Contact resistances in integrated circuits

1. A method of forming a low resistance contact between a poly-silicon resistor of an integrated circuit and a conducting material, the method comprising the steps of:

a) covering the resistor with an insulating layer, the resistor being disposed on a wafer;

b) etching at least one contact opening in the insulating layer to the resistor;

c) cleaning the insulating layer to remove any residues from the etching process;

d) dipping the wafer carrying said poly-silicon resistor into phosphoric acid after etching to the resistor; and

e) depositing a conducting layer in the at least one contact opening to form an electrical contact with said resistor.

2. The method as claimed in claim 1 , wherein the concentration of the phosphoric acid is approximately 85% phosphoric acid to 15% water.

3. The method as claimed in claim 1 , wherein the temperature of the phosphoric acid during step (d) is approximately 170° C.

4. The method as claimed in claim 1 , wherein the time for which the phosphoric acid is applied is less than 15 minutes.

5. The method as claimed in claim 4 , wherein the time for which the phosphoric acid is applied is between 5 and 10 minutes.

6. The method as claimed in claim 5 , further comprising the step of:

rinsing the wafer with a water rinse after the phosphoric acid has been applied.

7. The method as claimed in claim 1 , wherein said conducting layer is deposited using an evaporation method.

8. The method as claimed in claim 1 , wherein said cleaning step is carried out using hydrofluoric acid.

9. The method as claimed in claim 1 , wherein said etching step comprises a masking step to define areas for said contact openings.

10. The method as claimed in claim 9 , wherein said masking step uses a masking resist layer.

11. The method as claimed in claim 10 , wherein said masking resist layer is removed after cleaning of said contact openings.

12. The method as claimed in claim 1 , wherein said etching step is carried out using a plasma etch method.

13. The method as claimed in claim 1 , wherein said resistor is doped with a chemical selected from the group consisting of boron, phosphorus and arsenic.

14. The method as claimed in claim 1 , wherein said conducting material is aluminum.

15. The method as claimed in claim 14 , wherein said aluminum contains small concentrations of silicon.

16. The method as claimed in claim 1 , wherein said conducting layer is deposited using a sputter deposition method.

17. The method as claimed in claim 1 , wherein said etching step is carried out using a wet etch method.

18. The method as claimed in claim 17 , wherein said etching step is carried out using a combination of a plasma etch method and a wet etch method.

19. The method as claimed in claim 14 , wherein said aluminum contains small concentrations of copper.

20. A method of forming a low resistance contact between a poly-silicon resistor of an integrated circuit and a conducting material, the method comprising the steps of:

a) covering the resistor with an insulating layer;

b) etching at least one contact opening in the insulating layer to the resistor;

c) cleaning the insulating layer to remove any residues from the etching process;

d) applying phosphoric acid to the resistor; and

e) depositing a conducting layer which forms an electrical contact with said resistor.

21. The method as claimed in claim 20 , wherein step (d) is carried out by either dipping or spraying the wafer carrying said poly-silicon resistor into phosphoric acid after initiating etching.

22. The method as claimed in claim 20 , wherein the concentration of the phosphoric acid is approximately 85% phosphoric acid to 15% water.

23. The method as claimed in claim 21 , wherein the temperature of the phosphoric acid during step (d) is approximately 170° C.

24. The method as claimed in claim 1 , wherein the time for which the phosphoric acid is applied is less than 15 minutes.

25. The method as claimed in claim 21 , further comprising the step of rinsing the wafer with a water rinse after the phosphoric acid has been applied.

26. The method as claimed in claim 20 , wherein said conducting layer is deposited using either an evaporation method or a sputter deposition method.

27. The method as claimed in claim 20 , wherein said cleaning step is carried out using hydrofluoric acid.

28. The method as claimed in claim 20 , wherein:

said etching step comprises a masking step using a masking resist layer to define areas for said contact openings; and

said masking resist layer is removed after cleaning of said contact openings.

29. The method as claimed in claim 20 , wherein said etching step is carried out using either a plasma etch method or a wet etch method.

30. The method as claimed in claim 20 , wherein said etching step is carried out using a combination of plasma etch method and a wet etch method.

31. The method as claimed in claim 20 , wherein said resistor is doped with a chemical selected from the group consisting of boron, phosphorus and arsenic.

32. The method as claimed in claim 20 , wherein said conducting material is aluminum.

33. The method as claimed in claim 32 , wherein said aluminum contains small concentrations of silicon.

34. The method as claimed in claim 32 , wherein said aluminum contains small concentrations of copper.

35. The method as claimed in claim 1 , wherein:

said poly-silicon resistor is disposed on a wafer; and

step (d) comprises applying phosphoric acid onto the wafer.

36. A method of forming a low resistance contact between a poly-silicon resistor of an integrated circuit and a conducting material, the method comprising the steps of:

a) covering the resistor with an insulating layer;

b) etching at least one contact opening in the insulating layer to the resistor, said etching step comprising a masking step to define areas for said contact openings;

c) cleaning the insulating layer to remove any residues from the etching process;

d) applying phosphoric acid to the at least one contact opening after initiating etching; and

e) depositing a conducting layer which forms in the at least one contact opening to form an electrical contact with said resistor.

37. The method as claimed in claim 36 , wherein said masking step uses a masking resist layer.

38. The method as claimed in claim 37 , wherein said masking resist layer is removed after cleaning of said contact openings.