JP5699783B2 - Work polishing method and polishing apparatus - Google Patents

Description

  The present invention relates to a workpiece polishing method and a polishing apparatus, and more particularly to a workpiece polishing method and a polishing apparatus capable of accurately controlling the polishing amount of a workpiece such as a semiconductor wafer that requires high flatness.

In the manufacture of semiconductor wafers such as silicon wafers, which are typical examples of workpieces used for polishing, there is a double-side polishing process that simultaneously polishes the front and back surfaces of the wafer in order to obtain higher-precision wafer flatness quality and surface roughness quality. Generally adopted. The shape required for semiconductor wafers (mainly the flatness of the entire surface and the outer periphery) varies depending on the application, etc., and according to each request, the target of the polishing amount of the wafer is determined and the polishing amount is accurately determined. It is necessary to control.
In particular, in recent years, the demand for flatness of semiconductor wafers during exposure has become stricter due to the miniaturization of semiconductor elements and the increase in diameter of semiconductor wafers. Has been.

Conventionally, the polishing amount has been managed by adjusting the past batch processing results. That is, feedback control is performed in which a polishing rate is calculated from the previous polishing time record and polishing amount record, and the polishing time is set so as to ensure a predetermined polishing amount in the next batch.
However, double-sided polishing includes the time during which the wafer is mainly polished and the time during which the carrier plate is worn, so the polishing rate within the batch is not constant, and when performing a dressing process between batches, etc. In this case, the polishing rate also changes depending on the time between batches. Therefore, an error occurs when setting the polishing time in the next batch process from the results of the previous double-side polishing process.
Furthermore, because the polishing conditions differ between the last polishing and the polishing in the next batch due to deterioration of secondary materials such as the life of the polishing pad and the wear state of the carrier plate, the polishing time setting by feedback control is the amount of polishing. There was a problem with accuracy. In particular, since the polishing time is long in double-side polishing, a decrease in accuracy due to the deterioration of the auxiliary material becomes large.
On the other hand, for example, Patent Document 1 describes a method for controlling the polishing amount of a wafer from the amount of decrease in the surface plate driving torque of the double-side polishing apparatus during polishing.

JP 2002-254299 A

  However, the method described in Patent Document 1 has poor response to changes in the surface plate torque, and it is difficult to correlate the amount of change in torque with the amount of wafer polishing. In addition, when the wafer holding member (carrier plate) and the surface plate come into contact with each other, the polishing end point is judged as a large torque fluctuation. There is a problem that it cannot be detected.

  An object of the present invention is to provide a wafer polishing method and a polishing apparatus capable of accurately controlling the polishing amount when performing double-side polishing of a wafer.

The inventors have made extensive studies to solve the above problems.
As a result, in double-side polishing of workpieces, it was newly found that the change in the temperature change rate of the waste slurry is an accurate indicator of the wafer polishing amount.
Then, the inventors measure the temperature of the polishing slurry after polishing, and accurately control the polishing amount to achieve the target polishing amount using the rate of change in the temperature change rate as an index. I got new knowledge that I can do it.

The present invention is based on the above findings, and the gist of the present invention is as follows.
(1) The carrier plate is rotated between an upper surface plate and a lower surface plate to which a polishing pad is affixed while holding the workpiece on a carrier plate having one or more holding holes for holding the workpiece and supplying polishing slurry. In the method of simultaneously polishing the front and back surfaces of the workpiece,
Measure the temperature of the polishing slurry in the drainage tank or drainage channel subjected to polishing, calculate the measured temperature change rate of the polishing slurry and the change rate of the temperature change rate,
When the rate of change of the temperature change rate is equal to or greater than a predetermined value, it is determined that the thickness of the workpiece and the thickness of the carrier plate are equal, and the end or continuation of polishing is determined, A method for polishing a workpiece, wherein the polishing amount of the workpiece is controlled .

(2) A rotatable carrier plate in which one or more holding holes for holding a workpiece to be polished are formed, a lower surface plate on which the carrier plate is placed, and an upper surface plate that is paired with the lower surface plate In an apparatus for polishing both surfaces of a workpiece, including a drainage tank and a drainage channel ,
Means for measuring the temperature of the polishing slurry in the drainage tank or the drainage channel after polishing;
Means for calculating the measured temperature change rate of the polishing slurry and the change rate of the temperature change rate;
When the rate of change of the temperature change rate is equal to or greater than a predetermined value, it is determined that the thickness of the workpiece and the thickness of the carrier plate are equal, and the end or continuation of polishing is determined, Means for controlling the polishing apparatus;
An apparatus for polishing a workpiece, further comprising:

According to the present invention, it is possible to manufacture a highly flat semiconductor wafer having a shape according to demand by accurately controlling the amount of polishing in-line in double-side polishing of a wafer.
In addition, accurate control of the polishing amount eliminates the need for re-polishing due to insufficient polishing and improves the productivity in the wafer manufacturing process.
Furthermore, since the expected amount of wear is not exceeded, it is possible to prevent the occurrence of wafer defects and the wear of the carrier plate.

It is a schematic perspective view of the prototype double-side polishing apparatus. It is an AA arrow line view of FIG. It is a figure which shows the contact state of a wafer and a carrier plate, and a polishing pad. It is a figure which shows the time change of the temperature of the slurry used for grinding | polishing. It is a figure which shows the time change of the temperature of the slurry used for grinding | polishing, and the time change of a wafer shape. It is a schematic perspective view which shows the apparatus concerning one Embodiment of this invention. It is a figure which shows the time change of the temperature of the slurry with which it used for grinding | polishing, and the time change of the 1st derivative and the 2nd derivative by the time of slurry temperature.

Hereinafter, the process leading to the present invention will be described in detail.
The inventors have eagerly sought for alternative means since the amount of polishing of the wafer based on the conventional torque change described above is insufficient.
First, the inventors generate frictional heat between the wafer and carrier plate and the polishing pad and reaction heat between the polishing slurry and the object to be polished (wafer) during polishing. In order to find the possibility that some temperature change of each part of the wafer polishing apparatus and the supply material is compatible, in particular, pay attention to the temperature of the polishing slurry and measure this, the polishing apparatus shown in FIGS. Prototype.

FIG. 1 is a schematic perspective view showing a prototype of a workpiece polishing apparatus. Moreover, FIG. 2 is an AA arrow view of FIG.
As shown in FIGS. 1 and 2, the double-side polishing apparatus 1 includes one or a plurality of, in the illustrated example, five carrier plates 4 each having a holding hole 3 for holding a wafer 2, and these carrier plates 4. A lower surface plate 5 to be placed and an upper surface plate 6 paired with the lower surface plate 5 are provided.
A polishing pad 7 is applied to the opposing surfaces of the upper and lower surface plates 5 and 6.
Further, the carrier plate 4 is rotatable. In the illustrated example, each carrier plate 4 can be rotated by the sun gear 8 and the internal gear 9.
The carrier plate 4 has one or more holding holes 3, one in the illustrated example, and the holding hole 3 is eccentric with respect to the center of the carrier plate 4 in the illustrated example.
Further, this polishing apparatus has a drainage tank 10 and a drainage channel 11 in the illustrated example, and the polishing slurry used for polishing moves radially outward by centrifugal force, and the drainage channel from this drainage tank 10 11 is discharged.
Furthermore, this polishing apparatus is provided with temperature measuring means 12 for measuring the temperature of the carrier plate 4. In the illustrated example, the temperature measuring means 12 is installed so as to measure the slurry flowing through the drainage channel 11.

  The inventors measured the temperature of the slurry that flowed to the discharge path 11 after polishing using the above-described double-side polishing apparatus. It has been found that the temperature change shown in FIG. 4 occurs with the change.

That is, as shown in FIG. 3, at the initial stage of polishing, the polishing pad 7 slides with respect to the wafer 2, whereby frictional heat starts to be generated, and reaction heat between the polishing slurry and the wafer 2 is also generated. To start, as shown in FIG. 4, the slurry temperature rises with the lapse of the polishing time in the initial stage of polishing (step 1).
Thereafter, as the wafer is polished, the area where the carrier plate 4 and the polishing pad 7 come into contact gradually increases due to the elasticity of the polishing pad 7, as shown in FIG. As a result, frictional heat generated by sliding between the carrier plate 4 and the polishing pad 7 increases. In particular, since the temperature change of the carrier plate 4 due to the frictional heat is significant, the temperature of the polishing slurry gradually increases as shown in FIG. 4 (step 2).
Further, as shown in FIG. 3, as the wafer 2 is polished, the carrier plate 4 and the polishing pad 7 are in contact with each other over almost the entire surface (initial stage 3). The wafer 2 is further polished in a state where the entire surface is in contact with each other, and the wafer 2 and the carrier plate 4 have the same thickness (fixed state) (step 3 final stage). Between the initial stage and the final stage of Step 3, as shown in FIG. 4, the temperature change rate of the polishing slurry is remarkably reduced. This is because the contact area of the carrier plate 4 is constant, and the temperature change of the carrier plate 4 that particularly affects the slurry temperature is small.
As shown in FIG. 3, when the polishing is further continued from the fixed size state, the temperature change rate of the slurry is changed as shown in FIG. 4 due to the temperature increase of the carrier plate 4 due to the wear of the carrier plate 4 in particular. Increase (step 4).
That is, the inventors have shown that the contact state between the polishing pad 7 and the carrier plate 4 changes with time due to the elasticity of the polishing pad 7, the carrier plate 4 has a characteristic that the temperature easily rises, The present inventors have newly found that the slurry temperature exhibits a unique time change due to circumstances peculiar to the double-side polishing method and apparatus for the workpiece such as a long time.

The inventors stopped the polishing process at regular intervals in the double-side polishing process, measured the wafer thickness after polishing at each time point stopped using a wafer thickness measuring device provided outside the double-side polishing apparatus, The slurry temperature was measured by the temperature measuring means, and the time change of the slurry temperature was measured.
As a result, as shown in FIG. 5, it was found that the temperature change rate of the slurry used for polishing changes in a fixed size state where the thickness of the wafer and the thickness of the carrier plate are the same.
In this way, the inventors have obtained the knowledge that it is possible to determine the point in time when the sizing state is reached by detecting the rate of change in the temperature change rate of the polishing slurry, and complete the present invention. It is what led to let it be.
In FIG. 5, Gap (μm) means a difference between the thickness of the wafer and the thickness of the carrier plate. More specifically, it means the difference between the thickness of the wafer center and the height of the hole inner edge of the carrier plate loaded with the wafer.

FIG. 6 is a schematic perspective view of a double-side polishing apparatus according to one embodiment of the present invention.
The apparatus shown in FIG. 6 is further provided with means 13 for controlling the polishing amount of the wafer based on the change of the time change rate of the measured temperature of the polishing slurry in addition to the apparatus configuration shown in FIGS.
The apparatus shown in FIG. 6 is used to hold the wafer 2 on the carrier plate 4 having the holding holes 3 for holding the wafer 2 and supply the polishing slurry, and the upper surface plate 6 and the lower surface plate to which the polishing pad 7 is attached. By rotating the carrier plate 4 between the boards 5, the front and back surfaces of the wafer 2 can be polished simultaneously.
Not only the carrier plate 4 but also the upper and lower surface plates 5 and 6 can be rotated. In this case, the upper and lower surface plates 5 and 6 are rotated in opposite directions.
The type of the polishing slurry is not particularly limited, and colloidal silica having a particle size of about 0.5 to 2.0 μm can be used.
In the double-side polishing, the temperature of the polishing slurry (exhaust slurry) subjected to polishing can be measured by the temperature measuring means 12, and the change in the measured temperature change rate of the polishing slurry can be detected.
As the temperature measuring means 12, for example, a thermometer using an infrared sensor, a resistance thermometer, a thermocouple, or the like can be used, such as above the drainage tank 10 or the drainage channel 11, immediately after being subjected to polishing. It is preferable to install at a position where the slurry temperature can be measured.
Thereby, the change in the temperature change rate of the polishing slurry can be captured, and the polishing state can be determined as follows.
For example, the polishing rate can be determined by calculating the rate of change of the polishing slurry temperature with time and the rate of change of the rate of change with time (ratio of slurry temperature change rate).
Specifically, the first derivative and the second derivative according to the time of the temperature change of the slurry are calculated, and the time when the second derivative value exceeds the set upper limit threshold can be determined as the sizing state.
Here, the primary differentiation is obtained by calculating a temperature change amount, for example, at a time interval of 1 second using a calculation means, and dividing the change amount by the time interval.
The second derivative is obtained, for example, by calculating a change amount of the temperature change rate at a time interval of 1 second using a calculating means and dividing the change amount of the temperature change rate by the time interval.
When the point at which the second derivative value obtained as described above is 0.00001 ° C./s ² or more, for example, is detected, the wafer thickness is equal to the carrier plate thickness and the carrier plate thickness is equal. It can be judged.
If it is determined that the temperature change rate of the slurry has changed to a fixed size, the polishing amount of the wafer is controlled by determining the end or continuation of polishing according to the required wafer shape. be able to.
For example, when polishing is finished in a fixed size state, the polishing device control unit 13 stops the polishing device 1 when a change in the temperature change rate of the slurry, which should be determined to have reached the fixed size state, is detected. Thus, polishing can be completed.
Note that the temperature change rate of the slurry and the time change rate of the change rate may be calculated by the control unit 13 based on the temperature measured by the temperature measurement unit 12 or may be calculated in the temperature measurement unit 12. You may calculate by providing. Further, another calculation means may be interposed between the temperature measurement means 12 and the control means 13.

Therefore, according to the present invention, the amount of polishing can be accurately controlled in-line in double-side polishing of a wafer, and a semiconductor wafer with a high flatness having a shape as required can be manufactured. In addition, accurate control of the polishing amount eliminates the need for re-polishing due to insufficient polishing and improves the productivity in the wafer manufacturing process. Furthermore, since the expected amount of wear is not exceeded, it is possible to prevent the occurrence of wafer defects and the wear of the carrier plate.
In addition, since the polishing amount can be controlled independently of the past polishing results, there is no error due to the deterioration of the secondary material over time.
In addition, since the polishing amount is controlled based on the change in the temperature change rate of the slurry, not the slurry temperature itself or the change in the slurry temperature, no special selection or adjustment is required for the components or supply materials of the apparatus. .

  Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited thereto.

In order to confirm that the amount of polishing of the wafer can be accurately controlled according to the present invention, the apparatus shown in FIG. 6 was used to polish the wafer and measure the temperature of the polishing slurry used for polishing.
A 300 mm diameter, crystal orientation (100), p-type silicon wafer was used as a wafer to be polished.
As the carrier plate, a glass fiber reinforced plastic (GFRP) plate in which glass fibers are compounded with an epoxy resin having an initial thickness of 775 μm was used.
In the apparatus shown in FIG. 6, the polishing pad used was urethane foam polishing cloth MHN15 manufactured by Nita Haas, and Nalco 2350 manufactured by Nitta Haas was used as the polishing slurry. The upper and lower surface plates were rotated in opposite directions, the carrier plate was rotated in the same direction as the upper surface plate, and the wafer surface loaded in the carrier plate was polished.
As the temperature sensor, E52-P6D manufactured by OMRON Corporation was used.

Regarding the time change of the measured temperature of the polishing slurry, in order to detect the time change rate and the time change rate of the change rate, the calculation means capable of performing the calculation described below is the temperature measurement means and the polishing apparatus control means. And used in between.
<Detection method of change in polishing slurry temperature with time>
With respect to the slurry temperature measured by the temperature measuring means, the time derivative of the temperature was calculated for each of the first and second derivatives by this computing means.
In this test, the first derivative and the second derivative were obtained by the difference method. That is, the first derivative at a certain time t is obtained by dividing the amount of change in temperature in the time range of the time t ± 1 seconds by the time range, and the second derivative at a certain time t is the time t ± 1. The amount of change in the value of the first derivative in the time range of seconds was obtained by dividing by the time range.
First, the minimum value was obtained for the time change (first derivative) of the temperature. The minimum value was defined as the value of the first derivative at the time when the sign of the second derivative changed from negative to positive.
Next, the threshold value of the second derivative is set to 0.9 × 10 ⁻⁵ (° ^{C./s 2} ), and after the first derivative reaches the minimum value, the time when the second derivative exceeds this threshold is determined to be a fixed size. The position was determined to be in a state and polishing was finished.

As shown in FIG. 7, the time point when this threshold value was reached was detected, and at that time point, polishing was terminated by the polishing device control means.
The thickness of the wafer center after polishing was measured using Wafersight, and the hole inner edge height of the carrier plate was measured using a micrometer. The thickness of the wafer was 775.11 μm, and the thickness of the carrier plate Was 775 μm and Gap was 0.11 μm, and the polishing could be finished in a substantially constant size state.

1 Double-side polishing machine 2 Workpiece (wafer)
3 Holding hole 4 Carrier plate 5 Lower surface plate 6 Upper surface plate 7 Polishing pad 8 Sun gear 9 Internal gear 10 Drain tank 11 Drain channel 12 Temperature measuring means 13 Polishing device control means

Claims (2)

By holding the work on a carrier plate having one or more holding holes for holding the work and supplying the polishing slurry, by rotating the carrier plate between the upper surface plate and the lower surface plate to which the polishing pad is attached, In the method of simultaneously polishing the front and back surfaces of the workpiece,
Measure the temperature of the polishing slurry in the drainage tank or drainage channel subjected to polishing, calculate the measured temperature change rate of the polishing slurry and the change rate of the temperature change rate,
When the rate of change of the temperature change rate is equal to or greater than a predetermined value, it is determined that the thickness of the workpiece and the thickness of the carrier plate are equal, and the end or continuation of polishing is determined, A method for polishing a workpiece, wherein the polishing amount of the workpiece is controlled . A rotatable carrier plate in which one or more holding holes for holding a workpiece to be polished are formed, a lower surface plate on which the carrier plate is placed, an upper surface plate paired with the lower surface plate, and a drainage tank And an apparatus for polishing both surfaces of a workpiece, including a drainage channel ,
Means for measuring the temperature of the polishing slurry in the drainage tank or the drainage channel after polishing;
Means for calculating the measured temperature change rate of the polishing slurry and the change rate of the temperature change rate;
When the rate of change of the temperature change rate is equal to or greater than a predetermined value, it is determined that the thickness of the workpiece and the thickness of the carrier plate are equal, and the end or continuation of polishing is determined, Means for controlling the polishing apparatus;
An apparatus for polishing a workpiece, further comprising:

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