Research On Measurement Of Duty Cycles Of Cr-mask In The Fabrication Process Of Beam Sampling Grating

Measurement of duty cycles of Cr-mask in the fabrication process of beam samplinggrating (BSG) are investigated theoretically and experimentally in the thesis.BSG is specified to have0.1%-0.3%average diffraction efficiency with less than5%RMS diffraction uniformity of first order. Duty cycles will be different due to thenon-uniformity of exposure and grating period in the fabrication process of photoresistmask, resulting in the non-uniformity of diffraction efficiency. Cr-mask is applied tofabricate BSG, a proper etch depth can be determined to achieve average diffractionefficiency and diffraction efficiency uniformity requirements since the distribution of dutycycles is measured.Influence of grating structure on diffraction efficiency of Cr-mask grating and BSGare investigated based on rigorous coupled-wave analysis (RCWA). Distribution of dutycycles of mask can be calculated after zeroth-order diffraction efficiency is measured, thenthe average diffraction efficiency and diffraction efficiency RMS can be obtained at acertain etch depth, also a proper etch depth to achieve diffraction performancerequirements is known. Diffraction efficiency of BSG using TE and conical diffraction iscalculated respectively, there is little difference between two results, so TE diffraction canbe used to calculate diffraction efficiency of BSG for simple.Six Cr-mask grating are fabricated and diffraction efficiencies are measured. Dutycycles are calculated respectively using rectangle model and trapezium model. Results oftrapezium model can be excellent agree with value measured by SEM, also errors ofrectangle model is analyzed.Measurement system of mask and BSG is setup and a control program is written. Distribution of diffraction efficiency of a mask is measured, and with the duty cyclescalculated, the distribution of diffraction efficiency of BSG is simulated. The mask iswet-etched and the BSG first order diffraction efficiency is measured. The distribution ofBSG diffraction efficiency of simulation and measurement result are similar. Experimentshows that Cr-mask method to fabricate BSG to achieve diffraction efficiency uniformity isfeasible.