JPH07164308A - Sheet-shaped polishing member and wafer polishing device - Google Patents

Abstract

PURPOSE:To provide the polishing device which can carry out surface standard polishing without causing any shear drop around a wafer. CONSTITUTION:A sheet shaped foamed body 2 where minute independent bubbles are contained in chloroprene rubber, and a sheet shaped polishing member 5 comprising a flexible plate body 3 composed of a thin sheet of glass fiber contained epoxy resin, and velour type polishing cloth 4 bonded and laminated in the aforesaid order, are bonded over the surface of a polishing surface place via a sheet shaped foamed body. An oxide film formed uniformly over a silicone substrate scattering in thickness can be polished while the thickness of the oxide film is being uniformly maintained wherein oxide film projections over the surface of wafer are efficiently flattened.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sheet-like polishing member and a wafer polishing apparatus for polishing a wafer, and more specifically, a polishing member suitable for application to a planarization processing technique for improving the flatness of a semiconductor device, and The present invention relates to a polishing device.

[0002]

2. Description of the Related Art With the progress of high integration and large scale of semiconductor devices, miniaturization of wiring and multilayering of wiring have become more and more important. When the wiring is miniaturized, the end face is inevitably sharpened, and the covering property of the insulating film or the wiring to be deposited thereon is deteriorated. Also, when the wiring is multi-layered,
Since unevenness of the underlying wiring or insulating film is piled up, the unevenness of the surface becomes severe, and even if an attempt is made to form a wiring on the surface, the stepper cannot focus and the processing accuracy of the wiring deteriorates. In either case, the wiring is likely to be broken, and the reliability of the semiconductor device is reduced.

Various flattening techniques have been developed to solve this problem. For example, there is a glass flow method in which a glass film of PSG, BPSG, or the like is formed by CVD and then heated to 800 to 1100 ° C. to cause viscous flow for flattening. Although this method is simple in process, it has a drawback that the wiring material is limited such that Al wiring cannot be used because it is heated to a high temperature. Other than this, various methods have been developed, but each method has advantages and disadvantages, and there is no deciding technique.

In recent years, in order to overcome this situation, a flattening method applying a wafer polishing technique is being developed. That is, in the process of manufacturing a semiconductor device, a planarization processing technique for improving the flatness thereof, specifically, as a means for flattening the protruding portion of the silicon oxide film generated corresponding to the wiring on the wafer, It is intended to apply polishing technology.

However, in the planarization processing technique for manufacturing a semiconductor device, the cross-sectional shape of the wafer (hereinafter, referred to as wafer W) in the processing process corresponds to the thick portion of the wafer W shown in FIG. It is necessary to develop a technique for polishing a wafer W having a sectional shape shown in FIG. The reason for this is that conventionally, this wafer polishing technique has been developed in the direction of preferentially removing a large-thickness portion of the wafer for the purpose of equalizing the thickness on the entire surface of the wafer.

This surface reference polishing technique is specifically shown in FIG.
Oxide film 32 (interlayer insulating film) on the silicon substrate 31 shown in FIG.
The step, that is, the oxide film protrusion 33 is removed, and the thickness of the oxide film 32 is maintained uniform. In FIGS. 5 and 6, 34 is an element and 35 is a wiring.
Further, in these drawings, the global unevenness of the wafer W is exaggerated for convenience of explanation.

By the way, in such a wafer polishing apparatus, a commercially available polishing cloth is usually used as it is as a polishing member provided on a polishing platen. The polishing cloth includes a so-called suede type and a velour type, which are used according to the purpose of polishing. Suede-type polishing cloth is, so to speak, an artificial leather for industrial materials. And a surface layer having pores formed therein. The velor type polishing cloth is a so-called non-woven fabric having a single layer structure, and is a porous sheet-like material having a three-dimensional structure. Then, when polishing the wafer, a method is employed in which the wafer held by the holding member is brought into pressure contact with the polishing cloth on the polishing platen at a predetermined pressure and polishing is performed while supplying an appropriate polishing liquid onto the polishing cloth. .

The above-mentioned polishing cloth used for the primary polishing or secondary polishing of the wafer is made hard so that the thickness variation of the wafer after polishing is reduced, and the thick portion is preferentially polished. Designed to be removed.
For this reason, it has been difficult to perform the above-mentioned surface reference polishing with a wafer polishing apparatus provided with such a polishing cloth.

In order to improve this, for example, a polishing apparatus shown in FIG. 9 and a "wafer mirror polishing apparatus" of Japanese Patent Laid-Open No. 5-69310 have been proposed. In the polishing apparatus of FIG. 9, a soft mounting pad 42 as a wafer holding plate is provided on the lower surface of a pressing member 41 made of a hard material, and an annular template 43 is provided on the lower surface of the pad.
4 is provided with a soft polishing cloth 45 on the surface thereof.

Further, the polishing apparatus described in the above publication has a structure shown in FIG.
As shown in FIG. 0, a flexible elastic film 51 is used on the plane for holding the wafer W, and the elastic film 51 is attached to the ring-shaped body 52 with a uniform tension to hold the wafer W on the elastic film 51. A fluid supply means 53 for supplying a fluid for adjusting the pressing pressure of the wafer W is provided on the surface opposite to the surface on which the wafer W is pressed. In addition, 54 is a rotating shaft, 55 is an annular guide plate (template) adhered to the lower surface of the elastic film 51, and 56 is a polishing platen.

By the way, the amount of wafer removed by polishing is
Strongly depends on polishing pressure. Therefore, in the above-mentioned surface reference polishing technique, by making the distribution D of the polishing pressure on the back surface of the wafer W uniform (uniform load distribution) as shown in FIG. 11A, the entire surface of the wafer can be obtained as shown in FIG. 11B. It is extremely important to polish with a uniform polishing removal amount. In FIG. 11A, 61 is a wafer holding member, 6
2 is a polishing cloth.

[0012]

However, the polishing apparatus shown in FIG. 9 has the advantage of simplifying the wafer holding structure, but the influence of variations in the characteristics (thickness, elasticity, deterioration characteristics) of the mounting pad 42. It is easy to receive and it is difficult to make the polishing pressure uniform. Therefore, in the polishing pressure distribution D, when the polishing pressure becomes excessively large on the outer peripheral portion of the wafer as shown in FIG. 12A, a peripheral sag A is generated in the polishing wafer W as shown in FIG. Alternatively, as shown in FIG. 13A, when the polishing pressure is too low at the outer peripheral portion of the wafer, there is a problem that protrusions B are generated in the peripheral portion of the polishing wafer W as shown in FIG. 13B.

On the other hand, in the polishing apparatus described in the above publication, since the elastic film 51 that seals the ring-shaped body 52 is highly flexible, it is shown in FIGS. 12 (b) and 13 (b). In order to suppress the occurrence of the abnormal shape in the peripheral portion of the wafer, the distance between the lower surface of the outer peripheral edge of the elastic film 51 and the upper surface of the polishing platen 56 in FIG. 10 must be accurately set within a predetermined range. That is, if this interval is too large, the central portion of the elastic film 51 becomes convex due to the pressure of the fluid, so the cross-sectional shape of the wafer W after polishing becomes as shown in FIG. 13B, and this interval is too small. Then, the cross-sectional shape of the polished wafer W becomes as shown in FIG. 12B due to the downward load applied by the body portion 52 or the fluid pressure applied between the wafer W and the body portion 52. In either case, The uniformity of the oxide film thickness on the wafer cannot be maintained.

The present invention has been made in view of the above problems, and an object thereof is to provide a polishing member and a wafer polishing apparatus capable of performing surface reference polishing without peripheral sagging and peripheral protrusions of the wafer. Especially.

[0015]

A sheet-shaped polishing member according to claim 1 is a polishing member provided on a polishing surface plate, wherein a hard rubber is provided between a sheet-shaped foam made of a soft rubber-like elastic body and a polishing cloth. It is characterized in that flexible plate bodies made of thin plates are adhesively laminated.

In the sheet-shaped polishing member according to a second aspect, the sheet-shaped foam is a closed-cell foam made of natural rubber, synthetic rubber, or thermoplastic elastomer, and flexibility is imparted by the gas in the foam. The sheet-like polishing member has (1) a thickness of 0.2 to 2 mm, (2) a cell diameter of 0.05 to 1 mm, (3) a cell content rate (ratio of the cell volume to the foam volume. ) Is 70 to 98%, and (4) the compression elastic modulus is 10 to 100 g / mm ² .

The sheet-shaped polishing member according to a third aspect is characterized in that the polishing cloth is of a suede type or a velor type.

According to a fourth aspect of the present invention, there is provided a wafer polishing apparatus in which a sheet-like foam made of a soft rubber-like elastic body is provided on a surface of a polishing platen, and a flexible plate body made of a hard thin plate on the sheet-like foam. A polishing cloth is bonded and laminated on the flexible plate.

According to a fifth aspect of the present invention, in the wafer polishing apparatus, the sheet-shaped foam is a closed-cell foam made of natural rubber, synthetic rubber or thermoplastic elastomer, and flexibility is imparted by the gas in the foam. In the sheet-like foam, (1) thickness is 0.2 to 2 mm, (2) cell diameter is 0.05 to 1 mm, (3) cell content rate (ratio of cell volume to foam volume). Is 70 to 98%, and (4) the compression elastic modulus is 10 to 100 g / mm ² .

A wafer polishing apparatus according to a sixth aspect is characterized in that the polishing cloth is of a suede type or a velor type.

As the sheet-like foam used in the sheet-like polishing member of the present invention, it is preferable to use the closed-cell foam described in claim 2, and natural rubber, chloroprene rubber as synthetic rubber, and ethylene-propylene rubber. , Butyl rubber, etc., as styrene-based thermoplastic elastomer,
Ester type, urethane type, etc. can be used respectively. The hardness (Shore A) of natural rubber, synthetic rubber or thermoplastic elastomer (not expanded) is 3
The range of 0 to 90 is preferable. The elasticity of sheet foam is
The elasticity of the material itself and the elasticity of the gas in the foam are combined. Due to the viscoelastic properties of the material, changes in its elasticity over time are unavoidable, but the gas law in the foam (volume x pressure = constant) is almost established, so changes over time Almost never. Further, when the rigidity of the foam material itself is reduced by a means such as thinning the cell wall of the foam, the properties of the gas in the foam become prominent and the entire sheet-shaped foam is softened. You can do it.
Further, even if the cell wall is made thin, it is possible to prevent the sheet-like foam from collapsing during use due to the interaction of gas in the foam. Therefore, the sheet-like foam is a preferable material in that the compression elastic modulus can be reduced due to the property of the gas in the closed cells, and at the same time, the change over time can be suppressed.

The thickness of the sheet foam is preferably 0.2-2 mm. If the thickness is less than 0.2 mm, the deformation in conformity with the unevenness of the wafer cannot be achieved, and if it exceeds 2 mm, the sheet-like foam tends to be locally deformed during polishing, which makes accurate polishing impossible. Become. The bubble diameter of the sheet foam is preferably 0.05 to 1 mm. If the cell diameter is less than 0.05 mm, the cell content cannot be increased, and it becomes difficult to secure cushioning properties. If the cell diameter exceeds 1 mm, uniform deformation due to pressure becomes difficult, which is not preferable. The foam content of the sheet foam is 70.
It is preferable that the content is less than 98%. If the cell content is less than 70%, the cushioning property becomes small, and if it exceeds 98%, the ratio of the material forming the cell wall of the foam becomes small and it becomes difficult to repeatedly use it for a long time. . The compression elastic modulus of the sheet-shaped foam is preferably 10 to 100 g / mm ² . If the compression elastic modulus is less than 10 g / mm ² , the effect of improving the flexibility by the gas in the bubbles cannot be obtained, and if it exceeds 100 g / mm ² , it becomes too hard and the cushioning property is lost, which is not preferable.

As the flexible plate body made of a hard thin plate in the present invention, for example, a thin plate of hard plastic, hard rubber, metal or the like is used. As the hard plastic, epoxy resin, thermosetting resin such as phenol resin, heat-resistant hard resin such as polyethylene terephthalate, polybutylene terephthalate, polyimide, polysulfone are preferably used, and these are glass fiber, carbon. It may be reinforced with fibers, synthetic fibers, or woven or non-woven fabrics thereof. In the case of hard plastic or hard rubber (including the case of being reinforced with the above fibers or the like), the plate thickness is preferably 0.1 to 1.0 mm in order to ensure flexibility as a plate body. As the metal, steel represented by stainless steel is preferably used, but in this case,
0.05 to 0.2 to ensure flexibility as a plate
A thickness of mm is preferred.

[0024]

In the wafer polishing apparatus according to claim 4, as shown in FIG. 2, the sheet-like foam body 2, the flexible plate body 3 made of a thin plate made of hard plastic, and the polishing cloth 4 are bonded in this order. Since the polishing member 5 formed by laminating is adhered to the polishing platen 1, when the wafer W is pressed by the pressing member 14, the polishing member 5 has a uniform polishing pressure distribution over the entire back surface of the wafer. The wafer can be polished by flexing in a form adapted to the global unevenness of the wafer. However, when the flexible plate is not interposed, as shown in FIG. 4, the influence of the oxide film projections 33 escapes to the sheet-shaped foam 2 due to the flexibility of the polishing pad 4, and the oxide film projections 33 are formed. However, in the case of the present invention, as shown in FIG. 3, the upper layer of the polishing pad 4 is deformed into a recess having a size similar to that of the oxide film protrusion 33 (locally deformed). However, since the flexible plate body 3 does not locally deform and has a property of deforming with a large radius of curvature,
Since the flexible plate 3 is deformed into a form in which the deformation of the polishing cloth 4 is dispersed, the force is likely to be concentrated on the oxide film protruding portion, and the oxide film protruding portion is easily flattened. As described above, the wafer polishing apparatus of the present invention can easily flatten the oxide film protrusion while maintaining the uniformity of the oxide film thickness.

[0025]

The present invention will be described in more detail with reference to the embodiments shown in the drawings. Example 1 FIG. 1 is a schematic cross-sectional view showing a main part of a polishing apparatus, in which a sheet-like foam 2 made of a soft rubber-like elastic material is provided on the surface of a polishing platen 1.
Is adhered to the sheet-like foam 2, and a flexible plate 3 made of a thin plate of epoxy resin containing glass fiber is adhered to the sheet-like foam 2. Further, a known suede type or velor type is used on the flexible plate 3. The polishing cloth 4 is adhesively laminated to form a sheet-shaped polishing member 5. On the other hand, holding the wafer W
The rotating device 11 is provided with a pressing member 14 made of a hard material at a lower end portion of a rotating shaft 13 provided with a vacuum flow path 12 and capable of moving up and down, and a vacuum suction plate 15 at a lower end portion of the pressing member. The passage 12 is configured to communicate with the suction hole of the vacuum suction plate 15.

The polishing member 5 is prepared by adhering and laminating the sheet foam 2, the flexible plate 3 and the polishing cloth 4 in advance, and polishing the polishing member 5 through the sheet foam 2. It is preferable to adhere to the plate 1, and compared with the case where the sheet foam 2 and the like are sequentially adhered and laminated on the surface of the polishing platen 1,
Since the work of attaching the polishing member 5 is simplified and the wrinkle amount of the polishing member 5 is significantly reduced, the object of the present invention is to
It can be achieved more accurately. Further, the flexible plate body 3 and the sheet-shaped foam body 2 may be always attached to the polishing platen 1, and only the polishing cloth 4 may be replaced, whereby the cost of the polishing member 5 can be reduced. .

Next, experimental examples using the polishing apparatus of the present invention and comparative examples using the conventional polishing apparatus will be described. Experimental Example 1 A polishing member having the following structure was attached to a polishing platen 1 as shown in FIG. 1, and a cross-sectional shape of silicon having a thickness of about 660 μm and a diameter of 150 mm shown in FIG. 1.3 μm) was used as a polishing agent, and a fumed silica polishing agent (trade name: Semisperse ™ -25) was used as a polishing agent to perform mirror polishing under normal conditions, and the cross-sectional shapes of the wafers before and after polishing were compared. [Abrasive member] Sheet foam: Material Chloroprene rubber Thickness 0.8 mm Specific gravity 0.23 Cell diameter 0.05 to 0.16 mm (measured by an electron microscope) Cell content rate about 80% Compressive elastic modulus 60 g / mm before use ² , after use 12g /
mm ² Flexible plate: Material Glass fiber-containing epoxy resin plate Thickness 0.3 mm Polishing cloth: Velor type (non-woven fabric, for primary polishing of silicon wafer) Thickness 1.27 mm [Polishing condition]: Polishing pressure 300 gf / cm ² Relative speed 80m / min (polishing member and wafer) Polishing time 30 minutes

The polishing results are shown in FIG. In this figure, a curve L shows the relationship between the diametrical position of the pre-polishing wafer and the thickness of the silicon substrate, and a curve M shows the relationship between the diametrical position of the pre-polishing wafer and the thickness of the oxide film.
A curve N shows the same relationship as the curve M with respect to the wafer after polishing. In addition, these thicknesses were measured by an ellipsometer. As is clear from comparison between these curves, even if the thickness of the silicon substrate of the pre-polishing wafer varies, it is possible to perform polishing with a substantially uniform removal amount on the entire surface of the wafer. In other words,
When an oxide film formed to have a uniform thickness on a silicon substrate having a variation in wall thickness was polished, it was possible to perform surface reference polishing while maintaining the uniformity of the oxide film thickness. Further, in this embodiment, the vacuum suction plate 15 made of a hard material is used for the wafer fixing method, but the same effect can be obtained even when the mounting pad template method is used for the wafer fixing method. Has been confirmed.

Comparative Example 1 A polishing test was conducted in the same manner as in Experimental Example 1 except that only the polishing cloth of Experimental Example 1 was used as the polishing member. The result is shown in Fig. 8.
Shown in. In this figure, the curves P, Q and R correspond to the curves L, M and N of FIG. 7, respectively. Curves Q and R
As is clear from the comparison, the thickness of the oxide film is constant on the wafer before polishing, whereas there is a large variation in the thickness of the oxide film on the wafer after polishing. It was not possible to carry out polishing while maintaining the above.

Experimental Example 2 A silicon wafer having a thickness of about 660 μm and a diameter of 150 mm and having a mirror-finished surface has a width of 100 μm and a height of 1 μm.
m linear protrusions were formed, and an oxide film having a thickness of 3 μm was formed on the surface thereof by atmospheric pressure CVD, and polishing was performed under the same conditions as in Experimental Example 1 except that the polishing time was 5 minutes. went. As a result, the linear protrusions could be flattened to a height of 0.1 μm. On the other hand, when the flexible plate was not used, the height of the linear protrusion was 0.3 μm, and the effect of the flexible plate could be confirmed. The height of the linear protrusion was measured by a stylus type surface roughness meter.

[0031]

As is apparent from the above description, in the wafer polishing apparatus according to claim 4, the sheet-like foam, the flexible plate made of a thin plate made of hard rubber, and the polishing cloth are provided. Since the polishing member formed by bonding and laminating in this order is bonded to the polishing platen, the polishing member bends under a uniform polishing pressure distribution over the entire back surface of the wafer and in a form adapted to the global unevenness of the wafer. Therefore, the polishing removal amount can be uniformly polished on the entire surface of the wafer, and when the oxide film formed to have a uniform thickness on the silicon substrate having the thickness variation is polished, the surface that maintains the uniformity of the oxide film thickness There is an effect that the reference polishing can be performed accurately. Moreover, since the flexible plate body is deformed into a form in which the deformation of the polishing cloth is dispersed, it is possible to concentrate the force on the oxide film projecting portion, which has the effect of enhancing the flattening action.

[Brief description of drawings]

FIG. 1 is a schematic sectional view showing a main part of an embodiment of a wafer polishing apparatus according to the present invention.

FIG. 2 is a sectional view for explaining the operation of the wafer polishing apparatus of the present invention.

FIG. 3 is a partially enlarged view of FIG.

FIG. 4 is a sectional view for explaining the operation of the wafer polishing apparatus that does not use a flexible plate.

FIG. 5 is a cross-sectional view showing an example of a wafer before polishing.

FIG. 6 is a cross-sectional view of the polished wafer of FIG.

FIG. 7 is a graph showing the results of an experimental example of the present invention.

FIG. 8 is a graph showing the results of a comparative experiment example.

FIG. 9 is a schematic sectional view showing a main part of a conventional wafer polishing apparatus.

FIG. 10 is a schematic sectional view showing a main part of another conventional wafer polishing apparatus.

11A and 11B show a preferable polishing state, FIG. 11A is an explanatory view of a polishing pressure distribution, and FIG. 11B is a sectional view of a wafer after polishing.

FIG. 12 shows an example of an unfavorable polishing state,
(A) is an explanatory view of a polishing pressure distribution, and (b) is a sectional view of a wafer after polishing.

FIG. 13 shows another example of an unfavorable polishing state,
(A) is an explanatory view of a polishing pressure distribution, and (b) is a sectional view of a wafer after polishing.

[Explanation of symbols]

 1,44,56 Polishing surface plate 2 Sheet foam 3 Flexible plate 4,45,62 Polishing cloth 5 Polishing member 11 Holding / rotating device 12 Vacuum channel 13,54 Rotating shaft 14,41 Pressing member 15 Vacuum adsorption plate 31 Silicon substrate 32 Oxide film 33, 33a, 33b, 33c Oxide film protrusion 34 Element 35, 35a, 35b, 35c Wiring 42 Mounting pad 43 Template 51 Elastic film 52 Body 53 Fluid supply means 55 Guide plate (template) 61 Wafer holding member A Surrounding sag B Protrusion D Polishing pressure distribution W Wafer

Front page continuation (72) Inventor Fumio Suzuki Fukushima Nishigokawa-gun Saigo-mura Odakura Odaira No.150 Shindai semiconductor Co., Ltd. Semiconductor Shirakawa Laboratory

Claims (6)

[Claims] 1. A polishing member provided on a polishing surface plate, characterized in that a flexible plate body made of a hard thin plate is adhesively laminated between a sheet foam made of a soft rubber elastic body and a polishing cloth. A sheet-like polishing member. 2. The sheet-shaped foam is a closed-cell foam made of natural rubber, synthetic rubber or thermoplastic elastomer, and flexibility is imparted by the gas in the foam. , (1) Thickness is 0.2-2
mm, (2) Cell diameter is 0.05 to 1 mm, (3) Cell content (ratio of cell volume to foam volume) is 70 to 9
The sheet-like polishing member according to claim 1, wherein the sheet-like polishing member has a compression modulus of 8% and (4) is 10 to 100 g / mm ² . 3. The sheet-shaped polishing member according to claim 1, wherein the polishing cloth is of a suede type or a velour type. 4. A sheet-like foam made of a soft rubber-like elastic material on the surface of a polishing platen, a flexible plate made of a hard thin plate on the sheet-like foam, and polishing on the flexible plate. A wafer polishing apparatus characterized by being laminated with a cloth. 5. The sheet-shaped foam is a closed-cell foam made of natural rubber, synthetic rubber or thermoplastic elastomer, and flexibility is imparted by the gas in the foam. , (1) Thickness is 0.2-2m
m, (2) Cell diameter is 0.05 to 1 mm, (3) Cell content (ratio of cell volume to foam volume) is 70 to 98
%, And (4) the compressive elastic modulus is 10 to 100 g / mm ² , the wafer polishing apparatus according to claim 4. 6. The wafer polishing apparatus according to claim 4, wherein the polishing cloth is a suede type or a velor type.