Method of manufacturing semiconductor device

1. A method of manufacturing a semiconductor device comprising a PMOS transistor and an NMOS transistor, comprising:

forming a silicon layer over a substrate through a gate insulating film;

forming a first gate electrode and second gate electrode by patterning said silicon layer, said first gate electrode being a gate electrode of NMOS transistor, and said second gate electrode being a gate electrode of said PMOS transistor;

forming an interlayer film covering said first and said second gate electrodes;

forming a first metallic layer formed of a metal capable of forming a silicide over said first and said second gate electrodes;

executing a first heat treatment process to form a first silicide from said first metallic layer;

selectively forming an oxide layer on said silicon layer of said first and second gate electrodes subjected to said first heat treatment process, a thickness of said oxide layer on said first gate electrode being greater than a thickness of said oxide layer on said second gate electrode;

forming, on said oxide layer, a second metallic layer of a metal capable of forming a silicide over said first and second gate electrodes subjected to said first heat treatment;

executing a second heat treatment process; and

removing an unreacted portion of said metallic layer and said oxide layer after said first and said second heat treatment process.

2. The method according to claim 1 , further comprising introducing an impurity that promotes formation of an oxide layer, into said silicon layer of said first gate electrode, before said forming a first metallic layer.

3. The method according to claim 2 , wherein said introducing an impurity includes forming a mask over an area of said second gate electrode.

4. The method according to claim 2 , wherein said selectively forming an oxide layer on said silicon layer of said first gate electrode subjected to said first heat treatment process includes:

introducing said impurity into both of said first gate electrode and said second gate electrode before said forming a first metallic layer; and

removing a region where said impurity is introduced from said second gate electrode.

5. The method according to claim 2 , wherein said impurity is arsenic.

6. The method according to claim 5 , wherein said impurity, arsenic, is provided in said silicon layer in a concentration equal to or higher than 3×1015 atoms/cm2.

7. The method according to claim 1 , wherein said forming an oxide layer includes employing a chemical solution capable of oxidizing.

8. The method according to claim 1 , wherein said forming an oxide layer includes performing one of a heat treatment process or a plasma processing, utilizing an oxidizing gas.

9. The method according to claim 1 , wherein said first and said second metallic layer contain Ni.

10. The method according to claim 1 , wherein at least an upper surface of said gate insulating layer includes one of a Hf oxide, a Hf silicate, and a nitride thereof.

11. The method according to claim 1 , wherein said forming a first metallic layer includes:

forming a NiZr layer over said first and said second gate electrodes; and

forming said first metallic layer on said NiZr layer.