Patent Grant
8847181
The present application claims priority from Japanese Patent Application No. 2011-052917 filed Mar. 10, 2011, and Japanese Patent Application No. 2011-271331 filed Dec. 12, 2011.
1. Technical Field
This disclosure relates to a system and a method for generating extreme ultraviolet (EUV) light.
2. Related Art
In recent years, semiconductor production processes have become capable of producing semiconductor devices with increasingly fine feature sizes, as photolithography has been making rapid progress toward finer fabrication. In the next generation of semiconductor production processes, microfabrication with feature sizes of 60 nm to 45 nm, and microfabrication with feature sizes of 32 nm or less, will be required. In order to meet the demand for microfabrication with feature sizes of 32 nm or less, for example, an exposure apparatus is needed in which a system for generating EUV light at a wavelength of approximately 13 nm is combined with a reduced projection reflective optical system.
Three kinds of systems for generating EUV light are known in general, which include a LPP (Laser Produced Plasma) type system in which plasma is generated by irradiating a target material with a laser beam, a DPP (Discharge Produced Plasma) type system in which plasma is generated by electric discharge, and a SR (Synchrotron Radiation) type system in which orbital radiation is used.
An extreme ultraviolet light generation system according to one aspect of this disclosure may include: a laser apparatus configured to output a laser beam; a chamber provided with a window, through which the laser beam from the laser apparatus enters the chamber; a target supply unit configured to output a target toward a predetermined position inside the chamber; a laser beam focusing optical system positioned to reflect the laser beam toward a predetermined position inside the chamber; a detector for detecting an image of the laser beam at the predetermined position; a target position adjusting mechanism for adjusting a direction into which the target is to be outputted; a laser beam focus position adjusting mechanism for adjusting a focus position of the laser beam; and a controller for controlling the target position adjusting mechanism and the laser beam focus position adjusting mechanism based on the image detected by the detector.
An extreme ultraviolet light generation system according to another aspect of this disclosure may include: a first laser apparatus configured to output a first laser beam; a second laser apparatus configured to output a second laser beam; a chamber provided with a window, through which the first and second laser beams respectively from the first and second laser apparatuses enter the chamber; a target supply unit for outputting a target toward a predetermined position inside the chamber; a laser beam focusing optical system positioned to reflect the first and second laser beams toward a predetermined position; a detector for detecting an image of the second laser beam at the predetermined position; a target position adjusting mechanism for adjusting a direction into which the target is to be outputted; a laser beam focus position adjusting mechanism for adjusting a focus position of at least one of the first and second laser beams; and a controller for controlling the target position adjusting mechanism and the laser beam focus position adjusting mechanism based on the image detected by the detector.
A method according to yet another aspect of this disclosure for generating extreme ultraviolet light in a system including a laser apparatus, a chamber, a target supply unit, a laser beam focusing optical system, a detector, a target position adjusting mechanism, a laser beam focus position adjusting mechanism, and a controller may include: detecting an image of a laser beam reflected by the laser beam focusing optical system at a predetermined position; and controlling the target position adjusting mechanism and the laser beam focus position adjusting mechanism based on the detected image.
A method according to still another aspect of this disclosure for generating extreme ultraviolet light in a system including first and second laser apparatuses, a chamber, a target supply unit, a laser beam focusing optical system, a detector, a target position adjusting mechanism, a laser beam focus position adjusting mechanism, and a controller may include: outputting first and second laser beams respectively from the first and second laser apparatuses; detecting an image of the second laser beam reflected by the laser beam focusing optical system at a predetermined position; and controlling the target position adjusting mechanism and the laser beam focus position adjusting mechanism based on the detected image.
Hereinafter, selected embodiments of this disclosure will be described with reference to the accompanying drawings.
Hereinafter, selected embodiments of this 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 this disclosure. Further, the configuration(s) and operation(s) described in each embodiment are not all essential in implementing this disclosure. Note that like elements are referenced by like reference numerals and characters, and duplicate descriptions thereof will be omitted herein. This disclosure will be illustrated following the table of contents below.
Contents
An overview of the embodiments is as follows. In the selected embodiments to be described below, an EUV light generation apparatus used with a laser apparatus may be configured to detect an image of a laser beam by which a target has been irradiated. The EUV light generation apparatus may also be configured to control the position at which a laser beam is to be focused and the position of a target, based on the aforementioned detection result.
2. Terms
Terms used in this application may be interpreted as follows. The term “droplet” may refer to one or more liquid droplet(s) of a molten target material. Accordingly, the shape of a droplet may be substantially spherical due to its surface tension. The term “plasma generation region” may refer to a three-dimensional space in which plasma is to be generated. In a beam path of a laser beam, a direction or side closer to the laser apparatus is referred to as “upstream,” and a direction or side closer to the plasma generation region is referred to as “downstream.” The “predetermined repetition rate” does not have to be a constant repetition rate but may, in some examples, be a substantially constant repetition rate. The term “diffused target” refers to a target material in a state where at least one of pre-plasma and fragments of the target material is included. The term “pre-plasma” refers to a target material in a plasma state or in a state where plasma is mixed with its atoms or molecules. The term “fragments” may include fine particles such as clusters and microdroplets transformed from a target material as the target material is irradiated by the laser beam, or a mixture of such fine particles. The term “obscuration region” refers to a three-dimensional space defined by the specifications of an external apparatus, such as the exposure apparatus. Typically, the EUV light that passes through the obscuration region is not used for exposure in the exposure apparatus.
3. Overview of EUV Light Generation System
3.1 Configuration
The chamber 2 may have at least one through-hole formed in the wall thereof. The through-hole may be covered with a window 21, and a pulsed laser beam 31 may travel through the window 21 into the chamber 2. An EUV collector mirror 23 having a spheroidal surface may be disposed inside the chamber 2, for example. The EUV collector mirror 23 may have a multi-layered reflective film formed on the spheroidal surface, and the reflective film may include molybdenum and silicon that are laminated in alternate layers, for example. The EUV collector mirror 23 may have first and second foci. The EUV collector mirror 23 may preferably be disposed such that the first focus thereof lies in a plasma generation region 25 and the second focus thereof lies in an intermediate focus (IF) region 292 defined by the specification of an exposure apparatus 6. The EUV collector mirror 23 may have a through-hole 24 formed at the center thereof, and a pulsed laser beam 33 may travel through the through-hole 24.
Referring again to
Further, the EUV light generation apparatus 1 may include a connection part 29 for allowing the interior of the chamber 2 and the interior of the exposure apparatus 6 to be in communication with each other. A wall 291 having an aperture may be disposed inside the connection part 29. The wall 291 may be disposed such that the second focus of the EUV collector mirror 23 lies in the aperture formed in the wall 291.
Further, the EUV light generation system 1 may include a laser beam direction control unit 34, a laser beam focusing mirror 22, and a target collection unit 28 for collecting a target 27. The laser beam direction control unit 34 may include an optical element for defining the direction in which the laser beam travels and an actuator for adjusting the position and the orientation (or posture) of the optical element.
3.2 Operation
With reference to
The droplet generator 26 may output the targets 27 toward the plasma generation region 25 inside the chamber 2. The target 27 may be irradiated by at least one pulse of the pulsed laser beam 33. The target 27, which has been irradiated by the pulsed laser beam 33, may be turned into plasma, and rays of light, including EUV light 251, may be emitted from the plasma. The EUV light 251 may be reflected selectively by the EUV collector mirror 23. EUV light 252 reflected by the EUV collector mirror 23 may travel through the intermediate focus region 292 and be outputted to the exposure apparatus 6. The target 27 may be irradiated by multiple pulses included in the pulsed laser beam 33.
The EUV light generation controller 5 may integrally control the EUV light generation system 11. The EUV light generation controller 5 may process image data of the droplet 27 captured by the target sensor 4. Further, the EUV light generation controller 5 may control at least one of the timing at which the target 27 is outputted and the direction into which the target 27 is outputted (e.g., the timing with which and/or direction in which the target is outputted from the droplet generator 26), for example. Furthermore, the EUV light generation controller 5 may control at least one of the timing with which the laser apparatus 3 oscillates (e.g., by controlling laser apparatus 3), the direction in which the pulsed laser beam 31 travels (e.g., by controlling laser beam direction control unit 34), and the position at which the pulsed laser beam 33 is focused (e.g., by controlling laser apparatus 3, laser beam direction control unit 34, or the like), for example. The various controls mentioned above are merely examples, and other controls may be added as necessary.
4. EUV Light Generation System Including Laser Beam Irradiation Image Detector
Subsequently, an EUV light generation apparatus including a laser beam irradiation image detector for detecting an image of the laser beam passing around the target will be described with reference to the drawings.
4.1 Configuration
As illustrated in
The chamber 2 may include a main chamber 2a, into which the targets 27 are to be supplied, and a sub-chamber 2b, in which a laser beam focusing optical system 220 is disposed. The main chamber 2a and the sub-chamber 2b may be divided by a partition plate 201 having a through-hole formed at the center thereof, through which the pulsed laser beam 33 may pass. Alternatively, the main chamber 2a and the sub-chamber 2b may be separate chambers which may be integrated. However, this embodiment is not limited thereto, and the main chamber 2a and the sub-chamber 2b may be formed by dividing a single chamber into two with the partition plate 201.
The laser beam focusing optical system 220 disposed inside the sub-chamber 2b may include an off-axis paraboloidal concave mirror 222 and a high-reflection mirror 223, for example. The off-axis paraboloidal concave mirror 222 may be attached to a base plate 221 through a mirror holder 222a, for example. The high-reflection mirror 223 may be attached to the base plate 221 through a two-axis tilt stage 223a (this may correspond to a laser beam focus position adjusting mechanism), for example. The base plate 221 may be movable in the Z-direction through a single-axis stage 221a (this may correspond to a laser beam focus position adjusting mechanism), for example. The high-reflection mirror 223 may have its tilt angles θx and θy adjusted through the two-axis tilt stage 223a. Here, the tilt angle θx may be a pitch angle and the tile angle θy may be a yaw angle with respect to an angle formed by a normal line at the center of the reflective surface of the high-reflection mirror 223 and the installation surface of the two-axis tilt stage 223a on the base plate 221.
The pulsed laser beam 31 may be reflected by high-reflection mirrors 341 and 342 of the beam delivery unit 34 and may enter the sub-chamber 2b via the window 21. The pulsed laser beam 31 that has entered the sub-chamber 2b may be reflected by the off-axis paraboloidal concave mirror 222. With this, the pulsed laser beam 31 may be transformed into a converging pulsed laser beam 33. Thereafter, the pulsed laser beam 33 may be reflected by the high-reflection mirror 223, and may enter the main chamber 2a via a through-hole 201a.
The main chamber 2a may include the EUV collector mirror 23, a target supply unit 260, the target sensor 4, and a laser beam irradiation image detector 100. The EUV collector mirror 23 may be attached to the partition plate 201 through an EUV collector mirror holder 231, for example. The through-hole 24 in the EUV collector mirror 23 and the through-hole 201a in the partition plate 201 may each be sized not to block the pulsed laser beam 33 when the pulsed laser beam 33 passes through the respective through-holes. The target supply unit 260 may include the droplet generator 26 and a two-axis stage 261 (this may correspond to a target position adjusting mechanism). The droplet generator 26 may be attached to the main chamber 2a through the two-axis stage 261. The two-axis stage 261 may be configured to move the droplet generator 26 in the Y-direction and the Z-direction, whereby the position at which the target 27 passes through the plasma generation region 25 may be adjusted.
The laser beam irradiation image detector 100 may include an off-axis paraboloidal mirror 101, a beam splitter 102, an imaging lens 103, an image sensor 104, and a beam dump 105. The off-axis paraboloidal mirror 101 may be attached to the inner wall of the main chamber 2a through a support 101a, for example. The support 101a may be disposed in the obscuration region of the EUV light 252.
The beam splitter 102, the imaging lens 103, the image sensor 104, and the beam dump 105 may be disposed inside a detector chamber 110, which is in communication with the main chamber 2a through a connection hole 110a, for example. The pulsed laser beam 33 that has passed through the plasma generation region 25 may be reflected by the off-axis paraboloidal mirror 101. A pulsed laser beam 253, which includes the pulsed laser beam 33 reflected by the off-axis paraboloidal mirror 101, may enter the detector chamber 110 through the connection hole 110a. Then, the pulsed laser beam 253 may pass through the beam splitter 102, and thereafter may be imaged on the photosensitive surface of the image sensor 104 through the imaging lens 103. At this point, the image sensor 104 may be in a capture mode. For example, when the image sensor 104 is provided with a shutter or the like, the shutter may be operated such that the shutter remains open for a predetermined time in synchronization with the pulsed laser beam 253 being incident on the image sensor 104. In this way, the image sensor 104 may be arranged so as to detect an image of the pulsed laser beam 253 (that is, the pulsed laser beam 33 that has passed through the plasma generation region 25). The beam splitter 102 may transmit a part of the pulsed laser beam 253 and reflect the remaining part. The transmissivity of the beam splitter 102 may be adjusted so that the amount of light incident on the image sensor 104 is retained at or below the saturation amount of light. The pulsed laser beam reflected by the beam splitter 102 may be absorbed by the beam dump 105.
The EUV light generation controller 5 may include a reference clock generator 51a, an EUV light generation point controller 51, a laser beam focus control driver 52, a target controller 53, and a target supply driver 54. The EUV light generation controller 5 may integrally control the operation of the EUV light generation system 11a.
Specifically, the reference clock generator 51a may generate a reference clock that may serve as a reference for various operations. The EUV light generation point controller 51 may input various signals to the laser beam focus control driver 52, the target controller 53, and the laser apparatus 3, to thereby actuate them. The laser beam focus control driver 52 may actuate the single-axis stage 221a and the two-axis tilt stage 223a of the laser beam focusing optical system 220, based on control signals from the EUV light generation point controller 51. The target controller 53 may input a control signal to the target supply driver 54, based on the control signal inputted from the EUV light generation point controller 51 and the image data inputted from the target sensor 4. The target supply driver 54 may send an output signal to the droplet generator 26 to cause the droplet generator 26 to output the targets 27, based on the control signal inputted from the target controller 53. Further, the target supply driver 54 may actuate the two-axis stage 261, based on the control signal inputted from the target controller 53. The EUV light generation point controller 51 may send an output trigger for the pulsed laser beam 31 to the laser apparatus 3.
4.2 Operation
Subsequently, the operation of the EUV light generation system 11A shown in
The EUV light generation controller 5 may receive an EUV light generation request signal and an EUV light generation position specification signal from the exposure apparatus 6. The EUV light generation request signal may be a signal for requesting the EUV light to start being generated. The EUV light generation position specification signal may include information specifying the position inside the chamber 2 at which the EUV light is to be generated. The EUV light generation controller 5, which has received these signals, may output the output signal for the target 27 to the target supply unit 260. Then, the EUV light generation controller 5 may send the output trigger of the pulsed laser beam 31 (laser output timing) to the laser apparatus so that the target 27 is irradiated by the pulsed laser beam 33 when the target 27 arrives in the plasma generation region 25.
The pulsed laser beam 31 outputted from the laser apparatus 3 may travel, as the substantially collimated pulsed laser beam 31, through the beam delivery unit 34 that includes the high-reflection mirrors 341 and 342, and may enter the chamber 2 through the window 21.
The pulsed laser beam 31 may be transformed into the pulsed laser beam 33 that is to be focused in the plasma generation region 25 by the laser beam focusing optical system 220 that includes the off-axis paraboloidal concave mirror 222 and the high-reflection mirror 223. The pulsed laser beam 33 may be focused in the plasma generation region 25 in synchronization with the timing at which the target 27 passes through the plasma generation region 25.
When the target 27 is irradiated by the pulsed laser beam 33, the target 27 may be turned into plasma, and the EUV light 251, including the EUV light 252, may be emitted from the plasma.
Of the emitted EUV light 251, the EUV light 252 may be reflected selectively by the EUV collector mirror 23 so as to be focused in the intermediate focus (IF) region 292. The EUV light 252 that has passed through the intermediate focus region 292 may then enter the exposure apparatus 6.
The pulsed laser beam 33 that has passed through the plasma generation region 25 may be reflected by the off-axis paraboloidal mirror 101. Here the off-axis paraboloidal mirror 101 may be positioned such that the pulsed laser beam 33 is incident thereon at 45 degrees. The off-axis paraboloidal mirror 101 may transform the pulsed laser beam 33 into the collimated pulsed laser beam 253. The pulsed laser beam 253 may travel through the connection hole 110a and be incident on the beam splitter 102 disposed inside the detector chamber 110.
The beam splitter 102 may transmit a part of the pulsed laser beam 253 incident thereon, and reflect the remaining part. The remaining pulsed laser beam 253 reflected by the beam splitter 102 may be absorbed by the beam dump 105.
The pulsed laser beam 253 that has been transmitted through the beam splitter 102 may be focused on the photosensitive surface of the image sensor 104 through the imaging lens 103. With this, the pulsed laser beam 253 (that is, the pulsed laser beam 33 that has passed through the plasma generation region 25) may be imaged on the image sensor 104. In the case where the pulsed laser beam 33 has struck the target 27, the image of the pulsed laser beam 253 may include a shadow of the target 27.
The image data captured by the image sensor 104 may be sent to the EUV light generation point controller 51 of the EUV light generation controller 5. The EUV light generation point controller 51 may send control signals to the laser beam focus control driver 52 and the target supply driver 54 based on the image data. The control signal may be inputted to the target supply driver 54 through the target controller 53. With this, the laser beam focusing optical system 220 and the target supply unit 260 may be adjusted so that the pulsed laser beam 33 and the target 27 arrive at the EUV light generation position specified in the EUV light generation position specification signal.
Specifically, the laser beam focus control driver 52 may send actuation signals to the two-axis tilt stage 223a for the high-reflection mirror 223 and to the single-axis stage 221a. With this, the laser beam focusing optical system 220 may be controlled so that the pulsed laser beam 33 passes through the EUV light generation position. Further, the target supply driver 54 may send an actuation signal to the two-axis stage 261. With this, the orientation of the target supply unit 260 may be controlled so that the target 27 passes through the EUV light generation position.
The EUV light generation point controller 51 may send the output signal to the droplet generator 26 to cause the droplet generator 26 to output the target 27, based on the image data captured by the image sensor 104. The output signal may be inputted to the droplet generator 26 through the target controller 53 and the target supply driver 54. The EUV light generation point controller 51 may send the output trigger to the laser apparatus 3 to cause the laser apparatus 3 to output the pulsed laser beam 31, based on the image data. This may make it possible for the pulsed laser beam 33 to arrive at the EUV light generation position at substantially the same timing as the timing at which the target 27 arrives at the EUV light generation position.
With the above operation being repeated, each of the targets 27 passing through the EUV light generation position may be irradiated by the pulsed laser beam 33. As a result, the EUV light generation system 11A may be controlled such that the EUV light is generated at the specified EUV light generation position. Here, the EUV light generation position may be specified by an exposure apparatus controller 61 or may be specified by another external apparatus. Alternatively, the EUV light generation position may be a fixed position determined in advance.
4.3 Effect
As has been described so far, the image of the pulsed laser beam 33 that has passed through the plasma generation region 25 may be detected, the image including the shadow of the target 27. With this, both of the positional relationship between the target 27 and the pulsed laser beam when the target 27 is irradiated by the pulsed laser beam 33 and the position at which the pulsed laser beam 33 is focused can be detected directly.
Further, based on this detection result, the position at which the pulsed laser beam 33 is focused and the position at which the target 27 passes through the plasma generation region 25 may be controlled. Accordingly, the EUV light generation position may be controlled with high precision.
4.4 Image when Target is Irradiated by Laser Beam
As illustrated in
4.5 Control Flow
Subsequently, the operation of the EUV light generation system 11A shown in
4.5.1 Main Flow
Subsequently, the EUV light generation controller 5 may stand by until an EUV light generation request signal for requesting the generation of the EUV light is received from the exposure apparatus 6 (more specifically, the exposure apparatus controller 61) (Step S103; NO). Upon receiving the EUV light generation request signal (Step S103; YES), the EUV light generation controller 5 may sequentially execute an EUV light generation subroutine for generating the EUV light (Step S104), a laser beam irradiation image detection subroutine for detecting an image of the pulsed laser beam 33 passing around the target 27 (Step S105), and a position determination subroutine for determining whether or not the actual EUV light generation position falls within a permissible range (Step S106).
Thereafter, the EUV light generation controller 5 may determine, through the position determination subroutine (Step S106), whether or not the actual EUV light generation position falls within the permissible range, which may be either set in advance or inputted from an external apparatus such as the exposure apparatus 6 (Step S107). When the actual EUV light generation position falls within the permissible range (Step S107; YES), the EUV light generation controller 5 may send, to the exposure apparatus 6, an EUV light generation position normal signal indicating that the EUV light generation position falls within the permissible range (Step S108); and thereafter, the EUV light generation controller 5 may proceed to Step S112. In the mean time, when the actual EUV light generation position falls outside the permissible range (Step S107; NO), the EUV light generation controller 5 may send, to the exposure apparatus 6, an EUV light generation position abnormal signal indicating that the EUV light generation position does not fall within the permissible range (Step S109); and thereafter, the EUV light generation controller may proceed to Step S110.
In Step S110, the EUV light generation controller 5 may execute a target position control subroutine for controlling the position and the timing at which the target 27 passes through the plasma generation region 25. Subsequently, the EUV light generation controller 5 may execute a laser beam focus position control subroutine for controlling the position and the timing at which the pulsed laser beam 33 is focused (Step S111). Through these two subroutines (Steps S110 and S111), the EUV light generation system 11A may be controlled so that the target 27 is irradiated by the pulsed laser beam 33 at the specified EUV light generation position.
Thereafter, the EUV light generation controller 5 may determine whether or not this operation for controlling the EUV light generation position is to be terminated (Step S112). When the operation is to be terminated (Step S112; YES), the EUV light generation controller 5 may terminate this operation. On the other hand, when the operation is not to be terminated (Step S112; NO), the EUV light generation controller 5 may return to Step S102 and repeat the subsequent steps.
4.5.2 Parameter Initialization Subroutine
The parameter initialization subroutine shown in Step S101 of
Subsequently, the EUV light generation controller 5 may set an initial value Dd0 in a delay time Dd of an output signal to be inputted to the droplet generator 26 with reference to the reference clock (Step S122). The initial value Dd0 may be stored in a memory (not shown) or the like, for example. Further, the EUV light generation controller 5 may set an initial value Ld0 in a delay time Ld for an output trigger for the pulsed laser beam 31 with respect to the timing at which the target 27 passes through a predetermined position (Step S123). The initial value Ld0 may be stored in a memory (not shown) or the like, for example. Here, the delay time Ld may be in an amount required for the target 27 to be irradiated by the pulsed laser beam 33 at the EUV light generation position, that is, a duration from an output of a passing signal of the target 27 from the target sensor 4 until the output of the output trigger, for example.
Subsequently, the EUV light generation controller 5 may load a proportionality constant k, which may serve as a parameter when actuating various actuators for the two-axis stage 261 of the target supply unit 260, the single-axis stage 221a of the laser beam focusing optical system 220, and so forth (Step S124). The proportionality constant k may be stored in a memory (not shown) or the like, or may be given from an external apparatus, such as the exposure apparatus 6, for example.
Thereafter, the EUV light generation controller 5 may load permissible ranges for the actual EUV light generation position (Step S125). Subsequently, the EUV light generation controller 5 may return to the operation shown in
4.5.3 EUV Light Generation Position Setting Subroutine
The EUV light generation position setting subroutine shown in Step S102 of
Based on the determination result in Step S131, when the resetting data ΔEs has not been received (Step S131; NO), the EUV light generation controller 5 may return to the operation shown in
4.5.4 EUV Light Generation Subroutine
The EUV light generation subroutine shown in Step S104 of
Then, the EUV light generation controller 5 may stand by until a count value T in the timer T is at or exceeds the delay time Dd (Step S143; NO). When the count value T is at or exceeds the delay time Dd (Step S143; YES), the EUV light generation controller 5 may send the output signal to the target supply unit 260 to cause the target supply unit 260 to output the target 27 (Step S144).
Thereafter, the EUV light generation controller 5 may stand by until a passing signal indicating that the target 27 has passed through a predetermined position is received from the target sensor 4 (Step S145; NO). Upon receiving the passing signal (Step S145; YES), the EUV light generation controller 5 may reset the timer T (Step S146). Then, the EUV light generation controller 5 may stand by until the count value T in the timer T is at or exceeds the delay time Ld (Step S147; NO). When the count value T is at or exceeds the delay time Ld (Step S147; YES), the EUV light generation controller 5 may send an output trigger for a single pulse to the laser apparatus 3 (Step S148). Thereafter, the EUV light generation controller 5 may return to the operation shown in
4.5.5 Laser Beam Irradiation Image Detection Subroutine
The laser beam irradiation image detection subroutine shown in Step S105 of
4.5.6 Position Determination Subroutine
The position determination subroutine shown in Step S106 of
Further, the EUV light generation controller 5 may calculate a distance Lb between the EUV light generation position E and the position (the center L (Xb, Yb), for example) of the pulsed laser beam 33 (Step S162). The distance Lb may be obtained by calculating a difference in coordinates ΔL (ΔXb, ΔYb) of the pulsed laser beam 33 with respect to the EUV light generation position E. The difference in coordinates ΔL (ΔXb, ΔYb) may, for example, be obtained from the target EUV light generation position E (Xt, Yt) and the position (the center L (Xb, Yb), for example) of the pulsed laser beam 33. The calculated difference in coordinates ΔL and the calculated distance Lb may be stored in a memory (not shown) or the like, for example. Here, the deviation of the focus position in the Z-direction is not taken into consideration. However, when the deviation in the Z-direction is to be taken into consideration, the size of the image G33 of the pulsed laser beam 253 in the image data may be used.
Subsequently, the EUV light generation controller 5 may determine whether or not the distances Lt and Lb fall within the permissible ranges Ltr and Lbr, respectively (Step S163). When the distances Lt and Lb fall within the permissible ranges Ltr and Lbr, respectively (Step S163; YES), the EUV light generation controller 5 may set “true” in a position normal flag provided in a memory (not shown), for example (Step S164). Thereafter, the EUV light generation controller 5 may return to the operation shown in
4.5.7 Target Position Control Subroutine
The target position control subroutine shown in Step S110 of
4.5.7.1 Modification of Target Position Control Subroutine
The target position control subroutine shown in Step S110 of
4.5.8 Laser Beam Focus Position Control Subroutine
The laser beam focus position control subroutine shown in Step S111 of
As has been described so far, the EUV light generation position may be controlled with high precision by controlling the focus position of the pulsed laser beam 33 and the passing position of the target 27 based on the detection result of the image of the pulsed laser beam 253 passing though the EUV light generation position.
5. EUV Light Generation System Including Image Detector for Detecting Images when Target is Irradiated by Pre-Pulse and Main Pulse Laser Beams
Subsequently, an EUV light generation system 11B configured such that a target is irradiated by laser beams in multiple stages will be described in detail with reference to the drawings.
5.1 Configuration
The EUV light generation system 11B shown in
In the EUV light generation system 11B, the laser apparatus 3 may be replaced by a laser apparatus 3B, and the beam delivery unit 34 may be replaced by a beam delivery unit 34B.
The laser apparatus 3B may include a main pulse laser apparatus ML configured to output a pulsed laser beam (hereinafter, this will be referred to as a main pulse laser beam) 31 and a pre-pulse laser apparatus PL configured to output a pre-pulse laser beam 41. The beam delivery unit 34B may include a beam combiner 341B and high-reflection mirrors 342 and 343. The EUV light generation point controller 51 may be connected to each of the main pulse laser apparatus ML and the pre-pulse laser apparatus PL.
The reflective surface of the high-reflection mirror 343 may be coated with a film configured to reflect the pre-pulse laser beam 41 with high reflectivity. The beam combiner 341B may be coated with a film configured to transmit the pre-pulse laser beam 41 with high transmissivity on one surface thereof on which the main pulse laser beam 31 enters the beam combiner 341B. The beam combiner 341B may also be coated with a film configured to transmit the pre-pulse laser beam 41 with high transmissivity and reflect the main pulse laser beam 31 with high reflectivity on the other surface thereof.
The pre-pulse laser beam 41 outputted from the pre-pulse laser apparatus PL may be reflected by the high-reflection mirror 343. The reflected pre-pulse laser beam 41 may enter the beam combiner 341B. The main pulse laser beam 31 outputted from the main pulse laser apparatus ML may enter the beam combiner 341B through the surface opposite to the surface through which the pre-pulse laser beam 41 enters the beam combiner 341B. The beam combiner 341B may be embodied by a dichroic mirror, for example. The beam combiner 341B may be configured to reflect the main pulse laser beam 31 with high reflectivity and transmit the pre-pulse laser beam 41 with high transmissivity. The beam combiner 341B may be positioned such that the beam path of the reflected main pulse laser beam 31 coincides with the beam path of the transmitted pre-pulse laser beam 41. In this way, the beam combiner 341B may function as a beam path adjusting unit for making the beam path of the main pulse laser beam 31 coincides with the beam path of the pre-pulse laser beam 41. The pre-pulse laser beam 41 transmitted through the beam combiner 341B may then be reflected by the laser beam focusing optical system 220, to thereby be focused in the EUV light generation position as a pre-pulse laser beam 43.
5.2 Operation
Subsequently, the operation of the EUV light generation system 11B shown in
Upon receiving the EUV light generation request signal and the EUV light generation position specification signal from the exposure apparatus 6, the EUV light generation controller 5 may output an output signal for the target 27 to the target supply unit 260. Then, the EUV light generation controller 5 may send an output trigger for the pre-pulse laser beam 41 (laser output timing) to the pre-pulse laser apparatus PL so that the target 27 is irradiated by the pre-pulse laser beam 43 when the target 27 arrives in the plasma generation region 25.
Subsequently, the EUV light generation controller 5 may send an output trigger to the main pulse laser apparatus ML (laser output timing) such that, after the target 27 is irradiated by the pre-pulsed laser beam 43 and is diffused to a certain degree, the diffused target is irradiated by the main pulse laser beam 33. Whether the target 27 is diffused to a certain degree may be determined based on whether a predetermined delay time has elapsed since the timing at which the output trigger is sent to the pre-pulse laser apparatus PL.
The pre-pulse laser beam 41 may travel through the beam delivery unit 34B. Specifically, the pre-pulse laser beam 41 may be reflected by the high-reflection mirror 343 of the beam delivery unit 34B, be transmitted through the beam combiner 341B, and be reflected by the high-reflection mirror 342. Thereafter, the pre-pulse laser beam 41 may enter the chamber 2 through the window 21.
The pre-pulse laser beam 41 may be transformed into the pulsed laser beam 43 that may be focused in the plasma generation region 25 by the laser beam focusing optical system 220 that includes the off-axis paraboloidal concave mirror 222 and the high-reflection mirror 223. The target 27 may be supplied to the plasma generation region 25 in synchronization with the timing at which the pre-pulse laser beam 43 passes through the plasma generation region 25.
When the target 27 is irradiated by the pre-pulse laser beam 43, the target 27 may be diffused, resulting in the diffused target. The diffused target may be irradiated by the main pulse laser beam 33, whereby the target material may be turned into plasma with high efficiency. With this, an energy conversion efficiency (CE) into the EUV light may be improved.
The main pulse laser beam 33 may strike the diffused target in the same direction as the pre-pulse laser beam 43, for example. The diffused target may include fine particles or the like of the target material. Thus, apart of the main pulse laser beam 33 may pass through the diffused target without striking any of the fine particles. The part of the main pulse laser beam 33 which has passed through the diffused target may be reflected by the off-axis paraboloidal mirror 101. Here, the off-axis paraboloidal mirror 101 may be disposed such that the main pulsed laser beam 33 is incident thereon at 45 degrees. At this point, the main pulse laser beam 33 may be transformed into the collimated main pulse laser beam 253. The laser beam irradiation image detector 100 may detect the image of the main pulse laser beam 253 (that is, the main pulse laser beam 33 that has passed through the diffused target). In the case where the diffused target has been irradiated by the main pulse laser beam 33, the image of the main pulse laser beam 253 may include a shadow of the diffused target. Here, the beam path of the main pulse laser beam 33 may be set to a beam path that is offset from the beam path of the pre-pulse laser beam 43, in consideration of the position at which the diffused target is generated, the distance along which the diffused target drifts after the target 27 is irradiated by the pre-pulse laser beam 43 until the diffused target is irradiated by the main pulse laser beam 33, and so forth.
The EUV light generation point controller 51 may send control signals to the laser beam focus control driver 52 and the target supply driver 54, respectively. With this, the target supply unit 260 and the laser beam focusing optical system 220 may be controlled so that the diffused target is irradiated by the main pulse laser beam 33 in the EUV light generation position specified in the EUV light generation position specification signal received from the exposure apparatus controller 61.
Other configuration and operation may be similar to those of the EUV light generation system 11A shown in
5.3 Effect
As has been described so far, detecting the image of the main pulse laser beam 253 (that is, the main pulse laser beam 33 that has passed through the diffused target) may make it possible to detect directly both the position at which the diffused target is irradiated by the main pulse laser beam 33 and the position at which the main pulse laser beam 33 is focused.
Further, based on this detection result, the positions at which the pre-pulse laser beam 43 and the main pulse laser beam 33 are focused and the position at which the target 27 passes through the plasma generation region 25 may be controlled. Accordingly, the EUV light generation position may be controlled with high precision.
5.4 Image when Target is Irradiated by Main Pulse Laser Beam
As an example of the case where the diffused target is irradiated by the main pulse laser beam, the case where fragments are irradiated by the main pulse laser beam will be described.
As illustrated in
By analyzing the image detected by the image sensor 104, the difference in coordinates ΔL between the target EUV light generation position E (Xt, Yt) and a center Lm (Xb, Yb) of the main pulse laser beam 33 may be obtained. The center of the top-hat pre-pulse laser beam 43T (and of the main pulse laser beam 33) may be controlled based on the obtained result. Alternatively, the difference in coordinates ΔT between the target EUV light generation position E (Xt, Yt) and the center T (Xs, Ys) of the fragments 372 may be obtained, and the position of the target 27 may be controlled based on the obtained result.
On the other hand, as shown by a broken line 432 in
5.5 Control Flow
The operation of the EUV light generation system 11B shown in
5.5.1 Parameter Initialization Subroutine
As shown in
Then, the EUV light generation controller 5 may set an initial value Dd0 in a delay time Dd of an output signal inputted to the droplet generator 26 with respect to the reference clock (Step S222). The initial value Dd0 may be stored in a memory (not shown) or the like, for example. Further, the EUV light generation controller 5 may set an initial value Ldp0 in a delay time Ldp of an output trigger for the pre-pulse laser beam 41 with respect to the timing at which the target 27 passes through a predetermined position (Step S223). Further, the EUV light generation controller 5 may set an initial value Ldm0 in a delay time Ldm of the output trigger for the main pulse laser beam 31 with respect to the timing at which the target 27 passes through the predetermined position (Step S224). These initial values Ldp0 and Ldm0 may be stored in a memory (not shown) or the like, for example. Here, the delay time Ldp may be a delay time required for the target 27 to be irradiated by the pre-pulse laser beam 43 at the EUV light generation position, the delay time being a duration from the output of the signal for detecting that the target 27 has passed a predetermined position from the target sensor 4 until the target 27 is irradiated by the pre-pulse laser beam 43, for example. Further, the delay time Ldm may be a delay time of an irradiation timing of the main pulse laser beam 33 with respect to the pre-pulse laser beam 43.
Subsequently, the EUV light generation controller 5 may load a proportionality constant k serving as a parameter when actuating various actuators for the two-axis stage 261 of the target supply unit 260, the single-axis stage 221a of the laser beam focusing optical system 220, and so forth (Step S225). The proportionality constant k may be stored in a memory (not shown) or the like, or may be given from an external apparatus, such as the exposure apparatus 6, for example.
Thereafter, the EUV light generation controller 5 may load the permissible ranges for the actual EUV light generation position (Step S226). Then, the EUV light generation controller 5 may return to the operation shown in
5.5.2 EUV Light Generation Subroutine
As shown in
Then, the EUV light generation controller 5 may stand by until a count value T in the timer T is at or exceeds the delay time Dd (Step S243; NO). When the count value T is at or exceeds the delay time Dd (Step S243; YES), the EUV light generation controller 5 may send the output signal to the target supply unit 260 to cause the target supply unit 260 to output the target 27 (Step S244).
Thereafter, the EUV light generation controller 5 may stand by until the passing signal indicating that the target 27 has passed through a predetermined position is received from the target sensor 4 (Step S245; NO). Upon receiving the passing signal (Step S245; YES), the EUV light generation controller 5 may reset the timer T (Step S246). Then, the EUV light generation controller 5 may stand by until the count value T in the timer T is at or exceeds the delay time Ldp of the pre-pulse laser beam 41 (Step S247; NO). When the count value T is at or exceeds the delay time Ldp (Step S247; YES), the EUV light generation controller 5 may send an output trigger for a single pulse to the pre-pulse laser apparatus PL (Step S248).
Then, the EUV light generation controller 5 may stand by until the count value T in the timer T is at or exceeds the delay time Ldm of the main pulse laser beam 31 (Step S249; NO). When the count value T is at or exceeds the delay time Ldm (Step S249; YES), the EUV light generation controller 5 may send an output trigger for a single pulse to the main pulse laser apparatus ML (Step S250). Thereafter, the EUV light generation controller 5 may return to the operation shown in
As has been described so far, the positions at which the pre-pulse laser beam 43 and the main pulse laser beam 33 are focused and the position at which the target 27 passes through the plasma generation region 25 may be controlled, based on the detection result of the image of the main pulse laser beam 253 passing through the EUV light generation position. Accordingly, the EUV light generation position may be controlled with high precision.
6. EUV Light Generation System in which Beam Delivery System Includes Actuator for Adjusting Focus of Laser Beam
Subsequently, an EUV light generation system 11C will be described in detail with reference to the drawings. In the EUV light generation system 11C, a beam delivery unit 34C may be provided with a Z-direction laser beam focus adjusting unit 345 for controlling the focus position of the main pulse laser beam 33 and/or the pre-pulse laser beam 43.
6.1 Configuration
The EUV light generation system 11C shown in
In the EUV light generation system 11C, the beam delivery unit 34B may be replaced by the beam delivery unit 34C, and the laser beam focusing optical system 220 may be replaced by a laser beam focusing optical system 220C.
The beam delivery unit 34C may be similar in configuration to the beam delivery unit 34B. However, in the beam delivery unit 34C, the high-reflection mirror 342 may be held by a two-axis tilt stage 342a. Here, the high-reflection mirror 342 and the two-axis tilt stage 342a may be disposed inside the chamber 2.
Further, in the beam delivery unit 34C, a top-hat mechanism 344 may be provided between the high-reflection mirror 343 and the beam combiner 341B. Alternatively, the top-hat mechanism 344 may be provided between the pre-pulse laser apparatus PL and the high-reflection mirror 343. Here, when the pre-pulse laser apparatus PL is configured to output the pre-pulse laser beam 41 having top-hat type beam intensity distribution, the top-hat mechanism 344 may be omitted. Further, in the beam delivery unit 34C, a Z-direction laser beam focus adjusting unit 345 may be provided between the beam combiner 341B and the high-reflection mirror 342.
6.2 Operation
The two-axis tilt stage 342a for holding the high-reflection mirror 342 may be actuated under the control of the laser beam focus control driver 52. With this, the two-axis tilt stage 342a may function similarly to the two-axis tilt stage 223a holding the high-reflection mirror 223 in the laser beam focusing optical system 220 shown in
The top-hat mechanism 344 may be configured to transform the beam intensity distribution of the pre-pulse laser beam 41 into a top-hat type beam intensity distribution. The Z-direction laser beam focus point adjusting unit 345 may be configured to adjust the divergence of the main pulse laser beam 31 and of the pre-pulse laser beam 41, whereby the focus points of the main pulse laser beam 33 and of the pre-pulse laser beam 43 may be moved along the Z-direction.
The laser beam focusing optical system 220C may include an off-axis paraboloidal convex mirror 224 and an off-axis paraboloidal concave mirror 225. The off-axis paraboloidal convex mirror 224 may expand the pre-pulse laser beam 41 and the main pulse laser beam 31 incident thereon in diameter. The off-axis paraboloidal concave mirror 225 may focus the pre-pulse laser beam 41 and the main pulse laser beam 31, which have been expanded in diameter by the off-axis paraboloidal convex mirror 224, at the EUV light generation position as the pre-pulse laser beam 43 and the main pulse laser beam 33, respectively. The off-axis paraboloidal convex mirror 224 and the off-axis paraboloidal concave mirror 225 may be attached onto the base plate 221 such that a laser beam is incident on the respective mirrors at approximately 45 degrees. The base plate 221 may be attached to the sub-chamber 2b or to the partition plate 201.
6.3 Effect
In the EUV light generation system 11C shown in
Further, based on this detection result, the position at which the main pulse laser beam 33 is focused and the position at which the target 27 passes through the plasma generation region 25 may be controlled. Accordingly, the EUV light generation position may be controlled with high precision.
Further, the mechanisms (the two-axis tilt stage 342a and the Z-direction laser beam focus adjusting unit 345) for controlling the focus points of the main pulse laser beam 33 and of the pre-pulse laser beam 43 may be provided in the beam delivery unit 34C. This may allow the configuration of the laser beam focusing optical system 220C disposed inside the chamber 2 to be simplified.
7. Supplementary Descriptions
7.1 Two-Axis Tilt Stage
Now, an example of the aforementioned two-axis tilt stages 223a and 342a will be described with reference to the drawings.
7.2 Focus Position Adjusting Mechanism
Subsequently, an example of the aforementioned Z-direction laser beam focus adjusting unit 345 will be described with reference to
7.3 Modification of Focus Position Adjusting Mechanism
The Z-direction laser beam focus adjusting unit 345 may be modified as shown in
7.4 Top-Hat Mechanism
Subsequently, the aforementioned top-hat mechanism 344 will be described in detail with reference to the drawings.
7.5 First Modification of Top-Hat Mechanism
7.6 Second Modification of Top-Hat Mechanism
The above-described embodiments and the modifications thereof are merely examples for implementing this disclosure, and this disclosure is not limited thereto. Making various modifications according to the specifications or the like is within the scope of this disclosure, and other various embodiments are possible within the scope of this 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 being limited to the stated elements.” The term “have” should be interpreted as “having the stated elements but not being 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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| 2011-052917 | Mar 2011 | JP | national |
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