Spatio-temporal measurements of overshoot phenomenon in pulsed inductively coupled discharge*

Abstract

Pulse inductively coupled plasma has been widely used in the microelectronics industry, but the existence of overshoot phenomenon may affect the uniformity of plasma and generate high-energy ions, which could damage the chip. The overshoot phenomenon at various spatial locations in pulsed inductively coupled Ar and Ar/CF4 discharges is studied in this work. The electron density, effective electron temperature, relative light intensity, and electron energy probability function (EEPF) are measured by using a time-resolved Langmuir probe and an optical probe, as a function of axial and radial locations. At the initial stage of pulse, both electron density and relative light intensity exhibit overshoot phenomenon, i.e., they first increase to a peak value and then decrease to a convergent value. The overshoot phenomenon gradually decays, when the probe moves away from the coils. Meanwhile, a delay appears in the variation of the electron densities, and the effective electron temperature decreases, which may be related to the reduced strength of electric field at a distance, and the consequent fewer high-energy electrons, inducing limited ionization and excitation rate. The overshoot phenomenon gradually disappears and the electron density decreases, when the probe moves away from reactor centre. In Ar/CF4 discharge, the overshoot phenomenon of electron density is weaker than that in the Ar discharge, and the plasma reaches a steady density within a much shorter time, which is probably due to the more ionization channels and lower ionization thresholds in the Ar/CF4 plasma.

Comparison of pulse-modulated and continuous operation modes of a radio-frequency inductive ion source

“…It is not surprising that the wide practical use of RF discharges, in particular, in the problems of etching semiconductor wafers, has led to the appearance of numerous works [4][5][6][7][8][9][10][11][12][13][14][15][16][17] studying the pulse-modulated operation mode of plasma reactors.…”

“…The authors of [14,15] studied the pulse-modulated inductively coupled discharge in Ar and Ar/CF 4 mixture. They measured the time dependencies of input power, electron density, effective electron temperature, relative light intensity, and electron energy probability function.…”

“…References [4][5][6][7][8][9][10][11][12][13][14][15][16][17] primarily focus on ways to improve the operating modes of technological plasma reactors. Another type of plasma device widely used in terrestrial and space technologies is ion sources based on an inductive RF low-pressure discharge (p<1 mTorr).…”