Anisotropic etch method for a sandwich structure

Claim 1

A method to etch a sandwich structure of a first layer selected from the group of silicon dioxide and silicon nitride, on a second layer selected from the group of polycrystalline silicon and a refractory metal silicide, on a third layer selected from the group of silicon dioxide and silicon nitride, comprising the steps of: providing a patterned mask layer on the structure, leaving a region of the first layer exposed; providing a plasma etch reactor having a non-erodible electrode and using it for: etching the exposed first layer in a first atmosphere of He and 16:1 to 22:1 CHF 3 :SF 6 , in a 2.0 to 2.6 W/cm 2 plasma, at 400 to 600 mTorr and 15° to 25° C., until the second layer is exposed and a sidewall is formed in the first layer; etching the exposed second layer in a second atmosphere of 3.2:1 to 3.5:1 HBr:He, in a 1.0 to 1.2 W/cm 2 plasma, at 180 to 220 mTorr and 15° to 25° C., until any prograde in said second layer is counteracted; and etching the exposed second layer in a third atmosphere of 1.7:1 to 2.3:1 HBr:He, in a 1.2 to 1.4 W/cm 2 plasma, at 135 to 165 mTorr and 15° to 25° C., until the third layer is exposed and a sidewall is formed in the second layer.

Claim 2

A method to etch a sandwich structure of a first layer selected from the group of silicon dioxide and silicon nitride, on a second layer selected from the group of polycrystalline silicon and a refractory metal silicide, on a third layer selected from the group of silicon dioxide and silicon nitride, comprising the steps of: providing a patterned mask layer on the structure, leaving a region of the first layer exposed; providing a plasma etch reactor having a non-erodible electrode and using it for: etching the exposed first layer in a first atmosphere of He and 16:1 to 22:1 CHF 3 :SF 6 , in a 2.0 to 2.6 W/cm 2 plasma, at 400 to 600 mTorr and 15° to 25° C., until the second layer is exposed and a sidewall is formed in the first layer; etching the exposed second layer in a second atmosphere of 3.2:1 to 3.5:1 HBr:He, in a 1.0 to 1.2 W/cm 2 plasma, at 180 to 220 mTorr and 15° to 25° C., until any prograde in said second layer is counteracted; and etching the exposed second layer in a third atmosphere of 1.7:1 to 2.3:1 HBr:He, in a 1.2 to 1.4 W/cm 2 plasma, at 135 to 165 mTorr and 15° to 25° C., until the third layer is exposed and a sidewall is formed in the second layer.

Claim 4

A method to etch a sandwich structure of a first layer selected from the group of silicon dioxide and silicon nitride, on a second layer selected from the group of polycrystalline silicon and a refractory metal silicide, on a third layer selected from the group of silicon dioxide and silicon nitride, comprising the steps of: providing a patterned mask layer on the structure, leaving a region of the first layer exposed; providing a plasma etch reactor having a non-erodible electrode and using it for: etching the exposed first layer in a first atmosphere of an inert carrier gas and 16:1 to 22:1 CHF 3 :SF 6 , until the second layer is exposed and a sidewall is formed in the first layer; etching the exposed second layer in a second atmosphere of 3.2:1 to 3.5:1 HBr:inert assisting gas, until any prograde in said second layer is counteracted; and etching the exposed second layer in a third atmosphere of 1.7:1 to 2.3:1 HBr:inert assisting gas, until the third layer is exposed and a sidewall is formed in the second layer, and said sidewalls of said first and second layers are smoothed.

Claim 5

A method to etch a sandwich structure of a first layer selected from the group of silicon dioxide and silicon nitride, on a second layer selected from the group of polycrystalline silicon and a refractory metal silicide, on a third layer selected from the group of silicon dioxide and silicon nitride, comprising the steps of: providing a patterned mask layer on the structure, leaving a region of the first layer exposed; providing a plasma etch reactor having a non-erodible electrode and using it for: etching the exposed first layer in a first atmosphere of an inert carrier gas and 16:1 to 22:1 CHF 3 :SF 6 , until the second layer is exposed and a sidewall is formed in the first layer; etching the exposed second layer in a second atmosphere of 3.2:1 to 3.5:1 HBr:inert assisting gas, until any prograde in said second layer is counteracted; and etching the exposed second layer in a third atmosphere of 1.7:1 to 2.3:1 HBr:inert assisting gas, until the third layer is exposed and a sidewall is formed in the second layer, and said sidewalls of said first and second layers are smoothed.

Claim 13

A method to etch a sandwich structure of a first layer selected from the group of silicon dioxide and silicon nitride, on a second layer selected from the group of polycrystalline silicon and a refractory metal silicide, on a third layer selected from the group of silicon dioxide and silicon nitride, comprising the steps of: providing a patterned mask layer on the structure, leaving a region of the first layer exposed; providing a plasma etch reactor having a non-erodible electrode and using it for: etching the exposed first layer in a first atmosphere of an inert carrier gas and 16:1 to 22:1 CHF 3 :SF 6 , until the second layer is exposed and a sidewall is formed in the first layer; and etching the exposed second layer in a second atmosphere of 1.7:1 to 3.5:1 HBr:inert assisting gas, until the third layer is exposed and a sidewall is formed in the second layer, and said sidewalls of the first and second layers are smoothed.

Claim 14

A method to etch a sandwich structure of a first layer selected from the group of silicon dioxide and silicon nitride, on a second layer selected from the group of polycrystalline silicon and a refractory metal silicide, on a third layer selected from the group of silicon dioxide and silicon nitride, comprising the steps of: providing a patterned mask layer on the structure, leaving a region of the first layer exposed; providing a plasma etch reactor having a non-erodible electrode and using it for: etching the exposed first layer in a first atmosphere of an inert carrier gas and 16:1 to 22:1 CHF 3 :SF 6 , until the second layer is exposed and a sidewall is formed in the first layer; and etching the exposed second layer in a second atmosphere of 1.7:1 to 3.5:1 HBr:inert assisting gas, until the third layer is exposed and a sidewall is formed in the second layer, and said sidewalls of the first and second layers are smoothed.

Claim 20

A method according to claim wherein said etching in said second atmosphere includes an overetch step.