JP4955624B2 - Double-side polishing equipment - Google Patents

Description

  The present invention relates to a double-side polishing apparatus, and more particularly to a double-side polishing apparatus capable of efficiently manufacturing a semiconductor wafer having high flatness.

  As an example of a conventional wafer manufacturing method, a silicon wafer manufacturing method will be described. For example, first, a silicon single crystal ingot is grown by the Czochralski method (CZ method) and the obtained silicon single crystal ingot is sliced. Then, after the silicon wafer is manufactured, each process such as chamfering, lapping, etching and the like is sequentially performed on the silicon wafer, and then a polishing process for mirroring at least one main surface of the wafer is performed.

In this wafer polishing step, for example, when polishing both sides of a silicon wafer, a double-side polishing apparatus may be used.
As such a double-side polishing apparatus, a so-called 4-way double-side polishing apparatus having a planetary gear structure in which a carrier for holding a wafer is disposed between a sun gear at a central portion and an internal gear at an outer peripheral portion is usually used. ing.

  This 4-way double-side polishing machine inserts and holds a silicon wafer into a plurality of carriers in which wafer holding holes are formed, and polishes on the opposite surface of the wafer while supplying polishing slurry from above the held silicon wafer. The upper and lower surface plates with cloth attached are pressed against the front and back surfaces of each wafer and rotated in the relative direction. Simultaneously, the carrier is rotated and revolved by the sun gear and the internal gear, so that both sides of the silicon wafer are simultaneously It can be polished.

However, even when polishing is performed using the above-described double-side polishing apparatus, the polishing rate of the wafer varies every time polishing is performed due to deterioration of a processing jig such as a polishing cloth and a carrier and a material. For this reason, when polishing is performed with the polishing time fixed, there is a problem in that the thickness of the wafer after polishing due to the difference in polishing rate differs.
Thus, a double-side polishing apparatus that performs polishing while measuring the thickness of the wafer being polished is disclosed.

For example, as in the inventions described in Patent Documents 1 and 2, there is one that performs polishing while measuring the thickness of a semiconductor wafer that is being polished by using a light reflection interference method. The property can be made high.
Further, for example, according to the invention of Patent Document 1, the thickness of the semiconductor wafer is measured while forming the focal point by moving the measuring light beam along the thickness direction from the front surface to the back surface of the semiconductor wafer using light having a wavelength that passes through the wafer. Can be measured.

However, in the technique described in Patent Document 1, since the focal point is formed along the thickness, it is easily affected by the vibration of the wafer being polished, and the deviation between the actual wafer thickness and the measured value increases. Furthermore, it is easily affected by the attenuation of light depending on the distance from the object to be measured, and it is necessary to make the distance between the focal point and the incident / incident point closer. For this reason, there has been a problem that it is soiled by mist or the like due to polishing slurry in the optical path.
Further, in order to increase the measurement accuracy, it has been necessary to increase the frequency at which the measurement light takes in the measurement light from the specified region of the polishing surface during polishing. However, the confocal system as in Patent Document 1 has the disadvantages of poor response and low capture frequency.

JP 2002-59364 A JP 7-4921 A

  The present invention has been made in view of the above problems, and in a double-side polishing apparatus capable of performing polishing while measuring the thickness of the wafer, is affected by measurement errors represented by vibration of the wafer being polished. An object of the present invention is to provide a double-side polishing apparatus capable of polishing while measuring the thickness of the wafer with high accuracy.

In order to solve the above-described problems, in the present invention, at least a lower surface plate having a flat polishing upper surface that is rotationally driven, an upper surface plate having a flat polishing lower surface that is disposed opposite to the lower surface plate and is rotationally driven, and a wafer And a carrier having a wafer holding hole for holding a plurality of holes provided between a rotation center and a peripheral edge of the upper surface plate or the lower surface plate, and a plurality of holes formed from the plurality of holes. A wafer thickness measuring mechanism that measures the thickness in real time during polishing, and the wafer thickness measuring mechanism is fixed to a fixed end that is not the upper surface plate or the lower surface plate of the polishing apparatus. There is provided a double-side polishing apparatus characterized by that .

As described above, in the double-side polishing apparatus capable of simultaneously polishing both surfaces of the wafer, the thickness measurement frequency is increased by providing a plurality of holes for measuring the thickness of the wafer in the upper surface plate or the lower surface plate. Measurement accuracy can be improved. In particular, in a batch type polishing machine that polishes a plurality of wafers simultaneously, the wafer thickness can be measured simultaneously from the plurality of holes, which can contribute particularly to improvement in measurement accuracy.
In addition, by fixing the wafer thickness measurement mechanism to a location other than the upper or lower surface plate that is susceptible to vibration during polishing, the wafer thickness can be measured without being affected by vibration. And the thickness measurement accuracy can be improved.
Because of these effects, the thickness of the wafer being polished can be accurately known in real time, and thus a double-side polishing apparatus that can easily make the thickness of the polished wafer to a target thickness can be obtained. .

The wafer thickness measuring mechanism preferably includes a tunable infrared laser device having a wavelength that is optically transmitted to the wafer .
As described above, by using a wavelength tunable infrared laser device having a wavelength optically transmitted to the wafer as a wafer thickness measuring mechanism, the reflection spectrum on the wafer surface (the interference of light reflected on the wafer front surface and the back surface). The state of the wafer during polishing can be measured with high accuracy.

The laser light preferably has a wavelength of 1575 to 1775 nm .
As described above, if a high-speed infrared laser having a wavelength of 1575 to 1775 nm is used as a laser beam for measurement, the time resolution can be increased, and the thickness of the wafer being polished can be increased with high accuracy. Can be evaluated.

Further, it is preferable that the wafer thickness measuring mechanism measures a bulk thickness of the wafer .
Thus, by measuring the bulk thickness of the wafer, the actual thickness of the wafer being polished can be determined, thereby making the thickness of the polished wafer closer to the target. it can.

The plurality of holes are preferably provided at equal intervals around the upper surface plate .
As described above, by providing a plurality of holes at equal intervals, the thickness of the wafer can be easily measured, so that high-precision polishing is possible. By providing it in the periphery, the thickness of all held wafers can be measured during polishing in a four-way double-side polishing apparatus, for example, without adversely affecting polishing. Moreover, since it can suppress that the grinding | polishing slurry leaks from a hole by providing in an upper surface plate, the maintenance of a surface plate can be made easy. Further, it is possible to suppress the possibility of trouble in measuring the thickness of the wafer.

The fixed end to which the wafer thickness measuring mechanism is fixed is preferably a housing of the double-side polishing apparatus .
In this way, by fixing the wafer thickness measuring mechanism to the housing of the double-side polishing apparatus, the wafer thickness measuring mechanism is protected from vibration and dirt, and the wafer thickness is detected from the plurality of holes with high accuracy. be able to. Thereby, the influence of noise can be reduced, so that the thickness of the wafer being polished can be measured with higher accuracy.

  As described above, according to the present invention, in a double-side polishing apparatus that can perform polishing while measuring the thickness of a wafer, without being affected by measurement errors typified by vibration of the wafer being polished, Provided is a double-side polishing apparatus capable of performing polishing while measuring the thickness of a wafer with high accuracy.

Hereinafter, the present invention will be described in detail with reference to the drawings, but the present invention is not limited thereto.
As shown in FIG. 1, the double-side polishing apparatus 10 of the present invention has a lower surface plate 12 having a flat polishing upper surface 12 a that is rotationally driven to sandwich the wafer W, and is disposed opposite to the lower surface plate 12 and rotated. An upper surface plate 11 having a flat polishing lower surface 11a to be driven, a carrier 13 having a wafer holding hole for holding the wafer W, and a wafer thickness measuring mechanism 16 for measuring the thickness of the wafer W being polished. It is to be prepared.
A plurality of holes 14 and a polishing slurry supply mechanism 15 are provided on the upper surface plate 11 side in order to measure the thickness of the wafer being polished.

  The wafer thickness measuring mechanism 16 includes, for example, at least an optical unit 16a that irradiates the wafer W with laser light, a photodetector 16b that detects the laser light reflected from the wafer W, a laser light source unit 16c, and a detected laser. An arithmetic / control unit 16d for calculating the wafer thickness from light can be provided.

In this way, by fixing the wafer thickness measurement mechanism to a place (fixed end) other than the upper or lower surface plate that is susceptible to vibration during polishing, unnecessary data such as noise is included in the measured raw data. It can be prevented from being placed. For this reason, the accuracy of the measurement data can be greatly improved as compared with the conventional case, that is, the accurate thickness of the wafer can be measured.
Moreover, the frequency of thickness measurement can be increased by providing a plurality of holes for measuring the thickness of the wafer in the upper surface plate or the lower surface plate. In particular, it is suitable for batch polishing of a plurality of wafers at the same time, whereby the measurement accuracy can be improved.
Because of these effects, the thickness of the wafer being polished can be known more accurately than in the past, so the double-side polishing apparatus can easily make the polished wafer thickness close to the target thickness can do.

Here, the fixed end to which the wafer thickness measuring mechanism 16 is fixed can be the housing 18 of the double-side polishing apparatus.
As described above, when the wafer thickness measuring mechanism is fixed to the housing of the double-side polishing apparatus, the wafer thickness measuring mechanism can be protected from vibration and dirt. According to this, it is possible to suppress noise from being added to the thickness measurement data being polished and deterioration of the data. Therefore, the thickness of the wafer being polished can be measured with higher accuracy. Of course, it may be installed at a fixed end such as the ceiling of the building, but it is disadvantageous in terms of maintenance, vibration of the apparatus, and the like.

Further, the wafer thickness measuring mechanism 16 can measure the bulk thickness of the wafer.
If the wafer thickness measured by the wafer thickness measurement mechanism is the bulk thickness, the actual thickness of the wafer being polished will be measured, and therefore the thickness of the polished wafer will be closer to the target. It can be. Of course, the thickness of the SOI layer of the SOI wafer may be used.

Further, the wafer thickness measuring mechanism 16 can include a wavelength tunable infrared laser device having a wavelength that is optically transmitted to the wafer.
Thus, as a wafer thickness measurement mechanism, when using a wavelength variable infrared laser device having a wavelength that is optically transmitted to the wafer, the surface reflected light reflected on the wafer surface of the laser light incident on the wafer, It is possible to analyze how the back surface reflected light reflected on the back surface of the wafer interferes. According to this, the thickness of the wafer being polished can be evaluated with an accuracy of the order of several nm to several tens of μm.
Moreover, even if the thickness of the wafer to be polished changes greatly by using a tunable infrared laser device, it can be coped with by changing the wavelength of the incident laser light, and there is no need to change the light source itself. . For this reason, cost can be reduced.

And the wavelength of a laser beam can be 1575-1775 nm.
As described above, if the laser light has a wavelength of 1575 to 1775 nm, it is possible to suppress a decrease in the intensity of the reflected laser light due to part of the measurement laser light being absorbed by the wafer or the polishing slurry. Can be measured.

A plurality of holes 14 may be provided with equally spaced around the upper platen 1 1.
Thus, if the upper surface plate is provided with a plurality of holes at equal intervals, it is possible to suppress the occurrence of leakage of the polishing slurry from each of the plurality of measurement holes. For this reason, the maintenance of a surface plate can be performed easily. Further, it is possible to suppress the possibility of trouble in measuring the thickness of the wafer. For example, in a 4-way double-side polishing apparatus, it is convenient to measure the thickness of all wafers.

Further, when it is desired to change at least one of the polishing load, the rotation speed of the upper surface plate 11 and the rotation speed of the lower surface plate 12 during polishing, a double-side polishing apparatus 10 is equipped with a polishing machine control unit 17 as shown in the figure. Thus, the upper surface plate 11 and the lower surface plate 12 can be controlled. Accordingly, at least one of the polishing load, the rotational speed of the upper surface plate 11 and the rotational speed of the lower surface plate 12 can be changed.
According to this, during polishing of the wafer, it is possible to appropriately cope with a change in polishing conditions due to polishing cloth, a processing jig such as a carrier, which is determined from the measured wafer thickness, and material deterioration. Therefore, it is possible to stably obtain a wafer having a very high flatness of the surface after polishing.

  A method for polishing a wafer using such a double-side polishing apparatus will be described below, but the present invention is not limited to this.

First, the wafer W to be polished is set in the wafer holding hole of the carrier 13. At this time, a plurality of wafers W can be set.
The upper surface plate 11 and the lower surface plate 11 are sandwiched between the polishing lower surface 11 a of the upper surface plate 11, the upper surface 12 a of the lower surface plate 12 and the carrier 13, and the polishing slurry is supplied by the polishing slurry supply mechanism 15. Polishing is started while rotating 12 in a horizontal plane.

  At this time, the wafer W is fixed to a fixed end at a position different from the upper surface plate 11 or the lower surface plate 12 through a plurality of holes 14 provided in the upper surface plate 11 or the lower surface plate 12. Polishing is performed while measuring by the thickness measuring mechanism 16.

According to the method of polishing a wafer using such a double-side polishing apparatus, it is possible to know the state of the polished surface of the wafer without interrupting polishing, for example, it is possible to know the thickness of the wafer being polished at any time, Whether the target thickness of the wafer has been reached can be judged while polishing. Therefore, it is possible to determine whether or not the target thickness has been reached without interrupting the polishing, and the time required for polishing can be shortened.
Further, since the wafer can be set to the target thickness without fixing the polishing time, excessive or insufficient polishing does not occur, and deterioration of flatness can be suppressed.

EXAMPLES Hereinafter, although an Example and a comparative example are shown and this invention is demonstrated more concretely, this invention is not limited to these.
(Example)
Using a double-side polishing apparatus as shown in FIG. 1, the wafer was polished in a batch system (15 batches). At this time, the target value of the thickness of the polished wafer was set to 777 μm.
As a wafer to be polished, 600 p ^- type silicon single crystal wafers having a diameter of 300 mm were prepared by slicing and cutting with a wire saw from an ingot grown by the CZ method, and then chamfering, lapping and etching. This p ^- type is a p-type high resistivity wafer.
As a wafer thickness measurement mechanism, a mechanism equipped with an optical unit using a wavelength tunable infrared laser device that can tune the wavelength of laser light to 1575 to 1775 nm is prepared. Using such a wafer thickness measurement mechanism, the wafer thickness is measured. While measuring the thickness, 300 of 600 wafers were polished, and the thickness of the polished wafer was evaluated by AFS (capacitance flatness measuring device manufactured by ADE).

(Comparative example)
Using the same double-side polishing apparatus as in the example, the remaining 300 wafers were polished. However, in the comparative example, polishing was performed without operating the wafer thickness measuring mechanism. The polishing time was fixed.

FIG. 2 shows the relative frequency and cumulative relative frequency of the wafer thickness after polishing 300 wafers polished by the double-side polishing apparatus of the example and the comparative example.
It was found that the wafer polished by the double-side polishing apparatus of the example had a smaller variation in average finished thickness after polishing than the wafer of the comparative example, and was reduced by about 50%.
In addition, it was found that the double-side polishing apparatus of the example could achieve an accuracy with a standard deviation of 0.1 μm or less.

  Further, as shown in FIG. 3, the wafer polished by the double-side polishing apparatus of the example had a stable wafer thickness after polishing, whereas the wafer of the comparative example had large variations and was not stable. .

  The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and the present invention has any configuration that has substantially the same configuration as the technical idea described in the claims of the present invention and that exhibits the same effects. Are included in the technical scope.

It is the schematic which showed an example of the double-side polish apparatus of this invention. It is the graph which showed the relative frequency of the thickness after grinding | polishing each 300 wafers polished with the double-side polish apparatus of the Example and the comparative example, and a cumulative relative frequency. It is the graph which showed the thickness variation after grinding | polishing of the wafer grind | polished with the double-side polish apparatus of an Example and a comparative example.

Explanation of symbols

10: Double-side polishing device,
DESCRIPTION OF SYMBOLS 11 ... Upper surface plate, 11a ... Polishing lower surface, 12 ... Lower surface plate, 12a ... Polishing upper surface, 13 ... Carrier, 14 ... Multiple holes, 15 ... Slurry supply mechanism,
16 ... Wafer thickness measurement mechanism, 16a ... Optical unit, 16b ... Photo detector, 16c ... Laser light source unit, 16d ... Calculation / control mechanism,
17 ... polishing machine control unit, 18 ... housing,
W: Wafer.

Claims (2)

At least a lower surface plate having a flat polishing upper surface to be driven to rotate, an upper surface plate having a flat lower surface to be driven to rotate disposed opposite to the lower surface plate, and a carrier having a wafer holding hole for holding a silicon wafer; In a double-side polishing apparatus comprising:
A plurality of holes provided at equal intervals around the rotation center and peripheral edge of the upper surface plate;
A wafer thickness measuring mechanism that measures the thickness of the silicon wafer from the plurality of holes in real time during polishing;
The wafer thickness measurement mechanism is fixed to a fixed end of the polishing apparatus that is not the upper surface plate and the lower surface plate, and optically transmits to the silicon wafer using light reflection interferometry at 1575 to 1775 nm. A double-side polishing apparatus characterized by comprising a tunable infrared laser apparatus having a wavelength of 5 to measure the bulk thickness of the silicon wafer. The double-side polishing apparatus according to claim 1, wherein the fixed end to which the wafer thickness measuring mechanism is fixed is a housing of the double-side polishing apparatus.

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