Laser processing of silicon at submicron scale using photochromic films

Laser fabrication at submicron scale is experimentally demonstrated with the nonlinear optical switching effect of photochromism. The effect, which is a result of change in the optical properties of the photochromic material between the open-ring and closed-ring isomers during the photoisomerization, effectively reduces the laser beam size. The ultrafast response of the molecular photocyclization and cycloreversion reactions at a time scale of a few picoseconds ensures the instantaneous realization of the effect. Utilizing a photochromic film of cis-1,2-dicyano-1,2-bis(2,4,5-trimethyl-3-thienyl) ethane as the mask layer, laser processing of a silicon wafer demonstrated submicron scale feature size with improved surface quality as compared to the smallest features achievable using direct laser ablation without the photochromic film.