Patent Application
20130305989
The present invention relates generally to ion implantation systems, and more specifically to improved systems and methods for reducing residue buildup in such ion implantation systems.
In the manufacture of semiconductor devices and other products, ion implantation systems are used to implant dopant elements into work pieces (e.g., semiconductor wafers, display panels, glass substrates). These ion implantation systems are typically referred to as “ion implanters”.
Ion dose and ion energy are two variables commonly used to characterize an ion implantation carried out by an ion implanter. The ion dose is associated with the quantity of ions implanted into a region of a work piece, and is usually expressed as a number of dopant atoms per unit area of work piece material (e.g., 1018 boron atoms/cm2). Ion energy is associated with a depth at which the ions are implanted beneath a surface of a work piece. For example, formation of relatively-deep junctions for retrograde wells in semiconductor devices typically requires ion energies of up to a few million electron volts (MeV), while formation of relatively-shallow junctions may demand energies below 1 thousand electron volts (1 keV).
Historically, many ion implantations have been carried out using small molecules or so-called “monatomic species”. However, in recent years, substantial improvements in throughput have been demonstrated by using large molecules, such as molecular boron (e.g., decaborane (B10H14), octadecaborane (B18H22)) or molecular carbon (e.g., C7H7, C16H14), for example. The use of large molecules provides significant advantages from a throughput perspective, because it allows each wafer to receive a given dose in a shorter time (relative to beams generated from monatomic species).
However, one potential drawback of using these large molecules is that they tend to dissociate after being ionized. This dissociation causes at least some dissociated molecules to “stick” to the inside of the ion implanter (e.g., ion source), causing residue buildup. After some time (e.g., 10-20 hours), the residue can impede operation of the ion source and reduce beam current.
Existing ion implanters attempt to remove the residue by purely physical means or by generating a plasma using NF3 gas. However, both of these previous approaches have significant drawbacks. For example, purely physical means, such as bead blasting, typically requires a residue-coated component to be removed from the ion implantation apparatus in order for the component to be cleaned, which leads to machine downtime and potentially lost throughput for the fabrication facility. The use of plasma based on NF3 gas is expensive because NF3 requires special handling. In addition, in spite of the expense, NF3 is still unable to remove several types of residues (e.g., graphitic residues due to plasma sources using carbon) and is unfriendly to the environment in many respects.
Accordingly, a need exists for a method of cleaning residue from the ion source in order to meet the needs of the ion implantation industry.
The following presents a simplified summary of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not an extensive overview of the invention, and is neither intended to identify key or critical elements of the invention nor to delineate the scope of the invention. Rather, the purpose of the summary is to present some concepts of the invention in a simplified form as a prelude to the more detailed description that is presented later.
Some techniques disclosed herein facilitate cleaning of residue from a molecular beam component. For example, in an exemplary method, a molecular beam is provided along a beam path, causing residue build up on the molecular beam component. To reduce the residue, the molecular beam component is exposed to a plasma comprising fluorine. In some methods, different kinds of plasma can be selectively generated to clean different kinds of residue on the molecular beam component.
In an exemplary system, a reactive gas delivery system includes a flow controller that supplies various types of gas to one or more plasma chambers. The flow controller selectively delivers some of the gases, such as boron compounds and carbon compounds, to generate plasma discharges that are subsequently used to achieve ion implantation into one or more work pieces. The boron and/or carbon compounds can cause different types of residues to buildup in the system. Accordingly, the flow controller also can selectively deliver different types of cleaning gases to one or more plasma chambers to generate different plasma discharges to selectively remove the different types of residue from the system.
The following description and annexed drawings set forth in detail certain illustrative aspects and implementations of the invention. These are indicative of but a few of the various ways in which the principles of the invention may be employed.
The present invention is directed generally towards residue removal techniques that are applicable to ion implantation systems. More particularly, the system and methods of the present invention provide an efficient way to reduce residue generated by large molecular species, such as, for example: carborane; decaborane; octadecaborane and icosaboranes; hydrocarbons such as C7H7 and C10H14, as well as standard ionization gases for the production of small molecular ion implant species (e.g., BF2, and monatomic species), such as boron trifluoride, phosphine and arsine. It will be understood that the foregoing list of ion implantation species is provided for illustrative purposes only, and shall not be considered to represent a complete list of the ionization gases that could be used to generate ion implant species. Accordingly, aspects of the present invention will now be described with reference to the drawings, wherein like reference numerals are used to refer to like elements throughout.
To steer the beam 22 from the terminal 12 to the work piece 24, the beamline assembly 14 has a beamguide 26 and a mass analyzer 28. A dipole magnetic field is established in the mass analyzer 28 during operation. Ions having an inappropriate charge-to-mass ratio collide with the sidewalls 32a, 32b; thereby leaving only the ions having the appropriate charge-to-mass ratio to pass through a resolving aperture 30 and into the work piece 24. The beam line assembly 14 may also include various beam forming and shaping structures extending between the ion source 18 and the end station 16, which maintain the ion beam 22 and bound an elongated interior cavity or passageway 36 through which the beam 22 is transported to the work piece 24 supported in the end station 16. A vacuum pump 34 typically keeps the ion beam transport passageway 36 at vacuum to reduce the probability of ions being deflected from the beam path through collisions with air molecules.
The implanter 10 may employ different types of end stations 16. For example, “batch” type end stations can simultaneously support multiple work pieces 24 on a rotating support structure, wherein the work pieces 24 are rotated through the path of the ion beam until all the work pieces 24 are completely implanted. A “serial” type end station, on the other hand, supports a single work piece 24 along the beam path for implantation, wherein multiple work pieces 24 are implanted one at a time in serial fashion, with each work piece 24 being completely implanted before implantation of the next work piece 24 begins.
Absent countermeasures, various contaminants (e.g., boron, carbon, or other dopant material from the ion source 18) can deposit and form one or more types of residue on various ion implanter components adjacent to the beam 22. For example, when boron species are present in the beam 22, boron-based residue can build up in an ion source; while when carbon species are present in the beam 22 carbon-based residue can similarly build up. Other types of residue can also build up depending on the types of implantation carried out. Aspects of this disclosure relate to techniques for removing or otherwise limiting such residue.
In the illustrated embodiment, the flow control assembly 202 is shown coupled to first and second dopant gas supplies (206, 208), as well as first and second cleaning gas supplies (210, 212). Often, the gas supplies 206-212 are stored in gas canisters, although the desired gases can also be generated in situ by carrying out appropriate chemical reactions and/or ionizations. It will be appreciated that although the illustrated embodiment depicts only first and second dopant gas supplies (206, 208) and first and second cleaning gas supplies (210, 212), any number of such gas supplies may be included to carry out desired implantation and cleaning functionality.
During operation, the controller 204 instructs the flow control assembly 202 to supply dopant gases from the dopant gas supplies 206, 208 to a plasma chamber (not shown) in the ion source 18, which is in a vacuum state. The power system 20 is then energized to ionize the dopant gas molecules in the plasma chamber, thereby generating different types of plasma depending on which dopant gas is present in the plasma chamber. For example, in one embodiment, the first dopant gas supply 206 comprises molecular boron (e.g., decaborane (B10H14), octadecaborane (B18H22)) and the second dopant gas supply 208 comprises molecular carbon (e.g., C7H7, C16H14). During implantation of a first workpiece (or one or more batches of workpieces), the molecular boron can be supplied to the plasma chamber to generate a first plasma, which can be extracted to form a first type of ion beam 22 that is suitable for forming an n-type region on the work piece(s). When another workpiece (or another batch of workpieces) is to be subsequently implanted, the molecular carbon can be supplied to the plasma chamber to generate a second plasma, which can be extracted to form a second type of ion beam 22 that is suitable for forming compressive strain regions in semiconductor devices.
Because the first and second types of ion beams include different molecular species, the first and second ion beams can form different kinds of residue in the system. Unless appropriate measures are taken, these different kinds of residue can buildup to push beam current beneath desired levels. Based on whether residue is present (and/or based on whether a predetermined time between cleaning routines has occurred), the controller 204 can initiate a cleaning process to reduce any such residue.
If a first type of residue, such as boron-based residue, is present (and/or if a pre-determined time has elapsed from a previous cleaning operation), the controller 204 instructs the flow control assembly 202 to pump the plasma chamber down to vacuum and then supply a first cleaning gas from the first cleaning gas supply 210 to a second plasma source that is used exclusively for cleaning purposes. For example, in some embodiments, the first cleaning gas comprises a fluorocarbon (having molecular formula CaFb, where a and b are integers) and/or a hydro-fluorocarbon (having molecular formula CxFyHz, where x, y, and z are integers). When this first cleaning gas is ionized and plasma is generated therefrom, its free reactive fluorine atoms can remove the first type of residue (e.g., boron-based residue). In some embodiments, the first cleaning gas may be substantially, if not completely, free of NF3 gas; thereby alleviating the need for special gas handling techniques, reducing costs, and tending to make the inventive techniques more environmentally friendly in some respects than NF3-based cleaning techniques.
Conversely, if a second type of residue, such as carbon based residue is present (and/or if a pre-determined time has elapsed from a previous cleaning operation), the controller 204 can also instruct the flow control assembly 202 to pump the plasma chamber down to vacuum, and then supply a second cleaning gas from the second cleaning gas supply 212 to the second plasma source. The second cleaning gas may comprise oxygen, thereby generating a plasma comprising atomic oxygen that removes the second type of residue (e.g., carbon-based residue) from an ion source component. Like the first cleaning gas, the second cleaning gas may also be substantially, if not completely, free of NF3 gas.
By changing between different types of plasma discharges to selectively clean different types of residues, this disclosure facilitates reliable operation for the ion implantation system. Although this concept is discussed above with respect to only first and second cleaning plasma discharges to clean first and second types of residue, respectively, this concept is extendable to any number of cleaning plasma discharges operable to clean any number of types of residue, respectively.
To help determine whether one or more residues have been completely cleaned from the ion source components, the system may employ various residue detection systems. For example,
In one embodiment, the residue detection sensor 214 can enable optical spectroscopic analysis that makes use of a secondary plasma source (not shown) in the exhaust system 216. Accordingly, in this embodiment, the residue detection sensor 214 analyzes exhaust from the plasma chamber in the ion source for trace amounts of residue. When plasma is ignited in the secondary plasma source, residue (if present) emits photons/light at a predetermined quantized energy level indicative of residue. The light emitted from different types of residue serve as a kind of “fingerprint” by which different types of residue can be identified, thereby allowing the controller 204 to select an appropriate cleaning gas to remove the particular type of residue detected. Alternately, as the built up residue gets cleaned up, less and less residue flows into the exhaust system and once all the residue is gone the optical fingerprint drops below a certain preset threshold, which can allow the controller 204 to terminate the cleaning process, thereby providing real-time control of the length of cleaning required.
In another embodiment, the residue detection sensor 214 can enable residual mass analysis that makes use of a secondary plasma source and a quadrupole magnet (not shown) located in the exhaust system 216. In residual gas analysis (RGA), the molecular constituents of the exhaust are again analyzed for trace amounts of residue, but this time based on the respective atomic masses of the molecular constituents. Thus, in this embodiment, the masses that are detected serve as a kind of “fingerprint” by which different types of residue can be identified, thereby allowing the controller 204 to select an appropriate cleaning gas to remove the particular type of residue detected.
In still another embodiment, the residue detection sensor 214 can comprise a temperature sensor. When a residue molecule disassociates in the presence of reactive species, the chemical reactions are typically exothermic, which tend to heat up the surfaces upon which the residue had formed according to a characteristic temperature curve, which can be indicative of whether residue is being removed. Once the temperature sensor typically mounted to the ion source components shows no further rise in temperature, the exothermic chemical reactions between the residue and reactive cleaning plasma are complete, and the temperature sensor's data may be used to stop the cleaning process.
Now that some examples of ion implantations systems have been discussed, reference is made to
If a first type of implantation routine is selected, the method proceeds to 304 and one or more workpieces are implanted with a molecular boron ion beam. This implantation may cause a first type of residue to build up on one or more ion beam components.
At 306, the molecular beam component having the first type of residue thereon is exposed to a first afterglow (or a first cleaning plasma), which comprises reactive dissociated atomic fluorine radicals to facilitate removal of the residue. In some examples, the first cleaning plasma which gives rise to the first afterglow may be generated by using a gas mixture that comprises a fluorocarbon and/or hydro-fluorocarbon gas.
At 308, exposure to the first afterglow (or first cleaning plasma) is selectively ended based on whether a first predetermined condition is met. The first predetermined condition is indicative of an extent of removal of the residue. For example, in one embodiment, the first condition relates to whether a predetermined time has expired as measured from a starting time of the exposure to the first afterglow. In another embodiment, the first condition relates to whether optical spectroscopic analysis using a secondary plasma source located preferably, though not limited to, in the exhaust line indicates whether the first afterglow has completely removed the residue from the ion source component. In still another embodiment, the first condition relates to whether a residual gas mass analysis indicates whether the first afterglow has completely removed the residue from the ion source component. In still another embodiment, the first condition relates to whether a temperature measurement indicates whether the first afterglow has completely removed the residue from the ion source component. Note that the first condition could also relate to less than a complete removal of the residue in these and other embodiments.
At 310, the method determines if another implantation is required. If so, the method returns to 302 and selects another implantation routine to be carried out on the same or different workpiece as previously implanted.
Assuming a second implantation routine is selected at 302, at 312 one or more workpieces are implanted with a molecular carbon beam. This forms a second residue on the ion beam component.
At 314, the ion beam component is exposed to a second afterglow (or a second cleaning plasma) comprising reactive dissociated atomic oxygen radicals to facilitate removal of the second residue formed, for example, during the molecular carbon implant.
At 316, exposure to the second afterglow (or second cleaning plasma) is selectively ended based on whether a second predetermined condition is met, where the second predetermined condition is indicative of an extent of removal of the second residue. For example, in one embodiment, the second condition relates to whether a predetermined time has expired as measured from a starting time of the exposure to the second afterglow. In another embodiment, the second condition relates to whether optical spectroscopic analysis using a secondary plasma source indicates whether the second afterglow has completely removed the residue from the ion source component. In still another embodiment, the second condition relates to whether a residual gas mass analysis indicates whether the second afterglow has completely removed the residue from the ion source component. In still another embodiment, the second condition relates to whether a temperature measurement indicates whether the second afterglow has completely removed the residue from the ion source component. Note that the second condition could also relate to less than a complete removal of the residue in these and other embodiments.
Although not explicitly shown in
At 404, the first molecular beam is provided along a beam path, which causes a first residue to buildup on molecular beam components.
At 406, the molecular beam components are exposed to a first cleaning plasma to facilitate removal of the first residue. In the example implementation now described, the first cleaning plasma includes fluorine ions and/or fluorine radicals, such as can be generated from fluorocarbons or hydro-fluorocarbons, for example.
At 408, exposure to the first cleaning plasma is selectively ended based on whether a first predetermined condition is met. For example, the first condition can relate to time, a spectrographic optical analysis, a residual gas mass analysis, or a temperature analysis.
At 410, a second molecular ion beam is generated, which includes a second molecular species. In the example now described, the second molecular species is described as carbon, which is one non-limiting example.
At 412, the second molecular ion beam is provided along the beam path, causing a second residue to buildup on the molecular beam component.
At 414, the molecular beam component is selectively exposed to a second cleaning plasma that differs from the first cleaning plasma to facilitate removal of the second residue. In the example now described, the second cleaning plasma includes oxygen, which is one non-limiting example.
At 416, exposure to the second cleaning plasma is selectively ended based on whether a second predetermined condition is met. For example, the second condition can relate to time, a spectrographic optical analysis, a residual gas mass analysis, or a temperature analysis.
Although not explicitly shown in
Often, the method illustrated in
The ion source 500 comprises a first plasma chamber 502 situated adjacent a second plasma chamber 516. The first plasma chamber 502 includes a gas source supply line 506 and is a configured with a plasma generating component 504 for creating plasma from a first source gas. The gas supply line selectively carries a dopant gas (e.g., from the first and/or second dopant gas supply 206, 208 of
The plasma generating component 504 can comprise a cathode 508/anode 510 combination, as shown in
The first, or electron source, plasma chamber 502 defines an aperture 512 forming a passageway into a high vacuum region of an ion implantation system, i.e. a region wherein pressure is much lower than the pressure of the source gas in the first plasma chamber 502.
The electron source plasma chamber 502 also defines an aperture 514 forming an extraction aperture for extracting electrons from the electron source plasma chamber 502. In a preferred embodiment, the extraction aperture 514 is provided in the form of a replaceable anode element 510 as illustrated in
As previously stated, the ion source 500 also includes a second, or ion source chamber 516. The second ion source plasma chamber 516 includes a second gas source supply line 518 for introducing a source gas into the ion source plasma chamber 516 and is further configured to receive electrons from the electron source plasma chamber 502, thereby creating plasma therein via the collisions between the electrons and the second source gas. The second gas supply source line 518 can selectively carry a dopant gas (e.g., from the first and/or second dopant gas supply 206, 208 of
The second, or ion source, plasma chamber 516 defines an aperture 517 aligned with the extraction aperture 514 of the first plasma chamber 502, forming a passageway therebetween for permitting electrons extracted from the first plasma chamber 502 to flow into the second plasma chamber 516. Preferably, the ion source plasma chamber 516 is configured to have a positively biased electrode 519 for attracting electrons injected into the ion source plasma chamber 516 in a so-called non-reflex mode to create the desired collisions between electrons and gas molecules to create ionization plasma. Alternatively, the electrode 519 can be biased negatively to cause electrons to be repelled back into the ion source plasma chamber 516 in a so-called reflex mode.
An extraction aperture 520 is configured in the second plasma chamber 516 to extract ions for formation of an ion beam for implantation.
In one embodiment the second plasma chamber 516 is biased positively with respect to the first plasma chamber 502 utilizing an external bias power supply 515 (
It should be noted that the first plasma chamber 502 and the second plasma chamber 516 can have three open boundaries: a gas inlet (e.g., a first gas supply inlet 522 and a second gas supply inlet 524), an opening to a high vacuum area (e.g., pumping aperture 512 and extraction aperture 520) and a common boundary apertures 514 and 517 forming the common passageway between the first and second plasma chambers, 502 and 504, respectively.
Both plasma chambers 502, 516 also share a magnetic field oriented along the extraction aperture, provided by a standard Axcelis source magnet, depicted by reference numeral 530. It is well known that the ionization process (and in this case the electron generating process) becomes more efficient by inducing a vertical magnetic field in the plasma generating chamber. As such, in one embodiment electromagnet members 530 are positioned outside of the first and second plasma chambers, 502 and 516 respectively, preferably along the axis of the shared boundary therebetween. These electromagnet elements 530 induce a magnetic field that traps the electrons to improve the efficiency of the ionization process.
The configuration of
Although the invention has been illustrated and described with respect to one or more implementations, alterations and/or modifications may be made to the illustrated examples without departing from the spirit and scope of the appended claims. In particular regard to the various functions performed by the above described components or structures (blocks, units, engines, assemblies, devices, circuits, systems, etc.), the terms (including a reference to a “means”) used to describe such components are intended to correspond, unless otherwise indicated, to any component or structure which performs the specified function of the described component (e.g., that is functionally equivalent), even though not structurally equivalent to the disclosed structure which performs the function in the herein illustrated exemplary implementations of the invention. In addition, while a particular feature of the invention may have been disclosed with respect to only one of several implementations, such feature may be combined with one or more other features of the other implementations as may be desired and advantageous for any given or particular application. Furthermore, to the extent that the terms “including”, “includes”, “having”, “has”, “with”, or variants thereof are used in either the detailed description and the claims, such terms are intended to be inclusive in a manner similar to the term “comprising”.
This application is a divisional of U.S. application Ser. No. 12/616,662 filed on Nov. 11, 2009.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 12616662 | Nov 2009 | US |
| Child | 13948280 | US |
