Abstract During SiO2 etching, when the oxide surface etch rate is larger than the bulk etch rate and the photoresist adheres tenaciously to the surface, a near vertical wall or cusp will be formed. This will create potential fracture spots in sputtered or evaporated metal which covers the steps. In the fabrication of self-aligned gate IGFETs, where the gate material acts as a mask against either etching or ion implantation, holes in the step metal will allow regions under the nominal gate to be doped during the source-drain doping. The slope of an etched step can be controlled by fabricating a double layer in which the top layer etches faster than the bulk. The specification describes the use of the enhanced etch rate of ion bombarded SiO2 to generate controlled tapers on window openings.
The method of claim 1 in which the substrate is silicon.
Claim 2
Dependent Claim
35 words
The method of claim 1 in which the ion beam exposure results in a peak ion penetration at a point less than one third of the distance from the surface of the silicon dioxide layer.
Claim 3
Dependent Claim
15 words
The method of claim 1 in which the silicon dioxide layer is etched with HF.
Claim 4
Dependent Claim
38 words
The method of claim 2 in which the silicon dioxide layer has a thickness of the order of 0.7 microns and is exposed to 50 keV Ar ions at a dose of approximately 3 X 1013 cm 2.
Claim 5
Dependent Claim
23 words
The method of claim 1 in which the ion beam contains ions selected from the group consisting of boron, phosphorus, argon and silicon.
Claim 6
Independent Claim
138 words
A method for obtaining a tapered silicon dioxide layer on a supporting substrate comprising the steps of, depositing a silicon dioxide layer on the supporting substrate, exposing the silicon dioxide layer to an ion beam to penetrate a surface portion of the thickness of the layer, masking the silicon layer so that the edge of the open portion of the mask corresponds to the region of the layer desired to be tapered, exposing the unmasked portion of the silicon dioxide layer to an ion beam to penetrate through that region of the silicon dioxide layer, the ion beam exposure in each case having an ion dose sufficient to cause the etch rate of the implanted regions to exceed the normal etch rate by at least 50 percent, and etching the silicon dioxide layer to produce a typered layer.
Claim 7
Dependent Claim
31 words
The method of claim 7 in which the silicon layer is masked with a shadow mask and the entire surface of the silicon dioxide layer is subsequently at least partly etched.