Yun-Seong Lee

Numerical investigation on plasma and poly-Si etching uniformity control over a large area in a resonant inductively coupled plasma source

In high-density plasma etching processes for ultra-large-scale integrated (ULSI) circuits, the uniformity of the plasma over a large area is of major concern. Recently a resonant inductively coupled plasma source [S. S. Kim et al., Appl. Phys. Lett. 77, 492 (2000)] has been proposed for large-area plasma processing, which achieves large-area plasma uniformity by properly tuning its antenna with an external variable capacitor. In the present paper, the plasma transport and poly-Si etching characteristics of this plasma source have been numerically investigated using a self-consistent model for electron heating, plasma transport, and microscopic etching profiles. The numerical simulation results indicate that uniform poly-Si etching over 300 mm in diameter can be easily achieved in this plasma source.

Pressure limitation of electron density measurement using a wave-cutoff method in weakly ionized plasmas

Wave-cutoff method using microwave provides capabilities for diagnostics of various processing plasmas, and can give the precise absolute electron densities1. In this study, pressure limitation of electron density measurement using a wave-cutoff method is presented. As gas pressure increases, the wave-cutoff signal disappears. The disappearance of signal happens when the electron-neutral collision frequency is over the plasma frequency. At that time, the electron motion cannot catch up to the movement of the electromagnetic wave, and the electromagnetic waves begin to penetrate into plasma. In result, the wave-cutoff signal disappears.

Si etching rate calculation for low pressure high density plasma source using Cl2 gas

Based on a simplified Cl 2 plasma Si etching mechanism, we calculate the Si etching rate with a comprehensive analysis of the effect of ion bombardment. With its flux distribution, the bombarding ions are regarded as the sum of independent monoenergetic beams (SIMB) approach. The Si etching rate is examined over the radio-frequency (rf) frequency (ν rf ) range from 1 to 20 MHz (0.1ν pi ≲ν rf ≲2ν pi , where ν pi is the ion plasma frequency) under the typical low pressure high density plasma condition. To consolidate the SIMB approach, the etching rate is compared with the result from the monoenergetic single ion beam approach. The difference in the Si etching rate between the two approaches is notable at a low rf frequency range. The effect of threshold energy on the Si etching mechanism is also investigated. We conclude that under a low rf frequency, for a precise etching property examination, the effect of the bombarding ions should be investigated through the SIMB approach.

A restoration model of distorted electron density in wave-cutoff probe measurement

This study investigates the problem of electron density distortion and how the density can be restored in a wave-cutoff probe. Despite recent plasma diagnostics research using a wave-cutoff probe, the problem of electron density distortion caused by plasma conditions has not been resolved. Experimental results indicate that electron density measured using the wave-cutoff method is highly susceptible to variations in the probe tip gap. This electron density distortion is caused by the bulk plasma disturbance between probe tips, and it must be removed for calculating the absolute electron density. To do this, a detailed analytic model was developed using the power balance equation near probe tips. This model demonstrates the characteristics of plasma distortion in wave-cutoff probe measurement and successfully restored the absolute value of electron density with varying probe tip gaps.

On the possibility of the multiple inductively coupled plasma and helicon plasma sources for large-area processes

In this study, we attempted to determine the possibility of multiple inductively coupled plasma (ICP) and helicon plasma sources for large-area processes. Experiments were performed with the one and two coils to measure plasma and electrical parameters, and a circuit simulation was performed to measure the current at each coil in the 2-coil experiment. Based on the result, we could determine the possibility of multiple ICP sources due to a direct change of impedance due to current and saturation of impedance due to the skin-depth effect. However, a helicon plasma source is difficult to adapt to the multiple sources due to the consistent change of real impedance due to mode transition and the low uniformity of the B-field confinement. As a result, it is expected that ICP can be adapted to multiple sources for large-area processes.