Patent Application
20090095713
The present invention relates to a method and apparatus for cleaning the vacuum chamber and beamline of an ion implantation system used in the fabrication of a microelectronic device. In addition, the present invention relates to a method for the in situ cleaning of cryogenic pumps to remove purge resistant effluent material.
Ion implantation is used in integrated circuit fabrication to accurately introduce controlled amounts of dopant impurities into semiconductor wafers and is a crucial process in microelectronic/semiconductor manufacturing. In such implantation systems, an ion source ionizes a desired dopant element gas and the ions are extracted from the source in the form of an ion beam of desired energy. Extraction is achieved by applying a high voltage across suitably shaped extraction electrodes, which incorporate apertures for passage of the extracted beam. The ion beam is then directed at the surface of the workpiece, such as a semiconductor wafer, in order to implant the workpiece with the dopant element. The ions of the beam penetrate the surface of the workpiece to form a region of desired conductivity.
Several types of ion sources are commonly used in commercial ion implantation systems, including the Freeman and Bernas types using thermoelectrodes and powered by an electric arc, a microwave type using a magnetron, indirectly heated cathode sources, and RF plasma sources, all of which typically operate in a vacuum. The ion source generates ions by introducing electrons into a vacuum chamber filled with the dopant gas (commonly referred to as the “feedstock gas”). Collisions of the electrons with dopant atoms and molecules in the gas results in the creation of an ionized plasma consisting of positive and negative dopant ions. An extraction electrode with a negative or positive bias will respectively allow the positive or negative ions to pass through the aperture and out of the ion source as a collimated ion beam, which is accelerated towards the workpiece. Feedstock gases include, but are not limited to, BF3, B10H14, B12H22, PH3, AsH3, PF5, AsF5, H2Se, N2, Ar, GeF4, SiF4, O2, H2, and GeH4.
Presently, there are upwards of 10-15 implantation steps in the fabrication of state of the art devices. Increasing wafer sizes, decreasing critical dimensions, and growing circuit complexity are placing greater demands on ion implant tools, with respect to better process control, the deliverance of high beam currents at low energies, and a decrease in the mean time between failures (MTBF).
The parts of the ion implanter tool that require the most maintenance include: the ion source, which must be serviced after approximately 100 hours of operation, depending on its operating conditions; the extraction electrodes and the high voltage insulator, which usually require cleaning after a few hundred hours of operation; and the cryogenic pump
In the ideal case, all feedstock molecules would be ionized and extracted, but in reality a certain amount of feedstock decomposition occurs, which results in the deposition on and contamination of the vacuum chamber and beamline. For example, boron residue readily deposits on surfaces in the ion source region. The residue can form on low voltage insulators in the ion source, causing electrical short circuits, which can interrupt the arc required to produce thermionic electrons. This phenomenon is generally known as “source glitching,” and it is a major contributor to ion beam instability, and may eventually cause premature failure of the source. The residue also forms on the high voltage components of the ion implanter, such as the source insulator or the surfaces of the extraction electrodes, causing energetic high voltage sparking. Such sparks are another contributor to beam instability, and the energy released by these sparks can damage sensitive electronic components, leading to increased equipment failures and poor MTBF. While the ion source life expectancy for ion implantation systems using non halide-containing source materials is generally around 168 hours, with halide-containing materials such as GeF4, the ion source life can be as low as 10 hours due to the detrimental effects of residue deposition on source operation.
Presently, vacuum chambers are cleaned using gases such as NF3 and other nitrogen-containing gases as well as oxidizing species. For example, U.S. Pat. No. 6,135,128 in the name of Graf et al. relates to the cleaning of an ion source using NF3 gas. However, NF3 cleaning gas requires an energetic source to release atomic fluorine, which upon release tends to be too aggressive, attacking every component in the ion source region. In addition, the required energetic source, e.g., plasma, increases the cost of ownership (COO). U.S. Pat. No. 6,355,933 in the name of Tripsas et al. relates to the introduction of oxygenated gases to the ion source for reacting with deposit forming species. Although oxidizing gases prove useful for the removal of carbonaceous species, it is disadvantageous if any component of the vacuum chamber or beamline is fabricated from carbon/graphitic material. Moreover, the introduction of an oxidizing species to the vacuum chamber may promote the formation of a surface oxide layer, or “rust,” on most metallic components, said oxide layer potentially resulting in particle formation, entrapment of gas molecules, shorts and premature filament failure.
Cryogenic vacuum pumps (cryopumps) are widely used in high vacuum applications. Cryopumps are based on the principle of removing gases from a vacuum chamber by cryocondensing and/or cryosorbing the gases on cold surfaces inside the cryopump. In cryocondensation, gas molecules are condensed on previously condensed gas molecules, and thick layers of condensation can be formed, thereby, pumping large quantities of gas. Cryosorption is commonly used to pump gases that are difficult to condense at the normal operating temperatures of the cryopump. In this case, a sorbent material, such as activated charcoal, is attached to the coldest surface in the cryopump, typically a second stage of a cryoarray. Because the binding energy between a gas particle and the adsorbing surface is greater than the binding energy between the gas particles themselves, the gas particles that cannot be condensed are removed from the vacuum system by adhering to the sorbent material.
Presently, ion implant cryopumps use inert gas, e.g., N2, to purge away the cryogenically captured gas molecules and process residues accumulated during the process cycle. The inert gas purge assists in bringing the cryopump to ambient temperature, and adequately purges the evolving, previously cryosorbed gas molecules, including water vapor, hydrogen and organic compounds. The inert gas purge, however does not remove all the process effluents, hereinafter referred to as accumulated process effluents, some of which underwent reaction to form non-volatile species during the warm-up of the cryopump and/or adhered to the metallic components of the pump. Presently, the only method of removing the accumulated process effluents is through cryopump maintenance.
There are two types of cryopump maintenance evolutions, a vacuum side rebuild, and displacer side rebuild. Both forms of maintenance involve removal of the cryopump from the implanter. The vacuum side rebuild requires the pump be disassembled, cleaned, reassembled, and functionally tested and is recommended by the OEM on an annual basis. The displacer side maintenance involves disassembly, cleaning, reassembly, and functional testing of the displacer (gas flow cooling, actuating mechanism) of the cryopump and is recommended by the OEM on a tri-annual basis.
In addition to the operational difficulties caused by residues in the ion implanter and the cryopump, there are also significant personnel safety issues due to the emission of toxic or corrosive vapors when components are removed for cleaning. The safety issues arise wherever residues are present, but are of particular concern in the ion source region of the vacuum chamber because the ion source is the most frequently maintained component of the ion implanter. To minimize down time, contaminated ion sources are often removed from the implanter at temperatures significantly above room temperature, which increases the emission of vapors and exacerbates the safety issue.
It would therefore be a significant advance in the art of ion implantation to provide an in situ cleaning process for the effective, selective removal of unwanted residues deposited throughout the implanter, particularly in the ion source region of the vacuum chamber, during implantation. Such in situ cleaning would enhance personnel safety and contribute to stable, uninterrupted operation of the implantation equipment.
An alternative to in situ cleaning is to provide a separate cleaning station whereby contaminated components that have been removed from the implanter can be cleaned safely without any mechanical abrasion which might damage delicate components such as graphite electrodes. It would therefore also be a significant advance in the art of ion implantation to provide an off-line cleaning station that could be used to selectively and non-destructively clean components following removal from the implant system.
In addition, it would be a significant advance in the art to provide an in situ cleaning process for the removal of accumulated process effluents from the cryopump thereby reducing or eliminating the frequency of cryopump maintenance.
The present invention relates generally to a method and apparatus for cleaning internal components of an ion implantation tool. Specifically, the present invention relates to the in situ removal of residue from the vacuum chamber and components contained therein by contacting the vacuum chamber and/or components with a gas-phase reactive halide composition, e.g., XeF2, for sufficient time and under sufficient conditions to at least partially remove the residue from the components, and to do so in such a manner that residue is removed selectively with respect to the materials from which the components of the ion implanter are constructed.
In one aspect, the invention relates to a method of cleaning a vacuum chamber of a semiconductor manufacturing tool, at least one component, or combination thereof, said method comprising:
In another aspect, the present invention relates to a method of cleaning a vacuum chamber of a semiconductor manufacturing tool, at least one internal component, or combination thereof, said method comprising:
In yet another aspect, the present invention relates to an apparatus for cleaning a vacuum chamber of a semiconductor manufacturing tool, at least one internal component, or combination thereof, said apparatus comprising:
In a further aspect, the present invention relates to a method of cleaning a vacuum chamber of a semiconductor manufacturing tool, at least one component, or combination thereof, said method comprising:
In yet another aspect, the invention relates to a method of cleaning accumulated process effluent from the interior of a cryopump, said method comprising purging the cryopump with at least two purge gases, said purge gases including nitrogen and at least one reactive gas selected from the group consisting of oxygen, ozone, nitrogen oxides, species that generate oxygen radicals in situ, and combinations thereof, wherein said method is characterized by at least one of the following purge process sequences (I), (II), and (III):
A further aspect of the present invention relates to a method of ex situ cleaning at least one component of a semiconductor manufacturing tool, said method comprising:
Yet another aspect of the invention relates to improved methods of manufacturing microelectronic devices such as semiconductors using the inventive methods and systems described herein.
Other aspects, features and embodiments of the invention will be more fully apparent from the ensuing disclosure and appended claims.
The present invention relates to a method and apparatus for cleaning the vacuum chamber and/or beamline of an ion implantation system used in the fabrication of a microelectronic device. Specifically, the present invention relates to the in situ removal of residue from a vacuum chamber of the ion implanter and components contained therein by contacting the vacuum chamber and/or components with a gas-phase reactive halide composition, e.g., XeF2, NF3, F2, XeF6, XeF4, SF6, C2F6, IF5 or IF7, for sufficient time and under sufficient conditions to at least partially remove the residue from the components, and to do so in such a manner that residue is removed selectively with respect to the materials from which the components of the ion implanter are constructed.
As used herein, “vacuum chamber” includes the source vacuum chamber, and the ion source region including the source arc chamber, the source insulators, the extraction electrodes, the suppression electrodes, the high voltage insulators, source bushing and the source turbomolecular pump.
As used herein, “beamline” includes the ion source region and other components inside the vacuum system, including the beamline vacuum chamber, the accelerator column, interior ion optical components such as electrostatic steerers and lenses, the beamline turbomolecular pumps and the vacuum exhaust lines.
As used herein, “microelectronic device” corresponds to semiconductor substrates, flat panel displays, and microelectromechanical systems (MEMS), manufactured for use in microelectronic, integrated circuit, or computer chip applications. It is to be understood that the term “microelectronic device” is not meant to be limiting in any way and includes any substrate that will eventually become a microelectronic device or microelectronic assembly.
As used herein, “residue” corresponds to the unused portion of the implant gas (e.g., some portion of BF3, PH3, AsH3, GeF4, etc.), carrier gas residue (e.g., fluorine, chlorine, oxygen, nitrogen, argon, etc.), as well as chamber material that is sputtered/deposited (e.g., tungsten, molybdenum and/or aluminum-containing species). For example, the residue may include metals such as B, As, P, Ge, W, Mo and/or Al, compounds between the B, As, P and/or Ge species and the W, Mo and/or Al species, as well as permutations of the materials of construction. The residue may be conducting or non-conducting. Preferably, the residue is devoid of non-dopant components of the implant gas.
The reactive halide gas may for example include a XeF2 vapor. XeF2 will sublime at room temperature, but may be heated using a heater to increase the rate of sublimation. XeF2 is known to be an effective silicon etchant and has been used as a silicon selective etchant in Micro Electro Mechanical System (MEMS) device processing because it is extremely selective to SiO2 and other dielectric materials. Specifically, XeF2 reacts with silicon according to the following reaction.
2 XeF2 (g)+Si (s)→2 Xe (g)+SiF4 (g) (1)
Importantly, the silicon/XeF2 reaction can occur without activation, i.e., plasma or thermal heating.
In this application, the use of XeF2 as an etchant for metallic boron is disclosed. Although not wishing to be bound by theory, it is thought that the boron is etched according to the following reaction.
3 XeF2 (g)+2 B (s)→3 Xe (g)+2 BF3 (g) (2)
The use of XeF2 as an etchant for arsenic, phosphorus and germanium has not been reported to the best of our knowledge; however, XeF2 may prove to be an effective etchant for these materials as well according to the following reactions (3)-(5).
5 XeF2 (g)+2 As (s)→5 Xe (g)+2 AsF5 (g) (3)
5 XeF2 (g)+2 P (s)→5 Xe (g)+2 PF5 (g) (4)
2 XeF2 (g)+Ge (s)→2 Xe (g)+GeF4 (g) (5)
Similar to the silicon/XeF2 reaction, the reactions disclosed herein may occur with or without energetic activation.
Importantly, the method and apparatus taught herein is used to at least partially remove the residue from the components of the ion implanter, and to do so in such a manner that residue is removed selectively with respect to the materials from which the components of the ion implanter are constructed, e.g., aluminum, tungsten, molybdenum, etc.. As used herein, the term “at least partially remove” is defined as the removal of at least about 25 wt. %, more preferably at least about 50 wt. %, more preferably at least 75 wt. %, and most preferably at least about 90 wt. % of the residue to be removed. The extent of residue removal and/or ion implanter component removal may be determined using analytical techniques well known in the art including, but not limited to, temperature-programmed infrared spectroscopy (TPIR), Fourier Transform Infrared Spectroscopy (FTIR), electron paramagnetic spectroscopy (EPM), residual gas analysis (RGA), mass spectrometry, and combinations thereof.
Several novel ways to deliver the gas-phase reactive halide composition, e.g., a composition including XeF2, to the vacuum chamber and the beamline for in situ cleaning therein are proposed, including a stagnant mode, a continuous mode, and a direct introduction mode. Although reference is made hereinafter to a XeF2 composition, other reactive halide compositions may be used including, but not limited to, XeF6, XeF4, SF6, C2F6, IF5 or IF7. It is further noted that the XeF2 or alternative reactive halide compositions may comprise, consist essentially of or consist of XeF2 or alternative reactive halides. Preferably, the gas-phase reactive halide composition is devoid of or substantially free of an oxidizing species and a nitrogen-containing species, wherein the nitrogen-containing species comprises at least one additional element selected from the group consisting of O, F, and Br, unless indicated otherwise. Alternatively, the gas-phase reactive halide composition may include reducing species such as hydrogen and/or carbon monoxide.
In addition, it is noted that the apparatuses described herein may include improved low-pressure dopant gas supply arrangements which permit dopant gases to be delivered to the ion source unit at ground potential, as described in U.S. Provisional Patent Application No. 60/712,648 in the name of Robert Kaim et al. and entitled “Delivery of Low Pressure Dopant Gas to a High Voltage Ion Source,” which is hereby incorporated by reference herein in the entirety.
In the stagnant mode, an etchant container with the XeF2 composition disposed therein is communicatively attached to the chamber of the ion implanter to be cleaned, wherein the etchant container and the chamber to be cleaned have a valve disposed therebetween. During cleaning, the valve may be manually or remotely opened whereby the XeF2 vapor is permitted to fill the chamber to be cleaned until a pre-determined pressure is attained. The etchant container may be moderately heated to increase the sublimation rate and/or the sublimation pressure.
In a more preferred embodiment, the cleaning apparatus includes a separate holding chamber of sufficient volume positioned between the etchant container and vacuum chamber. The XeF2 may be flowed first into the holding chamber and stored therein until a pre-determined pressure threshold is reached. Such holding chamber serves to allow immediate gas flow to the vacuum chamber on demand and to shorten the “waiting-period” associated with sublimation. The walls of the holding chamber may be heated to permit higher pressure storage while avoiding condensation of XeF2 on interior surfaces of the chamber. The holding chamber may further comprise flow-regulating devices, such as a mass flow controller, to achieve reproducible delivery of XeF2 into the vacuum chamber.
Once the desired pressure in the vacuum chamber has been attained, the vacuum chamber is sealed and the XeF2 permitted to react for sufficient time and under sufficient conditions to at least partially remove the residue from the vacuum chamber and the components contained therein. The vacuum chamber can then be evacuated and the cleaning process repeated as needed. The evacuated gas mixture may be further directed to abatement units including, but not limited to, chemical and/or physical adsorption beds, incinerators, wet scrubbers, or a combination thereof.
The internal pressure, time, and number of repeat cleanings may be readily determined by those of ordinary skill in the art. The nature and extent of the cleaning of the residue may be empirically determined while varying the time and/or contacting conditions (such as temperature, pressure, concentration and partial pressure) of the XeF2 composition to identify the process conditions producing a desired residue removal result. For example, the pressure of the XeF2 composition in the vacuum chamber may be about 0.3 Torr to about 4.0 Torr, preferably about 0.3 Torr to about 0.7 Torr, and the length of cleaning about 1 to about 4 minutes, which may be repeated about two (2) to about ten (10) times. Preferably, the pressure of the XeF2 is about 0.35 Torr and the length of cleaning about 1 minute. Importantly, the pressure in the vacuum chamber during cleaning should be carefully monitored as the pressure will gradually increase as the cleaning reaction proceeds and should plateau when the reaction has run its course.
A residual gas analyzer may be used to measure the concentration of XeF2 and other reaction byproducts, which may also be useful for monitoring the progress of the cleaning process. A residual gas analyzer (RGA), as shown schematically in
Preferably, the XeF2 gas is generated without energetic activation, although activation is contemplated herein. Thus, effective cleaning can be performed at room temperature, although cleaning is contemplated at temperature in a range of about 0° C. to about 1000° C. depending on the circumstances. Preferably, in the stagnant mode, the temperature is in a range from about 0° C. to about 50° C.
Importantly, the process parameters are chosen to ensure that the reactive halide gas is essentially non-reactive with the vacuum chamber and the beamline components material of construction. As used herein, “essentially non-reactive” corresponds to less than about 5% of the total reactive halide gas reacts with the components of the vacuum chamber and the beamline, preferably less than about 2%, most preferably less than about 1%.
An example of the stagnant mode for cleaning an ion source region 10 is shown in
In the continuous mode, an etchant container with the cleaning gas composition disposed therein is directly or indirectly communicatively attached to the vacuum chamber or to the arc chamber, and a vacuum pump is withdrawing the cleaning gas and reaction products so that there is a continuous flow of gases through the vacuum chamber or the arc chamber. An inert carrier gas may be arranged to flow continuously over the XeF2 composition in the etchant container to deliver a steady stream of XeF2 to the chamber to be cleaned. The flow rate of the carrier gas, temperature of the etchant container, and cleaning time are experimental parameters readily determined by those skilled in the art. Similar to the stagnant mode, a holding chamber may be situated between the etchant container and the chamber to be cleaned.
An example of the continuous mode, wherein the etchant container is communicatively connected to the arc chamber, is shown in
In addition,
In yet another embodiment of the continuous mode, the etchant gas and the dopant gas are introduced simultaneously to the arc chamber permitting a continuous ion-implantation and cleaning process. The amount of cleaning gas and the process conditions must be tailored to insure the desired dopant species are not compromised, as readily determined by one skilled in the art.
In a still further embodiment of the continuous mode, cleaning may be effectuated by alternating the continuous flow of the dopant gas (i.e., BF3 or other dopant gases during ion implantation) and the continuous flow of the cleaning gas to the vacuum chamber or the arc chamber, with or without an intermediate evacuation step. The dopant gas and the cleaning gas may be alternating between one and five times, as readily determined by one skilled in the art. This alternating dopant gas/cleaning gas methodology is advantageous relative to the current industry practice of alternating dopant species, because the cleaning schedule may be decoupled from and interleaved with the processing schedule, and more frequent cleaning may occur.
In the direct introduction mode, an etchant container with pre-measured amounts of XeF2 composition, e.g., in the form of pellets, is introduced into the sealed vacuum chamber 100. The XeF2 completely sublimates in the vacuum chamber and the XeF2 is permitted to react for sufficient time and under sufficient conditions to at least partially remove the residue from the ion source region components. The amount of etchant and the time required for cleaning are readily determined by those skilled in the art. Methods for mechanical dispensing, i.e., etchant containers, are readily engineered by those skilled in the art. Following at least partial removal of the residue from the interior of the chamber to be cleaned, valve 92 is opened and the gases are evacuated using pump 96 via outlet line 94. Direct introduction cleaning may be repeated as necessary.
In another embodiment of the invention, the reactive halide gas may for example comprise a nitrogen trifluoride (NF3) vapor. NF3 is used in the semiconductor industry as a fluorine source for plasma etching, e.g., in situ chamber cleaning of CVD reactors. Additional applications include etching of polysilicon, silicon nitride, tungsten silicide and tungsten films. Specifically, NF3 dissociates into reactive halide species in the plasma, such as fluorine radicals and/or fluoride ions, said reactive halide species subsequently reacting with the residue to be removed. For example, if the residue includes boron, cleaning occurs according to the following reaction.
3 F2 (g)+2 B (s)→2 BF3 (g) (5)
Several novel ways to deliver the NF3 compound to the ion source region for in situ cleaning therein are proposed, including a direct dissociative plasma configuration.
In the direct dissociative plasma configuration, a NF3 source 222 is communicatively connected to the arc chamber 210, with a valve situated therebetween 220 (see
Additional cleaning gases contemplated for introduction using the direct dissociative plasma introduction mode, in addition to NF3, include XeF2, XeF6, XeF4, IF5, IF7, SF6 and C2F6.
In another embodiment of the invention, the reactive halide gas is fluorine, for example as delivered from Advanced Technology Materials VAC cylinder (Danbury, Conn., USA). Fluorine is an extremely corrosive gas and can be used with or without thermal or electrical activation. Without activation, the fluorine gas can be admitted directly to the vacuum chamber, wherein the gas is permitted to spontaneously react for sufficient time and under sufficient conditions to at least partially remove the residue. If additional activation is required, components may be heated or left at an elevated temperature and the gas permitted to react for sufficient time to at least partially remove the residue. In the alternative, a plasma may be generated within the arc chamber (as described previously) to further induce fluorine activation.
The embodiments described herein may be added directly to newly manufactured ion implantation tools or in the alternative, implanters already in use may be easily retrofitted with the cleaning systems described herein.
In a further embodiment, the etchant gas may be blended with the implanting species, e.g., boron trifluoride, so that etching and implanting may occur simultaneously, which is cost effective in terms of minimization of down time and elimination of additional expensive delivery systems. Thus, another embodiment of the invention relates to a method of implanting an implant species while simultaneously etching or cleaning the vacuum chamber and/or beamline, preferably using a blend of implanting species and an etchant gas.
The advantages of the present invention include, but are not limited to, selective cleaning of unwanted residue in the vacuum chamber and beamline of an ion implantation system, the ability to clean the residue without using plasma-induced radicals thereby minimizing damage to the components of the vacuum chamber and beamline, and effective cleaning at room temperature. Residue removal from the vacuum chamber and beamline using the methods introduced herein reduces source glitching and extraction arcing, thereby contributing to more stable operation of the ion implanter. Further, the ion source lifetime and MTBF are increased, with a concomitant decrease in preventative maintenance costs and time.
In situ cleaning of the vacuum chamber and beamline should be performed about 1 to 2 times per week, although the number of cleanings may be more or less often depending on how often the ion implanter is used. Typically, the length of the entire cleaning operation is about 1 hour, although the cleaning time may be more or less.
To perform any of the cleaning operations described herein, the ion source is left on or turned off (as indicated in the foregoing processes) and the source isolation valve is closed (for stagnant or continuous processes) or open (for continuous processes) prior to introduction of the etchant gas (or the etchant container in the direct introduction mode). Following residue removal, normal ion implanter operations may be resumed.
In yet another embodiment of the invention, off-line (ex situ) cleaning of the components of the ion source region using a vapor phase is disclosed. In this embodiment, components from any part of the ion implanter which are delicate (e.g., graphite-containing components) may be cleaned off-line thereby eliminating exposure to conventional off-line cleaners, such as harsh abrasives or liquids. Off-line cleaning using a vapor phase material is an advance in the art because abrasives can damage the delicate components and liquids which enter the pores of the delicate components during cleaning must be pumped out of the pores during pump down of the vacuum chamber.
In this embodiment, the ion source or any other power supplies are turned off, relevant isolation valves are closed, and the ion source or other vacuum chamber is vented to atmospheric pressure. Preferably, the ion source region is allowed to cool to room temperature before disengagement of the components to be cleaned from the ion source region. The components are removed from the implanter and positioned in a separate, off-line vacuum chamber with a simple pumping system and valves. Alternatively, the components may be positioned in some other high pressure vessel such as a supercritical fluid vessel altered for said ex situ cleaning. Etchant gas, for example XeF2, is introduced into the off-line vacuum chamber according to the teachings herein, for sufficient time and under sufficient conditions to at least partially remove the residue from the components. Following each cleaning phase, the toxic by-products are pumped away, optionally to abatement units, as previously described, to properly dispose of the toxic vapors. Preferably, the off-line vacuum chamber is a stand alone unit that is able to service numerous ion implanters, e.g., upwards of 10-12, in the fab.
In yet another embodiment, the present invention relates to the in situ cleaning of the cryogenic pump.
As used herein, “accumulated process effluents” correspond to those species that are not removable during the conventional cryopump purge process using nitrogen as the purge gas. For example, the accumulated process effluents may be species that underwent a chemical change while the cryopump was warmed to ambient temperature. Alternatively, the accumulated process effluents may correspond to species that have adhered to the metallic parts of the cryopump.
Nitrogen is the conventional gas of choice during the cryopump purging process whereby the temperature of the cryopump is raised from 10-14K to ambient temperature and the previously cryosorbed species are carried away within the purge gas to the exhaust system. In the present invention, a portion of the nitrogen purge gas may be replaced by a reactive gas to remove or inhibit accumulated process effluent buildup in the cryopump. Reactive gases contemplated herein include, but are not limited to, oxygen, ozone, nitrogen oxides, other species that generate oxygen radicals, and combinations thereof.
The purge gas(es) may be delivered to the cryopump using a process selected from the group consisting of: (i) 100% (“essentially pure”) nitrogen for x minutes followed by 100% (“essentially pure”) reactive gas for y minutes repeated n times, wherein n may be any integer between 1 and 10 and [n×(x+y)] equals the cumulative length of this purging process; (ii) 100% (“essentially pure”) nitrogen at time zero and 100% (“essentially pure”) reactive gas at the end of this cryopump purging process, whereby the percentage of nitrogen decreases and the percentage of reactive gas increases continuously or in steps (equal or non-equal in dimension) temporally from time zero to the end of this cycle purge; (iii) 100% (“essentially pure”) nitrogen at time zero and less than 100% reactive gas at the end of this cryopump purging process, whereby the percentage of nitrogen decreases and the percentage of reactive gas increases continuously or in steps (equal or non-equal in dimension) temporally from time zero to the end of this cycle purge; (iv) (100−z) % nitrogen and z% reactive gas continuously throughout the purging process; and (v) variations and combinations thereof. Preferably, “x” is in a range from about 10 minutes to about 120 minutes, preferably about 10 minutes to about 20 minutes, “y” is in a range from about 10 minutes to about 120 minutes, preferably about 10 minutes to about 20 minutes, and “z” is in a range from about 0.01% to about 99.99%.
As defined herein, “essentially pure” corresponds a gas containing less than 5 vol. % contaminating species, preferably less than 2 vol. %, more preferably less than 1 vol. %, and most preferably less than 0.5 vol. %. It is to be understood by one skilled in the art that a contaminating species may include reactive as well as non-reactive gas species.
The foregoing purge gas(es) delivery options ((i)-(v)) may be applied during warm-up of the cryopump to ambient temperature, following achievement of ambient temperature (i.e., the cryopump temperature was increased using 100% (“essentially pure”) nitrogen followed by the application of one or more of the foregoing purge gas delivery options) or a combination of both. Accordingly, for purposes of the present invention, time zero corresponds to the moment the pump is no longer cryogenically cooled, or the moment when the pump achieves ambient temperature, or some other moment when the accumulated process effluent can be most efficiently removed, as readily determined by one skilled in the art for the desired in situ cleaning.
Importantly, substitution of a reactive purge gas for at least a portion of the nitrogen purge gas will reduce buildup of the accumulated process effluent in the cryopump, which has the advantage of reducing or eliminating the frequency of cryopump maintenance and concomitantly decreases the tool downtime and the cost of ownership. In addition, the acidity level in the cold head of the cryopump may be decreased as a result of the use of the reactive gas(es).
The features and advantages of the invention are more fully shown by the illustrative examples discussed below.
Test samples were prepared using electron beam deposition of aluminum, boron, tungsten and silicon on glass microscope slides. The aluminum was used as a bottom layer barrier on the glass slide. Some samples were capped with a protective silicon layer while others were left uncapped and allowed to oxidize. The test samples were sequentially placed into an ex situ XeF2 reactor and etched for 16 one-minute pulse-etch cycles at a pressure of 300-400 mTorr at room temperature.
While the invention has been described herein with reference to various specific embodiments, it will be appreciated that the invention is not thus limited, and extends to and encompasses various other modifications and embodiments, as will be appreciated by those ordinarily skilled in the art. Accordingly, the invention is intended to be broadly construed and interpreted, in accordance with the ensuing claims.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/US2005/038102 | 10/21/2005 | WO | 00 | 3/13/2008 |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 10973673 | Oct 2004 | US |
| Child | 11577852 | US |
