In situ surface contamination removal for ion implanting
View Patent ↗Methods and apparatus that introduce, within the ion implant chamber or an isolated chamber in communication therewith, the capability to remove contaminants and oxide surface layers on a wafer surface prior to ion implantation, are disclosed. The mechanisms for removal of contaminants include conducting: a low energy plasma etch, heating the wafer and application of ultraviolet illumination, either in combination or individually. As a result, implantation can occur immediately after the cleaning/preparation process without the contamination potential of exposure of the wafer to an external environment. The preparation allows for the removal of surface contaminants, such as water vapor, organic materials and surface oxides.
1. An ion implantation method comprising:
biasing a wafer positioned in an implant chamber to a first bias voltage level, said first bias voltage level configured to perform a low energy plasma etch to remove contaminants from a surface of said wafer during a vacuum condition; and
biasing said wafer to a second bias voltage level larger in magnitude than said first bias voltage level after biasing said wafer to said first bias voltage level without breaking said vacuum condition, said second bias voltage level configured to accelerate ions within a plasma for ion implantation into said wafer.
2. The ion implantation method of claim 1 , wherein said first bias voltage level is no greater than −1,000 V.
3. The ion implantation method of claim 1 , wherein said first bias voltage level is between 0 V and −1,000 V and said second bias voltage level is about −5,000 V.
4. The ion implantation method of claim 1 , wherein said method further comprises providing at least one process gas to said implant chamber.
5. The ion implantation method of claim 4 , wherein a first process gas is provided during said biasing of said wafer at said first bias voltage level.
6. The ion implantation method of claim 5 , wherein said first process gas is selected from the group consisting of NF 3 , SiF 4 , BF 3 , F 2 , and H 2 .
7. The ion implantation method of claim 4 , wherein a second process gas is provided during said biasing of said wafer at said second bias voltage level.
8. The ion implantation method of claim 7 , wherein said second process gas is BF 3 .
9. The ion implantation method of claim 1 , further comprising monitoring change in secondary electron emission from said wafer.
10. The ion implantation method of claim 9 , further comprising controlling the duration of at least one of said first bias voltage level and said second bias voltage level based on said monitoring.