Abstract:
Method of infusing or introducing material into a substrate using a gas cluster ion beam. The method includes maintaining a reduced-pressure environment around a substrate holder and holding a substrate securely within that reduced-pressure environment. A gas-cluster ion beam formed from a pressurized gas mixture including an inert gas and at least one other atomic or molecular specie is provided to the reduced-pressure environment and accelerated. In one embodiment, the method includes irradiating the accelerated gas-cluster ion beam onto one or more surface portions of the substrate to form an infused region or gas-cluster ion-impact region therein by introducing part or all of the atomic or molecular specie into the surface. In another embodiment, the method includes modifying at least one electrical property of the surface of the substrate by irradiating the accelerated gas-cluster ion beam onto one or more surface portions of the substrate.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of U.S. patent application Ser. No. 11/150,698, now U.S. Pat. No. ______, which is a continuation-in-part of PCT Application No. PCT/US03/39754 filed 12 Dec. 2003, which claims the benefit of priority to U.S. Provisional Patent Application No. 60/433,866, and which is a continuation-in-part of U.S. patent application Ser. No. 11/080,800, now U.S. Pat. No. ______, and PCT Application No. PCT/US05/08246, each filed 11 Mar. 2005 and which claim the benefit of priority to U.S. Provisional Patent Application No. 60/552,505. The entire content of each of these applications is hereby incorporated by reference. 
     
    
     FIELD OF THE INVENTION  
       [0002]    This invention relates generally to the infusion or introduction of atomic and/or molecular species into a surface portion of a substrate. More particularly, it relates to the formation of an infused region or gas-cluster ion-impact region by energetic gas-cluster ion beam irradiation. 
       BACKGROUND OF THE INVENTION 
       [0003]    The characteristics of semiconductor materials such as silicon, germanium and gallium arsenide and other semiconductors have been exploited to form a large variety of useful devices in the fields of electronics, communications, electro-optics, and nano-technology. Ultra shallow junctions are required for future semiconductor devices. The formation of a shallowly doped semiconductor having an abrupt interface is difficult. Prior art methods have employed ion implantation techniques using very low energy conventional ions. Typical ion implanters suffer from greatly reduced ion beam currents at very low energies and therefore result in a low processing throughput. In efforts to increase the throughput of shallow doping processes, alternative techniques have been developed. These include plasma ion doping and decaborane ion implantation (or similar molecular implants). All these methods require a pre-amorphizing implant to prevent ion channeling of the doping implant species, which would otherwise produce undesirably deep junctions. A pre- amorphizing implant is an ion implantation step done prior to a doping step for the purpose of damaging the region to be doped so as to reduce or eliminate the crystallinity of the region to reduce the degree of channeling of the dopant, which would otherwise result in a dopant depth distribution with an undesirably deep tail due to channeled dopant atoms. Such pre-amorphizing damage implants are often done with inert gases like Ar or Xe or with non-electrically active ion species like Si or Ge. For some semiconductor devices, it is desirable to dope the semiconductor material with, for example, boron at very high doping concentrations. With conventional ion beams, including even molecular ion beams (decaborane, for example) the development of high doping levels using the low beam currents available at the very low ion energies required for shallow junction doping is a low productivity process. Additionally, the solid solubility limit of the dopant in silicon has been an upper limit for effective doping. Prior art indicates that the solid solubility limit of boron in silicon can be increased by introducing germanium atoms to the silicon. 
         [0004]    The use of a gas-cluster ion beam (GCIB) for etching, cleaning, and smoothing surfaces is known (see for example, U.S. Pat. No. 5,814,194, Deguchi, et al.) in the art. GCIBs have also been employed for assisting the deposition of films from vaporized carbonaceous materials (see for example, U.S. Pat. No. 6,416,820, Yamada, et al.) For purposes of this discussion, gas-clusters are nano-sized aggregates of materials that are gaseous under conditions of standard temperature and pressure. Such clusters may consist of aggregates of from a few to several thousand (or even tens of thousands) molecules or more, loosely bound to form the cluster. The clusters can be ionized by electron bombardment or other means, permitting them to be formed into directed beams of controllable energy. Such ions each typically carry positive charges of q·e (where e is the magnitude of the electronic charge and q is an integer of from one to several representing the charge state of the cluster ion). The larger sized clusters are often the most useful because of their ability to carry substantial energy per cluster ion, while yet having only modest energy per molecule. The clusters disintegrate on impact, with each individual molecule carrying only a small fraction of the total cluster energy. Consequently, the impact effects of large clusters are substantial, but are limited to a very shallow surface region. This makes ion clusters effective for a variety of surface modification processes, without the tendency to produce deeper subsurface damage and/or dopant channeling that is characteristic of conventional ion beam processing. 
         [0005]    Means for creation of and acceleration of such GCIBs are described in the reference (U.S. Pat. No. 5,814,194) previously cited and which is incorporated herein by reference. Presently available ion cluster sources produce clusters ions having a wide distribution of sizes, N, up to N of several thousand, or even tens of thousands, the distribution typically having a mean cluster size  N  at greater than 200, and commonly greater than several thousand (where N=the number of molecules in each cluster—in the case of monatomic gases like argon, an atom of the monatomic gas will be referred to as either an atom or a molecule and an ionized atom of such a monatomic gas will be referred to as either an ionized atom, or a molecular ion, or simply a monomer ion—throughout this discussion). 
       SUMMARY OF THE INVENTION 
       [0006]    It is therefore an object of this invention to provide shallow doping of semiconductor materials by energetic gas-cluster ion irradiation. 
         [0007]    It is another object of this invention to provide shallow, abrupt junction, doping of semiconductor materials wherein a pre-amorphizing step is not required. 
         [0008]    It is a further object of this invention to provide doping of semiconductors at high dopant concentrations by increasing the solid solubility limit of the dopant species in the semiconductor by incorporating germanium in the semiconductor. 
         [0009]    A still further object of this invention is to provide a method of improving a distribution of a dopant in a semiconductor substrate by irradiation with an energetic gas-cluster ion beam. 
         [0010]    It is an additional object of this invention to provide a channeling free method of doping a semiconductor that can be electrically activated without the requirement of performing a separate amorphizing step. 
         [0011]    It is therefore an object of this invention to provide for re-crystallizing or for improving the crystallinity of a semiconductor surface by energetic gas cluster ion irradiation. 
         [0012]    It is another object of this invention to provide for the activation of shallowly implanted dopant atoms in a semiconductor material with reduced redistribution of the dopant atoms by diffusion induced by the activation by utilizing energetic gas-cluster ions for the activation. 
         [0013]    A still further object of this invention is to provide for the production of an ultra-shallow junction by the introduction of dopant atoms in the ultra-shallow sub-surface regions of a semiconductor material and for the activation of the dopant and for re-crystallizing or for improving the crystallinity of the semiconductor surface by irradiation of energetic gas-cluster ions comprising dopant atoms or comprising dopant and inert atoms. 
         [0014]    The objects set forth above as well as further and other objects and advantages of the present invention are achieved by the embodiments of the invention described hereinbelow. 
         [0015]    Upon impact of an energetic gas-cluster on the surface of a solid target, penetration of the atoms of the cluster into the target surface is typically very shallow because the penetration depth is limited by the low energy of each individual constituent atom and depends principally on a transient thermal effect that occurs during the gas-cluster ion impact. Gas-clusters dissociate upon impact and the individual gas atoms then become free to recoil and possibly escape from the surface of the target. Other than energy carried away by the escaping individual gas atoms, the total energy of the energetic cluster prior to impact becomes deposited into the impact zone on the target surface. The dimensions of a target impact zone are dependent on approximately the cube root of the cluster energy (as opposed to the linear dependence on energy in conventional ion implantation) and range from a few tens of angstroms to a few hundreds of angstroms for cluster acceleration potentials of 40 kV and below for an ionic cluster comprised of 1000 atoms. Because of the deposition of most of the total energy carried by each cluster ion into a small impact zone on the target, an intense thermal transient occurs within the target material at the cluster ion impact site. The thermal transient dissipates quickly as energy is lost from the impact zone by conduction deeper into the target. Duration of the thermal transient is determined by the conductivity of the target material but will typically be less than 10 −6  second. 
         [0016]    Near a cluster impact site, a volume of the target surface can momentarily reach temperatures of many hundreds to several thousands of degrees Kelvin. As an example, impact of a cluster carrying 10 keV total energy is estimated to be capable of producing a momentary temperature increase of about 2000 degrees Kelvin throughout a highly agitated, approximately hemispherical zone extending to about 100 Angstroms below a silicon surface. 
         [0017]    Following initiation of an elevated temperature transient within the target volume below an energetic cluster impact site, the affected zone cools rapidly. Some of the cluster constituents escape during this process, while others remain behind and become incorporated in the surface. A portion of the original surface material may also be removed by sputtering or like effects. In general, the more volatile and inert constituents of the cluster are more likely to escape, while the less volatile and/or more chemically reactive constituents are more likely to become incorporated into the surface and a shallow sub-surface region. Although the actual process is likely much more complex, it is convenient to think of the cluster impact site and the surrounded affected zone as a “melt zone” wherein the cluster atoms may briefly interact and mix with the substrate surface and wherein the cluster materials either escape the surface or become infused into the surface to the depth of the affected zone. The term “infusion” or “infusing” is used by the inventors to refer to this process to distinguish it from ion “implantation” or “implanting”, a very different process that produces very different results. Unlike conventional ion implantation, GCIB infusion does not introduce significant amounts of energy into the bulk of the processed substrate and thus is an essentially room temperature process that does not result in any significant heating of the substrate (other than the highly localized effects at the cluster impact sites). 
         [0018]    If a damaged crystal lattice condition, such as that caused by ion implantation of dopant atoms, exists within a layer near the target surface, the transient temperature conditions produced by energetic cluster impact can be employed to cause recovery of the damaged lattice. For this to occur, a sufficient thermal transient must be created in a volume extending through the damaged region to the undamaged silicon crystal below. During dissipation of the transient temperature conditions, cooling must proceed from the undamaged crystal lattice below the damaged layer back through the damage layer to the surface. Upon restoration or partial restoration of the crystal lattice within the damaged region, dopant atoms will become incorporated into lattice sites and electrical activation will occur. 
         [0019]    Noble gases in the energetic cluster ion, such as argon and xenon, for example, being volatile and non-reactive have a high probability of escape from the affected zone, while materials such as boron, germanium, and silicon, for example, being less volatile and more likely to form chemical bonds, are more likely to remain in the affected zone, becoming incorporated in the surface of the substrate. If a gas containing an appropriate semiconductor dopant atom such as boron is added to, or used as, the gas to form the energetic gas-clusters, the energetic gas-cluster impact can deposit dopant atoms into a semiconductor lattice and simultaneously produce recovery or partial recovery of any damage to the lattice. 
         [0020]    Inert gases such as, for example, noble inert gases argon and xenon, can be mixed with gases containing elements that form semiconductors, germanium or silicon, for example, and/or with gases that contain elements that act as dopants (dopants are elements that, when introduced into a pure semiconductor material, act as electron donors or acceptors for modifying the electrical characteristics of the semiconductor material) for semiconductor materials, boron, phosphorous and arsenic, for example, to form compound gas-clusters containing different selected elements. Such clusters can be formed with existing gas-cluster ion beam processing equipment as will be described hereinafter, by using suitable source gas mixtures as the source gas for gas-cluster ion beam generation, or by feeding two or more gases (or gas mixtures) into the gas-cluster ion generating source and allowing them to mix in the source. Germanium-containing gases such as germane (GeH 4 ) or germanium tetrafluoride (GeF 4 ), for example, may be employed for incorporating germanium into gas-clusters. Silicon-containing gases such as silane (SiH 4 ) and silicon tetrafluoride (SiF 4 ), for example, may be employed for incorporating silicon into gas-clusters. Dopant-containing gases such as diborane (B 2 H 6 ), boron trifluoride (BF 3 ), phosphine (PH 3 ), phosphorous pentafluoride (PF 5 ), arsine (AsH 3 ), arsenic pentafluoride (AsF 5 ), as examples, may be employed for incorporating dopant atoms into gas-clusters. For example, argon and germane can be mixed to make a source gas for forming clusters for infusing germanium. As another example, argon and diborane can be mixed to form a source gas for forming clusters containing boron for infusing boron. As still another example, argon, diborane, and germane can be mixed to form a source gas for forming clusters containing both boron and germanium atoms for infusing both boron and germanium. 
         [0021]    For some semiconductor products, an important requirement for the introduction of dopants into the semiconductor surface or for the formations of films is that the maximum depth to which the dopant has been introduced be rather shallow, on the order of several tens of angstroms to a few hundred angstroms. Gas-cluster ion beams are particularly suited for shallow doping because, while the gas-cluster ions may be accelerated to several kilo-electron volts (or even several tens of kilo-electron volts) of energy, because the clusters typically consist of thousands of atoms, individual atoms have little energy and do not ballistically penetrate the irradiated surface to great depths as occurs in conventional ion implantation and other monomer ion processes. The depth of the effects produced by energetic gas-cluster impact can be controlled by controlling the energy of the gas-cluster and, through such control, films of 100 angstroms or even less can be formed and/or processed. In addition, it is noted that gas-cluster ion beams are very efficient at infusing cluster constituents into the surfaces they irradiate. Conventional ion beams typically implant one or at most a few atoms per ion. In the case of a GCIB, the efficiency is much higher. As an example, a gas-cluster ion beam formed of clusters formed from a mixture of 5% germane in argon will typically incorporate from 100 to 2000 germanium atoms per gas-cluster ion into the irradiated surface, the exact number being controllably and repeatably dependent on beam parameters. The infused films tend to be amorphous or polycrystalline, but they can be converted to crystalline films by applying a thermal annealing step (e.g., at a temperature at or below 600 C), either a rapid anneal or a furnace anneal, preferably a non-diffusing or low-diffusing anneal. If needed to optimize anneal conditions a post-infusion-amorphization step can be done by conventional ion implantation, or by GCIB infusion of, for example, germanium by employing germanium-containing energetic gas-cluster ions. With suitable clusters containing both a dopant (boron for example) and an amorphizing agent (germanium for example) a single GCIB infusion step can produce a very shallow doped and amorphized layer that can be annealed and activated without a separate amorphizing step. When GCIB infusion of both boron and germanium is performed in a silicon substrate, the presence of the germanium can also serve to increase the solid solubility of the boron in the silicon, permitting higher boron doping levels. 
         [0022]    Inert gas gas-cluster ion beam processing of a GCIB infusion doped semiconductor can be used to improve the depth-distribution profile of the dopant when it is desired to flatten the profile peak while yet retaining a shallow, abrupt depth-distribution tail. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0023]    For a better understanding of the present invention, together with other and further objects thereof, reference is made to the accompanying drawing and detailed description, wherein: 
           [0024]      FIG. 1  is a schematic showing the basic elements of a prior art GCIB processing apparatus that uses an electrostatically scanned beam; 
           [0025]      FIG. 2  is a schematic showing the basic elements of a prior art GCIB processing apparatus that uses a stationary beam with mechanical scanning of the workpiece and that includes provision for mixing source gases; 
           [0026]      FIG. 3  is a schematic of a portion of a semiconductor wafer receiving gas-cluster ion irradiation; 
           [0027]      FIG. 4  is a schematic enlarging a portion of the semiconductor wafer from  FIG. 3 , showing additional detail including a mixed-gas-cluster ion; 
           [0028]      FIG. 5  is a schematic of a portion of a semiconductor wafer, showing modification of the surface in the affected zone of a cluster impact, according to the invention; 
           [0029]      FIG. 6  is a schematic of a portion of a semiconductor wafer, showing modification of surface regions impacted by many gas-cluster ions forming a surface film according to the invention; 
           [0030]      FIG. 7  is a schematic of a portion of a semiconductor wafer, showing mask controlled localization of processing during irradiation by gas-cluster ions; 
           [0031]      FIG. 8  is a schematic of a portion of a semiconductor wafer after mask controlled localization of processing during gas-cluster ion irradiation to form an infused film by gas-cluster ion beam processing; 
           [0032]      FIG. 9  is a graph showing results of Secondary Ion Mass Spectrometry (SIMS) depth profile measurements comparing conventional ion implantation and GCIB infusion, both in a silicon substrate; 
           [0033]      FIG. 10  is a graph showing results of SIMS measurement of a series of boron infused films formed by application of the invention; 
           [0034]      FIG. 11  is a graph showing results of SIMS measurement of an infusion doped film formed by a specific application of the invention and showing effects of subsequent processing by argon GCIB; 
           [0035]      FIG. 12  is a graph showing results of SIMS measurements boron GCIB infusion doping following furnace anneal for three specific example applications of the invention; 
           [0036]      FIG. 13  is a graph showing results of SIMS and spreading resistance probe (SRP) measurement on boron infused silicon processed according to specific applications of the invention; 
           [0037]      FIG. 14  is a graph showing results of SIMS measurement of an infused film formed by a specific application of the invention; 
           [0038]      FIG. 15(A , B, C) is cross-sectional transmission electron micrographs showing amorphous layer formation in silicon by germanium GCIB Ge infusion; 
           [0039]      FIG. 16  is a graph showing results of SIMS measurements of an infused film formed by a specific application of the invention; and 
           [0040]      FIG. 17  is a graph showing results of SIMS measurements of the infused film of  FIG. 16  after annealing for activation. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0041]      FIG. 1  shows a schematic of the basic elements of a prior art configuration for a processing apparatus  100  for generating a GCIB in accordance with the present invention. Apparatus  100  may be described as follows: a vacuum (reduced-pressure) vessel  102  is divided into three communicating chambers, a source chamber  104 , an 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 or N 2 ) stored in a gas storage cylinder  111  is admitted under pressure through gas metering valve  113  and gas feed tube  114  into stagnation chamber  116  and is ejected into the substantially lower pressure vacuum through a properly shaped nozzle  110 . A supersonic gas jet  118  results. Cooling, which results from the expansion in the jet, causes a portion of the gas jet  118  to condense into clusters, each consisting of from several to several thousand weakly bound atoms or molecules. A gas skimmer aperture  120  partially separates the gas molecules that have not condensed into a cluster jet from the cluster jet so as to minimize pressure in the downstream regions where such higher pressures would be detrimental (e.g., ionizer  122 , high voltage electrodes  126 , and processing chamber  108 ). Suitable condensable source gases  112  include, but are not necessarily limited to argon, nitrogen, carbon dioxide, oxygen, and other gases. 
         [0042]    After the supersonic gas jet  118  containing gas-clusters has been formed, the clusters are ionized in an ionizer  122 . The ionizer  122  is typically an electron impact ionizer that produces thermoelectrons from one or more incandescent filaments  124  and accelerates and directs the electrons causing them to collide with the gas-clusters in the gas jet  118 , where the jet passes through the ionizer  122 . The electron impact ejects electrons from the clusters, causing a portion the clusters to become positively ionized. A set of suitably biased high voltage electrodes  126  extracts the cluster ions from the ionizer, forming a beam, then accelerates them to a desired mean energy (typically from 1 keV to several tens of keV) and focuses them to form a GCIB  128 . Filament power supply  136  provides filament voltage V f  to heat the ionizer filament  124 . Anode power supply  134  provides anode voltage V A  to accelerate thermoelectrons emitted from filament  124  to cause them to irradiate the cluster containing gas jet  118  to produce ions. Extraction power supply  138  provides extraction voltage V E  to bias a high voltage electrode to extract ions from the ionizing region of ionizer  122  and to form a GCIB  128 . Accelerator power supply  140  provides acceleration voltage V Acc  to bias a high voltage electrode with respect to the ionizer  122  so as to result in a total GCIB acceleration potential equal to V Acc . V Acc  is typically adjustable and controllable, having a typical range of from a few hundred volts to as much as several tens of kV or even as much as 100 kV. One or more lens power supplies ( 142  and  144  shown for example) may be provided to bias high voltage electrodes with focusing voltages (V L1  and V L2  for example) to focus the GCIB  128 . 
         [0043]    A workpiece  152 , which may be a semiconductor wafer or other workpiece to be processed by GCIB processing, is held on a workpiece holder  150 , disposed in the path of the GCIB  128 . Since most applications contemplate the processing of large workpieces with spatially uniform results, a scanning system is desirable to uniformly scan the GCIB  128  across large areas to produce spatially homogeneous results. Two pairs of orthogonally oriented electrostatic scan plates  130  and  132  can be utilized to produce a raster or other scanning pattern across the desired processing area. When beam scanning is performed, the GCIB  128  is converted into a scanned GCIB  148 , which scans the entire surface of workpiece  152 . 
         [0044]      FIG. 2  shows a schematic of the basic elements of a prior art mechanically scanning GCIB processing apparatus  200  for generating a GCIB in accordance with the present invention. Apparatus  200  may be described as having a stationary beam with a mechanically scanned workpiece  152 , and having a conventional faraday cup for beam measurement and a conventional thermionic neutralizer. GCIB formation is similar to as shown in  FIG. 1 , except there is additional provision for an optional second source gas  222  (typically different from the source gas  112 ) stored in a gas storage cylinder  221  with a gas metering valve  223  and connecting through gas feed tube  114  into stagnation chamber  116 . Although not shown, it will be readily appreciated by those of skill in the art that three or more source gases can easily be arranged for by adding additional gas storage cylinders, plumbing, and valves. This multiple gas arrangement allows for controllably selecting between two differing source gasses  112  and  222  or for controllably forming a mixture of two (or more) source gasses for use in forming gas-clusters. It is further understood that the source gases,  112 , and  222 , may themselves be mixtures of gases, for examples argon plus 1% diborane, or argon plus 5% germane. In addition, in the mechanically scanning GCIB processing apparatus  200  of  FIG. 2 , the GCIB  128  is stationary (not electrostatically scanned as in the GCIB processing apparatus  100 ) and the workpiece  152  is mechanically scanned through the GCIB  128  to distribute the effects of the GCIB  128  over a surface of the workpiece  152 . 
         [0045]    An X-scan actuator  202  provides linear motion of the workpiece holder  150  in the direction of X-scan motion  208  (into and out of the plane of the paper). A Y-scan actuator  204  provides linear motion of the workpiece holder  150  in the direction of Y-scan motion  210 , which is typically orthogonal to the X-scan motion  208 . The combination of X-scanning and Y-scanning motions moves the workpiece  152 , held by the workpiece holder  150  in a raster-like scanning motion through GCIB  128  to cause a uniform irradiation of a surface of the workpiece  152  by the GCIB  128  for uniform processing of the workpiece  152 . The workpiece holder  150  disposes the workpiece  152  at an angle with respect to the axis of the GCIB  128  so that the GCIB  128  has an angle of beam incidence  206  with respect to the workpiece  152  surface. The angle of beam incidence  206  may be 90 degrees or some other angle, but is typically 90 degrees or near 90 degrees. During Y-scanning, the workpiece  152  held by workpiece holder  150  moves from the position shown to the alternate position “A”, indicated by the designators  152 A and  150 A respectively. Notice that in moving between the two positions, the workpiece  152  is scanned through the GCIB  128  and in both extreme positions, is moved completely out of the path of the GCIB  128  (over-scanned). Though not shown explicitly in  FIG. 2 , similar scanning and over-scan is performed in the (typically) orthogonal X-scan motion  208  direction (in and out of the plane of the paper). 
         [0046]    A beam current sensor  218  is disposed beyond the workpiece holder  150  in the path of the GCIB  128  so as to intercept a sample of the GCIB  128  when the workpiece holder  150  is scanned out of the path of the GCIB  128 . The beam current sensor  218  is typically a faraday cup or the like, closed except for a beam-entry opening, and is affixed to the wall of the vacuum vessel  102  with an electrically insulating mount  212 . 
         [0047]    A controller  220 , which may be a microcomputer based controller connects to the X-scan actuator  202  and the Y-scan actuator  204  through electrical cable  216  and controls the X-scan actuator  202  and the Y-scan actuator  204  so as to place the workpiece  152  into or out of the GCIB  128  and to scan the workpiece  152  uniformly relative to the GCIB  128  to achieve uniform processing of the workpiece  152  by the GCIB  128 . Controller  220  receives the sampled beam current collected by the beam current sensor  218  by way of lead  214  and thereby monitors the GCIB and controls the GCIB dose received by the workpiece  152  by removing the workpiece  152  from the GCIB  128  when a predetermined desired dose has been delivered. 
         [0048]      FIG. 3  is an illustration of a surface region  300  of a portion of a semiconductor wafer  302  being impacted by a gas-cluster ion  306  comprising a mixture of noble gas and other gas molecules. The figure is not drawn to scale. The semiconductor wafer  302  has a surface  304  and is, for example, a single crystal material and may be at any of several stages of processing for fabricating an integrated circuit or semiconductor device. A gas-cluster ion  306  having a trajectory  308  is shown impacting surface  304  of semiconductor wafer  302 , where it forms a gas-cluster ion-impact region  310 . According to an embodiment of the invention, gas-cluster ion  306  has been formed so that it is a cluster that includes dopant atom species and/or a species to promote increased amorphization or to improve dopant solubility (germanium for example). For example, the cluster might include diborane, germane, and/or other species in addition to a noble gas such as argon. 
         [0049]      FIG. 4  is a schematic  320  enlarging a portion of the semiconductor wafer  302  from  FIG. 3 , showing additional detail. Gas-cluster ion  306  comprises multiple molecules of at least two gases that include at least a noble gas and a gas comprising either a dopant atom or a species to promote increased amorphization or to improve dopant solubility (germanium or silicon, for example). The gas-cluster ion  306  contains noble gas atoms  322  and gas molecules  324  comprising either a dopant atom species or a species to promote increased amorphization or to improve dopant solubility such as, for example, germanium or silicon. Optionally, the gas-cluster ion  306  may contain additional dopant atom species or amorphization-promoting or dopant solubility improving molecules  332  of a type different than that of gas molecules  324 . Thus, the cluster  306  may be comprised of at least a noble gas portion and multiple, fractional portions of distinct molecule species of dopant atoms or amorphization-promoting or dopant solubility improving atom species. Such a gas-cluster ion  306  may be formed in a GCIB processing apparatus  200  as shown in or similar to those shown in  FIG. 2 , for example. When it is desired to have a mixture of gasses in the gas-clusters, a premixed gas mixture with the desired mix can be provided in a single gas storage cylinder  111  ( FIG. 2 ) or alternatively, separate, differing source gases or source gas mixtures  112  and  222  can be provided in gas storage cylinders  111  and  221  ( FIG. 2 ) and then mixed in desired proportions as they flow to the stagnation chamber  116  ( FIG. 2 ) by suitable adjustment of gas metering valves  113  and  223  ( FIG. 2 ), which are preferably mass flow controller valves. Thus, it is possible to generate gas-cluster ion beams with a controllable mixture of two or more gasses. Referring again to  FIG. 4 , the gas-cluster ion  306  is shown (for example and not for limitation) to comprise noble gas atoms  322  and multiple types of dopant or amorphization promoting gas molecules  324 ,  332 . It is recognized that a wide range of mixtures of noble gas, dopant and amorphization promoting gas molecules are useful in the present invention and that the clusters used for the process of the invention can be formed from noble gas mixed with very high concentrations of dopant or amorphization promoting gas molecules, or at the other extreme, the ratio of dopant or amorphization promoting gas molecules to noble gas molecules may be so low that some or many gas-cluster ions do not contain even a single non-noble gas molecule, but wherein at least a portion of the gas-cluster ions in a gas-cluster ion beam comprise one or more molecules of dopant or amorphization promoting gas molecules. Typically, the concentration of amorphization promoting gas molecules, if present, will comprise on the order a few to several tens of molecular percent of the gas-cluster ions, while any dopant-containing gas molecules will be of lower molecular concentration (for example, not for limitation, from about 0.01 to about 20 molecular percent) in the gas-cluster ions. The gas-cluster ion-impact region  310  has a boundary  326 . The volume of the gas-cluster ion-impact region  310  and hence it&#39;s depth of penetration of the surface of the semiconductor is dependent on the preselected and controlled energy of the gas-cluster ion  306 . It is preferable to use gas-cluster ions having energies in the range of from about 1 keV to about 40 keV per ionic charge (acceleration potentials of from about 1 kV to about 40 kV). Upon impact of an energetic gas-cluster ion  306  on the surface  304 , the gas-cluster ion  306  dissociates and the individual dopant or amorphization promoting gas molecules from the dissociated cluster become free. Inert gas molecules typically recoil and escape from the surface  304  of the semiconductor wafer  302 . Some molecules including some of the dopant or amorphization promoting gas molecules become infused into the surface. Other than a small energy carried away by the escaping individual gas atoms, the total energy of the energetic gas-cluster ion  306  becomes deposited into the gas-cluster ion-impact region  310 . The dimensions of the gas-cluster ion-impact region  310  are dependent on the energy of the cluster but are small—on the order of tens or hundreds of angstroms in diameter—depending on the preselected gas-cluster ion energy. Because of the deposition of most of the total energy carried by the gas-cluster ion  306  into the small gas-cluster ion-impact region  310 , an intense thermal transient occurs within the material in the gas-cluster ion-impact region  310 . The heat deposited in the gas-cluster ion-impact region  310  dissipates by conduction in the directions  328  deeper into the surrounding semiconductor material. Duration of the thermal transient is determined by the thermal conductivity of the surrounding material but will typically be less than 10 −6  second. 
         [0050]    In the gas-cluster ion-impact region  310 , material can momentarily reach temperatures of many hundreds to several thousands of degrees Kelvin. As an example, impact of a gas-cluster ion  306  when carrying 10 keV total energy is estimated to be capable of producing a momentary temperature increase of about 2000 degrees Kelvin throughout an gas-cluster ion-impact region  310  extending to almost 100 Angstroms below the surface  304 . Without being bound to a particular theory, it is believed that during the thermal transient, thermal agitation is high enough to possibly melt the material in the gas-cluster ion-impact region  310 . As the gas-cluster ion-impact region  310  cools by thermal conduction in the directions  328 , part of the dopant or amorphization promoting material in the impacted cluster becomes infused into the cluster ion impact region  310  and is incorporated into the cooled surface. Another potential effect of the thermal transient is the restoration or partial restoration of crystallinity for damaged material within much of the gas-cluster ion-impact region. 
         [0051]      FIG. 5  is an illustration of a surface region  340  of a portion of a semiconductor wafer  302 , showing infusion of dopant or amorphization promoting atoms into a region impacted by a gas-cluster ion, according to the present invention. After the gas-cluster ion-impact event described in  FIG. 4 , upon dissipation of the thermal transient, an infused region  342  replaces the gas-cluster ion-impact region  310  of  FIG. 4 . Infused region  342  extends to a depth  344  below the surface  304  of semiconductor wafer  302 . 
         [0052]      FIG. 6  is an illustration of a surface region  360  of a portion of a semiconductor wafer  302 , showing an infused film  362  formed by completion of gas-cluster ion beam processing according to the present invention. With continued gas-cluster ion irradiation, infused regions similar to the infused region  342  ( FIG. 5 ) form, overlap, and eventually develop the infused film  362 , extending to a depth  364  below the surface  304  of the semiconductor wafer  302 . 
         [0053]      FIG. 7  is an illustration of a surface region  400  of a portion of a semiconductor wafer  302  being impacted by a gas-cluster ion  306  comprising a mixture of noble gas and other gas molecules. The figure is not drawn to scale. The semiconductor wafer  302  has a surface  304  and is typically a single crystal material and may be at any of several stages of processing for fabricating an integrated circuit or semiconductor device. A portion of the surface  304  of the semiconductor wafer  302  is covered by a mask  402  that masks part of the surface  304  from irradiation by energetic clusters. A gas-cluster ion  306  having a trajectory  308  is shown impacting surface  304  of semiconductor wafer  302  in an unmasked region, where it forms a gas-cluster ion-impact region  310 . Any clusters that strike the mask  402  are prevented by the mask from affecting the surface  304  of the semiconductor wafer  302 . The mask  402  can be either a hard mask like silicon dioxide, or a soft mask such as photoresist material. 
         [0054]      FIG. 8  is an illustration of a surface region  420  of a portion of a semiconductor wafer  302 , showing an infused film  422  formed by completion of gas-cluster ion beam processing of the masked wafer shown in  FIG. 7 , according to the present invention. With continued gas-cluster ion irradiation, infused regions similar to the infused region ( 342   FIG. 5 ) form, overlap, and eventually develop the infused film  422  only at the exposed surface regions of the mask  402 . 
         [0055]      FIGS. 6 and 8  show the formation of infused films ( 362  and  422 ) on semiconductor substrates. Doped films and/or amorphized films can be can be formed. The amount of processing that occurs is a function of both cluster ion energy and cluster ion dose. The process herein referred to as “infusion” occurs (the dopant and/or amorphization promoting atoms in the gas-cluster ions become mixed into the shallow subsurface regions of the irradiated surface ( 362  and  422  in  FIGS. 6 and 8  respectively). Specific examples of some of the useful processes will be given in additional detail hereinafter. Some re-crystallization and electrical activation can also be achieved in originally damaged material in the impact region at the surface by the gas-cluster ion beam processing. 
       Experimental Results 
       [0056]      FIG. 9  is a graph showing results of Secondary Ion Mass Spectrometry (SIMS) depth profile measurements comparing conventional ion implantation and GCIB infusion, both in a silicon substrate. A conventional 500 eV BF 3  implant and a GCIB boron infusion (according to the invention) performed using a mixture of 1% B 2 H 6  in argon are compared. Both doping processes were accomplished without a pre-amorphization step. While the as-implanted 500 eV boron profile shows a prominent channeling tail that results in a 1×10 18  at/cc concentration at approximately 400 angstroms, the GCIB as-infused profile shows a 1×10 18  at/cc concentration at approximately 120 angstroms and exhibits a very abrupt concentration gradient of approximately 25 angstroms/decade. The GCIB infusion was performed using 5 kV acceleration potential resulting in 5 keV energy for singly charged clusters and higher energies for multiply charged clusters. The cluster infusion dose of 3×10 14  clusters/cm 2  resulted in a boron dose of approximately 1.9×10 15  at/cm 2 . A gas-cluster ion beam processing system similar to that shown in  FIG. 2  was used to perform the GCIB infusion process. 
         [0057]      FIG. 10  is a graph showing results of SIMS measurement of a series of boron infused films formed by a method in accordance with the invention. GCIB boron infusion (according to the invention) was performed using a mixture of 1% B 2 H 6  in argon at five different gas-cluster acceleration potentials (2.5, 5, 10, 20, and 30 kV). All were accomplished without a pre-amorphization step. All were performed with 3×10 14  gas clusters/cm 2  infusion doses, which resulted in corresponding boron atom doses shown on the face of the  FIG. 10  graph. The boron 1×10 18  at/cc concentration depths were approximately (75, 120, 180, 240, and 280 angstroms, respectively). The GCIB infusions performed using acceleration potentials (2.5, 5, 10, 20, and 30 kV) resulted in cluster energies for singly charged clusters of (2.5, 5, 10, 20, and 30 keV respectively) and higher energies for multiply charged clusters. A gas-cluster ion beam processing system similar to that shown in  FIG. 2  was used to perform the GCIB infusion process. 
         [0058]      FIG. 11  is a graph showing results of SIMS measurement of an infusion doped film formed by a specific application of the invention and showing effects of subsequent processing by argon GCIB. In this example, a gas-cluster ion beam processing system similar to that shown in  FIG. 2  was used to perform a boron infusion doping of a silicon semiconductor wafer substrate. A mixture of 1% diborane (B 2 H 6 ) in argon was used as a source gas for gas-cluster formation and a GCIB infusion dose of 3×10 14  gas-cluster ions/cm 2  was irradiated to the substrate. One region of the substrate was subsequently additionally irradiated with an argon GCIB gas-cluster ion dose of 3×10 14  gas-cluster ions/cm 2  accelerated by a 5 kV acceleration potential. A second region of the substrate was subsequently additionally irradiated with an argon GCIB gas-cluster ion dose of 1×10 15  gas-cluster ions/cm 2 , accelerated by a 5 kV acceleration potential. The  FIG. 11  graph shows the original as-infused boron distribution and also shows that the two post-infusion operations of additional argon GCIB irradiation were effective in flattening the peak of the as-infused distribution and that for a given argon GCIB acceleration potential (5 kV) the depth of the tail of the distribution is substantially independent of the argon GCIB gas-cluster ion dose, both cases resulting in improving the initial as-infused distribution by flattening the peak while retaining a very abrupt concentration gradient in the tail. The 1×10 18  at/cc concentration of the argon processed samples both being approximately 150 angstroms deep. The tail of the redistributed boron distribution appears to depend primarily on the argon GCIB acceleration potential and not on the GCIB gas-cluster ion dose. In many semiconductor applications, the flattened profile peak obtained by the argon GCIB post-infusion doping processing is preferred over the original as-infused boron distribution profile. 
         [0059]      FIG. 12  is a graph showing results of SIMS measurements boron GCIB infusion doping following furnace anneal for three specific example applications of the invention. In all three examples, a gas-cluster ion beam processing system similar to that shown in  FIG. 2  was used to perform a boron infusion doping of a silicon semiconductor wafer substrate. A mixture of 1% diborane (B 2 H 6 ) in argon was used as a source gas for gas-cluster ion formation, a 5 kV acceleration potential was used to accelerate the GCIB and a GCIB infusion dose selected to result in a 5×10 15  boron atom/cm 2  doping of the silicon was irradiated to each of three substrates. One of the boron infused substrates was subsequently additionally post-infusion amorphized with a 30 keV conventional ion implantation of silicon ions to an implant dose of 1×10 15  Si ions/cm 2 . A second of the boron infused substrates was subsequently additionally post-infusion irradiated with a 5 keV conventional ion implantation of germanium ions to an implant dose of 5×10 14  Ge ions/cm 2 . All three infused substrates were subsequently annealed in a furnace at 550 degrees C. for 60 minutes. In the case of boron infusion without subsequent post-infusion amorphization, the annealed boron profile was essentially the same as the as-infused profile (not shown). In the case of the germanium ion implant post-infusion amorphization, there was seen a modest amount of boron redistribution, with the 1×10 18  boron atom/cc concentration depth increasing from approximately 140 angstroms to approximately 220 angstroms. In the case of the silicon ion implant post-infusion amorphization, there was seen a larger amount of boron redistribution, with the 1×10 18  boron atom/cc concentration depth increasing from approximately 140 angstroms to approximately 450 angstroms. These examples show that although conventional ion implantation can be used to facilitate dopant activation with annealing, it results some redistribution of the dopant after low temperature anneal. 
         [0060]      FIG. 13  is a graph showing results of SIMS and spreading resistance probe (SRP) measurement on boron infused silicon processed according to specific applications of the invention. In all the examples shown in  FIG. 13 , a gas-cluster ion beam processing system similar to that shown in  FIG. 2  was used to perform a boron infusion doping of a silicon semiconductor wafer substrate. A mixture of 1% diborane (B 2 H 6 ) in argon was used as a source gas for gas-cluster ion formation, a 5 kV acceleration potential was used to accelerate the GCIB and a GCIB infusion dose selected to result in a 5×10 15  boron atom/cm 2  doping of each silicon substrate (same boron infusion conditions as for the cases shown in  FIG. 12 ). In case (b) the boron infused substrate was furnace annealed at 550 degrees C. for 60 minutes. The boron distribution in this case (b) was substantially unchanged from the as-infused case (not shown). In case (a) the boron infused substrate was furnace annealed at 950 degrees C. for 60 minutes. In case (a) the high temperature anneal resulted in considerable diffusion of the dopant. SRP measurements for case (a) are indicated by the dash-dot curve (e) and show an activated dopant level of 3×10 19  boron atoms/cc, but with a deep junction of 3000-4000 angstroms. In case (d) the infused boron was subsequently post-infusion amorphized with 30 keV, 1×10 15  Si ions/cm 2  conventional ion implantation amorphization. After amorphization with silicon, the case (d) was furnace annealed for 60 minutes at 550 degrees C. SRP measurements for case (d) are indicated by the dashed curve (f) and show an electrical junction depth of approximately 50 angstroms. 
         [0061]      FIG. 14  is a graph showing results of SIMS measurement of an infused film formed by a specific application of the invention. In this example (identified as sample  144 - 3 ), a gas-cluster ion beam processing system similar to that shown in  FIG. 2  was used to process the surface of a silicon semiconductor wafer. A mixture of 5% germane (GeH 4 ) in argon was used as one source gas for gas-cluster formation, while a mixture of 1% diborane (B 2 H 6 ) in argon was used as a second source gas for gas-cluster formation. The two source gases were mixed as they flowed into the stagnation chamber—the germane mixture was fed at a rate of 30 sccm and the diborane mixture was fed at a rate of 300 sccm. The ionized gas-cluster ion beam was accelerated by 30 kV acceleration voltage and a dose of 1×10 15  gas-cluster ions/cm 2  was irradiated onto the silicon wafer. The SIMS analysis confirms that a surface infused with boron ions and simultaneously infused with germanium ions for amorphizing the layer (or for increasing the solid solubility limit of a dopant) has been formed. 
         [0062]      FIGS. 15A-15C  are cross-sectional transmission electron micrographs showing amorphous layer formation in silicon by germanium GCIB Ge infusion. The sample shown in  FIG. 15A  is as-infused (approximately 1×10 15  germanium atoms/cm 2  infused by GCIB infusion using 5% GeH 4  in argon as gas-cluster ion source gas) and clearly shows the amorphous layer  502  formation.  FIG. 15B  shows the germanium infused layer of FIG.  15 A after a 60 minute, 550 degree C. furnace anneal and shows the conversion of the amorphous layer  502  to a single-crystalline layer  504 .  FIG. 15C  shows the germanium infused layer of  FIG. 15A  after a 60 minute, 950 degree C. furnace anneal and also shows conversion of the amorphous layer to a single crystalline layer. 
         [0063]      FIG. 16  is a graph showing results of SIMS measurements of an infused film formed by a specific application of the invention. In this example, a gas-cluster ion beam processing system similar to that shown in  FIG. 2  was used to process the surface of a silicon semiconductor wafer. A mixture of 5% germane (GeH 4 ) in argon was used as one source gas for gas-cluster formation, while a mixture of 1% diborane (B 2 H 6 ) in argon was used as a second source gas for gas-cluster formation. The two source gases were mixed as they flowed into the stagnation chamber—the germane mixture was fed at a rate of 300 sccm and the diborane mixture was fed at a rate of 75 sccm. The ionized gas-cluster ion beam was accelerated by 5 kV acceleration voltage and a dose of 1×10 15  gas-cluster ions/cm 2  was irradiated onto the silicon wafer. The SIMS analysis confirms that a surface infused with boron ions and simultaneously infused with germanium ions for amorphizing the layer (as shown in  FIG. 15A ) or for increasing the solid solubility limit of the boron dopant has been formed. 
         [0064]      FIG. 17  is a graph showing results of SIMS measurements of the infused film of  FIG. 16  after annealing for activation. In this example the boron-germanium infused film was furnace annealed for 60 minutes at 550 degrees C. When compared to the SIMS plots of  FIG. 16 , it is seen that no significant movement of the dopant occurred as a result of the anneal. Evaluation of the film after anneal showed that the doped junction was electrically activated and remained very shallow and abrupt 
         [0065]    Although the invention has been described with respect to various embodiments, it should be realized this invention is also capable of a wide variety of further and other embodiments within the spirit of the invention.