Kenichi Nanbu

Direct simulation Monte Carlo analysis of flows and etch rate in an inductively coupled plasma reactor

The direct simulation Monte Carlo (DSMC) method was employed to predict the etch rate distribution on Si wafer. The etchant is assumed to be Cl. The production rate of Cl due to electron impact was obtained separately by preprocessing an inductively coupled chlorine plasma by use of the particle-in-cell/Monte Carlo method. Under the condition of constant total pressure, the etch rate increases with the mass flow rate of source gas Cl/sub 2/. The density of the etch product SiCl/sub 2/ rapidly decreases with increasing the flow rate. The density of the etchant hardly depends on the flow rate. The recombination 2Cl/spl rarr/Cl/sub 2/ on the inner walls of etching apparatus has a large effect on the etch rate; recombination probability of 0.1 results in 50% reduction of the etch rate. The etch rate distribution becomes more uniform when the reaction probability at the wafer surface is reduced.

DETAILED STRUCTURE OF THE AFTERGLOW OF RADIO-FREQUENCY CHLORINE DISCHARGE

The potential, ion density, electron density, and the rates of excitation, attachment, and ionization in the afterglow of radio-frequency chlorine discharge are examined using the particle-in-cell/Monte Carlo method. The gas pressure is 50 mTorr and the amplitude of rf voltage is 250 V before the power is turned off. The electron loss mechanism changes near time t=3 µs. For t 3 µs, the loss is caused by dissociative attachment of slow electrons.

Measurement of plasma parameters in an inductively coupled plasma reactor

The objective is to deepen the understanding of basic plasma properties in a high-density inductively coupled plasma (ICP) reactor. The experiment using a Langmuir probe, which is made of tungsten wire having length of 2.3 mm and diameter of 0.65 mm, is carried out to determine the characteristics of argon plasma. The axial and radial distributions of the plasma density, electron temperature, and plasma potential are measured. It was found that the electron density is in the range of 1.0×1010 to 1.0×1011u2009cm−3, electron temperature 4∼6u2009eV, and plasma potential 35∼45u2009V, respectively. These plasma parameters are spatially nonuniform in the axial direction; they depend on the distance between the plasma source and the measuring point. Next, etching of polycristalline silicon wafer by chlorine plasma is studied. The results obtained in this study indicate the effects of rf coil power, gas pressure, and substrate rf bias power on the distributions of the etch rate.