US20090047870A1

US20090047870A1 - Reverse Shallow Trench Isolation Process

Info

Publication number: US20090047870A1
Application number: US12/179,643
Authority: US
Inventors: Junaid Ahmed Siddiqui; Quamrul Arefeen; Chelsea L. Beck
Original assignee: DuPont Air Products NanoMaterials LLC
Current assignee: Air Products and Chemicals Inc
Priority date: 2007-08-16
Filing date: 2008-07-25
Publication date: 2009-02-19

Abstract

A method of polishing a substrate surface containing silicon nitride and silicon oxide or silicon dioxide, comprising movably contacting the surface with a polishing pad and having a polishing composition disposed between the polishing pad and the surface, said polishing composition comprising 1) hydrous ceria abrasive; 2) polyvinylpyridine, vinyl pyridine copolymers, or both, and 3) water, wherein at 2 psi downpressure the silicon nitride removal rate is at least 500 angstroms per minute and the selectivity of silicon nitride to silicon oxide is at least 30.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

This patent application claims the benefit of U.S. Provisional Patent Application Ser. No. 60/956,232 filed 16 Aug. 2007.

BACKGROUND OF THE INVENTION

The present invention is directed to a process of making a shallow-trench-isolation type structure comprising polishing a silicon nitride layer disposed over a silicon dioxide or silicon oxide film formed for example from tetraethoxysilane (TEOS) or plasma enhanced tetraethoxysilane (PETEOS) using an aqueous chemical mechanical planarization slurry comprising, or alternatively consisting essentially of or consisting of: 1) hydrous (not calcined) ceria abrasive; 2) an effective amount of vinyl pyridine polymers and/or copolymers, e.g., poly(4-vinylpyridine), poly(4-vinylpyridine co-styrene), or mixture thereof; and 3) a pH adjusting agent which is advantageously an alkyl ammonium hydroxide.
Classical shallow trench isolation (STI) is a well-known method in the fabrication of IC chips. U.S. Pat. No. 6,342,432 describes manufacturing a traditional shallow trench isolation wherein shallow trenches are etched in the substrate and an oxide liner is thermally grown on the trench walls. The trench is then filled with an insulating material. A typical method of trench formation comprises initially growing a pad oxide layer on the substrate, and depositing a nitride polish stop layer thereon. A photoresist mask is then applied to define the trench areas. The exposed portions of the nitride layer are then etched away, followed by the pad oxide layer. The etching continues into the substrate to form the shallow trench. When etching of the trench is completed, the photoresist is stripped off the nitride layer. Next, the substrate is oxidized to form an oxide liner on the walls and base of the trench to control the silicon-silicon dioxide interface quality. The trench is then filled with an insulating material (or “trench fill”), such as silicon dioxide derived from TEOS. The surface is then planarized to provide a flat surface at the trench edges, as by chemical-mechanical polishing (CMP) to the nitride polish stop, and the nitride and pad oxide are stripped off the active areas to complete the trench isolation structure. Disadvantageously, during planarization, an excess amount of the trench fill tends to be removed, resulting in the top of the trench fill being “dished” in the middle; i.e., lower than the top of the trench. This condition complicates subsequent processing, thereby lowering manufacturing yield and increasing production costs.
A typical STI process is shown in FIGS. 1A to 1F. To prevent dishing, conventional STI formation methodologies include the formation of an additional photolithographic mask, known as a planarization mask. As shown in FIG. 1A, a trench 100 a is formed in a semiconductor substrate 100 after deposition of a pad oxide layer 105 and a nitride polish stop layer 110.An oxide liner 115 is then thermally grown, and trench 100 a is filled with an insulating material 120 (typically silicon oxide). Insulating material 120 is then polished, as by CMP, to obtain a flat upper surface, as shown in FIG. 1B. The portion of insulating material 120 above trench 100 a is masked by photoresist mask 125 (see FIG. 1C), then the portions of insulating material 120 unprotected by mask 125 are etched, as shown in FIG. 1D. Mask 125 is then removed, and insulating material 120 is further polished, as by CMP, down to the level of polish stop layer 110 (see FIG. 1E). The silicon nitride layer has served as a stopping layer during the chemical-mechanical planarization process, as the overall polishing rate has decreased upon exposure of the silicon nitride layer. In this application, a high TEOS to silicon nitride selectivity was required for successful planarization. A typical goal was to achieve high TEOS removal rates (e.g., 1500 A/min to 2500 A/min) and stop at Si₃N₄(e.g., less than 20 A/min) at low polishing pressure, providing a high TEOS/Si₃N₄(greater than 5, typically greater than 10, often greater than 20) selectivity during polishing. When the silicon nitride layer is exposed, the largest area of the substrate exposed to the chemical-mechanical polishing system comprises silicon nitride. While this silicon nitride can be removed by etching, removing the silicon nitride layer by polishing to achieve a highly planar and uniform surface is desirable. After the silicon nitride polish stop 110 is removed, the trench fill 120 is above the top of trench 100, as shown in FIG. 1F. The amount of the protrusion may be very small. Even moderately selective polishing compositions, having a selectivity of between 4 and 25, more typically between 6 and 12, will result in considerable erosion of the protruding oxide.
However, as oxide line widths have become smaller in next-generation devices, in some circumstances it is desirable to utilize polishing systems having selectivity for silicon nitride over oxide polishing, in order to minimize defectivity in the oxide lines formed on the substrate surface. Several chemical-mechanical polishing compositions for substrates containing low dielectric constant materials (e.g., oxide) are known. Generally, prior art utilizes ceria abrasive to obtain a high silicon dioxide to silicon nitride polishing ratio (selectivity).
Conversely to get high silicon nitride to silicon dioxide ratios, the prior art slurries use an abrasive such as alumina, titania, and silica. U.S. Pat. No. 6,043,155 discloses a cerium oxide-based slurry for inorganic and organic insulating films, having selectivity for silicon dioxide versus silicon nitride polishing. U.S. Patent Application Publication 2002/0168857 A1 discloses a method for manufacturing a semiconductor device in which silicon dioxide is deposited on a silicon nitride film patterned with trenches, and a two-stage chemical-mechanical polishing process is then performed to selectively remove overlying silicon dioxide, thus leaving trenches filled with silicon dioxide. Thus, there remains a need in the art for polishing compositions and methods having the reverse selectivity, for selectively removing silicon nitride over underlying dielectric components. U.S. Patent Application Publication 2006/0099814 teaches a slurry containing ceria at a pH of about 7 or less, with examples having pH values of 4.9, and shows a silicon nitride to oxide selectivity of less than 25. U.S. Patent Application Publication 2006/0108326 teaches a slurry containing ceria and shows a silicon nitride to oxide selectivity of less than 25. What is needed is a silicon nitride to silicon oxide selectivity of greater than 30, preferably greater than 40, is needed, where the polishing rate of the silicon nitride must simultaneously be useful, e.g., above 500 angstroms per minute.

BRIEF SUMMARY OF THE INVENTION

The present invention is directed to a process of making a shallow-trench-isolation type structure comprising polishing a silicon nitride layer disposed over a silicon dioxide or silicon oxide film formed for example from TEOS or PETEOS using an aqueous chemical mechanical planarization slurry comprising, or alternatively consisting essentially of or consisting of: 1) hydrous (not calcined) ceria abrasive; 2) an effective amount of vinyl pyridine polymers and/or copolymers, e.g., poly(4-vinylpyridine), poly(4-vinylpyridine co-styrene), or mixture thereof; and 3) a pH adjusting agent which is advantageously an alkyl ammonium hydroxide.
The invention includes the use of poly(4-vinylpyridine) and poly(4-vinyl pyridine co-styrene) for suppressing the TEOS rate with no effect on the removal rate of silicon nitride. Hence poly(4-vinylpyridine) and copolymers of 4-vinylpyridine such as poly 4-vinyl pyridine co-polystyrene are selective with respect to silicon nitride with complete suppression of oxide removal rate. The homopolymer and copolymer offer different protection profiles, and a polishing composition most preferably has both poly(4-vinylpyridine) and one or more copolymers of 4-vinylpyridine such as poly(4-vinyl pyridine co-styrene). However, the invention has additional improvements on the art. The invention is robust such that while removal rates are tunable the amount of material needed to affect tenability is sufficiently large (a difference of at least 50 ppm from high silicon nitride to silicon oxide selectivity to low silicon nitride to silicon selectivity) and the composition provides high polishing rates with low downpressure. While the system allows excellent tenability over a considerable range, advantageously the silicon nitride to silicon oxide selectivity is preferably at least 30, more preferably at least 35, most preferably at least 40. At pH 3.9 to 4.1, the selectivity of silicon nitride to silicon oxide can exceed 40, and can even be made to exceed 60 or 80. At such high selectivities, the small protruding silicon oxide layer remaining after STI will not be damaged, and can be made thinner than would be possible if the slurry had a selectivity of 25 or less, especially 10 or less. At the same time, advantageously, by only changing the amount of vinyl pyridine-based polymers, the selectivity of silicon nitride to silicon oxide can be made equal to 1 (0.8 to 1.2, preferably 0.9 to 1.1). This allows use of the base slurry in a variety of manufacturing variants where a slurry that always polishes silicon nitride at rates greater than silicon oxide can not be used.
The polishing composition advantageously comprises, consists essentially of, or consists of: A) about 0.05% to 2%, preferably 0.2% to 1%, by weight of hydrous ceria; B) about 10 to 1000, preferably about 20 to about 600, more than 50 to about 300 ppm, or 60 to 200 ppm, or 80 to 150 ppm, of one or more of poly(4-vinylpyridine), a polymer made from monomers consisting essentially of 4-vinylpyridine, poly(4-vinylpyridine co-styrene), other 4-vinylpyridine-based copolymers, or mixture thereof; C) a carrier which is preferably high purity water; D) optionally a pH adjuster, preferably a halide-free ammonium-based compound such as an tetra-alkyl ammonium compound, to adjust the pH between 3.5 and 4.5, preferably between 3.8 and 4.2, if necessary; and E) optionally between 5 and 500 ppm of nonionic surfactants including for example Zonyl FSJ® (10 to 1000 ppm) and Zonyl FSN® (5 to 50 ppm) to reduce defect counts and increase slurry stability.
Zonyl FSN®: it is a non-ionic surfactant, and a mixture of telomeric monoether with polyethylene glycol of formula R_fCH₂CH₂O(CH₂CH₂O)_xH: Where R_f═F(CF₂CF₂)_y, x=0 to about 25, and y=1 to about 9. The structures of Zonyl FSJ®, an anionic phosphate fluorosurfactant, is R_f(CH₂CH₂O)_xP(O)(ONH₄)_y, where R_f═F(CF₂CF₂)_z, x=1 or 2, y=2 or 1, x+y=3, and z=1 to about 7. The polishing method comprises movably contacting a substrate comprising a surface having both silicon nitride and silicon oxide with a polishing pad and with a polishing composition of this invention disposed between the polishing pad and the substrate surface. Advantageously the pH or the polishing composition is between 3.5 and 4.5, more particularly between 3.8 and 3.9, between 3.9 and 3.99, 4.00, or between 4.01 and 4.1.
Preferred compositions have 60 or more ppm, for example 70 ppm, 80 ppm, 90 ppm, 100 ppm, 110 ppm, 120 ppm, 130 ppm, 140 ppm, or 150 ppm of poly(4-vinylpyridine). Most preferred are polishing compositions having 80 to 150 ppm of poly(4-vinylpyridine) or a copolymer containing at least 70 molar percent of 4-vinylpyridine copolymerized with other polymers.
The invention includes a method of polishing a substrate surface containing silicon nitride and silicon oxide or silicon dioxide, comprising movably contacting the surface with a polishing pad and having a polishing composition disposed between the polishing pad and the surface, said polishing composition comprising 1) hydrous ceria abrasive; 2) an effective amount of polyvinylpyridine, vinyl pyridine copolymers having more than 60 molar percent of monomers being vinyl pyridine, or both, and 3) water. Advantageously the polishing composition comprises at least 60 ppm, preferably at least 80 ppm, for example between 100 and 200 ppm of poly(4-vinylpyridine). In another embodiment the polishing composition comprises poly(4-vinylpyridine co-styrene). Advantageously the silicon nitride to silicon oxide selectivity is at least 30, and the silicon nitride removal rate is at least 500 angstroms per minute. More advantageously, the silicon nitride to silicon oxide selectivity is at least 40, and the silicon nitride removal rate is at least 600 angstroms per minute when polished at a 2 psi downpressure. In a preferred embodiment the silicon nitride to silicon oxide selectivity is at least 60. Typically the polishing composition is at pH 3.9 to 4.1. The composition is tunable. Advantageously, the silicon nitride to silicon oxide selectivity is variable from 0.8 to over 50 by changing only the amount of polyvinylpyridine, vinyl pyridine copolymers, or both present in the polishing composition. In a preferred embodiment the polishing composition comprises 1) about 0.05% to 2% by weight of hydrous ceria; 2) more than 50 to about 300 ppm of one or more of poly(4-vinylpyridine), a polymer made from monomers consisting essentially of 4-vinylpyridine, poly(4-vinylpyridine co-styrene), other 4-vinylpyridine-based copolymers, or mixture thereof; and 3) water. Alternatively the polishing composition comprises 1) about 0.05% to 2% by weight of hydrous ceria; 2) 80 to about 600 ppm of one or more of poly(4-vinylpyridine), a polymer made from monomers consisting essentially of 4-vinylpyridine, poly(4-vinylpyridine co-styrene), other 4-vinylpyridine-based copolymers, or mixture thereof; and 3) high purity water, wherein the pH is between 3.5 and 4.5. In a very preferred embodiment, the polishing composition consists essentially of 1) about 0.05% to 2% by weight of hydrous ceria; 2) 80 to about 600 ppm poly(4-vinylpyridine); and 3) high purity water, and a pH adjuster so that the pH is between 3.8 and 4.2. Advantageously the polishing composition consists essentially of 1) about 0.05% to 2% by weight of hydrous ceria; 2) 80 to about 600 ppm of a copolymer containing at least 70 molar percent of 4-vinylpyridine copolymerized with other polymers, poly(4-vinylpyridine), or mixture thereof; and 3) high purity water.
The invention also includes a method of polishing a substrate surface containing silicon nitride and silicon oxide such as silicon dioxide, said method comprising movably contacting the surface with a polishing pad and having a polishing composition disposed between the polishing pad and the surface, said polishing composition comprising 1) hydrous ceria abrasive; 2) polyvinylpyridine, vinyl pyridine copolymers, or both, and 3) water, wherein at 2 psi downpressure the silicon nitride removal rate is at least 500 angstroms per minute and the selectivity of silicon nitride to silicon oxide is at least 30, preferably at least 40 at 2 psi downpressure. Preferably the hydrous ceria was provided by milling submicron ceria in an aqueous milling medium of no high purity alpha alumina at a pH of between 10 and 11 for a time sufficient to allow the hydroxyl ions to react with the surface of the ceria. Advantageously the polishing composition contains substantially no polydiallyldimethylammonium halide, poly(amidoamine), poly(methacryloyloxyethyltrimethylammonium) chloride, poly(methacryloyloxyethyldimethylbenzylammonium) chloride, poly(vinylpyrrolidone), poly(vinylimidazole), poly(vinylamine), and copolymers of acrylamide and diallyldimethylammonium chloride; and/or no no oxidizing agents; and/or less than 20 ppm total of chloride and fluoride. The above polymers can cause coagulation of the slurry. The polishing composition may additionally comprise between 0.005% and 0.1% of an ethoxylated fluorosurfactant to further reduce defects.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

FIG. 1A to 1E shows an STI manufacturing process where compositions of this invention could be usefully employed.

DETAILED DESCRIPTION OF THE INVENTION

The invention includes a polishing composition having greater than 20 ppm of a vinyl pyridine homopolymer or a vinyl pyridine copolymer, or both, used with hydrous ceria (preferably of 100 to 200 nanometers diameter) that allows a silicon nitride to silicon oxide (a term known in the art to indicate a material formed for example from TEOS) selectivity of less than 1 to greater than 30, preferably greater than 40, where the polishing rate of the silicon nitride is economically useful, e.g., above 500 angstroms per minute, preferably above 600 angstroms per minute, more preferably over 700 angstroms per minute at 2 psi downpressure. Different selectivities will doubtless be observed between silicon nitride and other dielectric materials such as silicon dioxide and against conductors such as polysilicon.
In preferred embodiments the polymer in the polishing composition comprises, consists essentially of, or consists of poly(4-vinylpyridine co-styrene). In another preferred embodiment the polymer in the polishing composition comprises, consists essentially of, or consists of poly(4-vinylpyridine co-styrene). Advantageously the molar ratio of vinyl pyridine to styrene in the copolymer is at least 50:50, more preferably at least 60:40. In another embodiment, the polymer in the polishing composition comprises, consists essentially of, or consists of copolymers of 4-vinylpyridine and other monomers, where advantageously the copolymers have greater than 50 molar percent, preferably greater than 60 molar percent, of the polymer being 4-vinylpyridine.
The use of hydrous, as opposed to calcined or “pure” ceria, is critical to the invention. By hydrous we mean for example a ceria formed by for example a precipitation process, which preferably has not undergone heated drying in an air atmosphere at a temperature sufficient to drive off water, or exposure to strong oxidizing agents, or other process which results in a similar product. Even better, ceria milled in an aqueous liquid at pH 9-11 for a sufficient period of time is most hydrous and is preferred. Ceria formed by pyrogenic methods are not desired. Calcined ceria is similarly not preferred. In preferred embodiments, the composition comprises less than 0.2%, preferably less than 0.05%, and most preferably is free of any or each of 1) ceria formed pyrogenically; 2) calcined ceria; 3) ceria that has undergone heated drying in an air atmosphere at a temperature sufficient to drive off water; and 4) ceria that has undergone exposure to strong oxidizing agents such as ceria formed by oxidizing soluble cerium salts, unless any of the above has been subsequently treated to revert the ceria to a hydrous form. Hydrous ceria is very active against silicon oxide and silicon dioxide. One method of potentially identifying hydrous ceria is that, in the absence of polymer, the polishing rate of silicon oxide is substantially greater than the polishing rate of silicon nitride at pH 3.9 to 4.5. As we have tested only a limited number of ceria products, however, the above is no guarantee that the ceria is hydrous.
A method of providing the hydrous ceria includes milling the ceria at a high pH of between 10 and 11 in a milling medium of no high purity alpha alumina for a time sufficient to allow the hydroxyl ions to react with the surface of the ceria, such that in a low pH environment the ceria is hydrous.
Advantageously the ceria has a particle size between 50 and 300 nanometers, with about 100 to about 200 nanometers diameter being preferred, and 130 to 170 nanometers being most preferred.
A useful commercially available ceria is such as is described in U.S. Pat. No. 6,238,450. The ceria maintains a positive ionic surface charge at pH values of about 4 to a pH of 10, and the ceria agglomerated particles have been subjected to a mechano-chemical treatment which comprises milling a slurry of the particles using low-purity alumina or zirconia milling media at a pH of from 9 to 12.5, until an essentially de-agglomerated product with a BET surface area of at least 10 m²/gm is obtained. The pH at which the de-agglomeration occurs is preferably from 10 to 12.5 and the time required may be from seconds up to 15 days depending on the equipment used and the degree of de-agglomeration required. Conventional vibratory mills such as a Sweco mill may require seven days or more.
Another potentially useful ceria might be obtained following the process of U.S. Pat. No. 4,661,330 which discloses a method for preparing high surface area and high purity ceria. Ammonium ceria nitrate is refluxed for 24 hours with ammonium sulfate to obtain a hydrous ceria powder. This powder, provided it can be milled to a average particle size below 0.2 microns, is likely useful. In that patent, the hydrous ceria was subsequently calcinated at 538° C. in air to form ceria having a surface area of 150 m²/g. After calcining, the ceria would not be useful in preferred variants of this invention.
The 4-vinylpyridine-based polymers of the present invention, when present in amounts up to 100 ppm, have substantially no detrimental effect on the silicon nitride polishing rate. By substantially no detrimental effect we mean the silicon nitride polishing rate is greater than about 50% of the comparative silicon nitrate removal rate when polishing under identical parameters with a slurry devoid of the vinyl pyridine-based polymers. The poly(4-vinylpyridine) and poly(4-vinylpyridine co-styrene) have a low affinity to the silicon nitride. Therefore, the presence of this polymer does not radically affect the polishing rate of the silicon nitride.
In contrast, the data in Table 1 of U.S. Patent Application Publication 2006/0099814 and 2006/0108326 show that polyethyleneimine in amounts of as little as 10 ppm results not only in a large reduction in the amount of oxide but also over a 95% reduction in the silicon nitride removal rate. It is difficult to manufacture and use polishing compositions where a variation of a few ppm will drastically affect the system performance. Absorption or reaction of the polymers during shipping and storage, and during mixing and storage in a plant, can result in a loss of a few ppm of such surface-active material, resulting in undesirable and significant variations in slurry performance. Even with polyvinylpyridine, tests for particle size distribution showed the polymer was coating the Accusizer™sensors. Preferably the polishing composition has substantially no, e.g., less than 10 ppm, more preferably less than 1 ppm, most preferably zero ppm, of polymers such as polyethyleneimine. Preferably the polishing composition has little, e.g., less than 10 ppm, more preferably less than 1 ppm, most preferably zero ppm, of polymers such as polydiallyldimethylammonium halide, poly(amidoamine), poly(methacryloyloxyethyltrimethylammonium) chloride, poly(methacryloyloxyethyldimethylbenzylammonium) chloride, poly(vinylpyrrolidone), poly(vinylimidazole), poly(vinylamine), and copolymers of acrylamide and diallyldimethylammonium chloride. The above polymers can cause coagulation of the slurry.
The combination of vinyl pyridine-based polymers and copolymers, in amounts greater than 20 ppm, preferably greater than 40 ppm, and often more than 60 ppm, in combination with the hydrous ceria allows silicon nitride to silicon oxide (e.g., from TEOS or PETEOS) selectivity to be 25 or more, preferably 30 or more, more preferably 40 or more, while still maintaining a silicon nitride removal rate of 400 angstroms per minute or more, preferably 600 to 1500 angstroms per minute, most preferably 800 to 1000 angstroms per minute at 2 psi downpressure. Generally, polishing rates increase with increasing down pressure. At 4 psi downpressure, which is not recommended as it is very high and substrate damage will be more frequent, about a 2× increase in removal rates may be realized. Nevertheless the desirable silicon nitride to silicon oxide selectivity of greater than 30, preferably greater than 40, can be maintained.
In compositions having normal (calcined) ceria, in the absence of polymers, generally the silicon nitride to silicon dioxide selectivity is near 1.5, and the selectivity of silicon nitride to silicon oxide is between 1.5 and 2. Using hydrous ceria, however, in the absence of polymers, the silicon nitride to silicon dioxide selectivity is below 0.4. Adding the polymer changes this selectivity to above 25. Therefore the compositions of this invention are tunable for silicon nitride to silicon oxide selectivity from 0.4 to above 30, while at the same time maintaining silicon nitride rates of over 600 angstroms per minute and which do not vary by more than about 50% over the range of selectivities. The compositions of this invention, most importantly, are tunable to a nitride to oxide selectivity of about 1. This is highly desirable in the industry.
Advantageously the compositions of this invention have little (less than 0.1%) or no oxidizing agents, including peroxides and the like.
Advantageously in one embodiment the compositions of this invention have little (less than 20 ppm, more preferably less than 5 ppm) or no halides, especially chloride and fluoride. Such halides may damage certain low k dielectric materials. If acid is needed, for example to obtain the proper pH, the acid should contain an anion such as sulfate.
Various corrosion reducing agents can be added. Such agents typically bind to copper and reduce corrosion. However, because the composition of this invention has no oxidizers, such corrosion reducing agents are typically not needed or desired.
Non-ionic surfactants, including particularly between 0.005% and 0.1% of an acetylenic alcohol comprising at least two hydroxyl substituents, more particularly the Zonyl™ type acetylenic diol surfactants which may or may not have an ethoxylated portion, are useful to reduce defects.
The polishing composition optionally can further comprise a biocide. The biocide can be any suitable biocide, for example an isothiazolinone biocide. The amount of biocide used in the polishing composition typically is about 1 ppm to about 500 ppm, and preferably is about 10 ppm to about 200 ppm.
The polishing composition also can be provided as a concentrate which is intended to be diluted with an appropriate amount of water prior to use. In such an embodiment, the polishing composition concentrate can comprise the hydrous ceria abrasive, the 4-vinyl pyridine-based homopolymer or copolymer, a base or other appropriate pH adjusting agent, and water in amounts such that, upon dilution of the concentrate with an appropriate amount of water, each component of the polishing composition will be present in the polishing composition in an amount within the appropriate range recited above for each component. The concentrate may contain an amount that is about 2 times (or about 3 times, about 4 times, or about 5 times) greater than the concentration recited above for each component so that, when the concentrate is diluted with an equal volume of water (e.g., 2 equal volumes water, 3 equal volumes of water, or 4 equal volumes of water, . . . ), each component will be present in the polishing composition in an amount within the ranges set forth above for each component.

EXAMPLES

In the examples, the following components and suppliers were used. Colloidal silica Syton® OX-K was obtained from DuPont Air Products NanoMaterials L.L.C., Tempe, Ariz., or Mirrasol®-30180 was obtained from Precision C, LLC, 102 Old Mill Road, Cartersville, Ga. 30120. Ceria (calcined) was obtained from Baikowski Japan, Co., Ltd, 6-17-13 Higashinarashino Chiba, JP 275-001. Ceria (hydrous) was obtained from Saint-Gobain Inc., 1 New Bond Street, Worcester, Mass. 01615
As used herein, silicon oxide or the dielectric “oxide” layer is formed from deposition of tetraethoxy silane or tetraethyl orthosilicate (TEOS), more particularly plasma enhanced deposition of tetraethoxy silane (PETEOS). Other compounds and methods are available to form similar silicon oxide layers. As used herein, “A/min” is angstrom(s) per minute. Back pressure and down force is provided in pounds per square inch (psi) units. Platen rotational speed of polishing tool is provided in rpm (revolution(s) per minute). Slurry flow is provided in milliliters per minute (ml/min). Reported removal rates of TEOS and silicon nitride are those observed at 2 psi down pressure. While larger rates are obtainable at higher down pressure, down pressures in excess of 3 psi are discouraged. Removal rates at 2 psi down pressure are advantageously 500 A/min to 800 A/min for Si₃N₄and less than 20 A/min for oxide.
In the examples, the polishing pad used during CMP was Politex® and IC1000 obtained from Rodel, Inc, Phoenix, Ariz. Oxide wafers were 15,000 A PETEOS on silicon. Silicon nitride blanket wafers were 10,000 A Si₃N₄on silicon on silicon, and were obtained from Silicon Valley Microelectronics, 1150 Campbell Ave, Calif., 95126. The CMP tool that was used is a Mirra®, manufactured by Applied Materials, 3050 Boweres Avenue, Santa Clara, Calif., 95054. A Rodel Politex® embossed pad, supplied by Rodel, Inc, 3804 East Watkins Street, Phoenix, Ariz., 85034, was used on the platen for the blanket wafer polishing studies. Pads were broken-in by polishing twenty-five dummy oxide (deposited by plasma enhanced CVD from a TEOS precursor, PETEOS) wafers. In order to qualify the tool settings and the pad break-in, two PETEOS monitors were polished with Syton® OX-K colloidal silica, supplied by DuPont Air Products NanoMaterials L.L.C., at baseline conditions.
In blanket wafers studies, groupings were made to simulate successive film removal: Si₃N₄and PETEOS. The tool mid-point conditions were: table speed; 123 rpm, head speed; 112 rpm, membrane pressure, 2.0 psi; inter-tube pressure, 0.0 psi; and slurry flow of 200 ml/min.

Comparative Example 1

In a 3-liter beaker, a ceria dispersion (18.26 weight %), purchased from Saint-Gobain Inc., 1 New Bond Street, Worcester, Mass. 01615, were added to deionized water and allowed to stir using a magnetic stirrer for five minutes. To this mixture, tetramethylammonium hydroxide (5 wt % solution) was added to bring the final pH to 4.00. Example 2 was the same as example 1 in table 1, but had 100 PPM of poly(4-vinylpyridine) added. Example 3 was the same as example 1 in table 1, except 100 PPM of poly(4-vinylpyridine co-polystyrene) was added. Comparative Example 4 was the same as example 2 in table 1, except that ceria particles were replaced with silica (180 nanometers) particles.
Compositions and polishing data are provided in Table 1.

TABLE 1

Effect of Adding Poly(4-vinylpyridine) and Poly(4-vinylpyridine
co-styrene) on Si₃N₄/TEOS selectivity at 2 psi down pressure

	Exam-			Exam-
	ple #1	Exam-	Exam-	ple # 4
Sample	Control	ple # 2	ple # 3	Control

Abrasive, ceria (D = 200 NM)	0.5	0.5	0.5
Abrasive, Silica (D50 = 180 NM)				0.5
Poly (4-vinyl pyridine), PPM	0	100	0	100
Poly (4-vinyl pyridine co-	0	0	100	0
styrene), PPM
Tetramethyl ammonium	05	05	05	05
hydroxide, , ppm
pH	4.0	3.8	3.8	4.0
RR of Silicon nitride (A/min)	809	740	692	37
RR of PETEOS (A/min)	2150	28	57	5
Selectivity (Si₃N₄/PETEOS)	0.4	26	12	7.4

It can be seen that Poly(4-vinyl pyridine) at 100 ppm reduces TEOS removal to below 30 angstroms per minute (a reduction of over 85%), while reducing the silicon nitride removal rate by less than 20% and allowing a silicon nitride removal rate in excess of 600 angstroms per minute. These parameters are highly desirable in the industry.
The effect of using hydrous ceria is also evident. In compositions having normal (calcined) ceria, in the absence of polymers, generally the silicon nitride to silicon dioxide selectivity is near 1.5, and the selectivity of silicon nitride to silicon oxide is between 1.5 and 2. Using hydrous ceria, however, in the absence of polymers, the silicon nitride to silicon dioxide selectivity is below 0.4. Adding the polymer changes this selectivity to above 25. Therefore the compositions of this invention are tunable for silicon nitride to silicon oxide selectivity from 0.4 to above 30, while at the same time maintaining silicon nitride rates of over 600 angstroms per minute and which do not vary by more than about 50% over the range of selectivities. The compositions of this invention, most importantly, are tunable to a nitride to oxide selectivity of about 1. This is highly desirable in the industry.

Example 5

In Example 5 et seq. a slightly different manufacturing method was used. In a 3-liter beaker, a ceria dispersion (18.26 weight %), purchased from Saint-Gobain Inc., 1 New Bond Street, Worcester, Mass. 01615, was added to 1 deionized water and allowed to stir using a magnetic stirrer for five minutes. To this mixture, poly(4-vinyl pyridine) was added during a period of 4 minutes, followed by addition of tetramethylammonium hydroxide to bring the final pH to 4.0. In Examples 5, 6 and 7, the amount of ceria was varied. Polishing data is presented in Table 2.

TABLE 2

Effect of Differing Percent Solid Ceria on Si₃N₄/TEOS
selectivity Using Poly(4-vinylpyridine)

Sample	Example # 5	Example # 6	Example 7

Abrasive, ceria (D = 200 NM)	0.5	0.7	1.0
Poly (4-vinyl pyridine), PPM	50	50	50
Tetramethyl ammonium	2.73 g	2.79 g	2.85 g
hydroxide, pH adjuster, 5%
solution
pH	4.01	4.00	4.1
RR of Silicon nitride Avg. of 3	710	825	906
runs (A/min)
RR of PETEOS Avg. of 3 runs	9	4.5	5
(A/min)
Selectivity Avg. of 3 runs	58	79	181
(Si₃N₄/PETEOS)

Example 8 and comparative example 9 further show the benefit of hydrous ceria (from Saint Gobain) versus a calcined ceria (obtained from Baikowski). Compositional and polishing rate data are presented in Table 3.

TABLE 3

Effect of Comparison of 0.5% Ceria Particles on
Si₃N₄/TEOS selectivity

	Example # 8	Example # 9
Sample	Saint-Gobain	Baikowski

Abrasive, ceria (D = 200 NM)	0.5	0.5
Poly (4-vinyl pyridine), PPM	50	50
Tetramethyl ammonium	2.74 g	1.04 g
hydroxide
pH	4.0	4.03
RR of Silicon nitride Avg. of 3	710	239
runs (A/min)
RR of PETEOS Avg. of 3 runs	9	22
(A/min)
Selectivity (Si₃N₄/PETOS)	79	10

The invention is intended to be limited by the disclosure and/or the claims, as the law of various jurisdictions proscribe, and is intended to be illustrated by but is not intended to be limited by the Examples.

Claims

1. A method of polishing a substrate surface containing silicon nitride and silicon oxide, comprising movably contacting the surface with a polishing pad and having a polishing composition disposed between the polishing pad and the surface, said polishing composition comprising 1) hydrous ceria abrasive; 2) polyvinylpyridine, vinyl pyridine copolymers having more than 60 molar percent of monomers being vinyl pyridine, or both, and 3) water, wherein the polishing composition comprises at least 60 ppm of poly(4-vinylpyridine).

2. The method of claim 1 wherein the polishing composition comprises at least 80 ppm of poly(4-vinylpyridine).

3. The method of claim 1 wherein the polishing composition comprises between 100 and 200 ppm of poly(4-vinylpyridine).

4. The method of claim 1 wherein the polishing composition comprises poly(4-vinyl pyridine co-styrene).

5. The method of claim 1 wherein the silicon nitride to silicon oxide selectivity is at least 30, and wherein the silicon nitride removal rate is at least 500 angstroms per minute.

6. The method of claim 1 wherein the silicon nitride to silicon oxide selectivity is at least 40, and wherein the silicon nitride removal rate is at least 600 angstroms per minute when polished at a 2 psi downpressure.

7. The method of claim 1 wherein the silicon nitride to silicon oxide selectivity is at least 60.

8. The method of claim 1 wherein the polishing composition is at pH 3.9 to 4.1.

9. The method of claim 1 wherein the silicon nitride to silicon oxide selectivity is variable from 0.8 to over 50 by changing only the amount of polyvinylpyridine, vinyl pyridine copolymers, or both present in the polishing composition.

10. The method of claim 1 wherein the polishing composition comprises 1) about 0.05% to 2% by weight of hydrous ceria; 2) more than 60 to about 300 ppm of one or more of poly(4-vinylpyridine), a polymer made from monomers consisting essentially of 4-vinylpyridine, poly(4-vinylpyridine co-styrene), other 4-vinylpyridine-based copolymers, or mixture thereof; and 3) water.

11. The method of claim 1 wherein the polishing composition comprises 1) about 0.05% to 2% by weight of hydrous ceria; 2) 80 to about 600 ppm of one or more of poly(4-vinylpyridine), a polymer made from monomers consisting essentially of 4-vinylpyridine, poly(4-vinylpyridine co-styrene), other 4-vinylpyridine-based copolymers, or mixture thereof; and 3) high purity water, wherein the pH is between 3.5 and 4.5.

12. The method of claim 1 wherein the polishing composition consists essentially of 1) about 0.05% to 2% by weight of hydrous ceria; 2) 80 to about 600 ppm poly(4-vinylpyridine); and 3) high purity water, wherein the pH is between 3.8 and 4.2.

13. The method of claim 1 wherein the polishing composition consists essentially of 1) about 0.05% to 2% by weight of hydrous ceria; 2) 80 to about 600 ppm of a copolymer containing at least 70 molar percent of 4-vinylpyridine copolymerized with other polymers, poly(4-vinylpyridine), or mixture thereof; and 3) high purity water.

14. A method of polishing a substrate surface containing silicon nitride and silicon oxide, comprising movably contacting the surface with a polishing pad and having a polishing composition disposed between the polishing pad and the surface, said polishing composition comprising 1) hydrous ceria abrasive; 2) polyvinylpyridine, vinyl pyridine copolymers, or both, and 3) water, wherein at 2 psi downpressure the silicon nitride removal rate is at least 500 angstroms per minute and the selectivity of silicon nitride to silicon oxide is at least 30 and wherein the polishing composition comprises at least 60 ppm of poly(4-vinylpyridine).

15. The method of claim 14 wherein the selectivity of silicon nitride to silicon oxide at 2 psi downpressure is at least 40.

16. The method of claim 15 wherein the hydrous ceria was provided by milling submicron ceria in an aqueous milling medium of no high purity alpha alumina at a pH of between 10 and 11 for a time sufficient to allow the hydroxyl ions to react with the surface of the ceria.

17. The method of claim 15 wherein the polishing composition contains substantially no polydiallyldimethylammonium halide, poly(amidoamine), poly(methacryloyloxyethyltrimethylammonium) chloride, poly(methacryloyloxyethyldimethylbenzylammonium) chloride, poly(vinylpyrrolidone), poly(vinylimidazole), poly(vinylamine), and copolymers of acrylamide and diallyldimethylammonium chloride.

18. The method of claim 15 wherein the polishing composition contains no oxidizing agents.

19. The method of claim 15 wherein the polishing composition contains less than 20 ppm total of chloride and fluoride.

20. The method of claim 15 wherein the polishing composition additionally comprises between 0.005% and 0.1% of an ethoxylated fluorosurfactant.