JP5007791B2 - Wafer polishing method - Google Patents

Description

  The present invention relates to a method for polishing a wafer such as a sapphire substrate used for manufacturing a nitride semiconductor light emitting device, and more particularly to an improvement in a polishing method capable of simultaneously polishing a number of wafers without generating concentric irregularities. .

  When manufacturing a nitride semiconductor light emitting device used as a light emitting device, it is important to grow a high-quality epitaxial film, and there is no residual processing strain even on wafers such as sapphire substrates used for epitaxial film growth. A smooth surface free of defects is required.

  Wafers such as sapphire substrates for nitride semiconductor light emitting devices are conventionally processed into wafers with a specific crystal orientation exposed on the surface with a wire saw or the like, and mechanical polishing with loose abrasive grains and colloidal silica. It is used as a substrate on which an epitaxial film is grown after performing single-side mirror polishing by mechanochemical polishing.

In a single-side mirror polishing method for a wafer such as a sapphire substrate, normally, as shown in FIG. 3, a plurality of wafers W are fixed to a circular block 30 such as ceramic with wax or the like, and the circular block 30 is shown in FIG. The polishing head unit 10 is held on the lower surface of the polishing head unit 10, the polishing head unit 10 is pressed against the rotating surface plate 20 on which the polishing cloth 21 is mounted, and the colloidal silica 40 is supplied to the polishing cloth 21 of the rotating surface plate 20. The circular block 30 on which the wafer W is fixed is rotated.

When such single-sided mirror polishing is performed, the center of rotation of the polishing head unit 10 and the center of rotation of the rotating surface plate 20 are always constant, so that the contact locus of the wafer W on the polishing pad 21 is transferred to the wafer W, and FIG. The concentric irregularities 50 as shown in FIG. 1 may occur on the polished surface of the wafer W, and processing strain may remain on the surface of the wafer W.

  However, even if concentric irregularities 50 are generated on the surface of the wafer W, there has conventionally been no means for detecting them, so that the concentric irregularities 50 are formed as they are as substrates for epitaxial film growth. In recent years, the development of optical surface inspection devices has clarified the correspondence between concentric irregularities and defects in epitaxial films, and a wafer without concentric irregularities is desired.

  For this reason, the wafer after single-sided mirror polishing is inspected, and if concentric irregularities occur, it is necessary to replace the polishing cloth and re-polished the wafer with irregularities once again, which is the cost of inspection and re-polishing. Invited high.

  Incidentally, a method of uniformly polishing the wafer by reciprocating the surface plate in the direction perpendicular to the direction of movement of the surface plate at the center of the polishing member (corresponding to the polish head portion) (see Japanese Patent Laid-Open No. 4-210369), Alternatively, a method of polishing the wafer by simultaneously swinging the head portion and the rotating surface plate in directions orthogonal to each other (see JP-A-6-170724) has been developed.

However, any of these methods is merely a polishing method in which a single wafer is attached to a polishing member (head portion). Moreover, in order to satisfy the above conditions for the surface plate and the polishing member (head portion), one method is required. Since only a maximum of two sets of polishing members (head portions) can be incorporated in the surface plate, it was not a method capable of polishing a large number of wafers simultaneously.
JP-A-4-210369 JP-A-6-170724

  The present invention has been made paying attention to such a problem, and the object of the present invention is to provide a wafer polishing method capable of simultaneously polishing a large number of wafers without generating concentric concavities and convexities. Another object of the present invention is to provide a low-cost sapphire substrate (wafer) and the like that enable manufacture of a simple nitride semiconductor light emitting device.

  Accordingly, as a result of intensive studies by the inventor in order to solve the above-mentioned problems, the rotating surface plate is rotated in a direction that forms an angle of about 45 degrees with the rotation direction of the rotating surface plate at the center of the polishing head portion to which the wafer is fixed. When reciprocating, a maximum of four sets of polishing heads can be incorporated in one rotating surface plate, and it is found that a large number of wafers can be polished at the same time without generating concentric irregularities. It came to. The present invention has been completed based on such findings.

That is, the invention according to claim 1
On the premise of a wafer polishing method in which a wafer is fixed to a polishing head part, and the polishing head part is pressed against a rotating surface plate equipped with a polishing cloth to polish the wafer.
Four polishing heads that reciprocate the rotary platen in a direction that forms an angle of approximately 45 degrees with the rotation direction of the rotary platen at the center of the polishing head unit, and that are symmetrical with respect to the rotary platen. The portion is pressed against the rotating surface plate .

Next, the invention according to claim 2
Based on the wafer polishing method according to the invention of claim 1 ,
A plurality of wafers are fixed to the polishing head part,
The invention according to claim 3
On the premise of the wafer polishing method according to the invention of claim 1 or 2 ,
The reciprocating distance of the rotating surface plate is ± 1 mm or more.

According to the wafer polishing method of the present invention,
Since the rotary platen is reciprocated in a direction that forms an angle of approximately 45 degrees with the rotation direction of the rotary platen at the center of the polishing head, it becomes possible to polish the wafer without generating concentric concavities and convexities. Since a maximum of four polishing head portions can be incorporated into the rotating surface plate, a large number of wafers can be polished simultaneously.

  Therefore, it has the effect of providing a sapphire substrate (wafer) or the like that enables the manufacture of a high-quality nitride semiconductor light-emitting element at a low cost.

  Hereinafter, embodiments of the present invention will be described in detail.

  First, as shown in FIG. 1, the wafer polishing method according to the present invention fixes a wafer (not shown) to the polishing head unit 10 and is mounted with a polishing cloth (not shown). 20 is a method of polishing the wafer by pressing the polishing head portion 10 against an arrow that forms an angle of θ = approximately 45 degrees with the rotation direction indicated by the arrow B of the rotating surface plate 20 at the center A of the polishing head portion 10. The rotary surface plate 20 is reciprocated in the direction indicated by C.

Here, in order to polish (mirror finish) a plurality of wafers at the same time, each wafer (not shown) fixed to each polishing head unit 10 has the same swinging condition, as shown in FIG. The number of polishing head portions 10 is four with respect to the rotating surface plate 20, and the above-described direction is indicated by an arrow C that forms an angle of about 45 degrees with the rotation direction indicated by the arrow B of the rotating surface plate 20 at the center A of the polishing head portion 10. It is confirmed that it is most efficient to reciprocate (swing) the rotating surface plate 20. However, it is necessary that the four polishing head portions 10 be arranged so as to be symmetrical with respect to the rotating surface plate 20. That is, as in the prior art, the rotary platen 20 is reciprocated (oscillated) in a direction that forms an angle of 0 degrees or 90 degrees with the rotation direction indicated by the arrow B of the rotary platen 20 at the center A of each polishing head unit 10. ), The number of polishing head portions 10 for the same rocking condition of each wafer fixed to each polishing head portion 10 becomes two as understood from FIG. It is confirmed that the polishing process efficiency is inferior to the polishing method.

  Next, the reciprocating distance of the rotating surface plate is arbitrarily set, but is preferably set to ± 1 mm or more from the viewpoint of suppressing the occurrence of concentric irregularities.

  In addition, the number of semiconductor wafers such as sapphire substrates to be fixed to each polish head is in principle arbitrary, but the viewpoint of providing semiconductor wafers such as sapphire substrates that can manufacture high-quality nitride semiconductor light-emitting elements at low cost Therefore, it is desirable to mirror-polish by fixing as many as possible near the outer periphery of the circular block. In addition, the polishing head part generally rotates passively with the rotation of the rotating platen, and the rotational speed of the polishing head part changes with time, but in order to stabilize the processing conditions of the surface of a semiconductor wafer such as a sapphire substrate. In this case, it is preferable to forcibly rotate the polish head portion at a rotational speed close to the rotational speed of the rotating platen.

  Next, the upper limit of the reciprocating speed (swinging speed) in the rotating platen is not particularly specified. However, if the speed is extremely high, the polishing cloth will be worn more seriously and the flatness of the wafer will be deteriorated. About 1/10 or less of the rotational speed of the rotating surface plate at the center is sufficient. In addition, the lower limit of the reciprocating motion speed (swinging speed) on the rotating platen is not particularly specified, but if the polishing speed is exceeded, concentric irregularities will not be observed, and the cost of the substrate will increase due to expensive polishing equipment. From the viewpoint of avoidance, it is preferably about several mm / min or more.

  Examples of the present invention will be specifically described below.

  6 pieces of 3 inch diameter sapphire substrates are fixed to 4 pieces of 300 mm diameter ceramic circular blocks (see FIG. 3), respectively, and the above ceramic circular blocks are respectively held on the bottom surface of the 4 polish heads. I let you. The four polish head portions are arranged so as to have symmetry with respect to the rotating surface plate as shown in FIG.

Next, the four polishing heads were pressed against a rotating platen having a diameter of 800 mm and a rotation speed set to 60 rpm, and one-side mirror polishing was performed for 1 hour while supplying colloidal silica. Incidentally, the rotational speed of the polish head is 58 rpm, the unit load of the sapphire substrate is 350 g / cm ² , the reciprocating speed (rocking speed) of the rotating surface plate is 200 mm / min, and the reciprocating distance of the rotating surface plate is ± 20 mm. Each is set.

  Then, after performing the above-mentioned single-side mirror polishing, the sapphire substrate was peeled off from each ceramic circular block and cleaned, and then inspected with an optical surface inspection device (OSA-C1 manufactured by Candela). Concentric unevenness was not confirmed in one of the 24 sapphire substrates. Further, the same single-side mirror polishing was performed on the 216 sapphire substrates in total under the same conditions without changing the polishing cloth of the rotating surface plate, but no concentric irregularities were found. .

  The polishing rate at this time is 3.0 μm / hr on average, and it has been confirmed that the rocking speed (200 mm / min) of the rotating platen is sufficiently faster than the polishing rate (average 3.0 μm / hr). .

  Six sapphire substrates each having a diameter of 3 inches were fixed to four ceramic circular blocks having a diameter of 300 mm with wax, and the ceramic circular blocks were respectively held on the lower surfaces of the four polish head portions. The four polish head portions are arranged so as to have symmetry with respect to the rotating surface plate as shown in FIG.

Next, the four polishing heads were pressed against a rotating platen having a diameter of 800 mm and a rotation speed set to 60 rpm, and one-side mirror polishing was performed for 1 hour while supplying colloidal silica. The rotational speed of the polishing head is 58 rpm, the unit load of the sapphire substrate is 350 g / cm ² , the reciprocating speed (rocking speed) of the rotating surface plate is 200 mm / min, and the reciprocating distance of the rotating surface plate is ± 1 mm. Each is set.

  Then, after performing the above-mentioned single-side mirror polishing, the sapphire substrate was peeled off from each ceramic circular block and cleaned, and then inspected with an optical surface inspection device (OSA-C1 manufactured by Candela). Concentric unevenness was not confirmed in one of the 24 sapphire substrates. Further, the same single-side mirror polishing was performed on the 216 sapphire substrates in total under the same conditions without changing the polishing cloth of the rotating surface plate, but no concentric irregularities were found. .

  The polishing rate at this time is 2.8 μm / hr on average, and it has been confirmed that the rocking speed (200 mm / min) of the rotating surface plate is sufficiently faster than the polishing rate (average 2.8 μm / hr). .

  Six sapphire substrates each having a diameter of 3 inches were fixed to four ceramic circular blocks having a diameter of 300 mm with wax, and the ceramic circular blocks were respectively held on the lower surfaces of the four polish head portions. The four polish head portions are arranged so as to have symmetry with respect to the rotating surface plate as shown in FIG.

Next, the four polishing heads were pressed against a rotating platen having a diameter of 800 mm and a rotation speed set to 60 rpm, and one-side mirror polishing was performed for 1 hour while supplying colloidal silica. Incidentally, the rotational speed of the polish head is 58 rpm, the unit load of the sapphire substrate is 350 g / cm ² , the reciprocating speed (swinging speed) of the rotating surface plate is 1 mm / min, and the reciprocating distance of the rotating surface plate is ± 1 mm. Each is set.

  Then, after performing the above-mentioned single-side mirror polishing, the sapphire substrate was peeled off from each ceramic circular block and cleaned, and then inspected with an optical surface inspection device (OSA-C1 manufactured by Candela). Concentric unevenness was not confirmed in one of the 24 sapphire substrates. Further, the same single-side mirror polishing was performed on the 216 sapphire substrates in total under the same conditions without changing the polishing cloth of the rotating surface plate, but no concentric irregularities were found. .

The polishing rate at this time is 2.9 μm / hr on average, and it has been confirmed that the rocking speed (1 mm / min) of the rotating platen is sufficiently faster than the polishing rate (average 2.9 μm / hr). .
[Comparative Example 1]
Except that the rotary platen is not reciprocated (oscillated), 24 round sapphire substrates were subjected to one-side mirror polishing under the same conditions as in Examples 1, 2, and 3, and then each ceramic circular block After removing the sapphire substrate from the substrate and cleaning it, it was inspected with an optical surface inspection device (OSA-C1 manufactured by Candela). As a result, 6 out of 24 processed sapphire substrates were found to have concentric irregularities. It was done.

  Furthermore, the same single-side mirror polishing was performed on the total number of 216 sapphire substrates 9 times under the same conditions without changing the polishing cloth of the rotating platen. In 15 out of 24 sheets, concentric irregularities were observed in all 24 sheets after the fourth time.

  As a result, the superiority of the polishing method according to Examples 1 to 3 as compared with Comparative Example 1 was confirmed.

  According to the wafer polishing method of the present invention, a large number of wafers such as sapphire substrates can be simultaneously polished without generating concentric concavities and convexities.

  Therefore, it has industrial applicability applied as a polishing method for providing an inexpensive sapphire substrate or the like for manufacturing a nitride semiconductor light emitting device.

1 is a schematic plan view showing a wafer polishing method according to the present invention. Explanatory drawing which shows the grinding | polishing method of a wafer. The schematic plan view of the circular block to which the wafer was fixed. The schematic plan view which shows the concentric unevenness | corrugation formed in the wafer with the conventional grinding | polishing method.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Polish head part 20 Rotating surface plate A Center part of polish head part B Arrow which shows the rotation direction of a rotating surface plate C Arrow which shows the reciprocating motion (oscillation) direction of a rotating surface plate

Claims (3)

In the wafer polishing method, the wafer is fixed to the polishing head part, and the polishing head part is pressed against a rotating surface plate equipped with a polishing cloth to polish the wafer.
Four polishing heads that reciprocate the rotary platen in a direction that forms an angle of approximately 45 degrees with the rotation direction of the rotary platen at the center of the polishing head unit, and that are symmetrical with respect to the rotary platen. A method for polishing a wafer , comprising pressing a portion against the rotating surface plate . 2. The wafer polishing method according to claim 1 , wherein a plurality of wafers are fixed to the polishing head portion. 3. The wafer polishing method according to claim 1, wherein a reciprocating distance of the rotating surface plate is ± 1 mm or more.

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