离焦激光直写的线宽稳定方法

Research of Linewidth Stabilizing Method During Defocusing Laser Direct Writing

为了提高激光直写加工衍射光学元件时的线条质量,提出一种离焦激光直写的线宽稳定方法。该方法通过同时调节激光功率和离焦量,使光刻胶的曝光阈值处于线宽对曝光量的变化率较小位置,从而可以弱化线宽对实际曝光量或光刻胶阈值等变化的敏感度,提高利用离焦方法进行衍射光学元件制作时的线宽稳定性。推导了稳定线宽后的光功率控制模型和线宽模型,模型中的变量仅为离焦量,降低了光功率控制的复杂性。利用632.8 nm的He-Ne激光和NA=0.1的物镜在CCD上对采用该方法后的离焦线宽模型进行验证,实验结果与理论模型吻合较好。该方法对于线宽稳定度较高的衍射光学元件制作具有重要价值。

A linewidth stabilizing method for defocusing laser direct writing is proposed for further improvement of line quality of diffractive optical elements. The writing power and defocusing amount are synchronously adjusted to set photoresist threshold at the position where the linewidth variation rate is small, thereby the linewidth sensitivity to variation of actual exposure dose and photoresist threshold is weakened, and then tbe linewidtb stability during defocusing laser direct writing is guaranteed. Both the power control model and linewidth model of the proposed method are established with defocusing amount as the unique variable. The verification of linewidth model was carried out on CCD with laser wavelength of 632. 8 nm and objects of numerical aperture 0. 1, and it shows that the experimental result is in good agreement with that by theoretical model. The proposed method is of great significance for fabrication of high-stability diffractive optical elements.