Spatially resolved optical emission study of sputtering in reactive plasmas

The study of material sputtering under low-pressure reactive ion etching conditions in various gases (Cl-2, SiCl4, O-2) was performed using optical emission spectroscopy with high spatial resolution. Sputtering-induced secondary photon emission (atomic and molecular) from the processed materials (Si, Al2O3, GaAs) was found to be strongly localized near the target surface. A spatial distribution of atomic line emission intensity was shown to be essentially nonmonotonical with distance from the surface. This effect was explained by a cascade feeding from the upper lying atomic levels, which is enhanced in plasma (collisional) environment. A simplified model accounting for the cascading has been developed, and velocities of sputtered excited atoms (in the range of 2-7 x 10(6) cm/s) and molecules (about 2-5 x 10(5) cm/s) have been evaluated from the emission spatial decay parameters, The excited sputtered atoms and molecules are produced in different types of collisions. Fast elicited atoms can be produced only in the first few collisions of the incident ion in the surface top layers, whereas excited molecules are knocked off by secondary (slow) atoms originated from a collision cascade inside the solid. Based on this concept of the process, simple expressions for atomic and molecular excitation yields as functions of the incident ion flux and surface coverage were deduced. The technique can he used for in situ surface probing during plasma processing. (C) 1998 American Vacuum Society.16251452

Study of conditions for anisotropic plasma etching of tungsten and tungsten nitride using SF6/Ar gas mixtures

Results of the study of reactive ion etching of tungsten, tungsten nitride, and silicon in SF6/Ar gas mixtures are presented. For plasma diagnostics, optical emission spectroscopy (actinometry) was used. Using the actinometry technique, it was possible to show that etching mechanisms were different for Si-F and W-F chemistries. Anisotropic etching of tungsten/tungsten nitride using conventional reactive ion etcher has been obtained, and conditions of achieving anisotropic etching have been analyzed. A correlation is found between anisotropy of tungsten etching and the ratio of Si/W etch rates. Mechanisms of fluorine redistribution between the bottom/sidewall surfaces due to surface diffusion and/or reflection are proposed as possible reasons for the observed correlation.1493G179G18

Efficacy of ECR-CVD silicon nitride passivation in InGaP/GaAs HBTs

High quality passivation silicon nitride films have been obtained requiring no surface pretreatment and being fully compatible with monolithic microwave integrated circuits. The nitride film is deposited by electron cyclotron resonance-chemical vapor deposition directly over GaAs-n substrate and over InGaP/GaAs heterojunction structures, which are used for heterojunction bipolar transistors (HBTs). Metal/ nitride/ GaAs-n capacitors were fabricated for all the samples. Effective charge densities of 3 X 10(11) cm(-2) and leakage current densities of 1 mu A/cm(2) were determined. Plasma analysis showed a reduced formation of molecules such as NH in the gas phase at low pressures, allowing the deposition of higher quality films. The process was used for InGaP/GaAs HBT fabrication with excellent results, such as higher current gain of passivated device comparing to unpassivated HBTs. (c) 2006 American Vacuum Society.2441762176

Anisotropic etching of silicon for a micromachining application using plasmas of SF6/CH4/O-2/Ar and SF6/CF4/O-2/Ar

We investigated the reactive ion etching of silicon using SF6/CH4(CF4)/O-2/Ar gas mixtures containing fluorine for MEMS applications. Etch rates and anisotropy of etch profiles were examined as a function of gas composition, material of electrode, and RF power. Etch depths were measured using a profilometer, and etch profiles were analyzed by scanning electron microscope. As a mask material, an aluminium film deposited by evaporation, was used. High anisotropy of etching of 0.95 was achieved at etch depths up to 20-30 micrometers and etch rates of approximately 0.3-0.6 mum/min. Highly anisotropic etching is based on a mechanism that enhance the ion bombarding and protects the sidewalls due to polymerization and/or oxidation mechanisms in order to avoid the lateral etch. However, under the anisotropic etching conditions, considerable damages of the etched surfaces (roughness formation), were observed. After etching experiments, wet / dry cleaning procedures were applied to remove surface residues resulting from the reactive ion etching and to improve the etched surface morphology.50220320

A contribution of vibrationally excited Cl-2 molecules to GaAs reactive ion etching in Cl-2/Ar

The experimental results on GaAs RIE in Cl-2/Ar are considered within the framework of the ion-neutral synergy model. It has been shown, that the model gives a good agreement with the etch rate data obtained for low Cl-2 partial pressure, but fails at the increased chlorine percentage. A possible contribution of vibrationally excited Cl-2 molecules to GaAs etch rate has been considered.357BL940L94

Silicon nitride etching in high- and low-density plasmas using SF(6)/O(2)/N(2) mixtures

Results of a comparative study of SiN(x) SiO(2) and Si etching in high- and low-density O(2)-N(2) based plasmas with small additions of SF(6) are presented. Higher selectivities of SiN(x) etching over both SiO(2) (up to 50-70) and Si (up to 20) are obtained in a high-density reactor as compared with low-density reactive ion etching. Plasma and surface processes responsible for etching are analyzed. Kinetics of NO molecules responsible for enhanced nitride etching is shown to be distinctly different for low- and high-density plasma conditions. Possible ways of further optimization of the process are discussed. (C) 2003 American Vacuum Society.21246146