Multilayer ceramic coatings from silicate esters and metal oxides

Abstract: This invention relates to materials produced by diluting in a solvent a preceramic mixture of a partially hydrolyzed silicate ester and a metal oxide precursor selected from the group consisting of an aluminum alkoxide, a titanium alkoxide, and a zirconium alkoxide. 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/metal oxide 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, 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", pp 349-65, 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. David W. Johnson, JR. has described in an article entitled "Sol-Gel Processing of Ceramics and Glass" [AM. Ceram. Soc. Bull., 64 [12] 1597-1602 (1985)] that TiO₂-SiO₂ coatings on silicon (Si) wafers have been produced by hydrolysing the ethoxides of titanium (Ti) and silicon (Si). At least one of the constituents was partially hydrolysed before the mixing and the solutions were applied by a spinning process for the Si wafers which were dried under a heat lamp and then heated to temperatures of from 200 to 400°C. Film thicknesses varied from 50-100 nm. 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. Dietz et al., United States Patent No. 3,859,126, issued January 7, 1975, teaches the formation of a composition comprising PbO, B₂O₃, and ZnO, with optional various oxides including SiO₂. Rust et al., United States Patent No. 3,061,587, October 30, 1963, teaches a process for forming ordered organo silicon-aluminum oxide copolymers by reacting dialkyl diacyloxysilane or dialkyl dialkoxysilane, with trialkylsiloxy dialkoxy aluminum. Glasser et al. ("Effect of The H₂O/TEOS Ratio Upon The Preparation And Nitridation Of Silica Sol/Gel Films", Journal of Non-Crystalline Solids 63, (1984) p. 209-221) utilized tetraethoxysilane without additional metal oxides to produce films for subsequent high temperature nitridation. The instant invention 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 discovered is a method of forming coatings from a silicate ester and one or more metal oxides, which are subsequently coated with one or more silicon, or silicon and nitrogen, or silicon and carbon and nitrogen-containing, ceramic or ceramic-like coatings. According to the present invention, in its broadest aspects, there is provided a process for providing an electronic device with a multilayer protective coating, which process comprises, in a first stage (I), providing said device with a first coating by diluting with a solvent a preceramic mixture consisting of hydrolyzed or partially hydrolyzed silicate ester with zirconium, aluminium and/or titanium alkoxide, applying the resulting diluted preceramic mixture solution to said device, drying said solution to evaporate the solvent and thereby to deposit a preceramic coating on said device and ceramifying said preceramic coating to silicon dioxide and metal oxide by heating the coated device to a temperature between 200 and 1,000°C, whereby a ceramic or ceramic-like planarizing first coating is produced on said device, wherein, in a second stage (II), said device is provided with a silicon-containing second coating consisting of: (i) a silicon-containing coating by chemical vapour decomposition of a silane, halosilane, halodisilane, halopolysilane, or mixture thereof, at a temperature between 200 and 1000°C, in the presence of the ceramic coated device, whereby a silicon-containing second coating is produced on said ceramic coated device; or (ii) a silicon nitrogen-containing coating by (a) chemical vapour decomposition or plasma-enhanced or metal-assisted chemical vapour decomposition of a silane, halosilane, halodisilane, halopolysilane or mixture thereof and ammonia, at a temperature between 200 and 1,000°C, in the presence of the ceramic or ceramic-like coated device, whereby a silicon nitrogen-containing second coating is produced on said ceramic coated device, or (b) diluting a preceramic silicon nitrogen-containing polymer in a solvent, coating the ceramic coated device with the resulting diluted solution, drying said diluted solution to evaporate the solvent and thereby to deposit a preceramic silicon nitrogen-containing coating on the coated electronic device, and heating the electronic device having said silicon nitrogen-containing coating thereon in an inert or ammonia-containing atmosphere at a temperature between 200 and 1,000°C to produce a ceramic or ceramic-like silicon nitrogen-containing second coating on said device; or (iii) a silicon carbon-containing coating by chemical vapour decomposition or plasma-enhanced or metal-assisted chemical vapour decomposition of a silane, halosilane, halodisilane, halopolysilane, or mixture thereof, and an alkane of 1 to 6 carbon atoms or an alkylsilane, in the vapour phase, at a temperature between 200 and 1,000°C, in the presence of the device coated with said first coating, whereby a silicon carbon-containing second coating is produced on said device; or (iv) a silicon carbon nitrogen-containing coating by chemical vapour deposition or plasma-enhanced or metal-assisted chemical vapour deposition of (a) hexamethyldisilazane or (b) a silane, halosilane, halodisilane, halopolysilane or mixture thereof in the presence of an alkane of 1 to 6 carbon atoms or an alkylsilane and further in the presence of ammonia, in the presence of the ceramic coated device, whereby a silicon carbon, nitrogen second coating is obtained on said ceramic coated device. A preferred temperature range for obtaining the vapour decomposition of the silane, halosilane, halodisilane, halopolysilane or mixture thereof, to produce the silicon-containing coating is between 200 and 600°C, more preferably between 200°C and 400°C. According to a preferred aspect of the invention the second coating produced in the above second stage (II) consists in a passivating coating selected from the group consisting of (i) a silicon nitrogen-containing coating, (ii) a silicon carbon-containing coating and (iii) a silicon carbon nitrogen-containing coating. According to a preferred embodiment, the silicon nitrogen-coating is obtained by chemical vapour deposition or plasma-enhanced or metal-assisted chemical vapour deposition of a silane, halosilane, halodisilane, halopolysilane, or mixture thereof, in the presence of ammonia at a temperature between 200 and 400°C or by ceramification of a silicon nitrogen-containing preceramic polymer at a temperature between 200 and 400°C. According to a further feature of the invention, in a third stage (III), there is applied to the passivating coating (II) a silicon-containing third coating selected from the group consisting of (i) a silicon-containing coating, (ii) a silicon carbon-containing coating, (iii) a silicon nitrogen-containing coating and (iv) a silicon carbon nitrogen-containing coating using the same means as are employed for applying said silicon-containing second coating according to stage (II) above. The invention also covers the use of an electronic device with a multilayer coating obtainable on said device by a process as defined above for producing an electronic device with enhanced protection against environmental stress. The instant invention relates to the low temperature formation of multilayer protective coatings for the protection of electronic devices. The multi-layer coatings of the present invention consists of (1) a coating prepared by contacting a hydrolyzed or partially hydrolyzed silicate ester with zirconium, aluminum, and/or titanium alkoxides to produce a homogeneous preceramic coating and (2) a topcoat of silicon-containing material, or silicon nitrogen-containing material, or silicon carbon-containing material, derived by heating a silane, halosilane, halodisilane, halopolysilane or mixtures thereof to provide protection. The first layer is a SiO₂/TiO₂, or SiO₂/ZrO₂, or SiO₂/TiO₂/ZrO₂, or SiO₂/Al₂O₃, or SiO₂/TiO₂/ZrO₂/Al₂O₃ planarizing and passivating coating that is applied by known techniques, including flow coating, spin coating, dip coating and spray coating of an electronic device and then ceramifying. The second layer of the dual-layer coatings of the instant invention is a protective barrier coating of silicon-containing material derived from the CVD or plasma enhanced CVD of silanes, alkylsilanes, halosilanes, halodisilanes, silazanes, or mixtures of alkanes, silanes, and ammonia. The instant invention also relates to the low temperature formation of a three layer coating system for electronic devices wherein the first layer is a SiO₂/TiO₂, or SiO₂/ZrO₂, or SiO₂/TiO₂/ZrO₂, or SiO₂/Al₂O₃, or SiO₂/TiO₂/ZrO₂/Al₂O₃ coating. 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 the three layer coatings of the present invention is a top coating of (a) silicon-containing material applied by CVD, plasma enhanced CVD, 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 (c) silicon nitrogen-containing material applied by CVD or plasma enhanced CVD of a silane, 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 CVD or plasma enhanced CVD of mixtures of a silane, an alkylsilane an alkane and ammonia. The instant invention relates to the discovery that a hydrolyzed or partially hydrolyzed silicate ester can be contacted with zirconium, aluminum or titanium alkoxides to prepare novel preceramic polymers that can be converted at low temperatures to ceramic or ceramic-like materials useful as planarizing coatings for irregular surfaces of electronic devices. In the instant invention, by "alkoxide" is meant any alkoxy, acyloxy, dialkoxy, trialkoxy, or tetraalkoxy organic group which is bonded to a metal and which can be hydrolyzed and subsequently pyrolyzed under the ceramification conditions stated herein to produce a metal oxide. By the instant invention, ceramic or ceramic-like planarizing coating compositions such as SiO₂/ZrO₂, SiO₂/TiO₂, SiO₂/TiO₂/ZrO₂, and SiO₂/Al₂O₃ have been prepared, These metal oxide ceramic or ceramic-like coatings minimize mechanical stresses due to the irregular topography of an integrated circuit or electronic device and also help prevent microcracking of subsequent multilayer coatings under thermal cycling conditions. The first layer comprising the SiO₂ in its coating can be obtained from a solvent solution of a material containing silicon and oxygen, wherein, upon heat treatment, the material ceramifies to form an SiO₂-containing material. Such materials can include, but are not limited to, organic orthosilicates, Si(OR)₄, or condensed esters of the type (RO)₃SiOSi(OR)₃, and any other source of SiOR such that upon hydrolysis and subsequent pyrolysis a material of essentially SiO₂ is produced. Thus, materials containing carbon, such as SiOC-containing materials, can be included in this group if the carbon-containing group is hydrolyzable under the thermal conditions so as to volatilize out leaving essentially SiO₂. By "silicate esters" is meant herein materials which upon hydrolysis and pyrolysis yield essentially SiO₂. By "hydrolyzed or partially hydrolyzed silicate ester" in the instant invention is meant any SiO₂-containing material, as described above, which has been treated with aqueous, basic, or acidic conditions so as to hydrolyze or partially hydrolyze the ester. In the instant invention, by "ceramic-like" is meant those pyrolyzed silicon-nitrogen containing 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 devices including, but not limited to, electronic devices, silicon based devices, gallium arsenide devices, focal plane arrays, opto-electronic devices, photovoltaic cells and optical devices. The invention further relates to the discovery that these ceramics can be used as multilayer coatings for electronic devices. The instant invention also relates to the formation of silicon- and nitrogen-containing passivating coatings and silicon-containing top coatings for ceramic or ceramic-like coated electronic devices wherein the top coating is prepared by CVD, plasma enhanced CVD or metal catalyzed CVD techniques. In the case of highly reactive alkoxides of aluminum, titanium, and zirconium, such as the propoxides, iospropoxides, butoxides, and isobutoxides, and also the zirconium pentanedionate (also called acetylacetonate), the metal alkoxides and the silicate ester can be pre-mixed and heated to reflux in ethanol for 24 hours to afford a homogeneous reaction mixture which can be hydrolyzed uniformly and at a controllable rate. The refluxing produces a condensation reaction, the product of which can be hydrolyzed uniformly. However, attempts to pre-hydrolyze a mixture of the above mentioned highly reactive alkoxides and silicate ester without the condensation reaction results in preferential and rapid hydrolysis of the metal alkoxide over that of the silicate ester, resulting in rapid, non-homogeneous gellation of the reaction mixture. The coatings produced by the instant invention exhibit strong adhesion to electronic devices, and are abrasion and moisture resistant. The choice of the electronic 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. In addition, the instant invention relates to a method of forming a multilayer, ceramic or ceramic-like, coating which method comprises (A) coating an electronic device with a planarizing coating by means of diluting with a solvent a preceramic mixture of a hydrolyzed or partially hydrolyzed silicate ester and a metal oxide precursor selected from the group consisting of an aluminum alkoxide, a titanium alkoxide, and a zirconium alkoxide, coating an electronic device with said diluted preceramic polymer solution, drying the diluted preceramic polymer solution so as to evaporate the solvent and thereby deposit a homogeneous preceramic coating on the electronic device, ceramifying the polymer to silicon dioxide and metal oxide by heating the coated device to produce a ceramic or ceramic-like coating, and (B) applying to the ceramic coated device a silicon-containing coating by means of decomposing in a reaction chamber a silane, halosilane, halodisilane or mixture thereof in the vapor phase at a temperature between 200 and 1000°C., in the presence of the ceramic coated device, whereby an electronic device containing a multilayer, ceramic coating thereon is obtained. The method for coating the electronic device with the preceramic solvent solution can be, but is not limited to, flow coating, spin coating, spray or dip coating techniques. The instant invention further relates to a method of forming a multilayer, ceramic or ceramic-like, protective coating comprising (A) coating an electronic device with a coating by means of diluting to low solids in a solvent a hydrolyzed or partially hydrolyzed silicate ester preceramic polymer, which has been contacted with zirconium pentanedionate, coating an electronic device with said diluted preceramic polymer solution, drying the diluted preceramic polymer solution so as to evaporate the solvent and thereby deposit a preceramic coating on the electronic device, ceramifying the polymer to silicon dioxide and zirconium dioxide by heating the coated device to produce a ceramic or ceramic-like coating, and (B) applying to the ceramic or ceramic-like coating on the electronic device a silicon-containing coating by means of decomposing in a reaction chamber a silane, halosilane, halodisilane or mixture of halosilanes in the vapor phase, at a temperature between 200 and 400°C., in the presence of the coated device, whereby an electronic device containing a multilayer, ceramic or ceramic-like, protective coating thereon is obtained. The instant invention further relates to a method of forming a multilayer, ceramic or ceramic-like coating which method comprises (A) coating an electronic device with a coating by means of diluting to low solids in a solvent a hydrolyzed or partially hydrolyzed silicate ester preceramic polymer which has been contacted with titanium dibutoxy diacetylacetonate, coating an electronic device with said diluted preceramic polymer solution, drying the diluted preceramic polymer solution so as to evaporate the solvent and thereby deposit a preceramic coating on the electronic device, ceramifying the polymer to silicon dioxide and titanium dioxide by heating the coated device to produce a ceramic or ceramic-like coating, and (B) applying to the coated device a silicon-containing coating by means of decomposing in a reaction chamber a silane, halosilane, halodisilane or mixture of halosilanes in the vapor phase, at a temperature between 200 and 400°C., in the presence of the coated device, whereby an electronic device containing a multilayer, ceramic or ceramic-like coating thereon is obtained. The instant invention further relates to a method of forming a multilayer, ceramic or ceramic-like coating which method comprises (A) coating an electronic device with a coating by means of diluting to low solids in a solvent a hydrolyzed or partially hydrolyzed silicate ester preceramic polymer which has been contacted with an aluminum alkoxide, coating an electronic device with said diluted preceramic polymer solution, drying the diluted preceramic polymer solution so as to evaporate the solvent and thereby deposit a preceramic coating on the electronic device, ceramifying the polymer to silicon dioxide and aluminum oxide by heating the coated device to produce a ceramic or ceramic-like coating, and (B) applying to the ceramic or ceramic-like coating on the electronic device a silicon-containing coating by means of decomposing in a reaction chamber a silane, halosilane, halodisilane or mixture of halosilanes in the vapor phase, at a temperature between 200 and 400°C., in the presence of the coated device, whereby an electronic device containing a multilayer, ceramic or ceramic-like protective coating thereon is obtained. The instant invention further relates to a method of forming a multilayer, ceramic or ceramic-like coating which method comprises (A) coating an electronic device with a coating by means of diluting with a solvent a preceramic mixture of a hydrolyzed or partially hydrolyzed silicate ester and a metal oxide precursor selected from the group consisting of an aluminum alkoxide, titanium alkoxide, and zirconium alkoxide, coating an electronic device with said diluted preceramic mixture solution, drying the diluted preceramic polymer mixture solution so as to evaporate the solvent and thereby deposit a preceramic coating on the electronic device, ceramifying the preceramic coating to silicon dioxide and metal oxide by heating the coated device to produce a ceramic or ceramic-like coating, and (B) applying to the coated device a passivating coating which comprises a silicon nitrogen-containing material by means of diluting to low solids in a solvent a preceramic silicon nitrogen-containing polymer, coating the ceramic coated device with the diluted preceramic silicon nitrogen-containing polymer solution, drying the diluted preceramic silicon nitrogen-containing polymer solution so as to evaporate the solvent and thereby deposit a preceramic silicon nitrogen-containing coating on the coated electronic device, heating the coated device in an inert or ammonia-containing atmosphere to produce a ceramic or ceramic-like silicon nitrogen-containing coating, and (C) applying to the coated device a silicon-containing coating by means of decomposing in a reaction chamber a silane, halosilane, halodisilane, halopolysilane or mixture thereof in the vapor phase, at a temperature between 200 and 900°C., in the presence of the coated device, whereby an electronic device containing a multilayer, ceramic or ceramic-like coating thereon is obtained. The ceramification of the planarizing and passivating coatings utilized in the multilayer coatings of the instant invention can be achieved at temperatures between 200 and 1000°C. and preferably at temperatures between 200 and 400°C. In the instant invention, a preceramic polymer containing a hydrolyzed or partially hydrolyzed silicate ester is diluted after the incorporation of, for example, zirconium tetra acetylacetonate, Zr(CH₃COCH₂COCH₃)₄, or titanium dibutoxy diacetylacetonate, Ti(CH₃COCH₂COCH₃)₂(OCH₂CH₂CH₂CH₃)₂, and/or aluminum acetylacetonate, Al(CH₃COCH₂COCH₃)₃, to low solids (eg., 0.1 to 10 weight %) in a solvent such as ethanol. The diluted preceramic polymer solvent solution is refluxed for twenty-four hours and then coated onto an electronic device and the solvent allowed to evaporate by drying. As discussed above, certain metal alkoxides are too reactive toward hydrolysis and therefore should be pre-mixed with the silicate ester and the mixture refluxed in a solvent such as ethanol prior to hydrolysis. The method of coating the diluted preceramic polymer solution onto the electronic device can be, but is not limited to, spin coating, dip coating, spray coating, or flow coating. By this means is deposited a homogeneous preceramic coating which is ceramified by heating the coated device for approximately twenty hours at 200°C. or for one hour at 400°C. This represents a significant processing temperature reduction over that of the prior art. Thin ceramic or ceramic-like planarizing coatings of less than 2 micrometres (microns) [or approximately 500 nanometres (5000 A)] are thus produced on the devices. The planarizing coatings thus produced can then be coated with a passivating silicon nitrogen-containing coating of the present invention or with a CVD or PECVD applied silicon-containing coating, silicon carbon-containing coating, silicon nitrogen-containing coating, silicon carbon nitrogen-containing coating, or a combination of these coatings. Sample formulations of the planarizing coatings of the instant invention include, but are not limited to, those depicted in Table I. where wt% is weight per cent; ZrO₂ is zirconium dioxide produced from zirconium alkoxide; TiO₂ is titanium dioxide produced from titanium alkoxide; Al₂O₃ is aluminum oxide produced from aluminum pentanedionate. While Table 1 indicates a metal alkoxide composition in the coatings of 10 weight per cent, the concentration range of metal oxide may vary from 0.1 weight per cent metal alkoxide up to approximately 30 weight percent. By varying the ratio of hydrolyzed or partially hydrolyzed silicate ester to metal alkoxide (and thus to the resulting metal oxide) specific formulations with desired coefficients of thermal expansion (CTE) can be designed. It is desirable in coating electronic devices that the CTE of the coating allow for sufficient thermal expansion so as to minimize the formation of microcracks upon exposure of the coated device to temperature variations. Table II shows the CTE values for several common ceramic materials used in coating electronic devices and also the CTE values of ceramic planarizing coatings of the instant invention. The source for the reference data appearing above is "Ceramic Source", American Chemical Society, vol. 1., 1985, p. 350-1. The CTE values for the compositions of the instant invention are calculated. The chemical compounds in which the aluminum, zirconium, and titanium are operative in the present invention are not limited to the oxide or dioxide forms listed above but include any and all forms and mixtures of the metals which can be blended with the hydrolyzed or partially hydrolyzed silicate ester and ceramified to produce the mixed oxide planarizing coating system of the instant invention. The second and passivating silicon nitrogen-containing layer of the composite coatings in the instant invention provides resistance against ionic impurities. Preceramic silicon nitrogen-containing polymers suitable for use in this present invention are well known in the art, including, but not limited to, silazanes, disilazanes, polysilazanes, cyclic silazanes and other silicon nitrogen-containing materials. The preceramic silicon nitrogen-containing polymers suitable for use in this invention must be capable of being converted to a ceramic or ceramic-like material at elevated temperatures. Mixtures of preceramic silazane polymers and/or other silicon- and nitrogen-containing materials may also be used in this invention. Examples of preceramic silazane polymers or polysilazanes suitable for use in this invention include polysilazanes as described by Gaul in U.S. Patents 4,312,970 (issued January 26, 1982), 4,340,619 (issued July 20, 1982), 4,395,460 (issued July 26, 1983), and 4,404,153 (issued September 13, 1983). Suitable polysilazanes also include those described by Haluska in U.S. Patent 4,482,689 (issued November 13, 1984) and by Seyferth et al. in U.S. Patent 4,397,828 (issued August 9, 1983), and Seyferth et al. in U.S. Patent 4,482,669 (issued November 13, 1984). Other polysilazanes suitable for use in this invention are disclosed by Cannady in U.S. Patents 4,540,803 (issued September 10, 1985), 4,535,007 (issued August 13, 1985), and 4,543,344 (issued September 24, 1985), and by Baney et al. in EP-A2 0 175 384. Also suitable for use in this invention are dihydridosilazane polymers prepared by the reaction of H₂SiX₂, where X = a halogen atom, and NH₃. These (H₂SiNH) n polymers are well known in the art, but have not been used for the protection of electronic devices. (See, for example, Seyferth, U.S. Patent Number 4,397,828, issued August 9, 1983.) Also to be included as preceramic silicon nitrogen-containing polymer materials useful within the scope of the present invention 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 materials are disclosed and claimed in U.S. Patent No. 4,745,205, titled "Novel Preceramic Polymers Derived From Cyclic Silazanes And Halogenated Disilanes And A Method For Their Preparation", and U.S. Patent No. 4,742,143, titled "Novel Preceramic Polymers Derived From Cyclic Silazanes And Halosilanes And A Method For Their Preparation", respectively, filed in the name of Loren A. Haluska. 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. 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 polymeric ceramic or ceramic-like coating material is produced. Alternatively, in the three layer coating of the instant invention, the second and passivating coating can be selected from the group consisting of silicon nitrogen-containing material, silicon carbon nitrogen-containing material, and silicon carbon-containing material. The silicon nitrogen-containing material is deposited by the CVD or plasma enhanced CVD of the reaction product formed by reacting silane, halosilanes, halopolysilanes, or halodisilanes and ammonia. The silicon carbon-containing material is deposited by the CVD or plasma enhanced CVD of the reaction product formed by reacting silane, halosilanes, halopolysilanes, or halodisilanes and an alkane of one to six carbon atoms or alkylsilane. The silicon carbon nitrogen-containing material is deposited by the CVD or PECVD of hexamethyldisilazane or the CVD or PECVD of mixtures of a silane, an alkylsilane, an alkane of one to six carbon atoms, and ammonia. The second and passivating coating of the multilayer coatings of the instant invention can be produced by applying to the planarizing coating a passivating ceramic or ceramic-like coating selected from the group consisting of (i) a silicon nitrogen-containing coating, (ii) a silicon carbon-containing coating, and (iii) a silicon carbon nitrogen-containing coating, wherein the silicon nitrogen-containing coating is applied onto the ceramic or ceramic-like coated electronic device by a means selected from the group consisting of (a) chemical vapor deposition of a silane, halosilane, halodisilane, halopolysilane or mixtures thereof in the presence of ammonia, (b) plasma enhanced chemical vapor deposition of a silane, halosilane, halodisilane, halopolysilane or mixtures thereof in the presence of ammonia, (c) ceramification of a silicon and nitrogen-containing preceramic polymer; and wherein the silicon carbon nitrogen-containing coating is applied onto the ceramic or ceramic-like coated electronic device by a means selected from the group consisting of (1) chemical vapor deposition of hexamethyldisilazane, (2) plasma enhanced chemical vapor deposition of hexamethyldisilazane, (3) chemical vapor deposition of a silane, alkylsilane, halosilane, halodisilane, halopolysilane or mixture thereof in the presence of an alkane of one to six carbon atoms or an alkylsilane and further in the presence of ammonia, and (4) plasma enhanced chemical vapor deposition of a silane, alkylsilane, halosilane, halodisilane, halopolysilane or mixture thereof in the presence of an alkane of one to six carbon atoms or an alkylsilane and further in the presence of ammonia; and wherein the silicon carbon-containing coating is deposited by a means selected from the group consisting of (i) chemical vapor deposition of a silane, alkylsilane, halosilane, halodisilane, halopolysilane or mixtures thereof in the presence of an alkane of one to six carbon atoms or an alkylsilane and (ii) plasma enhanced chemical vapor deposition of a silane, alkylsilane, halosilane, halodisilane, halopolysilane or mixtures thereof in the presence of an alkane of one to six carbon atoms or an alkysilane, to produce the passivating ceramic or ceramic-like coating. The preceramic silazane or other silicon nitrogen-containing polymer solvent solution is coated (by any method discussed above) onto the electronic device previously coated with the SiO₂/metal alkoxide coating, such as, SiO₂/Zr(CH₃COCH₂COCH₃)₄, or SiO₂/Zr(CH₃COCH₂COCH₃)₄/Ti(CH₃COCH₂COCH₃)₂(OCH₂CH₂CH₂CH₃)₂ and subsequently ceramified to SiO₂/metal oxide, such as, SiO₂/ZrO₂, or SiO₂/ZrO₂/TiO₂, respectively. The solvent is then allowed to evaporate by drying. By this means is deposited a preceramic silicon nitrogen-containing polymer coating which is ceramified by heating the coated device for approximately one hour at temperatures up to 400°C. under argon. Thin ceramic passivating coatings of less than 2 micrometres (microns) [or approximately 500 nanometres (5000 Angstroms)] are thus produced on the device. The third layer of the multilayer coatings of the instant invention can be produced by applying to the passivating ceramic or ceramic-like coating a silicon-containing coating selected from the group consisting of (i) a silicon coating, (ii) a silicon carbon-containing coating, (iii) a silicon nitrogen-containing coating, and (iv) a silicon carbon nitrogen-containing coating, wherein the silicon coating is applied onto the passivating coating by a means selected from the group consisting of (a) chemical vapor deposition of a silane, halosilane, halodisilane, halopolysilane or mixtures thereof, (b) plasma enhanced chemical vapor deposition of a silane, halosilane, halodisilane, halopolysilane or mixtures thereof, or (c) metal assisted chemical vapor deposition of a silane, halosilane, halodisilane, halopolysilane or mixtures thereof, and wherein the silicon carbon-containing coating is applied by a means selected from the group consisting of (1) chemical vapor deposition of a silane, halosilane, halodisilane, halopolysilane or mixtures thereof in the presence of an alkane of one to six carbon atoms or an alkylsilane, (2) plasma enhanced chemical vapor deposition of a silane, alkylsilane, halosilane, halodisilane, halopolysilane or mixtures thereof in the presence of an alkane of one to six carbon atoms or an alkylsilane; and wherein the silicon nitrogen-containing coating is deposited by a means selected from the group consisting of (A) chemical vapor deposition of a silane, halosilane, halodisilane, halopolysilane or mixtures thereof in the presence of ammonia, (B) plasma enhanced chemical vapor deposition of a silane, halosilane, halodisilane, halopolysilane or mixtures thereof in the presence of ammonia, and (C) ceramification of a silicon and nitrogen-containing preceramic polymer, and wherein the silicon carbon nitrogen-containing coating is deposited by a means selected from the group consisting of (i) chemical vapor deposition of hexamethyldisilazane, (ii) plasma enhanced chemical vapor deposition of hexamethyldisilazane, (iii) chemical vapor deposition of a silane, alkylsilane, halosilane, halodisilane, halopolysilane or mixture thereof in the presence of an alkane of one to six carbon atoms or an alkylsilane and further in the presence of ammonia, and (iv) plasma enhanced chemical vapor deposition of a silane, alkylsilane, halosilane, halodisilane, halopolysilane or mixture thereof in the presence of an alkane of one to six carbon atoms or an alkylsilane and further in the presence of ammonia; to produce the silicon-containing coating on the electronic device. The silicon-containing protective third layer or topcoat of the composite coatings of the present invention can be obtained at relatively low reaction temperature by the metal-assisted CVD process claimed in the parallel U.S. Patent Application Serial No. 835,029, filed February 2, 1986 in the name of Sudarsanan Varaprath and entitled "Silicon-Containing Coatings and a Method for Their Preparation", or by conventional non-metal assisted CVD and plasma enhanced CVD techniques. The high temperature conditions of the conventional CVD technique normally limit the type of substrate materials which can be coated. Thus, electronic devices which cannot be heated over 400°C. without damage cannot be coated by conventional, CVD techniques. 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. 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 as dielectric layers, and as a diffusion barrier against ionic impurities such as Na⁺ and Cl⁻. The SiO₂/metal oxide coatings and the silicon nitrogen-containing ceramic or ceramic like coatings of the instant invention are also useful as interlevel dielectrics within the body of the electronic device and between the metallization layers, thereby replacing spin-on glass films. The coatings of the present invention are useful for functional purposes in addition to protection of electronic devices from the environment. The coatings of the present invention are also useful as dielectric layers 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. Example 1 A reaction mixture of 0.3125 grams of ethyl orthosilicate and 0.0396 grams of zirconium tetra acetylacetonate, dissolved in 35.2 grams of ethanol was refluxed for 24 hours. The reaction mixture was then cooled to room temperature and to the reaction mixture was then added 0.033 grams of water and one drop of 5% hydrochloric acid and the solution was heated to 60 - 75°C. for 45 minutes to produce a hydrolyzed preceramic polymer solution. The hydrolyzed preceramic polymer solvent solution was then spin coated onto a CMOS electronic device. By this means was deposited a preceramic polymer coating which was ceramified by heating the coated device in a two inch Lindberg furnace for approximately twenty hours at 200°C. Additional coatings were also ceramified at 400°C. for one hour. Thin ceramic planarizing coatings of less than 2 micrometres (microns) [or approximately 400 nanometres (4000 A)] were thus produced on the devices. By this method coatings were also applied to aluminum panels. Example 2 A solution of 8.6 milliliters of ethyl orthosilicate, 8.6 milliliters of ethanol, 2.8 milliliters of water and one drop of 5% hydrochloric acid was heated at 60°C. for thirty minutes. The solution was diluted with 60 milliliters of ethanol and 0.04 grams of dibutoxy diacetylacetonate titanium, Ti(OC₄H₉)₂(O₂C₅H₇)₂, and allowed to stand at room temperature for 24 hours to produce a preceramic polymer solution. The preceramic polymer solution was then spin coated onto an electronic device. By this means was deposited a preceramic polymer coating which was ceramified by heating the coated device for approximately twenty hours at 200°C. or for one hour at 400°C. Thin ceramic planarizing coatings of less than 2 micrometres (microns) [or approximately 400 nanometres (4000 A)] were thus produced on the devices. By this method coatings were also applied to aluminum panels. Example 3 A solution of 5.04 milliliters of ethyl orthosilicate, 5.04 milliliters of ethanol, 9.9 milliliters of water and two drops of 5% hydrochloric acid was heated at 60-70°C. for thirty minutes. The solution was diluted to 3.3 weight per cent solids with the addition of 60 milliliters of ethanol followed by the addition of one drop of 5% hydrochloric acid. The solution was allowed to sit at ambient temperatures for 4 days. Ten grams of the solution was mixed with 0.235 grams of aluminum tris pentanedionate and 26.2 grams of ethanol to produce a clear, stable preceramic polymer solution. The preceramic polymer solution was then spin coated onto an electronic CMOS device. By this means was deposited a preceramic polymer coating which was ceramified by heating the coated device for approximately twenty hours at 200°C. or for one hour at 400°C. Thin ceramic planarizing coatings of less than 2 micrometres (microns) [or approximately 400 nanometres (4000 Angstroms)] were thus produced on the devices. By this method coatings were also applied to aluminum panels. Example 4 A 7:1:1:1 weight per cent mixture of ethyl orthosilicate, titanium dibutoxy diacetylacetonate, zirconium tetra acetylacetonate, and aluminum acetylacetonate, respectively, was prepared by refluxing at low solids, 1.0 weight per cent, in ethanol for a period of 24 hours. This solution was hydrolyzed by the addition of one equivalent of water for each alkoxy group in the presence of a small amount of hydrochloric acid and heating the solution to 60-75°C. for 45 minutes to produce a hydrolyzed preceramic polymer solution. The preceramic polymer solvent solution was then spin coated onto an electronic CMOS device. By this means was deposited a preceramic polymer coating which was ceramified by heating the coated device for approximately twenty hours at 200°C. or for one hour at 400°C. Thin ceramic planarizing coatings of less than 2 micrometres (microns) [or approximately 400 nanometres (4000 Angstroms)] were thus produced on the devices. By this method coatings were also applied to aluminum panels. Example 5 A preceramic silazane polymer, prepared by the method of Cannady in Example 1 in U.S. Patent No. 4,540,803, was diluted to 1.0 weight per cent in toluene. The diluted preceramic silazane polymer solvent solution was then flow coated onto the coated electronic devices of Examples 1 through 4 and the solvent was allowed to evaporate by drying in the absence of air. By this means was deposited a preceramic polymer passivating coating which was ceramified by heating the coated device for approximately one hour at 400°C. under argon. Thin silicon nitrogen-containing ceramic or ceramic-like passivating coatings of less than 2 micrometres (microns) [or approximately 300 nanometres (3000 Angstroms)] were thus produced on the devices. By this method coatings were also applied to aluminum panels. Example 6 Using the procedure of Example 5, a preceramic silazane polymer containing about 5 per cent titanium, prepared by the method of Haluska in Example 13 in U.S. Patent No. 4,482,689, was flow coated onto the SiO₂/metal oxide coated electronic device and the solvent allowed to evaporate by drying. By this means was deposited a preceramic polymer coating which was ceramified by heating the coated device for approximately one hour at temperatures up to 400°C. under argon. Thin silicon nitrogen-containing ceramic or ceramic-like passivating coatings of less than 2 micrometres (microns) [or approximately 300 nanometres (3000 Angstroms)] were thus produced on the devices. By this method coatings were also applied to aluminum panels. Example 7 Using the procedure of Example 5, a preceramic silazane polymer, prepared by the method of Gaul in Example 1 in U.S. Patent No. 4,395,460, was coated onto the SiO₂/metal oxide coated electronic device and the solvent allowed to evaporate by drying. By this means was deposited a preceramic polymer coating which was ceramified by heating the coated device for approximately one hour at temperatures up to 400°C. under argon. Thin silicon nitrogen-containing ceramic or ceramic-like passivating coatings of less than 2 micrometres (microns) [or approximately 300 nanometres (3000 Angstroms)] were thus produced on the devices. By this method coatings were also applied to aluminum panels. Example 8 A 1-2 weight % solution in diethyl ether of dihydridosilazane polymer, prepared by the method of Seyferth in Example 1 in U.S. Patent No. 4,397,828, was flow coated onto CMOS devices coated by the methods of Examples 1-4, above. The coated devices were heated in nitrogen for one hour at 400°C. The coating and pyrolysis treatment did not adversely affect the function of the devices, as determined by a CMOS circuit tester. The coated devices withstood 0.1M NaC1 exposure for over four and one half hours before circuit failure. A nonprotected CMOS device will fail to function after exposure to a 0.1M NaC1 solution for less than one minute. By this method coatings were also applied to aluminum panels. Example 9 The electronic devices coated with the planarizing and/or passivating coatings of Examples 1 through 8 were then overcoated with the barrier coats as follows; Hexafluorodisilane, 6.67 KPa (50 Torr), was placed in a Pyrex glass reaction container along with a CMOS electronic device, previously coated as above. The hexafluorodisilane was transferred to the glass container in such a manner as to preclude exposure to the atmosphere. The container was sealed and heated in an oven for 30 minutes at a temperature of approximately 360°C. During this time, the hexafluorodisilane starting material decomposed and formed a silicon-containing topcoat on the previously coated electronic device. The reaction by-products, mixtures of various halosilanes, and any unreacted starting material were removed by evacuation after the container had been reattached to the vacuum line. The ceramic coated electronic device, onto which the decomposed hexafluorodisilane starting material had deposited a silicon-containing topcoating, was then removed. The coated electronic device was tested and all electronic circuits were operable. The instrument that was utilized to test the CMOS devices before and after coating was a Teradyne Analogical Circuit Test Instrument J133C equipped with a CMOS 4000 AE Series Family Board and a CMOS 4011 A Quad 2 Input Nand Gate Device Board. This unit tests the DC parameters of the device. The test is a go/no go type test.

Claims: A process for providing an electronic device with a multilayer protective coating, which process comprises, in a first stage (I), providing said device with a first coating by diluting with a solvent a preceramic mixture consisting of hydrolyzed or partially hydrolyzed silicate ester with zirconium, aluminium and/or titanium alkoxide, applying the resulting diluted preceramic mixture solution to said device, drying said solution to evaporate the solvent and thereby to deposit a preceramic coating on said device and ceramifying said preceramic coating to silicon dioxide and metal oxide by heating the coated device to a temperature between 200 and 1,000°C, whereby a ceramic or ceramic-like planarizing first coating is produced on said device, wherein, in a second stage (II), said device is provided with a silicon-containing second coating consisting of: (i) a silicon-containing coating by chemical vapour decomposition of a silane, halosilane, halodisilane, halopolysilane, or mixture thereof, at a temperature between 200 and 1000°C, in the presence of the ceramic coated device, whereby a silicon-containing second coating is produced on said ceramic coated device; or (ii) a silicon nitrogen-containing coating by (a) chemical vapour decomposition or plasma-enhanced or metal-assisted chemical vapour decomposition of a silane, halosilane, halodisilane, halopolysilane or mixture thereof and ammonia, at a temperature between 200 and 1,000°C, in the presence of the ceramic or ceramic-like coated device, whereby a silicon nitrogen-containing second coating is produced on said ceramic coated device, or (b) diluting a preceramic silicon nitrogen-containing polymer in a solvent, coating the ceramic coated device with the resulting diluted solution, drying said diluted solution to evaporate the solvent and thereby to deposit a preceramic silicon nitrogen-containing coating on the coated electronic device, and heating the electronic device having said silicon nitrogen-containing coating thereon in an inert or ammonia-containing atmosphere at a temperature between 200 and 1,000°C to produce a ceramic or ceramic-like silicon nitrogen-containing second coating on said device; or (iii) a silicon carbon-containing coating by chemical vapour decomposition or plasma-enhanced or metal-assisted chemical vapour decomposition of a silane, halosilane, halodisilane, halopolysilane, or mixture thereof, and an alkane of 1 to 6 carbon atoms or an alkylsilane, in the vapour phase, at a temperature between 200 and 1,000°C, in the presence of the device coated with said first coating, whereby a silicon carbon-containing second coating is produced on said device; or (iv) a silicon carbon nitrogen-containing coating by chemical vapour deposition or plasma-enhanced or metal-assisted chemical vapour deposition of (a) hexamethyldisilazane or (b) a silane, halosilane, halodisilane, halopolysilane or mixture thereof in the presence of an alkane of 1 to 6 carbon atoms or an alkylsilane and further in the presence of ammonia, in the presence of the ceramic coated device, whereby a silicon carbon, nitrogen second coating is obtained on said ceramic coated device. A process according to Claim 1, in which said silicon-containing second coating is obtained by vapour decomposition of said silane, halosilane, halodisilane, halopolysilane, or mixture thereof, at a temperature between 200 and 600°C. A process according to Claim 2, wherein said temperature is in the range between 200°C and 400°C. A process according to Claim 1, wherein said second stage (II) consists in applying to the ceramic or ceramic-like planarizing first coating obtained in said first stage (I) a passivating coating selected from the group consisting of (i) a silicon nitrogen-containing coating, (ii) a silicon carbon-containing coating and (iii) a silicon carbon nitrogen-containing coating. A process according to Claim 4, wherein said silicon nitrogen-containing coating is obtained by chemical vapour deposition or plasma-enhanced or metal-assisted chemical vapour deposition of a silane, halosilane, halodisilane, halopolysilane, or mixture thereof, in the presence of ammonia at a temperature between 200 and 400°C or by ceramification of a silicon nitrogen-containing preceramic polymer at a temperature between 200 and 400°C. A process according to Claim 4 or Claim 5, further characterised in that, in a third stage (III) there is applied to the passivating coating (II) obtained according to Claim 4 or Claim 5 a silicon-containing third coating selected from the group consisting of (i) a silicon-containing coating, (ii) a silicon carbon-containing coating, (iii) a silicon nitrogen-containing coating and (iv) a silicon carbon nitrogen-containing coating using the same means as are employed for applying said silicon-containing second coating according to stage (II) of Claim 1. Use of an electronic device with a multilayer protective coating obtainable on said device by a process as claimed in any of Claims 1-6 for producing an electronic device with enhanced protection against environmental stress.

Inventors: HALUSKA LOREN ANDREW, MICHAEL KEITH WINTON, TARHAY LEO, HALUSKA, LOREN ANDREW, MICHAEL, KEITH WINTON, TARHAY, LEO
Applicants: DOW CORNING, DOW CORNING CORPORATION
Application year: 1987
Main classification: C23C28
IPC codes: H01L21, H01L23, C23C16, C23C18