Patent ID: 7378226

Claim:
A plasma-free method for forming, on a substrate, a big-layer lift-off mask having an upper and a lower layer, both layers having a geometrically similar dog-bone shape, the upper layer being symmetrically formed on the lower layer, the lower layer being formed on said substrate and being uniformly undercut relative to said upper layer and wherein said dog-bone shape is characterized by a narrow central linear portion formed between flared distal portions, said central portion of the lower layer being substantially narrower than the central portion of said upper layer and thereby forming a narrow ridge that supports and maintains the central portion of said upper layer at a fixed height above said substrate and eliminates the accumulation of unwanted deposition residues, comprising: providing a substrate; forming on said substrate a lower layer of PMGI or its derivatives; forming on said PMGI layer an upper layer of radiation-sensitive resist material; exposing a dog-bone shaped region of said radiation-sensitive material with appropriate radiation, the central portion of said region having an initial width and a length; developing said exposed upper layer, said developing process including the application of a solvent that removes all unexposed portions of said exposed upper layer as well as at least all portions of said lower PMGI layer not directly beneath said exposed layer and said solvent producing, thereby, an initial undercut of said PMGI layer relative to said upper layer; then performing, in the absence of said solvent and without the application of a plasma, an ozone-assisted additional undercut process of said lower PMGI layer by placing said layers in an ozone chamber, in the presence of an ozone oxidizing ambient wherein there is an ozone density, an ozone flow rate, an ozone processing time and a processing temperature, said process, thereby, producing a further undercut by a controlled rate of dissolution of the PMGI layer; and, using only the application of said ozone, producing a well controlled and void free undercut of the PMGI relative to the exposed upper layer while also continuing the dimensional reduction of said upper layer, the final width, W 2 , of the central portion of the PMGI subsequent to said undercut being less than the final width, W 1 , of the upper layer and said PMGI central region forming, thereby, a void free supporting ridge beneath said central portion of the upper layer and eliminating from beneath said central portion voids within which unwanted deposition residue can form.