Self-biasing active load circuit and related power supply for use in a charged particle beam processing system

A load circuit device having a self-biasing active load circuit, and a related high voltage power supply configured to bias an optical element in a charged particle beam processing system, such as a gas cluster ion beam (GCIB) processing system. The high voltage power supply comprises a variable voltage supply having a load terminal at a load potential and a reference terminal at a reference potential, and a self-biasing active load circuit connected between the load terminal and the reference terminal, and configured to sustain a variable voltage drop between the load potential and the reference potential while maintaining a substantially constant current.

BACKGROUND OF THE INVENTION

1. Field of Invention

The invention relates to a self-biasing active load circuit and a related high voltage power supply and, in particular, to a high voltage power supply configured to bias an optical element in a charged particle beam processing system.

2. Description of Related Art

Gas-cluster ion beams (GCIB's) are used for many applications, including etching, cleaning, smoothing, and forming thin films. For purposes of this discussion, gas clusters are nano-sized aggregates of materials that are gaseous under conditions of standard temperature and pressure. Such gas clusters may consist of aggregates including a few to several thousand molecules, or more, that are loosely bound together. The gas clusters can be ionized by electron bombardment, which permits the gas clusters to be formed into directed beams of controllable energy. Such cluster ions each typically carry positive charges given by the product of the magnitude of the electron charge and an integer greater than or equal to one that represents the charge state of the cluster ion.

The larger sized cluster ions are often the most useful because of their ability to carry substantial energy per cluster ion, while yet having only modest energy per individual molecule. The ion clusters disintegrate on impact with the substrate. Each individual molecule in a particular disintegrated ion cluster carries only a small fraction of the total cluster energy. Consequently, the impact effects of large ion clusters are substantial, but are limited to a very shallow surface region. This makes gas cluster ions effective for a variety of surface modification processes, but without the tendency to produce deeper sub-surface damage that is characteristic of conventional ion beam processing.

Conventional cluster ion sources produce cluster ions having a wide size distribution scaling with the number of molecules in each cluster that may reach several thousand molecules. Clusters of atoms can be formed by the condensation of individual gas atoms (or molecules) during the adiabatic expansion of high pressure gas from a nozzle into a vacuum. A skimmer with a small aperture strips divergent streams from the core of this expanding gas flow to produce a collimated beam of clusters. Neutral clusters of various sizes are produced and held together by weak inter-atomic forces known as Van der Waals forces. This method has been used to produce beams of clusters from a variety of gases, such as helium, neon, argon, krypton, xenon, nitrogen, oxygen, carbon dioxide, sulfur hexafluoride, nitric oxide, and nitrous oxide, and mixtures of these gases.

Typically, a GCIB processing system comprises one or more optical elements to extract the cluster ions from the ionizer, accelerate the extracted cluster ions to a desired energy, and focus the energetic, extracted cluster ions to define the GCIB. The kinetic energy of the cluster ions in the GCIB may range from about 1000 electron volts (1 keV) to several tens of keV. For example, the GCIB may be accelerated to 1 to 100 keV.

Therefore, by design, one or more optical elements operate at a high voltage, and generally float above the desired voltage due to the relatively high impedance of most high voltage power supply outputs. In order to shunt excess current, a resistor load is disposed between the terminals of the high voltage power supply. However, when varying the desired voltage across a range of possible operating voltages, the power dissipation in the resistor load can become excessive, particularly at high voltages since the power dissipation scales as the square of the voltage (i.e., P=V2/R, where P represents power dissipation, V represents voltage, and R represents resistance). This excessive power dissipation may be impractical at high voltages.

SUMMARY OF THE INVENTION

The invention relates to a high voltage power supply and, in particular, to a high voltage power supply configured to bias an optical element in a charged particle beam processing system. The invention further relates to a load circuit device that is configured to be used with a high voltage power supply to provide the biasing function.

According to one embodiment, a high voltage power supply is described. The high voltage power supply comprises a variable voltage supply having a load terminal at a load potential and a reference terminal at a reference potential, and a self-biasing active load circuit connected between the load terminal and the reference terminal, and configured to sustain a variable voltage drop between the load potential and the reference potential while maintaining a substantially constant current.

According to another embodiment, an optical element for use in a charged particle processing system is described. The optical element comprises: a high voltage electrode configured to be arranged along a beam line in a charged particle beam processing system; a variable voltage supply having a load terminal at a load potential and a reference terminal at a reference potential, and configured to couple the load potential to the high voltage electrode; and a self-biasing active load circuit connected between the load terminal and the reference terminal, and configured to sustain a variable voltage drop between the load potential and the reference potential while maintaining a substantially constant current.

According to yet another embodiment, a GCIB processing system configured to treat a substrate is described. The GCIB processing system comprises: a vacuum vessel; a gas cluster ion beam (GCIB) source disposed in the vacuum vessel and configured to produce a GCIB; and a substrate holder configured to support the substrate inside the vacuum vessel for treatment by the GCIB. The GCIB source comprises: a nozzle assembly comprising a gas source, a stagnation chamber and a nozzle, and configured to introduce under high pressure one or more gases through the nozzle to the vacuum vessel in order to produce a gas cluster beam, a gas skimmer positioned downstream from the nozzle assembly, and configured to reduce the number of energetic, smaller particles in the gas cluster beam, an ionizer positioned downstream from the gas skimmer, and configured to ionize the gas cluster beam to produce the GCIB, and beam optics positioned downstream from the ionizer, the beam optics comprising one or more optical elements configured to extract the GCIB, accelerate the GCIB, or focus the GCIB, or perform any combination of two or more thereof. At least one of the one or more optical elements comprises: a high voltage electrode configured to be arranged along a beam line in a GCIB processing system, a variable voltage supply having a load terminal at a load potential and a reference terminal at a reference potential, and configured to couple the load potential to the high voltage electrode, and a self-biasing active load circuit connected between the load terminal and the reference terminal, and configured to sustain a variable voltage drop between the load potential and the reference potential while maintaining a substantially constant current.

In accordance with still another embodiment, a load circuit device is described. The load circuit device comprises a self-biasing active load circuit configured to be connected between a first circuit node at a first potential and a second circuit node at a second potential, and configured to sustain a variable voltage drop between said first potential and said second potential while maintaining a substantially constant current.

DETAILED DESCRIPTION OF SEVERAL EMBODIMENTS

A high voltage power supply configured to bias an optical element in a charged particle beam processing system, such as a gas cluster ion beam (GCIB) processing system, is disclosed in various embodiments. A load circuit device comprising a self-biasing active load circuit that can be added to a high voltage power supply to configure it to bias the optical element is also disclosed in various embodiments. However, one skilled in the relevant art will recognize that the various embodiments may be practiced without one or more of the specific details, or with other replacement and/or additional methods, materials, or components. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of various embodiments of the invention. Similarly, for purposes of explanation, specific numbers, materials, and configurations are set forth in order to provide a thorough understanding of the invention. Nevertheless, the invention may be practiced without specific details. Furthermore, it is understood that the various embodiments shown in the figures are illustrative representations and are not necessarily drawn to scale.

In the description and claims, the terms “coupled” and “connected,” along with their derivatives, are used. It should be understood that these terms are not intended as synonyms for each other. Rather, in particular embodiments, “connected” may be used to indicate that two or more elements are in direct physical or electrical contact with each other while “coupled” may further mean that two or more elements are not in direct contact with each other, but yet still co-operate or interact with each other.

As described above, there is a general need for electrically biasing one or more optical elements in a charged particle beam processing system, such as a GCIB processing system, to, among other things, extract, accelerate and focus the charged particle beam, or GCIB. However, conventional beam optics for biasing an optical element across a range of voltages suffer from high power dissipation due to the shunt of excess current through a resistor load. Accordingly, a high voltage power supply configured to bias an optical element in a charged particle beam processing system is described herein. A load circuit device comprising a self-biasing active load circuit that can be added to a high voltage power supply to configure it to bias the optical element is also disclosed herein. Although the load circuit device may be utilized with any charged particle beam processing system including but not limited to an ion implant equipment processing system, ion beam processing system, and GCIB processing system, the load circuit device is described in the context of a GCIB processing system.

Referring now to the drawings wherein like reference numerals designate corresponding parts throughout the several views, a GCIB processing system100for treating a substrate is depicted inFIG. 1according to an embodiment. The GCIB processing system100comprises a vacuum vessel102, substrate holder150, upon which a substrate152to be processed is affixed, and vacuum pumping systems170A,170B, and170C. Substrate152can be a semiconductor substrate, a wafer, a flat panel display (FPD), a liquid crystal display (LCD), or any other workpiece. GCIB processing system100is configured to produce a GCIB for treating substrate152.

Referring still to GCIB processing system100inFIG. 1, the vacuum vessel102comprises three communicating chambers, namely, a source chamber104, an ionization/acceleration chamber106, and a processing chamber108to provide a reduced-pressure enclosure. The three chambers are evacuated to suitable operating pressures by vacuum pumping systems170A,170B, and170C, respectively. In the three communicating chambers104,106,108, a gas cluster beam can be formed in the first chamber (source chamber104), while a gas cluster ion beam can be formed in the second chamber (ionization/acceleration chamber106) wherein the gas cluster beam is ionized and accelerated. Then, in the third chamber (processing chamber108), the accelerated gas cluster ion beam may be utilized to treat substrate152.

As shown inFIG. 1, GCIB processing system100can comprise one or more gas sources configured to introduce one or more gases or mixture of gases to vacuum vessel102. For example, a first gas composition stored in a first gas source111is admitted under pressure through a first gas control valve113A to a gas metering valve or valves113. Additionally, for example, a second gas composition stored in a second gas source112is admitted under pressure through a second gas control valve113B to the gas metering valve or valves113. Furthermore, for example, the first gas composition or the second gas composition or both can comprise a film-forming gas composition, an etching gas composition, a dopant composition, etc. Further yet, for example, the first gas composition or second gas composition or both can include a condensable inert gas, carrier gas or dilution gas. For example, the inert gas, carrier gas or dilution gas can include a noble gas, i.e., He, Ne, Ar, Kr, Xe, or Rn.

The high pressure, condensable gas comprising the first gas composition or the second gas composition or both is introduced through gas feed tube114into stagnation chamber116and is ejected into the substantially lower pressure vacuum through a properly shaped nozzle110. As a result of the expansion of the high pressure, condensable gas from the stagnation chamber116to the lower pressure region of the source chamber104, the gas velocity accelerates to supersonic speeds and gas cluster beam118emanates from nozzle110.

The inherent cooling of the jet as static enthalpy is exchanged for kinetic energy, which results from the expansion in the jet, causes a portion of the gas jet to condense and form a gas cluster beam118having clusters, each consisting of from several to several thousand weakly bound atoms or molecules. A gas skimmer120, positioned downstream from the exit of the nozzle110between the source chamber104and ionization/acceleration chamber106, partially separates the gas molecules on the peripheral edge of the gas cluster beam118, that may not have condensed into a cluster, from the gas molecules in the core of the gas cluster beam118, that may have formed clusters. Among other reasons, this selection of a portion of gas cluster beam118can lead to a reduction in the pressure in the downstream regions where higher pressures may be detrimental (e.g., ionizer122, and processing chamber108). Furthermore, gas skimmer120defines an initial dimension for the gas cluster beam entering the ionization/acceleration chamber106.

After the gas cluster beam118has been formed in the source chamber104, the constituent gas clusters in gas cluster beam118are ionized by ionizer122to form GCIB128. The ionizer122may include an electron impact ionizer that produces electrons from one or more filaments124, which are accelerated and directed to collide with the gas clusters in the gas cluster beam118inside the ionization/acceleration chamber106. Upon collisional impact with the gas cluster, electrons of sufficient energy eject electrons from molecules in the gas clusters to generate ionized molecules. The ionization of gas clusters can lead to a population of charged gas cluster ions, generally having a net positive charge.

As shown inFIG. 1, beam optics130are utilized to ionize, extract, accelerate, and focus the GCIB128. The beam optics130includes a filament power supply136that provides voltage VFto heat the ionizer filament124.

Additionally, the beam optics130includes a set of suitably biased high voltage electrodes126in the ionization/acceleration chamber106that extracts the cluster ions from the ionizer122. The high voltage electrodes126then accelerate the extracted cluster ions to a desired energy and focus them to define GCIB128. The kinetic energy of the cluster ions in GCIB128typically ranges from about 1000 electron volts (1 keV) to several tens of keV. For example, GCIB128can be accelerated to 1 to 100 keV.

As illustrated inFIG. 1, the beam optics130further includes an anode power supply134that provides voltage VAto an anode of ionizer122for accelerating electrons emitted from filament124and causing the electrons to bombard the gas clusters in gas cluster beam118, which produces cluster ions.

Additionally, as illustrated inFIG. 1, the beam optics130include an extraction power supply138that provides voltage VEto bias at least one of the high voltage electrodes126to extract ions from the ionizing region of ionizer122and to form the GCIB128. For example, extraction power supply138provides a voltage to a first electrode of the high voltage electrodes126that is less than or equal to the anode voltage of ionizer122.

Furthermore, the beam optics130can include an accelerator power supply140that provides voltage VAccto bias one of the high voltage electrodes126with respect to the ionizer122so as to result in a total GCIB acceleration energy equal to about VAccelectron volts (eV). For example, accelerator power supply140provides a voltage to a second electrode of the high voltage electrodes126that is less than or equal to the anode voltage of ionizer122and the extraction voltage of the first electrode.

Further yet, the beam optics130can include lens power supplies142,144that may be provided to bias some of the high voltage electrodes126with potentials (e.g., VL1and VL2) to focus the GCIB128. For example, lens power supply142can provide a voltage to a third electrode of the high voltage electrodes126that is less than or equal to the anode voltage of ionizer122, the extraction voltage of the first electrode, and the accelerator voltage of the second electrode, and lens power supply144can provide a voltage to a fourth electrode of the high voltage electrodes126that is less than or equal to the anode voltage of ionizer122, the extraction voltage of the first electrode, the accelerator voltage of the second electrode, and the first lens voltage of the third electrode.

Note that many variants on both the ionization and extraction schemes may be used. While the scheme described here is useful for purposes of instruction, another extraction scheme involves placing the ionizer and the first element of the extraction electrode(s) (or extraction optics) at Vacc. This typically requires fiber optic programming of control voltages for the ionizer power supply, but creates a simpler overall optics train. The invention described herein is useful regardless of the details of the ionizer and extraction lens biasing.

As will be described below, any one of the power supplies described above (e.g., extraction power supply138, accelerator power supply140, and/or lens power supplies142,144) may comprise a high voltage power supply having a variable voltage supply, and a self-biasing active load circuit connected between a load terminal and a reference terminal for the variable voltage supply. The self-biasing active load circuit can be configured to sustain a variable voltage drop between the load potential and the reference potential while maintaining a substantially constant current.

A beam filter146in the ionization/acceleration chamber106downstream of the high voltage electrodes126can be utilized to eliminate monomers, or monomers and light cluster ions from the GCIB128to define a filtered process GCIB128A that enters the processing chamber108. In one embodiment, the beam filter146substantially reduces the number of clusters having100or less atoms or molecules or both. The beam filter may comprise a magnet assembly for imposing a magnetic field across the GCIB128to aid in the filtering process.

Referring still toFIG. 1, a beam gate148is disposed in the path of GCIB128in the ionization/acceleration chamber106. Beam gate148has an open state in which the GCIB128is permitted to pass from the ionization/acceleration chamber106to the processing chamber108to define process GCIB128A, and a closed state in which the GCIB128is blocked from entering the processing chamber108. A control cable conducts control signals from control system190to beam gate148. The control signals controllably switch beam gate148between the open or closed states.

A substrate152, which may be a wafer or semiconductor wafer, a flat panel display (FPD), a liquid crystal display (LCD), or other substrate to be processed by GCIB processing, is disposed in the path of the process GCIB128A in the processing chamber108. Because most applications contemplate the processing of large substrates with spatially uniform results, a scanning system may be desirable to uniformly scan the process GCIB128A across large areas to produce spatially homogeneous results.

An X-scan actuator160provides linear motion of the substrate holder150in the direction of X-scan motion (into and out of the plane of the paper). A Y-scan actuator162provides linear motion of the substrate holder150in the direction of Y-scan motion164, which is typically orthogonal to the X-scan motion. The combination of X-scanning and Y-scanning motions translates the substrate152, held by the substrate holder150, in a raster-like scanning motion through process GCIB128A to cause a uniform (or otherwise programmed) irradiation of a surface of the substrate152by the process GCIB128A for processing of the substrate152.

The substrate holder150disposes the substrate152at an angle with respect to the axis of the process GCIB128A so that the process GCIB128A has an angle of beam incidence166with respect to a substrate152surface. The angle of beam incidence166may be 90 degrees or some other angle, but is typically 90 degrees or near 90 degrees. During Y-scanning, the substrate152and the substrate holder150move from the shown position to the alternate position “A” indicated by the designators152A and150A, respectively. Notice that in moving between the two positions, the substrate152is scanned through the process GCIB128A, and in both extreme positions, is moved completely out of the path of the process GCIB128A (over-scanned). Though not shown explicitly inFIG. 1, similar scanning and over-scan is performed in the (typically) orthogonal X-scan motion direction (in and out of the plane of the paper).

A beam current sensor180may be disposed beyond the substrate holder150in the path of the process GCIB128A so as to intercept a sample of the process GCIB128A when the substrate holder150is scanned out of the path of the process GCIB128A. The beam current sensor180is typically a faraday cup or the like, closed except for a beam-entry opening, and is typically affixed to the wall of the vacuum vessel102with an electrically insulating mount182.

As shown inFIG. 1, control system190connects to the X-scan actuator160and the Y-scan actuator162through electrical cable and controls the X-scan actuator160and the Y-scan actuator162in order to place the substrate152into or out of the process GCIB128A and to scan the substrate152uniformly relative to the process GCIB128A to achieve desired processing of the substrate152by the process GCIB128A. Control system190receives the sampled beam current collected by the beam current sensor180by way of an electrical cable and, thereby, monitors the GCIB and controls the GCIB dose received by the substrate152by removing the substrate152from the process GCIB128A when a predetermined dose has been delivered.

In the embodiment shown inFIG. 2, the GCIB processing system100′ can be similar to the embodiment ofFIG. 1and further comprise a X-Y positioning table253operable to hold and move a substrate252in two axes, effectively scanning the substrate252relative to the process GCIB128A. For example, the X-motion can include motion into and out of the plane of the paper, and the Y-motion can include motion along direction264.

The process GCIB128A impacts the substrate252at a projected impact region286on a surface of the substrate252, and at an angle of beam incidence266with respect to the substrate252surface. By X-Y motion, the X-Y positioning table253can position each portion of a surface of the substrate252in the path of process GCIB128A so that every region of the surface may be made to coincide with the projected impact region286for processing by the process GCIB128A. An X-Y controller262provides electrical signals to the X-Y positioning table253through an electrical cable for controlling the position and velocity in each of X-axis and Y-axis directions. The X-Y controller262receives control signals from, and is operable by, control system190through an electrical cable. X-Y positioning table253moves by continuous motion or by stepwise motion according to conventional X-Y table positioning technology to position different regions of the substrate252within the projected impact region286. In one embodiment, X-Y positioning table253is programmably operable by the control system190to scan, with programmable velocity, any portion of the substrate252through the projected impact region286for GCIB processing by the process GCIB128A.

The substrate holding surface254of positioning table253is electrically conductive and is connected to a dosimetry processor operated by control system190. An electrically insulating layer255of positioning table253isolates the substrate252and substrate holding surface254from the base portion260of the positioning table253. Electrical charge induced in the substrate252by the impinging process GCIB128A is conducted through substrate252and substrate holding surface254, and a signal is coupled through the positioning table253to control system190for dosimetry measurement. Dosimetry measurement has integrating means for integrating the GCIB current to determine a GCIB processing dose. Under certain circumstances, a target-neutralizing source (not shown) of electrons, sometimes referred to as electron flood, may be used to neutralize the process GCIB128A. In such case, a Faraday cup (not shown, but which may be similar to beam current sensor180inFIG. 1) may be used to assure accurate dosimetry despite the added source of electrical charge, the reason being that typical Faraday cups allow only the high energy positive ions to enter and be measured.

In operation, the control system190signals the opening of the beam gate148to irradiate the substrate252with the process GCIB128A. The control system190monitors measurements of the GCIB current collected by the substrate252in order to compute the accumulated dose received by the substrate252. When the dose received by the substrate252reaches a predetermined dose, the control system190closes the beam gate148and processing of the substrate252is complete. Based upon measurements of the GCIB dose received for a given area of the substrate252, the control system190can adjust the scan velocity in order to achieve an appropriate beam dwell time to treat different regions of the substrate252.

Alternatively, the process GCIB128A may be scanned at a constant velocity in a fixed pattern across the surface of the substrate252; however, the GCIB intensity is modulated (may be referred to as Z-axis modulation) to deliver an intentionally non-uniform dose to the sample. The GCIB intensity may be modulated in the GCIB processing system100′ by any of a variety of methods, including varying the gas flow from a GCIB source supply; modulating the ionizer122by either varying a filament voltage VFor varying an anode voltage VA; modulating the lens focus by varying lens voltages VL1and/or VL2; or mechanically blocking a portion of the gas cluster ion beam with a variable beam block, adjustable shutter, or variable aperture. The modulating variations may be continuous analog variations or may be time modulated switching or gating.

The processing chamber108may further include an in-situ metrology system. For example, the in-situ metrology system may include an optical diagnostic system having an optical transmitter280and optical receiver282configured to illuminate substrate252with an incident optical signal284and to receive a scattered optical signal288from substrate252, respectively. The optical diagnostic system comprises optical windows to permit the passage of the incident optical signal284and the scattered optical signal288into and out of the processing chamber108. Furthermore, the optical transmitter280and the optical receiver282may comprise transmitting and receiving optics, respectively. The optical transmitter280receives, and is responsive to, controlling electrical signals from the control system190. The optical receiver282returns measurement signals to the control system190.

The in-situ metrology system may comprise any instrument configured to monitor the progress of the GCIB processing. According to one embodiment, the in-situ metrology system may constitute an optical scatterometry system. The scatterometry system may include a scatterometer, incorporating beam profile ellipsometry (ellipsometer) and beam profile reflectometry (reflectometer), commercially available from Therma-Wave, Inc. (1250 Reliance Way, Fremont, Calif. 94539) or Nanometrics, Inc. (1550 Buckeye Drive, Milpitas, Calif. 95035).

For instance, the in-situ metrology system may include an integrated Optical Digital Profilometry (iODP) scatterometry module configured to measure process performance data resulting from the execution of a treatment process in the GCIB processing system100′. The metrology system may, for example, measure or monitor metrology data resulting from the treatment process. The metrology data can, for example, be utilized to determine process performance data that characterizes the treatment process, such as a process rate, a relative process rate, a feature profile angle, a critical dimension, a feature thickness or depth, a feature shape, etc. For example, in a process for directionally depositing material on a substrate, process performance data can include a critical dimension (CD), such as a top, middle or bottom CD in a feature (i.e., via, line, etc.), a feature depth, a material thickness, a sidewall angle, a sidewall shape, a deposition rate, a relative deposition rate, a spatial distribution of any parameter thereof, a parameter to characterize the uniformity of any spatial distribution thereof, etc. Operating the X-Y positioning table253via control signals from control system190, the in-situ metrology system can map one or more characteristics of the substrate252.

In the embodiment shown inFIG. 3, the GCIB processing system100″ can be similar to the embodiment ofFIG. 1and further comprise a pressure cell chamber350positioned, for example, at or near an outlet region of the ionization/acceleration chamber106. The pressure cell chamber350comprises an inert gas source352configured to supply a background gas to the pressure cell chamber350for elevating the pressure in the pressure cell chamber350, and a pressure sensor354configure to measure the elevated pressure in the pressure cell chamber350.

The pressure cell chamber350may be configured to modify the beam energy distribution of GCIB128to produce a modified process GCIB128A′. This modification of the beam energy distribution is achieved by directing GCIB128along a GCIB path through an increased pressure region within the pressure cell chamber350such that at least a portion of the GCIB traverses the increased pressure region. The extent of modification to the beam energy distribution may be characterized by a pressure-distance integral along the at least a portion of the GCIB path, where distance (or length of the pressure cell chamber350) is indicated by path length (d). When the value of the pressure-distance integral is increased (either by increasing the pressure and/or the path length (d)), the beam energy distribution is broadened and the peak energy is decreased. When the value of the pressure-distance integral is decreased (either by decreasing the pressure and/or the path length (d)), the beam energy distribution is narrowed and the peak energy is increased. Further details for the design of a pressure cell may be determined from U.S. Pat. No. 7,060,989, entitled “METHOD AND APPARATUS FOR IMPROVED PROCESSING WITH A GAS-CLUSTER ION BEAM”; the content of which is incorporated herein by reference in its entirety.

Control system190comprises a microprocessor, memory, and a digital I/O port capable of generating control voltages sufficient to communicate and activate inputs to GCIB processing system100(or100′,100″) a as well as monitor outputs from GCIB processing system100(or100′,100″). Moreover, control system190can be coupled to and can exchange information with vacuum pumping systems170A,170B, and170C, first gas source111, second gas source112, first gas control valve113A, second gas control valve113B, beam optics130, beam filter146, beam gate148, the X-scan actuator160, the Y-scan actuator162, and beam current sensor180. For example, a program stored in the memory can be utilized to activate the inputs to the aforementioned components of GCIB processing system100according to a process recipe in order to perform a GCIB process on substrate152(or252).

However, the control system190may be implemented as a general purpose computer system that performs a portion or all of the microprocessor based processing steps of the invention in response to a processor executing one or more sequences of one or more instructions contained in a memory. Such instructions may be read into the controller memory from another computer readable medium, such as a hard disk or a removable media drive. One or more processors in a multi-processing arrangement may also be employed as the controller microprocessor to execute the sequences of instructions contained in main memory. In alternative embodiments, hard-wired circuitry may be used in place of or in combination with software instructions. Thus, embodiments are not limited to any specific combination of hardware circuitry and software.

The control system190can be used to configure any number of processing elements, as described above, and the control system190can collect, provide, process, store, and display data from processing elements. The control system190can include a number of applications, as well as a number of controllers, for controlling one or more of the processing elements. For example, control system190can include a graphic user interface (GUI) component (not shown) that can provide interfaces that enable a user to monitor and/or control one or more processing elements.

Control system190can be locally located relative to the GCIB processing system100(or100′,100″), or it can be remotely located relative to the GCIB processing system100(or100′,100″). For example, control system190can exchange data with GCIB processing system100using a direct connection, an intranet, and/or the internet. Control system190can be coupled to an intranet at, for example, a customer site (i.e., a device maker, etc.), or it can be coupled to an intranet at, for example, a vendor site (i.e., an equipment manufacturer). Alternatively or additionally, control system190can be coupled to the internet. Furthermore, another computer (i.e., controller, server, etc.) can access control system190to exchange data via a direct connection, an intranet, and/or the internet.

Substrate152(or252) can be affixed to the substrate holder150(or substrate holder250) via a clamping system (not shown), such as a mechanical clamping system or an electrical clamping system (e.g., an electrostatic clamping system). Furthermore, substrate holder150(or250) can include a heating system (not shown) or a cooling system (not shown) that is configured to adjust and/or control the temperature of substrate holder150(or250) and substrate152(or252).

Vacuum pumping systems170A,170B, and170C can include turbo-molecular vacuum pumps (TMP) capable of pumping speeds up to about 5000 liters per second (and greater) and a gate valve for throttling the chamber pressure. In conventional vacuum processing devices, a 1000 to 3000 liter per second TMP can be employed. TMPs are useful for low pressure processing, typically less than about 50 mTorr. Although not shown, it may be understood that pressure cell chamber350may also include a vacuum pumping system. Furthermore, a device for monitoring chamber pressure (not shown) can be coupled to the vacuum vessel102or any of the three vacuum chambers104,106,108. The pressure-measuring device can be, for example, a capacitance manometer or ionization gauge.

Referring now toFIG. 4, a section300of a gas cluster ionizer (122,FIGS. 1,2and3) for ionizing a gas cluster jet (gas cluster beam118,FIGS. 1,2and3) is shown. The section300is normal to the axis of GCIB128. For typical gas cluster sizes (2000 to 15000 atoms), clusters leaving the skimmer aperture (120,FIGS. 1,2and3) and entering an ionizer (122,FIGS. 1,2and3) will travel with a kinetic energy of about 130 to 1000 electron volts (eV). At these low energies, any departure from space charge neutrality within the ionizer122will result in a rapid dispersion of the jet with a significant loss of beam current.FIG. 4illustrates a self-neutralizing ionizer. As with other ionizers, gas clusters are ionized by electron impact. In this design, thermo-electrons (seven examples indicated by310) are emitted from multiple linear thermionic filaments302a,302b,and302c(typically tungsten) and are extracted and focused by the action of suitable electric fields provided by electron-repeller electrodes306a,306b,and306cand beam-forming electrodes304a,304b,and304c.Thermo-electrons310pass through the gas cluster jet and the jet axis and then strike the opposite beam-forming electrode304bto produce low energy secondary electrons (312,314, and316indicated for examples).

Though (for simplicity) not shown, linear thermionic filaments302band302calso produce thermo-electrons that subsequently produce low energy secondary electrons. All the secondary electrons help ensure that the ionized cluster jet remains space charge neutral by providing low energy electrons that can be attracted into the positively ionized gas cluster jet as required to maintain space charge neutrality. Beam-forming electrodes304a,304b,and304care biased positively with respect to linear thermionic filaments302a,302b,and302cand electron-repeller electrodes306a,306b,and306care negatively biased with respect to linear thermionic filaments302a,302b,and302c.Insulators308a,308b,308c,308d,308e,and308felectrically insulate and support electrodes304a,304b,304c,306a,306b,and306c.For example, this self-neutralizing ionizer is effective and achieves over 1000 micro Amps argon GCIBs.

Alternatively, ionizers may use electron extraction from plasma to ionize clusters. The geometry of these ionizers is quite different from the three filament ionizer described here but the principles of operation and the ionizer control are very similar. For example, the ionizer design may be similar to the ionizer described in U.S. Pat. No. 7,173,252, entitled “IONIZER AND METHOD FOR GAS-CLUSTER ION-BEAM FORMATION”; the content of which is incorporated herein by reference in its entirety.

The gas cluster ionizer (122,FIGS. 1,2and3) may be configured to modify the beam energy distribution of GCIB128by altering the charge state of the GCIB128. For example, the charge state may be modified by adjusting an electron flux, an electron energy, or an electron energy distribution for electrons utilized in electron collision-induced ionization of gas clusters.

Referring now toFIG. 5, a high voltage power supply500is described according to an embodiment. The high voltage power supply500comprises a variable voltage supply510, and a self-biasing active load circuit520configured to shunt excess current.

The variable voltage supply510comprises a load terminal at a load potential and a reference terminal at a reference potential, wherein the variable voltage supply510is configured to bias an optical element530, such as a high voltage electrode, at the load potential. As illustrated inFIG. 5, the high voltage power supply500is configured to bias optical element530at a negative voltage relative to the reference potential. The self-biasing active load circuit520is connected between the load terminal and the reference terminal, and configured to sustain a variable voltage drop between the load potential and the reference potential while maintaining a substantially constant current. The self-biasing active load circuit520further comprises one or more active load elements525, wherein each active load element525may be designed to sustain up to a maximum voltage drop. For example, as illustrated inFIG. 5, the self-biasing active load circuit520comprises an array of active load elements525connected in series.

In accordance with the invention, a load circuit device comprising a self-biasing active load circuit520may be added to an existing power supply to form a high voltage power supply500, or the high voltage power supply500may be manufactured to initially include the self-biasing active load circuit520. Thus, embodiments of the invention are directed to both a load circuit device itself, and a high voltage power supply that includes a self-biasing active load circuit. For the load circuit device itself, the self-biasing active load circuit is configured to be connected between a first circuit node at a first potential and a second circuit node at a second potential, and is configured to sustain a variable voltage drop between said first potential and said second potential while maintaining a substantially constant current.

Referring now toFIG. 6, an electrical schematic is provided for an active load element600according to an embodiment. The active load element600comprises an insulated gate bipolar transistor610having a collector611coupled to a first terminal601of the active load element600, an emitter612coupled to a second terminal602of the active load element600, and a gate615. The insulated gate bipolar transistor610may comprise a model IRG4PH50U insulated gate bipolar transistor commercially available from International Rectifier (El Segundo, Calif.).

Additionally, the active load element600comprises a current sensing circuit620coupled to the gate615, and configured to sense a current through the insulated gate bipolar transistor610and to self-bias the gate615to a lower potential when the sensed current increases and self-bias the gate615to a higher potential when the sensed current decreases. The current sensing circuit620comprises a sensing device622, and a first resistor624and a second resistor626to serve as a current divider. The sensing device622may comprise a model 2N3904 NPN general purpose amplifier commercially available from Fairchild Semiconductor (South Portland, Me.). The first resistor624may include a 10 kΩ resistor, and the second resistor626may comprise a 1.5 kΩ resistor.

Additionally yet, the active load element600comprises a start-up circuit element630connected between the first terminal601and both the collector611and the gate615, and configured to initially charge the gate615once the variable voltage drop is applied across the active load circuit600at the first terminal601and the second terminal602. The start-up circuit element630may include a first resistor632and a second resistor634to serve as a current divider. The first resistor632may include a 10 MΩ resistor, and the second resistor634may comprise a 100 kΩ resistor.

Furthermore, the active load element600comprises a varistor640connected in parallel with the insulated gate bipolar transistor610, and configured to protect the insulated gate bipolar transistor610during initial transients of the active load circuit600once the variable voltage drop is applied across the first terminal601and the second terminal602. The varistor640may comprise a LA Series varistor commercially available from Littelfuse (Des Plaines, Ill.).

Further yet, the active load element600comprises a reverse current diode650connected in parallel with the insulated gate bipolar transistor610, and configured to protect the insulated gate bipolar transistor610in an event where a reverse current through the active load element600occurs.

Referring now toFIG. 7, resistance (mega-Ohms, MΩ) and current (milli-Amps, mA) are provided for an array of active load elements (e.g.,525,600) connected in series, wherein each active load element is designed according to the features described above to sustain a maximum voltage drop of about 1 kV. As shown inFIG. 7, the current is approximately constant across the 30 kV range of voltage.

Although only certain embodiments of this invention have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the embodiments without materially departing from the novel teachings and advantages of this invention. Accordingly, all such modifications are intended to be included within the scope of this invention.