CRADA SC94-1259 final report: Dielectric mirror masks for laser processing of microelectronics

Two methods were examined for the fabrication of dielectric mirror masks. In the first method, a commercial laser mirror was patterned with photoresist and the dielectric film etched with ammonium bifluoride. The ammonium bifluoride etch showed strong kinetic anisotropy with the fastest etch rate in the vertical direction. However, horizontal etching still resulted in significant undercutting of the photomask. In the second method, a photoresist coated laser mirror was etched with an argon plasma. The argon plasma caused significant damage to the photoresist and underlying dielectric layer without adequate removal of the dielectric film in the open areas of the mask. Neither of the two methods examined were able to produce usable dielectric masks. During the course of this project, it was discovered that a foreign company, Balzers AG of Liechtenstein, had recently developed successful fabrication procedures for dielectric mirror masks. A mask purchased from Balzers for testing showed distinguishable pattern features down to 2 {mu}m in size. This mask was used in ablative projection etching experiments to form microstructures in Mylar polymer films. A thin film resistor pattern with 7.0 {mu}m wide lines was etched 5.4 {mu}m deep into a Mylar substrate. The etch pattern showed uniform linewidths but exhibited some thinning of the lines in areas where U-turns occurred. The ablative projection etching technique shows promise as a method for the rapid fabrication of contact masks in microstructuring applications