Selective formation of titanium silicide and titanium nitride by hydrogen gas control

A method for fabricating a semiconductor structure, the method comprising:

• forming a source/drain (S/D) region on a substrate;
• depositing a titanium silicide layer over the S/D region with a first deposition process comprising a first hydrogen-to-precursor flow rate ratio;
• and
• depositing a titanium nitride layer over the titanium silicide layer with a second deposition process comprising a second hydrogen-to-precursor flow rate ratio,
• wherein the first hydrogen-to-precursor flow rate ratio is greater than the second hydrogen-to-precursor flow rate ratio.

A method comprising:

• forming a fin with a source/drain (S/D) region on a substrate;
• forming a gate structure over the fin;
• forming a spacer on a sidewall of the gate structure;
• depositing a silicide layer on the S/D region and on a first portion of the spacer with a first deposition process comprising a first precursor gas flow;
• and
• depositing a nitride layer on a second portion of the spacer with a second deposition process comprising a second precursor gas flow,
• wherein the first and second deposition processes are performed in a single reaction chamber and a flow rate of the second precursor gas flow is higher than a flow rate of the first precursor gas flow.