US20140252953A1 - Plasma generator - Google Patents
Plasma generator Download PDFInfo
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- US20140252953A1 US20140252953A1 US14/348,071 US201214348071A US2014252953A1 US 20140252953 A1 US20140252953 A1 US 20140252953A1 US 201214348071 A US201214348071 A US 201214348071A US 2014252953 A1 US2014252953 A1 US 2014252953A1
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- plasma
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J37/00—Discharge tubes with provision for introducing objects or material to be exposed to the discharge, e.g. for the purpose of examination or processing thereof
- H01J37/32—Gas-filled discharge tubes
- H01J37/32009—Arrangements for generation of plasma specially adapted for examination or treatment of objects, e.g. plasma sources
- H01J37/32082—Radio frequency generated discharge
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- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05H—PLASMA TECHNIQUE; PRODUCTION OF ACCELERATED ELECTRICALLY-CHARGED PARTICLES OR OF NEUTRONS; PRODUCTION OR ACCELERATION OF NEUTRAL MOLECULAR OR ATOMIC BEAMS
- H05H1/00—Generating plasma; Handling plasma
- H05H1/24—Generating plasma
- H05H1/26—Plasma torches
- H05H1/30—Plasma torches using applied electromagnetic fields, e.g. high frequency or microwave energy
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J37/00—Discharge tubes with provision for introducing objects or material to be exposed to the discharge, e.g. for the purpose of examination or processing thereof
- H01J37/30—Electron-beam or ion-beam tubes for localised treatment of objects
- H01J37/3002—Details
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J37/00—Discharge tubes with provision for introducing objects or material to be exposed to the discharge, e.g. for the purpose of examination or processing thereof
- H01J37/32—Gas-filled discharge tubes
- H01J37/32431—Constructional details of the reactor
- H01J37/32798—Further details of plasma apparatus not provided for in groups H01J37/3244 - H01J37/32788; special provisions for cleaning or maintenance of the apparatus
- H01J37/32853—Hygiene
- H01J37/32862—In situ cleaning of vessels and/or internal parts
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- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05H—PLASMA TECHNIQUE; PRODUCTION OF ACCELERATED ELECTRICALLY-CHARGED PARTICLES OR OF NEUTRONS; PRODUCTION OR ACCELERATION OF NEUTRAL MOLECULAR OR ATOMIC BEAMS
- H05H1/00—Generating plasma; Handling plasma
- H05H1/24—Generating plasma
- H05H1/46—Generating plasma using applied electromagnetic fields, e.g. high frequency or microwave energy
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05H—PLASMA TECHNIQUE; PRODUCTION OF ACCELERATED ELECTRICALLY-CHARGED PARTICLES OR OF NEUTRONS; PRODUCTION OR ACCELERATION OF NEUTRAL MOLECULAR OR ATOMIC BEAMS
- H05H1/00—Generating plasma; Handling plasma
- H05H1/24—Generating plasma
- H05H1/46—Generating plasma using applied electromagnetic fields, e.g. high frequency or microwave energy
- H05H1/4645—Radiofrequency discharges
- H05H1/4652—Radiofrequency discharges using inductive coupling means, e.g. coils
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05H—PLASMA TECHNIQUE; PRODUCTION OF ACCELERATED ELECTRICALLY-CHARGED PARTICLES OR OF NEUTRONS; PRODUCTION OR ACCELERATION OF NEUTRAL MOLECULAR OR ATOMIC BEAMS
- H05H1/00—Generating plasma; Handling plasma
- H05H1/24—Generating plasma
- H05H1/46—Generating plasma using applied electromagnetic fields, e.g. high frequency or microwave energy
- H05H1/4645—Radiofrequency discharges
- H05H1/466—Radiofrequency discharges using capacitive coupling means, e.g. electrodes
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05H—PLASMA TECHNIQUE; PRODUCTION OF ACCELERATED ELECTRICALLY-CHARGED PARTICLES OR OF NEUTRONS; PRODUCTION OR ACCELERATION OF NEUTRAL MOLECULAR OR ATOMIC BEAMS
- H05H2242/00—Auxiliary systems
- H05H2242/20—Power circuits
Definitions
- the invention relates to an arrangement and method for removal of contaminant deposits, and in particular to a plasma generator for removing contaminant deposits.
- Charged particle lithography systems generate charged particles such as electrons, and generate beams of charged particles which are focused, modulated and projected onto a wafer in the lithography process.
- the charged particle beams interact with hydrocarbons present in the lithography system, and the resulting Electron Beam Induced Deposition (EBID) forms a carbon-containing layer on surfaces in the system. This layer of carbon-containing material affects the stability of the charged particle beamlets.
- the charged particle beams and beamlets are typically formed using aperture plates, and they may also be focused and modulated by arrays of lenses and electrodes formed in aperture plates.
- a build-up of carbon-containing layers in and around apertures through which the charged particle beams or beamlets pass also reduces the size of the apertures and reduces transmission of beams or beamlets through these apertures. Removal of EBID, in particular in areas with relatively high hydrocarbon partial pressures and relatively high beam current densities, is therefore highly desirable.
- Such deposits can be lessened or removed by atomic radical cleaning. This may be achieved using a plasma generator to produce a stream of atomic radicals that chemically react with the deposits, forming volatile molecular compounds.
- the invention is directed to an improved plasma generator and an improved method for generating plasma. These may be of particular utility in cleaning contaminants such as EBID, and in a charged particle lithography system.
- the invention provides an arrangement for generating plasma, the arrangement comprising a primary plasma source arranged for generating plasma, a hollow guiding body arranged for guiding at least a portion of the plasma generated by the primary plasma source to a secondary plasma source, and an outlet for emitting at least a portion of the plasma or components thereof (e.g. atomic radicals) from the arrangement.
- This dual plasma source design enables the plasma generator to have a larger primary plasma source located remotely from the outlet and a smaller secondary plasma source located close to the outlet, due to the interaction between the two sources. This is particularly advantageous in situations where there is limited space at the location where the plasma is required, e.g. for cleaning contaminant deposits on equipment located in a cramped space.
- the formation of plasma in the secondary plasma source close to the outlet enables smaller loss of plasma due to decay of the plasma during transport from the remote primary chamber.
- This design also enables the heat load produced by the primary plasma source to be located remotely from the outlet.
- the primary plasma source may comprise a primary source chamber in which the plasma may be formed and a first coil for generating the plasma in the primary source chamber, the chamber comprising an inlet for receiving an input gas, and one or more outlets for removal of at least a portion of the plasma from the source chamber and into the guiding body.
- the secondary plasma source may comprise a secondary source chamber occupying at least a portion of the guiding body.
- the secondary plasma source may omit a coil for enhancing or generating plasma.
- the secondary plasma source may comprise a secondary source chamber and the arrangement may be adapted to generate a high brightness plasma in the secondary source chamber.
- a plasma generator may operate by capacitive coupling where an electric field is generated by a radio frequency (RF) voltage between two electrodes which induces the plasma formation, or by inductive coupling where a magnetic field is generated by an RF current through a coil which induces the plasma formation.
- the primary plasma source in operation, may be adapted to generate a primary plasma via inductive coupling, and the secondary plasma source to generate a secondary plasma via capacitive coupling.
- the arrangement thus forms a hybrid plasma generator using both inductive and capacitive coupling to generate plasma.
- the arrangement may further comprise an electrode located near the outlet of the arrangement, wherein, in operation, the coil of the primary plasma source is capacitively coupled to the electrode via the plasma generated by the primary plasma source and/or the secondary plasma source.
- the electrode may be maintained at a fixed potential with respect to a voltage supplied to the coil of the primary plasma source, or it may be grounded with respect to a voltage supplied to the coil of the primary plasma source.
- the arrangement may also comprise an aperture array near the outlet, and may also comprise an additional electrode arranged for repelling or attracting plasma ions in the guiding body.
- the plasma formed by the plasma generator includes ions and radicals, and this arrangement enables retention of ions in the plasma generator or reduction of their energy, while permitting emission of radicals from the plasma generator.
- the primary plasma source may comprise a primary source chamber in which primary plasma is generated and the secondary plasma source may comprise a secondary source chamber in which the primary plasma is enhanced and/or secondary plasma is generated, the primary source chamber being larger than the secondary source chamber.
- the primary source chamber may have a larger cross-section than the secondary source chamber, and may have a greater internal volume. The larger primary source chamber can then be located further from the outlet than the secondary source chamber, allowing constructions where the smaller secondary source chamber can fit into narrow restricted spaces close to the location where the plasma is required.
- the arrangement may further comprise a pressure regulator for regulating pressure in the primary source chamber, and a flow or pressure restriction may be provided between the primary and secondary source chambers.
- the restriction may be adapted to maintain an operating pressure in the secondary source chamber at a lower pressure than in the primary source chamber.
- the arrangement may also be adapted for regulating the pressure in the secondary source chamber, or for regulating the pressure in both the primary and secondary source chambers.
- the secondary source chamber may have a length longer than the primary source chamber in a direction of the flow of plasma from the primary source chamber.
- the primary source chamber may have a diameter of 20 mm or more, and the secondary source chamber may have a diameter of less than 20 mm.
- the secondary source chamber may have an end section for directing plasma in a desired direction.
- the secondary source chamber may be arranged to generate plasma at a position close to an outlet of the arrangement, and the primary plasma source may be located further from the outlet than the secondary plasma source. This results in a design with a secondary plasma chamber closer to the outlet where the plasma is emitted, so that less of the plasma generated in the secondary chamber is lost by decay and other processes during transfer to the outlet.
- the hollow guiding body may comprise a funnel section located at the outlet of the primary plasma source arranged for guiding plasma generated by primary plasma source into the guiding body.
- the guiding body may comprise a quartz material or an inner surface comprising a quartz material, and the guiding body may be in the form of a tube or duct.
- the guiding body may have a bend or elbow to direct plasma from the outlet onto an area to be cleaned by the plasma.
- the primary plasma source may comprise a primary source chamber in which the plasma may be formed, and an aperture plate positioned between the primary source chamber and the guiding body, the aperture plate having one or more apertures for permitting flow of the plasma from the primary source chamber into the guiding body.
- the arrangement may further comprise an aperture plate at or near the outlet of the guiding body to confine at least a portion of the plasma in the guiding body from exiting through the outlet.
- the invention in another aspect relates to a method for generating a plasma, comprising flowing an input gas into a primary source chamber, energizing a first coil to form a primary plasma in the primary source chamber, flowing at least a portion of the primary plasma into a secondary source chamber, and generating a secondary plasma in the secondary source chamber.
- the step of flowing the primary plasma into the secondary source chamber may comprise flowing the plasma into a guiding body, at least a portion of the guiding body forming the secondary source chamber.
- the first plasma may be flowed from the primary source chamber through a restriction into a secondary source chamber.
- the method may comprise forming the primary plasma in the primary source chamber via inductive coupling, and generating the secondary plasma in the secondary source chamber via capacitive coupling.
- the secondary source chamber may omit a coil for forming a plasma.
- the method may further comprise regulating pressure in the primary source chamber and the secondary source chamber, and the step of regulating the pressure may comprise maintaining a lower pressure in the secondary source chamber than in the primary source chamber.
- the primary plasma may be a relatively low brightness plasma and the secondary plasma may be a relatively high brightness plasma.
- the method may further comprise stabilizing the formation of plasma in the secondary source chamber with the primary plasma flowing from the primary source chamber, and may further comprise maintaining a lower pressure in the secondary source chamber than in the primary source chamber.
- the invention in another aspect relates to a cleaning apparatus for cleaning contaminants from a surface, the apparatus comprising an arrangement for generating plasma as described herein, and means for directing the plasma onto the surface to be cleaned.
- the invention in yet another aspect relates to a charged particle lithography machine, comprising a beamlet generator for generating a plurality of charged particle beamlets and a plurality of beamlet manipulator elements for manipulating the beamlets, each beamlet manipulator element comprising a plurality of apertures through which the beamlets pass, the machine further comprising an arrangement for generating plasma as described herein, adapted to generate plasma and direct the plasma onto a surface of one or more of the beamlet manipulator elements.
- FIG. 1 is a schematic diagram of an embodiment of a radio frequency (RF) plasma generator
- FIGS. 2A , 2 B and 2 C are schematic diagrams of an embodiment of a plasma generator including a guiding body
- FIGS. 3A and 3B are schematic diagrams of the embodiment of FIG. 2 in operation
- FIG. 4 is a schematic diagram of an embodiment including aperture plates and an electrode at the outlet;
- FIG. 5 is a schematic diagram of another embodiment including aperture plates and electrodes at the outlet;
- FIG. 6 is a photograph of a plasma chamber with a guiding body showing plasma forming in the primary plasma chamber
- FIG. 7 is a photograph of the plasma chamber of FIG. 6 showing plasma forming in the guiding body.
- FIG. 8 is a schematic diagram of an embodiment of a charged particle lithography machine.
- FIG. 1 shows a radio frequency (RF) plasma generator comprising a chamber 2 with an RF coil 4 around the outside of the chamber.
- An input gas such as oxygen or hydrogen or other suitable gas is passed into the chamber via inlet 5 and the coil 4 is energized with an RF voltage to produce a plasma including radicals, such as oxygen atom radicals, which exit the chamber via one or more outlets 6 .
- RF radio frequency
- Contaminants such as electron beam induced deposition (EBID), generally comprising carbon containing compounds, form on surfaces in a charged particle lithography system, such as the surfaces of beamlet manipulator elements (such as beamlet modulators, deflectors, lenses, aperture arrays, beam stop arrays, etc.).
- EBID electron beam induced deposition
- beamlet manipulator elements such as beamlet modulators, deflectors, lenses, aperture arrays, beam stop arrays, etc.
- radicals such as oxygen atom radicals
- Plasma typically comprises a mixture of gas molecules, ions, electrons, and atomic radicals.
- atomic ions may also be used.
- ions may be accelerated by electric fields generated in or around the plasma generator system, and have sufficient kinetic energy to sputter the surface to be cleaned. This can result in removing not just the contaminant deposits, but also part of the surface underlying the deposits, so damaging the surface.
- Uncharged radicals generally have a lower kinetic energy. i.e. the thermal energy of the radicals, and are more suitable in many cleaning applications for this reason.
- Excellent cleaning rates of greater than 5 micron per hour can be achieved by atomic radical cleaning where there is a direct view from the plasma generator source to the contaminated area to be cleaned.
- this method cannot be easily implemented in situations where the deposits are formed on surfaces with cannot be easily accessed and in which there is little room to locate the plasma generator with a direct line from the source to the area to be cleaned.
- the beam stop array and beamlet aperture array are areas that exhibit these problems, typically having a restricted space available above the surface of the beam stop of 5 mm of less.
- plasma sources are constructed with a long tube of length 20 cm or more and a diameter of about 10 cm.
- a plasma source for cleaning the beam stop array and beamlet aperture array in a charged particle lithography system there is typically very limited space (e.g. about 10 ⁇ 10 ⁇ 10 mm 3 ) available to implement a plasma source in the vicinity of these elements.
- the problem in designing a miniature plasma source for use in locations with very restricted space lies in the aspect ratio of the area to volume of the plasma generator. For a large plasma source this ratio is small, but as the size of the plasma source is reduced the ratio increases. This results in minor instabilities coupling into or out of the plasma in the source chamber via its surface, having an increasingly large effect. As a consequence, the plasma may be hard to ignite and easily extinguished due to these instabilities.
- a much larger source may be used (e.g. about 100 ⁇ 100 ⁇ 100 mm 3 ) to be situated at approximately 200 mm from the elements to be cleaned.
- the plasma radicals must then be transported from the plasma generator to the site of the cleaning.
- the present invention provides a plasma generator which permits direct access to the contaminated area even where only a limited volume is available at the cleaning site to locate the cleaning apparatus.
- a plasma source is placed near the contaminated area to be cleaned, and a guiding path is attached to the plasma generator and the plasma radicals produced are transported towards the area to be cleaned.
- FIGS. 2A , 2 B and 2 C schematically show arrangements for removal of contaminant deposits, in particular for removal of contaminants deposited on surfaces that are located in areas with restricted or difficult access.
- the arrangements comprise a plasma generator similar to that shown in FIG. 1 , further referred to as the primary source chamber 15 , which functions as a primary plasma source 1 .
- the arrangement further comprises a hollow guiding body 11 , such as tube or duct, for guiding plasma towards a predetermined destination area. It will be recognized that various configurations are possible, and three possible configurations are shown, and features of any of these embodiments may be used in any of the other embodiments.
- the guiding body 11 includes a funnel portion 10 where the guiding body 11 is coupled to the primary source chamber 15 , and the chamber end wall with outlets 6 function as an aperture plate to permit the plasma and radicals to enter the guiding body 11 from the chamber 15 .
- the guiding body 11 includes an elbow 12 near the end of the guiding body to direct plasma exiting the guiding body.
- the arrangement in FIG. 2B omits the funnel portion, the chamber end wall, and the elbow, so that a straight guiding body 11 having a smaller cross section than the primary source chamber 15 is coupled directly to the primary source chamber 15 .
- the arrangement in FIG. 2C features a continuous hollow body, a wider portion forming the primary source chamber 15 and a narrower portion forming the guiding body 11 .
- a hollow body having a uniform cross section may also be used, one portion of the hollow body functioning as the primary source chamber 15 and another portion functioning as the guiding body 11 .
- the guiding body 11 may be straight or may comprise one or more bends such as an elbow 12 or bend 13 to direct the plasma in a desired direction.
- the guiding body 11 is as straight as possible to increase the average lifetime of radicals being transferred through the tube.
- the guiding body has an outlet 14 which may be located in close proximity of the contaminant deposit to be reduced or removed. Typically, the outlet 14 is in direct contact with a vacuum environment.
- the plasma and radicals generated in primary source chamber 15 of primary source 1 are guided towards the contaminant deposit to be reduced or removed via the guiding body 11 .
- the guiding body 11 may be made of quartz, or with inner surface coated with quartz, to suppress extinction of the radicals when they interact with these parts of the device.
- Embodiments of the invention are described herein with reference to plasma formed from oxygen. However, it will be understood that the invention may also employ plasmas from other gases, such as hydrogen or nitrogen.
- FIG. 3A shows the arrangement of FIG. 2A in operation. It will be understood that arrangements shown in FIGS. 2B and 2C may also be operated in a similar manner.
- Oxygen is supplied to the primary source chamber 15 and RF coil 4 is energized to inductively heat the oxygen, and a plasma 20 is generated in primary source chamber 15 .
- the oxygen pressure may be adjusted, for example, to produce a relatively high pressure in the chamber 15 .
- the plasma 20 and in particular radicals produced therein, may exit the primary source chamber 15 as schematically represented by dashed arrow 21 and flow into the guiding body 11 .
- the plasma generator may also be made more effective by more efficient transport of plasma through the guiding body 11 , and/or generation of plasma in the guiding body 11 so that the guiding body is not merely conveying plasma formed in the primary source chamber 15 , but additional plasma is formed in the guiding body, close to the location where it is needed for cleaning.
- a secondary plasma source 25 is formed, with a portion of the guiding body functioning as a secondary source chamber 16 .
- plasma may be guided from the primary source chamber 15 into the guiding body 11 and through the guiding body to the outlet 14 .
- the pressure should preferably decrease from the primary source chamber 15 to the guiding body 11 and to the environment outside the outlet 14 in order to promote flow of plasma from the chamber 15 to the outlet 14 .
- the pressure can be optimized through the device, e.g. by use of aperture plates (such as aperture plate 31 at the entrance to the guiding body 11 and aperture plate 32 at the outlet 14 ) and/or by adjusting the relative sizes and geometry of the primary source chamber 15 , guiding body 11 and the outlet 14 .
- plasma By adjusting pressures in the primary source chamber 15 and in the guiding body 11 , plasma can be formed in the guiding body.
- the pressures may be adjusted to obtain conditions where a high brightness plasma is formed in the guiding body at a relatively lower pressure than the primary source chamber. This results in the formation of plasma in the guiding body closer to the location where it is needed to produce more effective cleaning.
- the pressure in the guiding body 11 may be relatively low in comparison to the primary source chamber 15 , depending on the geometry of the tube and size of the outlet 14 , and the ambient pressure of the surrounding environment.
- a relatively high pressure in the primary source chamber 15 will displace more plasma into the guiding body 11 , thus shortening the path for the radicals to reach the outlet 14 and the cleaning site, and thus reducing the loss of radicals due to recombination and other effects, and thereby increasing the cleaning rate.
- the ambient pressure may be low inside the lithography machine vacuum chamber, e.g. 10 ⁇ 3 millibar or lower.
- the pressure in the guiding body 11 may be higher, e.g. 10 ⁇ 2 millibar, but lower than the pressure in the primary plasma chamber 15 , aiding the formation of plasma in the guiding body itself, even though there is no RF coil around the guiding body. This may be due to the relatively lower pressure in the guiding body 11 and may be assisted by the flow of plasma from the primary source chamber 15 , conveying the effect of the RF coil at the primary source chamber, e.g. by capacitive coupling, into the guiding body.
- Plasma is an electrical conductor, and thus may conduct RF current resulting from excitation of the RF coils 4 surrounding the primary source chamber 15 , into the guiding body 11 where it may generate more plasma.
- the resulting effect is to generate plasma in the guiding body 11 , a portion of the guiding body functioning as a “passive” secondary plasma source 25 .
- the guiding body is not merely conveying plasma formed in by primary plasma source 1 , but additional plasma is formed in a secondary plasma source 25 in the guiding body 11 , close to the location where it is needed for cleaning.
- the plasma formed in the secondary plasma source 25 may be high brightness plasma suitable for effective cleaning of the EBID deposits.
- plasma 20 is formed in the primary source chamber 15
- plasma (or components of the plasma) 21 flows into the guiding body 11
- plasma 22 is subsequently formed in a secondary source chamber 16 in the guiding body 11 .
- the plasma 21 acts as “seed” plasma to enhance plasma formation in the secondary source chamber 16 near to the outlet 14 , where it acts as a source of atomic radicals close to the location where they are needed.
- An alternative is to operate the system at a low pressure in the primary source chamber 15 and guiding body 11 to reduce the loss of radicals by decreasing the recombination probability, and thereby increasing the cleaning rate.
- the embodiment shown in FIG. 4 employs an optional aperture plate 31 between the primary source chamber 15 and guiding body 11 at the exit of the primary source.
- the gas flow conductance of the aperture plate 31 can be adjusted (by adjusting the number and size of the apertures in the plate) to adjust the relative pressures in the source chamber 15 and guiding body 11 .
- the aperture plate 31 also operates to partly confine the plasma in the primary source chamber 15 by reducing the quantity of ions flowing from the chamber 15 into the guiding body 11 , due partly to recombination of ions and electrons due to collisions, while permitting flow of radicals into the guiding body 11 .
- the aperture plate 31 may be omitted altogether where maximum flow of plasma into guiding body 11 is desired to maximize formation of secondary plasma 22 in the guiding body 11 .
- An optional aperture plate 32 may also be placed near the end of the guiding body 11 (as shown in the FIG. 5 embodiment), preferably at the outlet 14 .
- the aperture plate 32 at the outlet 14 can be used to assist in regulating pressure in the guiding body 11 , typically in conjunction with aperture plate 31 .
- Aperture plate 32 may also operate to partly confine the plasma inside the guiding body 11 , limiting the ability of high kinetic energy ions from striking the area to be cleaned, or this function may be performed by the electrode 32 . These high energy ions may sputter the top surface of the area to be cleaned and this can lead to damage of the part being cleaned.
- the gas flow conductance of the aperture plates can be adjusted so that the pressure in both the primary source chamber 15 and the guiding body 11 (i.e. secondary source chamber 16 ) is optimal, to improve the efficiency of the plasma generator.
- the aperture plates 31 and/or 32 may be made from a conducting material such as a metal, or a non-conducting material such as a plastic, ceramic or quartz.
- the aperture plate 32 may be made from a conducting material to function also as an electrode, which may be grounded or connected to a common voltage.
- a separate electrode 30 may be installed near the outlet 14 , as shown in the embodiment of FIG. 4 , which may be grounded or connected to a common voltage.
- Such an electrode 30 (or grounded aperture plate 32 ) near the outlet 14 operates to generate plasma in the guiding body 11 and/or enhance plasma flowing into the guiding body 11 , through capacitive coupling.
- Plasma is a conductor, and as it flows from the primary source chamber 15 into the guiding body 11 towards the electrode 30 , it creates a capacitive coupling between the RF coil 4 of the primary plasma source 1 and the electrode 30 at the outlet 14 at the end of the secondary source chamber 25 .
- the RF voltage supplied to the RF coil 4 generates an electric field between the RF coil 4 and electrode 30 conducted by the seed plasma 21 flowing into the guiding body 11 , which excites the plasma in the guiding body 11 between the RF coil 4 and electrode 30 which enhances or induces formation of plasma 22 in the guiding body 11 .
- Plasma generation via such capacitive coupling is typically difficult to achieve unless the guiding body is short, i.e. short distance from the primary plasma source to the cleaning site, particularly when there is grounded metal near to the plasma generator, which is usually the case where the plasma generator is surrounded by other equipment.
- the electrode 30 may also operate to partly confine the plasma 22 inside the guiding body 11 , e.g. taking the form of a mesh or aperture plate.
- the electrode 40 also functions to avoid or reduce capacitive coupling between the RF coil 4 and the part being cleaned where the part is conductive and grounded. This can avoid damage to the part being cleaned where it is vulnerable to stray electrical current, e.g. a beamlet modulation array of a charged particle lithography machine.
- a “hybrid” plasma generator which uses both inductive and capacitive coupling to generate plasma as described herein, can overcome this difficulty.
- the system generates a primary plasma 20 in the primary source chamber 15 using inductive coupling, where a magnetic field generated by an RF current through the coil 4 induces plasma formation, and a secondary plasma 22 in the guiding body 11 /second plasma chamber 16 using capacitive coupling, where an electric field is generated by an RF voltage between the coil 4 and electrode 30 induces plasma formation.
- the primary inductively-coupled plasma can “grow” in the guiding body 11 towards the electrode 30 near the cleaning site, changing from inductively coupled to capacitively coupled.
- This process starts with a primary inductively-coupled plasma that can be formed in a grounded environment, i.e. where there are grounded conductors nearby. In such a grounded environment, it is very difficult to sustain a capacitively-coupled plasma.
- the primary plasma 20 in the primary source chamber 15 heats the nearby volume in the guiding body 11 , partly due to flow of hot plasma 21 into the guiding body, and the plasma grows a little more in the guiding body.
- the plasma is a conductor and its growth/formation in the guiding body extends the electric field from the RF coil 4 of the primary source 1 further into the guiding body 11 , aiding further plasma growth/formation. This process continues until the plasma reaches the electrode 30 and a high brightness plasma can be formed in the guiding body 11 /second plasma chamber 16 .
- FIG. 4 has a bend 13 at the end of the guiding body 11 near the outlet 14 , rather than a 90 degree elbow 12 , while the embodiment of FIG. 5 has a straight guiding body 11 .
- Any of the configurations shown in any of the drawings may be used with any of the embodiments, with or without the funnel section 10 or aperture plates 31 and/or 32 or electrodes 30 and/or 34 .
- the embodiment shown in FIG. 5 employs an additional electrode 34 to further reduce the quantity of atomic ions exiting the outlet 14 of the plasma generator and/or reduce their velocity.
- the additional electrode 34 may be energized with a voltage V to repel or attract the ions, e.g. a positive voltage to repel negative ions, or an RF voltage opposite to the voltage supplied to the RF coil 4 .
- the electrode 30 , aperture plate 32 , and additional electrode 34 may be used in various combinations to achieve the desired results, i.e. to extend plasma formation into the guiding body 11 while controlling the emission of energetic ions while permitting the emission of atomic radicals.
- These elements operate as a atomic radical/ion filter, to let radicals pass while reducing or preventing ion emission.
- This new design provides an arrangement with two plasma sources, a smaller secondary plasma source 25 located close to the plasma outlet 14 and a larger primary plasma source 1 further from the outlet 14 , the arrangement including a guiding body 11 for guiding plasma generated by the primary plasma source 1 to the secondary plasma source 25 to stabilize plasma formation by the secondary plasma source 25 .
- the design is simple with very few parts, the secondary plasma source 25 operating by capacitive coupling to an electrode 30 /aperture plate 32 .
- FIG. 6 is a photograph of a plasma chamber in the center of the photograph, with an guiding body in the form of an extension tube extending towards the bottom of the photograph. Greenish low brightness plasma is flowing from the primary plasma chamber into the guiding body towards the outlet at the bottom of the photograph.
- FIG. 7 is a photograph of the plasma chamber of FIG. 6 at the top of the photograph, with the guiding body extending towards the bottom of the photograph.
- the faint greenish low brightness plasma in the guiding body has been replaced by high brightness plasma which is forming in the guiding budy and exiting the outlet at the bottom of the photograph.
- FIG. 8 shows a simplified schematic diagram of an electron-optical column of a charged particle lithography element.
- Such lithography systems are described for example in U.S. Pat. Nos. 6,897,458; 6,958,804; 7,019,908; 7,084,414; and 7,129,502, U.S. patent publication no. 2007/0064213, and co-pending U.S. patent application nos. 61/031,573; 61/031,594; 61/045,243; 61/055,839; 61/058,596; and 61/101,682, which are all assigned to the owner of the present invention and are all hereby incorporated by reference in their entireties.
- the lithography element column comprises an electron source 110 producing an expanding electron beam 130 , which is collimated by collimator lens system 113 .
- the collimated electron beam impinges on an aperture array 114 a, which blocks part of the beam to create a plurality of sub-beams 134 , which pass through a condenser lens array 116 which focuses the sub-beams.
- the sub-beams impinge on a second aperture array 114 b which creates a plurality of beamlets 133 from each sub-beam 134 .
- the system generates a very large number of beamlets 133 , preferably about 10,000 to 1,000,000 beamlets.
- a beamlet blanker array 117 comprising a plurality of blanking electrodes, deflects selected ones of the beamlets.
- the undeflected beamlets arrive at beam stop array 118 and pass through a corresponding aperture, while the deflected beamlets miss the corresponding aperture and are stopped by the beam stop array.
- the beamlet blaker array 117 and beam stop 118 operate together to switch the individual beamlets on and off.
- the undeflected beamlets pass through the beam stop array 119 , and through a beam deflector array 119 which deflects the beamlets to scan the beamlets across the surface of target or substrate 121 .
- the beamlets pass through projection lens arrays 120 and are projected onto substrate 121 which is positioned on a moveable stage for carrying the substrate.
- the substrate usually comprises a wafer provided with a charged-particle sensitive layer or resist layer.
- the lithography element column operates in a vacuum environment.
- a vacuum is desired to remove particles which may be ionized by the charged particle beams and become attracted to the source, may dissociate and be deposited onto the machine components, and may disperse the charged particle beams.
- a vacuum of at least 10 ⁇ 6 bar is typically required.
- the charged particle lithography system is located in a vacuum chamber. All of the major elements of the lithography element are preferably housed in a common vacuum chamber, including the charged particle source, projector system for projecting the beamlets onto the substrate, and the moveable stage.
Abstract
Description
- 1. Field of the Invention
- The invention relates to an arrangement and method for removal of contaminant deposits, and in particular to a plasma generator for removing contaminant deposits.
- 2. Description of the Related Art
- The accuracy and reliability of charged particle lithography systems is negatively influenced by contamination. An important contribution to contamination in such lithography system is caused by the build-up of deposits of contaminants. Charged particle lithography systems generate charged particles such as electrons, and generate beams of charged particles which are focused, modulated and projected onto a wafer in the lithography process. The charged particle beams interact with hydrocarbons present in the lithography system, and the resulting Electron Beam Induced Deposition (EBID) forms a carbon-containing layer on surfaces in the system. This layer of carbon-containing material affects the stability of the charged particle beamlets. The charged particle beams and beamlets are typically formed using aperture plates, and they may also be focused and modulated by arrays of lenses and electrodes formed in aperture plates. A build-up of carbon-containing layers in and around apertures through which the charged particle beams or beamlets pass also reduces the size of the apertures and reduces transmission of beams or beamlets through these apertures. Removal of EBID, in particular in areas with relatively high hydrocarbon partial pressures and relatively high beam current densities, is therefore highly desirable.
- Such deposits can be lessened or removed by atomic radical cleaning. This may be achieved using a plasma generator to produce a stream of atomic radicals that chemically react with the deposits, forming volatile molecular compounds.
- The invention is directed to an improved plasma generator and an improved method for generating plasma. These may be of particular utility in cleaning contaminants such as EBID, and in a charged particle lithography system.
- In one aspect the invention provides an arrangement for generating plasma, the arrangement comprising a primary plasma source arranged for generating plasma, a hollow guiding body arranged for guiding at least a portion of the plasma generated by the primary plasma source to a secondary plasma source, and an outlet for emitting at least a portion of the plasma or components thereof (e.g. atomic radicals) from the arrangement. This dual plasma source design enables the plasma generator to have a larger primary plasma source located remotely from the outlet and a smaller secondary plasma source located close to the outlet, due to the interaction between the two sources. This is particularly advantageous in situations where there is limited space at the location where the plasma is required, e.g. for cleaning contaminant deposits on equipment located in a cramped space. The formation of plasma in the secondary plasma source close to the outlet enables smaller loss of plasma due to decay of the plasma during transport from the remote primary chamber. This design also enables the heat load produced by the primary plasma source to be located remotely from the outlet.
- The primary plasma source may comprise a primary source chamber in which the plasma may be formed and a first coil for generating the plasma in the primary source chamber, the chamber comprising an inlet for receiving an input gas, and one or more outlets for removal of at least a portion of the plasma from the source chamber and into the guiding body. The secondary plasma source may comprise a secondary source chamber occupying at least a portion of the guiding body. The secondary plasma source may omit a coil for enhancing or generating plasma. The secondary plasma source may comprise a secondary source chamber and the arrangement may be adapted to generate a high brightness plasma in the secondary source chamber.
- A plasma generator may operate by capacitive coupling where an electric field is generated by a radio frequency (RF) voltage between two electrodes which induces the plasma formation, or by inductive coupling where a magnetic field is generated by an RF current through a coil which induces the plasma formation. In some embodiments, in operation, the primary plasma source may be adapted to generate a primary plasma via inductive coupling, and the secondary plasma source to generate a secondary plasma via capacitive coupling. The arrangement thus forms a hybrid plasma generator using both inductive and capacitive coupling to generate plasma. The arrangement may further comprise an electrode located near the outlet of the arrangement, wherein, in operation, the coil of the primary plasma source is capacitively coupled to the electrode via the plasma generated by the primary plasma source and/or the secondary plasma source. The electrode may be maintained at a fixed potential with respect to a voltage supplied to the coil of the primary plasma source, or it may be grounded with respect to a voltage supplied to the coil of the primary plasma source.
- The arrangement may also comprise an aperture array near the outlet, and may also comprise an additional electrode arranged for repelling or attracting plasma ions in the guiding body. The plasma formed by the plasma generator includes ions and radicals, and this arrangement enables retention of ions in the plasma generator or reduction of their energy, while permitting emission of radicals from the plasma generator.
- The primary plasma source may comprise a primary source chamber in which primary plasma is generated and the secondary plasma source may comprise a secondary source chamber in which the primary plasma is enhanced and/or secondary plasma is generated, the primary source chamber being larger than the secondary source chamber. The primary source chamber may have a larger cross-section than the secondary source chamber, and may have a greater internal volume. The larger primary source chamber can then be located further from the outlet than the secondary source chamber, allowing constructions where the smaller secondary source chamber can fit into narrow restricted spaces close to the location where the plasma is required.
- The arrangement may further comprise a pressure regulator for regulating pressure in the primary source chamber, and a flow or pressure restriction may be provided between the primary and secondary source chambers. The restriction may be adapted to maintain an operating pressure in the secondary source chamber at a lower pressure than in the primary source chamber. The arrangement may also be adapted for regulating the pressure in the secondary source chamber, or for regulating the pressure in both the primary and secondary source chambers.
- The secondary source chamber may have a length longer than the primary source chamber in a direction of the flow of plasma from the primary source chamber. The primary source chamber may have a diameter of 20 mm or more, and the secondary source chamber may have a diameter of less than 20 mm. The secondary source chamber may have an end section for directing plasma in a desired direction.
- The secondary source chamber may be arranged to generate plasma at a position close to an outlet of the arrangement, and the primary plasma source may be located further from the outlet than the secondary plasma source. This results in a design with a secondary plasma chamber closer to the outlet where the plasma is emitted, so that less of the plasma generated in the secondary chamber is lost by decay and other processes during transfer to the outlet.
- The hollow guiding body may comprise a funnel section located at the outlet of the primary plasma source arranged for guiding plasma generated by primary plasma source into the guiding body. The guiding body may comprise a quartz material or an inner surface comprising a quartz material, and the guiding body may be in the form of a tube or duct. The guiding body may have a bend or elbow to direct plasma from the outlet onto an area to be cleaned by the plasma.
- The primary plasma source may comprise a primary source chamber in which the plasma may be formed, and an aperture plate positioned between the primary source chamber and the guiding body, the aperture plate having one or more apertures for permitting flow of the plasma from the primary source chamber into the guiding body. The arrangement may further comprise an aperture plate at or near the outlet of the guiding body to confine at least a portion of the plasma in the guiding body from exiting through the outlet.
- In another aspect the invention relates to a method for generating a plasma, comprising flowing an input gas into a primary source chamber, energizing a first coil to form a primary plasma in the primary source chamber, flowing at least a portion of the primary plasma into a secondary source chamber, and generating a secondary plasma in the secondary source chamber. The step of flowing the primary plasma into the secondary source chamber may comprise flowing the plasma into a guiding body, at least a portion of the guiding body forming the secondary source chamber. The first plasma may be flowed from the primary source chamber through a restriction into a secondary source chamber.
- The method may comprise forming the primary plasma in the primary source chamber via inductive coupling, and generating the secondary plasma in the secondary source chamber via capacitive coupling.
- The secondary source chamber may omit a coil for forming a plasma. The method may further comprise regulating pressure in the primary source chamber and the secondary source chamber, and the step of regulating the pressure may comprise maintaining a lower pressure in the secondary source chamber than in the primary source chamber. The primary plasma may be a relatively low brightness plasma and the secondary plasma may be a relatively high brightness plasma.
- The method may further comprise stabilizing the formation of plasma in the secondary source chamber with the primary plasma flowing from the primary source chamber, and may further comprise maintaining a lower pressure in the secondary source chamber than in the primary source chamber.
- In another aspect the invention relates to a cleaning apparatus for cleaning contaminants from a surface, the apparatus comprising an arrangement for generating plasma as described herein, and means for directing the plasma onto the surface to be cleaned.
- In yet another aspect the invention relates to a charged particle lithography machine, comprising a beamlet generator for generating a plurality of charged particle beamlets and a plurality of beamlet manipulator elements for manipulating the beamlets, each beamlet manipulator element comprising a plurality of apertures through which the beamlets pass, the machine further comprising an arrangement for generating plasma as described herein, adapted to generate plasma and direct the plasma onto a surface of one or more of the beamlet manipulator elements.
- Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings in which:
-
FIG. 1 is a schematic diagram of an embodiment of a radio frequency (RF) plasma generator; -
FIGS. 2A , 2B and 2C are schematic diagrams of an embodiment of a plasma generator including a guiding body; -
FIGS. 3A and 3B are schematic diagrams of the embodiment ofFIG. 2 in operation; -
FIG. 4 is a schematic diagram of an embodiment including aperture plates and an electrode at the outlet; -
FIG. 5 is a schematic diagram of another embodiment including aperture plates and electrodes at the outlet; -
FIG. 6 is a photograph of a plasma chamber with a guiding body showing plasma forming in the primary plasma chamber; -
FIG. 7 is a photograph of the plasma chamber ofFIG. 6 showing plasma forming in the guiding body; and -
FIG. 8 is a schematic diagram of an embodiment of a charged particle lithography machine. - The following describes certain embodiments of the invention, given by way of example only and with reference to the figures.
-
FIG. 1 shows a radio frequency (RF) plasma generator comprising achamber 2 with anRF coil 4 around the outside of the chamber. An input gas such as oxygen or hydrogen or other suitable gas is passed into the chamber viainlet 5 and thecoil 4 is energized with an RF voltage to produce a plasma including radicals, such as oxygen atom radicals, which exit the chamber via one ormore outlets 6. In the following description, except where the context indicates otherwise, the term plasma is used for simplicity to denote a plasma and/or radicals produced in such a plasma generator. - Contaminants such as electron beam induced deposition (EBID), generally comprising carbon containing compounds, form on surfaces in a charged particle lithography system, such as the surfaces of beamlet manipulator elements (such as beamlet modulators, deflectors, lenses, aperture arrays, beam stop arrays, etc.). For removing contaminants such as EBID deposits, radicals, such as oxygen atom radicals, may be used, reacting with carbon in the EBID deposits to form carbon monoxide. Plasma typically comprises a mixture of gas molecules, ions, electrons, and atomic radicals. For cleaning EBID deposits, atomic ions may also be used. However, due to their electrical charge, ions may be accelerated by electric fields generated in or around the plasma generator system, and have sufficient kinetic energy to sputter the surface to be cleaned. This can result in removing not just the contaminant deposits, but also part of the surface underlying the deposits, so damaging the surface. Uncharged radicals generally have a lower kinetic energy. i.e. the thermal energy of the radicals, and are more suitable in many cleaning applications for this reason.
- Excellent cleaning rates of greater than 5 micron per hour can be achieved by atomic radical cleaning where there is a direct view from the plasma generator source to the contaminated area to be cleaned. However, this method cannot be easily implemented in situations where the deposits are formed on surfaces with cannot be easily accessed and in which there is little room to locate the plasma generator with a direct line from the source to the area to be cleaned. The beam stop array and beamlet aperture array are areas that exhibit these problems, typically having a restricted space available above the surface of the beam stop of 5 mm of less. Typically, plasma sources are constructed with a long tube of
length 20 cm or more and a diameter of about 10 cm. - For example, for cleaning the beam stop array and beamlet aperture array in a charged particle lithography system there is typically very limited space (e.g. about 10×10×10 mm3) available to implement a plasma source in the vicinity of these elements. The problem in designing a miniature plasma source for use in locations with very restricted space lies in the aspect ratio of the area to volume of the plasma generator. For a large plasma source this ratio is small, but as the size of the plasma source is reduced the ratio increases. This results in minor instabilities coupling into or out of the plasma in the source chamber via its surface, having an increasingly large effect. As a consequence, the plasma may be hard to ignite and easily extinguished due to these instabilities.
- Instead, a much larger source may be used (e.g. about 100×100×100 mm3) to be situated at approximately 200 mm from the elements to be cleaned. The plasma radicals must then be transported from the plasma generator to the site of the cleaning.
- The present invention provides a plasma generator which permits direct access to the contaminated area even where only a limited volume is available at the cleaning site to locate the cleaning apparatus. A plasma source is placed near the contaminated area to be cleaned, and a guiding path is attached to the plasma generator and the plasma radicals produced are transported towards the area to be cleaned.
-
FIGS. 2A , 2B and 2C schematically show arrangements for removal of contaminant deposits, in particular for removal of contaminants deposited on surfaces that are located in areas with restricted or difficult access. The arrangements comprise a plasma generator similar to that shown inFIG. 1 , further referred to as theprimary source chamber 15, which functions as aprimary plasma source 1. The arrangement further comprises a hollow guidingbody 11, such as tube or duct, for guiding plasma towards a predetermined destination area. It will be recognized that various configurations are possible, and three possible configurations are shown, and features of any of these embodiments may be used in any of the other embodiments. The arrangement inFIG. 2A the guidingbody 11 includes afunnel portion 10 where the guidingbody 11 is coupled to theprimary source chamber 15, and the chamber end wall withoutlets 6 function as an aperture plate to permit the plasma and radicals to enter the guidingbody 11 from thechamber 15. The guidingbody 11 includes anelbow 12 near the end of the guiding body to direct plasma exiting the guiding body. The arrangement inFIG. 2B omits the funnel portion, the chamber end wall, and the elbow, so that astraight guiding body 11 having a smaller cross section than theprimary source chamber 15 is coupled directly to theprimary source chamber 15. The arrangement inFIG. 2C features a continuous hollow body, a wider portion forming theprimary source chamber 15 and a narrower portion forming the guidingbody 11. A hollow body having a uniform cross section may also be used, one portion of the hollow body functioning as theprimary source chamber 15 and another portion functioning as the guidingbody 11. - The guiding
body 11 may be straight or may comprise one or more bends such as anelbow 12 or bend 13 to direct the plasma in a desired direction. Preferably, the guidingbody 11 is as straight as possible to increase the average lifetime of radicals being transferred through the tube. The guiding body has anoutlet 14 which may be located in close proximity of the contaminant deposit to be reduced or removed. Typically, theoutlet 14 is in direct contact with a vacuum environment. - The plasma and radicals generated in
primary source chamber 15 ofprimary source 1 are guided towards the contaminant deposit to be reduced or removed via the guidingbody 11. The guidingbody 11 may be made of quartz, or with inner surface coated with quartz, to suppress extinction of the radicals when they interact with these parts of the device. Embodiments of the invention are described herein with reference to plasma formed from oxygen. However, it will be understood that the invention may also employ plasmas from other gases, such as hydrogen or nitrogen. -
FIG. 3A shows the arrangement ofFIG. 2A in operation. It will be understood that arrangements shown inFIGS. 2B and 2C may also be operated in a similar manner. Oxygen is supplied to theprimary source chamber 15 andRF coil 4 is energized to inductively heat the oxygen, and aplasma 20 is generated inprimary source chamber 15. The oxygen pressure may be adjusted, for example, to produce a relatively high pressure in thechamber 15. Theplasma 20, and in particular radicals produced therein, may exit theprimary source chamber 15 as schematically represented by dashedarrow 21 and flow into the guidingbody 11. - Major losses of radicals are typically observed in these arrangements during transport from the
primary source chamber 15 to theoutlet 14 at the site where the cleaning is to take place. Several processes will cause annihilation of the atomic radicals, such as volume recombination, surface adsorption and surface recombination. The losses of such a system are significant, e.g. using power of 600 W for the source chamber, the efficiency of transport of the radicals is only 0.4%. The losses in the guidingbody 11 can be compensated by using a more intense plasma source, but the thermal load caused by using such high power for the plasma generator becomes a serious problem for many applications, particularly when used in a vacuum environment as required for lithography applications. By carefully designing the pressure and temperature of the primary source chamber and guiding body, the losses can be minimized. - The plasma generator may also be made more effective by more efficient transport of plasma through the guiding
body 11, and/or generation of plasma in the guidingbody 11 so that the guiding body is not merely conveying plasma formed in theprimary source chamber 15, but additional plasma is formed in the guiding body, close to the location where it is needed for cleaning. In this case asecondary plasma source 25 is formed, with a portion of the guiding body functioning as asecondary source chamber 16. - This may be accomplished in different ways. By adjusting pressure in the primary source chamber and pressure in the guiding body relative to the surrounding environment, plasma may be guided from the
primary source chamber 15 into the guidingbody 11 and through the guiding body to theoutlet 14. The pressure should preferably decrease from theprimary source chamber 15 to the guidingbody 11 and to the environment outside theoutlet 14 in order to promote flow of plasma from thechamber 15 to theoutlet 14. Depending on the plasma formation, the pressure can be optimized through the device, e.g. by use of aperture plates (such as aperture plate 31 at the entrance to the guidingbody 11 andaperture plate 32 at the outlet 14) and/or by adjusting the relative sizes and geometry of theprimary source chamber 15, guidingbody 11 and theoutlet 14. - By adjusting pressures in the
primary source chamber 15 and in the guidingbody 11, plasma can be formed in the guiding body. The pressures may be adjusted to obtain conditions where a high brightness plasma is formed in the guiding body at a relatively lower pressure than the primary source chamber. This results in the formation of plasma in the guiding body closer to the location where it is needed to produce more effective cleaning. - The pressure in the guiding
body 11 may be relatively low in comparison to theprimary source chamber 15, depending on the geometry of the tube and size of theoutlet 14, and the ambient pressure of the surrounding environment. A relatively high pressure in theprimary source chamber 15 will displace more plasma into the guidingbody 11, thus shortening the path for the radicals to reach theoutlet 14 and the cleaning site, and thus reducing the loss of radicals due to recombination and other effects, and thereby increasing the cleaning rate. - In a lithography machine cleaning application, the ambient pressure may be low inside the lithography machine vacuum chamber, e.g. 10−3 millibar or lower. The pressure in the guiding
body 11 may be higher, e.g. 10−2 millibar, but lower than the pressure in theprimary plasma chamber 15, aiding the formation of plasma in the guiding body itself, even though there is no RF coil around the guiding body. This may be due to the relatively lower pressure in the guidingbody 11 and may be assisted by the flow of plasma from theprimary source chamber 15, conveying the effect of the RF coil at the primary source chamber, e.g. by capacitive coupling, into the guiding body. Plasma is an electrical conductor, and thus may conduct RF current resulting from excitation of the RF coils 4 surrounding theprimary source chamber 15, into the guidingbody 11 where it may generate more plasma. - The resulting effect is to generate plasma in the guiding
body 11, a portion of the guiding body functioning as a “passive”secondary plasma source 25. The guiding body is not merely conveying plasma formed in byprimary plasma source 1, but additional plasma is formed in asecondary plasma source 25 in the guidingbody 11, close to the location where it is needed for cleaning. By adjusting the relative pressures in the system, tuned by adjusting the entry pressure of the input gas to theprimary source chamber 15, and adapting the dimensions of the guidingbody 11 andoutlet 14, the plasma formed in thesecondary plasma source 25 may be high brightness plasma suitable for effective cleaning of the EBID deposits.FIG. 4 shows this effect in whichplasma 20 is formed in theprimary source chamber 15, plasma (or components of the plasma) 21 flows into the guidingbody 11, andplasma 22 is subsequently formed in asecondary source chamber 16 in the guidingbody 11. Theplasma 21 acts as “seed” plasma to enhance plasma formation in thesecondary source chamber 16 near to theoutlet 14, where it acts as a source of atomic radicals close to the location where they are needed. - An alternative is to operate the system at a low pressure in the
primary source chamber 15 and guidingbody 11 to reduce the loss of radicals by decreasing the recombination probability, and thereby increasing the cleaning rate. - The embodiment shown in
FIG. 4 employs an optional aperture plate 31 between theprimary source chamber 15 and guidingbody 11 at the exit of the primary source. The gas flow conductance of the aperture plate 31 can be adjusted (by adjusting the number and size of the apertures in the plate) to adjust the relative pressures in thesource chamber 15 and guidingbody 11. The aperture plate 31 also operates to partly confine the plasma in theprimary source chamber 15 by reducing the quantity of ions flowing from thechamber 15 into the guidingbody 11, due partly to recombination of ions and electrons due to collisions, while permitting flow of radicals into the guidingbody 11. The aperture plate 31 may be omitted altogether where maximum flow of plasma into guidingbody 11 is desired to maximize formation ofsecondary plasma 22 in the guidingbody 11. - An
optional aperture plate 32 may also be placed near the end of the guiding body 11 (as shown in theFIG. 5 embodiment), preferably at theoutlet 14. Theaperture plate 32 at theoutlet 14 can be used to assist in regulating pressure in the guidingbody 11, typically in conjunction with aperture plate 31.Aperture plate 32 may also operate to partly confine the plasma inside the guidingbody 11, limiting the ability of high kinetic energy ions from striking the area to be cleaned, or this function may be performed by theelectrode 32. These high energy ions may sputter the top surface of the area to be cleaned and this can lead to damage of the part being cleaned. Furthermore, when bothaperture plates 31 and 32 are used, the gas flow conductance of the aperture plates can be adjusted so that the pressure in both theprimary source chamber 15 and the guiding body 11 (i.e. secondary source chamber 16) is optimal, to improve the efficiency of the plasma generator. - The aperture plates 31 and/or 32 may be made from a conducting material such as a metal, or a non-conducting material such as a plastic, ceramic or quartz. The
aperture plate 32 may be made from a conducting material to function also as an electrode, which may be grounded or connected to a common voltage. Alternatively, aseparate electrode 30 may be installed near theoutlet 14, as shown in the embodiment ofFIG. 4 , which may be grounded or connected to a common voltage. - Such an electrode 30 (or grounded aperture plate 32) near the
outlet 14 operates to generate plasma in the guidingbody 11 and/or enhance plasma flowing into the guidingbody 11, through capacitive coupling. Plasma is a conductor, and as it flows from theprimary source chamber 15 into the guidingbody 11 towards theelectrode 30, it creates a capacitive coupling between theRF coil 4 of theprimary plasma source 1 and theelectrode 30 at theoutlet 14 at the end of thesecondary source chamber 25. The RF voltage supplied to theRF coil 4 generates an electric field between theRF coil 4 andelectrode 30 conducted by theseed plasma 21 flowing into the guidingbody 11, which excites the plasma in the guidingbody 11 between theRF coil 4 andelectrode 30 which enhances or induces formation ofplasma 22 in the guidingbody 11. Plasma generation via such capacitive coupling is typically difficult to achieve unless the guiding body is short, i.e. short distance from the primary plasma source to the cleaning site, particularly when there is grounded metal near to the plasma generator, which is usually the case where the plasma generator is surrounded by other equipment. Theelectrode 30 may also operate to partly confine theplasma 22 inside the guidingbody 11, e.g. taking the form of a mesh or aperture plate. The electrode 40 also functions to avoid or reduce capacitive coupling between theRF coil 4 and the part being cleaned where the part is conductive and grounded. This can avoid damage to the part being cleaned where it is vulnerable to stray electrical current, e.g. a beamlet modulation array of a charged particle lithography machine. - However, a “hybrid” plasma generator, which uses both inductive and capacitive coupling to generate plasma as described herein, can overcome this difficulty. The system generates a
primary plasma 20 in theprimary source chamber 15 using inductive coupling, where a magnetic field generated by an RF current through thecoil 4 induces plasma formation, and asecondary plasma 22 in the guidingbody 11/second plasma chamber 16 using capacitive coupling, where an electric field is generated by an RF voltage between thecoil 4 andelectrode 30 induces plasma formation. The primary inductively-coupled plasma can “grow” in the guidingbody 11 towards theelectrode 30 near the cleaning site, changing from inductively coupled to capacitively coupled. This process starts with a primary inductively-coupled plasma that can be formed in a grounded environment, i.e. where there are grounded conductors nearby. In such a grounded environment, it is very difficult to sustain a capacitively-coupled plasma. Theprimary plasma 20 in theprimary source chamber 15 heats the nearby volume in the guidingbody 11, partly due to flow ofhot plasma 21 into the guiding body, and the plasma grows a little more in the guiding body. The plasma is a conductor and its growth/formation in the guiding body extends the electric field from theRF coil 4 of theprimary source 1 further into the guidingbody 11, aiding further plasma growth/formation. This process continues until the plasma reaches theelectrode 30 and a high brightness plasma can be formed in the guidingbody 11/second plasma chamber 16. - The embodiment in
FIG. 4 has abend 13 at the end of the guidingbody 11 near theoutlet 14, rather than a 90degree elbow 12, while the embodiment ofFIG. 5 has astraight guiding body 11. Any of the configurations shown in any of the drawings may be used with any of the embodiments, with or without thefunnel section 10 or aperture plates 31 and/or 32 orelectrodes 30 and/or 34. - The embodiment shown in
FIG. 5 employs anadditional electrode 34 to further reduce the quantity of atomic ions exiting theoutlet 14 of the plasma generator and/or reduce their velocity. Theadditional electrode 34 may be energized with a voltage V to repel or attract the ions, e.g. a positive voltage to repel negative ions, or an RF voltage opposite to the voltage supplied to theRF coil 4. Note that theelectrode 30,aperture plate 32, andadditional electrode 34 may be used in various combinations to achieve the desired results, i.e. to extend plasma formation into the guidingbody 11 while controlling the emission of energetic ions while permitting the emission of atomic radicals. These elements operate as a atomic radical/ion filter, to let radicals pass while reducing or preventing ion emission. - This new design provides an arrangement with two plasma sources, a smaller
secondary plasma source 25 located close to theplasma outlet 14 and a largerprimary plasma source 1 further from theoutlet 14, the arrangement including a guidingbody 11 for guiding plasma generated by theprimary plasma source 1 to thesecondary plasma source 25 to stabilize plasma formation by thesecondary plasma source 25. The design is simple with very few parts, thesecondary plasma source 25 operating by capacitive coupling to anelectrode 30/aperture plate 32. -
FIG. 6 is a photograph of a plasma chamber in the center of the photograph, with an guiding body in the form of an extension tube extending towards the bottom of the photograph. Greenish low brightness plasma is flowing from the primary plasma chamber into the guiding body towards the outlet at the bottom of the photograph. -
FIG. 7 is a photograph of the plasma chamber ofFIG. 6 at the top of the photograph, with the guiding body extending towards the bottom of the photograph. The faint greenish low brightness plasma in the guiding body has been replaced by high brightness plasma which is forming in the guiding budy and exiting the outlet at the bottom of the photograph. -
FIG. 8 shows a simplified schematic diagram of an electron-optical column of a charged particle lithography element. Such lithography systems are described for example in U.S. Pat. Nos. 6,897,458; 6,958,804; 7,019,908; 7,084,414; and 7,129,502, U.S. patent publication no. 2007/0064213, and co-pending U.S. patent application nos. 61/031,573; 61/031,594; 61/045,243; 61/055,839; 61/058,596; and 61/101,682, which are all assigned to the owner of the present invention and are all hereby incorporated by reference in their entireties. - In the embodiment shown in
FIG. 8 , the lithography element column comprises anelectron source 110 producing an expandingelectron beam 130, which is collimated bycollimator lens system 113. The collimated electron beam impinges on anaperture array 114 a, which blocks part of the beam to create a plurality ofsub-beams 134, which pass through a condenser lens array 116 which focuses the sub-beams. The sub-beams impinge on a second aperture array 114 b which creates a plurality of beamlets 133 from each sub-beam 134. The system generates a very large number of beamlets 133, preferably about 10,000 to 1,000,000 beamlets. - A beamlet blanker array 117, comprising a plurality of blanking electrodes, deflects selected ones of the beamlets. The undeflected beamlets arrive at
beam stop array 118 and pass through a corresponding aperture, while the deflected beamlets miss the corresponding aperture and are stopped by the beam stop array. Thus, the beamlet blaker array 117 and beam stop 118 operate together to switch the individual beamlets on and off. The undeflected beamlets pass through thebeam stop array 119, and through abeam deflector array 119 which deflects the beamlets to scan the beamlets across the surface of target orsubstrate 121. Next, the beamlets pass through projection lens arrays 120 and are projected ontosubstrate 121 which is positioned on a moveable stage for carrying the substrate. For lithography applications, the substrate usually comprises a wafer provided with a charged-particle sensitive layer or resist layer. - The lithography element column operates in a vacuum environment. A vacuum is desired to remove particles which may be ionized by the charged particle beams and become attracted to the source, may dissociate and be deposited onto the machine components, and may disperse the charged particle beams. A vacuum of at least 10−6 bar is typically required. In order to maintain the vacuum environment, the charged particle lithography system is located in a vacuum chamber. All of the major elements of the lithography element are preferably housed in a common vacuum chamber, including the charged particle source, projector system for projecting the beamlets onto the substrate, and the moveable stage.
- The invention has been described by reference to certain embodiments discussed above. It will be recognized that these embodiments are susceptible to various modifications and alternative forms well known to those of skill in the art without departing from the spirit and scope of the invention. Accordingly, although specific embodiments have been described, these are examples only and are not limiting upon the scope of the invention, which is defined in the accompanying claims.
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---|---|---|---|---|
KR101314666B1 (en) * | 2011-11-28 | 2013-10-04 | 최대규 | Hybride plasma reactor |
US9123507B2 (en) | 2012-03-20 | 2015-09-01 | Mapper Lithography Ip B.V. | Arrangement and method for transporting radicals |
WO2014168876A2 (en) | 2013-04-08 | 2014-10-16 | Perkinelmer Health Sciences, Inc. | Capacitively coupled devices and oscillators |
EP3113583B1 (en) * | 2014-02-24 | 2020-08-12 | National University Corporation Nagoya University | Radical source and molecular beam epitaxy device |
US20160042916A1 (en) * | 2014-08-06 | 2016-02-11 | Applied Materials, Inc. | Post-chamber abatement using upstream plasma sources |
CN106255304A (en) * | 2016-07-19 | 2016-12-21 | 中国人民解放军装甲兵工程学院 | Plasma density computational methods in a kind of cylinder |
WO2018235194A1 (en) * | 2017-06-21 | 2018-12-27 | 株式会社日立ハイテクノロジーズ | Charged-particle beam device and cleaning method |
Citations (7)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US5518572A (en) * | 1991-06-10 | 1996-05-21 | Kawasaki Steel Corporation | Plasma processing system and method |
US6136387A (en) * | 1997-06-04 | 2000-10-24 | Tokyo Electron Limited | Ion flow forming method and apparatus |
US6297595B1 (en) * | 1995-11-15 | 2001-10-02 | Applied Materials, Inc. | Method and apparatus for generating a plasma |
US6897458B2 (en) * | 2002-10-30 | 2005-05-24 | Mapper Lithography Ip B.V. | Electron beam exposure system |
US20090250340A1 (en) * | 2005-09-09 | 2009-10-08 | Naruyasu Sasaki | Ion source and plasma processing apparatus |
US20110284774A1 (en) * | 2009-05-27 | 2011-11-24 | Gigaphoton Inc. | Target output device and extreme ultraviolet light source apparatus |
US20110298376A1 (en) * | 2009-01-13 | 2011-12-08 | River Bell Co. | Apparatus And Method For Producing Plasma |
Family Cites Families (21)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US3157308A (en) | 1961-09-05 | 1964-11-17 | Clark Mfg Co J L | Canister type container and method of making the same |
US3159408A (en) | 1961-10-05 | 1964-12-01 | Grace W R & Co | Chuck |
GB1222243A (en) * | 1967-07-05 | 1971-02-10 | Kearns Tribune Corp | Generating plasma |
US4524308A (en) | 1984-06-01 | 1985-06-18 | Sony Corporation | Circuits for accomplishing electron beam convergence in color cathode ray tubes |
AU6449994A (en) | 1993-04-30 | 1994-11-21 | Board Of Regents, The University Of Texas System | Megavoltage scanning imager and method for its use |
JPH07245193A (en) * | 1994-03-02 | 1995-09-19 | Nissin Electric Co Ltd | Plasma generating device and plasma processing device |
EP0766405A1 (en) | 1995-09-29 | 1997-04-02 | STMicroelectronics S.r.l. | Successive approximation register without redundancy |
EP2302458B1 (en) | 2002-10-25 | 2016-09-14 | Mapper Lithography Ip B.V. | Lithography system |
US7129502B2 (en) | 2003-03-10 | 2006-10-31 | Mapper Lithography Ip B.V. | Apparatus for generating a plurality of beamlets |
EP1627412B1 (en) | 2003-05-28 | 2007-04-04 | Mapper Lithography Ip B.V. | Charged particle beamlet exposure system |
ATE381728T1 (en) | 2003-07-30 | 2008-01-15 | Mapper Lithography Ip Bv | MODULATOR CIRCUITS |
EP1855833B1 (en) * | 2005-03-11 | 2020-02-26 | PerkinElmer, Inc. | Plasma devices and method of using them |
US7709815B2 (en) | 2005-09-16 | 2010-05-04 | Mapper Lithography Ip B.V. | Lithography system and projection method |
DE102008004602B4 (en) * | 2008-01-16 | 2022-01-05 | Daimler Ag | Indoor wire arc torch |
KR101481950B1 (en) | 2008-02-26 | 2015-01-14 | 마퍼 리쏘그라피 아이피 비.브이. | Projection lens arrangement |
WO2009106560A1 (en) | 2008-02-26 | 2009-09-03 | Mapper Lithography Ip B.V. | Projection lens arrangement |
US8445869B2 (en) | 2008-04-15 | 2013-05-21 | Mapper Lithography Ip B.V. | Projection lens arrangement |
KR20110030466A (en) | 2008-05-23 | 2011-03-23 | 마퍼 리쏘그라피 아이피 비.브이. | Imaging system |
KR101647768B1 (en) | 2008-06-04 | 2016-08-11 | 마퍼 리쏘그라피 아이피 비.브이. | Method of and system for exposing a target |
JP5420670B2 (en) | 2008-10-01 | 2014-02-19 | マッパー・リソグラフィー・アイピー・ビー.ブイ. | Electrostatic lens structure |
US10168208B2 (en) | 2015-04-03 | 2019-01-01 | Hitachi High-Technologies Corporation | Light amount detection device, immune analyzing apparatus and charged particle beam apparatus that each use the light amount detection device |
-
2012
- 2012-09-28 WO PCT/EP2012/069226 patent/WO2013045636A2/en active Application Filing
- 2012-09-28 WO PCT/EP2012/069234 patent/WO2013045643A2/en active Application Filing
- 2012-09-28 JP JP2014532410A patent/JP2014535125A/en active Pending
- 2012-09-28 TW TW101136127A patent/TW201330705A/en unknown
- 2012-09-28 CN CN201280058528.3A patent/CN103959919A/en active Pending
- 2012-09-28 US US14/348,062 patent/US9224580B2/en active Active
- 2012-09-28 US US14/348,071 patent/US20140252953A1/en not_active Abandoned
Patent Citations (7)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US5518572A (en) * | 1991-06-10 | 1996-05-21 | Kawasaki Steel Corporation | Plasma processing system and method |
US6297595B1 (en) * | 1995-11-15 | 2001-10-02 | Applied Materials, Inc. | Method and apparatus for generating a plasma |
US6136387A (en) * | 1997-06-04 | 2000-10-24 | Tokyo Electron Limited | Ion flow forming method and apparatus |
US6897458B2 (en) * | 2002-10-30 | 2005-05-24 | Mapper Lithography Ip B.V. | Electron beam exposure system |
US20090250340A1 (en) * | 2005-09-09 | 2009-10-08 | Naruyasu Sasaki | Ion source and plasma processing apparatus |
US20110298376A1 (en) * | 2009-01-13 | 2011-12-08 | River Bell Co. | Apparatus And Method For Producing Plasma |
US20110284774A1 (en) * | 2009-05-27 | 2011-11-24 | Gigaphoton Inc. | Target output device and extreme ultraviolet light source apparatus |
Cited By (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US20230209694A1 (en) * | 2021-12-23 | 2023-06-29 | Finesse Technology Co., Ltd. | Hybrid plasma source and operation method thereof |
US11895765B2 (en) * | 2021-12-23 | 2024-02-06 | Finesse Technology Co., Ltd. | Hybrid plasma source and operation method thereof |
Also Published As
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US20140231667A1 (en) | 2014-08-21 |
WO2013045643A3 (en) | 2013-06-20 |
WO2013045636A4 (en) | 2013-09-12 |
WO2013045636A3 (en) | 2013-07-18 |
WO2013045643A2 (en) | 2013-04-04 |
CN103959919A (en) | 2014-07-30 |
TW201330705A (en) | 2013-07-16 |
JP2014535125A (en) | 2014-12-25 |
US9224580B2 (en) | 2015-12-29 |
WO2013045636A9 (en) | 2013-11-28 |
WO2013045636A2 (en) | 2013-04-04 |
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