Ion beam implanters are widely used in the process of doping semiconductor wafers. An ion beam implanter generates an ion beam comprised of desired species of positively charged ions. The ion beam impinges upon an exposed surface of a workpiece such as a semiconductor wafer, substrate or flat panel, thereby “doping” or implanting the workpiece surface with desired ions. The workpiece is supported on a workpiece support or pedestal of an electrostatic chuck to intersect the ion beam within an evacuated implantation chamber. The pedestal can be tilted to adjust an implantation angle of the workpiece with respect to the ion beam striking the workpiece. An implantation angle of zero degrees (0°) means that the implantation surface of the workpiece is normal to a beam line of the ion beam within the implantation chamber. To minimize the detrimental effects of channeling small positive and negative implantation angles are often used for workpiece implantation.
Some ion implanters utilize serial implantation wherein one relatively large wafer workpiece is positioned on the pedestal and implanted or “doped” with desired ions. After implantation is completed, the workpiece is removed from the pedestal and another workpiece is positioned on the pedestal.
The pedestal and electrostatic chuck are supported by a workpiece support structure extending into the evacuated implantation chamber. Specifically, the electrostatic chuck is supported on a scan arm. Certain facilities, including cooling fluid and/or gas and electrical power, must be routed to the electrostatic chuck. This routing of facilities is referred to as “feedthrough.” In some prior art ion implanters, the routing of facilities to the electrostatic chuck required harnesses or umbilical cords carrying facilities to be routed though a wall of the implantation chamber to the electrostatic chuck. This required additional seals and complexity.
Since the scan arm extends from an exterior region into the implantation chamber interior region through an opening in the implantation chamber, a seal must be provided between the scan arm and the implantation chamber. Typically, ferrofluidic seals or sliding seals are utilized for the scan arm—implantation chamber seal. An example of a magnetic fluid seal system including a ferrofluidic seal utilized for a scan arm or shaft—implantation chamber seal is disclosed in U.S. application Ser. No. 10/371,606, filed Feb. 21, 2003 and assigned to the assignee of the present invention. application Ser. No. 10/371,606 is incorporated in its entirety by reference herein.
In addition to changing the tilt or implantation angle of a workpiece with respect to an ion beam entering the implantation chamber, it is highly desirable that the workpiece support structure can move the workpiece within the implantation chamber interior region in all three dimensions with respect to the ion beam beam line and, more specifically, once an implantation angle is selected, it is desirable to have the workpiece move in a linear path with respect to the ion beam within the plane of the workpiece and wherein an absolute rotation angle of the workpiece with respect to the ion beam during implantation is zero (twist angle=0°) so that the workpiece is uniformly implanted with ions as the workpiece moves though the ion beam.
What is desired is a workpiece support structure, including a scan arm—implantation chamber seal that permits movement of the workpiece within the implantation chamber in a linear path with respect to the ion beam within the plane of the workpiece and wherein a twist angle of the workpiece during implantation is zero.
What is also desired is a workpiece support structure wherein, except for the scan arm and the electrostatic chuck, all components of the workpiece support structure are external to the implantation chamber, thereby minimizing the required size of the implantation chamber, the capacity of the pumping system need to evacuate the implantation chamber interior region, and facilitating the servicing of workpiece support structure components when required. What is also needed is a workpiece support structure that permits a straight line routing of facilities to the electrostatic chuck without the need to pass the facilities through rotary joints or having harnesses or umbilical cords passing through walls of the implantation chamber.