In situ surface contaminant removal for ion implanting
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. Technical Field
The present invention relates generally to ion implantation, and more particularly, to in situ surface contaminant removal for ion implanting.
2. Related Art
Semiconductor wafers that are to be ion implanted typically have contaminant materials and oxides on the wafer surface. These materials can contaminate the implant process and cause dose non-uniformity and reduced dose retained in the silicon.
Conventional surface preparation procedures include pre-cleaning techniques that are external to an ion implantation chamber. One of these approaches includes stripping of native oxide from the wafer, and exposing the wafer to a high vacuum environment to allow water vapor to evaporate off of the wafer surface. Unfortunately, externally removing oxides still allows for oxide re-growth as the wafer is transported to the implant tool. Accordingly, the performance of devices on the wafer may be limited by the external environment in which they are cleaned. In addition, since the external environment is typically not controlled, the repeatability of the transport conditions also may affect performance.
In view of the foregoing, there is a need in the art for a way to prepare a wafer surface for ion implantation in situ.
SUMMARY OF THE INVENTIONThe invention includes a method 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. 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.
A first aspect of the invention is directed to an ion implanting apparatus comprising: an implant chamber; means for generating ions for implanting a wafer in the chamber; and means for removing contaminants from a surface of the wafer in situ within the implant chamber.
A second aspect of the invention is directed to a method of removing contaminants from a surface of a wafer in situ of an ion implant apparatus, the method comprising: placing the wafer in an isolated chamber that is in communication with an implant chamber; and removing contaminants from a surface of the wafer in situ within one of the isolated chamber and the implant chamber.
A third aspect of the invention is directed to a method of removing contaminants from a surface of a wafer, the method comprising: placing the wafer in an isolated chamber that is in communication with an implant chamber; and removing contaminants from a surface of the wafer in situ within one of the isolated chamber and the implant chamber by conducting at least one of: exposing the surface to ultraviolet (UV) illumination; heating a platen that holds the wafer in the implant chamber; and controlling a radio frequency (RF) source of the implant chamber to conduct a low energy plasma etch
The foregoing and other features of the invention will be apparent from the following more particular description of embodiments of the invention.
BRIEF DESCRIPTION OF THE DRAWINGSThe embodiments of this invention will be described in detail, with reference to the following figures, wherein like designations denote like elements, and wherein:
Referring to the attached drawings,
The invention also includes a number of mechanisms for removing contaminants from a surface 60 of wafer 48.
A first mechanism includes exposing wafer 48 to ultraviolet light. In this case, one or more ultraviolet illumination devices 70 may be employed for exposing surface 60 to ultraviolet (UV) illumination. In one embodiment, as shown in
A second mechanism for removing contaminants from surface 60 includes, as shown in
A third mechanism for removing contaminants includes, as shown in
A method of removing contaminants from a surface of a wafer 46 according to the invention includes placing wafer 48 in isolated chamber 50 that is in communication with implant chamber 20, and then removing contaminants from surface 60 of wafer 48 in situ within one of isolated chamber 50 and implant chamber 20. The removing step includes conducting at least one of: exposing surface 60 to ultraviolet (UV) illumination; heating wafer 48; and controlling RF source 26 of implant chamber 20 to conduct low energy plasma etch 98.
While this invention has been described in conjunction with the specific embodiments outlined above, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, the embodiments of the invention as set forth above are intended to be illustrative, not limiting. Various changes may be made without departing from the spirit and scope of the invention as defined in the following claims.
Claims
1. An ion implanting apparatus comprising:
- an implant chamber;
- means for generating ions for implanting a wafer in the chamber; and
- means for removing contaminants from a surface of the wafer in situ within the implant chamber.
2. The apparatus of claim 1, wherein the contaminant removing means includes means for exposing the surface to ultraviolet (UV) illumination.
3. The apparatus of claim 2, wherein the exposing means is mounted externally of the implant chamber and includes a UV illumination device to transmit UV light through a window of the implant chamber.
4. The apparatus of claim 2, wherein the exposing means includes one of an internally-mounted UV illumination device and means for producing an ion plasma configured to emit UV light.
5. The apparatus of claim 4, wherein the producing means includes one of:
- a) a radio frequency (RF) source configured to resonate radio frequency currents in a radio frequency antenna to pass into the implant chamber and excite and ionize a process gas to generate plasma within the implant chamber; and
- b) a direct current (DC) pulse generator for generating a pulsed DC voltage in a wafer cathode to excite and ionize the process gas to generate plasma within the implant chamber.
6. The apparatus of claim 2, wherein the exposing means further includes means for exposing the wafer to a vacuum of better than 1×10−5 Torr.
7. The apparatus of claim 1, wherein the contaminant removing means includes a heater for heating the wafer.
8. The apparatus of claim 7, further comprising a temperature controller for the heater.
9. The apparatus of claim 7, further comprising a gas portal for introducing a gas between a platen that holds the wafer and the wafer to improve heat transfer.
10. The apparatus of claim 1, wherein the contaminant removing means includes means for conducting a low energy plasma etch.
11. The apparatus of claim 10, wherein the low energy plasma etch uses no greater than −1000 V of wafer bias.
12. The apparatus of claim 10, wherein the low energy plasma etch includes using one of:
- BF3, NF3 and F2 as a plasma for a subsequent BF3 plasma implantation.
13. The apparatus of claim 10, wherein the ion generating means includes at least one of:
- a) a radio frequency (RF) source configured to resonate radio frequency currents in a radio frequency antenna to pass into the implant chamber and excite and ionize a process gas to generate plasma within the implant chamber; and
- b) a direct current (DC) pulse generator for generating a pulsed DC voltage in a wafer cathode to excite and ionize the process gas to generate plasma within the implant chamber.
14. A method of removing contaminants from a surface of a wafer in situ of an ion implant apparatus, the method comprising:
- placing the wafer in an isolated chamber that is in communication with an implant chamber; and
- removing contaminants from a surface of the wafer in situ within one of the isolated chamber and the implant chamber.
15. The method of claim 14, wherein the contaminant removing step includes exposing the surface to ultraviolet (UV) illumination.
16. The method of claim 15, wherein the exposing step includes exposing the surface to UV light through a window of one of the isolated chamber and the implant chamber.
17. The method of claim 15, wherein the exposing step includes exposing the surface to one of an internally-mounted UV illumination device and means for producing a UV light emitting plasma.
18. The method of claim 17, wherein the producing means includes one of:
- a) a radio frequency (RF) source configured to resonate radio frequency currents in a radio frequency antenna to pass into the implant chamber and excite and ionize a process gas to generate plasma within the implant chamber; and
- b) a direct current (DC) pulse generator for generating a pulsed DC voltage in a wafer cathode to excite and ionize the process gas to generate plasma within the implant chamber.
19. The method of claim 15, wherein the exposing step further includes exposing the wafer to a vacuum of better than 1×10−5 Torr.
20. The method of claim 14, wherein the contaminant removing step includes heating the wafer.
21. The method of claim 20, wherein the heating step includes heating a platen that holds the wafer in the implant chamber, and further comprising controlling a temperature of the heating.
22. The method of claim 20, further comprising introducing a gas between the platen and the wafer to improve heat transfer.
23. The method of claim 14, wherein the contaminant removing step includes controlling a radio frequency (RF) source of the implant chamber to conduct a low energy plasma etch.
24. The method of claim 23, wherein the low energy plasma etch uses no greater than −1000 V wafer bias.
25. The method of claim 23, wherein the low energy plasma etch includes using one of: BF3, NF3 or F2 as a plasma for a subsequent BF3 plasma implantation.
26. A method of removing contaminants from a surface of a wafer, the method comprising:
- placing the wafer in an isolated chamber that is in communication with an implant chamber; and
- removing contaminants from a surface of the wafer in situ within one of the isolated chamber and the implant chamber by conducting at least one of:
- exposing the surface to ultraviolet (UV) illumination;
- heating a platen that holds the wafer in the implant chamber; and
- controlling a radio frequency (RF) source of the implant chamber to conduct a low energy plasma etch.
27. The method of claim 26, wherein the exposing step includes exposing the surface to UV light through a window of one of the isolated chamber and the process chamber.
28. The method of claim 26, wherein the exposing step includes exposing the surface to one of an internally-mounted UV illumination device and means for producing UV light emitting plasma.
29. The method of claim 28, wherein the producing means includes one of:
- a) a radio frequency (RF) source configured to resonate radio frequency currents in a radio frequency antenna to pass into the implant chamber and excite and ionize a process gas to generate plasma within the implant chamber; and
- b) a direct current (DC) pulse generator for generating a pulsed DC voltage in a wafer cathode to excite and ionize the process gas to generate plasma within the implant chamber.
30. The method of claim 26, wherein the heating step further includes controlling a temperature of the heating.
31. The method of claim 26, wherein the heating step further includes introducing a gas between the platen and the wafer to improve heat transfer.
32. The method of claim 26, wherein the controlling step includes using no greater than 0.1 V.
33. The method of claim 26, wherein the controlling step includes using one of: BF3, NF3 or F2 as a source gas for a subsequent BF3 plasma implantation.
Type: Application
Filed: Aug 20, 2004
Publication Date: Feb 23, 2006
Inventors: Steve Walther (Andover, MA), Sandeep Mehta (Boxford, MA), Naushad Variam (Marblehead, MA), Ukyo Jeong (Andover, MA)
Application Number: 10/922,710
International Classification: H01L 21/302 (20060101); C23F 1/00 (20060101); C03C 25/68 (20060101);