TWI843891B - Grinding composition and grinding method - Google Patents

Abstract

The subject of the present invention is to provide a polishing composition suitable for forming the above-mentioned wiring pattern including silicon material by polishing the polishing object by CMP method (the aforementioned polishing object is a film including silicon material having silicon-silicon bonds formed on a pattern including an insulating film), and can also suppress a significant decrease in the polishing rate. The solution of the present invention is the polishing composition of the present invention, which includes: abrasive grains, and a first water-soluble polymer including a polymer compound containing a lactam ring and having a weight average molecular weight of less than 300,000, and a second water-soluble polymer including a polymer compound containing a lactam ring and having a weight average molecular weight smaller than the first water-soluble polymer, and an alkaline compound, and water.

Description

Grinding composition and grinding method

The present invention relates to a polishing composition and a polishing method.

In recent years, with the multi-layer wiring on the surface of semiconductor substrates, the so-called chemical mechanical polishing (CMP) technology has been used to polish semiconductor substrates for flattening during device manufacturing. CMP is a method of flattening the surface of a polishing object (object to be polished) such as a semiconductor substrate using a polishing composition (slurry) containing abrasive particles such as silicon dioxide, aluminum oxide, and tin oxide, an anti-corrosion agent, and a surfactant. The polishing object (object to be polished) is a wiring, plug, etc. made of silicon, polysilicon, silicon oxide film (silicon oxide), silicon nitride, or metal. There have been various proposals for the polishing composition used when polishing semiconductor substrates by CMP.

For example, Patent Document 1 describes a polishing composition for improving the polishing characteristics of polysilicon, especially the step elimination efficiency. The polishing composition includes abrasive particles (colloidal silica) and an oxidant, and the pH is above 6. It is described that according to this polishing composition, since the surface of the polishing object, i.e., polysilicon, is chemically acted on in the composition with an oxidant of pH 6 or above, chemical polishing is performed, and the step elimination characteristics of the polishing object with steps are improved. In addition, Patent Document 1 describes a polishing composition containing 500 ppm of polyvinyl pyrrolidone with a weight average molecular weight of 40,000 as an example of an additive, i.e., a water-soluble polymer, which is blended to further improve the step elimination efficiency. This polishing composition has a pH of 9 and contains 0.1% by mass of oxygen peroxide.

Patent document 2 describes an additive for CMP polishing agent that includes an organic compound having an acetylene bond, a water-soluble vinyl polymer, and water, and has a pH of 4 to 9, and can polish an inorganic insulating film for semiconductors by combining it with a semiconductor oxide slurry. It also describes that by adding this additive, the polishing uniformity of the entire wafer surface can be improved, and the flattening characteristics of the entire wafer surface can be improved. In addition, polyvinyl pyrrolidone is not exemplified as a water-soluble vinyl polymer.

Patent document 3 describes a polishing composition for rough grinding of silicon wafers, which includes abrasive grains, a nitrogen-containing water-soluble polymer (polyvinyl pyrrolidone, content of 0.005 mass % or less) formed by two identical structures (a first nitrogen-containing water-soluble polymer and a second nitrogen-containing water-soluble polymer) with different weight average molecular weights, an alkaline compound, and water. In addition, it is described that the blending ratio of the two types of nitrogen-containing water-soluble polymers is 5:1 to 1:20 for the first nitrogen-containing water-soluble polymer (weight average molecular weight of 300,000 or more): the second nitrogen-containing water-soluble polymer (weight average molecular weight of less than 300,000). [Prior art document] [Patent document]

[Patent Document 1] Japanese Patent Publication No. 2015-86355 [Patent Document 2] Japanese Patent Publication No. 2008-85058 [Patent Document 3] WO2019/116833 Brochure

[Problems to be solved by the invention]

In the manufacturing steps of semiconductor devices, for example, a polishing object is polished by CMP method to form a wiring pattern including a polysilicon film, and the polishing object is formed on a pattern including a silicon nitride film (insulating film). Problems generated during this polishing include dishing like a plate on the wiring pattern including the polysilicon film, etching caused by scraping off the silicon nitride film between wirings, and the polysilicon film to be scraped off remains, resulting in a state where the silicon nitride film between wiring patterns is not exposed.

Although the polishing composition described in Patent Document 1 is intended to suppress dishing, the polishing rate of polysilicon film is significantly reduced by including an oxidizing agent. The CMP polishing agent described in Patent Document 2 includes tantalum oxide as abrasive particles. Tantalum oxide is generally expensive and easily precipitates, so its storage stability is deteriorated. The polishing composition described in Patent Document 3 is not suitable for "polishing a polishing object by CMP method to form a wiring pattern composed of a silicon material having a silicon-silicon bond, and the polishing object is formed on a pattern composed of an insulating film to form a film composed of a silicon material having a silicon-silicon bond."

The subject of the present invention is to provide a polishing composition suitable for forming a wiring pattern composed of a silicon material having a silicon-silicon bond by polishing a polishing object by a CMP method (suppressing the above-mentioned problem), wherein the polishing object is formed on a pattern composed of an insulating film, and a film composed of a silicon material having a silicon-silicon bond is formed, and a significant decrease in the polishing rate can also be suppressed. [Means for solving the subject]

In order to solve the above-mentioned problem, one aspect of the present invention is a polishing composition comprising: abrasive grains, a first water-soluble polymer comprising a polymer compound containing a lactam ring and having a weight average molecular weight of less than 300,000, a second water-soluble polymer comprising a polymer compound containing a lactam ring and having a weight average molecular weight smaller than that of the first water-soluble polymer, an alkaline compound, and water. [Effect of the invention]

According to the present invention, a polishing composition suitable for forming a wiring pattern composed of a silicon material having a silicon-silicon bond by polishing a polishing object by a CMP method can be provided, wherein the polishing object is a polishing composition in which a film composed of a silicon material having a silicon-silicon bond is formed on a pattern composed of an insulating film, and a significant decrease in the polishing rate can be suppressed.

[One aspect of the present invention]

As described above, a polishing composition according to one aspect of the present invention comprises: silica abrasive grains, a first water-soluble polymer comprising a polymer compound containing a lactam ring and having a weight average molecular weight of less than 300,000, a second water-soluble polymer comprising a polymer compound containing a lactam ring and having a weight average molecular weight smaller than that of the first water-soluble polymer, an alkaline compound, and water. According to a polishing composition according to one aspect of the present invention, the polishing characteristics of a polishing object comprising a film formed of a silicon material having a silicon-silicon bond are improved by comparing the polishing composition comprising both the first water-soluble polymer and the second water-soluble polymer with a polishing composition not comprising or only comprising either the first water-soluble polymer and the second water-soluble polymer.

The first water-soluble polymer and the second water-soluble polymer are both composed of a polymer compound containing a lactam ring, and both have a weight average molecular weight of less than 300,000. The weight average molecular weight of the second water-soluble polymer is smaller than the weight average molecular weight of the first water-soluble polymer. By comparing a polishing composition containing both the first water-soluble polymer and the second water-soluble polymer (having a weight average molecular weight of less than 300,000) with a polishing composition containing neither or only one of them, when a polishing method of "polishing a polishing object by a CMP method to form a wiring pattern containing a silicon material having a silicon-silicon bond, wherein the polishing object is formed on a pattern containing an insulating film, and a film containing a silicon material having a silicon-silicon bond is formed", depression of the wiring pattern is suppressed, erosion of the insulating film is suppressed, and a state in which the insulating film between the wiring patterns is not exposed is suppressed.

Even if the polymer compound containing a lactam ring is formed and contains two water-soluble polymers with different weight average molecular weights, when the weight average molecular weight of one of the water-soluble polymers is 300,000 or more, when the above-mentioned polishing method is implemented, it is easy to become a state where the insulating film between the wiring patterns is not exposed. The polishing composition of one aspect of the present invention contains both the first water-soluble polymer and the second water-soluble polymer, and since it is not necessary to contain an oxidant in order to obtain the above-mentioned action and effect, it will not produce a significant reduction in polishing speed like the polishing composition of patent document 1 containing an oxidant.

[Detailed description of one aspect of the present invention] The following is a detailed description of one aspect of the present invention. <Polishing object> As an application of the polishing composition of one aspect of the present invention, polishing of a polishing object including a film, the film being composed of a silicon material having a silicon-silicon bond can be listed. As silicon materials having a silicon-silicon bond, for example, polysilicon (Poly-Si), amorphous silicon, single crystal silicon, n-type doped single crystal silicon, p-type doped single crystal silicon, SiGe and other Si-based alloys can be listed. It is particularly suitable for use in polishing a film including polysilicon. The polishing object includes a film, the film being made of a silicon material having a silicon-silicon bond, and materials other than the silicon material having a silicon-silicon bond include, for example, silicon oxide, silicon nitride, silicon carbonitride (SiCN), metal, and the like.

<Abrasive grains> The polishing composition of one aspect of the present invention comprises silica abrasive grains (abrasive grains comprising silica particles). When using indium oxide as abrasive grains, it is not preferable to use indium oxide because indium oxide residues are easily left on the polished object after polishing. The type of silica particles is not particularly limited, and although fumed silica, colloidal silica, etc. can be listed, colloidal silica is preferred. As the manufacturing method of colloidal silica, the soda silica method and the sol-gel method can be listed, and even if the colloidal silica is manufactured by any manufacturing method, it is suitable for use as silica particles constituting one aspect of the polishing composition of the present invention.

However, from the perspective of reducing metal impurities, colloidal silica produced by the sol-gel method is preferred. Colloidal silica produced by the sol-gel method is preferred because it contains less metal impurities that diffuse in semiconductors or corrosive ions such as chloride ions. The production of colloidal silica by the sol-gel method can be carried out using conventionally known methods. Specifically, colloidal silica can be obtained by using a hydrolyzable silicon compound (such as alkoxysilane or its derivatives) as a raw material and performing a hydrolysis and condensation reaction.

The silica particles may have a cationic group. That is, the silica particles may be cationic modified silica particles or cationic modified colloidal silica. As the colloidal silica having a cationic group (cationic modified colloidal silica), colloidal silica having an amine group fixed on the surface may be preferably selected. As a method for producing colloidal silica having such a cationic group, there can be cited a method described in Japanese Patent Application Publication No. 2005-162533, in which a silane coupling agent having an amino group such as aminoethyltrimethoxysilane, aminopropyltrimethoxysilane, aminoethyltriethoxysilane, aminopropyltriethoxysilane, aminopropyldimethylethoxysilane, aminopropylmethyldiethoxysilane, aminobutyltriethoxysilane is immobilized on the surface of silica particles. In this way, colloidal silica having an amino group immobilized on the surface (amino-modified colloidal silica) can be obtained.

Colloidal silica may have anionic groups. That is, the silica particles may be anionic modified silica particles or anionic modified colloidal silica. As colloidal silica having anionic groups (anionic modified colloidal silica), colloidal silica having anionic groups such as carboxylic acid groups, sulfonic acid groups, phosphonic acid groups, aluminum acid groups, etc. fixed on the surface may be preferably selected. There is no particular limitation on the method for producing colloidal silica having such anionic groups. For example, a method of reacting a silane coupling agent having anionic groups at the ends with colloidal silica may be cited.

As a specific example, if sulfonic acid groups are immobilized on colloidal silica, the method described in "Sulfonic acid-functionalized silica through of thiol groups", Chem. Commun. 246-247 (2003) can be used. Specifically, by coupling a silane coupling agent having a thiol group such as 3-butylpropyltrimethoxysilane to colloidal silica, and then oxidizing the thiol group with hydrogen peroxide, colloidal silica with sulfonic acid groups immobilized on the surface (sulfonic acid modified colloidal silica) can be obtained.

If carboxylic acid groups are immobilized on colloidal silica, for example, the method described in "Novel Silane Coupling Agents Containing a Photolabile 2-Nitrobenzyl Ester for Introduction of a Carboxy Group on the Surface of Silica Gel", Chemistry Letters, 3, 228-229 (2000) can be used. Specifically, by coupling a silane coupling agent containing photoreactive 2-nitrobenzyl ester to colloidal silica and then irradiating the colloidal silica with carboxylic acid groups immobilized on the surface (carboxylic acid modified colloidal silica) can be obtained.

The shape of the silicon dioxide particles is not particularly limited, and may be spherical or non-spherical. Specific examples of non-spherical shapes include a polygonal prism such as a triangular prism or a quadrangular prism, a cylindrical shape, a doll shape in which the center of a cylindrical shape is more bulging than the ends, a donut shape that passes through the center of a disk, a plate shape, a so-called coil shape with a contraction in the center, a so-called converged spherical shape formed by integrating a plurality of particles, a so-called konpeito shape with a plurality of protrusions on the surface, an olive ball shape, and the like, and there is no particular limitation.

The size of the silica particles is not particularly limited. However, the average primary particle size of the silica particles is preferably 20 nm or more, more preferably 40 nm or more, more preferably 50 nm or more, and particularly preferably 60 nm or more. In addition, the average primary particle size of the silica particles is preferably 250 nm or less, more preferably 200 nm or less, more preferably 150 nm or less, and particularly preferably 100 nm or less. If it is such a range, the surface of the grinding object after grinding with the grinding composition can be used to suppress defects such as scratches. That is, the average primary particle size of the silica particles is preferably 20 nm or more and 250 nm or less, more preferably 40 nm or more and 200 nm or less, more preferably 50 nm or more and 150 nm or less, and particularly preferably 60 nm or more and 100 nm or less. Here, the average primary particle size of the silica particles is calculated based on the specific surface area of the silica particles measured by the BET method, for example.

The average secondary particle size of the silicon dioxide particles is preferably 50 nm or more, more preferably 80 nm or more, more preferably 100 nm or more, and particularly preferably 120 nm. In addition, the average secondary particle size of the silicon dioxide particles is preferably 500 nm or less, more preferably 400 nm or less, more preferably 300 nm or less, and particularly preferably 250 nm or less. If it is such a range, the surface of the grinding object after grinding with the grinding composition can be used to suppress defects such as scratches. That is, the average secondary particle size of the silicon dioxide particles is preferably 50 nm or more and 500 nm or less, more preferably 80 nm or more and 400 nm or less, more preferably 100 nm or more and 300 nm or less, and particularly preferably 120 nm or more and 250 nm or less. In addition, the average secondary particle size of the silicon dioxide particles can be measured by a dynamic light scattering method represented by a laser diffraction scattering method, for example.

The average degree of convergence of the silica particles is preferably 5.0 or less, more preferably 3.0 or less, and even more preferably 2.5 or less. As the average degree of convergence of the silica particles decreases, the occurrence of defects on the surface of the object being polished can be further reduced. In addition, the average degree of convergence of the silica particles is preferably 1.0 or more, more preferably 1.2 or more. As the average degree of convergence of the silica particles increases, there is an advantage of increasing the polishing speed of the polishing composition. In addition, the average degree of convergence of the silica particles is obtained by dividing the value of the average secondary particle size of the silica particles by the value of the average primary particle size.

The aspect ratio of the silica particles is not particularly limited, but is preferably less than 2.0, more preferably less than 1.8, and even more preferably less than 1.5. If it is within this range, the defects on the surface of the polished object can be further reduced. In addition, the aspect ratio is obtained by using a scanning electron microscope to obtain the smallest rectangle circumscribed with the image of the silica particles, and the average of the values obtained by dividing the length of the long side of the rectangle by the length of the short side of the same rectangle. It can be obtained using general image analysis software. The aspect ratio of the silica particles is not particularly limited, but is preferably greater than 1.0.

In the particle size distribution obtained by the laser diffraction scattering method of the silica particles, the ratio of the diameter of the particle when the integrated particle weight reaches 90% of the total particle weight (D90) to the diameter of the particle when the integrated particle weight reaches 10% of the total particle weight (D10) from the microparticle side, i.e. D90/D10, is not particularly limited, but is preferably 1.1 or more, more preferably 1.2 or more, and even more preferably 1.3 or more. In addition, in the silica particles in the polishing composition, the particle size distribution obtained by the laser diffraction scattering method is not particularly limited to the ratio of the diameter (D90) of the particle when the integrated particle weight reaches 90% of the total particle weight to the diameter (D10) of the particle when the integrated particle weight reaches 10% of the total particle weight, i.e. D90/D10. If it is within such a range, the defects on the surface of the polishing object can be further reduced. The size of the silica particles (average primary particle size, average secondary particle size, aspect ratio, D90/D10, etc.) can be appropriately controlled by selecting the manufacturing method of the silica particles.

The content (concentration) of silica particles in the polishing composition of one aspect of the present invention is preferably 0.01 mass% or more, more preferably 0.05 mass% or more, further preferably 0.1 mass% or more, and particularly preferably 0.5 mass% or more. In addition, the content of silica particles in the polishing composition is preferably 20 mass% or less, more preferably 10 mass% or less, further preferably 5 mass% or less, and particularly preferably 3 mass% or less. If the content of silica particles is within such a range, the surface defects of the polishing object after polishing with the polishing composition can be further suppressed. In addition, when the polishing composition contains two or more silica particles, the content of silica particles means the total amount of these. The polishing composition of one aspect of the present invention may contain other abrasive particles in addition to silicon dioxide particles. Examples of other abrasive particles include metal oxide particles such as aluminum oxide particles, zirconium oxide particles, and titanium dioxide particles.

<First water-soluble polymer, second water-soluble polymer> The polishing composition of one aspect of the present invention comprises: a first water-soluble polymer comprising a polymer compound containing a lactam ring and having a weight average molecular weight of less than 300,000, and a second water-soluble polymer comprising a polymer compound containing a lactam ring and having a weight average molecular weight smaller than that of the first water-soluble polymer. The weight average molecular weight of the first water-soluble polymer is preferably 25,000 or more and less than 300,000, more preferably 30,000 or more and 200,000 or less, and even more preferably 35,000 or more and 150,000 or less. The weight average molecular weight of the second water-soluble polymer is preferably 1,000 or more and less than 25,000, more preferably 3,000 or more and 20,000 or less, and even more preferably 5,000 or more and 15,000 or less.

As a combination of the weight average molecular weight of the first water-soluble polymer and the weight average molecular weight of the second water-soluble polymer, it is preferred that the weight average molecular weight of the first water-soluble polymer is 25,000 to 300,000, and the weight average molecular weight of the second water-soluble polymer is 1,000 to 25,000. It is more preferred that the weight average molecular weight of the first water-soluble polymer is 30,000 to 200,000, and the weight average molecular weight of the second water-soluble polymer is 3,000 to 20,000. For example, the weight average molecular weight of the first water-soluble polymer is 35,000 to 150,000, and the weight average molecular weight of the second water-soluble polymer is 5,000 to 15,000.

As the first water-soluble polymer and the second water-soluble polymer, there can be listed homopolymers composed of monomers comprising a polymer compound containing a lactam ring, or copolymers composed of monomers comprising a polymer compound containing a lactam ring and monomers comprising a compound not containing a lactam ring. As monomers comprising a polymer compound containing a lactam ring, there can be listed vinyl pyrrolidone, vinyl caprolactam, vinyl valerolactamide, vinyl lauryl lactamide, and vinyl piperidone.

As a homopolymer composed of a monomer comprising a high molecular compound containing a lactam ring, at least one selected from the group consisting of polyvinyl pyrrolidone, polyvinyl caprolactam, polyvinyl valerolactamide, polyvinyl lauryl lactam, and polyvinyl piperidone can be cited. The first water-soluble polymer and the second water-soluble polymer are particularly preferably polyvinyl pyrrolidone.

In one aspect of the polishing composition of the present invention, the total content of the first water-soluble polymer and the second water-soluble polymer is preferably less than 0.05 mass %. If it is within this range, it is beneficial to maintain a high polishing rate of polysilicon. In one aspect of the polishing composition of the present invention, the ratio (W1/W2) of the content of the first water-soluble polymer (W1) to the content of the second water-soluble polymer (W2) is preferably 1/15 to 15/1, more preferably 1/10 to 10/1, and particularly preferably 1.

<Alkaline compound> The polishing composition of one aspect of the present invention includes an alkaline compound. As an alkaline compound included in the polishing composition of one aspect of the present invention, for example, at least one alkaline compound selected from the group consisting of hydroxides of alkaline metals, alkaline metal salts of inorganic acids, ammonium salts of inorganic acids, alkaline metal salts of organic acids, ammonium salts of organic acids, and ammonia can be listed. By using such alkaline compounds, not only can the pH be adjusted in an alkaline region that easily dissolves silicon contained in the polishing object, but also the alkaline compound will not be adsorbed on the surface of the abrasive grains or the surface of the polishing object during polishing, but will mostly dissolve in the dispersion medium, so it will not hinder the removal of silicon, and efficient polishing can be achieved.

Examples of alkali metal hydroxides include lithium hydroxide, sodium hydroxide, potassium hydroxide, etc. Examples of alkali metal salts of inorganic acids include alkali metal salts of nitrites such as sodium nitrite and potassium nitrite; alkali metal salts of nitrates such as sodium nitrate and potassium nitrate; alkali metal salts of molybdenum acid such as sodium molybdate and potassium molybdate; alkali metal salts of hypochlorous acid such as sodium hypochlorite and potassium hypochlorite; sodium sulfate and potassium sulfate; Alkali metal salts of sulfuric acid such as sodium carbonate and potassium carbonate; alkaline metal salts of carbonate such as sodium carbonate and potassium carbonate; alkaline metal salts of hydrochloric acid such as sodium chloride and potassium chloride; alkaline metal salts of phosphoric acid such as sodium phosphate and potassium phosphate; alkaline metal salts of silicic acid such as sodium silicate and potassium silicate; alkaline metal salts of boric acid such as sodium borate and potassium borate, etc. Examples of ammonium salts of inorganic acids include ammonium chloride, ammonium sulfate, ammonium amide sulfate, ammonium nitrate, monoammonium dihydrogen phosphate, diammonium hydrogen phosphate, triammonium phosphate, ammonium diphosphite, ammonium carbonate, ammonium hydrogen carbonate, ammonium sulfide, ammonium borate, and ammonium borofluoride.

Examples of the alkali metal salts of organic acids include sodium acetate, potassium acetate, sodium propionate, potassium propionate, sodium glycerate, potassium glycerate, sodium appletetracarboxylate, potassium appletetracarboxylate, sodium citrate, potassium citrate, sodium lactate, potassium lactate, sodium tartrate, potassium tartrate, sodium salicylate, potassium salicylate, sodium malonate, potassium malonate, sodium succinate, potassium succinate, sodium maleate, potassium maleate, sodium phthalate, potassium phthalate, sodium oxalate, Potassium oxalate, sodium glutarate, potassium glutarate, sodium hydroxybutyrate, potassium hydroxybutyrate, sodium sorbate, potassium sorbate, sodium 2,4,6-octatriene-1-carboxylate, potassium 2,4,6-octatriene-1-carboxylate, sodium oleostearate, potassium oleostearate, sodium 2,4,6,8-decatetraene-1-carboxylate, potassium 2,4,6,8-decatetraene-1-carboxylate, sodium vitamin A acid, potassium vitamin A acid, potassium acylimidodiacetate, etc.

Examples of ammonium salts of organic acids include ammonium oxalate, ammonium acetate, diammonium oxalate, ammonium hydrogen oxalate, ammonium benzoate, monoammonium citrate, diammonium citrate, triammonium citrate, ammonium lactate, ammonium phthalate, ammonium succinate, monoammonium tartrate, diammonium tartrate, and ammonium aspartate. Among these alkaline compounds, in order to prevent malfunction of the semiconductor device obtained by polishing, it is preferred to use at least one selected from potassium hydroxide, inorganic acid potassium salts, inorganic acid ammonium salts, organic acid potassium salts, organic acid ammonium salts, and ammonia.

<Water> The polishing composition of one aspect of the present invention includes water as a dispersion medium. From the viewpoint of suppressing contamination or other components that hinder the polishing object, it is preferable to include water that contains as few impurities as possible as a dispersion medium. As such water, it is preferable to use water having a total transition metal ion content of 100 ppb or less. Here, the purity of the water can be improved by, for example, removing impurity ions using an ion exchange resin, removing foreign matter using a filter, distillation, etc. Specifically, as water, it is preferable to use deionized water (ion exchange water), pure water, ultrapure water, distilled water, etc. Generally, it is preferred that 90% by volume or more of the dispersing medium contained in the polishing composition is water, more preferably 95% by volume or more, still more preferably 99% by volume or more, and particularly preferably 100% by volume of water.

<Erosion inhibitor> The polishing composition of one aspect of the present invention preferably further comprises: an erosion inhibitor composed of a surfactant or a compound having a guanidine group. As the erosion inhibitor comprising a surfactant, anionic surfactants, cationic surfactants, nonionic surfactants, and amphoteric surfactants can be used, but anionic surfactants are preferably used.

Examples of the corrosion inhibitors containing anionic surfactants include alkyl sulfates (salts), alkyl phosphates (salts), alkyl naphthalene sulfonic acids (salts), alkyl benzene sulfonic acids (salts), polyoxyalkylene alkyl sulfates (salts), polyoxyalkylene styrenated phenyl sulfates (salts), polyoxyalkylene alkyl sulfosuccinic acids (salts), polyoxyalkylene allyl phenyl ether phosphates (salts), polyoxyalkylene alkyl phosphoric acids (salts), polyoxyalkylene alkyl acetic acids (salts), polyoxyalkylene alkyl sulfosuccinic acids (salts), alkyl sulfosuccinic acids (salts), alkyl naphthalene sulfonic acids (salts), alkyl diphenyl ether disulfonic acids (salts), etc. Among them, branched sodium alkylbenzene sulfonate (C9-17), sodium dodecylbenzene sulfonate, or polyoxyethylene (n=45-55) allyl phenyl ether amine phosphate salt is preferably used.

As corrosion inhibitors containing compounds having guanidine groups, creatinine, arginine, and guanidine acetic acid (Glycocyamine) can be listed. Among them, creatinine or arginine is preferably used. When the polishing composition of one aspect of the present invention contains a corrosion inhibitor, the corrosion inhibitor is composed of a surfactant, and its content is preferably 0.00001 mass% or more, more preferably 0.00005 mass% or more, and more preferably 0.0001 mass% or more. In addition, when the polishing composition contains a corrosion inhibitor, the corrosion inhibitor is composed of a surfactant, and its content is preferably 0.01 mass% or less, more preferably 0.005 mass% or less, and more preferably 0.001 mass% or less. When the content is less than 0.00001 mass %, substantially no corrosion inhibition effect is obtained, and when the content exceeds 0.01 mass %, the polishing rate of the polysilicon film is reduced.

When the polishing composition of one aspect of the present invention includes an erosion inhibitor, the erosion inhibitor is composed of a compound having a guanidine group, and the content rate thereof is preferably 0.001 mass % or more, more preferably 0.01 mass % or more, and even more preferably 0.05 mass % or more. Furthermore, when the polishing composition includes an erosion inhibitor, the erosion inhibitor is composed of a compound having a guanidine group, and the content rate thereof is preferably 5 mass % or less, more preferably 2 mass % or less, and even more preferably 1 mass % or less. When the content is less than 0.001 mass %, the erosion inhibition effect is substantially not obtained, and when the content exceeds 5 mass %, the polishing speed of the polysilicon film is reduced.

<Other additives> The polishing composition of one aspect of the present invention preferably does not contain an oxidizing agent. The polishing composition of one aspect of the present invention may further contain known additives such as a chelating agent, a thickening agent, a dispersant, a surface protective agent, a wetting agent, a surfactant (different from that included as a corrosion inhibitor), and a dissolving aid within the scope that does not impair the effect of the present invention. The content of the above-mentioned additives can be appropriately set according to the purpose of their addition.

<pH of polishing composition> The pH of the polishing composition of one aspect of the present invention is preferably 8 or more. If the pH is 8 or more, the polishing speed is further increased compared to the case where the pH is less than 8. This pH is more preferably 8.5 or more, more preferably 9.0 or more, and particularly preferably 9.5 or more. On the other hand, from the perspective of safety, the pH of the polishing composition is preferably 13.0 or less, more preferably 12.0 or less, and further preferably 11.5 or less. That is, the preferred pH range of the polishing composition of one aspect of the present invention is 8.0 or more and 13.0 or less, more preferably 8.5 or more and 12.0 or less, further preferably 9.0 or more and 11.5 or less, and particularly preferably 9.5 or more and 11.5 or less. Therefore, the amount of the alkaline compound blended is preferably adjusted in such a manner as to be within the above pH range.

<Method for producing a polishing composition> The method for producing a polishing composition of one aspect of the present invention is not particularly limited, and can be obtained by, for example, mixing silica particles, a first water-soluble polymer, a second water-soluble polymer, an alkaline compound, and other additives as necessary in a dispersion medium, i.e., water. The details of each component are as described above. The temperature when mixing the components is not particularly limited, but is preferably above 10°C and below 40°C, but heating may be performed to increase the dissolution rate. In addition, the mixing time is not particularly limited if uniform mixing is possible.

<Polishing method> A polishing method for polishing a polishing object including a film using a polishing composition according to one aspect of the present invention, wherein the film is made of a silicon material having a silicon-silicon bond, is described below. As a polishing device, a general polishing device having a polishing platen to which a polishing pad (polishing cloth) can be attached, which includes a bracket for holding a substrate having a polishing object and a motor with a variable number of revolutions. As a polishing pad, general non-woven fabrics, polyurethanes, porous fluororesins, etc. can be used without particular limitation. In the polishing pad, it is preferable to implement groove processing such as retaining the polishing liquid.

Regarding the polishing conditions, for example, the rotation speed of the polishing platen is preferably above 10 rpm (0.17 s ^-1 ) and 500 rpm (8.3 s ^-1 ). The pressure applied to the substrate having the polishing object (polishing pressure) is preferably above 0.5 psi (3.4 kPa) and below 10 psi (68.9 kPa). The method of supplying the polishing composition to the polishing pad is not particularly limited, and a continuous supply method such as a pump is adopted. Although the supply amount is not limited here, it is preferred that the surface of the polishing pad is usually coated with a polishing composition of one embodiment of the present invention. After the polishing is completed, the substrate is washed in running water, and the water droplets attached to the substrate are shaken off and dried by a rotary dryer, etc., to obtain a substrate having a metal layer.

The polishing composition of one aspect of the present invention may be a one-liquid type or a multi-liquid type that is initially a two-liquid type. In addition, the polishing composition of one aspect of the present invention may be prepared by diluting the original liquid of the polishing composition with a diluent such as water, for example, by 10 times or more. [Example 1]

The following describes the embodiments and comparative examples of the present invention, but the present invention is not limited to the embodiments shown below. In addition, in the embodiments shown below, in order to implement the present invention, although there are better technical limitations, such limitations are not essential requirements of the present invention. In addition, the following embodiments can be modified or improved in various ways, and the forms with such modifications or improvements can also be included in the present invention.

<Preparation of polishing composition> (Example 1) Colloidal silica having an average primary particle size of 90 nm was added in an amount of 1.5% by mass relative to the total amount of the polishing composition, polyvinyl pyrrolidone having a weight average molecular weight of 40,000 as a first water-soluble polymer was added in an amount of 0.00300% by mass relative to the total amount of the polishing composition, and polyvinyl pyrrolidone having a weight average molecular weight of 10,000 as a second water-soluble polymer was added in an amount of 0.00300% by mass relative to the total amount of the polishing composition, and water as a dispersant was added to obtain a mixed solution. Ammonia was then added to the obtained mixed solution in such a manner that the pH became 10.4, and the mixture was stirred and mixed at room temperature (25°C) for 30 minutes to prepare a polishing composition. In the polishing composition, the ratio (W1/W2) of the content of the first water-soluble polymer (W1) to the content of the second water-soluble polymer (W2) is 1. The pH of the polishing composition (liquid temperature: 25°C) was confirmed by a pH meter (manufactured by Horiba, Ltd., model: LAQUA).

(Example 2) The amount of polyvinyl pyrrolidone with a weight average molecular weight of 40,000 and polyvinyl pyrrolidone with a weight average molecular weight of 10,000 was added to the total amount of the polishing composition to be 0.00200 mass %. Other than that, the polishing composition was prepared in the same manner as in Example 1.

(Example 3) Instead of colloidal silica with an average primary particle size of 90 nm, colloidal silica with an average primary particle size of 70 nm was used. The amount of polyvinyl pyrrolidone with a weight average molecular weight of 40,000 and polyvinyl pyrrolidone with a weight average molecular weight of 10,000 was added to the total amount of the polishing composition in such a manner that it became 0.00025 mass %. In addition, instead of ammonia, potassium hydroxide was added in such a manner that the pH became 10.7. Except for these points, the polishing composition was prepared in the same manner as in Example 1.

(Example 4) Instead of using polyvinyl pyrrolidone with a weight average molecular weight of 40,000, polyvinyl pyrrolidone with a weight average molecular weight of 100,000 is used. Other than that, the same steps as in Example 1 are followed to prepare the grinding composition.

(Example 5) Instead of colloidal silica having an average primary particle size of 90 nm, colloidal silica having an average primary particle size of 70 nm is used. The amount of the polishing composition to be added is 0.00050 mass % relative to the total amount of polyvinyl pyrrolidone having a weight average molecular weight of 40,000. The amount of the polishing composition to be added is 0.00005 mass % relative to the total amount of polyvinyl pyrrolidone having a weight average molecular weight of 10,000. The ratio (W1/W2) is 10. Except for these points, the polishing composition is prepared in the same manner as in Example 1.

(Example 6) Instead of colloidal silica having an average primary particle size of 90 nm, colloidal silica having an average primary particle size of 70 nm is used. The amount of polyvinyl pyrrolidone added to the total amount of the polishing composition with a weight average molecular weight of 40,000 is adjusted to 0.00005 mass %. The amount of polyvinyl pyrrolidone added to the total amount of the polishing composition with a weight average molecular weight of 10,000 is adjusted to 0.00050 mass %. The ratio (W1/W2) is 1/10. Except for these points, the polishing composition is prepared in the same manner as in Example 1.

(Example 7) Instead of colloidal silica having an average primary particle size of 90 nm, colloidal silica having an average primary particle size of 70 nm was used. The amount of polyvinyl pyrrolidone added to the total amount of the polishing composition was 0.00005 mass %. The amount of polyvinyl pyrrolidone added to the total amount of the polishing composition was 10000 mass %. The ratio (W1/W2) was 1. Ammonia was added only in an amount of 0.194 mass % relative to the total amount of the polishing composition. The pH of the obtained polishing composition was confirmed to be 10.3. Except for these points, the polishing composition was prepared in the same manner as in Example 1.

(Example 8) Potassium hydroxide was added instead of ammonia. Except for these points, the polishing composition was prepared in the same manner as in Example 7. The pH of the polishing composition was confirmed to be 10.7.

(Example 9) Colloidal silica having an average primary particle size of 70 nm was added in an amount of 1.5% by mass relative to the total amount of the polishing composition, polyvinyl pyrrolidone having a weight average molecular weight of 40,000 as a first water-soluble polymer was added in an amount of 0.00005% by mass relative to the total amount of the polishing composition, polyvinyl pyrrolidone having a weight average molecular weight of 10,000 as a second water-soluble polymer was added in an amount of 0.00005% by mass relative to the total amount of the polishing composition, and sodium branched alkylbenzene sulfonate (C9-17) as an erosion inhibitor was added in an amount of 0.0005% by mass relative to the total amount of the polishing composition, and water as a dispersant was added to obtain a mixed solution. Then, potassium hydroxide was added to the obtained mixed solution in an amount of 0.194 mass % relative to the total amount of the polishing composition, and the mixture was stirred and mixed at room temperature (25°C) for 30 minutes to prepare a polishing composition. The pH of the obtained polishing composition was confirmed to be 10.7. In the polishing composition, the ratio (W1/W2) of the content rate of the first water-soluble polymer (W1) to the content rate of the second water-soluble polymer (W2) was 1.

(Example 10) Sodium dodecylbenzenesulfonate was used as a corrosion inhibitor. Other than this, the polishing composition was prepared in the same manner as in Example 9. The pH of the polishing composition obtained was confirmed to be 10.7. (Example 11) Polyoxyethylene (n=45-55) allylphenyl ether amine phosphate was used as a corrosion inhibitor. Other than this, the polishing composition was prepared in the same manner as in Example 9. The pH of the polishing composition obtained was confirmed to be 10.7.

(Example 12) Use polyoxyethylene (n=8) styrenated phenyl ether ammonium sulfate as a corrosion inhibitor. Except for this point, the polishing composition is prepared in the same manner as in Example 9. The pH of the obtained polishing composition is confirmed to be 10.7. (Example 13) As a corrosion inhibitor, creatinine is added in an amount of 0.1% by mass relative to the total amount of the polishing composition. Except for this point, the polishing composition is prepared in the same manner as in Example 9. The pH of the obtained polishing composition is confirmed to be 10.7. (Example 14) As a corrosion inhibitor, arginine is added in an amount of 0.1% by mass relative to the total amount of the polishing composition. Except for these points, the polishing composition was prepared in the same manner as in Example 9. The pH of the obtained polishing composition was confirmed to be 10.8.

(Comparative Example 1) No polyvinyl pyrrolidone was added. Potassium hydroxide was added in place of ammonia to a pH of 10.7. Except for these points, the polishing composition was prepared in the same manner as in Example 1. (Comparative Example 2) No polyvinyl pyrrolidone was added. Except for these points, the polishing composition was prepared in the same manner as in Example 1.

(Comparative Example 3) The amount of polyvinyl pyrrolidone with a weight average molecular weight of 40,000 to be added to the total amount of the polishing composition was 0.01000 mass %. In addition, polyvinyl pyrrolidone with a weight average molecular weight of 10,000 was not added. Except for these points, the polishing composition was prepared in the same way as in Example 1. (Comparative Example 4) The amount of polyvinyl pyrrolidone with a weight average molecular weight of 10,000 to be added to the total amount of the polishing composition was 0.00250 mass %. In addition, polyvinyl pyrrolidone with a weight average molecular weight of 40,000 was not added. Except for these points, the polishing composition was prepared in the same way as in Example 1.

(Comparative Example 5) The amount of polyvinyl pyrrolidone with a weight average molecular weight of 40,000 to be added to the total amount of the polishing composition was adjusted to 0.00250 mass %. In addition, polyvinyl pyrrolidone with a weight average molecular weight of 10,000 was not added. Except for these points, the polishing composition was prepared in the same manner as in Example 1. (Comparative Example 6) Instead of polyvinyl pyrrolidone with a weight average molecular weight of 40,000, polyvinyl pyrrolidone with a weight average molecular weight of 300,000 was added. Except for these points, the polishing composition was prepared in the same manner as in Example 1.

<Measurement of polishing rate> Using each polishing composition obtained, CMP polishing was performed on a non-doped polysilicon film (hereinafter referred to as "Non-Doped poly-Si film"), a film including a pattern of a polysilicon film doped with phosphorus (hereinafter referred to as "Doped poly-PTW film"), a silicon oxide film, and a silicon nitride film to investigate the polishing rate.

(Wafer for polishing rate measurement) The polishing rate of each film was measured using the CMP evaluation wafer shown below. Non-Doped poly-Si film polishing: Blank wafer (300mm) with a 5,000Å thick polysilicon film formed on the surface of a silicon wafer, manufactured by Advanced Material Technology Co., Ltd. Doped poly-PTW film polishing: 854 mask pattern, a 1000Å thick silicon nitride film formed on a silicon wafer, and a groove with a depth of 800Å was dug out, and a 2000Å thick Poly-Si film doped with phosphorus (phosphorus concentration 0.1 mass%) was formed to fill the uneven wafer (300mm), manufactured by Advantech Co., Ltd.

For polishing silicon oxide film: A blank wafer (300mm) with a 10,000Å thick silicon oxide film (TEOS film) formed on the surface of the silicon wafer, manufactured by Advantech Co., Ltd. For polishing silicon nitride film: A blank wafer (300mm) with a 3,500Å thick silicon nitride film (SiN film) formed on the surface of the silicon wafer, manufactured by Advanced Material Technology Co., Ltd.

(Polishing device and polishing conditions) The polishing device and polishing conditions used are as follows. Polishing device: Reflexion LK, 300mm CMP single-side polishing device made by Applied Materials Pad: IC1010, hard polyurethane pad made by NITTA HAAS Co., Ltd. Polishing pressure: 2.2psi Polishing platen rotation number: 73rpm Carrier rotation number: 67rpm Polishing composition supply: overflow Polishing composition supply amount: 200ml/min Polishing time: 60 seconds The value of the film thickness (Å) of each film before polishing minus the film thickness (Å) of each film after polishing is divided by the polishing time (min), and the calculated value is defined as the polishing speed (Removal Rate; RR). The film thickness (Å) of each film before and after polishing was determined using an optical interferometer film thickness measurement device (manufactured by KLA-Tencor Corporation, model: ASET-f5x).

<Polishing test> Using each polishing composition obtained, a pattern including a silicon nitride film was formed on a silicon wafer through an oxide film, and a polishing object formed with a polysilicon film was polished by CMP method to form a wiring pattern including a polysilicon film. As shown in FIG1 , the polishing object 10 is a pattern 3 including a silicon nitride film formed on a silicon wafer 1 through an oxide film 2, and a polysilicon film 4 is formed thereon. The thickness T1 of the pattern 3 including the silicon nitride film is 1000Å, the line width H1 is 10μm or 0.25μm, and the interval H2 is 10μm or 0.25μm. In addition, the thickness T2 of the polysilicon film 4 is 2000Å. When the polishing object 10 is polished ideally, the polysilicon film 4 does not remain on the pattern 3 made of the silicon nitride film, and the upper surface of the pattern 3 is completely exposed, and the wiring pattern 41 made of the polysilicon film is formed, and the line pattern 31 made of the silicon nitride film exists between adjacent wiring patterns 41. FIG2 is a plan view showing this state.

(Polishing device and polishing conditions) The polishing device and polishing conditions used are as follows. Polishing device: Reflexion LK, 300mm CMP single-side polishing device made by application materials Pad: IC1010, hard polyurethane pad made by NITTA HAAS Co., Ltd. Polishing pressure: 2.2psi Polishing platen rotation speed: 73rpm Carrier rotation speed: 67rpm Polishing composition supply: overflow Polishing composition supply amount: 200ml/min Polishing time: 15 seconds

(Performance evaluation) The surface state of the polished object after the polishing test was observed with an atomic force microscope (trade name WA-1300, manufactured by Hitachi Construction Machinery Fintech Co., Ltd.) to investigate the remaining state of the polysilicon film 4 to be scraped off, and to measure the amount of depression of the 10μm wide wiring pattern 41 and the amount of erosion of the 0.25μm wide line pattern 31. The remaining state of the polysilicon film 4 to be scraped off was evaluated as follows. ◎: The state where no polysilicon film remains on the polishing object (e.g., the state in FIG. 2) ○: The state where the polysilicon film remains partially on the polishing object, but there is no problem (e.g., the state in FIG. 3) ×: The state where the polysilicon film remains much on the polishing object and there is a problem (e.g., the state in FIG. 4) The measured values of the polishing speed and the polishing test results obtained are shown in Table 1 together with the composition of each polishing composition.

When polishing using each polishing composition of Examples 1 to 4, 6, 8 to 10, and 12 to 14, no residue of the polysilicon film 4 to be scraped off remains, and the state shown in FIG. 2 is obtained (indicated by "◎" in Table 1). In addition, the amount of depression of the wiring pattern 41 is lower than 173Å in Example 1 to 161Å or less, and the amount of erosion of the line pattern 31 is lower than 132Å in Example 1 to 88Å or less.

When the polishing composition of Examples 5, 7, and 11 was used for polishing, a portion of the polysilicon film 4 to be scraped off remained, but the pattern 31 formed of the silicon nitride film between the wiring patterns 41 was almost exposed (for example, the state of FIG. 3 ), which was a state without problems (indicated as "○" in Table 1). In addition, the amount of depression of the wiring pattern 41 was 157Å, which was lower than 173Å of Example 1, and the amount of erosion of the line pattern 31 was 87Å or less, which was lower than 132Å of Example 1.

When the polishing compositions of Comparative Examples 1, 2, 4, and 5 were used for polishing, there was no residue of the polysilicon film 4 to be scraped off, and the state shown in FIG. 2 (indicated as "◎" in Table 1) was obtained. However, in Comparative Example 1, the amount of depression of the wiring pattern 41 was as high as 173Å, and the amount of erosion of the line pattern 31 was as high as 1132Å. In Comparative Example 2, the amount of erosion of the line pattern 31 was as high as 133Å. In Comparative Example 4, the amount of erosion of the line pattern 31 was as high as 98Å. In Comparative Example 5, the amount of erosion of the line pattern 31 was as high as 127Å.

When the polishing compositions of Comparative Examples 3 and 6 are used for polishing, most of the polysilicon film 4 that should be scraped off remains. For example, as shown in FIG. 4 , many portions of the pattern 31 formed of the silicon nitride film between the wiring patterns 41 are not exposed at all in the longitudinal direction of the wiring (indicated as "×" in Table 1).

From the above results, it is understood that the polishing compositions of Examples 1 to 14 can reduce the residual polysilicon film to be scraped off and obtain the effect of inhibiting the pitting and corrosion. On the other hand, the polishing compositions of Comparative Examples 1 to 6 did not obtain any effect. In addition, the polishing rate of the polysilicon film of the polishing compositions of Examples 1 to 14 was 2256 to 2903 Å/min, which is the same as the polishing rate of the polysilicon film of the polishing compositions of Comparative Examples 1 and 2 that do not contain polyvinyl pyrrolidone (2432 to 2646 Å/min).

Furthermore, when the polishing compositions of Example 7 and Example 8, which only contain different types of alkaline compounds, are compared, the polishing composition of Example 8 containing potassium hydroxide has a higher effect of reducing the residual amount of the polysilicon film 4 to be scraped off, and the amount of depression of the wiring pattern 41 and the amount of erosion of the line pattern 31 are also smaller. From this result, it is understood that potassium hydroxide is more preferable as an alkaline compound than ammonia.

Furthermore, it was found that when comparing the polishing compositions of Example 8 and Examples 9 to 14, which differ only in whether they contain or not contain an erosion inhibitor, the amount of erosion can be further reduced when polishing is performed using the polishing composition of Examples 9 to 14 containing an erosion inhibitor, compared to the case where polishing is performed using the polishing composition of Example 8 not containing an erosion inhibitor.

1: Silicon wafer 2: Oxide film 3: Pattern formed by silicon nitride film 4: Polysilicon film 10: Polishing object 31: Line pattern formed by silicon nitride film 41: Wiring pattern formed by polysilicon film

[FIG. 1] is a cross-sectional view showing a polishing object subjected to a polishing test in the embodiment and an ideal polishing state of the polishing object. [FIG. 2] is a plan view showing a state (◎) where no polysilicon film remains on the polishing object after the polishing test in the embodiment. [FIG. 3] is a plan view showing a state (○) where a polysilicon film remains partially on the polishing object after the polishing test in the embodiment, but there is no problem. [FIG. 4] is a plan view showing a state (×) where a large amount of polysilicon film remains on the polishing object after the polishing test in the embodiment.

1: Silicon Wafer

2: Oxide film

3: Patterns including silicon nitride film

4: Polysilicon film

10: Grinding object

31: Linear pattern including silicon nitride film

41: Wiring pattern including polysilicon film

Claims (11)

A polishing composition comprising: silica abrasive grains, a first water-soluble polymer comprising a polymer compound containing a lactam ring and having a weight average molecular weight of 25,000 or more and less than 300,000, a second water-soluble polymer comprising a polymer compound containing a lactam ring and having a weight average molecular weight of 1,000 or more and less than 25,000, an alkaline compound, and water; the ratio (W1/W2) of the content rate (W1) of the first water-soluble polymer to the content rate (W2) of the second water-soluble polymer is 1/15 or more and 15/1 or less. The polishing composition of claim 1, wherein the first water-soluble polymer and the second water-soluble polymer are homopolymers composed of monomers containing a compound containing a lactam ring, or copolymers composed of monomers containing a compound containing a lactam ring and monomers containing a compound not containing a lactam ring. As in claim 2, the polishing composition, wherein the monomer comprising the aforementioned compound containing a lactam ring comprises at least one selected from the group consisting of vinyl pyrrolidone, vinyl caprolactam, vinyl valerolactamide, vinyl lauryl lactam, and vinyl piperidone. The polishing composition of claim 2, wherein the homopolymer comprises at least one selected from the group consisting of polyvinyl pyrrolidone, polyvinyl caprolactam, polyvinyl valerolactamide, polyvinyl lauryl lactam, and polyvinyl piperidone. The polishing composition as claimed in claim 1, wherein the first water-soluble polymer and the second water-soluble polymer are polyvinyl pyrrolidone. A polishing composition as claimed in any one of claims 1 to 5, wherein the total content of the first water-soluble polymer and the second water-soluble polymer is less than 0.05 mass %. The polishing composition of any one of claims 1 to 5 further comprises: an erosion inhibitor composed of a surfactant or a compound having a guanidine group. As in claim 7, the polishing composition, wherein the aforementioned surfactant is a cationic surfactant. As in claim 7, the grinding composition, wherein the compound having a guanidine group is creatinine or arginine. A polishing method, comprising the step of polishing a polishing object including a film using a polishing composition as described in any one of claims 1 to 9, wherein the film is made of a silicon material having silicon-silicon bonds. A polishing method, comprising the step of using a polishing composition as described in any one of claims 1 to 9 to polish an object to be polished by CMP to form a wiring pattern composed of a silicon material, wherein the object to be polished is formed on a pattern composed of an insulating film to form a film composed of a silicon material having a silicon-silicon bond.

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