Radiant energy – Irradiation of objects or material – Irradiation of semiconductor devices
Reexamination Certificate
1998-08-12
2001-01-09
Anderson, Bruce C. (Department: 2881)
Radiant energy
Irradiation of objects or material
Irradiation of semiconductor devices
C250S442110
Reexamination Certificate
active
06172372
ABSTRACT:
BACKGROUND OF THE INVENTION
The prior art is familiar with systems which scan ion beams across target objects so as to selectively dope the target surface. U.S. Pat. No. 5,028,795, entitled “Ion Implantation Apparatus” describes one such system. In the '795 patent, two multipole electrostatic deflectors are used to scan the beam in two dimensions across the target surface.
The prior art is also familiar with magnetically-controlled ion beam scanning systems. U.S. Pat. No. 4,922,106, entitled “Ion Beam Scanning Method and Apparatus,” describes one such system. In the '106 patent, a magnetic deflector with two truncated sector-shaped poles is used to control the ion beam so as to maintain a parallel beam path and a scan direction.
The prior art is further aware of systems which mechanically scan the target object in one direction, and which electrostatically or magnetically scan the beam in the other direction. In combination, therefore, such systems provide a raster scan that fully covers the target object surface. U.S. Pat. No. 4,726,689, entitled “Linear Gas Bearing with Integral Vacuum Seal for use in Serial Process Ion Beam Implantation Apparatus,” describes one related system. In the '689 patent, linear gas bearings are used to provide both linear axial motion and a high differential pressure link between ambient pressure and the internal chamber vacuum.
Increasing requirements for scanning speed and accuracy require improvements to the above systems so as to provide low friction shaft control with minimal shaft vibration. One object of the invention is thus to provide such improvements.
One problem with the prior art systems is that the steps of loading and unloading workpieces onto the shaft are difficult and time-consuming, reducing production efficiency. It is thus another object of the invention to provide new and improved methods for loading and unloading objects onto ion scanning shafts, thus improving production throughput. Still another object of the invention is to provide “batch” loading of workpieces onto scanning shafts. These and other objects will become apparent in the description which follows.
SUMMARY OF THE INVENTION
As discussed above, U.S. Pat. No. 5,028,795 describes scanning and applying an ion beam to target objects, and is accordingly incorporated herein by reference. U.S. Pat. No. 4,922,106 describes magnetically scanning ion beams in one dimension, and is accordingly incorporated herein by reference. U.S. Pat. No. 4,726,689 describes coupling a shaft into an ion beam processing chamber via linear gas bearings, and is accordingly incorporated herein by reference.
The following patents provide other useful information for the invention: U.S. Pat. No. 5,223,109; U.S. Pat. No. 4,936,968; U.S. Pat. No. 4,683,378; U.S. Pat. No. 4,457,803; U.S. Pat. No. 5,583,344; U.S. Pat. No. 4,680,474; and U.S. Pat. No. 4,980,562. These patents are herein incorporated by reference.
As used herein, “workpiece” refers to the part or object to be processed within a processing chamber. For example, in semiconductor manufacturing, a substrate which is scanned and doped by ion beams is one such workpiece.
In one aspect, the invention provides an ion beam processing system which mounts a workpiece onto a shaft that extends through both sides of the processing chamber. Linear gas (or air) bearings are coupled between the shaft and the chamber walls—such as described in the above-referenced U.S. Pat. No. 4,726,689—to provide good decoupling between outside ambient and the typically-evacuated region internal to the chamber. The shaft is counter-balanced in this configuration since it extends through the wall on both sides of the chamber.
The operation of the shaft is to provide both linear and rotational motions. That is, a linear drive unit couples to the shaft, external to the chamber, so as to drive the shaft in one direction that is substantially perpendicular to the ion beam (“perpendicular” is used in this sentence to refer to ion beams that are within about ten degrees from the surface normal of the target surface). A corresponding ion beam source and scanning unit—such as described in the above-referenced patents—scans the beam in the other dimension such that, in combination with the linear drive, a raster scan can be obtained onto workpieces mounted to the shaft within the chamber.
A rotational drive unit is also connected to the shaft to provide selective incident angles for the ion beam. A beam which is normal to the workpiece will tend to channel into the target, an unwanted effect. Therefore, a slight angle of incidence between about three and ten degrees is desirable and obtainable through rotation of the shaft by the rotational drive unit.
The rotational drive unit can further be used to mount and dismount workpieces onto the shaft. That is, it is convenient to mount the workpiece onto the shaft in one orientation (generally such that the workpiece can be positioned at its preferred mounting position by operation of gravity), and then to rotate the workpiece so as to scan the workpiece along another axis. Therefore, in other aspects, the shaft is rotated to accommodate mounting and dismounting of workpieces thereon, selectively.
U.S. Pat. No. 4,726,689 teaches counter-balancing a shaft within an ion implantation chamber by the competing forces of gravity and the pressure differential created by the shaft as a seal between the vacuum chamber and outer ambient pressure. Counter-balancing reduces the forces required to drive the shaft linearly or rotationally. One problem with the prior art counter-balancing technique is that it requires a certain orientation of the shaft—i.e., the shaft longitudinal axis must be substantially parallel to the gravity vector—greatly reducing system flexibility.
In accord with another aspect of the invention, “active” counter-balancing is provided to achieve greater flexibility and control of the shaft. In certain aspects, active counter-balancing is achieved through mechanical weights, air and/or pneumatic subsystems, motors with lead screws or other high-torque motors, magnetic counter-balancing, and unidirectional gravitational counterbalance. Note, in addition, that the certain aspects described herein are “self-counterbalancing” such as when the shaft extends through both sides of the processing chamber.
In still another aspect of the invention, a two phase scanning system is provided. In this aspect, a shaft is coupled, via linear gas bearings, through opposing sides of a processing chamber. Two mounting surfaces are included on the shaft: one mounting surface provides for loading and unloading of processing workpieces; while the other mounting surface provides for processing of other workpieces. In this manner, utilization of a process chamber, e.g., an ion beam implantation system, is much higher than prior art systems which are essentially inactive during load and unload of workpieces.
The invention is next described further in connection with preferred embodiments, and it will become apparent that various additions, subtractions, and modifications can be made by those skilled in the art without departing from the scope of the invention.
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Forn PCT/ISA/210 (second sheet) in International Search Report, Application No. PCT/US98/16630, Oct. 19, 1998 (Date of search completion).
Anderson Bruce C.
Varian Semiconductor Equipment Associates Inc.
Wolf Greenfield & Sacks P.C.
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