Etch process employing asymmetric bipolar pulsed DC

• US 5,770,023 A
• Filed: 02/12/1996
• Issued: 06/23/1998
• Est. Priority Date: 02/12/1996
• Status: Expired due to Term

• Current Assignee: MKS Instruments Incorporated
• Original Assignee: ENI
• Inventors: Sellers, Jeff C.
• Primary Examiner(s): Kunemund, Robert
• Assistant Examiner(s): MCDONALD, RODNEY GLENN
• Application Number:
  US08/600,194
• Time in Patent Office: 862 Days
• Field of Search: 204/192.1, 204/192.12, 204/192.3, 204/192.32, 204/192.37, 204/298.08, 216/67, 156/643.1
• US Class Current: 204/192.3
• CPC Class Codes: C23C 14/0036 Reactive sputtering
• CPC Class Codes: C23C 14/022 by means of bombardment with energetic particles or radiation

Abstract

An asymmetric bipolar plasma etching process is employed for etching a workpiece positioned within a plasma chamber, to prepare the workpiece for a subsequent coating process. The etching process involves applying a negative high voltage to the workpiece, relative to an anode portion of the chamber. Pulses of a positive voltage are applied to the workpiece at a predetermined pulse width and a predetermined level relative to the anode, so that the applied voltage appears as a train of asymmetric bipolar pulses. The waveform has a major negative-going portion and a minor positive-going portion. The negative-going portion can have a voltage of minus 300 to minus 4,000 volts, and the positive-going pulses can have a voltage of plus 50 to plus 300 volts, and a typical pulse width between about 0.25 and 3 microseconds. The etching process can be followed by a sputter coating process in the same chamber. Another coating technique could also be used.

Claims

1. Asymmetric bipolar plasma etching process for etching a workpiece to be later coated, and which is positioned within a plasma chamber, comprising the steps of:

applying a negative dc forward etching current at an applied forward voltage level between said workpiece and an anode in said chamber such that said applied forward voltage level causes noble gas ions in said chamber to impinge upon said workpiece with sufficient energy to flee impurities from the surface of said workpiece; and

applying onto said forward etching current pulses of a positive reverse voltage at a suitable pulse width and a suitable reverse bias level relative to said anode, so that the voltage applied between said workpiece and said anode is a train of asymmetric bipolar pulses with the reverse bias voltage having a pulse duty cycle that is significantly below 50%;

wherein said applied forward voltage is between negative 300 and negative 4,000 volts and said reverse bias voltage is selected at a smaller level between positive 50 volts and positive 300 volts.

2. Process according to claim 1 wherein said negative voltage is on the order of 1,500 to 1,800 volts.

7. Process according to claim 1 wherein said pulses have a pulse rate of between 40 KHz and 200 Khz.

8. Process according to claim 1 wherein said reverse bias voltage is about +75 volts.

9. Process according to claim 1 wherein said applied forward voltage is at least minus 1,200 volts.

10. Process according to claim 9, wherein said applied forward voltage is between about minus 1,200 volts and minus 1,800 volts.

3. A combined etching and sputtering process in which a workpiece is first subjected to plasma etching in a plasma chamber that contains a sputtering target to remove impurities from the surface of the article, and then is subjected to reactive sputtering to produce a coating on the article;

comprising the steps of

a) etching said article in a plasma chamber by

i) applying a negative dc forward etching current at an applied forward voltage level between said workpiece and an anode in said chamber such that said forward voltage level causes noble gas ions in said chamber to impinge upon said workpiece with sufficient energy to free impurities from the surface of said workpiece;

while

ii) applying onto said forward etching current pulses of a positive reverse bias voltage at a suitable pulse width and pulse rate and a suitable reverse bias level relative to said anode, so that the voltage applied between said workpiece and said anode is a train of asymmetric bipolar pulses wherein the positive reverse bias voltage has a pulse duty cycle significantly below fifty percent;

wherein said forward applied voltage is between negative 300 and negative 4,000 volts and said reverse bias voltage is provided at a substantially smaller level between positive 50 volts and positive 300 volts; and

with said pulse width being between 0.25 μ

sec and 3 μ

sec; and

directly after said workpiece has been etched sufficiently to carry out a sputter coating operation thereon,

b) carrying out a reactive sputtering process in the very same plasma chamber, by

i) introducing into said chamber a reactive gas; and

ii) applying a dc sputtering current between said target and an anode in said chamber at an applied voltage level that causes noble gas ions in the chamber to impinge upon said target with sufficient energy to free atoms of said target material from said target;

iii) wherein the free atoms of said target material react with said reactive gas to form a compound that is then deposited on the etched surface of said workpiece.

4. Combined etching and sputtering process according to claim 3, wherein said step ii) of applying a dc sputtering current includes supplying said sputtering current to said target at a forward negative voltage level relative to said anode, and applying onto said sputtering current pulses of a positive reverse bias voltage relative to said anode at a predetermined pulse rate having a pulse duty cycle that is significantly below fifty percent and a predetermined pulse width so that accumulations of said compound which have deposited on said target are bombarded by said noble gas ions with sufficient energy to free molecules of said compound from said target.

5. Combined etching and sputtering process according to claim 4 wherein said pulses of positive voltage have a pulse width between about 0.25 and 3 μ

sec.

6. Combined etching and sputtering process according to claim 4, wherein said negative applied voltage is between 300 and 700 volts and said positive voltage is between 50 and 300 volts.