OF SILICON DIOXIDE ON A METHOD FOR THE FORMATION OF SEMICONDUCTOR SUBSTRATE LAYERS.

Description

TITLE INV. DES. PRIORITY INTERNATIONAL BUSINESS MACHINES CORP. ARMONK NYUSA METHOD FOR FORMING SILICON DIOXIDE LAYERS ON A SEMICONDUCTOR SUBSTRATE. KEMLAGE BERNARD MICHAEL USA SUN. BREV. No. 66,964 OF 16 AUGUST 1979 Rome, December 10, 1906 Register A Protocol No. ?3G9O a / 80 MINISTRY OF INDUSTRY, COMMERCE AND CRAFTS Provincial Office of Industry, Commerce and Crafts of Milan COPY OF THE MINUTES OF FILING FOR INDUSTRIAL INVENTION PATENT In the year 1980, on the twenty-fifth day of the month at the hours and minutes of the month of log] I, the company INTERNATIONAL BUSINESS .MACHINES CORPORATION of American nationality with headquarters in Armonk - New York 10504 (USA) Via through the agent Dr.Ing. CAMILLO SAVI at IBM Italia SpA and with domicile for legal purposes in Milan - Via Andrea Doria 56 at the office of the * agent has presented to me, the undersigned: - Stamped application for the granting of a PATENT FOR a principal industrial invention I having as TITLE' THE METHOD FOR THE FORMATION OF SILICON DIOXIDE LAYERS ON A SEMICONDUCTOR SUBSTRATE Patent Application Priority in : USAN 66,964 dated .16 August 1979 designated inventor(s): 'Bernard Michael Kemlage writing pages, in duplo. accompanied by: - Description In duplicate of n - Drawings, tables no. 2 - Declaration referring to Power of Attorney. • Priority document and Italian translation. Deed of transfer with certified translation (reservation), - Proof of payment on postal account no. 00668004 made out to the Registry Office for Government Concession Taxes of Rome of Lit. 122,000.*= issued by the Post Office of Milan 14 on 15 July 1980 n. 733 and of Lit. 5,500.“ issued by the Post Office of Milan 14 on 23 July 1980 n. 228 for payment of deposit tax and Γ, 2\ 3, 4 Λ, and ^annual tn - Revenue stamp of Lit. 2000.* Inventor's designation act The application, descriptions and drawings listed above have been signed by the applicant and countersigned and stamped with the official stamp ' ' '''T^ THE OFFICER R, Peter the 1st p. the Director (Salvatore Ravalli) THE HEAD OF THE PATENT OFFICE Boleti / ) , w;*;: > ' · · ·”· ;·.·* For certified copy on the original(s) >, .ir:· / CS HON. MINISTRY OF INDUSTRY, TRADE AND CRAFTS CENTRAL PATENT OFFICE - ROME The applicant International Business Machines Corporation, of US nationality, with registered office in ARMONK, NEW YORK 10504 (USA) and elected domiciled for all legal purposes in Milan, at its Agent Dr. Ing. Camillo THE Savi, c / o IBM Italia SpA, Via A. Doria 56, 20124 Milan, requests, through the aforementioned agent, that the U PI CA,MILAN r- 'wifioafiiivF'i· '**·-' * .Ili . . ?:.Γ;7Γ mCvu Cl L..„..... the Patent Certificate for the industrial invention having j as its title: Method for forming silicon dioxide layers on a semiconductor substrate for the purpose of manufacturing, selling and using e-: i exclusively said invention, priority of the patent application filed in the United States of America to. serial 66,964 of August 16, 1979. , Please attach the following documents to this letter: 1) Description in two copies of 17 pages of writing. |2) Drawings n. 2 plates in two copies, j 3) Statement of reference to the General Power of Attorney. ί ' J 4) Proof of payment on postal account no. 00668004 in the name of the Registry Office for Government Tax Concessions - Rome of Lit. 122,000.=, issued by the Post Office of Milan 14 on 15 July 1980 no. 733 and of Lit. 5,500'.= issued by the Post Office of Milan 14 on 23 July 1980 fi tì- d il £L d n. 228, for payment of deposit fee and 1. ,2,3,4,5,6 Annuality. 5) Revenue stamp of Lit. 2,000 for issuing the Certificate. 6) Priority document and Italian translation. ?) Deed of Transfer with certified translation (reservation) 8) Act of designation of inventor. Designated Inventor(s): Bernard Michael Kemlage. / p. Inlernatlonat Business Machines Corporation Docket FI979O19 / CS DESCRIPTION of the invention entitled: Method for forming silicon dioxide layers on a semiconductor substrate* in the name of: International Business Machines Corporation residing in ARMONK, New York 10504 (USA) of US nationality filed on 2 5 |_UG 1980 with 11 3 Ρ9θ Summary of the invention A chemical vapor deposition process is described in which a barrier layer of silicon nitride, or the like, in the order of 50 - 3000 x 6 is formed on a silicon substrate and in which low-pressure chemical vapor deposition of a chlorosilane and a nitrous oxide oxidizer gas is employed to form silicon dioxide on the silicon nitride layer. This process overcomes the problem of low-pressure chemical vapor deposition of silicon dioxide that does not use the silicon nitride layer. The problem of degradation of the silicon dioxide layer during successive oxidation cycles p. International Business Machines Corporation Description of the invention 2. The invention relates to methods of forming silicon dioxide layers chemically deposited by low-pressure vapor and, more specifically, to a reactive chemical deposition of silicon dioxide on a silicon nitride layer by the reaction of a chlorosilane and an oxidizing gas under low-pressure conditions. Reference to related patent applications U.S. patent application of Β. M. Kemlage, IBM Docket No. FI979O18, Serial No. 66,965, filed concurrently with this application, under the title Low Pressure Chemical Vapor Deposition of Silicon Dioxide with Oxygen Enhancement of the ρ. Inlernatinnat Business Machines Corporation Basic technique 3. Silicon dioxide is widely used as an insulating and / or masking layer in the formation of semiconductor devices and integrated circuits. An important method for the formation of silicon dioxide is thermal growth, which involves the thermal oxidation of silicon in the presence of oxygen or steam at relatively high temperatures of over 900°C, and typically 1000°C and higher. This method is a high-temperature technique that may result in shifting of the P-N junction boundaries during the oxidation process. An additional problem is that silicon dioxide can only be grown on silicon. Another method for growing a silicon dioxide layer involves the use of a chemical vapor deposition reaction that involves the gas-phase oxidation of silicon tetrachloride, silicon dioxide, dichlorosilane, or the like. This method has been used for many years at atmospheric pressure and, more recently, at low pressures of the order of less than 1 torr. XI. Chemical vapor deposition method of silicon dioxide by gas-phase oxidation p. International Business Machines Corporation of silicon tetrachloride or aliano, has Typically 4. resulted in undesirably high temperatures such as those between 900°C and 1200°C. These temperatures would give rise to the problem of a shift in the boundaries of the P-N junctions, which should be avoided. At low temperatures, below 900°C, gas-phase oxidation of silene or silicon tetrachloride resulted in silicon dioxide films of lower quality than those obtained with thermally grown silicon dioxide films. ZI US Patent 4002512 by MJ Lim, entitled Method of Forming Silicon Dioxlde, known on date 11 / 1 / 1977, describes a low-temperature method for the formation of high-quality silicon dioxide films using dichloroethylene which is oxidized by means of a gas such as Og, COg, NgO, HgO, etc., combined with an inert carrier gas such as He, A, Ng, Hg, eoo. The use of a low-pressure hot-wall system for chemical vapor deposition of silicon dioxide is described in a paper presented by J. Sandor to the Electrocheraical Society Meeting, Los Angeles, California, May 6-10, 1962, ρ. International Business Machines Corporation by J. Oroshnik and others, in Journal Eleotro-Cheralcal 5. Society of Southern State Science, vol. 115, p. 649, 1968, and by R. S. Rosler in a paper entitled *Low Pressure CVD Production Processes for Poly, Nitrlde, and Oxide, in Solld State Technology, April 1977, pp. 63-70. RS Rosler's article reviews various low-pressure chemical vapor deposition methods for forming polycrystalline silicon, silicon nitride, and silicon dioxide films in the semiconductor industry. On page 68 Rosler describes the low-pressure reactions of diolrosilane and nitrous oxide in the temperature range of 800°C -920°C. The gas-phase reaction of chlorosilane, and more particularly diolrosilane, with nitrous oxide has led to the production of high-quality silicon dioxide glove layers with respect to their refractive index, but susceptible to degradation during subsequent oxidation cycles at temperatures above 900°C. The degradation phenomenon is believed to be an undercutting process resulting in the flaking of the silicon dioxide layer that has been so affected. p. Iniernational Business Machines Corporation The resulting structures are shown in Figures 1 and 2. Figure 3 is a plan view of an uncut silicon dioxide layer obtained by the method of the invention. Silicon nitride provides an effective barrier to the penetration of impurities into the surface of a semiconductor body. ZI U.S. Patent No. 3,494,809 to C.A. Rose under the title Semiconductor Processing proposes the use of silicon nitride on the back side of semiconductor wafers during the epitaxial growth phases on the front surface of the wafer, oxidation, etching and diffusion. According to the present invention, the degradation problem is overcome by using a silicon nitride film on which the silicon dioxide layer is deposited. This layer must have a thickness greater than about 50 Angstrom. 81 can use a thermally grown silicon dioxide layer between the silicon substrate and the silicon nitride layer. ρ. International Business Macfilnos Corporation Brief description of the drawings Figures 1 and 2 are 216x photographs of degraded, low-pressure vapor chemically deposited silicon dioxide films; Figure 3 is a 216x photograph of a silicon dioxide film that has not been degraded and was obtained according to the method of the invention; Figure 4 is a schematic cross-section showing the undercut phenomena; Figures 5 and 6 illustrate the structures resulting from the method of the present invention with silicon dioxide films that do not flake off after the oxidation cycle. p. International Business Machines Corporation The silicon dioxide layers, ^10^, after- 8. chemically extracted from low-pressure steam by the gas-phase reaction of chlorosilane, in particular dichlorosilane, and nitrous oxide, were undercut by an oxidation cycle or with dry hydrochloric acid at 1050 C. This undercutting proceeds so far as to cause actual cleavage of the 81O2 layer. The characteristics of the β10 2 films, as deposited, appear excellent. The surfaces are flat and defect-free, the refractive index δ 1.456, and analysis with an infrared spectrophotometer produces a plot identical to that of high-quality SiO2 layers formed by other means. The etch rate in 5:1 buffered hydrofluoric acid δ is slightly slower than that of other high-quality vapor-deposited SiO2 layers, and no etch is observed in pyrophosphate solution when the layer is used as a mask. The pinhole density δ was measured as zero by discharging the metal oxide capacitors. The films, as deposited, were placed in argon annealing furnaces at 1000°C for 30 minutes. International Business Machines Corporation ti and at 1100°C for 60 minutes. 9. Annealing had no apparent effect on any of the film characteristics. The surfaces remained defect-free, and the thickness and refractive index remained unchanged, suggesting that the SiO2 was deposited in a densified state. The same is true for annealing in hydrogen at 1150°C for 30 minutes. The SiO2 layer was found to react in the presence of hydrochloric acid, H2O, and O2 at high temperatures. The reaction ranged from intense wrinkling to flaking films. Figure 4 illustrates the undercut phenomenon in which the silicon substrate 10 is etched to form an opening 11 at the interface between the silicon dioxide layer 12 and the silicon substrate. The portion 13 of the silicon dioxide layer may peel off above the opening 11. X undercutting phenomena occur due to oxidations of 0 2 and 2t of hydrochloric acid carried out at 1050°C, but do not occur at 50°C. Dry 0 2 oxidations at 1100°C form dense roughness in the films after 60 minutes with no increase in density after 220 minutes. The same p. International Business Machines Corporation formation of dense roughness yes has oon oxidations ln humid environment at 1100%. Increasing the oxidation temperature in a humid environment to 1100% results in complete undercutting. This latter condition of a 1100% dry-wet-air oxidation cycle (5 minutes - 10 minutes - 5 minutes) was used as a test criterion for films deposited under various conditions. Films annealed in 1100% argon for 60 minutes, in 1100% oxygen for 220 minutes, or in 1150% hydrogen for 30 minutes were tested. These procedures did not bring any visible benefits. X Process parameters that have been tested include growth rate (25^ / min - 220^ / min), H^OtSl^Cl^ ratios (10*1 - 3*1), system pressure (300 mtorr - 600 mtorr) and temperatures (890% - 940%). Of these, only temperature influences the results. It has been established that the problem depends more on the thickness for depositions carried out at low temperatures. For thicknesses lower than 1500&, bubbles form. From about 1500& to about 2500&, these bubbles increase in density to form plaques that appear oriented towards the substratum. 10. 4 1 > ρ. International Business Machines Corporation to. For thicknesses greater than 250c£, the 11 are observed. undercutting and cleavage phenomena. Using a scanning electron microscope, it was determined that the roughness and plaques were likely due to chemical etching of the silicon substrate. Roughness and plaques are flat, etched cavities in the silicon substrate. The problem is believed to be caused by the inclusion of chlorine in the deposited SiO^ film. This bound chlorine can occur due to incomplete oxidation of chlorosilane, for example to chlorosilane Sih 2C1 2, probably in the form of SiO Cl . A physical analysis of the deposited SiO_ xy * films by Auger and RSman spectroscope confirmed the presence of chlorine. A clear presence of chlorine was observed at the SiO 2 / Sl interface, but no exact concentration determination could be made using the Auger method. Raman spectroscopy, on the other hand, has established in tested samples a chlorine inclusion of about 2.7% in the whole membrane of the layer. YES 2, as filed. In an attempt to obtain a barrier of protection against the attack of the substrate of p. International Business Machines Corporation silicon, polycrystalline silicon was discarded, as the problem initially arose for polycrystalline silicon. Thermal SiOg and chemically vapor-deposited SiOg were found to be slightly effective only when the barrier thickness was very large and equivalent to the thickness of the chemically vapor-deposited SiOg film itself. It was established that silicon nitride was an effective barrier when deposited at a thickness greater than 50 Angstroms, or directly on silicon, as shown in figure 5, or on an intermediate buffer layer of silicon dioxide, as shown in figure 6. The preferred thickness of the silicon nitride layer 14 is approximately 100 to 500 Angstroms. Silicon nitride can be up to 3000 × 8 thick. Thicknesses greater than 3000 pounds give rise to tension problems. Chemically vapor-deposited SiOg layers of up to 2.0 ρm were successfully vapor-oxidized at 1100°C for 60 minutes without echo undercutting that in pinholes of the nitride. 12. silicon. p. International Business Machines Corporation Silicon nitride is preferably deposited in one atmosphere using a mixture of SiH. and NH^ at a deposition temperature range of about 700°C - 1000°C. The silicon dioxide substrate 15 is preferably formed by thermal oxidation of the silicon substrate in steam at 1000°C. The thickness of the 810 6 is between about 100 and 5000 * Angstrom. The use of the silicon nitride layer allows for quality silicon dioxide layers of thicknesses ranging from 1000 - 100,000 Angstroms. The following examples are given simply to facilitate the understanding of the invention and those skilled in the art may make modifications to them without departing from the spirit or purpose of the invention. Example 1 Silicon nitride was deposited on a series of wafers with reagents t εΐΗ,ΝΗ in a carrier gas4 3 tn 2 temperature t 800°C growth rate! about 10oS / min. The wafer series containing Si layers.,N. of 3 4 13. p. International Business Machines Corporation 0, 25, 50, 100, 200, and 500 μm thick wafers directly onto the silicon substrate were used for the deposition of 1 shot of LPCVD-SiO^ from a high-temperature LPCVD-SiO^ system. These wafers were steam annealed at 1100°C to determine the barrier effectiveness. For all wafers with Si^N^ thickness greater than 5oR, the barrier proved to be fully effective for eliminating undercutting. Example 2 A series of wafers identical to those in example η. 1 were prepared except that 810 was formed and thermally increased in thickness. Λ of 1000& between the silicon wafer and the barrier Yes.N., All subsequent proceedings were 3 4 the same. The same results were obtained as in example η. 1. The silicon oxide had no effect on the Ei^N^ barrier layer at all. It will be obvious to the expert that, although the invention has been shown and described in detail in relation to some of its preferred embodiments, there are numerous modifications of the whole and of the details which can be made without departing from the spirit or scope of the invention. 14. p. International Business Machines Corporation of the Invention.

Claims

1. CLAIMS 1. A method of forming a silicon dioxide layer on a semiconductor substrate wherein said layer is not subject to degradation during successive oxidation cycles comprising the steps of forming a silicon nitride layer of thickness greater than about 50 Angstroms on a surface of said substrate; and mixing a gas-phase chlorosilicon with a nitrous oxide oxidizing gas at a temperature of about 800°C to 1200°C at a pressure of less than about 5 torr to deposit said silicon dioxide layer on said silicon nitride layer.

2. The method of claim 1 wherein said δ silicon nitride layer is deposited by mixing silene and ammonium in a nitrogen carrier gas at temperatures between about 700°C and 1000°C.

3. The method of claim 1 wherein said silicon nitride layer has a thickness of from about 50 to 3,000 Angstroms and said silicon dioxide layer has a thickness of from about 1,000 to 100,000 Angstroms.

15.

4. The method according to claim 1 wherein ρ. International Business Machines Corporation said substrate is silicon and a silicon dioxide layer is formed thereon by thermal oxidation thereon prior to said formation of a silicon nitride layer.

5. The method of claim 4 wherein the thickness of said silicon dioxide layer formed by thermal oxidation has a thickness of between about 100 and 5000 Angstroms.

6. The method of claim 1 wherein said chlorosilane is dichlorosilane and is combined with said oxidizing gas at a temperature of about 850°C - 1000%.

7. A method of forming a silicon dioxide layer on a semiconductor substrate wherein said layer is not subject to degradation during successive oxidation cycles comprising the steps of forming a silicon nitride layer of thickness greater than about 50 Angstroms on a surface of said substrate and combining gas-phase dichlorosilane and nitrous oxide at a temperature of about 850% to 1000% at a pressure of less than about 5 torr to deposit said silicon dioxide layer on said silicon nitride layer.

16.

8. The method of claim 7 wherein p. International Business Machines Corporation said silicon nitride layer is deposited by a mixture of silica and ammonium in a nitrogen carrier gas at temperatures between about 700°C and 1000°C.

9. The method of claim 7 wherein said substrate is silicon and a silicon dioxide layer is formed by thermal oxidation prior to forming the silicon nitride layer.

10. The method of claim 9 wherein said silicon dioxide layer formed by thermal oxidation has a thickness of from about 100 to 5,000 Angstroms, said silicon nitride layer has a thickness of from about 50 to 3,000 Angstroms, and said silicon dioxide layer deposited on said silicon nitride layer has a thickness of from about 1,000 to 100,000 Angstroms. 17.