Radiant energy – Irradiation of objects or material
Reexamination Certificate
2000-12-06
2002-11-26
Lee, John R. (Department: 2881)
Radiant energy
Irradiation of objects or material
C250S492200, C250S492220, C204S192100
Reexamination Certificate
active
06486478
ABSTRACT:
FIELD OF THE PRESENT INVENTION
The present invention is directed to a gas cluster ion beam apparatus. More particularly, the present invention is directed to a gas cluster ion beam apparatus that enables effective separation of monomer or molecular ions from the gas cluster ion beam.
Moreover, the present invention is directed to a gas cluster ion beam apparatus capable of controlling multiple independent adjustments through an automated electronic control system.
BACKGROUND OF THE PRESENT INVENTION
Energetic-ion sputtering has been conventionally used for etching and thinning in manufacturing and depth-profiling in analytic instruments. However, energetic-ion sputtering causes subsurface damage and accumulated roughness because energetic-ion sputtering uses monomer ions. Individual monomer atoms or molecules have energies on the order of thousands of electron volts that cause the residual surface damage.
To avoid the residual surface damage, gas cluster ion beam process devices have been developed. One example of such an apparatus, as well as the creation and acceleration of such a conventional gas cluster ion beam, is described in U.S. Pat. No. 5,814,194to Deguchi et al. The entire contents of U.S. Pat. No. 5,814,194 are hereby incorporated by reference. Another example of a gas cluster ion beam apparatus is described in U.S. Pat. No. 5,459,326 to Yamada. The entire contents of U.S. Pat. No. 5,459,326 are hereby incorporated by reference.
Gas cluster ion beams can be used for etching, cleaning, and smoothing of material surfaces in certain applications. These conventional gas cluster ion beams comprise gas clusters having nano-sized aggregates of materials that are gaseous under conditions of standard temperature and pressure. Such clusters are typically formed of aggregates of approximately 20 to approximately several thousand atoms or molecules loosely bound together. The gas clusters can be ionized by electron bombardment or other means, permitting the gas clusters to be formed into directed beams of known and controllable energy. The larger sized gas clusters are the most useful because the larger sized gas clusters are able to carry substantial energy per cluster ion, while yet having only modest energy per atom or molecule.
The gas clusters disintegrate on impact with each individual atom or molecule carrying only a small fraction of the total cluster energy. Consequently, the impact effects of large clusters, while substantial, are limited to only a very shallow surface region, thereby enabling ion clusters to be effective for a variety of surface modification processes, without the tendency to produce deeper subsurface damage. As noted above, deeper subsurface damage is a characteristic of monomer or molecular ion beam processing.
One characteristic of gas cluster ion interactions with surfaces is ultra-shallow interaction depth. The gas cluster ion interactions also exhibit inherent smoothing and planarization behaviors. These behaviors can be extraordinary when the gas cluster ion impacts upon rough or non-planar surfaces. Since the atoms within a cluster are able to interact with each other as the cluster disintegrates upon impact, some of the energy carried by the cluster is converted into energy of individual atoms within the cluster. This converted energy is dissipated in all directions within the plane of the target surface, thereby producing excellent smoothing behavior on most materials, including diamond. Lastly, the gas cluster ion interactions demonstrate an ability to produce enhanced surface chemical reactions with reactive cluster species.
Gas cluster ions deposit their total energy into the impact site upon the target surface. The atoms within a gas cluster ion have small individual energies that prevent the atoms from penetrating beyond very shallow depths of a few atomic layers. Consequently, a gas cluster ion deposits considerable energy into a much shallower region on the target surface than would a monomer or molecular ion of equal energy. Similarly, since the gas cluster ion has much greater mass and momentum, a gas cluster ion impact can generate much more intense pressure pulse effects than those associated with monomer ion bombardment.
Computer simulations of gas cluster ion impacts predict peak momentary temperatures of the order of 100,000°K in combination with pressure pulses in the range of millions of pounds per square inch. These transient high temperature and pressure conditions within the impact volume occur while the gas atoms from the cluster are being dynamically mixed with the target material atoms, thereby enabling highly enhanced chemical reaction properties to be observed or realized.
Conventionally, gas cluster ion sources produce gas clusters ions having a wide distribution of sizes, N (where N=the number atoms or molecules in each cluster). Such atoms in a cluster are not individually energetic enough (on the order of a few electron volts) to significantly penetrate a surface to cause the residual surface damage typically associated with the other types of ion beam processing, such as energetic-ion sputtering.
However, the gas cluster ion can be made sufficiently energetic (some thousands of electron volts), to effectively etch, smooth or clean surfaces. This allows the gas cluster ion to be used to smooth surfaces of various materials to nearly an atomic scale by utilizing all-dry vacuum methods. Such materials include, but are not limited to, silicon, compound semiconductors, dielectric wafers, films and high-dielectrics, thin metal and ferromagnetic films, and electro-optics.
An example of a prior art gas cluster ion beam apparatus
100
is illustrated in FIG.
1
. As illustrated in
FIG. 1
, the gas cluster ion beam apparatus
100
includes a vacuum vessel
102
that is divided into three communicating chambers, a source chamber
104
, a ionization/acceleration chamber
106
, and a processing chamber
108
. The three chambers are evacuated to suitable operating pressures by vacuum pumping systems
146
a
,
146
b
, and
146
c
, respectively. A condensable source gas
112
(for example argon, Ar) is admitted under pressure through gas feed tube
114
to stagnation chamber
116
and is ejected into the substantially lower pressure vacuum through a properly shaped nozzle
110
.
The gas feed tube
114
, the stagnation chamber
116
, and the nozzle
110
together constitute the gas feed assembly, thereby producing a supersonic gas jet
118
. Cooling, resulting from the expansion in the jet, causes a portion of the gas jet
118
to condense into clusters, each cluster consisting of from several to several thousand weakly bound atoms or molecules.
In
FIG. 1
, a gas skimmer
120
, having an aperture, separates the gas products that have not been formed into a cluster jet from the cluster jet. This separation minimizes the pressure in the downstream regions where higher pressures would be detrimental (e.g., ionizer
122
, high voltage electrodes
126
, and process chamber
108
). Suitable condensable source gases
112
include, but are not necessarily limited to, argon; nitrogen and other inert gases; oxygen; carbon dioxide; oxides of nitrogen; and sulfur hexafluoride.
After the supersonic gas jet
118
containing gas clusters has been formed, the clusters are ionized in ionizer
122
. The ionizer
122
is typically an electron impact ionizer that produces thermoelectrons from one or more incandescent filaments
124
. The ionizer
122
accelerates and directs the electrons causing the electrons to collide with the gas clusters in the gas jet
118
, at the point where the jet passes through the ionizer
122
. The impact of the electrons causes electrons from the clusters to be ejected, thereby causing a portion of the clusters to become positively ionized. The positive ionization is usually, but not necessarily, with a single charge.
A set of suitably biased high voltage electrodes
126
extracts the cluster ions from the ionizer, forming a beam. The biased high voltage electrodes
126
then accelerates the cluster ions to
Bachand James G.
Crawford Lester G.
Greer James A.
Gwinn Matthew C.
Libby Bruce K.
Burke Michelle J.
Cohen Jerry
Epion Corporation
Lee John R.
Perkins Smith & Cohen LLP
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