JP6572790B2 - Wafer double-side polishing method - Google Patents

Description

  The present invention relates to a double-side polishing method for simultaneously polishing the front and back surfaces of a wafer, and in particular, a double-side polishing method for a wafer capable of obtaining excellent flatness in the overall shape of the wafer and sufficiently suppressing sagging on the outer periphery of the wafer. It is about.

  For example, in the manufacturing process of a semiconductor wafer such as a silicon wafer obtained by slicing a silicon single crystal, double-side polishing that simultaneously polishes the front and back surfaces of the wafer is performed for the purpose of improving the flatness of the wafer shape and the surface roughness. Generally adopted.

  In both-side polishing, generally, the upper and lower surface plates with a polishing cloth are applied to narrow the wafer, and while supplying slurry to the wafer, the upper and lower surface plates are rotated to move the front and back surfaces of the wafer simultaneously. This is a polishing method. FIG. 12 is a diagram showing how the shape of the wafer changes as the polishing time elapses in the order of FIGS. 12A to 12E in a general double-side polishing process. is there. FIG. 12 also shows the magnitude relationship between the thickness of the wafer and the thickness of the carrier plate at each time point in FIGS. 12 (a) to 12 (e). 12A to 12E, the vertical axis indicates the thickness of the wafer, and the horizontal axis indicates the position from the wafer center when the radius of the wafer is R. In other words, these figures show the state of the cross-sectional shape in the vertical direction of the wafer by the thickness at each position from the center of the wafer, and the right enlarged view enlarges one end of the wafer outer periphery (edge part). It is a thing.

  As shown in FIG. 12, in the double-side polishing, the front and back surfaces of the wafer are simultaneously polished with the polishing cloth affixed to the upper surface plate and the lower surface plate, and as the polishing time elapses, FIGS. 12 (a) to 12 (e). The shape changes like this. In the initial stage of the polishing step shown in FIG. 12A, the wafer whole surface shape (global shape) is a convex shape with a large thickness near the center, and a large sag (Roll off) is also seen on the outer periphery of the wafer. In this initial stage, the thickness of the wafer is sufficiently thicker than the thickness of the carrier plate. In the subsequent stage of FIG. 12B, the overall shape of the wafer approaches a flat shape rather than the above-mentioned convex shape, but the sagging of the wafer outer periphery seen in the initial stage remains. When the polishing further proceeds and the stage of FIG. 12C is reached, the thickness of the wafer and the thickness of the carrier plate are substantially equal, and the entire surface shape of the wafer becomes a substantially flat shape. In addition, since the polishing cloth is an elastic body and is polished by applying a certain pressure, the polishing cloth sinks a certain amount during polishing, particularly at the stage of FIGS. 12 (a) and 12 (b). A greater stress is applied to the outer periphery of the wafer than in the vicinity of the center. On the other hand, when the thickness of the wafer and the thickness of the carrier plate are substantially equal, the stress from the polishing cloth applied to the outer periphery of the wafer is distributed to the carrier plate, and the stress is reduced. For this reason, at the stage of FIG. 12C, the sagging amount seen on the wafer outer periphery is also small.

  Thereafter, when the polishing proceeds to the stage of FIG. 12D, the shape near the center of the wafer is recessed, and the periphery of the wafer is rounded up. From this stage, the polishing further progresses to the stage shown in FIG. 12 (e). The shape in the stage shown in FIG. 12 (d) is further recessed near the center of the wafer, and the round-up amount on the outer periphery of the wafer is further increased. growing. Further, the thickness of the wafer is further reduced with respect to the thickness of the carrier plate.

  From the above, in order to obtain a wafer with high flatness and little sagging on the outer periphery of the wafer, it is common to perform polishing while controlling the thickness of the wafer to be approximately equal to the thickness of the carrier plate. This control is conventionally performed by adjusting the polishing time.

  However, in the control by adjusting the polishing time, it is difficult to control accurately due to the shift of the timing of stopping the apparatus and the influence of the polishing environment. Further, with the recent miniaturization of microelectronic device structures and the increase in the diameter of semiconductor wafers, higher control of the shape of the manufactured wafer, particularly flatness and nanotopology, is required. For this reason, in order to obtain a wafer having better flatness and nanotopology, various attempts for improvement in the polishing process have been studied.

  For example, when the pressure from the polishing cloth applied to the wafer surface during polishing is unevenly distributed in the wafer surface, the polishing rate and the polishing amount are also uneven in the wafer surface, and the wafer is not polished flatly. As a method for solving such a problem, before the polishing cloth to be attached to the surface plate is attached to the surface plate, using a device different from the polishing device, a temperature higher than the use temperature at the time of polishing and / or Or the method of compressing with the pressure more than the pressure at the time of grinding | polishing or more is disclosed (for example, refer patent document 1). The polishing cloth, which is a viscoelastic body, undergoes a rapid deformation immediately after the load is applied, and then slowly deforms thereafter. Moreover, the displacement amount (thickness reduction amount) of the polishing cloth when a load is applied largely depends on the time during which the load is applied, but the polishing load existence time becomes non-uniform depending on the position of the polishing cloth. Sometimes. If the presence time of the polishing load is not uniform depending on the position of the polishing cloth, the amount of displacement of the polishing cloth is not uniform at each position of the polishing cloth, and the flatness of the wafer to be polished is impaired. In the method of Patent Document 1, the polishing cloth before being attached to the surface plate is compressed under high temperature and high pressure conditions using an apparatus other than the polishing apparatus, and the deformation of the polishing cloth that proceeds rapidly immediately after polishing is completely removed. Thus, creep deformation of the polishing cloth that occurs during polishing is suppressed, thereby improving the flatness of the wafer.

JP-A-11-267978 (Claim 2, paragraphs [0006] to [0008], paragraph [0022])

  However, in the polishing method disclosed in Patent Document 1, although the flatness of the entire shape of the wafer can be increased, sufficient investigation has not been made to the effect of suppressing the sagging of the outer periphery of the wafer. In addition, in the general method of adjusting the above polishing time and controlling the thickness of the wafer and the thickness of the carrier plate to be equal, the pressure applied during polishing even when these are equal in thickness As a result, the polishing cloth, which is an elastic body, enters the gap between the carrier plate and the wafer, so that the stress applied to the outer periphery of the wafer is not sufficiently distributed to the carrier plate, and the stress may not be reduced. For this reason, there is a case in which the effect of suppressing sagging of the outer periphery of the wafer may not be sufficiently obtained even by adjusting the polishing time more accurately, for example, only by the usual method of controlling the relationship between the two and performing polishing. . As described above, since the conventional method cannot sufficiently suppress the sagging of the outer periphery of the wafer, it is difficult to perform polishing while achieving both the flatness of the outer periphery of the wafer and the flatness of the entire shape of the wafer. It was difficult to respond adequately.

  An object of the present invention is to provide a double-side polishing method for a wafer which can obtain excellent flatness in the entire shape of the wafer and can sufficiently suppress sagging on the outer periphery of the wafer.

According to a first aspect of the present invention, a wafer is narrowed by a doughnut-shaped upper and lower surface plates each having a central hole at the center and a polishing cloth affixed to the polishing surface. In the double-side polishing method for polishing both surfaces of the wafer by rotating the upper and lower surface plates while supplying the slurry to the polishing plate, the polishing is applied to both the upper and lower surface polishing cloths. Either or both of the outer peripheral side compression part and the inner peripheral side compression part, which are formed by compressing the outer periphery or inner periphery of the cloth in the vertical direction using an abrasive cloth compression jig, are provided, and the horizontal direction of the outer peripheral side compression part When the compression width in A is A, the compression width in the horizontal direction of the inner circumferential side compression portion is B, and the diameter of the wafer is D, the compression width A satisfies 0.15 × D ≦ A ≦ 0.25 × D , It said compression width B is 0.15 × D ≦ B ≦ And satisfies the .25 × D.

The second aspect of the present invention is an invention based on the first aspect , wherein the compression amount in the vertical direction of the inner peripheral side compression portion and the outer peripheral side compression portion is 0. 0 of the thickness of the polishing pad before compression. It is characterized by being 77% or more.

A third aspect of the present invention is an invention based on the first or second aspect , and further includes an outer peripheral side compression portion and an inner peripheral side compression on both of the polishing cloths attached to the upper surface plate and the lower surface plate, respectively. Both parts are provided.

A fourth aspect of the present invention is an invention based on the first to third aspects, and is characterized in that the polishing cloth is a non-woven cloth polishing cloth, a polyurethane polishing cloth or a suede polishing cloth.

A fifth aspect of the present invention is an invention based on the first to fourth aspects, wherein the abrasive cloth compression jig is a ring-shaped jig composed of one part, or by coupling. The jig is composed of two or more parts having one ring shape.

A sixth aspect of the present invention is an invention based on the first to fifth aspects, wherein the polishing cloth compression jig has a thickness of 0.3 mm or more and is a jig formed of an inorganic material or It is a resin jig.

In the double-side polishing method according to the first aspect of the present invention, the wafer is narrowed with a doughnut-shaped upper surface plate and lower surface plate each having a central hole at the center and a polishing cloth affixed to the polishing surface. This is a double-sided polishing method that polishes both sides of the wafer by rotating the upper and lower surface plates while supplying slurry to the wafer from the supply holes. The polishing cloths attached to the upper and lower surface plates respectively. Either one or both of an outer peripheral side compression part and an inner peripheral side compression part formed by compressing and molding the outer periphery or inner periphery of the polishing cloth in the vertical direction using an abrasive cloth compression jig is formed. At that time, the compression width in the horizontal direction of the outer peripheral side compression portion is A, and the compression width B in the horizontal direction of the inner periphery side compression portion is 0.15 × D ≦ A, which is a predetermined condition with respect to the diameter D of the wafer. Control is performed to satisfy the conditions of ≦ 0.25 × D and 0.15 × D ≦ B ≦ 0.25 × D. In this way, by properly controlling the compression width in the horizontal direction and compressing a part of the polishing cloth for polishing, even if the polishing cloth sinks a certain amount during polishing, the outer periphery of the wafer is near the center It is possible to suppress the application of a large stress compared to the above stress. Thereby, the flatness in the wafer outer periphery and the flatness in the whole surface shape of the wafer can be made compatible in the polished wafer.

In the double-side polishing method according to the second aspect of the present invention, the compression amount in the vertical direction of the inner peripheral side compression portion and the outer peripheral side compression portion is controlled to be a predetermined ratio with respect to the thickness of the polishing cloth before compression. To do. This makes it easier to make the stress applied to the outer periphery of the wafer during polishing and the stress applied to the vicinity of the center of the wafer more uniform.

In the double-side polishing method of the third aspect of the present invention, both the outer peripheral side compression portion and the inner peripheral side compression portion are formed on both of the polishing cloths attached to the upper surface plate and the lower surface plate, respectively. The effect of suppressing a large stress on the outer periphery of the wafer is further enhanced.

In the double-side polishing method of the fourth aspect of the present invention, since a predetermined polishing cloth such as a non-woven cloth polishing cloth is used as the polishing cloth, when forming the compression width, the horizontal compression width and the vertical compression amount are set. Easy to adjust and form. Further, the compressed portion is difficult to be restored during polishing and the like, and the surface roughness is excellent.

In the double-side polishing method according to the fifth aspect of the present invention, a ring-shaped jig composed of one or more parts is used as the polishing cloth compression jig used for forming the inner peripheral compression section and the outer compression section. Is used. In this way, by using a ring-shaped jig, by using a simple method of narrowing the jig with the polishing cloth stuck to the upper or lower surface plate without using another device, The compression part can be formed on the polishing cloth with high accuracy.

In the double-side polishing method of the sixth aspect of the present invention, the polishing cloth compression jig is made to have a thickness equal to or greater than a predetermined value, so that the amount of compression of the polishing cloth in the vertical direction can be controlled to a desired amount and accurately. be able to. In addition, by using a jig made of a desired material as the polishing cloth compression jig, it is possible to prevent the wafer being polished from being contaminated by the material used to manufacture the polishing cloth compression jig. Can do.

It is the schematic sectional drawing which showed an example of the grinding | polishing apparatus used with the method of embodiment of this invention. It is the schematic which looked at the state in which grinding | polishing of the wafer is performed by the method of this invention embodiment from the upper surface. It is the sectional view on the AA line in FIG. It is explanatory drawing which showed typically the principle by which the stress concerning a wafer outer periphery is reduced compared with the conventional method. It is the schematic diagram which showed an example of the polishing cloth compression jig | tool used by this invention embodiment. It is the XY sectional view taken on the line in FIG. 2 is a graph showing test results in Example 1. FIG. 6 is a graph showing test results in Example 2. 10 is a graph showing test results in Example 3. It is the graph which showed the evaluation result regarding the outer periphery shape comparison in Example 4. FIG. It is the graph which showed the relationship between the compression amount in the perpendicular direction of the polishing cloth used in the Example, compression surface pressure, and the leaving time after compression part formation. It is a figure showing a mode that a wafer shape changes as progress of polish time in a general double-side polish process.

  Next, an embodiment for carrying out the present invention will be described with reference to the drawings.

  The present invention supplies the slurry to the wafer from the slurry supply hole by narrowing the wafer with a doughnut-shaped upper and lower platen each having a central hole at the center and a polishing cloth affixed to the polishing surface. However, this is an improvement of the double-side polishing method in which the upper surface plate and the lower surface plate are rotationally driven to simultaneously polish both surfaces of the wafer.

  The apparatus used for carrying out the double-side polishing method of the present invention is not particularly limited except for the structure of the polishing cloth described later, and a general double-side polishing apparatus can be used. For example, the apparatus 10 shown in FIG. 1 is a schematic view showing an example of a double-side polishing apparatus used in the embodiment of the present invention. In this apparatus 10, except for the configuration of the polishing cloth 11, a general double-side polishing apparatus and It is comprised by the same structure. 1 to 3 indicate the same parts or members.

  As shown in FIG. 1, the apparatus 10 has two surface plates composed of a doughnut-shaped upper surface plate 12 and a lower surface plate 13 each having a polishing cloth 11 affixed to the polishing surface and a central hole provided in the center. Prepare. A sun gear 21 is provided at the center between the upper surface plate 12 and the lower surface plate 13, and an internal gear 22 is provided at the periphery. The inner diameter of the internal gear 22 is larger than the outer diameter of the upper surface plate 12 or the lower surface plate 13. On the lower surface plate 13 to which the polishing cloth 11 is attached, a carrier plate 14 is installed so as to be sandwiched between both surface plates 12 and 13, and a wafer 16 as an object to be polished is disposed in a holding hole of the carrier plate 14. Is done.

  On the other hand, the upper platen 12 is provided with a slurry supply hole 18 for supplying a slurry (polishing liquid) 17, and a supply pipe 19 is provided above the supply hole 18, and the slurry supplied from the supply pipe 19 17 is supplied to the wafer 16 through the supply hole 18. The upper surface plate 12 is placed opposite to the lower surface plate 13 so that the polishing cloth 11 affixed to the upper surface plate 12 is in contact with the front surface of the wafer 16, and pressurizes the upper surface plate 12. The wafer 16 in 14 is narrowed by both surface plates 12 and 13.

  On the outer periphery of the carrier plate 14, outer peripheral teeth that mesh with the sun gear 21 and the internal gear 22 are provided. In addition, a shaft 20 is provided in the center hole of both the surface plates 12, 13, and the carrier plate 14 rotates while the sun plate 21 rotates while the upper surface plate 12 and the lower surface plate 13 are rotated by a power source (not shown). Revolve to the center. At this time, the wafer 16 moves in the carrier plate 14 by the rotation of the carrier plate 14 as shown in FIG.

  The present invention is an improvement of the double-side polishing method using such an apparatus, and its characteristic configuration is that the outer periphery of the polishing cloth 11 is attached to both the polishing cloth 11 affixed to the upper surface plate 12 and the lower surface plate 13, respectively. Alternatively, either one or both of the outer peripheral side compression portion 11a and the inner peripheral side compression portion 11b formed by compressing and molding the inner periphery in the vertical direction using a polishing cloth compression jig is provided with a predetermined compression width. .

  In this way, by controlling the compression width in the horizontal direction and compressing a part of the polishing cloth for polishing, the stress applied to the outer periphery of the wafer can be reduced as compared with the case where the compression part is not formed. it can. When the wafer is narrowed by the upper and lower surface plates in a state where the compression portion is not formed, the wafer is pressed against the polishing cloth which is an elastic body, and the polishing cloth sinks a certain amount. For this reason, as shown in FIG. 4A, a greater stress is applied to the outer periphery of the wafer 16 from the polishing pad 11 than in the vicinity of the center of the wafer 16. On the other hand, as shown in FIG. 4B, by forming the outer peripheral side compression portion 11a or the inner peripheral side compression portion 11b with an appropriate compression width, a larger stress is applied to the outer periphery of the wafer 16 than in the vicinity of the center of the wafer 16. It is suppressed from hanging. Thereby, during polishing, the stress applied to the vicinity of the center of the wafer 16 and the outer periphery of the wafer 16 is substantially uniform in the plane. As a result, good flatness is obtained on the entire wafer surface, and sagging of the outer periphery of the wafer 16 is suppressed. In general, GBIR, which will be described later, is used as an index representing the flatness of the entire shape of the wafer 16, and SFQR or ESFQR is used as an index representing the flatness of the outer periphery of the wafer 16. That is, in the double-side polishing method of the present invention, GBIR and SFQR or ESFQR can be made compatible in the polished wafer 16.

  Here, when the compression width in the horizontal direction of the outer peripheral compression portion 11a is A, the compression width in the horizontal direction of the inner peripheral compression portion 11b is B, and the diameter of the wafer 16 is D, the compression width A is: 0.05 × D ≦ A is satisfied, and the compression width B is controlled to satisfy 0.30 × D ≧ B. During polishing, the wafer 16 travels to the innermost and outer peripheral portion of the polishing pad 11 along the track shown in FIG. By controlling the compression portion as described above, the outer peripheral portion of the wafer 16 passes through the outer peripheral side compression portion 11a or the inner peripheral side compression portion 11b formed on the polishing cloth 11 during polishing. The stress applied to the outer periphery of the wafer 16 is reduced. The reason why the compression width A and the compression width B are controlled in this way is that when the compression width A is too small with respect to the diameter D of the wafer 16, a portion passing through the outer peripheral compression portion 11 a on the outer periphery of the wafer 16 is polished during polishing. This is because the effect of reducing the large stress applied to the outer periphery of the wafer is not sufficiently obtained. On the other hand, if the compression width B is too large with respect to the diameter D of the wafer 16, the stress from the polishing pad 11 is applied to the uncompressed portion of the polishing pad 11 due to the contact surface with the wafer 16 becoming small. Concentrated and a strong stress is applied to the wafer 16 from the portion. Therefore, the flatness of the entire shape of the wafer 16 is impaired, and GBIR is deteriorated. Further, when GBIR deteriorates, the flatness of the outer periphery of the wafer 16 is also impaired, and an influence of about several nm is exerted in ESFQR evaluation. Of these, the compression width B is preferably 0.05 × D ≦ A ≦ 0.30 × D, and more preferably 0.15 × D ≦ A ≦ 0.25 × D. Control is performed so as to satisfy 0.05 × D ≦ B ≦ 0.30 × D, more preferably 0.15 × D ≦ B ≦ 0.25 × D. Note that the compression width A or the compression width B when the wafer 16 travels to the innermost peripheral portion of the polishing pad 11 during polishing is the outermost peripheral portion or the innermost peripheral portion of the polishing pad 11, as shown in FIG. It is the width in the horizontal direction of the outer peripheral side compression part 11a or the inner peripheral side compression part 11b measured from the respective parts. That is, the compression width A and the compression width B in this case coincide with the actual width in the horizontal direction of the outer peripheral side compression portion 11a or the inner peripheral side compression portion 11b. However, the compression width A and the compression width B in the case where the wafer 16 does not travel to the outermost or innermost peripheral portion of the polishing pad 11 during polishing are as follows. The width in the horizontal direction of the outer peripheral side compression part 11a or the inner peripheral side compression part 11b, which is measured starting from the point on the outermost peripheral side or the point on the innermost peripheral side of the polishing cloth 16 to be performed. That is, the compression width A and the compression width B in this case are the horizontal direction of the non-running portion where the wafer 16 does not travel during polishing from the actual width in the horizontal direction of the outer peripheral side compression portion 11a or the inner peripheral side compression portion 11b. The value obtained by subtracting the width at.

  Moreover, it is preferable that the compression amount in the vertical direction of the outer peripheral side compression portion 11a and the inner peripheral side compression portion 11b formed on the polishing pad 11 is 0.77% or more of the thickness of the polishing pad 11 before compression. This is because if the amount of compression in the vertical direction is too small, it may be difficult to obtain an effect of reducing a large stress applied to the outer periphery of the wafer when the polishing cloth sinks during polishing. Of these, the amount of compression in the vertical direction is particularly preferably 0.90% or more of the thickness of the polishing pad before compression. Moreover, the cross-sectional shape of the outer peripheral side compression part 11a and the inner peripheral side compression part 11b was formed so that it might incline toward the inner periphery or outer periphery from the compression start position from the center of polishing cloth 11, as shown in FIG. In addition to the shape, the shape may be such that the compression surface of the compression portion is horizontal without being inclined. In addition, the compression amount in the said vertical direction in the case of forming the outer peripheral side compression part 11a and the inner peripheral side compression part 11b so that it may incline toward the inner periphery or outer periphery of the polishing pad 11 is a compression amount in the said compression part. The value measured at the point where is the largest.

  Moreover, although the said compression part may form any one of the outer peripheral side compression part 11a and the inner peripheral side compression part 11b with respect to the polishing cloth 11 of 1 sheet, the viewpoint that the above-mentioned effect is fully expressed. Therefore, it is preferable to form both the outer peripheral side compression part 11a and the inner peripheral side compression part 11b.

The outer peripheral side compression portion 11a and the inner peripheral side compression portion 11b can be formed using, for example, a ring-shaped polishing cloth compression jig 31 as shown in FIGS. Specifically, for example, after the polishing cloth 11 is affixed to the polishing surfaces of the upper surface plate 12 and the lower surface plate 13, the outer peripheral side polishing shown in FIG. The cloth compression jig 31a or the inner peripheral polishing cloth compression jig 31b is arranged, and these are narrowed by the upper surface plate 12 and the lower surface plate 13 under predetermined conditions. Thereby, the desired compression part mentioned above can be easily formed in the outer periphery or inner periphery of the polishing pad 11. The compression conditions at this time are controlled to a compression temperature of 20 to 30 ° C., a compression time of 1 hour or more, and a surface pressure of 500 g / cm ² , for example, in order to prevent the compressed portion from partially recovering during polishing and changing dimensions. It is preferable to do this.

  The polishing cloth compression jig 31 may be a ring-shaped jig composed of one part as shown in FIG. 5, but is composed of, for example, two or more parts that are combined into a single ring shape. It may be a jig. The cross-sectional shape of the polishing cloth compression jig 31 is not particularly limited, and can be, for example, the shape shown in FIG. 6A or the shape shown in FIG. 6B according to the cross-sectional shape of the compression part to be formed. .

  The polishing cloth compression jig 31 may be manufactured using stainless steel, titanium, or the like, but prevents the wafer being polished from being contaminated by the material used for manufacturing the jig. From the viewpoint of doing, it is preferably a jig made of an inorganic material or a resin jig. Examples of the inorganic material include silicon nitride and zirconia. Examples of the resin include polyvinyl chloride (PVC) and polytetrafluoroethylene polytetrafluoroethylene. Further, the thickness of the polishing cloth compression jig 31 is 0.3 mm or more in order to control the compression amount in the vertical direction of the outer peripheral side compression portion 11a or the inner peripheral side compression portion 11b to the above-described desired compression amount. Is preferred.

  Further, the polishing cloth 11 attached to the upper surface plate 12 and the lower surface plate 13 is not particularly limited, but it is easy to form a compressed portion, the compressed portion is difficult to restore to the original thickness, and has excellent surface roughness. In view of the above, it is preferable to use a non-woven polishing cloth, a polyurethane polishing cloth or a suede polishing cloth.

  In the polishing method of the present invention, the specific procedure and other conditions when performing polishing other than the configuration of the polishing cloth described above are not particularly limited, and can be performed under well-known conditions. As described above, in the double-side polishing method of the present invention, excellent flatness can be obtained in the entire shape of the wafer in the polished wafer, and sagging on the outer periphery of the wafer can be sufficiently suppressed.

  Next, examples of the present invention will be described in detail.

<Example 1>
The double-side polishing apparatus 10 shown in FIG. 1 is used to perform double-side polishing of the wafer by changing the compression width A and compression width B of the outer peripheral side compression portion 11a and the inner peripheral side compression portion 11b of the polishing pad 11 for each test example. Then, the transition of the flatness due to the variable of the compression width was verified. The results are shown in Table 1 below and FIG. In Test Examples 2 to 9 in Example 1, as shown in Table 1, the compression width A and the compression width B were changed under the condition of compression width A = compression width B. In Test Example 1, double-side polishing of the wafer was performed without forming the compression part.

Specifically, first, as the polishing cloth 11, a non-woven polishing cloth having a polishing cloth thickness of 1.3 mm, a hardness (AskerC) of 83, and a compression ratio of 3.3% (trade name: suba800 manufactured by Nittah Haas) ), And the polishing cloth 11 was applied to the polishing surfaces of both surface plates 12 and 13 included in the apparatus 10. Thereafter, two polishing cloth compression jigs 31a and 31b shown in FIG. 5 are arranged on the outer periphery and inner periphery of the polishing cloth 11 affixed to the lower surface plate 13, respectively, and the compression temperature is 25 ° C., the surface pressure is 500 g / cm ² , and the compression is performed. The pressure was reduced under the condition of 1 hour. Thereby, the outer peripheral side compression part 11a and the inner peripheral side compression part 11b were formed in both of the polishing cloth 11 stuck on the polishing surface of both the surface plates 12 and 13. FIG. As the polishing cloth compression jigs 31a and 31b, PVC jigs having a cross-sectional shape shown in FIG.

Next, a carrier plate 14 having a thickness of 778 μm is placed on the polishing cloth 11 on the lower surface plate 13 side on which the outer peripheral side compression portion 11a and the inner peripheral side compression portion 11b are formed. A silicon wafer having a diameter of 300 mm and a thickness of 790 μm was placed in the holding hole as an object to be polished (wafer 16). Next, the wafer 16 placed in the holding hole of the carrier plate 14 is narrowed together with the carrier plate 14 under the condition of a processing surface pressure of 300 g / cm ² , and the slurry is supplied from the slurry supply hole 18 (trade name, manufactured by Nitta Haas) : Nalco2350) 17, the upper surface plate 12 and the lower surface plate 13 were rotated and the wafer 16 was polished on both sides. The target thickness at this time was 780 μm.

  About the flatness of the wafer after double-side polishing, it evaluated by measuring GBIR and SFQRmax using the measuring apparatus (KLA Tencor company name: Wafer Sight2). The measurement conditions at this time were set to 296 mm excluding the wafer outer periphery of 2 mm. In addition, the values of GBIR and SFQRmax shown in Table 1 and FIG. 7 are values obtained by performing double-side polishing on the same condition for each pair of polishing cloths on which the compression part is formed under the above-described conditions, and averaging them. It is. The coefficient α shown in Table 1 and FIG. 7 is a coefficient α when the compression width A or the compression width B is expressed as a length with respect to the wafer diameter D, that is, A = α × D or B = α × D, respectively. is there. GBIR (Grobal Backside Ideal focal plane Range) is a value used as an index indicating the flatness of the entire shape of the wafer. This GBIR is obtained by calculating the difference between the maximum thickness and the minimum thickness of the entire wafer on the basis of the back surface of the wafer when it is assumed that the back surface of the wafer is completely adsorbed.

  SFQR (Site Front least Quares Randge) is an index indicating the local flatness of a wafer according to the SEMI standard. This SFQR calculates the reference plane in the site by the least square method from all the data indicating the surface position of each point in the surface reference site, and takes the sum of the maximum value and the minimum value of the deviation from this plane. SFQRmax indicates the maximum value of SFQR at all sites in the wafer.

  As is clear from Table 1 and FIG. 7, when the compression width A and the compression width B are increased so that the coefficient α satisfies the predetermined condition, GBIR does not substantially change and SFQRmax shows a good value. (Test Example 2 to Test Example 7). In particular, the best results were obtained when the coefficient α was 0.20 (Test Example 5). On the other hand, the flatness deteriorates from the time when the coefficient α exceeds 0.30. In Test Example 8 in which the coefficient α is 0.35, SFQRmax shows a bad value as in Test Example 1 in which the compression width is not formed. Moreover, in Test Example 9 where the coefficient α was 0.40, both GBIR and SFQRmax showed significantly worse values than Test Example 1. From these results, it was confirmed that the compression width is preferably controlled so that the coefficient α satisfies the predetermined condition in order to improve the flatness of the polished surface.

<Example 2>
As shown in Table 2 below, the compression width A and compression width B of the outer peripheral side compression portion and inner peripheral side compression portion provided on the polishing cloth are changed for each test example under the condition of compression width A ≠ compression width B. Then, by performing double-side polishing of the wafer, the transition of the flatness due to the variable compression width was verified. The results are shown in Table 2 below and FIG. The conditions other than the compression width and the evaluation method in each test example of Example 2 were performed in the same manner as in Example 1 described above.

  As is apparent from Table 2 and FIG. 8, if the coefficient α is controlled so as to be within a predetermined range, the flatness of the polished surface can be improved without forming the compression width A and the compression width B to the same compression width. It was confirmed that it can be improved.

<Example 3>
The compression part was formed only on either the outer periphery or the inner periphery of the polishing cloth, and the compression width was changed within the range shown in Table 3 below, and the wafer was subjected to double-side polishing, and the transition of the flatness was verified. The results are shown in Table 3 below and FIG. In addition, about conditions other than the compression width | variety and evaluation method in each test example of this Example 3, it carried out similarly to the above-mentioned Example 1. FIG.

  As apparent from Table 3 and FIG. 9, even when the compression part is formed only on either the outer periphery or the inner periphery of the polishing cloth and the compression width is controlled so that the coefficient α satisfies the predetermined condition, Although some cases in which the flatness is slightly reduced are observed, it was confirmed that the effect of improving the flatness of the polished surface can be sufficiently obtained as in Test Examples 2 to 7.

<Example 4>
From the results of Example 1 described above, the highest evaluation was obtained in Test Example 5 in which the coefficient α was 0.20. Therefore, double-side polishing of the wafer was performed again under the same conditions as in Test Example 5, The amount of outer peripheral sag was evaluated. The results are shown in Table 4 below and FIG. In addition, the result shown in Table 4 and FIG. 10 is a value obtained by performing double-side polishing under the same conditions for 25 sheets for each test example and averaging them.

  In Table 4, Test Example 24 is an example in which double-side polishing of the wafer was performed without forming a compression portion on the polishing cloth, as in Test Example 1 in Example 1 described above, and Test Example 25 was performed as described above. In this example, the compression part is formed under the same conditions as in Test Example 5 in Example 1, and the wafer is subjected to double-side polishing. About the conditions at the time of grinding | polishing and the evaluation method of GBIR and SFQRmax, both Test Example 24 and Test Example 25 were performed similarly to each test example in Example 1. The evaluation of the amount of peripheral sag was also performed using the above-described measuring device (model name: Wafer Sight2 manufactured by KLA Tencor).

  As is apparent from Table 4, with respect to the value of GBIR, almost the same results were obtained in Test Example 24 and Test Example 25. On the other hand, SFQRmax indicates that the flatness is higher as the numerical value is smaller. Therefore, the flatness is improved in Test Example 25 in which a desired compression portion is formed on the polishing cloth than in Test Example 24. I know that. FIG. 10 shows the shape of the outer peripheral portion of the wafer. It was confirmed that the sagging amount on the outer periphery of the wafer was improved by forming a desired compression portion on the polishing cloth.

<Example 5>
Using the same polishing cloth as the polishing cloth used in each test example of Examples 1 to 3, the compression amount in the vertical direction when forming the compression portion on the polishing cloth, the compression surface pressure, and the compression portion were formed. And the relationship with the standing time from the start to the double-side polishing. The result is shown in FIG. FIG. 11 shows the results when the compression surface pressure is 100 to 1000 g / cm ² and the standing time from the formation of the compression portion to the start of double-side polishing is 10 minutes to 6 hours. Even when the standing time exceeded 6 hours, there was no change in the amount of compression when left standing for 6 hours (not shown). Further, as in each of the test examples of Examples 1 to 3, the compression time when forming the compression part was 1 hour, and the compression temperature was 25 ° C. (room temperature).

In each of the test examples of Examples 1 to 3 described above, in the test example in which the effect of improving the flatness in the wafer shape was observed, the compression surface pressure was set to 500 g / cm ² and the compression part was formed. Double-side polishing was carried out for 10 minutes (compression amount 17 μm = compression rate 1.3%) and for 6 hours (compression amount 10 μm = compression rate 0.77%) in the longest test example. According to the results shown in FIG. 11, in these test examples, the amount of compression of the polishing cloth in the vertical direction is 10 μm or more, and the amount of compression with respect to the thickness (100%) of the polishing cloth before compression is determined from the value. When calculated, the amount of compression of the polishing cloth in the vertical direction was 0.77% or more with respect to the thickness of the polishing cloth before compression. From this, it was confirmed that the compression amount in the vertical direction of the compression part is preferably 0.77% or more with respect to the thickness of the polishing pad before compression.

  INDUSTRIAL APPLICABILITY The present invention can be used for double-side polishing of a wafer for obtaining wafer flatness, for example, in a semiconductor wafer manufacturing process represented by a silicon wafer.

DESCRIPTION OF SYMBOLS 11 Polishing cloth 11a Outer peripheral side compression part 11b Inner peripheral side compression part 12 Upper surface plate 13 Lower surface plate 14 Carrier plate 16 Wafer 17 Slurry 18 Slurry supply hole

Claims (6)

While narrowing the wafer with a doughnut-shaped upper surface plate and lower surface plate each having a central hole in the center and a polishing cloth affixed to the polishing surface, while supplying the slurry to the wafer from the slurry supply hole, In the double-side polishing method for polishing both surfaces of the wafer by rotating and driving the upper surface plate and the lower surface plate,
An outer peripheral side compression portion formed by compressing the outer periphery or inner periphery of the polishing cloth in the vertical direction using an abrasive cloth compression jig on both the polishing cloths attached to the upper surface plate and the lower surface plate, respectively. Either one or both of the inner peripheral side compression sections are provided,
When the width in the horizontal direction of the outer peripheral side compression portion is the compression width A, the width in the horizontal direction of the inner peripheral compression portion is the compression width B, and the diameter of the wafer is D, the compression width A is 0.15 ×. A double-side polishing method for a wafer, wherein D ≦ A ≦ 0.25 × D is satisfied, and the compression width B satisfies 0.15 × D ≦ B ≦ 0.25 × D. Compression amount in the vertical direction of the inner peripheral side compression portion and the outer peripheral-side compression section, of the wafer of claim 1 Symbol mounting, characterized in that said at least 0.77% of the thickness before compression of the polishing cloth Double-side polishing method. To both the polishing cloth affixed respectively to the upper platen and lower platen, No possible mounting according to claim 1 or 2 SL, characterized in that both of the outer peripheral side compression portion and an inner peripheral side compression portion is provided Wafer double-side polishing method. The polishing cloth nonwoven based polishing cloth double-side polishing method for a wafer according to any one of claims 1 to 3, characterized in that a polyurethane polishing cloth or a suede type polishing cloth. The polishing cloth compressing jig is a ring-shaped jig composed of one part, or a jig composed of two or more parts that are combined into a single ring shape. The method for polishing a wafer on both sides according to any one of claims 1 to 4 . The polishing cloth compression jig is a at the 0.3mm or more thickness, claims 1, characterized in that it is formed of an inorganic material jig or resin jig according to 5 any one Wafer double-side polishing method.

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