Radiant energy – Irradiation of objects or material – Irradiation of semiconductor devices
Reexamination Certificate
1999-04-19
2001-07-31
Berman, Jack (Department: 2878)
Radiant energy
Irradiation of objects or material
Irradiation of semiconductor devices
C250S442110
Reexamination Certificate
active
06268609
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to ion implantation processes for implanting ions into a workpiece, such as wafers or substrates, in the fabrication of semiconductor devices. More specifically, the present invention relates to reducing the heating of a surface of a wafer in a ion implanter during ion implantation processing
BACKGROUND OF THE INVENTION
Ion implantation techniques are commonly used as one of the processes in the manufacture of integrated circuits. Ion implanters are used to modify the electrical transport properties, i.e. conductivity, in predefined regions of semiconductor material by doping the predefined regions with impurity atoms. Ion implantation techniques generally involve generating a beam of a particular species of ions in an ion beam generator and directing the ion beam through a vacuum chamber into a target wafer supported on a substrate holder or platen assembly. The ion beam may be scanned across the wafer using either electrostatic and/or magnetic deflection of the ion beam. Other ion implantation systems involve either mechanically scanning the wafer relative to the ion beam or a combination of mechanical scanning of the wafer with electrostatic and/or magnetic deflection of the ion beam. Ion implanters for processing single wafers one after the other often use a hybrid scanning system in which the beam is scanned at a relatively fast rate in one direction across the wafer and the wafer is mechanically reciprocated to and fro in a transverse direction through the scanned beam.
In any of these systems, and in particular in high current and/or high energy ion implantation applications, during processing, the temperature at any point on the surface of the wafer may rise to a temperature that causes damage to the structures thereon. The temperature of the surface of the wafer at any point is a function of the ion beam power and the technique used for ion beam scanning and/or wafer scanning. Steps have been taken in the prior art to limit the maximum temperature at the surface of the substrate during processing. These attempts to limit wafer surface temperature include for example the use of wafer clamping systems to clamp wafers to a heat sinking surface and to enhance thermal conductance through the back surface of the wafer. In spite of these known wafer cooling systems, wafer processing speeds may still be limited by the need to avoid overheating the wafer or parts thereof.
SUMMARY OF THE INVENTION
An object of an embodiment of the invention is to provide a method and apparatus for reducing the maximum temperature reached on the surface of a wafer, and each point on the surface of the wafer experiencing substantially the same thermal cycle on each mechanical scan, during ion implantation when using single wafer implanters using hybrid scanning systems.
According to the invention there is provided a method for ion implantation of a workpiece in an ion implanter, comprising the steps of generating an ion beam for implantation of ions into a workpiece, the workpiece having a surface defining a plane; scanning the ion beam relative to the surface of the workpiece in a first direction in the plane; repeatedly reciprocating the workpiece in a second direction transverse to said first direction to traverse to and fro through said scanned ion beam; and rotating said workpiece 180 degrees about a central axis of the workpiece between each successive traverse of the wafer through the scanned ion beam, so that the wafer always presents the same leading edge to the beam on each traverse.
Additionally, according to the invention an apparatus is provided for ion implantation of a workpiece in an ion implanter, comprising an ion beam generator for generating an ion beam for implantation of ions into a workpiece, the workpiece having a surface defining a plane; an ion beam scanner for scanning the ion beam relative to the surface of the workpiece in a first direction in the plane; and an arm assembly for repeatedly reciprocating the workpiece in a second direction transverse to said first direction to traverse to and fro through said scanned ion beam, said arm assembly comprising a rotational drive mechanism for rotating said workpiece about a central axis of the workpiece, and a controller arranged to operate said rotational drive mechanism to rotate the workpiece
180
degrees between each successive traverse of the wafer through the scanned ion beam, so that the wafer always presents the same leading edge to the beam on each traverse.
This arrangement provides sufficient time between each traverse or sweep of the workpiece through the scanned ion beam for heat to dissipate at points on the surface of the wafer near the trailing edge of the wafer. Accordingly, during successive sweeps, the maximum temperature reached at any point on the surface of the wafer is substantially minimized and the thermal cycle at any point on the surface of the wafer is substantially the same, which substantially reduces the risk of damage to the structures on the surface of the wafer.
REFERENCES:
patent: 5003183 (1991-03-01), Nagami et al.
patent: 5194748 (1993-03-01), Aitken
patent: 5229615 (1993-07-01), Brune et al.
patent: 5929456 (1999-07-01), Tamai
patent: WO99/13488 (1998-09-01), None
“Wafer Cooling in a High Current ion Implanter”.
Farley Marvin
Ryding Geoffrey
Smick Theodore H.
Applied Materials Inc.
Berman Jack
Tennant Boult Wade
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