JPH0413093B2 - - Google Patents

Description

[Detailed description of the invention]

[Object of the Invention] (Industrial Application Field) The present invention relates to a polishing surface plate applied to polishing, lapping, etc., and particularly relates to a polishing surface plate that improves the flatness of a polished surface. (Prior Art) Polishing is conventionally known as a means for precisely polishing semiconductor substrates such as silicon wafers, glass, metal plates, and the like. In polishing, the object to be polished is mounted on the surface of a polishing surface plate that is driven to rotate on a horizontal plane through a polishing cloth, and the polishing liquid is supplied between the polishing cloth and the silicon wafer. It performs polishing, and the polishing process is similar to wrapping.
Polishing is carried out in a temperature range of 200°C. As the polishing liquid, for example, water mixed with abrasive grains is used, and as the polishing cloth, polyester nonwoven fabric or the like is used. and,
The object to be polished is polished with a polishing liquid, and polishing debris is removed with a polishing cloth. By the way, for items that require ultra-precision polishing such as silicon wafers, mechanochemical polishing is performed using SiO ₂ powder as abrasive grains and involving a chemical reaction between the silicon wafer and a polishing liquid. When polishing silicon wafers using such mechanochemical polishing, the optimum temperature range (35
~45℃), and strict temperature control is required in the polishing section. As a means of temperature control, it is known that the polishing surface plate has a liquid cooling structure. That is, a polishing surface plate is constituted by a disk for mounting an object to be polished, and a liquid cooling jacket rotatably attached to the back surface of the disk. Further, the liquid cooling suppresses an excessive temperature rise due to polishing heat (mainly frictional heat). In order to enhance the effect of this liquid cooling, conventionally the disk was made of brass etc. with good thermal conductivity.
The jacket is made of gray cast iron, which has relatively low thermal expansion. (Problem to be Solved by the Invention) However, in the conventional polishing surface plate made by joining a brass disk and a gray cast iron jacket, the disk expands greatly due to the difference in thermal expansion during polishing. However, there was a problem in that the disk surface was deformed into a convex shape, and as a result, the flatness of the object to be polished, such as a silicon wafer, could not be increased beyond a certain level. The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a polishing surface plate that can suppress convex deformation of a disk and improve the flatness of a workpiece. [Structure of the Invention] (Means and Effects for Solving Problems) The inventor has studied the flatness (height of convex deformation of the upper surface) of the disk and the object to be polished from the viewpoint of the constituent materials of the disk and jacket. I went. As a result, the coefficient of thermal expansion of brass, which is commonly used for discs, is approximately 20×10 ^-6 /℃, and the coefficient of thermal expansion of gray cast iron, which is often used for jackets, is approximately 11.5×10 ^-6 /℃, which is 20 When polishing is performed at a temperature range of ~200℃, the flatness is approximately several hundred μm with a polishing surface plate with an outer diameter of 900 mm, and the flatness is approximately several hundred μm with an outer diameter of 100 mm.
The inventors have found that the flatness of several micrometers is the limit for each object to be polished. In line with the recent trend toward miniaturization of electronic components, silicon wafers and the like are required to have a high flatness of 1 μm or less, and the conventional structure described above cannot meet this requirement. However, in the past, heat dissipation was emphasized as a disk material, and there was a tendency for materials to be used only if their thermal conductivity was comparable to that of brass. The reality is that measures are being taken to improve flatness within this range. For example, countermeasures include making the disk concave at room temperature so that the disk has a high degree of flatness when the temperature rises during polishing. However, such means have problems such as large variations in flatness and lack of reliability. Therefore, the inventor considered constructing the disk with a low thermal expansion material as a direct measure to prevent thermal deformation. However, in a polishing surface plate, the entire back surface of the disk is bonded to the jacket, and the inventors have discovered that the flatness cannot necessarily be improved due to the relationship between the coefficients of thermal expansion of the two. Ivy. In other words, it has been found that simply constructing a disk from a low thermal expansion material does not improve the flatness of the disk. After further investigation, we found that the temperature rise during polishing of the Dix and the jacket is different, and the coefficients of thermal expansion of their constituent materials are also different. It turned out to be extremely difficult to improve. Furthermore, it has been found that since the coefficient of thermal expansion of the material changes depending on the temperature, the state of thermal deformation between the disk and the jacket becomes even more complicated. However, the temperature during polishing, lapping, etc. is in the range of 20 to 200°C, and within this temperature range, the degree of change in the thermal expansion coefficient of the metal with respect to temperature rise is relatively small. Therefore, within this temperature range, even if the disk and jacket made of different materials experience different temperature increases, it is possible to relatively accurately determine their thermal deformation. Therefore, the inventor came up with the idea that by setting a temperature range and a reference thermal expansion coefficient, it is possible to improve the flatness of a polishing surface plate made of a disk and a jacket combined. The present invention was made based on such an idea, and includes a rotating disk carrying an object to be polished;
In this polishing surface plate having a liquid cooling jacket rotatably attached to the back surface of the disk, the disk is made of a low thermal expansion material with an average coefficient of thermal expansion of 5×10 ^-6 /℃ or less between 20 and 200℃. If the average coefficient of thermal expansion of the disk is α ₁ , the temperature rise during polishing is T ₁ °C, and the temperature rise of the jacket is T ₂ °C, then the coefficient of thermal expansion of the jacket constituent material α ₂ is According to the present invention, the polishing surface plate is characterized in that α ₂ ≒T ₁ /T ₂ α ₁ is set.
By constructing the disk, which particularly causes convex deformation, from a low thermal expansion material with an average coefficient of thermal expansion of 5×10 ^-6 /°C or less within the above temperature range, deformation of the same portion can be significantly suppressed. The flatness of the disk can be maintained at a high level. Moreover, the amount of thermal expansion during polishing is approximately the same between the disk and the jacket, as shown in the above equation, using the coefficients of thermal expansion α ₁ , α ₂ and temperature increases T ₁ , T ₂ between the disk and the jacket as elements. The flatness of the disk and, by extension, the flatness of the workpiece can be improved. In addition, low thermal expansion materials used as disk materials include:
For example, Si-Ni-Co cast iron (SiO.5~1.0%, Ni35
%, Co2%) etc. can be applied. In addition, FC20 and other jacket materials are also available.
General cast iron such as FCD40 or cast steel such as SC46 can be used. (Example) Hereinafter, an example of the present invention will be described with reference to FIGS. 1 to 4. Figure 1 shows the vertical cross-sectional shape of the polishing surface plate in this embodiment.
FIG. 2 shows the planar shapes. As shown in FIGS. 1 and 2, the polishing surface plate of this embodiment has a water cooling jacket 2 of approximately the same diameter connected to the back surface of a disk 1 for mounting an object to be polished by a plurality of connecting bolts 3. It is structured as follows. Water cooling holes 4 are formed inside the jacket 2. A rotating shaft 5 is connected to the center of the jacket 2 by a bolt 6. The wall thickness of the disk 1 is constant, and water cooling holes 4 face over a wide range on the back surface thereof. In this one, the constituent material of disk 1 is
It is made of 0.6Si−36Ni−2Co cast iron. This cast iron
The average coefficient of thermal expansion α ₁ from 20 to 200℃ is 2.5×10 ^-6 /℃,
Young's modulus is 12×10 ³ Kgf/mm ² . The material of the jacket 2 is FCD45. The thermal expansion coefficient α ₂ of this FCD45 is 12.0×
10 ^-6 /°C, Young's modulus is 18.5×10 ³ Kgf/mm ² .
FIG. 3 is a side sectional view showing the polishing action using the above polishing surface plate, and FIG. 4 is a plan view thereof. During polishing, as shown in FIGS. 3 and 4, the polishing surface plate is rotated at high speed on a horizontal plane via the rotating shaft 5. As shown in FIGS. A polishing cloth 7 made of, for example, polyester non-woven fabric is applied to the surface of the disk 1 of this polishing surface plate.
Attach. Then, on the top surface of disk 1, there are several
Workpieces, such as silicon wafers 8, are each held by adhesive on top plates 9 arranged in parallel. The top plate 9 is rotationally driven via a rotating shaft 10, and thereby the silicon wafer 8
slides and rotates on the polishing cloth 7. And polishing cloth 7
The polishing liquid 1 is supplied to the top surface of the polishing liquid through the polishing liquid supply pipe 11.
Supply 2. The polishing liquid 12 is, for example, a mixture of water and SiO ₂ powder, and the silicon wafer 8 is thereby polished by a mechanochemical polishing action. Incidentally, the disk 1 of the polishing surface plate is constantly cooled by cooling water supplied to the water cooling hole 4 of the jacket 2. When we investigated the temperature rise during polishing, we found that the polishing surface plate, which was at 15℃ before polishing, rose in temperature during polishing due to polishing heat, and the temperature of disk 1 was 45℃ and jacket 2 was 21℃. Summer. That is, the temperature of disk 1 increased by 30°C, and the temperature of jacket 2 increased by 6°C. When the flatness (height of convex deformation on the upper surface) of the disk 1 with an outer diameter of 900 mm was examined under this temperature condition, it was found to be 20 μm, which is the same as before polishing. The reason why the flatness of disk 1 can be maintained at such a high level is due to the degree of thermal expansion of disk 1 (30×2.5×10 ^-6 ) due to a temperature rise of 30°C and the degree of thermal expansion of jacket 2 due to a temperature rise of 6°C. This is because (6×12.0×10 ⁻⁶ ) is approximately the same value. Further, when the flatness of a φ100 mm wafer polished on the disk 1 was examined, extremely high values of 1 to 0.5 μm were obtained. In order to compare the effects of the above embodiments, we investigated the flatness, etc. of a conventional polishing surface plate, and the following results were obtained. That is, the constituent material of the disk 1 was brass. The average coefficient of thermal expansion of brass at 20 to 200℃ is 2×
10 ⁻⁶ /°C, Young's modulus is 9.8×10 ³ Kgf/mm ² .
Furthermore, the constituent material of the jacket 2 was FC30.
The thermal expansion coefficient of FC30 is 11.5×10 ^-6 /℃, Young's modulus is
It is 13×10 ³ Kgf/mm ² . When we investigated the temperature rise during polishing on such a polishing surface plate, it was 15℃ before use, but it was 45℃ for disk 1 and 21℃ for jacket 2, which is the same as in the above example. be. However, in the case of this conventional example, the flatness of the disk 1, which was 20 .mu.m before use, became 550 .mu.m after use, resulting in a significant decrease in flatness. Furthermore, the flatness of the φ100mm wafer was as low as 7μm. As is clear from the above comparison, according to the polishing surface plate of the above embodiment, the flatness of the disk is several ten times higher than that of the conventional polishing plate, and it is possible to obtain extremely high flatness of the wafer. Summer. In addition, in the above embodiment, the constituent material of the disk 1 is
Although the 0.6Si-36Ni-2Co cast iron is used, the present invention is not limited to this.
^ASTM
Various materials can be used, such as austenitic spheroidal graphite cast iron known as A571-57 Type D-5 and Niresist D5. These components and thermal expansion coefficients are shown in Tables 1 to 4 in Table 1 below. In addition, although FCD45 was used for jacket 2, it is not limited to this.
It is possible to use a material whose thermal expansion based on the temperature difference between the disc 1 and the disc 1 can be the same as that of the disc 1, such as general cast iron such as JIS FC20 or FCD40 material, or cast steel such as SC46. These components and thermal expansion coefficients are shown in Tables 5 to 12 in Table 1 below. Furthermore, Table 2 below shows the flatness of the disk and jacket made of various materials.

【table】

[Table] Next, other embodiments of the present invention will be described with reference to FIGS. 5 to 7. FIG. 5 shows the planar configuration of the polishing surface plate, and FIGS. 6 and 7 show enlarged cross-sectional shapes of the main parts. In this embodiment, the disk 1 is joined to the jacket 2 by a connecting mechanism 13 that allows expansion in the radial direction. The coupling mechanism 13 consists of a dovetail groove 14 formed on the joint surface of the disk 1 and an engaging protrusion 15 protruding from the joint surface of the jacket 2. The protrusion 15 is fastened to the jacket 2 with a bolt 16. A plurality of these dovetail grooves 14 and protrusions 16 are arranged at intervals in the circumferential direction of the polishing surface plate. Further, each dovetail groove 14 is formed along the radial direction of the polishing surface plate, and is provided with an interval C in the radial direction with respect to the protrusion 15, respectively. The other configurations are almost the same as those of the above embodiment, so the explanation thereof will be omitted. According to the polishing surface plate of the embodiment shown in FIGS. 5 and 6, even if the disk 1 expands in each radial direction due to thermal expansion during polishing, the connection mechanism 13 Relative positional deviation in the radial direction between the disk 1 and the jacket 2 is allowed. Therefore,
The flatness of the disk 1 can be maintained at a high level even during use. In particular, if the disk 1 and the jacket 2 are made of a material with a small coefficient of thermal expansion, the effect of maintaining the flatness and altitude will be remarkable. Table 3 below shows disk 1 and jacket 2.
The composition of an example of a surface plate with an outer diameter of 900 mm made of low expansion cast iron is shown in comparison with a conventional example.

[Table] Table 4 below also shows the connection mechanism 13 that can absorb thermal deformation shown in FIGS. 5 to 7 for the disk 1 and jacket 2 made of the composition materials shown in Table 3. The changes in the flatness of the disk 1 during polishing in this case are shown in comparison with a conventional example in which the disks are connected by bolts.

〔Effect of the invention〕

As described above, according to the present invention, the disk that particularly causes convex deformation among the polishing surface plates is made of a low thermal expansion material having an average coefficient of thermal expansion of 5×10 ^-6 /℃ or less within the above temperature range. With this configuration, deformation of the same portion can be significantly suppressed, and the high degree of flatness of the disk can be maintained. Moreover, the amount of thermal expansion during polishing was set to be approximately the same value for the disk and jacket, taking into account the coefficient of thermal expansion and temperature rise between the disk and jacket, so the flatness of the disk and, by extension, the workpiece The flatness of objects can be improved,
This is highly effective in performing precision polishing in polishing, lapping, etc.

[Brief explanation of drawings]

Fig. 1 is a longitudinal cross-sectional view showing one embodiment of the present invention, Fig. 2 is a partially omitted view, Fig. 3 is a longitudinal cross-sectional view showing the state of use, Fig. 4 is a plan view, and Fig. 5 is a longitudinal cross-sectional view showing an embodiment of the present invention. The figure is a partially omitted plan view showing another embodiment of the present invention.
The figure is a sectional view showing an enlarged main part, and FIG. 7 is a sectional view taken along the line -- in FIG. 6. DESCRIPTION OF SYMBOLS 1... Disk, 2... Jacket, 4... Water cooling hole, 5... Rotating shaft, 7... Polishing cloth, 8... Object to be polished (silicon wafer), 12... Polishing liquid supply pipe, 12... Polishing liquid, 13... Connection mechanism, 14
...Dovetail groove, 15...button.

Claims (1)

[Scope of Claims] 1. A polishing surface plate having a rotating disk carrying a workpiece to be polished and a liquid cooling jacket attached to the back surface of the disk so as to be integrally rotatable, with the disk being rotated between 20 and 200 times. It is made of a low thermal expansion material with an average coefficient of thermal expansion of 5×10 ^-6 /℃ or less, and the average coefficient of thermal expansion of the disk is α ₁ , the temperature rise during polishing is T ₁ ℃, and the same temperature of the jacket A polishing surface plate characterized in that the thermal expansion coefficient α ₂ of the jacket constituent material is set to α ₂ ≒T ₁ /T ₂ α ₁ when the rise is T ₂ °C. 2. The polishing surface plate according to claim 1, wherein the disk is joined to the jacket by a connecting mechanism that allows expansion in the radial direction. 3. The coupling mechanism consists of a dovetail groove formed on one joint surface of the disk or jacket, and a protrusion protruding from the other joint surface that engages with the dovetail groove, and these dovetail grooves and protrusion 3. The polishing surface plate according to claim 2, wherein a plurality of dovetail grooves are arranged at intervals in the direction, and each dovetail groove is formed along the radial direction.