JP5750877B2 - Wafer single-side polishing method, wafer manufacturing method, and wafer single-side polishing apparatus - Google Patents

Description

  The present invention relates to a wafer single-side polishing method, a wafer manufacturing method, and a wafer single-side polishing apparatus. In particular, the present invention relates to a wafer single-side polishing method capable of effectively reducing scratches on a wafer surface after polishing by reducing scratches generated on the wafer surface in an initial stage of polishing.

  Chemical mechanical polishing (CMP) is used for surface polishing of a wafer such as a semiconductor wafer that requires high flatness. CMP uses a polishing liquid that has an etching action on an object to be polished, and typically etches the object to be polished by a chemical action, and typically uses a machine based on relative movement between the polishing liquid containing abrasive grains and the object to be polished. This is a polishing technique that performs mechanical polishing.

  A typical single-side polishing apparatus that performs CMP includes a polishing head that holds a wafer, and a polishing platen (rotary surface plate) that faces the polishing head and has a polishing cloth fixed to the surface. Then, the polishing head is controlled, the surface to be polished of the wafer is pressed against the polishing cloth on the polishing platen, and the polishing head and the polishing platen are rotated while supplying the polishing liquid onto the polishing cloth. Apply polishing.

Here, a conventional single-side polishing method will be described with reference to FIG. As shown in FIG. 3A, the surface to be polished of the wafer is pressed against a polishing cloth (not shown) on the polishing platen 12 having a radius R larger than the diameter of the wafer W so that the polishing platen 12 and the wafer W are in the same direction. Rotate each. In FIG. 3A, the rotation direction of the polishing platen 12 is indicated by a solid line arrow, and the rotation direction of the wafer W is indicated by a broken line arrow. Both the polishing platen 12 and the wafer W are rotated counterclockwise as viewed from above the polishing apparatus. Yes. The rotation center of the wafer W is O ₁ and the rotation center of the polishing platen 12 is O ₂ . In the conventional single-side polishing method, as shown in FIG. 3A, the rotation center O ₁ of the wafer W is separated from the relatively outer peripheral portion on the polishing platen, for example, the rotation center O ₂ of the polishing platen 12 by R / 2. The polishing process was started by pressing the wafer W against the polishing platen 12 so as to be positioned and then starting to rotate. After the start of polishing, the polishing process is generally performed while the wafer W is fixed to the outer peripheral region of the polishing platen 12 or while the wafer W is swung on the polishing platen 12. This is because the relative speed between the wafer W and the polishing platen 12 becomes uniform within the wafer in the outer peripheral region of the polishing platen, and more uniform polishing is possible.

  As an example of a conventional single-side polishing method, Patent Document 1 discloses that a load current value of one or both of a motor for rotating a polishing platen and a motor for rotating a polishing head is constant. A technique for polishing while adjusting the pressing force is described.

JP 2009-38232 A

  The polishing method shown in FIG. 3A is preferable from the viewpoint of realizing uniform polishing. However, when the present inventors observed the appearance of a wafer that was stopped at the initial stage of polishing by this method, a large number of scratches were generated on the polished surface of the wafer as shown in FIG. I found out. For wafers that had been polished to a predetermined thickness without being stopped at the initial stage, the number of scratches was reduced, but some remained. Since scratches on the wafer surface deteriorate the performance of semiconductor devices manufactured from the wafer or the manufacturing yield of semiconductor devices, it is desirable to reduce the scratches.

  In addition, it has been found that the tendency to generate many scratches in the initial stage is particularly remarkable in a large-diameter wafer having a diameter of 450 mm or more. At present, when a large-diameter wafer is required for improving the productivity of semiconductor devices, it is particularly necessary to reduce scratches on the surface of the large-diameter wafer.

  Patent Document 1 is a technique for suppressing the generation of scratches by adjusting the pressing force of the wafer against the polishing platen from the middle of polishing, and there is no problem recognition that scratches occur on the wafer surface in the initial stage of polishing. It does not disclose any means for solving the problem.

  Therefore, in view of the above problems, the present invention provides a single-side polishing method for a wafer, which can effectively reduce scratches on the wafer surface after completion of polishing by reducing scratches generated on the wafer surface in an initial polishing stage. It is an object of the present invention to provide a manufacturing method and a wafer single-side polishing apparatus.

  When the inventors measured the load current value of the motor that rotates the polishing platen 12 in the conventional single-side polishing method described with reference to FIG. 3A, as shown in FIG. A large load current was observed. This indicates that an excessive polishing torque was generated at the start of polishing. The present inventors considered that this excessive polishing torque is a cause of scratches generated on the wafer surface in the initial stage of polishing, and conducted intensive studies to reduce the load current value at the start of polishing. It is found that the initial object can be achieved by positioning the wafer in the central region of the platen, and then continuing the polishing process while moving the wafer to the outside of the polishing platen, thereby completing the present invention. It came.

This invention is based on said knowledge and examination, The summary structure is as follows.
(1) A wafer having a radius r held by a polishing head is pressed against a polishing cloth fixed to the surface of the polishing platen, and the polishing head and the polishing platen are rotated while supplying a polishing liquid, thereby A method for polishing a single side of a wafer, wherein the surface to be polished is polished.
Starting the polishing process under an arrangement in which the initial position of the rotation center of the wafer is within the center region of the polishing platen where the distance P from the rotation center of the polishing platen is 0 < P <r;
Continuing the polishing process while moving the rotation center of the wafer from the initial position to the radially outer side of the polishing platen;
A method for polishing a single side of a wafer, comprising:

(2) In the polishing process continuation step, the rotation center of the wafer is moved to a predetermined position outside the central region,
The wafer single-side polishing method according to (1), further comprising the step of fixing the rotation center of the wafer at the predetermined position and continuing the polishing process.

  (3) The wafer single-side polishing method according to (2), wherein the predetermined position is an outer peripheral region of P ≧ R / 2, where R is a radius of the polishing platen.

  (4) In the polishing process starting step, the surface to be polished of the wafer and a polishing cloth on the polishing platen are brought into contact, and then the polishing head and the polishing platen are rotated. The method for polishing one side of a wafer according to any one of claims 1 to 4.

( 5 ) The wafer single-side polishing method according to any one of (1) to ( 4 ), wherein in the polishing process continuation step, the rotation center of the wafer is linearly moved from the initial position.

( 6 ) The single-side polishing method of a wafer according to any one of (1) to ( 5 ), wherein the wafer is a large-diameter wafer having a diameter of 450 mm or more.

( 7 ) A method for producing a wafer, comprising a polishing step by the single-side polishing method for a wafer according to any one of (1) to ( 6 ) above.

( 8 ) a polishing head for holding a wafer having a radius r;
A polishing platen facing the polishing head and having a polishing cloth fixed to the surface;
First and second motors for rotating the polishing head and the polishing platen, respectively;
A polishing liquid supply mechanism for supplying a polishing liquid onto the polishing cloth;
A movable mechanism that enables relative movement between the polishing head and the polishing platen;
A control unit for controlling the movable mechanism;
A single-side polishing apparatus for a wafer having
The controller, when starting the polishing process, arranges the rotation center of the wafer in the central region of the polishing platen where the distance P from the rotation center of the polishing platen is 0 < P <r, and during the polishing process, The single-side polishing apparatus for a wafer, wherein the movable mechanism is controlled so as to move the rotation center of the wafer from the initial position to the outside in the radial direction of the polishing platen.

  According to the present invention, by starting the polishing process in the central region of the polishing platen, it is possible to prevent excessive polishing torque from being generated at the start of polishing, and as a result, to reduce scratches generated on the wafer surface in the initial polishing stage. Thus, scratches on the wafer surface after polishing can be effectively reduced.

1 is a schematic side view of a representative single-side polishing apparatus according to the present invention. BRIEF DESCRIPTION OF THE DRAWINGS It is the top view which saw through the polishing platen and the wafer from the upper part of the single-side polish apparatus explaining the typical single-side polishing method according to this invention, (a) showed the positional relationship of the wafer and polishing platen at the time of a grinding | polishing start. FIG. 4B is a diagram showing the positional relationship between the wafer and the polishing platen when the wafer is moved to the outer periphery of the polishing platen and polishing is continued. (A) is the top view which saw through the polishing platen and the wafer from the upper side of the single-side polishing apparatus explaining the conventional single-side polishing method, and (b) is the load current of the motor that rotates the polishing platen in the conventional single-side polishing method. The graph which shows a time-dependent change of a value, (c) is the visual appearance figure of the wafer surface when grinding | polishing is complete | finished in the grinding | polishing initial stage in the conventional single-side grinding | polishing method. FIG. 3 is a schematic top view of a wafer and a polishing platen for explaining a mode in which polishing torque is generated, where (a) shows polishing by a single-side polishing method according to the present invention, and (b) shows polishing by a conventional single-side polishing method. The case of starting is shown. It is a graph which shows a time-dependent change of the load current value of the motor which rotates a polishing platen when the distance L between the rotation centers of a wafer and a polishing platen is made into various values, (a) is L = r (comparative example), (B) is for L = r / 2 (example), (c) is for L = r / 4 (example), and (d) is for L≈0 (example). It is a graph which shows the scratch incidence of the wafer in an Example and a comparative example.

  Hereinafter, the present invention will be described in more detail with reference to the drawings. In principle, the same components are denoted by the same reference numerals, and description thereof is omitted.

(Wafer single-side polishing equipment)
A typical single-side polishing apparatus according to the present invention will be described with reference to FIG. The single-side polishing apparatus 100 for a wafer W includes a polishing head 10 that holds a wafer W having a radius r, and a polishing platen 12 that has a polishing cloth 11 that faces the polishing head 10 and is fixed to the surface. The first motor 13 rotates the polishing head 10, and the second motor 14 rotates the polishing platen 12. As a movable mechanism that enables relative movement between the polishing head 10 and the polishing platen 12, this single-side polishing apparatus 100 is a swing guide for linearly moving the polishing head 10 in a horizontal direction (a direction parallel to the polishing platen 12). 16 and a swing motor 17 and an up / down motor 18 for vertically moving the polishing head 10 in a vertical direction (a direction perpendicular to the polishing platen 12). When the swing motor 17 is driven, the polishing head 10 moves along the swing guide 16, and as a result, the in-plane position of the wafer W on the polishing platen 12 can be changed. Further, when the up / down motor 17 is driven, the contact and non-contact between the wafer W and the polishing cloth 11 on the polishing platen 12 can be controlled. While the wafer W is pressed against the polishing pad 11 by the vertical motor 17 and the polishing liquid is supplied onto the polishing pad 11 from the polishing liquid supply mechanism 15, the polishing head 10 and the polishing platen 12 are moved by the first motor 13 and the second motor 14. When rotated, the surface to be polished of the wafer can be polished.

  The control unit 19 controls driving of the swinging motor 17 and the vertical motor 18 that are movable mechanisms. The first motor 13 and the second motor 14 may be controlled by a separate control unit (not shown). However, if the control unit 19 performs the control, the relative movement and rotation of the polishing head 10 and the polishing platen 12 are combined. Can be controlled. A feature of the single-side polishing apparatus 100 is the control of the movable mechanism by the control unit 19, which will be described in detail later. At the start of polishing processing, polishing with a distance P from the rotation center of the polishing platen 12 satisfying 0 ≦ P <r. The center of rotation of the wafer is arranged in the central region of the platen, and the center of rotation of the wafer W is moved from the initial position to the outside in the radial direction of the polishing platen 12 during the polishing process. With this single-side polishing apparatus 100, a single-side polishing method described in detail below can be carried out.

(Wafer single-side polishing method)
A typical wafer single-side polishing method according to the present invention will be described with reference to FIG. In this single-side polishing method, the wafer W having a radius r held by the polishing head 10 is pressed against the polishing cloth 11 fixed to the surface of the polishing platen 12, and the polishing head 10 and the polishing platen 12 are rotated while supplying the polishing liquid. As a result, the surface to be polished of the wafer W is polished.

FIGS. 2A and 2B are diagrams showing the in-plane position of the wafer W on the polishing platen 12. Normally, the polishing platen 12 has a radius R sufficiently larger than the radius r of the wafer W, and in the present embodiment, R> 2r will be described. In FIG. 2, the rotation direction of the polishing platen 12 is indicated by a solid line arrow, and the rotation direction of the wafer W is indicated by a broken line arrow, and both the polishing platen 12 and the wafer W are rotated in the same direction (counterclockwise) when viewed from above the polishing apparatus. . The rotation center of the wafer W is O ₁ , the rotation center of the polishing platen 12 is O _2, and the distance between both rotation centers is L. Note that, as in the present embodiment, the rotation center and the geometric center are usually the same for both the wafer W and the polishing platen, but the present invention is not limited to this.

FIG. 2A is a diagram showing the positional relationship between the wafer and the polishing platen at the start of polishing. Thus, under the arrangement in which the initial position of the rotation center O ₁ of the wafer W is within the center region 12a of the polishing platen where the distance P from the rotation center O ₂ of the polishing platen 12 is 0 ≦ P <r, Start polishing. For example, in a state where the polishing head 10 and the polishing platen 12 are not rotated, the wafer W is pressed against the polishing pad 11 so that the wafer W and the polishing platen 12 have the positional relationship shown in FIG. Thereafter, the polishing head 10 and the polishing platen 12 are rotated to start polishing.

FIG. 2B is a diagram showing the positional relationship between the wafer and the polishing platen when the wafer is moved to the outer peripheral portion of the polishing platen and polishing is continued. As described above, after the polishing is started, the polishing process is continued while moving the rotation center O _{1 of the} wafer from the initial position to the radially outer side of the polishing platen 12.

  The technical significance of adopting the above characteristic process in the single-side polishing method of the present invention will be described together with the function and effect with reference to FIG.

As described above, when the polishing process is started by pressing the wafer W against the outer periphery of the polishing platen 12, excessive polishing torque is generated, and polishing is performed by the motor (the second motor 14 in FIG. 1) that rotates the polishing platen 12. An excessive load current was observed at the beginning of the process. This is considered to be due to the following reasons. First, the rotation directions of the wafer W and the polishing platen 12 at the start of polishing are as shown in FIG. Here, since the rotation direction of the wafer W is the same as the rotation direction of the polishing platen 12 in the left half region in FIG. 4B with the rotation center O ₁ of the wafer W as a reference, the wafer W and the polishing platen 12 are the same. And the relative speed becomes relatively small. However, since the right half region of the wafer W is the left half region with respect to the rotation center O ₂ of the polishing platen 12, the rotation direction of the wafer W is opposite to the rotation direction of the polishing platen 12. For this reason, since the relative speed between the wafer W and the polishing platen 12 is increased, a very large frictional resistance is generated in this region at the start of polishing, which is a major factor in generating an excessive polishing torque. Furthermore, the polishing liquid does not sufficiently permeate between the wafer W and the polishing pad 11 at the start of polishing, and the friction coefficient is high, which is a major factor for increasing the frictional resistance.

Therefore, in the present invention, the wafer W is positioned in the central region of the polishing platen 12 at the start of polishing. As an example, FIG. 4A shows a case where polishing is started in a state where the rotation center O ₁ of the wafer W coincides with the rotation center O ₂ of the polishing platen 12. In this case, since the rotation direction is the same as the rotation direction of the polishing platen 12 in the right half as well as the left half of the wafer W, the relative speed between the wafer W and the polishing platen 12 is reduced, and the frictional resistance is also reduced. Become. Therefore, an excessive polishing torque generated when polishing is started on the outer peripheral portion of the polishing platen 12 is not generated, and scratches generated on the wafer surface due to the excessive polishing torque at the start of polishing are effectively reduced. It becomes possible.

  It is obvious that the above-described effects can be obtained regardless of the rotational speeds of the wafer W and the polishing platen 12. For example, if the angular velocity of the wafer W and the angular velocity of the polishing platen 12 are set equal, the wafer W The relative speed with respect to the polishing platen 12 becomes zero at all the positions, and no matter how high the friction coefficient is, no polishing torque is generated.

In the present invention, the central region 12a of the polishing platen 12, the distance P from the rotation center _{O 2} is defined as a set of 0 ≦ P <r a is a point P (see FIG. 2 (a)), in the central region 12a The polishing process is started in a state where the rotation center O ₁ of the wafer W is positioned at the position. In this case, the distance L between the rotation centers is also 0 ≦ L <r. If L <r, as shown in FIG. 2 (a), of the wafer W, the rotation center O ₁ of the wafer W in the right half as a reference, and the right half the rotational center O ₂ of the polishing platen 12 as a reference The part which becomes becomes. In this portion, since the rotation direction of the wafer W is the same as the rotation direction of the polishing platen 12, the above-described effects are obtained.

On the other hand, when polishing is continued in the central region 12a, the relative speed with the polishing platen 12 is not uniform within the surface to be polished of the wafer. Further, in order to minimize the polishing torque at the start of polishing, when the angular velocities of the wafer W and the polishing platen 12 are close to each other, a sufficient polishing amount cannot be obtained and the angular velocities are equalized. The effective polishing amount is zero. Therefore, in the present invention, after the polishing is started, the polishing process is continued while moving the rotation center O ₁ of the wafer W from the initial position (FIG. 2A) to the radially outer side of the polishing platen 12 (FIG. 2). (See (b)).

  As described above, in the present invention, by starting the polishing process in the central region of the polishing platen, an excessive polishing torque is prevented from being generated at the start of polishing, and as a result, scratches generated on the wafer surface in the initial polishing stage are reduced. As a result, scratches on the wafer surface after the polishing can be effectively reduced. In particular, polishing in the central region of the polishing platen is a process that cannot normally be taken from the viewpoint of making the polishing amount of the wafer uniform. In the present invention, the wafer W is placed in the central region only at the start of polishing, and thereafter By moving the polishing platen to the outside in the radial direction, the requirement for uniform polishing is also satisfied.

From the viewpoint of obtaining the above-described effects of the present invention more remarkably, it is preferable that the initial position of the rotation center O ₁ of the wafer W is a region where 0 ≦ P ≦ r / 2 in the central region 12a.

The initial position of the rotation center O ₁ of the wafer W, of the central region 12a, preferably a region to be 0 <P. That is, from the viewpoint of obtaining the effects of the present invention more remarkably, the polishing starts, the rotation center O ₁ of the wafer W, but it is preferred to as much as possible close to the rotational center O ₂ of the polishing platen 12, both the center of rotation Are preferably not matched (ie, L ≠ 0). When L = 0, only the rotation center O ₁ of the wafer W is not polished at the stage before the wafer is moved. Therefore, after the polishing process is completed, the polishing is performed on the rotation center O ₁ of the wafer W and other portions. This is because there is a possibility that a difference in amount is generated and uniform polishing is hindered. If the angular velocity of the wafer W and the angular velocity of the polishing platen 12 are set to be completely equal, there is no concern as described above.

  The time from the start of the polishing process in the central region 12a of the polishing platen 12 to the start of movement outward in the radial direction is not particularly limited. However, it is preferable to start the movement after the polishing liquid sufficiently penetrates between the wafer W and the polishing pad 11 by the rotational movement, because the movement can be performed with less polishing resistance and the generation of scratches due to the movement can be suppressed. . Specifically, the time from the start of the polishing process to the start of movement depends on the composition of the polishing liquid used, but if it is approximately 10 seconds, the polishing liquid can be sufficiently infiltrated.

In polishing continuing step (FIG. 2 (b)), the rotation center O ₁ of the wafer W is moved to a predetermined position outside the central region 12a, the rotation center O ₁ of the wafer W is fixed to the predetermined position, It is preferable to continue the polishing process. Thereby, more uniform polishing can be realized after starting polishing with a low polishing torque.

Further, the predetermined position outside the central region 12a is preferably the outer peripheral region 12b of P ≧ R / 2. The outer peripheral region 12b is a set of points P where P = R / 2 indicated by a broken line in FIG. In FIG. 2 (b), it moves the rotation center O ₁ of the wafer W to the position of P = R / 2 is the innermost edge of the peripheral region 12b, are continuing to polishing. Thereby, more uniform polishing can be realized. However, the wafer W does not protrude from the polishing platen 12.

In the polishing process continuation step, it is preferable to linearly move the rotation center O ₁ of the wafer W from the initial position. The method of linearly moving on the polishing platen 12 is the simplest and simple in the structure of the apparatus, and can be accurately moved to a predetermined position.

A method for moving the rotation center O ₁ of the wafer W from the initial position to the outside in the radial direction of the polishing platen 12 is not particularly limited as long as it is a relative movement between the wafer W and the polishing platen 12. For example, as shown in FIG. 1, while the polishing platen 12 is fixed, the polishing head 10 can be moved to move the wafer W relative to the polishing platen 12.

  The relative speed between the wafer W and the polishing platen 12 in the above movement is not particularly limited. However, if the relative speed is excessively high, there is a possibility of causing scratches on the surface of the wafer W. Therefore, the speed is at most 30 mm / sec or less. It is desirable to move with.

  In order to perform the polishing process, two conditions are: 1) the surface to be polished of the wafer W and the polishing cloth 11 on the polishing platen 12 are in contact, and 2) the polishing head 10 and the polishing platen 12 are rotated. Is at least necessary. Therefore, in the polishing process start step of the present invention, which of the above two conditions is satisfied first is not limited. Whether the wafer W starts to rotate after contacting the polishing cloth 11 or the wafer W is in contact with the polishing cloth 11 in the rotating state, the wafer W can be positioned in the central region of the polishing platen 12 at the start of polishing. This is because the effects of the present invention are achieved. However, as in this embodiment, it is preferable to bring the surface to be polished of the wafer W into contact with the polishing cloth 11 on the polishing platen 12 and then rotate the polishing head 10 and the polishing platen 12. That is, since the polishing cloth 11 that is an elastic body has a displacement immediately after contact, the parallelism between the wafer W and the polishing platen 12 cannot be secured sufficiently, and a biased pressure distribution is generated on the wafer. This is because cracks may occur. In particular, this tendency increases as the diameter of the wafer W increases.

By applying the single-side polishing method of the present invention to polishing a large-diameter wafer having a diameter of 450 mm or more, a particularly remarkable effect can be obtained. The larger the object to be polished, the larger the load current value necessary for polishing and the larger the contact area with the polishing pad 11, so that a larger polishing torque is generated at the start of polishing, and the problem to be solved by the present invention is. This is because it appears more prominently. For example, in the wafer diameter 450 m m, even if you set the surface pressure of (g / cm ²⁾ to the same extent as the surface pressure (g / cm ²⁾ during polishing with a diameter of 300mm wafers, the total weight (kg) 2 .25 times and the radius is 1.5 times. As a result, the supply of the polishing liquid to the processing point is remarkably impaired, and the friction between the polishing cloth and the wafer W increases accordingly. Due to these complex factors, the problem to be solved by the present invention becomes more prominent in the case of a large-diameter wafer having a diameter of 450 mm or more.

(Wafer manufacturing method)
The method for producing a wafer according to the present invention includes a polishing step by the single-side polishing method for a wafer according to the present invention described so far. By manufacturing a wafer by this method, scratches generated on the wafer surface in the initial stage of polishing can be reduced, and as a result, a wafer having effectively reduced scratches on the wafer surface after polishing can be obtained.

  The method for producing a wafer of the present invention includes a step of preparing a pre-stage wafer for polishing. For example, a slicing process → rough chamfering process → lapping process → single-side grinding process → finishing chamfering process → mirror polishing (EM) process of chamfered portion → etching process is performed. Next, a rough polishing process and a final polishing process are performed in this order on the wafer surface. The single-side polishing method of the present invention can be applied to this final polishing step. In this way, a polished wafer can be obtained. Furthermore, an epitaxial wafer may be manufactured by epitaxially growing a single crystal silicon layer (epitaxial film) having a thickness of several μm on the wafer surface, or an annealed wafer may be manufactured by annealing in hydrogen or air. . The single-side polishing method of the present invention can also be applied to the rough polishing step.

  Although the present invention has been described above, these are examples of typical embodiments, and the present invention is not limited to these embodiments, and various modifications can be made within the scope of the invention. It can be changed.

  In order to further clarify the effects of the present invention, comparative evaluations in which experiments of Examples and Comparative Examples described below were conducted will be described.

(Example)
First, a silicon wafer having a diameter of 450 mm (radius r = 225 mm), whose front and back surfaces were roughly polished, was prepared. The surface of this silicon wafer was finish-polished by the single-side polishing method according to the present invention described below. For the final polishing, a single-side polishing apparatus having the configuration shown in FIG. 1 was used. The radius R of the polishing platen was 1200 mm, and a suede type polishing cloth was used. The polishing liquid supplied onto the polishing cloth was an alkaline aqueous solution mainly composed of potassium hydroxide (KOH) containing fine colloidal silica as abrasive grains. The polishing head was controlled by the vertical motor, and the wafer W was pressed against the polishing cloth. At that time, the distance L between the rotation center of the wafer W and the rotation center of the polishing platen on the polishing platen was set to L≈0 (specifically, 30 mm). Thereafter, while supplying the polishing liquid, rotation was started at a rotation speed of the wafer of 40 rpm and a rotation speed of the polishing platen of 40 rpm, and polishing processing was started. Thereafter, polishing is continued for 10 seconds without changing the distance L between the rotation centers of the wafer and the polishing platen, and then the polishing head is moved at a speed of 10 mm / s to polish the rotation center of the wafer outward in the radial direction of the polishing platen. It was moved linearly to a position separated by R / 2 from the center of rotation of the platen. Thereafter, the polishing process was continued for 180 seconds without changing the distance between the rotation centers. A total of 30 wafers were polished.

  As another example, the wafer was polished by the same method as above except that the center distance L at the start of the polishing process was changed to various values. Specifically, 30 polishing processes were performed for L = r / 4, L = r / 2, L = 7r / 9, and L = 8r / 9, respectively.

(Comparative example)
The wafer was polished by the same method as in the example except that the center distance L at the start of the polishing process was changed to various values to make it outside the scope of the present invention. Specifically, 30 polishing processes were performed for L = r, L = 10r / 9, and L = 11r / 9, respectively.

(Measurement of platen load current)
In Examples and Comparative Examples in which the center-to-center distance L at the start of polishing was varied, the load current value of a motor that rotates the polishing platen during polishing (hereinafter referred to as “platen load current”) was measured. . As a comparative example, FIG. 5A shows the change over time in the platen load current value when L = r, and the change over time when L = r / 2, L = r / 4, and L≈0 as an example. FIG. 5B, FIG. 5C, and FIG. 5D respectively.

As shown in FIG. 5A, when L = r, which is a comparative example, an excessive platen load current equivalent to that in the conventional single-side polishing method shown in FIG. It was. On the other hand, as shown in FIGS. 5B, 5C, and 5D, in the case of L = r / 2, L = r / 4, and L≈0 as an example, the platen load current at the start of polishing Was found to be significantly suppressed.

(Scratch rate)
FIG. 6 shows the ratio of wafers where scratches were observed on the polished surface of the wafer after completion of polishing in each of Examples and Comparative Examples in which the center-to-center distance L at the start of polishing processing was various values.

  As shown in FIG. 6, in the comparative example of L ≧ r, the scratch rate was as high as 9 to 10%, whereas in the example of L <r, the scratch rate was as low as 6% or less. In particular, a lower scratch rate could be obtained when r ≦ r / 2.

  According to the present invention, by starting the polishing process in the central region of the polishing platen, it is possible to prevent excessive polishing torque from being generated at the start of polishing, and as a result, to reduce scratches generated on the wafer surface in the initial polishing stage. Thus, scratches on the wafer surface after polishing can be effectively reduced.

DESCRIPTION OF SYMBOLS 10 Polishing head 11 Polishing cloth 12 Polishing platen 12a Central area | region of polishing platen 12b Outer peripheral area | region of polishing platen 13 1st motor 14 2nd motor 15 Polishing liquid supply mechanism 16 Oscillation guide (movable mechanism)
17 Swing motor (movable mechanism)
18 Vertical motor (movable mechanism)
19 Control unit 100 Single-side polishing apparatus W Wafer O Rotation center of ₁ wafer Rotation center of O ₂ polishing platen

Claims (8)

The wafer having a radius r held by the polishing head is pressed against a polishing cloth fixed to the surface of the polishing platen, and the polishing head and the polishing platen are rotated while supplying the polishing liquid. A method of polishing a wafer on one side,
Starting the polishing process under an arrangement in which the initial position of the rotation center of the wafer is within the center region of the polishing platen where the distance P from the rotation center of the polishing platen is 0 < P <r;
Continuing the polishing process while moving the rotation center of the wafer from the initial position to the radially outer side of the polishing platen;
A method for polishing a single side of a wafer, comprising: In the polishing continuation step, the rotation center of the wafer is moved to a predetermined position outside the central region,
2. The wafer single-side polishing method according to claim 1, further comprising the step of fixing the rotation center of the wafer at the predetermined position and continuing the polishing process.   3. The wafer single-side polishing method according to claim 2, wherein when the radius of the polishing platen is R, the predetermined position is an outer peripheral region of P ≧ R / 2.   4. The polishing process according to claim 1, wherein in the polishing process starting step, a surface to be polished of the wafer and a polishing cloth on the polishing platen are brought into contact with each other, and then the polishing head and the polishing platen are rotated. Wafer single-side polishing method. Wherein the polishing continues step, the rotation center of the wafer, single side polishing method for a wafer according to any one of claims 1 to 4 linearly moves from the initial position. The single-side polishing method for a wafer according to any one of claims 1 to 5 , wherein the wafer is a large-diameter wafer having a diameter of 450 mm or more. A method for manufacturing a wafer, comprising a polishing step by the single-side polishing method for a wafer according to any one of claims 1 to 6 . A polishing head for holding a wafer of radius r;
A polishing platen facing the polishing head and having a polishing cloth fixed to the surface;
First and second motors for rotating the polishing head and the polishing platen, respectively;
A polishing liquid supply mechanism for supplying a polishing liquid onto the polishing cloth;
A movable mechanism that enables relative movement between the polishing head and the polishing platen;
A control unit for controlling the movable mechanism;
A single-side polishing apparatus for a wafer having
The controller, when starting the polishing process, arranges the rotation center of the wafer in the central region of the polishing platen where the distance P from the rotation center of the polishing platen is 0 < P <r, and during the polishing process, The single-side polishing apparatus for a wafer, wherein the movable mechanism is controlled so as to move the rotation center of the wafer from the initial position to the outside in the radial direction of the polishing platen.

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