JP2000158341A - Polishing method and polishing system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stabilize pH of an abrasive slurry for a long time without adding other material by reserving the abrasive slurry for polishing a work piece in an inert gas atmosphere. SOLUTION: Before starting a polishing work, a valve 27 is closed, a valve 26 is opened for a CMP(chemical and mechanical polishing) device body 12. During the polishing work, an abrasive slurry discharged from the CMP device body 12 is guided to a recovering tank 20 or a disposal unit 24, and the used slurry supplied to the recovering tank 20 is filtered or reproduced, and fed to a supply tank 18 as a reproduced slurry. In this supply tank 18, the reproduced slurry supplied from the recovering tank 20 and a new slurry reserved in an atmosphere of nitrogen gas from a reservoir 16 are mixed, are adjusted in temperature, are supplied to a filter unit 22, and are filtered again, and the filtered slurry is supplied to the CMP device body 12.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a polishing method and a polishing system for polishing a workpiece such as a semiconductor wafer using a polishing slurry. In particular, the present invention relates to a polishing method and a polishing system having a recycling function of reusing a used polishing slurry.

[0002]

2. Description of the Related Art As a polishing apparatus for flattening the surface of a semiconductor wafer or the like, a CMP apparatus (chemical mechanical polishing apparatus) is widely used at present. In a CMP apparatus, a polishing operation is performed while supplying a polishing slurry between a rotating polishing pad and a semiconductor wafer. In such a polishing apparatus, the pH of the polishing slurry greatly affects the polishing characteristics. That is, the polishing rate and the selectivity greatly change depending on the pH value of the polishing slurry.

Therefore, in the invention disclosed in Japanese Patent Application Laid-Open No. HEI 8-115892, an ammonium salt and pure water are added to a polishing slurry to reduce the p of the slurry.
H is controlled.

[0004]

However, if another substance such as an ammonium salt is added to control the pH of the polishing slurry, the concentration of the polishing slurry and the balance of other components will fluctuate. As a result, other problems such as a change in the degree of adhesion of contaminants to the workpiece occur.

The present invention has been made in view of the above situation, and has as its object to provide a polishing method and a polishing system capable of stabilizing the pH of a polishing slurry for a long period of time without adding other substances. I do.

[0006]

In order to solve the above-mentioned problems, in a polishing method according to a first aspect of the present invention, a polishing slurry is stored in an inert gas atmosphere.

A polishing system according to a second aspect of the present invention includes a polishing apparatus for polishing a workpiece using a polishing slurry; a tank for storing the polishing slurry to be supplied to the polishing apparatus; An inert gas supply mechanism for supplying gas.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Before describing embodiments of the present invention,
The theory and principle underlying the present invention will be briefly described.
The present invention has been made by focusing on the fact that the pH of the polishing slurry is stable in an inert gas atmosphere. For example, as shown in FIG. 1, cerium oxide (CeO
₂ ) The slurry was prepared in a nitrogen atmosphere (A) and an air atmosphere (B).
An experiment was conducted on the change in pH when the sample was stored in step (1). FIG.
Shows the experimental results. In this experiment, the pH value was measured while stirring the polishing slurry in each container.
As can be seen from the figure, the pH of the polishing slurry
Increases greatly over time. On the other hand, when the polishing slurry is stored in a nitrogen (inert gas) atmosphere, almost no change in pH is confirmed. That is, it became clear that the pH stability of the polishing slurry was improved in an inert gas atmosphere.

[0009]

Embodiments of the present invention will be described below. The embodiment described below is a CM for polishing the surface of a semiconductor wafer.
This is an application of the technical idea of the present invention to the P system. It is needless to say that the present invention can be applied to polishing of various samples (workpieces) such as a magnetic disk and a glass substrate in addition to polishing of a semiconductor wafer.

FIG. 3 shows a CM according to the first embodiment of the present invention.
1 shows the overall configuration of a P system. The CMP system according to the present embodiment includes a CMP apparatus main body 12 for polishing the surface of a semiconductor wafer using a polishing pad, a storage tank 16 for storing new slurry, a supply tank 18 connected to the storage tank 16, A filter unit 22 connected to the tank 18;
The apparatus includes a recovery tank 20 connected between the P apparatus main body 12 and the supply tank 18, and a disposal unit 24 connected to the CMP apparatus main body 12. The CMP system of this embodiment further includes a nitrogen gas supply unit 15 connected to the storage tank 16, the supply layer 18, and the recovery tank 20.

In the storage tank 16, as a new slurry,
For example, a cerium oxide (CeO ₂ ) slurry is stored. The storage tank 16 is connected to a nitrogen gas supply unit 15 via a nitrogen gas supply pipe 17, and stores (purges) the slurry in an atmosphere of nitrogen gas supplied from the nitrogen gas supply unit 15. On a pipe 17 between the nitrogen gas supply unit 15 and the storage tank 16, a valve 16a for controlling the supply of the nitrogen gas is provided.

The supply tank 18 mixes the new slurry supplied from the storage tank 16 with the regenerated slurry supplied from the recovery tank 20. Among the used slurries discharged from the CMP apparatus main body 12, the slurry supplied to the disposal unit 24 is a slurry that is not at an appropriate concentration, such as a discharged slurry immediately after the CMP apparatus main body 12 is washed with pure water, Discarded without being used. On the other hand, the slurry supplied to the recovery tank 20 is a slurry having an appropriate concentration, and after being subjected to a filtration regeneration process in the recovery tank 20, the slurry is returned to the supply tank 18 as a regenerated slurry.

The supply tank 18 is connected to a nitrogen gas supply unit 15 via a nitrogen gas supply pipe 17, and stores the slurry in an atmosphere of nitrogen gas supplied from the nitrogen gas supply unit 15. Nitrogen gas supply unit 1
A valve 18a for controlling the supply of nitrogen gas is provided on the pipe 17 between the supply tank 5 and the supply tank 18. Supply tank 1
Reference numeral 8 also controls the temperature of the slurry supplied to the CMP apparatus main body 12 by a temperature adjusting mechanism such as a heater or a cooling water channel (not shown).

The filter unit 22 filters the polishing slurry immediately before being supplied to the CMP apparatus main body 12, and removes secondary growth abrasive grains and abnormal growth abrasive grains of the slurry. Note that the filter unit 22 is also connected to the collection tank 20 by a bypass pipe.

A valve 26 is provided in the middle of the pipe connecting between the CMP apparatus main body 12 and the filter unit 22 so that the polishing slurry supplied from the filter unit 22 can be supplied to the CMP apparatus main body 12 and the recovery tank 20. It leads to either one. That is, the flow path of the polishing slurry can be arbitrarily switched between the CMP apparatus main body 12 side and the recovery tank 20 side. C
Further, pure water for cleaning is supplied to the MP apparatus main body 12 via a valve 27.

A valve 28a is provided between the CMP apparatus main body 12 and the recovery tank 20, and a valve 28b is provided between the CMP unit main body 12 and the waste unit 24. These two valves 28
a and 28b are selectively opened and closed to obtain CM
The flow path of the liquid (slurry, pure water) discharged from the P device main body 12 is switched between the recovery tank 20 side and the disposal unit 24 side. The slurry supplied to the recovery tank 20 circulates through the system for recycling. Further, the slurry and pure water supplied to the disposal unit 24 are disposed at a predetermined timing.

The recovery tank 20 is also provided with a nitrogen gas supply pipe 17.
Is connected to the nitrogen gas supply unit 15 through
The slurry is stored in an atmosphere of nitrogen gas supplied from the nitrogen gas supply unit 15. On the pipe 17 between the nitrogen gas supply unit 15 and the supply tank 18, a valve 20a for controlling the supply of nitrogen gas is provided.

FIG. 4 shows the configuration of the CMP apparatus main body 12. The main body 12 of the CMP apparatus of this embodiment has a polishing platen 62.
And the polishing pad 6 attached to the lower surface of the polishing platen 62
8, an elastic member 66 disposed between the polishing platen 62 and the polishing pad 68, a wafer table 32, a wafer holder 34, and a retainer 78 for fixing the wafer 80 on the wafer holder 34. ing.

The elastic member 66 is formed in a ring shape and is fixed to the polishing platen 62 with a double-sided tape or the like. The polishing pad 68 is similarly formed into a ring shape, and the inner peripheral ring 70 is formed.
, The outer ring 74 and the bolts 72 and 76 are pulled up and fixed to the bottom surface of the polishing platen 62. Wafer holder 3
4 is rotatably mounted on the wafer table 32.

The polishing table 62, the wafer table 32,
The wafer holding unit 34 includes rotation axes AA ′, BB ′,
It is configured to rotate around CC ′. A slurry supply hole 64 is formed in the central axis of the polishing platen 62, and the polishing slurry is supplied between the polishing pad 68 and the wafer 80 through the slurry supply hole 64.

FIG. 5 shows the internal structure of the recovery tank 20. In the collection tank 20, a filter cartridge 46 having a filter 44 is disposed. The filter cartridge 46 is a cartridge body 4 that holds the filter 44.
8 and a handle 72 provided to set the main body 48 in the collection tank 20 and to facilitate taking out.

The collection tank 20 includes a first filter tank 74,
And a second filter tank 76. The used slurry is supplied to the first filter tank 74 via the pipe 29. The second filter tank 76 includes the filter 4
The slurry after filtration by 4 is stored. The second filter tank 76 is connected to the supply tank 18 via the pipe 21.

In the recovery tank 20, two sensors 38, 4
0 is set. The sensor 38 is a float type lower limit sensor. When the lower limit sensor 38 detects the surface position of the slurry, the discharge of the slurry (delivery to the supply tank 18 by a pump not shown) is stopped. . The sensor 40 is a float-type upper limit sensor, and detects that the level of the slurry in the second filter tank 76 has reached a pumping start position (delivery to the supply tank 18 by a pump (not shown)).

In the upper part of the recovery tank 20, one end of a pipe 17 connected to the nitrogen gas supply unit 15 is inserted, from which nitrogen gas is taken in, and the slurry can be stored in a nitrogen gas atmosphere. .

Next, the overall operation of the CMP system configured as described above will be briefly described. Prior to starting the polishing operation, the valve 27 is closed and the valve 26 is opened to the CMP apparatus main body 12. During polishing work,
The polishing slurry discharged from the CMP apparatus main body 12 is guided to the recovery tank 20 or the disposal unit 24. Collection tank 20
The used slurry supplied to the recovery tank 20 is filtered and regenerated in the recovery tank 20 and sent to the supply tank 18 as regenerated slurry.

In the supply tank 18, the new slurry supplied from the storage tank 16 and the regenerated slurry supplied from the recovery tank 20 are mixed and the temperature is adjusted, and then the filter unit 22 is pumped (not shown). Send to Then, the slurry filtered again by the filter unit 22 is supplied to the CMP apparatus main body 12.

When the polishing operation in the CMP apparatus main body 12 is completed, the valve 2 is used to clean the polished wafer and the apparatus.
6 is opened to the collection tank 20 and the valve 27 is opened to allow the pure water to flow into the CMP apparatus main body 12.
Supply within. During the cleaning of the CMP apparatus main body 12, the valve 28a is closed and the valve 28b is opened, and the discharged liquid (pure water) of the CMP apparatus main body 12 is discarded through the discarding unit 24.

Next, the operation and effect of the above-described CMP system of this embodiment will be described. FIG. 6 shows the supply tank 18.
And the recovery tank 20 in a nitrogen atmosphere (in the case of the embodiment)
And changes with time of the slurry pH in each case when the atmosphere was changed to the air atmosphere (in the case of the comparative example). In this case,
Actually, the polishing operation was not performed, and the polishing slurry was simply circulated in the order of the supply tank 18, the filter 22, and the recovery tank 20. As can be seen from the graph of FIG. 6, when the polishing slurry is circulated in the atmosphere, the slurry pH increases with time. On the other hand, when circulating in a nitrogen atmosphere, the pH change of the slurry is extremely small and stable for a long time.

As described above, if the pH value of the polishing slurry is stabilized, the polishing rate of a workpiece such as a semiconductor wafer is stabilized. In the present embodiment, the selectivity of the film to be polished can be further improved by controlling the pH of the polishing slurry. For example, a trench isolation method (ST
I method: a silicon oxide film (SN) formed on a silicon nitride film (SiNx) by a shallow trench isolation method.
In the case where iO ₂ ) is polished, the polishing slurry p
By maintaining H in an optimal state, polishing characteristics (selectivity)
Can be improved.

FIG. 7 shows the effect of the pH of the polishing slurry on the polishing rates of the oxide film and the nitride film. In the figure,
The pH dependence of the oxide film polishing rate is indicated by a circle, and the pH dependence of the nitride film polishing rate is indicated by a triangle. As you can see from the figure,
When the pH of the polishing slurry is below a certain value, the polishing rate of the silicon nitride film becomes extremely low. That is, if the pH of the slurry is equal to or less than that value, the silicon oxide film (insulating film)
Is removed, but the silicon nitride film (polishing stop film) is hardly removed. Therefore, even when a slight error occurs in the control of the polishing time, excessive polishing does not occur. In the case of the present embodiment, a good selectivity can be obtained when the pH of the polishing slurry is 7 or less, preferably 6.5 or less.

FIG. 8 shows an outline of the steps of the above-described trench isolation method. The trench isolation method is used as a method for electrically isolating a large number of element formation regions on a silicon substrate. In this method, a trench (groove) is dug in a silicon substrate, and the trench is buried with an insulating film (silicon oxide film), and then the surface of the substrate is planarized using a CMP apparatus.

More specifically, first, as shown in FIG. 8A, a polishing stopper film 102 made of a thin silicon nitride film is formed on a silicon substrate 100. Next, as shown in FIG. 1B, patterning is performed by photolithography, and a trench 104 is formed by etching. Next, as shown in FIG. 3C, an insulating film 106 made of a silicon oxide film is deposited in the trench 104.
At this time, the insulating film 106 is formed in a place other than the trench 104.
Is formed. Then, as shown in FIG.
Using a P device, the insulating film 106 is polished to planarize the substrate surface. At this time, the silicon nitride film 102 functions as a polishing stop film. The technique of using a silicon nitride film as a polishing stopper film is also used for flattening an interlayer insulating film.

FIG. 9 shows the change over time of the pH of the polishing slurry when the polishing operation is actually performed using the CMP system of this embodiment shown in FIG. As can be seen from the figure, even during the actual polishing operation, the pH of the polishing slurry is about 6.2.
６6.7 (approximately 6.3 to 6.6), and does not show large fluctuation. In FIG. 9, the reason why the pH value fluctuates jaggedly is that new polishing slurry is supplied to the supply tank 18 at a predetermined timing. That is, in the system of FIG. 3, when the amount of the polishing slurry in the supply tank 18 decreases, the supply tank 18 is automatically refilled with new polishing slurry from the storage tank 16.
Then, when the new slurry is sent into the supply tank 18, the pH of the slurry temporarily decreases.

FIGS. 10 and 11 show changes over time in the polishing rates of the oxide film and the nitride film when the polishing operation is actually performed using the CMP system of the present embodiment shown in FIG. The data in these figures are the results of experiments performed under the following conditions. That is, a sample a having a silicon oxide film formed on a silicon substrate (no pattern) and a sample b having a silicon nitride film formed on a silicon substrate (no pattern) are prepared, and the sample a and the sample b are polished alternately. did. The polishing time was 1 minute / time for sample a, and 10 minutes / time for sample b. Also,
The interval from the end of one polishing to the start of the next polishing was 5 minutes. Such a polishing operation is performed from 9:00 to 1
2:00, 13:00 to 17:00 (7 hours / day), and only the slurry was circulated in the system during the lunch break and at night. The polishing rate was determined by measuring the change in film thickness before and after polishing with an optical film thickness meter and dividing the difference in film thickness before and after polishing by the polishing time.

FIG. 10 shows that the polishing rate of the oxide film is stable at a high level (about 2000 ° / min or more). From FIG. 11, it can be seen that the polishing rate of the nitride film is stable at a low level (about 15 ° / min or less). Such a result is caused by storing the polishing slurry in the storage tank 16, the supply tank 18, and the recovery tank 20 in a nitrogen atmosphere and controlling the pH to an optimum state (6.5 or less).

FIG. 12 shows the change over time in the polishing selectivity of the silicon nitride film and the silicon oxide film in the CMP system of this embodiment. As shown in FIG. 12, in a case where a silicon oxide film formed on a silicon nitride film is polished, the silicon nitride film functions well as a polishing stopper film.

FIG. 13 shows, as a comparative example, the CM shown in FIG.
The graph shows the change over time in the pH of the polishing slurry when the polishing operation is performed by storing the polishing slurry in the atmosphere in all of the storage tanks 16 and the like of the P system. As can be seen from the figure, when the polishing slurry is stored in an air atmosphere, the pH greatly fluctuates with the cumulative polishing time, and sometimes shows a pH of 7 or more. As shown also in FIG.
If H exceeds 7, the polishing rate of the silicon nitride film sharply increases, so that the silicon nitride film does not serve as a polishing stopper film.

FIG. 14 shows a CM according to the second embodiment of the present invention.
1 shows a configuration of a main part of a CMP apparatus main body applied to a P system. In addition, other configurations except for a part of the CMP apparatus main body are as follows.
This is the same as the first embodiment shown in FIG. 4, and the description of the overlapping portion will be omitted. Features of the CMP apparatus main body of this embodiment (first
The difference from the embodiment is that the nitrogen gas is introduced to the inside of the main body of the CMP apparatus. That is, in the present embodiment, in the rotation axis of the wafer table 32 and the polishing table 6
Nozzle 11 for supplying nitrogen gas into the rotating shaft 2
0 and 112 are provided.

These nozzles 110 and 112 are connected to the nitrogen gas supply unit 15 shown in FIG. 3 so that the space between the polishing pad 68 to which the slurry is supplied and the wafer 80 is maintained in a nitrogen gas atmosphere. I have. As in the present embodiment, the stability of the pH of the polishing slurry can be further improved by setting the polishing portion to an inert gas (nitrogen gas) atmosphere.

[0040]

As described above, according to the present invention,
Since the polishing slurry is stored in an atmosphere of an inert gas such as nitrogen gas, long-term stability of the pH of the slurry can be improved. Therefore, the polishing rate of the workpiece can be maintained at a favorable value, and as a result, the selection ratio can be optimized.

In a polishing system that reuses used slurry, it is very important to extend the life of the slurry with long-term stability of the slurry pH. That is, the present invention is particularly effective in a recycling system aiming at effective utilization of the slurry.

[Brief description of the drawings]

BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is an explanatory diagram showing a state of a basic experiment (slurry pH change over time) of the present invention.

FIG. 2 is a graph showing the results of the experiment in FIG. 1 (change in slurry pH with time).

FIG. 3 is an explanatory diagram illustrating a schematic configuration of a CMP system according to a first embodiment of the present invention.

FIG. 4 is a side view (partial cross section) showing a configuration of the CMP apparatus main body according to the first embodiment.

FIG. 5 is a cross-sectional view illustrating a structure of a recovery tank according to the first embodiment.

FIG. 6 is a graph showing the operation of the first embodiment, and shows the slurry p in a state of being circulated in the CMP system.
The change with time of H is shown.

FIG. 7 is a graph showing the operation of the first embodiment, and shows the change in the polishing rate of the oxide film and the nitride film with respect to the slurry pH.

FIG. 8 is a process diagram showing a schematic process of an STI method (shallow trench isolation method).

FIG. 9 is a graph showing the operation of the first embodiment, and shows the change over time (nitrogen atmosphere) of the slurry pH during the actual polishing operation.

FIG. 10 is a graph showing the operation of the first embodiment, and shows the change over time (nitrogen atmosphere) in the polishing rate of the oxide film.

FIG. 11 is a graph showing the operation of the first embodiment, and shows the change over time (nitrogen atmosphere) in the polishing rate of the nitride film.

FIG. 12 is a graph showing the operation of the first embodiment, and shows the change over time (nitrogen atmosphere) in the selectivity between the oxide film and the nitride film.

FIG. 13 is a graph showing the operation of the conventional technique (Comparative Example), and shows the slurry pH during the actual polishing operation.
Over time (atmospheric atmosphere).

FIG. 14 is a diagram showing a CMP according to a second embodiment of the present invention;
It is a side view (partial section) showing the composition of an apparatus main part.

[Explanation of symbols]

 12 CMP apparatus main body 15 Nitrogen gas supply unit 16 Storage tank 18 Supply tank 20 Recovery tank 68 Polishing pad 80 Wafer 110, 112 Nozzle (for nitrogen gas supply)

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Yasuo Minamikawa 1-8 Fuso-cho, Amagasaki-shi, Hyogo Sumitomo Metal Industries, Ltd. Semiconductor Equipment Division F-term (reference) 3C047 GG14

Claims (9)

[Claims] 1. A polishing method for polishing a workpiece using a polishing slurry, wherein the polishing slurry is stored in an inert gas atmosphere. 2. The polishing method according to claim 1, wherein said polishing slurry is a cerium oxide slurry. 3. The polishing method according to claim 1, wherein the used polishing slurry is reused. 4. The polishing method according to claim 1, wherein the workpiece is a SiO ₂ film formed on a SiN film, and the polishing slurry is maintained at a pH of 7 or less. 5. A polishing apparatus for polishing a workpiece using a polishing slurry; a tank for storing polishing slurry to be supplied to the polishing apparatus; and an inert gas supply mechanism for supplying an inert gas to the tank. A polishing system, comprising: 6. A tank for storing a new polishing slurry; a collection tank for collecting and regenerating used polishing slurry used in the polishing apparatus; and a tank supplied from the storage tank and the collection tank. The polishing system according to claim 5, further comprising a supply tank that mixes the slurry and supplies the mixed slurry to the polishing apparatus. 7. The polishing system according to claim 5, wherein the polishing slurry is a cerium oxide slurry. 8. The polishing apparatus according to claim 5, wherein the polishing apparatus is for polishing a SiO ₂ film formed on a SiN film, and maintains the polishing slurry at a pH of 7 or less. Polishing system. 9. The polishing apparatus includes a nozzle for guiding the inert gas near a polishing surface of the workpiece, and the inert gas supply mechanism supplies the inert gas to a nozzle of the polishing apparatus. Claim 5, characterized in that:
9. The polishing system according to 6, 7, or 8.