Method for coating a substrate with a silicon nitrogen-containing material.

Abstract: This invention relates to materials produced by diluting in a solvent a platinum or rhodium catalyzed preceramic mixture of a hydrogen silsesquioxane resin. The preceramic mixture solvent solution is applied to a substrate and ceramified by heating. One or more ceramic coatings containing silicon carbon, silicon nitrogen, or silicon carbon nitrogen can be applied over the ceramified SiO₂ coating. A CVD or PECVD top coating can be applied for further protection. The invention is particularly useful for coating electronic devices.

Description: Electronic devices, to be serviceable under a wide variety of environmental conditions, must be able to withstand moisture, heat, and abrasion resistance, among other stresses. A significant amount of work has been reported directed toward the preparation of coatings for electronic devices which can increase the reliability of the devices. None of the conventional coatings available today, including ceramic and metal packaging, can perform well enough by itself to protect an electronic device against all environmental stresses. A common cause of failure of electronic devices is microcracks or voids in the surface passivation of the semiconductor chip allowing the introduction of impurities. Thus, a need exists for a method which will overcome the formation of microcracks, voids or pinholes in inorganic coatings of electronic devices. Passivating coatings on electronic devices can provide barriers against ionic impurities, such as chloride ion (Cl-) and sodium ion (Na+), which can enter an electronic device and disrupt the transmission of electronic signals. The passivating coating can also be applied to electronic devices to provide some protection against moisture and volatile organic chemicals. Amorphous silicon (hereinafter a-Si) films have been the subject of intense research for various applications in electronic industries, however, the use of a-Si films for environmental or hermetic protection of electronic devices is unknown. A number of possible processes have been previously disclosed for forming a-Si films. For instance, for producing films of amorphous silicon, the following deposition processes have been used: chemical vapor deposition (CVD), plasma enhanced CVD (PECVD), reactive sputtering, ion plating and photo-CVD, etc. Generally, the plasma enhanced CVD process is industrialized and widely used for depositing a-Si films. Known to those skilled in the art is the utility of substrate planarization as an interlayer within the body of an electronic device and between the metallization layers. Gupta and Chin (Microelectronics Processing, Chapter 22, "Characteristics of Spin-On Glass Films as a Planarizing Dielectric", pp349-65, American Chemical Society, 1986) have shown multilevel interconnect systems with isolation of metallization levels by conventional interlevel dielectric insulator layers of doped or undoped SiO₂ glass films. However, CVD dielectric films provide only at best a conformal coverage of substrate features which is not conducive to continuous and uniform step coverage by an overlying metallization layer. The poor step coverage results in discontinuous and thin spots in the conductor lines causing degradation of metallization yields as well as device reliability problems. Spin-on glass films have been utilized to provide interlayer isolation between the metallization layers, the top layer of which is later patterned by lithographic techniques. Topcoat planarization on the surface of an electronic device as opposed to planarizing interlevel dielectric layers, however, is unknown. Under the teachings of the prior art, a single material most often will not suffice to meet the ever increasing demands of specialty coating applications, such as those found in the electronics industry. Several coating properties such as microhardness, moisture resistance, ion barrier, adhesion, ductility, tensile strength, thermal expansion coefficients, etc.; need to be provided by successive layers of different coatings. Silicon and nitrogen-containing preceramic polymers, such as silazanes have been disclosed in various patents, including U.S. Patent No. 4,404,153, issued September 13, 1983 to Gaul, wherein there is disclosed a process for preparing R'₃SiNH- containing silazane polymers by contacting and reacting chlorine-containing disilanes with (R'₃Si)₂NH where R' is vinyl, hydrogen, an alkyl radical of 1 to 3 carbon atoms or the phenyl group. Gaul also teaches therein the use of the preceramic silazane polymers to produce silicon-carbon-nitrogen-containing ceramic materials. Gaul in U.S. Patent 4,312,970, issued January 26, 1982, obtained ceramic materials by the pyrolysis of preceramic silazane polymers, which polymers were prepared by reacting organochlorosilanes and disilazanes. Gaul in U.S. Patent 4,340,619, issued July 20, 1982, obtained ceramic materials by the pyrolysis of preceramic silazane polymers, which polymers were prepared by reacting chlorine-containing disilanes and disilazanes. Cannady in U.S. Patent 4,540,803, issued September 10, 1985, obtained ceramic materials by the pyrolysis of preceramic silazane polymers, which polymers were prepared by reacting trichlorosilane and disilazanes. Frye and Collins teach in United States Patent No. 3,615,272, issued October 26, 1971, and also in Frye et al., J. Am. Chem. Soc., 92, p.5586, 1970, the formation of hydrogen silsesquioxane resin. Copending parent application No. 87309356.1 relates to the enhancement of the protection of electronic devices by the low temperature formation of thin multilayer ceramic or ceramic-like coatings on the surface of the device. What has been recovered is a method of forming coatings for electronic devices from catalyzed hydrogen silsesquioxane resin and one or more silicon- and nitrogen-containing ceramic or ceramic-like coatings. Copending parent Application No. 87309356.1 relates to the low temperature formation of monolayer and multilayer coatings for the protection of electronic devices. The monolayer coatings comprise a coating prepared by depositing on an electronic device a platinum or rhodium catalyzed solvent solution of hydrogen silsesquioxane resin, (HSiO 3/2 ) n . The dual-layer coatings comprise (1) a coating prepared by depositing on an electronic device a platinum or rhodium catalyzed solvent solution of hydrogen silsesquioxane resin, (HSiO 3/2 ) n , and (2) a topcoat of silicon-containing material, or silicon nitrogen-containing material, or silicon carbon-containing material, or silicon carbon nitrogen-containing material. The first layer is a SiO₂ planarizing and passivating coating that is applied by known techniques, including flow coating, spin coating, dip coating and spray coating of an electronic device. The second layer is a barrier coating of silicon-containing material derived from CVD or plasma enhanced CVD of halosilanes or halodisilanes, silazane, or mixtures of alkanes silanes and ammonia. Copending parent Application No 87309356.1 also relates to the formation of a three layer coating system for the protection of electronic devices wherein the first layer is a platinum and/or rhodium catalyzed SiO₂-containing planarizing coating obtained from solvent solution of hydrogen silsesquioxane resin (HSiO 3/2 ) n , wherein upon heat treatment, the material ceramifies to form an essentially SiO₂-containing material. The second layer, used for passivation, is a ceramic or ceramic-like coating obtained by the ceramification of a preceramic silicon nitrogen-containing polymer coating, or is a silicon nitrogen-containing, silicon carbon nitrogen-containing, or silicon carbon-containing layer deposited by thermal, UV, CVD, plasma enhanced CVD, or laser techniques. The third layer in these three layer coatings is a top coating of (a) silicon-containing material applied by CVD, plasma enhanced CND, or metal assisted CVD of a halosilane, halodisilane, halopolysilane, or mixtures thereof, or (b) silicon carbon-containing material, applied by CVD or plasma enhanced CVD of a halosilane, halodisilane, halopolysilane, or mixtures thereof, and an alkane or alkylsilane, or (c) silicon nitrogen-containing material applied by CVD or plasma enhanced CVD or a halosilane, halodisilane, halopolysilane, or mixtures thereof, and ammonia, or (d) silicon carbon nitrogen-containing material applied by CVD or plasma enhanced CVD of hexamethyldisilazane or mixtures of silanes, alkanes, alkylsilanes and ammonia. The catalyzed planarizing SiO₂ layers exhibit improved weight loss reduction over that of the uncatalyzed SiO2 planarizing layer. The instant invention relates to the discovery that catalyzed silicon dioxide (SiO2-containing) ceramic or ceramic-like coatings can be coated with a silicon nitrogen-containing material for the protection of electronic devices as well as other integrated circuits. In the instant invention, by "ceramic-like" is meant those pyrolyzed materials which are not fully free of residual carbon and/or hydrogen but which are otherwise ceramic-like in character. By "electronic device" in the instant invention is meant device including, but not limited to, electronic device, silicon based devices, gallium arsenide devices, focal plane arrays, opto-electronic devices, photovoltaic cells and optical devices. The coatings of the instant invention are also useful as dielectric layers, doped dielectric layers to produce transistor-like devices, pigment loaded binder systems containing silicon to produce capacitors and capacitor-like devices, multilayer devices, 3-D devices, silicon-on-insulator (SOI) devices, super lattice devices and the like. The present invention provides a method of coating a substrate with a ceramic or ceramic-like silicon nitrogen-containing material, wherein said method comprises the steps of: (1) diluting with a solvent a silicon and nitrogen-containing preceramic polymer produced by reacting a cyclic silazane or a mixture of cyclic silazanes with a silicon-containing material selected from the group consisting of halodisilanes and halosilanes; (2) coating a substrate with the diluted preceramic polymer solvent solution; (3) drying the diluted preceramic polymer solvent solution in the absence of air so as to evaporate the solvent and thereby deposit a preceramic polymer coating on the substrate; and (4) heating the coated substrate in the absence of air to produce a ceramic or ceramic-like coated substrate. The process according to this invention can be employed as part of a process for forming on a substrate a multilayer, ceramic or ceramic-like, coating according to copending parent application no 87309356.1 which process comprises (A) coating an electronic device with a coating by means of diluting hydrogen silsesquioxane resin (HSiO 3/2 ) n with a solvent, catalyzing the diluted hydrogen silsesquioxane resin solution with a metal catalyst selected from the group consisting of platinum catalysts and rhodium catalysts, and applying the catalyzed diluted hydrogen silsesquioxane resin solution to an electronic device; drying the catalyzed diluted hydrogen silsesquioxane resin (HSiO 3/2 ) n solution so as to evaporate the solvent and thereby deposit a catalyzed hydrogen silsequioxane resin (HSiO 3/2 ) n preceramic material coating on the electronic device, ceramifying the catalyzed hydrogen silsequioxane resin (HSiO 3/2 ) n preceramic material coating to silicon dioxide by heating the coated device to a temperature between 150 and 1000°C. to produce a ceramic or ceramic-like coating, and (B) applying to the ceramic or ceramic-like coated device a silicon nitrogen-containing coating by the process according to the present invention. Preferably the coated device is heated to a temperature of 150 to 1000°C in an inert or ammonia-containing atmosphere to produce the ceramic or ceramic-like silicon nitrogen-containing coating on the electronic device. The process according to the present invention can also be employed as part of a process for forming on a substrate a multilayer, ceramic or ceramic-like, coating which process comprises effecting step (A) as just defined and then (B) applying to the ceramic or ceramic-like coated device a passivating coating which comprises a silicon nitrogen-containing material by the process according to the present invention, and (C) applying to the ceramic or ceramic-like coated device a silicon-containing coating by means of decomposing in a reaction chamber a silane, halosilane, halodisilane or halopolysilane, or mixture thereof, in the vapor phase, at a temperature between 200 and 600°C., in the presence of the ceramic or ceramic-like coated device, whereby an electronic device containing a multilayer, ceramic or ceramic-like, coated thereon is obtained. According to another possibility for forming on a substrate a multilayer, ceramic or ceramic-like, coating step (C) comprises applying to the ceramic or ceramic-like coated device a silicon nitrogen-containing coating by means of decomposing in a reaction chamber a silane, halosilane, halodisilane, halopolysilane, or mixture thereof and ammonia, in the vapor phase, at a temperature between 150 and 1000°C., in the presence of the ceramic or ceramic-like coated device, whereby an electronic device containing a multilayer, ceramic or ceramic-like, coating thereon is obtained. Alternatively, step (C) comprises applying to the ceramic or ceramic-like coated device a silicon carbon-containing coating by means of decomposing in a reaction chamber a silane, halosilane, halodisilane, halopolysilane, alkysilane, or mixtures thereof, and an alkane of one to six carbon atoms or an alkysilane, in the vapor phase, at a temperature between 150 and 1000°C., in the presence of the ceramic or ceramic-like coated device, whereby an electronic device containing a multilayer, ceramic or ceramic-like, coating thereon is obtained. According to the process disclosed in parent application No 87309356.1 hydrogen silsesquioxane resin (HSiO 3/2 ) n is diluted (e.g., 0.1 to 10 weight %) with a solvent such as n-heptane or toluene. To the solution of silsesquioxane resin is added the platinum catalysts or rhodium catalyst in the form of, for example, 60 parts per million of (CH₃CH₂S)₂PtC1₂ in 0.01 gram of toluene. The catalyzed preceramic solvent solution is then coated onto an electronic device and the solvent allowed to evaporate by drying at ambient conditions. The process of coating the catalyzed preceramic polyer solution onto the electronic device can be, but is not limited to, spin coating, dip coating, spray coating, or flow coating. The catalyzed hydrogen silsesquioxane resin (HSiO 3/2 ) n preceramic material is oxidized in air to a SiO₂-containing material. By this means is deposited a preceramic polymer coating which is ceramified by heating the coated device, for example, for approximately one hour at 400°C. A thin ceramic or ceramic-like planarizing coating of less than 2 microns (or approximately 3000 to 5000 Angstroms) is thus produced on the device. The planarizing coating thus produced can then be coated with a passivating silicon nitrogen-containing ceramic or ceramic-like coating according to the present invention or with a CVD applied silicon-containing coating, silicon carbon-containing coating, or silicon nitrogen-containing coating or a combination of these coatings. Another significant result of catalyzing the silsesquioxane resin with platinum and/or rhodium is the beneficial reduction in the amount of weight loss observed on exposure to increasing temperatures. Thus, the silsesquioxane resin exposed to increasing temperatures in thermogravimetric analysis (TGA) under helium atmosphere but in absence of platinum catalyst, exhibited a 20% weight loss while the silsesquioxane resin catalyzed with the platinum catalyst exhibited only a 14% weight loss. The significant improvement of 6% in reduction of weight loss resulting from the platinum catalyst is indicative of improved crosslinking of the resin to form higher molecular weight polymers with higher char yields, a feature important in ceramification. Furthermore, TGA experiments run in air on the uncatalyzed and platinum catalyzed silsesquioxane resin demonstrate a 9% weight loss in the former but a 6% weight gain in the latter, i.e., the catalyzed sample displayed an initial 4% loss as unreacted material volatilized but upon continued heating from about 400°C. to 1000°C., the sample gained 6% weight above the starting weight as a result of oxidation. With rhodium catalysis, another sample of hydrogen silsesquioxane resin heated to 1000°C. under helium exhibited a 30% weight loss but a 68% weight loss was observed under identical conditions without the rhodium catalysis. When catalyzed with rhodium and oxidized in air, the hydrogen silsesquioxane resin exhibited a 7% weight gain, similar to the gain observed with platinum catalysis, due to oxygen incorporation. However, in the absence of rhodium catalyst, the same resin lot showed a 28% weight loss upon heating to 1000°C. in air. Thus, the platinum catalyst or rhodium catalyst facilitates the oxidation of any residual SiH moieties first to SiOH and then further to SiOSi. This oxidative weight gain phenomenon was not observed in the uncatalyzed silsesquioxane resin samples. The higher molecular weights and reduction in weight loss achievable by the present invention are important advances over the prior art because subsequent ceramification of the higher molecular weight polymers can produce higher ceramic yields. The cure of the hydrogen silsesquioxane resin is not limited herein to oxidative curing in air. The above discussion illustrates the utility of the present invention to cure the hydrogen silsesquioxane resin with platinum catalysts or rhodium catalysts in the absence of air. In ambition, the resin can be cured with platinum or rhodium catalysts in an ammonia-containing atmosphere. The platinum catalysts and rhodium catalysts operative in the present invention include, but are not limited to, (CH₃CH₂S)₂PtCl₂, platinum acetylacetonate, and rhodium catalyst RhCl₃(CH₃CH₂CH₂CH₂S)₃, obtained from Dow Corning Corporation, Midland, Michigan. Any platinum or rhodium compound or complex which can be solubilized in the hydrogen silsesquioxane resin will serve to catalyze the cure and is within the scope of this patent. Also to be included as preceramic silicon nitrogen-containing polymer materials useful within the scope of the present invention for the protection of electronic devices are the novel preceramic polymers derived from cyclic silazanes and halogenated disilanes, and also the novel preceramic polymers derived from cyclic silazanes and halosilanes. These material are disclosed and claimed in EP-A2 0266912 and EP-A2 0266918. The above described novel preceramic silicon nitrogen-containing polymers derived from cyclic silazanes and halosilanes and/or halogenated disilanes are also useful for the protection of any substrate able to withstand the temperatures necessary for ceramification of the preceramic polymers. Still other silicon- and nitrogen-containing materials may be suitable for use in the present invention. In the instant invention, a preceramic polymer containing silicon and nitrogen is diluted to low solids (e.g., 0.1 to 5 weight %) in a solvent such as toluene or n-heptane. The silicon nitrogen-containing polymer solvent solution is coated (by any method discussed above) onto the electronic device previously coated with the ceramified SiO₂-containing material and the solvent allowed to evaporate by drying in an inert or ammonia-containing atmosphere. By this means is deposited a preceramic polymer coating which is ceramified by heating the coating device for approximately one hour at temperatures up to 400°C. under argon. Thin ceramic or ceramic-like passivating coatings of less than 2 microns (or approximately 3000 to 5000 A) are thus produced on the devices. A preferred temperature range for ceramifying or partially ceramifying the silicon nitrogen-containing preceramic polymer is from 200 to 400°C. A more preferred temperature range for ceramifying the silicon nitrogen-containing preceramic polymer is from 300 to 400°C. However, the method of applying the heat for the ceramification or partial ceramification of the silicon nitrogen-containing coating is not limited to conventional thermal methods. The silicon nitrogen-containing polymer coatings useful as planarizing and passivating coatings in the instant invention can also be cured by other radiation means, such as, for example, exposure to a laser beam. However, the present invention is not limited to ceramification temperatures below 400°C. Ceramification techniques utilizing temperatures up to and including at least 1000°C., will be obvious to those skilled in the art, and are useful in the present invention where the substrate can withstand such temperatures. By "cure" in the present invention is meant coreaction and ceramification or partial ceramification of the starting material by heating to such an extent that a solid polymer ceramic or ceramic-like coating material is produced. The silicon-containing third layer or topcoat of the composite coating described above can be obtained at relatively low reaction temperature by the metal-assisted CVD process, mentioned supra and claimed in EP A2 0234593, or by conventional non-metal assisted CVD or plasma enhanced CVD techniques. The metal-assisted CVD process is particularly suited for the deposition of coatings from SiCl₄, SiBr₄ , HSiI₃, HSiCl₃ and HSiBr₃. The choice of substrates and devices to be coated by the instant invention is limited only by the need for thermal and chemical stability of the substrate at the lower decomposition temperature in the atmosphere of the decomposition vessel. The process of the present invention provides onto the electronic devices coated with ceramified hydrogen silsesquioxane resin (HSiO 3/2 ) n material and ceramified silicon nitrogen-containing material, a silicon-containing topcoating of a thickness which can be varied as desired depending upon the concentration of the silicon halides that are being reduced. The top coatings of the instant invention can be deposited by an known state-of-the-art technique. Coatings produced by the instant invention possess low defect density and are useful on electronic devices as protective coatings, as corrosion resistant and abrasion resistant coatings, as temperature and moisture resistant coatings, and as a diffusion barrier against ionic impurities such as Na+ and Cl-, and as dielectric layers. The coatings are also useful as dielectric layers, doped dielectric layers to produce transistor-like devices, pigment loaded binder systems containing silicon to produce capacitors and capacitor-like devices, multilayer devices, 3-D devices, silicon-on-insulator (SOI) devices, and super lattice devices. Another unique aspect of the coatings produced by the present invention is their transparency to electromagnetic radiation. Thus a particular advantage of the coatings of the present invention is utilization on focal plane arrays, photovoltaic cells, or opto-electronic devices in which electromagnetic radiation can pass into or emanate from the coated device.

Claims: A method of coating a substrate with a ceramic or ceramic-like silicon nitrogen-containing material, wherein said method comprises the steps of: (1) diluting with a solvent a silicon and nitrogen-containing preceramic polymer produced by reacting a cyclic silazane or a mixture of cyclic silazanes with a silicon-containing material selected from the group consisting of halodisilanes and halosilanes; (2) coating a substrate with the diluted preceramic polymer solvent solution; (3) drying the diluted preceramic polymer solvent solution in the absence of air so as to evaporate the solvent and thereby deposit a preceramic polymer coating on the substrate; and (4) heating the coated substrate in the absence of air to produce a ceramic or ceramic-like coated substrate. A method according to claim 1 wherein, in step (4) the coated substrate is heated to a temperature of 150 to 1000°C in an inert or ammonia - containing atmosphere. A method according to claim 1 or 2, wherein the heating in step (4) is conducted at 200 to 400°C. A method according to claim 3, wherein the heating in step (4) is conducted at 300 to 400°C. A method according to any of claims 1 to 4, wherein in step (1) the preceramic polymer is diluted to a solids content of 0.1 to 5 weight %.

Inventors: HALUSKA, LOREN ANDREW, MICHAEL, KEITH WINTON, TARHAY, LEO
Applicants: DOW CORNING CORPORATION
Application year: 1991
Main classification: C04B41
IPC codes: C23C18, H01L21, H01L23, C04B41, H05K3