KR100447540B1 - pollishing slurry for silicon wafer - Google Patents

Abstract

The present invention relates to a slurry for removing SP1 defects in a silicon wafer, comprising 0.25 to 12 percent by weight of silica particles containing nitrogenated organic salts and organic acids that are directly related to the removal of SP1 defects and having an average particle diameter of 10 to 50 nm. Ammonia is used so as to have a pH of 10.5 to 11.5, and a slurry composed of cellulose polymers so as to have a viscosity of 2 to 40 cP is used for intermediate polishing and final polishing in a three-step polishing process of a silicon wafer. This relatively reduced effect, especially when used as an intermediate polishing agent has an excellent effect of controlling less than 10 SP1 defects that cause problems in DRAM manufacturing compared to the conventional process. As a result, defects on the surface of the wafer are reduced, thereby improving planarization.

Description

Polishing slurry for silicon wafer

The present invention relates to a slurry for removing defects of SP1 of a silicon wafer and a method of using the same, in particular, in addition to nitrogenated organic salts such as choline chloride used to remove SP1 defects, which are surface defects caused by mechanical polishing during polishing of silicon wafers. In particular, the present invention relates to a polishing slurry for silicon wafers that effectively removes metal oxides or metal impurities such as alumina particles, including organic salts such as citric acid.

In general, a silicon wafer serving as a substrate in semiconductor manufacturing is a multi-step process of single crystal growing, slicing, lapping, etching, mirror polishing, and cleaning. It is manufactured through.

The final polishing process, which is the final stage of the various manufacturing processes, is a process in which the surface of a silicon wafer is polished with a fine particle abrasive to make it a mirror surface, and the surface or subsurface defects generated in the previous stage, namely, The defects of scratches, cracks, grain distortion, surface roughness and topography are removed and processed into a defect-free mirror wafer.

This polishing process requires two important consumables in addition to polishers and ultra pure water: pads, soft or hard polyurethane polishing cloths, and slurry, abrasives.

On the other hand, the polishing of the wafer surface is described as a process of chemical mechanical polishing (CMP), in which the pad plays a role of mechanical polishing and the slurry plays a mechanical and chemical role. Large wafer size and thus high quality requirements have led to improved pad and slurry performance.

In particular, because the slurry is regarded as the final regulator of wafer quality, products with various physicochemical properties have been released and are being studied continuously.

These slurries are combined with the basic composition of abrasive particles, ultrapure water and pH adjuster. The abrasive particles are a mixture of silica or silica and alumina, and it is common to use potassium hydroxide, sodium hydroxide or aqueous ammonia as the pH adjuster. to be.

In addition to these components, a polishing accelerator for improving the polishing rate and a dispersing agent for enhancing the dispersibility of the particles may be added.

Mirror polishing as described above is divided into stock removal polishing and final polishing, and each of the two or three polishing steps is successively performed. Is used.

In recent years, as quality items for wafers have been advanced and newly introduced, the multi-step process is an intermediate step between initial polishing and final polishing, and polishing conditions (polishing pressure, surface rotational speed) and consumables placement (hard polishing cloth, final slurry). Applying the intermediate polishing step to adjust the quality is going to improve the trend.

In the initial polishing, a slurry having a particle level of 0.1 micron and a strong alkali is used to polish a rough surface of several microns to remove bulk defects.

It is common for particles to use spherical monodisperse silica, and bases to use organic strong bases such as inorganic strong bases of NaOH and KOH or tetramethylammonium hydroxide (TMAH). In addition, the pad for initial polishing uses a hard polyurethane material to induce a large amount of bulk removal (thickness removal of 18 to 22 microns).

The final polishing slurry is to remove scratches, microroughness of less than several microns and residual contaminants, and to polish the surface with a mirror surface having no defects and roughness of several nanometers or less (0.2 to 0.5 micron thickness). For the purpose of particle or alkaline, it has physically and chemically weaker reactivity compared to initial polishing.

Therefore, the final polishing particles use spherical monodisperse silica of 30-40 nanometer (nm) level and use a weak base of ammonia water as a pH regulator. In addition, water-soluble polymers or surfactants are used to stabilize the dispersion of particles. Sometimes. At this time, the pad is made of a soft urethane material.

In order to examine the limitations of the past technology and to refer to the development, various patent cases were examined. Various patent cases regarding the composition of the initial and final slurry and patent cases of the polishing process are as follows.

Trennnick et al. US3715842 At 100 nm or less of silica particles were dispersed in water, and ammonia was added at 0.05% or more to pH 7 or more. HPC) was added to 0.05 to 2.5 weight percent to prepare a slurry for final polishing. The slurry by this method has a large particle size and a wide particle size distribution, which makes it difficult for intermediate polishing or final polishing of a silicon wafer.

Chromwell et al. Prepared a slurry by dispersing a mixture of microfine silica and quaternary ammonium silicate in water in US3807979 at a pH of 10.2 to 10.6.

Payne et al. Use particles ranging in size from 4 to 100 nm in a series of patents (US4169337, US4462188, US4588421) and add 2 or 4 percent of amines such as aminoethanolamine or ethylenediamine. A slurry was added in which 2 or 4 percent of a quaternary ammonium salt such as tetramethylammonium chloride or tetramethylammonium hydroxide (TMAH) was added.

The method used by Koyama et al. In US Pat. No. 4,46,646,79 is used to treat the surface of silica particles with a silane compound such as methyltrimethoxysilane or hexamethyldisilazane, thereby reducing the number of silanol groups on the surface of silica. after the 0.3~3 gae / Å ^2, was to use a mixture of an alumina sol. This method is disadvantageous in terms of economics because it uses expensive silane compounds.

Sasaki et al. Proposed a method for making colloidal silica from water glass in US5226930. Silica by this method is difficult to be used for the final polishing of a silicon wafer because the particle size is 5 to 1000 µm.

US5352277 also proposes a slurry using colloidal silica, a water soluble polymer, and a water soluble salt. Silica is 5-500nm to 20-50%, the amount of water-soluble polymer is about 100ppm, salt is selected from the cation of Na, K, NH4, the anion of Cl, F, NO ₃ , ClO ₄ The concentration was 20-100 ppm. This slurry was used to reduce roughness values of 5 nm and above.

Longcki et al. Used in WO96 / 38262 a few hundred nanometers of silica with 0.2 to 0.5 weight percent, amine with 0.01 to 0.1 percent, and PVA of 0.02 to 0.05 weight percent and pH 8 to 11 To prepare the final polishing slurry. When the 150 mm wafer was polished, the haze level of the wafer surface became cloudy or smeared, and the haze level was 0.06 ppm. The 0.1-0.3 micron LPD showed an average quality of 90 or less, but no attention was paid to other defects.

Krishna et al. EP0684634A2 in The existing two-stage polishing process using Syton HT50 in the initial (primary) polishing and Glanzox 3900 in the final (secondary) polishing, reduces the LPD and improves the haze by adjusting the input method of the slurry without the addition of a polishing machine. Showed.

In other words, the initial (primary) polishing is performed using Syton HT50, and the intermediate polishing is performed by replacing Glanzox 3900 with the same grinder. Final (tertiary) polishing was achieved with the reduction of LPD using Glanzox 3900 as with intermediate polishing. In addition to haze and LPD, however, no mention was made as to the causes or effects of SP1 defects.

Inoue et al. Proposed a secondary or final polishing composition in JP 2000-0006327. The abrasive for the composition used silica having primary particles of 35 nm and secondary particles of 70 nm, and TMAH (samethylammonium hydroxide) as a base at 0.001 to 0.3 weight percent. In addition, it was mentioned that the hydrophilicity of the surface of the wafer was improved by adding ethyl cellulose hydroxide (HEC) having a molecular weight of 1.3 million or more, but did not deviate from the composition of the general polishing slurry. As a result of the polishing by this composition, haze was evaluated in three categories in the item of the groove of the mixture, and surface roughness was evaluated by quantifying by the Ra value, but the haze evaluation of the mixture was not quantified. This lack of clearness makes it difficult to judge the goodness of the grooves and surface roughness of the inclusions, especially SP1 surface defects.

As seen from the above example, the conventionally used polishing slurry is mainly composed of colloidal silica, and two or less kinds of slurry are applied according to the polishing step.

Even in the mass production system in which multi-stage polishing is operated, only two types of initial polishing slurry and final polishing slurry are applied. Two types of slurry are used, which are classified into physical properties such as particle size, viscosity, particle amount, and pH, depending on the environment of the system and polishing results (haze, light print defect, and metal impurities). Various products are used by manufacturers.

However, in recent years, in addition to defects such as haze or LPD, in which the wafer surface becomes cloudy or stained, surface defects such as SP1, a kind of microroughness that causes the haze, have been introduced from semiconductor manufacturers. Carefully managed. In response to these wafer quality requirements, wafer manufacturers are attempting to improve the performance of the final slurry or to adjust process parameters to reduce wafer defects, particularly SP1 defects.

MEMC's process, which changes the use of slurries and the operation of the grinding machine as suggested in US245592, has recently been applied in a similar way to wafer manufacturers.

However, the improved intermediate (secondary) polishing uses the final polishing slurry formulated to be suitable for the soft polishing cloth, and the hard polishing cloth is used to remove much of the surface distortion. There is a limit to the removal of surface defects such as SP1 defects by causing adverse effects. In particular, there is a problem in that the silicon wafer cannot adequately and sufficiently remove metal oxides or metal impurities such as alumina particles.

The present invention is to minimize the above-described SP1 defects, and in particular, in addition to nitrogenated organic salts such as choline chloride used to remove SP1 defects, which are surface defects caused by mechanical polishing during silicon wafer polishing, particularly citric acid. It is an object to effectively remove metal oxides or metal impurities such as alumina particles, including organic salts.

The object of the present invention is to add dozens of SP1 defects on the wafer surface by adding ammonia, cellulose, nitrogenated organic salts, organic acids, and alkylphenyl nonionic surfactants to an aqueous colloidal silica solution mixed with ultrapure water and spherical monodisperse silica particles. Achieved by a slurry of a silicon wafer having a composition that is controlled at a level.

Hereinafter, the slurry for removing defects of SP1 of a silicon wafer and a method of using the same according to the present invention will be described in detail.

The application of slurry in the polishing process of wafer mass production uses slurry with a particle size of 100 nm for primary polishing (initial polishing), and slurry with a particle size of 40 nm for secondary polishing (intermediate polishing) and tertiary polishing. A three step process used for (final polishing) is applied, and the present invention relates to a composition of a slurry for reducing the SP1 defects and a method of using the slurry.

The slurry of the present invention consists of ultrapure water, spherical monodisperse silica particles, ammonia, cellulose, nitrogenated organic salts, organic acids and alkylphenyl nonionic surfactants.

It is known that defects below the surface of the wafer are affected by mechanical polishing effects, that is, polishing pressure, particle amount, and particle size, which causes light scattering, which causes haze, etc., and causes obstacles in LPD analysis. to provide.

Silica particles are made of colloidal silica with an average size of 10 to 50 nm in order to reduce the effects of mechanical polishing, that is, the surface and subsurface damage caused by the particles. By mixing with ultrapure water, an aqueous colloidal silica solution is obtained.

Ammonia has no surface penetrating effect compared to alkali metal bases, and rather, forms a complex with a metal to suppress metal residue, and serves to maintain a pH of 10.5 to 11.5.

In order to reduce the mechanical polishing effect and to obtain a desired level of polishing, celluloses, which are water-soluble polymers having a molecular weight of 100,000 or more and having a long chain structure, are used to generate a laminar flow. The cellulose may be hydroxypropyl cellulose, hydroxybutyl methyl cellulose, hydroxypropyl methyl cellulose, hydroxyethyl cellulose, hydroxyethyl cellulose adjusted to lipophilic, hydroxymethyl cellulose, methyl cellulose, etc. In order to maintain high viscosity, the molecular weight should be 100,000 to 1 million, hydroxymethyl cellulose and hydroxypropyl cellulose in a ratio of 2: 1, the amount of which is 0.02 to 2 weight percent of the total, and the viscosity is 2 to 40. Let it be cP.

In addition, the nitrification organic salt is 0.02 to 1.2 weight percent, and the organic acid is 0.0005 to 0.5 weight percent, so that the concentration of particles and metal impurities remaining on the surface after polishing is used. In this case, cholin chloride is used as the nitrified organic salt, and choline chloride is a salt that is used independently as a detergent for removing particles or metal impurities from the metal surface, and citric acid is used as the organic acid. This citric acid is particularly effective in removing metal oxides or metal impurities such as alumina particles.

The alkylphenyl nonionic surfactant is an alkyl phenyl ethylene oxide having 50 to 100 ethylene oxide monomers and the amount of the monomers is 10 wt% or more of the total molecular weight, and the amount is 0.01 to 0.5 weight percent of the total.

On the other hand, a base and a dispersant are used to disperse the silica particles in the colloidal silica aqueous solution, the base is a pH of 10.5 to 11.5 using ammonia water, the dispersing agent is an alkylphenyl having 50 to 100 ethylene oxide groups Ethylene oxide is used at 0.01 to 0.5 weight percent to prevent silica particles from aggregating during storage in the container.

In particular, the polymer cellulose may be precipitated as a solid due to a decrease in solubility or dispersibility under the slurry composition. When precipitated as particles, the polymer cellulose is accelerated to agglomerate of silica particles and loses its performance as an abrasive. Therefore, the use of alkylphenylethylin oxide may increase the dispersibility of cellulose, and consequently, obtain an effect of increasing the dispersibility of the polishing composition.

The components directly related to the SP1 defect in the composition of the present invention as described above are nitrogenated organic salts, in particular choline chloride and organic acids, and the reduction of the SP1 defect in the composition in which they are used together is large.

The topography of the surface, such as the SP1 defect to be solved in the present invention, is influenced by the silicic acid of the highly reactive activity, which is a polishing remover. In other words, the silicic acid may be polymerized by polymerization independently, and monomers or polymerized polymers may re-react with the particle surface or form crosslinks between particles to aggregate and cause pad clogging.

The agglomerated particles cannot be uniformly polished, and mechanical defects are applied below the surface to form defects. And re-adsorption with the surface creates non-uniform oxide film on the surface, resulting in the SP1 defect of the pit or the jut.

In order to suppress such a reaction, screening of the hydroxyl group, which is a reactive activator of silicic acid, is suppressed. Nitrogenated organic salts can be used for this action, of which choline chloride with ethanol group has a good effect.

In the present invention, when the citric acid which is an organic acid is also used together, it has a great effect.

Slurry made with the composition of the present invention described above is a conventional polishing slurry for the primary polishing (initial polishing) and the first polishing slurry for the secondary (medium) and tertiary (final) polishing. When the slurry of the present invention was polished by applying the slurry of the present invention to the intermediate polishing and the final polishing, the SP1 defects were 50 or similar to the existing results.

In particular, when the existing slurry was used for the initial polishing and the final polishing, and the slurry of the present invention was applied to the intermediate polishing, the SP1 defects were reduced by about 50 percent compared to the previous ones. When using the slurry of the present invention independently in the interpolation between the polishing was confirmed that the excellent mechanical polishing control effect.

Hereinafter, the present invention will be described in detail and in detail. However, the following examples do not limit the scope of the present invention.

Example 1

Colloidal silica of 20 to 30nm was diluted with ultrapure water to have a particle content of 6% by weight, and ammonia was added to 3% by weight (wt%) to have a pH of 11.0 or more. Choline chloride was used at 0.3 weight percent and citric acid was used at 0.2 weight percent. The molecular weight of 450,000 hydroxymethylcellulose was added to 0.6 weight percent and the molecular weight of 100,000 hydroxypropylcellulose was added to 0.3 weight percent so that the viscosity was 25 cP. And alkylphenyl ethylene oxide was added to 0.2 weight percent.

The slurry thus prepared was diluted 20-fold with ultrapure water and used for intermediate polishing. A P-type 200mm flat wafer of (10) orientation was used for a speedpamp multihead with a hard urethane polishing cloth. (speedfam multihead) was polished with a grinder.

The initial polishing slurry was used for the initial polishing and the final polishing slurry was used for the final polishing.

When 11 of the 80 polished wafers were measured for SP1 defects with KLA-Tencor SP1, fewer than 20 SP1 defects occurred and the average was controlled at 7 levels.

Example 2

The slurry prepared in Example 1 was diluted 20 times with ultrapure water and used for intermediate polishing and final polishing, and a p-type 200mm flat wafer with a (10) orientation was used for hard or soft urethane softening. Polishing was performed in a speedfam multihead grinder with abrasion.

When 10 of the 80 polished wafers were measured for SP1 defects with KLA-Tencor SP1, there were less than 70 SP1 defects and the average was controlled at 30 levels.

Example 3

Colloidal silica of 20 to 30nm was diluted with ultrapure water to have a particle content of 6% by weight, and ammonia was added to 3% by weight so that the pH was 11.0 or more. Choline chloride was used at 0.3 weight percent and citric acid was used at 0.5 weight percent. A molecular weight of 500,000 hydroxypropylcellulose was added to 0.9 weight percent to a viscosity of 20 cP. And alkyl phenyl ethylene oxide was added to 0.1 weight percent.

The slurry thus prepared was diluted 20 times with ultrapure water and used for intermediate polishing and final polishing. A hard or soft urethane polishing cloth was attached to a (10-) orientation p-type 200mm flat wafer. Polishing was performed in a speedfam multihead grinder.

When 10 of the 80 polished wafers were measured for SP1 defects with KLA-Tencor SP1, there were less than 70 SP1 defects and the average was 40 levels.

[Comparative Example]

A p-type 200mm flat wafer with a (1 0 0) orientation was diluted 40 times with a commercial slurry of 5 weight percent silica with an average particle diameter of 40 nm, pH 10.7 and a viscosity adjusted to 60 cP. Intermediate and final polishing was performed on a speedfam multihead grinder.

When five of the final polished wafers were measured for SP1 defects with KLA-Tencor SP1, there were less than 100 SP1 defects and the average was controlled to 50 levels.

As described above in detail through the configuration and examples of the present invention, the present invention is particularly effective in addition to nitrification organic salts such as choline chloride used to remove SP1 defects, which are surface defects caused by mechanical polishing during silicon wafer polishing. It is a very useful and effective invention to effectively remove metal oxides or metal impurities such as alumina particles, including organic salts such as citric acid.

As a result, defects on the surface of the wafer are reduced, thereby improving planarization.

Claims (2)

An aqueous colloidal silica solution obtained by mixing silica particles and ultrapure water having an average particle diameter of 10 to 50 nm and a content of 0.25 to 12 weight percent (wt%); Ammonia to maintain a pH of 10.5 to 11.5; Hydroxypropyl cellulose, hydroxybutyl methyl cellulose, hydroxypropyl methyl cellulose, hydroxyethyl cellulose, hydroxyethyl cellulose controlled by lipophilic, hydroxymethyl cellulose, methyl cellulose, or both Cellulose in an amount of 0.02 to 2 weight percent of the total so that the viscosity of the slurry is 2 to 40 cP; Nitrogenated organic salts containing 0.02 to 1.2% by weight and using choline chloride; An alkyl phenyl ethylene oxide having 50 to 100 ethylene oxide monomers, the amount of which is at least 10% by weight (wt%) of the total molecular weight, the amount of which is 0.01 to 0.5% by weight of the alkyl phenyl nonionic surfactant In the slurry consisting of a composition made by mixing, A slurry for polishing a silicon wafer, wherein the content is 0.0005 to 0.5 weight percent and removes metal oxides or metal impurities such as alumina particles, including organic acids using citric acid. delete