Patent Grant
9055657
The present application claims priority from Japanese Patent Application No. 2012-124277 filed May 31, 2012, the entire contents of which are hereby incorporated by reference.
1. Technical Field
The present disclosure relates to an apparatus for generating extreme ultraviolet (EUV) light and a method for the same.
2. Related Art
A lithography apparatus used for fabrication of an integrated circuit or the like is an apparatus for transferring a desired pattern onto a substrate. A patterning device called a mask or a reticle is used for producing a circuit pattern on a substrate. Transfer of such a pattern onto the substrate is attained by imaging on a radiation-sensitive material (resist) layer provided on the substrate (for example, a silicon wafer substrate).
A critical dimension (CD) that is a theoretically predicted limit value of pattern transfer is given by the following formula (1).
CD=K1·λ/NA (1)
Here, λ is a wavelength of light for light exposure used for pattern transfer, NA is a numerical aperture of a projection system used for the pattern transfer, and K1 is a process-dependent coefficient called a Rayleigh constant. CD is a critical dimension of a print. As can be seen from formula (1), a decrease of a transferable size can be achieved by any of the three, that is, a decrease of the wavelength λ of light for light exposure, an increase of the numerical aperture NA, or a decrease of the K1 value.
It has been proposed that an apparatus for generating EUV light with a wavelength in a range of 10 nm to 20 nm, preferably, in a range of 13 nm to 14 nm, is used in order to reduce a wavelength of light for light exposure and thereby reduce a transferable size. For a typical EUV light generation apparatus, there can be provided a laser produced plasma (LPP) type EUV light generation apparatus, a discharge plasma type EUV light generation apparatus, an electron storage ring generated synchrotron radiation type EUV light generation apparatus, or the like.
Typically, a tin (Sn) droplet is irradiated with a laser light beam to produce plasma and thereby generate light with a wavelength in a range of EUV in an LPP type EUV light generation apparatus. Such a laser beam may be supplied by, for example, a CO2 laser apparatus.
An extreme ultraviolet light generation apparatus may include a droplet production device, a first laser device, a second laser device, and a beam shaping unit. The droplet production device may be configured to produce a droplet of a target substance. The first laser device may be configured to generate a first laser beam and irradiate the droplet with the first laser beam to diffuse the target substance. The second laser device may be configured to generate a second laser beam and irradiate the target substance diffused by irradiation of the first laser beam with the second laser beam to produce plasma of the target substance and generate extreme ultraviolet light from the target substance. The beam shaping unit may be configured to elongate a beam spot of the first laser beam in a traveling direction of the droplet produced by the droplet production device.
An extreme ultraviolet light generation apparatus may include a droplet production device, a first laser device, and a second laser device. The droplet production device may be configured to produce a droplet of a target substance. The first laser device may be configured to generate a plurality of first laser beams and irradiate the droplet with the first laser beams to diffuse the target substance. The second laser device may be configured to generate a second laser beam and irradiate the target substance diffused by irradiation of the first laser beams with the second laser beam to produce plasma of the target substance and generate extreme ultraviolet light from the target substance. Beam spots of the plurality of first lease beams may be located in the traveling direction of the droplet.
An extreme ultraviolet light generation method may include producing a droplet of a target substance, generating a first laser beam, shaping a beam spot of the first laser beam to be elongated in a traveling direction of the droplet, irradiating the target substance with the first laser beam to diffuse the target substance, generating a second laser beam, and irradiating the target substance diffused by irradiation of the first laser beam with the second laser beam to produce plasma of the target substance and generate extreme ultraviolet light from the target substance.
An extreme ultraviolet light generation method may include producing a droplet of a target substance, generating a plurality of first laser beams, irradiating the droplets with the first laser beams with each of beam spots of the first laser beams being located in a traveling direction of the droplets, generating a second laser beam, and irradiating the target substance diffused by irradiation of the first laser beams with the second laser beam to produce plasma of the target substance and generate extreme ultraviolet light from the target substance.
Hereinafter, selected embodiments of the present disclosure will be described with reference to the accompanying drawings.
Hereinafter, selected embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. The embodiments to be described below are merely illustrative in nature and do not limit the scope of the present disclosure. Further, the configuration(s) and operation(s) described in each embodiment are not all essential in implementing the present disclosure. Note that like elements are referenced by like reference numerals and characters, and duplicate descriptions thereof will be omitted herein.
Contents
The chamber 2 may be provided with at least one through-hole that penetrates through a wall thereof. The through-hole may be sealed with a window 21. An EUV light focusing mirror 23 having a reflection surface with, for example, a shape of rotationally elliptical surface, may be arranged inside the chamber 2. The mirror with a shape of rotationally elliptical surface may have a primary focal point and a secondary focal point. A multilayer reflective coating provided by laminating, for example, molybdenum and silicon alternately may be formed on a surface of the EUV light focusing mirror 23. It is preferable for the EUV light focusing mirror 23 to be arranged in such a manner that, for example, the primary focal point is located at or near a plasma generation position (plasma generation site 25) and the secondary focal point is located at a position of a focal point (intermediate focal point (IF) 292) of EUV light reflected by the EUV focusing mirror 23. The through-hole 24 may be provided at a central portion of the EUV light focusing mirror 23 and pulsed laser light 33 may pass through the through-hole 24.
As further referring to
The LPP type EUV light generation apparatus 1 may include a communicating tube 29 for communicating an inside of the chamber 2 with the inside of a light exposure apparatus 6. A wall 291 with an aperture may be included inside the communicating tube 29 and the wall 291 may be placed in such a manner that the aperture is present at a position of the secondary focal point.
The LPP type EUV light generation apparatus 1 may include a laser light traveling direction control actuator 34, a laser light focusing mirror 22, a target recovery unit 28 for droplets 27, and the like.
1.2 Operation
As referring to
The droplet generator 26 may output a droplet target toward the plasma generation site 25 inside the chamber 2. The droplet target may be irradiated with at least one beam of pulsed laser light 33. A droplet target irradiated with the laser light may produce plasma so that EUV light may be generated from the plasma. One droplet target may be irradiated with a plurality of pulsed laser light beams.
The EUV light generation control system 5 may manage controlling of the whole of the EUV light generation system. The EUV light generation control system 5 may process information of an image of droplet 27 captured by the droplet imaging device 4 or the like. The EUV light generation control system 5 may also conduct, for example, at least one of a control of timing of emission of the droplet target 27 and a control of a direction of emission of the droplet target 27. The EUV light generation control system 5 may further conduct, for example, at least one of a control of timing of laser oscillation of the laser device 3, a control of a traveling direction of the pulsed laser light 31, and a control of a change in a focusing position. Various controls described above are merely illustrative and another control may be added as necessary.
2. EUV Light Generation Apparatus Including Pre-Pulsed Laser Device>
2.1 Configuration
An EUV light generation apparatus 1 may include an EUV light generation control system 5, a droplet generator 26, a main pulsed laser device 3a, a pre-pulsed laser device 3b, an EUV chamber 2, high-reflectance mirrors 7a and 7b, a beam combiner 35, and a beam shaping unit 44.
The EUV light generation control system 5 may include an EUV light generation apparatus controller 5a, a trigger generator 5b, and a delay circuit 5c. The droplet generator 26 may include a droplet generator controller 26a.
The beam combiner 35 may include a high-reflectance mirror 7c and a dichroic mirror 7d. The beam combiner 35 may be fixed to the EUV chamber 2. The dichroic mirror 7d may be such that a diamond substrate is coated with a coating for highly reflecting pre-pulsed laser light and transmitting main pulsed laser light.
The beam shaping unit 44 may be an optical system for beam-shaping a beam spot of a pre-pulsed laser light beam at a position 25 of irradiation of a droplet 27 into a desired beam spot shape. The details will be described below.
For example, a concave lens may be arranged in the beam shaping unit 44 in such a manner that a pre-pulsed laser light beam is focused on an elongated beam spot in a direction of a droplet sequence.
The EUV chamber 2 may include a window 36c, a laser light focusing optical system 36, an EUV focusing mirror 23, an EUV focusing mirror holder 37, a plate 41, a droplet production device 26b, an EUV light sensor 38, a damper 39, and a damper supporting member 40.
The droplet production device 26b may be arranged to supply a plurality of droplets 27 into a plasma production area 25.
The droplet production device 26b may be a target production device for producing droplets 27 based on a continuous jet method (hereinafter, abbreviated as a CJ method). The details will be described below.
The laser light focusing optical system 36 may include an off-axis parabolic mirror 36a, a plane mirror 36b, a plate 42, and a stage 43 that is moveable in XYZ directions. The laser light focusing optical system 36 may be arranged inside the EUV chamber 2. Each optical element may be arranged in such a manner that a position of a focal point of the laser light focusing optical system 36 is generally coincident with the plasma production area 25.
The high-reflectance mirror 7a and the high-reflectance mirror 7c may be arranged in such a manner that main pulsed laser light transmits through the dichroic mirror 7d and the window 36c and enters the laser light focusing optical system 36.
The high-reflectance mirror 7b and the dichroic mirror 7d may be arranged in such a manner that pre-pulsed laser light is reflected from the dichroic mirror 7d, transmits through the window 36c, and enters the laser light focusing optical system 36.
Herein, the dichroic mirror 7d and the high-reflectance mirror 7c may be arranged in such a manner that an optical path of pre-pulsed laser light reflected from the dichroic mirror 7d is generally coincident with an optical path of main pulsed laser light transmitting through the dichroic mirror 7d.
The pre-pulsed laser device 3b may be a YAG laser device for outputting pulsed laser light with a wavelength of 1.06 μm.
The main pulsed laser device 3a may be a CO2 laser device for outputting pulsed laser light with a wavelength of 10.6 μm.
2.2 Operation
The EUV light generation apparatus controller 5a may receive an EUV light generation signal from a light exposure apparatus controller 6a. Subsequently, the EUV light generation apparatus controller 5a may cause the droplet production device 26b to produce a droplet-shaped target sequence based on the CJ method via the droplet generator controller 26a. Such a droplet-shaped target sequence may be supplied to the plasma production area 25 as a droplet sequence.
The EUV light generation apparatus controller 5a may input a trigger outputted from the trigger generator 5b into the pre-pulsed laser device 3b through the delay circuit 5c as a first trigger. Thereby, pre-pulsed laser light may be outputted from the pre-pulsed laser device 3b. The pre-pulsed laser light may be inputted into the window 36c through the high-reflectance mirror 7b, the beam shaping unit 44, and the dichroic mirror 7d. The pre-pulsed laser light may be focused into a beam spot with a longitudinally elongated shape by the laser light focusing optical system 36 and irradiate a plurality of droplets 27 disposed on a path of the droplets 27 in the plasma production area 25 in a direction of arrangement thereof. Then, the plurality of droplets 27 disposed on the path of the droplets 27 may be broken to diffuse as a target substance including fine particles (micro-droplets) or clusters.
On the other hand, a second trigger signal delayed by a predetermined delay time by the delay circuit 5c may be inputted into the main pulsed laser device 3a. Main pulsed laser light may be outputted from the main pulsed laser device 3a based on the second trigger signal. The main pulsed laser light may be inputted into the window 36c through the high-reflectance mirror 7a, the high-reflectance mirror 7c, and the dichroic mirror 7d. The main pulsed laser light may be focused into a spot with a predetermined diameter by the laser light focusing optical system 36 and irradiate a diffused target when a predetermined period of time has passed after irradiation with pre-pulsed laser light. Due to such irradiation, plasma of the diffused target may be produced to generate EUV light.
2.3 Effect
A plurality of droplets 27 on the path that have arrived at the plasma production area 25 may be irradiated with the pre-pulsed laser light. As a result, the plurality of droplets 27 irradiated with the pre-pulsed laser light may be broken to diffuse. Such a diffused target may have a higher absorbance and be irradiated with the main pulsed laser light, so that a conversion efficiency (CE) may be improved and production of debris may be suppressed.
2.4 Target Production Device Based on Continuous Jet Method
A droplet generator 26 may include a droplet production device 26b, a pressure controller 26i, an inert gas cylinder 26d, an electric power source 26c, and the piezoelectric element 26f.
An input side of the pressure controller 26i may be connected to the inert gas cylinder 26d via a pipeline and an output side of the pressure controller 26i may be connected to the droplet production device 26b via a pipeline.
The piezoelectric element 26f may be fixed to the nozzle 26g and connected to the electric power source 26c for applying a voltage to the piezoelectric element 26f.
The electric power source 26c may be connected to a droplet generator controller 26a.
When a droplet production signal is inputted from the EUV light generation apparatus controller 5a, the droplet generator controller 26a may send the signal to the pressure controller 26i. Thereby, the pressure controller 26i may apply a pressure to a target substance that is present inside the droplet production device 26b via an inert in such a manner that the inside of the droplet production device 26b is at a predetermined pressure.
When a pressure is applied to the target substance, a jet 27a of the target substance may be outputted from a pore of the nozzle 26g.
On the other hand, a pulsed signal with a predetermined frequency may be inputted from the droplet generator controller 26a to the electric power source 26c.
The electric power source 26c may apply a predetermined voltage to the piezoelectric element 26f at a frequency identical to a frequency of the pulsed signal via an electric current introduction terminal and thereby cause the nozzle 26g to vibrate.
The jet 27a may be divided by vibration of the nozzle 26g to form a droplet sequence.
In the CJ method, conditions for producing droplets may be restricted. According to Reyleigh's small disturbance stability theory, a target jet with a diameter d flowing at a velocity v is vibrated at a frequency f to cause a disturbance. In such a case, when a wavelength λ of vibration caused in a target flow (λ=v/f) satisfies a predetermined condition (3<λ/d<8), droplets with a generally uniform size are repeatedly formed at the frequency f. The frequency f is called a Reyleigh frequency.
In a case where a focused light beam diameter of main pulsed laser light is 300 μm, 7 and 23 droplets are present within an irradiation area for main pulsed laser light when the droplet diameters are 20 μm and 5.7 μm, respectively.
Thus, when one sequence of a plurality of droplets is thus preset within an area of a focused light beam diameter of main pulsed laser light, it is preferable to irradiate all the droplets with pre-pulsed laser light.
As illustrated in
In order to reduce a droplet diameter, a droplet distance can be reduced.
Here, a focused spot diameter Dp of pre-pulsed laser light may be controlled to be slightly greater than a diameter of one droplet and a spot diameter Dm of main pulsed laser light may be set to be comparable with a diameter of a target diffused by the pre-pulsed laser light. Dm may be greater than “4 Dp˜5 Dp” (
When a droplet distance is small, a situation can be supposed that, for example, only one droplet is irradiated with pre-pulsed laser light on a condition that a plurality of droplets are present in the spot diameter Dm of main pulsed laser light.
In
2.5 Beam Shaping Unit for Pre-Pulsed Laser Light>
The optical system may include a laser light focusing optical system 36, a dichroic mirror 7d, and a beam shaping unit 44.
The laser light focusing optical system 36 may include an off-axis parabolic mirror 36a and a plane mirror 36b, as illustrated in
The laser light focusing optical system 36 may be arranged in such a manner that an axis of a droplet sequence in a traveling direction thereof is generally coincident with a focal plane of the laser light focusing optical system 36 so that a laser beam is focused in a desired plasma production area 25.
The dichroic mirror 7d may be such that a substrate thereof is made of a material that highly transmits main pulsed laser light. The dichroic mirror 7d may be coated with a coating that highly reflects pre-pulsed laser light and highly transmits main pulsed laser light.
The beam shaping unit 44 may be placed on an optical path between the dichroic mirror 7d and the pre-pulsed laser device 3b.
The beam shaping unit 44 may include a concave cylindrical lens 44a.
The concave cylindrical lens 44a may be arranged in such a manner that an axis of a droplet sequence in a traveling direction thereof is generally orthogonal to a focal axis of the concave cylindrical lens 44a and a plurality of droplets are irradiated with a focused light beam of pre-pulsed light.
As illustrated in
On the other hand, main pulsed laser light may highly transmit through the dichroic mirror 7d, and then, be focused at a position of a focal point by the laser light focusing optical system 36. At that time, a focused light spot diameter of main pulsed laser light may be controlled based on a wavelength and an NA. Specifically, a focused light spot diameter of main pulsed laser light may be controlled by utilizing that it is proportional to a wavelength and inversely proportional to a numerical aperture (NA). For example, when both laser light beams have an identical NA and an identical M2, a spot diameter of main pulsed laser light with a wavelength of 10.6 μm can be about 10 times greater than that of pre-pulsed laser light with a wavelength of 1.06 μm.
A focused light spot of main pulsed laser light may be circular and include all the area irradiated with a focused light beam of pre-pulsed laser light with an elongated circular shape.
As illustrated in
A plurality of droplets present in an area (spot diameter) irradiated with main pulsed laser light can be irradiated with pre-pulsed laser light to have formed a diffused target. Since such a distributed and diffused target is irradiated with main pulsed laser light, the CE may be improved and production of debris may be suppressed.
3. Other Embodiments of Beam Shaping Unit for Pre-Pulsed Laser Light
Similarly to the case of
A configuration illustrated in
A first prism 44b and a second prism 44c are placed at a predetermined distance and one irradiation beam of pre-pulsed laser light may be divided into three beams. Each of two divided beams produced as transmitting through the first prism 44b and the second prism 44c may be refracted at a predetermined angle.
As illustrated in
3.1 Beam Shaping Unit for Producing a Plurality of Beams
Alternatively, a plurality of mirrors placed at different angles may be arranged between each pre-pulsed laser device 3c, 3d, or 3e and a dichroic mirror 7d.
3.2 Beam Shaping Unit for Producing Sheet Beam>
Also in the present embodiment, a plurality of droplets irradiated with pre-pulsed laser light may be included in a focused light beam of main pulsed laser light. As illustrated in
The configuration illustrated in
The micro-fly-eye lens 44d may be an optical element processed by providing on a substrate a plurality of, typically several hundred or more, rectangular concave lenses that have a similarity shape with the focused light beam 51c of pre-pulsed laser light in
A pre-pulsed laser light beam can be divided into a plurality of beams by the micro-fly-eye lens 44d and the plurality of divided beams can be expanded by respective lenses. Then, the plurality of beams expanded by respective lenses may be incident on and highly reflected from the dichroic mirror 7d, and subsequently, overlapped by a laser light focusing optical system 36 at a position of a focal point thereof to produce a sheet-shaped beam (Koehler illumination).
Since a droplet sequence is irradiated with pre-pulsed laser light with a rectangular or top-hat shape, a condition of a produced diffused target can be stabilized when positions of a plurality of droplets 27 are present in an area of uniform pre-pulsed laser light.
Although a micro-fly-eye lens is used in the present embodiment, a diffractive optical element may be used in such a manner that pre-pulsed laser light is focused into a beam spot with a sheet-like and top hat shape.
4. Embodiments of Irradiation with a Plurality of Pre-Pulsed Laser Light
The focused light spot of pre-pulsed laser light 51d may be located at an upstream side in a traveling direction of a droplet sequence with respect to the focused light spot 50 of main pulsed laser light.
At that time, the diffused target 27d and the droplets 27 have moved in a traveling direction as indicated by an arrow 52 and the droplets 27 can be present on a focused light spot of pre-pulsed laser light and irradiated with second pre-pulsed laser light.
The configuration illustrated in
An optical path of pre-pulsed laser light may be bent by a predetermined angle by the prism 44e.
The focused light spot 51d of pre-pulsed laser light may be located at an upstream side of a droplet sequence with respect to the focused light spot 50 of main pulsed laser light.
A difference between the EUV light generation apparatus according to the embodiment of
Timing of outputs of three trigger signals to a pre-pulsed laser device and one trigger signal to a main pulsed laser device may be set in the delay circuit 5c by an EUV light generation apparatus controller 5a.
For the case illustrated in
For the case illustrated in
For the case illustrated in
As illustrated in
As described above, a plurality of droplets may be irradiated with a plurality of pre-pulsed laser light beams at different times to diffuse a target substance.
5. EUV Light Generation Apparatus Including Polarization Adjustment Unit
As illustrated in
Next, the operation of each component will be described. The polarization adjustment unit 45 may adjust a direction of polarization of pre-pulsed laser light. The beam shaping unit 46 may adjust a beam shape of main pulsed laser light.
An embodiment illustrated in
The pre-pulsed laser device may be a laser device for outputting pulsed laser light with linear polarization.
The polarization adjustment unit 45 may be the λ/2 plate 45a.
Pre-pulsed laser light with linear polarization having a polarization direction perpendicular to the plane of paper may be incident on the λ/2 plate 45a.
The pre-pulsed laser light may transmit through the λ/2 plate 45a so that the polarization direction thereof may be rotated by 90° to produce a polarization direction that is a direction included in the plane of paper. When a plurality of droplets 27 are irradiated with pre-pulsed laser light with linear polarization, a target irradiated with the pre-pulsed laser light with linear polarization may be diffused in a direction orthogonal to a direction of the polarization.
Such a diffused target 27g may be irradiated with main pulsed laser light to produce plasma and thereby generate EUV light.
A placement angle (an angle of a polarization direction with respect to an optical axis) θ (45° in the figure) of the λ/2 plate 45a may be adjusted in such a manner that a direction of polarization of pre-pulsed laser light 53 may be generally coincident with a traveling direction 52 of droplets.
Since the diffused target 27g can generally fill an area of a focused light spot of main pulsed laser light as illustrated in
In the present embodiment, the placement angle of the λ/2 plate 45a is adjusted in such a manner that the direction of polarization of pre-pulsed laser light is generally coincident with the traveling direction of droplets. However, adjustment and placement thereof may be conducted to, for example, rotate about an optical path or axis of pre-pulsed laser light, without being limited to the present embodiment. Basically, it is sufficient to include a mechanism that can adjust a polarization direction.
Although a case where droplets are irradiated with pre-pulsed laser light with linear polarization is illustrated in the present embodiment, droplets may be irradiated with pre-pulsed laser light with elliptical polarization, without being limited to the present embodiment. When droplets are irradiated with pre-pulsed laser light with elliptical polarization, it is sufficient that a direction of a longitudinal axis of the ellipse thereof is generally coincident with a traveling direction of droplets.
6. Embodiments of Beam Shaping Unit for Main Pulsed Laser Light
The optical system illustrated in
The beam shaping unit 46 may be a convex cylindrical mirror 46a. Preferably, it may be a convex cylindrical mirror 46a with an off-axis parabolic surface.
A beam of main pulsed laser light may be expanded in a direction that is generally identical to a traveling direction 52 of droplets 27 by the convex cylindrical mirror 46a in the beam shaping unit 46.
Main pulsed laser light may be focused into a beam spot with an elongated circular shape on a focal plane of a laser light focusing optical system 36.
Since a longitudinally diffused target 27h may be irradiated with a main pulsed laser light beam with an elongated circular shape as illustrated in
The optical system illustrated in
Such a micro-fly-eye lens may be an optical element processed in such a manner that a plurality (several hundred or more) of concave lenses with a rectangular shape (that is a similarity shape with that of a focused light beam of main pulsed laser light in
A pre-pulsed laser light beam may be divided into a plurality of beams by the micro-fly-eye lens and the plurality of divided beams may be expanded by respective lenses. Then, the plurality of beams expanded by respective lenses can be incident on and highly transmit through a dichroic mirror 7d and then overlapped by a laser light focusing optical system 36 at a position of a focal point to provide a beam with a rectangular shape (Koehler illumination).
Pre-pulsed laser light may transmit through a λ/2 plate 45a in such a manner that a direction of polarization thereof is rotated by 90° to provide a polarization direction that is a direction parallel to the plane of paper. A target having a form of a plurality of droplets 27 can principally be diffused in a direction orthogonal to a polarization direction by irradiation with pre-pulsed laser light with linear polarization.
Such a diffused target can be irradiated with main pulsed laser light with a rectangular shape 50b to produce plasma and thereby generate EUV light.
Since a diffused target can be irradiated with a main pulsed laser light beam that is a focused light beam with a rectangular shape corresponding to the diffused target as illustrated in
The above-described embodiments and the modifications thereof are merely examples for implementing the present disclosure, and the present disclosure is not limited thereto. Making various modifications according to the specifications or the like is within the scope of the present disclosure, and other various embodiments are possible within the scope of the present disclosure. For example, the modifications illustrated for particular ones of the embodiments can be applied to other embodiments as well (including the other embodiments described herein).
The terms used in this specification and the appended claims should be interpreted as “non-limiting.” For example, the terms “include” and “be included” should be interpreted as “including the stated elements but not limited to the stated elements.” The term “have” should be interpreted as “having the stated elements but not limited to the stated elements.” Further, the modifier “one (a/an)” should be interpreted as “at least one” or “one or more”.
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