Dopant activation anneal to achieve less dopant diffusion (better USJ profile) and higher activation percentage
A method and apparatus for forming a semiconductor device. A semiconductor substrate is implanted with dopants. The substrate is subjected to a cleaning process employing electrically neutral nitrogen and fluorine radicals to produce an oxygen-free surface having dangling bonds. Before any further exposure to oxidizing gases, the substrate is annealed by thermal treatment to activate and distribute the dopants. A gate oxide layer is formed over the annealed surface. The apparatus performs all such treatments without breaking vacuum.
1. A method of processing a doped semiconductor substrate, comprising:
disposing the doped semiconductor substrate in a processing chamber;
providing a cleaning gas comprising a mixture of ammonia, nitrogen trifluoride, and a carrier gas to the processing chamber;
converting a portion of the cleaning gas to neutral radicals by applying RF power;
forming a sublimation layer on the doped semiconductor substrate by exposing the substrate to the cleaning gas while cooling the substrate;
forming an oxygen-free surface on the doped semiconductor substrate by heating the sublimation layer; and
activating the dopants in the doped semiconductor substrate by an annealing process, wherein a partial pressure of oxidizing gases is maintained below about 1 mTorr during the aforementioned disposing, providing, converting, forming, forming, and activating.
2. The method of claim 1 , wherein the substrate temperature is maintained below about 100° C. while forming the sublimation layer.
3. The method of claim 1 , wherein heating the sublimation layer comprises positioning the sublimation layer proximate to a hot showerhead.
4. A process for forming a device on a substrate, comprising:
implanting dopants into a surface of the substrate;
terminating the implanted surface with dangling bonds by exposing the substrate to a reducing gas at a temperature less than about 100° C.;
activating the dopants by heating the implanted surface of the substrate; and
forming an oxide layer over the implanted surface.
5. The process of claim 4 , wherein the reducing gas comprises nitrogen and fluorine.
6. The process of claim 5 , wherein terminating the implanted surface with dangling bonds comprises forming a sublimation layer over the implanted surface, and removing the sublimation layer by positioning the sublimation layer proximate to a hot showerhead and heating the sublimation layer to a temperature at or above 100° C.
7. The process of claim 4 , wherein the reducing gas comprises electrically neutral radicals.
8. The process of claim 7 , wherein the reducing gas comprises nitrogen and fluorine radicals, and the reducing gas forms a sublimation layer on the substrate that is subsequently removed by heating to a temperature at or above 100° C.
9. The process of claim 8 , wherein the implanted surface of the substrate is hydrogen-terminated at the time the dopants are activated by heating.
10. The process of claim 4 , wherein implanting dopants into the substrate surface, terminating the substrate surface with dangling bonds, and activating the dopants are all performed in a substantially oxygen-free atmosphere that is maintained during and between the implanting, terminating, and activating processes.
11. The process of claim 10 , wherein forming an oxide layer over the implanted surface comprises exposing the implanted surface to an oxidizing gas in the presence of RF power.
12. A method of forming a device on a substrate, comprising:
implanting dopants into a surface of the substrate;
disposing the substrate in a processing chamber configured to produce a charge-free reducing gas comprising neutral radicals;
applying RF energy at a remote location to form neutral radicals comprising nitrogen and fluorine;
flowing the neutral radicals into the processing chamber and exposing the doped surface of the substrate to the neutral radicals;
reacting the neutral radicals with the substrate surface at a temperature less than about 100° C. to form a thin film;
removing the thin film by heating a fixture of the processing chamber, positioning the fixture near the substrate surface, and heating the substrate surface;
generating dangling bonds on the substrate surface;
activating the dopants using a furnace annealing process; and
forming an oxide layer over the implanted surface.
13. The method of claim 12 , wherein the furnace annealing process comprises heating the substrate surface to a temperature less than about 850° C.