JP2010131683A - Grinding method of silicon wafer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of grinding a silicon wafer capable of improving quality of a surface shape of the wafer, further miniaturizing an electronic circuit, and solving such a problem that fine particles increase on the rear of the wafer after a grinding process is completed when all grinding processes are done in double-side grinding. <P>SOLUTION: All of the grinding processes of silicon wafers except the final process are done in double-side grinding, whereby the quality of the surface shape of the wafer can be improved and the electronic circuit can be more miniaturized. In addition, since the final grinding is done in one-side grinding only on the front face, dust generated due to a scratch failure caused by the wafer colliding against a wall of a holding hole does not occur in the final grinding process. As a result, such a problem when all grinding processes are done in double-side grinding that the fine particles increase on the rear of the wafer after the grinding process can be solved. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for polishing a silicon wafer, and more particularly to a method for polishing a silicon wafer that can improve the quality of the surface shape of the silicon wafer.

In manufacturing a silicon wafer, block cutting, outer diameter grinding, slicing, chamfering, etching or surface grinding are sequentially performed on a silicon single crystal ingot, and then polishing is performed to remove wafer damage during etching or surface grinding. Thereby, a silicon wafer having a mirror-finished surface is manufactured.
In the polishing process, 3 to 4 stages of multi-step polishing including primary polishing, secondary polishing, tertiary polishing, and finish polishing are generally performed. In multi-stage polishing, as the polishing stage progresses, quality improvements related to the surface shape of the silicon wafer such as flatness, nanotopology, surface roughness, and haze are achieved.

  In order to further improve the quality of the surface shape of the wafer, conventional double-side polishing using a planetary gear type (sun gear type) double-side polishing apparatus has been adopted only for the primary polishing, and after the secondary polishing, One-side polishing for polishing the surface is performed (for example, Patent Documents 1 and 2). The planetary gear type double-side polishing apparatus has a planetary gear structure in which a sun gear is arranged at the center and an internal gear is arranged at the outer periphery. At the time of use, while holding the silicon wafer in the plurality of wafer holding holes of the carrier plate and supplying the slurry containing abrasive grains, the upper and lower surface plates on which the polishing cloth is stretched are pressed against both the front and back surfaces of each wafer, The carrier plate rotates and revolves between the sun gear and the internal gear. Thereby, the front and back surfaces of each silicon wafer are polished simultaneously.

Conventionally, the reason why single-side polishing is adopted in each polishing after the secondary polishing is as follows.
(1) In the device formation process, devices are actually formed only on the surface of the silicon wafer.
(2) Generally, the amount of polishing required to improve the surface roughness, haze, and the like of a silicon wafer is as small as several μm to several tens of μm (the polishing amount is smaller as the subsequent polishing is performed). Therefore, even when only single-side polishing (back surface-based surface polishing) is employed, the wafer flatness and nanotopology after the primary polishing do not change so much. Nanotopology is the surface roughness (absolute value of change amount) at the nm level.
(3) In double-side polishing, a carrier plate with a holding hole for holding a silicon wafer is used. For this reason, the silicon wafer collides with the formation wall of the holding hole at the time of polishing, and a scratch defect occurs, so that the quality of the silicon wafer is lowered and there is a risk of dust generation.
(4) In double-side polishing, a double-side polishing apparatus having a complicated structure is used. Therefore, the equipment cost increases and the front and back surfaces of the wafer are polished, so that the running cost for consumables such as a polishing cloth is increased rather than single-side polishing.

Japanese Patent Laid-Open No. 9-97775 Japanese Patent No. 4038429

  However, in recent years, there has been a demand from the device formation department to sufficiently increase the nanotopology of the back surface of a silicon wafer, and thus the flatness of the wafer. In addition, management of minute particles on the back surface of the wafer is also required. These are indispensable in order to cope with further miniaturization of electronic circuits formed on the wafer surface. In other words, the current technical level has reached the point where it is impossible to realize miniaturization of the electronic circuit on the wafer surface unless both the nanotopology on the wafer back surface and the fine particles on the wafer back surface are controlled.

  Therefore, as a result of diligent research, the inventor has performed double-side polishing as the polishing of the silicon wafer, and the polishing is changed at all times except for the final polishing among the multi-stage polishing performed continuously three times or more by changing the polishing conditions. It has been found that the above-mentioned problems can be solved if it is adopted. In addition, dust generation due to a scratch failure generated when the silicon wafer collides with the formation wall of the holding hole does not occur in the final polishing. For this reason, the inventors have found that the number of fine particles on the back surface of the wafer after the polishing step can be further reduced as compared with the case where all the polishing operations are performed on both sides, thereby completing the present invention.

  This invention can improve the quality of the surface shape of the silicon wafer, thereby enabling further miniaturization of the electronic circuit formed on the wafer surface, and becomes a problem when all the polishing is double-sided polishing. An object of the present invention is to provide a method for polishing a silicon wafer that can eliminate an increase in minute particles on the back surface of the wafer after the polishing step.

  The invention according to claim 1 is a silicon which polishes the front and back surfaces by pressing the polishing cloth against the front and back surfaces of the silicon wafer and sliding the silicon wafer and the polishing cloth relatively while supplying the polishing liquid. A method for polishing a wafer, wherein the polishing of the front and back surfaces of the silicon wafer is a multi-stage polishing performed continuously three times or more by changing the polishing conditions, and the multi-stage polishing is performed for all rounds except the final round. However, this is a silicon wafer polishing method in which double-side polishing is performed to simultaneously polish the front and back surfaces of the silicon wafer, and the final polishing is single-side polishing in which the wafer surface is polished.

According to the first aspect of the present invention, as the polishing of the silicon wafer, multi-stage polishing that is continuously performed by changing the polishing conditions for each time is adopted, and this multi-stage polishing is performed for all times except the final time. Polishing is double-sided polishing. As a result, the nanotopology on the back surface of the wafer and the generation amount of minute particles on the back surface of the wafer are reduced. As a result, the quality of the surface shape of the silicon wafer can be improved, and the electronic circuit formed on the wafer surface can be further miniaturized.
In addition, since the final polishing is a single-side polishing that polishes only the wafer surface, the dust generated by double-sided polishing due to a scratch defect caused by a silicon wafer hitting the holding hole formation wall is the final polishing. Does not occur. As a result, it is possible to eliminate an increase in minute particles on the back surface of the wafer after completion of the polishing process, which becomes a problem when all polishing is performed on both sides.

As the silicon wafer, a single crystal silicon wafer or the like can be adopted.
The “front and back surfaces of the silicon wafer” is any of the front surface, back surface, and front and back surfaces of the wafer.
As the polishing liquid, for example, a colloidal shape in which silica particles (polishing abrasive grains) having an average particle diameter of about 0.02 to 0.1 μm are dispersed in an alkaline etching liquid (KOH solution or the like) having a pH concentration of 9 to 11. Things can be adopted. However, since the abrasive grains reduce the surface roughness of the wafer, it is preferable that the abrasive grains are not mixed in the polishing liquid.
As the polishing cloth, a nonwoven fabric pad in which a nonwoven fabric is impregnated and cured with a urethane resin, a foamable urethane pad obtained by slicing a foamed urethane block, or the like can be used. Alternatively, a suede pad in which foamed polyurethane is laminated on the surface of a base material in which polyester felt is impregnated with polyurethane, and a surface layer portion of the polyurethane is removed to form an opening in the foamed layer may be used.

The relative sliding between the silicon wafer and both polishing cloths may be sliding between the silicon wafer and both polishing cloths by rotating only the silicon wafer, or sliding by rotating only both polishing cloths. In addition, sliding by rotation of both the silicon wafer and both polishing cloths may be used.
Examples of the “changing polishing conditions” include, for example, the type of polishing cloth, the type of polishing liquid, the polishing amount, the polishing rate, the polishing pressure, the polishing time, the rotation speed of the silicon wafer, the rotation speed of the polishing cloth, and the rotation of the silicon wafer. Direction, rotation direction of the polishing cloth, and the like.
As the double-side polishing, for example, planetary gear type double-side polishing having a sun gear can be employed. In addition, non-sun gear type double-side polishing without a sun gear may be used.
“Multi-stage polishing (double-side polishing) performed continuously three times or more” may be performed by only one double-side polishing apparatus or by a plurality of polishing apparatuses.
“Consecutively three or more times” here refers to a case where substantial processing such as mechanical, chemical, or thermal processing is performed on a silicon wafer. Therefore, it includes a case where a silicon wafer cleaning process, an inspection process, and the like are performed between successive “pre-polishing” and “post-polishing”.

The polishing condition to be changed may be only the polishing condition of the wafer surface. Further, only the polishing conditions on the back surface of the wafer may be used. Furthermore, the polishing conditions for both the front and back surfaces of the wafer may be used.
The number of times of double-side polishing is, for example, three times or four times. In any case, double-side polishing is performed on the silicon wafer at all times.

  According to a second aspect of the present invention, the polishing cloth is adhered while holding the silicon wafer in a wafer holding hole formed in a carrier plate and supplying the polishing liquid in at least one double-side polishing. Between the upper surface plate and the lower surface plate to which the polishing cloth is adhered, both sides of a sun gear type that allows the carrier plate to perform a circular motion without rotation in a plane parallel to the surface of the carrier plate. 2. The method for polishing a silicon wafer according to claim 1, wherein the polishing is performed.

  According to the second aspect of the present invention, the silicon wafer is held between the upper surface plate and the lower surface plate, and while maintaining this state, the carrier plate is circularly moved without rotation, and both surfaces are polished. According to the circular motion that does not rotate, all the points on the carrier plate perform exactly the same small circular motion. This is a kind of rocking motion. That is, it can be considered that the locus of the swing motion becomes a circle. Due to the movement of the carrier plate, the silicon wafer is polished while being rotated in the wafer holding hole during polishing. Thereby, it can grind | polish uniformly over the substantially whole region of a wafer grinding | polishing surface. For example, polishing sag at the outer periphery of the wafer can be reduced.

The circular motion without rotation refers to a circular motion (rotational rocking) in which the carrier plate rotates constantly while maintaining a state where the carrier plate is eccentric by a predetermined distance from the rotation axes of the upper surface plate and the lower surface plate. The number of wafer holding holes formed in the carrier plate may be one (single wafer type) or plural (batch). The size of the wafer holding hole is arbitrarily changed according to the size of the silicon wafer to be polished.
In the case of non-sun gear type double-side polishing, it is not always necessary to rotate the upper and lower surface plates simultaneously. This is because the non-sun gear-type double-side polishing presses the polishing cloths of the upper surface plate and the lower surface plate against the front and back surfaces of the silicon wafer to move the carrier plate.

  The invention according to claim 3 is the method for polishing a silicon wafer according to claim 1 or 2, wherein the polishing liquid does not contain abrasive grains.

  According to the third aspect of the present invention, since the polishing liquid that does not include abrasive grains is employed, it is possible to prevent the surface roughness of the silicon wafer such as surface roughness and haze from being lowered due to the abrasive grains. .

  According to the first aspect of the present invention, as the polishing of the silicon wafer, multi-stage polishing that is continuously performed by changing the polishing conditions for each time is adopted, and the multi-stage polishing is performed all times except the final time. Is double-side polished. Thereby, the quality of the surface shape of the silicon wafer can be improved, and the electronic circuit formed on the wafer surface can be further miniaturized. In addition, since the final polishing is a single-side polishing that polishes only the wafer surface, dust generated by double-sided polishing due to a scratch defect that occurs when the silicon wafer collides with the holding hole formation wall is the final polishing. Does not occur. As a result, it is possible to eliminate an increase in minute particles on the back surface of the wafer after completion of the polishing process, which becomes a problem when all polishing is performed on both sides.

  According to the second aspect of the present invention, the sun gear is not incorporated as at least one double-side polishing, and the front and back surfaces of the wafer are simultaneously polished by moving the carrier plate between the upper surface plate and the lower surface plate. Since the sun gear type double-side polishing is adopted, it is possible to polish uniformly over substantially the entire area of the wafer polishing surface. As a result, polishing sagging on the outer periphery of the wafer can be reduced.

  According to the third aspect of the present invention, since the polishing liquid that does not include abrasive grains is employed, it is possible to prevent the surface roughness of the silicon wafer such as surface roughness and haze from being lowered due to the abrasive grains. .

  Examples of the present invention will be specifically described below.

A method for polishing a silicon wafer according to Embodiment 1 of the present invention will be described.
The silicon wafer to be used is manufactured by the following process. A silicon single crystal ingot having a diameter of 300 mm, an initial oxygen concentration of 1.0 × 10 ¹⁸ atoms / cm ³ and a specific resistance of 10 mΩ · cm is pulled up by the Czochralski method. As shown in the flow sheet of FIG. 1, the obtained silicon single crystal ingot is subjected to block cutting, outer diameter grinding, slicing, chamfering, etching, primary polishing (sun gear type double side polishing), and secondary polishing (sun gearless type). Double-side polishing) and finish polishing (single-side polishing) are sequentially performed.

Next, with reference to FIG. 2 and FIG. 3, the primary polishing process of the silicon wafer W will be described.
The front and back surfaces of the etched silicon wafer W are subjected to primary double-side polishing using a sun gear type double-side polishing apparatus.
2 and 3, reference numeral 40 denotes a sun gear type double-side polishing apparatus. The sun gear type double-side polishing apparatus 40 is provided in parallel with each other, and an upper surface plate 42 in which polishing cloths 41 and 41 are respectively attached to respective opposing surfaces. And a lower surface plate 43, a small-diameter sun gear 44 interposed between the upper surface plate 42 and the lower surface plate 43 so as to be rotatable around an axis, and a large diameter provided so as to be rotatable around the axis. The internal gear 45 and the wafer holding holes 46a for holding the four silicon wafers W are formed, and the outer gear 46b meshed with the sun gear 44 and the internal gear 45 is formed at each outer edge. And four disk-shaped carrier plates 46.
The sun gear type double-side polishing apparatus 40 employs a 28B double-side polishing apparatus manufactured by Speed Fam Co., Ltd. For both polishing cloths 41, 41, Suba 800 manufactured by Rodel Nitta Co. is used. The thickness of the silicon wafer W is 730 μm, and the thickness of the carrier plate 46 is 600 μm.

In the primary polishing process, both surfaces of the silicon wafer W are polished simultaneously using the sun gear double-side polishing apparatus 40. That is, the silicon wafer W is inserted into each wafer holding hole 46a of the carrier plate 46 so as to be rotatable. At this time, the back surface of each wafer is upward. Next, in this state, polishing cloths 41 and 41 are pressed at 200 g / cm ² on both front and back surfaces of each wafer. Further, between the upper surface plate 42 and the lower surface plate 43, 1 weight of silica particles having an average particle diameter of about 40 nm (dynamic scattering method) based on a KOH solution of 0.3% by weight at a use point is used. The carrier plate 46 is rotated and revolved while supplying 2% / min colloidal silica). As a result, both the front and back surfaces of the four silicon wafers W held in the wafer holding holes 46a are collectively polished while being pressed against a pair of upper and lower polishing cloths 41, 41. Instead of the polishing liquid made of colloidal silica, a polishing liquid only containing a KOH solution not containing polishing abrasive grains may be employed. In this case, the surface roughness of the silicon wafer such as surface roughness and haze due to the abrasive grains can be prevented from being lowered. The polishing rate of the front and back surfaces of the wafer is 1 μm / min, and the polishing amount is 30 μm.

Next, with reference to FIGS. 4 to 6, a secondary polishing process of the silicon wafer W subjected to the primary polishing will be described. Secondary double-side polishing using a non-sun gear type double-side polishing apparatus is continuously performed on the front and back surfaces of the silicon wafer W after the primary polishing. However, a step of cleaning the silicon wafer W may be inserted between the primary polishing and the secondary polishing.
4 to 6, reference numeral 10 denotes a sun gearless double-side polishing apparatus. Specifically, a double-side polishing apparatus (LPD300) manufactured by Fujikoshi Co., Ltd. is employed.
The sun-gear-type double-side polishing apparatus 10 has a disk-shaped glass epoxy carrier plate 11 in plan view in which five wafer holding holes 11a are formed around the plate axis (circumferential direction) every 72 degrees. Further, the silicon wafer W having a diameter of 300 mm inserted and held in the respective wafer holding holes 11a is sandwiched from above and below and moved relative to the silicon wafer W to polish the wafer surface. A surface plate 12 and a lower surface plate 13 are provided. The thickness (600 μm) of the carrier plate 11 is slightly smaller than the thickness (730 μm) of the silicon wafer W.

On the lower surface of the upper surface plate 12 and the upper surface of the lower surface plate 13, Suba400 manufactured by Rodel Nitta Co. is stretched as polishing cloths 14 and 15 for individually polishing the front and back surfaces of the silicon wafer W (FIG. 5). The upper surface plate 12 is rotationally driven in the horizontal plane by the upper rotation motor 16 via a rotating shaft 12a extending upward. The upper surface plate 12 is moved up and down in the vertical direction by an elevating device 18 that moves forward and backward in the axial direction. The elevating device 18 is used when the silicon wafer W is supplied to and discharged from the carrier plate 11. The upper surface plate 12 and the lower surface plate 13 are pressed against the front and back surfaces of the silicon wafer W by a pressing means such as an air bag system (not shown) incorporated in the upper surface plate 12 and the lower surface plate 13.
The lower surface plate 13 is rotated in the horizontal plane by the lower rotation motor 17 via the output shaft 17a. The carrier plate 11 is circularly moved in a plane (horizontal plane) parallel to the surface of the plate 11 by the carrier circular motion mechanism 19 so that the plate 11 itself does not rotate. Next, the carrier circular motion mechanism 19 will be described in detail.

The carrier circular motion mechanism 19 has an annular carrier holder 20 that holds the carrier plate 11 from the outside (FIG. 6). The carrier circular motion mechanism 19 and the carrier holder 20 are connected via a connection structure 21. The connection structure 21 is a means for connecting the carrier plate 11 to the carrier holder 20 so that the carrier plate 11 does not rotate and can absorb the elongation of the carrier plate 11 during thermal expansion.
That is, the connecting structure 21 corresponds to each pin 23 among the multiple pins 23 projecting from the inner peripheral flange 20a of the carrier holder 20 at predetermined angles in the holder circumferential direction and the outer peripheral portion of the carrier plate 11. And a long hole-shaped pin hole 11b perforated in a number corresponding to the position.

  These pin holes 11b have their hole length directions aligned with the plate radial direction so that the carrier plate 11 connected to the carrier holder 20 via the pins 23 can move slightly in the radial direction. By inserting the pins 23 into the respective pin holes 11b and attaching the carrier plate 11 to the carrier holder 20, elongation due to thermal expansion of the carrier plate 11 during double-side polishing is absorbed. The base portion of each pin 23 is screwed into a screw hole formed in the inner peripheral flange 20a via an outer screw engraved on the outer peripheral surface of this portion. Further, a flange 23 a on which the carrier plate 11 is placed is provided directly above the external screw at the base of each pin 23. Therefore, the height position of the carrier plate 11 placed on the flange 23 can be adjusted by adjusting the screwing amount of the pin 23.

On the outer periphery of the carrier holder 20, four bearing portions 20b projecting outward every 90 degrees are disposed. An eccentric shaft 24a protruding from an eccentric position on the upper surface of the small-diameter disc-shaped eccentric arm 24 is inserted into each bearing portion 20b. A rotating shaft 24b is suspended from the center of each lower surface of the four eccentric arms 24 (FIGS. 4 and 5). These rotary shafts 24b are inserted into bearing units 25a arranged in a total of four at 90 degrees on the annular device base body 25 with their tips protruding downward. Sprockets 26 are fixed to the tip portions protruding downward from the respective rotary shafts 24b.
Each sprocket 26 has a series of timing chains 27 in a horizontal state. The timing chain 27 may be changed to a power transmission system having a gear structure. The four sprockets 26 and the timing chain 27 constitute synchronizing means for simultaneously rotating the four rotary shafts 24b so that the four eccentric arms 24 perform a circular motion in synchronization.

  Of these four rotating shafts 24 b, one rotating shaft 24 b is formed to be longer, and its tip protrudes downward from the sprocket 26. A power transmission gear 28 is fixed to this portion. The gear 28 meshes with a large-diameter driving gear 30 fixed to an output shaft extending upward of a circular motion motor 29 such as a geared motor.

  Therefore, if the output shaft of the circular motion motor 29 is rotated, the rotational force is transmitted to the timing chain 27 via the gears 30 and 28 and the sprocket 26 fixed to the long rotating shaft 24b. By rotating 27, the four eccentric arms 24 are synchronously rotated in the horizontal plane around the rotation shaft 24b via the other three sprockets 26. As a result, the carrier holder 20 collectively connected to each eccentric shaft 24a, and thus the carrier plate 11 held by the holder 20, performs a circular motion without rotation in a horizontal plane parallel to the plate 11. . That is, the carrier plate 11 turns while maintaining a state that is eccentric from the axis e of the upper surface plate 12 and the lower surface plate 13 by a distance L. This distance L is the same as the distance between the eccentric shaft 24a and the rotating shaft 24b. By this circular motion not accompanied by rotation, all points on the carrier plate 11 draw a locus of a small circle of the same size.

Next, a secondary double-side polishing method for the silicon wafer W using the sun gearless double-side polishing apparatus 10 will be described.
As shown in FIGS. 4 to 6, first, a silicon wafer W is inserted into each wafer holding hole 11 a of the carrier plate 11 so as to be rotatable. At this time, the back surface of each wafer is upward. Next, in this state, the polishing cloth 14 on the wafer back side rotating at 5 rpm with the upper surface plate 12 is pressed against the back surface of each wafer at 150 g / cm ² , and the wafer surface side rotating at 25 rpm with the lower surface plate 13 The polishing cloth 15 is pressed against each wafer surface at 150 g / cm ² .

  Then, with both polishing cloths 14 and 15 pressed against both front and back surfaces of the wafer, the polishing liquid (based on a KOH solution of less than 0.1% by weight at the point of use and an average particle diameter of about 20 nm (dynamic scattering) The timing chain 27 is rotated by the circular motion motor 29 while supplying the colloidal silica mixed with 0.5% by weight of the silica particles of method) at 2 liters / minute. Thereby, each eccentric arm 24 rotates synchronously in the horizontal plane, and the carrier holder 20 and the carrier plate 11 collectively connected to each eccentric shaft 24a are rotated in a horizontal plane parallel to the surface of the plate 11. Perform no circular motion at 24 rpm. As a result, the respective front and back surfaces of each silicon wafer W are polished while turning in the horizontal plane in the corresponding wafer holding holes 11a. As the polishing liquid, an abrasive-free type may be employed. The polishing time in the secondary polishing step is 15 minutes.

Next, with reference to FIG. 7, the final polishing (tertiary polishing) process of the silicon wafer W subjected to the secondary polishing will be described. The silicon wafer W after the secondary polishing is continuously subjected to finish polishing only on its surface using the single-side polishing apparatus 50. However, a cleaning process of the silicon wafer W may be performed between the secondary polishing and the final polishing. As the single-side polishing apparatus, a single-side polishing apparatus LG704 manufactured by Lapmaster is used.
The single-side polishing apparatus 50 is disposed so as to face an upper surface of a polishing surface plate 52 having a polishing cloth (Seagull 7355) 51 made by Toray Cortex Co., Ltd. on the upper surface, and four silicons on the lower surface. The wafer W includes a polishing head 54 attached with wax via a carrier plate 53.

In the final polishing process, only the surface of the silicon wafer W is mirror-polished using the single-side polishing apparatus 50. That is, the polishing head 54 is rotated at a predetermined rotation speed and gradually lowered, and the surface of each silicon wafer W is subjected to finish polishing by pressing the surface of the silicon wafer W against the rotating polishing cloth 51 at a predetermined rotation speed of 150 g / cm ² . At that time, a polishing liquid made of colloidal silica used in the secondary polishing is supplied onto the polishing pad 51 at a rate of 2 liters / minute. Instead of the polishing liquid made of colloidal silica, a polishing liquid only containing a KOH solution not containing polishing abrasive grains may be employed.

Thus, as the polishing of the silicon wafer W, the multi-stage polishing which is continuously performed by changing the polishing conditions every time is adopted, and the multi-stage polishing includes the primary polishing and the secondary polishing excluding the final finishing polishing. Is a double-sided polishing. Therefore, the nanotopology on the back surface of the wafer and the generation amount of minute particles on the back surface of the wafer can be reduced. As a result, the quality of the surface shape of the silicon wafer W can be improved, and the electronic circuit formed on the wafer surface can be further miniaturized.
In addition, since the final polishing is single-sided polishing, dust generation peculiar to double-side polishing does not occur in the final polishing due to a scratch defect that occurs when the silicon wafer W collides with the formation wall of the wafer holding hole. As a result, it is possible to eliminate an increase in minute particles on the back surface of the wafer after completion of the polishing process, which becomes a problem when all polishing is performed on both sides.

Hereinafter, with reference to FIG. 8 and FIG. 9, the polishing method of the silicon wafer of this invention is demonstrated concretely based on a test example and a comparative example.
A silicon single crystal ingot having a diameter of 300 mm, an initial oxygen concentration of 1.0 × 10 ¹⁸ atoms / cm ³ and a specific resistance of 10 mΩ · cm obtained under the conditions of Example 1 was processed into a wafer, and the surface was finally mirror-polished. Two selected silicon wafers (thickness: 730 μm) were used in the experiments of Comparative Example 1 and Test Example 1.

(Comparative Example 1)
Next, the silicon wafer was subjected to three-stage polishing including primary polishing, secondary polishing and finish polishing.
Among these, in the primary polishing step, the same sun gear double-side polishing apparatus 40 as the primary polishing in Example 1 was used, and double-side polishing of the silicon wafer was performed under the same polishing conditions as in Example 1.
In the secondary polishing step, only the surface of the silicon wafer was polished under the same conditions as those in the secondary polishing step of Example 1 except that a single-side polishing device LG704 manufactured by Lapmaster was used as the polishing device.
Further, in the tertiary polishing step, only the surface of the silicon wafer was polished under the same conditions as in the tertiary polishing step of Example 1, except that the same single-side polishing apparatus as in the secondary polishing step of Comparative Example 1 was used. .

(Test Example 1)
In Test Example 1, double-side polishing of a silicon wafer was performed using the same apparatus and the same conditions as in Example 1 in primary to final polishing. The results are shown in the graph of FIG. 8 and FIGS. 9a and 9b together with that of Comparative Example 1. The graph of FIG. 8 shows the flatness of the silicon wafer, and FIGS. 9a and 9b show the LPD (Light Point Defect; minimum measured value 130 nm) on the back side of the silicon wafer measured with SP2 manufactured by KLA-TENCOR. Represents the distribution.
As apparent from the graph of FIG. 8, the SFQR (Site Front Last-Squares Site Range) was smaller in the silicon wafer of Test Example 1 than in the silicon wafer of Comparative Example 1. In Comparative Example 1, 2300 LPDs of 130 nm or more were present on the back surface of one silicon wafer (FIG. 9a). In contrast, in Test Example 1, it was found that there were only 29 LPDs on the back surface of one silicon wafer (FIG. 9b).

1 is a flow sheet of a wafer manufacturing method including a silicon wafer polishing method according to Embodiment 1 of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view including a cutaway view of a part of a sun gear double-side polishing apparatus used in a silicon wafer polishing method according to Embodiment 1 of the present invention. It is a principal part longitudinal cross-sectional view of the sun gear type double-side polish apparatus used with the grinding | polishing method of the silicon wafer which concerns on Example 1 of this invention. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a sun gearless double-side polishing apparatus used in a silicon wafer polishing method according to Embodiment 1 of the present invention. It is a principal part longitudinal cross-sectional view of the sun gearless double-side polish apparatus used with the grinding | polishing method of the silicon wafer which concerns on Example 1 of this invention. It is a principal part expanded sectional view which shows the kinetic force transmission structure which transmits a kinetic force to the carrier plate incorporated in the non-sun gear type double-side polish apparatus used with the grinding | polishing method of the silicon wafer which concerns on Example 1 of this invention. It is a longitudinal cross-sectional view of the single-side polish apparatus used with the grinding | polishing method of the silicon wafer which concerns on Example 1 of this invention. It is the graph which compared the flatness of the silicon wafer obtained by the grinding | polishing method of the silicon wafer which concerns on Example 1 of this invention, and the silicon wafer produced by the conventional method. It is a top view which shows the LPD detection point on the back surface of the silicon wafer obtained by the grinding | polishing method of the silicon wafer which concerns on the comparative example 1 of this invention. It is a top view which shows the LPD detection point on the back surface of the silicon wafer obtained by the grinding | polishing method of the silicon wafer which concerns on Test Example 1 of this invention.

Explanation of symbols

10 Sun gear-free double-side polishing machine,
11,46 carrier plate,
11a, 46a Wafer holding hole,
12,42 Upper surface plate,
13,43 Lower surface plate,
14, 15, 41, 51 Abrasive cloth,
40 Sun gear double-side polishing machine,
50 single-side polishing equipment,
W Silicon wafer.

Claims (3)

A method for polishing a silicon wafer, wherein a polishing cloth is pressed against the front and back surfaces of a silicon wafer and the silicon wafer and the polishing cloth are relatively slid while supplying a polishing liquid, and the front and back surfaces are polished.
The polishing of the front and back surfaces of the silicon wafer is a multistage polishing performed continuously three times or more by changing the polishing conditions.
The multi-stage polishing is a polishing of a silicon wafer in which all polishing except the final polishing is double-side polishing for simultaneously polishing the front and back surfaces of the silicon wafer, and the final polishing is single-side polishing for polishing the wafer surface. Method.   The upper surface plate and the polishing cloth to which the polishing cloth is adhered while holding the silicon wafer in a wafer holding hole formed in a carrier plate and supplying the polishing liquid at least once. The sun gear-type double-sided polishing that causes the carrier plate to perform a circular motion without rotation in a plane parallel to the surface of the carrier plate between the lower surface plate to which is attached. Silicon wafer polishing method.   The method for polishing a silicon wafer according to claim 1, wherein the polishing liquid contains no abrasive grains.

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