Plasma etching of poly-Si/SiO2/Si structures: Langmuir-probe and optical-emission-spectroscopy monitoring
Tóm tắt
An in-depth experimental evaluation is presented of the Langmuir probe as a tool for monitoring the etching of polysilicon-gate MOS structures with an inductively coupled high-density plasma excited in a mixture of SF6, O2, and Ar. It is shown that Langmuir-probe measurements made in parallel with optical actinometry offer ways of accurate end-point detection and etch-rate monitoring. It is established that the surface reactions involved lead to considerable changes in major parameters of the charged plasma species in the course of the process, affecting both the densities of electrons and ions and the electron energy distribution function (EEDF). It is found that the effective electron temperature and EEDF of the working plasma differ greatly from those of an Ar plasma under the same excitation conditions. It is concluded that wafer-surface charging could be minimized by varying the electron temperature and energy distribution. On the basis of optical-actinometry measurements, relationships are identified between the fluorine-atom density in the bulk plasma and the etch rate of the polysilicon or the oxide, taking account of the influence of ion bombardment. A conception is put forward of how the etch selectivity could be controlled.
Tài liệu tham khảo
International Technology Roadmap for Semiconductors, 1999, 2001, 2005 Editions.
Orlikovskii, A.A. and Rudenko, K.V., In situ Diagnostics of Plasma Processes in Microelectronics: The Current Status and Immediate Prospect, Part III, Mikroelektronika, 2001, vol. 30, no. 5, pp. 323–344 [Russ. Microelectron. (Engl. Transl.), vol. 30, no. 5, pp. 275–294].
Orlikovskii, A.A. and Rudenko, K.V., In situ Diagnostics of Plasma Processes in Microelectronics: The Current Status and Immediate Prospects. Part I, Mikroelektronika, 2001, vol. 30, no. 2, pp. 85–105 [Russ. Microelectron. (Engl. Transl.), vol. 30, no. 2, pp. 69–87].
Valiev, K.A., Orlikovsky, A.A., Rudenko, K.V., Semin, Yu.F., and Sukhanov, Ya.N., RF Patent 2 248 645, Byull. FIPS, 2005, no. 8.
Zaidel’, A.N., Prokof’ev, V.K., Raiskii, S.M., Slavnyi, V.A., and Shreider, E.A., Tables of Spectral Lines, New York: IFI/Plenum, 1990.
Pearse, R.W.B. and Gaydon, A.G., The Identification of Molecular Spectra, New York: Wiley, 1976, 4th ed.
Hebner, G.A. and Abraham, I.C., J. Appl. Phys., 2002, vol. 91, no. 12, pp. 9539–9546.
Ershov, A.P., Kalinin, A.V., Sukhanov, Y.N., and Rudenko, K.V., Langmuir-Probe End-Point Detection for Etching of SiO2 on Silicon, Vestn. Mosk. Univ., Ser. 3: Fiz., Astron., 1995, vol. 36, no. 6, pp. 18–22.
Maishev, Yu.P., Farenik, V.I., Shevchenko, A.V., Budyanskii, A.M., Dudin, S.V., and Zykov, A.V., Langmuir-Probe Plasma Diagnostics in Ion-Beam or Plasma Etching, in Tr. FTIAN, 1999, vol. 15, pp. 86–116.
Lieberman, M.A. and Lichtenberg, A.J., Principles of Plasma Discharges and Materials Processing, New York: Wiley, 2005, 2nd ed.
Langmuir Probe Analysis for High Density Plasmas, Chen, F.F., Ed., Los Angeles: University of California, 2000.
Kono, A., Negative Ions in Processing Plasmas and Their Effect on Plasma Structure, Appl. Surf. Sci., 2002, vol. 192, pp. 115–134.
Chabert, P., Sheridan, T.E., Boswell, R.W., and Perrin, J., Electrostatic Probe Measurements of the Negative Ion Fraction in an SF6 Helicon Discharge, Plasma Sources Sci. Technol., 1999, vol. 8, pp. 561–566.
Sukhanov, Y.N., Ershov, A.P., Rudenko, K.V., and Orlikovsky, A.A., On the Parameters of Inductively Coupled and Microwave BF3 Plasmas Used for Plasma Immersion Ion Implantation, Plasma Process. Polym., 2005, vol. 2, pp. 472–479.
Rudenko, K.V., Myakon’kikh, A.V., Orlikovsky, A.A., and Pustovit, A.N., New Method for the Langmuir Probe Diagnostics of Polymerizing Plasmas, Mikroelektronika, 2007, vol. 36, no. 1 (in press) [Russ. Microelectron. (Engl. Transl.), vol. 36, no. 1 (in press)].
Orlikovsky, A.A., Rudenko, K.V., and Averkin, S.N., Fine-Line Plasma-Enhanced Processes on the Basis of a Set of Pilot Units with a Scalable Inductively Coupled Plasma Source for Use in Microelectronics, Khim. Vys. Energ., 2006, vol. 40, no. 3, pp. 220–232 [High Energy Chem. (Engl. Transl.), vol. 40, no. 3, pp. 182–193].
Ershov, A.P., Dovzhenko, V.A., Kuzovnikov, A.A., and Oks, S.N., Processing the Current-Voltage Characteristics of a Langmuir Probe in a Non-Maxwellian Plasma, Fiz. Plazmy, 1981, vol. 7, no. 3, p. 609.
Coburn, J.W. and Chen, M., Optical Emission Spectroscopy of Reactive Plasmas: A Method for Correlating Emission Intensities to Reactive Particle Density, J. Appl. Phys., 1980, vol. 51, no. 6, pp. 3134–3136.
Granier, A., Chereau, D., Henda, K., Safari, R., and Leprince, P., Validity of Actinometry to Monitor Oxygen Atom Concentration in Microwave Discharges Created by Surface Wave in O2-N Mixtures, J. Appl. Phys., 1994, vol. 75, no. 1, pp. 104–114.
Jenq, J.S., Ding, J., Taylor, J.W., and Hershkowitz, N., Absolute Fluorine Atom Concentrations in RIE and ECR CF4 Plasmas Measured by Actinometry, Plasma Sources Sci. Technol., 1994, vol. 3, p. 154.
Kawai, Y., Sasaki, K., and Kadota, K., Comparison of Fluorine Atom Density Measured by Actinometry and Vacuum Ultraviolet Absorption Spectroscopy, Jpn. J. Appl. Phys., Part 2, 1997, vol. 36, no. 9A/B, pp. L1261–L1264.
Walkup, R.E., Saenger, K.L., and Selwyn, G.S., Studies of Atomic Oxygen in O2 + CF4 RF Discharges by Two-Photon Laser-Induced Fluorescence and Optical Emission Spectroscopy, J. Chem. Phys., 1986, vol. 84, pp. 2668–2674.
Kagan, Yu.M. and Perel’, V.I., Examining Plasmas with Probes, Usp. Fiz. Nauk, 1962, vol. 81, no. 3, pp. 409–452.
Park, B.-K., Kim, D.-G., and Kim, G.-H., Analysis of Langmuir Probe Data Using Wavelet Transform, IEEE Trans. Plasma Sci., 2004, vol. 32, no. 2, pp. 355–361.
Savitzky, A. and Golay, M.J.E., Smoothing and Differentiation of Data by Simplified Least Squares Procedures, Anal. Chem., 1964, vol. 36, no. 8, pp. 1627–1639.
Ershov, A.P. and Kuzovnikov, A.A., Electron Energy Distribution Function of a Low-Pressure RF Xenon Plasma, Fiz. Plazmy, 1985, vol. 11, no. 5, pp. 618–621.
Godyak, V.A., Piejak, R.B., and Alexandrovich, B.M., Electron Energy Distribution Function Measurements and Plasma Parameters in Inductively Coupled Argon Plasma, Plasma Sources Sci. Technol., 2002, vol. 11, pp. 525–543.
Sukhanov, Ya.N., Ershov, A.P., Rudenko, K.V., and Orlikovsky, A.A., Comparative Study of Inductively Coupled and Microwave BF3 Plasmas for Microelectronic Technology Applications, in Proc. SPIE—Int. Soc. Opt. Eng., 2004, vol. 5401, pp. 55–63.
Hwang, G.S. and Giapis, K.P., Pattern-Dependent Charging in Plasmas: Electron Temperature Effects, Phys. Rev. Lett., 1997, vol. 79, pp. 845–848.
Flamm, D.L., Donnelly, V.M., and Mucha, J.A., The Reaction of Fluorine Atoms with Silicon, J. Appl. Phys., 1981, vol. 52, no. 5, pp. 3633–3639.
Rudenko, K.V., Orlikovsky, A.A., and Roeder, G., Monitoring of the p-Si/SiO2/Si Plasma Etching by the Optical Emission Actinometry, in Proc. FTIAN, 2006, vol. 16, pp. 32–37.
Kimura, T. and Ohe, K., Investigation of Electronegativity in a Radio-Frequency Xe/SF6 Inductively Coupled Plasma Using a Langmuir Probe, Appl. Phys. Lett., 2001, vol. 79, no. 18, pp. 2874–2876.