Densely spaced fins for semiconductor fin field effect transistors

1. A method of forming a fin-based field effect transistor (finFET) device, comprising:

forming one or more first fins comprising silicon on a substrate;

forming epitaxial layers on sides of the one or more first fins;

filling a plurality of spaces between each of the epitaxial layers with an oxide filler material removing, via a timed etch process and not an end-pointed reactive ion etching (RIE) process, a portion of the oxide filler material from the plurality of spaces between each of the one or more first fins to form a plurality of second fins to create first opening in the oxide filler material;

etching a second opening within the first opening, wherein:

the etching of the first opening exposes a top surface of the oxide filler material;

the second opening is etched in the oxide filler material to a predetermined depth to expose the plurality of second fins for forming a device region; and

forming a gate structure covering a portion of the plurality of second fins to define source and drain regions; and

forming a contact on the plurality of second fins.

2. The method of claim 1 , wherein the first fins include a base of silicon germanium and a cap of silicon nitride, and

the epitaxial layers are formed only on the silicon germanium portions of the first fins.

3. The method of claim 1 , further comprising:

forming filler material on the plurality of second fins to expand a volume of the source and drain regions.

4. The method of claim 3 , wherein forming the filler material comprises epitaxially growing a silicon-based material on the plurality of second fins.

5. The method of claim 1 , wherein forming the epitaxial layers on the sides of the one or more first fins comprises:

etching the one or more first fins from a silicon-based layer;

filling spaces around the one or more fins with an oxide layer;

etching a portion of the oxide layer to define a device region having the one or more fins exposed; and

forming the epitaxial layers on the sides of the one or more fins in the device region.

6. The method of claim 5 , wherein etching the portion of the oxide layer includes forming a sacrificial layer on the oxide layer and forming a photoresist layer on the sacrificial layer, the photoresist layer having a region without photoresist defining the device region.

7. The method of claim 1 , wherein forming the one or more first fins comprises:

forming a plurality of third fins by performing an etching process;

forming a silicon-based spacer layer on the plurality of third fins;

etching the silicon-based spacer layer and the plurality of third fins to form a plurality of fin-shaped spacers; and

performing an etching process using the fin-shaped spacers as a mask to form the one or more first fins.

8. The method of claim 7 , wherein the silicon-based spacer layer is made of silicon nitride.

9. The method of claim 7 , wherein the fin-shaped spacers are formed on a layer of silicon dioxide, the layer of silicon dioxide is formed on a layer of silicon nitride, and the layer of silicon nitride is formed on a layer of silicon germanium, and

the layer of silicon germanium and the layer of silicon nitride form the one or more first fins.

10. The method of claim 9 , further comprising:

forming the layer of silicon germanium epitaxially on a silicon substrate.