Semiconductor structure having NFET extension last implants

1. A method of forming a semiconductor structure comprising:

(a) obtaining an extra thin semiconductor on insulator (ETSOI) wafer having a PFET portion where a p-type field effect transistor (PFET) will be formed and an NFET portion where an n-type field effect transistor (NFET) will be formed;

(b) forming at least one gate structure in the PFET portion and at least one gate structure in the NFET portion;

(c) depositing a high quality nitride over the PFET portion and the NFET portion, the high quality nitride being unetchable in dilute hydrofluoric acid (HF);

(d) depositing a low quality nitride over the high quality nitride, the low quality nitride being etchable in dilute HF;

(e) etching the PFET portion to remove the high quality nitride and low quality nitride except for high quality nitride and low quality nitride adjacent to the at least one gate structure in the PFET portion;

(f) etching the PFET portion and the NFET portion to remove the low quality nitride;

(g) forming a doped faceted epitaxial silicon/germanium (SiGe) on the ETSOI adjacent to the high quality nitride and the at least one gate structure in the PFET portion to form a faceted raised source/drain (RSD) in the PFET portion and an amorphous portion on the high quality nitride;

(h) depositing a low quality nitride over the PFET portion and the NFET portion;

(i) etching the PFET portion to remove the low quality nitride while maintaining the low quality nitride adjacent to the high quality nitride and at least one gate structure to form disposable spacers from the low quality nitride adjacent to the high quality nitride and etching the NFET portion to remove the low quality nitride and high quality nitride except for high quality nitride and low quality nitride adjacent to the at least one gate structure in the NFET portion, the low quality nitride adjacent to the at least one gate structure in the NFET portion forming disposable spacers;

(j) ion implanting into the RSD in the PFET portion to render amorphous a top portion of the RSD in the PFET portion;

(k) etching the disposable spacers adjacent the at least one gate structure in the NFET portion and the PFET portion to leave at least the high quality nitride adjacent to the at least one gate structure in the PFET portion and at least the high quality nitride adjacent to the at least one gate structure in the NFET portion;

(l) forming a faceted epitaxial silicon RSD on the ETSOI adjacent to the at least one gate structure in the NFET portion;

(m) performing a rapid thermal anneal;

(n) ion implanting extensions into the ETSOI underneath the at least one gate structure in the NFET portion; and

(o) performing a short time scale anneal to activate the NFET extension implants but not diffuse them.

2. The method of claim 1 wherein step (i) comprises two etching steps such that a first etching step comprises etching the low quality nitride from the PFET portion and the NFET portion and a second etching step comprises etching the high quality nitride from the NFET portion wherein the second etching step has different etching parameters than the first etching step.

3. The method of claim 1 wherein forming in step (i) comprises a cyclic epitaxial process.

4. The method of claim 3 wherein epitaxial material is not formed on the RSD in the PFET portion during the cyclic epitaxial process.

5. The method of claim 1 wherein the epitaxial silicon formed in step (I) is undoped silicon.

6. The method of claim 5 further comprising the steps between step (I) and step (m) of forming oxide spacers adjacent to the high quality nitride in the NFET portion, masking the PFET portion and ion implanting into the RSD in the NFET portion and step (m) of performing a rapid thermal anneal includes driving in dopants of the RSD into the ETSOI in the PFET portion and NFET portion.

7. The method of claim 1 wherein the epitaxial silicon formed in step (l) is doped silicon and step (m) of performing a rapid thermal anneal includes driving in dopants of the RSD into the ETSOI in the PFET portion and NFET portion.

8. The method of claim 1 wherein the short time anneal in step (o) is a laser anneal or a flash anneal such that the anneal time is less than 10 milliseconds.

9. The method of claim 1 further comprising a step (p) of forming nitride spacers adjacent to the at least one gate structure in the PFET portion and the at least one gate structure in the NFET portion.

10. The method of claim 1 wherein dilute HF may be defined as having a range of HF:H 2 O (water) from 1:10 to 1:100 and the high quality nitride is a nitride that has an etch rate in dilute hydrofluoric (HF) acid of less than about 1 nanometer per minute.

11. The method of claim 10 wherein the low quality nitride has an etch rate in dilute HF of more than about 10 nanometers per minute.