High aspect ratio channel fabrication with near-infrared laser-induced backside wet etching

Laser-induced backside wet etching (LIBWE) is one of the most promising manufacturing processes for fabricating high aspect ratio microfeatures of glass. However, cracks inside the glass during the LIBWE process due to high thermal stress limits the manufacturable shape. In this study, we propose a new technique to prevent the crack generation in the near-infrared (NIR) LIBWE process by adding phosphoric acid to the absorbent. It was possible to increase the maximum fabricable depth by approximately five times compared to the absorbent without phosphoric acid. The nature of the crack suppression mechanism in the absorbent with added phosphoric acid was investigated by in situ observation of the process and chemical analysis. To investigate the effects of phosphoric acid on LIBWE with added phosphoric acid, the influences of phosphoric acid concentration on maximum fabricable depth, fabrication speed and sidewall roughness were studied. Based on the investigated principle and process characteristics, we found that high aspect ratio microchannels of different shapes could be produced.