April 13, 1971 E, PAMMER ETAL 3,574,677 METHOD o1" I’ROUUCLNG A PROTEOTLVE LAYER FROM A SEMICONDUCTOR COMPOUND FOR SEMICONDUCTOR PURPOSES Filed Apr11'28, 1967 3,574,677 ‘United States Patent O?ce Patented Apr. 13, 1971 1 2 oxide. The corresponding effect is also on the electro 3,574,677 > METHOD OF PRODUCING A PROTECTIVE LAYER static charging of the insulating layers. Also, the silicon FROM A SEMICONDUCTOR NITROGEN COM layers permit a limiting frequency which is ap POUND FOR SEMICONDUCTOR POSES proximately 3—5 times higher. Planar transistors may Erich Pammer and Horst Panholzer, Munich, Germany, also be advantageously produced with such protective assignors to Siemens Aktiengesellschaft, Berlin, Ger layers. The present invention has among its objects the pro~ Filed Apr. 28, 1967, Ser. No. 634,614 duction of such layers in an advanta Claims priority, application Germany, May 2, 1966, geous Way, permitting not only lower growing tempera— rm. Cl. B44d’1/02, 1/18 tures for these layers than possible with known methods, US. Cl. 117—201 _ 7 ‘Claims but also obtaining better structural characteristics for the protective layer. The layer may be used as a mask as well as for the protection of the obtained structural com ABSTRACT OF THE DISCLOSURE ponents. Other semiconductor-nitrogen compounds, for 15 example Ge3N4 may also be favorably produced as a A method of producing a protective layer at the sur protective layer by the method of the invention. The face of a semiconductor crystal. Organic silicon nitro invention relates to a method for producing a protective gen compounds are pyrolytically (thermally) precipi layer from a silicon or nitrogen compound tated from gaseous phase to form silicon nitride on the at the surface of a semiconductor crystal, preferably semiconductor. 20 silicon, germanium or an AIHBV compound, by means of thermal precipitation of the silicon or germanium nitro It is known that SiOZ layers on the surface of semicon gen compound from a gaseous phase. To this end, the ductor components protect p-n junctions against moisture present invention provides the use of a reaction gas whose and other disturbances. For this reason such protective one active component is a metal free, gaseous compound layers are found on the surfaces of planar transistors, 25 between the nitrogen and the semiconductor, for example, such as silicon planar transistors. The protective layers silicon. also serve an important function in the production of Contrary to the aforementioned production of the pro such transistors by diffusion. During the production of tective layer from a mixture of and silicon planar transistors, the semiconductor surface is pro hydride, according to the method of the invention, the vided with an SiOg layer, for example by thermal oxi 30 silicon nitrogen compound is already contained in the dation. Subsequently, individual areas of the semicon reaction gas. This difference over the known technique ductor surface have the SiOz layer removed therefrom, permits our method to use not only lower reaction in order to obtain a local penetration of the activator temperatures, but also simultaneously prevents the oc substance from a gaseous phase, into the semiconductor currence of intermediary products which still contain material. By contrast to those areas from which the SiO2 35 Si-H compounds, and which may become incorporated layer had been removed, the activator cannot or can only in the silicon nitride of the protective layer. Therefore, to a very insigni?cant degree ‘penetrate into the semicon— ‘ the protective layer, produced according to the invented ductor surface which is coated with the SiO2 layer. Since method, is more compact than the known Si3N4 layers, the p-n junctions thus produced Will not reach the freed so that still better masking characteristics are obtainable. semiconductor surface, but will remain beneath the pro 40 On the other hand, tests have shown the aforementioned tective layer, the SiO2 layer protects the p-n junctions improvements present no obstacle for etching-in dif in the ?nished semiconductor component. fusion windows, for example by hydrofluoric acid con However, the masking capacity of an Si02 protective taining etchants. layer is better with respect to individual activators. Hence, Among the volatile compounds, which can be used other protective layer materials were repeatedly sought. 45 for producing silicon-nitride protective layers, accord~ Lately, the use of silicon nitride layers has been sug ing to the present method, the following should be con gested for this purpose. The silicon nitride layers are sidered: alkylaminosilane, alkylaminosilazane, siliconiso precipitated from a gaseous phase, through reaction of nitrile (silicon isocyanate). These compounds are pref SiH, and ammonia at the surface of the semiconductor erably admixed to a ?ow of inert carrier gas, for ex crystals, at increased temperature. In layers thus pro ample nitrogen a noble gas or hydrogen. The reaction duced, diffusion windows for the actual semiconductor occurs at the surface of the heated semiconductor crys surface, required for the diffusion of activators, may be tal. An advantage of using such compounds is that lower produced by etching with HF-containing acid mixtures. melting semiconductor materials, such as germanium, Silicon nitride has better masking properties than SiOg can be coated with the protective layers. On the heated mainly during the diffusion of metallic activators, e.g. surface, the aforementioned compounds thermally dis~ Zinc or gallium, and results in higher blocking voltages sociate into dense silicon nitride layers, which adhere than may be obtained in semiconductor components, pro very strongly to the substrate. To produce other pro vided with comparable SiO‘z protective layers. The use of tective layers, as for example from germanium-nitride, silicon nitride protective layers is analogous to the SiOg analogous germanium compounds may be used. protective layers. For example, field effect transistors 60 During the reaction of halide silanes, for example of possess an even higher control sensitivity, if the control SiCl4 with ammonium, a white, non-volatile polymeric electrode is separated from the semiconductor body by a solid body of the formula (Si(NH)2),, forms in admix silicon nitride layer, instead of an equally dimensioned ture with solid ammonium chloride, via unstable inter SiOz layer. The dielectric strength of such nitride layers mediary products, such as Si(NH2)4 etc. By heating to is better than that of the corresponding SiO2 layers. This 65 higher temperatures, this compnnd converts through sev is particularly advantageous in ?eld effect transistors eral intermediary stages, by splitting out ammonia, into whose control electrode is separated from the semicon pulverulent, hexagonal silicon nitride, Si3N4. The process ductor by an insulation layer comprised of silicon nitride, may be illustrated by the following equation: as contrasted to transistors separated by an SiO2 layer, in lieu thereof. Contaminations present in silicon nitride 70 have a considerably lower tendency for the to mi grate than the contaminations contained in silicon di 3,574,677

(Si(NH)2)x and its resulting products are not suitable of the layers obtained, depends largely on the precipita due to their non-volatility for the production of uniform, tion temperature. adhesive and gas-tight silicon-nitride layers to be used as ‘Especially suitable as volatile Si-nitrogen compounds making protective layers for a localized diffusion in semi are: conductor surfaces. Neither does the reaction of silicon with nitrogen or ammonia (which reaction is usually at (a) alkyl and arylaminosilanes or alkly and arylamino 1300“ C.) produce a silicon-nitride layer able to per alkylsilane form the desired function. The Si3N4 which results from Si(NRR')4 such processes is a porous layer at the semiconductor or surface, or is even localized as loose crystal needles. The 10 "R(4_n)Si(NRR’)n high temperatures, needed in the known method, also R=H, alkyl, phenyl promote an undesirable out-diffusion of doping materials R'=H, alkyl, phenyl from the semiconductor crystals to be coated. n=l, 2, 3, 4. If, however, in accordance with the method of the (b) Alkyl: and arylaminosilazane invention, gaseous, oxygen-free silicon nitrogen com 15 pounds are used from the start and if their vapors are (R'RN)3_mSiRm—§—SiRm'(NRR’)3-111’ passed, if necessary, together with foreign gases onto m, m"=1, 2, 3 heated semiconductor surfaces, a pyrolytic precipitation (0) Cyclic Si-N compounds of (a) and (b) for example occurs with a deposit of a strongly adhering, clear ho mogeneous layer of silicon nitride which Will be precipi tated on said semiconductor surfaces. R H R” The drawing illustrates apparatus suitable for execut ing the method of the present invention. ‘In a cylindrical reaction vessel 1, comprised for ex ample of quartz, the semiconductor crystal 3 which is to be coated with the silicon nitride layer, is arranged on a pedestal 2 of the type used in conventional semiconduc tor epitaxy from a gaseous phase. Heating of the crystal may be effected by means of a resistance heater 4, using (d) Silicon-isocyanate (melting point 26", boiling point the pedestal 2 as a heat resistor, or by means of the 30 185.6“) induction ?eld of a coil 5 which heats, the pedestal, which Si(NOO)4 is comprised of a conductive and heat-resistant material, (e) In place of alkyl-aminoalkylsilanes, a gaseous mix to reaction temperature. The consumed reaction gases ture of alkylaminosilane may be brought into reaction leave from the reaction vessel via outlet 6 while the fresh with ammonia or alkylamines and hydrogen. At gas is introduced into the reaction vessel at point 7 in 35 temperatures above 700° this also results in the coating such a way that said fresh gas may enter into sufficient of silicon . contact with the semiconductor crystal to be coated. The schematically: liquid silicon nitrogen compound 8 is located in a vapor SiR4 + NH; } Si-nitride ization vessel 8a, whose temperature is kept constant via or +hydrocarbon a thermostatic bath 15. A carrier gas is passed through 40 +hydrogen this vessel at 8b by means including valve 13 and gas flow meter 12 and leaves the vaporization vessel at point In selecting a carrier gas the nature of the volatile 9, loaded with entrained vapor of the volatile silicon silicon nitrogen compound must be taken into account. nitrogen compound. A supply path 10 for the pure car To be considered is Whether silicon atoms are bound rier gas is connected in parallel thereto. The flow of the only to nitrogen or whether Si-—C or Si-H compounds carrier gas may be controlled by means of gas flow are also present. In the ?rst instance noble gases, hydrogen meters 11 and 12 and regulated by means of control or nitrogen alone or mixtures thereof, may be used as a valves 13 and 14. The conditions are the same as in carrier gas; in the second instance, an addition of am hetero-epitaxy. monia or gaseous alkylamine is necessary for the above Several examples to illustrate the invention follow: carrier gases when the atom ratio N:Si is less than 1.521. The use of a hydrogen and/or NH3 containing atmosphere EXAMPLE 1 is always advantageous for facilitating the separation of R alkyl groups. S : N/ —-—>Si-hitride+hydrocarbon The analogy of the method of our invention with con R 4 ventional epitaxy from gaseous phase of silicon, ger Si-nitride layers with variable characteristics are ob manium and other semiconductor layers raises the pos tained according to the temperature range and type as sibility of obtaining silicon nitride, which in a mono crystalline state in a semiconductor, in the form of a well as the admixture of the foreign gas. monocrystalline layer on a semiconductor body of, for EXAMPLE 2 example silicon or silicon-carbide. For example, it is A carrier gas (N2, argon, NH3 or mixtures thereof) possible to obtain on a substrate comprised of silicon or are passed into a fritted wash bottle through liquid tetra silicon carbide with (111) precipitation surface, mono kisdimethylaminosilane (melting point 15° C., boiling crystalline Si3N4 layers, if the combination of the reaction point 180° C.) so that the gas becomes loaded with the gas is gradually changed during the precipitation process, vapors of the compound. The ratio of gas to vapor is 65 so that initially, virtually only the semiconductor of the preferably adjusted by a regulated temperature bath (pos substrate is precipitated with a slight mixture with the sibly by a “bypass”). The gas mixture is now passed into silicon nitride and only then gradually increasing the a reactor with the silicon or semiconductor discs which share of silicon-nitride while correspondingly decreasing are positioned on a heated substrate (usually carbon the share of the substrate semiconductor during precipi heaters coated with quartz glass). The temperature of 70 tation, until ?nally only silicon nitride is precipitated. [the discs may be between 500° C., and 1200° C. although The adjusting forces of the silicon, or of the silicon carbide it is usually approximately 700° C. Slowly, a dense, trans lattice, may in this way ?nally result in an oriented pre parent coating of silicon nitrides is precipitated on the cipitation of the silicon nitride. The use of such mono discs. The thickness of the layer increases linearly with the crystalline silicon nitride layers as semiconductors is en time. The dissolving speed, especially in etching solutions, tirely feasible. a, 574,677 5 6 We claim: References Cited 1. A method of producing a silicon nitride protective layer compound at the surface of a semiconductor crystal, UNITED STATES PATENTS by thermal precipitation from the reaction gas, which 3,149,398 9/1964 Sprague et a1. ______117—106X comprises thermally decomposing a reaction gas con 3,246,214 4/1966 Hugle ______3l7—235 sisting essentially of a metal-free volatile compound of 3,386,918 6/1968 Hough et a1 ______117—106UX nitrogen and silicon which contains an Si-N bond and FOREIGN PATENTS at least one organic radical, said compound being selected from the group consisting of alkyl and arylaminosilane, 1,190,308 3/1959 France ______117-—106 ' alkyl and arylaminoalkylsilane, and alkyl and arylamino 10 OTHER REFERENCES silazane. Ephraim, F.: , 6th ed., by P. C. L. 2. The method of claim 1, wherein the semiconductor Thorne and E. R. Roberts; ‘Oliver-Boyd; London, England, crystal is selected from silicon, germanium and AIIIBv 1954, pp. 662-3. compounds. Storr, R., Wright, A. N., Winkler, C. A.: Reactions of 3. The method of claim 2, wherein an aminosilazane 15 Active Nitrogen with Boron Trichloride and Germane, is used to precipitate silicon nitride. in Canadian Journal of Chemistry, 40 pp. 1299-1301, 4. The method of claim 2 in which tetra‘kisdimethyl 1962. aminosilane is used to precipitate silicon nitride. Semiconductor Device, in Chemical Abstracts, 63 5. The method of claim 2, wherein an aminosilane (1965), 1321b, in Electronics, 39, Jan. 10, 1966, p. 164. is used to precipitate silicon nitride. 20 6. The method of claim 5, wherein an alkylaminosilane ALFRED L. LEAVITT, Primary Examiner is reacted with ammonia at pyrolytic temperature to pre cipitate the silicon nitride layer. C. K. WEIFFENBACH, Assistant Examiner 7. The method of claim 5, wherein an alkylaminosilane is reacted with alkylamine and hydrogen at pyrolyltic US. Cl. X.R. temperature to precipitate the silicon nitride layer. 23-191; 1l7—106, 135.1 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION

Patent No. 3 , 574 , 677 Dated April 13 , 1971

1nventor(s) Erich Pammer et a1 _

It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Priority date should read -— April 29, 1966 -—.

Signed and sealed this 31st day of August 1971.

(SEAL) Attest: EDWARD M.FLETCHER,JR. ROBERT GOTTSCHLAK Attesting Officer Acting Commissioner of Pat