Investigation of etching optimization in capacitively coupled SF6–O2 plasma

Khaled Ali Alshaltami,Stephen Daniels

doi:10.1063/1.5066286

Abstract

The selective etching process is widely used for achieving the desired etch rate in semiconductor fabrication. Parameters such as input power, operating pressure, gas mixture, chamber geometry, and amplitude of the radio-frequency voltage govern the etch rate and etch quality in plasma. In this work, we experimentally investigated the optimum plasma etching conditions required to achieve an anisotropic etch profile and analyzed how the optimum etching can be carried out using an appropriate operating pressure and oxygen concentration. Optical emission spectroscopy was used to measure the concentrations of oxygen and fluorine, and Langmuir probe was used to measure the electron density in the plasma. The oxygen concentration was varied from zero to 100 vol. % for pressures in the range of 20–600 mTorr. The optimum etch conditions are used to study the ion energy distribution given by Kawamura et al., Plasma Sources Sci. Technol. 8, R45 (1999). The results suggest that in addition to O2% and pressure, the DC bias is another crucial parameter for achieving the optimum etch conditions.

Highlights

The rapid development of technologies that use semiconductors has led to enhanced requirements for the synthesis of optimized semiconductors, such as in terms of the dimensions of the material and surface properties
The results suggest that O2 concentration is the principal factor influencing the etch profile, while the etch rate is strongly affected by the system pressure
Sheath voltage is a function of DC bias and DC bias changes with pressure and O2% as shown in Fig. 2 and Fig. 3 In accordance with our results, we found that as we increase the pressure for a given power and O2%, DC bias decreases, plasma density increases up to the optimum condition the sheath thickness should decrease with the pressure as per Eq (2) provided electron temperature is more or less constant

Summary

Introduction

The rapid development of technologies that use semiconductors has led to enhanced requirements for the synthesis of optimized semiconductors, such as in terms of the dimensions of the material and surface properties. Change in input power, pressure, and flow rate can influence the ion density and the number of free radicals in the plasma. The results suggest that O2 concentration is the principal factor influencing the etch profile, while the etch rate is strongly affected by the system pressure. Morshed et al. studied the effect of oxygen flow rates on the fluorine density in SF6 plasma. The results show that the etch profiles can be controlled by changing the flow rate of oxygen in the plasma. We experimentally investigated the anisotropic etch profile in two geometrically different capacitively coupled plasma sources. The results obtained indicate that the etch profile varies as a function of F and O densities in the plasma chamber. The peak etch rates for both chambers were obtained at 20 vol % oxygen concentration in the plasma

Methods

Results

Conclusion