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Protective Electronic Coatings Using Filled Polysilazanes

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Protective Electronic Coatings Using Filled Polysilazanes Europaisches Patentamt 19 European Patent Office Office europeen des brevets © Publication number : 0 675 537 A2 12 EUROPEAN PATENT APPLICATION © Application number : 95302008.8 <&) int. ci.6: H01L 23/29 @ Date of filing : 27.03.95 (30) Priority: 01.04.94 US 221597 © Inventor : Haluska, Loren Andrew 4510 James Street Midland, Michigan (US) @ Date of publication of application Inventor : Michael, Keith Winton 04.10.95 Bulletin 95/40 2715 Siebert Midland, Michigan (US) @ Designated Contracting States : DE FR GB IT NL © Representative : Vandamme, Luc Johan Roger Dow Corning Limited, Cardiff Road © Applicant : DOW CORNING CORPORATION Barry, South Glamorgan CF63 2YL, Wales (GB) Midland, Michigan 48686-0994 (US) © Protective electronic coatings using filled polysilazanes. © The present invention relates to a method of forming protective coatings on electronic subs- trates and to the substrates coated thereby. The method comprises applying a coating compris- ing a polysilazane and a filler on a substrate and then heating the coated substrate at a tempera- ture sufficient to convert the polysilazane to a ceramic. CM < co If) If) h- LU Jouve, 18, rue Saint-Denis, 75001 PARIS 1 EP 0 675 537 A2 2 The present invention relates to a method of filler materials. The expression "filler" describes a forming protective coatings using compositions com- finely divided solid phase which is distributed within prising polysilazanes and fillers. These coatings are the polysilazane and the final ceramic coating. The useful on a variety of electronic substrates. expression "electronic substrate" includes electronic The use of polysilazanes to form ceramic coat- 5 devices or electronic circuits such as silicon based ings on electronic devices is known in the art. For in- devices, gallium arsenide based devices, focal plane stance, WO 93/02472 discloses such a process arrays, opto-electronic devices, photovoltaic cells wherein a solution of a polysilazane resin is applied and optical devices. to an electronic substrate followed by heating the In our process, a protective ceramic coating is coated substrate in air at a temperature in the range 10 formed on a substrate by a process which comprises of 150-800°C. This publication, however, does not de- applying a coating composition comprising a polysi- scribe the use of fillers within the coating. lazane and a f illeronto the substrate and then heating Similarly, the use of fillers within ceramic coat- the coated substrate at a temperature sufficient to ings derived from polysilazanes is also known in the convert the polysilazane to a ceramic. art (JP-A(s) 52287 and 221466). These documents, 15 The polysilazanes (or silazane polymers) useful however, do not describe the use of such materials as in this invention are well known in the art and their protective coatings on electronic substrates. structure is not particularly critical. These polysila- JP-A 3250082 also describes the incorporation of zanes generally contain units of the type [R2SiNH], an electroconductive powder within a ceramic de- [RSi(NH)1.5] and/or [R3Si(NH)1/2] wherein each R is in- rived from a polysilazane. However, it does not de- 20 dependency selected from hydrogen atoms, alkyl scribe protective coatings on electronic substrates. radicals containing 1 to 20 carbon atoms, aryl radicals We have now found that useful coatings for the and alkenyl radicals. Naturally, the polysilazanes protection of electronic devices can be formed from useful in this invention may contain other silazane compositions comprising polysilazanes and fillers. units. Examples include [MeSi(NH)15], [Me2SiNH), The present invention relates to a method of 25 [ViSi(NH)1.5], [Vi2SiNH], [PhMeSiNH], [PhViSiNH], forming a protective coating on the surface of an elec- [MeViSiNH], [HSi(NH)1.5] and [H2SiNH]. As used here- tronic substrate and to the substrates coated thereby. in, Me is a methyl radical, Vi is a vinyl radical and Ph The method comprises first applying a composition is a phenyl radical. Mixtures of polysilazanes may comprising a polysilazane and a filler on the surface also be employed in the practice of this invention. of the electronic substrate. The coated substrate is 30 The polysilazanes of this invention can be pre- then heated at a temperature sufficient to convert the pared by techniques well known in the art. The actual composition to a ceramic coating. method used is not critical. Suitable preceramic sila- Desirable protective coatings can be formed on zane polymers or polysilazanes may be prepared by electronic substrates from a composition comprising the methods in U.S. Patents 4,540,803 and a polysilazane and a filler. Coatings derived there- 35 4,543,344. Other polysilazanes suitable for this in- from are thicker (e.g., > 40 micrometers) than those vention can be prepared by the methods of U.S. Pa- derived from polysilazanes alone (e.g., < 2 microme- tents 4,312,970; 4,340,619; 4,395,460 and ters). We have found a variety of coatings can result 4,404,153. Suitable polysilazanes also include those with electrical properties depending on the filler prepared by U.S. Patents 4,482,689 and 4,397,828. which are crack and pore-free. 40 Still other polysilazanes include those of European Because of these advantages, our coatings are Patent 351,747; U.S. Patent 4,543,344; European particularly valuable as protective coatings on elec- Patent 332,374; U.S. Patents 4,656,300 or 4,689,252 tronic substrates. Such coatings could serve as pas- and U.S. Patent No. 5,030,744. sivation or dielectric coatings, interlevel dielectric lay- Especially preferred polysilazanes are those ers, doped dielectric layers to produce transistor like 45 which have no carbon in the repeating units of the devices, pigment loaded binder systems containing polymer since the resultant coatings have little car- silicon to produce capacitor and capacitor like devic- bon contamination. Endblocking groups such as es, multilayer devices, 3-D devices, silicon on insula- Me3Si(NH)1/2 are acceptable in such polymers since tor devices, coatings for superconductors, super lat- they will be removed during the subsequent pyrolysis tice devices, tamperproof coatings and the like. so steps. As used herein, the expression "ceramic coating" The most preferred polymers are those of U.S. describes the hard coating obtained after heating the Patents 4,340,619 and 4,540,803. The former sila- polysilazane - filler composition. This coating con- zane polymers are prepared by contacting and react- tains both amorphous silica (Si02) materials as well ing in an inert, essentially anhydrous atmosphere a as amorphous silica-like materials that are not fully 55 chlorine containing disilane or mixture of chlorine free of residual carbon (e.g., Si-C), nitrogen (e.g., Si- containing disilanes of the general formula (ClxRySi)2 N), silanol (Si-OH) and/or hydrogen (e.g., Si-H) which with a disilazane having the general formula are obtained upon heating the polysilazane and the (R3'Si)2NH at a temperature in the range of 25°C. to 2 3 EP 0 675 537 A2 4 300°C. while distilling volatile byproducts, wherein R (materials which render heat on oxidation) such as is a vinyl group, an alkyl group of 1-3 carbon atoms magnesium, iron, tin, silicon, zinc, precipitated diato- or a phenyl group; R' is a vinyl group, hydrogen atom, mite, aluminum silicate or other silicates, pigments, an alkyl group of 1-3 carbon atoms ora phenyl group; phosphors, wollastonite, mica, kaolin, clay and talc. x has a value of 0.5-3; y has a value of 0-2.5 and the 5 Also, some organic materials such as cellulose, poly- sum of x+y equals 3. An especially preferred embodi- amides and phenol resins may be used. ment of the former polymers involves the reaction of The preferred fillers used herein depend on the methylchlorodisilanes with hexamethyldisilazane to intended use for the coating. For instance, if the coat- produce methylpolydisilylazane. The product sila- ing is used as an interlevel dielectric, a material such zane polymers may have a relatively high chloride ion 10 as silica or alumina may be desirable so that the coat- content and it is preferred that it be lowered before ing has a low dielectric constant (DK) of less than 8. use in the present invention. A method for such re- Similarly, if a coating having a high DK of greater than moval is described in U.S. Patent 4,772,516 which 12 is desired, a material such as barium titantate or comprises treating the product polymers with ammo- lead niobate may be desirable. Similarly, if an opaque nia for a time sufficient to remove the chlorine. 15 coating is desired, an optically or radiopaque material The latter silazane polymers above are prepared may be desired. by a method which comprises contacting and reacting The number average particle size and shape of in an inert essentially anhydrous atmosphere, tri- the above fillers can vary over a wide range depend- chlorosilane with a disilazane at a temperature in the ing on factors such as the type of filler, the desired range of 25°C. to 300°C. while distilling volatile by- 20 coating thickness or the like. Since the coatings are products. The disilazane used in the process has the generally less than 500 micrometers thick, particle si- formula (R3Si)2NH where R is selected from vinyl rad- zes less than this are generally used. Preferred num- ical, hydrogen atom, phenyl radical and alkyl radicals ber average particle sizes are in the range of less than containing 1 to 3 carbon atoms. An especially prefer- 50 micrometers and the most preferred number aver- red embodiment of the latter polymers involves the 25 age particle size is in the submicrometer range to 10 reaction of trichlorosilane with hexamethyldisilazane micrometers.
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