JPH11233462A - Both surfaces polishing method of semiconductor wafer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To leave machined strain on a sand blast treatment surface when both surfaces polishing method excellent in precision is adopted. SOLUTION: Polishing cloths 1, 2 which are different in slurry holding force and in polishing speed are used. The cloth 1 whose polishing speed is extremely low is used facing a surface W1 having a working strain layer of a wafer W, cloth 2 whose polishing speed is high is used facing a polishing surface W2 on the opposite side, and both surfaces are simultaneously polished. As a result, polishing amount of the surface W1 having the machined strain layer of the wafer W is made extremely little as compared with that of the polishing surface W2 on the opposite side.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for polishing a silicon semiconductor substrate on which one surface is mirror-finished and a pattern is formed on the surface to manufacture an IC element, and a mirror polishing method for manufacturing the silicon semiconductor substrate.

[0002]

2. Description of the Related Art Conventionally, a polishing method for producing a silicon semiconductor substrate that requires at least one surface to be mirror-finished is performed by pressing a wafer attached to a plate against a polishing cloth while supplying a slurry. One side is mirror-finished, or the wafer held by the wafer carrier is pressed between a pair of upper and lower metal platens on which the polishing cloth is attached, and is moved relatively to the polishing cloth attached to the surface plate. By doing so, both surfaces were simultaneously mirror-finished with an equal amount of polishing. After that, in the substrate according to the above two methods, a pattern is formed on the mirror surface side of the silicon semiconductor substrate having only one mirror surface, and on one surface of the silicon semiconductor substrate having both mirror surfaces. Speaking of the difference between the two polishing methods in terms of flatness, which is one of the important characteristics, the double-side polishing method does not require the wafer to be attached to the plate as in the single-side polishing method. The flatness is good because it is not affected by variations in sticking the wafer to the plate, such as uneven application of the adhesive. On the other hand, the polishing cloth is indeed a wide variety of practically used ones. In general, depending on the manufacturing method and its structure, a non-woven fabric is used as a base material and a urethane resin is foamed on the surface thereof. Mold) and a `` nonwoven fabric mold '' in which a polyester nonwoven fabric is impregnated with urethane resin.
It is said that the urethane foam type is roughly classified into three types, and these various types are selected depending on the purpose depending on the purpose.

[0003]

However, such a conventional double-side polishing method has good flatness but has the following problems. The silicon semiconductor substrate has a gettering effect (absorption of contaminants and absorption of crystal defects) on the side opposite to the surface on which the pattern is formed before polishing in the process.
It is common to form a layer with significant processing strain by sandblasting for the purpose of. The single-side polishing method has no effect on the sandblasted surface since the surface opposite to the surface originally sandblasted is polished and finished, whereas the double-side polishing method is polished at the same speed from both sides of the wafer Therefore, the polishing allowance is usually 10 μm in consideration of the variation in the processing of the process up to that point.
Considering that the significant work strain layer formed by the sand blasting process is very small of several μm or less, although the front and back are necessary, the work strain is completely or partially eliminated. This problem is essential, and as a countermeasure, it is attempted to form a processing strain deeply with polishing progressing from both sides and disappearing, but deep sandblasting is performed in subsequent steps. Problems such as the occurrence of scratches and the like due to peeling of the wafer surface, and adhesion to the mirror surface during cleaning are raised again. It is also conceivable to perform sandblasting after finishing the mirror finish,
At that time, the processed mirror surface becomes the holding surface of the wafer, and there are some scratches which are almost impossible at present, and there are some which are very difficult to cope with the problem. Another problem is that it is practical in operation. In the double-side polishing method, the upper platen must be pulled up after polishing is completed, and the wafer must be taken out of the wafer carrier manually or automatically. At the time of this removal, the wafer that should be on the polishing cloth surface on the lower platen side rises together with the upper platen while sticking to the polishing cloth on the upper platen side, and not only is it difficult to take out the work, There is a troublesome problem that the wafer is dropped and damaged during the unloading operation.

An object of the present invention is to leave a processing distortion on a sandblasted surface when employing a double-side polishing method superior in accuracy. A second object of the present invention is to prevent the wafer from being stuck to the polishing pad on the upper platen side, in addition to the object of the first embodiment.

[0005]

In order to achieve the above-mentioned object, according to the first aspect of the present invention, a silicon semiconductor wafer is sandwiched between a pair of upper and lower platens to which polishing cloths are respectively attached. Pressing, in the method of simultaneously moving both sides while supplying the slurry, and polishing simultaneously on both surfaces, the material and shape of the polishing cloth material to be attached to the surface plate are different at the same time or independently of the upper and lower surface plates, It is characterized in that polishing is performed with different polishing speeds (polishing amounts per time) from both sides of the wafer in contact with the polishing cloth. Here, the difference in the material and shape of the polishing cloth material means that, in general, the polishing cloth is manufactured by forming different materials and shapes in a layered form, but attention is paid to the material and shape of the surface layer directly in contact with the wafer. It is a difference. The invention described in claim 2 is claim 1
In the configuration of the invention described in the above, in the difference in the shape of the polishing cloth material attached to the surface plate, the total area of the slurry flow channel finally applied to the polishing cloth surface on the upper surface plate side, the lower surface plate It is characterized by adding a configuration that is larger than that of the side.

[0006]

[Action] Regardless of the type of cloth selected as the polishing cloth,
As the usage time increases, clogging and crushing phenomenon occur, and as a result, the holding power of the slurry decreases and the polishing rate decreases. In consideration of this phenomenon, the invention of claim 1 uses a polishing cloth having a different polishing rate because the slurry holding force is different from the beginning, and the polishing rate of the wafer having a processing strain layer is reduced. By using an extremely small polishing cloth and simultaneously polishing both sides using a polishing cloth with a high polishing rate on the opposite polishing surface, the surface of the wafer having the work strained layer is on the opposite side. The amount of polishing is extremely small as compared with the polished surface. As a practical correspondence to make both the material and the shape of the upper and lower polishing cloths different, for example, the polishing cloth on the upper platen side is “urethane foam type”, while the polishing cloth on the lower platen side is “nonwoven fabric type”. Adopting or using the same urethane foam type as the material even if the size and number of foams on the upper platen side are extremely different from those on the lower side, that is, those with different shapes Etc. Since these differences result in extreme differences in the polishing rate, the processing strain equivalent to the conventional one can be left by forming the processing strain only slightly deeply. In addition, as a method of changing the polishing amount on the upper surface and the lower surface when polishing the wafer, it is attempted to change the relative speed between the polishing cloth and the upper and lower surfaces of the wafer. Since it acts on the carrier and is limited by the strength problem of the thin wafer carrier, it cannot have a great change. According to a second aspect of the present invention, in the structure of the first aspect, the difference in the shape of the polishing cloth material stuck on the surface plate causes the slurry flow finally applied to the surface of the polishing cloth on the upper surface plate. Since the total area of the groove for the road is larger than that of the lower platen, the area of the slurry passage groove is larger in the upper platen than in the lower platen. The adsorbing power is reduced by the amount corresponding to the atmospheric pressure.

[0007]

Embodiments of the present invention will be described below with reference to the drawings. First, an outline of an apparatus for polishing a silicon semiconductor wafer on both sides will be described with reference to FIG. This apparatus is composed of a pair of upper and lower metal platens U to which a polishing cloth is attached.
T, LT, a plurality of carriers C holding the wafer W,
This is a double-side polishing machine for a silicon semiconductor wafer comprising a sun gear S and an internal gear I for causing the carrier C to carry out planetary movement between the upper and lower platens UT and LT. The structure is similar to that of the silicon semiconductor wafer rubbing apparatus. Usually, the slurry is supplied from the upper platen UT through the slurry introduction pipe P and the introduction hole H. Also,
A polishing cloth 1 is attached to the upper platen UT so as to face the upper surface W1 of the wafer W, and a polishing cloth 2 is attached to the lower platen LT so as to face the lower surface W2 of the wafer W.

[0008]

[Embodiment 1] In general polishing, a two-stage polishing system is generally used, and the same applies to the embodiment of the present invention. The first embodiment is an example in which the materials and shapes of the polishing cloths 1 and 2 are different in the primary polishing method, and only the shape (the material is the same) is different in the secondary polishing. (still,
(Of course, the load, slurry, and other conditions are all the same.) Specific examples of the materials and shapes of these polishing cloths 1 and 2 are shown in Table 1 below.

[0009]

[Table 1]

The urethane foam type polishing cloth can easily change the form of the urethane foam part, that is, the number and size of the foam parts, according to the manufacturing method. "Extremely low" indicates specially manufactured. In addition, the urethane foam type (usual size and number of foams) indicates a conventional one manufactured so as to be able to hold the slurry better.

Therefore, the above example is based on the upper surface W1 of the wafer W.
Is a sandblasted surface, and the lower surface W2 is a surface on which a pattern is formed by being polished to an original mirror surface,
The lower surface W2 has a primary polishing and secondary polishing of 7 to 8 μm.
On the other hand, the upper surface W1 subjected to sandblasting can be estimated to have an extremely small machining allowance (amount) of about 0.5 to 1 μm due to a difference in slurry holding power. This can be sufficiently dealt with by forming the processing strain somewhat deeper in advance during the sandblasting process, and the gettering effect having the conventional processing strain can be secured.

[0012]

Embodiment 2 In Embodiment 2, the materials of the polishing cloths 1 and 2 to be used are the same as those in Embodiment 1, but when the shape is viewed macroscopically, both the primary polishing and the secondary polishing are performed on the upper surface plate. Before the polishing cloth 1 is attached to the UT, a groove 1a for a slurry flow path is cut and formed by a special tool as shown in FIG. On the other hand, in the slurry flow channel groove (not shown) of the polishing pad 2 attached to the lower surface plate LT, the area of the formed groove is larger than the area of the slurry flow channel groove 1a on the upper surface plate UT side. Small or not formed at all as shown in Table 2 below.

[0013]

[Table 2]

Conventionally, it is said that the grooves processed variously in the polishing cloth are originally for uniformly distributing the slurry and also increase the polishing rate, but the urethane foam type polishing as in this embodiment is considered. When the structure (shape, number) of the foamed portion of the cloth is made different, such an effect is small, and only the reduction of the wafer suction force due to the large area of the groove becomes apparent.

Accordingly, the area occupied by the slurry flow channel groove 1a formed on the surface of the polishing cloth 1 on the upper surface plate UT side is equal to the lower surface plate L
Atmospheric pressure is greater than the area (zero in this embodiment) occupied by the slurry flow channel (not shown) formed on the surface of the polishing cloth 2 on the T side, so that the suction force is reduced. As a result, 1
Next, when the upper platen UT is pulled up after the completion of the secondary polishing and the wafer W is to be taken out from the wafer carrier C, an operation problem such that the wafer W sticks to the upper polishing cloth 1 and rises together. Can be avoided.

The groove 1a for the slurry flow channel shown in Table 2 is shown in FIG.
As shown in the figure, both primary and secondary polishing have a pitch of 15 mm and a groove width of 2.
mm and 0.6 mm deep. (A) of FIG.
FIG. 2 is an overall view of the polishing cloth 1 attached to the upper platen UT side, which is a concentric circular polishing cloth having a thickness of 1.5 mm determined by the size of the apparatus. On the surface of the polishing cloth 1, grooves 1a are formed in a grid pattern at a pitch of 15 mm as shown in FIG. 4B, and a groove V of 2 mm is formed as shown in FIG.
It is formed in the shape of a letter. Further, reference numeral 1b denotes an adhesive sheet for attaching the polishing cloth 1 to the upper surface plate UT.

The overall shape of the slurry flow channel 1a is not limited to the lattice shape, and the same operation and effect can be obtained even if it is concentric, rhombic, spiral, or the like.

[0018]

As described above, the present invention according to claim 1 of the present invention uses a polishing cloth having a difference in slurry holding power and a different polishing rate, and a surface of a wafer having a work distortion layer. A polishing cloth with an extremely low polishing rate is disposed opposite to the polishing surface, and a polishing cloth with a high polishing rate is disposed opposite the polishing surface on the opposite side, and both sides are polished at the same time. Is extremely small compared to the opposite polished surface, so that the processing distortion of the sandblasted surface can be left. Therefore, the desired gettering effect can be ensured with the conventional processing distortion.
It is said that one of the reasons that a double-sided mirror-finished substrate is quantitatively less than a single-sided mirror-finished substrate despite its good processing accuracy is that it is difficult to identify the front and back surfaces. I have. In this regard, the remaining processing surface called sand blast causes a difference in surface quality and can be identified.

According to a second aspect of the present invention, in addition to the effect of the first aspect, the polishing pad on the upper platen has a larger area for the groove for the slurry flow path than the polishing cloth on the lower platen. However, since the suction force is reduced by communicating with the atmospheric pressure, it is possible to reliably prevent the wafer from sticking to the polishing cloth on the upper stool. Therefore, it is easy to take out the wafer from the wafer carrier by lifting the upper platen after the polishing is completed, and the wafer is not dropped and damaged during the taking out operation.

[Brief description of the drawings]

FIG. 1 is a sectional view of an apparatus for polishing a silicon semiconductor wafer on both sides.

FIG. 2A is an overall view showing a polishing cloth on an upper platen side;
(B) is a partially enlarged view of (a), and (c) is a sectional view showing a partially enlarged view.

[Explanation of symbols]

 UT Upper surface plate LT Lower surface plate W Wafer W1 Upper surface W2 Lower surface 1 Polishing cloth 1a Slurry flow channel 2 Polishing cloth

Claims (2)

[Claims] 1. A silicon semiconductor wafer (W) is sandwiched between a pair of upper and lower platens (UT, LT) to which polishing cloths (1, 2) are respectively attached, and relatively moved while supplying slurry. In the method of polishing both surfaces simultaneously, the material and the shape of the polishing cloth (1, 2) to be attached to the surface plate (UT, LT) are simultaneously or independently set.
LT), and polishing at different polishing rates from both sides (W1, W2) of the wafer (W) in contact with the polishing cloth (1, 2). Method. 2. The method according to claim 1, wherein the difference in the shape of the polishing cloth (1, 2) material adhered to the surface plate (UT, LT) results in a final application to the surface of the polishing cloth (1) on the upper surface plate (UT) side. 2. The method for polishing both sides of a silicon semiconductor wafer according to claim 1, wherein the total area of the formed slurry flow grooves (1a) is larger than that of the lower surface plate (LT).