JP2900777B2 - Polishing member and wafer polishing apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[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. Conventionally, this wafer polishing technique has been developed in order to equalize the thickness over the entire surface of the wafer and to preferentially remove a thick portion of the wafer.

[0005] 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 between the thin portion and the thin portion, there is a need to develop a technique for polishing a wafer W having a sectional shape shown in FIG.

Specifically, this polishing technique removes a step in an oxide film 32 (interlayer insulating film) on a silicon substrate 31 shown in FIG. 3, that is, an oxide film projection 33, and makes the thickness of the oxide film 32 uniform. To maintain. 3 and 4, reference numeral 34 denotes an element, and reference numeral 35 denotes a wiring. Also,
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. These polishing cloths are of a so-called suede type and a velor type, and are respectively 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. When the wafer is polished, a method is employed in which the wafer held by the holding member is pressed against a polishing cloth on a polishing platen at a predetermined pressure, and polishing is performed while supplying an appropriate polishing liquid onto the polishing cloth. .

The polishing cloth used for the primary or secondary polishing of the wafer is made of a hard material so that the thickness variation of the wafer after polishing is reduced. It is designed to be polished and removed. For this reason, it was difficult to perform the above-mentioned surface-based 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. 7 has been proposed. This polishing apparatus is composed of a pressing member 71 made of a hard material.
A soft mounting pad 72 as a wafer holding plate is provided on the lower surface of the substrate, and an annular template 73 is provided on the lower surface of the pad.
, And a soft polishing cloth 75 is provided on the surface of the polishing platen 74.

By the way, the removal amount of the wafer by polishing is as follows.
It depends strongly on polishing pressure. Accordingly, 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. 8A, reference numeral 81 denotes a wafer holding member;
Is a polishing cloth.

[0010]

However, the polishing apparatus shown in FIG. 7 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 72. Susceptible to
It is difficult to equalize the polishing pressure. For this reason, as shown in FIG. 9A, when a mounting pad having a thickness variation is used as shown in FIG. 9A in the polishing pressure distribution D, the polishing pressure in the wafer surface becomes non-uniform, and as shown in FIG. When the undulation A occurs on the polishing wafer W, or when the polishing pressure becomes too small at the outer peripheral portion of the wafer as shown in FIG. 10A, the undulation A is generated at the peripheral portion of the polishing wafer W as shown in FIG. There is a problem that the projection B occurs.

SUMMARY OF THE INVENTION The present invention has been made in consideration 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 undulations and peripheral projections of a wafer. It is in.

[0012]

According to a first aspect of the present invention, there is provided a polishing member provided on a polishing platen, wherein a sheet-like foam of closed cells made of a soft rubber-like elastic material and a polishing cloth are provided.
And the sheet-like foam is the independent
The flexibility is given by bubbles (gas in foam)
There is a feature.

[0013] abrasive member according to claim 2 is the foam the sheet foam as defined in claim 1 is composed of natural rubber, synthetic rubber or thermoplastic elastomer, 0.2 thickness (1) 2 mm, (2) bubble diameter is 0.05 to 1 mm, (3) bubble content (ratio of bubble volume to foam volume) is 70 to 98%, and (4) compression elastic modulus is 10 to 100 g / mm ² . There is a feature.

A polishing member according to a third aspect is characterized in that, in the first aspect, the polishing cloth is of a suede type or a velor type.

The wafer polishing apparatus according to the fourth aspect of the present invention is a wafer polishing apparatus, wherein the surface of the polishing platen is made of a soft rubber-like elastic body for sealing closed cells.
And a polishing cloth laminated on the sheet-like foam.
And the sheet-like foam is closed cells (foamed
(A gas in the body) .

[0016] wafer polishing apparatus according to claim 5, a foamed body, wherein the sheet-like foam as claimed in claim 4 is made of natural rubber, synthetic rubber or thermoplastic elastomer
Te, (1) a thickness of 0.2 to 2 mm, (2) cell diameter 0.05 to 1 mm, (3) the bubble content (percentage of the bubble volume for foam volume) 70-98%, (4 ) The compression modulus is 10 to 100 g / mm ² .

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

The sheet-like foam used in the polishing member of the present invention is, for example, chloroprene rubber, ethylene-propylene rubber, butyl rubber or the like as natural rubber or synthetic rubber, and styrene or ester-based thermoplastic elastomer. , Urethane-based or the like can be used. The hardness (Shore A) of natural rubber, synthetic rubber or thermoplastic elastomer (not foamed) is 30.
The range of ~ 90 is preferred. 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, its elasticity is inevitable over time, but the gas in the foam almost conforms to the law of gas (volume x pressure = constant). Almost no. 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 large, and the entire sheet-like foam can be softened. it can.
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.

The thickness of the sheet-like foam is preferably 0.2 to 2 mm. 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 preferably 0.05 to 1 mm. When the bubble diameter is less than 0.05 m, the bubble content cannot be increased, and it is difficult to secure the cushioning property. When the bubble diameter exceeds 1 mm, uniform deformation under pressure becomes difficult, which is not preferable. The foam content of the sheet-like foam is 70
When the cell content is less than 70%, the cushioning property is reduced. When the cell content is more than 98%, the proportion of the material forming the cell walls of the foam is reduced, and long-term repeated use becomes difficult. . It is preferable that the compression elastic modulus of the sheet foam is 10 to 100 g / mm ² . Is less than the compression modulus of 10 g / mm ^2, not be obtained flexibility enhancing effect of the gas in the bubbles, 100 g / mm ² to exceed the hard becomes too cushioning eliminates undesirable.

[0020]

The wafer polishing apparatus according to the fourth aspect has a structure in which a polishing cloth 3 is provided on a polishing platen 1 via a sheet-like foam 2 made of a soft rubber-like elastic material as shown in FIG. Therefore, when the wafer W is pressed by the pressing member 14, the polishing member 4 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 (the thickness of the wafer). Wafer) can be polished.

[0021]

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 known polishing cloth 3 such as a suede type or a velor type is bonded and laminated on the sheet-like foam 2, and the sheet-like polishing member 4 is constituted by the sheet-like foam 2 and the polishing cloth 3. It was done. On the other hand, wafer W
The holding / rotating device 11 is provided with a pressing member 14 made of a hard material on a lower end portion of a rotatable shaft 13 provided with a vacuum flow path 12 and capable of moving up and down.
A vacuum suction plate 15 at the lower end of the pressure member, and a template 16 on the outer peripheral side of the suction plate.
2 is made to communicate with the suction hole of the vacuum suction plate 15.

The polishing member 4 is prepared by bonding and laminating the sheet-like foam 2 and the polishing cloth 3 in advance, and the polishing member 4 is bonded to the polishing platen 1 via the sheet-like foam 2. Preferably, compared to the case where the sheet-like foam 2 is bonded to the surface of the polishing platen 1 and then the polishing cloth 3 is bonded and laminated.
The operation of attaching the polishing member 4 is simplified, and the amount of wrinkles generated by the polishing member 4 is greatly reduced.
It can be achieved more accurately.

Next, an experimental example using the polishing apparatus of the present invention and a comparative example 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 silicon wafer W having a cross-sectional shape of about 660 μm in thickness and 150 mm in diameter shown in FIG. A film having a thickness of 1.2 μm)
Polishing was performed under normal conditions using colloidal silica as an abrasive, and the cross-sectional shapes of the wafer before and after polishing were compared. [Polishing member] Sheet-shaped 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% Compressive elasticity 60 g / mm before use ² , 12g after use
mm ² polishing cloth: velor type (non-woven fabric) thickness 1.27 mm [polishing condition]: polishing pressure 500 gf / cm ² relative speed 110 mm / min (polishing member and wafer) polishing time 30 minutes

FIG. 5 shows the polishing result. In this figure, the curve Lb shows the relationship between the position in the diameter direction and the wafer thickness of the wafer before polishing, and the curve La shows the same relationship for the wafer after polishing. The thickness of the wafer was measured by an electronic micrometer. As is clear from the comparison between the curves Lb and La, the polishing could be performed in a form in which the global concavo-convex shape of the wafer before polishing and its dimensions were left as they were. As described above, according to the present invention, polishing in which the cross-sectional shape is maintained even when the thickness of the wafer varies, that is, polishing with a uniform removal amount can be performed over the entire surface of the wafer. In other words, when an oxide film having a uniform thickness is polished on a silicon substrate having a thickness variation, it is possible to accurately perform surface-based polishing while maintaining the uniformity of the oxide film thickness. FIG.
In the polishing, sagging occurs at the outermost peripheral portion, and the shape is not completely maintained, but there is no problem because this wafer region is an unused portion, and by an appropriate technique not described in this specification, Drip can be eliminated. 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.

Comparative Example 1 A polishing test was performed in the same manner as in Experimental Example 1 except that only the polishing cloth of Experimental Example 1 was used as a polishing member. The result is shown in FIG.
Shown in In this figure, the curve Mb shows the relationship between the diameter position and the wafer thickness of the wafer before polishing, and the curve Ma shows the same relationship for the wafer after polishing. As is clear from the comparison between the curves Mb and Ma, the global unevenness of the wafer before polishing disappeared after polishing, and it was difficult to perform polishing with a uniform removal amount on the entire surface of the wafer.

[0027]

As apparent from the above description, according to the wafer polishing apparatus of the fourth aspect, the polishing member conforms to the global unevenness of the wafer under a uniform polishing pressure distribution over the entire back surface of the wafer. Since the wafer can be polished by bending in the above-mentioned form, the polishing removal amount can be uniformly polished on the entire surface of the wafer, and when polishing an oxide film formed with a uniform thickness on a silicon substrate having a thickness variation, There is an effect that polishing can be performed while maintaining the uniformity of the oxide film thickness.

[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 sectional view of a wafer before polishing.

FIG. 4 is a cross-sectional view of the wafer after polishing.

FIG. 5 is a graph showing the results of an experimental example of the present invention.

FIG. 6 is a graph showing the results of a comparative example.

FIG. 7 is a schematic sectional view showing a main part of a conventional wafer polishing apparatus.

8A and 8B show a preferable polishing state, in which FIG. 8A is an explanatory diagram of a polishing pressure distribution, and FIG.

FIG. 9 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. 10 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]

 1,74 Polishing surface plate 2 Sheet foam 3,75,82 Polishing cloth 4 Polishing member 11 Holding / rotating device 12 Vacuum flow path 13 Rotating shaft 14,71 Pressing member 15 Vacuum suction plate 16,73 Template 31 Silicon substrate Reference Signs List 32 oxide film 33 oxide film protrusion 34 element 35 wiring 72 mounting pad 81 wafer holding member A undulation B protrusion D polishing pressure distribution W wafer

──────────────────────────────────────────────────続 き Continuing from the front page (72) Fumio Suzuki, Inventor 150 Odakura, Odakura, Nishigo-mura, Nishishirakawa-gun, Fukushima Prefecture Shin-Etsu Semiconductor Co., Ltd. Semiconductor Shirakawa Research Laboratories (58) Field surveyed (Int. Cl. ⁶ , DB name) B24B 37/00 B24D 11/00 H01L 21/304 622

Claims (6)

(57) [Claims] 1. A polishing member provided on a polishing platen, wherein a sheet-like foam of closed cells made of a soft rubber-like elastic material is provided.
And a polishing cloth are laminated and adhered, and the sheet-like foam is
A polishing member, wherein flexibility is imparted by the closed cells . Wherein said sheet-like foam was a foamed body made of natural rubber, synthetic rubber or thermoplastic elastomer
Te, (1) a thickness of 0.2 to 2 mm, (2) cell diameter 0.05 to 1 mm, (3) the bubble content (percentage of the bubble volume for foam volume) 70-98%, (4 ) abrasive member according to claim 1, the compression modulus of 10 to 100 g / mm ^2, characterized in that. 3. The polishing member according to claim 1, wherein the polishing cloth is of a suede type or a velor type. 4. A sheet-like foam of closed cells made of a soft rubber-like elastic material on a surface of a polishing platen , and a sheet-like foam on the sheet-like foam.
Abrasive cloth is laminated and bonded, and the sheet-like foam is
A wafer polishing apparatus characterized in that flexibility is imparted by the closed cells . Wherein said sheet-like foam was a foamed body made of natural rubber, synthetic rubber or thermoplastic elastomer
Te, (1) a thickness of 0.2 to 2 mm, (2) cell diameter 0.05 to 1 mm, (3) the bubble content (percentage of the bubble volume for foam volume) 70-98%, (4 ) the polishing apparatus according to claim 4, the compression modulus of 10 to 100 g / mm ^2, characterized in that. 6. The polishing apparatus according to claim 4, wherein said polishing cloth is of a suede type or a velor type.