JP2004025352A - Polishing method and device of semiconductor wafer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polishing method and device of semiconductor wafer wherein making it difficult to transfer of the shape of a wafer-retaining side surface to a ground surface hardly occur, and the uneven abrasion of the circumferential part of a wafer in batch polishing is eliminated. <P>SOLUTION: The silicon wafer W is sucked/retained to and by an abrasive head 12 in a vacuum degree of -60KPa to-KPa, and polished. Consequently, the wafer W not only revolves around according to the rotation of the abrasive head 12, but also slowly rotates around the waver central axis in spite of the vacuum sucking method. Accordingly, the polishing is performed based on the surface, and the lower surface shape of a carrier plate 14 is hardly transferred to the ground surface of the wafer W. Further, in a batch type polishing device 10, the uneven abrasion of the circumferential part of the silicon wafer W is suppressed. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method and apparatus for polishing a semiconductor wafer, and more particularly to a semiconductor wafer polishing technique for polishing a semiconductor wafer while rotating the semiconductor wafer during polishing.
[0002]
[Prior art]
After chamfering, the surface of the etched silicon wafer is subjected to mechanical and chemical polishing in the next polishing step. As a result, the surface of the silicon wafer is finished to a smooth and distortion-free mirror surface.
A general polishing apparatus is provided with a polishing platen on which a polishing cloth is adhered on an upper surface, and a polishing head which is arranged above the polishing platen so as to face and has a silicon wafer held by a predetermined holding structure on a lower surface. I have. At the time of polishing, a silicon wafer rotating integrally with the polishing head is brought into sliding contact with the surface (polishing surface) of the polishing cloth while supplying an abrasive (slurry) containing abrasive grains to the polishing cloth. Grind.
[0003]
By the way, as a method of holding a silicon wafer on a polishing head, for example, (1) a method in which a silicon wafer is vacuum-adsorbed to a lower surface of a carrier plate attached to a lower portion of the polishing head by a negative pressure is known. In addition, (2) a waxless mounting method is known in which an annular template for accommodating a silicon wafer is provided on the surface of the polishing head on the wafer holding side, and a back pad is interposed between the silicon wafer and the polishing head. I have.
(1) In the vacuum suction method, a silicon wafer is completely sucked to a carrier plate at a high degree of vacuum of about −60 KPa or less (adsorption with a suction force that does not move the wafer during polishing), and polishing is performed while maintaining this state. On the other hand, (2) In the waxless mounting method, a back pad having a thickness of about 200 to 400 μm is used. At the time of polishing, pure water is supplied to the back pad, and the silicon wafer housed inside the template is held (water-filled) from the back side of the wafer and polished by the surface tension.
[0004]
[Problems to be solved by the invention]
However, the conventional silicon wafer polishing apparatus has the following problems.
That is, (1) In the conventional vacuum suction method, the silicon wafer is polished at a high degree of vacuum while completely adsorbing the silicon wafer to the polishing head. Therefore, the silicon wafer being polished simply rotates (revolves) integrally with the rotation of the polishing head, and does not independently rotate (spin) about the wafer central axis. As a result, this polishing is based on the back surface, and the lower surface shape of the carrier plate may be directly transferred to the polished surface of the silicon wafer. Moreover, in a batch-type polishing apparatus for simultaneously polishing a plurality of silicon wafers, the polishing pressure acting on the carrier plate from the polishing head is larger at the plate outer peripheral portion than at the plate central portion. For this reason, one-sided loss (excessive polishing) is likely to occur in a part of the outer peripheral portion of the wafer after polishing.
(2) In the conventional waxless mounting method, a thick pad of about 400 μm is used as a back pad. For this reason, polishing has become the surface reference, and the polishing pressure directly acting on the silicon wafer has been reduced. As a result, there is a risk that the shape of the wafer surface before polishing is maintained as it is after polishing, or that irregularities on the wafer surface are amplified after polishing.
[0005]
Therefore, the inventor of the present invention has conducted extensive research and found that (1) if the wafer is polished by suctioning the wafer to the polishing head at a degree of vacuum of −60 KPa to −5 KPa, the wafer can be centered on the center axis of the wafer while using the vacuum suction method. It was found that the polishing was performed at a low speed, and the polishing was performed from the back surface to the surface. It has also been found that this makes it difficult for the shape of the lower surface of the carrier plate to be transferred to the polished surface of the wafer, and that during polishing using a batch-type polishing apparatus, the loss of the outer peripheral portion of the wafer is eliminated. Completed.
Further, the inventor has found that (2) the polishing pressure acting on the wafer can be increased while polishing on the surface basis by reducing the thickness of the back pad to 200 μm or less during polishing by the waxless mounting method. As a result, the unevenness of the wafer surface before polishing is maintained after polishing, or the possibility that the uneven shape is amplified is reduced, and as a result, the flatness of the wafer surface after polishing is found to be increased. Completed the invention.
[0006]
[Object of the invention]
The present invention makes it difficult to transfer the shape of the surface on the wafer holding side of the polishing head to the polished surface of the semiconductor wafer in the vacuum suction type polishing, and also to eliminate the loss of the wafer outer peripheral portion during the batch type polishing. It is an object of the present invention to provide a semiconductor wafer polishing method and an apparatus therefor.
In addition, the present invention suppresses the shape of the wafer surface before polishing from being maintained or amplified even after polishing, even though the polishing is performed on a surface basis, in the waxless mounting type polishing. It is an object of the present invention to provide a method and an apparatus for polishing a semiconductor wafer, which can increase the flatness of the semiconductor wafer.
[0007]
[Means for Solving the Problems]
The invention according to claim 1 is a method for polishing a semiconductor wafer, comprising: supplying an abrasive to a polishing cloth; and bringing a semiconductor wafer held by a polishing head into sliding contact with the polishing cloth, thereby polishing the semiconductor wafer. A method for polishing a semiconductor wafer, wherein the semiconductor wafer is adsorbed to the polishing head at a degree of vacuum of -60 KPa to -5 KPa.
[0008]
The polishing method applied here may be a single wafer type in which semiconductor wafers are polished one by one. Alternatively, a batch type in which a plurality of semiconductor wafers are polished simultaneously may be used.
As the semiconductor wafer, for example, a silicon wafer, a gallium arsenide wafer, or the like can be employed.
As the polishing cloth, for example, an "MH pad" or "IC pad" made of a hard foamed urethane foam, a "Suba pad" in which a nonwoven fabric is impregnated with a urethane resin, and the like can be used.
As the abrasive, for example, a mixture of calcined silica, colloidal silica (abrasive grains), amine (processing accelerator), organic polymer (haze inhibitor), and the like can be used. Colloidal silica is a transparent or opaque milky white colloid liquid that is dispersed in water as primary particles without causing aggregation of silica fine particles.
[0009]
The degree of vacuum that acts during polishing is −60 KPa to −5 KPa, preferably −40 KPa to −15 KPa. If the pressure is lower than −60 KPa, the semiconductor wafer does not rotate, so that the polishing is performed on the basis of the back surface, and the transfer of the shape of the lower surface of the carry plate and the one-sided reduction are likely to occur. If it exceeds -5 KPa, polishing becomes a surface reference, and unevenness on the wafer surface is amplified.
During polishing, the polishing pressure acting on the semiconductor wafer from the polishing head is 100 to 700 g / cm ² , preferably 350 to 450 g / cm ² . If it is less than 100 g / cm ² , polishing becomes a surface standard, and unevenness on the wafer surface is easily amplified. On the other hand, if it exceeds 700 g / cm ² , since it is difficult to rotate, polishing is based on the back surface, so that one-sided reduction or transfer of the lower surface shape of the carrier plate is likely to occur.
[0010]
The invention according to claim 2 provides a state in which an annular template is provided on the surface of the polishing head on the wafer holding side, and the surface opposite to the polishing surface is brought into contact with the polishing head inside the template. Then, the semiconductor wafer is polished by sliding the semiconductor wafer against the polishing cloth while supplying the polishing agent to the polishing cloth while accommodating the semiconductor wafer.
The template has a hole inside the plate slightly larger than the diameter of the semiconductor wafer. The semiconductor wafer is accommodated in the hole. The height of the template is not limited. However, the height is preferably substantially the same as the thickness of the semiconductor wafer. As a material of the template, for example, glass epoxy resin, various ceramics, or the like can be used.
To accommodate a semiconductor wafer inside the template, with the surface opposite to the polishing surface being in contact with the polishing head, means that the semiconductor wafer has a surface opposite to the polishing surface that is the wafer of the polishing head. It means that it is directly applied to the holding side surface and is accommodated inside the template.
[0011]
The invention according to claim 3 provides an annular template on the surface of the polishing head on the wafer holding side, accommodates the semiconductor wafer inside the template, and has a thickness between the semiconductor wafer and the polishing head. This is a method of polishing a semiconductor wafer in which a back pad of 200 μm or less is interposed, and then the semiconductor wafer is brought into sliding contact with the polishing cloth and polished while supplying an abrasive to the polishing cloth.
As a material of the back pad, for example, a nonwoven fabric such as a suede cloth can be adopted. Also, its hardness is not limited.
If the thickness of the back pad exceeds 200 μm, the polishing pressure acting on the semiconductor wafer becomes small, and polishing becomes a surface reference, so that unevenness on the wafer surface is easily amplified.
[0012]
The invention according to claim 4 is a polishing surface plate on which a polishing cloth is stuck, a polishing head having a surface on a wafer holding side for holding a semiconductor wafer opposed to the polishing surface plate, and a wafer of the polishing head. An apparatus for polishing a semiconductor wafer, comprising: suction means for vacuum-sucking a semiconductor wafer at -60 KPa to -5 KPa on a surface on a holding side.
The polishing apparatus may be one in which a polishing head is arranged above the polishing apparatus so as to face the other, or may be one in which the polishing head is arranged upside down. Further, a polishing apparatus that reciprocates the polishing head along the polishing cloth or a polishing apparatus that does not reciprocate the polishing head may be used. When the semiconductor wafer is reciprocated, polishing may be performed with a part of the outer peripheral portion of the semiconductor wafer protruding outside the polishing pad, or may be performed without such polishing.
[0013]
An invention according to claim 5, wherein a polishing platen to which a polishing cloth is adhered, a polishing head having a surface on a wafer holding side for holding a semiconductor wafer opposed to the polishing platen, and a wafer of the polishing head An apparatus for polishing a semiconductor wafer, comprising: an annular template provided on a holding-side surface and containing a semiconductor wafer in a state in which a surface opposite to a polishing surface is in contact with the polishing head.
[0014]
The invention according to claim 6 is a polishing surface plate on which a polishing cloth is stuck, a polishing head having a surface on a wafer holding side for holding a semiconductor wafer opposed to the polishing surface plate, and a wafer of the polishing head. In a semiconductor wafer polishing apparatus, comprising: an annular template provided on a holding side surface, in which a semiconductor wafer is housed inside; and a back pad interposed between the semiconductor wafer and the polishing head. This is a semiconductor wafer polishing apparatus in which the thickness of the pad is 200 μm or less.
[0015]
[Action]
According to the first and fourth aspects of the present invention, the semiconductor wafer is polished by being adsorbed to the polishing head at a degree of vacuum of -60 KPa to -5 KPa lower than that at the time of complete adsorption. Therefore, in spite of the vacuum suction method, the semiconductor wafer not only revolves with the rotation of the polishing head but also slowly rotates around the center axis of the wafer. As a result, the polishing is performed on the basis of the surface, and it becomes difficult for the shape of the surface of the polishing head on the wafer holding side to be transferred to the wafer polishing surface of the semiconductor wafer. In addition, during batch-type polishing, it is possible to suppress the loss of the outer peripheral portion of the semiconductor wafer.
[0016]
According to the second, third, fifth, and sixth aspects of the present invention, the semiconductor wafer is accommodated inside the template by bringing the surface opposite to the polishing surface into direct contact with the polishing head. The semiconductor wafer is accommodated through a thin back pad having a thickness of 200 μm or less. Thereafter, this state is maintained, and the wafer is polished by sliding the polishing surface of the wafer against a polishing cloth. This reduces the possibility that the shape of the wafer surface before polishing is maintained or amplified even after polishing, even though the polishing is based on the surface. As a result, the flatness of the polished wafer surface can be increased.
[0017]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. First, a first embodiment will be described with reference to FIG. FIG. 1 is a vertical sectional view of a main part of a semiconductor wafer polishing apparatus according to a first embodiment of the present invention.
In FIG. 1, reference numeral 10 denotes a semiconductor wafer polishing apparatus (hereinafter, polishing apparatus). The polishing apparatus 10 is a vacuum suction type polishing apparatus capable of simultaneously polishing one side of a silicon wafer (CZ wafer) W having a diameter of 6 inches made of four single-crystal silicon.
The polishing apparatus 10 includes a polishing platen 11, a polishing head 12 disposed above the polishing platen 11, and having a surface (lower surface) on the wafer holding side for holding the silicon wafer W opposed to the polishing platen 11. And a suction means V for applying a degree of vacuum for vacuum suction of the silicon wafer W on the lower surface of the polishing head 12. The polishing platen 11 and the polishing head 12 have a thick disk shape, and opposing surfaces are flat.
[0018]
The polishing platen 11 is rotatable about a rotation axis by rotating means (not shown). A polishing cloth 13 is adhered to the upper surface of the polishing platen 11 via a thick sponge rubber. The polishing cloth 13 is a Suba600 (1270 μm thick, 80 ° hardness (Asker)) manufactured by Rodale in which a nonwoven fabric is impregnated with a urethane resin and cured.
The polishing head 12 is configured to be able to move up and down by lifting means (not shown). A carrier plate 14 for holding a wafer is detachably attached to the lower surface of the polishing head 12. On the lower surface of the carrier plate 14, wafer holding areas for adsorbing the silicon wafer W are arranged at 90-degree intervals on an imaginary circle centered on the center of the plate. In each wafer holding region of the carrier plate 14, a predetermined number of communication holes 14a are formed at a predetermined distance from each other, penetrating both sides of the plate. Similarly, a template 21 is fixed to each wafer holding area so that the silicon wafer W does not protrude from the holding area. The template 21 is a plate made of glass epoxy resin having a circular ring shape in plan view. The thickness of the template 21 is substantially the same as the silicon wafer W or is thinner by 1 to 200 μm.
[0019]
Inside the polishing head 12, a suction path 12a whose lower part is branched into many is formed. The upper part of the suction passage 12a is formed along the center axis of the rotating shaft, and communicates with the suction part of the suction means V via a communication pipe arranged outside. The branched lower portion of the suction passage 12a is divided into four groups, and the lower end of each group is communicated with a communication hole 14a formed in a corresponding wafer holding area of the carrier plate 14. A negative pressure is generated by the operation of the suction means V, and this negative pressure acts on the communication holes 14a in each wafer holding area via the communication pipe and the suction path 12a. As a result, the silicon wafer W is attracted to each wafer holding area.
The feature of the first embodiment is that the degree of negative pressure (degree of vacuum) generated by the suction means V is -60 KPa to -5 KPa, which is lower than the conventional -60 KPa for completely sucking the silicon wafer W onto the carrier plate 14. This is the point that has been set. Thereby, during polishing, the four silicon wafers W slowly rotate around their own wafer central axes.
[0020]
Next, the operation of the polishing apparatus 10 according to the first embodiment will be described.
As shown in FIG. 1, at the time of polishing the silicon wafer W, the suction means V is operated, and the four silicon wafers W stored in the holes 21 a of each template 21 are placed in each wafer holding area on the lower surface of the carrier plate 14. Adsorb each. At this time, each silicon wafer W is sucked at a low degree of vacuum of −60 KPa to −5 KPa.
Thereafter, the rotating polishing head 12 is lowered while the polishing agent is supplied at 1.0 liter / minute to the center of the polishing cloth 13, and the polishing of the polishing cloth 13 rotating integrally with the polishing platen 11 is performed. The silicon wafer W is brought into sliding contact with the working surface. The rotation speed of the polishing platen 11 is 5 to 20 rpm, the rotation speed of the polishing head 12 is 3 to 20 rpm, and the polishing pressure is 200 to 400 g / cm ² . The polishing time is about 10 minutes.
[0021]
Thus, the silicon wafer W at the time of polishing is adsorbed on the lower surface of the carrier plate 14 at a low degree of vacuum of −30 KPa. Therefore, the silicon wafer W not only revolves with the rotation of the polishing head 12 but also slowly rotates at about 1 rpm about the center axis of the wafer in spite of the vacuum suction method. As a result, the polishing of the silicon wafer W is changed from the conventional back surface reference to the front surface reference, and as a result, the shape of the lower surface of the carrier plate 14 is less likely to be transferred to the polished surface of the silicon wafer W.
Moreover, when such a batch-type polishing apparatus 10 is used, the polishing pressure from the polishing head 12 is larger at the outer peripheral portion of the carrier plate 14 than at the central portion thereof. As a result, in the related art, a part of the outer peripheral portion of the polished wafer is liable to be partially reduced. However, in the first embodiment, although the silicon wafer W rotates at a low speed of 1 rpm, the outer peripheral portion of the wafer is polished substantially uniformly, and such a loss can be eliminated.
[0022]
Next, a second embodiment of the present invention will be described with reference to FIG.
FIG. 2 is a vertical sectional view of a main part of a semiconductor wafer polishing apparatus according to a second embodiment of the present invention.
As shown in FIG. 2, in a second embodiment, in a polishing apparatus 20 of a waxless mount type, a surface (upper surface) opposite to a polished surface is formed on a hole 21 a inside a template 21 by using a carrier plate 14. This is an example in which a silicon wafer W is housed in direct contact with the lower surface. Therefore, in the second embodiment, there is no back pad normally used in the waxless mounting method.
In the polishing apparatus 20, a template 21 for accommodating a silicon wafer W is fixed to each wafer holding area on the lower surface of the polishing head 12. The template 21 is a circular ring-shaped glass epoxy plate. Of course, the polishing apparatus 20 is of a wackless mount type. Therefore, the suction means V, the suction passage 12a in the polishing head 12, and the communication hole 14a in the template 14 used in the first embodiment are removed.
[0023]
At the time of polishing by the polishing apparatus 20 of the second embodiment, a predetermined amount of water is supplied to the holes 21a of each template 21, and the upper surface of the wafer is brought into direct contact with the lower surface of the carrier plate 14 to fill the silicon wafer W with water. Thereafter, the silicon wafer W is slid against the polishing pad 13 and polished while supplying a predetermined amount of polishing agent.
As described above, since the silicon wafer W is directly filled with water on the lower surface of the carrier plate 14, the polishing pressure from the polishing head 12 acting directly on the silicon wafer W is lower than that of a conventional polishing apparatus using a back pad. It becomes big. As a result, the silicon wafer W slowly rotates at about 1 rpm about the center axis of the wafer. This reduces the risk that the shape of the surface of the silicon wafer W before polishing is maintained or amplified after polishing, even though the polishing is performed on the basis of the surface. As a result, the flatness of the polished wafer surface can be increased.
Other configurations, operations, and effects are in ranges that can be inferred from the first embodiment, and a description thereof will not be repeated.
[0024]
Next, a third embodiment of the present invention will be described with reference to FIG.
FIG. 3 is a longitudinal sectional view of a main part of a semiconductor wafer polishing apparatus according to a third embodiment of the present invention.
As shown in FIG. 3, the semiconductor wafer polishing apparatus 30 of the third embodiment is an example in which the thickness of the back pad 31 is smaller than that of a conventional product (about 400 μm).
That is, in the polishing apparatus 30, the back pad 31 having a thickness t of 200 μm is adhered to the entire lower surface of the carrier plate 14, and the template 21 is fixed to each wafer holding region on the lower surface of the back pad 31. The back pad 31 is made of a suede cloth. At the time of polishing, a predetermined amount of pure water is supplied to the back pad 31 to fill the silicon wafer W with water. Polishing is performed while maintaining this state. The polishing pressure acting on the silicon wafer W during polishing is smaller than in the case of the above-described second embodiment. However, when the thickness is reduced to about 200 μm, which is about half the thickness of the conventional back pad, the one-sided loss of the outer peripheral portion of the polished silicon wafer W is almost eliminated.
Other configurations, operations, and effects are substantially the same as those of the second embodiment, and thus description thereof is omitted.
[0025]
【The invention's effect】
According to the first and fourth aspects of the present invention, the semiconductor wafer is adsorbed to the polishing head at a low degree of vacuum of −60 KPa to −5 KPa and polished. Rotates. Therefore, the polishing of the semiconductor wafer is based on the surface, and the shape of the surface of the polishing head on the wafer holding side is difficult to be transferred to the polishing surface of the semiconductor wafer. it can.
[0026]
According to the second, third, fifth and sixth aspects of the present invention, when a semiconductor wafer is accommodated inside the template, the surface opposite to the polished surface of the semiconductor wafer is directly attached to the polishing head. It is housed in a contact state or is housed through a thin back pad having a thickness of 200 μm or less. As a result, the risk of maintaining or amplifying the shape of the wafer surface before polishing is reduced even though the polishing is performed on the basis of the surface. Therefore, the flatness of the polished wafer surface can be improved.
[Brief description of the drawings]
FIG. 1 is a vertical sectional view of an essential part of a semiconductor wafer polishing apparatus according to a first embodiment of the present invention.
FIG. 2 is a vertical sectional view of a main part of a semiconductor wafer polishing apparatus according to a second embodiment of the present invention.
FIG. 3 is a longitudinal sectional view of a main part of a polishing apparatus for a semiconductor wafer according to a third embodiment of the present invention.
[Explanation of symbols]
10,20,30 polishing equipment for semiconductor wafers,
11 polishing table,
12 polishing head,
13 polishing cloth,
21 templates,
31 back pad,
V adsorption means,
W Silicon wafer (semiconductor wafer).

Claims (6)

By supplying an abrasive to the polishing cloth, by bringing the semiconductor wafer held by the polishing head into sliding contact with the polishing cloth, in a semiconductor wafer polishing method for polishing this semiconductor wafer,
A method for polishing a semiconductor wafer, wherein the semiconductor wafer is adsorbed on the polishing head at a degree of vacuum of −60 KPa to −5 KPa. An annular template is provided on the surface of the polishing head on the wafer holding side, and the semiconductor wafer is accommodated inside the template in a state where the surface opposite to the polishing surface is in contact with the polishing head. A semiconductor wafer is polished by sliding a semiconductor wafer against a polishing cloth while supplying an abrasive to the semiconductor wafer. An annular template is provided on the surface of the polishing head on the wafer holding side, and a semiconductor wafer is accommodated inside the template, and a back pad having a thickness of 200 μm or less is interposed between the semiconductor wafer and the polishing head, Then, a semiconductor wafer polishing method for polishing the semiconductor wafer by bringing the semiconductor wafer into sliding contact with the polishing cloth while supplying an abrasive to the polishing cloth. A polishing platen on which a polishing cloth is stuck;
A polishing head in which the surface on the wafer holding side that holds the semiconductor wafer on the polishing platen is arranged to face,
A semiconductor wafer polishing apparatus, comprising: suction means for vacuum-suctioning the semiconductor wafer at -60 KPa to -5 KPa on a surface of the polishing head on the wafer holding side. A polishing platen on which a polishing cloth is stuck;
A polishing head in which the surface on the wafer holding side that holds the semiconductor wafer on the polishing platen is arranged to face,
A polishing apparatus for a semiconductor wafer, comprising: an annular template provided on a surface of the polishing head on the wafer holding side, the semiconductor wafer being housed in a state where a surface opposite to the polishing surface is in contact with the polishing head. A polishing platen on which a polishing cloth is stuck;
A polishing head in which the surface on the wafer holding side that holds the semiconductor wafer on the polishing platen is arranged to face,
An annular template provided on the wafer holding side surface of the polishing head and containing the semiconductor wafer inside,
In a semiconductor wafer polishing apparatus comprising a back pad interposed between the semiconductor wafer and the polishing head,
An apparatus for polishing a semiconductor wafer, wherein the thickness of the back pad is 200 μm or less.

Images