Plasma anodisation is an attractive technique for growing insulating layers of SiO2 at much lower temperatures then those needed for thermal oxide growth. Defects can be generated in silicon when it is subjected to prolonged high temperature oxidation processes, which in turn lead to degradation in both yield and performance of small geometry devices. An additional disadvantage of thermal oxide growth lies in the lateral oxidation behaviour (i.e. oxidation underneath the mask or ‘bird-beaking’ effect) which limits the minimum device separation which can be achieved. Although plasma anodisation has been widely investigated (see and references therein), previous studies have highlighted the severe difficulty of producing effective masks for this process, particularly during the high power anodisation studies which are the subject of this paper. Most of the established masks against thermal oxidation appear to be consumed during the plasma anodisation process. Therefore an important issue with regard to plasma anodisation is to find material systems in which the vertical oxidation rate of the mask is low compared to silicon and the lateral oxidation of both the mask and the silicon substrate under the mask are minimal. For the present study, two materials systems have been investigated; Si3N4/SiO2 strips on Si and Al/SiO2 strips on Si.
Lateral oxidation of InAlAs in InP-based heterostructures for long wavelength vertical cavity surface emitting laser applications
