Low-cost photomask fabrication using laser ablation

Abstract

A specific fabrication process has been developed to produce low-cost photomasks using standard consumer products. This process is based on an indirect route, using a numerically-controlled excimer laser (KrF) etching technique. It begins with RF-sputtering deposition of a titanium film (200 nm-thick) on float glass substrate. Then a nitrocellulose lacquer, serving as a self-developing resist, is spin-coated on titanium. It is ablated with partially-overlapping laser impacts and undergoes self-combustion under laser beam. Proper heat treatments are applied before and after laser ablation to circumvent smearing and adhesion problems. Finally the titanium layer is wet etched through the openings in the resist by dilute hydrofluoric acid. Both nitrocellulose lacquer characterization and laser parameters are discussed. The resolution achieved here (10 µm, limited by diffraction effects of the laser optics and by side heating of the resist due to the titanium film) is suitable for the fabrication of microwave devices.To confirm the suitability of the proposed process, several photomasks have been fabricated to pattern coplanar tunable stub resonators on ferroelectric KTa 0.5 Nb 0.5 O 3 thin films. The dielectric permittivity of the KTa 0.5 Nb 0.5 O 3 material is controlled by DC biasing. A 18 % tunability of the stub resonance frequency has been measured in X-band (close to 10 GHz), validating thereby the whole patterning process.

A Twofold Approach in Loss Reduction of KTa0.5Nb0.5O3 Ferroelectric Layers for Low-Loss Tunable Devices at Microwaves

“…To this end, the titanium and silver bilayers were first fully removed by chemical wet etching. Then, the laser microetching technique [20], [23], [24] was implemented to confine the ferroelectric layer only underneath and close to the CPW resonator; KTN was removed in non-critical areas (i.e. underneath the ground plane and the feeding line of the stub, see Fig.…”