JP6003800B2 - Wafer double-side polishing method and double-side polishing system - Google Patents

Description

  The present invention relates to a double-side polishing method for simultaneously polishing both surfaces of a wafer while measuring the thickness of the wafer.

With the miniaturization of the semiconductor circuit line width, the flatness required for the semiconductor wafer as the substrate is becoming increasingly severe. Under such circumstances, when polishing a large-diameter wafer, a double-side polishing method with higher processing accuracy is adopted instead of the conventional single-side polishing.
Here, the double-side polishing apparatus includes a planetary gear type double-side polishing apparatus as shown in FIG. 8 and a swing type double-side polishing apparatus as shown in FIG. The planetary gear type double-side polishing machine has an upper and lower surface plate, the upper surface plate can move up and down, and the upper surface plate is pressed against the lower surface plate to apply a load to the wafer sandwiched between the upper and lower surface plates. Can do. As shown in FIG. 8, the double-side polishing apparatus 101 includes a sun gear 107 provided on the inner side of the lower surface plate and an internal gear 108 provided on the outer side of the lower surface plate.

  In addition, there is a carrier 105 that holds the wafer between the upper and lower surface plates, and the outer peripheral portion thereof can mesh with the sun gear and the internal gear to rotate. This carrier rotates and revolves between the upper and lower surface plates according to the number of rotations of the sun gear and the internal gear. A wafer as an object to be polished is inserted and held in a holding hole 106 provided in the carrier, so that it is polished without jumping out from the double-side polishing apparatus during polishing.

On the other hand, as shown in FIG. 9, the oscillating double-side polishing apparatus 111 disposes a carrier 105 that holds a wafer between rotating upper and lower surface plates, and polishes the wafer by making a circular motion without rotating the carrier 105. To do.
The planetary gear type double-side polishing machine can set the number of rotations and revolutions of the carrier higher than that of the swing type double-side polishing machine. As a result, the rotation type of the wafer during polishing is promoted to promote the rotation type of the wafer. A wafer with higher flatness than a polishing machine can be polished. Therefore, as a double-side polishing apparatus in recent years, a planetary gear type double-side polishing machine has become mainstream.

  Here, in the planetary gear type double-side polishing apparatus, it is known that the flatness of the polished wafer varies depending on the thickness of the wafer at the end of polishing, that is, the relationship between the finished thickness of the wafer and the thickness of the carrier. . For example, when the finished thickness is increased with respect to the thickness of the carrier, the pressure at the outer peripheral portion of the wafer becomes higher than that at the central portion due to the influence of the sinking of the wafer into the polishing cloth due to the polishing load. As a result, polishing of the outer peripheral portion of the wafer is promoted, so that the outer peripheral portion becomes thinner than the central portion, so-called peripheral sagging occurs, and the overall shape tends to be convex.

Conversely, when the finished thickness is reduced relative to the thickness of the carrier, the pressure at the outer peripheral portion becomes smaller than that at the central portion due to a so-called retainer effect that alleviates the influence of the carrier sinking into the polishing cloth. As a result, the outer periphery of the wafer becomes thicker than the center, and the overall shape tends to be concave.
For this reason, in order to polish a wafer with high flatness, it is necessary to finish the wafer with a thickness optimum for the thickness of the carrier.

  Conventionally, in order to finish a wafer with an optimum thickness, the polishing rate is calculated from the thickness of the wafer and the time spent for polishing before and after polishing, and this is accumulated as an expected polishing rate for polishing conditions. Based on the accumulated expected polishing rate, the polishing rate of the polishing to be performed is predicted, and polishing is performed with a polishing time obtained by dividing the necessary polishing amount by the predicted polishing rate. For this reason, for example, if there is a variation in polishing speed due to a change in polishing cloth over time, a deviation occurs between the target wafer thickness and the actual wafer thickness, resulting in a wafer with poor flatness.

  In addition, since it is necessary to accumulate the expected polishing rate under various polishing conditions in advance, it is costly. If there is no expected polishing rate under the polishing conditions to be performed in the future, the polishing rate is roughly determined. As a result, the difference between the target wafer thickness and the actual wafer thickness becomes large, and a wafer with poor flatness can be easily formed.

  For this reason, as shown in FIG. 7, by using a double-side polishing apparatus 101 equipped with a thickness measuring means 102 for measuring the thickness of the wafer W in-situ during polishing, For example, it is possible to finish the wafer with a desired thickness without being affected by fluctuations in the polishing rate due to changes in the polishing cloth over time. As a result, it is always possible to polish a highly flat wafer (see Patent Document 1).

JP 2010-34462 A

  However, there is a problem that the investment burden becomes very large if the thickness measuring device 102 using the wavelength tunable infrared laser as shown in FIG. In particular, since the laser light source 103 of the thickness measuring unit 102 is expensive, a method of dividing the laser light from the laser light source 103 into a plurality of parts by a beam splitter and simultaneously using it by a plurality of double-side polishing apparatuses can be considered. Since the amount of each laser beam sent to each double-side polishing machine is reduced, a reflected signal with sufficient intensity can be obtained especially for thick wafers and wafers with a relatively high impurity concentration, that is, with a low resistivity. There is a problem that the thickness cannot be measured accurately.

  The present invention has been made in view of the above problems, and in double-side polishing performed while measuring the thickness of the wafer using a wavelength tunable infrared laser, the accuracy of measuring the thickness of a wafer having a particularly low resistivity is lowered. An object of the present invention is to provide a double-side polishing method and double-side polishing system for a wafer that can reduce the equipment cost without doing so.

  To achieve the above object, according to the present invention, a wafer held by a carrier is sandwiched between upper and lower surface plates to which a polishing cloth is attached, the carrier is rotated and revolved, an abrasive is supplied, A method for polishing both surfaces of a wafer using a plurality of double-side polishing apparatuses that simultaneously polish both surfaces of the wafer while measuring a thickness by a light reflection interference method using a wavelength tunable infrared laser, the plurality of double-side polishing apparatuses Measuring the thickness of the wafer while irradiating the tunable infrared laser used in each of the lasers by switching the single-sided polishing apparatus from one laser light source, and polishing the wafer to a target thickness A double-side polishing method for a wafer is provided.

Further, according to the present invention, the wafer held by the carrier is sandwiched between the upper and lower surface plates to which the polishing cloth is attached, the carrier is rotated and revolved, the abrasive is supplied, and the thickness of the wafer is changed to the wavelength variable infrared ray. A system for polishing both sides of the wafer using a plurality of double-side polishing apparatuses that simultaneously polish both sides of the wafer while measuring by light reflection interferometry using a laser,
A laser path switching unit that switches between the one laser light source and the double-side polishing apparatus to be irradiated from the one laser light source, and the wavelength-tunable infrared laser used in each of the plurality of double-side polishing apparatuses The wafer is characterized in that the thickness of the wafer is measured while irradiating the single-side laser light source by switching from the one laser light source to the target thickness, and the wafer is double-side polished to a target thickness. A double-side polishing system is provided.

  With such a double-side polishing method and double-side polishing system, it is possible to significantly reduce equipment costs by sharing an expensive laser light source among a plurality of double-side polishing apparatuses, and without reducing the thickness of the wafer. The wafer can be polished on both sides to the target thickness by measuring.

At this time, the wavelength of the wavelength tunable infrared laser is preferably set to 1000 nm to 1700 nm.
In this way, the wavelength-tunable infrared laser can be optically transmitted to the wafer, so that the reflection spectrum on the wafer surface can be analyzed, thereby measuring the thickness of the wafer being polished with high accuracy. can do.

Further, when switching the double-side polishing apparatus to be irradiated from the one laser light source, the switching destination is sequentially selected from the plurality of double-side polishing apparatuses at regular intervals, preferably every 1 second or more and 60 seconds or less. It is preferable.
If it does in this way, it will become possible to switch to more double-side polish apparatuses with one laser light source, and it will become possible to reduce equipment cost more.

Further, when switching the double-side polishing apparatus to be irradiated from the one laser light source, switching is performed so that the number of times of measuring the thickness of the wafer in each of the plurality of double-side polishing apparatuses is at least twice per minute. Is preferred.
In this way, the thickness of the wafer can be reliably measured without degrading accuracy.

  In the present invention, in double-side polishing of a wafer performed by using a plurality of double-side polishing apparatuses, irradiation with a tunable infrared laser used in each of the plurality of double-side polishing apparatuses is performed by switching from one laser light source to an irradiation target double-side polishing apparatus. While measuring the thickness of the wafer and double-side polishing the wafer to the target thickness, sharing the expensive laser light source with multiple double-side polishing equipment can greatly reduce the equipment cost and the thickness of the wafer Can be measured without degrading accuracy, and the wafer can be polished on both sides to the target thickness.

It is a flowchart of an example of the double-sided polishing method of the wafer of this invention. 1 is a schematic view of a double-side polishing system having a plurality of double-side polishing apparatuses and thickness measuring means used in a wafer double-side polishing method of the present invention. It is the figure which expanded the double-side polish apparatus shown in FIG. It is a figure which shows the approximate line calculated | required by the least squares method from the measurement result of the wafer thickness in the example in the wafer grinding | polishing. It is a figure which shows the approximate line calculated | required by the least squares method from the measurement result of the wafer thickness in the grinding | polishing of the wafer in a comparative example. It is a figure which shows the relative frequency and cumulative relative frequency of the wafer thickness after grinding | polishing in an Example and a comparative example. It is the schematic of the double-side polish apparatus and laser light source which are used with the double-side polish method of the conventional wafer. 1 is a schematic view showing a general planetary gear type double-side polishing apparatus. It is the schematic which shows a general rocking | swiveling type double-side polish apparatus.

Hereinafter, although an embodiment is described about the present invention, the present invention is not limited to this.
First, a double-side polishing system equipped with a plurality of double-side polishing apparatuses and thickness measuring means used in the wafer double-side polishing method of the present invention will be described. In the present invention, as shown in FIG. 2, when the wafer is polished on both sides, the laser light source 21 of the thickness measuring means 20 is shared by the plurality of double-side polishing apparatuses 1, 1 ′.

  As shown in FIG. 3, the double-side polishing apparatus 1 has a cylindrical upper surface plate 2 and a lower surface plate 3, and a polishing cloth 4 is attached to the upper and lower surface plates 2 and 3 so that their polishing surfaces face each other. It is attached. Here, the polishing cloth 4 is a non-woven fabric impregnated with a urethane resin or a urethane foam. A sun gear 7 is attached to the inside of the lower surface plate 3 and an internal gear 8 is attached to the outside. The upper and lower surface plates 2, 3, the sun gear 7, and the internal gear 8 have the same rotation center axis and can rotate independently of each other around the axis.

  The carrier 5 is provided with a holding hole 6 for holding the wafer W, and a plurality of carriers 5 are sandwiched between the upper and lower surface plates 2 and 3. A plurality of holding holes 6 are provided in one carrier 5 so that a plurality of wafers W can be polished for each batch. The carrier 5 meshes with the sun gear 7 and the internal gear 8, and rotates and revolves between the upper and lower surface plates according to the rotational speeds of the sun gear 7 and the internal gear 8.

  Further, in order to measure the thickness of the wafer being polished by the thickness measuring means 20, a plurality of holes 11 are provided on the upper surface plate 2 side. The thickness measuring means 20 detected a laser light source 21, optical units 22 and 22 'for irradiating the wavelength variable infrared laser on the wafer W, and a photodetector (not shown) for detecting reflected light reflected from the wafer W. A thickness measurement computer 24 for calculating the wafer thickness from the reflected light and controlling the thickness measurement is provided.

  The wavelength tunable infrared laser emitted from one laser light source 21 is irradiated to the wafer W in the plane sandwiched between the upper and lower surface plates through the hole 11, and the thickness reflected by analyzing the reflected light is obtained. be able to. A plurality of double-side polishing apparatuses 1, 1 ′ are provided with a laser path switch 23 so that the thickness of the wafers being polished can be sequentially measured using the same laser light source 21.

Hereinafter, the wafer double-side polishing method of the present invention will be described more specifically with reference to FIGS.
As described above, the wafer flatness after polishing varies depending on the difference between the carrier and wafer thickness. Therefore, based on the information on the wafer thickness and flatness obtained by actual polishing, the optimum target thickness (finished thickness) Is set in the thickness measuring means 20 ((A) of FIG. 1).

  Next, polishing is started using a plurality of double-side polishing apparatuses while measuring the thickness of the wafer ((B) in FIG. 1). Specifically, as shown in FIG. 3, first, the wafer W is inserted and held in the holding hole 6 of the carrier 5 of each double-side polishing apparatus 1, 1 ′. Thereafter, the upper surface plate 2 descends to sandwich the wafer W and the carrier 5 and apply a polishing load. By rotating the upper surface plate 2 and the lower surface plate 3 in the opposite directions while pouring the abrasive supplied from the nozzle 10 between the upper and lower surface plates through the through holes 9 provided in the upper surface plate 2, the wafers are rotated. Start double-sided polishing of W.

Here, the polishing load, the platen rotation speed, and the carrier rotation speed are controlled by the control unit 12 provided in each double-side polishing apparatus 1, 1 ′.
During polishing of the wafer W, the wavelength variable infrared laser used in each of the plurality of double-side polishing apparatuses 1 and 1 ′ is irradiated from one laser light source 21 so as to switch the double-side polishing apparatuses 1 and 1 ′ to be irradiated. Then, the thickness of the wafer W is measured.

The irradiation destination of the wavelength tunable infrared laser can be switched by, for example, a laser path switch 23 of the thickness measuring unit 20 as shown in FIG.
Here, switching the double-side polishing apparatus to which the wavelength tunable infrared laser is irradiated means that one of the plurality of double-side polishing apparatuses 1 and 1 'is used without dividing the wavelength tunable infrared laser into a plurality of parts by, for example, a beam splitter. This means that the two-side polishing apparatus is arbitrarily selected as the irradiation destination, and only the selected double-side polishing apparatus is irradiated with the wavelength tunable infrared laser. Then, after measuring the wafer thickness with the selected double-side polishing apparatus, the laser path switching unit 23 is used to switch the laser irradiation destination to another double-side polishing apparatus to measure the wafer thickness.

  At this time, in the double-side polishing apparatus selected as the irradiation destination of the wavelength tunable infrared laser, it is assumed that the thickness measurement control is effective as shown in FIG. 1, and as described above, the laser light source 21 of the thickness measuring means 20 is used. The thickness of the wafer W is measured using the wavelength tunable infrared laser transmitted from (FIG. 1C). Further, in the double-side polishing apparatus other than the double-side polishing apparatus selected as the irradiation destination of the wavelength tunable infrared laser, the thickness measurement control is not effective and the polishing is continued for a preset time ((D) in FIG. 1). .

When the thickness measurement result of the wafer W reaches a preset target thickness, a polishing stop signal is sent from the thickness measuring means 20 to the double-side polishing apparatus 1 via the control unit 12 to finish polishing (FIG. 1). (E)).
With such a double-side polishing method of the present invention, it is possible to irradiate a wavelength-variable infrared laser to any one double-side polishing apparatus without causing a decrease in the amount of laser light, and a wafer having a low resistivity. Even in the case of polishing, the wafer thickness can be accurately measured with a plurality of double-side polishing apparatuses, and a wafer having a target thickness can be obtained. Further, by sharing a particularly expensive laser light source among the thickness measuring means among a plurality of double-side polishing apparatuses, the equipment cost can be greatly reduced.

  Here, the wavelength is preferably set to 1000 nm to 1700 nm so that the wavelength tunable infrared laser can be optically transmitted to the wafer. In this way, it is possible to analyze the reflection spectrum on the wafer surface (the state of interference of light reflected from the wafer surface and the back surface), thereby measuring the thickness of the wafer being polished with high accuracy. Can do.

  In addition, when switching the irradiation side double-side polishing apparatus from one laser light source, the thickness of the wafer being polished can be measured by selecting the switching destination sequentially from a plurality of double-side polishing apparatuses at regular intervals. Without reducing the accuracy, it is possible to switch to more double-side polishing apparatuses with one laser light source, and the equipment cost can be further reduced. Here, it is preferable that the fixed time at the time of switching is 1 second or more and 60 seconds or less because it is possible to more accurately perform the measurement of the wafer thickness. It can be determined appropriately according to the polishing conditions.

The selection of the switching destination and the switching interval when switching the irradiation destination of the wavelength tunable infrared laser is controlled by setting in advance in the thickness measuring computer 24 of the thickness measuring means 20 shown in FIG. Can do.
At this time, it is preferable to set so that the number of times of measuring the thickness of the wafer in each of the plurality of double-side polishing apparatuses is switched to twice or more per minute. In this way, the thickness of the wafer can be reliably measured without degrading accuracy.

  For example, by dividing the section from the start of polishing to the end of polishing as a plurality of polishing steps, in each double-side polishing apparatus, as shown in FIG. That is, it can be set to determine whether or not to measure the thickness ((F) in FIG. 1). At this time, the target thickness is set for each polishing step, and the time for polishing while measuring the thickness in the polishing step is set so that the wafer thickness being polished reaches the target thickness for each polishing step. (H in FIG. 1).

  In addition to the method of determining whether the thickness of the wafer W being polished has reached a preset target thickness, by comparing the thickness measured by the thickness measuring means 20 with the target thickness, for example, By calculating the approximate line obtained by the least square method by taking the measured values obtained by measuring the thickness on the vertical axis, the polishing time on the horizontal axis, and calculating the thickness near the center of the dispersion of the measured values. Then, the thickness corresponding to the current polishing time on the approximate line can be calculated as the estimated thickness ((G) in FIG. 1). With this method of calculating the approximate line, the accuracy of thickness measurement can be further increased.

  Furthermore, in order to increase the accuracy of thickness measurement, the number of thickness measurement data when obtaining an approximate line by the least square method is at least 20 points, and the variation (standard deviation) in the difference between the approximate line and the measured value is 0.5 μm. It is preferable to be within.

  In the present invention, since the laser light source is shared by a plurality of double-side polishing apparatuses, the number of times of thickness measurement is reduced as compared with the conventional method that does not share the laser light source, but the estimated thickness calculated based on the actually measured thickness is as follows. By determining the end of polishing based on the thickness, highly accurate thickness measurement can be performed more reliably.

  In the example shown in FIG. 2, the laser irradiation from one laser light source is switched between two double-side polishing apparatuses, but is not limited thereto, and is switched between three or more double-side polishing apparatuses. Also good. Further, although one thickness measuring computer 24 is used for each double-side polishing apparatus, the thickness measurement of each double-side polishing apparatus may be controlled by one thickness measuring computer 24. .

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples of the present invention, but the present invention is not limited to these.

(Example)
Using a double-side polishing system having two double-side polishing apparatuses and one laser light source as shown in FIG. 2, according to the double-side polishing method for a wafer of the present invention, a silicon wafer having a diameter of 300 mm and a final target thickness of 775 μm is double-side polished. At this time, the thickness of the polished wafer was evaluated.
Here, 1 × 2 Mechanical Fiber Switch manufactured by AC Photonics was used as the laser path switch 23 of the thickness measuring unit. Further, the irradiation side double-side polishing apparatus was sequentially switched every 5 seconds.

  Judgment on whether the wafer thickness has reached the target thickness is based on the measured values obtained by thickness measurement on the vertical axis and the polishing time on the horizontal axis. The polishing is terminated when the thickness corresponding to the current polishing time on the approximate line reaches the target thickness.

(Comparative example)
A silicon wafer was double-side polished under the same conditions as in Example except that one double-side polishing apparatus having thickness measuring means as shown in FIG.

FIG. 4 shows the result of the wafer thickness transition during polishing in the example, and FIG. 5 shows the result of the comparative example. Comparing FIG. 4 and FIG. 5, it can be seen that the number of thickness measurement points is smaller than in the comparative example because the laser irradiation destination from one laser light source is switched between two double-side polishing apparatuses in the example.
FIG. 6 shows the results of the relative frequency and cumulative relative frequency of the wafer thickness after polishing. As shown in FIG. 6, in the example, even when the number of measurements is smaller than that in the comparative example, a wafer having a target thickness of 775 μm can be obtained with the same distribution as in the comparative example, and both cost reduction and polishing accuracy can be achieved. It was confirmed that

  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.

1, 1 '... Double-side polishing machine, 2 ... Upper surface plate, 3 ... Lower surface plate, 4 ... Polishing cloth,
5 ... Carrier, 6 ... Holding hole, 7 ... Sun gear, 8 ... Internal gear,
9 ... Through-hole, 10 ... Nozzle, 11 ... Multiple holes, 12 ... Control unit,
20 ... Thickness measuring means, 21 ... Laser light source, 22, 22 '... Optical unit,
23: Laser path switcher 24: Thickness measuring computer

Claims (4)

A wafer held by a carrier is sandwiched between upper and lower surface plates to which a polishing cloth is attached, the carrier is rotated and revolved, an abrasive is supplied, and the thickness of the wafer is reflected by a light reflection interference method using a wavelength tunable infrared laser. A method for polishing both sides of the wafer using a plurality of double-side polishing apparatuses that simultaneously polish both sides of the wafer while measuring in
Measure the thickness of the wafer while irradiating the tunable infrared laser used in each of the plurality of double-side polishing apparatuses by switching the double-side polishing apparatus to be irradiated from one laser light source, and target the wafer Polish both sides to thickness ,
When switching the double-side polishing apparatus to be irradiated from the one laser light source, the switching destination is sequentially selected from the plurality of double-side polishing apparatuses at regular intervals of 1 second or more and 60 seconds or less, each double-sided polishing process of the wafer number of times to measure the thickness of the wafer and wherein the switching Rukoto so that every minute or two double-side polishing apparatus.   2. The double-side polishing method for a wafer according to claim 1, wherein the wavelength of the wavelength tunable infrared laser is set to 1000 nm to 1700 nm. A wafer held by a carrier is sandwiched between upper and lower surface plates to which a polishing cloth is attached, the carrier is rotated and revolved, an abrasive is supplied, and the thickness of the wafer is reflected by a light reflection interference method using a wavelength tunable infrared laser. A system for polishing both sides of the wafer using a plurality of double-side polishing apparatuses that simultaneously polish both sides of the wafer while measuring in
A laser path switching unit that switches between the one laser light source and the double-side polishing apparatus to be irradiated from the one laser light source, and the wavelength-tunable infrared laser used in each of the plurality of double-side polishing apparatuses Measure the thickness of the wafer while irradiating the two-side polishing apparatus to be irradiated from the one laser light source by means of a vessel, and polish the wafer to the target thickness on both sides ,
When switching the double-side polishing apparatus to be irradiated from the one laser light source, the switching destination is sequentially selected from the plurality of double-side polishing apparatuses at regular intervals of 1 second or more and 60 seconds or less, each the wafer side polishing system, wherein the number of times of measuring the thickness of the wafer is switched shall so per minute or more two double-side polishing apparatus. 4. The wafer double-side polishing system according to claim 3 , wherein the wavelength tunable infrared laser has a wavelength of 1000 nm to 1700 nm.

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