Selective removal of a silicon oxide layer
A method of fabricating a device, including the steps of forming a first silicon oxide layer within a first region of the device and a second silicon oxide layer within a second region of the device, implanting doping ions of a first type into the first region, implanting doping ions of a second type into the second region, and etching the first and second regions for a determined duration such that the first silicon oxide layer is removed and at least a part of the second silicon oxide layer remains.
1. A method of fabricating a device comprising a first transistor and a second transistor, and comprising active regions, the method comprising:
forming a first silicon oxide layer within a first region of said device and a second silicon oxide layer within a second region of said device;
implanting doping ions of a first type into said first region such that ions are implanted into said first silicon oxide layer and not into said second silicon oxide layer;
implanting doping ions of a second type into said second region such that ions are implanted into said second silicon oxide layer and not into said first silicon oxide layer, wherein said steps of implanting doping ions of said first and second types form active regions of said device; and
simultaneously etching said first and second silicon oxide layers for a determined duration, wherein a first etch rate of the first silicon oxide layer being greater than a second etch rate of the second silicon oxide layer causes said first silicon oxide layer to be completely removed and at least a part of said second silicon oxide layer on a gate electrode of the second transistor to remain.
2. The method as claimed in claim 1 , wherein said first type of doping ions are heavier than said second type of doping ions.
3. The method as claimed in claim 1 , wherein the quantity of said first type of doping ions implanted into said first region is greater than the quantity of said second type of doping ions implanted into said second region.
4. The method as claimed in claim 1 , wherein the energy with which said first type of doping ions are implanted into said first region is greater than the energy with which said second type of doping ions are implanted into said second region.
5. The method as claimed in claim 1 , wherein said first silicon oxide layer is a high thermal oxide formed by high temperature deposition.
6. The method as claimed in claim 1 , wherein said device is a CMOS device, said first transistor is a first MOS transistor, said second transistor is a second MOS transistor, and said first silicon oxide layer is formed over a polysilicon gate electrode of the first MOS transistor and said second silicon oxide layer is formed over a polysilicon gate electrode of the second MOS transistor.
7. The method as claimed in claim 6 , wherein said step of implanting doping ions of a first type into said first region also forms source and drain regions of said first MOS transistor and said step of implanting doping ions of a second type into said second region also forms source and drain regions of said second MOS transistor.
8. The method as claimed in claim 7 , further comprising, the steps of:
depositing a first metal layer over said first and second regions;
performing a first annealing step so as to form a first silicide gate electrode of a first silicide and silicide source and drain regions of said first silicide in said first MOS transistor;
etching said first and second regions such that said at least part of said second silicon oxide layer is removed;
depositing a second metal layer over said first and second regions; and
performing a second annealing step so as to form a second silicide gate electrode of a second silicide in said second MOS transistor.
9. The method as claimed in claim 8 wherein said first annealing step also forms silicide source and drain regions of said first silicide in said second MOS transistor.
10. The method of claim 1 , wherein the gate of the first transistor and the gate of the second transistor are formed of different silicides.
11. The method of claim 1 , wherein the first silicon oxide layer is formed over a gate electrode of the first transistor.
12. The method of claim 11 , wherein the gate electrodes of the first and second transistors are polysilicon gate electrodes.
13. A method of fabricating a device comprising a first transistor and a second transistor, the method comprising:
implanting dopants of a first type into a first protective layer and not into a second protective layer, wherein the implanting dopants of the first type forms a first active region of the device;
implanting dopants of a second type into the second protective layer and not into the first protective layer, wherein the implanting dopants of the second type forms a second active region of the device; and
simultaneously etching the first and second protective layers for a time duration, wherein a first etch rate of the first protective layer being greater than a second etch rate of the second protective layer causes the first protective layer to be completely removed and at least a part of the second protective layer on a gate electrode of the second transistor to remain.
14. The method of claim 13 , wherein the first type of dopant is heavier than the second type of dopant.
15. The method of claim 14 , wherein the gate electrodes of the first and second transistors are polysilicon gate electrodes.
16. The method of claim 13 , wherein an energy with which the first type of dopants are implanted into the first protective layer is greater than an energy with which the second type of dopants are implanted into the second protective layer.
17. The method of claim 13 , wherein the first protective layer and the second layer comprise silicon oxide.
18. The method of claim 13 , wherein the first protective layer is a high thermal oxide formed by high temperature deposition.
19. The method of claim 13 , wherein the device is a CMOS device, said first transistor is a first MOS transistor, said second transistor is a second MOS transistor, and the first protective layer is formed over a polysilicon gate electrode of a the first MOS transistor and the second protective layer is formed over a polysilicon gate electrode of a the second MOS transistor.
20. The method of claim 19 , wherein the first active region comprises source and drain regions of the first MOS transistor and the second active region comprises source and drain regions of the second MOS transistor.
21. The method of claim 19 , further comprising:
depositing a first metal layer over the polysilicon gate electrode of the first MOS transistor and the at least part of the second protective layer;
annealing the device a first time to form a first silicide gate electrode of a first silicide in the first MOS transistor;
etching the device such that the at least part of the second protective layer is removed;
depositing a second metal layer over the first silicide gate electrode and the polysilicon gate electrode of the second MOS transistor; and
annealing the device a second time to form a second silicide gate electrode of a second silicide in the second MOS transistor.
22. The method of claim 21 , wherein annealing the device the first time forms silicide source and drain regions of said first silicide in said first and second MOS transistors.