Patent Grant
7819981
The present invention relates to a method and apparatus for cleaning the ion source region 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 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.
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. 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 ion source region. 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.
In addition to the operational difficulties caused by residues in the ion implanter, 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 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, 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.
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 cleaning of the ion source region using a gas-phase reactive halide composition, wherein the gas-phase reactive halide composition is contacted with the residue in the ion source region for sufficient time and under sufficient conditions to at least partially remove the residue from all components in the ion source region.
In one aspect, the present invention relates to a method of cleaning at least one component of a semiconductor manufacturing tool, said method comprising:
In another aspect, the present invention relates to a method of cleaning an ion source region of a semiconductor manufacturing tool, said method comprising:
In yet another aspect, the present invention relates to an apparatus for cleaning a vacuum chamber of an ion source region of a semiconductor manufacturing tool, said apparatus comprising:
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:
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 ion source region 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 the 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, 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, “ion source region” includes the vacuum chamber, the source arc chamber, the source insulators, the extraction electrodes, the suppression electrodes, the high voltage insulators and the source bushing.
The reactive halide gas may for example include a XeF2 vapor. XeF2 will sublime at room temperature, but may be heated using a heating means 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.
2XeF2(g)+Si(s)→2Xe(g)+SiF4(g) (1)
Importantly, the silicon/XeF2 reaction can occur without activation, i.e., plasma or thermal heating.
In this application, we disclose the use of XeF2 as an etchant for metallic boron. Although not wishing to be bound by theory, it is thought that the boron is etched according to the following reaction.
3XeF2(g)+2B(s)→3Xe(g)+2BF3(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) and (4).
5XeF2(g)+2As(s)→5Xe(g)+2AsF5(g) (3)
5XeF2(g)+2P(s)→5Xe(g)+2PF5(g) (4)
Similar to the silicon/XeF2 reaction, the reactions disclosed herein may occur with or without energetic activation. As used herein, the “residue” may comprise, consist essentially of or consist of silicon, boron, phosphorus, germanium or arsenic.
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, etc. As used herein, the term “at least partially remove” is defined as the removal of at least about 25%, more preferably at least about 50%, and most preferably at least about 75% of the residue to be removed.
Several novel ways to deliver the gas-phase reactive halide composition, e.g., a composition including XeF2, to the ion source region 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, SF6, C2F6, IF5 or IF7. It is further noted that the XeF2 composition may comprise, consist essentially of or consist of XeF2.
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.
Importantly, the process parameters are chosen to ensure that the reactive halide gas is essentially non-reactive with the ion source region 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 ion source region, 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 XeF2 composition disposed therein is directly or indirectly communicatively attached to the vacuum chamber or to the arc chamber, whereby the etchant container and the chambers to be cleaned has at least one valve disposed therebetween. 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 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.
3F2(g)+2B(s)→2BF3(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, 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 ion source region, 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.
The advantages of the present invention include, but are not limited to, selective cleaning of unwanted residue in the ion source region of an ion implantation system, the ability to clean the residue without using plasma-induced radicals thereby minimizing damage to the components of the ion source region, and effective cleaning at room temperature. Residue removal from the ion source region using the method 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 ion source region 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 turned off and the source isolation valve is closed prior to introduction of the etchant gas (or the etchant container in the direct introduction mode). Following residue removal, the ion source is restarted and 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 ion source region.
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. 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 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.
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.
| Number | Name | Date | Kind |
|---|---|---|---|
| 5144147 | Shiozaki et al. | Sep 1992 | A |
| 5370568 | Ivins et al. | Dec 1994 | A |
| 5413670 | Langan et al. | May 1995 | A |
| 5421957 | Carlson et al. | Jun 1995 | A |
| 5554845 | Russell | Sep 1996 | A |
| 5554854 | Blake | Sep 1996 | A |
| 5565038 | Ashley | Oct 1996 | A |
| 5620526 | Watatani et al. | Apr 1997 | A |
| 5633506 | Blake | May 1997 | A |
| 5767021 | Imai et al. | Jun 1998 | A |
| 5940724 | Warren | Aug 1999 | A |
| 5943594 | Bailey et al. | Aug 1999 | A |
| 5977552 | Foad | Nov 1999 | A |
| 5988187 | Trussell et al. | Nov 1999 | A |
| 6033973 | Takemura | Mar 2000 | A |
| 6135128 | Graf et al. | Oct 2000 | A |
| 6143191 | Baum et al. | Nov 2000 | A |
| 6221169 | Bernstein et al. | Apr 2001 | B1 |
| 6224785 | Wojtczak et al. | May 2001 | B1 |
| 6254792 | Van Buskirk et al. | Jul 2001 | B1 |
| 6259105 | Eddy et al. | Jul 2001 | B1 |
| 6267909 | Currie et al. | Jul 2001 | B1 |
| 6290864 | Patel et al. | Sep 2001 | B1 |
| 6306807 | Wojtczak et al. | Oct 2001 | B1 |
| 6322600 | Brewer et al. | Nov 2001 | B1 |
| 6322756 | Arno et al. | Nov 2001 | B1 |
| 6344432 | Wojtczak et al. | Feb 2002 | B1 |
| 6355933 | Tripsas et al. | Mar 2002 | B1 |
| 6379575 | Yin et al. | Apr 2002 | B1 |
| 6559462 | Carpenter et al. | May 2003 | B1 |
| 6566315 | Wojtczak et al. | May 2003 | B2 |
| 6620256 | Arno et al. | Sep 2003 | B1 |
| 6620258 | Arno et al. | Sep 2003 | B1 |
| 6699399 | Qian et al. | Mar 2004 | B1 |
| 6709610 | Van Buskirk et al. | Mar 2004 | B2 |
| 6756600 | Ng et al. | Jun 2004 | B2 |
| 6767836 | San et al. | Jul 2004 | B2 |
| 6812648 | Luten et al. | Nov 2004 | B2 |
| 6841141 | Arno et al. | Jan 2005 | B2 |
| 6843258 | Shang et al. | Jan 2005 | B2 |
| 6843858 | Rossman | Jan 2005 | B2 |
| 6846424 | Baum et al. | Jan 2005 | B2 |
| 6851432 | Naghshineh et al. | Feb 2005 | B2 |
| 6880561 | Goto et al. | Apr 2005 | B2 |
| 6887337 | Lebouitz et al. | May 2005 | B2 |
| 6902629 | Zheng et al. | Jun 2005 | B2 |
| 6921062 | Gregg et al. | Jul 2005 | B2 |
| 7037376 | Harvey et al. | May 2006 | B2 |
| 7037813 | Collins et al. | May 2006 | B2 |
| 7080545 | Dimeo, Jr. et al. | Jul 2006 | B2 |
| 7168436 | Mouri et al. | Jan 2007 | B2 |
| 7201174 | Fukiage | Apr 2007 | B2 |
| 7201807 | Yim et al. | Apr 2007 | B2 |
| 7228724 | Chen et al. | Jun 2007 | B2 |
| 7288491 | Collins et al. | Oct 2007 | B2 |
| 7296458 | Dimeo, Jr. et al. | Nov 2007 | B2 |
| 7296460 | Dimeo, Jr. et al. | Nov 2007 | B2 |
| 7300038 | Gregg et al. | Nov 2007 | B2 |
| 7487956 | Gregg et al. | Feb 2009 | B2 |
| 7556244 | Gregg et al. | Jul 2009 | B2 |
| 20020011463 | Buskirk et al. | Jan 2002 | A1 |
| 20020033229 | Lebouitz et al. | Mar 2002 | A1 |
| 20020083961 | Tsuga | Jul 2002 | A1 |
| 20030098038 | Siegele et al. | May 2003 | A1 |
| 20030183244 | Rossman | Oct 2003 | A1 |
| 20040006249 | Hoshino et al. | Jan 2004 | A1 |
| 20040108296 | Kanayama et al. | Jun 2004 | A1 |
| 20050016838 | Murata et al. | Jan 2005 | A1 |
| 20050230046 | Lebouitz et al. | Oct 2005 | A1 |
| 20050252529 | Ridgeway et al. | Nov 2005 | A1 |
| 20050260354 | Singh et al. | Nov 2005 | A1 |
| 20060005856 | Sun et al. | Jan 2006 | A1 |
| 20060019039 | Hanawa et al. | Jan 2006 | A1 |
| 20060086376 | Dimeo, Jr. et al. | Apr 2006 | A1 |
| 20060169915 | Olson et al. | Aug 2006 | A1 |
| 20060272775 | Horsky et al. | Dec 2006 | A1 |
| 20060272776 | Horsky et al. | Dec 2006 | A1 |
| 20070108395 | Horsky et al. | May 2007 | A1 |
| 20070117396 | Wu et al. | May 2007 | A1 |
| 20070210260 | Horsky et al. | Sep 2007 | A1 |
| 20070241689 | Horsky et al. | Oct 2007 | A1 |
| 20070259111 | Singh et al. | Nov 2007 | A1 |
| 20080121811 | Horsky et al. | May 2008 | A1 |
| 20080142039 | Chen et al. | Jun 2008 | A1 |
| 20080191153 | Marganski et al. | Aug 2008 | A1 |
| 20080223409 | Horsky et al. | Sep 2008 | A1 |
| 20090095713 | Dimeo, Jr. et al. | Apr 2009 | A1 |
| 20100022095 | Wu et al. | Jan 2010 | A1 |
| Number | Date | Country |
|---|---|---|
| 0 945 892 | Sep 1999 | EP |
| 2412488 | Sep 2005 | GB |
| 08-055804 | Feb 1996 | JP |
| 2000222724 | Aug 2000 | JP |
| WO 0250883 | Jun 2002 | WO |
| WO 2005059942 | Jun 2005 | WO |
| WO 2005072252 | Aug 2005 | WO |
| 2009102762 | Aug 2009 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 20060086376 A1 | Apr 2006 | US |
