Patent ID: 7635546

Claim:
A method for fabricating a phase shifting photomask, comprising: providing a quartz substrate substantially transparent to light produced by an illumination source of a lithographic system, the substrate comprising a film stack, the film stack further comprising: a sacrificial upper layer; a first layer having a pre-determined value of transparency to the light; and a second layer substantially transparent to the light; forming a patterned etch mask on the sacrificial upper layer; etching exposed portions of the sacrificial upper layer; etching exposed portions of the second layer; etching exposed portions of the first layer using the substrate as an etch stop layer, wherein etching the exposed portions of the first layer comprises providing in a processing chamber chlorine (Cl 2 ) and argon (Ar) at a flow ratio Cl 2 :Ar in a range from about 1:20 to about 20:1, wherein the Ta etch has a selectivity for Ta over quartz of at least about 10:1; removing the patterned etch mask; and removing the sacrificial upper layer, wherein the remaining film stack and substrate having characteristics that result in a 180 degrees phase shift of light passing through the film stack relative to light passing through an opening in the film stack; wherein: the patterned etch mask comprises photoresist; the sacrificial upper layer is formed from chromium (Cr) and has a thickness of about 20 to about 200 nm; the first layer is formed from tantalum (Ta) and has a pre-determined thickness in a range from about 5 to about 50 nm; and the second layer is formed from silicon dioxide (SiO 2 ) and has a pre-determined thickness in a range from about 50 to about 300 nm.