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Development and investigation of a high density, inductively coupled plasma source
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Type
Thesis
Author
Tsakadze, Erekle
Supervisor
Xu, Shuyan
Abstract
There has been a great deal of interest in high-density, low temperature RF plasma sources for various low-pressure vacuum technologies. Inductively coupled plasma (ICP) sources featuring high (>1011-1012 cm-3) ion densities and low plasma potentials have been proven superior in generation of large-area and large-volume plasmas for fabrication and processing of unique materials and ultra-fine selective etching of semiconductor wafers. The uniformity of the electromagnetic fields, RF power density and plasma parameters is a key factor for plasma processing applications.
In this thesis a novel low-frequency (0.5 MHz), inductively coupled plasma source with internal RF currents has been developed and investigated. Two different theoretical models of generation of high-density plasmas in a cylindrical metal-walled vessel have been investigated. First model describes the plasma generation by means of internal RF current sheet with spatially varying phase (Internal Rotating Current), while the second model concentrate on the generation of a plasma sustained by an internal RF current sheet with spatially constant phase (Internal Oscillating Current). A global electromagnetic model of inductively coupled plasma sustained with internal RF currents sheet is developed. The electromagnetic field structure, profiles of the RF power transferred to the plasma electrons, electron number density, and working points of the discharge are studied invoking particle and power balance. It is revealed that the internal RF currents with spatially variable / invariable phases significantly improve the radial uniformity of the electromagnetic fields and the power density in the chamber as compared with conventional plasma sources with external flat spiral inductive coils. It is shown that the model with internal oscillating current configuration offers a possibility to control the RF power deposition in azimuthal direction, while power absorbed by plasma electrons generated by internal rotating current is azimuthaly invariable. Comparative study of the field distribution, the efficiency of power deposition, and the properties of plasma generated in both models with that of conventional external flat spiral coil ICP sources having the same geometrical size is also presented.
To exam the theoretical predictions of the properties of the plasma generated by internal RF current with spatially constant phase, a new plasma source with internal coil configuration has been developed. Numerous diagnostic tools have been used for the study. In particular, specially designed and calibrated magnetic probes have been used to investigate electromagnetic field profiles in the vacuum vessel. Optical properties of argon plasma have been investigated using an optical emission spectroscopy (OES) technique. Global plasma parameters such as electron number density, effective electron temperature, plasma potential and electron energy distribution/probability functions have been obtained from RF compensated Langmuir probe measurements. The measurements reveal high degree of radial and axial uniformity of the plasma density in the vacuum chamber. It has been found that the EEDF's in the studied plasma source appear to be Druyvestein-like rather than Maxwellian. Variation of global plasma parameters and optical properties of plasma with power and gas filling pressure have been experimentally investigated. It has been found that plasma density is almost linear function of power absorbed by plasma electrons, which is consistent with the theoretical estimation. Study of hysteresis phenomenon, which is peculiar for inductively coupled plasma sources, reveals that mode transition can occur at very low powers of ~ 400W at gas filling pressure p ~ 50 mTorr. Investigation of the optical properties of the plasma generated by new plasma source with internal oscillating current configuration shows that intensities of different spectral lines in electrostatic (E) and in electromagnetic (H) modes are higher than ones in conventional ICP source with external coil configuration. New plasma source also features high degree of stability and reproducibility during the operating process.
In conclusion, experimental investigation and theoretical study of newly developed inductively coupled plasma source with internal RF current with spatially constant phase has been performed. Another model of plasma generation by internal rotating current has been also studied theoretically. It has been demonstrated that ICP source with internal oscillating and rotating RF currents can be promising for various plasma processing applications.
In this thesis a novel low-frequency (0.5 MHz), inductively coupled plasma source with internal RF currents has been developed and investigated. Two different theoretical models of generation of high-density plasmas in a cylindrical metal-walled vessel have been investigated. First model describes the plasma generation by means of internal RF current sheet with spatially varying phase (Internal Rotating Current), while the second model concentrate on the generation of a plasma sustained by an internal RF current sheet with spatially constant phase (Internal Oscillating Current). A global electromagnetic model of inductively coupled plasma sustained with internal RF currents sheet is developed. The electromagnetic field structure, profiles of the RF power transferred to the plasma electrons, electron number density, and working points of the discharge are studied invoking particle and power balance. It is revealed that the internal RF currents with spatially variable / invariable phases significantly improve the radial uniformity of the electromagnetic fields and the power density in the chamber as compared with conventional plasma sources with external flat spiral inductive coils. It is shown that the model with internal oscillating current configuration offers a possibility to control the RF power deposition in azimuthal direction, while power absorbed by plasma electrons generated by internal rotating current is azimuthaly invariable. Comparative study of the field distribution, the efficiency of power deposition, and the properties of plasma generated in both models with that of conventional external flat spiral coil ICP sources having the same geometrical size is also presented.
To exam the theoretical predictions of the properties of the plasma generated by internal RF current with spatially constant phase, a new plasma source with internal coil configuration has been developed. Numerous diagnostic tools have been used for the study. In particular, specially designed and calibrated magnetic probes have been used to investigate electromagnetic field profiles in the vacuum vessel. Optical properties of argon plasma have been investigated using an optical emission spectroscopy (OES) technique. Global plasma parameters such as electron number density, effective electron temperature, plasma potential and electron energy distribution/probability functions have been obtained from RF compensated Langmuir probe measurements. The measurements reveal high degree of radial and axial uniformity of the plasma density in the vacuum chamber. It has been found that the EEDF's in the studied plasma source appear to be Druyvestein-like rather than Maxwellian. Variation of global plasma parameters and optical properties of plasma with power and gas filling pressure have been experimentally investigated. It has been found that plasma density is almost linear function of power absorbed by plasma electrons, which is consistent with the theoretical estimation. Study of hysteresis phenomenon, which is peculiar for inductively coupled plasma sources, reveals that mode transition can occur at very low powers of ~ 400W at gas filling pressure p ~ 50 mTorr. Investigation of the optical properties of the plasma generated by new plasma source with internal oscillating current configuration shows that intensities of different spectral lines in electrostatic (E) and in electromagnetic (H) modes are higher than ones in conventional ICP source with external coil configuration. New plasma source also features high degree of stability and reproducibility during the operating process.
In conclusion, experimental investigation and theoretical study of newly developed inductively coupled plasma source with internal RF current with spatially constant phase has been performed. Another model of plasma generation by internal rotating current has been also studied theoretically. It has been demonstrated that ICP source with internal oscillating and rotating RF currents can be promising for various plasma processing applications.
Date Issued
2001
Call Number
QC718.4 Tsa
Date Submitted
2001