JPH11286739A - Lapping machine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lapping machine which works the surface of a plate-work for which particularly extremely high grades of flatness and parallelism are required and which is provided with cast iron lapping surface plates having particularly little dimensional change to the temp. variation. SOLUTION: In the lapping machine provided with the cast iron alloy-made surface plates 1, 2 containing 1.0-4.0 wt.% carbon, <38 wt.% total of nickel and cobalt and as the other element, <=2.0 wt.% silicon, <=2.0 wt.% manganese, <=0.1 wt.% sulfur, <=0.15 wt.% phosphorus, <=0.1 wt.% magnesium and the balance iron with few content of impurities, this surface plates 1, 2 in the lapping machine, has the characteristic, the grain diameter of spheroidal graphite contained in the structure of this alloy is <=50 μm and the number of the grains is <=150/mm<2> and this coefficient of thermal expansion is <=5×10<-6> / deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a material for a surface plate of a lapping machine for simultaneously processing both sides of a plate-like work requiring extremely high flatness and parallelism. The present invention relates to a lapping machine having a surface plate having a low coefficient of thermal expansion and a small deformation due to heat.

[0002]

2. Description of the Related Art Conventionally, glass, metal materials, semiconductor materials,
For planar processing of plate-like materials such as ceramics and carbon materials that require extremely high flatness and parallelism, place a platen on the top and bottom or one of them, and hold the workpiece between or on top of it. So-called lapping, in which the platen and the workpiece are pressed and rotated while the abrasive fine powder slurry as the abrasive is supplied quantitatively, and the action is used to make the thickness uniform and improve the flatness and parallelism. Processing methods have been implemented.

[0003] In recent years, in particular, the need to increase the storage capacity of ICs and LSIs and to improve the productivity has led to the uniformization of the thickness of silicon wafers or compound-based wafers (hereinafter collectively referred to as wafers) as raw materials, Processing accuracy,
The tendency for the size of the wafer itself to increase at the same time as the improvement in dimensional stability is remarkable, and extremely precise control is also required for the main conditions in lapping processing, the accuracy and stability of the equipment itself, and various other incidental conditions. It is coming. In particular, in the case of silicon wafers, the technology for manufacturing a silicon single crystal ingot as a raw material has been improved, and the production of large-diameter wafers having a diameter of 12 inches or 16 inches has been performed. Therefore, in order to carry out lapping of such a large-diameter wafer with high production efficiency, a large-sized lapping machine equipped with a large-diameter lapping plate having a carrier diameter of 24 inches or 32 inches has recently become popular.

The lapping plate referred to here is a disk having a certain thickness made of a metal such as cast iron, copper, tin and soft iron, or a non-metal such as ceramics and glass. For example, a thin lattice-shaped groove is formed on the surface used for processing, and this is arranged on both upper and lower surfaces or on one surface. In the case of a double-sided processing machine, the workpiece is pressed and clamped between them, and the workpiece and / or the platen are rotated.In the case of a single-sided processing machine, the workpiece is pressed against the surface plate with a holder. Then, the abrasive slurry is quantitatively supplied to the processed surface. The surface of the workpiece is gradually removed by the action of the abrasive grains and is created with a flat and uniform surface roughness, but in this type of processing, the flatness of the workpiece processing surface is The flatness of the surface plate is transferred as it is. Therefore,
The shape and flatness of the surface plate must be kept extremely accurately. In particular, when a hard and brittle material such as a silicon wafer is used as a workpiece, a platen made of cast iron is generally used.

As the general cast iron platen material, a so-called cast iron containing about 1 to 5% by weight of carbon is used, and its thermal expansion coefficient α is about 10 to 11 × 10 ⁻⁶ / ° C. is there. As long as a cast iron surface plate of this material is used, for example, a surface plate of 24B size (outer diameter Φ1592 mm)
In the case of (1), a temperature difference of about 1 ° C. in the thickness direction (70 mm) of the surface plate causes a warpage of about 70 μm. Meanwhile, as mentioned above,
The flatness of the workpiece in the lapping is the same as the flatness of the surface plate, and the TTV allowed in the lapping of an 8-inch silicon wafer is at most about 0.7 μm. Such warpage is not at all permissible. Therefore, in actual use, it is necessary to adjust the temperature to the operating temperature and then perform the actual machining after newly performing surface polishing on the surface plate with a common slide etc. Met. Because such work is required,
The surface plate was also heavily worn, and it was necessary to replace an expensive surface plate about once every few months. This was not only complicated in actual work but also caused a large economic loss.

That is, in the case of a silicon wafer, the temperature of the platen is reduced as described above due to the polishing heat generated by the processing or the heat generated by the motor or reduction gear for rotating the platen. It could not be denied that the temperature rose by about 5 to 10 ° C. with time, causing warpage of the shape and seriously affecting the dimensional accuracy of the processed wafer. In order to eliminate such adverse effects, a method for controlling the temperature rise by passing a cooling medium inside the surface plate and processing the surface plate at a stable temperature in a cooled state, or maintaining the temperature of the surface plate at a stable temperature Have already been proposed (for example, JP-A-63-245368, JP-A-4-53671, and Japanese Patent Application No. 9-317735). Although these are effective, they all add some kind of device to the existing device, and it is hardly an essential measure.

[0007] In order to solve these various problems,
As an essential measure, attempts have been made to use cast iron constituting the surface plate as an alloy having a low coefficient of linear expansion α against heat. For example, Japanese Patent Publication No. 60-51547 or Japanese Patent Publication No.
As disclosed in Japanese Patent Publication No. 90541, an alloy comprising carbon steel as a base and nickel and cobalt added as subcomponents has been proposed as a material having a thermal expansion coefficient α of 5 × 10 ⁻⁶ / ° C. or less. These low thermal expansion cast iron alloys
It contains about 1 to 5% of carbon and a large amount of nickel and cobalt components. In the case of general cast iron, the added carbon content is dispersed in the structure during the melting process, and is uniformly precipitated as graphite crystals during the cooling process. When this cast iron is used as a lapping platen, the aforementioned spherical graphite present on the surface of the platen falls off due to the rubbing action accompanying polishing and forms fine pores, leading to an appropriate surface roughness and abrasive trapping property, and lapping. It can be used as a surface plate. On the other hand, in the case of the above-mentioned low thermal expansion cast iron alloy, graphite spheroidization of carbon is not sufficient because there are many components other than iron, for example, amorphous carbon, or segregated into needle-like crystals, It has been difficult to use it as a lapping plate for precision machining because it adversely affects the properties of the platen, for example, causes abnormal scratches on the surface of the workpiece or deteriorates the TTV. That is, even if a cast iron material having only a low coefficient of thermal expansion is used, it cannot be applied to a lapping plate for ultraprecision machining.

[0008]

In view of the above-mentioned problems of the conventional lapping machine, the present inventors have conducted intensive studies and as a result, have devised the alloy component ratio to lower the thermal expansion coefficient. At the same time, using a Fe-Ni-Co-based cast iron alloy, which has the required physical properties such as rigidity and machinability as a surface plate and regulates the state of carbon in the structure of the cast iron alloy, as a lapping surface plate, It has been found that a lapping machine for the purpose of precision machining can be obtained, and the purpose is to perform processing without frequent modification of the shape of the surface plate with little change due to temperature. To provide a lapping machine capable of performing the lapping process.

[0009]

SUMMARY OF THE INVENTION The above-mentioned object is achieved when the carbon content is in the range of 1.0 to 4.0% by weight, and the total content of nickel and cobalt is within 38% by weight. Element content other than silicon content 2.0% by weight or less, manganese content 2.0% by weight or less, sulfur content 0.1% by weight or less, phosphorus content 0.15% by weight or less, magnesium content 0.1% by weight or less The remainder is a lapping machine equipped with a cast iron alloy platen made of iron containing a trace amount of impurities, wherein the particle size of the spheroidal graphite contained in the structure of the alloy constituting the platen is 50 μm.
m or less, the number of particles is 150 / mm ² or less, and the coefficient of thermal expansion is 5 × 10 ⁻⁶ / ° C. or less.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in FIG. 1, a lapping machine used in the present invention is provided with a rotatable upper platen 1 and a lower platen 2 which are rotatable on upper and lower opposing surfaces, and a wafer or the like therebetween. The workpiece 3 is rotated while sandwiching the workpiece 3 to supply an abrasive and perform polishing.
Cast iron having a thickness of about 70 mm is used. In the processing, since the surface accuracy of the surface plate is transferred as it is, it must be little changed even under disturbance conditions such as temperature change. In the present invention, the cast iron alloy used for the lapping plate has features that can correspond to the above matters. That is, based on carbon steel excellent in rigidity, nickel and cobalt were added to a total of 38% by weight or less of Fe.
The use of a -Ni-Co austenitic cast iron alloy makes it possible to reduce the coefficient of thermal expansion (line) to a low level of 5 ^10-6 / C or less.

Further, in order to uniformly disperse and precipitate carbon as graphite spherulites in the structure of the cast iron alloy and to impart castability, machinability and vibration damping properties as in general cast iron, a silicon content of 2% is required. .
0% by weight or less, manganese content of 2.0% by weight or less, sulfur content of 0.1% by weight or less, phosphorus content of 0.15% by weight or less, and magnesium content of 0.1% by weight or less. It is important. By doing so, the above-mentioned properties are imparted and an intended alloy having a low coefficient of thermal expansion, that is, a low-expansion alloy can be obtained.

The particle size and distribution density of the fine spherical graphite particles do not particularly affect the physical properties and performance in the case of general cast iron applications, but have important significance in the case of surface plate applications. That is, in the present invention, the particle size of the spheroidal graphite contained in the alloy structure is required to be 50 μm or less. When this appears on the surface of the lapping plate, it is peeled off and removed by the rubbing action of the lapping, and the traces become micropores.
If the size of the abrasive fine powder used as an abrasive for lapping is smaller than the pores, it may be trapped and deposited in the pores during processing and adversely affect the surface of the workpiece, but if the size is small, It is possible to effectively prevent such a phenomenon from occurring. If the thickness is more than 50 μm, abrasive grains are deposited, deteriorated in the pores, hardened or agglomerated, and cannot be used for lapping for precision processing.

Further, in the present invention, it is necessary that the number of the above-mentioned spheroidal graphite is uniformly dispersed at 150 or less / mm ² . If the dispersion or distribution is non-uniform, it may cause abnormal streaks (scratch) at the time of lapping, which is not preferable and cannot be actually used. Hereinafter, embodiments of the present invention will be described with reference to Examples and Comparative Examples, but the present invention is not limited thereto.

[0014]

EXAMPLES AND COMPARATIVE EXAMPLES Example 1 to 2% by weight of carbon, 36% by weight of total nickel and cobalt, 2% by weight or less of silicon, 2% by weight or less of manganese, sulfur A cast iron alloy containing 0.1% by weight or less, phosphorus 0.15% by weight or less, magnesium 0.1% by weight or less, and the balance being iron was prepared. The coefficient of thermal expansion of this cast iron alloy was 5 × 10 ⁻⁶ / ° C., no spherical graphite having a particle size of 50 μm or more was contained, and the number of spherical graphite contained did not exceed 150 / mm ² . Using this cast iron alloy, a surface plate of 24B size (OD 1592
(mm, thickness 70 mm) at the top and bottom. Using this lapping machine, lapping of an 8-inch (200 mm) size silicon wafer was performed. At the start of processing, no work such as preheating and heat keeping of the surface plate was performed, and no dummy processing was performed. From the first batch after the start of processing, the shape accuracy of TTV, etc., and the surface roughness, which are within the quality standard, are almost 1
A yield of 00% could be obtained.

Comparative Example Carbon content 3.6% by weight, silicon content 2.5% by weight, manganese content 0.2% by weight, sulfur content 0.04% by weight or less, phosphorus content 0.1% by weight or less A cast iron alloy containing 0.06% by weight of magnesium and the balance of iron was prepared.
The coefficient of thermal expansion of this cast iron alloy was 11 × 10 ⁻⁶ / ° C. Using this cast iron alloy, a lapping machine having a 24B-size platen (outer diameter 1592 mm, thickness 70 mm) similar to that of the example was manufactured. Using this lapping machine, lapping of an 8-inch (200 mm) size silicon wafer was performed. At the start of processing, work such as preheating and heat retention of the surface plate is not performed.
No dummy processing was performed. Up to three batches after the start of processing, the shape accuracy was not stable and the product yield was extremely poor, and it was only from the fifth batch that stable product quality could be obtained at a high yield.

[0016]

As is clear from the above examples and comparative examples, when the lapping machine according to the present invention is used, for example, processing such as preheating, heat keeping and temperature control of the surface plate, or the temperature of the surface plate by dummy operation It is possible to immediately start the actual operation of the machine without homogenizing the machine. Therefore, the operating rate of the machine stand and the product yield can be significantly improved.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a double-sided lapping machine.

[Explanation of symbols]

 1 Upper surface plate 2 Lower surface plate 3 Workpiece

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Takeshi Amano 2647 Hayakawa Hayakawa, Ayase City, Kanagawa Prefecture Inside (72) Inventor Tomohiro Aizawa 2647 Hayakawa, Ayase City, Kanagawa Prefecture Speed Fam Corporation (72) Inventor Takayoshi Ito Hitachi Zosen Metal Works Co., Ltd. (1,180)

Claims (2)

[Claims] (1) The carbon content is in the range of 1.0 to 4.0% by weight, the total content of nickel and cobalt is within 38% by weight, and the other element content is silicon content. 2.
0% by weight or less, manganese content 2.0% by weight or less, sulfur content 0.1% by weight or less, phosphorus content 0.15% by weight or less, magnesium content 0.1% by weight or less, the balance being iron containing trace impurities. A lapping machine equipped with a cast iron alloy surface plate, wherein the particle size of the spheroidal graphite contained in the structure of the alloy constituting the surface plate is 50 μm or less and the number of particles is 150 particles / m 2.
m ² or less and its coefficient of thermal expansion is 5 × 10 ⁻⁶ / ° C.
A lapping machine characterized by the following. 2. The lapping machine according to claim 1, wherein the lapping machine is of a type having a platen on both upper and lower surfaces.