Method for photolithographically forming a selfaligned mask using back-side exposure and a non-specular reflecting layer

Claim 1

A method for forming a mask, comprising the steps of: (a) forming an island structure of opaque material on a principal surface of a transparent substrate; (b) depositing at least one layer of a transparent material on the principal substrate surface and over the island structure; (c) depositing a layer of photoresist material having a selected thickness over the at least one layer; (d) depositing a layer of a substantially non-specular reflective material over said layer of photoresist; (e) exposing a back-side substrate surface, opposite to the principal substrate surface, to ultra-violet (UV) light of a selected intensity for a selected duration such that the opaque island structure casts a shadow thereby exposing a portion of the photoresist layer corresponding substantially to an area outside of the boundaries of the shadow of the island structure; and (f) removing the exposed photoresist portions by selective development to form a mask which is aligned with the island structure and is narrower than the island structure by the selected overlap distance on each side thereof.

Claim 2

A method for forming a mask, comprising the steps of: (a) forming an island structure of opaque material on a principal surface of a transparent substrate; (b) depositing at least one layer of a transparent material on the principal substrate surface and over the island structure; (c) depositing a layer of photoresist material having a selected thickness over the at least one layer; (d) depositing a layer of a substantially non-specular reflective material over said layer of photoresist; (e) exposing a back-side substrate surface, opposite to the principal substrate surface, to ultra-violet (UV) light of a selected intensity for a selected duration such that the opaque island structure casts a shadow thereby exposing a portion of the photoresist layer corresponding substantially to an area outside of the boundaries of the shadow of the island structure; and (f) removing the exposed photoresist portions by selective development to form a mask which is aligned with the island structure and is narrower than the island structure by the selected overlap distance on each side thereof.

Claim 19

A method for fabricating a thin-film transistor, comprising the steps of: (a) forming an opaque gate electrode on a principal surface of a transparent substrate; (b) depositing a first layer of insulation material on the principal substrate surface and over the gate electrode; (c) depositing a layer of semiconductor material on the first insulation layer; (d) depositing a second layer of insulation material on the semiconductor layer; (e) depositing a first layer of photoresist on the second insulation layer; (f) depositing a layer of a substantially non-specular reflective material over said first layer of photoresist. (g) exposing a back-side substrate surface, opposite to the principal substrate surface, to UV light of a selected intensity for a selected duration such that said opaque gate electrode casts a shadow thereby exposing a portion of the first photoresist layer substantially outside of the boundaries of the shadow of the gate electrode and causing exposure of an additional portion of said photoresist layer within a selected overlap distance form said boundaries of said shadow formed by the illumination of the gate electrode, said additional portion of said photoresist layer being exposed by UV light reflected and scattered from said non-specular reflective layer; (h) removing at least the exposed first photoresist portions by selective development to leave a first remaining photoresist portion and to expose a segment of the second insulation layer not covered by the first remaining photoresist portion; (i) selectively etching the second insulation layer segment to leave a remaining second insulation segment, under the first remaining photoresist portion, and to expose a portion of the semiconductor layer not covered by the remaining second insulation segment being aligned with the gate electrode and being narrower than the gate electrode by a selected overlap distance on each side thereof; (j) removing the first remaining photoresist portion; (k) depositing a layer of doped semiconductor material on the exposed semiconductor portion and over the remaining second insulation segment; (l) depositing a layer of conductive material on the doped semiconductor material; (m) selectively etching a portion of the conductive layer and a portion of the doped semiconductor layer to expose at least a top surface of the remaining second insulation segment and to form self-registered source and drain electrodes from the etched conductive layer which each overlap the gate electrode the selected overlap distance.

Claim 20

A method for fabricating a thin-film transistor, comprising the steps of: (a) forming an opaque gate electrode on a principal surface of a transparent substrate; (b) depositing a first layer of insulation material on the principal substrate surface and over the gate electrode; (c) depositing a layer of semiconductor material on the first insulation layer; (d) depositing a second layer of insulation material on the semiconductor layer; (e) depositing a first layer of photoresist on the second insulation layer; (f) depositing a layer of a substantially non-specular reflective material over said first layer of photoresist. (g) exposing a back-side substrate surface, opposite to the principal substrate surface, to UV light of a selected intensity for a selected duration such that said opaque gate electrode casts a shadow thereby exposing a portion of the first photoresist layer substantially outside of the boundaries of the shadow of the gate electrode and causing exposure of an additional portion of said photoresist layer within a selected overlap distance form said boundaries of said shadow formed by the illumination of the gate electrode, said additional portion of said photoresist layer being exposed by UV light reflected and scattered from said non-specular reflective layer; (h) removing at least the exposed first photoresist portions by selective development to leave a first remaining photoresist portion and to expose a segment of the second insulation layer not covered by the first remaining photoresist portion; (i) selectively etching the second insulation layer segment to leave a remaining second insulation segment, under the first remaining photoresist portion, and to expose a portion of the semiconductor layer not covered by the remaining second insulation segment being aligned with the gate electrode and being narrower than the gate electrode by a selected overlap distance on each side thereof; (j) removing the first remaining photoresist portion; (k) depositing a layer of doped semiconductor material on the exposed semiconductor portion and over the remaining second insulation segment; (l) depositing a layer of conductive material on the doped semiconductor material; (m) selectively etching a portion of the conductive layer and a portion of the doped semiconductor layer to expose at least a top surface of the remaining second insulation segment and to form self-registered source and drain electrodes from the etched conductive layer which each overlap the gate electrode the selected overlap distance.