JP3410719B2 - Wax coating method for wafer - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for polishing a silicon semiconductor wafer. More specifically, the present invention relates to a method of applying wax to a wafer when the wafer is attached to a holding plate when the wafer is polished.

[0002]

2. Description of the Related Art Generally, the polishing of a silicon semiconductor wafer is
A plurality of wafers are attached to a holding plate with wax and held, and the holding plate is pressed against the rotating metal surface plate to which the polishing cloth is attached while flowing the polishing slurry, and the polishing surfaces of these wafers are placed on the cloth. And then slide it to polish. In this case, in order to keep the flatness of the wafer after polishing, the flatness is also required for the wax application surface for sticking and holding the wafer on the holding plate.
Regarding the specific method of applying wax to a wafer, the wafer is adsorbed and held on a rotating table that can be rotated at high speed, the wax is dropped on the center of the wafer, and then the wafer is rotated at high speed (spin method), and the centrifugal force is applied. To form a uniform and uniform wax film on the entire surface of the wafer by spraying, or liquid wax is sprayed from above the fixed and held wafer by a nozzle or the like (spray method) to form a wax film on the entire surface of the wafer. . In the latter method, a high voltage is applied between the nozzle and the wafer to charge the mist-like wax so that the wax is efficiently and uniformly applied in the plane of the wafer.

[0003]

However, in such conventional wafer polishing, the wafer adhered to the plate is pressed against the cross surface and slides in the slurry at the same time when the polishing is started. However, since the cross surface in contact with the wafer is easily deformed (depressed) due to the pressure, the contact surface pressure rises more than the inside of the wafer, especially near the outer periphery of the wafer, and further the slurry is sufficient in the outer periphery of the wafer. In addition, the wafer is polished more than the inside of the wafer. As a result, the wafer after polishing has a thin outer peripheral portion (referred to as “peripheral sag”), and the flatness of the entire wafer is reduced. It gets worse. The outer peripheral portion (a few mm from the outer peripheral edge) of the wafer having the problem of flatness has not been used as a device-formable area, but this is replaced with a device-formable area, and as many as possible from one wafer. It has been a conventional problem to improve the flatness of the outer peripheral portion of the wafer in order to obtain the above IC chip.

The invention according to claim 1 of the present invention is intended to prevent "peripheral sagging" after polishing. In addition to the object of the invention described in claim 1, the invention described in claim 2 aims to adjust the wax thickness to an optimum value in consideration of various polishing conditions. In addition to the object of the invention described in claim 1, the invention described in claim 3 is intended to adjust to an optimum wax thickness in consideration of various polishing conditions with a simple structure.

[0005]

[Means for Solving the Problems] Means taken by the present invention for solving the above problems are as follows. Claim 1
Then, in a wax application method for applying a wafer when a silicon semiconductor wafer is attached to a holding plate, the wax is applied to the wafer attachment surface so that the thickness is less than the application thickness inside the wafer over the entire periphery of the periphery. A wafer wax coating method is used, which is characterized by coating. According to a second aspect of the present invention, the wafer wax application method according to the first aspect is adopted, in which after the entire periphery of the wafer is masked by the masking means, the wax is applied to the wafer attachment surface by a spray method. According to a third aspect of the present invention, in applying the wax to the wafer adhering surface by a spray method, the wax is applied by adjusting the distance between the wafer adhering surface and the spray nozzle. adopt.

[0006]

The following effects are brought about by adopting the method of claim 1. Wax is applied over the entire circumference of the periphery of the wafer so that it is thinner than the coating thickness on the inside of the wafer. ), The outer peripheral portion and the inner portion of these wafers have the same polishing amount, so that “peripheral sagging” after the polishing can be prevented. More specifically, since the wax A near the outer peripheral portion W2 is thinner than the inner portion W1, the wafer W is bent and adhered to the holding plate side at the time of attachment, and the polishing surface of the outer peripheral portion W2 is polished. Polishing pressure (contact surface pressure) equivalent to that of the inner W1 polishing surface
Is obtained. Next, the following effects are brought about by adopting the method of claim 2. After the masking means is used to mask the entire periphery of the wafer adhering surface in the vicinity of the outer circumference of the wafer, wax is applied by a spray method. Therefore, by appropriately selecting the shape of the masking means and the gap between the wafer and polishing conditions (polishing Pressure, amount of slurry, sliding speed, etc.)
The wax thickness can be adjusted to an optimum value, and as a result, "peripheral sagging" can be virtually eliminated. Further, by adopting the method of claim 3, the following effects are brought about. By adjusting the distance between the wafer adhering surface and the spray nozzle, the application range (concentric circle with the wafer) of the wax sprayed in a conical shape on the wafer surface can be adjusted without using the masking means of claim 2. It becomes adjustable, and polishing conditions (polishing pressure, slurry amount, sliding speed, etc.) are the same as in the method of claim 2.
The wax thickness can be adjusted to the optimum wax thickness with a simple structure.
As a result, "surrounding sagging" can be virtually eliminated.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. In this embodiment, as shown in FIG. 1, a silicon semiconductor wafer W is sucked and held horizontally by a vacuum chuck 1, and a spray nozzle 2 for wax A is installed above the central portion of the wafer W. From the wax A to the horizontal surface of the wafer W
Is sprayed in a conical shape, so that the wax A is uniformly applied in the entire surface of the bonding surface of the wafer W.

In the space from the sticking surface of the wafer W to the nozzle 2, a masking means 3 is installed so that a slight gap G can be maintained between the sticking surface of the wafer W and the nozzle 2. The masking means 3 is a doughnut-shaped jig made of a material such as a synthetic resin or a metal to open a central portion facing the inside W1 of the wafer W and leave a portion corresponding to the outer peripheral portion W2 of the wafer W in an annular shape. A plurality of sizes and shapes of the circular annular portion 3a are prepared according to the diameter and shape of the wafer W to be used.

When the wafer W to be used is, for example, 200 mm (8 inches) without an orientation flat as shown in FIG. 2, it has a perfect circular shape with an outer diameter of 210 mm, an inner diameter of 188 mm and a thickness of 2 mm. The masking means 3 formed in an annular shape is used. Further, in the case of the wafer W having the orientation flat OF as shown in FIG. 3, the masking means 3 in which the linear portion 3b corresponding to the orientation flat OF is formed on a part of the circular annular portion 3a is used. To do.

Further, the masking means 3 is supported by an elevating means 4 such as an air cylinder so as to be adjustable in the vertical direction, and a gap G between the masking means 3 and the sticking surface of the wafer W is shown in FIG. Fine adjustment is possible with the adjuster 5 (screw structure) shown.

Next, a method for applying the wax A on the wafer W will be described. First, as shown in FIG. 1, the vacuum chuck 1 holds the wafer W in a horizontal state by suction, and masking is performed by the masking means 3 over the entire periphery of the bonding surface in the vicinity of the outer peripheral portion W2. In this state, the wax A is sprayed from the spray nozzle 2 onto the attachment surface of the wafer W in a conical shape with a spraying time adjusted so as to have a predetermined wax thickness (wax weight).

In the case of this embodiment, the gap G between the adhering surface of the wafer W and the masking means 3 is 0.5 mm, the masking means 3 is
The spraying time was set so that the thickness of the wax in the inside W1 of the wafer W facing the central opening of the wafer W was 1.5 μm.

As a result, the wax W is applied to the inside W1 of the wafer W through the central opening portion of the masking means 3 without any obstruction, and when the wax thickness becomes 1.5 μm as set, The wax thickness on the outer peripheral portion W2 of the wafer W covered by the masking means 3 is 0 to 0.3 μm, which is extremely thin compared to the inner portion W1, and the difference in coating thickness between the inner portion W1 and the outer peripheral portion W2 is 1.2 to
It could be 1.5 μm.

The wafer W obtained by the above-mentioned coating method was attached to a holding plate (not shown) and polished under conventional conventional polishing conditions. At this time, since the wax A applied to the outer peripheral portion W2 of the wafer W is thinner than the inner portion W1, the wafer W is bent and adhered to the holding plate side at the time of attachment, and the outer peripheral portion W2 of the outer peripheral portion W2 is polished at the time of polishing. A polishing surface (contact surface pressure) equivalent to that of the inner W1 polishing surface can be obtained.

As a result, regarding the flatness of the wafer W after polishing, the "peripheral sag" which was 1.2 μm in the related art was improved to 0.2 μm when the width dimension of the outer peripheral portion W2 was 6 mm from the outer peripheral edge. Therefore, since the wax A is applied by a spray method, the shape of the masking means 3 and the gap G with the wafer W are appropriately selected to optimize the polishing conditions (polishing pressure, slurry amount, sliding speed, etc.). The wax thickness can be adjusted to a proper value, and as a result, "surrounding sagging" can be virtually eliminated.

On the other hand, what is shown in FIGS. 4 and 5 is another embodiment of the present invention. In this device, the spray nozzle 2 is supported by an elevating means 6 such as an air cylinder so as to be adjustable and movable with respect to a bonding surface of the wafer W without installing the masking means 3 described above. By adjusting the distance between the sticking surface and the spray nozzle 2, it becomes possible to adjust the application range (concentric circle with the wafer W) of the wax A which is sprayed in a conical shape on the sticking surface of the wafer W. As a result, the structure in which the outer peripheral portion W2 of the wax A is made thinner than that of the inner part W1 is different from the embodiment shown in FIGS. 1 to 3, and the other structures are the same as those of the embodiment shown in FIGS. Is the same as.

The wafer W used in this embodiment is
Indicates that there is no orientation flat as shown in FIG. 5, and that having an orientation flat OF as shown in FIG. 3 cannot be used.

Therefore, as shown in FIGS. 4 and 5, the polishing conditions (polishing pressure, slurry amount) are the same as those of the embodiment shown in FIGS. 1 to 3 without using the masking means 3 of the embodiment. , The sliding speed, etc.) can be adjusted to an optimum wax thickness, and as a result, "peripheral sagging" can be virtually eliminated. As a result, there is an advantage that the structure can be simplified by the amount that it is not necessary to provide the masking means 3 as compared with the embodiment shown in FIGS.

In the embodiment shown above, the masking means 3 is a donut type jig, but the masking means 3 is not limited to this, and the wafer W is formed around the outer peripheral portion W2 of the wafer W.
Other structures may be used as long as the wax A can be applied so as to be thinner than the application thickness of the inside W1.

[0020]

As described above, according to the first aspect of the present invention, the wax is applied over the entire circumference of the periphery of the wafer so as to be thinner than the coating thickness inside the wafer. As a result, even at the outer peripheral portion of the wafer, a polishing pressure (contact surface pressure) almost equal to that of the inner polishing surface is obtained, and the polishing amounts at the outer peripheral portion and the inner portion of these wafers become equal to each other. Can be prevented. Therefore, more IC chips can be obtained from one wafer without the peripheral portion becoming the device formation impossible area.

According to the invention of claim 2, in addition to the effect of the invention of claim 1, since the masking means masks the entire periphery of the wafer adhering surface in the vicinity of the outer periphery of the wafer, wax is applied by a spray method. By appropriately selecting the shape of the masking means and the gap with the wafer, it is possible to adjust the wax thickness to an optimum value in consideration of various polishing conditions (polishing pressure, slurry amount, sliding speed, etc.). As a result, it is possible to virtually eliminate "surrounding droop".

According to the invention of claim 3, in addition to the effect of the invention of claim 1, by adjusting the distance between the wafer adhering surface and the spray nozzle, spraying is performed in a conical shape without using masking means. Since the range of wax coating on the wafer surface (concentric with the wafer) can be adjusted, the wax structure can be adjusted to the optimum wax thickness in consideration of various polishing conditions (polishing pressure, slurry amount, sliding speed, etc.). it can. As a result, it is possible to virtually eliminate "surrounding droop".

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional front view of an apparatus used for a wafer wax coating method according to an embodiment of the present invention.

2 is a cross-sectional plan view of FIG.

FIG. 3 is a cross-sectional plan view showing a modified example of a wafer.

FIG. 4 is a vertical sectional front view of an apparatus used for a wafer wax coating method according to another embodiment of the present invention.

5 is a cross-sectional plan view of FIG.

[Explanation of symbols]

W Silicon semiconductor wafer W1 Wafer inside W2 Wafer outer peripheral portion A Wax 2 Spray nozzle 3 Masking means

─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP 2001-189292 (JP, A) JP 2002-52462 (JP, A) JP 59-32135 (JP, A) (58) Fields investigated ( Int.Cl. ⁷ , DB name) H01L 21/304

Claims (3)

(57) [Claims] 1. A wax coating method for coating a wafer (W) when a silicon semiconductor wafer (W) is attached to a holding plate, wherein the wafer (W) attachment surface has an entire periphery near an outer peripheral portion (W2). Wax coating method for a wafer, wherein the wax (A) is coated so as to be thinner than the coating thickness inside the wafer (W) (W1). 2. The masking means (3) masks the entire periphery of the outer peripheral portion (W2) of the wafer (W),
The method for applying a wax to a wafer according to claim 1, wherein the wax (A) is applied to the surface on which the wafer (W) is adhered by a spray method. 3. When the wax (A) is applied to the wafer (W) sticking surface by a spray method, the distance between the wafer (W) sticking surface and the spray nozzle (2) is adjusted to apply the wax. The method of applying a wax to a wafer according to claim 1, which is performed.