Radiant energy – Irradiation of objects or material – Irradiation of semiconductor devices
Reexamination Certificate
2000-09-26
2003-06-24
Lee, John R. (Department: 2881)
Radiant energy
Irradiation of objects or material
Irradiation of semiconductor devices
C165S009100
Reexamination Certificate
active
06583428
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to batch ion implantation systems, and more particularly to an apparatus for the backside cooling of a wafer in a batch ion implanter and a seal apparatus therefor.
BACKGROUND OF THE INVENTION
In the manufacture of semiconductor devices, ion implantation is used to dope semiconductors with impurities. Ion beam implanters are used to treat silicon wafers with an ion beam, in order to produce n or p type extrinsic material doping or to form passivation layers during fabrication of an integrated circuit. When used for doping semiconductors, the ion beam implanter injects a selected ion species to produce the desired extrinsic material. Implanting ions generated from source materials such as antimony, arsenic or phosphorus results in “n type” extrinsic material wafers, whereas if “p type” extrinsic material wafers are desired, ions generated with source materials such as boron, gallium or indium may be implanted.
Typical ion beam implanters include an ion source for generating positively charged ions from ionizable source materials. The generated ions are formed into a beam and directed along a predetermined beam path to an implantation station. The ion beam implanter may include beam forming and shaping structures extending between the ion source and the implantation station. The beam forming and shaping structures maintain the ion beam and bound an elongated interior cavity or passageway through which the beam passes en route to the implantation station. When operating an implanter, this passageway must be evacuated to reduce the probability of ions being deflected from the predetermined beam path as a result of collisions with air molecules.
The mass of an ion relative to the charge thereon (e.g., charge-to-mass ratio) affects the degree to which it is accelerated both axially and transversely by an electrostatic or magnetic field. Therefore, the beam which reaches a desired area of a semiconductor wafer or other target can be made very pure since ions of undesirable molecular weight will be deflected to positions away from the beam and implantation of other than desired materials can be avoided. The process of selectively separating ions of desired and undesired charge-to-mass ratios is known as mass analysis. Mass analyzers typically employ a mass analysis magnet creating a dipole magnetic field to deflect various ions in an ion beam via magnetic deflection in an arcuate passageway which will effectively separate ions of different charge-to-mass ratios.
Ion implanters may be separated into two different categories. The first category includes serial ion implanters, in which semiconductor wafers or other workpieces are completely implanted with ions in serial fashion. This type of implanter includes a single workpiece mount adapted to hold or support the workpiece being implanted. The second category of ion implanters includes batch implanters, wherein a plurality of wafers or other workpieces may be implanted with ions in a single batch. The workpieces being implanted are mounted in individual workpiece mounts in a rotatable process disk. The workpiece mounts are typically located on individual pedestals extending outward from a center portion of the process disk at a slight angle so as to use centrifugal force to keep the workpieces seated in the mounts as the process disk is rotated in a controlled fashion via a drive motor. The ion source is located so as to present ions along a beam path offset from the rotational axis of the process disk, and thereby to implant ions onto the workpieces as they rotate into the beam path. This method of ion implantation is sometimes referred to as spinning disk ion implantation.
As ions are implanted in the workpieces, heat is generated therein, which may cause workpiece damage or other deleterious effects if not removed from the workpiece. Conventional batch ion implantation systems and apparatus remove heat from the process disk onto which the workpieces are mounted, using internal passages through which cooling fluid such as water is circulated. Heat is removed from the workpieces to the process disk through vulcanized rubber or RTV pads on which the workpieces are seated. The RTV pads provide some heat removal by transferring heat from the workpieces to the process disk. However, improved heat transfer is desirable, in order to minimize thermal damage to the workpieces. In addition, the relatively sticky RTV presently employed for heat sinking may cause other problems. In particular, the workpieces may stick to the RTV, making removal of the workpieces from the batch implanter difficult. Furthermore, particles tend to adhere to the RTV, which may be transferred to the workpieces causing undesirable contamination thereof. Moreover, the RTV pads may cause capacitive charging of the workpieces. Thus, there is an unresolved need for improved batch ion implantation systems and apparatus which eliminate or minimize the problems associated with conventional RTV workpiece heat sink pads, and which provide for improved heat transfer away from the workpieces.
SUMMARY OF THE INVENTION
The present invention is directed to a system and apparatus which provides improved heat transfer from workpieces in a batch ion implantation operation, while eliminating RTV pads heretofore employed and the problems associated therewith. The invention provides an apparatus by which a cooling gas is supplied from a stationary source to the back side of the workpieces being implanted in a rotating or spinning batch implanter process disk. The provision of the cooling gas allows for improved heat transfer from the workpieces to the process disk, which may be advantageously combined with circulation of cooling fluid through passages in the process disk to remove heat therefrom. The invention further includes the use of a rotary feedthrough in order to transfer the cooling gas from a stationary housing to a gas chamber in a rotating shaft which spins the batch implanter process disk. In addition, a seal apparatus is provided which seals the cooling gas applied to the back sides of the workpieces from the vacuum in which the front sides of the workpieces are implanted. The invention thus improves heat transfer and reduces or eliminates particulate transfer, wafer sticking, and wafer capacitive charging associated with conventional batch implanters.
In accordance with one aspect of the present invention, there is provided an ion implantation system comprising a housing with an outer wall having an outer surface and an inner surface defining an interior cavity, and a first gas chamber extending through the outer wall between a first gas inlet opening in the outer surface of the outer wall and an outlet opening in the inner surface. A shaft is rotatably mounted in the interior cavity of the housing for rotation about an axis, which includes an outer surface extending axially between a first end and a second end. The shaft includes a second gas chamber extending there through between a second gas inlet opening through the outer surface of the shaft and the second end thereof. A process disk is mounted onto or otherwise operatively engaged with the second end of the shaft for rotation about the axis, including a third gas chamber in fluid communication with the second gas chamber of the shaft.
The process disk comprises one or more pedestals extending laterally outwardly from a center portion, wherein the pedestals may each include a workpiece mount radially disposed from the axis and adapted to support a workpiece thereon. The pedestals comprise a gas feed port in the corresponding workpiece mount, wherein the third gas chamber provides fluid communication between the second gas chamber in the shaft and the gas feed ports in the workpiece mounts. The system may further comprise a drive, such as a motor, adapted to provide rotation of the shaft with respect to the housing, and a cooling gas source adapted to provide gas to the gas inlet opening in the housing, whereby cooling gas may be provided to the back sides
Chipman David J.
Lagos Bryan C.
Mitchell Robert J.
Rosen Gary
Stone Dale K.
Axcelis Technologies Inc.
Eschweiler & Associates LLC
Kalivoda Christopher M.
Lee John R.
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