Fluid simulation of a pulse-modulated, inductively coupled plasma discharge with radio frequency bias
Introduction
Pulse-modulated inductively coupled plasma (ICP) discharge is widely used in the manufacturing of microelectronic devices (e.g., the deposition and etching processes) owing to its high electron density under low-gas-pressure conditions [1], [2], [3]. During deposition and etching processes, the ion energy distribution (IED) at the substrate is an important factor [4], [5], [6]. IED is difficult to control independently in pure ICP discharge. For inductive discharge, radio frequency (RF) bias is used to control the ion energy on the substrate [5], [7]. Therefore, it is important to understand the relationship between the RF-bias conditions and the plasma profile [8], [9], [10].
In this study, we simulated a pulse-modulated ICP discharge with RF bias for semiconductor device processes and investigated the plasma characteristics. The systems for semiconductor device processes were modeled as cylinders. Therefore, it was possible to apply axial symmetry to these systems. A two-dimensional axisymmetric structure was used in the simulation.
Kinetic, hybrid, and fluid models are commonly used in plasma discharge simulations. Detailed explanations of these methods are given in Refs. [11], [12]. The simulation in this study was based on the fluid model. Although fluid simulations have some accuracy limitations since EEDF is assumed, they provide quick computation and satisfactory solutions for moderate-pressure conditions. COMSOL Multiphysics 5.2a was used for the simulation in this study.
The contents of this study are as follows. Section 2 details the simulation model used in this study, and Section 3 gives the simulation results, discussion, and conclusions.
Section snippets
Model description
The schematic of the ICP simulated in this study is shown Fig. 1. The geometry was a modified gaseous electronics conference (GEC) cell, which is considered to only dominant plasma discharge regions in the original structure. A pulse-modulated RF power of 13.56 MHz was applied to the coils, and a 3.4 MHz RF-bias voltage was applied to the bottom electrode. The radius of the bottom electrode was 5.72 cm, and the gap between the bottom electrode and the ceramic window was 4.05 cm. The dielectric
Results and discussion
The plasma characteristics in a pulse-modulated ICP discharge were investigated, and the results were compared with those of other simulations conducted under RF-bias conditions. The simulation conditions were as follows. Argon gas was used in the plasma discharge, and its flow rate was 100 sccm. At the outlet, a gas pressure of 30 mTorr was applied. A 13.56 MHz sinusoidal power of 100 W was applied to the coil and it is pulse modulated wave. The pulse frequency was 100 kHz, and the duty cycle
Conclusions
This study shows the outcomes of two-dimensional fluid simulation for pulse modulated ICP discharge.
The plasma characteristics in the pulsed-modulated ICP were investigated. The profiles of the plasma parameters changed instantaneously with the power conditions. The slopes of the spatial maximum and spatial averaged electron densities were significantly different. When power was changed to ON from OFF, the spatial averaged electron density momentarily decreased, and the electron temperature
Acknowledgements
This work was supported by R&D Program of 'Human Resources Development and Invigoration of Education - Research - Industry Networks' through the National Fusion Research Institute of Korea (NFRI) funded by the Government fund.
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