Real-time optical characterization of laser oxidation process in bimetallic direct write gray scale photomasks

Numerical analysis of the sub-wavelength fabrication of MTMO grayscale photomasks by direct laser writing

“…According to the experiment results in Ref. [19], under a given high laser power, the laser-induced oxidation rate of metal films in molten state is significantly larger than that in solid state due to the increased diffusion of ions. In this paper, we study only the light-induced oxidation above melting temperature.…”

“…In other words, the indium film is not fully oxidized at a laser power lower than the threshold power, the oxidation layer will become thicker with the increase of the pulse duration. Moreover, a saturation point at a certain optical density was always produced for a given specific laser power even for a much longer pulse duration [19], which suggests the indium film will not be oxidized continuously if we further decrease the laser power. However, different oxidation findings were described in Ref.…”

“…Figure 3(b) shows the temperature distribution along the radial direction at the interface between the indium film and the substrate and the time of 1 μs with the laser power of 4.0, 5.0, 6.0, 8.0, 10.0 mW, from which one can know the melting area. The temperature fields show that the indium film can be molten when the laser power is higher than 4.0 mW, and the oxidation environments should be similar by then [19]. The major factor that determines the oxidation rate is the laser power distribution which can be represented by the absorbed power density Q.…”