JP6822432B2 - Wafer single-sided polishing method - Google Patents

Description

The present invention relates to a single-sided polishing method for a wafer.

One of the surface polishing methods for wafers that require high flatness, such as semiconductor wafers, is a single-sided polishing method that polishes only one side of the wafer. The single-sided polishing method is widely used from rough polishing using a relatively hard polishing pad to finish polishing using a relatively soft polishing pad.

Conventionally, a single-sided polishing apparatus 200 as shown in FIG. 4 has been used for rough polishing. The single-side polishing apparatus 200 includes a rotary surface plate 10 to which a polishing pad 12 for polishing one surface of the wafer W is attached. Further, the single-side polishing apparatus 200 includes a backing pad 22 which is the other holding surface of the wafer W and a retainer ring 24 attached to the outer edge portion of the backing pad 22 on the holding surface side, and is arranged to face the rotary surface plate 10. The polishing head 20 is provided. Here, the retainer ring 24 is generally made of a hard resin material or the like. Further, the single-sided polishing apparatus 200 includes a slurry supply unit 30 that supplies a polishing slurry 32 containing a water-soluble polymer onto the polishing pad 12. Here, the polishing slurry 32 contains silica particles that function as abrasive grains, a water-soluble basic compound that functions as an etching agent for a wafer, and a water-soluble polymer that functions as a protective agent for a wafer. Further, the polishing head 20 includes a shaft portion 26 for raising and lowering and rotating the polishing head 20, and a rotating frame portion 28 provided at the lower end of the shaft portion 26 and having a backing pad 22 attached to the lower surface. Further, the single-sided polishing apparatus 200 is connected to the rotary surface plate 10 and includes a surface plate rotating shaft 14 for rotating the rotary platen 10. The shaft portion 26 and the surface plate rotating shaft 14 are connected to a drive mechanism (not shown) such as a motor. In the single-sided polishing apparatus 200, the rotary surface plate 10 and the polishing head 20 rotate together, so that the rotary surface plate 10 and the polishing head 20 rotate relative to each other, and the polishing slurry 32 is transferred from the polishing slurry supply unit 30 onto the polishing pad 12. While supplying, only one surface of the wafer W is polished.

In such a single-sided polishing apparatus 200, the shape of the wafer after polishing may fluctuate depending on the usage time of the backing pad 22 and the retainer ring 24, which is a problem in stabilizing the flatness of the wafer. There is. Patent Document 1 describes a technique for improving the flatness of a wafer in a single-sided polishing apparatus 200 as shown in FIG. 4 by the following method. That is, in the single-sided polishing apparatus 200 as shown in FIG. 4, polishing conditions such as the rotation speed, polishing pressure, and type of backing pad 22 of the rotary surface plate 10 and the polishing head 20 are adjusted. In such an adjustment, the amount of change in the depth of the recess for accommodating and holding the wafer W, which is defined by the inner peripheral surface of the retainer ring 24 and the surface of the backing pad 22 on the retainer ring side, before and after polishing is small. It is done like this. As a result, the maximum absolute value of the ESFQD (Edge Site flatness Front reference leastsQuare Deviation) of the wafer is suppressed. The "ESFQD" is an index showing the flatness of the wafer, and the smaller the maximum value of the absolute value, the higher the flatness of the wafer.

JP-A-2017-87328

In Patent Document 1, in order to improve the flatness of the wafer after polishing, the maximum absolute value of the ESFQD of the wafer is suppressed. Certainly, when a wafer immediately after rough polishing is used as a polished wafer, it is required to reduce the maximum value of ESFQD of the wafer immediately after rough polishing. However, the ESFQD of the wafer immediately after rough polishing does not necessarily have to have a small maximum value. For example, when an epitaxial wafer is obtained by subjecting a wafer immediately after rough polishing to epitaxial growth, it is necessary to make the shape of the wafer immediately after rough polishing a sagging shape. That is, it is necessary to set the ESFQD of the wafer after rough polishing to a negative predetermined value. This is because the epitaxial growth rate of the outer peripheral portion of the wafer is higher than that of the central portion, so that a flat epitaxial wafer cannot be obtained unless the outer peripheral sagging shape is obtained. Therefore, it is not always necessary to reduce the ESFQD in the wafer immediately after rough polishing, and it is required to approach the desired ESFQD corresponding to the epitaxial wafer or the polished wafer with high accuracy.

In view of the above problems, an object of the present invention is to provide a single-sided polishing method for a wafer capable of obtaining a wafer having a desired ESFQD with high accuracy.

In Patent Document 1, the amount of change in the depth of the recess before and after polishing is controlled, which corresponds to controlling the amount of protrusion of the wafer defined by the difference between the center thickness of the wafer and the thickness of the retainer ring. .. This amount of protrusion changes each time the wafer is subjected to polishing due to variations in the center thickness of the wafer to be polished and wear of the retainer ring over time. Therefore, the ESFQD of the wafer after polishing varies from a desired value each time the wafer is subjected to polishing. By the way, it is practically difficult to perform high-precision control in μm units so that the protrusion amount is always constant. For example, although it is conceivable to use a single-sided polishing device capable of controlling the distance between the surface to be polished of the wafer and the lower surface of the retainer ring by independently raising and lowering the chuck holding the retainer ring and the wafer. Such a single-sided polishing device requires many sensors and control units, and the structure becomes complicated.

Therefore, the present inventors have studied a single-sided polishing method for a wafer, which can obtain a wafer having a desired ESFQD with high accuracy without controlling the protrusion amount of the wafer. Then, it was found that the correlation between the amount of protrusion of the wafer and ESFQD largely depends on the concentration of the water-soluble polymer as a protective agent for the wafer contained in the polishing slurry. Therefore, by appropriately determining the concentration of the water-soluble polymer according to the protrusion amount of the wafer, it is not possible to obtain a wafer having a desired ESFQD with high accuracy without controlling the protrusion amount of the wafer. I got the idea.

The present invention has been completed based on the above idea, and its gist structure is as follows.
[1] A rotary surface plate to which a polishing pad for polishing one surface of the wafer is attached, and
A polishing head provided with a backing pad serving as a holding surface for the other surface of the wafer and a retainer ring attached to an outer edge portion of the backing pad on the holding surface side, and arranged to face the rotary surface plate.
A slurry supply unit that supplies a polishing slurry containing a water-soluble polymer onto the polishing pad,
It is a method of single-sided polishing of a wafer using a single-sided polishing device of a wafer.
The first step of calculating the protrusion amount of the wafer based on the following equation (1), and
The second step of determining the concentration of the water-soluble polymer contained in the polishing slurry based on the protrusion amount, and
The rotary surface plate and the polishing head are relatively rotated to polish one side of the wafer while supplying the polishing slurry having the concentration of the water-soluble polymer determined in the second step onto the polishing pad. 3 steps and
A method for single-sided polishing of a wafer, which comprises.
Record
[Extrusion amount] = [Wafer center thickness]-[Retainer ring thickness] ・ ・ ・ (1)

[2] The method for single-sided polishing of a wafer according to the above [1], wherein in the second step, the concentration of the water-soluble polymer is determined based on the following formula (2).
Record
[Desirable ESFQD] = A x ([Protrusion amount] -B) x ([Concentration of water-soluble polymer] -C) + D ... (2)
However, A, B, C, and D are coefficients obtained by linear regression analysis of the actual values of single-sided polishing of the wafer.

[3] The method for single-sided polishing of a wafer according to the above [2], wherein the protrusion amount is 75 μm or more and 200 μm or less.

[4] The single-sided polishing apparatus further includes a plurality of slurry tanks each storing polishing slurries having different concentrations of water-soluble polymers.
Prior to the polishing in the third step, the step of selecting a slurry tank in which the polishing slurry having the concentration of the water-soluble polymer determined in the second step is stored is further included from the plurality of slurry tanks.
The single-sided polishing method for a wafer according to any one of the above [1] to [3], wherein the polishing slurry stored in the selected slurry tank is supplied in the third step.

According to the single-sided polishing method for a wafer of the present invention, a wafer having a desired ESFQD can be obtained with high accuracy.

It is a schematic diagram which shows the single-sided polishing apparatus 100 of the wafer which can be used in one Embodiment of this invention. It is a flowchart which shows the single-sided polishing method of the wafer by one Embodiment of this invention. It is a graph which shows the correlation of the protrusion amount of a wafer and the average value of ESFQD by the study of these inventors. It is a schematic diagram which shows the conventional single-sided polishing apparatus 200.

Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

First, the single-sided polishing apparatus 100 for wafers used in one embodiment of the present invention will be described with reference to FIG. The single-side polishing apparatus 100 includes a rotary surface plate 10 to which a polishing pad 12 for polishing one surface of the wafer W is attached, and a backing pad 22 and a backing pad 22 which are the other holding surfaces of the wafer W. A retainer ring 24 attached to an outer edge portion on the side is provided, and a polishing head 20 arranged to face the rotary surface plate 10 and a polishing slurry supply unit 30 for supplying the polishing slurry 32 onto the polishing pad 12 are provided. The polishing slurry 32 contains at least a water-soluble polymer, and can further contain abrasive grains and an etching agent, and the water-soluble polymer can function as a protective agent for the wafer W. The retainer ring 24 may be configured to have an inner diameter equal to or larger than the diameter of the wafer W.

Further, the polishing head 20 can include a shaft portion 26 for raising and lowering and rotating the polishing head 20, and a rotating frame portion 28 provided at the lower end of the shaft portion 26 and having a backing pad 22 attached to the lower surface. .. Further, the single-sided polishing apparatus 100 can include a surface plate rotating shaft 14 that is connected to the rotating surface plate 10 and rotates the rotating surface plate 10. The shaft portion 26 and the surface plate rotating shaft 14 can be connected to a drive mechanism (not shown) such as a motor.

Further, the single-sided polishing apparatus 100 can be provided with slurry tanks 40A to 40X for storing polishing slurries having different concentrations of water-soluble polymers. These slurry tanks 40A to 40X can be connected to the polishing slurry supply pipes 44A to 44X for supplying the polishing slurry to the polishing slurry supply unit 30 via the on-off valves 42A to 42X, respectively.

Further, the single-sided polishing apparatus 100 can be controlled by using the control unit 50. The control unit 50 includes a control unit (not shown) that controls the opening and closing of the on-off valves 42A to 42X and the rotation of the shaft portion 26 and the surface plate rotating shaft 14 (not shown), and a calculation unit (not shown) that calculates polishing conditions. It may be provided. The control unit 50 can be realized by a central processing unit (CPU) or the like inside the computer.

In the following, with reference to FIGS. 1 and 2, an example of a single-sided polishing method for a wafer that can be performed by using the single-sided polishing apparatus 100 described above will be described. The wafer that can be used for the single-sided polishing method of the wafer of the present invention is not particularly limited, and examples thereof include a silicon wafer and a SiC wafer.

With reference to FIG. 2, in the first step, the protrusion amount of the wafer W is calculated based on the following equation (1) (step S10).

[Extrusion amount] = [Wafer center thickness]-[Retainer ring thickness] ・ ・ ・ (1)

Here, with reference to FIG. 1, in the first step, the control unit 50 reads the center thickness of the wafer W from the storage unit (not shown) (step S11), and the control unit 50 retains from the storage unit. A step of reading out the thickness (step S12) and a step of calculating the protrusion amount of the wafer W based on the above equation (1) by the control unit 50 using the read-out center thickness of the wafer W and the thickness of the retainer (step S13). And can be done by. The "center thickness of the wafer W" may be stored in the storage unit after the center thickness of the wafer before rough polishing is measured in advance by a known spectral interference displacement device. Further, the "retainer ring thickness" can be an average value of the thicknesses at eight points at equal intervals in the circumferential direction of the retainer ring, which are measured in advance using a known spectral interference displacement device, and the value is stored in the storage unit. You can store it in. However, the first step in the present invention is not limited to this, and for example, instead of steps S11 to S13, each time the wafer W is subjected to single-side polishing, the center thickness of the wafer W and the thickness of the retainer are known for spectral interference displacement. It may be measured by the device.

Next, with reference to FIG. 2, in the second step, the concentration of the water-soluble polymer contained in the polishing slurry is determined based on the protrusion amount calculated in the first step (step S20).

Here, the second step is preferably performed by determining the concentration of the water-soluble polymer contained in the polishing slurry based on the following equation (2) using the predetermined coefficients A, B, C and D. .. In addition, this determination may be made by using the control unit 50.

[Desirable ESFQD] = A x ([Protrusion amount] -B) x ([Concentration of water-soluble polymer] -C) + D ... (2)

Hereinafter, the experiments by the present inventors who have obtained the findings of the present invention will be described. First, various polishing slurries were prepared. Then, a plurality of combinations of the polishing head 20 and the wafer W provided with the retainer ring 24 so that the protrusion amount of the wafer becomes a specific value within a predetermined range (for example, 75 μm or more and 200 μm or less) are prepared. In the experiment, first, one-sided polishing is performed on these wafers W with constant polishing conditions such as pressing force and rotation speed, except for the amount of protrusion and the polishing slurry. Next, the average value of ESFQD of the polished wafer is obtained. As a result, the average value of ESFQD corresponding to the concentration of the predetermined water-soluble polymer and the amount of protrusion can be obtained. This series of operations is repeated by moving the concentration of the water-soluble polymer and the amount of protrusion within the predetermined range described above. Focusing on the water-soluble polymer that functions as a protective agent contained in the polishing slurry, a correlation of the average value of ESFQD with respect to the protrusion amount of the wafer can be obtained according to each concentration of the water-soluble polymer as shown in FIG. It was. From this result, it was found that the correlation between the protrusion amount of the wafer and ESFQD largely depends on the concentration of the water-soluble polymer as a protective agent contained in the polishing slurry. Then, when the linear regression analysis was performed on the correlation shown in FIG. 3 with the protrusion amount as the explanatory variable and the mean value of ESFQD as the objective variable, the above equation (2) was obtained. Therefore, A, B, C, and D in the above equation (2) are coefficients obtained by linear regression analysis of the actual values of single-sided polishing of the wafer in this way. Here, A is the physical characteristics (hardness, compressibility, thickness) of the backing pad and the polishing pad, the polishing conditions (polishing load, the number of rotations of the polishing head and the rotating surface plate, the polishing time), and the dilution rate with pure water or the like. Depends on. B and C depend on the type of water-soluble polymer. D depends on the end face shape of the wafer and the ESFQD of the wafer before being subjected to polishing (that is, the ESFQD of the material).

In addition, "ESFQD (Edge Site flatness Front reference leastsQuare Deviation)" in this specification means ESFQD defined in SEMI M67. Specifically, a flatness measuring device (manufactured by KLA-Tencor: WaferSight2) was used for the measurement of ESFQD. ESFQD is an index showing the site flatness at the outer peripheral portion (edge) of the wafer. The ESFQD divides the outer peripheral portion of the wafer into a large number (for example, 72) fan-shaped regions (sites), and uses the in-site plane calculated by the least squares method as the reference for the data in the site, and starts from this in-site plane. It is the maximum displacement amount including the code of, and each site has one data. That is, the ESFQD is the SFQD value of each site (the deviation of the larger positive or negative from the least squares surface in the region). The ESFQD site excludes a region 2 mm in the radial direction from the outermost circumference, and has two straight lines with a sector length of 30 mm extending inward from the outer peripheral reference end to the center side in the radial direction, and 5 ° in the outer circumference direction of the wafer. It is a substantially rectangular area surrounded by an arc corresponding to (± 2.5 °).

The "concentration of the water-soluble polymer" in the above formula (2) is preferably 0 ppm or more and 60 ppm or less, and more preferably 20 ppm or more and 50 ppm or less. This is because if it is 20 ppm or more, roll-off can be easily suppressed, and if it is 50 ppm or less, a more sufficient polishing rate can be secured.

The "concentration of the water-soluble polymer" means the concentration measured by the following method. That is, the sample obtained by adjusting the pH of the stock solution of the polishing slurry with sodium hydroxide and sulfuric acid to 3.0 is passed through a gas containing no carbon dioxide (for example, N ₂ ) and centrifuged (manufactured by AS ONE Corporation). : By centrifuging at 14000 rpm for 30 minutes using MCD-2000), a supernatant from which the water-soluble polymer adsorbed on the silica particles contained in the polishing slurry has been removed is obtained. Then, the concentration of the water-soluble polymer adsorbed on the silica particles is measured with respect to the supernatant using a total organic carbon measuring meter (TOC meter Seabass model 810).

The "protrusion amount" in the above formula (2) is preferably 75 μm or more and 200 μm or less. This is because if it is 75 μm or more, the polishing rate can be secured, and if it is 200 μm or less, cracking or chipping of the wafer can be suppressed.

By using the above formula (2), the concentration of the water-soluble polymer capable of accurately realizing the desired ESFQD can be determined, but the present invention is not limited to this. That is, the present invention is based on the finding that the correlation between the protrusion amount of the wafer W and the ESFQD changes depending on the concentration of the water-soluble polymer contained in the polishing slurry, and the invention is based on the finding that the protrusion amount of the wafer W changes. It is important to properly determine the concentration of the water-soluble polymer that achieves the desired ESFQD.

Next, referring to FIGS. 1 and 2, in the third step, the rotary surface plate 10 and the polishing head 20 are relatively rotated, and the concentration of the water-soluble polymer determined in the second step is placed on the polishing pad 12. Polishing one side of the wafer W while supplying the polishing slurry 32 of the above (step S30). The relative rotation of the rotary surface plate 10 and the polishing head 20 may be performed by the control unit 50 rotating the surface plate rotation shaft 14 and the shaft unit 26, respectively. Further, the polishing slurry 32 may be supplied by the control unit 50 opening an on-off valve (not shown) of the slurry supply unit. Further, when the predetermined polishing time elapses, the control unit 50 stops the rotation of the surface plate rotating shaft 14 and the shaft unit 26, and closes the on-off valve of the slurry supply unit 30 to end the single-sided polishing. Good.

Here, prior to the polishing in the third step, the control unit 50 stores the polishing slurry having the concentration of the water-soluble polymer determined in the second step from the slurry tanks 40A to 40X (the present embodiment). Then, the step of selecting the slurry tank 40A) may be further included (step S31). In this case, in the third step, the control unit 50 opens the on-off valve 42A of the slurry tank 40A selected in step S31, so that the polishing slurry 32 stored in the selected slurry tank 40A is placed on the polishing pad 12. One side of the wafer W can be polished while being supplied (step S32).

Next, the polishing slurry 32 that can be used in one embodiment of the present invention will be described.

The stock solution of the polishing slurry 32 can contain silica particles that function as abrasive grains, a water-soluble basic compound that functions as an etching agent for the wafer, and a water-soluble polymer that functions as a protective agent for the wafer. .. Such a polishing slurry may be used as it is as a stock solution, or may be appropriately diluted with an aqueous medium such as pure water, ultrapure water, or ion-exchanged water. In the following, each component that can be contained in the stock solution of the polishing slurry 32 will be described.

Examples of the silica particles include colloidal silica, fumed silica, and precipitated silica. As the silica particles, one of these may be used alone, or two or more of them may be used in combination. It is particularly preferable to use colloidal silica from the viewpoint of suppressing the generation of scratches on the surface of the wafer and improving the polishing performance. The concentration of silica particles is preferably 8% by mass or more and 15% by mass or less in the stock solution of the polishing slurry. If it is 8% by mass or more, a sufficient polishing rate can be secured, so that the manufacturing cost can be suppressed, and if it is 15% by mass or less, the cost of the polishing slurry and the generation of scratches on the wafer surface are suppressed. Because it can be done. The average primary particle size of the silica particles is preferably 15 nm or more and 40 nm or less. If it is 15 nm or more, a sufficient polishing rate can be secured, so that the manufacturing cost can be suppressed, and if it is 40 nm or less, the cost of the polishing slurry and the occurrence of scratches on the wafer surface can be suppressed. Is.

In the present specification, the "average primary particle diameter" is calculated based on the BET method, and a molecule having a known adsorption area is adsorbed on the particle surface at the liquid nitrogen temperature, and the adsorption amount is used. The specific surface area of the particles is obtained, and this means the value obtained by converting the specific surface area into the diameter of the spherical particles.

The water-soluble basic compound can generate hydroxide ions in water that can chemically polish a polishing target such as a silicon wafer. Furthermore, it also has an action of assisting the dispersion of silica particles. From the viewpoint of obtaining such an action more stably, it is preferable that the water-soluble basic compound is dissolved in the composition. Examples of water-soluble basic compounds include ammonia, ammonium carbonate, ammonium hydrogencarbonate, organic amine compounds, tetramethylammonium hydroxide, sodium hydroxide, and potassium hydroxide, one or more of these. Can be used in. Organic amine compounds include methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine, triethylamine, ethanolamine, diisopropylethylamine, ethylenediamine, diethylenetriamine, triethylenetetramine, tris (2-aminoethyl) amine, N, N, N', N'-tetramethylethylenediamine, hexamethylenediamine, 1,4,7-triazacyclononane, 1,4,7-trimethyl-1,4,7-triazacyclononane, 1,4-diazabicyclooctane, Examples thereof include piperazine and piperidine, and these can be used in one kind or two or more kinds.

The pH of the polishing slurry is preferably adjusted to 8 or more and 12 or less. When the pH is 8 or more, the etching action on the wafer can be exhibited, and when the pH is 12 or less, the dissolution of the silica particles which are abrasive grains is prevented and the deterioration of the mechanical polishing action by the abrasive grains is suppressed. Because it can be done.

Examples of the water-soluble polymer include polymers such as polyvinylpyrrolidone, polyethylene glycol, polyvinyl alcohol, polypropylene glycol, polyethylene glycol, and hydroxyethyl cellulose having a molecular weight of 10,000 or more, and one of them can be used. It may be used alone or in combination of two or more. From the viewpoint of improving the polishing rate, the molecular weight is more preferably 20000 or more.

The raw materials of the polishing slurry are other than the above components for the purpose of adjusting the properties of the polishing slurry, capturing metal ions, and assisting the adsorption of the water-soluble polymer to the polishing target (a silicon wafer is exemplified as a specific example). May contain the following additives. For example, alcohols, chelates, and nonionic surfactants are mentioned, and one or more of these additives may be added. Examples of alcohols include methanol, ethanol, propyl alcohol, ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, and glycerin, and one or more of these can be added. Examples of chelates include ethylenediaminetetraacetic acid (EDTA), nitrilotriacetic acid (NTA), hydroxyethylenediaminetetraacetic acid, propanediaminetetraacetic acid, diethylenetriaminetetraacetic acid, and triethylenetetraminehexacetic acid, as well as ammonium and sodium salts thereof. , And metal salts such as potassium salts, and one or more of these can be added. Examples of nonionic surfactants include polyoxyethylene alkyl ethers, polyoxyethylene alkenyl ethers, polyoxyalkylene alkyl ethers, polyoxyalkylene alkenyl ethers, alkyl polyglycosides, and polyether-modified silicones. One or more can be added.

The method for producing the polishing slurry 32 is not particularly limited, and for example, each of the above-mentioned components may be suitably mixed using a known mixing device such as a blade type stirrer, an ultrasonic disperser, or a homomixer.

Although the single-sided polishing method for the wafer of the present invention has been described above by taking the present embodiment as an example, the present invention is not limited to the above embodiment, and modifications can be made as appropriate within the scope of the claims.

(Example of Invention)
In order to confirm the effect of the present invention, as an example of the invention, single-sided polishing of the wafer was performed according to the single-sided polishing apparatus shown in FIG. 1 and the flowchart shown in FIG. 2, and the variation in ESFQD of the wafer after polishing was evaluated.

In the above evaluation, the following conditions were adopted. As the polishing slurry, three types of polishing slurries having concentrations of the water-soluble polymer (polyvinylpyrrolidone, molecular weight: 20000) measured by the above-mentioned method of 27 ppm, 33 ppm, and 50 ppm were diluted 30 times with pure water. I prepared something. All the polishing slurries contained colloidal silica as silica particles, the concentration in the stock solution was 13% by mass, and the average primary particle diameter measured by the BET method was 35 nm. The water-soluble base compound was tetramethylammonium hydroxide, and the pH was adjusted to 10.5.

As the polishing pad, a polishing pad manufactured by Fujibo (registered trademark: POLYPAS) was used. As the backing pad and retainer ring, a Fujibo template (POLYPAS_Template) in which these were integrated was used. A single crystal silicon wafer was used as the wafer. The polishing load was 150 g / cm ² , the rotation speed of the polishing head and the rotary surface plate was 12 rpm, and the allowance amount was 500 nm to 1000 nm.

As the wafers to be polished and the retainer rings, 200 wafers (600 wafers in total) were prepared in which the protrusion amount calculated by the formula (1) was the value shown in Table 1. Table 1 shows the average value of 200 sheets. However, the thickness of the retainer ring was set to a constant value. Further, regarding the coefficient of the above-mentioned formula (2), the polishing conditions are determined in advance as constant, and in the formula (2), A is 0.0053 / ppm, B is 50 μm, C is 12.4 ppm, and D is −. It was 25 nm and the desired ESFQD was -15 nm.

(Comparison example)
In the comparative example, 200 wafers (600 wafers in total) having a protrusion amount of the value shown in Table 1 were prepared as wafers and retainer rings to be polished. Table 1 shows the average value of 200 sheets. However, the thickness of the retainer ring was set to a constant value. Then, one-sided polishing of the wafer was performed using only one type of polishing slurry having a polyvinylpyrrolidone concentration of 33 ppm without using the formula (2). Other conditions are the same as those of the invention example.

(Explanation of evaluation method and evaluation result)
In the invention example and the comparative example, the ESFQD of the polished wafer was measured by a spectroscopic interference displacement device. Then, the average value of the amount of deviation from the desired ESFQD (= [desired ESFQD]-[measured ESFQD]) was calculated. The measurement results are shown in Table 1.

As shown in Table 1, in the example of the invention, since the concentration of the water-soluble polymer was determined based on the equations (1) and (2), when the protrusion amount of the wafer was 100 μm, 140 μm, or 179 μm. However, the ESFQD of the polished wafer could be brought close to the desired ESFQD (-15 nm) with high accuracy. On the other hand, in the comparative example in which the concentration of the water-soluble polymer was not determined based on the equation (2), when the protrusion amount was 100 μm or 179 μm, the deviation amount was larger than that in the invention example, and after polishing. The ESFQD of the wafer could not be brought close to the desired ESFQD with high accuracy.

According to the single-sided polishing method for a wafer of the present invention, a wafer having a desired ESFQD can be obtained with high accuracy.

100 Single-sided polishing device 10 Rotating surface plate 12 Polishing pad 14 Surface plate rotating shaft 20 Polishing head 22 Backing pad 24 Retaining 26 Shaft part 28 Rotating frame part 30 Polishing slurry supply part 32 Polishing slurry 40A to X Slurry tank 42A to X On-off valve 44A to X Polishing slurry supply pipe 50 Control unit W wafer

Claims (4)

A rotary surface plate to which a polishing pad for polishing one surface of the wafer is attached,
A polishing head provided with a backing pad serving as a holding surface for the other surface of the wafer and a retainer ring attached to an outer edge portion of the backing pad on the holding surface side, and arranged to face the rotary surface plate.
A slurry supply unit that supplies a polishing slurry containing a water-soluble polymer onto the polishing pad,
It is a method of single-sided polishing of a wafer using a single-sided polishing device of a wafer.
The first step of calculating the protrusion amount of the wafer based on the following equation (1), and
The second step of determining the concentration of the water-soluble polymer contained in the polishing slurry based on the protrusion amount, and
The rotary surface plate and the polishing head are relatively rotated to polish one side of the wafer while supplying the polishing slurry having the concentration of the water-soluble polymer determined in the second step onto the polishing pad. 3 steps and
A method for single-sided polishing of a wafer, which comprises.
Record
[Extrusion amount] = [Wafer center thickness]-[Retainer ring thickness] ・ ・ ・ (1) The single-sided polishing method for a wafer according to claim 1, wherein in the second step, the concentration of the water-soluble polymer is determined based on the following equation (2).
Record
[Desirable ESFQD] = A x ([Protrusion amount] -B) x ([Concentration of water-soluble polymer] -C) + D ... (2)
However, A, B, C, and D are coefficients obtained by linear regression analysis of the actual values of single-sided polishing of the wafer. The single-sided polishing method for a wafer according to claim 2, wherein the protrusion amount is 75 μm or more and 200 μm or less. The single-sided polishing apparatus further includes a plurality of slurry tanks each storing polishing slurries having different concentrations of the water-soluble polymer.
Prior to the polishing in the third step, the step of selecting a slurry tank in which the polishing slurry having the concentration of the water-soluble polymer determined in the second step is stored is further included from the plurality of slurry tanks.
The single-sided polishing method for a wafer according to any one of claims 1 to 3, wherein in the third step, the polishing slurry stored in the selected slurry tank is supplied.

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