Phase shift mask using liquid phase oxide deposition

Abstract

Selective deposition of silica from a liquid phase solution of silica in hydrofluorosilicic acid through openings in a pattern of polyimide or similar organic material provides an optically improved phase shift mask structure for making lithographic exposures since deposition can be made substantially anisotropic to yield deposits of substantially uniform thickness. Deposition from the liquid phase is readily controlled and highly predictable control of deposition rate can be achieved by control of temperature of a low temperature deposition process. Therefore the optical quality of the mask need not be compromised by other structures, such as etch stop layers, otherwise necessary to achieve high phase shift accuracy and the deposits of phase shift material are substantially homogeneous. The process of deposition from the liquid phase can be stopped and started at will and the mask can be fabricated by a process which is substantially free from material-dependent or material-based process restrictions. The index of refraction of the deposited material can also be adjusted by annealing.

Dependencies are inferred from the claim text.