JP2016001705A - Wafer polishing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wafer polishing method which can improve a collection rate of a first abrasive while preventing mixture of a second abrasive when collecting the first abrasive.SOLUTION: A wafer polishing method comprises: a first polishing process of supplying a first abrasive and performing rough polishing of a wafer by the first abrasive; a residual abrasive collection process of collecting the first abrasive remaining on a surface plate after stopping supply of the first abrasive; and a second polishing process of switching the abrasive to be supplied to a second abrasive and performing fine polishing of the wafer by the second abrasive, in which the collection of the first abrasive remaining on the surface plate in the residual abrasive collection process is performed by increasing the rotational number of the surface plate compared with the rotational number of the surface plate at the time of stopping supply of the first abrasive.

Description

  The present invention relates to a wafer polishing method in which a wafer is slid in contact with a polishing cloth while supplying an abrasive.

  In general, a silicon wafer manufacturing method includes a slicing step of slicing a silicon ingot to obtain a thin disk-shaped wafer, and a chamfering step of chamfering the outer periphery of the wafer obtained by the slicing step to prevent cracking and chipping. A lapping process for flattening the chamfered wafer, an etching process for removing processing distortion remaining on the chamfered and lapped wafer, a polishing process for mirroring the surface of the etched wafer, and the polished wafer. And a cleaning step of removing the abrasive and foreign matter adhering to the substrate.

  The above shows only the main processes. In addition, a heat treatment process, a surface grinding process, a process for protecting the surface of the wafer at the time of automatic transfer, and the like are added, and the order of the processes is changed. Moreover, the same process may be implemented in multiple times. Thereafter, an inspection or the like is performed and the device is sent to a device manufacturing process. An insulating film or a metal wiring is formed on the surface of the wafer, and a device such as a memory is manufactured.

  The polishing step is a step of mirror-finishing the surface by bringing the wafer into sliding contact with the polishing cloth while supplying the abrasive. In wafer polishing, polishing is usually performed through a plurality of stages from rough polishing to fine polishing.

  In the polishing step, there are a method in which the abrasive is used only once, and a method in which the abrasive is recovered in the tank and reused as disclosed in Patent Document 1. The method of recovering and reusing the abrasive is to apply the load to the wafer with the polishing head while supplying the stored abrasive to the polishing cloth affixed on the surface plate, In this method, the surface of the silicon wafer is rotated to be brought into sliding contact with a polishing cloth for polishing, and the supplied abrasive is collected in the tank and reused for polishing.

  At this time, in order to improve processing efficiency, rough polishing and fine polishing may be performed on the same surface plate. In this case, the polishing agent supplied to the polishing cloth can be switched from rough polishing to fine polishing by switching from the first polishing agent for rough polishing to the second polishing agent for fine polishing.

  When switching from the first abrasive to the second abrasive in this way, the first abrasive remaining on the surface plate and the newly supplied second abrasive are mixed on the surface plate. End up. Since such a mixture of both abrasives cannot be recovered, it cannot be used. Therefore, after the supply of the first abrasive is stopped, water is supplied onto the surface plate, and the supplied water is supplied to the first abrasive. A method of discharging the abrasive together with the abrasive and removing the first abrasive from the surface plate and starting the supply of the second abrasive has been used.

JP 2013-55143 A

  In recent years, in the wafer polishing method as described above, the polishing apparatus has been increased in size for the purpose of increasing the diameter of the wafer itself and increasing the number of wafers that can be polished per batch in order to improve productivity. It is out. Due to the increase in size of the polishing apparatus, the size of the surface plate also increases, and the distance from the center of the surface plate to the outer periphery of the surface plate increases, so that the first abrasive remaining on the surface plate increases. In particular, in the case of a (solid) disk-shaped surface plate having no opening in the center, since the region where the abrasive remains remains wider than the donut-shaped surface plate, the residual amount also increases.

  When a large amount of the first abrasive remains on the surface plate in this way, water is supplied onto the surface plate, and the remaining first abrasive is not recovered and drained. Since a large amount of the first abrasive is discarded, the recovery rate of the first abrasive is greatly reduced. In addition, since the amount of the first abrasive to be discarded increases as the platen size increases, there is a problem that the recovery rate of the first abrasive is further reduced and the cost is increased.

  The present invention has been made in view of the above-described problems. When the first abrasive is recovered, the second abrasive is prevented from being mixed, and the recovery rate of the first abrasive is An object of the present invention is to provide a method for polishing a wafer capable of increasing the thickness.

In order to achieve the above object, according to the present invention, the wafer is loaded with a polishing head while supplying the polishing agent stored in the tank to the polishing cloth affixed on the surface plate. A method of polishing a wafer that is slid in contact with the polishing cloth, and the supplied abrasive is recovered in the tank and reused.
A first polishing step of supplying a first polishing agent to perform rough polishing of the wafer with the first polishing agent; and after stopping the supply of the first polishing agent, remaining on the surface plate A residual polishing agent recovery step of recovering the first polishing agent, and a second polishing step of switching the supplied polishing agent to a second polishing agent and finely polishing the wafer with the second polishing agent. And
The recovery of the first abrasive remaining on the surface plate in the residual abrasive recovery step is performed by adjusting the rotation speed of the surface plate and the rotation of the surface plate at the time when the supply of the first abrasive is stopped. Provided is a method for polishing a wafer, which is carried out by setting the number higher than the number.

  With such a wafer polishing method, when the first abrasive is recovered, the second abrasive is prevented from being mixed and the first abrasive recovery rate is increased. Can do.

At this time, in the residual abrasive recovery step,
It is preferable that the rotation speed of the surface plate be within a range of 25 to 35 rpm.
By doing in this way, the recovery rate of a 1st abrasive | polishing agent can be made more reliably.

At this time, in the residual abrasive recovery step,
The number of rotations of the polishing head is preferably 10 to 20 rpm, and the time is preferably 4 to 8 seconds.
By doing in this way, it can prevent that the flatness of a wafer deteriorates.

At this time, in the residual abrasive recovery step,
The load of the polishing head is preferably 30 to 80 g / cm ² .
By doing in this way, it can prevent reliably that the flatness of a wafer will deteriorate.

  As described above, according to the present invention, when recovering the first abrasive, it is possible to prevent the second abrasive from being mixed and to increase the recovery rate of the first abrasive.

It is the schematic which showed an example of the single-side polish apparatus to which this invention is applied. It is the graph which showed an example of frequency distribution of the measurement result of the flatness of a wafer in an Example. It is the graph which showed an example of frequency distribution of the measurement result of the flatness of a wafer in a comparative example.

Hereinafter, the present invention will be described in detail as an example of embodiments with reference to the drawings and tables, but the present invention is not limited to this.
As described above, in the conventional wafer polishing method, even if a large amount of the first abrasive remains on the surface plate, it cannot be recovered and discarded together with the water supplied on the surface plate. Therefore, there has been a problem that the recovery rate of the first abrasive is greatly reduced and the cost is increased. The amount of the first abrasive that is discarded increases as the platen size increases.

  Therefore, the present inventors have conducted intensive studies to solve the above-described problems. As a result, in the wafer polishing method, the number of rotations of the surface plate is made higher than the number of rotations of the surface plate at the time when the supply of the first abrasive is stopped, thereby remaining on the surface plate or the polishing cloth. It was conceived that the abrasive 1 could be shaken off from the surface plate and quickly collected in the pipe, thereby improving the recovery rate effectively. And the best form for implementing these was scrutinized and the present invention was completed.

A single-side polishing apparatus that can be used to carry out the wafer polishing method of the present invention will be described with reference to FIG.
As shown in FIG. 1, the single-side polishing apparatus 1 includes a surface plate 3 on which a polishing cloth 2 is attached, a nozzle 4, a polishing head 5, and tanks 7a and 7b. The tank 7a stores a first abrasive 8 used for rough polishing, and the tank 7b stores a second abrasive 12 used for fine polishing. Note that which abrasive is supplied can be controlled by the control means 11. In the single-side polishing apparatus 1, the wafer 6 is held by the polishing head 5, and the first polishing agent 8 or the second polishing agent 12 is supplied onto the polishing cloth 2 through the nozzle 4, and the surface plate 3 and the polishing head 5. Each is rotated to bring the surface of the wafer 6 into sliding contact with the polishing pad 2 for polishing.

  In addition, the single-side polishing apparatus 1 is configured so that the wafer 6 has a target polishing allowance, the polishing time, the load applied by the polishing head 5 to the wafer 6, the rotational speed of the polishing head 5 and the rotational speed of the surface plate 3, Control means 11 for controlling the supply of the first abrasive 8 and the second abrasive 12 is provided. The supplied first and second abrasives 8 and 12 flow down to the surface plate receiver 9 except for a portion that cannot be recovered due to, for example, partly scattering during polishing or exhausted as mist. 10 is collected in each tank 7a, 7b and reused for subsequent polishing. Note that the separator 13 can change the route whether the first abrasive 8 or the second abrasive 12 is collected or drained into the tank 7a or the tank 7b, respectively.

  Next, the wafer polishing method of the present invention will be described. Here, a case where a single-side polishing apparatus 1 as shown in FIG. 1 is used will be described.

  First, a wafer 6 to be polished is prepared, and the wafer 6 is held by the polishing head 5.

(First polishing process)
In the first polishing process, the wafer 6 is roughly polished.
While supplying the first abrasive 8 stored in the tank 7a to the polishing cloth 2 affixed on the surface plate 3, the wafer 6 is slid in contact with the polishing cloth 2 by the polishing head 5 and rough polished. At this time, the supplied first polishing agent 8 is collected in the tank 7a and then supplied again onto the polishing pad 2, whereby the wafer 6 is polished while reusing the first polishing agent 8. In this way, polishing is performed until the wafer 6 reaches a target thickness. Then, when the target thickness is reached, the supply of the first abrasive 8 is stopped.

(Residual abrasive recovery process)
After the supply of the first abrasive 8 is stopped, the rotational speed of the surface plate 3 is set at the time when the supply of the first abrasive 8 is stopped in a state where neither the abrasive nor water is supplied onto the surface plate 3. By making it higher than the rotation speed of the board 3, the first abrasive 8 remaining on the surface plate 3 and the polishing cloth 2 is quickly and easily recovered.

  At this time, the rotation speed of the surface plate 3 can be set within a range of 25 to 35 rpm. If the rotational speed of the surface plate 3 is 25 rpm or more, the first abrasive 8 adhered to the surface plate 3 can be shaken off from the surface plate 3, and if it is 35 rpm or less, deterioration of the flatness of the wafer 6 is suppressed. In addition, the first abrasive 8 can be reliably recovered without being scattered around.

  When the supply of the first polishing agent 8 is stopped during the residual polishing agent recovery process, if there is no polishing agent between the polishing cloth 2 and the wafer 6, heat generated between the wafer 6 and the polishing cloth 2 is generated. Although the amount increases, this process can be performed quickly and in a short time so that the heat generation does not affect the flatness of the wafer 6. Here, the flatness of the wafer 6 is, for example, a GBIR (Global Backside Ideal Range) in a state where the wafer back surface is corrected to a flat surface, and has one reference surface within the wafer surface, and the difference between the maximum and minimum position displacements relative to the reference surface. And is an index indicating the flatness of the wafer).

  At this time, in the residual abrasive recovery process, the rotational speed of the polishing head 5 can be set to 10 to 20 rpm. Moreover, the time of a residual abrasive | polishing agent collection | recovery process can be 4 to 8 second. By doing so, it is possible to suppress the occurrence of abnormal heat generation in the wafer 6 during polishing, and thus it is possible to reliably prevent the flatness of the wafer 6 from being deteriorated.

Moreover, in the residual abrasive | polishing agent collection | recovery process, the load applied to the wafer 6 with the grinding | polishing head 5 can be 30-80 g / cm < ² >. By doing in this way, deterioration of the flatness of the wafer 6 can be prevented more reliably.

  In addition, about the conditions of said each value, it calculated | required by performing experiment which is mentioned later.

(First abrasive removal step)
Further, after the residual abrasive recovery step, by supplying water or a hydrophilic agent, the first abrasive that removes the first abrasive 8 remaining on the surface plate 3, the polishing cloth 2, or the wafer 6 is removed. A removal step can be performed. In this case, the supplied water and hydrophilic agent are drained together with the remaining first abrasive 8. At the time of this drainage, as shown in FIG.
In the present invention, most of the first abrasive 8 on the surface plate 3 or the polishing cloth 2 has already been recovered in the residual abrasive recovery step before the first abrasive removal step. Even if the remaining first abrasive 8 is discharged together with water in the first abrasive removal step, the recovery rate of the first abrasive 8 can be increased.

  Note that the first polishing agent removing step is not necessarily performed, and the second polishing step can be performed following the residual polishing agent collecting step, and can be selected as appropriate.

(Second polishing step)
In the second polishing step, the wafer 6 is precisely polished.
The original tank that supplies the abrasive to the polishing cloth 2 affixed on the surface plate 3 is switched from the tank 7 a to the tank 7 b, and the wafer 6 is finely polished while supplying the second abrasive 12. At this time, similarly to the first polishing step, the supplied second abrasive 12 is collected in the tank 7b and then supplied again onto the polishing cloth 2, thereby reusing the second abrasive 12. However, the wafer 6 may be polished.

  After the second polishing step is completed, the wafer 6 is separated from the polishing cloth 2 and the first polishing agent 8 is recovered in the residual abrasive recovery step. A step of collecting the second abrasive 12 remaining on the top may be performed. At this time, since the wafer 6 and the polishing pad 2 are not in sliding contact with each other, the flatness of the wafer 6 is not affected.

  With the wafer polishing method as described above, it is possible to increase the recovery rate of the first abrasive 8 while preventing the second abrasive 12 from being mixed in at the end of the first polishing step. Therefore, the number of additions and replacements of the abrasive can be reduced, and the number of uses and the amount of the first abrasive 8 can be reduced.

Next, an experiment conducted when determining the range of each condition in the residual abrasive recovery process will be described.
(Experiment 1)
In the wafer polishing method of the present invention, the first polishing step and the residual abrasive recovery step were performed. Following the residual abrasive recovery process, the first abrasive removal process is performed, and the flatness of the wafer 6 from which the first abrasive 8 has been removed from the surface, and the first abrasive 8 at that time, is also shown. The recovery rate was measured.

In the first polishing step, when the supply of the first abrasive 8 was stopped, the rotation speed of the surface plate 3 was 19 rpm, the rotation speed of the polishing head 5 was 10 rpm, and the load of the polishing head 5 was 80 g / cm ² . Sometimes, in the residual abrasive recovery process, the rotation of the polishing head 5 is fixed at 10 rpm, the load of the polishing head 5 is fixed at 80 g / cm ² , the time is changed between 2 and 12 seconds, and the rotation speed of the surface plate 3 Was varied between 20 and 40 rpm. The GBIR of the wafer 6 polished by the polishing method under these conditions and the recovery rate of the first abrasive 8 were measured and are shown in Table 1. The recovery rate of the first abrasive 8 is 12 batches as 2 batches, and after polishing a total of 24 wafers 6, the amount of loss of the first abrasive 8 is taken as a loss amount, and the calculation formula is Abrasive recovery rate = (first abrasive initial amount−loss amount) / first abrasive initial amount.

(Experiment 2)
Experiment 1 except that the rotation speed of the polishing head 5 at the time when the supply of the first abrasive 8 was stopped in the first polishing process was 20 rpm, and the rotation of the polishing head 5 was 20 rpm in the residual abrasive recovery process. Similarly, the time was changed between 2 and 12 seconds, and the rotation speed of the surface plate 3 was changed between 20 and 40 rpm. The GBIR of the wafer 6 polished by the polishing method under these conditions and the recovery rate of the first abrasive 8 were measured and are shown in Table 2.

(Experiment 3)
In the first polishing step, the experiment was performed except that the rotation speed of the polishing head 5 was 30 rpm when the supply of the first abrasive 8 was stopped, and the rotation speed of the polishing head 5 was 30 rpm in the residual abrasive recovery process. As in 1, the time was changed between 2 and 12 seconds, and the rotation speed of the surface plate 3 was changed between 20 and 40 rpm. The GBIR of the wafer 6 polished by the polishing method under these conditions and the recovery rate of the first abrasive 8 were measured and are shown in Table 3.

As shown in Tables 1 to 3, if the rotational speed of the surface plate 3 is increased, the recovery rate of the first abrasive 8 tends to increase. In particular, the rotational speed of the surface plate 3 is preferably 25 rpm or more. I understood.
Further, in order to suppress the deterioration of GBIR, the rotation speed of the surface plate 3 is preferably 35 rpm or less and the rotation speed of the polishing head 5 is preferably 20 rpm or less.

  Furthermore, in order to suppress the deterioration of GBIR, it is preferable that the heat generated in the residual abrasive recovery process is set so as not to affect GBIR. In particular, it is preferable that the time of the residual abrasive recovery process is 4 to 8 seconds.

  Table 4 shows a summary of more preferable conditions in Experiments 1 to 3. Under such conditions, as can be seen from the results in Table 4, the wafer 6 having a high abrasive recovery effect and suppressing the GBIR deterioration of the wafer 6 can be reliably obtained. Is not limited to this condition.

(Experiment 4)
Next, in the first polishing step, when the supply of the first abrasive 8 is stopped, the rotation speed of the surface plate 3 is 19 rpm, the rotation speed of the polishing head 5 is 20 rpm, and in the residual abrasive recovery process, The rotation of the polishing head 5 was 20 rpm, the time was 8 seconds, and the rotation speed of the surface plate 3 was 35 rpm. At this time, the load of the polishing head 5 in the first polishing step and the residual abrasive recovery step was changed from 30 to 100 g / cm ² . The GBIR of the wafer 6 polished by the polishing method of the present invention under these conditions and the recovery rate of the first abrasive 8 were measured and are shown in Table 5.

As shown in Table 5, if the load of the polishing head 5 is in the range of 30 to 80 g / cm ² , the wafer has a high abrasive recovery effect and good GBIR after polishing in the first polishing step. It was found that 6 could be obtained more reliably.

  EXAMPLES Hereinafter, although an Example and comparative example of this invention are shown and this invention is demonstrated more concretely, this invention is not limited to these.

(Example)
As the single-side polishing apparatus, a single-side polishing machine SRED made by Fujikoshi Machinery was used. The polishing cloth used was a soft non-woven fabric, and the polishing agent used was KOH-based colloidal silica. Then, according to the wafer polishing method of the present invention, polishing of silicon wafers having a diameter of 300 mm, a conductivity type of P-, and a crystal orientation <110> is repeated batchwise, and the number of polished wafers per batch is set to 2 and 12 batches A total of 24 wafers were polished under the following conditions.

  In the wafer polishing method of the present invention, the first polishing step and the residual abrasive recovery step were performed. Following the residual abrasive recovery process, a first abrasive removal process was performed.

Table 6 shows the condition of each value in the example. As shown in Table 6, in the first polishing step, the rotation speed of the surface plate at the time when the supply of the first abrasive was stopped was 19 rpm, the rotation speed of the polishing head was 20 rpm, and the load was 80 g / cm ² . In the residual abrasive recovery process, the rotation speed of the polishing head was 20 rpm, the load of the polishing head was 80 g / cm ² , the time was 5 seconds, and the rotation speed of the surface plate was 30 rpm. In addition, in each step, the presence or absence (ON / OFF) of supply of an abrasive, water, or a hydrophilic agent, and whether the abrasive is recovered or drained are also shown.

The recovery rate of the first abrasive when polished under such conditions was measured and shown in Table 7.
Further, GBIR of the obtained wafer was measured, and the measurement result is shown in FIG. Table 8 shows the maximum value, minimum value, average value, and standard deviation of GBIR of the wafer in the measurement results at this time.

  The wafer GBIR was measured with a flatness tester WaferSight 2 manufactured by KLA-Tencor.

  As shown in Table 7, the recovery rate of the first abrasive in the example was 96.3%, and the recovery rate of the first abrasive was improved by 5.0% compared to the comparative example described later.

(Comparative example)
As shown in Table 9, polishing was carried out in the same manner as in Example except that the residual abrasive recovery step was not performed, and 12 batches were obtained as 2 batches to obtain a total of 24 wafers.

In the comparative example, as shown in Table 7, the recovery rate of the first abrasive was 91.3%, which was 5.0% lower than the example.
Further, GBIR of the obtained wafer was measured using a measuring apparatus, and the GBIR of the wafer as a result of the measurement is shown in FIG. Further, the average value, maximum value, minimum value, and standard deviation of GBIR of the wafer in FIG.

  As shown in FIGS. 2 and 3 and Table 8, it can be seen that GBIR in the example is below the same level as in the comparative example. That is, in the example, it was confirmed that the effect of suppressing the deterioration of GBIR can be realized by setting appropriate conditions in addition to the improvement of the recovery rate.

  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.

DESCRIPTION OF SYMBOLS 1 ... Single-side polishing apparatus, 2 ... Polishing cloth, 3 ... Surface plate, 4 ... Nozzle, 5 ... Polishing head,
6 ... Wafer, 7a, 7b ... Tank, 8 ... First polishing agent, 9 ... Surface plate receiver,
DESCRIPTION OF SYMBOLS 10 ... Pipe, 11 ... Control means, 12 ... 2nd abrasive | polishing agent, 13 ... Separator.

Claims (4)

While supplying the polishing agent stored in the tank to the polishing cloth affixed on the surface plate, a load is applied to the wafer with a polishing head, the wafer is slid in contact with the polishing cloth, and the supply is performed. A method of polishing a wafer for recovering and reusing the polished abrasive in the tank,
A first polishing step of supplying a first polishing agent to perform rough polishing of the wafer with the first polishing agent; and after stopping the supply of the first polishing agent, remaining on the surface plate A residual polishing agent recovery step of recovering the first polishing agent, and a second polishing step of switching the supplied polishing agent to a second polishing agent and finely polishing the wafer with the second polishing agent. And
The recovery of the first abrasive remaining on the surface plate in the residual abrasive recovery step is performed by adjusting the rotation speed of the surface plate and the rotation of the surface plate at the time when the supply of the first abrasive is stopped. A method for polishing a wafer, which is performed by increasing the number of the wafers. In the residual abrasive recovery step,
2. The wafer polishing method according to claim 1, wherein the rotation speed of the surface plate is set in a range of 25 to 35 rpm. In the residual abrasive recovery step,
The method for polishing a wafer according to claim 1 or 2, wherein the number of rotations of the polishing head is 10 to 20 rpm, and the time is 4 to 8 seconds. In the residual abrasive recovery step,
The wafer polishing method according to claim 1, wherein the load applied to the wafer by the polishing head is 30 to 80 g / cm ² .

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