Keisuke Namba

Chemical Kinetics of Chlorine in Electron Cyclotron Resonance Plasma Etching of Si.

Electron cyclotron resonance (ECR) plasma etching of Si in Cl2 has been studied from the viewpoint of plasma chemistry. Experiments were performed over a wide pressure range (0.2?10 mTorr), using a divergent magnetic-field ECR plasma reactor supplied with 2.45-GHz microwaves; a floating electrode or substrate holder was located ?30 cm downstream (B?150 G) of the 875-G ECR resonance region, and samples of polycrystalline Si were etched with no additional wafer biasing. Several diagnostics were employed to characterize the plasma around the wafer position, including two-photon laser-induced fluorescence (LIF) for detection of Cl atoms and Fourier transform infrared (FTIR) absorption spectroscopy for etch products or SiClx (x=1?4) molecules. The Si etch rate behavior obtained is interpreted in terms of a modified adsorption-reaction-ion-stimulated desorption process model based on these diagnostics.

Multicusp Electron-Cyclotron-Resonance Plasma Source Working with Microwaves Radially Injected through an Annular Slit

A new-type electron-cyclotron-resonance (ECR) plasma source has been developed for materials processing. The reactor employed magnetic multicusp fields and microwaves radially injected through an annular slit; this configuration yielded stable, uniform discharges without contamination of the microwave entrance window by sputtered particles. Electrostatic probe and optical emission measurements were made to obtain the plasma properties in Ar. These measurements showed that high-density, uniform plasmas were produced by optimizing the width of the annular slit. Moreover, the electron temperature exhibited its strong peak around the ECR zone near the chamber wall. A simple model indicates the mechanisms responsible for the plasma uniformity obtained: the plasma was dominantly produced around the ECR zone, and then diffused preferentially toward the center of the chamber because of strong magnetic fields generated near the wall surface.

In situ monitoring of product species in plasma etching by Fourier transform infrared absorption spectroscopy

In situ Fourier transform infrared (FTIR) absorption spectroscopy has been used to detect reaction products resulting from the etching of Si in Cl2 plasmas. Silicon tetrachloride SiCl4 was the only gas-phase product species detected during etching. Unsaturated silicon chlorides SiClx (x=1–3) were not observed in the plasma within the present level of detection. By comparing the absorbances of SiCl4 in Cl2 plasma etching of Si and in pure SiCl4 gases, it is suggested that the concentrations of SiCl4 or product species during etching are comparable to the feedstock Cl2 gas densities, e.g., [SiCl4] ~1 ×1013 cm-3 at a pressure of 0.5 mTorr. In contrast, on the surface-etched Si, unsaturated silicon chlorides SiClx (x=1–3) as well as SiCl4 were found to occur by FTIR reflection absorption spectroscopy (RAS). Moreover, absorption features of silicon oxides were observed both in the gas phase and on the surface, presumably arising from reactions between Si produced from etching and oxygen included in the reactor chamber owing to a small leak.