JP3820432B2 - Wafer polishing method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a wafer polishing method using a wax-free method, and more particularly, to a template assembly in which a backing material is interposed in a donut hole of a blank material affixed to a rotating processing plate, while maintaining the shape of the wafer. BACKGROUND OF THE INVENTION 1. Field of the Invention
[0002]
[Prior art]
In general, a semiconductor wafer is sliced, cut and chamfered from a cylindrical ingot, and then lapped while rubbing the polishing (lap) surface plate and the wafer through a polishing liquid containing abrasive grains, and the lapping is performed. After the wafer is subjected to a chemical etching process, the wafer is guided to a finishing process.
[0003]
In the finishing process, a polishing solution in which SiO ₂ fine particles are suspended in a weak alkaline solution is used between the polishing (polishing) pad and the wafer. Polished.
[0004]
The chemical mechanical polishing method of a semiconductor wafer is performed while applying a constant load and a relative speed between the wafer and the polishing cloth while supplying an abrasive. As the abrasive, a dispersion in which baked silica, colloidal silica or the like is dispersed in an alkaline solution is mainly used.
It is considered that mirror polishing of a silicon wafer forms a soft silicic hydrated film on the wafer surface by an alkaline solution, and the hydrated film is removed by abrasive particles to proceed with processing.
[0005]
In such a chemical mechanical polishing method, a method of polishing a plurality of wafers by pasting them on a glass plate or a ceramic plate with a wax adhesive has been the mainstream.
In such a wax method, it is important to make the thickness of the adhesive layer uniform because the non-uniformity of the thickness of the adhesive layer (wax layer) directly reflects the flatness, parallelism, etc. of the wafer after polishing. Further, since it is necessary to remove the wax from the wafer after the wafer polishing, there is a problem that the process becomes complicated.
[0006]
In order to eliminate such drawbacks, a waxless mount system that holds a wafer without using wax has been proposed.
For such a waxless mounting method, a waxless holding method by vacuum adsorption and a waxless holding method in which a wafer is water-sealed using a backing pad made of a porous resin, for example, a polyurethane resin porous body, are used. Both have the advantage that it is not necessary to apply and remove the wax to the wafer.
[0007]
From the viewpoint of production efficiency, the above-described polishing apparatus has been mainly a batch type polishing method in which a plurality of wafers are held in a template for polishing, but in recent years, the wafer diameter has been increased and the flatness has been improved. Against the background of demand for wafers, a single wafer polishing method is being studied in which a single wafer is held in a template and polishing is performed with the wafer rotation center and the rotation center of the processing plate supporting the wafer being aligned. .
[0008]
When adopting a waxless mounting method in which polishing is performed while holding the backing pad and the template one by one in such a single wafer polishing method, the polishing cloth, backing pad, and processing plate mechanism having excellent elasticity can be used in the wafer surface. A relatively uniform pressure is applied, and as a result, the in-plane distribution of the machining allowance becomes uniform. As a result, the copying polishing is performed so as to maintain the flatness of the wafer in the previous process.
[0009]
As a characteristic of copying polishing, polishing is performed so as to maintain the flatness of the wafer in the previous process. Therefore, when the flatness in the previous process is excellent, the wafer can be polished while maintaining the flatness, and as a result, flatness is achieved. There is an advantage that an excellent wafer can be obtained. On the other hand, when the flatness in the previous step is insufficient, polishing is performed so as to maintain the flatness of the wafer in the previous step, and the resulting flatness of the wafer remains insufficient.
[0010]
For this reason, the conventional polishing improves the surface roughness (mirror surface), and corrective polishing for polishing to improve the variation of the in-plane shape (improving flatness, for example, preferentially scraping the peripheral portion). In addition, the machining allowance is made uniform (thickness is controlled) while maintaining the flatness shape in the previous step, and both of the mirror polishing to be mirror-finished are appropriately selected or combined depending on the flatness state in the previous step.
[0011]
In these polishings, the thickness of the backing pad is reduced to, for example, 250 μm or less so that the in-plane shape of the wafer appears directly on the polishing surface side.
And, as a backing pad, a backing pad in which a nonwoven fabric such as artificial leather sheet or polyester fiber is impregnated with polyurethane resin and the surface thereof has a fine foam structure is used. Further, in JP-A-6-23664, for example, a thickness of about 40 μm is used. After applying a foaming resin composition of polyester-based polyurethane to the surface of the substrate layer and heating it to 60 ° C. for foaming, the thickness of the foaming layer is cut to a predetermined thickness with a grinding machine, Polishing is performed using a backing pad having a thickness of about 120 to 250 μm, with the substrate layer of the pad being in contact with the pressure plate side, and the foam layer being disposed on the contact surface side with the wafer.
[0012]
According to this invention, since the foam layer is located on the contact surface side with the wafer, even if the contact portion with the wafer is compressed and deformed during polishing, the area of the contact portion does not increase so much. It is supposed to be able to polish excellently.
[0013]
[Problems to be solved by the invention]
However, the conventional correction polishing cannot always be corrected to high flatness due to the mechanical accuracy of the polishing machine, and after processing to high flatness in the previous process such as lapping, etching process, and surface grinding, the high flatness It was found that the preferred flatness can be improved by performing mirror polishing in the polishing step while maintaining the above.
[0014]
Therefore, in the future, follow-up polishing in the polishing process will attract attention, but it is very difficult to make the machining allowance uniform while maintaining the high flatness shape of the previous process, and more specifically, using a thick backing pad, more specifically modified polishing Even if priority is given to profiling using a backing pad having a thicker thickness, for example, several hundred μm to 1 mm, the surface shape of the plate is transferred to the wafer, and the contact changes partially depending on the wafer shape. I could not polish.
[0015]
The reason for this is that artificial leather sheets and non-woven fabrics have high elastic strength, so that the irregularities on the back side of the wafer are not picked up, but the irregularities appear on the wafer polishing surface and deform the wafer. Therefore, it was not possible to carry out copying polishing with uniform removal allowance.
[0016]
Further, when using a backing pad according to Japanese Patent Laid-Open No. 6-23664 in which the foam layer is located on the contact surface side with the wafer, the foam layer can be used even when the thickness of the foam layer is increased to, for example, 1 mm or more. Is a closed cell that is distributed side by side in the cross-sectional direction, the surface pressure of the contact portion does not increase so much in proportion to the compression of the foam layer, and as a result, the in-plane shape of the wafer cannot be absorbed in the backing pad, As a result, the substrate is pressed and supported on the substrate layer side, and it is not possible to carry out copying polishing with uniform removal allowance.
[0017]
An object of the present invention is to provide a wafer polishing method capable of performing copying polishing with a uniform machining allowance in view of the drawbacks of the prior art.
[0018]
[Means for Solving the Problems]
Since the present invention is to achieve the foregoing object, a wafer template assembly was interposed a backing material donut hole of sticking the blank to the machining plate rotates, the wafer is uniformly polished balls or allowance to maintain the shape In the profile polishing method, the thickness deviation of the wafer (the difference between the max value and min value of the wafer in-plane thickness; Total Thickness Variation: TTV) and the thickness variation between the wafers, more specifically, Is a sheet-like elastic body having a thickness of 1 to 2 mm in the donut hole of the blank material, and is formed of an artificial leather sheet or a non-woven fabric of polyester fiber thereon, the thickness of which is larger than the thickness deviation of the wafer, And a backing pad set smaller than the thickness of the sheet-like elastic body is interposed, and the thickness of the backing pad But it is characterized by polishing the wafer with the set template assembly to 3 00~800μm.
[0019]
Sponge-like silicone is preferably used as the sponge-like elastic body. Silicone rubber sponge is particularly preferable because it is a member that easily absorbs the wafer shape, is easily available, and can be used easily. Silicone rubber sponge is also referred to simply as silicone sponge, and is a sponge mainly made of modified silicone rubber, and is a material with high flexibility.
[0020]
That is, the present invention does not directly use a sheet-like elastic body as a backing material, but a conventionally known backing material is used, and an independent sheet-like elastic body is interposed between the processing plate and the backing material. Is.
[0021]
In addition, it is preferable to use the sheet-like elastic body whose apparent specific gravity is set to 0.2 to 0.4 g / cm ³ .
In the case of such an invention, the sheet-like elastic body is preferably set to have an Asker C hardness of 15 to 35 (SRIS-C), and the backing pad is a non-woven fabric such as an artificial leather sheet or polyester fiber. The thickness is formed, and the thickness is larger than the thickness deviation of the wafer and smaller than the thickness of the sheet-like elastic body, preferably 300 to 800 μm, more preferably 500 to 600 μm.
[0022]
According to this invention, since the unevenness on the back side of the wafer is polished while being absorbed by the sheet-like elastic body via the backing pad, it is possible to carry out the follow-up polishing with a uniform removal allowance with high accuracy.
[0023]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are not intended to limit the scope of the present invention unless otherwise specified, and are merely illustrative examples. Only.
[0024]
FIG. 2 shows a single wafer type waxless chemical mechanical polishing apparatus according to an example and a comparative example of the present invention. A wax-free polishing apparatus using a backing pad has a polishing cloth 2 (polishing pad) as shown in FIG. ) And a plurality of processes in which a doughnut-shaped blank material 13 holding one wafer 10 is bonded to one hole 13a via a backing pad 6 on the lower surface side. A plate 4 and a slurry tube 5 for supplying a slurry (polishing suspension) to the polishing cloth 2, and the wafer 10 is pressed against the polishing cloth 2 on the rotary table 1 side through the polishing cloth 2 to make the unevenness of the wafer. The blank 13 used in the apparatus is made of glass epoxy resin, polycarbonate sheet, polyester sheet or the like. .
[0025]
The backing pad 6 is formed of a backing pad, for example, a polyurethane resin porous body, in which a non-woven fabric such as an artificial leather sheet or polyester fiber is impregnated with polyurethane resin and the surface thereof has a fine foam structure.
In the present invention shown in the right (A) of the figure, a sheet-like elastic body 7 is interposed between the processing plate 4 and the backing pad 6, and the prior art shown in the left (B) of the figure is the processing plate 4. A sheet-like elastic body 7 is not interposed between the backing pad 6 and the backing pad 6.
[0026]
The wafer 10 is held integrally with the backing pad 6 (with the sheet-like elastic body 7 interposed) with the rotational center of the processing plate 4 being coincident, and a plurality of processings are performed with respect to the rotational center of the turntable 1. The center of rotation of the plate 4 is disposed at a position displaced in the radial direction, and both are rotated in the direction of the arrows so that the wafer 10 fitted in the hole 13a of the blank 13 is relatively with respect to the polishing pad 2. Polishing while rotating and revolving.
[0027]
Using such an apparatus, chemical mechanical polishing is performed while supplying a polishing solution (slurry) in which SiO ₂ fine particles are suspended in a weak alkaline solution between the polishing cloth 2 and the wafer 10.
FIG. 1 shows the polishing steps of the present invention and the prior art. Each step of (A) showing the present invention and (B) showing the prior art is (a) is a wafer cross-sectional shape before polishing, and (b) Is a state in which the wafer is incorporated in the template assembly, (C) is an initial stage of polishing, (D) is during polishing, and (E) is a wafer cross-sectional shape after polishing.
As is clear from this figure, in the present invention of (A), the peripheral convex portion on the wafer back side is efficiently absorbed by the sheet-like elastic body 7 through the backing pad 6, and the center concave shape on the wafer back side is maintained. Thus, the wafer 10 can be polished and the machining allowance becomes uniform.
[0028]
On the other hand, in the prior art (B), the peripheral convex portion on the wafer rear side is pressed against the processing plate 4 via the backing pad 6, the concaves on the wafer rear side are reduced, and the concaves on the polishing side are enlarged accordingly. Since the wafer 10 is polished, the flatness increases as a result, but the in-plane machining allowance is not uniform. Moreover, what was high flatness before grinding | polishing may be deteriorated conversely by the press relationship with a process plate.
The wafer shape and thickness (outer wall thickness 800 μm, center wall thickness 700 μm, etc.) shown in FIG. 1 are reference values used to explain the difference from the prior art. It is not shown.
[0029]
Next, the following confirmation experiment of the present invention was carried out using the apparatus.
First, the blank material 13 of the template assembly is a glass epoxy material with an outer diameter of 335 mm, an inner diameter of 301.5 mm, and a thickness of 2.27 mm (however, this is a case where a 1 mm silicon rubber sponge is used as the sheet-like elastic body, When a silicon rubber sponge is not used or when a thick one is used, the wafer is affixed to the processing plate 4 using a donut shape that is arbitrarily adjusted so that the wafer protrudes about 200 μm.
[0030]
In the hole 13a of the blank material 13, a silicon rubber sponge sheet 7 having a hardness of 25 (SRIS-C) as an elastic body is formed into a circle having a diameter of 300 mm and a thickness of 1 mm, and a porous polyurethane resin having a thickness of 560 μm. More specifically, an R301 backing pad 6 manufactured by Rodel was interposed.
SRIS-C is so-called Asker C hardness, which is measured using a spring type hardness tester according to JISK6301.
The silicon rubber sponge sheet 7 uses a member whose apparent specific gravity is set to 0.2 to 0.4 g / cm ³ .
[0031]
Using the above template assembly, the wafer after etching having a diameter of 300 mmφ, a wafer center thickness of 775 μm ± 25 μm, and a TTV of about 1.8 μm is made about 2 μm in the process shown in FIG. When 100 wafers were polished, the removal allowance TTV of the wafer after polishing was 0.3 μm, and the shape change rate (shape change rate = removal allowance TTV / average allowance allowance × 100) indicating the uniformity of the allowance was 15% or less. Thus, it was possible to carry out the preferred copying polishing. Example 1
Here, the machining allowance TTV measures the thickness of a plurality of points in the surface of the wafer before processing, measures the same point after processing, and determines the machining allowance of each point from the difference. The difference between the max value and min value of the machining allowance in this plane was taken as the machining allowance TTV.
Other examples and comparative examples of the present invention are shown below, but the wafer and polishing conditions are the same as in Example 1 except that the template assembly is changed.
[0032]
When the thickness of the silicon rubber sponge sheet of Example 1 was increased to 2 mm and 100 sheets were polished using a silicon rubber sponge sheet having a hardness of 35 (SRIS-C) as an elastic body, a shape showing the uniformity of the machining allowance It was possible to carry out a more preferable copying polishing with a change rate of 10% or less. (Example 2)
Therefore, when the thickness of the silicon rubber sponge sheet was increased to 3 mm and 100 sheets were polished, the shape change rate indicating the uniformity of the machining allowance was 10% or less. Etc. occurred and could not be stably polished. (Comparative Example 1)
[0033]
Next, when the silicon rubber sponge sheet of Example 1 was polished using a silicon rubber sponge sheet having a hardness of 15 (SRIS-C) as an elastic body, the shape showing the uniformity of the removal allowance of 100-sheet polishing wafers It was possible to carry out preferable copying polishing with a change rate of 20% or less. Example 3
Next, when the silicon rubber sponge sheet of Example 1 was used and polished using a 350 μm thick R301 backing material manufactured by Rodel, the shape change rate indicating the uniformity of the removal allowance of the 100-sheet polishing wafer was obtained. It was possible to carry out preferable copying polishing of 20% or less. Example 4
[0034]
Next, when the silicon rubber sponge sheet of Example 1 was used and polishing was performed using a R301 backing material having a thickness of 750 μm manufactured by Rodel, the shape change rate indicating the uniformity of the removal allowance of the 100-sheet polishing wafer was obtained. It was possible to carry out preferable copying polishing of 15% or less. (Example 5)
[0035]
Next, as shown in FIG. 1 (A), when the silicon rubber sponge sheet of Example 1 was used and polishing was carried out using a 1 mm thick R301 backing material manufactured by Rodel, 100 wafers were removed. The rate of change in shape, which shows the uniformity of the cost, increased significantly to about 25%. (Comparative Example 2)
This is considered that the effect of the silicone rubber sponge sheet did not appear so much.
[0036]
Finally, as shown in FIG. 1B, when a similar polishing was performed using a backing material having a thickness of 250 μm disclosed in Japanese Patent Laid-Open No. Hei 6-23664, a shape showing the uniformity of the removal allowance of a 100-sheet polishing wafer. The rate of change increased significantly to about 50%. (Comparative Example 3)
[0037]
In this example, a wafer that was lapped and etched before polishing was used. However, even when a wafer after surface grinding or a wafer with poor TTV before polishing was used, the shape change rate was greatly reduced. It was the same even if the polishing allowance was increased.
In the conventional polishing using a backing pad, the shape change rate was 20 to 40% even if the thickness was 1 mm or more. In the case of the present invention consisting of a combination of “sheet-like elastic body and backing pad”, The shape change rate was 10 to 20%, which was greatly reduced.
[0038]
【The invention's effect】
As described above, according to the present invention, it is possible to perform polishing with a uniform machining allowance without changing the shape of the wafer. In particular, it is possible to perform profile polishing with a stable shape change rate of about 15%. As a result, the wafer having a high degree of flatness in the previous step can be mirror-finished as it is.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing a template assembly of the present invention (A) and a prior art (B) and an operation view showing a process step.
FIG. 2 is an overall view showing a single wafer waxless chemical mechanical polishing apparatus applied to the present invention.
[Explanation of symbols]
4 Processing plate 6 Backing pad 7 Silicon rubber sponge sheet 10 Wafer 13 Blank material

Claims (4)

In a polishing method in which a wafer is polished with a template assembly in which a backing material is interposed in a donut hole of a blank material affixed to a rotating processing plate, a 1-2 mm thick sponge-like sheet-like elasticity is applied to the donut hole of the blank material The body is laid and formed with an artificial leather sheet or a non-woven fabric of polyester fiber, and a backing pad having a thickness larger than the thickness deviation of the wafer and smaller than the thickness of the sheet-like elastic body is interposed. wafer polishing method characterized in that the thickness of said backing pad to polish the wafer at the set template assembly to 3 00~800μm.   The wafer polishing method according to claim 1, wherein the hardness of the sheet-like elastic body is set to 15 to 35 (SRIS-C) in Asker C hardness.   The wafer polishing method according to claim 1 or 2, wherein an apparent specific gravity of the sheet-like elastic body is set to 0.2 to 0.4 g / cm3.   The wafer polishing method according to claim 1, wherein the sponge-like elastic body is a silicon rubber sponge.

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