JP2006228823A - Composition for polishing metal film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a composition for polishing a metal film of which the selectivity can be controlled to any value. <P>SOLUTION: The composition for polishing a metal film contains fumed silica as abrasive grains. The specific surface area of the fumed silica is not less than 50 m<SP>2</SP>/g nor more than 190 m<SP>2</SP>/g, and a half-value width in the particle size distribution is less than 0.1 μm. By adjusting the specific surface area and the half-value width in the particle size distribution of the fumed silica within a predetermined range, the selectivity which is a ratio of a metal film polishing speed to an oxide film polishing speed can be controlled to any value. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a polishing composition used for CMP polishing treatment, and more particularly to a metal film polishing composition used when polishing a metal film.

  In the field of semiconductor manufacturing, with the high integration by miniaturization and multilayering of semiconductor elements, the planarization technology of semiconductor layers and metal layers has become an important elemental technology. When forming an integrated circuit on a wafer, if the layers are stacked without flattening the unevenness due to the electrode wiring or the like, the step becomes large and the flatness becomes extremely poor. Further, when the step becomes large, it becomes difficult to focus on both the concave portion and the convex portion in photolithography, and miniaturization cannot be realized. Therefore, it is necessary to perform a planarization process for removing irregularities on the wafer surface at an appropriate stage during the lamination. For the flattening process, an etching back method for removing uneven portions by etching, a film forming method for forming a flat film by plasma CVD (Chemical Vapor Deposition), a fluidizing method for flattening by heat treatment, a concave portion by selective CVD, etc. There is a selective growth method for embedding.

  The above method has problems that it is appropriate depending on the type of film such as an insulating film and a metal film, and that the region that can be flattened is extremely narrow. As a planarization technique that can overcome such problems, there is planarization by CMP (Chemical Mechanical Polishing).

  In the flattening process by CMP, while the polishing composition in which fine silica particles (abrasive grains) are suspended is supplied to the surface of the polishing pad, the pressed polishing pad and the silicon wafer as the object to be polished are relatively moved. By polishing the surface, the wafer surface over a wide range can be flattened with high accuracy.

  In the planarization process of a metal film such as tungsten (W), the selection ratio, which is the ratio between the metal film polishing rate and the oxide film polishing rate, is greatly related to the process capability and the yield. The selectivity is emphasized as a characteristic of the composition. However, although the selectivity required by each semiconductor product is different, the selectivity performance exhibited by each polishing composition is one, so it is necessary to perform adjustment according to the conditions of the planarization process. . Specifically, in order to polish the W thin film quickly in the initial stage of polishing, it is necessary to increase the polishing load, the number of rotations of the polishing pad, the number of rotations of the carrier, the slurry flow rate, etc., and polishing is performed when the oxide film is exposed. However, when polishing is performed under the polishing conditions in the initial stage of polishing as described above, dishing and erosion of W occur. Therefore, it is necessary to change the conditions such as lowering the polishing load, the polishing pad rotational speed, the carrier rotational speed, and the slurry flow rate from the initial polishing conditions.

  The slurry described in Patent Document 1 includes an oxidizing agent and a catalyst having a multi-oxidation site, and increases the polishing rate of tungsten and titanium. The slurry described in Patent Document 2 includes alcohol amine and increases the polishing rate of polysilicon. The selection ratio is changed by increasing the value.

Japanese Patent Laid-Open No. 10-265766 Japanese translation of PCT publication No. 2002-525383

  The selection ratio of the metal film polishing composition is unknown unless polishing is actually performed using the composition, and optimization is difficult because trial and error are necessary to optimize the polishing conditions.

  In addition, when the selection ratio is changed, as described in Patent Documents 1 and 2, it is necessary to add a new additive or change the chemical component composition. There is a problem that it gets worse and contamination occurs.

  An object of the present invention is to provide a metal film polishing composition capable of arbitrarily controlling the selection ratio.

The present invention is a metal film polishing composition containing fumed silica as abrasive grains,
The fumed silica has a specific surface area of 50 m ² / g or more and 190 m ² / g or less, and a half-value width in a particle size distribution is less than 0.1 μm.

The present invention is further characterized by further containing an oxidizing agent and an organic acid.
In addition, the present invention is characterized in that the oxidizing agent is one or more selected from the group consisting of iodate, peroxide, nitrate, oxide metal and chloride metal.

  Further, in the present invention, the organic acid is malonic acid, lactic acid, pyrophosphoric acid, acetic acid, phosphoric acid, carboxylic acid, phthalic acid, oxalic acid, amino acid, malic acid, citric acid, tartaric acid, nicotinic acid, adipic acid, and these It is characterized in that it is one or more selected from the group consisting of these derivatives.

According to this invention, it is a composition for metal film polishing which contains a fumed silica as an abrasive grain.
The specific surface area of the fumed silica is 50 m ² / g or more and 190 m ² / g or less, and the half width in the particle size distribution is less than 0.1 μm.

  By controlling the specific surface area of the fumed silica and the half width in the particle size distribution, the selection ratio which is the ratio between the metal film polishing rate and the oxide film polishing rate can be arbitrarily controlled.

  If the selection ratio can be controlled, trial and error for finding the optimum polishing conditions is unnecessary, and even if the polishing stage changes such as the initial stage or the final stage, it is not necessary to change the polishing conditions.

  According to the invention, the metal film polishing composition can further improve the polishing characteristics by further containing an oxidizing agent and an organic acid.

  As the oxidant, one or more selected from the group consisting of iodate, peroxide, nitrate, oxide metal, and chloride metal can be used. As the organic acid, malonic acid, One or two selected from the group consisting of lactic acid, pyrophosphoric acid, acetic acid, phosphoric acid, carboxylic acid, phthalic acid, oxalic acid, amino acid, malic acid, citric acid, tartaric acid, nicotinic acid, adipic acid, and derivatives thereof More than seeds can be used.

The present invention includes fumed silica as abrasive grains, the specific surface area of the fumed silica is 50 m ² / g or more and 190 m ² / g or less, and the half width in the particle size distribution is less than 0.1 μm. A metal film polishing composition.

  The ratio between the metal film polishing rate and the oxide film polishing rate is adjusted by adjusting the specific surface area of fumed silica and the half-value width in the particle size distribution (hereinafter simply referred to as “half-value width”) to a predetermined range. It is possible to control the selection ratio. FIG. 1 is a schematic diagram for explaining the half width. As shown in FIG. 1, the half width is a distribution width that is half (1/2) of the maximum value in a curve representing a mountain-shaped distribution such as a particle size distribution.

The specific surface area of fumed silica is preferably 50 m ² / g or more and 190 m ² / g or less, and the half-value width is preferably less than 0.1 μm. The half width is more preferably less than 0.075 μm, particularly preferably less than 0.06 μm, and particularly preferably 0.02 μm or more.

  The selection ratio of the metal film polishing composition is unclear unless polishing is actually performed using the composition, and trial and error are necessary to optimize the polishing conditions. By selecting the specific surface area and half-value width of fumed silica within an appropriate range, the selection ratio can be controlled to a desired value, and the polishing conditions can be easily optimized.

  Moreover, in order to obtain a desired selection ratio, it is not necessary to change the chemical composition or add new additives, so the polishing characteristics other than the selection ratio such as the surface roughness of the object to be polished may vary greatly, and contamination Thus, the polishing conditions can be easily optimized.

  The content of fumed silica is not particularly limited, and is preferably about the same as an existing metal film polishing composition, for example, 0.1 wt% or more and 26 wt% or less. If it is less than 0.1% by weight, the function as abrasive grains is not sufficient, and if it exceeds 26% by weight, the content of other components is affected.

  The present invention can improve polishing characteristics such as a polishing rate by including an oxidizing agent and an organic acid in addition to fumed silica. Examples of the oxidizing agent include one or more selected from the group consisting of iodate, peroxide, nitrate, oxide metal, and chloride metal. Examples of the organic acid include malonic acid, lactic acid, and pyrophosphoric acid. , Acetic acid, phosphoric acid, carboxylic acid, phthalic acid, oxalic acid, amino acid, malic acid, citric acid, tartaric acid, nicotinic acid, adipic acid, and one or more selected from the group consisting of these derivatives It is done.

  The contents of the oxidizing agent and the organic acid are not particularly limited, and may be the same as those of the existing metal film polishing composition.

  2-5 is a figure which shows the particle size distribution of the composition for metal film polishing. The vertical axis represents frequency (%), and the horizontal axis represents particle size (μm).

The particle size distribution was measured under the following conditions.
-Fumed silica Specific surface area: 50 m ² / g (Example 1), 90 m ² / g (Example 2), 130 m ² / g (Example 3), 200 m ² / g (Comparative Example 1)
Content: 5% by weight
・ Oxidizing agent (potassium iodate, hydrogen peroxide solution)
Content: 3% by weight (potassium iodate), 2% by weight (hydrogen peroxide solution)
・ Organic acid (malonic acid)
Content: 2% by weight
Particle size measurement: Laser diffraction / scattering particle size distribution analyzer (Horiba, Ltd .: LA920)

FIG. 2 shows the particle size distribution of Example 1 in which the specific surface area of fumed silica is 50 m ² / g. It can be seen from the graph shown in FIG. 2 that the half-value width W1 of the particle size distribution is 0.025 μm. FIG. 3 shows the particle size distribution of Example 2 in which the specific surface area of fumed silica is 90 m ² / g. From the graph shown in FIG. 3, it can be seen that the half width W2 of the particle size distribution is 0.045 μm. FIG. 4 shows the particle size distribution of Example 3 in which the specific surface area of fumed silica is 130 m ² / g. It can be seen from the graph shown in FIG. 4 that the half-value width W3 of the particle size distribution is 0.05 μm. FIG. 5 shows the particle size distribution of Comparative Example 1 in which the specific surface area of fumed silica is 200 m ² / g. It can be seen from the graph shown in FIG. 5 that the half width W4 of the particle size distribution is 0.1 μm.

  Next, using each example, a tungsten (W) film as a metal film and a TEOS (Tetraethoxysilane) film as an oxide film were polished, and the polishing rate was measured. The polishing rate is the film thickness (Å) removed by polishing per unit time. In Comparative Example 1, since the viscosity was very high and there were many aggregated particles, the polishing rate could not be measured.

  FIG. 6 is a diagram showing the results of measuring the polishing rate of the W film when each example is used. FIG. 7 is a diagram showing the results of measuring the TEOS film polishing rate when each example is used.

The polishing rate during W film polishing and TEOS film polishing was measured under the following conditions.
Polishing pad rotation speed: 120 rpm
Carrier rotation speed: 64 rpm
Slurry flow rate: 26 ml / min
Polishing time: 60 seconds Polishing load: 5 psi (3.4 × 10 ⁴ Pa)

  As shown in FIG. 6, it can be seen that the larger the specific surface area of fumed silica, the higher the polishing rate of the W film. Further, as shown in FIG. 7, it can be seen that the polishing rate of the TEOS film is substantially constant regardless of the specific surface area of the fumed silica.

  FIG. 8 is a diagram showing a selection ratio which is a ratio between the W film polishing rate and the TEOS film polishing rate. It can be seen from the above characteristics indicating the polishing rate that the selectivity of each example increases as the specific surface area of fumed silica increases, and decreases as the specific surface area of fumed silica decreases.

  The metal film is oxidized by the oxidizing agent and the surface state becomes very brittle. When fumed silica with the same concentration, small half width, and different specific surface area is used, fumed silica with a large specific surface area has a larger number of particles compared to those with a small specific surface area. It is considered that the polishing rate becomes faster because it exists in the object. On the other hand, it is considered that the surface of the oxide film is harder than that of the metal film under acidity, and does not depend on the number of particles, that is, does not depend on the specific surface area and has a constant polishing rate.

Thus, by adjusting the specific surface area of the fumed silica and the half-value width in the particle size distribution to a predetermined range, the selection ratio of the metal film polishing composition containing fumed silica can be controlled. Conventionally, when performing metal film polishing, it has been necessary to find the optimum polishing conditions for each polishing stage by trial and error, and to perform planarization while changing the found polishing conditions. For example, in the initial stage, polishing is performed under the conditions of a polishing pad rotational speed of 65 rpm, a carrier rotational speed of 65 rpm, a slurry flow rate of 150 ml / min, and a polishing load of 5 psi (3.4 × 10 ⁴ Pa), and in the final stage, the polishing pad rotational speed of 60 rpm. Then, polishing is performed by changing the conditions to a carrier rotation speed of 60 rpm, a slurry flow rate of 100 ml / min, and a polishing load of 3 psi (2.1 × 10 ⁴ Pa).

  Since the metal film polishing composition of the present invention can control the selection ratio, trial and error for finding the optimum polishing conditions is not necessary, and even if the polishing stage changes, the slurry having a different selection ratio. It is only necessary to supply, and it is not necessary to change the polishing conditions.

  In the above, a tungsten film is used as the metal film. This is because a remarkable effect is seen with respect to the polishing of the tungsten film. Even when a metal film such as is used, the same effect is obtained.

It is a schematic diagram for demonstrating a half value width. It is a figure which shows the particle size distribution of the composition for metal film polishing (Example 1). It is a figure which shows the particle size distribution of the composition for metal film polishing (Example 2). It is a figure which shows the particle size distribution of the composition for metal film polishing (Example 3). It is a figure which shows the particle size distribution of the composition for metal film polishing (comparative example 1). It is a figure which shows the polishing rate measurement result of W film | membrane when using each Example. It is a figure which shows the polishing rate measurement result of a TEOS film when using each Example. It is a figure which shows the selection ratio which is ratio of W film | membrane polishing rate and TEOS film | membrane polishing rate.

Claims (4)

A metal film polishing composition containing fumed silica as abrasive grains,
A metal film polishing composition, wherein the fumed silica has a specific surface area of 50 m ² / g or more and 190 m ² / g or less, and a half-value width in a particle size distribution is less than 0.1 μm.   The metal film polishing composition according to claim 1, further comprising an oxidizing agent and an organic acid.   3. The metal film polishing apparatus according to claim 2, wherein the oxidizing agent is one or more selected from the group consisting of iodate, peroxide, nitrate, oxide metal, and chloride metal. Composition.   The organic acid is a group consisting of malonic acid, lactic acid, pyrophosphoric acid, acetic acid, phosphoric acid, carboxylic acid, phthalic acid, oxalic acid, amino acid, malic acid, citric acid, tartaric acid, nicotinic acid, adipic acid, and derivatives thereof The metal film polishing composition according to claim 2, wherein the composition is one or more selected from the above.

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