PMGI bi-layer lift-off process

Claim 3

A method of forming a lift-off structure as recited in claim 1 wherein said solvent utilized during said soaking step is chlorobenzene.

Claim 4

A method of forming a lift-off structure as recited in claim 1 wherein said solvent utilized during said soaking step is toluene.

Claim 5

A bi-layer lift-off process for a wafer having a planarization layer of PMGI and a thin novalac positive photoresist layer on said planarization layer of PMGI comprising the steps of: placing a mask on said photoresist layer; exposing said mask with nominal light; removing said mask from said photoresist layer; developing said photoresist layer with a developer to create a pattern in said photoresist layer outlined by said mask; subjecting said wafer to a chlorobenzene soak for a predetermined time at a predetermined temperature to create a structure having a decreased solubility of said photoresist layer and an increased solubility of said planarization layer of PMGI; developing the PMGI revealed through said photoresist layer to create a desired undercut profile between said photoresist and said planarization layer of PMGI and an exposed portion of the wafer, said developing step performed by a developer after flood exposure of nominal light on the wafer with said photoresist layer having positive masking characteristics in relation to said planarization layer of PMGI; evaporating metal onto said exposed portion of wafer to form a gate; and lifting off said layer of PMGI and said photoresist layer from the wafer by utilizing said undercut profile to enhance being able to grip said planarization layer of PMGI during said lifting off steps.

Claim 6

A bi-layer lift-off process for a wafer having a planarization layer of PMGI and a thin novalac positive photoresist layer on said planarization layer of PMGI comprising the steps of: placing a mask on said photoresist layer; exposing said mask with nominal light; removing said mask from said photoresist layer; developing said photoresist layer with a developer to create a pattern in said photoresist layer outlined by said mask; subjecting said wafer to a chlorobenzene soak for a predetermined time at a predetermined temperature to create a structure having a decreased solubility of said photoresist layer and an increased solubility of said planarization layer of PMGI; developing the PMGI revealed through said photoresist layer to create a desired undercut profile between said photoresist and said planarization layer of PMGI and an exposed portion of the wafer, said developing step performed by a developer after flood exposure of nominal light on the wafer with said photoresist layer having positive masking characteristics in relation to said planarization layer of PMGI; evaporating metal onto said exposed portion of wafer to form a gate; and lifting off said layer of PMGI and said photoresist layer from the wafer by utilizing said undercut profile to enhance being able to grip said planarization layer of PMGI during said lifting off steps.

Claim 7

A bi-layer lift-off process as recited in claim 4 wherein the step of subjecting said wafer to a chlorobenzene soak occurs for 3-10 minutes at a temperature of 27° C.

Claim 8

A lift-off structure for FET processing comprising a compound semiconductor, a layer of PMGI juxtaposed to said substrate and a defined novelac photoresist layer adjacent to said layer of PMGI wherein an undercut profile is formed in said layer of PMGI beneath said defined layer during development of said PMGI layer due to solubility effects of a chlorobenzene soak, said undercut profile facilitating lift-off.

Claim 9

A lift-off structure for FET processing comprising a compound semiconductor, a layer of PMGI juxtaposed to said substrate and a defined novelac photoresist layer adjacent to said layer of PMGI wherein an undercut profile is formed in said layer of PMGI beneath said defined layer during development of said PMGI layer due to solubility effects of a chlorobenzene soak, said undercut profile facilitating lift-off.