No abstract

Articles you may be interested in MOS-diode characteristics of ultrathin Al 2 O 3 gate dielectrics after exposure to an electron-cyclotron-resonance plasma stream

A low-energy (10–20 eV) neutral stream generated by charge exchange reactions in an electron cyclotron resonance (ECR) plasma stream is extracted by eliminating charged particles and used for Si etching. The formation of a cusp magnetic field over the substrate eliminates charged particles because electrons are led outside the substrate by the magnetic field. In addition, residual ions are repelled by a positive voltage supplied to the substrate, and it becomes possible to irradiate the etching samples with only the neutral stream. The etch rate for Si is about 100 Å/min with a gaseous mixture of Cl2 and a small amount of SF6, and a microwave power of 400 W. We confirm that neutral stream etching allows us to attain anisotropic etching shapes without distortion, and that it can be used for delineating fine patterns.

Oxidation using electron cyclotron resonance (ECR) plasma stream provides a large silicon dioxide growth rate at the initial growth stage (>6 nm/min), a very small activation energy of 0.02 eV for oxidation, and a high-quality interface with interface trap density of 3×1010 cm-2·eV-1. The plasma stream was extracted by a divergent magnetic field from the ECR region and irradiated on a single-crystalline silicon substrate with ion energies of 10–30 eV. The high-quality interface was obtained by oxidation without substrate heating and only postoxidation annealing at 400°C in hydrogen ambient.

The characteristics of Si etching with electron cyclotron resonance (ECR) plasma of SF6–CF4 are studied in order to improve anisotropy in dry etching using fluoride gases. Si undercutting is decreased by increasing the amount of CF4. Si patterns with vertical sidewalls are obtained with an etch rate of 40 nm/min. Oxygen addition to SF6–CF4 increases Si/SiO2 etching selectivity to more than 10, but does not cause any undercutting. It is concluded that carbon (C) that decomposes from CF4 protects the pattern sidewall from undercutting by fluorine radicals. These results are applied to the anisotropic etching of WSiN as the gate material for GaAs metal-semiconductor field effect transistors (MESFETs). WSiN patterns are more vertical when the chamber inner wall exposed to SF6–CF4 ECR plasma is stainless steel rather than quartz. This is attributed to the reduction of the amount of CO, which possibly forms volatile tungsten-carbonyl [W(CO)6] and, along with fluorine radicals, causes undercutting. It is confirmed that the stainless steel inner wall does not cause serious wafer contamination by metallic elements when WSiN patterns are almost vertically etched.