Forming of a single-crystal semiconductor layer portion separated from a substrate

Abstract

A method for forming a single-crystal semiconductor layer portion above a hollowed area, including growing by selective epitaxy on an active single-crystal semiconductor region a sacrificial single-crystal semiconductor layer and a single-crystal semiconductor layer, and removing the sacrificial layer. The epitaxial growth is performed while the active region is surrounded with a raised insulating layer and the removal of the sacrificial single-crystal semiconductor layer is performed through an access resulting from an at least partial removal of the raised insulating layer.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A to 1E, previously described, illustrate in cross-section view different steps of the forming of a MOS transistor according to a known method;

FIG. 2, previously described, is a top view of FIG. 1C;

FIG. 3, previously described, is a cross-section view of the structure of FIG. 1E along plane III-III′ of FIG. 2;

FIGS. 4A to 4F are cross-section views of different steps of the forming of a MOS transistor according to an embodiment of the present invention;

FIG. 5 is a cross-sectional view of the structure of FIG. 4F in a perpendicular cross-section plane; and

FIGS. 6A and 6B show a variation of preliminary steps of implementation of a method according to the present invention.

Claims

1. A method for forming a single-crystal semiconductor layer portion above a hollowed area, comprising: growing by selective epitaxy, on an active single-crystal semiconductor region, a sacrificial single-crystal semiconductor layer and a single-crystal semiconductor layerremoving the sacrificial single-crystal semiconductor layer,wherein the epitaxial growth is performed while the active region is surrounded with a raised insulating layer and the removal of the sacrificial single-crystal semiconductor layer is performed through an access resulting from an at least partial removal of the raised insulating layer.

2. The method of claim 1, wherein the active single-crystal semiconductor region and the single-crystal semiconductor layer are made of silicon, and the sacrificial layer is made of silicon-germanium.

3. The method of claim 1, wherein the active region is initially delimited by an insulation area at the same level as its upper surface, and comprising, before epitaxy of said layers, lowering an upper surface of the active region by a height lower than a depth of said insulation areas.

4. The method of claim 3, wherein the lowering height of the upper surface of the active region is substantially equal to the sum of the thicknesses of the epitaxial layers.

5. The method of claim 1, wherein the active region is initially delimited by an insulation area formed above a semiconductor layer or substrate.

6. The method of claim 1, wherein the empty interval left by the removal of the sacrificial layer is filled with an insulator.

7. The method of claim 1, wherein the empty interval left by the removal of the sacrificial layer is filled with an electrically or thermally conductive material such as a metal.

8. A method for forming a MOS transistor, comprising forming a transistor channel by forming a single-crystal semiconductor layer portion above a hollowed area, comprising: growing by selective epitaxy, on an active single-crystal semiconductor region, a sacrificial single-crystal semiconductor layer and a single-crystal semiconductor layerremoving the sacrificial single-crystal semiconductor layer,wherein the epitaxial growth is performed while the active region is surrounded with a raised insulating layer and the removal of the sacrificial single-crystal semiconductor layer is performed through an access resulting from an at least partial removal of the raised insulating layer.

9. The method of claim 8, wherein removal of the sacrificial layer is performed after forming of an insulated gate on said single-crystal semiconductor layer.

10. The method of claim 8, wherein the forming of a gate is followed by a step of epitaxial growth of a single-crystal semiconductor material of same nature as that of the channel to form raised source/drain areas.

11. A method for forming a MOS transistor with several gates, comprising a method for forming the insulated single-crystal semiconductor layer of claim 1.

12. The method of claim 8, comprising forming a MOS transistor with several gates.