Coherent light generators – Particular active media – Gas
Reexamination Certificate
2001-06-15
2004-07-13
Jackson, Jerome (Department: 2815)
Coherent light generators
Particular active media
Gas
C372S058000, C372S038020, C372S038040
Reexamination Certificate
active
06763048
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for adjusting the bandwidth of a natural or line-narrowed emission line of a F
2
laser (e.g., &lgr;
1
=157.63094 nm) by adjusting the gas mixture to a selected composition.
2. Discussion of the Related Art
Line-narrowing is an important feature of excimer laser systems being used for optical lithography. Commonly the bandwidth of the natural emission of the DUV or VUV laser being used is too broad to be used with projection illumination systems. A very small bandwidth is especially valuable when using high numerical aperture (NA) refractive imaging systems, wherein bandwidths below 1 pm are desired when the NA of the projection lens is very high, such as 70 or more. Line-narrowing of natural emission lines of excimer lasers is usually done by sophisticated dispersive arrangements within the laser resonator. For example, line-narrowing of the natural emission of the ArF laser is shown in U.S. Pat. No. 5,901,163 as being performed by a prism beam expander-grating rear optics line-narrowing module in combination with an etalon outcoupler, and U.S. Pat. Nos. 6,154,470, 5,150,370, 5,596,596, 5,642,374, 5,559,816, and 5,852,627, and EP 0 472 727 B1, which are hereby incorporated by reference into the present application in this discussion and in the discussion of the preferred embodiment as disclosing variations of features of the preferred embodiment. All of these optical elements are expensive and suffer more or less from degradation due to exposure to the high intensity, intra-resonator UV emission of the laser. It is desired to have a narrow band laser, particularly for DUV and/or VUV microlithography, that has a natural bandwidth that is less than 0.6 pm, i.e., without additional intra-resonator line-narrowing optics, and/or has a bandwidth that is adjustable in a range from around 1 pm to 0.5 pm or less without having to adjust any intra-resonator line-narrowing elements.
One laser that is coming into high prominence for microlithography purposes is the molecular fluorine (F
2
) laser emitting around 157 nm. The value of the natural bandwidth of the F
2
laser to be used, as well as the feasibility and limits of adjusting the bandwidth, are considerations for optical imaging system designs for 157 nm wafer illumination. It is desired, then, to have an F
2
laser system that is capable of emitting at bandwidths that meet the specifications of these optical systems.
RECOGNIZED IN THE PRESENT INVENTION
It is recognized in the present invention that for bandwidths from 0.6 to 1.0 pm, catadioptic projection systems are used. For bandwidths less than around 0.5 to 0.6 pm, a second material may be used (e.g., BaF
2
along with CaF
2
) for dichroic correction. For line widths less than, e.g., around 0.2 pm, an optical design based only on one optical material may be used. Currently, CaF
2
is the most available of these materials in high quality and volume. In addition, the smaller the natural bandwidth of the laser, the easier it is to provide additional line-narrowing optics to meet the specifications of particular optical systems.
It is recognized herein that the natural bandwidth of the molecular fluorine F
2
laser main emission line at &lgr;
1
is around 0.6+/−0.1 pm using a gas mixture of approximately F
2
(5% in Ne):He (buffer)=70 mbar:2730 mbar. It is further recognized herein that the bandwidth depends on the definite gas mixture which is used as the laser active medium for producing the F
2
laser emission. Especially, a remarkable dependence of the natural bandwidth on the total pressure within the laser tube, or d(BW)/dP.
SUMMARY OF THE INVENTION
In view of the above, a molecular fluorine laser system is provided including a discharge tube filled with a gas mixture including molecular fluorine and at least one buffer gas and having a total pressure of less than substantially 2500 mbar, multiple electrodes within the discharge tube, a pulsed discharge circuit connected to the electrodes for energizing the gas mixture, a line-selection optic for selecting one of multiple closely-spaced lines around 157 nm emitted from the discharge tube, and a laser resonator including the line-selection optic and the discharge tube for generating a beam of laser pulses having a wavelength around 157 nm at a bandwidth of less than 0.6 pm.
A molecular fluorine laser system is further provided including a discharge tube filled with a gas mixture including molecular fluorine and at least one buffer gas and having a total pressure of less than 2000 mbar, multiple electrodes within the discharge tube and connected to a pulsed discharge circuit for energizing the gas mixture, a line-selection optic for selecting one of multiple closely-spaced lines around 157 nm emitted from the discharge tube, and a laser resonator including the line-selection optic and the discharge tube for generating a laser beam having a wavelength around 157 nm at a bandwidth of less than 0.6 pm.
A molecular fluorine laser system is also provided including a discharge tube filled with a gas mixture including molecular fluorine and at least one buffer gas and having a total pressure of less than substantially 1500 mbar, multiple electrodes within the discharge tube and connected to a pulsed discharge circuit for energizing the gas mixture, a line-selection optic for selecting one of multiple closely-spaced lines around 157 nm emitted from the discharge tube, and a laser resonator including the line-selection optic and the discharge tube for generating a laser beam having a wavelength around 157 nm at a bandwidth of less than 0.6 pm.
A molecular fluorine laser system is further provided including a discharge tube filled with a gas mixture including molecular fluorine and at least one buffer gas and having a total pressure of less than substantially 1000 mbar, multiple electrodes within the discharge tube and connected to a pulsed discharge circuit for energizing the gas mixture, a line-selection optic for selecting one of multiple closely-spaced lines around 157 nm emitted from the discharge tube, and a laser resonator including the line-selection optic and the discharge tube for generating a laser beam having a wavelength around 157 nm at a bandwidth of less than 0.6 pm.
A molecular fluorine laser system is also provided including a discharge tube filled with a gas mixture including molecular fluorine and at least one buffer gas and having a total pressure of less than substantially 2500 mbar, multiple electrodes within the discharge tube and connected to a pulsed discharge circuit for energizing the gas mixture, a line-narrowing module for selecting one of multiple closely-spaced lines around 157 nm emitted from the discharge tube, and for optically narrowing the bandwidth of the selected line, and a laser resonator including the line-narrowing module and the discharge tube for generating a beam of laser pulses having a wavelength around 157 nm at a bandwidth of less than 0.5 pm.
A molecular fluorine laser system is further provided including a discharge tube filled with a gas mixture including molecular fluorine and at least one buffer gas and having a total pressure of less than 2000 mbar, multiple electrodes within the discharge tube and connected to a pulsed discharge circuit for energizing the gas mixture, a line-narrowing module for selecting one of multiple closely-spaced lines around 157 nm emitted from the discharge tube, and for optically narrowing the bandwidth of the selected line, and a laser resonator including the line-narrowing module and the discharge tube for generating a beam of laser pulses having a wavelength around 157 nm at a bandwidth of less than 0.5 pm.
A molecular fluorine laser system is also provided including a discharge tube filled with a gas mixture including molecular fluorine and at least one buffer gas and having a total pressure of less than substantially 1500 mbar, multiple electrodes within the discharge tube and connected to a pulsed discharge circuit for energizi
Govorkov Sergei
Paetzel Rainer
Vogler Klaus
Jackson Jerome
Lambda Physik AG
Nguyen Joseph
Stallman & Pollock LLP
LandOfFree
Line narrowing of molecular fluorine laser emission does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Line narrowing of molecular fluorine laser emission, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Line narrowing of molecular fluorine laser emission will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3185950