Laser produced plasma euv light source
An EUV light source is disclosed that may include a laser source, e.g. CO2 laser, a plasma chamber, and a beam delivery system for passing a laser beam from the laser source into the plasma chamber. Embodiments are disclosed which may include one or more of the following; a bypass line may be provided to establish fluid communication between the plasma chamber and the auxiliary chamber, a focusing optic, e.g. mirror, for focusing the laser beam to a focal spot in the plasma chamber, a steering optic for steering the laser beam focal spot in the plasma chamber, and an optical arrangement for adjusting focal power.
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The present application is a continuation of U.S. patent application Ser. No. 11/358,992, entitled LASER PRODUCED PLASMA EUV LIGHT SOURCE, filed on Feb. 21, 2006, Attorney Docket No. 2005-0081-01, which is a continuation-in-part application of U.S. patent application Ser. No. 11/174,442, entitled SYSTEMS AND METHODS FOR REDUCING THE INFLUENCE OF PLASMA-GENERATED DEBRIS ON THE INTERNAL COMPONENTS OF AN EUV LIGHT SOURCE, filed on Jun. 29, 2005, Attorney Docket No. 2004-0110-01 which is a continuation-in-part application of U.S. patent application Ser. No. 10/979,945, entitled LPP EUV LIGHT SOURCE, filed on Nov. 1, 2004, Attorney Docket No. 2004-0088-01, the disclosures of each of which are hereby incorporated by reference herein.
U.S. patent application Ser. No. 11/358,992 is also a continuation-in-part application of U.S. patent application Ser. No. 11/067,099, entitled SYSTEMS FOR PROTECTING COMPONENTS OF AN EUV LIGHT SOURCE FROM PLASMA-GENERATED DEBRIS, filed on Feb. 25, 2005, Attorney Docket No. 2004-0117-01 the disclosure of which is hereby incorporated by reference herein.
The present invention is also related to U.S. patent application Ser. No. 10/900,839, entitled EUV LIGHT SOURCE, filed on Jul. 27, 2004, Attorney Docket No. 2004-0044-01, U.S. patent application Ser. No. 10/803,526, entitled HIGH REPETITION RATE LPP EUV LIGHT SOURCE, filed on Mar. 17, 2004, Attorney Docket No. 2003-0125-01, and U.S. patent application Ser. No. 10/798,740, entitled COLLECTOR FOR EUV LIGHT, filed on Mar. 10, 2004, Attorney Docket No. 2003-0083-01, the disclosures of each of which are hereby incorporated by reference herein.
The present application is also related to co-pending U.S. non-provisional patent application entitled LASER PRODUCED PLASMA EUV LIGHT SOURCE WITH PRE-PULSE filed concurrently herewith, attorney docket number 2005-0085-01, the entire contents of which are hereby incorporated by reference herein.
The present application is also related to co-pending U.S. nonprovisional patent application entitled SOURCE MATERIAL DISPENSER FOR EUV LIGHT SOURCE filed concurrently herewith, attorney docket number 2005-0102-01, the entire contents of which are hereby incorporated by reference herein.
The present application is also related to co-pending U.S. provisional patent application entitled EXTREME ULTRAVIOLET LIGHT SOURCE filed concurrently herewith, attorney docket number 2006-0010-01, the entire contents of which are hereby incorporated by reference herein.
FIELD OF THE INVENTIONThe present invention relates to extreme ultraviolet (“EUV”) light sources which provide EUV light from a plasma that is created from a source material and collected and directed to a focus for utilization outside of the EUV light source chamber, e.g., for semiconductor integrated circuit manufacturing photolithography e.g., at wavelengths of around 50 nm and below.
BACKGROUND OF THE INVENTIONExtreme ultraviolet (“EUV”) light, e.g., electromagnetic radiation having wavelengths of around 50 nm or less (also sometimes referred to as soft x-rays), and including light at a wavelength of about 13.5 nm, can be used in photolithography processes to produce extremely small features in substrates, e.g., silicon wafers.
Methods to produce EUV light include, but are not necessarily limited to, converting a material into a plasma state that has an element, e.g., xenon, lithium or tin, with an emission line in the EUV range. In one such method, often termed laser produced plasma (“LPP”) the required plasma can be produced by irradiating a target material, such as a droplet, stream or cluster of material having the required line-emitting element, with a laser beam.
For this process, the plasma is typically produced in a sealed vessel, e.g., vacuum chamber, and monitored using various types of metrology equipment. In addition to generating EUV radiation, these plasma processes also typically generate undesirable by-products in the plasma chamber which can include heat, high energy ions and scattered debris from the plasma formation, e.g., atoms and/or clumps/microdroplets of source material that is not fully ionized in the plasma formation process.
These plasma formation by-products can potentially damage or reduce the operational efficiency of the various plasma chamber optical elements including, but not limited to, collector mirrors including multi-layer mirrors (MLM's) capable of EUV reflection at normal incidence and/or grazing incidence, the surfaces of metrology detectors, windows used to image the plasma formation process, and the laser input window. The heat, high energy ions and/or source material debris may be damaging to the optical elements in a number of ways, including heating them, coating them with materials which reduce light transmission, penetrating into them and, e.g., damaging structural integrity and/or optical properties, e.g., the ability of a mirror to reflect light at such short wavelengths, corroding or eroding them and/or diffusing into them. For some source materials, e.g. tin, it may be desirable to introduce an etchant, e.g. HBr into the plasma chamber to etch debris that deposits on the optical elements. It is further contemplated that the affected surfaces of the elements may be heated to increase the reaction rate of the etchant.
In addition, some optical elements, e.g., the laser input window, form a part of the vacuum chamber, and heretofore, have typically been placed under a considerable stress due to a pressure differential between the relatively high vacuum in the plasma chamber and the pressure, e.g. atmospheric pressure, outside the plasma chamber. For these elements, deposits and heat can combine to fracture (i.e., crack) the element resulting in a loss of vacuum and requiring a costly repair. To accommodate this stress and prevent fracture, laser input windows have generally been rather thick, and, as a consequence, are subject to thermal lensing. This thermal lensing, in turn, can reduce the ability to properly steer and focus a laser beam to a desired location within the plasma chamber. For example, for use in some LPP EUV light sources, it is contemplated that a laser beam be focused to a spot diameter of about 300 μm or less.
In addition to reducing problems associated with thermal lensing, a laser beam delivery system for an EUV light source may have components that are exposed to the plasma chamber environment. These components may include the laser input window and in some cases focusing and/or steering optics. For these components, it may be desirable to use materials that are compatible with the etchant and heat used in debris mitigation.
With the above in mind, Applicants disclose systems and methods for effectively delivering and focusing a laser beam to a selected location in an EUV light source.
SUMMARY OF THE INVENTIONAn EUV light source is disclosed that may include a laser source, e.g. CO2 laser, a plasma chamber, and a beam delivery system having at least one auxiliary chamber. The auxiliary chamber may have an input window for passing a laser beam from the laser source into the auxiliary chamber and an exit window for passing the laser beam into the plasma chamber.
In one embodiment, a bypass line may be provided to establish fluid communication between the plasma chamber and the auxiliary chamber. A valve may be provided to close the bypass line. In a particular embodiment, a focusing optic, e.g. mirror, may be disposed in the auxiliary chamber for focusing the laser beam to a focal spot in the plasma chamber. In another embodiment, the focusing optic, e.g. mirror, may be disposed in the plasma chamber.
In another aspect, a focusing optic that is moveable to selectively move the location of the focal spot may be provided. In one embodiment, a target delivery system, e.g. droplet generator, may be provided for delivering a plasma source material to a plasma formation site in the plasma chamber together with a target position detector for generating a signal indicative of target position. With this arrangement, the focusing optic may be moveable in response to the signal from the target position detector to locate the focal spot along a target trajectory.
In still another aspect of an embodiment, a steering optic, e.g. flat mirror mounted on a tip-tilt actuator, may be provided for steering the laser beam focal spot in the plasma chamber. In a particular embodiment, the steering optic and focusing optic may be moveable together in a first direction to move the focal spot along a path parallel to the first direction. Like the focusing optic, the steering optic may be moveable in response to a signal from as target position detector to locate the focal spot along a target trajectory. An optical assembly, e.g. z-fold telescope, may be provided to adjust focal power.
For one or more of the above described embodiments, a plasma may be created in the plasma chamber comprising a plasma formation material, e.g. Sn, and an etchant for the plasma formation material, e.g. HBr, HI, Br2, Cl2, HCl, H2 or combinations thereof, may be introduced into the plasma chamber. In a particular embodiment, a heating subsystem may be provided to heat deposited plasma formation material on the exit window to a temperature greater than 150° C. to increase a rate of a chemical reaction between deposited plasma formation material and the etchant.
In one aspect, an EUV light source may include a laser source having a discharge chamber operating at a discharge pressure, e.g. CO2 laser, a plasma chamber, and a beam delivery system having at least one auxiliary chamber. The auxiliary chamber may have an input window for passing a laser beam from the laser source into the auxiliary chamber and an exit window for passing the laser beam into the plasma chamber. For this aspect, the light source may further include a bypass line establishing fluid communication between the discharge chamber and the auxiliary chamber. A valve operable to close the bypass line may be provided. In one particular embodiment, the auxiliary chamber may include a first compartment, a second compartment, and a sealing assembly for reconfiguring the auxiliary chamber between a first configuration wherein the first compartment is in fluid communication with the second compartment and a second configuration wherein the first compartment is sealed from the second compartment. For example, a window may be disposed in the auxiliary chamber that is moveable between a first position wherein the first compartment is in fluid communication with the second compartment and a second position wherein the first compartment is sealed from the second compartment.
In another aspect, a light source that produces EUV by plasma formation and generates debris may include a plasma chamber, a CO2 laser source producing a laser beam having a wavelength, λ, e.g. about 10.6 μm, and a laser input window for the plasma chamber. The light source may introduce an etchant, e.g. HBr, HI, Br2, Cl2, HCl, H2 or a combination thereof, for the plasma formation material, e.g. Sn, into the plasma chamber and a subsystem may be provided for heating deposited plasma formation material on the window to an elevated temperature, t, e.g., a temperature greater than about 150° C., to increase a rate of a chemical reaction between deposited plasma formation material and the etchant. For this aspect, the window provided may be substantially transparent to light at the wavelength, λ, and the window may have a surface that is chemically stable when exposed to the etchant at the temperature, t. In one embodiment, the window may be made of a material such as KBr, CsBr or CsI. In another embodiment, the window may be made by coating a material with KBr, CsBr or CsI. In a particular embodiment, a coating system to coat the window with a material selected from the group of materials consisting of KBr, CsBr and CsI after the window may be installed in the plasma chamber.
With initial reference to
The light source 20 may also include a target delivery system 24, e.g., delivering targets, e.g. targets of a source material including tin, lithium, xenon or combinations thereof, in the form of liquid droplets, a liquid stream, solid particles or clusters, solid particles contained within liquid droplets or solid particles contained within a liquid stream. The targets may be delivered by the target delivery system 24, e.g., into the interior of a chamber 26 to an irradiation site 28 where the target will be irradiated and produce a plasma.
A beam delivery system 50 having an auxiliary chamber 52 may be provided to deliver a laser beam from the laser source 22, e.g. a beam of laser pulses, along a laser optical axis into the plasma chamber 26 to the irradiation site 28. At the irradiation site, the laser, suitably focused, may be used to create a plasma having certain characteristics which depend on the source material of the target. These characteristics may include the wavelength of the EUV light produced by the plasma and the type and amount of debris released from the plasma. As shown, the beam deliver system 50 may have an input window 54 for passing a laser beam from the laser source 22 into the auxiliary chamber 52 and an exit window 56 for passing the laser beam into the plasma chamber 26.
Continuing with
The light source 20 may also include an EUV light source controller system 60, which may also include, e.g., a target position detection feedback system 62 and a laser firing control system 65, along with, e.g., a laser beam positioning system controller 66. The light source 20 may also include a target position detection system which may include one or more droplet imagers 70 that provide an output indicative of the position of a target droplet, e.g., relative to the irradiation site 28 and provide this output to the target position detection feedback system 62, which can, e.g., compute a target position and trajectory, from which a target error can be computed, if not on a droplet by droplet basis then on average. The target error may then be provided as an input to the light source controller 60, which can, e.g., provide a laser position, direction and timing correction signal, e.g., to the laser beam positioning controller 66 that the laser beam positioning system can use, e.g., to control the laser timing circuit and/or to control a laser beam position and shaping system 68, e.g., to change the location and/or focal power of the laser beam focal spot within the chamber 26.
As shown in
For the light source 20 shown in
Continuing with
For the embodiment shown in
Continuing with
As indicated above, the optical components in the focus and steering assembly 451/551 and mirrors 460a,b/560a,b of the focal power adjustment assembly may be moveable to adjust the position and focal power of the focal spot in the chamber 426/526. Adjustments to the focus and steering assembly and/or the focal power adjustment assembly may be made during light source setup and maintained at constant settings during operational use, or, adjustments to the focus and steering assembly and/or the focal power adjustment assembly may be made during light source operational use (i.e. during utilization of EUV light by a downstream apparatus, e.g. lithography scanner), for example, on a pulse by pulse basis and/or after a so-called “burst” of pulses, when a pulsed laser source 22 (see
As further shown, a detector 706, which may be a fluorescent converter such as a Zr coated Ce:YAG fluorescent converter may be positioned at or near the intermediate focus 40′, e.g. downstream of the intermediate focus 40′, as shown, to measuring in-band EUV light output intensity and producing an output signal indicative thereof. For the embodiment shown, the detector 706 may be periodically interposed within the EUV output beam, e.g. temporarily taking the light source “off line” or may sample a portion of the EUV light output, for example, using a pick-off type beam splitter (not shown). Although a fluorescent converter is shown, it is to be appreciated that other types of detectors known to those skilled in the art may be used to measure EUV output intensity, in-band or otherwise, as described herein.
Output signals from the detector 706 may be used to provide a more accurate coupling between the input laser and source material droplet. In particular, output signals from the detector 706 may be used to make adjustments to the focus and steering assembly and/or the focal power adjustment assembly described above or to the target delivery control mechanism 92′ to provide a laser—droplet interaction in which the laser is substantially centered relative to the droplet. This procedure may be performed during light source setup and maintained at constant settings during operational use, or, adjustments to the focus and steering assembly, the focal power adjustment assembly and/or the target delivery control mechanism 92′ may be made during light source operational use (i.e. during utilization of EUV light by a downstream apparatus, e.g. lithography scanner), for example, on a pulse by pulse basis and/or after a so-called “burst” of pulses, when a pulsed laser source 22 (see
Referring back to
Another technique which may be employed to reduce moisture absorption involves in-situ coating a ZnSe window with KBr, CsBr or CsI after the window is installed in the vacuum chamber and the air is pumped out.
It will be understood by those skilled in the art that the aspects of embodiments of the present invention disclosed above are intended to be preferred embodiments only and not to limit the disclosure of the present invention(s) in any way and particularly not to a specific preferred embodiment alone. Many changes and modification can be made to the disclosed aspects of embodiments of the disclosed invention(s) that will be understood and appreciated by those skilled in the art. The appended claims are intended in scope and meaning to cover not only the disclosed aspects of embodiments of the present invention(s) but also such equivalents and other modifications and changes that would be apparent to those skilled in the art. While the particular aspects of embodiment(s) described and illustrated in this patent application in the detail required to satisfy 35 U.S.C. §112 are fully capable of attaining any above-described purposes for, problems to be solved by or any other reasons for or objects of the aspects of an embodiment(s) above described, it is to be understood by those skilled in the art that it is the presently described aspects of the described embodiment(s) of the present invention are merely exemplary, illustrative and representative of the subject matter which is broadly contemplated by the present invention. The scope of the presently described and claimed aspects of embodiments fully encompasses other embodiments which may now be or may become obvious to those skilled in the art based on the teachings of the Specification. The scope of the present invention is solely and completely limited by only the appended claims and nothing beyond the recitations of the appended claims. Reference to an element in such claims in the singular is not intended to mean nor shall it mean in interpreting such claim element “one and only one” unless explicitly so stated, but rather “one or more”. All structural and functional equivalents to any of the elements of the above-described aspects of an embodiment(s) that are known or later come to be known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the present claims. Any term used in the specification and/or in the claims and expressly given a meaning in the Specification and/or claims in the present application shall have that meaning, regardless of any dictionary or other commonly used meaning for such a term. It is not intended or necessary for a device or method discussed in the Specification as any aspect of an embodiment to address each and every problem sought to be solved by the aspects of embodiments disclosed in this application, for it to be encompassed by the present claims. No element, component, or method step in the present disclosure is intended to be dedicated to the public regardless of whether the element, component, or method step is explicitly recited in the claims. No claim element in the appended claims is to be construed under the provisions of 35 U.S.C. §112, sixth paragraph, unless the element is expressly recited using the phrase “means for” or, in the case of a method claim, the element is recited as a “step” instead of an “act”.
Claims
1. An EUV light source comprising;
- a laser source;
- a plasma chamber; and
- a focusing mirror for focusing a laser beam from said laser source to a focal spot within said plasma chamber.
2. An EUV light source as recited in claim 1 wherein said focusing mirror is an off-axis parabolic mirror.
3. An EUV light source as recited in claim 1 wherein said focusing optic is moveable to selectively move the focal spot.
4. An EUV light source as recited in claim 3 further comprising a target delivery system for delivering a plasma source material to a plasma formation site in the plasma chamber.
5. An EUV light source as recited in claim 4 wherein said target delivery system comprises a droplet generator.
6. An EUV light source as recited in claim 4 further comprising a target position detector for generating a signal indicative of target position.
7. An EUV light source as recited in claim 6 wherein said focusing optic is moveable in response to said signal from said target position detector to locate the focal spot along a target trajectory.
8. An EUV light source as recited in claim 6 further comprising a steering optic disposed in said plasma chamber for steering the laser beam focal spot in said plasma chamber.
9. An EUV light source as recited in claim 8 wherein said steering optic and said focusing optic are moveable together in a first direction to move the focal spot along a path parallel to the first direction.
10. An EUV light source as recited in claim 8 wherein said steering optic is independently moveable in two dimensions.
11. An EUV light source as recited in claim 8 wherein said steering optic is moveable in response to said signal from said target position detector to locate the focal spot along a target trajectory.
12. An EUV light source comprising;
- a laser source;
- a plasma chamber;
- a focusing optic for focusing a laser beam from said laser source to a focal spot within said plasma chamber; and
- an actuator moving said focusing optic to selectively move the focal point within the plasma chamber.
13. An EUV light source as recited in claim 12 further comprising a target position detector for generating a signal indicative of target position and wherein said focusing optic is moveable in response to said signal from said target position detector to locate the focal spot along a target trajectory.
14. An EUV light source as recited in claim 12 further comprising a steering optic for steering the laser beam focal spot in said plasma chamber and wherein said steering optic and said focusing optic are moveable together in a first direction to move the focal spot along a path parallel to the first direction.
15. An EUV light source comprising;
- a laser source;
- a plasma chamber;
- a focusing optic for focusing a laser beam from said laser source to a focal spot within said plasma chamber; and
- an optical assembly to adjust a focal power of said focal spot.
16. An EUV light source as recited in claim 15 wherein said optical assembly comprises a z-fold telescope.
17. An EUV light source as recited in claim 16 wherein said z-fold telescope comprises two spherical mirrors.
18. An EUV light source as recited in claim 15 wherein said focusing optic is a mirror.
19. An EUV light source as recited in claim 15 further comprising a conical shroud positioned in said chamber to at least partially shield said focusing optic from debris generated in said plasma chamber.
20. An EUV light source as recited in claim 19 further comprising a system for flowing a gaseous etchant in said shroud.
21. An LPP EUV light source comprising:
- a laser source generating a laser beam;
- a source material droplet generator to generate droplets for exposure to said laser beam and produce an EUV emission;
- a detector for measuring an angular EUV emission distribution and outputting a signal indicative thereof; and
- a control system responsive to said signal to increase a coupling between said laser beam and said droplets.
Type: Application
Filed: Oct 5, 2009
Publication Date: Feb 4, 2010
Applicant: Cymer, Inc. (San Diego, CA)
Inventors: Alexander I. Ershov (Escondido, CA), William N. Partlo (Poway, CA), Norbert Bowering (Bielefeld), Bjorn Hansson (Bromma)
Application Number: 12/587,258
International Classification: C23F 1/08 (20060101);