Etching of mask-making resists

Following development of the exposed features, etching of the resist patterns on the mask for many years was done with wet etchants based on a mixture of ceric ammonium nitrate [Ce(NFl4)2(N03)6] and nitric acid, perchloric acid, or 

Levinson, Principles of Lithography, 2nd ed., SPIE Press, Bellingham, WA, p. 259 (2005). ibid., pp. 259 261. 

Furthermore, because chromium has proven difficult to dry etch, there have been considerable efforts expended in finding alternative mask opaque absorber materials. Molybdenum silicide (MoSi) appears to be gaining traction in certain applications, particularly in attenuated phase-shifting mask (att-PSM) and EUV mask applications (see Section 14.3), and even for binary masks.  

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