Method of making short channel thin film field effect transistor

Claim 1

A method of forming a current conduction channel having a length substantially less than a predetermined minimum feature size in a generally planar, thin film structure, said channel extending from an etchable initially deposited material across a subjacent semiconductor material to a subsequently deposited material, comprising the steps of: (a) forming a thick film of photoresist atop the initially deposited etchable material; (b) optically exposing the photoresist utilizing relatively coarse resolution exposure means having said predetermined minimum feature size; (c) wetting the photoresist with a solvent to cause the photoresist to swell and thereafter developing the photoresist, thereby forming an inwardly tapered surface on the photoresist having an overhang in portions thereof remote from the etchable material; (d) etching the initially deposited etchable material sufficiently to uncover subjacent material and to undercut a portion of the photoresist remaining above the etchable material; and (e) shadow depositing material atop uncovered subjacent material beyond the shadow of the undercut and overhanging photoresist, thereby forming said channel whose length is substantially equal to the shadow formed by the undercut and overhanging photoresist, and substantially less than said predetermined feature size.

Claim 2

A method of forming a current conduction channel having a length substantially less than a predetermined minimum feature size in a generally planar, thin film structure, said channel extending from an etchable initially deposited material across a subjacent semiconductor material to a subsequently deposited material, comprising the steps of: (a) forming a thick film of photoresist atop the initially deposited etchable material; (b) optically exposing the photoresist utilizing relatively coarse resolution exposure means having said predetermined minimum feature size; (c) wetting the photoresist with a solvent to cause the photoresist to swell and thereafter developing the photoresist, thereby forming an inwardly tapered surface on the photoresist having an overhang in portions thereof remote from the etchable material; (d) etching the initially deposited etchable material sufficiently to uncover subjacent material and to undercut a portion of the photoresist remaining above the etchable material; and (e) shadow depositing material atop uncovered subjacent material beyond the shadow of the undercut and overhanging photoresist, thereby forming said channel whose length is substantially equal to the shadow formed by the undercut and overhanging photoresist, and substantially less than said predetermined feature size.

Claim 9

A method of forming a generally horizontal thin film field effect transistor having deposited source and drain electrodes in contact with a deposited layer of semiconductor material and separated from one another by a current channel in the semiconductor material whose length between the electrodes is smaller than a predetermined minimum feature size, comprising the steps of: (a) forming a gate electrode upon a substrate from a first thin film of deposited conductive material; (b) depositing a thin film of insulating material atop the gate electrode, thereby forming a gate insulator layer; (c) depositing a thin film of non-single-crystals semiconductor material, a portion of which acts as said current channel, atop the film of insulating material; (d) depositing a second thin film of conductive material atop to the semiconductor material; (e) depositing a thick film of photoresist adjacent the second thin film of conductive material; (f) exposing the thick film of photoresist utilizing relatively coarse resolution exposure means having said predetermined minimum feature size; and (g) developing the photoresist, thereby defining the general location of one of the source and drain electrodes; (h) etching the second thin film of deposited conductive material to uncover the subjacent semiconductor material and to undercut a portion of the photoresist remaining above the general location of said one of the source and drain electrodes; and (i) shadow depositing a third thin film of conductive material atop the uncovered semiconductor material beyond the shadow of the undercut, thereby forming said channel having a length substantially less than said peredetermined feature size, and thereby forming at least a portion of the other of the source and drain electrodes.

Claim 10

A method of forming a generally horizontal thin film field effect transistor having deposited source and drain electrodes in contact with a deposited layer of semiconductor material and separated from one another by a current channel in the semiconductor material whose length between the electrodes is smaller than a predetermined minimum feature size, comprising the steps of: (a) forming a gate electrode upon a substrate from a first thin film of deposited conductive material; (b) depositing a thin film of insulating material atop the gate electrode, thereby forming a gate insulator layer; (c) depositing a thin film of non-single-crystals semiconductor material, a portion of which acts as said current channel, atop the film of insulating material; (d) depositing a second thin film of conductive material atop to the semiconductor material; (e) depositing a thick film of photoresist adjacent the second thin film of conductive material; (f) exposing the thick film of photoresist utilizing relatively coarse resolution exposure means having said predetermined minimum feature size; and (g) developing the photoresist, thereby defining the general location of one of the source and drain electrodes; (h) etching the second thin film of deposited conductive material to uncover the subjacent semiconductor material and to undercut a portion of the photoresist remaining above the general location of said one of the source and drain electrodes; and (i) shadow depositing a third thin film of conductive material atop the uncovered semiconductor material beyond the shadow of the undercut, thereby forming said channel having a length substantially less than said peredetermined feature size, and thereby forming at least a portion of the other of the source and drain electrodes.

Claim 14

A method of forming a generally horizontal thin film field effect transistor having reduced parasitic capacitance between the gate electrode and one or both of the source and drain electrodes, comprising the steps of: (a) forming horizontally spaced apart thin film source and drain electrodes atop an insulating substrate, said source and drain electrodes being separated by a distance substantially equal to the minimum feature size of the photomask used to pattern at least one of the source and drain electrodes; (b) depositing a thin film of non-single-crystal semiconductor material atop and in contact with the source and drain electrodes, thereby forming a current channel therebetween; (c) depositing a thin film of insulating material atop the semiconductor material; (d) depositing a thin film of etchable conductive material atop the deposited insulating material; (e) forming a thick film of photoresist atop the deposited etchable conductive material; (f) exposing the photresist through a relatively coarse resolution exposure means having said minimum predetermined feature size to define the general location of a gate electrode substantially directly above the current channel between the source and drain electrodes; (g) developing the photoresist; and (h) etching the etchable conductive material to uncover the subjacent insulating material and to undercut a portion of the photoresist remaining above the general location of the gate electrode, thereby defining a gate electrode having at least one dimension less than the minimum feature size of the exposure means, said dimension also being less than the length of the current channel between the source and drain electrodes, whereby parasitic capacitance between the gate electrode and at one of the source and drain electrodes due to overlap is minimized.

Claim 15

A method of forming a generally horizontal thin film field effect transistor having reduced parasitic capacitance between the gate electrode and one or both of the source and drain electrodes, comprising the steps of: (a) forming horizontally spaced apart thin film source and drain electrodes atop an insulating substrate, said source and drain electrodes being separated by a distance substantially equal to the minimum feature size of the photomask used to pattern at least one of the source and drain electrodes; (b) depositing a thin film of non-single-crystal semiconductor material atop and in contact with the source and drain electrodes, thereby forming a current channel therebetween; (c) depositing a thin film of insulating material atop the semiconductor material; (d) depositing a thin film of etchable conductive material atop the deposited insulating material; (e) forming a thick film of photoresist atop the deposited etchable conductive material; (f) exposing the photresist through a relatively coarse resolution exposure means having said minimum predetermined feature size to define the general location of a gate electrode substantially directly above the current channel between the source and drain electrodes; (g) developing the photoresist; and (h) etching the etchable conductive material to uncover the subjacent insulating material and to undercut a portion of the photoresist remaining above the general location of the gate electrode, thereby defining a gate electrode having at least one dimension less than the minimum feature size of the exposure means, said dimension also being less than the length of the current channel between the source and drain electrodes, whereby parasitic capacitance between the gate electrode and at one of the source and drain electrodes due to overlap is minimized.