SILICON DIOXIDE TRENCH FILLING PROCESS IN A RADIOFREQUENCY HOLLOW-CATHODE REACTOR

A process is described for void-free silicon dioxide filling Of trenches using a hollow cathode reactor. The process is carried out in a modified hollow cathode of a type similar to those used in previous studies. Silane gas is fed in through the top target of the hollow cathode which supports a low frequency (1 MHz), low pressure (approximately 0.2 Pa) oxygen and xenon discharge. The combination of low gas pressure, low excitation frequency, and silane feed position combine to produce high ion bombardment and a low rate of gas phase reaction. This produces what is believed to be an ion induced reaction with surface adsorbates, leading to directional oxide film growth. The faceting caused by ion-bombardment etching also serves to locally planarize the deposit. So far, trenches with 1 mum openings and aspect ratios up to 2.5:1 have been successfully filled at rates over 400 angstrom/min. Refractive index measurements of the deposited oxides have given results similar to thermally grown silicon dioxide.