JP2007063374A - Additive for polishing composition - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an additive for a polishing composition capable of achieving stable polishing characteristics. <P>SOLUTION: The additive for a polishing composition is added to a polishing composition (slurry) which was used at least once. This additive is an aqueous solution of one or a plurality of amine compounds, wherein the amine compound comprises a quaternary ammonium salt. Highly alkaline tetramethylammonium hydroxide (TMAH) is particularly preferred as the quaternary ammonium salt. When an amine compound is contained in the polishing composition in advance, the same amine compound as contained in the polishing composition is preferably contained. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an additive for polishing composition added to a polishing composition used at least once.

  Polishing of silicon wafers by CMP achieves high-precision flattening by performing multi-stage polishing of three stages or four stages. The primary polishing and secondary polishing performed in the first stage and the second stage mainly aim at surface smoothing and require a high polishing rate.

  In primary polishing and some secondary polishing, a slurry that is a polishing composition is generally circulated and repeatedly used. However, when used repeatedly, the pH of the slurry is lowered and the polishing characteristics are lowered. In particular, the reduction of the polishing rate is remarkable. Slurries whose properties have deteriorated to a certain extent need to be replaced with new slurries, but problems such as interruption of the process and an increase in cost occur for replacement.

  In order to prevent the polishing properties such as the polishing rate from deteriorating without replacement work, an inorganic alkaline solution such as potassium hydroxide or sodium hydroxide is added to the circulating slurry as needed, or the new slurry itself It is effective to add.

  Moreover, the polishing liquid for semiconductor wafer described in Patent Document 1 is used when polishing using a polishing tool in which abrasive grains are fixed, and sodium carbonate or potassium carbonate is mixed with sodium hydroxide or potassium hydroxide. Things are used.

JP 2002-252189 A

  When an inorganic alkaline solution such as potassium hydroxide or sodium hydroxide or a new slurry itself is added as needed, it is possible to suppress a decrease in the average polishing rate when polishing multiple times, but the polishing rate before and after the addition There is a problem that the variation in the polishing rate is large, such as a change in the thickness.

  An object of the present invention is to provide an additive for a polishing composition capable of realizing stable polishing characteristics.

The present invention relates to an additive for polishing composition added to a polishing composition used at least once.
An aqueous solution of one or more amine compounds,
The amine compound is an additive for a polishing composition containing a quaternary ammonium salt.

  Further, the present invention is an aqueous solution of two or more kinds of amine compounds, and the amine compound includes a quaternary ammonium salt, a primary amine compound having water solubility and water dispersibility, a secondary amine compound, a third It includes a primary amine compound and one or more amine compounds selected from polymer compounds having an amino group in the main chain or side chain.

  Moreover, this invention is an aqueous solution of 2 or more types of amine compounds, The said amine compound contains a quaternary ammonium salt and the same amine compound as the amine compound contained in the said polishing composition, It is characterized by the above-mentioned.

  In the invention, the quaternary ammonium salt is tetramethylammonium hydroxide.

  According to the present invention, the polishing composition additive is added to the polishing composition used at least once. The additive for polishing composition is an aqueous solution of one or more amine compounds, and the amine compound contains a quaternary ammonium salt.

  Accordingly, when the polishing composition is used a plurality of times, it is possible to realize stable polishing characteristics by preventing a decrease in the polishing rate and suppressing variations.

  According to the invention, when the polishing composition additive is an aqueous solution of two or more amine compounds, the amine compound is a quaternary ammonium salt, a primary having water solubility and water dispersibility. It is preferable to include one or more amine compounds selected from an amine compound, a secondary amine compound, a tertiary amine compound, and a polymer compound having an amino group in the main chain or side chain.

  According to the invention, when the polishing composition additive is an aqueous solution of two or more amine compounds, the amine compound is the same as the quaternary ammonium salt and the amine compound contained in the polishing composition. It preferably contains an amine compound.

  According to the invention, the quaternary ammonium salt is particularly preferably tetramethylammonium hydroxide.

  The present invention is an additive for a polishing composition added to a polishing composition (slurry) used at least once. The additive for polishing composition of the present invention is an aqueous solution of one or more amine compounds, and the amine compound contains a quaternary ammonium salt.

  For example, when a slurry that has been used once is collected and used repeatedly such that it is repeatedly used under the same conditions or the same polishing apparatus, the slurry that has been used once is collected and then subjected to another condition or another polishing. In the case of multistage use that is used multiple times in an apparatus or the like, by adding the additive for polishing composition of the present invention, it is possible to prevent deterioration of polishing characteristics and suppress variation.

  Since at least a quaternary ammonium salt is used as the amine compound, when two or more amine compounds are used, in addition to the quaternary ammonium salt, a water-soluble or water-dispersible primary amine compound or secondary amine compound is used. It is preferable to use one or more compounds selected from an amine compound, a tertiary amine compound, and a polymer compound such as polyalkyleneimine having an amino group in the main chain or side chain. Specific examples include ammonia, choline, monoethanolamine, aminoethylethanolamine, aminoethylpiperazine, piperazine, polyethyleneimine, and the like. As the quaternary ammonium salt, strong alkaline tetramethylammonium hydroxide (TMAH) is used. Is particularly preferred.

  Furthermore, when an amine compound is previously contained in the polishing composition, it is preferable that the same amine compound as the amine compound contained in the polishing composition is included.

  Therefore, when an amine compound is previously contained in the polishing composition, the additive for the polishing composition contains only the quaternary ammonium salt as the amine compound, or is included in the polishing composition with the quaternary ammonium salt. It is particularly preferred to contain the same amine compound as the amine compound being used.

  The pH of the additive for polishing composition is preferably 11 or more, and is more preferably 13 or more considering that it is diluted by being added to the polishing composition.

  Moreover, it is also possible to prevent metal contamination of the polishing wafer by adding an organic acid (chelating agent) to the polishing composition additive. This organic acid has an effect of forming a complex in the solution with metal ions generated in the polishing agent and from the polishing apparatus / environment and preventing metal contamination on the wafer surface and inside. The organic acid to be added is selected from a monocarboxylic acid having 2 to 6 carbon atoms, a dicarboxylic acid having 2 to 6 carbon atoms, a tricarboxylic acid having 3 to 6 carbon atoms, and ascorbic acid, and generally called a chelating agent. Acetic acid, hydroxyethylethylenediamine triacetic acid, diethylenetriaminepentaacetic acid, nitrilotriacetic acid, triethylenetetramine hexaacetic acid, hydroxyethyliminodiacetic acid, dihydroxyethylglycine, ethylene glycol-bis (β-aminoethyl ether) -N, N′-4 One or more selected from acetic acid and 1,2-diaminocyclohexane-N, N, N ′, N′-4 acetic acid can be added. The concentration of the organic acid depends on the polishing agent, the polishing apparatus / environment, and the required wafer purity, but is preferably 1 ppm or more and less than 1000 ppm.

  As described above, the additive for polishing composition is an aqueous solution of one or two or more amine compounds, and the amine compound contains a quaternary ammonium salt. By adding to the used slurry, it is possible to prevent a decrease in polishing characteristics and suppress variations.

  The timing for adding the polishing composition additive to the polishing composition will be described. FIG. 1 is a diagram showing the addition timing in the case of circulation use, and FIG. 2 is a diagram showing the addition timing in the case of using multiple stages (three stages). The timing of addition to the polishing composition is (1) before supplying the polishing composition to the polishing machine, (2) while the polishing composition is stored in the slurry tank, and (3) after recovering the polishing composition. Before returning to the slurry tank, (4) immediately after completion of polishing (between the polishing machine and the recovery tank) is preferable, and it can be added directly to the polishing composition and can be easily mixed by stirring. (2) Polishing composition Particularly preferred is the timing of addition while is stored in the slurry tank.

  It is desirable to adjust the addition amount of the polishing composition additive and the like appropriately by monitoring the pH, composition or polishing rate of the polishing composition and reducing the fluctuation.

Hereinafter, examples and comparative examples of the present invention will be described.
First, a polishing composition used for polishing and to which an additive for polishing composition is added will be described. The polishing composition was used after being diluted 40 times during polishing. The composition shown below is a diluted composition with the balance being water.

(Polishing composition)
Abrasive grain: 70 nm colloidal silica silica particles 0.30% by weight
Polishing accelerator: Piperazine 0.25% by weight

It shows about the composition of an example and a comparative example.
(Comparative Example 1)
No additive (Comparative Example 2)
Inorganic alkali: Potassium hydroxide 5.0% by weight
(Comparative Example 3)
Amine compound: Piperazine 3.0% by weight
Example 1
Amine compound: Tetramethylammonium hydroxide 1.5% by weight
Amine compound: Piperazine 3.0% by weight
(Example 2)
Amine compound: tetramethylammonium hydroxide 3.0% by weight

  In Comparative Example 1, no additive was used, and in Comparative Example 2, a potassium hydroxide aqueous solution was used as an inorganic alkali instead of an amine compound. In Comparative Example 3, piperazine was used as the amine compound, but no quaternary ammonium salt was used.

  In Example 1, tetramethylammonium hydroxide which is a quaternary ammonium salt and piperazine which is the same amine compound as the amine compound contained in the polishing composition were used as the amine compound. In Example 2, only tetramethylammonium hydroxide, which is a quaternary ammonium salt, was used as the amine compound.

For evaluation of the polishing characteristics, after dummy polishing was performed for 60 minutes, polishing was performed for 5 batches for 30 batches each. During the 5 batches of polishing, the additives of Comparative Examples 2 and 3 and Examples 1 and 2 were added to the slurry as needed to maintain the pH constant to maintain the pH of 10.5.
The polishing composition was recycled and an additive for the polishing composition was added when the tank was stored.

  The polishing rate was measured for each batch, and the average value of polishing rates in 5 batches and the variation in polishing rate between each batch were evaluated. In addition, the pad lifetime was evaluated by increasing the number of batches.

[Polishing rate]
The polishing rate is represented by the thickness (μm / min) of the wafer removed by polishing per unit time. The thickness of the wafer removed by polishing was calculated by measuring the reduction in wafer weight and dividing by the area of the polished surface of the wafer.

・ Polishing conditions Polishing pad: MH-S15A (Suba800 is used for pad lifetime evaluation) (made by Nitta Haas)
Polishing equipment: Strasbaugh20 "single wafer type platen rotation speed: 115rpm
Pressure head rotation speed: 100rpm
Slurry flow rate: 300ml / min (100ml / min at pad lifetime evaluation)
Load surface pressure: 30kPa (300gf / cm ² )
Polishing time: 30min
Rinse time: 15 sec
Silicon wafer: 6inch × 1
Slurry pH: 10.5 (excluding Comparative Example 1)

  FIG. 3 is a graph showing changes in the average polishing rate and the variation in polishing rate due to the additive. The vertical axis (left) shows the average value of the polishing rate (μm / min) in 5 batches, and the vertical axis (right) shows the coefficient of variation (%) representing the variation among the 5 batches.

  When no additive is used as in Comparative Example 1, the polishing rate gradually decreases as the number of batches increases, so the average value of the polishing rate is low and the coefficient of variation is about 2%. The variation was also large.

  In the case of Comparative Example 2, the use of potassium hydroxide suppressed the decrease in the average polishing rate to some extent, but the variation coefficient was about 1.7% and the variation was large.

  In the case of Comparative Example 3, the composition was only piperazine, and the amount of piperazine added to maintain the pH of 10.5 was larger than in the other examples. Although the decrease in the average value of the polishing rate was suppressed, the variation coefficient exceeded 2%, and the variation was larger than that of Comparative Example 1.

  In the case of Examples 1 and 2, a decrease in the average value of the polishing rate was suppressed, and the variation coefficient was about 0.7% and the variation was very small. The average value of the polishing rate of Example 1 was higher than that of Example 2.

  FIG. 4 is a graph showing the evaluation results of the pad lifetime. The vertical axis represents the polishing rate, and the horizontal axis represents the number of batches. As the number of batches increases, the polishing rate decreases, but in the case of Example 1, the decrease is gradual compared to the case of Comparative Example 2, the polishing rate becomes stable, and the pad surface is clogged (glazing). ) Is unlikely to occur.

  In the primary polishing of a silicon wafer, generally, a slurry is circulated. Therefore, the silicon compound generated from the polished silicon wafer is contained in the slurry in the same manner as the silica abrasive grains in the slurry. The dispersion state of the silicon compound and the silica abrasive grains becomes unstable due to long-term circulation and forms coarse foreign matters. This foreign matter adversely affects the surface roughness of the wafer or adheres to the surface of the polishing pad to cause glazing.

In order to confirm the dispersion stability of the silica abrasive grains and the polished silicon compound in the slurry, each zeta potential was measured when the additive was added. Measuring device is Dispersion
Technology DT-1200 was used. As the silica abrasive grains, pH-neutral colloidal silica abrasive grains (particle diameter 70 nm) were used, and as the silicon compound, silicon powder (particle diameter 3 μm) was used.

  FIG. 5 is a graph showing a change in zeta potential of colloidal silica, and FIG. 6 is a graph showing a change in zeta potential of silicon powder. Each vertical axis represents zeta potential, and the horizontal axis represents pH. The pH was changed by changing the amount of additive added.

  When the addition amount of Example 1 was increased, the value of the zeta potential tended to be almost constant or more stable. When the addition amount of Comparative Example 2 was increased, both colloidal silica and silicon powder tended to be unstable. It was found that by using the additive of Example 1, not only the colloidal silica abrasive grains but also the silicon compound produced by polishing maintained a more electrically stable state in the slurry. This is a result confirming the evaluation result of the pad lifetime, and it became clear that glazing was prevented by using Example 1.

It is a figure which shows the addition timing in the case of circulation use. It is a figure which shows the addition timing in the case of multistage use. It is a graph which shows the change of the average value of the polishing rate by an additive, and the dispersion | variation in polishing rate. It is a graph which shows the evaluation result of pad lifetime. It is a graph which shows the change of the zeta potential of colloidal silica. It is a graph which shows the change of the zeta potential of silicon powder.

Claims (4)

In the additive for polishing composition added to the polishing composition used at least once,
An aqueous solution of one or more amine compounds,
The additive for polishing compositions, wherein the amine compound contains a quaternary ammonium salt.   An aqueous solution of two or more amine compounds, the amine compound comprising a quaternary ammonium salt, a water-soluble and water-dispersible primary amine compound, a secondary amine compound, a tertiary amine compound, and The additive for polishing composition according to claim 1, comprising one or more amine compounds selected from polymer compounds having an amino group in the main chain or side chain.   The aqueous solution of two or more kinds of amine compounds, wherein the amine compound includes a quaternary ammonium salt and the same amine compound as the amine compound contained in the polishing composition. Polishing composition additive.   The additive for polishing composition according to any one of claims 1 to 3, wherein the quaternary ammonium salt is tetramethylammonium hydroxide.

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