and the conventional one, and the warpage amount is 18 in the conventional product (Sn: 0.01 to 0.02%). ~ 1
It is as large as 9 mm and has a great variation in hardness from 210 to 450 Hv. On the other hand, in the present embodiment, the amount of warpage is small at 2 to 4 mm, and the hardness is also small at 370 to 440 Hv. That is, the solidification structure is made uniform by the heat treatment by the addition of Sn, and the time difference between the start and end of martensite transformation can be reduced (hardness can be stabilized by making the martensite structure uniform). Deformation due to heat treatment can be minimized. For this reason, the polishing platen, which is conventionally uneven in hardness and has a large amount of warpage, has been improved, and by using a polishing platen having a small hardness variation and a small amount of warpage, uneven wear and flatness of the surface plate itself have been improved. The problem of deterioration has been solved, and the yield of silicon wafers has been greatly improved.

[0016]

As described above, according to the present invention, tin is contained in spheroidal graphite cast iron in a weight ratio of 0.05 to 0.3%, and the structure is tempered by tempering and tempering to form a tempered martensite structure. This is a surface plate having a hardness of 390 or more and a hardness variation within ± 20. By containing tin, the time difference between the start and end of martensitic transformation of the platen by quenching can be reduced, the deformation due to heat treatment can be minimized, and the hardness of the platen can be made substantially uniform. It was realized.

Claims (3)

[Claims] 1. C: 2.0 to 3.5% by weight, S:
i: 2.0 to 2.7%, Mn: 0.5 to 1.0%, N
i: On a polishing platen made of spheroidal graphite cast iron containing 0.2 to 0.6%, with the balance being iron and incidental impurities, tin is added to the spheroidal graphite cast iron in a weight ratio of 0.05 to 0.3%. A polishing platen characterized by being formed by containing it. 2. The polishing platen according to claim 1, wherein the structure becomes a tempered martensite structure by heat treatment of quenching and tempering. 3. The polishing platen according to claim 1, wherein Vickers hardness is 390 or more and hardness variation is within ± 20.