JP6491812B2 - Membrane, polishing head, workpiece polishing apparatus and method, and silicon wafer - Google Patents

Description

  The present invention relates to a polishing apparatus and a polishing method for single-side polishing a disk-shaped workpiece such as a semiconductor wafer, a polishing head for the polishing apparatus, a membrane for the polishing head, and a silicon wafer having a predetermined flatness. Is.

  In the manufacture of semiconductor wafers such as silicon wafers, which are typical examples of workpieces used for polishing, in recent years, the demand for flatness of semiconductor wafers during exposure has been severe due to the downsizing of semiconductor elements and the increase in diameter of semiconductor wafers. It has become to.

  2. Description of the Related Art Conventionally, as a technique for polishing one surface of a workpiece, a workpiece polishing method in which a workpiece is pressed from the back surface by a membrane is known. For example, Patent Document 1 proposes that the flatness of the membrane bonded to the rigid ring is 40 μm or less, so that the machining allowance on the entire surface of the workpiece is made uniform and the flatness of the workpiece to be polished is improved. ing.

JP 2010-247254 A

  However, as a result of repeated studies by the present inventors, the technique described in Patent Document 1 has a tendency that the polishing allowance of the outer peripheral portion of the work tends to be small, and the flatness of the work after polishing is not sufficient. Turned out to. Further, in the method described in Patent Document 1, when a membrane having a desired flatness is produced, the membrane is integrally formed with a rigid ring using a mold. Therefore, there is a problem that the cost is increased.

  An object of the present invention is to solve the above-described problems, and an object of the present invention is to provide a workpiece polishing apparatus and polishing method capable of obtaining a workpiece with high flatness, a polishing head for the polishing apparatus, and a polishing head for the polishing head. Is to provide a membrane. Another object of the present invention is to provide a silicon wafer having a predetermined flatness.

  As a result of intensive studies to solve the above problems, the inventors of the present invention obtain a workpiece with higher flatness when the thickness of the membrane used for polishing has a predetermined nonuniformity in the radial direction. Therefore, the present inventors have completed the present invention by obtaining new knowledge that it is effective.

The gist configuration of the present invention is as follows.
The membrane for a polishing head of the present invention is a membrane made of a flexible material that is attached to the lower surface of a polishing head used for polishing a disc-shaped workpiece and holds the back surface of the workpiece in contact and presses against a polishing pad. ,
Of the contact area of the membrane to the workpiece, an area from the outer edge of the contact area to 20 mm radially inward of the membrane is defined as the outer periphery of the membrane, and 20 mm radially outward from the center of the membrane. When the region is the inner periphery of the membrane,
The maximum thickness at the outer periphery of the membrane is smaller than the minimum thickness at the inner periphery of the membrane.
Here, “the contact area of the membrane with the workpiece” means an area surrounded by a circle having the same size as the radius of the workpiece to be polished with the center of the disc-shaped membrane as the center of the circle. And

Further, in the membrane for a polishing head of the present invention, the maximum thickness in the radial direction of the membrane is Trmax, the minimum thickness is Trmin, and the average thickness is Travel in the contact region, and the thickness in the radial direction of the membrane is uniform. Property hr (%) is expressed by the relational expression (1),
hr = {(Trmax−Trmin) / Trave} × 100
, Hr is preferably 2.8% or more.
The maximum thickness in the radial direction of the membrane is Trmax, the minimum thickness is Trmin, and the average thickness is Travel, which means the maximum thickness, the minimum thickness, and the average thickness of the membrane diameter.

  Furthermore, in the membrane for a polishing head according to the present invention, it is preferable that the thickness of the membrane gradually decreases from the center of the membrane to the outer edge of the contact region as it goes radially outward.

In addition, in the membrane for a polishing head of the present invention, on the circumference of 5 mm radially inward from the outer edge of the contact area of the membrane, the maximum thickness in the circumferential direction of the membrane is Tcmax, the minimum thickness is Tcmin, and the average The thickness is Tcave, and the thickness uniformity hc (%) in the circumferential direction of the membrane is expressed by the relational expression (2),
hc = {(Tcmax−Tcmin) / Tcave} × 100
Hc is preferably 10.2% or less.

  Here, the polishing head of the present invention is a polishing head used for polishing a disk-shaped workpiece, and the membrane, a holding plate that holds an outer edge portion of the membrane, and a pressure supply unit that supplies pressure to the membrane And.

  Further, the workpiece polishing apparatus of the present invention is a disk-shaped workpiece polishing apparatus, wherein the polishing plate is provided on the upper surface, and the polishing head is provided above the surface plate. And.

Here, the workpiece polishing method of the present invention is a disc-shaped workpiece polishing method,
Supplying pressure to a membrane made of a flexible material attached to the lower surface of the polishing head, holding the back surface of the workpiece in contact with the membrane and pressing it against the polishing pad;
Polishing the workpiece by rotating the polishing head, and
Of the contact area of the membrane to the workpiece, an area from the outer edge of the contact area to 20 mm radially inward of the membrane is defined as the outer periphery of the membrane, and 20 mm radially outward from the center of the membrane. When the region is the inner periphery of the membrane,
The maximum thickness at the outer periphery of the membrane is smaller than the minimum thickness at the inner periphery of the membrane.

Furthermore, the silicon wafer of the present invention is a silicon wafer having a diameter of 450 mm or more, and a GBIR defined by SEMI standards is 0.2 μm or less, and an area of 2 mm radially inward from the outer edge of the silicon wafer is excluded. The maximum value of SFQR defined by the SEMI standard is 0.04 μm or less.
Here, the GBIR (Global Backside Ideal Plane Range) is specifically the difference between the maximum displacement and the minimum displacement of the entire silicon wafer on the assumption that the back surface of the silicon wafer is completely adsorbed. It is obtained by calculating the difference.
In addition, SFQR (Site Front Least Squares Range) is a plane in a site where data is calculated by a least square method in a set site, and a + side from this plane (that is, the main surface of the wafer is defined as a plane). It is a value evaluated for each site expressed by the sum of absolute values of the maximum displacement amount of each of the maximum displacement amount on the upper side and the lower side (same as the lower side), and the maximum value of SFQR. Is the maximum value in the SFQR of all sites on the wafer. The flatness SFQRmax defined in the present invention is a value when the site size of 26 × 8 mm ² is measured using a flatness measuring device (manufactured by KLA-Tencor: WaferSight).

  ADVANTAGE OF THE INVENTION According to this invention, the grinding | polishing apparatus and grinding | polishing method of a workpiece | work which can obtain a workpiece | work with high flatness, the grinding | polishing head for this grinding | polishing apparatus, and the membrane for this grinding | polishing head can be provided. In addition, according to the present invention, a silicon wafer having a predetermined flatness can be provided.

It is a schematic sectional drawing which shows the double-side polish apparatus of the workpiece | work concerning one Embodiment of this invention. (A)-(c) It is a schematic diagram which shows a mode that a membrane press-contacts to a silicon wafer. It is a figure which shows the relationship between the uniformity of the circumferential direction of a membrane, and the uniformity of a machining allowance. It is a figure which shows the three-dimensional distribution of grinding allowance. (A) ~ (e) cross-sectional shape (lower diagram) of the surface of the membrane and the silicon wafer Ken Migakutodai cross-sectional shape is a diagram showing a (top). It is a figure which shows the evaluation result of SFQR. It is a figure which shows the evaluation result of GBIR.

Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a schematic sectional view showing a double-side polishing apparatus 1 for a workpiece according to one embodiment of the present invention. As shown in FIG. 1, the double-side polishing apparatus 1 includes a polishing head 2 and a surface plate 3. The polishing head 2 is provided above the surface plate 3, and a polishing pad 4 is pasted on the upper surface of the surface plate 3. The surface plate 3 is connected to a motor (not shown) that rotates the surface plate 3.

  Here, as shown in FIG. 1, the polishing head 2 includes a housing top portion 5a and a housing side portion 5b surrounding other components, and is connected to a motor or the like (not shown) for rotating the polishing head 2. A shaft 6 is provided. The housings 5a and 5b prevent internal components from unwanted exposure and wear.

  As shown in FIG. 1, the polishing head 2 has a retainer ring 7 that surrounds a disk-shaped workpiece (a silicon wafer in this example). The retainer ring 7 holds the silicon wafer W so that it does not fall off the polishing head 2. Moreover, as shown in FIG. 1, the retainer ring 7 is connected to the lower side of the housing side portion 5b.

  Here, as shown in FIG. 1, the polishing head 2 includes an internal head 12 having a disk-shaped member 8, a ring-shaped member 9, and a disk-shaped holding plate 10 inside housings 5a and 5b. A membrane 11 is attached to the lower surface of the internal head 12, which is the lower surface of the polishing head 2, to hold the back surface of the silicon wafer W (the polishing surface is the front side) and press it against the polishing pad 4. The membrane 11 is made of a flexible material. As shown in FIG. 1, the ring-shaped member 9 is connected to the lower surface of the disk-shaped member 8, and the holding plate 10 is screwed to and connected to the lower surface of the ring-shaped member 9. The outer edge portion of the membrane 11 is held and fixed so as to be sandwiched between the ring-shaped member 9 and the holding plate 10.

  As shown in FIG. 1, the housing side portion 5 b and the internal head 12 are connected by a flexible member 13. Thereby, the first pressure supply portion 14 is defined by the housing top portion 5 a, the housing side portion 5 b, the disk-like member 8, and the flexible member 13. As shown in FIG. 1, a first air supply line 15 is formed on the shaft 6 and the housing top 5 a, and the first pressure supply unit 14 is connected to the first air (not shown) via the first air supply line 15. Connected to the supply device. With this configuration, the volume in the first pressure supply unit 14 expands due to the supply of air from the first air supply device, the flexible member 13 bends, and the internal head 12 connected to the flexible member 13. Is pressed downward in the figure. The downward movement of the internal head 12 is limited within a predetermined range by the stopper 18, and therefore the pressing force on the silicon wafer W is also limited within the predetermined range.

  As shown in FIG. 1, the outer edge of the membrane 11 is held above the holding plate 10, and a region that can contact the silicon wafer W extends below the holding plate 10. As shown in FIG. 1, the second pressure supply section 16 is partitioned by the disk-shaped member 8, the ring-shaped member 9, the holding plate 10, and the membrane 11.

As shown in FIG. 1, a second air supply line 17 is formed on the shaft 6 and the housing top 5 a, the disk-shaped member 8, and the holding plate 10, and the second pressure supply unit 16 is connected to the second air supply line. 17 is connected to a second air supply device (not shown). With this configuration, the volume in the second pressure supply unit 16 is expanded by the supply of air from the second air supply device, and the membrane 11 is bent. In this way, the internal head 12 provided with the membrane 11 by the first pressure supply unit 14 is applied to the silicon wafer W while applying pressure so as to urge the membrane 11 toward the silicon wafer W by the second pressure supply unit 16. The membrane 11 can be brought into pressure contact with the back surface of the silicon wafer W by applying a pressure so as to be biased in the direction of. Thereby, the silicon wafer W can be pressed downward in the figure where the polishing pad 4 is disposed.
In this way, the polishing pad 4 and the front surface of the silicon wafer W are rotated by rotating the polishing head 2 and the surface plate 3 while supplying the polishing slurry onto the polishing pad 4 while applying pressure to the silicon wafer W. Can be slid to polish one side of the silicon wafer W.

In the present embodiment, of the contact area of the membrane 11 with respect to the silicon wafer W, an area from the outer edge of the contact area to 20 mm inward in the radial direction of the membrane 11 is defined as the outer peripheral portion of the membrane 11. When the area from the center to the radially outer side of 20 mm is used as the inner peripheral portion of the membrane 11, it is important that the maximum thickness at the outer peripheral portion of the membrane 11 is thinner than the minimum thickness at the inner peripheral portion of the membrane 11.
Hereinafter, the effect of this embodiment is demonstrated.

FIGS. 2A to 2C are schematic views showing a state in which the membrane 11 whose outer edge is held by the holding plate 10 is pressed against the silicon wafer W when air is supplied to the second pressure supply unit 16. is there.
FIG. 2A shows a case where the thickness of the membrane 11 is substantially equal between the outer peripheral portion and the inner peripheral portion. As shown in FIG. 2A, the outer edge portion of the membrane 11 is held and fixed by the holding plate 10, and therefore extends below the holding plate 10 in the membrane 11 that is a flexible member. The portion is deformed so as to form an arc with a cross-sectional shape when receiving a certain pressure by supplying air. Further, the downward movement of the internal head 12 is limited to a certain range by the stopper 18. For this reason, in the membrane 11, the pressure on the inner peripheral portion of the silicon wafer W is relatively increased, while the pressure on the outer peripheral portion of the silicon wafer W is relatively decreased. Therefore, when single-side polishing of the silicon wafer W is performed, the polishing allowance of the outer peripheral portion of the silicon wafer W tends to be small.
FIG. 2B shows a case where the thickness of the outer peripheral portion of the membrane 11 is reduced as compared with the inner peripheral portion, and FIG. 2C shows the thickness of the outer peripheral portion of the membrane 11 from FIG. This shows a case where is further reduced as compared with the inner periphery. Here, the membrane 11 is more stretchable in the portion where the thickness is thinner, and therefore the portion where the thickness is thinner will better stretch when subjected to the same pressure. Therefore, as shown in FIG. 2 (b), since the outer peripheral portion of the membrane 11 is thin, the outer peripheral portion is stretched when subjected to pressure compared to the inner peripheral portion where the membrane 11 is thick. It is relatively larger than the elongation of the peripheral part, and the membrane 11 comes into contact with the inner peripheral part and the outer peripheral part more evenly. Therefore, the difference between the pressure at the outer peripheral portion and the pressure at the inner peripheral portion when the membrane 11 is pressed against the silicon wafer W is reduced. Further, as shown in FIG. 2 (c), when the thickness of the outer peripheral portion of the membrane 11 is further reduced relative to the thickness of the inner peripheral portion, the elongation of the outer peripheral portion of the membrane 11 is further increased relatively. Therefore, the membrane 11 comes into contact with the inner peripheral portion and the outer peripheral portion more evenly. Accordingly, the pressure applied to the outer peripheral portion of the silicon wafer W can be made substantially equal to the pressure applied to the central portion of the silicon wafer W.

  According to the present embodiment, since the maximum thickness at the outer peripheral portion of the membrane 11 is thinner than the minimum thickness at the inner peripheral portion of the membrane 11, the membrane 11 can be pressed sufficiently uniformly over the entire surface of the silicon wafer W. By polishing with, a silicon wafer with higher flatness can be obtained. Furthermore, when the membrane 11 is replaced, it is only necessary to use a mold once used to create the membrane 11, and it is not necessary to perform integral molding with other members, so that replacement at a low cost is possible. According to the polishing apparatus of this embodiment, there is no need for any contrivance in the apparatus itself, and the above effect can be obtained by a simple method in which the membrane 11 has a predetermined non-uniform thickness in the radial direction. it can.

Here, in the present invention, in the contact region, the thickness uniformity hr (%) in the radial direction of the membrane defined by the relational expression (1) is 2.8% or more. Preferably, it is 22% or more, more preferably 34% or more. As described above (as will be described in Examples below), the lower the uniformity in the radial direction of the membrane (the larger the numerical value of hr), the more the membrane can be stretched at the outer periphery of the workpiece, This is because the flatness of the workpiece after polishing becomes higher.
On the other hand, if the thickness uniformity in the radial direction of the membrane is too low (the value of hr is too large), the elongation at the outer periphery of the membrane becomes too large, and the amount of polishing at the outer periphery of the workpiece increases. Accordingly, the hr (%) is preferably not more than 37% because the shape of the workpiece may become uneven.

  In the present invention, it is preferable that the thickness of the membrane 11 gradually decreases from the center of the membrane 11 to the outer edge of the contact region as it goes radially outward. When the thickness is uniform, as shown in FIG. 2A, the pressure gradually decreases from the center of the membrane 11 to the outer edge. Therefore, the elongation of the membrane 11 gradually increases from the center of the membrane 11 to the outer edge so as to cancel out the pressure. This is because the membrane 11 can press the entire surface of the work W more uniformly.

Furthermore, in the present invention, the thickness uniformity in the circumferential direction of the membrane 11 defined by the above relational expression (2) on the circumference of 5 mm radially inward from the outer edge of the contact region of the membrane 11. hc (%) is preferably 10.2% or less, more preferably 6.5% or less, and even more preferably 1.4% or less. This is because the flatness of the workpiece W after polishing is higher when the thickness uniformity in the circumferential direction of the membrane 11 is higher (the numerical value of hc is smaller), as will be described in the examples described later.
In addition, since the uniformity in the circumferential direction is higher (the smaller the numerical value of hc), the lower limit of hc is not particularly limited.

In the present invention, membrane 11 is flexible material is preferably used as a JIS-A hardness of 30 to 90 °, as the specific material are not particularly limited, for example, ethylene-flop Ropirengomu It is preferable to use silicone rubber, butyl rubber or the like.

  Further, the membrane 11 of the present invention can basically be manufactured by a known method. For example, by injecting silicone rubber, which is the material of the membrane, into the mold for casting, and adjusting the flatness of the mold and the pressure distribution of the press machine, the maximum value of the outer peripheral thickness is Membranes thinner than the minimum thickness can be produced.

Furthermore, in the present invention, the thickness of the membrane 11 is preferably 0.5 to 1.5 mm. Moreover, in this invention, it is preferable that the thickness in the outer peripheral part of the membrane 11 shall be 1.3%-66% of the thickness in an inner peripheral part.
By setting the ratio to 1.3% or more, the pressure at the outer peripheral portion exerted on the workpiece W by the membrane 11 can be made closer to the pressure at the inner peripheral portion. On the other hand, by setting the pressure to 66% or less, the membrane This is because, by reducing the thickness of the outer peripheral portion having the property of being difficult to stretch due to the structure of rubber, the outer peripheral portion can be uniformly pressurized and can be uniformly pressurized.
In reducing the thickness of the membrane 11, the thickness on the side where the workpiece W is pressed may be reduced, the thickness on the side receiving pressure from the second pressure supply unit 16 may be reduced, or both of them may be reduced. May be reduced.

Here, as will be described in detail in the examples described later, according to the present invention, a wafer that achieves high flatness can be obtained even in a large-diameter silicon wafer having a diameter of 450 mm or more. Has a diameter of 450 mm or more, a GBIR defined by SEMI standards of 0.2 μm or less, and a maximum SFQR value of 0.04 μm or less excluding an annular region 2 mm radially inward from the outer edge of the workpiece. A silicon wafer can be obtained.
Thereby, the yield in a device manufacturing process etc. can be improved.

Next, a method for polishing a workpiece according to an embodiment of the present invention will be described.
In the workpiece polishing method of this embodiment, polishing is performed using the apparatus shown in FIG. Since the apparatus configuration shown in FIG. 1 has already been described, the description thereof will be omitted.

In the workpiece polishing method of the present embodiment, first, air is supplied to the first pressure supply unit 14 via the first air supply line 15 by the first air supply device, and the volume of the first pressure supply unit 14 is expanded. The internal head 12 is pressed downward.
In addition, the second air supply device supplies air to the second pressure supply unit 16 via the second air supply line 17, expands the volume of the second pressure supply unit 16, and supplies pressure to the membrane 11. The membrane 11 is urged downward.
Thus, the silicon wafer W can be pressed against the membrane 11 by supplying pressure to the membrane 11 while pressing the internal head 12 to which the membrane 11 is attached in the direction of the silicon wafer W below.
Then, the polishing slurry is supplied onto the polishing pad 4, and the polishing head 2 and the surface plate 3 are rotated by driving means such as a motor while the membrane 11 is pressed against the silicon wafer from the back surface of the silicon wafer W. One side of the silicon wafer W can be polished by sliding the polishing pad 4 and the polishing surface of the silicon wafer W.

Here, the workpiece polishing method of this embodiment is characterized in that the maximum thickness at the outer peripheral portion of the membrane 11 is thinner than the minimum thickness at the inner peripheral portion of the membrane 11.
As a result, the membrane 11 can be pressed sufficiently uniformly over the entire surface of the silicon wafer W, and a silicon wafer with higher flatness can be obtained by polishing in this state. Furthermore, when the membrane 11 is replaced, it is only necessary to use a mold once used to create the membrane 11, and it is not necessary to perform integral molding with other members, so that replacement at a low cost is possible. According to the polishing method of the present embodiment, there is no need to add a process, and the above effect can be obtained by a simple method using a membrane 11 whose thickness has a predetermined nonuniformity in the radial direction. .

Although the embodiments of the present invention have been described above, the present invention can be widely applied to any polishing head, polishing apparatus, and polishing method that presses the back surface of the work W using the membrane 11 to perform single-side polishing of the work W. The present invention is not limited to the above-described embodiment. For example, in the above embodiment, the method of pressurizing the membrane 11 with air has been described. However, a method of pressurizing the membrane 11 with a pressurized fluid may be used. In the above embodiment, the example in which the membrane 11 directly presses the workpiece W has been shown. However, in the apparatus shown in FIG. 1, a foaming polyurethane backing pad is applied to the lower surface of the membrane 11, and the backing pad is It can also comprise so that the workpiece | work W may be pressed through. In the above-described embodiment, the example in which the first pressure supply unit 14 bends the flexible member with air has been described. However, the internal head 12 is configured to be biased downward by another elastic body or the like. You can also.
Examples of the present invention will be described below, but the present invention is not limited to these examples.

<Example 1>
In order to evaluate the relationship between the uniformity in the circumferential direction of the membrane and the polishing allowance, a plurality of membranes having different uniformity in the circumferential direction were produced, and a test for measuring each polishing allowance was performed. Here, EPDM rubber was used as the membrane. In addition, a p-type silicon wafer having a diameter of 450 mm, a thickness of 925 μm, and a crystal orientation (100) was used as the disk-shaped workpiece. Further, the polishing was performed using the apparatus shown in FIG. In this test, an alkaline aqueous solution mainly composed of potassium hydroxide (KOH) containing abrasive grains (fine colloidal silica) is used as the polishing slurry, the pressing force is 10 kPa, the rotation speed of the polishing head is 30 rpm, and the rotation of the surface plate The number was 30 rpm, and the polishing time was 240 sec.
Here, the circumferential uniformity of the membrane is defined by the above formula (2), and a smaller numerical value indicates higher uniformity. Further, the machining allowance uniformity U (%) excludes an annular region from the outer edge of the silicon wafer to 2 mm inward in the radial direction, and for the entire remaining region, the maximum machining allowance is dmax, the minimum machining allowance is dmin, and the average machining allowance. Is set to dave,
U = {(dmax−dmin) / (2 × dave)} × 100
The smaller the numerical value, the higher the uniformity.
The membrane thickness was measured by using a contact-type thickness meter. Moreover, each said stock removal was measured using the nano metro by Kuroda, and the three-dimensional distribution was also measured using the nano metro by Kuroda.

  FIG. 3 is a diagram showing the relationship between the uniformity in the circumferential direction of the membrane and the uniformity of the machining allowance. FIG. 4 shows the three-dimensional distribution of polishing allowance particularly when the uniformity in the circumferential direction of the membrane is 15.2%, 11.1%, 10.2%, 6.5%, and 1.4%. FIG.

  As shown in FIGS. 3 and 4, it can be seen that the higher the uniformity in the circumferential direction of the membrane, the higher the uniformity of the polishing allowance of the silicon wafer. In particular, the polishing allowance was 20% or less when the uniformity in the circumferential direction of the membrane was 1.4% to 10.2%. In addition, the radial uniformity (defined by the above formula (1)) was 1.5% to 2%.

<Example 2>
Next, a test for evaluating the relationship between the uniformity in the radial direction of the membrane and the polishing allowance was performed. The polishing conditions are the same as in the previous test. Here, the uniformity in the radial direction of the membrane is defined by the above formula (1), and the smaller the numerical value, the higher the uniformity.
5A to 5E, the radial uniformity of the membrane is 37%, 34%, and 22%. 2.8%, in the case of 2%, respectively, a diagram showing the surface of the cross-sectional shape of the membrane (bottom view) and the cross-sectional shape (top view) of a polishing allowance of the silicon wafer.

As shown in FIGS. 5A to 5E, it can be seen that the lower the uniformity in the radial direction of the membrane, the higher the uniformity of the polishing allowance of the silicon wafer. In particular, the uniformity of polishing allowance range radial uniformity of the membrane is 2.8% to 37% becomes 20% or less. In addition, the uniformity in the circumferential direction (defined by the above formula (2)) at this time was 12% to 15%.

<Example 3>
Next, the test which compares the flatness and surface roughness (RMS) of the silicon wafer obtained by this invention and the silicon wafer concerning a prior art example was done. As a silicon wafer of the present invention, a polished silicon wafer obtained by the above test was used. This silicon wafer has a diameter of 450 mm, a membrane with a radial uniformity of 20% and a circumferential uniformity of 7%, and is obtained when polishing is performed under the above polishing conditions. It is a thing.
In addition, as a silicon wafer according to the conventional example, a silicon wafer polished using a polishing apparatus having a membrane integrally molded with a rigid ring was prepared. The membrane used for polishing according to the conventional example had a substantially uniform thickness in the radial direction.
Here, the flatness of the silicon wafer was measured by measuring the maximum values of GBIR and SFQR. First, GBIR was measured using (KLA-Tencor, Inc .: WaferSight). In addition, the maximum value of SFQR is obtained by using a Nanometer 450TT manufactured by Kuroda Seiko Co., Ltd., and obtaining a plurality of 26 mm × 8 mm rectangular samples for the area excluding the 2 mm annular area radially inward from the outer edge of the silicon wafer. Measured.
Furthermore, about the surface roughness (RMS) of the silicon wafer, the roughness of the front and back surfaces of the silicon wafer was measured using Chapman MPS manufactured by Chapman Instruments.
Hereinafter, the evaluation results will be described.

FIG. 6 is a diagram illustrating the evaluation result of the maximum value of SFQR. As shown in FIG. 6, the silicon wafer obtained by the present invention has a maximum SFQR distributed in a range of 0.04 μm or less, and it can be seen that the flatness is higher than that of the conventional silicon wafer. .
Moreover, FIG. 7 is a figure shown about the evaluation result of GBIR. As shown in FIG. 7, it can be seen that the silicon wafer obtained by the present invention has a smaller GBIR and higher flatness than the conventional silicon wafer.
Therefore, although the silicon wafer obtained by the present invention is a large-diameter silicon wafer having a diameter of 450 mm or more, GBIR is 0.2 μm or less and the maximum value of SFQR is 0.04 μm or less. It can be seen that the degree can be achieved.
Further, the surface roughness (RMS) of the silicon wafer is such that the surface roughness on the front side which is the polished surface is 2 nm or less, and the ratio A / B of the surface roughness A to the surface roughness B on the back surface is 0. .4 or less.

  ADVANTAGE OF THE INVENTION According to this invention, the grinding | polishing apparatus and grinding | polishing method of a workpiece | work which can obtain a workpiece | work with high flatness, the grinding | polishing head for this grinding | polishing apparatus, and the membrane for this grinding | polishing head can be provided. In addition, according to the present invention, a silicon wafer having a predetermined flatness can be provided.

DESCRIPTION OF SYMBOLS 1 Double-side polish apparatus 2 Polishing head 3 Surface plate 4 Polishing pad 5a Housing top part 5b Housing side part 6 Shaft 7 Retainer ring 8 Disc-shaped member 9 Ring-shaped member 10 Holding plate 11 Membrane 12 Internal head 13 Flexible member 14 First pressure Supply unit 15 First air supply line 16 Second pressure supply unit 17 Second air supply line 18 Stopper

Claims (5)

A membrane made of a flexible material that is attached to the lower surface of a polishing head used for polishing a disk-shaped workpiece and holds the back surface of the workpiece in contact and presses against a polishing pad,
Of the contact area of the membrane to the workpiece, an area from the outer edge of the contact area to 20 mm radially inward of the membrane is defined as the outer periphery of the membrane, and 20 mm radially outward from the center of the membrane. When the region is the inner periphery of the membrane,
The maximum thickness at the outer periphery of the membrane is thinner than the minimum thickness at the inner periphery of the membrane,
Within the contact area, the maximum thickness in the radial direction of the membrane is Trmax, the minimum thickness is Trmin, the average thickness is Travel, and the thickness uniformity hr (%) in the radial direction of the membrane is expressed by the relational expression (1),
hr = {(Trmax−Trmin) / Trave} × 100
And hr is 2.8% or more and 37% or less, and
On the circumference of 5 mm radially inward from the outer edge of the contact area of the membrane, the maximum thickness in the circumferential direction of the membrane is Tcmax, the minimum thickness is Tcmin, the average thickness is Tcave, and the thickness in the circumferential direction of the membrane is The uniformity hc (%) is expressed by the relational expression (2),
hc = {(Tcmax−Tcmin) / Tcave} × 100
In when defining, hc is state, and are 15% more than 12% or less,
A membrane for a polishing head , wherein the flexible material has a JIS-A hardness of 30 to 90 ° .   2. The membrane for a polishing head according to claim 1, wherein the thickness of the membrane gradually decreases from the center of the membrane to the outer edge of the contact region as it goes radially outward. A polishing head used for polishing a disk-shaped workpiece,
The membrane according to claim 1 or 2,
A holding plate for holding the outer edge of the membrane;
A polishing head, comprising: a pressure supply unit that supplies pressure to the membrane. A disk-shaped workpiece polishing apparatus,
A surface plate on which the polishing pad is applied on the upper surface;
An apparatus for polishing a workpiece, comprising: the polishing head according to claim 3 provided above the surface plate. A method for polishing a disk-shaped workpiece,
Supplying pressure to a membrane made of a flexible material attached to the lower surface of the polishing head, holding the back surface of the workpiece in contact with the membrane and pressing it against the polishing pad;
Polishing the workpiece by rotating the polishing head, and
Of the contact area of the membrane to the workpiece, an area from the outer edge of the contact area to 20 mm radially inward of the membrane is defined as the outer periphery of the membrane, and 20 mm radially outward from the center of the membrane. When the region is the inner periphery of the membrane,
The maximum thickness at the outer periphery of the membrane is thinner than the minimum thickness at the inner periphery of the membrane,
Within the contact area, the maximum thickness in the radial direction of the membrane is Trmax, the minimum thickness is Trmin, the average thickness is Travel, and the thickness uniformity hr (%) in the radial direction of the membrane is expressed by the relational expression (1),
hr = {(Trmax−Trmin) / Trave} × 100
And hr is 2.8% or more and 37% or less, and
On the circumference of 5 mm radially inward from the outer edge of the contact area of the membrane, the maximum thickness in the circumferential direction of the membrane is Tcmax, the minimum thickness is Tcmin, the average thickness is Tcave, and the thickness in the circumferential direction of the membrane is The uniformity hc (%) is expressed by the relational expression (2),
hc = {(Tcmax−Tcmin) / Tcave} × 100
In when defining, hc is state, and are 15% more than 12% or less,
The method for polishing a workpiece, wherein the flexible material has a JIS-A hardness of 30 to 90 ° .