Al Etching Characteristics Employing Helicon Wave Plasma

Abstract

Characteristics of helicon wave plasma employing Cl₂ gas and its application to Al etching have been studied. Production of Cl ions dominates that of Cl atoms at 1200W RF power at 2 mTorr. Liberated oxygen from a quartz tube sputtered with Cl ions oxidizes Al and the probe surface. This is overcome by adding 10% BCl₃ to Cl₂. Electron density, temperature and ion current in Cl₂ plasma at 2 mTorr are 5×10¹⁰ cm^-3, 5.5 eV and 15 mA/cm², respectively. Formation of negative chlorine is dominant at higher pressure. Although the Al etch rate is 5000 Å/min, selectivity to resist and SiO₂ is poor due to high substrate bias voltage. Initiation time depends strongly on bias voltage, while net etching time is not changed. This implies that Al etching follows a chemical reaction even at 2 mTorr. Considerably uniform etch rate was achieved in zero magnetic field in a reactor. Slight variation which may result in the helicon wave plasma was observed.