JP2908316B2 - Polishing surface plate for Si wafer - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polishing platen used for lapping of a Si wafer or the like. 2. Description of the Related Art Generally, in lapping of Si wafers or the like, slurry-like abrasive grains are supplied between a pair of upper and lower polishing platens and a workpiece, and the platen is rotated while applying a processing pressure. A method is used in which a required amount of removal is removed from a workpiece by using a cutting blade of an abrasive by using motion, and thereby the flatness of the surface plate is transferred to the workpiece. Such polishing is performed by Si
It is often used to flatten the surface of workpieces such as glass, jewelry, metal, and ceramics as well as wafers. In particular, recently, the demand for Si wafers has been increasing year by year in connection with the development of electronics. There is a tendency. Usually, in polishing a Si wafer, Al ₂ O ₃ and ZrO ₂ are used as abrasive grains, the grain size of which is # 1000 mesh and the average grain size is 16 μm. Conventionally, cast iron (JIS-FCD45) containing spheroidal graphite is often used as a polishing platen in this case. This JIS-FCD45 base (base material)
Hardness is Hv (Vickers hardness load 5)
(Measured at 00 g) is about 140, and the graphite particle size is 100 to 1
It is a material having physical properties of 50 μm. When polishing a Si wafer using a polishing platen made of this material, in the polishing state, Al ₂ O ₃ and ZrO ₂ , which are abrasive grains, are selectively present and distributed in a portion where graphite grains are present. S in state
Polishing is performed on the i-wafer. In this case, the abrasive grains are S
In addition to polishing the i-wafer, polishing (wear) is simultaneously performed on the polishing platen based on JIS-FCD45. That is, in the case of a base plate having a relatively soft base such as a ferrite structure, wear due to hard abrasive grains is likely to progress, and the flatness of the polishing base plate is deteriorated. As described above, during polishing, the flatness of the polishing platen is directly transferred to the surface of the workpiece, and as a result, the flatness of the workpiece is deteriorated and high-precision polishing cannot be performed. There's a problem. [0005] In addition, conventionally used JIS-FCD
The graphite particle size of the 45 platen is as large as 100 to 150 μm, and the abrasive particles are selectively present in the graphite portion, so that they are relatively unevenly distributed. There is also a problem that the flow of the abrasive grains becomes non-uniform, the processing speed is reduced, and the non-uniform wear of the surface plate is advanced, and as a result, the surface of the Si wafer is liable to be flawed. SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and maintains flatness and smoothness by minimizing the amount of wear caused by abrasive grains during polishing. In addition, an object of the present invention is to provide a polishing platen in which the distribution of the abrasive grains is dispersed as finely as possible to promote the flow of the abrasive grains uniformly. In order to achieve the above object, a polishing plate for Si wafer according to the present invention comprises a base material having a Vickers hardness number of 200 or more in a base material having a spheroidization ratio of 80% or more. Table 1 shows a spheroidal graphite cast iron structure in which spheroidal graphite having a graphite particle size of 100 μm or less and graphite particles of 70 particles / mm ² or more exists in a dispersed state.
At least 15 mm from the surface
It is characterized in that that. The above-mentioned spheroidal graphite cast iron preferably contains carbon, silicon, manganese and magnesium as essential components, and the balance substantially consists of iron. C: 2.7-3.5%, S
i: 2.0 to 2.7%, Mn: 0.5 to 1.0%, P: 0.03% or less,
S: 0.03% or less, Mg: 0.03 to 0.07%, Ni: 0.2 to 0.
It is preferable that 6%, Cu: 0.3 to 0.7%, and the balance be Fe. The polishing platen according to the present invention is characterized in that the base of the platen has a hardness of at least Hv 200 or more in order to minimize the amount of wear caused by the abrasive grains. In order to improve abrasion resistance, it is preferable to form pearlite, bainite, martensite or tempered martensite by heat treatment. Polishing is performed by supplying abrasive grains to the surface of a workpiece through a polishing platen, and the flatness of the polishing platen and the uniform and fine dispersion of the abrasive grains and the smooth flow. Is essential. The former, that is, the flatness, has a great influence on the wear resistance of the polishing platen base, and the latter, that is, the uniformity and dispersibility, are greatly affected by the graphite shape, particle size, and particle distribution.
In order to uniformly disperse the abrasive grains and promote uniform flow of the abrasive grains, the base of the surface plate was made of spheroidal graphite cast iron rather than flake graphite cast iron, and the graphite particle size was adapted to the size of the abrasive grains It is important to have dimensions. It is also preferable that the graphite particles are also distributed as small and uniformly as possible. In particular, in the case of Si wafers, the abrasive grains have an average grain size of 16 μm, so that the graphite grain size is larger than the abrasive grains, and the graphite grain size is 100 μm or less, preferably 30
５０50 μm. The distribution (cross-sectional density) of the graphite particles is preferably 70 particles / mm ² or more, and the spheroidization ratio is preferably 80% or more. However, the spheroidization rate is not particularly limited to this range. It is necessary to have the above properties over at least 15 mm depth direction from the surface of the polishing platen. Hereinafter, preferred embodiments of the present invention will be described. The polishing platen according to the present invention has a weight ratio of C: 2.
7 to 3.5%, Si: 2.0 to 2.7%, Mn: 0.5 to 1.0%, P,
S <0.03%, Mg: 0.03 to 0.07%, more preferably N
It is preferable that i: 0.2 to 0.6%, Cu: 0.3 to 0.7%, and the balance be Fe. As described above, the polishing platen includes:
Good wear resistance to abrasive grains such as Al ₂ O ₃ and ZrO ₂ is required. For this reason, the conventional surface plate material JIS-
It is important to use a spheroidal graphite cast iron having a predetermined hardness (Hv> 200) and excellent mechanical properties for the FCD 45 by heat treatment to form a metal structure having good wear resistance. The purpose of addition of each composition component and the reason for limiting the composition range will be described below. [0016] C exceeds 3.5%, the mechanical properties, not particularly tensile strength to the target 70 kgf / mm ² or more, whereas, 70 / mm ² or more distributed as graphite grains in the following C2.7% It is not preferable because it does not become. Si is added to improve the spheroidization rate and castability. However, when Si exceeds 2.7%, ferrite is present even by heat treatment, and the hardness tends to decrease.
It becomes difficult to do so. Further, the temperature at which austenite is formed increases, and the heat treatment temperature increases. As a result, an oxide is easily formed, and it is necessary to remove the oxide from the surface plate, which is not desirable. If the content of Si is less than 2.0%, the castability is particularly deteriorated.
An undesired shrinkage cavity is likely to be generated as a surface plate. When the Mn is 0.5% or less, the surface plate (thickness: 40-60 m)
As in the case of m), ferrite is likely to be generated during air cooling toward the center of a thick casting, and wear resistance is deteriorated. On the other hand, if it exceeds 1%, the hardened phase tends to segregate at the grain boundaries and becomes brittle, which is not desirable. P and S are preferably reduced as much as possible in order to reduce the formation of inclusions. Since the inclusions are hard and irregularly present, they easily scratch the Si wafer. For this reason, 0.03% or less is good for all. When the content exceeds 0.03%, inclusions (Fe ₃ P, MnS,
MgS, etc.) is undesirable. Mg is an alloying element necessary for spheroidizing graphite. If it is less than 0.03%, the spheroidization ratio is difficult to be in a preferable range (for example, 80% or more). Is not preferable because it is easy to generate. Ni and Cu are used to make the structure uniform, for example, to make the structure uniform in the depth direction from the surface to eliminate the variation in hardness, and particularly to maintain Hv 30 to 50 in a region 20 mm from the surface. It is an effective element. 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 adding 0.6% or more is not so effective in these effects and is not economical. On the other hand, Cu is 0.3% like Ni
Below, the effect on uniformity is small, and conversely Cu is 0.7%
With the above addition, a Cu phase is precipitated on the matrix, the structure becomes uneven, and there is a tendency that the wear resistance is deteriorated. Ni and Cu are not necessarily indispensable elements in the present invention, but are desirable alloy components for uniformity of the structure and prevention of scale. In the case of the above composition, in the case of heat treatment, the temperature of the heat treatment needs to be a temperature capable of turning the structure into austenite, and is about 850 ° C. or higher, preferably about 9 ° C.
It is around 30 ° C. Embodiment 1 A spheroidal graphite cast iron having the components shown in Table 1 was cast to produce a casting of a surface plate for an abrasive. Prior to machining such as slitting, it was heated to 930 ° C. and air-cooled. in this case,
The microscope was inspected at a depth of 20 mm from the surface, but the spherical graphitization rate was 90%, the graphite particle size was 30 to 50 μm, and the distribution was 150 particles / mm ² . The base had a fine pearlite structure and a hardness of Hv250 by air cooling. This material was finished into a platen by machining. This was used for polishing a Si wafer, and the results are shown in Table 2 below. Conventional FCD45
Defects are reduced to 75% (FCD45 is reduced to 100%) and the life of the platen (hereinafter, also referred to as life)
Was improved by 150% (FCD45 was set to 100%).
Further, the wear amount was reduced by 40% (the FCD45 was set to 100%), which showed desirable characteristics as a surface plate. (Example 2) Spheroidal graphite cast iron having the components shown in Table 1 was cast,
A platen was made. The spheroidization ratio of graphite in the depth direction of 20 mm from the surface is 85%, the graphite particle diameter is 30 to 50 μm, and the graphite particles are 7%.
The distribution was 0 / mm ² . The cast product was heated to 930 ° C., then cooled in a furnace, the base was made into a ferrite structure, and machining such as slitting was performed. After the machining, an austenite structure was formed at 930 ° C., and an austempering treatment was performed at 300 ° C. to obtain a bainite structure. The hardness was Hv350. Oh
The change in the flatness of the surface caused by the tempering treatment was polished to correct the flatness, thereby obtaining a polished platen. The Si wafer was polished using this polishing platen. As shown in Table 2, the flaw on the Si wafer surface was reduced to 65% (FCD45 was set to 100%), and the life was improved by 170% (FCD45).
Is 100%), and the wear amount is reduced by 50% (FCD
45 is set to 100%). (Example 3) A platen was cast using the spheroidal graphite cast iron shown in Table 1. The cast product had a spheroidization ratio of 90% in a depth direction of 20 mm from the surface, a graphite particle size of 30 to 50 μm, and a distribution of 70 graphite particles / mm ² . This cast product was heated to 930 ° C., cooled in a furnace, and the base was made into a ferrite structure. After the working, it was made to have an austenite structure at 930 ° C. and an austemper at 350 ° C. to have a bainite structure. The hardness was Hv300. Austemper
The surface flatness change caused by the treatment was used as a surface plate corrected by polishing. As shown in Table 2, the defects on the surface of the Si wafer were reduced to 70%, and the life was improved by 160%. It showed desirable characteristics as a surface plate, such as a 50% reduction in the amount of wear. Example 4 Spherical cast iron having the composition shown in Table 1 was cast to produce a surface plate. The cast product has a spheroidization ratio of 80% from the surface to at least 20 mm in the depth direction, a graphite particle size of 30 to 50 μm, and a distribution of 100 graphite particles / mm ² . 9 for casting
Heated to 30 ° C and cooled in the furnace to make the base a ferrite structure,
Machined slits. 930 again after machining
C. and quenched in oil. Hardness was Hv550. After quenching, it was polished to correct the surface flatness and finished to a surface plate. When polishing a Si wafer using this,
As shown in Table 2, compared to the conventional FCD45 platen,
Defects on wafer surface reduced to 45%, life is 220
%, And the abrasion amount was also reduced to 20%, showing desirable characteristics as a surface plate. (Example 5) A casting of a surface plate was manufactured using spheroidal graphite cast iron having the composition shown in Table 1. The casting has a spheroidizing ratio of 80% from the surface to at least 20 mm in the depth direction, and a graphite particle size of 50 to 50 mm.
1000 μm, 100 graphite particles / mm ^{2 are} distributed. The cast product was heated to 930 ° C. and cooled in a furnace to make the base into a ferrite structure, and machined as a surface plate such as a slit. After processing, it was heated again to 930 ° C. and quenched in oil. The hardness was Hv500. After quenching, it was polished to correct the surface flatness and finished as a polished platen. Using this, a Si wafer was polished.
As shown in Table 2, the defect on the surface of the Si wafer was reduced to 50%, the life was improved to 200%, and the abrasion was reduced to 25%. Example 6 A slab casting was manufactured using spheroidal graphite cast iron having the composition shown in Table 1. The casting has a spheroidizing ratio of 73% from the surface to at least 20 mm in the depth direction, and a graphite particle size of 30 to
50 μm, 100 graphite particles / mm ^{2 were} distributed. The cast product is heated to 930 ° C. and then quenched.
The substrate was tempered at 50 ° C. to have a tempered martensite composition, and was machined as a platen such as a slit. Hardness was Hv386. Thereafter, polishing was performed to correct the flatness of the surface, and finished as a polished platen. Using this, a Si wafer was polished.
As shown in Table 2, the defect on the surface of the Si wafer was reduced to 50%, the life was improved to 200%, and the abrasion was reduced to 25%. (Comparative Example) A slab casting was manufactured using spheroidal graphite cast iron having the composition shown in Table 1. The cast product has a spheroidization ratio of 75% and a graphite particle size of 100 at least 20 mm in the depth direction from the surface.
The graphite particles were 60 particles / mm ² at で 150 μm. The casting was heated to 930 ° C. and cooled in a furnace to make the base into a ferrite structure. The hardness was Hv140. After the heat treatment, it was machined as a surface plate such as a slit. Polishing of the Si wafer using this surface plate was inferior to the surface plate of the example, as shown in Table 2, in terms of defects such as scratches on the surface of the Si wafer, life of the surface plate, and abrasion loss. [Table 1] [Table 2] As is clear from the results of the above examples and comparative examples, the polishing platen of the present invention has a change in flatness, life and wear of the platen compared to the conventional platen. All of them show desirable characteristics in terms of the amount, and have an excellent effect that no flaw is formed on the surface of the member to be polished.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Takanori Nishimura 2-4 Suehirocho, Tsurumi-ku, Yokohama-shi, Kanagawa Prefecture Inside the Keihin Office of Toshiba Corporation (72) Inventor Masaharu Kinoshita 378 Ogunimachi, Ogunimachi, Ogunimachi, Nishiokitama-gun, Yamagata Prefecture Toshiba Ceramics Co., Ltd. Oguni Works (72) Inventor Norio Masuda 378 Ogunimachi, Oguni-machi, Nishiokitama-gun, Yamagata Prefecture Toshiba Ceramics Co., Ltd. Oguni Works (56) References JP-A-59-43816 (JP, A) (58) Survey Field (Int.Cl. ⁶ , DB name) B24B 37/04

Claims (1)

(57) [Claims] Vickers The spheroidization rate in a base material with a hardness of 200 or more
A spheroidal graphite cast iron structure in which spheroidal graphite having a graphite particle size of 80% or more, a graphite particle size of 100 μm or less and a graphite particle number of 70 particles / mm ² or more exists in a dispersed state at least 15 mm from the surface.
A polishing surface plate for a Si wafer, characterized in that it has a standing surface. 2. The spheroidal graphite cast iron has a weight ratio of C: 2.7 to 3.5%,
Si: 2.0 to 2.7%, Mn: 0.5 to 1.0%, P: 0.03% or less, S: 0.03% or less, Mg: 0.03 to 0.07%, Ni: 0.2
2. The Si wafer according to claim 1, wherein the Si wafer comprises 0.3 to 0.7%, Cu: 0.3 to 0.7%, and the balance is Fe and incidental impurities.
Polishing surface plate for c .