JPH1110523A - Grinding device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a grinding device which can keep a stable grinding state and hence make a ground surface sufficiently flat and does not reduce grinding capacity by preventing a reduction in grinding speed during grinding. SOLUTION: A girding device has a rotary surface plate 2 provided with an expanded abrasive cloth 11 on the top surface and a holding part 7 for holding a work 6 to be ground, and the work 6 is ground by putting the ground surface of the work 6 into a sliding contact with the abrasive cloth 11 while abrasives 3 are being supplied on the abrasive cloth 11. The abrasive cloth 11 is made of foam material having a density of 0.825-0.860 g/cm<3> .

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a polishing apparatus,
In particular, the present invention relates to a polishing apparatus suitable for flattening a substrate having a step in a semiconductor device manufacturing process.

[0002]

2. Description of the Related Art In recent years, in the field of semiconductor devices, in order to flatten the surface of a wafer, a convex portion of a step is chemically mechanically polished (hereinafter referred to as CMP).
). FIG.
FIG. 1 is a side view showing a conventional polishing apparatus used for performing CMP disclosed in, for example, Japanese Patent Application Laid-Open No. H8-241878.

This polishing apparatus mainly comprises a rotary platen 2 on which a polishing cloth 1 is stretched, a polishing agent supply means 8 for supplying a polishing slurry 3 onto the polishing cloth 1, and a wafer (semiconductor substrate) 6 held in close contact. And a rotary grinding head 5 in which grinding abrasive grains 4 such as diamond are embedded.

The rotary platen 2 is connected to a motor (not shown) through a shaft 2S provided at the center of the lower part of the rotary platen 2 so as to be rotatable in a counterclockwise direction (A direction in the figure). I have. The wafer holding table 7 is connected to a drive mechanism (not shown) via a shaft 7S provided at the center of the upper part of the wafer holding table 7, so that the wafer holding table 7 is rotated counterclockwise (direction D in FIG. ), And can also be moved in the vertical direction (direction E in the figure), so that the wafer 6 and the polishing pad 1 can be slid in contact with or separated from each other.

The rotary grinding head 5 is connected to a drive mechanism (not shown) through a shaft 5S provided at the center of the upper portion of the rotary grinding head 5 so that, similarly to the rotary platen 2 and the wafer holding table 7, the counterclockwise In addition to being rotatable in the circumferential direction (direction B in the drawing), it is also movable in the vertical direction (direction C in the drawing), so that the abrasive grains 4 and the polishing pad 1 can be slid into contact with or separated from each other. It has become.

To actually perform polishing by this polishing apparatus, first, the wafer 6 is held in close contact with the wafer holding table 7 and rotated. Further, the abrasive 3 is supplied onto the polishing pad 1 from the abrasive supply means 8 while rotating the rotary platen 2. Then, the wafer 6 is polished by bringing the polishing surface of the wafer 6 into sliding contact with the polishing cloth 1 via the polishing agent 3. Polishing cloth 1
Is worn by the polishing of the wafer 6, so that the abrasive grains 4 of the rotary grinding head 5 are brought into sliding contact with the surface of the polishing cloth 1, whereby the surface of the polishing cloth 1 is ground and the surface roughness is recovered. I do.

As a method of recovering the surface roughness of the polishing cloth 1, as shown in FIG. 6, a rotary grinding head 5, 5 'in which two different grinding abrasive grains 4, 4' are respectively embedded is stepwise. There is known a method of recovering the surface roughness of the polishing pad 1 by using a polishing device that makes sliding contact with the polishing pad.

The polishing pad 1 is made of, for example, a flexible material such as foamed polyurethane whose surface is controlled to a predetermined roughness so as not to damage the wafer 6. FIG. 7 is a cross-sectional view showing a conventional polishing cloth 1 using foamed polyurethane, and the polishing cloth 1 has pores 9 generated in a manufacturing process. Here, it is the exposed portion 10 of the polyurethane other than the holes 9 in the surface of the polishing pad 1 that plays the role of polishing the wafer 6.

By controlling the surface roughness of the exposed portion 10 to a predetermined value, stable polishing can be performed. As a method for polishing the wafer 6, the abrasive grains 4 of the rotary grinding head 5 are brought into sliding contact with the polishing cloth 1 and ground when the wafer 6 is polished, so that the surface roughness of the polishing cloth 1 is lower than the surface roughness before the start of polishing. By using a method in which polishing is performed under the condition of maintaining substantially equal and constant, it is possible to control to a desired surface grain size (for details, refer to JP-A-8-241878).

[0010]

The problem with the conventional polishing apparatus is that even if the surface roughness of the polishing pad 1 is controlled to be constant, the proportion of the holes 9 to the surface area of the polishing pad 1 increases. This is because the proportion of the exposed portion 10 relatively decreases and the polishing rate decreases. When the polishing rate decreases, the polishing time must be extended in order to obtain a predetermined polishing amount, and as a result, there is a problem that the processing capability of the polishing apparatus is reduced. In addition, in this polishing apparatus, there is a problem that work such as pilot polishing for checking a polishing rate is increased, and the operability of CMP is reduced.

In order to prevent the polishing rate of the polishing cloth 1 having a low density from decreasing, a method of increasing the polishing rate by increasing the surface roughness is conceivable. However, as described in the above-mentioned publication, the polishing is performed up to the stepped recess. Therefore, there is a problem that sufficient flatness cannot be obtained.

[0012] The present invention has been made in view of the above circumstances, and by preventing the polishing rate from decreasing during polishing, a stable polishing state can be maintained. Therefore, the flatness of the polished surface can be reduced. An object of the present invention is to provide a polishing apparatus which can be obtained sufficiently and does not lower the processing capacity.

[0013]

As a result of various studies, the present inventors have reached the following conclusions. With respect to the surface area of the polishing pad, a value indicating the ratio of the holes to the surface area can be expressed as the density of the polishing pad. The proportion of the pores in the surface area and the density of the polishing pad are in inverse proportion, and the density of the polishing pad becomes relatively small as the proportion of the pores increases.

FIG. 1 is a diagram showing the relationship between the number of polished wafers at two different densities of the polishing pad and the polishing rate when the surface roughness of the polishing pad is set to a predetermined value. . In this figure, the density of the polishing cloth is 0.809 g / c.
In the case of m ³ , the polishing rate decreased with an increase in the number of polished wafers, while the density of the polishing cloth was 0.84.
In the case of 8 g / cm ^3, the polishing rate only slightly decreases as the cumulative number of wafers increases.

As a result of further study, it was found that the polishing rate was reduced.
Means that the polishing cloth density is 0.825 g / cm ^ThreeRaw if less than
It turned out to be. The polishing cloth density is O. 860g
/ Cm^ThreeIf it exceeds, the percentage of vacancies will decrease too much
It was also found to be unsuitable as a polishing cloth.

Accordingly, the present invention provides the following polishing apparatus. That is, the polishing apparatus according to claim 1 includes a rotary platen having a polishing cloth stretched on an upper surface thereof, and a holding unit for holding an object to be polished, and the polishing apparatus supplies the polishing agent onto the polishing cloth while polishing. A polishing apparatus for polishing a polished object by bringing a polished surface of the polished object into sliding contact with a cloth, wherein the polishing cloth has a density of 0.82.
5 g / cm ³ or more and O. It is a foamable material of 860 g / cm ³ or less.

According to a second aspect of the present invention, in the polishing apparatus, the cellular material is a cellular resin.

According to a third aspect of the present invention, in the polishing apparatus, the foamable resin is a resin containing polyurethane as a main component.

According to a fourth aspect of the present invention, in the polishing apparatus, the object to be polished is a semiconductor substrate.

[0020] In the polishing apparatus of the present invention, the polishing pad is made of a polishing cloth having a density of 0.825 g / cm ³ or more and an O.D. By using a porous material of 860 g / cm ³ or less, the ratio of the exposed portion to the surface area of the polishing cloth falls within a certain range, and the polishing rate is stabilized. As a result, variation in the polishing amount is reduced, and a stable polishing amount can be achieved, and the flatness of the polished surface of the object to be polished is improved.

Here, the density is 0.825 g / cm ³ or more and the O.D. The reason for limiting the amount to 860 g / cm ³ or less is as follows.
If it is less than 825 g / cm ³ , the polishing rate decreases, a long polishing time is required to obtain a sufficient flat surface, and the processing capacity of the apparatus decreases. If it exceeds 860 g / cm ³ , the proportion of vacancies will be too small, and the properties as a cellular material will be lost.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the polishing apparatus according to the present invention will be described below with reference to the drawings. FIG. 2 is a side view showing a polishing apparatus according to an embodiment of the present invention. In the figure, reference numeral 11 denotes a polishing apparatus having a density of 0.825 g / cm ³ or more and an O.D. 8
This is a polishing cloth made of a cellular foam material of 60 g / cm ³ or less. As the foamed material, a foamed resin is suitable, and in particular, a resin containing polyurethane as a main component such as foamed polyurethane (also referred to as polyurethane home) is suitable.

When the surface roughness of the polishing pad 11 is set to a predetermined value, the polishing rate is determined by the exposed portion mainly composed of polyurethane on the surface of the polishing pad 11, and this exposed portion is determined by the surface of the polishing pad 11. Is determined by the pores generated by the foaming process of the chemical reaction. Further, since the ratio of the holes has an inverse relationship with the density of the polishing pad 11, the ratio of the holes can be expressed by the density of the polishing pad 11.

Therefore, the density of the polishing pad 11 is set to 0.82
5 g / cm ³ or more and O. By limiting it to 860 g / cm ³ or less, the ratio of the exposed portion mainly composed of polyurethane to the surface of the polishing cloth 11 falls within a certain range, and a stable polishing rate can be obtained. The operation of this polishing apparatus is exactly the same as that of a conventional polishing apparatus.

FIG. 3 is a diagram showing the relationship between the amount of polishing and the cumulative number of polishing (sheets) when the wafer 6 is polished using the polishing cloth 11 of this embodiment. Here, the density is 0.832g
/ Cm ³ of polishing cloth 11 was used. On the other hand, FIG. 4 is a diagram showing the relationship between the amount of polishing and the cumulative number of polishing when the wafer 6 is polished using the conventional polishing cloth 1. Here, the polishing pad 1 having a density of 0.797 g / cm ³ out of the range of the present invention is used.
Was used. Further, the polishing amount is represented as an index with respect to a required polishing amount.

According to FIG. 3 and FIG. 4, when the polishing pad 11 of this embodiment is used, the accumulated polishing number is 150 to 400.
, The polishing amount is almost 1 and the variation is as small as 417 °, and the polishing state is kept almost constant. In contrast, when the conventional polishing cloth 1 is used, the accumulated number of polishing increases. As the amount of polishing decreases, the polishing amount gradually decreases.
8 and the variation was as large as 875 °, which indicates that the polished state was greatly reduced as compared with the initial polished state.

As a result, in the polishing cloth 11 of this embodiment,
Compared to the conventional polishing cloth 1, the polishing amount can be maintained at a substantially constant value even if the cumulative number of polishing increases, and a substantially constant polishing state can be maintained. Therefore, the variation in the polishing amount can be reduced by half.

As described above, according to the polishing apparatus of the present embodiment, the density is 0.825 g / cm ³ or more and the O.D. 8
Since the polishing cloth 11 made of a porous material of 60 g / cm ³ or less is used, the polishing rate can be stabilized, so that the variation in the polishing amount can be reduced, and a stable polishing amount can be achieved. Can be.

By polishing the semiconductor substrate such as the wafer 6 using the polishing apparatus of the present embodiment, a polished surface having excellent flatness can be obtained. It is possible to provide a semiconductor substrate which can cope with the development of semiconductor devices, and can greatly contribute to the progress of semiconductor devices.

[0030]

As described above, according to the polishing apparatus of the present invention, the polishing pad can be used with a density of 0.825 g / cm ³ or more and an O.D. 860 g / cm ³ or less as a foamed material,
The ratio of the exposed portion to the surface area of the polishing cloth can be kept within a certain range. Therefore, the polishing rate can be stabilized, the flatness of the polished surface of the object to be polished can be sufficiently obtained, and the processing capability of the apparatus does not decrease. Further, pilot polishing and the like can be reduced, continuous operation can be performed, and the operability of CMP can be improved.

[Brief description of the drawings]

FIG. 1 is a diagram showing the relationship between the cumulative number of polished wafers and the polishing rate at each of two different densities of a polishing cloth.

FIG. 2 is a side view showing a polishing apparatus according to an embodiment of the present invention.

FIG. 3 is a diagram illustrating a relationship between a polishing amount and a cumulative polishing number when a wafer is polished using the polishing cloth according to the embodiment of the present invention.

FIG. 4 is a diagram illustrating a relationship between a polishing amount and a cumulative polishing number when a wafer is polished using a conventional polishing cloth.

FIG. 5 is a side view showing an example of a conventional polishing apparatus.

FIG. 6 is a side view showing another example of the conventional polishing apparatus.

FIG. 7 is a sectional view showing a conventional polishing cloth.

[Explanation of symbols]

 Reference Signs List 2 rotating surface plate 2S shaft part 3 abrasive 4 grinding abrasive 5 rotating grinding head 5S shaft part 6 wafer (semiconductor substrate) 7 wafer holding table (holding part) 7S shaft part 8 abrasive supply means 11 polishing cloth A, B, D Counterclockwise direction C, E Vertical direction

Claims (4)

[Claims] A rotating platen having a polishing cloth stretched on an upper surface thereof;
A holding unit for holding the object to be polished, a polishing apparatus that polishes the object to be polished by sliding the polishing surface of the object to be polished to the polishing cloth while supplying an abrasive on the polishing cloth, The polishing cloth has a density of 0.825 g / cm ³ or more and an O.D. A polishing apparatus comprising a multi-cellular material of 860 g / cm ³ or less. 2. The polishing apparatus according to claim 1, wherein said foamable material is a foamed resin. 3. The polishing apparatus according to claim 2, wherein the foamable resin is a resin containing polyurethane as a main component. 4. The polishing apparatus according to claim 1, wherein the object to be polished is a semiconductor substrate.