Processing of Lithographically Defined Apex Glass Structures with Smooth and Transparent Sidewalls

Abstract

We demonstrate a process to improve the surface roughness and optical transparency of the sidewalls of structures made in ApexTM photosensitive glass. Improved sidewall roughness is achieved through a post- etch anneal that reflows the surface of the glass microstructure and reduces the size of roughened glass nodules on the HF etched surface. The same anneal process is equally suited for bonding between substrates as the surface of the glass is melted allowing the glass to reflow across the seam of the bond. The process involves four basic steps: the glass sample is exposed to mid UV light to photo-activate metallic particles, followed by a two-stage baking process to allow for formation of metallic nanoclusters in the glass matrix. The amorphous glass is then etched in a diluted 3–4% (by volume) HF solution. Finally the glass structure undergoes a post-etch annealing processes at 630°C for 15 min to smoothen the etched surface and enhance the transparency of the glass sidewalls. The surface roughness obtained was approximately 200  36 nm. The surface roughness prior to post etch annealing was over 1 μm with a standard deviation of 0.4 μm. Thermal loading was observed between structures of varying size at these temperatures. The improvement of transparency in the sidewalls renders the glass structures useful for micro-optical sensors. Future work will investigate the use of this process for the development of visible and near IR microspectrometer curvets.