JP3821944B2 - Wafer single wafer polishing method and apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a single wafer polishing method and apparatus capable of obtaining high flatness, and more particularly to a single wafer polishing method suitable for obtaining high flatness in wafer single wafer polishing by a waxless mount method. The present invention relates to a polishing method and an apparatus therefor.
[0002]
[Prior art]
Generally, a semiconductor wafer is sliced, cut and chamfered from a cylindrical ingot, and then lapped while rubbing a polishing (lap) surface plate and an as-cut wafer through a polishing liquid containing abrasive grains, and The lapped wafer is subjected to a chemical etching process and then 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 between a polishing (polishing) pad and a wafer is used to create a smooth, undistorted mirror surface by a chemical mechanical polishing method. Mirror 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 a 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.
Mirror polishing of a silicon wafer is considered to be performed by forming a soft hydration film on the wafer surface with an alkaline solution and removing the hydrated film with abrasive particles.
[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 mounting system that holds a wafer without using wax has been proposed.
For such a waxless mount method, a waxless holding method by vacuum adsorption and a waxless holding method in which a wafer is water-bonded 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 wax on the wafer.
[0007]
The above-mentioned polishing apparatus has been mainly a batch type polishing method in which a plurality of wafers are held on a template and polished from the standpoint of production efficiency. However, in recent years, the wafer diameter is increased and the flatness is more excellent. In response to the demand for wafers, a single wafer polishing method is being studied in which a single wafer is held on a template and polishing is performed with the wafer rotation center and the rotation center of the polishing head supporting the wafer aligned. .
[0008]
When using a single wafer type polishing method with a backing pad and a template that is polished while being held by a template, a polishing cloth with excellent elasticity, a backing pad, and a polishing head mechanism can be used. A relatively uniform pressure is applied. As a result, the in-plane distribution of the machining allowance becomes uniform, and as a result, polishing is performed so as to maintain the flatness of the wafer in the previous process.
[0009]
[Problems to be solved by the invention]
However, the conventional technology has the following problems.
In the conventional technology, 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 polishing can be performed without deteriorating the flatness, and as a result, the flatness is obtained. It is possible to obtain an excellent wafer. On the other hand, when the flatness in the previous process is insufficient, the conventional technique performs polishing so as to maintain the flatness of the wafer in the previous process, and the resulting flatness of the wafer is insufficient. There is a problem that the flatness cannot be improved.
[0010]
In order to eliminate such drawbacks, the liquid pressure (water bag) or air pressure is applied from the back side of the polishing head in order to forcibly change the distribution of the polishing load applied from the back side of the polishing head, in other words, the in-plane load of the wafer. Although a technique for obtaining an in-plane load corresponding to the unevenness of the wafer flatness during the previous process by using (airbag) is also disclosed, when pressing an air bag or a water bag against the polishing head, the device It is difficult to obtain an arbitrary in-plane load distribution that is likely to be complicated in configuration and accurate.
[0011]
In the chemical mechanical polishing method using the wackless mount method in particular, the present invention provides high accuracy by adding a simple structure or an inexpensive and general-purpose member when the flatness of the wafer in the previous process is insufficient. An object of the present invention is to provide a wafer single wafer polishing method and apparatus capable of obtaining flatness.
[0012]
[Means for Solving the Problems]
In order to achieve the above object, according to the present invention, the wafer rotation center and the polishing pad supporting the wafer are aligned with the rotation center of the polishing head supporting the wafer without using wax. In a single wafer polishing method for holding and polishing,
At the position corresponding to the convex side portion of the flatness of the wafer in the pre-polishing step, a rotationally symmetric thin layer sheet that is harder than the backing pad is interposed, and the hard rotationally symmetric thin layer sheet is When the wafer central part is concave and the outer peripheral side is convex so that the processing pressure of the convex part increases, the wafer is turned into a ring-circular rotationally symmetric body having a radial width corresponding to the convex part on the outer peripheral side of the wafer. In the case where the central portion is convex, polishing is performed by selecting and interposing a shape of the sheet body on a rotationally symmetric body having a circular circular shape, thereby improving the flatness of the wafer . In this case, the thin layer sheet body is preferably formed of a thick paper or a resin sheet that is larger than the flatness deviation of the convex portion and has a surface pressure distribution of 100 μm or less.
[0013]
The invention according to claim 3 relates to an apparatus for effectively carrying out the invention, and is a polishing head without using wax in a state in which the rotation center of the wafer is coincident with the rotation center of the polishing head supporting the wafer. In a single wafer polishing machine that holds and holds a wafer with a backing pad,
The position that corresponds to the convex portion of the flatness of the wafer during polishing previous step, with interposed a thin layer sheet of rigid rotational symmetry than the backing pad, a thin layer sheet of the rigid rotational symmetry When the central part of the wafer is concave and the outer peripheral side is convex so that the processing pressure of the convex side part increases, the ring circular rotationally symmetric body having a radial width corresponding to the convex part on the outer peripheral side of the wafer In the case where the central portion of the wafer is convex, polishing is performed by selecting the shape of the sheet member in a circularly circular rotationally symmetric body to improve the flatness of the wafer.
And said thin layer sheet, it is preferable and the following surface pressure distribution 100μm large that is formed by the extent of the wall thickness of the paper or resin sheet varies from flatness deviation of the convex portion.
[0014]
The sheet body used in the present invention is a thin layer sheet harder than a backing pad (for example, a polyurethane resin porous body), more specifically, although it depends on the material of the sheet, the flatness deviation (usually normal) Is preferably about 0.5 to 30 μm) and is made of a thick paper or resin sheet that changes the surface pressure distribution of about 100 μm or less. A sheet body thinner than the deviation of the convex side of the wafer has little effect of increasing the surface pressure, and excessive thickness leads to excessive polishing. Specifically, resin sheets such as polyethylene terephthalate, polypropylene, and vinyl chloride resin are used, but are not limited thereto.
[0015]
Further, the width (or radius) in the radial direction is preferably set to a width smaller than the width of the convex portion without setting the full width of the convex portion of the wafer.
[0016]
The present invention will be described with reference to FIGS.
As described above, in the case of a single-wafer polishing apparatus using a chemical mechanical polishing method, particularly a waxless single-wafer apparatus, a polishing cloth having excellent elasticity, a backing pad, and a mechanism of a polishing head are used. Even with a wafer having a flatness deviation of about 30 μm, a relatively uniform pressure is applied to the wafer surface.
However, in the portion where the sheet 12 inserted between the backing pad 6 and the polishing head 4 is present, a larger pressure is applied to the wafer 10 than the region where the sheet 12 does not exist due to the thickness of the sheet 12, and the machining allowance increases. .
[0017]
Consider a rotationally symmetric shape in which the central portion of the wafer 10 is convex as shown in FIG. In this case, if the polishing is performed as usual, the polishing is performed so that the shape of the previous process is maintained as described above, and therefore the polishing is performed while the convex shape of the central portion is maintained. In order to improve and improve the flatness, it is sufficient that the allowance for the central portion is larger than that for the outer peripheral portion. In order to make the machining allowance of the central part larger than that of the outer peripheral part, the surface pressure of the central part during polishing may be made larger than that of the outer peripheral part. Therefore, as shown in FIG. 1, a sheet 12 having a shape and size corresponding to the convex shape at the center is inserted between the polishing head 4 and the backing pad 6. As a result, the surface pressure of the central portion where the sheet 12 is inserted increases, and the machining allowance becomes larger than that of the outer peripheral portion, so that the flatness can be improved.
[0018]
Conversely, as shown in FIG. 2, the shape of the wafer 10 obtained in the previous step is considered to be a rotationally symmetric shape in which the central portion of the wafer 10 is concave. In this case, the flatness can be improved if the allowance for the outer peripheral portion is larger than that for the central portion. Therefore, as shown in FIG. 2, a sheet 12 having a shape and size corresponding to the concave shape of the outer peripheral portion is inserted between the polishing head 4 and the backing pad 6. As a result, the surface pressure of the outer peripheral portion into which the sheet 12 is inserted is increased, the machining allowance is increased compared to the central portion, and the flatness can be improved. Such a polishing method is preferably a single wafer type in which one wafer is processed by one polishing head. By using a single wafer type, a sheet corresponding to the wafer shape can be easily selected.
Also, there are vacuum adsorption and water pasting types for holding the wafer. Since the polishing head rotates, the method for holding the wafer is not particularly limited. However, when the wafer is held by the water-attached type, the wafer rotates in the wafer holding member during polishing, and the rotationally symmetric shape can be improved efficiently.
[0019]
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.
FIG. 3 shows a single wafer type waxless chemical mechanical polishing apparatus according to an embodiment of the present invention. A wax-free polishing apparatus using a backing pad is applied with a polishing cloth 2 (polishing pad) as shown in FIG. A plurality of polishing heads 4 in which a template 13 holding one wafer 10 in one holding hole 13a is bonded via a backing pad 6 on the lower surface side, and the polishing cloth. 2 is a polishing apparatus for supplying a slurry (polishing suspension) to 2 and pressing the wafer 10 against the rotary table 1 through the polishing cloth 2 to smooth the unevenness of the wafer 10, and The template 13 used in such an apparatus is formed from a glass epoxy resin, a polycarbonate sheet, a polyester sheet, etc., and a backing pad. It is formed from a porous resin such as polyurethane resin porous body.
[0020]
The wafer 10 is held integrally with the backing pad 6 so that the rotation center with the polishing head 4 coincides, and the rotation centers of the plurality of polishing heads 4 are displaced in the radial direction with respect to the rotation center of the turntable 1. The wafer 10 placed in the position and rotated in the direction of the arrow with each other is polished while rotating and revolving relatively with respect to the polishing pad 2 relative to the polishing cloth 2.
[0021]
Using such an apparatus, the processing speed V (removal rate) when chemical mechanical polishing is performed while supplying a polishing solution in which SiO ₂ fine particles are suspended in a weak alkaline solution between the polishing pad 4 and the wafer 10 is supplied. Can be approximated by the following equation 1).
V = K ・ p ・ v ・ t …… 1)
K: proportional constant p: machining pressure v: relative speed t: machining time
Now, in the case of a waxless single wafer type apparatus as in this apparatus, even if the flatness deviation of the wafer 10 at the time of polishing is about 0.5 to 30 μm, a polishing cloth having excellent elasticity, a backing pad 6, In addition, a relatively uniform pressure is applied to the surface of the wafer 10 by the mechanism of the polishing head 4.
Therefore, in the present embodiment, by inserting the sheet 12 between the backing pad 6 and the polishing head 4, and selecting the shape of the sheet 12 so that the processing pressure p of the portion increases depending on the thickness of the sheet 12, The surface pressure of the convex portion is increased, in other words, a larger pressure is applied to the wafer 10 than in the region where the sheet 12 does not exist, and the processing speed V (removal allowance) is set to increase.
[0023]
Therefore, even if the shape of the wafer 10 obtained in the previous step is convex as shown in FIG. 1 (right figure in FIG. 3), as shown in FIG. 10 Even if the central part is concave (the left figure in FIG. 3), uneven loading is generated in the surface by the insertion of the sheet 12, and the removal is adjusted and polished.
[0024]
Next, a comparative experiment was performed between the present invention and the prior art.
First, the surface pressure during polishing using this apparatus will be shown. FIG. 4 shows the surface pressure distribution when the wafer 10 is set on the wafer 10 with nothing interposed between the polishing head 4 and the backing pad 6 as in the prior art.
Further, FIG. 5 assumes a case where the central portion of the wafer 10 is convex, and a circular sheet 12 (resin sheet having a thickness of about 90 μm) having a diameter slightly smaller than the convex portion is provided between the polishing head 4 and the backing pad 6. This is the surface pressure distribution when the wafer 10 is inserted and set. The surface pressure of the convex portion in this figure is high.
In the conventional method of FIG. 4, pressure is applied almost uniformly over the entire surface of the wafer 10. On the other hand, when the sheet 12 is inserted between the backing pad 6 and the polishing head 4 of FIG. It can be seen that the pressure increases in the part.
[0025]
As described above, since the machining allowance increases when the surface pressure is high, it is understood that the machining allowance increases at the portion where the sheet 12 is inserted, and the wafer flatness can be improved.
[0026]
【The invention's effect】
As described above, according to the present invention, when the flatness of the wafer in the previous process is insufficient, it is possible to obtain a high-precision flatness with the addition of a simple structure or an inexpensive and general-purpose member. This is effective for a waferless mount type single wafer polishing apparatus in which a relatively uniform pressure is applied to the wafer surface by the mechanism of the polishing cloth, backing pad and polishing head having excellent elasticity.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a main part of a polishing head portion showing a sheet shape of a wafer having a convex central portion and its loading position according to an embodiment of the present invention.
FIG. 2 is a cross-sectional view of a main part of a polishing head portion showing a wafer sheet shape having a concave central portion and a loading position thereof according to an embodiment of the present invention.
FIG. 3 is an overall view showing a single wafer type waxless chemical mechanical polishing apparatus according to an embodiment of the present invention.
FIG. 4 is a surface pressure distribution diagram when a wafer is set without interposing anything between a polishing head and a backing pad according to the prior art.
FIG. 5 is a surface pressure distribution diagram when a wafer is set with a sheet interposed between a polishing head and a backing pad according to the present invention.
[Explanation of symbols]
1 Lower rotary table 2 Polishing cloth 4 Polishing head 5 Slurry tube 6 Backing pad 10 Wafer 12 Sheet 13 Template

Claims (4)

In the single wafer polishing method in which the wafer is held by the polishing head and the backing pad without using wax in a state in which the rotation center of the wafer and the rotation center of the polishing head supporting the wafer are matched,
At the position corresponding to the convex side portion of the flatness of the wafer in the pre-polishing step, a rotationally symmetric thin layer sheet that is harder than the backing pad is interposed, and the hard rotationally symmetric thin layer sheet is When the wafer central part is concave and the outer peripheral side is convex so that the processing pressure of the convex part increases, the wafer is turned into a ring-circular rotationally symmetric body having a radial width corresponding to the convex part on the outer peripheral side of the wafer. When the central part is convex, the wafer is characterized by improving the flatness of the wafer by polishing by selectively inserting the shape of the sheet on a circularly circular rotationally symmetric body Leaf polishing method. The laminate sheet material, by forming on the order of the thickness of the paper or resin sheet and change the following surface pressure distribution 100μm large than flatness deviation of the convex portion, the surface pressure of the convex portion 2. The wafer single wafer polishing method according to claim 1 , wherein polishing is performed to improve the flatness of the wafer. In a single wafer polishing apparatus that performs polishing by holding a wafer with a polishing head and a backing pad without using wax in a state in which the rotation center of the polishing head that supports the wafer coincides with the rotation center of the wafer ,
At the position corresponding to the convex side portion of the flatness of the wafer in the pre-polishing step, a rotationally symmetric thin layer sheet that is harder than the backing pad is interposed, and the hard rotationally symmetric thin layer sheet is When the wafer central part is concave and the outer peripheral side is convex so that the processing pressure of the convex part increases, the wafer is turned into a ring-circular rotationally symmetric body having a radial width corresponding to the convex part on the outer peripheral side of the wafer. When the central part is convex, the wafer is characterized by improving the flatness of the wafer by polishing by selectively inserting the shape of the sheet on a circularly circular rotationally symmetric body Leaf polishing machine. The thin-layer sheet is interposed with a thin-layer sheet body formed of thick paper or a resin sheet that is larger than the flatness deviation of the convex side portion and changes in surface pressure distribution of 100 μm or less. The wafer single wafer polishing apparatus according to claim 3 .

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