JP2891083B2 - Sheet-shaped polishing member and wafer polishing device - Google Patents

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 particularly to a polishing member suitable for application to a planarization processing technique for improving the flatness of a semiconductor device. It relates to a polishing apparatus.

[0002]

2. Description of the Related Art With the progress of high integration and large scale of semiconductor devices, miniaturization of wirings and multi-layering of wirings have become more and more important. When the wiring is miniaturized, the end face must be sharpened, and the covering property of the insulating film or the wiring to be deposited thereon is reduced. Also, when wiring is multi-layered,
Since the unevenness of the lower wiring or the insulating film is piled up, the unevenness of the surface becomes severe. Even if an attempt is made to form the wiring on the surface, the stepper becomes out of focus and the processing accuracy of the wiring is reduced. In any case, disconnection of the wiring is likely to occur, and the reliability of the semiconductor device is reduced.

In order to solve this problem, various flattening techniques have been developed. For example, there is a glass flow method in which a glass film such as PSG or BPSG is formed by CVD, and then heated to 800 to 1100 ° C. to make it viscous flow to flatten. This method is simple in process, but has the drawback that the wiring material is limited, such as the use of Al wiring because it is heated to a high temperature. In addition, various methods have been developed, but each has its advantages and disadvantages, and there is no decisive technology.

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

However, in the planarization processing technology for manufacturing semiconductor devices, the cross-sectional shape of a wafer (hereinafter, referred to as a wafer W) in the processing process is different from the thick portion of the wafer W shown in FIG. Even if there is a difference from the thin portion, there is a need to develop a technique for polishing a wafer W having a cross-sectional shape shown in FIG. The reason is that conventionally, this wafer polishing technique has been developed for the purpose of equalizing the thickness over the entire surface of the wafer and for removing the thick portion of the wafer preferentially.

This surface-based polishing technique is specifically described in FIG.
Oxide film 32 (interlayer insulating film) on silicon substrate 31 shown in FIG.
Is removed, that is, the oxide film projections 33 are removed, and the thickness of the oxide film 32 is maintained uniform. In FIGS. 5 and 6, reference numeral 34 denotes an element, and reference numeral 35 denotes a wiring.
In these figures, the global unevenness of the wafer W is exaggerated for convenience of explanation.

In such a wafer polishing apparatus, a commercially available polishing cloth is usually used as a polishing member provided on a polishing platen. This polishing cloth is a so-called suede type (Suede Ty).
pe) and the velor type (Velour Type)
e), which are selectively used according to the purpose of polishing. Suede-type polishing cloths are artificial leathers for industrial materials.It is composed of a base layer consisting of a three-dimensional nonwoven fabric made of synthetic fibers and special synthetic rubber, and a resin such as polyurethane with excellent wear resistance. And a surface layer on which fine pores (holes) are formed. The velor-type polishing cloth is a so-called nonwoven fabric having a single-layer structure, and is a porous sheet material having a three-dimensional structure. Then, when polishing the wafer, the wafer held by the holding member is pressed against a polishing cloth on a polishing platen at a predetermined pressure,
A method of polishing while supplying an appropriate polishing liquid onto a polishing cloth is employed.

The polishing cloth used for the primary polishing or the secondary polishing of the wafer is made of a hard material so that the thickness variation of the wafer after polishing is reduced, and the thick portion is preferentially polished. Designed to eliminate.
For this reason, with a wafer polishing apparatus provided with such a polishing cloth, the surface-based polishing described above was difficult.

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

[0010] The polishing apparatus described in the above publication is similar to the polishing apparatus shown in FIG.
As shown in FIG. 0, a flexible elastic film 51 is used on a plane for holding the wafer W, and the elastic film 51 is attached to the ring-shaped body 52 with uniform tension to hold the wafer W of 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 a surface opposite to the surface on which the wafer W is provided. Reference numeral 54 denotes a rotating shaft, 55 denotes an annular guide plate (template) adhered to the lower surface of the elastic film 51, and 56 denotes a polishing platen.

By the way, the removal amount of the wafer by polishing is as follows.
It depends strongly on polishing pressure. Therefore, in the above-mentioned surface-based polishing technique, the distribution D of the polishing pressure on the back surface of the wafer W is made uniform (uniformly distributed load) as shown in FIG. It is extremely important to polish with a uniform polishing removal amount over the entire area. In FIG. 11A, reference numeral 61 denotes a wafer holding member;
2 is a polishing cloth.

[0012]

However, the polishing apparatus shown in FIG. 9 has an advantage that the structure for holding the wafer is simplified, but the influence of variations in the characteristics (thickness, elasticity, and deterioration characteristics) of the mounting pad 42. And uniform polishing pressure is difficult. For this reason, when the polishing pressure becomes excessive at the outer peripheral portion of the wafer as shown in FIG. 12A in the polishing pressure distribution D, peripheral sag A occurs on the polishing wafer W as shown in FIG. Alternatively, when the polishing pressure is too small at the outer peripheral portion of the wafer as shown in FIG. 13A, there is a problem that a projection B is generated at the peripheral portion of the polished wafer W as shown in FIG.

On the other hand, in the polishing apparatus described in the above-mentioned publication, since the elastic film 51 sealing the ring-shaped body 52 is rich in flexibility, it is shown in FIGS. 12 (b) and 13 (b). In order to suppress the occurrence of such a shape abnormality in the peripheral portion of the wafer, the distance between the lower surface of the outer peripheral end of the elastic film 51 and the upper surface of the polishing platen 56 in FIG. That is, if the interval is excessively large, the central portion of the elastic film 51 becomes convex due to the pressure of the fluid, so that the cross-sectional shape of the polished wafer W becomes as shown in FIG. In this case, the cross-sectional shape of the polished wafer W becomes as shown in FIG. 12B due to the load applied downward by the body portion 52 or the fluid pressure applied between the wafer W and the body portion 52. The uniformity of the thickness of the oxide film on the wafer cannot be maintained.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to provide a polishing member and a wafer polishing apparatus capable of performing surface reference polishing without causing peripheral sagging and peripheral projection of the wafer. It is in.

[0015]

According to a first aspect of the present invention, in a polishing member provided on a polishing platen, a sheet-like foam made of a soft rubber-like elastic body and a polishing cloth are provided. comprising a flexible plate body composed of a thin plate adhered laminated
A polishing member, wherein the sheet-like foam is made of natural rubber, synthetic
Generation of closed cells made of rubber or thermoplastic elastomer
It is a foam with flexibility given by the gas in the foam
And (1) a thickness of 0.2 to 2 mm, (2) a cell diameter of 0.05 to 1 mm, and (3) a cell content (a ratio of cell volume to foam volume).
If) is 70-98%, (4) the compression modulus of 10 to 100 g / mm ^2, it is characterized.

The sheet-like abrasive member according to claim 2, wherein the polishing pad, and characterized in that the suede type or velor type.

The wafer polishing apparatus according to claim 3, a sheet-like foam on the surface of the polishing platen by a soft rubber-like elastic material, a flexible plate body composed of a rigid sheet to the sheet-like foam on, polishing formed by bonding laminating a polishing pad on the flexible plate on the body
The sheet-like foam is a natural rubber, a synthetic rubber
Or closed-cell foam made of thermoplastic elastomer
Which is made more flexible by the gas in the foam.
And (1) a thickness of 0.2 to 2 mm, (2) a cell diameter of 0.05 to 1 mm, and (3) a cell content (a ratio of cell volume to foam volume).
If) is 70-98%, (4) the compression modulus of 10 to 100 g / mm ^2, it is characterized.

The wafer polishing apparatus according to claim 4, wherein the polishing pad, and characterized in that the suede type or velor type.

[0019] Independent constituting the sheet-like abrasive member of the present invention
Natural rubber, synthetic rubber such as chloroprene rubber, ethylene-propylene rubber, butyl rubber, and the like can be used as the material of the foamed foam , and styrene-based, ester-based, and urethane-based thermoplastic elastomers can be used. The hardness (Shore A) of natural rubber, synthetic rubber or thermoplastic elastomer (not foamed) is preferably in the range of 30 to 90. The elasticity of the sheet-like foam is a composite of the elasticity of the material itself and the elasticity of the gas in the foam. Due to the viscoelastic properties of the material,
Although the change with time of the elasticity is unavoidable, the gas in the foam hardly changes with time because the gas law (volume × pressure = constant) is almost satisfied. Furthermore, when the rigidity of the foam material itself is reduced by means such as thinning the cell walls of the foam, the properties of the gas in the foam become remarkable, and the entire sheet-like foam is softened. I can do it. Further, even when the cell wall is thinned, the sheet-like foam is prevented from being crushed during use due to the interaction of the gas in the foam. Therefore, the sheet-like foam is a preferable material in that the compression elastic modulus can be reduced by the property of the gas in the closed cells, and the change with time can be suppressed.

[0020] The thickness of the sheet-like foam 0.2~2m
m. If the thickness is less than 0.2 mm, deformation in accordance with the unevenness of the wafer cannot be performed. If the thickness exceeds 2 mm, local deformation of the sheet-like foam during polishing tends to occur, and high-precision polishing becomes impossible. Become. The cell diameter of the sheet-like foam is 0.05 to 1 mm . Bubble diameter 0.05
If it is less than mm, the bubble content cannot be increased, and it is difficult to secure cushioning properties. If it exceeds 1 mm, it becomes difficult to uniformly deform under pressure, which is not preferable.
The foam content of the sheet-like foam is 70 to 98% . If the bubble content is less than 70%, the cushioning property is reduced,
If it exceeds 98%, the proportion of the material forming the cell wall of the foam becomes small, and it becomes difficult to use the cell for a long period of time. The compression elastic modulus of the sheet-like foam is 10 to 100 g / mm ² .
You. 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 not preferable.

The flexible plate made of a hard thin plate in the present invention includes, for example, hard plastic, hard rubber,
A thin plate of metal or the like is used. As the hard plastic, a thermosetting resin such as an epoxy resin and a phenol resin, a heat-resistant hard resin such as polyethylene terephthalate, polybutylene terephthalate, polyimide, and polysulfone are preferably used. Fibers, synthetic fibers, or those reinforced with woven or nonwoven fabrics thereof may be used. In the case of hard plastic and hard rubber (including the case of reinforcing with the above-mentioned fiber etc.),
The thickness is preferably 0.1 to 1.0 mm from the viewpoint of securing the flexibility of the plate. As the metal, steel typified by stainless steel is preferably used. In this case, in order to secure flexibility as a plate, 0.05 to 0.2 mm
It is preferable to have a thickness of

[0022]

In the wafer polishing apparatus according to the third aspect , as shown in FIG. 2, a sheet-like foam 2 and a flexible plate 3 made of a thin plate made of a hard plastic and a polishing cloth 4 are bonded in this order. Since the laminated polishing member 5 is bonded 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. Can be bent in a form adapted to the global unevenness of the wafer to polish the wafer. However, when the flexible plate is not interposed, the influence of the oxide film projections 33 escapes to the sheet-like foam 2 due to the flexibility of the polishing pad 4, as shown in FIG. 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 concave portion having a size similar to the size of the oxide film projection 33 (deformation locally). However, since the flexible plate 3 has a property of being deformed with a large radius of curvature without being locally deformed,
Since the flexible plate 3 is deformed into a form in which the deformation of the polishing pad 4 is dispersed around the periphery, the force is easily concentrated on the oxide film protrusion, and the oxide film protrusion is easily flattened. As described above, in the wafer polishing apparatus of the present invention, the oxide film protrusion can be easily flattened while maintaining the uniformity of the oxide film thickness.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS 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 sectional view showing a main part of a polishing apparatus, and a sheet-like foam 2 made of a soft rubber-like elastic material is provided on a surface of a polishing platen 1.
And a flexible plate 3 made of a thin plate of epoxy resin containing glass fiber is adhered onto the sheet-like foam 2, and a known type such as a suede type or a velor type is further placed on the flexible plate 3. The polishing cloth 4 is bonded and laminated to form a sheet-like polishing member 5. On the other hand, holding of the wafer W
The rotating device 11 is provided with a pressing member 14 made of a hard material at the lower end of a rotatable shaft 13 provided with a vacuum flow path 12 and a vacuum suction plate 15 at the lower end of the pressing member. The passage 12 communicates with a suction hole of a vacuum suction plate 15.

The polishing member 5 is prepared by bonding and laminating the sheet-like foam 2, the flexible plate 3 and the polishing cloth 4 in advance, and the polishing member 5 is polished and fixed through the sheet-like foam 2. It is preferable to adhere to the plate 1, as compared with the case where the sheet-like foam 2 and the like are sequentially adhered and laminated on the surface of the polishing platen 1.
The operation of attaching the polishing member 5 is simplified, and the amount of wrinkles generated by the polishing member 5 is greatly reduced.
It can be achieved more accurately. In addition, the flexible plate 3 and the sheet-like foam 2 can be always stuck to the polishing platen 1 and only the polishing cloth 4 can be replaced, whereby the cost of the polishing member 5 can be reduced. .

[0025] Next, an experimental example using the polishing apparatus of the present invention,
And a comparative example using a conventional polishing apparatus will be described. Experimental Example 1 A polishing member having the following configuration was attached to a polishing platen 1 as shown in FIG.
The cross section has a thickness of about 660 μm and a diameter shown in FIG.
150mm silicon (thermal oxide film on mirror surface wafer surface
(Formed with a thickness of 1.3 μm) as a polishing agent
Smoked silica abrasive (trade name: Semisperse)
Mirror polishing under normal conditions using TM-25), before polishing
The cross-sectional shapes of the wafers were compared. [Polishing member] Sheet foam: Material Chloroprene rubber Thickness 0.8 mm Specific gravity 0.23 Cell diameter 0.05 to 0.16 mm (measured by electron microscope) Cell content about 80% Compression elasticity 60 g / mm before use², 12g / mm after use²  Flexible plate: Material Epoxy resin plate with glass fiber Thickness 0.3mm Polishing cloth: Velor type (for primary polishing of nonwoven fabric, silicon wafer) 1.27mm thick [Polishing conditions]: Polishing pressure 300gf / cm²  Relative speed 80m / min (polishing member and wafer) Polishing time 30min

[0026] shows the polishing results are shown in Figure 7. In this figure, curve L represents the relationship between the diameter position and the thickness of the silicon substrate for the wafer before polishing, and curve M represents the relationship between the diameter position and the thickness of the oxide film for the wafer before polishing.
The curve N shows the same relationship as the curve M for the polished wafer. In addition, these thicknesses were measured by an ellipsometer. As is clear from the comparison of these curves, even if the thickness of the silicon substrate of the wafer before polishing varies, it was 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 with a uniform thickness on a silicon substrate having a thickness variation was polished, surface-based polishing was performed 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. However, the same effect can be obtained when the mounting pad / template method is used for the wafer fixing method. Has been confirmed.

[0027] except for using only the polishing cloth of Example 1 as Comparative Example 1 abrasive member was polished tested in the same manner as described in Example 1. The result is shown in FIG.
Shown in In this figure, curves P, Q, R correspond to curves L, M, N of FIG. 7, respectively. Curves Q and R
As is clear from the comparison, the thickness of the oxide film is constant in the wafer before polishing, while the thickness of the oxide film is large in the wafer after polishing. Was not able to be polished.

The diameter 150mm in Experimental Example 2 thickness of about 660Myuemu, width 100μm on the surface of the silicon wafer subjected to mirror finish, height 1μ
m, a 3 μm-thick oxide film was formed on the surface by atmospheric pressure CVD, and polishing was performed under exactly the same conditions as in Experimental Example 1 except that the polishing time was 5 minutes. went. As a result, the linear protrusion was flattened to a height of 0.1 μm. On the other hand, when the flexible plate was not used, the height of the linear projection 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.

[0029]

As is clear from the above description, in the wafer polishing apparatus according to the third aspect , an independent wafer having predetermined characteristics is provided.
A foamed sheet-like foam, a flexible plate made of a thin plate made of hard rubber or the like, and a polishing cloth are bonded and laminated in this order to a polishing member on a polishing platen via the sheet-like foam. Bonding
Because the structure has a uniform polishing pressure distribution over the entire back surface of the wafer, and the polishing member bends in a form that conforms to the global unevenness of the wafer, the polishing removal amount can be uniformly polished over the entire surface of the wafer, When an oxide film formed with a uniform thickness is polished on a silicon substrate having a thickness variation, there is an effect that surface-based polishing can be performed accurately while maintaining the uniformity of the oxide film thickness. In addition, since the flexible plate deforms into a form in which the deformation of the polishing cloth is dispersed around the flexible plate, it is possible to concentrate the force on the oxide film protrusion, and there is an effect that the flattening action is enhanced.

[Brief description of the 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. 2;

FIG. 4 is an operation explanatory sectional view of a wafer polishing apparatus that does not use a flexible plate.

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

FIG. 6 is a sectional view of a polished wafer of FIG. 5;

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 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.

FIGS. 11A and 11B show a preferable polishing state, wherein FIG. 11A is an explanatory diagram of a polishing pressure distribution, and FIG. 11B is a cross-sectional view of the 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 cross-sectional view of a wafer after polishing.

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

[Explanation of symbols]

 1, 44, 56 Polishing surface plate 2 Sheet-like foam 3 Flexible plate 4, 45, 62 Polishing cloth 5 Polishing member 11 Holding / rotating device 12 Vacuum flow path 13, 54 Rotating shaft 14, 41 Pressing member 15 Vacuum suction 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 Peripheral sag B Projection D Polishing pressure distribution W Wafer

────────────────────────────────────────────────── ─── Continuing on the front page (72) Fumio Suzuki, Inventor 150 Odakura, Odakura, Nishigo-mura, Nishishirakawa-gun, Fukushima Prefecture Shin-Etsu Semiconductor Co., Ltd. Semiconductor Shirakawa Laboratory (56) JP-A-63-196369 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) B24B 37/00 H01L 21/304 622

Claims (4)

(57) [Claims] 1. A polishing member disposed on a polishing platen, a flexible plate body composed of a rigid sheet formed by adhesively laminated between the sheet-like foam by soft rubber-like elastic body and the polishing pad
A polishing member, wherein the sheet-like foam is made of natural rubber, synthetic
Generation of closed cells made of rubber or thermoplastic elastomer
It is a foam with flexibility given by the gas in the foam
And (1) a thickness of 0.2 to 2 mm, (2) a cell diameter of 0.05 to 1 mm, and (3) a cell content (a ratio of cell volume to foam volume).
If) is 70-98%, (4) the compression modulus of 10 to 100 g / mm ^2, the sheet-like abrasive member, characterized in that. 2. A sheet-like polishing member according to claim 1, wherein said polishing cloth is of a suede type or a velor type. 3. A sheet foam made of a soft rubber-like elastic material on a surface of a polishing platen, a flexible plate made of a hard thin plate on the sheet foam, and a polishing made on the flexible plate. A wafer polishing apparatus formed by bonding and laminating a cloth,
Foam is natural rubber, synthetic rubber or thermoplastic elastomer
Closed-cell foam consisting of
Ri is obtained by imparting flexibility, and (1) a thickness of 0.2 to 2 mm, (2) cell diameter 0.05 to 1 mm, (3) the bubble content (bubble volume to the foam volume Percent
If) is 70-98%, (4) the compression modulus of 10 to 100 g / mm ^2, the wafer polishing apparatus characterized by. Wherein said polishing cloth, the wafer polishing apparatus according to claim 3, characterized in that it is of suede type or velor type.