Radiant energy – Radiant energy generation and sources – With container for radioactive source and radiation...
Reexamination Certificate
1999-10-06
2001-12-18
Berman, Jack (Department: 2881)
Radiant energy
Radiant energy generation and sources
With container for radioactive source and radiation...
C250S492210, C250S492300, C250S42300F
Reexamination Certificate
active
06331713
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to an ion source assembly, in particular for use in an ion implanter.
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 a required dopant.
A number of arrangements for generating a source of ions in an ion implanter are known. Hot cathode sources, such as the so-called Freeman or Bernas sources, use a directly heated filament to generate a source of thermionic electrons. The cathode is held at a high negative potential relative to an anti-cathode (usually formed from the walls of an arc chamber) and an arc current flows through an admitted gas supply to generate a plasma.
Alternatively, a microwave or rf source can be used. Here, a microwave or rf field excites free electrons which then ionise an admitted gas to again produce a source of ions for implanting.
In one common arrangement, known as a triode structure, a suppression or extraction electrode is used to extract the ions from the ion source where they are formed. The extraction electrode is arranged adjacent to an extraction aperture formed in a face plate mounted upon the arc chamber of the ion source. The potential difference between the arc chamber and the extraction electrode defines the energy of the resultant ion beam. The triode structure also includes a ground electrode prevent electrons from being swept away and thus allows ion beam neutrality to be preserved. The face plate, suppression or extraction electrode and ground electrode are henceforth termed an extraction assembly.
To permit acceleration of ions out of the ion source, the extraction electrode needs to be at a net negative potential with respect to the ion source itself. Thus, the ion source is typically electrically insulated from the extraction electrode by high voltage bushing formed from, for example, a ceramic based material A second, less common form of ion source assembly employs a tetrode structure. Here, instead of a dual purpose extraction/suppressor electrode such as is used in the triode structure described above, separate suppressor and extraction electrodes are employed. The suppressed electrode is electrically insulated from the suppressor electrode and is held at a net negative potential (for positively charged ions) with respect to it. Examples of tetrode structures are shown in U.S. Pat. No. 5,866,909 and WO99/23685.
In both the triode and tetrode structures, the ion source, isolated from the extraction assembly, is mounted coaxially within a first end of an elongate, usually cylindrical vacuum chamber. The other, second end of the vacuum chamber is mounted, often non-removably, around an inlet into a mass analyser.
The various parts of the ion source assembly (consisting of the ion source, extraction assembly, insulators and vacuum chamber) require frequent cleaning and servicing to prevent contamination of the resultant ion beam. For this reason, the ion source assembly must be dismantled.
Such a process is difficult and time consuming. The trend to larger ion implanters has in turn caused larger ion source assemblies to evolve, which tend to be relatively heavy. To dismantle such assemblies can require two persons or even lifting equipment. Furthermore, the particular shape of some components of typical ion source assemblies can in any event make them difficult to remove without damage. For example, the extraction electrode in the tetrode structure shown in WO99/23685 is mounted upon the base of a ‘cup’ shaped electrode support of relatively small diameter. The elongate ion source then extends into the cup such that a front face of the ion source is generally parallel with, and adjacent to, the base of the cup (and the extraction electrode in particular). Then, even when the ion source is removed, the extraction electrode can only be accessed via the narrow diameter of the cup.
SUMMARY OF THE INVENTION
It is an object of the present invention to address these and other problems with the prior art. More specifically, it is an object of the invention to provide an ion source assembly permitting easier access to the components thereof. According to the present invention, there is provided an ion source assembly for an ion implanter comprising a source sub assembly including an ion source for generating ions to be implanted; an extraction electrode for extracting ions from the ion source; and a first electrical insulator arranged to support the extraction electrode relative to the ion source and to electrically insulate the said extraction electrode from the ion source; and a chamber having a chamber wall with an inner and outer surface, and being arranged to receive ions extracted from the ion source, the chamber wall defining an exit aperture to permit egress of the said ions to the ion implanter; wherein the source sub assembly is movable relative to the chamber, the ion source assembly further comprising constraining apparatus arranged to connect the chamber wall with the source sub assembly such that the source sub assembly is constrained to move along a fixed locus of points relative to the chamber to allow access to the inner wall thereof, at least some of any loss in the potential energy of the source sub assembly during movement thereof being stored by the said constraining apparatus.
The use of a constraining apparatus, such as for example a hinge, mounted between the first sub assembly and the chamber allows ready access to the internal components of the ion source assembly. In particular, to gain access to the inside of the chamber, the first sub assembly may simply be pulled away from the chamber, the constraining means acting to support the one part relative to the other part. This in turn avoids the problem of having to remove and carry away the bulky ion source, and then the extraction electrode, before access to the inside of the chamber could be gained. The risk of damage to the components of the source sub assembly is likewise reduced.
Preferably, the source sub assembly is movable in use between a first position in which it is fixedly mounted upon the chamber walls and a second position in which it is movable relative to the chamber along the said fixed locus of points. For example, the constraining means may constrain the source sub assembly to move in a substantially horizontal plane, whereby, in the said first position, the weight of the source sub assembly is borne across the chamber, and in the said second position, the weight of the source sub assembly is substantially all borne by the said hinge means. Alternatively, for example, the constraining apparatus may constrain the sub assembly to move in both a horizontal and vertical plane. Then, it is preferable that the constraining apparatus should also include an energy storage device such as a spring or gas strut to store any loss in potential energy of the source sub assembly as it moves downwards in a vertical plane. This stored energy can be utilised when moving the source sub assembly back upwards in a vertical plane to assist the person moving it.
Thus, when the source sub assembly is dismounted from the chamber, the user who wishes to clean the components of the ion source assembly does not need to support the weight of the source sub assembly. The source sub assembly, in the preferred embodiment, acts as a movable “door” hinged upon the chamber which is typically fixedly mounted to the ion implanter.
Preferably, the ion source assembly further comprises extraction electrode support means arranged to support the said extract electrode relative to the said first electrical insulator. In that case, the ion source may be generally elongate and have a first end along the axis of elongation, the said first end preferably inclu
Farley Marvin
Rose Peter
Ryding Geoffrey
Satoh Shu
Smick Theodore H.
Applied Materials Inc.
Berman Jack
Fernandez K.
Tennant Boult Wade
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