Use of reflective and amorphous materials for dark field stepper alignment on silicon carbide substrates

A method of performing fine alignment for stepper lithography using a dark field alignment system (DFAS) has been developed for low reflectivity substrates. This patented process is useful for substrates such as silicon carbide (SiC), which do not provide adequate reflected light in DFAS systems for alignment mark detection. The method involves forming alignment mark structures from thin films of materials that have the following two characteristics: adequate reflectance to broadband illumination typical of DFAS systems and a fine-grained or amorphous morphology. Alignment mark materials must also be resistant to grain growth during high temperature (950 °C) anneals common to SiC processing to avoid any increase in surface roughness which can lower mark contrast. This study includes modeling of the reflectivity of several candidate materials and characterization of film surfaces using atomic force microscopy.