Selective germanium P-contact metalization through trench
Techniques are disclosed for forming transistor devices having reduced parasitic contact resistance relative to conventional devices. The techniques can be implemented, for example, using a standard contact stack such as a series of metals on, for example, silicon or silicon germanium (SiGe) source/drain regions. In accordance with one example such embodiment, an intermediate boron doped germanium layer is provided between the source/drain and contact metals to significantly reduce contact resistance. Numerous transistor configurations and suitable fabrication processes will be apparent in light of this disclosure, including both planar and non-planar transistor structures (e.g., FinFETs), as well as strained and unstrained channel structures. Graded buffering can be used to reduce misfit dislocation. The techniques are particularly well-suited for implementing p-type devices, but can be used for n-type devices if so desired.
1. A semiconductor device, comprising:
a substrate;
p-type source and drain regions in the substrate and adjacent to a corresponding channel region in the substrate;
n-type source and drain regions in the substrate and adjacent to a corresponding channel region in the substrate;
a gate electrode above each channel region, wherein a gate dielectric layer is provided between the gate electrode and the channel region;
an insulation layer over the substrate, the insulation layer having a contact trench formed over at least each of the p-type source and drain regions;
a boron doped germanium layer entirely within the contact trenches and on at least a portion of the corresponding p-type source and drain regions, the boron doped germanium layer comprising a germanium concentration in excess of 50 atomic % and a boron concentration in excess of 2E20 cm −3 ; and
a metal source/drain contact at least partially within each of the contact trenches and on the boron doped germanium layer.
2. The device of claim 1 wherein the device comprises FinFET transistor architecture, such that each channel region is associated with a semiconductor body that extends from the substrate through the insulation layer, and the corresponding gate electrode is formed over three surfaces of the semiconductor body to form three gates.
3. The device of claim 1 wherein the boron doped germanium layer is only on p-type source/drain regions of the device, and the contacts associated therewith each comprise a metal-germanide.
4. The device of claim 1 wherein the insulation layer comprises silicon dioxide.
5. The device of claim 1 , further comprising at least one of:
a graded buffer between the substrate and at least one of the p-type and n-type source/drain regions; and
a graded buffer between at least one of the p-type and n-type source/drain regions and the boron doped germanium layer.
6. The device of claim 5 wherein the graded buffer between at least one of the p-type and n-type source/drain regions and the boron doped germanium layer has a germanium concentration that is graded from a base level concentration compatible with the at least one of the p-type and n-type source/drain regions to a high concentration in excess of 95 atomic %.
7. The device of claim 6 wherein the high concentration reflects pure germanium.
8. The device of claim 5 wherein the graded buffer between the at least one of the p-type and n-type source/drain regions and the boron doped germanium layer has a boron concentration that is graded from a base level concentration compatible with the at least one of the p-type and n-type source/drain regions to a high concentration in excess of 1E20 cm −3 .
9. The device of claim 1 wherein the boron doped germanium layer has a graded concentration of at least one of germanium and boron.
10. The device of claim 1 wherein the p-type and n-type source/drain regions comprise silicon germanium having a germanium concentration that is graded from a base level concentration compatible with the substrate to a high concentration in excess of 50 atomic %, and the boron doped germanium layer has a germanium concentration in excess of 95 atomic %.
11. The device of claim 1 wherein the p-type and n-type source/drain regions comprise boron doped silicon germanium having a boron concentration that is graded from a base level concentration compatible with the substrate to a high concentration in excess of 1E20 cm −3 .
12. The device of any of claim 1 wherein the p-type and n-type source/drain regions comprise silicon or silicon germanium, and the device further comprises a buffer between at least one of the p-type and n-type source/drain regions and the boron doped germanium layer, the buffer having a germanium concentration that is graded from a base level concentration compatible with the at least one p-type and n-type source/drain regions to a high concentration in excess of 50 atomic %, and a boron concentration that is graded from a base level concentration compatible with the at least one of the p-type and n-type source/drain regions to a high concentration in excess of 1E20 cm −3 .
13. The device of claim 1 wherein the boron doped germanium layer comprises a germanium concentration in excess of 98 atomic %, and a boron concentration in excess of 2E20 cm −3 .
14. A semiconductor device, comprising:
a substrate having a plurality of fins extending from the substrate, each fin including a channel region;
a gate electrode around each channel region so as to provide a tri-gate structure, wherein a gate dielectric layer is provided between the gate electrode and the channel region and spacers are provided on sides of the gate electrode;
p-type source and drain regions in the substrate and adjacent to a corresponding channel region;
n-type source and drain regions in the substrate and adjacent to a corresponding channel region;
an insulation layer over the substrate, the insulation layer having a contact trench formed over at least each of the p-type source and drain regions;
a boron doped germanium layer entirely within the contact trenches and on at least a portion of the corresponding p-type source and drain regions, the boron doped germanium layer comprising a germanium concentration in excess of 50 atomic % and a boron concentration in excess of 2E20 cm −3 ; and
a metal source/drain contact at least partially within each of the contact trenches.
15. The device of claim 14 , the device further comprising:
a buffer between at least one of the p-type and n-type source/drain regions and the boron doped germanium layer, wherein the buffer has a germanium concentration that is graded from a base level concentration compatible with the at least one of the p-type and n-type source/drain regions to a high concentration in excess of 95 atomic %, and a boron concentration that is graded from a base level concentration compatible with the at least one of the p-type and n-type source/drain regions to a high concentration in excess of 2E20 cm −3 .
16. The device of claim 14 wherein the boron doped germanium layer has a graded concentration of at least one of germanium and boron.
17. The device of claim 14 wherein the p-type and n-type source/drain regions comprise silicon germanium having a germanium concentration that is graded from a base level concentration compatible with the substrate to a high concentration in excess of 50 atomic %, and the boron doped germanium layer has a germanium concentration in excess of 98 atomic %.
18. The device of claim 17 wherein the p-type and n-type source/drain regions have a boron concentration that is graded from a base level concentration compatible with the substrate to a high concentration in excess of 2E20 cm −3 .
19. The device of claim 14 wherein the p-type and n-type source/drain regions comprise silicon germanium having a fixed germanium concentration, and the device further comprises a buffer between the p-type and n-type source/drain regions and the boron doped germanium layer, the buffer having a germanium concentration that is graded from a base level concentration compatible with the p-type and n-type source/drain regions to a high concentration in excess of 50 atomic %, and a boron concentration that is graded from a base level concentration compatible with the p-type and n-type source/drain regions to a high concentration in excess of 2E20 cm −3 , the buffer having a thickness of less than 100 Angstroms.
20. A method for forming a transistor device, comprising:
providing a substrate;
providing p-type source and drain regions in the substrate and adjacent to a corresponding channel region in the substrate;
providing n-type source and drain regions in the substrate and adjacent to a corresponding channel region in the substrate;
providing a gate electrode above the channel region, wherein a gate dielectric layer is provided between the gate electrode and the channel region; and
providing an insulation layer over the substrate;
forming a contact trench in the insulation layer over at least each of the p-type source and drain regions;
providing a boron doped germanium layer entirely within the contact trenches and on at least a portion of the corresponding p-type source and drain regions, the boron doped germanium layer comprising a germanium concentration in excess of 50 atomic % and a boron concentration in excess of 2E20 cm −3 ; and
providing metal-germanide source/drain contacts on the boron doped germanium layer.