Determining the profile parameters of photoresist grating with spectrum deductive method

Abstract

ABSTRACT In process of fabricating the pulse compression grating (PCG), before the photoresist grating’s profile is etched into the substrate with multilayer dielectric stack, the profile paramete rs, i.e. the groove depth, residual thickness and duty cycle which directly affect the diffraction efficiency of the PCG are required to be measured. A non-destructive detecting method to determine the profile parameters which is based on analyzing the 0 th order diffracted spectrum of the photoresist grating is present in this paper. An optimization function of variable profile parameters is defined in this method. By means of the direct search algorithm approach, the profile parameters are derived from the spectrum of the 0 th order diffracted light for the 1740lp/mm photo-resist gra ting with definite dielectric stack and the Littrow incidence angle. Numerical simulation results show that: when the value of optimization function is set under 1%, the difference of the groove depth and the differen ce of duty cycle between the deduced value an d the target value are less than 10nm and 2% respectively. The 0th order diffraction spectrum from 400nm to 700nm is obtained by the spectrometer. Then the profile parameters of the photo-resist grating are deduced from the measuring spectrum. The deducted result is compared with the result provided by the SEM. It shows that the spectrum deductive method is an effective method in determining the depth and duty cycle of photoresist grating with multilayer dielectric stack. At the end of the paper, the factors affecting the precision of deducing are discussed, too. Keywords: photoresist grating, deductive method, profile parameters, diffraction spectrum, multilayer dielectric stack