In microfabrication for optical or electron devices, dry etching processes of III-V compound semiconductors are important for fine pattern fabrication.
In this process, usually, reactive gases are used as process gas. In our previously study, we proposed the use of an I2 crystal with high volatility as the solid source of etching gas in the process chamber for dry etching of InP. In addition, we succeed in a dry etching of GaAs by using ICl3 powder as a source of chlorine. By the way, materials for the optical and electron devices are not only the compound semiconductors but also other materials such as fluoride or oxide. We think that the reactivity of H2O vapor by presence of OH is useful for dry etching process. We would like to propose a novel dry etching process using H2O and report H2O plasma characteristics of optical emission and mass spectrum analysis.
We used the ICP etching system. The H2O was supplied as vapor through a mass flow controller using a water tank with a heating system. We observed the emission of the plasma through a sapphire window by using an optical fiber probe.
We measured emission spectra of H2O at the position on the tray. Typical discharged conditions were H2O flow rates: 5sccm, ICP power: 100-300W and process pressure: 1 Pa. The emission signals originated from OH (307, 283nm), H (656nm) and O (777nm) were observed and the intensity of OH was much larger than those of H and O. We also measured the mass spectrum of the neutral particles in the H2O-ICP. H, H2, O, O2, OH and H2O signals were observed. It is considered that the H2O is dissociated in the plasma.
Next, we measured ICP power dependence of optical emission intensity of OH, H and O at 1 Pa. The emission intensity of these species increased with increasing ICP power. We also measured process pressure dependence of the optical emission intensity of OH, H and O at 0.35-1 Pa. The emission intensity of OH has a minimum value and that of H has a maximum value at 0.8 Pa, respectively. The emission intensity of O decreased slightly with the increasing process pressure.
We expect that the H2O plasma is useful for dry etching process. In addition, we think that the OH plasma generated by using the proposed process may be useful for sterilization.
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