Study on the potentialities of sub-100nm optical lithography of alternating and phase-edge phase shift mask for ArF lithography

The patterning potentialities of sub-100nm pattern for ArF lithography was evaluated with conventional alternating PSM (alt-PSM) for dense lines and spaces (L/S) and phase edge PSM (PE-PSM) for isolated lines of memory device. In dense L/S pattern, 1 100nm pattern was defined with relatively small depth of focus(DOF) window(∼ 0.2 μm) due to phase error of mask. As pattern sizes was changed from 130nm to 200nm, critical dimension (CD) difference between two neighboring spaces was varied and it was assumed that micro loading effect was occurred in Qz etching. The linearity was guaranteed to dense L/S of 110nm and isolated line of 90nm, and Iso-Dense bias was controlled within 15nm. The 60nm and 70nm isolated lines of PE-PSM ware defined with good process windows in the case of OA―X size(X-direction size of Cr open area) of 0.5 μm. The 55nm isolated line was also defined. The pattern shift of isolated lines was occurred with 4∼7nm as phase of mask was varies within 190 ∼ 200°. Though the alt-PSM with high numerical aperture (NA) for ArF lithography was strong candidates for sub-100nm lithography of memory device, the issues of mask fabrication such as tighter phase control and minimizing etch loading effect would be big obstacles. On the contrary, there were many possibilities of sub-100nm patterning in PE-PSM with good process windows, however tighter control of pattern shift due to phase error must be studied intensively.