VERY LOW PRESSURE HIGH POWER IMPULSE TRIGGERED MAGNETRON SPUTTERING

• US 20100264016A1
• Filed: 06/10/2010
• Published: 10/21/2010
• Est. Priority Date: 12/14/2007
• Status: Active Grant

• Current Assignee: Regents of the University of California (University of California)
• Original Assignee: Regents of the University of California (University of California)
• Inventors: Andersson, Joakim, Anders, Andre
• Granted Patent: US 8,568,572 B2
• Time in Patent Office: Days
• US Class Current: 204/192.120
• CPC Class Codes: C23C 14/16 on metallic substrates or on substrates of boron or silicon
• CPC Class Codes: C23C 14/354 Introduction of auxiliary energy into the plasma
• CPC Class Codes: H01J 37/3467 Pulsed operation, e.g. HIPIMS

Abstract

A method and apparatus are described for very low pressure high powered magnetron sputtering of a coating onto a substrate. By the method of this invention, both substrate and coating target material are placed into an evacuable chamber, and the chamber pumped to vacuum. Thereafter a series of high impulse voltage pulses are applied to the target. Nearly simultaneously with each pulse, in one embodiment, a small cathodic arc source of the same material as the target is pulsed, triggering a plasma plume proximate to the surface of the target to thereby initiate the magnetron sputtering process. In another embodiment the plasma plume is generated using a pulsed laser aimed to strike an ablation target material positioned near the magnetron target surface.

Claims

1. A very low pressure high power impulse magnetron sputtering method for film coating of a selected material onto a substrate, the steps including:

a) placing the substrate to be film coated and a target comprising the selected coating material into a vacuum chamber, the substrate spaced a distance from the target;

b) evacuating the chamber to very low pressure;

c) applying a target pulse of a negative voltage to the target for a defined target pulse duration, while maintaining another member proximate the target at positive potential relative to the target, thus serving as the anode of the discharge, the target pulse of negative voltage of sufficient amplitude so as to create a condition supportive of self-sputtering of the target material after magnetron discharge has been initiated;

d) initiating the sputtering and ionization of said target material by providing a triggering pulse of a short duration to a triggering plasma source positioned proximate the target to generate a triggering plasma which blankets the target, wherein said target pulse and the triggering pulses overlap for at least a portion of their durations; and

,

c) thereafter repeating process steps c), and d) until the film coating is complete.

2. The method of claim 1 wherein the vacuum chamber is evacuated to a pressure between 10⁻

6 Torr and 10<sup>−

8</sup> Torr.

3. The method of claim 1 wherein the target material is selected from the group comprising silver, copper, nickel and bismuth.

4. The method of claim 1 where the negative voltage applied to the target is in the range of 500V to 1500V.

5. The method of claim 4 wherein the applied voltage is of sufficient amplitude so as to result in a power density to the target of at least 100 W cm⁻

2.

6. The method of claim 4 wherein the applied voltage is of sufficient amplitudes so as to result in a power density on target of between 100 W cm⁻

2 to 5,000 W cm<sup>−

2</sup>.

7. The method of claim 1 wherein the vacuum chamber is evacuated to a pressure at or below 8×

10<sup>−

4</sup> Torr.

8. The method of claim 2 including the further step of continuously supplying the chamber with a small but continuous stream of an inert process gas while at the same time continuing to evacuate the chamber such that the pressure in the chamber remains at or below 8×

10<sup>−

4</sup> Torr.

9. The method of claim 8 wherein the inert process gas is argon.

10. The method of claim 8 wherein the target material is selected from the group comprising niobium, aluminum, titanium, tungsten and chromium.

11. The method of claim 1 wherein the duration of the first pulse of negative voltage to the target is initiated for a first duration which is longer that the second pulse of a second duration.

12. The method of claim 11 wherein the first pulse is initiated prior to the second pulse.

13. The method of claim 11 wherein the first pulse is initiated subsequent to the initiation of the second pulse.

14. The method of claim 1 wherein the triggering plasma source is a cathodic arc plasma source.

15. The method of claim 1 wherein the triggering plasma source is a laser ablation source comprising a laser and an ablation target comprised of the same material as the sputtering target, the laser aimed such that when pulsed, the issuing laser beam strikes the ablation target, the said laser beam pulse duration of said second duration.

16. The method of claim 1 wherein the triggering plasma source comprises at least two arc plasma sources positioned in the chamber in close proximity to the face of said target.

17. The process of claim 1 in which the substrate is negatively biased with respect to the plasma potential.

18. An apparatus for very low pressure high power impulse triggered magnetron sputtering, said apparatus including:

a) a vacuum chamber;

b) means for positioning a substrate within said chamber;

c) a pump for evacuating the chamber to pressures below 8×

10<sup>−

4</sup> Torr;

d) a support stage for holding a target material within the chamber, said support stage including a multiplicity of permanent magnets, and serving as the positive member for the sputtering discharge;

e) a target material mounted to said support stage;

f) a switched dc power source capable of applying a pulsed voltage to said target on said support stage;

g) a triggering plasma source positioned proximate to the exposed face of said target; and

,

h) a dc source of pulsed power connected to said triggering plasma source for generating a triggering plasma when power is supplied to said source.

19. The apparatus of claim 18 wherein the said triggering plasma source is a cathodic arc source.

20. The apparatus of claim 18 wherein the triggering plasma source includes a laser facing and aligned with an ablation target.

21. A process for initiation of a self sustaining sputtering reaction at very low pressures including the steps of:

a) providing a magnetron target;

b) reducing the ambient pressure at said magnetron target to 8×

10<sup>−

4</sup> Torr or below;

c) applying a pulsed negative voltage to the said magnetron target, said pulse width of a selected interval, the pulsed negative voltage of sufficient amplitude so as to create a condition supportive of self sputter of the target material after discharge has been initiated; and

,

c) initiating the sputtering of said target material by providing a pulsed plasma of the same material as the target, which pulsed plasma blankets the target, the pulse width used to generate the plasma of shorter duration that the pulse of said negative voltage applied to the said magnetron target.

22. A process for sputtering a target material onto a substrate in a low pressure environment including the steps of reducing the gas pressure of said sputtering environment to the point where the mean free path of sputtered material is greater than or equal to the distance between the target and the substrate, and thereafter initiating a triggering plasma to trigger a sputtering plasma.

23. The process of claim 22 wherein the pressure maintained within the sputtering environment is between 8×

10<sup>−

4</sup> to 10<sup>−

11</sup> Torr.

24. The process of claim 22 wherein the pressure maintained within the sputtering environment is between 10⁻

6 and 10<sup>−

8</sup> Torr.

25. The process of claim 23 wherein the pressure maintained within the sputtering environment is between 8×

10<sup>−

4</sup> to 10<sup>−

5</sup> Torr.

26. A high power pulsed magnetron sputtering apparatus including a pulsed triggering plasma source for triggering a sputtering plasma.

27. The magnetron sputtering apparatus of claim 26 wherein the triggering plasma source for triggering the sputtering plasma is a miniature cathodic arc source.

28. The magnetron sputtering apparatus of claim 26 wherein the triggering plasma source for triggering the sputtering plasma is a laser ablation source.

29. The magnetron sputtering apparatus of claim 26 wherein the triggering plasma source produces triggering plasma of a material different than the target material so as to inject a dopant material to the deposited films.