JP4654275B2 - 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 that can efficiently polish a semiconductor wafer having high flatness at low cost.

  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 is performed to mirror at least one main surface of the wafer.

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 applied are pressed against the front and back surfaces of each wafer and rotated in a 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, polishing is performed while measuring the thickness of a semiconductor wafer being polished by using a light reflection interference method.
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.

JP 2002-59364 A JP 7-4921 A Patent 3327817

  In a double-side polishing machine that performs polishing while measuring the thickness of the wafer being polished by optical reflection interferometry in real time as described above, a hole is made on the polishing platen at the position overlapping the hole for the optical path. Attached to the polishing surface plate as a window material by attaching a material that is optically transparent to the polishing cloth, does not damage the polished object, such as scratches, and is not easily violated by slurry such as abrasives. Used as a polishing cloth.

With such a polishing apparatus, the thickness during polishing of the wafer was measured by the reflection interference method through this window material, and the polishing was automatically stopped when the target thickness was reached.
For example, in the invention described in Patent Document 2, a window is provided on the non-polished surface side of the wafer, and light having a wavelength that passes through the wafer is used as measurement light. The invention described in Patent Document 3 uses a window material or a plug integrated with a polishing cloth on the upper surface of the lower surface plate in contact with the polishing surface side of the film-coated wafer as a wafer thickness measurement window. is doing.

However, in the invention described in the patent document as described above, since the polishing cloth and the window material are integrated, it is necessary to replace the polishing cloth only by destroying the window material. In addition, the window material is more consumed than the abrasive cloth is consumed, and the window material reaches the end of its life before the end of the life of the polishing cloth, both of which are discarded, resulting in a lot of waste.
Further, as seen in the invention described in Patent Document 3, since the window is located on the polishing surface side of the object to be polished, that is, on the upper side of the surface plate, and the optical path system is on the vertical lower side, the confidentiality of the window material is reduced. In order to increase it, it was necessary to use a strong sealing material plug. For this reason, the replacement is not easy, the maintenance takes time, and the efficiency is lowered.

  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 a wafer being polished, has little waste, low running cost, and maintenance. An object of the present invention is to provide a double-side polishing apparatus capable of performing polishing while measuring the thickness of a 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 In the double-side polishing apparatus provided with a carrier having a wafer holding hole for holding a plurality of holes provided between a rotation center and a peripheral edge of the surface plate, the upper surface plate or the lower surface plate, The polishing surface of the upper and lower surface plate has a polishing cloth having a hole having a diameter larger than the hole at a position corresponding to the plurality of holes, and a diameter larger than the hole and smaller than the hole of the polishing cloth than the polishing cloth. A thin window material, and further includes a wafer thickness measurement mechanism that measures the thickness of the wafer in real time during polishing from the plurality of holes. Separated from the polishing cloth, Providing a double-sided polishing apparatus characterized by a serial on the platen or the lower platen those fixed through an adhesive layer.

Thus, on the polishing surface of the upper or lower surface plate provided with a plurality of holes for measuring the thickness of the wafer, a polishing cloth having a hole having a diameter larger than the hole at a position corresponding to the hole, and a hole It is assumed that a window material that is larger in diameter and smaller in diameter than the hole in the polishing cloth and thinner than the polishing cloth is attached.
With such a structure, the window material and the polishing cloth can be separated and bonded separately. Therefore, when the window material is destroyed, it is possible to eliminate the need to dispose of the polishing cloth that has not reached the end of its life by peeling and replacing only the window material. In addition, since only the window material that is heavily consumed can be replaced, the cost for disposal of the waste can be reduced, and the running cost can be reduced.
Further, since the window material and the polishing cloth are independent, maintenance is easy. Further, since only the window material can be replaced, if the measurement of the thickness of the wafer being polished begins to be hindered due to the lifetime of the window material, only the window material can be replaced without changing the polishing cloth. For this reason, it is possible to provide a double-side polishing machine capable of reducing the waste and polishing the wafer while measuring the thickness with high accuracy. In the present invention, since a plurality of holes are required, and thus a plurality of window materials are necessary, and thickness measurement is accurately performed, the window material and the polishing cloth are separated as described above. Therefore, it is highly necessary to set the life individually.
In addition, by providing a wafer thickness measurement mechanism that can measure the thickness of the wafer being polished in real time, it is possible to know the wafer thickness being polished at any time. It can be judged while polishing. Therefore, it is possible to obtain a wafer having high flatness without causing excess or deficiency of the wafer polishing amount or thickness.

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 higher accuracy.

Moreover, it is preferable that the said window material is an optically transparent thing with respect to the laser beam which the said wavelength tunable infrared laser apparatus emits .
In this way, if the window material is optically transmissive to the laser light, the absorption and reflection of the laser light at the window material can be suppressed, so that the intensity of the measurement laser light is prevented from being attenuated. can do. Thereby, the measurement accuracy of the wafer can be further increased.

The window material is preferably made of plastic .
Thus, by using an inexpensive plastic having excellent stability as the window material, it is possible to reduce the replacement frequency of the window material, and to reduce the labor and cost required for the replacement.

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, it is possible to monitor the actual thickness of the wafer being polished, thereby making the thickness of the polished wafer closer to the target. it can.

In the double-side polishing apparatus according to the present invention, the thickness of the window material is t _w [μm], the refractive index is n _w , the thickness of the adhesive layer is t ₂ [μm], and the thickness of the wafer is t _s [μm], refractive index is n _s , thickness of the polishing cloth is t ₁ [μm], compressibility is ζ ₁ [% / g / cm ² ], and maximum polishing load is P [g / cm ² ]. When a _{t 1 × ζ 1 × P /} 100> t w + t 2, and it is preferable to satisfy the relation of _{t w n w> t s n} s or _{t w n w <t s n} s .
In this way, if the relationship of t ₁ × ζ ₁ × P / 100> t _w + t ₂ is satisfied, the window material can be prevented from protruding from the polishing cloth during polishing. It can suppress that the flatness of a wafer deteriorates in a part.
_Further, as long as it satisfies the relation of _{t w n w> t s n} s or _{t w n w <t s n} s, for example, in the case of using a laser beam to measure the thickness of the wafer, the window material It is possible to prevent the measurement accuracy from being deteriorated due to the fact that the reflected light and the peak of the reflected light from the wafer overlap and become difficult to measure.
By these, it becomes easier to make a wafer with high flatness while measuring the thickness of the wafer with high accuracy.

The plurality of holes are preferably provided at equal intervals around the upper surface plate .
Thus, by providing a plurality of holes at equal intervals, even when batch polishing a plurality of wafers at the same time, it is possible to easily measure the thickness of all the wafers. Accurate polishing is possible. In addition, by providing the upper surface plate, it is not necessary to take special measures against the abrasive slurry leakage in the window material, and it is possible to suppress the occurrence of abrasive slurry leakage from the hole, so that maintenance of the surface plate can be performed. It can be easy. Further, it is possible to suppress the possibility of trouble in measuring the thickness of the wafer.

  As described above, according to the present invention, in the double-side polishing apparatus that can perform polishing while measuring the thickness of the wafer being polished, there is little waste, the running cost is low, and maintenance is easy. 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 FIGS. 1, 2, and 3. However, the present invention is not limited to these.
FIG. 1 is a schematic view showing an example of the double-side polishing apparatus of the present invention. Moreover, FIG. 2 is the figure which showed the mode that the outline of the window material of this invention, and this window material was affixed on the upper surface plate.

The double-side polishing apparatus 10 of the present invention includes at least a lower surface plate 12 having a flat polishing upper surface 12a that is rotationally driven, and an upper surface plate 11 having a flat polishing lower surface 11a that is disposed opposite to the lower surface plate 12 and is rotationally driven. A carrier 13 having a wafer holding hole for holding the wafer W, a plurality of holes 14 provided in the upper surface plate 11, and a thickness for measuring the thickness of the wafer W from the plurality of holes 14 in real time during polishing. A wafer thickness measuring mechanism 16 and a polishing slurry supply mechanism 15 for supplying polishing slurry are provided.
A polishing cloth 11b having holes larger in diameter than the holes 14 is attached to the polishing surface of the upper surface plate 11 at positions corresponding to the plurality of holes 14, and a polishing cloth 12b is attached to the polishing surface of the lower surface plate 12. Yes. Further, a window material 17 having a diameter larger than that of the plurality of holes 14 and smaller than that of the polishing cloth 11b and thinner than that of the polishing cloth 11b is bonded to the polishing surface side of the plurality of holes 14 via an adhesive layer 18. ing. Further, the window member 17 is separated from the polishing pad 11 b and is fixed to the upper surface plate 11 via an adhesive layer 18.

  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.

Thus, since the double-side polishing apparatus of the present invention has a structure in which the window material and the polishing cloth are separated, it is not necessary to discard the polishing cloth that has not reached the end of life by replacing only the discarded window material, and the polishing cloth The replacement frequency can be greatly reduced. For this reason, the waste of the polishing cloth can be greatly reduced. In particular, since a plurality of holes and windows for measuring the wafer thickness are provided as in the present invention for accurate measurement, this requirement is strong.
Moreover, since it is a structure which can affix only a window material to a surface plate, replacement | exchange is easy and a maintenance can also be performed easily.
Furthermore, by measuring the thickness of the wafer being polished by the wafer thickness measuring mechanism, polishing can be stopped when the thickness of the wafer being polished reaches the target, The occurrence of surface roughness can be prevented, and a flat wafer can be obtained.

Here, as the adhesive layer 18, it is desirable to use a double-sided tape.
If it is a double-sided tape, a window material can be attached easily and is inexpensive. Furthermore, when an optical system is used as the wafer thickness measuring mechanism, the double-sided tape is thin and has little unevenness, so the variation in mounting angle is so small that it can be ignored. .

Further, as shown in FIG. 3 showing a view of the upper surface plate 11 and the carrier 13 as viewed from the polishing surface side, the plurality of holes 14 may be provided at equal intervals around the upper surface plate. it can.
In this way, by providing a plurality of holes in the upper surface plate, the window material is also fixed to the upper surface plate, so that measures such as slurry leakage are unnecessary, and the scattered polishing slurry can be removed when replacing the window material. It can be easily washed with water or the like, and maintenance becomes easy.

  Furthermore, the wafer thickness measuring mechanism 16 maintains a distance that allows a person to work safely in the vertical direction from above the upper surface plate 11 or from the lower surface plate 12 of the double-side polishing device 10, and is different from the main body of the double-side polishing device 10. It is desirable to fix to the fixed end. In this way, if the wafer thickness measurement mechanism is not rotated with the upper or lower surface plate, it can be made less susceptible to vibrations from the upper and lower surface plates, thereby enabling highly accurate wafer thickness measurement. It can be carried out. Furthermore, the contamination by the polishing slurry can be reduced by taking a certain distance.

Here, the wafer thickness measuring mechanism 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.

Further, the wafer thickness measuring mechanism 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 measured with an accuracy of the order of several nanometers to several tens of micrometers.
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.

Further, the window material can be optically transmissive to laser light emitted from the wavelength tunable infrared laser device.
Thus, by making the window material optically transmit the laser beam, it is possible to suppress the attenuation of the intensity of the measurement laser beam due to the absorption and reflection of the laser beam at the window material. Thereby, the thickness of the wafer can be measured with higher accuracy.

The window material can be made of plastic. Here, the plastic window material includes a film made of plastic.
Thus, since the plastic window material is excellent in stability, the replacement frequency of the window material can be reduced. Moreover, since it is cheap, the cost for replacement can be reduced.

Here, the thickness of the window material is t _w [μm], the refractive index is n _w , the thickness of the adhesive layer is t ₂ [μm], the thickness of the wafer is t _s [μm], the refractive index is n _s , When the thickness of the polishing cloth is t ₁ [μm], the compressibility is ζ ₁ [% / g / cm ² ], and the maximum polishing load is P [g / cm ² ], t ₁ × ζ ₁ × P / 100> t _w a + _{t 2,} and can be made to satisfy the relation of _{t w n w> t s n} s or _{t w n w <t s n} s.
Thus, by satisfying the relationship of t ₁ × ζ ₁ × P / 100> t _w + t ₂ , it is possible to suppress the window material from protruding from the polishing cloth in the thickness direction during polishing. It can suppress that the flatness of a wafer deteriorates in the window material part. Therefore, it is possible to obtain a wafer with more excellent flatness.
_Further, by satisfying the relationship of _{t w n w> t s n} s or _{t w n w <t s n} s, for example, in the case of using a laser beam to measure the thickness of the wafer, the reflection on the window material It is possible to prevent the detection intensity from being lowered due to overlap of light and the peak of reflected light from the wafer. For this reason, the wafer thickness can be measured with higher accuracy.

  A wafer polishing method using such a double-side polishing apparatus will be briefly described below, but 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, polishing is performed while the thickness of the wafer W is measured by the wafer thickness measuring mechanism 16 from the plurality of holes 14 provided in the upper surface plate 11 or the lower surface plate 12.

  According to the wafer polishing method using such a double-side polishing apparatus, the state of the polished surface of the wafer can be known with high accuracy without interrupting polishing. Therefore, it can be determined while polishing whether the target thickness of the wafer has been reached. In particular, since the measurement is performed from a plurality of holes, the thickness of all the wafers can be accurately measured even in a batch system in which a plurality of wafers are polished simultaneously. Therefore, it is possible to determine whether or not the target thickness has been reached without interrupting the polishing, to shorten the time required for polishing, and to suppress the occurrence of excessive or insufficient polishing. . Therefore, a wafer with high flatness can be obtained easily and stably. In addition, the cost of window material and polishing cloth can be reduced.

Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited thereto.
(Example)
A double-side polishing apparatus as shown in FIG. 1 was prepared.
First, as a plurality of holes, 15 holes having a diameter of 20 mm were formed on the circumference with the center of the upper surface plate as a fulcrum. Then, a polishing cloth (Nitta Haas polishing pad MH, thickness 1500 μm) having a hole (diameter 40 mm) cut 20 mm larger in diameter than the outer peripheral portion of the hole portion, and 10 mm from the hole opened in the surface plate as a window material A large-diameter Toray PTS film (diameter 30 mm, thickness 150 μm) is cut into a disk shape, and double-sided tape (Sumitomo 3M 442JS3, thickness 110 μm) is pasted along the outer periphery of the PTS film. I prepared a few. And the window material was affixed on the hole part of the upper surface plate with the double-sided tape.

As a wafer to be polished, 1000 p ^- type silicon single crystal wafers having a diameter of 300 mm, which were cut out from an ingot grown by the CZ method and then chamfered, lapped and etched, were prepared. This p ^- type is a p-type high resistivity wafer.
In addition, 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 1755 nm is prepared, and such a wafer thickness measurement mechanism is used. While measuring the thickness of the wafer, 1000 pieces were polished by a batch method (15 pieces per batch).

As a result of evaluating the surface shape of a wafer polished by using such a double-side polishing apparatus with an AFS (capacitance flatness measuring apparatus manufactured by ADE), for example, a conventional structure in which a polishing cloth and a window material are integrated. A flat wafer was obtained with less variation than the polishing apparatus.
Further, the deterioration of the window material did not change so much and the replacement frequency did not change so much, but the replacement frequency of the polishing cloth became about ½ compared with the conventional case. As described above, waste can be greatly reduced as compared with the conventional case, and the cost of the polishing cloth can be reduced.

  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 figure which showed the outline (a) of the window material of this invention, and the mode (b) which affixed this window material on the upper surface plate. It is the figure which looked at the upper surface plate and carrier of the double-side polish apparatus of this invention from the grinding | polishing surface side.

Explanation of symbols

10: Double-side polishing device,
DESCRIPTION OF SYMBOLS 11 ... Upper surface plate, 11a ... Polishing lower surface, 11b ... Polishing cloth, 12 ... Lower surface plate, 12a ... Polishing upper surface, 12b ... Polishing cloth, 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 ... Window material, 18 ... Adhesive layer,
W: Wafer.

Claims (6)

At least a lower surface plate having a flat polishing upper surface to be rotationally driven, an upper surface plate having a flat polishing lower surface disposed opposite to the lower surface plate and rotationally driven, and a carrier having a wafer holding hole for holding a wafer. In the double-side polishing apparatus provided,
The upper surface plate or the lower surface plate is provided with a plurality of holes provided between a rotation center and a peripheral edge of the surface plate, and the polishing surface of the upper and lower surface plates has a position corresponding to the plurality of holes. And a polishing cloth having a hole larger in diameter than the hole, and a window material having a diameter larger than the hole and a diameter smaller than the hole of the polishing cloth and thinner than the polishing cloth,
And a wafer thickness measuring mechanism that measures the thickness of the wafer from the plurality of holes in real time during polishing,
The window material is separated from the polishing cloth and fixed to the upper surface plate or the lower surface plate via an adhesive layer ,
And the thickness of the window material is t _w [μm], the refractive index is n _w , and the thickness of the adhesive layer is t ₂ [μm],
The thickness of the wafer is _ts [μm], the refractive index is _ns ,
The thickness of the polishing cloth is t ₁ [μm], the compressibility is ζ ₁ [% / g / cm ² ],
When the polishing maximum load is P [g / cm ² ],
sided, characterized in that _{t 1 × ζ 1 × P /} 100> a _t w + t _2, and satisfies the relation of _{t w n w> t s n} s or _{t w n w <t s n} s Polishing equipment.   The double-side polishing apparatus according to claim 1, wherein the wafer thickness measuring mechanism includes a wavelength tunable infrared laser apparatus having a wavelength that is optically transmitted to the wafer.   The double-side polishing apparatus according to claim 2, wherein the window material optically transmits laser light emitted from the wavelength tunable infrared laser apparatus.   The double-side polishing apparatus according to claim 1, wherein the window material is made of plastic.   The double-side polishing apparatus according to any one of claims 1 to 4, wherein the wafer thickness measuring mechanism measures a bulk thickness of the wafer. The double-side polishing apparatus according to any one of claims 1 to 5 , wherein the plurality of holes are provided at equal intervals around the upper surface plate.

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