The effects of ICP dry etching and HF wet etching on the morphology of SiO2 surface

Both dry etching and wet etching are an integral part for the fabrication of semiconductor devices. However, both types of etching can cause problems such as surface degradation, uncontrollability of etching depth and undercut. For instance, aqueous HF (wet etching) and dry etching are used to etch SiO2 films. During HF partial etch (SiO2 is not fully removed), it introduces some interesting phenomena such as adhesion degradation on SiO2 surface morphology which is not present when SiO2 is fully etched. This paper reports the first study of systematical characterization of the SiO2 surface morphology after partial dry and HF wet etching and compares their different effects on the strength of adhesion on polaric and nonpolar liquids. To study the strength of adhesion, this experiment utilized two different types of resist such as PMMA resist and PMGI based LOR resist. Atomic Force Microscopy (AFM) was used to determine the surface morphology before and after dry etching and HF wet etching process. Telescope-Goniometer was used to measure the contact angles as an indicator of liquid-solid adhesion. From the comparison study it's evident that partial wet etching by HF changes the surface morphology of the SiO2 significantly and degrades the adhesion between the resist and the surface. On the other hand, dry etching does not alter the SiO2 surface morphology significantly and it is recommended to use dry etching instead of HF wet etching to avoid the degradation in adhesion strength on SiO2 surface whenever possible. Next, as a more general approach, adhesion promoter was used to restore the adhesion between the resist and SiO2 surface.