JP2004356336A - Double-sided polishing method of semiconductor wafer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a double-sided polishing method of a semiconductor wafer which can efficiently control a flatness and states of front and rear faces of the semiconductor wafer. <P>SOLUTION: While supplying an abrasive, a polishing cloth 15 for polishing a front face and a polishing cloth 14 for polishing a rear face and a silicon wafer W are relatively rotated, respectively, and the polishing clothes 14 and 15 are pressed against the front and rear faces of the silicon wafer W respectively to carry out double-sided polishing. After a first-time double-sided polishing, a second-time double-sided polishing is carried out under the polishing conditions for the front and rear faces of the wafer different from those in the first-time double-sided polishing. Specifically, the type of the polishing clothes, the type of the abrasive, the polishing time period, the number of rotation of upper and lower surface plates, etc. are changed. Consequently, a flatness and states of front and rear faces of the semiconductor wafer can be efficiently controlled. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for polishing both sides of a semiconductor wafer, and more particularly to a method for polishing both sides of a semiconductor wafer for efficiently controlling the flatness of the semiconductor wafer and the state of both the front and back surfaces of the semiconductor wafer.
[0002]
[Prior art]
In the production of a conventional double-side polished wafer, a single crystal silicon ingot is sliced to produce a silicon wafer, and then each step of chamfering, lapping, acid etching or surface grinding is sequentially performed on the silicon wafer. Next, double-side polishing is performed to mirror both the front and back surfaces of the wafer.
As this double-side polishing, conventionally, (1) a double-side polishing method using a planetary gear type double-side polishing device and (2) a double-side polishing method using a sun gear-free double-side polishing device are known.
(1) The planetary gear type double-side polishing apparatus usually has a planetary gear structure in which a sun gear is arranged at a central portion and an internal gear is arranged at an outer peripheral portion. In this double-side polishing apparatus, a silicon wafer is inserted and held inside a plurality of wafer holding holes formed in a carrier plate. Then, while supplying a slurry containing abrasive grains to the silicon wafer from above, the upper platen and the lower platen having a polishing cloth spread on each opposing surface are pressed against both front and back surfaces of each wafer, and the carrier plate is moved to the sun gear. By rotating and revolving between the internal gear and the internal gear, both surfaces of each silicon wafer are simultaneously polished.
[0003]
(2) As a non-sun gear type double-side polishing apparatus, for example, a “double-side polishing apparatus” described in Patent Document 1 is known. This non-sun gear type double-side polishing apparatus does not have a sun gear at the center of the apparatus unlike the planetary gear type. To that extent, the space for forming each wafer holding hole on the carrier plate is enlarged. As a result, even if the carrier plate has the same outer diameter as that of the sun gear type, the size of the silicon wafer that can be handled can be increased in the non-sun gear type double-side polishing apparatus. For example, it is advantageous when a large-diameter wafer having a diameter of 300 mm or more is polished on both sides.
[Patent Document 1] JP-A-11-254302
[0004]
The configuration of the sunless-type double-side polishing apparatus has a carrier plate having a plurality of wafer holding holes for holding a silicon wafer, and is arranged in a vertical direction of the carrier plate. An upper platen and a lower platen on which a polishing cloth for polishing both front and back surfaces of a silicon wafer is spread, and a carrier plate held between the upper platen and the lower platen, in a plane parallel to the surface of the carrier plate. Carrier exercise means for exercise.
The motion of the carrier plate is a circular motion without rotation of the carrier plate such that the silicon wafer held between the upper surface plate and the lower surface plate is rotated in the corresponding wafer holding hole. Also, during double-side polishing of the wafer, the upper and lower stools rotate in opposite directions about respective vertical rotation axes.
[0005]
Therefore, at the time of wafer double-side polishing, a silicon wafer is inserted and held in each wafer holding hole of the carrier plate, a slurry containing abrasive grains is supplied to the silicon wafer, and the carrier is rotated while rotating the upper platen and the lower platen. By causing the plate to perform a circular motion without rotation, each silicon wafer is simultaneously polished on both sides.
Since the sun gear is not incorporated in the non-sun gear type double-side polishing apparatus, the space for forming each wafer holding hole on the carrier plate is enlarged accordingly. As a result, even if the outer diameter is the same as that of the sun gear type, the size of the silicon wafer that can be handled can be increased in a double-side polishing apparatus (hereinafter, sometimes referred to as a non-sun gear type double-side polishing apparatus). .
Conventionally, double-side polishing of a silicon wafer has been performed only by primary polishing. Thereafter, only the surface of the silicon wafer has been subjected to polishing after the secondary polishing (for example, secondary polishing, and subsequent finish polishing) only on the surface of the silicon wafer by the single-side polishing apparatus.
[0006]
[Problems to be solved by the invention]
However, the following problems have been encountered in both conventional double-side polishing methods for silicon wafers using a double-side polishing apparatus of (1) planetary gear type and (2) sunless type.
That is, in the conventional double-side polishing method, the double-side polishing is performed only once. After that, only the surface of the wafer is processed by a single-side polishing apparatus, for example, secondary polishing and finish polishing. Therefore, it was not possible to control the roughness of the wafer back surface only by double-side polishing using a double-side polishing apparatus.
[0007]
[Object of the invention]
An object of the present invention is to provide a method for polishing both surfaces of a semiconductor wafer, which can efficiently control the flatness of the semiconductor wafer and the state of the front and back surfaces of the semiconductor wafer.
[0008]
[Means for Solving the Problems]
According to the first aspect of the present invention, the relative movement between the semiconductor wafer and the two polishing cloths is performed while pressing the polishing surface of the polishing cloth against both the front and back surfaces of the semiconductor wafer and supplying the polishing agent to both the polishing surfaces. A method for polishing both sides of a semiconductor wafer simultaneously by polishing both the front and back surfaces of the semiconductor wafer, wherein the double-side polishing of the semiconductor wafer is performed a plurality of times by changing the polishing conditions of the wafer surface and / or the polishing conditions of the wafer back surface. This is a method for polishing both sides of a wafer.
[0009]
As the semiconductor wafer, for example, a silicon wafer, a gallium arsenide wafer, or the like can be employed. The size of the semiconductor wafer is not limited. For example, a 6-inch wafer or an 8-inch wafer can be adopted. In addition, a large-diameter wafer having a diameter of 300 mm or more may be used.
As the type of abrasive used, for example, a slurry in which colloidal silica particles (polishing abrasive particles) having an average particle size of about 0.1 to 0.02 μm are dispersed in an alkaline etching solution having a pH concentration of 9 to 11 is employed. be able to. Further, abrasive grains may be dispersed in an acidic etching solution. The supply amount of the abrasive varies depending on the size of the semiconductor wafer and the like. Usually, it is 1.0 to 2.0 liter / min.
The type and material of the polishing cloth are not limited. For example, 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 block of foamed urethane, or the like can be used. In addition, 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.
[0010]
The relative movement between the semiconductor wafer and both polishing cloths may be rotation of only the semiconductor wafer or rotation of both polishing cloths. Alternatively, each of the semiconductor wafer and both polishing cloths may be rotated.
The double-side polishing apparatus is not limited. For example, a planetary gear type double-side polishing apparatus having a sun gear can be employed. In addition, a non-sun gear type double-side polishing apparatus having no sun gear may be employed.
The polishing of the semiconductor wafer may be performed by a single wafer type polishing apparatus for polishing semiconductor wafers one by one, or may be performed by a batch type polishing apparatus for simultaneously polishing a plurality of semiconductor wafers. The double-side polishing performed a plurality of times may be performed by one double-side polishing apparatus, or may be performed by a plurality of polishing apparatuses.
The polishing conditions to be changed may be only the polishing conditions for the wafer surface. Further, only the polishing conditions for the back surface of the wafer may be used. Further, both the polishing conditions for the front surface of the wafer and the polishing conditions for the rear surface of the wafer may be used. Specific polishing conditions to be changed include, for example, a polishing amount, a polishing rate, a polishing pressure, a rotation direction of a polishing cloth, a rotation direction of a semiconductor wafer, and the like.
The number of times of double-side polishing may be a plurality of times. For example, twice or three times.
[0011]
The invention according to claim 2, wherein the semiconductor wafer is held in a wafer holding hole formed in a carrier plate, and while the polishing agent is supplied, the upper surface plate and the polishing pad on which the polishing pad is adhered. 2. The double-side polishing method for a semiconductor wafer according to claim 1, wherein the carrier plate is caused to make a circular motion without rotation in a plane parallel to the surface of the carrier plate between the lower platens to which the carrier plate is adhered.
The double-side polishing apparatus is not limited as long as it does not include a sun gear, and is a non-sun gear type double-side polishing apparatus that simultaneously moves the carrier plate between the upper surface plate and the lower surface plate to polish both the front and rear surfaces of the wafer.
The circular motion with no rotation refers to a circular motion in which the carrier plate constantly turns while maintaining a state where the carrier plate is eccentric by a predetermined distance from the rotation axis of the upper surface plate and the lower surface plate. Due to this movement, all points on the carrier plate will trace a small circle of the same size.
The number of wafer holding holes formed in the carrier plate may be one (single wafer type) or plural. The size of the wafer holding hole is arbitrarily changed depending on the size of the semiconductor wafer to be polished.
In the case of non-sun gear type double-side polishing, the upper platen and the lower platen do not always need to be simultaneously rotated. This is because the sun-gearless double-side polishing apparatus employs a configuration in which the carrier plate is moved while the respective polishing cloths of the upper surface plate and the lower surface plate are pressed against the front and back surfaces of the semiconductor wafer.
[0012]
According to a third aspect of the present invention, there is provided the double-side polishing method for a semiconductor wafer according to the first or second aspect, wherein the double-side polishing is performed by a single double-side polishing apparatus.
[0013]
The method according to any one of claims 1 to 3, wherein the semiconductor wafer has one surface or both surfaces covered with an oxide film. It is.
The oxide film may cover only the front surface of the wafer or only the back surface of the wafer. Further, both sides of the semiconductor wafer may be used.
The type of the oxide film is not limited. For example, a silicon oxide film in the case of a silicon wafer can be employed. The thickness of the oxide film is not limited.
[0014]
According to a fifth aspect of the present invention, the polishing condition of the front surface and / or the polishing condition of the rear surface of the wafer to be changed is a kind of the polishing cloth. 2. A double-side polishing method for a semiconductor wafer according to item 1.
As a method of changing the type of the polishing cloth, for example, one of a non-woven fabric pad, a foamable urethane pad, and a suede pad is a polishing cloth for surface polishing, and another is a polishing cloth for polishing a back surface. it can.
Further, a polishing cloth of a material having a different hardness, a polishing cloth of a material having a different density, a polishing cloth of a material having a different compression rate, a polishing cloth of a material having a different compression elastic modulus, or the like can be used.
[0015]
The hardness of the polishing cloth is not limited. However, usually, a material having a hardness of 50 to 100 ° (Asker hardness tester) is used. The hardness ratio between one polishing cloth and the other polishing cloth is not limited. However, usually those having a ratio of 1: 1.05 to 1.60 are used.
The compression ratio of the polishing cloth is not limited. For example, it is 1.0 to 8.0%.
The density of the polishing cloth is not limited. For example, 0.30 to 0.80 g / cm ³ It is. The density ratio between one polishing cloth and the other polishing cloth is, for example, 1: 1.1 to 2.0.
The ratio of the compressibility of the polishing cloth is, for example, 1: 1.2 to 8.0.
The ratio between the compression elastic modulus of one polishing cloth and the compression elastic modulus of the other polishing cloth is, for example, 1: 1.1 to 1.5.
[0016]
The invention according to claim 6, wherein the polishing condition of the front surface of the wafer and / or the polishing condition of the rear surface of the wafer to be changed is a type of the polishing agent, according to any one of claims 1 to 4. Is a method for polishing both sides of a semiconductor wafer.
As the polishing agent, for example, only an alkaline liquid containing no free abrasive grains may be used. Alternatively, a slurry in which abrasive grains having an average particle size of about 0.02 to 0.1 μm are dispersed in an alkaline liquid may be used. Examples of the abrasive grains include any of diamond, silica (silicon dioxide), silicon carbide, alumina (aluminum oxide), ceria (cerium oxide), zirconia, manganese oxide, calcium carbonate, barium carbonate, magnesium oxide, and alumina-silica. Can be adopted. Further, a mixture of two or more of these at a predetermined compounding ratio may be used.
[0017]
The semiconductor wafer according to any one of claims 1 to 4, wherein the changed polishing conditions for the front surface of the wafer and the polishing conditions for the rear surface of the wafer are polishing times. Is a double-side polishing method.
For example, the time for the second double-side polishing is set longer than the time for the first double-side polishing. Or shorten it.
[0018]
In the invention described in claim 8, the polishing conditions for the front surface of the wafer and / or the polishing conditions for the rear surface of the wafer to be changed are the rotation speed of the upper surface plate and / or the rotation speed of the lower surface plate. The semiconductor wafer is a double-side polishing method according to any one of the above.
The rotation speeds of the upper stool and the lower stool are not limited. For example, the rotation speed of the platen on the low-speed rotation side may be changed within a range of 5 to 15 rpm, and the rotation speed of the platen on the high-speed rotation side may be changed at 20 to 30 rpm. At this time, the rotation speed ratio between the upper stool and the lower stool is also not limited. For example, from 1: 4 to 1: 5.
[0019]
[Action]
According to the present invention, while supplying the abrasive, the polishing cloth for the front surface polishing and the polishing cloth for the back surface polishing, and the semiconductor wafer are relatively rotated, respectively, these polishing cloths on the front and back surfaces of the semiconductor wafer Press to polish both sides. After the first double-side polishing, the second and subsequent double-side polishing is performed. At this time, in the second and subsequent double-side polishing, the polishing conditions for the front surface of the wafer and / or the polishing conditions for the rear surface of the wafer are changed to perform double-side polishing. Specifically, the type of polishing cloth (Claim 5), the type of abrasive (Claim 6), the polishing time (Claim 7), and the number of rotations of the upper and lower platens (Claim 8) are changed. As a result, the flatness of the semiconductor wafer and the state of the front and back surfaces of the semiconductor wafer can be efficiently controlled.
[0020]
In particular, according to the invention described in claim 2, the semiconductor wafer is held between the upper stool and the lower stool, and the carrier plate is caused to make a circular motion without rotation of the plate while maintaining this state. Polish on both sides. According to the non-rotating circular motion, all points on the carrier plate make exactly the same motion. This can be said to be a kind of rocking movement. That is, the trajectory of the swinging motion can be considered to be a circle. Due to such movement of the carrier plate, the semiconductor wafer is polished while rotating in the wafer holding hole during polishing. Thereby, it is possible to perform polishing uniformly over substantially the entire area of the wafer polishing surface. For example, it is possible to reduce polishing sag on the outer peripheral portion of the wafer.
[0021]
According to the third aspect of the present invention, since the double-side polishing is performed a plurality of times using only one double-side polishing apparatus, the equipment cost can be reduced, and the polishing time through the plurality of times can be reduced. Can be shortened.
[0022]
Further, according to the invention described in claim 4, one surface or both front and back surfaces of the semiconductor wafer are covered with the oxide film. Therefore, the surface having an oxide film and the surface having no oxide film can be polished to a predetermined degree during the different times of double-side polishing.
[0023]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
As shown in FIG. 1, in the first embodiment, each step of slicing, chamfering, lapping, etching, surface grinding, primary double-side polishing, oxide film removal, secondary double-side polishing, and finish cleaning is performed. A silicon wafer is produced. Hereinafter, each step will be described in detail.
The single crystal silicon ingot pulled up by the CZ (Czochralski) method is sliced into a large number of silicon wafers having a thickness of about 730 μm and a diameter of 200 mm or 300 mm in a slicing step (S101).
Next, the silicon wafer is chamfered (S102). That is, the outer peripheral portion of the wafer is roughly chamfered to a predetermined shape by the metal chamfering grindstones # 600 to # 1500. Thereby, the outer peripheral portion of the wafer is formed into a predetermined rounded shape (for example, a MOS type chamfered shape).
[0024]
Next, the chamfered silicon wafer is wrapped in a lapping step (S103). In the lapping step, the silicon wafer is arranged between lapping plates kept parallel to each other, and a lapping liquid, which is a mixture of alumina abrasive grains, a dispersant, and water, is poured between the lapping plate and the silicon wafer. Then, the wafer is rotated and rubbed under pressure to mechanically wrap both sides of the wafer. The wrap amount is about 40 to 80 μm on both the front and back surfaces of the wafer.
Subsequently, the wrapped silicon wafer is etched (S104) to remove the damage. A silicon natural oxide film having a thickness of about 40 nm is formed on the surface after the etching.
[0025]
Subsequently, the etched silicon wafer is subjected to surface grinding for grinding the wafer surface using the surface grinding apparatus shown in FIG. 2 (S105).
The surface grinding device 50 mainly includes a lower surface plate 51 and a grinding head 52 disposed above the lower surface plate 51. The silicon wafer W is vacuum-sucked on the upper surface of the lower platen 51. An annular grinding wheel 53 is fixed to the outer peripheral portion of the lower surface of the grinding head 52. The grinding wheel 53 has a large number of grinding tips 53a made of resinoid grinding wheels arranged in an annular shape. The count of the abrasive grains of the resinoid grinding wheel is # 4000. While rotating the grinding head 52 at 6000 rpm, it is gradually lowered at 0.3 μm / sec to grind the surface of the silicon wafer W on the lower platen 51. At this time, the rotation speed of the lower stool 51 is 40 rpm. A silicon oxide film remains on the back surface of the silicon wafer W whose surface has been ground.
[0026]
Next, the surface-ground silicon wafer W is subjected to primary double-side polishing (S106). Hereinafter, a double-side polishing apparatus used in the primary double-side polishing step will be specifically described with reference to FIGS. This double-side polishing apparatus is also used in a secondary double-side polishing step.
3 and 4, reference numeral 10 denotes a double-side polishing apparatus (hereinafter, referred to as a double-side polishing apparatus) to which the semiconductor wafer polishing method according to the first embodiment is applied. Specifically, a double-side polishing machine (LPD300) manufactured by Fujikoshi Corporation is employed.
The double-side polishing apparatus 10 includes a carrier plate 11 made of glass epoxy, which has a disc shape in a plan view, in which five wafer holding holes 11a are formed every 72 degrees around the plate axis (in the circumferential direction). An upper surface plate 12 for polishing a wafer surface by sandwiching a silicon wafer W having a diameter of 300 mm, which is rotatably inserted and held in the wafer holding hole 11a from above and below, and moving the silicon wafer W relative to the silicon wafer W. And a lower surface plate 13. The thickness (600 μm) of the carrier plate 11 is slightly smaller than the thickness (730 μm) of the silicon wafer W.
[0027]
As shown in FIG. 5A, a Bellatrix VN573 is adhered to the lower surface of the upper stool 12 as a back surface polishing cloth 14 for polishing the back surface (the silicon oxide film Wa side) of the silicon wafer W. On the upper surface of the lower stool 13, SUBA800 is spread as a front-side polishing cloth 15 for mirror-finishing the wafer surface. The hardness of the back side polishing cloth 14 is 91 ° (Asker hardness tester), and the density is 0.4 g / cm. ³ The compression ratio is 2.3%, the compression modulus is 89%, and the thickness is 1.0 μm. On the other hand, the hardness of the front side polishing cloth 15 is 83 ° (Asker hardness tester), and the density is 0.4 g / cm. ³ The compression ratio is 3.2%, the compression modulus is 74%, and the thickness is 1.2 μm.
When the holding power of the abrasive containing the abrasive grains is referred to with respect to the two polishing cloths 14, 15, the softer front-side polishing cloth 15 naturally holds the abrasive compared to the harder back-side polishing cloth 14. Power increases. The greater the holding power of the abrasive, the more abrasive grains adhere to the polishing surface and the higher the polishing rate.
[0028]
As shown in FIGS. 3 and 4, the upper platen 12 is driven to rotate in a horizontal plane by an upper rotation motor 16 via a rotation shaft 12a extending upward. The upper platen 12 is vertically moved up and down 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 both the front and back surfaces of the silicon wafer W by a pressing means such as an airbag system (not shown) incorporated in the upper surface plate 12 and the lower surface plate 13.
The lower surface plate 13 is rotated in a horizontal plane by a lower rotation motor 17 via an output shaft 17a. The carrier plate 11 makes a circular motion in a plane (horizontal plane) parallel to the plane 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 with reference to FIGS. 3, 4, 6, and 7. FIG.
[0029]
As shown in these figures, the carrier circular motion mechanism 19 has an annular carrier holder 20 for holding the carrier plate 11 from outside. The carrier circular motion mechanism 19 and the carrier holder 20 are connected via a connection structure 21. The connecting structure 21 is 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 expansion of the carrier plate 11 during thermal expansion.
That is, as shown in FIG. 7, the connecting structure 21 includes a plurality of pins 23 projecting from the inner peripheral flange 20 a of the carrier holder 20 at predetermined angles in the holder circumferential direction, Each pin 23 has a slot-shaped pin hole 11b formed in a number corresponding to a position corresponding to the pin 23.
[0030]
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 mounting the carrier plate 11 on the carrier holder 20 by loosely inserting the pins 23 into the respective pin holes 11b, the expansion due to the thermal expansion of the carrier plate 11 during double-side polishing is absorbed. The base of each pin 23 is screwed into a screw hole formed in the inner peripheral flange 20a via an external screw carved on the outer peripheral surface of this portion. A flange 23a on which the carrier plate 11 is placed is provided directly above the external screw at the base of each pin 23. Therefore, by adjusting the screwing amount of the pin 23, the height position of the carrier plate 11 placed on the flange 23 can be adjusted.
[0031]
Four bearing portions 20 b protruding outward at every 90 degrees are provided on the outer peripheral portion of the carrier holder 20. An eccentric shaft 24a protruding from an eccentric position on the upper surface of the small-diameter disk-shaped eccentric arm 24 is inserted into each bearing portion 20b. At the center of each lower surface of the four eccentric arms 24, a rotating shaft 24b is vertically provided. These rotary shafts 24b are inserted into a ring-shaped device base 25 with a total of four bearings 25a arranged at 90 ° intervals, with their tips protruding downward. Sprockets 26 are fixed to the respective tips of the rotating shafts 24b projecting downward. A timing chain 27 is stretched over each sprocket 26 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 a synchronizing means for simultaneously rotating the four rotary shafts 24b so that the four eccentric arms 24 perform a circular motion in synchronization.
[0032]
Further, one of the four rotating shafts 24b is formed to be longer, and the tip thereof protrudes downward from the sprocket 26. A power transmission gear 28 is fixed to this portion. The gear 28 is meshed with a large-diameter drive gear 30 fixed to an output shaft extending above a circular motion motor 29 such as a geared motor. Instead of being synchronized by the timing chain 27, the eccentric arms 24 may be individually rotated by, for example, disposing a circular motion motor 29 in each of the four eccentric arms 24. However, the rotation of each motor 29 needs to be synchronized.
[0033]
Therefore, when 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 rotary shaft 24b, and this timing chain As the orbit 27 rotates, the four eccentric arms 24 rotate in the horizontal plane around the rotation shaft 24b in synchronization with the other three sprockets 26. As a result, the carrier holder 20 connected collectively to the respective eccentric shafts 24a and the carrier plate 11 held by the holder 20 perform 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 of being eccentric by the distance L from the axis a of the upper stool 12 and the lower stool 13. This distance L is the same as the distance between the eccentric shaft 24a and the rotating shaft 24b. By this circular motion without rotation, all the points on the carrier plate 11 draw a locus of a small circle of the same size.
FIG. 8 shows the positions of the polishing agent supply holes in the double-side polishing apparatus 10. For example, a plurality of abrasive supply holes formed in the upper platen 12 are arranged at the center positions of these silicon wafers W. That is, the abrasive supply hole (SL) is located at the center of the upper platen 12, in other words, at the center of the carrier plate 11. As a result, the thin film of the abrasive is always held on the back surface of the silicon wafer W during polishing.
[0034]
Next, a primary double-side polishing method of the silicon wafer W using the double-side polishing apparatus 10 will be described.
First, the silicon wafer W is rotatably inserted into each of the wafer holding holes 11a of the carrier plate 11. At this time, the back surface of each wafer is directed upward. Then, in this state, the back side polishing cloth 14 rotating at 5 rpm together with the upper surface plate 12 is applied to the back side of each wafer at 200 g / cm. ² And the surface side polishing cloth 15 rotating at 25 rpm together with the lower platen 13 on the surface of each wafer at 200 g / cm. ² Press with.
[0035]
Then, the timing chain 27 is rotated by the circular motion motor 29 while the abrasive is supplied at 2 liters / minute from the upper platen 12 while the polishing cloths 14 and 15 are pressed against the front and back surfaces of the wafer. As a result, the eccentric arms 24 rotate synchronously in a horizontal plane, and the carrier holder 20 and the carrier plate 11 which are collectively connected to the eccentric shafts 24a rotate in a horizontal plane parallel to the surface of the plate 11. No circular motion is performed at 24 rpm. As a result, each silicon wafer W is polished on both front and back surfaces of each silicon wafer W while turning in a horizontal plane in the corresponding wafer holding hole 11a. The abrasive used here is a non-abrasive type. The polishing time in the first double-side polishing step is 15 minutes.
[0036]
At this time, the hardness of the back side polishing cloth 14 of the upper surface plate 12 is higher than that of the front side polishing cloth 15 of the lower surface plate 13. Moreover, a silicon oxide film Wa is formed on the back surface of the wafer. Therefore, the back surface of the wafer, which is the surface of the silicon oxide film Wa, is hardly polished, and primary double-side polishing in which the wafer surface is a mirror surface can be performed.
Next, the silicon oxide film Wa is removed from the back surface of the silicon wafer W after the primary double-side polishing (S107). Specifically, the silicon wafer W is immersed in a hydrofluoric acid solution having a concentration of 0.5 wt% and a temperature of 22 ° C. for only 30 seconds. After removing the silicon oxide film Wa, rinsing with pure water is performed for one minute or more.
[0037]
Subsequently, the silicon wafer W after the pure water rinsing is subjected to secondary double-side polishing.
The conditions for the secondary double-side polishing are the same as those for the primary double-side polishing, except that the polishing time is reduced from 15 minutes to 5 minutes. As shown in FIG. 5B, in the second double-side polishing, the silicon oxide film Wa is removed from the back surface of the silicon wafer W.
Actually, when the glossiness of the front and back surfaces of the silicon wafer W after the secondary double-side polishing was measured, the wafer back surface after the secondary double-side polishing was measured by the glossiness measurement device of Nippon Denshoku Co., Ltd. The average was 340% (390% or more was a mirror surface). On the other hand, the glossiness of the wafer surface was 390% on average. The flatness was 0.2 μm or less on average in SBIR and 0.5 μm or less on average in GBIR.
[0038]
As described above, since the double-side polishing of the silicon wafer W was performed twice while changing the polishing conditions for the front surface and the rear surface of the wafer, the flatness of the silicon wafer W and the state of the front and rear surfaces of the silicon wafer W were efficiently reduced. You can control well.
Further, at the time of the primary double-side polishing, the carrier plate 11 is made to make a circular motion without rotation of the plate 11 to polish the front and rear surfaces of the wafer. Since the silicon wafer W is polished on both sides by such a special movement of the carrier plate 11, it is possible to uniformly polish the silicon wafer W over substantially the entire front and back surfaces of the wafer.
After that, the silicon wafer W polished on both sides is subjected to finish cleaning (S109). Specifically, RCA cleaning is used.
[0039]
Next, a method for polishing both surfaces of a semiconductor wafer according to a second embodiment of the present invention will be described.
In the second embodiment, items related to the silicon oxide film Wa such as the formation of the silicon oxide film Wa in the first embodiment, the double-side polishing through the silicon oxide film Wa, and the removal of the silicon oxide film Wa are deleted. . As the polishing cloth for the primary double-side polishing apparatus, a back-side polishing cloth 14 having a hardness of 95 ° and a front-side polishing cloth 15 having a hardness of 83 ° are employed, while the polishing cloth for the secondary double-side polishing apparatus is employed. Is characterized in that a back side polishing cloth 14 having a hardness of 70 ° and a front side polishing cloth 15 having a hardness of 84 ° are mounted. The hardness is measured by an Asker hardness tester.
Other configurations, operations, and effects are substantially the same as those of the first embodiment, and thus description thereof is omitted.
[0040]
Next, a method for double-side polishing a semiconductor wafer according to a third embodiment of the present invention will be described.
In the third embodiment, while removing the matter relating to the silicon oxide film Wa of the first embodiment, the above-mentioned non-abrasive abrasive is used as the abrasive during the primary polishing, and the abrasive is used as the abrasive during the secondary polishing. It is characterized in that a polishing agent of the type having abrasive grains is used, and further, the first double-side polishing and the second double-side polishing are performed by one double-side polishing apparatus 10.
Other configurations, operations, and effects are substantially the same as those of the first embodiment, and thus description thereof is omitted.
[0041]
Next, a method for double-side polishing a semiconductor wafer according to a fourth embodiment of the present invention will be described.
In the fourth embodiment, while the matter relating to the silicon oxide film Wa of the first embodiment is deleted, the rotation speed of the upper platen during the primary polishing is set to 25 rpm, and the rotation speed of the lower platen is set to 5 rpm. At this time, the rotation speed of the upper platen is set to 20 rpm, the rotation speed of the lower platen is set to 15 rpm, and the first and second double-side polishing are performed by one double-side polishing apparatus 10. .
Other configurations, operations, and effects are substantially the same as those of the first embodiment, and thus description thereof is omitted.
[0042]
【The invention's effect】
According to the present invention, since the double-side polishing of the semiconductor wafer is performed a plurality of times by changing the polishing conditions of the wafer front surface and / or the polishing conditions of the rear surface of the wafer, the flatness of the semiconductor wafer and the state of the front and rear surfaces of the semiconductor wafer are changed. Can be controlled efficiently.
[0043]
In particular, according to the invention described in claim 2, the semiconductor wafer is held between the upper stool and the lower stool, and the carrier plate is caused to make a circular motion without rotation of the plate while maintaining this state. Since both sides are polished, the polishing can be performed uniformly over substantially the entire area of the wafer polishing surface. As a result, it is possible to reduce polishing sag on the outer peripheral portion of the wafer.
[0044]
According to the third aspect of the present invention, since the double-side polishing is performed a plurality of times using only one double-side polishing apparatus, the equipment cost can be reduced, and the polishing time through the plurality of times can be reduced. Can be shortened.
[0045]
Furthermore, according to the invention as set forth in claim 4, since one surface or both the front and back surfaces of the semiconductor wafer are covered with the oxide film, the surface having the oxide film and the surface not having the oxide film are subjected to the polishing at different times. It can be polished to a predetermined degree.
[Brief description of the drawings]
FIG. 1 is a flow sheet showing a method for manufacturing a semiconductor wafer to which a double-side polishing method for a semiconductor wafer according to a first embodiment of the present invention is applied.
FIG. 2 is a perspective view of the surface grinding device according to the first embodiment of the present invention in a used state.
FIG. 3 is an overall perspective view of a double-side polishing apparatus used for a double-side polishing method for a semiconductor wafer according to the first embodiment of the present invention.
FIG. 4 is a longitudinal sectional view during double-side polishing of the wafer by the double-side polishing apparatus according to the first embodiment of the present invention.
FIG. 5A is an enlarged sectional view of a main part showing a state during primary double-side polishing. (B) is a principal part enlarged sectional view showing a state during secondary double-side polishing.
FIG. 6 is a schematic plan view of the double-side polishing apparatus according to the first embodiment of the present invention.
FIG. 7 is an enlarged cross-sectional view of a main part of transmitting a kinetic force to transmit a kinetic force to the carrier plate according to the first embodiment of the present invention.
FIG. 8A is a cross-sectional view showing a position of a polishing agent supply hole according to the first embodiment of the present invention.
(B) is a plan view showing a position of a polishing agent supply hole according to the first embodiment of the present invention.
[Explanation of symbols]
11 Carrier plate,
11a wafer holding hole,
12 Upper platen,
13 Lower surface plate,
14 Back side polishing cloth,
15 front side polishing cloth,
W silicon wafer (semiconductor wafer),
Wa Silicon oxide film.

Claims (8)

The polishing surface of the polishing cloth is pressed against the front and back surfaces of the semiconductor wafer, respectively, and the polishing agent is supplied to both polishing surfaces, and the relative movement between the semiconductor wafer and the two polishing cloths causes the front and back surfaces of the semiconductor wafer to move. A double-side polishing method for a semiconductor wafer to be polished simultaneously,
A method for double-side polishing a semiconductor wafer, wherein the double-side polishing of the semiconductor wafer is performed a plurality of times by changing the polishing conditions for the front surface of the wafer and / or the polishing conditions for the rear surface of the wafer. While holding the semiconductor wafer in a wafer holding hole formed in the carrier plate and supplying the abrasive, between the upper platen on which the polishing cloth is attached and the lower platen on which the polishing cloth is attached 2. The method for polishing both surfaces of a semiconductor wafer according to claim 1, wherein the carrier plate is caused to make a circular motion without rotation in a plane parallel to the surface of the carrier plate. The double-side polishing method for a semiconductor wafer according to claim 1, wherein the double-side polishing is performed by a single double-side polishing apparatus. The method for polishing a semiconductor wafer according to any one of claims 1 to 3, wherein the semiconductor wafer has one surface or both front and back surfaces covered with an oxide film. The double-sided surface of the semiconductor wafer according to any one of claims 1, 2, and 4, wherein the changed polishing condition of the front surface of the wafer and / or the polishing condition of the rear surface of the wafer is a type of the polishing cloth. Polishing method. The method for polishing a double-sided semiconductor wafer according to any one of claims 1 to 4, wherein the changed polishing conditions for the front surface of the wafer and / or the polishing conditions for the rear surface of the wafer are types of the polishing agent. The method for polishing a double-sided semiconductor wafer according to any one of claims 1 to 4, wherein the changed polishing conditions for the front surface of the wafer and / or the polishing conditions for the rear surface of the wafer are polishing times. The polishing condition for the wafer front surface and / or the polishing condition for the back surface of the wafer to be changed is a rotation speed of the upper stool and / or a rotation speed of the lower stool, according to any one of claims 1 to 4. Polishing method for double-sided semiconductor wafers.

Images