Vertical transport field-effect transistor including dual layer top spacer
A vertical transport field-effect transistor includes a top source/drain region separated from an underlying gate stack by a multi-layer top spacer that includes an oxygen barrier layer beneath a top dielectric layer. Techniques for fabricating the transistor include depositing the oxygen barrier layer over the gate stack prior to depositing the top dielectric layer. The oxygen barrier layer blocks oxygen diffusion during deposition of the top dielectric layer, thereby avoiding damage to underlying interfacial and gate dielectric layers.
1. A method of fabricating a vertical transport field-effect transistor structure, comprising:
obtaining a first structure including:
a vertically extending semiconductor fin including a top region, a bottom region, and a channel region between the top region and the bottom region,
a bottom source/drain region adjoining the bottom region of the semiconductor fin,
a gate dielectric layer adjoining the channel region of the semiconductor fin,
an electrically conductive gate electrode layer adjoining the gate dielectric layer, each of the gate dielectric layer and the gate electrode layer including exposed top edge portions, the top region of the semiconductor fin extending above the exposed top edge portions of the gate dielectric layer and the gate electrode layer, and
a bottom electrically insulating spacer between the bottom source/drain region and the gate electrode layer;
depositing an oxidation barrier layer on the first structure, the oxidation barrier layer extending over the gate electrode layer and the exposed top edge portions of the gate dielectric layer and the gate electrode layer;
depositing a top dielectric layer on the oxidation barrier layer;
exposing the top region of the semiconductor fin, wherein exposing the top region of the semiconductor fin includes removing a first portion of the oxidation barrier layer and a first portion of the top dielectric layer above the channel region of the semiconductor fin;
epitaxially growing a top source/drain region on the top region of the semiconductor fin such that a second portion of the oxidation barrier layer and a second portion of the top dielectric layer comprise a top spacer between the top source/drain region and the gate electrode layer.
2. The method of claim 1 , wherein the oxygen barrier layer includes aluminum oxide.
3. The method of claim 2 , wherein obtaining the first structure includes:
epitaxially growing the bottom source/drain region directly on a semiconductor substrate;
depositing the bottom electrically insulating spacer over the bottom source/drain region;
depositing the gate dielectric layer directly on the bottom electrically insulating spacer and the semiconductor fin, and
depositing the gate electrode layer directly on the gate dielectric layer.
4. The method of claim 3 , wherein the top dielectric layer includes silicon nitride.
5. The method of claim 4 , wherein the first structure further includes a dielectric cap on the semiconductor fin, further including removing the dielectric cap prior to epitaxially growing the top source/drain region.
6. The method of claim 5 , wherein the semiconductor substrate comprises silicon.
7. The method of claim 1 , wherein the semiconductor fin is integral with the semiconductor substrate, further wherein epitaxially growing the top source/drain region includes growing the top source/drain region on first and second sidewall portions of the semiconductor fin extending above the top spacer.
8. The method of claim 7 , wherein the semiconductor fin extends about two to twenty nanometers above the top spacer.