Radiant energy – Luminophor irradiation
Reexamination Certificate
2000-09-01
2002-11-05
Anderson, Bruce (Department: 2881)
Radiant energy
Luminophor irradiation
C200S252000, C200S341000
Reexamination Certificate
active
06476399
ABSTRACT:
TECHNICAL FIELD
The present invention generally relates to ion beam processing and, more particularly, to a system and method for removing contaminant particles relative to an ion beam.
BACKGROUND
In the manufacture of semiconductor devices, an ion implanter is employed to dope a semiconductor wafer or glass substrate with impurities. In particular, ion beam implanters are used to treat silicon wafers with an ion beam, in order to produce n or p type extrinsic materials doping or to form passivation layers during fabrication of an integrated circuit. When used for doping semiconductors, an ion beam implanter injects a selected ion species to produce a 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 is 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 extremely pure since ions of undesirable molecular weight are 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 effectively separates ions of different charge-to-mass ratios.
The ion beam is focused and directed at a desired surface region of the substrate. Typically, the energetic ions of the ion beam are accelerated to a predetermined energy level to penetrate into the bulk of a workpiece. The ions are embedded into the crystalline lattice of the material to form a region of desired conductivity, with the beam energy determining the depth of implantation. Examples of ion implantation systems include those available from Axcelis Technologies of Beverly, Massachusetts.
Operation of an ion implanter or other ion beam equipment (e.g., linear accelerators) may result in the production of contaminant particles. The contaminant particles, for example, may be less than about 1 &mgr;m in size. The momentum of the ions in the beam that strike the particles, in turn, cause the particles to be transported with the beam, although typically at a speed much less than the ions. Consequently, particles entrained in an ion beam may be transported with the beam toward the wafer (or other substrate), resulting in undesired contamination at the wafer.
In an ion implantation system, for example, one source of contaminant particles is photoresist material. Photoresist material is coated on wafer surfaces prior to implantation and is utilized to define circuitry on the completed integrated circuit. As ions strike the wafer surface, particles of photoresist coating may be dislodged from the wafer and may become entrained in the ion beam. Contaminant particles that collide with and adhere to a semiconductor wafer or other substrate during ion implantation may be a source of yield loss in the fabrication of semiconductor and other devices that require submicroscopic pattern definition on the treated wafers.
As semiconductor devices are manufactured at reduced sizes with greater precision, higher accuracy and efficiency are required of apparatuses for manufacturing such semiconductor devices. Accordingly, it is desirable to reduce the level of contaminant particles in an ion beam so as to mitigate wafer contamination.
SUMMARY
One aspect of the present invention relates to a system and method for facilitating removal of contaminant particles relative to an ion beam. An ion beam travels through a region in which particles are charged to a polarity different from that of the ion beam. An electric field is generated downstream relative to where the particles are charged, the electric field urging contaminant particles traveling with the ion beam away from a direction of travel of the ion beam. The electric field also may provide an acceleration region for accelerating the ion beam to a desired level. As a result, particles may be removed or urged away from a direction of travel for an ion beam, in accordance with the present invention, thereby mitigating contamination of a workpiece.
Another aspect of the present invention provides a system for inhibiting transport of particles with an ion beam. The system includes a particle charging system for charging particles to a polarity different from that of the ion beam. An electric field generator generates an electric field downstream relative to the particle charging system for urging a charged particle located in the ion beam away from a direction of travel for the ion beam.
Yet another aspect of the present invention provides a system for inhibiting transport of particles with an ion beam. The system includes a plasma generator for emitting plasma into a plasma region that generally surrounds the ion beam. An electric field generator generates an electric field generally parallel to a direction of travel for the ion beam and downstream relative to the plasma region. Particles located in the plasma region are charged negatively, with the electric field urging negatively charged particles located in the ion beam away from the direction of travel for the ion beam.
Another aspect of the present invention provides an ion implantation system. The system includes an ion source for emitting ions to treat a substrate located at an implantation station and an analyzing magnet system for diverting ions of a desired mass to an implantation trajectory. A particle removal system inhibits transport of particles with the diverted ions from the analyzing magnet system. The particle removal system includes a particle charging system for charging particles to a polarity different from that of the diverted ions. An electric field is generated downstream relative to the particle charging system. The electric field is operable to urge at least some of the charged particles away from a direction of travel for the diverted ions. A substrate is supported at the implantation station for treatment with ions from the particle removal system, whereby particle contamination at the substrate is mitigated.
Still another aspect of the present invention provides a method for inhibiting transport of particles with an ion beam. The method includes charging particles to a polarity different from the ion beam and generating an electric field downstream relative to a region in which the particles are charged. At least some of the charge particles are urged away from a direction of travel for the ion beam.
Another aspect of the present invention provides a method for inhibiting transport of particles with an ion beam. The method includes emitting electrons into a region through which the ion beam travels for negatively charging particles. An electric field is generated that is operable to urge the charged particles away from a direction of travel for the ion beam.
REFERENCES:
Benveniste Victor M.
Graf Michael A.
Harrington Eric R.
Rathmell Robert D.
Anderson Bruce
Axcelis Technologies Inc.
Eschweiler & Associates LLC
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