Micro and Nano Engineering Center


At Michigan State University


MICROWAVE PLASMA SOURCE DEVELOPMENT

In the late 1960's and the early 1970's plasma etching was introduced as an alternative to "wet"-chemical etching for integrated circuit (IC) manufacturing. Since then the sophisticated process requirements for manufacturing microelectronic devices have stimulated the continued development of plasma etching technology. Today, plasma processing is an important enabling technology for manufacturing computer chips and other electronic devices.

Fig 1: Cross section of MSU ECR reactor evaluated by SEMATECH/SRC/Lucent Technologies for sub-0.35 micrometer polysilicon gate etch[1].

Recently, modern plasma assisted etch process requirements such as large-area, single-wafer, submicron, silicon integrated circuit (IC) processing, and low-damage etching of electronic and photonic structures have lead to the development of a new generation of low-pressure, high-density plasma (HDP) sources. These plasma sources must operate at low neutral pressures of 10-4 - 5 x 10-3 Torr, with high plasma densities of 1011 - 1012/cm3, while still maintaining low plasma potentials. They must be capable of uniformly etching 100-350 nanometer feature sizes over large surfaces, must produce high process throughput and must provide an independent substrate bias control of the ion energies. Current applications of these HDP sources are large-area (200-300 millimeter diameters), submicron (0.13 - 0.30 micron) polysilicon etching for state-of-the-art computer chips and dry etching for the fabrication of a large variety of III-V semiconductor heterostructures and electro-optic devices.

MNEC engineers have invented and developed a microwave excited HDP source. This source, which is shown in Figure 1, sometimes is identified as a multipolar electron cyclotron resonance (ECR) plasma source.

Fig 2: 0.25 micrometer profiles etched in silicon.

It utilizes a tuned microwave cavity applicator that efficiently couples microwave energy into a discharge volume inside a quartz chamber. A multipolar static ECR magnetic field is impressed on the discharge by rare-earth magnets equally spaced in a circle around and adjacent to the quartz discharge chamber. A microwave discharge is formed inside the quartz chamber and diffuses onto the large area silicon substrate. An applied 13.56 MHz bias on the substrate provides an independent adjustment of the ion energies before they strike the substrate.

This HDP source can be built in many different sizes ranging from a few to over 24 inches in diameter. It has been successfully evaluated in single-wafer submicron polysilicon etching (see Figure 2) and other etching applications such as the etching of III-V and II-VI semiconductor heterostrucrues and electro-optic devices (see Figure 3).

Fig 3: InGaAs/InGaP/InP quantum-well laser (top disk: electrode and bottom disk: laser) courtesy of S. J. Pearton.
 
 

MNEC investigators have made numerous contributions to the invention, the development, the application and the fundamental understanding of these low-pressure ECR microwave plasma sources. See NSF Grant - DMI 9713298, plasma etching and the References for additional information on this plasma source technology and associated MNEC faculty research activities.
 

References

High-density plasma source development

  1. J.T.C. Lee, "A comparison of HDP sources for polysilicon etching," Solid State Technol., vol. 39, no. 8, pp. 63-69, Aug. 1996.
  2. J. Asmussen, "Electron cyclotron resonance microwave discharges for etching and thin-film deposition," J. Vac. Sci. Technol., vol. A7, no. 3, pp. 883-893, May/June 1989.
  3. M.A. Lieberman, and R.A. Gottscho, "Design of high-density plasma sources for materials processing," in Physics of Films, M. H. Francombe and J.L. Vossen, Eds. New York: Academic, 1994.
  4. O. Popov, "Electron cyclotron resonance plasma sources and their use in plasma-assisted chemical vapor deposition of thin films," in Physics of Films, M.H. Francombe and J.L. Vossen, Eds. New York: Academic, 1994, vol. 17.
  5. F.C. Sze, and J. Asmussen, "Experimental scaling laws for multipolar electron cyclotron resonance plasma sources," J. Vac. Sci. Technol., vol. A11, no. 4, pp. 1289-1295, July/August 1993.
  6. J. Asmussen, "Microwave plasma disk processing machines," in High Density Plasma Sources, O.A. Popov, Ed. Park Ridge, NJ: Noyes, 1995, ch. 6, pp. 251.
  7. F.C. Sze, D.K. Reinhard, B. Musson, J. Asmussen, and M. Dahimene, "Experimental performance of a large-diameter multipolar microwave plasma disk reactor," J. Vac. Sci. Technol., vol. B8, no. 6, pp. 1759-1762, Nov./Dec. 1990.

Silicon etching

  1. I. Tepermeister, N. Blayo, F.P. Klemens, D.E. Ibbotson, R.A., Gottscho, J.T.C. Lee, and H.H. Swain, "Comparison of advanced plasma sources for etching applications. I. Etch rate, uniformity, and profile control in a helicon and a multipolar electron cyclotron resonance source," J. Vac. Sci. Technol., vol. B12, no. 4, pp. 2310-2321, July/August 1994.
  2. I. Tepermeister, D.E. Ibbotson, J.T.C. Lee, and H.H. Swain, "Comparison of advanced plasma sources for etching applications. II. Langmuir probe studies of a helicon and a multipolar electron cyclotron resonance source," J. Vac. Sci. Technol., vol. B12, no. 4, pp. 2322-2332, July/August 1994.
  3. G.W. Gibson, H.H. Swain, I. Tepermeister, D.E. Ibbotson, and J.T.C. Lee, "Comparison of advanced plasma sources for etching applications. III. Ion energy distribution functions for a helicon and a multipolar electron cyclotron resonance source," J. Vac. Sci. Technol., vol. B12, no. 4, pp. 2333-2341, July/August 1994.
  4. N. Blayo, I. Tepermeister, J.L. Benton, G.S. Higashi, T. Boone, A. Onuoha, F.R. Klemens, D.E. Ibbotson, and J.T.C. Lee, "Comparison of advanced plasma sources for etching applications. IV. Plasma induced damage in a helicon and a multipolar electron cyclotron resonance source," J. Vac. Sci. Technol., vol. B12, no. 3, pp. 1340-1350, May/June 1994.
  5. K.T. Sung, W.H. Juan, S.W. Pang, and M. Dahimene, "Dependence of etch characteristics on charge particles as measured by Langmuir probe in a multipolar electron cyclotron resonance source," J. Vac. Sci. Technol., vol. A12, no. 1, pp. 69-74, Jan./Feb. 1994.
  6. W.H. Juan, and S.W. Pang, "High aspect ratio polyimide etching using an oxygen plasma generated by an electron cyclotron resonance source," J. Vac. Sci. Technol., vol. B12, no. 1, pp. 422-426, Jan./Feb. 1994.
  7. B.D. Musson, F.C. Sze, D.K. Reinhard, and J. Asmussen, "Anisotropic etching of submicron silicon features in a 23 cm diameter microwave multicusp electron cyclotron resonance plasma reactor," J. Vac. Sci. Technol., vol. B9, no. 6, pp. 3521-3525, Nov./Dec. 1991.

Etching of III-V and II-VI semiconductors

  1. S.J. Pearton, and F. Ren, "Review science of dry etching of III-V materials," J. Mater. Sci. Mater. Electron., vol. 5, pp. 1-12, 1994.
  2. C. Constantine, D. Johnson, S.J. Pearton, U.K. Chakrabarti, A.B. Emerson, W.S. Hobson, and A.P. Kinsella, "Plasma etching of III-V semiconductors in CH4/H2/Ar electron cyclotron resonance discharges," J. Vac. Sci. Technol., vol. B8, no. 4, pp. 596-606, July/August 1990.
  3. T.R. Fullowan, S.J. Pearton, K.F. Kopf, and P.R. Smith, "All-nAs/InGaAs based heterojunction bipolar transistors fabricated by electron cyclotron resonance etch," J. Vac. Sci. Technol., vol. B9, no. 3, pp. 1445-1448, May/June 1991.
  4. S.J. Pearton, F. Ren, J.R. Lothian, T.R. Fullowan, R.F. Kopf, U.K. Chakrabarti, S.P. Hui, A.B. Emerson, R.L. Kostelak, and S.S. Pei, "Dry etch processing of GaAs/AIGaAs hgh electron mobility transistor structures," J. Vac. Sci Technol., vol. B9, no. 5, pp. 2487-2496, Sept./Oct. 1991.
  5. S.J. Pearton, F. Ren, T.R. Fullowan, J.R. Lothian, A. Katz, R.F. Kopf, and C.R. Abernathy, "III-V semiconductor device dry etching using ECR discharges," Plasma Sources, Sci. Technol., vol. 1, pp. 18-27, Feb. 1992.
  6. C.B. Vartuli, S.J. Pearton, C.R. Abernathy, R.J. Shul, A.J. Howard, S.P. Kilcoyne, J.E. Parmeter, and M. Hagerott-Crawford, "High-density plasma etching of III-V nitrides," J. Vac. Sci. Technol., vol. A14, no. 9, pp. 1011-1014, May/June 1996.
  7. S.J. Pearton, W.S. Hobson, and A.F.J. Levi, "Comparison of plasma chemistries for patterning InP-based laser structures," Plasma Sources Sci. Technol., vol. 3, pp. 19-24, 1994.
    S.J. Pearton, C.R. Abernathy, R.F. Kopf, F. Ren, and W.S. Hobson, "Comparison of multipolar and magnetic mirror electron cyclotron resonance sources for CH4/H2 dry etching of III-V semiconductors," J. Vac. Sci. Technol., vol. B12, no. 3, pp. 1333-1339, May/June 1994