Radiant energy – Ion collectors
Reexamination Certificate
2000-10-11
2003-05-20
Anderson, Bruce (Department: 2881)
Radiant energy
Ion collectors
C250S491100, C250S492210, C250S397000
Reexamination Certificate
active
06566661
ABSTRACT:
FIELD OF THE INVENTION
The invention is concerned with ion implanters and particularly with an arrangement for checking the angle of the wafer on a holder to be implanted and the alignment of a travelling Faraday in the implant chamber, used for setting up the ion beam prior to implantation.
BACKGROUND OF THE INVENTION
Ion implanters have been used for many years in the processing of semiconductor wafers. Typically a beam of ions of a required species is produced and directed at a wafer or other semiconductor substrate, so that ions become implanted under the surface of the wafer. Implantation is typically used for producing regions in the semiconductor wafer of altered conductivity state, by implanting in the wafer ions of required dopant.
Known ion implanters include batch type implanters and single wafer type implanters. In single wafer type implanters, the ion beam is usually scanned transversely in one orthogonal direction at a relatively high scanning rate, and the single wafer being implanted is mechanically translated to and fro across the scanned beam substantially in a second orthogonal direction. The ion beam can be scanned electrostatically or electromagnetically and it is normal practice to collimate the scanned beam so that the beam impinging on the wafer remains parallel to a desired beam direction during scanning.
The angle at which the ion beam strikes the wafer during an implantation process is important. Many implants are conducted with the ion beam precisely normal to the wafer surface, i.e. where the ion beam has zero angle relative to a normal to the wafer surface. In other processes, implants may be conducted with the normal to the wafer surface at a predetermined angle to the ion beam, for example if it is desired to minimise channelling effects as ions penetrate into the crystal structure of the wafer, or else if it is desired to implant into the walls of trenches or other physical structures on the wafer surface prepared by previous processes, or avoid shadowing by such structures.
It is often important to control the angle of implantation closely, especially for ensuring zero implant angle in certain processes.
It is known in single wafer type implanters for the wafer holder to be adjustable about an axis parallel to the plane of the wafer on the holder, for the purpose of adjusting the implant angle. For example, WO 99/13488 discloses an implant chamber for a single wafer type ion implanter in which the wafer is mounted on a holder and the holder can be translated to and fro through the plane of a scanned ion beam entering the implant chamber. The scanning mechanism can itself be rotated about an axis substantially through the plane of the wafer, so as not only to adjust the angle of the wafer relative to the ion beam, but also to change the direction of the mechanical reciprocating translation of the wafer, so that the wafer holder is always reciprocated in the plane of the wafer.
The above referred International patent application also discloses the provision of a travelling Faraday which can be moved to different positions in the direction of scanning of the beam, for the purpose of checking the rate of dose delivery at different points over the range of scanning of the beam. The travelling Faraday in the above International patent application is also used, in association with a further travelling Faraday upstream in the beam direction, for confirming beam parallelism and scan uniformity.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an arrangement in an implanter for accurately confirming the angle relative to the beam of a wafer on the wafer holder, so as to ensure an implant is performed at the correct implant angle. A further object of the present invention is the provision of an arrangement to confirm the alignment of a travelling Faraday used in an implant chamber, so that measurements by the travelling Faraday can be correctly referred to a datum alignment in the implant chamber.
Accordingly, in one aspect, the invention provides an ion implanter having an evacuatable implant chamber, a holder inside the chamber for holding a semiconductor wafer at a selected wafer angle during implantation, said holder being adjustable about at least one axis parallel to the plane of a wafer on the holder for changing said wafer angle, a source of focused electromagnetic radiation mounted relative to said implant chamber and arranged to direct said radiation for reflection at a surface of a wafer held on said holder or at a surface of the holder which is parallel or at a known angle to the plane of a wafer when held on said holder, and a sensor mounted relative to said implant chamber to receive radiation from said source reflected specularly by the wafer surface or by said holder surface, said sensor providing a signal, in response to the reflected radiation, which is indicative of a predetermined wafer angle. The arrangement disclosed above enables the angle of the wafer to be set to the predetermined angle by monitoring the signal from the sensor.
Preferably, said source of electromagnetic radiation and said sensor are mounted outside the implant chamber and the chamber has at least one window transparent to said radiation through which the focused radiation from said radiation source is directed into the chamber, and the reflected radiation leaves the chamber for reception by said sensor. Then, the presence of additional sensing equipment within the implant chamber is avoided, which is important to minimise contamination during implant processes, and also for serviceability of the angle sensing equipment.
In preferred embodiments, the radiation source is arranged to produce an illuminated spot of said reflected radiation on said sensor. Typically the source is a laser arranged to provide a substantially parallel beam of said radiation.
The sensor may have a sensitive area providing a signal representative of the position of the illuminated spot on said area at least in a direction perpendicular to the axis of adjustability of the wafer holder. In this way, the sensor can provide an output signal having a range of values for comparison by control equipment with a desired datum value corresponding to the desired predetermined angle of the wafer.
In a preferred embodiment, the implanter includes a drive unit to adjust the rotary position of the holder about said axis, and a controller responsive to the signal from said sensor to control said drive unit to adjust said holder position to bring said illuminated spot to a desired position on the sensitive area of the sensor corresponding to the predetermined wafer angle.
Normally, the implanter has a source of ions to be implanted, and a scanner and collimator combination to produce a parallel scanned beam of said ions in said implant chamber for implantation in a wafer on said holder. Then preferably, said scanner and collimator combination define an ideal beam direction for said parallel scanned beam, and said radiation source and said sensor are mounted so as to be referenced to said ideal beam direction defined by the scanner and collimator combination, whereby said predetermined wafer angle is referenced to said ideal beam direction.
In one embodiment, said scanner and collimator combination scans the beam in a scan direction perpendicular to the beam direction in a beam scanning plane, and the implanter further includes an actuator for translating the wafer holder through the beam scanning plane in a translation plane containing said scan direction and having a translation angle to the normal to the beam scanning plane, a first rotary drive unit to adjust said translation angle and effecting a corresponding adjustment of said wafer angle, a second rotary drive unit to change the angle of the wafer holder relative to the actuator about an axis parallel to said scan direction to adjust the angle of a wafer on the holder relative to said translation angle, and a controller responsive to the signal from the said sensor to control said first rotary drive unit to adjust said tran
Anderson Bruce
Boult Wade & Tennant
Hashmi Zia R.
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