Processing of photosensitive APEX™ glass structures with smooth and transparent sidewalls

Abstract

Improvement of the surface roughness and optical transparency of microstructures lithographically fabricated in APEX TM glass was accomplished through a post-etch anneal. An optimal dose of UV radiation is found to be 24 J g −1 for a wavelength of 280 nm, after which etch rate in HF acid and selectivity saturate. The anneal process, while originally designed to improve the surface roughness by reflowing, can be used to join multiple structures for the creation of optically transparent three-dimensional devices. The resulting glass microstructures demonstrate an average sidewall RMS surface roughness that is reduced from 0.7 μm to 32.7 nm which is adequate for optical signal detection across a wide frequency band that includes the visible spectrum.

In-plane spectroscopy of microfluidic channels using photosensitive glass

“…A process to fabricate microstructures from Apex ™ photosensitive glass with smooth sidewalls and transparent in the near UV, visible and Near IR regions was presented in [9]. Briefly, the process starts by irradiating photosensitive glass to UV light to receive a certain dose, during this step a reaction occurs in which cerous (Ce 3+ ) ions are photo oxidized to Ce 3++ ion and electron pairs as suggested by Brandily-Anne et.…”

“…Depending on the glass composition, and method of exposure, the surface roughness after this step is in the range 0.7-5 11m [6,9].…”

“…When Apex ™ glass is then annealed at 530-545 °c [9], or 560-570 °c for Foturan glass [13], the RMS surface roughness is reduced to a value on the order of tens of nanometers. A microcuvette with internal dimensions of 600 X 600 X 500 11m was fabricated using the process in [9], and bonded to a glass substrate of the same type.…”

“…Photodefinable glass processing [6][7][8][9] demonstrates superiority in producing optically smooth and transparent sidewalls thicker than lOO Jim and aspect ratios up to 50: 1 [8], they further allow for the fabrication of embedded channels in the glass [7]. In addition, microstructures made in photostructurable glasses may be mass produced at low cost.…”

“…In addition, microstructures made in photostructurable glasses may be mass produced at low cost. The four-stage process shown in [9] This work demonstrates the use of the process outlined in [9] for performing an in-plane spectral analysis on stacked microfluidic systems through the glass sidewalls eliminating the need for a non-planar observation of the system as currently employed in microfluidic technologies, this is demonstrated in figure 1. This application is demonstrated by presenting measurements of the visible and Near-Infrared (NIR) absorption spectra as well as the Raman spectra of fluids in microstructures fabricated using the process shown in [9].…”