JPH0950974A - Polishing cloth and method for manufacturing semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the fluctuation of the elastic modulus of a polishing cloth as a whole even when the cloth is worn to a thin thickness by giving a hardness gradient to the cloth in the thickness direction. SOLUTION: A polishing cloth 6 is manufactured by laminating a hard layer composed of polyurethane as an upper layer 6a on a soft layer composed of polyurethane formed as a lower layer 6a. In the initial state, the elastic modulus of the upper layer 6b is lower than that of the lower layer 6a and the cloth 6 is deformed by the pressure applied to a polishing head at the polishing time, because the hard upper layer 6b having a hardness gradient is formed on the soft lower layer 6a. Since the deforming of the cloth 6 is limited to the upper layer 6b, the elastic modulus of the cloth 6 when the cloth 6 is deformed becomes that of the upper layer 6b. When the upper layer 6b is worn, the deforming region reaches the lower layer 6a and the elastic modulus when the cloth 6 is deformed becomes the composite elastic modulus of the upper and lower layers 6b and 6a. Since the elastic modulus of the upper layer 6b when the layer 6b is worn is higher than the initial elastic modulus of the layer 6b, the composite elastic modulus does not change from the initial value.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polishing cloth and a method for manufacturing a semiconductor device, and more particularly to a polishing cloth suitable for polishing an interlayer insulating film applied to the field of manufacturing semiconductor devices and a semiconductor using this polishing cloth. The present invention relates to a method of manufacturing a manufacturing device.

[0002]

2. Description of the Related Art Conventionally, a polishing technique has been used in order to flatten the unevenness formed on a substrate such as a semiconductor substrate during the manufacture of a semiconductor device (for example, Japanese Patent Laid-Open No. 60-3983).
5). On the other hand, in the field of semiconductor devices, the scale of integrated circuits is increasing, but in order to increase the scale, it is necessary to make the area of the integrated circuit chip as small as possible, and there is a need for multilayer wiring technology. Has been done. In this multilayer wiring technique, it is necessary to make the surface of the underlayer as flat as possible in order to prevent disconnection of the multilayer wiring. In recent years, a mechanochemical polishing technique using fine particles of silicon oxide in a basic solvent has been developed as a planarization technique.

[0003]

However, in this mechanochemical polishing technique, a polyurethane cloth is generally used as the polishing cloth used for polishing, and the shape after polishing is dependent on the hardness of this resin. Is known to be greatly affected. For example, as shown in FIG. 6A, the wiring layer 2 made of aluminum is formed on the semiconductor substrate 1.
Consider a case where the wafer 4 having the interlayer insulating layer 3 made of silicon oxide film is polished. Polishing cloth 6
When a relatively soft material is used for the substrate, it is possible to follow the local unevenness of the film thickness of the semiconductor substrate 1 as shown in FIG. 6 (a), but the polishing cloth 6 is deformed by the pressing pressure, resulting in unevenness. As a result, the flatness after polishing depends on the uneven shape.

Further, when a hard polishing cloth is used, FIG.
As shown in (b), since the polishing pad 6 is not deformed, the bottom portion of the unevenness is not polished, but it cannot follow the local fluctuation of the film thickness of the wafer 4, and therefore the flatness after polishing is not achieved. The sex is not good. Further, in order to avoid the occurrence of these problems, as shown in FIG. 6 (c), there has been proposed a polishing cloth 6 using soft polyurethane for the lower layer 6a and hard polyurethane for the upper layer 6b.

However, when the polishing cloth 6 is used for polishing, the deformation of the polishing cloth 6 due to the pressing pressure during polishing extends not only to the hard polyurethane of the upper layer 6b but also to the soft polyurethane of the lower layer 6a. That is, the elastic modulus of the polishing cloth is a physical property calculated by the composite elastic modulus of the upper layer 6b and the lower layer 6a. Therefore, it was revealed that when the upper layer 6b having a high elastic modulus is reduced by polishing, the elastic modulus of the polishing cloth becomes close to that of the lower layer 6a and the flatness of the wafer 4 after polishing deteriorates. Therefore, there is a need for a polishing cloth and a manufacturing technique for the polishing cloth, in which the elastic modulus of the polishing cloth as a whole does not fluctuate even when it is consumed and the thickness thereof is reduced.

[0006]

In order to solve the above problems, the invention according to claim 1 is a method for carrying out polishing while holding a material to be polished, bringing a polishing cloth into contact with the material to be polished, and supplying an abrasive. In the polishing cloth used in the above, the polishing cloth is characterized by having a hardness gradient in the thickness direction so that the composite elastic modulus of the polishing cloth does not change between the initial state and the worn state.

According to a second aspect of the present invention, the polishing cloth has a hardness gradient formed by laminating polishing cloths having different hardnesses, and the polishing cloth has a composite elastic modulus. The initial state and the worn state did not change.

According to a third aspect of the present invention, the polishing cloth has a hardness gradient provided by controlling the density of the material, and the polishing cloth has a structure in which the composite elastic modulus of the polishing cloth is in an initial state. I tried not to change it when worn.

According to a fourth aspect of the invention, the polishing cloth has a hardness gradient by controlling the degree of cross-linking of the material. I tried not to change between the condition and the worn condition.

According to a fifth aspect of the present invention, in the step of forming the insulating film for flattening the insulating film on the material to be polished, polishing is performed using a polishing cloth having a hardness gradient in the thickness direction. With the configuration of the method for manufacturing a semiconductor device, the elastic modulus of the polishing cloth does not change even when worn, and polishing with good flatness between wafers can be performed.

The polishing cloth according to the present invention and the polishing method using the same will be described below with reference to embodiments.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION First Embodiment A first embodiment of the present invention will be described with reference to FIGS. 1 and 2. As shown in FIG. 1A, a polishing cloth 6 was prepared by laminating a soft layer made of polyurethane as a lower layer 6a and a hard layer made of polyurethane as an upper layer 6b. Specifically, in the polyurethane soft layer of the lower layer 6a, a polyol formed by using ethylene glycol as a diol component and adipic acid as a dicarboxylic acid is added with 4,4-methylenediphenyldiisocyanate and ethylene glycol as a chain extender. The polyurethane thus prepared was prepared by adding a tri- or more-functional triisocyanate obtained by reacting glycerin and hexamethylene diisocyanate to carry out a crosslinking reaction.

The polyurethane hard layer of the upper layer 6b is a polyurethane prepared by using 1,4 butanediol as a diol component and terephthalic acid as a dicarboxylic acid in a polyol prepared by changing the addition amounts of ethylene glycol and 4,4 methylenediphenyl diisocyanate. Resin 0.2m
10 sheets having a thickness of m were prepared. The lower layer 6a and the upper layer 6b formed by this method were pressure-bonded to each other to form a bonded polishing cloth 6.

The polishing cloth having a hardness gradient structure according to the first embodiment has an initial state, as shown in FIG. 1A, in which the upper layer 6b of the hard layer having the hardness gradient is formed on the lower layer 6a of the soft layer.
Are formed. The upper layer 6b of the hard layer has a low elastic modulus and the lower layer 6a has a high elastic modulus, and is deformed by the pressure applied to the polishing head during polishing. Since the polishing cloth deformation region is limited to the upper layer 6b, the elastic modulus at the time of deformation is the elastic modulus of the upper layer 6b of the hard layer (see FIG. 1B). In the state where the upper layer 6b is worn as shown in FIG. 2A, the deformation region is up to the lower layer polishing cloth, and the elastic modulus at the time of deformation is the composite elastic modulus of the hard layer upper layer 6a and the soft layer lower layer 6a (see FIG. 2 (b)). Since the upper layer 6b of the hard layer at this time has a higher elastic modulus than the initial elastic modulus, the composite elastic modulus does not change from the initial value, and if the material to be polished is polished using this polishing cloth, the flatness No deterioration occurs.

Second Embodiment The second embodiment embodies a structure of a polishing cloth in which the degree of crosslinking of the upper layer 6b is controlled to give a hardness gradient. Specifically, the polyurethane of the lower layer 6a is a polyurethane prepared by adding 4,4-methylenediphenyl diisocyanate and a glycol prepared by using ethylene glycol as a diol component and adipic acid as a dicarboxylic acid and ethylene glycol as a chain extender. Trifunctional or more triisocyanate obtained by reacting glycerin and hexamethylene diisocyanate was added and a cross-linking reaction was carried out to prepare. Upper layer 6
The polyurethane hard layer of b is produced by adding ethylene glycol as a diol component and terephthalic acid as a dicarboxylic acid to a polyol produced by adding ethylene glycol and 4,4-methylenediphenyldiisocyanate obtained by modifying an unterminated isocyanate group with acrylic acid. did.

[0016] Then, it is made to be able to be crosslinked by ultraviolet rays and electron beams by modifying with acrylic. Then, the surface of the upper layer 6b was irradiated with ultraviolet rays to be crosslinked. The ultraviolet rays cause a crosslinking reaction in the upper layer portion, but the ultraviolet rays do not reach the lower layer gradually and the crosslinking reaction does not occur. Therefore, the degree of crosslinking differs in the depth direction, and the resin hardness has a hardness distribution in the depth direction.
After that, the upper layer resin and the lower layer resin were pressure bonded to produce a polishing cloth.

The effect that the total elastic modulus of the polishing cloth does not change from the initial state after several polishing operations is similar to that of the first embodiment, and a polishing cloth suitable for mass production can be provided.

Third Embodiment In the third embodiment, a method of manufacturing a semiconductor device using the polishing cloth shown in the above-described first and second embodiments is embodied. Prior to the description of the polishing process, the configuration of the polishing apparatus used to carry out the present invention will be described with reference to FIG. The wafer (material to be polished) 4 is fixed by a vacuum chuck type wafer holding table 7.

On the other hand, a polishing cloth 6 is fixed to the polishing table 5, and an abrasive 8 is supplied onto the polishing cloth 6 from an abrasive supply pipe 9. Then, the wafer holder 7 is rotationally driven by a holder rotating shaft 7a connected thereto, and the polishing table 5 is rotationally driven by a polishing table rotating shaft 5a connected thereto to perform polishing. During polishing, an appropriate polishing operation is performed by controlling the pressure with which the wafer holding table 7 is pressed against the polishing table 5.

Suitable polishing conditions include, for example, the following. Polishing conditions Number of rotations of wafer holder rotation axis 37 [rpm] Number of rotations of wafer holder 17 [rpm] Polishing pressure 5.5 × 10 ³ [Pa] Polishing agent flow rate 200 [ml / min]

Here, a process applied to the removal of the convex insulating film in the process of forming the interlayer film in the method of manufacturing a semiconductor device using the above-described polishing apparatus will be described with reference to FIG. First, as shown in FIG. 4A, after forming a first silicon oxide film 1a on a semiconductor substrate 1 made of silicon, an aluminum wiring layer 2 was formed by photolithography and reactive ion etching.

Next, as shown in FIG. 4B, a second silicon oxide film (interlayer insulating layer) 3 was formed under the following conditions. Deposition conditions of silicon oxide film Source gas TEOS = 800 [sccm] Oxygen O ₂ = 600 [sccm] Pressure 1330 [Pa] Temperature 400 [° C.] RF output 700 [W] However, TEOS is Tetra Ethyl Ortho
Abbreviation for Silicate.

Thereafter, the second film formed as described above
In order to polish and remove the convex portions of the silicon oxide film 3, the wafer 4 was held on the wafer holding table 7 of the polishing apparatus, and the surface to be polished of the wafer 4 was polished using the above-mentioned polishing apparatus. As a result, the convex portion of the second silicon oxide film 3 was removed as shown in FIG. After that, even if the polishing agent was removed using a hydrofluoric acid aqueous solution, the surface of the interlayer insulating film 3 was not roughened.

By polishing the wafer 4 as described above, the second silicon oxide film (interlayer insulating film) is obtained.
3 is flattened. As a result of continuously polishing for 700 minutes using these conditions, as shown in FIG. 5, when the conventional polishing cloth is used, the upper polishing cloth film thickness is 1 / th that of the initial polishing cloth.
When the value becomes 3, the flatness is greatly deteriorated, but the polishing cloth of the first embodiment does not change the elastic modulus, and the result that the flatness is not impaired in the polishing step is obtained compared to the initial state.

[0025]

According to the polishing cloth of the present invention, the initial elastic modulus and the elastic modulus after abrasion do not change, and if a material to be polished is polished using this polishing cloth, polishing with good flatness can be achieved. It

[Brief description of drawings]

FIG. 1A is a cross-sectional view of a polishing cloth in an initial state of the present invention, and FIG. 1B is a graph showing a gradient of elastic modulus with respect to its thickness.

FIG. 2 (a) is a cross-sectional view of the abrasive cloth of the present invention after abrasion, and FIG. 2 (b) is a graph showing a gradient of elastic modulus with respect to its thickness.

FIG. 3 is a side view of a polishing apparatus used in the present invention.

FIG. 4 is a side sectional view of a wafer showing a manufacturing process of a semiconductor device.

FIG. 5 is a graph showing the flatness of the polished surface of the material to be polished and the polishing time dependency.

6A and 6B are side sectional views of a conventional polishing cloth and a material to be polished, wherein FIG. 6A is an example using a soft polishing cloth, FIG. 6B is an example using a hard polishing cloth, and FIG. ) Indicates an example using a multilayer polishing cloth.

[Explanation of symbols]

 1 Semiconductor Substrate 1a First Silicon Oxide Film 2 Aluminum Wiring Layer 3 Second Silicon Oxide Film (Interlayer Insulation Layer) 4 Wafer (Material to be Polished) 5 Polishing Table 5a Polishing Table Rotating Table 6 Polishing Cloth 6a Lower Layer 6b Upper Layer 7 Wafer Holding table 7a Holding table rotating table 8 Abrasive 9 Abrasive supply pipe

Claims (5)

[Claims] 1. A polishing cloth used for a method of holding a material to be polished, bringing a polishing cloth into contact with the material to be polished, and performing polishing while supplying an abrasive, wherein the polishing cloth has a hardness gradient in a thickness direction. Characteristic polishing cloth. 2. The polishing cloth according to claim 1, wherein the polishing cloth has a hardness gradient obtained by laminating polishing cloths having different hardnesses. 3. The polishing cloth according to claim 1, wherein the polishing cloth is provided with a hardness gradient by controlling the density of the material. 4. The polishing cloth according to claim 1, wherein the polishing cloth is provided with a hardness gradient by controlling the degree of crosslinking of the material. 5. A method of manufacturing a semiconductor device, characterized in that, in the step of forming an insulating film for flattening an insulating film on a material to be polished, polishing is performed using a polishing cloth having a hardness gradient in the thickness direction. .