Arthur Sherman - Chemical Vapor Deposition for Microelectronics, страница 12

These gasesare then fluid dynamically transported to the wafer where deposition occurs.If the wafer had been present in the region where the plasma was being generated, serious damage would have been done to it. It is the separation of thegeneration and deposition processes that makes this concept feasible.For the deposition of silicon nitride, the reactant gases were SiH 4 and N2flowing at a pressure of 0.1 mTorr.

With the excitation frequency fixed at2.45 GHz, a steady magnetic field of 875 gauss produced the condition ofelectron cyclotron resonance. The plasma produced by this condition thenflows along a divergent magnetic nozzle until it impinges on the wafer beingcoated. The wafer which is electrically floated in the chamber charges negatively("'15V) and causes some ion bombardment of the growing film.62Chemical Vapor Deposition for MicroelectronicsSilicon nitride films produced by this technique proved to be comparableto those created in parallel-plate reactors in terms of stoichiometry and hydrogen content, as evidenced by the data presented in Figures 17 and 18.400SiH4 ' 10 cc/min.N2 ,10 cc/min.c::oMS"'-.0<:300~(JJoWm~c::/.2000oMoW'Men0p..(JJlOaat/'.~....--.--><2.2Si 3 N4'x~~x __x(JJ"'0c::'M2.1(JJ>OMoW--x__(J2.0\d~~Q)aa100200300Microwave power (w)1.9~Figure 17: Deposition rate and refractive index for silicon nitride films as afunction of microwave power for ECR reactor (after Matsu0 26 ).SiH4 , 10 cc/min.N2' 10 - 20 cc/min.Without heating.20010050201051.92.02.

IRefractive indexFigure 18: BOE etch rate versus refractive index for silicon nitride films forEC R reactor (after Matsu0 26 ).Silicon nitride filmsreactors will be discussedtypically have a refractivegen incorporated into thedeposited in parallel-plate, plasma-enhanced CVDin greater detail in a later chapter. However, theyindex on the order of 2.0, partly because of hydrolayer, and the ECR films appear similar.

Also, asFundamentals of Plasma-Assisted CVD63will be discussed again later, the buffered oxide etch (BOE) rate for such filmsis some indication of their hydrogen content, high rates indicating very highatomic percentages of hydrogen. Etch rates for silicon nitride films producedin parallel-plate reactors will frequently range up to 100 A/min, so the ECRfilms appear to be of good bulk quality.There are a number of interesting observations that can be made regarding these results.

First, the deposition rate achieved in these experiments iscomparable to those obtainable by conventional PECVD, in spite of the factthat the ECR unit operates at 0.1 mTorr and the conventional unit at 300mTorr. This indicates a much higher degree of excitation of the ECR plasma.In spite of this, we are still comparing a single-wafer CVD machine to thebatch parallel-plate units, both with the same deposition rates.

Therefore, itis unlikely such a machine will be of much interest for production of films forintegrated circuit passivation.In addition, due to the low plasma pressure and guiding magnetic field,such a reactor deposits in an anisotropic fashion. In other words, the filmwin either be thicker or denser on a horizontal surface exposed to the ECRplasma than it will be on vertical surfaces. This makes such films of limitedvalue for coati ng integrated circuits with the usual topography.2.5.2 Parallel Electrode, Hot-Wall PECVD ReactorInstead of arranging the electrodes as long, narrow rectangular plates positioned along the length of a hot tube (see Figure 15), it would be highly desirable to arrange them normal to the tube axis, as shown inFigure 19.RFn---------.---------.----,-...-.

VacuumMetal SusceptorDiffusion FurnaceFigure 19: Hot tube parallel-plate PECVD reactor.The great advantage of th is arrangement over the one cu rrently used commercially is that for a given tube size, many more wafers could be loaded ineach batch. Unfortunately, although a number of U.S. and Japanese equipment vendors have tried to develop such a design, it has not proven practical.Major difficulties were experienced due to the complexity of the electrodestructure and in maintaining uniform discharges along the side of the tube.64Chemical Vapor Deposition for Microelectronics2.5.3 Ionic Systems ConceptIn order to carry out plasma-enhanced silicon nitride deposition with lowhydrogen content and on room-ternperature wafers, this small cornpany hasdeveloped a system in which nitrogen is ionized in an RF (13.56 MHz) glowdischarge in one chamber, and then the excited gas flows into a second chamberwhere silane is added.

The mixture then flows over room-temperature wafers.Since excited nitrogen is metastable, it can remain excited as it flows into thesecond chamber where it can decompose the silane. This then provides thereacting mixture necessary to grow silicon nitride films at rates of 150 to 300A/min.

Again, separation of generation and deposition has permitted unusualresults to be achieved.REFERENCES1. Sherman, A., Plasma-assisted chemical vapor deposition processes andtheir semiconductor applications. Thin Solid Films 113:135 (1984).2. Rosier, R.S., Benzing, W.C. and Baldo, J., A production reactor for lowtemperature plasma-enhanced silicon nitride deposition. Solid StateTechnology 19(6):45 (1976).3. Carlson, D.E. and Wronski, C.R., Amorphous silicon solar cell. Appl.Phys. Lett. 28:671 (1976).4. Wroge, D.M. and Hess, D.W., Plasma-enhanced deposition of iron/ironoxide films. Proceedings of the Symposium on Plasma Etching andDeposition. Electrochemical Society, Pennington, NJ, 81-1 :30 (1981 ).5.

Reif, R., Plasma enhanced chemical vapor deposition of thin crystallinesemiconductor and conductor films. J. Vac. Sci. Techno I. A2(2):429(1984).6. Hess, D.W., Plasma-enhanced chemical vapor deposition of metal andmetal sil icide films. Mat. Res. Soc. Symp. Proc., Vol. 38, 1985, Materials Research Society.7. Van de Ven, E.P.G.T., Plasma deposition of silicon dioxide and siliconnitride films. Solid State TechnoI. 24(1) :167 (1981).8.

Chapman, B., Glow Discharge Processes, John Wiley & Sons, NY (1980).9. Fishman, F.J., Kantrowitz, A.R. and Petschek, H.E., Magnetohydrodynamic shock wave in a collision-free plasma. Rev. Mod. Phys. 32:959(1960).10. Sutton, G.W. and Sherman, A., Engineering Magnetoh ydro dynamics,McGraw-Hili, NY (1965).11. Brown, S.C., Breakdown in Gases: Alternating and High-Frequency Fields.In Handbuch der Physik, Vol. 22, ed. S. Flugge (1956) Springer-Verlag.12. Brown, S.C., Basic Data of Plasma Physics, John Wiley & Sons, NY (1959).13. Thornton, J.A., Plasmas in Deposition Processes. In Deposition Technologies for Films and Coatings, ed.

Bunshah, R.F., Noyes Publications,NJ (1982).14. Butler, H.S. and Kino, G.S., Plasma sheath formation by radio-frequencyfields, Phys. Fluids 6:1346 (1963).Fundamentals of Plasma-Assisted CVD15.16.17.18.19.20.21.22.23.24.25.26.65Koenig, H.R.

and Maissel, L.I., Application of RF discharges to sputtering.IBMJ. Res. Develop. 14:168 (1970).Francis, G., The Glow Discharge at Low Pressure. In Handbuch der Physik,Vol. 22, ed. S. Flugge (1956) Springer-Verlag.Horwitz, C.M., RF sputtering-voltage division between two electrodes.J. Vac. Sci.

Technol. A, 1(1 ):60 (1983).Coburn, J.W. and Kay, E., Positive-ion bombardment of substrates inRF diode glow discharge sputtering. J. Appl. Phys. 43:4965 (1972).Logan, J.S., Control of RF sputtered film properties through substratetuning.IBMJ. Res. Develop. 14:172 (1970).Smith, D.L. and Bruce, R.H., Si and AI etching and product detection ina plasma beam under ultrahigh vacuum. J. Electrochem. Soc. 129:2045 (1982).Bruce, R.H., Ion response to plasma excitation frequency. J.

Appl. Phys.52:7064 (1981 ).Bruce, R.H., Frequency dependence of CCI 4 etching. Proceedings of theSymposium on Plasma Etching and Deposition, Electrochemical Society, Pennington, NJ, 81-1 :243 (1981).Minkiewicz, V.J., Chen, M., Coburn, J.W., Chapman, B.N.

and Lee, K.Magnetic field control of reactive plasma etching. Appl. Phys. Lett.35:393 (1979).Reinberg, A.R., RF Plasma deposition of inorganic films for semiconductor applications. Electrochem. Soc. Extended Abstracts Volume1974-1, pg. 21. This figure was originally presented at the Spring1974 Meeting of The Electrochemical Society, Inc. held in San Francisco, California.Reinberg, A.R., Radial Flow Reactor, U.S. Patent 3,757,733, Sept. 11,1973.Matsuo, S. and Kiuchi, M., Low temperature deposition apparatus usingan electron cyclotron resonance plasma.

Proc. Symp. on Very-LargeScale Integration Science and Technology, Electrochemical Society,Pennington, NJ, pg. 83 (1982). These figures \Nere originally presentedat the Fall 1982 Meeting of The Electrochemical Society, Inc. heldin Detroit, Michigan.3Thermal CVD of Dielectrics andSemiconductors3.1 INTRODUCTIONIn the present chapter, we will turn our attention to films deposited bythermal CVD that are either dielectrics or semiconductors. There are, as onewould expect, many films that can be deposited by this technique.

In addition, there are many gaseous reactants that one can use to create each film,the choice depending on the film characteristics desired. Rather then attemptto catalogue all of the possible films and reactants, we will choose instead tofocus on silicon dioxide, silicon nitride, polysilicon, and epitaxial silicon asthe films of interest. At the same time, we will only look at those reactantgases that have been used for integrated circuit manufacture. An excellentsurvey of the film types that can be deposited by CVD and the many reactants that have been used to obtain them has been given by Kern.!3.2 81 LICON DIOXIDESilicon dioxide films have been an essential factor in the manufactureof integrated circuits from the earliest days of the industry.