Wafer-based Light Source Parameter Control

Abstract

The present disclosure relates to wafer-based light source parameter control. For example, a lithography method includes generating a pulsed light beam from a light source; scanning the pulsed light beam across a substrate of a lithography exposure apparatus to expose the substrate with the pulsed light beam, including exposing each sub-region of the substrate with the pulsed light beam. A sub-region is a part of the entire region of the substrate. For each sub-region of the substrate, receiving a lithography performance parameter associated with the sub-region of the substrate; analyzing the received lithography performance parameter, and based on the analysis, modifying a first spectral characteristic of the pulsed light beam and maintaining a second spectral characteristic of the pulsed light beam.

Description

[0001] This application is a divisional application of an application with an application date of October 04, 2017, an application number of 2017800638353, and an invention title of "Wafer-based Light Source Parameter Control". Technical Field

[0002] The disclosed subject matter relates to an apparatus for compensating for variations in lithography performance parameters during wafer scanning by adjusting spectral characteristics of a pulsed light beam directed toward a wafer. Background Art

[0003] In semiconductor lithography (or lithographic technology), the fabrication of integrated circuits (ICs) requires various physical and chemical processes performed on a semiconductor (e.g., silicon) substrate (also referred to as a wafer). A lithographic exposure apparatus or scanner is a machine that applies a desired pattern onto a target portion of the substrate. The wafer is fixed to a platform such that the wafer generally extends in a plane defined by orthogonal X L and Y L directions of the scanner. The wafer is irradiated with a light beam having a wavelength in the deep ultraviolet (DUV) range. The light beam travels along an axial direction that corresponds to the Z L direction of the scanner. The Z L direction of the scanner is orthogonal to the lateral X L -Y L plane. The light beam passes through a beam delivery unit, is filtered by a reticle (or mask), and is then projected onto the prepared wafer. In this way, the chip design is patterned onto a photoresist, the photoresist is then etched and cleaned, and then the process is repeated. Summary of the Invention

[0004] In some general aspects, a lithographic apparatus includes: a light source configured to generate a pulsed light beam; a spectral characteristic selection system optically interacting with the pulsed light beam; a scanning optical system configured to scan the pulsed light beam across a substrate located in the lithographic apparatus; a metrology device configured to determine at least one lithography performance parameter at each sub-region of the substrate, where the sub-region is a part of the entire region of the substrate; and a control system connected to the spectral characteristic selection system, the light source, and the metrology device. The control system is configured to, at each substrate sub-region: receive the determined lithography performance parameter; analyze the determined lithography performance parameter; and based on the analysis of the determined lithography performance parameter: modify a first spectral characteristic of the pulsed light beam by sending a first signal to the spectral characteristic selection system; and while modifying the first spectral characteristic of the pulsed light beam, maintain a second spectral characteristic of the pulsed light beam by sending a second signal to the spectral characteristic selection system.

[0005] The implementation may include one or more of the following features. For example, each sub-region of the substrate may be an exposure field of the substrate, or each sub-region may correspond to a single pulse of the light beam.

[0006] The spectral feature selection system may include a spectral feature actuation mechanism, the spectral feature actuation mechanism including an actuation system configured to cause one or more elements of the spectral feature actuation mechanism to be changed so as to change the interaction with the pulsed light beam. The control system may be connected to the actuation system of the spectral feature actuation mechanism such that a first signal is sent to the actuation system of the spectral feature actuation mechanism and a second signal is sent to the actuation system of the spectral feature actuation mechanism.

[0007] The lithography performance parameter may be a physical property of the substrate. The control system may be configured to receive a determined value of the physical property of the substrate for each sub-region of the substrate. The physical property of the substrate may include one or more of the average offset of the position of the substrate from the desired position and the platform vibration of the substrate. The physical property of the substrate may be the position of the substrate that varies from the central sub-region of the substrate to the sub-regions at the edge of the substrate.

[0008] The spectral feature selection system may include a dispersive optical element and a beam expander, the beam expander including at least three refractive optical elements. The pulsed light beam interacts with the dispersive optical element and each of the plurality of refractive optical elements. The spectral feature selection system may include an actuation system including a plurality of actuators, each of the plurality of actuators causing one of the at least three refractive optical elements to rotate relative to the pulsed light beam. The at least three refractive optical elements may include a first refractive optical element furthest from the dispersive optical element, a second refractive optical element adjacent to the first refractive optical element, and a third refractive optical element adjacent to the second refractive optical element. The first refractive optical element may be associated with a first fast actuator including a first rotating table that rotates about a first rotation axis and includes a region mechanically linked to the first refractive optical element to cause the first refractive optical element to rotate about the first rotation axis. The third refractive optical element may be associated with a second fast actuator including a second rotating table that rotates about a second rotation axis and includes a region mechanically linked to the third refractive optical element to cause the third refractive optical element to rotate about the first rotation axis.

[0009] Rotation of the first refractive optical element can cause the second spectral characteristic of the pulsed beam to change in a relatively coarse manner, and rotation of the third refractive optical element can cause the second spectral characteristic of the pulsed beam to change in a relatively fine manner. Rotation of the second refractive optical element can cause the first spectral characteristic of the pulsed beam to change in a relatively fine manner. The beam expander can include a fourth refractive optical element, and rotation of the fourth refractive optical element can cause the first spectral characteristic of the pulsed beam to change in a relatively coarse manner. The spectral characteristic selection system can include a reflective optical element between the beam expander and the dispersive optical element.

[0010] The control system can analyze the determined lithography performance parameter by determining whether the lithography performance parameter is outside an acceptable range. If it is determined that the lithography performance parameter is outside the acceptable range, the control system can modify the first spectral characteristic of the pulsed beam by sending a signal to the spectral characteristic selection system.

[0011] The scanning optical system can be configured to move one or more of the pulsed beam and the substrate relative to each other in a transverse plane such that the pulsed beam interacts with each sub-region of the substrate. The transverse plane can be perpendicular to the axial direction along which the pulsed beam is directed.

[0012] The light source can include: a first gas discharge stage including a first gas discharge chamber that houses an energy source and contains a gas mixture containing a first gain medium; and a second gas discharge stage including a second gas discharge chamber that houses an energy source and contains a gas mixture containing a second gain medium. The first gas discharge stage is configured to generate a first pulsed beam. The second gas discharge stage is configured to receive the first pulsed beam and amplify the first pulsed beam, thereby generating a pulsed beam from the light source.

[0013] In other general aspects, a lithography method includes: generating a pulsed beam from a light source; and scanning the pulsed beam across a substrate of a lithography exposure apparatus to expose the substrate with the pulsed beam, including exposing each sub-region of the substrate with the pulsed beam, where the sub-region is a part of the entire area of the substrate. The method includes, for each sub-region of the substrate: receiving a lithography performance parameter associated with the sub-region of the substrate; analyzing the received lithography performance parameter; and based on the analysis, modifying at least the first spectral characteristic of the pulsed beam and maintaining at least the second spectral characteristic of the pulsed beam.

[0014] The implementation can include one or more of the following features. For example, the pulsed beam can be generated by directing the pulsed beam through the spectral characteristic selection system. The method can include selecting the first spectral characteristic of the pulsed beam by selectively reflecting the pulsed beam from a diffractive surface of the spectral characteristic selection system.

[0015] A sub-region of the substrate can be an exposure field of the substrate or can correspond to a single pulse of the beam.

[0016] The lithography performance parameters at each sub-region of the substrate can be received by receiving the lithography performance parameters at each sub-region of the substrate during scanning of the pulsed beam across the substrate.

[0017] Receiving the lithography performance parameters at each sub-region of the substrate can include receiving one or more of the following: errors in substrate physical properties, contrast of features formed on the substrate, critical dimension at the substrate region exposed to the pulsed beam, placement (X, Y positions relative to the desired / target position) of features formed on the substrate relative to a target or relative to underlying features (i.e., overlay), photoresist distribution, sidewall angle, and variation in the position of the substrate.

[0018] The lithography performance parameters at the sub-region can be received by receiving one or more of the average offset of the position of the substrate from the desired position and the platform vibration of the substrate. The lithography performance parameters at the sub-region can be received by receiving the position of the substrate varying from a central sub-region of the substrate to a sub-region at the edge of the substrate.

[0019] The lithography performance parameters at each sub-region of the substrate can be received by receiving the lithography performance parameters at each sub-region of the substrate before scanning of the pulsed beam across the substrate.

[0020] The first spectral feature can be modified by modifying the wavelength of the pulsed beam, and the second spectral feature can be maintained by keeping the bandwidth of the pulsed beam within a bandwidth range.

[0021] The bandwidth of the pulsed beam can be kept within the bandwidth range by keeping the bandwidth of the pulsed beam within + / - 10 femtoseconds (fs) or + / - 1 fs.

[0022] The first spectral characteristic of a pulsed light beam can be changed by rotating a first prism system through which the pulsed light beam passes; and the second spectral characteristic of the pulsed light beam can be maintained by rotating a second prism system through which the pulsed light beam passes. The first prism system and the second prism system can be components within a spectral characteristic selection system. The first prism system through which the pulsed light beam passes can be rotated by rotating two prisms through which the pulsed light beam passes; and the second prism system through which the pulsed light beam passes can be rotated by rotating at least two other prisms through which the pulsed light beam passes. One prism in the first prism system can be rotated by actuating the prism in the first prism system with an actuation step size greater than the actuation step size of another prism in the first prism system. The other two prisms in the second prism system can be rotated by actuating one prism in the second prism system with an actuation step size greater than the actuation step size of another prism in the second prism system.

[0023] The first spectral characteristic of a pulsed light beam can be changed by rotating a mirror off which the pulsed light beam is reflected; and the second spectral characteristic of the pulsed light beam can be maintained by rotating a prism system through which the pulsed light beam passes. The mirror and the prism system are components within a spectral characteristic selection system.

[0024] The method can further include: estimating, at least at each sub-region of a substrate, the first spectral characteristic of a pulsed light beam generated from a light source; determining whether the estimated first spectral characteristic is within an acceptable range; and modifying the first spectral characteristic of the pulsed light beam if it is determined that the estimated first spectral characteristic is not within the acceptable range.

[0025] The method can include: estimating, at least at each sub-region of a substrate, the second spectral characteristic of a pulsed light beam generated from a light source; determining whether the estimated second spectral characteristic is within an acceptable range; and modifying the second spectral characteristic of the pulsed light beam if it is determined that the estimated second spectral characteristic is not within the acceptable range.

[0026] The second spectral characteristic of the pulsed light beam can be maintained by adjusting the second spectral characteristic to compensate for a change in the second spectral characteristic caused by the modification of the first spectral characteristic of the pulsed light beam. And the second spectral characteristic of the pulsed light beam can be adjusted while modifying the first spectral characteristic of the pulsed light beam.

[0027] The received lithography performance parameters can be analyzed by determining whether the physical properties of a substrate are outside an acceptable range based on the lithography performance parameters.

[0028] The first spectral characteristic of the pulsed beam can be modified, thereby causing a modification of the first condition of the pulsed beam at the substrate, and the second spectral characteristic of the pulsed beam can be maintained, thereby causing the second condition of the pulsed beam at the substrate to be maintained at a specific level.

[0029] The pulsed beam can be generated from a light source by generating a first pulsed beam from a first gas discharge stage, including selecting the first spectral characteristic of the pulsed beam; directing the first pulsed beam to a second gas discharge stage; and amplifying the first pulsed beam in the second gas discharge stage, thereby generating the pulsed beam from the light source.

[0030] The at least first spectral characteristic of the pulsed beam can be modified and the at least second spectral characteristic of the pulsed beam can be maintained by directing the pulsed beam through a plurality of prisms towards a diffractive optical element such that the pulsed beam retro-reflects off the diffractive optical element and passes through the plurality of prisms again; and simultaneously rotating at least two right-angled prisms such that the angle of incidence of the pulsed beam on the diffractive optical element changes, but the total magnification of the pulsed beam on the diffractive optical element remains unchanged.

[0031] In other general aspects, a lithography method includes: generating a pulsed beam from a light source; receiving a matching scheme associating the edge roll-off slope of a substrate with each sub-region of the substrate, where the sub-region is a part of the entire region of the substrate; scanning the pulsed beam across the substrate of a lithography exposure apparatus to expose the substrate with the pulsed beam, including exposing each sub-region of the substrate with the pulsed beam; modifying at least the wavelength of the pulsed beam based on the exposed sub-regions so as to adjust the focus position at the substrate to compensate for the edge roll-off slope; and maintaining at least the bandwidth of the pulsed beam while modifying the wavelength of the pulsed beam to adjust the focus position at the substrate and compensate for the edge roll-off slope of the exposed sub-regions. Description of the Drawings

[0032] Figure 1 is a block diagram of a lithography system that generates a pulsed beam directed to a lithography exposure apparatus;

[0033] Figure 2 is a schematic diagram depicting a drawing of a wafer imaged within the Figure 1 lithography exposure apparatus of, which shows the sub-regions of the wafer;

[0034] Figure 3 is by Figure 1 an exemplary spectrum curve of the pulsed beam generated by the lithography system of;

[0035] Figure 4 is an exemplary lithography exposure apparatus that can be used in the Figure 1 lithography system of;

[0036] Figure 5A is a block diagram of an exemplary spectral feature selection device that can be used in a Figure 1 lithography system;

[0037] Figure 5B is Figure 5A a block diagram of an exemplary prism within the spectral feature selection device, and shows the beam magnification and beam refraction angle through the prism;

[0038] Figure 6A is a block diagram of an exemplary spectral feature selection device that includes a fast actuator associated with at least one prism and can be used in the lithography system of FIG. 1;

[0039] Figure 6B is a view taken along the Figure 6A 6B-6B cross-section of one prism of the device;

[0040] Figure 6C is a view taken along the Figure 6B Z SF direction of the prism, showing the rotation of the prism;

[0041] Figure 7A is a block diagram of an exemplary spectral feature selection device that includes a fast actuator associated with at least one prism and can be used in the lithography system of FIG. 1;

[0042] Figure 7B is a view taken along the Figure 7A 7B-7B cross-section of one prism of the device;

[0043] Figure 7C is a view taken along the Figure 7B Z SF direction of the prism, showing the rotation of the prism;

[0044] Figure 8A is a block diagram of an exemplary spectral feature selection device that includes a fast actuator associated with at least one prism and can be used in the lithography system of FIG. 1;

[0045] Figure 8B is a view taken along the Figure 8A 8B-8B cross-section of one prism of the device;

[0046] Figure 8C is a view taken along the Figure 8B Z SF direction of the prism, showing the rotation of the prism;

[0047] Figure 8D is a close-up view taken along the Figure 8B 8B-8B cross-section shown;

[0048] Figure 9 is a block diagram of an exemplary light source that can be used in a Figure 1 lithography system;

[0049] Figure 10 is a block diagram of an exemplary control system that can be used in a Figure 1 lithography system;

[0050] Figure 11 is a flowchart of an exemplary process performed by a Figure 1 lithography system to quickly and independently control at least two spectral characteristics of a pulsed beam to compensate for property variations at a wafer in each sub-region of the wafer; and

[0051] Figure 12 is a flowchart of an exemplary process performed by a Figure 1 lithography system to control one or more spectral characteristics of a pulsed beam. DETAILED DESCRIPTION

[0052] Referring Figure 1 to, lithography system 100 includes an illumination system 150 that produces a pulsed beam 110 having a wavelength nominally at a center wavelength and that is directed to a lithography exposure tool or scanner 115. The pulsed beam 110 is for patterning microelectronic features on a substrate or wafer 120 mounted on a platform 122 in the scanner 115. The dimensions of these microelectronic features patterned on the wafer 120 are limited by a critical dimension (CD).

[0053] As the pulsed beam 110 is scanned across the wafer 120, the scanner 115 or control system 185 periodically requests changes in spectral characteristics of the beam 110, such as wavelength or bandwidth, to compensate for changes in lithography performance parameters that occur at the wafer 120. For example, one or more lithography performance parameters can vary with each sub-region of the wafer 120 being scanned by the pulsed beam 110. A sub-region of the wafer 120 is an area of the wafer 120 that is part of the overall area of the wafer being scanned and can be the exposure field of the wafer 120 or an area of the wafer that interacts with a single pulse of the beam 110. A sub-region of the wafer 120 can be the location on the wafer 120 where it is exposed to the beam 110 at any particular time.

[0054] Such lithography performance parameters at the wafer 120 can be considered as characteristics associated with the wafer 120, or as characteristics associated with the beam 110 that interacts with the wafer 120. For example, chromatic aberration, changes in the position of the wafer 120, and errors in the focal plane of the beam 110 caused by the bandwidth, pressure, temperature, wafer topography, or surface shape of the beam 110 are lithography performance parameters that may fluctuate unexpectedly during the scan across the wafer 120.

[0055] The pressure and temperature parameters are the pressure and temperature in the environment near the wafer 120 within the scanner 115, respectively. Changes in pressure and temperature cause an effective change in the wavelength of the beam 110, and thus cause a change in the focal plane of the beam 110.

[0056] In a specific example, most projection lenses (used in the path of the beam 110 traveling towards the wafer 120) have chromatic aberration, and if there is a wavelength error in the beam 110, the chromatic aberration produces imaging errors on the wafer 120. One error caused by chromatic aberration is the focus error, and other errors tend to be much smaller. For example, if the wavelength of the beam 110 deviates from the target wavelength, the image on the wafer 120 will have a significant focal plane error. Therefore, it is desirable to be able to change the wavelength of the beam 110 when scanning the beam 110 across the wafer 120 to compensate for these focal plane errors caused by chromatic aberration.

[0057] As another example, a lithography performance parameter that can vary from one sub-region of the wafer 120 to another is the position of the wafer 120 along the Z L direction. The position of the wafer 120 includes an offset (such as an average offset), which is a fixed offset from the desired position, and the position of the wafer 120 also includes platform vibration or oscillation, which is an oscillation in position about this fixed offset. The platform vibration along the Z L direction can be characterized by the moving standard deviation (MSD) value derived from the platform error signal. A higher platform vibration value blurs the image and thus results in CD non-uniformity. The average offset along the Z L direction is characterized by the moving average (MA) value. The topography of the wafer 120 may contribute to or cause an undesirable effect called the edge roll-off slope, where the wafer exhibits different surface geometries in sub-regions along its edge (and farthest from its central sub-region). In particular, the best focus position of the wafer 120 can have a value that varies significantly from near the center of the wafer 120 along the edge or near the edge of the wafer 120 (this effect can be seen in Figure 2 , as discussed below).

[0058] Reference Figure 2, shows an exemplary plot 200 of wafer 220, where lithography performance parameter PP is plotted for each sub-region of wafer 220 (e.g., each exposure field 223). Higher PP values are darker and lower PP values are lighter. Plot 200 of wafer 220 shows how PP varies across exposure fields 223 of wafer 220. Exposure fields 223 of wafer 220 are regions of wafer 220 that are exposed in a single scan of the exposure slit or window within scanner 115.

[0059] The lithography system 100 and related methods described herein are designed such that the first spectral characteristic (such as wavelength) of beam 110 can be modified when scanning beam 110 across wafer 120 and in accordance with instructions from scanner 115 to compensate for variations in these performance parameters at wafer 120. The modification of the first spectral characteristic of beam 110 is achieved and under the control of spectral characteristic selection device 130, which is configured to interact with pulsed beam 110A that serves as the seed beam for forming beam 110 output from illumination system 150. Due to the design of spectral characteristic selection device 130, other spectral characteristics of beam 110 can be coupled to the first spectral characteristic such that by changing the first spectral characteristic, the second spectral characteristic is inadvertently or undesirably changed. Thus, lithography system 100 is designed to maintain the second spectral characteristic (such as bandwidth) of beam 110 within an acceptable value range during the scan across wafer 120, even when the first spectral characteristic (such as wavelength) is being modified. To maintain the second spectral characteristic of beam 110 within an acceptable value range, lithography system 100 adjusts the second spectral characteristic of beam 110 to compensate for the undesired change in the second spectral characteristic caused by the change in the first spectral characteristic. The modification of the second spectral characteristic (and other spectral characteristics) is also achieved and under the control of spectral characteristic selection device 130.

[0060] In accordance with instructions from scanner 115, the modification of the first spectral characteristic and the adjustment of the second spectral characteristic occur at each location or sub-region of wafer 120 (e.g., at each exposure field), and thus occur while scanning beam 110 across wafer 120. For example, the wavelength and bandwidth of beam 110 can be adjusted for each sub-region of wafer 120 (such as each exposure field). These adjustments occur in a rapid manner such that the adjustments can stabilize to steady-state values within the time it takes to proceed from one sub-region of wafer 120 to another sub-region of wafer 120.

[0061] To achieve rapid bandwidth adjustment for each sub-region of the wafer 120, the spectral feature selection device 130 has been redesigned to provide more rapid adjustment of the bandwidth of the pulsed beam 110 while scanning the beam 110 across the wafer 120, so as to be able to adjust the bandwidth for each sub-region of the wafer 120.

[0062] The spectral feature selection device 130 may include a coarse spectral feature adjustment system 130A and a fine spectral feature adjustment system 130B. The coarse spectral feature adjustment system 130A is for coarse, large-range, and slow control of spectral features such as bandwidth, and is a collection of optical components that interact with the pulsed beam 110A generated by the light source 104. Coarse control means that the adjustment step of the spectral feature is relatively large compared to the adjustment step used in fine control. The fine spectral feature adjustment system 130B is for fine, narrow-range, and rapid control of spectral features such as bandwidth. Fine control means that the adjustment step of the spectral feature is relatively small compared to the adjustment step used in coarse control. The fine spectral feature adjustment system 130B may include an optical system that optically interacts with the pulsed beam 110A to control one or more spectral features. The fine bandwidth adjustment system 130C may include a non-optical system that interacts with other aspects of the light source 105 in a rapid manner to control one or more spectral features such as bandwidth. For example, the fine spectral feature adjustment system 130C may be configured to adjust aspects of the timing associated with the gas discharge chamber within the light source 105, thereby adjusting the bandwidth of the pulsed beam 110.

[0063] Details regarding the lithography system 100 are described next.

[0064] Referring again to Figure 1 , the illumination system 150 includes a light source 105 that generates a pulsed beam 110 at a variable pulse repetition rate. The illumination system 150 includes a control system 185 that communicates with the light source 105 and other features within the illumination system 150. The illumination system 150 also communicates with the scanner 115 to control the operation of the illumination system 150 and aspects of the pulsed beam 110.

[0065] The control system 185 is operably connected to the pulsed light source 105 and the spectral feature selection device 130. And, the scanner 115 includes a lithography controller 140 that is operably connected to the control system 185 and components within the scanner 115.

[0066] The pulse repetition rate of the pulsed beam 110 is the rate at which the light source 110 generates pulses of the beam 110. Thus, for example, the repetition rate of the pulsed beam 110 is 1 / Δt, where Δt is the time between pulses. The control system 185 is generally configured to control the repetition rate of the generation of the pulsed beam 110, including changing the repetition rate of the pulsed beam when the pulsed beam exposes the wafer 120 in the scanner 115.

[0067] In some implementations, the scanner 115 triggers the light source 105 (through communication between the controller 140 and the control system 185) to generate the pulsed beam 110, and thus the scanner 115 controls the repetition rate, spectral characteristics such as bandwidth or wavelength, and / or dose through the controller 140 and the control system 185. For example, the controller 140 sends a signal to the control system 185 to maintain the repetition rate of the beam 110 within a specific acceptable rate range. The scanner 115 generally maintains a constant repetition rate for each pulse burst of the beam 110. The pulse burst of the beam 110 can correspond to an exposure field on the wafer 120. For example, the pulse burst can include any number of pulses from 10 to 500 pulses.

[0068] The critical dimension (CD) is the smallest feature size that the system 100 can print on the wafer 120. The CD depends on the wavelength of the beam 110. Thus, in order to maintain a uniform CD of the microelectronic features printed on the wafer 120 and other wafers exposed by the system 100, the center wavelength of the beam 110 should be maintained at the expected or target center wavelength or within a wavelength range near the target wavelength. Thus, in addition to maintaining the center wavelength at the target center wavelength or within an acceptable wavelength range near the target center wavelength, it is also desirable to maintain the bandwidth (the wavelength range in the beam 110) of the beam 110 within an acceptable bandwidth range.

[0069] To maintain the bandwidth of the beam 110 within an acceptable range or to adjust the bandwidth of the beam 110, the control system 185 is configured to determine the amount of adjustment to the bandwidth of the pulsed beam 110. The control system 185 is configured to send a signal to the spectral characteristic selection device 130 to move at least one optical element (e.g., a prism) of the device 130 so that when the pulsed beam 110 exposes the wafer 120, the bandwidth of the pulsed beam 110 is changed by the determined amount of adjustment, thereby compensating for the bandwidth change caused by the modification of the pulse repetition rate of the pulsed beam 110.

[0070] The bandwidth of the pulsed beam 110 can be changed between any two bursts of the pulse. In addition, the time it takes for the bandwidth to change from a first value to a second value and stabilize at the second value should be less than the time between the pulse bursts. For example, if the time period between bursts is 50 milliseconds (ms), then the total time for changing the bandwidth from the first value to the second value and stabilizing at the second value should be less than 50 ms. The control system 185 and the spectral feature selection device 130 are designed to be able to achieve such a rapid change in bandwidth, as discussed in detail below.

[0071] The controller 140 of the scanner 115 sends a signal to the control system 185 to adjust or modify an aspect (such as bandwidth or repetition rate) of the pulsed beam 110 being scanned across the wafer 120. The signal sent to the control system 185 can cause the control system 185 to modify the electrical signal sent to the pulsed light source 105 or the electrical signal sent to the device 130. For example, if the pulsed light source 105 includes a gas laser amplifier, the electrical signal provides a pulsed current to the electrodes in one or more gas discharge chambers of the pulsed light source 105.

[0072] The wafer 120 is placed on a wafer stage 122 (also referred to as a worktable), and the stage 122 is connected to a locator that is configured to accurately position the wafer 120 according to certain parameters and under the control of the controller 140.

[0073] The lithography system 100 may also include a measurement system 170, and the measurement system 170 may include a subsystem that measures one or more spectral features (such as bandwidth or wavelength) of the measurement beam 110. Due to various interferences applied to the lithography system 100 during operation, the value of the spectral feature (such as bandwidth or wavelength) of the beam 110 at the wafer 120 may not correspond to or match the desired spectral feature (i.e., the spectral feature desired by the scanner 115). Therefore, during operation, the spectral feature (such as the feature bandwidth) of the beam 110 is measured or estimated by the value of the spectral estimation metric, so that the operator or an automated system (such as a feedback controller) can use the measured or estimated bandwidth to adjust the characteristics of the light source 105 and adjust the spectrum of the beam 110. The subsystem of the measurement system 170 measures the spectral features (such as bandwidth and / or wavelength) of the beam 110 based on this spectrum.

[0074] Measurement system 170 receives the portion of beam 110 redirected by the beam splitter device, which is placed in the path between light source 105 and scanner 115. The beam splitter device directs a first portion or percentage of beam 110 into measurement system 170 and directs a second portion or percentage of beam 110 towards scanner 115. In some implementations, most of the beam 110 in the second portion is directed towards scanner 115. For example, the beam splitter device directs a portion (e.g., 1 - 2%) of beam 110 into measurement system 170. The beam splitter device can be, for example, a beam splitter.

[0075] The pulses of beam 110 are centered at a wavelength in the deep ultraviolet (DUV) range, such as a wavelength of 248 nanometers (nm) or 193 nm. The size of the microelectronic features patterned on wafer 120 depends on the wavelength of pulsed beam 110, with lower wavelengths resulting in smaller minimum feature sizes or critical dimensions. When the wavelength of pulsed beam 110 is 248 nm or 193 nm, the minimum size of the microelectronic features can be, for example, 50 nm or less. The bandwidth used to analyze and control pulsed beam 110 can be the actual instantaneous bandwidth of its spectrum 300 (or emission spectrum), as Figure 3 shown. Spectrum 300 contains information on how the optical energy or power of beam 110 is distributed over different wavelengths (or frequencies). Spectrum 300 of beam 110 is depicted in the form of a graph, where the spectral intensity (not necessarily having absolute calibration) is plotted as a function of wavelength or optical frequency. Spectrum 300 can be referred to as the spectral shape or intensity spectrum of beam 110. The spectral characteristics or features of beam 110 include any aspect or representation of the intensity spectrum. For example, bandwidth is a spectral feature. The bandwidth of a beam is a measure of the width of that spectral shape, and this width can be given in terms of the wavelength or frequency of the laser. Any suitable mathematical structure (i.e., metric) related to the details of spectrum 300 can be used to estimate the value characterizing the bandwidth of the beam. For example, the full width at half maximum (FWXM) of the spectrum at a fraction (X) of the maximum peak intensity of the spectral shape can be used to characterize the beam bandwidth. As another example, the width of the spectrum (called EY) containing a fraction (Y) of the integrated spectral intensity can be used to characterize the beam bandwidth.

[0076] Beam 110 is directed through beam preparation system 112, which can include optical elements that modify various aspects of beam 110. For example, beam preparation system 112 can include reflective and / or refractive optical elements, an optical pulse stretcher, and an optical aperture (including an automatic shutter).

[0077] The spectral feature selection device 130 is placed at the first end of the light source 105 to interact with the light beam 110A generated by the light source 105. The light beam 110A is a light beam generated at one end of a resonator within the light source 105 and can be a seed beam generated by a master oscillator, as described below. The spectral feature selection device 130 is configured to finely adjust the spectral characteristics of the pulsed light beam 110 by tuning or adjusting one or more spectral features of the pulsed light beam 110A, such as bandwidth or wavelength.

[0078] Also refer to Figure 4 , the wafers 120, 220 are irradiated by the light beam 110. The lithographic exposure apparatus 115 includes an optical arrangement that includes an illuminator system 129 having, for example, one or more condenser lenses, a mask 134, and an objective lens arrangement 132. The mask 134 is movable in one or more directions, such as along the Z L direction (which generally corresponds to the axial direction of the light beam 110) or in the X L -Y L plane perpendicular to the Z L direction. The objective lens arrangement 132 includes a projection lens and enables image transfer from the mask 134 to the photoresist on the wafer 120. The illuminator system 129 adjusts the angular range of the light beam 110 incident on the mask 134. The illuminator system 129 also equalizes (makes uniform) the intensity distribution of the light beam 110 across the mask 134.

[0079] Among other features, the lithographic apparatus 115 may include a lithography controller 140, air conditioning equipment, and a power supply for various electrical components. The lithography controller 140 controls how the layer is printed on the wafer 120.

[0080] In some implementations, an immersion medium may be provided to cover the wafer 120. The immersion medium may be a liquid (such as water) for liquid immersion lithography. In other implementations where the lithography is a dry system, the immersion medium may be a gas such as dry nitrogen, dry air, or clean air. In other implementations, the wafer 120 may be exposed within a pressure-controlled environment, such as a vacuum or a partial vacuum.

[0081] Again refer to Figure 4, The process program or selection scheme determines the exposure length on the wafer 120, the mask 134 used, and other factors affecting the exposure. During lithography, multiple pulses of the light beam 110 irradiate the same area of the wafer 120 to form an irradiation dose. The number of pulses N of the light beam 110 irradiating the same area can be referred to as the exposure window 400, and the size of the window 400 can be controlled by an exposure slit 405 placed in front of the mask 134. The slit 405 can be designed as a shutter and can include multiple blades that can be opened and closed. Also, the size of the exposure field is determined by the distance between the blades in the non-scanning direction and the scanning length (distance) in the scanning direction. In some implementations, the value of N is ten, for example, 10 - 100 pulses. In other implementations, the value of N is greater than 100 pulses, for example, 100 - 500 pulses.

[0082] One or more of the wafer stage 122, the mask 134, and the objective lens arrangement 132 are fixed to associated actuation systems, thereby forming a scanning arrangement (or scanning optical system). In the scanning arrangement, one or more of the mask 134, the objective lens arrangement 132, and the wafer 120 (via the stage 122) move relative to each other during exposure to scan the exposure window 400 across the exposure field 223.

[0083] Referring again to Figure 1 , the lithography system 100 further includes a wafer metrology device 145 configured to determine the value of the lithography performance parameter PP for each sub-region of the wafers 120, 200 (e.g., for each exposure field 223). The metrology device 145 is connected to the control system 185 such that the control system 185 receives the value of the lithography performance parameter PP for each wafer sub-region. The control system 185 can store the value of the lithography performance parameter PP for each wafer sub-region.

[0084] In some implementations, the metrology device 145 is configured to be used in an offline mode, in which the wafers 120, 220 are analyzed after the wafers 120, 220 have been patterned by the light beam 110. The data obtained through such scanning can be used by the control system 185 for one or more wafers to be scanned in the future.

[0085] In other implementations, the metrology device 145 is used in an online mode, in which the wafers 120, 220 are analyzed while the wafers 120, 220 are being patterned by the light beam 110. For example, the exposure fields of the wafers 120, 220 can be detected between bursts of the light beam 110.

[0086] Referring again to Figure 1 , the metrology device 145 can be any device capable of detecting the lithography performance parameter PP.

[0087] For example, if the performance parameter PP being monitored is wafer topography, the metrology device 145 can be a scanner 115, which can perform such monitoring during exposure or between scans of the wafer 120. The topography of the wafer 120 can be controlled by adjusting the wavelength of the beam 110.

[0088] The metrology device 145 can be a stand-alone system, such as a high-resolution scanning electron microscope (SEM) designed for high-resolution imaging, so as to be able to display feature sizes smaller than, for example, 1 nm. The SEM is an electron microscope that produces an image of a sample (in this case the wafer 120) by scanning the wafer 120 with a focused electron beam. The SEM can achieve a resolution better than 1 nanometer (nm).

[0089] The wafer 120 can be observed in any suitable environment, such as in high vacuum, in low vacuum, (in an environmental SEM) under humid conditions, and over a wide range of low or high temperatures. The most common detection method is secondary electrons emitted by atoms excited by an electron beam. The number of secondary electrons is a function of the angle between the surface of the wafer 120 and the electron beam. In other systems, backscattered electrons or X-rays can be detected.

[0090] The metrology device 145 can employ scanning white light interferometry, which provides quantitative non-contact three-dimensional measurements of the wafer 120. In this technique, a white light beam passes through a filter and then through a microscope objective to reach the surface of the wafer 120. The light reflected back from the surface of the wafer 120 is combined with a reference beam and captured for software analysis within the device 145. After obtaining data for each point, the device 145 can generate a three-dimensional image (topography) of the surface of the wafer 120. Such a topography map of the wafer 120 also enables the measurement of these other lithography performance parameters: local step height, critical dimension (CD), overlay, multilayer film thickness and optical properties, combined topography and film thickness, and wafer bow.

[0091] In other implementations, the metrology device 145 is a scatterometer that transmits energy pulses towards the wafer 120 and measures the reflected or diffracted energy from the wafer 120. The scatterometer can combine the measurement of overlay, focal length, and CD in one sensor. In some implementations, the metrology device 145 is a YieldStar S-250D (manufactured by ASML Netherlands BV of Veldhoven, the Netherlands), which is an independent metrology tool that allows the measurement of overlay and focus on a product using diffraction-based overlay and diffraction-based focus techniques, as well as an optional function for measuring CD.

[0092] In some implementations, the metrology device 145 is a overlay metrology device that determines whether the individual material patterns placed on each layer of the wafer 120 are correctly aligned. For example, the overlay metrology device determines whether the contacts, lines, and transistors of each layer of the wafer are aligned with each other. Any type of misalignment between the patterns can result in short circuits and connection failures, which in turn affect the yield and profit rate. Thus, in practice, after each layer is formed on the wafer 120 but after the second layer is formed, the overlay metrology device is used. The overlay metrology device measures the relative position of the most recently formed (i.e., current) layer on the wafer with respect to the previously formed layer on the wafer, where the most recently formed layer is formed on the previously formed layer. For each position on the wafer where the light beam exposes the wafer (if the characteristics of the light beam 110 measured at the wafer 120 correspond to that position), the relative position between the current wafer layer and the previously formed wafer layer is measured.

[0093] The metrology device 145 can measure the critical dimension (CD), which is related to the printed feature size. SEM and scatterometry tools can be used to measure the CD. The metrology device 145 can measure the overlay to check for image placement errors with respect to the design intent and / or the previously patterned layer. Optical and diffraction-based tools can be used to measure the overlay.

[0094] Reference Figure 5A , in some implementations, the spectral feature selection device 130 includes a set of optical features or components 500, 505, 510, 515, 520 arranged to optically interact with the pulsed light beam 110A and a control module 550 of electronics in any combination form of firmware and software. The optical components 500, 505, 510, 515, 520 can be configured to provide a coarse spectral feature adjustment system 130A; and, if the adjustment of these components is fast enough, the optical components 500, 505, 510, 515, 520 can be configured to provide a fine spectral feature adjustment system 130B. Although not shown in Figure 5A , the spectral feature selection device 130 can include other optical features or other non-optical features for providing fine spectral feature control.

[0095] The control module 550 is connected to one or more actuation systems 500A, 505A, 510A, 515A, 520A that are physically coupled to corresponding optical components 500, 505, 510, 515, 520. The optical components of the device 130 include a dispersive optical element 500, which can be a grating, and a beam expander 501 made of a set of refractive optical elements 505, 510, 515, 520, which can be prisms. The grating 500 can be a reflective grating designed to disperse and reflect the beam 110A; thus, the grating 500 is made of a material suitable for interacting with the pulsed beam 110A having a wavelength in the DUV range. Each of the prisms 505, 510, 515, 520 is a transmissive prism for dispersing and redirecting the beam 110A as the beam 110A passes through the prism body. Each prism can be made of a material (such as, for example, calcium fluoride) that permits transmission of the wavelength of the beam 110A. Although four refractive optical elements 505, 510, 515, 520 are shown, fewer than four or more than four can be used in the beam expander 501.

[0096] The prism 520 is located at the position farthest from the grating 500, while the prism 505 is located at the position closest to the grating 500. The pulsed beam 110A enters the device 130 through the aperture 555 and then travels successively through the prism 520, the prism 510, and the prism 505, and then impinges on the diffraction surface 502 of the grating 500. As the beam 110A passes through each successive prism 520, 515, 510, 505, the beam 110A is optically amplified and redirected (refracted at a specific angle) toward the next optical component. When the beam 110A exits the device 130, the beam 110A is diffracted and reflected back from the grating 500 before passing through the aperture 555 and successively passes through the prism 505, the prism 510, the prism 515, and the prism 520. Each time the beam 110A passes through the successive prisms 505, 510, 515, 520 from the grating 300, the beam 110A is optically compressed as it travels toward the aperture 555.

[0097] Reference Figure 5B , rotation of the prism P (which can be any one of the prisms 505, 510, 515, or 520) of the beam expander 501 changes the angle of incidence of the beam 110A on the incident surface H(P) of the rotated prism P. In addition, the two local optical qualities (i.e., the optical magnification OM(P) and the beam refraction angle δ(P)) of the beam 110A passing through the rotated prism P are functions of the angle of incidence of the beam 110A on the incident surface H(P) of the rotated prism P. The optical magnification OM(P) of the beam 110A passing through the prism P is the ratio of the transverse width Wo(P) of the beam 110A exiting the prism P to the transverse width Wi(P) of the beam 110A entering the prism P.

[0098] A change in the local optical magnification OM(P) of the light beam 110A at one or more prisms P within the beam expander 501 causes an overall change in the optical magnification OM 565 of the light beam 110A passing through the beam expander 501. The optical magnification OM 565 of the light beam 110A passing through the beam expander 501 is the ratio of the transverse width Wo of the light beam 110A leaving the beam expander 501 to the transverse width Wi of the light beam 110A entering the beam expander 501.

[0099] In addition, a change in the local beam refraction angle δ(P) of one or more prisms P within the beam expander 501 causes an overall change in the incident angle 562 of the light beam 110A at the surface 502 of the grating 500.

[0100] The wavelength of the light beam 110A can be adjusted by changing the incident angle 562 at which the light beam 110A impinges on the diffraction surface 502 of the grating 500. The bandwidth of the light beam 110A can be adjusted by changing the optical magnification 565 of the light beam 110.

[0101] The spectral feature selection device 130 is redesigned to more rapidly adjust the bandwidth of the pulsed light beam 110 as the light beam 110 is scanned across the wafer 120 by the scanner 115. The spectral feature selection device 130 can be redesigned to have one or more new actuation systems for more effectively and rapidly rotating one or more of the optical components 500, 505, 510, 515, 520.

[0102] For example, the spectral feature selection device 130 includes a new actuation system 520A for more effectively and rapidly rotating the prism 520. The new actuation system 520A can be designed in a manner that increases the speed of rotation of the prism 520. Specifically, the axis of rotation of the prism 520 mounted to the new actuation system 520A is parallel to the rotatable motor shaft 522A of the new actuation system 520A. In other implementations, the new actuation system 520A can be designed to include an arm that is physically linked to the motor shaft 522A at one end and physically linked to the prism 520 at the other end to provide an additional means for rotating the prism 520. In this way, the optical magnification OM of the light beam 110A is made more sensitive to the rotation of the prism 520.

[0103] In some implementations, the prism 505 is flipped relative to the existing design of the beam expander to provide more rapid bandwidth adjustment. In these cases, the bandwidth changes relatively more quickly (compared to the existing design of the device 130) with a relatively small rotation of the prism 520. Compared to the existing spectral feature selection device, in the redesigned spectral feature selection device 130, the change in the optical magnification per unit rotation of the prism 520 increases.

[0104] The device 130 is designed to adjust the wavelength of the beam 110A generated within one or more resonators of the light source 105 by adjusting the incident angle 562 at which the beam 110A impinges on the diffraction surface 502 of the grating 500. Specifically, this can be accomplished by rotating one or more of the prisms 505, 510, 515, 520 and the grating 500 so as to adjust the incident angle 562 of the beam 110A.

[0105] In addition, the bandwidth of the beam 110A generated by the light source 105 is adjusted by adjusting the optical magnification OM 565 of the beam 110A. Thus, the bandwidth of the beam 110A can be adjusted by rotating one or more of the prisms 505, 510, 515, 520, which causes a change in the optical magnification 565 of the beam 110A.

[0106] Since the rotation of a particular prism P causes a change in both the local beam refraction angle δ(P) and the local optical magnification OM(P) at that prism P, the control of wavelength and bandwidth is coupled in this design.

[0107] In addition, the bandwidth of the beam 110A is relatively sensitive to the rotation of the prism 520 and relatively insensitive to the rotation of the prism 505. This is because any change in the local optical magnification OM(520) of the beam 110A due to the rotation of the prism 520 is multiplied by the product of the changes in the optical magnifications OM(515), OM(510), OM(505) in the other prisms 515, 510, 505 respectively, since these prisms are between the rotated prism 520 and the grating 500 and the beam 110A must pass through these other prisms 515, 510, 505 after passing through the prism 520. On the other hand, the wavelength of the beam 110A is relatively sensitive to the rotation of the prism 505 and relatively insensitive to the rotation of the prism 520.

[0108] For example, to change the bandwidth without changing the wavelength, the optical magnification 565 should be changed without changing the incident angle 562, and this can be achieved by rotating the prism 520 by a large amount and the prism 505 by a small amount.

[0109] The control module 550 is connected to one or more actuation systems 500A, 505A, 510A, 515A, 520A that are physically coupled to the respective optical elements 500, 505, 510, 515, 520. Although an actuation system is shown for each optical component, some of the optical components in the device 130 may remain stationary or not be physically coupled to an actuation system. For example, in some implementations, the grating 500 may remain stationary, and the prism 515 may remain stationary and not be physically coupled to an actuation system.

[0110] Each of the actuation systems 500A, 505A, 510A, 515A, 520A includes one or more actuators connected to its respective optical component. Adjustment of the optical component causes adjustment of a particular spectral characteristic (wavelength and / or bandwidth) of the light beam 110A. The control module 550 receives a control signal from the control system 185, the control signal including a particular command to operate or control one or more of the actuation systems. The actuation systems can be selected and designed to work in concert.

[0111] Each actuator of the actuation systems 500A, 505A, 510A, 515A, 520A is a mechanical device for moving or controlling the respective optical component. The actuator receives energy from the module 550 and converts the energy into some kind of motion imparted to the respective optical component. For example, the actuation system can be any one of a force device and a rotating stage for rotating one or more prisms of a beam expander. The actuation system can include, for example, an electric motor (such as a stepper motor), a valve, a pressure control device, a piezoelectric device, a linear motor, a hydraulic actuator, a voice coil, etc.

[0112] The grating 500 can be an echelle grating with a high blaze angle, and a beam 110A incident on the grating 500 at any angle of incidence 562 that satisfies the grating equation will be reflected (diffracted). The grating equation provides the relationship between the spectral order of the grating 500, the diffracted wavelength (the wavelength of the diffracted beam), the angle of incidence 562 of the beam 110A onto the grating 500, the angle of emergence of the beam 110A diffracted away from the grating 500, the vertical divergence of the beam 110A incident on the grating 500, and the groove pitch of the diffracting surface of the grating 500. Additionally, if the grating 500 is used such that the angle of incidence 562 of the beam 110A onto the grating 500 is equal to the angle of emergence of the beam 110A from the grating 500, then the grating 500 and the beam expanders (prisms 505, 510, 515, 520) are arranged in an autocollimation configuration and the wavelength of the beam 110A reflected from the grating 500 is the autocollimation wavelength. It can be assumed that the vertical divergence of the beam 110A incident on the grating 500 is close to zero. To reflect the nominal wavelength, the grating 500 is aligned with respect to the beam 110A incident on the grating 500 such that the nominal wavelength is reflected back through the beam expanders (prisms 505, 510, 515, 520) to be amplified in the light source 105. Then, by changing the angle of incidence 562 of the beam 110A onto the grating 500, the autocollimation wavelength can be tuned across the entire gain bandwidth of the resonator within the light source 105.

[0113] Each of the prisms 505, 510, 515, 520 is wide enough in the transverse direction of the beam 110A such that the beam 110A is contained within the surface through which the beam 110A passes. Each prism optically expands the beam 110A along the path from the aperture 555 towards the grating 500, and thus the size of each prism increases continuously from the prism 520 to the prism 505. Thus, the prism 505 is larger than the prism 510, the prism 510 is larger than the prism 515, and the prism 520 is the smallest prism.

[0114] The prism 520, which is the farthest from the grating 500 and has the smallest size, is mounted on the actuation system 520A, and specifically to the rotation axis 522A. This causes the prism 520 to rotate, and this rotation changes the optical magnification of the light beam 110A incident on the grating 500, thereby changing the bandwidth of the light beam 110A output from the device 130. The actuation system 520A is designed as a fast actuation system 520A because it includes a rotary stepper motor, and the rotary stepper motor includes the rotation axis 522A to which the prism 520 is fixed. The rotation axis 522A rotates about its axis, which is parallel to the rotation axis of the prism 520. In addition, because the actuation system 520A includes a rotary stepper motor, it has no mechanical memory and no energy ground state. Each position of the rotation axis 522A has the same energy as each other position of the rotation axis 522A, and the rotation axis 522A has no preferred stationary position with low potential energy.

[0115] In some implementations, the actuation system 510A (to which the prism 510 is mounted) can be a fast actuation system similar to the fast actuation system 520A. In this way, the actuation system 510A can include a rotation axis 512A, and the rotation axis 512A causes the prism 510 to rotate, and this rotation changes the optical magnification of the light beam 110A incident on the grating 500, thereby modifying the bandwidth of the light beam 110A output from the device 130. Therefore, the actuation system 510A is designed as a fast actuation system (similar to system 520A) because it includes a rotary stepper motor, and the rotary stepper motor includes the rotation axis 512A to which the prism 510 is fixed. The rotation axis 512A rotates about its axis, which is parallel to the rotation axis of the prism 510. In addition, because the actuation system 510A includes a rotary stepper motor, it has no mechanical memory and no energy ground state. Each position of the rotation axis 512A has the same energy as each other position of the rotation axis 512A, and the rotation axis 512A has no preferred stationary position with low potential energy.

[0116] As described above, the bandwidth of the light beam 110A is relatively sensitive to the rotation of the prism 520 and relatively insensitive to the rotation of the prism 505. This is because any change in the local optical magnification OM(520) of the light beam 110A caused by the rotation of the prism 520 is multiplied by the product of the changes in the optical magnifications OM(515), OM(510), and OM(505) in the other prisms 515, 510, and 505, respectively, since these prisms are between the rotated prism 520 and the grating 500 and the light beam 110A must pass through these other prisms 515, 510, 505 after passing through the prism 520. On the other hand, the wavelength of the light beam 110A is relatively sensitive to the rotation of the prism 505 and relatively insensitive to the rotation of the prism 520. Thus, the wavelength can be roughly changed by rotating the prism 505, and the prism 520 can be rotated (in a rough manner). The incident angle 562 of the light beam 110A is changed due to the rotation of the prism 505, and the rotation of the prism 520 cancels the change in magnification caused by the rotation of the prism 505. In addition, the newly designed fast-actuating system 520A enables the bandwidth to be changed quickly to quickly cancel unwanted magnification changes. Additionally, if more precise control of the bandwidth is needed, the newly designed fast-actuating system 510A can be used to quickly rotate the prism 510. The wavelength can also be more precisely controlled by rotating the prism 515 using the actuating system 515A, where the actuating system 515A can include a piezoelectric platform.

[0117] The prism 520 can be used for rough, large-range, and slow bandwidth control. In contrast, the bandwidth can be controlled more precisely and in a narrow range and even faster by controlling the prism 510.

[0118] In some implementations, the spectral feature selection device 130 can include a beam deflector, such as a mirror, placed at the position 503 between the beam expander 501 and the grating 500 and along the travel path of the light beam 110A between the beam expander 501 and the grating 500. The mirror rotates under the control of its own actuator system to change the incident angle 562 of the light beam 110A incident on the diffraction surface 502 of the grating 500. In this way, the mirror can be used to adjust the wavelength of the light beam 110A without causing unwanted changes in the optical magnification 565 or the bandwidth of the light beam 110A.

[0119] Reference Figure 6A and 6B, in a first implementation, the spectral feature selection device 630 is designed to have a grating 600 and four prisms 605, 610, 615, 620. The grating 600 and the four prisms 605, 610, 615, 620 are configured to interact with the beam 110A after the beam 110A generated by the light source 105 passes through the aperture 655 of the device 630. The beam 110A travels along a path in the X SF -Y SF plane from the aperture 655, passes through the prism 620, the prism 615, the prism 610, the prism 605, and then reflects from the grating 600, and then returns through the prisms 605, 610, 615, 620, and then passes through the aperture 655 and leaves the device.

[0120] The prisms 605, 610, 615, 620 are right-angled prisms through which the pulsed beam 110A is transmitted such that the pulsed beam 110A changes its optical magnification when passing through each right-angled prism. The right-angled prism 620 farthest from the dispersive optical element 600 has the smallest hypotenuse among the plurality, and each successive right-angled prism closer to the dispersive optical element 600 has a hypotenuse of a larger or equal size than the adjacent right-angled prism farther from the dispersive optical element.

[0121] For example, the prism 605 closest to the grating 600 is also the largest in size. For example, its hypotenuse has the largest range among the four prisms 605, 610, 615, 620. The prism 620 farthest from the grating 600 is also the smallest in size. For example, its hypotenuse has the smallest range among the four prisms 605, 610, 615, 620. Adjacent prisms may have the same size. However, each prism closer to the grating 600 should be at least as large or larger than its adjacent prism because the beam 110A is optically magnified when passing through the prisms 620, 615, 610, and 605, and thus when the beam 110A is closer to the grating 600, the lateral range of the beam 110A expands. The lateral range of the beam 110A is the range in a plane perpendicular to the propagation direction of the beam 110A. And, the propagation direction of the beam 110A is in the X SF -Y SF plane of the device 630.

[0122] The prism 605 is physically coupled to an actuator system 605A that rotates the prism 605 about an axis parallel to the Z SF axis of the device 630, and the prism 610 is physically coupled to an actuator system 610A that rotates the prism 610 about an axis parallel to the Z SFrotates about an axis parallel to the axis, and the prism 620 is physically coupled to the fast-actuation system 620A. The fast-actuation system 620A is configured to rotate the prism 605 about an axis parallel to the Z SF axis of the device 630.

[0123] The fast-actuation system 620A includes a rotary stepper motor 621A having a rotary shaft 622A and a rotary plate 623A fixed to the rotary shaft 622A. The rotary shaft 622A and thus the rotary plate 623A rotate about an axis AR, the axis AR being parallel to the centroid of the prism 620 (corresponding to the axis of rotation AP) and also parallel to the Z SF axis of the device 630. Although not necessary, the axis AR of the prism 620 may be along the X SF -Y SF plane corresponding to or aligned with the centroid of the prism 620 (axis of rotation AP). In some implementations, the centroid of the prism 620 (or axis of rotation AP) is offset from the axis AR along the X SF -Y SF plane. By offsetting the axis AR from the centroid of the prism 620, the position of the beam 110A can be adjusted to a specific position on the surface of the grating 600 whenever the prism 620 rotates.

[0124] By mounting the prism 620 to the rotary plate 623A, when the shaft 622A and the rotary plate 623A rotate about their axis AR, the prism 620 directly rotates about its axis of rotation AP. In this way, compared to a system using a linear stepper motor with a linearly translatable axis (using a flexure to convert to rotational motion), rapid rotation or control of the prism 620 can be achieved. Since the rotational step of the shaft 622A (and plate 623A) is directly related to the rotational step of the prism 620 (without applying any linear motion), the rotary stepper motor 621A can rotate the prism 620 at a speed such that the beam 110A can be adjusted more rapidly and thus the spectral characteristics (such as bandwidth) of the beam 110 can be adjusted more rapidly. The rotational design of the stepper motor 621A imparts a pure rotational motion to the prism 620, and the prism 620 is mounted without using any linear motion or flexure motion found in existing actuators for the prism 620. Additionally, using the rotary shaft 622A enables the prism 620 to rotate approximately a full 360°, which is different from existing actuators using a linear stepper motor plus a flexure design (where the prism 620 can only rotate about an angle determined by the flexure). In some implementations, to achieve tuning of the bandwidth of the beam 110A within an acceptable range, the prism 620 can rotate 15 degrees. The prism 620 can rotate more than 15 degrees, but it is not necessary for the current bandwidth range requirements.

[0125] In some implementations, the stepper motor 621A can be a direct drive stepper motor. A direct drive stepper motor is a conventional electromagnetic motor that uses a built-in stepper motor function for position control. In other implementations where higher motion resolution may be required, the stepper motor 621A can use piezoelectric motor technology.

[0126] The stepper motor 621A can be, for example, a rotary stage that is controlled by a motor controller using a variable frequency drive control method to provide rapid rotation of the prism 620.

[0127] As described above, the advantage of using the rotary stepper motor 621A is to obtain more rapid rotation of the prism 620 because the axis of rotation AP of the prism 620 is parallel to the axis of rotation 622A and the axis AR. Thus, for each unit rotation of the axis 622A, the prism 620 rotates by an incremental unit, and the prism 620 rotates as fast as the axis of rotation 622A can rotate. In some implementations, to increase the stability of this configuration and increase the stability of the prism 620, the fast actuation system 620A includes a position monitor 624A that is configured to detect the position of the axis of rotation 622A of the rotary stepper motor 621A. The error between the measured position of the axis of rotation 622A and the expected or target position of the axis of rotation 622A is directly related to the position error of the prism 620, and thus, this measurement can be used to determine the rotational error of the prism 620 (i.e., the difference between the actual rotation and the commanded rotation) and correct this error during operation.

[0128] The control module 550 is connected to the position monitor 624A to receive the value of the position of the axis of rotation 622A, and the control module 550 is also able to access the stored or current value of the commanded position of the axis of rotation 622A such that the control module 550 can perform calculations to determine the difference between the measured value of the position of the axis of rotation 622A and the commanded position, and also determine how to adjust the axis of rotation 622A to reduce this error. For example, the control module 550 can determine the magnitude and direction of rotation of the axis of rotation 622A to counteract the error. Alternatively, the control system 185 can perform this analysis.

[0129] The position monitor 624A can be a very high-resolution optical rotary encoder integrally constructed with the rotating plate 623A. The optical rotary encoder uses optical sensing technology and the rotation of an internal encoding disk having opaque lines and patterns thereon. For example, the plate 623A rotates in a light beam such as a light-emitting diode (thus called a rotary encoder), and the markings on the plate 623A serve as masks for blocking and unblocking light. The internal photodiode detector senses the alternating light beam, and the electronics of the encoder convert the pattern into an electrical signal, which is then transmitted to the control module 550 via the output of the encoder 624A.

[0130] In some implementations, the control module 550 can be designed to have a fast internal dedicated controller solely for operating the rotary stepper motor 621A. For example, the fast internal dedicated controller can receive high-resolution position data from the encoder 624A and can directly send signals to the rotary stepper motor 621A to adjust the position of the shaft 622A and thus adjust the position of the prism 620.

[0131] Also refer to Figure 6C , the illumination system 150 changes the spectral characteristics of the light beam 110A, such as the bandwidth, under the control of the control system 185 docked with the control module 550. For example, to roughly and widely control the bandwidth of the light beam 110A and the light beam 110, the control module 550 sends a signal to the rotary stepper motor 621A of the fast actuation system 620A to rotate the rotary shaft 622A from a first angle θ1 (on the left side of Figure 6C ) to a second angle θ2 (where Δθ = θ2 – θ1) (on the right side of Figure 6C ). And this angular change of the shaft 622A is directly applied to the plate 623A fixed to the shaft 622A and thus also to the prism 620 fixed to the plate 623A. The rotation of the prism 620 from θ1 to θ2 causes a corresponding change in the optical magnification OM 565 of the pulsed light beam 110A interacting with the grating 600 from OM1 to OM2, and the change in the optical magnification 565 of the pulsed light beam 110A causes a change in the bandwidth of the pulsed light beam 110A (and the light beam 110). The bandwidth range that can be achieved by rotating the prism 620 using this fast actuation system 620A can be a wide range and can be from about 100 femtoseconds (fm) to about 450 fm. The total achievable bandwidth range can be at least 250 fm.

[0132] Rotating the prism 620 associated with the fast-actuating system 620A by one rotation unit about the rotation axis 622A causes a change in the bandwidth of the pulsed beam 110A that is less than the resolution of the bandwidth measurement device (for example, as part of the measurement system 170, which is discussed below), and the bandwidth measurement device measures the bandwidth of the pulsed beam 110. The prism 620 can be rotated up to 15 degrees to achieve such a bandwidth change. In practice, the amount of rotation of the prism 620 is only constrained by the optical layout of the other components of the device 630. For example, too large a rotation may cause the beam 110A to be displaced by such a large amount that the beam 110A does not illuminate the next prism 615. In some implementations, in order to tune the bandwidth of the beam 110A within an acceptable range, the prism 620 can be rotated 15 degrees without the risk of the beam 110A leaving any of the other prisms 605, 610, or 615. The prism 620 can be rotated more than 15 degrees, but this is not necessary for the current bandwidth range requirements.

[0133] Referring again to Figure 6A , the prism 610 can be mounted to the actuating system 610A, and the actuating system 610A causes the prism 410 to rotate, and this rotation of the prism 610 can provide fine control of the wavelength of the beam 110A. The actuating system 610A can include a rotary stepper motor controlled by a piezoelectric motor. The piezoelectric motor operates using the inverse piezoelectric effect, where the material generates acoustic or ultrasonic vibrations in order to produce linear or rotary motion.

[0134] Alternatively, the prism 610 can be mounted to a fast-actuating system 610A that includes a rotary stepper motor (similar to the rotary stepper motor 621A having a rotation axis 622A and a rotating plate 623A fixed to the rotation axis 622A). The rotation axis and thus the rotating plate rotate about an axis parallel to the centroid of the prism (corresponding to the rotation axis AP) and also parallel to the Z SF axis of the device 630. In this way, the rotation of the prism 610 can provide finer control of the bandwidth of the beam 110A.

[0135] In some implementations, a prism 615 that is closer to the grating 600 and has a size greater than or equal to the size of the prism 620 can be fixed in space. The size of the next prism 610 closer to the grating 600 is greater than or equal to the size of the prism 615.

[0136] The size of the prism 605 closest to the grating 610 is greater than or equal to the size of the prism 610 (prism 605 is the largest prism of the beam expander). The prism 605 can be mounted to an actuation system 605A, and the actuation system 605A causes the prism 605 to rotate, and this rotation of the prism 605 can provide coarse control of the wavelength of the light beam 110A. For example, the prism 605 can be rotated by 1 - 2 degrees to tune the wavelength of the light beam 110A (and thus the light beam 110) from approximately 193.2 nanometers (nm) to approximately 193.5 nm. In some implementations, the actuation system 605A includes a rotary stepper motor, and the rotary stepper motor includes a mounting surface (such as a plate 623A) to which the prism 605 is fixed and a motor shaft that rotates the mounting surface. The motor of the actuation system 605A can be a piezoelectric motor that is 50 times faster than existing linear stepper motor and flexure combination designs. Similar to the actuation system 620A, the actuation system 605A can include an optical rotary encoder that provides angular position feedback to the control system 185 or the control module 650.

[0137] Reference Figure 7A and 7B , in another implementation of the spectral feature selection device 730, the fast actuation system 720A is designed to rotate the prism 720 of the beam expander that is farthest from the grating 700 about the axis line AR. Optionally or additionally, the actuation system 710A associated with the prism 710 can also be a fast actuation system designed to be similar to the fast actuation system 720A or 620A.

[0138] The device 730 includes an extension arm 725A, and the extension arm 725A has a first region 740A that is mechanically linked to the rotating plate 723A at the position of the axis line AR. The extension arm 725A has a second region 745A that deviates from the axis line AR in a direction in the X SF -Y SF plane (and thus in a direction perpendicular to the axis line AR), such that the second region 745A does not intersect the axis line AR. The prism 720 is mechanically linked to the second region 745A.

[0139] The center of mass of the prism 720 (prism axis AP) and the axis line AR both remain parallel to the Z SF axis of the device 730; however, the center of mass of the prism 720 deviates from the axis line AR. The extension arm 725A rotates about the axis line AR by an angle Δθ to impart a combined motion to the prism 720: a rotation R of the prism 720 about the axis line AR by an angle Δθ in the X SF -Y SF plane (see Figure 7C ) and a translation along a direction in the X SF -Y SFLinear translation T of the direction in the plane to the prism 720. In Figure 7C the example, the prism 720 rotates R from the first angle θ1 to the second angle θ2 and translates T from the first position Pos1 in the X SF -Y SF plane to the second position Pos2 in the X SF -Y SF plane.

[0140] Thus, the linear translation T to the prism 720 translates the light beam 110A in a direction parallel to the long axis 701 of the surface 702 of the grating 700. The long axis 701 also lies in the X SF -Y SF plane of the device 730. By performing such a translation of the light beam 110A, which region of the grating 700 can be controlled to be irradiated at the lower end of the range of possible optical magnifications OM. Moreover, the grating 700 and the surface 702 of the grating are non-uniform; that is, some regions of the surface 702 of the grating 700 impart different variations to the wavefront of the light beam 110A than other regions of the surface 702 of the grating 700, and some regions of the surface 702 impart more distortion to the wavefront of the light beam 110A than other regions of the surface 702. The control system 185 (or the control module 550) can control the fast-actuating system 720A so as to adjust the linear translation T to the prism 720 and adjust the translation of the light beam 110A along the long axis 701 to utilize the non-uniformity of the surface 702 of the grating 700 and irradiate the higher-distortion region of the surface 702 of the grating 700 near one end of the grating surface 702 to increase the spectral bandwidth, even greater than what would be achieved by simply reducing the optical magnification.

[0141] Additionally, during the rotation of the position of the prism 720 relative to the light beam 110A, the linear translation T to the prism 720 also translates the hypotenuse H of the prism 720 (see Figure 7C ). Thus, during the operation of the device 730, the translation of the hypotenuse H exposes a new region of the hypotenuse H to the light beam 110A. During the life of the device 730, the prism 720 rotates from one end of its rotation range to the other end, and still more regions are exposed to the light beam 110A, which reduces the amount of damage imparted by the light beam 110A to the prism 720.

[0142] Similar to device 630, spectral feature selection device 730 also includes grating 600, and the beam expander includes prisms 705, 710, 715 positioned between prism 720 and grating 700 along the path of beam 110A. Grating 700 and the four prisms 705, 710, 715, 720 are configured to interact with beam 110A generated by light source 105 after beam 110A passes through aperture 755 of device 730. Beam 110A travels along a path in the X SF -Y SF plane from aperture 755, passes through prism 720, prism 715, prism 710, prism 705, and then reflects from grating 700, and passes through consecutive prisms 705, 710, 715, 720, and then passes through aperture 755 to exit device 730.

[0143] Referring to 8A - 8D, in other implementations, fast actuation system 820A is designed to be similar to fast actuation system 720A but with an additional auxiliary actuator 860A. Auxiliary actuator 860A is physically coupled to prism 820 that is furthest from grating 800. Auxiliary actuator 860A is configured to rotate prism 820 about an axis AH that lies in the X SF -Y SF plane and also in the plane of the hypotenuse H of prism 820.

[0144] In some implementations, although not necessary, auxiliary actuator 860A is controlled by control module 650 (or control system 185). Auxiliary actuator 860A can be a manual screw and flexure design that is not controlled by control module 550 or control system 185. For example, actuator 860A can be set before using system 820A, or actuator 860A can be manually changed between uses of system 820A.

[0145] Thus, prism 820 can rotate about axis AH that lies in the X SF -Y SF plane so as to be able to better control the position of beam 110A entering prism 820 and the hypotenuse H of prism 820, in order to better maintain the path of beam 110A through each of prisms 815, 810, 805, and grating 800. Specifically, the rotation of prism 820 about axis AH enables beam 110A to be more finely adjusted. For example, prism 820 can rotate about axis AH to ensure that the retroreflected (i.e., diffracted) beam 110A from grating 800 remains in the X SF -Y SF plane, and even if prism 820 rotates about axis AP or AR, the retroreflected beam 110A does not travel along the Z SFAxis shift. If the AP or AR axis is not perfectly aligned with the Z SF axis, it is beneficial to adjust the Z SF axis. Additionally, it is beneficial to rotate the prism 820 about the AH axis because the extension arm 825A is a cantilever and can sag or move along the Z SF axis in such a way that it deflects about the axis AH and the assist actuator 860A can be used to counteract this deflection.

[0146] Reference Figure 9 , the exemplary light source 905 is a pulsed laser source that generates a pulsed laser beam as the beam 110. The light source 905 is a two-stage laser system including a master oscillator (MO) 900 that provides a seed beam 110A to a power amplifier (PA) 910. The master oscillator 900 generally includes a gain medium in which amplification occurs and an optical feedback mechanism such as an optical resonator. The power amplifier 910 generally includes a gain medium in which amplification occurs when seeded with a seed laser beam from the master oscillator 900. If the power amplifier 910 is designed as a regenerative ring resonator, it is described as a power ring amplifier (PRA), and in this case, sufficient optical feedback can be provided from the ring design. The spectral feature selection device 130 receives the beam 110A from the master oscillator 900 in order to be able to finely tune spectral parameters of the beam 110A, such as the center wavelength and bandwidth, with a relatively low output pulse energy. The power amplifier 910 receives the beam 110A from the master oscillator 900 and amplifies the output to obtain the power required for output to be used in lithography.

[0147] The master oscillator 900 includes a discharge chamber having two elongated electrodes, a laser gas serving as a gain medium, and a fan that circulates the gas between the electrodes. The laser resonator is formed between the spectral feature selection device 130 on one side of the discharge chamber and an output coupler 915 on the second side of the discharge chamber to output the seed beam 110A to the power amplifier 910.

[0148] The light source 905 may further include a line center analysis module (LAM) 920 that receives the output from the output coupler 915, and one or more beam modification optical systems 925 that modify the size and / or shape of the beam as needed. The line center analysis module 920 is an example of a type of measurement system within a measurement system 170 that can be used to measure the wavelength (e.g., center wavelength) of the seed beam.

[0149] The power amplifier 910 includes a power amplifier discharge chamber, and if it is a regenerative ring amplifier, the power amplifier also includes a beam reflector or beam steering device 930 that reflects the beam back into the discharge chamber to form a circulating path. The power amplifier discharge chamber includes a pair of elongated electrodes, a laser gas serving as a gain medium, and a fan for circulating the gas between the electrodes. The seed beam 110A is amplified by repeatedly passing through the power amplifier 910. The beam modification optical system 925 provides a means (e.g., a partially reflective mirror) to intracouple the seed beam 110A and outcouple a portion of the amplified radiation from the power amplifier to form the output beam 110.

[0150] The laser gas used in the discharge chambers of the master oscillator 900 and the power amplifier 910 can be any suitable gas for generating a laser beam around the desired wavelength and bandwidth. For example, the laser gas can be argon fluoride (ArF) that emits light at a wavelength of about 193 nm or krypton fluoride (KrF) that emits light at a wavelength of about 248 nm.

[0151] The line center analysis module 920 monitors the wavelength of the output (beam 110A) of the master oscillator 900. The line center analysis module 920 can be placed at other locations within the light source 905 or can be placed at the output of the light source 905.

[0152] The repetition rate of the pulses generated by the power amplifier 910 is determined by the control system 185 controlling the repetition rate of the master oscillator 900 according to instructions from the controller 140 in the scanner 115. The repetition rate of the pulses output from the power amplifier 910 is the repetition rate seen by the scanner 115.

[0153] As described above, the bandwidth can be roughly and finely controlled using only optical elements such as Figure 5A . On the other hand, the bandwidth can be roughly and widely controlled by adjusting the angle of the prism 520 using the fast actuation system 520A, and can be quickly and finely controlled within a narrow range by controlling the differential timing between the activation of the electrodes within the MO 900 and the PRA 910.

[0154] Reference Figure 10 provides details regarding the control system 185 related to aspects of the systems and methods described herein. The control system 185 can include Figure 10 other features not shown. Generally, the control system 185 includes one or more of digital electronic circuits, computer hardware, firmware, and software.

[0155] The control system 185 includes a memory 1000, which can be a read-only memory and / or a random access memory. Storage devices suitable for tangibly implementing computer program instructions and data include all forms of non-volatile memory, and by way of example, include semiconductor memory devices such as EPROM, EEPROM, and flash memory devices; magnetic disks such as internal hard disks and removable disks; magneto-optical disks; and CD-ROM disks. The control system 185 may also include one or more input devices 1005 (such as a keyboard, touch screen, microphone, mouse, handheld input device, etc.) and one or more output devices 1010 (such as a speaker or a display).

[0156] The control system 185 includes one or more programmable processors 1015, and one or more computer program products 1020 tangibly implemented in a machine-readable storage device for execution by a programmable processor (such as processor 1015). Each of the one or more programmable processors 1015 can execute an instruction program to perform a desired function by operating on input data and generating an appropriate output. Typically, the processor 1015 receives instructions and data from the memory 1000. Any of the foregoing may be supplemented or incorporated by a specially designed ASIC (application specific integrated circuit).

[0157] In addition to other components, the control system 185 further includes a spectral feature analysis module 1025, a measurement module 1027, a lithography analysis module 1030, a decision module 1035, a light source actuation module 1050, a lithography actuation module 1055, and a beam preparation actuation module 1060. Each of these modules can be a set of computer program products executed by one or more processors such as processor 1015. In addition, any one of the modules 1025, 1030, 1035, 1050, 1055, 1060 can access the data stored in the memory 1000.

[0158] The spectral feature analysis module 1025 receives the output from the measurement system 170. The measurement module 1027 receives data from the measuring device 145. The lithography analysis module 1030 receives information from the lithography controller 140 of the scanner 115. The decision module 1035 receives the output from the analysis modules (such as modules 1025, 1027, and 1030) and determines which drive module or modules need to be activated based on the output from the analysis modules. The light source actuation module 1050 is connected to one or more of the light source 105 and the spectral feature selection device 130. The lithography actuation module 1055 is connected to the scanner 115, and specifically to the lithography controller 140. The beam preparation actuation module 1060 is connected to one or more components of the beam preparation system 112.

[0159] Although Figure 10 Only a few modules are shown in Figure 10 , but the control system 185 may include other modules. Additionally, although the control system 185 is depicted as a box in which all components appear to be co-located, the control system 185 may be composed of components that are physically remote from each other. For example, the light source actuation module 1050 may be physically co-located with the light source 105 or the spectral feature selection device 130.

[0160] Generally, the control system 185 receives at least some information about the light beam 110 from the measurement system 170, and the spectral feature analysis module 1025 performs an analysis on the information to determine how to adjust one or more spectral features (e.g., bandwidth) of the light beam 110 provided to the scanner 115. Based on this determination, the control system 185 sends signals to the spectral feature selection device 130 and / or the light source 105 to control the operation of the light source 105 via the control module 550. Generally, the spectral feature analysis module 1025 performs the analysis required to estimate one or more spectral features (e.g., wavelength and / or bandwidth) of the light beam 110. The output of the spectral feature analysis module 1025 is an estimated value of the spectral feature that is sent to the decision module 1035.

[0161] The spectral feature analysis module 1025 includes a comparison block that is connected to receive the estimated spectral feature and is also connected to receive a spectral feature target value. Generally, the comparison block outputs a spectral feature error value that represents the difference between the spectral feature target value and the estimated value. The decision module 1035 receives the spectral feature error value and determines how best to correct the system 100 in order to adjust the spectral feature. Thus, the decision module 1035 sends a signal to the light source actuation module 1050, and the light source actuation module 105 determines how to adjust the spectral feature selection device 130 (or the light source 105) based on the spectral feature error value. The output of the light source actuation module 1050 includes a set of actuator commands that are sent to the spectral feature selection device 130. For example, the light source actuation module 1050 sends these commands to the control module 550, and the control module 550 is connected to the actuation system within the device 530.

[0162] In addition, for example, the lithography analysis module 1030 can receive instructions from the lithography controller 140 of the scanner 115 to change one or more spectral characteristics of the pulsed beam 110 or to change the pulse repetition rate of the beam 110. The lithography analysis module 1030 performs an analysis on these instructions to determine how to adjust the spectral characteristics and sends the analysis result to the decision module 1035. The control system 185 causes the light source 105 to operate at a given repetition rate. More specifically, the scanner 115 sends a trigger signal to the light source 105 for each pulse (i.e., in a pulse-to-pulse manner) through the control system (through the lithography analysis module 1030), and the time interval between these trigger signals can be arbitrary, but when the scanner 115 sends trigger signals at regular intervals, the rate of these signals is the repetition rate. The repetition rate can be the rate requested by the scanner 115.

[0163] Reference Figure 11 , the process 1100 is performed by the lithography system 100 to quickly and independently control at least two spectral characteristics of the pulsed beam 110 to compensate for variations in one or more lithography performance parameters at each sub-region of the wafer 120. The independent control of at least two spectral characteristics means that if the first spectral characteristic should be adjusted for a specific sub-region of the wafer 120 and the second spectral characteristic should be maintained for this specific sub-region of the wafer 120, then the process 1100 takes the steps required to keep the second spectral characteristic within an acceptable range, and this operation is performed for each sub-region of the wafer 120. Thus, after any adjustment is required in a specific sub-region of the wafer 120 and before analyzing the next sub-region of the wafer 120, the first spectral characteristic and the second spectral characteristic reach stable values. This rapid analysis and adjustment are performed for each sub-region of the wafer 120 because the spectral characteristic selection system 130 has been redesigned to provide a more rapid adjustment of the spectral characteristics of the pulsed beam 110. The process 1100 can be performed by the control system 185.

[0164] For example, the pulsed beam 110 is generated (1105) by the light source 105. The pulsed beam 110 can be generated (1105) by guiding the seed beam 110A through the spectral characteristic selection system 130.

[0165] For example, the pulsed beam 110 can be generated from the light source 905 by generating a first pulsed beam 910A from a first gas discharge stage (such as the master oscillator 900), including selecting the first spectral characteristic of the pulsed beam 910A; guiding the first pulsed beam 910A to a second gas discharge stage (such as the power amplifier 910); and amplifying the first pulsed beam in the second gas discharge stage, thereby generating the pulsed beam 910 from the light source 905.

[0166] The pulsed beam 110 is directed towards the wafer 120, which is mounted on the stage 122 of the scanner 115. For example, the pulsed beam 110 generated by the light source 105 is modified as needed and redirected towards the scanner 115 through the beam preparation system 112.

[0167] For example, the pulsed beam 110 is scanned (1110) across the wafer 120 by moving the pulsed beam 110 and the wafer 120 relative to each other along a transverse plane (X L -Y L plane). Specifically, the lithography controller 140 can send one or more signals to the actuation systems associated with the wafer stage 122, the mask 134, and the objective arrangement 132, so as to move one or more of the mask 134, the objective arrangement 132, and the wafer 220 (via the stage 122) relative to each other during exposure to scan the exposure window 400 across each sub-region of the wafer 220 (for each exposure field 223).

[0168] A first sub-region of the wafer 120 is selected for exposure (1115) by the beam 110 for lithography processing. The selected sub-region of the wafer 120 can be an exposure field (such as the exposure field 223 of the wafer 220). Alternatively, the sub-region of the wafer 120 can correspond to the portion of the wafer 120 that interacts with a single pulse of the beam 110.

[0169] Receive (1120) the lithography performance parameters at the wafer 120 for the selected sub-region of the wafer 120. For example, the control system 185 receives the performance parameters of the sub-region of the wafer 120 from the lithography controller 140, and the lithography controller 140 receives data from the metrology device 145. The performance parameters at the wafer 120 can be received (1120) at each sub-region of the wafer 120 while scanning the pulsed beam 110 across the wafer 120, or can be received before scanning the pulsed beam 110 across the wafer 120.

[0170] The received (1120) performance parameters can be one or more of the following: errors in the physical properties of the wafer, the contrast of the features formed on the wafer, the critical dimension of the sub-region exposed to the pulsed beam 110, the placement of the features formed on the wafer 120 relative to the target or relative to the underlying features (e.g., overlay) (X, Y positions relative to the desired / target position), the photoresist distribution, the sidewall angle, and the change in the position of the wafer 120.

[0171] The control system 185 analyzes the received lithography performance parameters (1125), for example, to determine whether it is outside the acceptable value range. If the lithography performance parameter is outside the acceptable value range (1125), the control system 185 determines how to modify the first spectral characteristic of the beam 110 in order to compensate for the unacceptable change in the lithography performance parameter in this sub-region of the wafer 120. The control system 185 sends a signal to the spectral characteristic selection device 130 to change (1130) the first spectral characteristic of the beam 110 by a specific amount that will compensate for the unacceptable change in the lithography performance parameter.

[0172] In addition, the control system 185 also analyzes whether the modification to the first spectral characteristic of the beam 110 affects the value of the second spectral characteristic of the beam 110 and acts in a way that keeps the second spectral characteristic of the beam 110 within an acceptable range. For example, the control system 185 can determine that the second spectral characteristic of the beam 110 needs to be changed to counteract the unwanted modification to the second spectral characteristic of the beam 110 caused by the modification to the first spectral characteristic of the beam 110. Therefore, the control system 185 sends a signal to the spectral characteristic selection device 130 to change (1130) the second spectral characteristic of the beam by a specific amount that will compensate for this unwanted modification.

[0173] The control system 185 determines whether additional sub-regions of the wafer 120 need to be exposed (1135) by the beam 110 for lithography processing, and if additional sub-regions of the wafer 120 need to be exposed (1135), the control system 185 selects the next sub-region (1140) of the wafer 120 as the sub-region to be exposed by the beam 110 for lithography processing. Thus, the process 1100 continues until the entire wafer 120 has been processed.

[0174] In addition, the process 1100 can modify (1130) the first spectral characteristic of the pulsed beam 110 by selectively reflecting the pulsed beam 110A from the diffraction surface (such as surface 502) of the spectral characteristic selection system 130.

[0175] By directing the pulsed beam through a plurality of prisms (such as prisms 505, 510, 515, 520) towards a diffractive optical element (such as grating 500) such that the pulsed beam is retro-reflected off the diffractive optical element and passes through the plurality of prisms again, the first spectral characteristic of the pulsed beam can be modified (1130) and the second spectral characteristic of the pulsed beam can be maintained (113). Additionally, at least two prisms in the beam expander can be rotated such that the incident angle 562 of the pulsed beam 110 on the diffractive optical element changes, but the total magnification 565 of the pulsed beam on the diffractive optical element remains unchanged.

[0176] The first spectral characteristic of the beam 110 (1130) can be modified by modifying the wavelength of the pulsed beam. Additionally, the second spectral characteristic (1130) can be maintained by keeping the bandwidth of the pulsed beam 110 within a bandwidth range. For example, the bandwidth of the pulsed beam 110 can be kept within + / - 10 femtoseconds (fs) or + / - 1 fs.

[0177] The first spectral characteristic of the pulsed beam 110 (1130) can be modified by rotating the first prism system of the spectral characteristic selection device 130 through which the pulsed beam 110A passes. For example, the control system 185 can send a signal to Figure 5A the control module 550 of the spectral characteristic selection device 130 to rotate one or more prisms of the beam expander 501. For example, the prism 505 can be rotated for a relatively coarse wavelength modification, and the prism 510 can be rotated for a relatively fine wavelength modification. As another example, the prism 505 can be rotated for a relatively coarse wavelength modification, and the prism 515 can be rotated for a relatively fine wavelength modification.

[0178] Additionally, the second spectral characteristic of the pulsed beam 110 (1130) can be maintained by rotating the second prism system of the spectral characteristic selection device 130 through which the pulsed beam 110A passes. For example, the control system 185 can send a signal to Figure 5A the control module 550 of the spectral characteristic selection device 130 to rotate one or more prisms of the beam expander 501. For example, using the fast actuator discussed above, the prism 520 can be rotated for a relatively coarse bandwidth adjustment, and the prism 510 can be rotated for a relatively fine bandwidth adjustment.

[0179] A relatively coarse wavelength modification can be achieved by an actuation step associated with the prism that is relatively larger than the actuation step for providing a relatively fine wavelength modification. Similarly, a relatively coarse bandwidth adjustment can be achieved by an actuation step associated with the prism that is relatively larger than the actuation step for providing a relatively fine bandwidth modification.

[0180] The first spectral characteristic of the pulsed beam 110 (1130) can be modified by rotating a mirror placed between the prism 505 and the grating 500 of the spectral characteristic selection device 130 through which the pulsed beam 110A passes. For example, the control system 185 can send a signal to Figure 5A the control module 550 of the spectral characteristic selection device 130 to rotate the mirror.

[0181] The control system 185 can maintain the second spectral characteristic (1130) of the pulsed beam 110 by adjusting the second spectral characteristic to compensate for the change in the second spectral characteristic caused by the modification of the first spectral characteristic of the pulsed beam 110 (1130). Additionally, the second spectral characteristic of the pulsed beam 110 can be adjusted (1130) while the first spectral characteristic of the pulsed beam 110 is being modified (1130).

[0182] The modification (1130) of the first spectral characteristic of the pulsed beam 110 can cause a modification of the first condition of the pulsed beam 110 at the wafer 120. For example, if the first spectral characteristic is the wavelength of the beam 110, the modification of the wavelength causes a modification of the focal plane of the beam 110 at the wafer 120. The maintenance (1130) of the second spectral characteristic of the pulsed beam 110 can cause the second condition of the pulsed beam 110 at the wafer 120 to be maintained at a specific level. For example, if the second spectral characteristic is the bandwidth of the beam 110, by maintaining the bandwidth of the beam 110, the contrast property or the depth of focus of the beam 110 at the wafer 120 can thus be maintained.

[0183] Although the examples given above relate to Figure 5A the spectral characteristic selection device, however Figure 6A any design of the spectral characteristic selection devices of FIGS. 7A and 8A can be used to perform one or more steps in the process 1100.

[0184] Additionally, during the process 1100, the control system 185 also performs a parallel process 1150 for controlling one or more spectral characteristics of the pulsed beam 110 while scanning the beam 110 across the wafer 120 as shown in Figure 12 FIG. The process 1150 is performed independent of whether the lithography performance parameters are outside the acceptable range and thus does not consider the lithography performance parameters. However, the analysis performed by the control system 185 during the process 1150 can be used by the control system 185 to further determine how to analyze the received lithography performance parameters (1125) and modify the first spectral characteristic and maintain the second spectral characteristic (1130).

[0185] Process 1150 includes measuring one or more spectral characteristics (1155) of the pulsed beam 110 and determining whether any of the measured spectral characteristics are outside an acceptable range of values (1160). For example, the spectral characteristics analysis module 1025 of the control system 185 may receive spectral characteristic measurements (1155) from the measurement system 170. The spectral characteristics analysis module 1025 may determine whether any of the spectral characteristics are outside an acceptable range of values (1160). If any of the spectral characteristics are outside an acceptable range of values, those spectral characteristics are adjusted (1165). For example, the decision module 1035 may send a signal to the light source actuation module 1050, and the light source actuation module 1050 may send a signal to the spectral characteristic selection device 130 to adjust one or more spectral characteristics of the beam 110 (1165). This adjustment may be coordinated with any adjustment that needs to be made to account for changes in wafer characteristics (1130).

[0186] Process 1150 may be performed at regular intervals during the scan, e.g., for each exposure field 223 or for each sub-region where steps 1120, 1125, 1130 are performed. Additionally, the control system 185 may coordinate the adjustment (1130) of the first spectral characteristic needed to compensate for changes in lithography performance parameters with any adjustment needed to ensure that the first spectral characteristic is within an acceptable range of values.

[0187] Other implementations are within the scope of the following claims.

Claims

1. An apparatus, comprising: A spectral feature selection system that optically interacts with a pulsed beam; A measurement system configured to measure one or more spectral features of the pulsed beam; A metrology device configured to determine at least one lithography performance parameter for each sub-region of a substrate, where the sub-region is a part of the entire region of the substrate, and where the lithography performance parameter is a characteristic associated with the substrate or with the pulsed beam that interacts with the substrate; And A control system connected to the spectral feature selection system, the measurement system, and the metrology device, and configured for each substrate sub-region: Receive the determined lithography performance parameter from the metrology device and receive the measured one or more spectral features of the pulsed beam from the measurement system; Analyze the determined lithography performance parameter for each sub-region of the substrate and analyze the measured one or more spectral features of the pulsed beam; And Based on these analyses: Send a first signal to the spectral feature selection system to modify a first spectral feature of the pulsed beam, where the modification of the first spectral feature takes into account the analysis of the measured one or more spectral features, and where the first signal is sent based on a determination that the lithography performance parameter is outside an acceptable range; and Keep a second spectral feature of the pulsed beam within a range of values of the second spectral feature by sending a second signal to the spectral feature selection system when the first spectral feature of the pulsed beam is modified.

2. The apparatus according to claim 1, wherein the control system is configured to send the first signal to the spectral feature selection system to modify the first spectral feature by determining whether any of the measured one or more spectral features is outside an acceptable range of values, wherein the first signal takes into account the analysis of the measured one or more spectral features.

3. The apparatus according to claim 1, wherein the first spectral feature of the pulsed beam is the wavelength of the pulsed beam, and the second spectral feature of the pulsed beam is the bandwidth of the pulsed beam.

4. The apparatus according to claim 1, wherein the measurement system is configured to receive a portion of the pulsed beam directed to the substrate.

5. The apparatus according to claim 1, wherein the lithography performance parameters include one or more of the following: the average offset of the position of the substrate from the desired position, the platform vibration of the substrate, the position of the substrate varying from a central sub-region of the substrate to a sub-region at the edge of the substrate, the error in the physical properties of the substrate, the contrast of the features formed on the substrate, the critical dimension at the substrate region exposed to the pulsed beam, the placement of the features formed on the substrate relative to a target or relative to underlying features, the photoresist distribution, the sidewall angle, and the variation in the position of the substrate.

6. A method, comprising: Measure one or more spectral features of a pulsed beam directed at a substrate of a lithography exposure apparatus; Receive at least one lithography performance parameter associated with each sub-region of the substrate when the pulsed beam interacts with each sub-region of the substrate, where the sub-region is a part of the entire region of the substrate, and where the lithography performance parameter is a characteristic associated with the substrate or with the pulsed beam that interacts with the substrate; Receive the measured one or more spectral features of the pulsed beam; Analyze the determined lithography performance parameter at each sub-region of the substrate; Analyze the measured one or more spectral features of the pulsed beam; And Based on these analyses: Modify a first spectral feature of the pulsed beam, where the modification of the first spectral feature takes into account the analysis of the measured one or more spectral features, and where the modification of the first spectral feature is based on a determination that the lithography performance parameter is outside an acceptable range; and Keep a second spectral feature of the pulsed beam within a range of values of the second spectral feature when the first spectral feature of the pulsed beam is modified.

7. The method according to claim 6, wherein the modification of the first spectral characteristic taking into account the analysis of the measured one or more spectral characteristics includes determining whether any of the measured one or more spectral characteristics is outside an acceptable range of values.

8. The method according to claim 6, wherein modifying the first spectral characteristic of the pulsed beam includes modifying the wavelength of the pulsed beam, and maintaining the second spectral characteristic of the pulsed beam includes maintaining the bandwidth of the pulsed beam within a range of values of the bandwidth.

9. The method according to claim 6, wherein measuring the one or more spectral characteristics of the pulsed beam includes measuring the wavelength of the pulsed beam.

10. The method according to claim 6, wherein measuring the one or more spectral characteristics of the pulsed beam includes measuring the bandwidth of the pulsed beam.

11. The method according to claim 6, wherein modifying the first spectral characteristic of the pulsed beam includes ensuring that the first spectral characteristic is within an acceptable range of values.

12. The method according to claim 6, wherein measuring the one or more spectral characteristics of the pulsed beam includes estimating a metric value of the spectrum of the pulsed beam.

13. A lithographic apparatus, comprising: A spectral feature selection system that optically interacts with a pulsed beam; A metrology device configured to determine at least one lithography performance parameter at each sub-region of a substrate, where the sub-region is a part of the entire region of the substrate, and where the lithography performance parameter is a characteristic associated with the substrate or with the pulsed beam that interacts with the substrate; And A control system, connected to the spectral feature selection system and the measurement device, and configured to, at each substrate sub-region: Receive the determined lithography performance parameters; Analyze the determined lithography performance parameters; And Based on the analysis of the determined lithography performance parameters: Modify the wavelength of the pulsed beam by sending a first signal to the spectral feature selection system, wherein the modification of the wavelength causes a change in the bandwidth of the pulsed beam; and Maintain the bandwidth of the pulsed beam within an acceptable range of values when the wavelength is modified.

14. The apparatus according to claim 13, wherein maintaining the bandwidth of the pulsed beam within an acceptable range of values includes adjusting the bandwidth of the pulsed beam to compensate for a change in bandwidth caused by the modification of the wavelength, wherein adjusting the bandwidth includes sending a second signal to the spectral characteristic selection system when the wavelength of the pulsed beam is modified.

15. The apparatus according to claim 14, wherein: Modifying the wavelength of the pulsed beam includes rotating the wavelength prism through which the pulsed beam passes to change the angle of incidence between the pulsed beam and the grating; and Adjusting the bandwidth of the pulsed beam includes rotating the bandwidth prism through which the pulsed beam passes by an amount that cancels the magnification change caused by the rotation of the wavelength prism.

16. The apparatus according to claim 13, wherein the lithography performance parameter includes one or more of the following: the average offset of the position of the substrate from the desired position, the platform vibration of the substrate, the position of the substrate varying from a central sub-region of the substrate to a sub-region at an edge of the substrate, an error in a physical property of the substrate, the contrast of a feature formed on the substrate, the critical dimension at a substrate region exposed to the pulsed beam, the placement of a feature formed on the substrate relative to a target or relative to a feature below, the photoresist distribution, the sidewall angle, and a change in the position of the substrate.

17. The apparatus according to claim 13, wherein the spectral feature selection system includes: A grating and a beam expander including a plurality of prisms, configured such that the pulsed beam interacts with each of the grating and the prisms of the beam expander; And An actuation system in communication with the control system, the actuation system including a plurality of actuators, each actuator being coupled to one of the prisms to rotate the one prism relative to the pulsed beam under the control of the control system.

18. A method, comprising: When the pulsed beam interacts with each sub-region of the substrate, receive at least one lithography performance parameter associated with that sub-region, where the sub-region is a part of the entire region of the substrate, and where the lithography performance parameter is a characteristic associated with the substrate or with the pulsed beam that interacts with the substrate; Analyze the determined at least one lithography performance parameter; And Based on the analysis of the determined lithography performance parameters: Modify the wavelength of the pulsed beam, wherein the modification of the wavelength causes a change in the bandwidth of the pulsed beam, and wherein the modification of the wavelength is based on the determination that the lithography performance parameter is outside an acceptable range; and Maintain the bandwidth of the pulsed beam within an acceptable range of values when the wavelength is modified.

19. The method according to claim 18, wherein maintaining the bandwidth of the pulsed beam within an acceptable range of values includes adjusting the bandwidth of the pulsed beam to compensate for a change in the bandwidth caused by the modification of the wavelength.

20. The method according to claim 19, wherein: Modifying the wavelength of the pulsed beam includes rotating the wavelength prism through which the pulsed beam passes to change the angle of incidence between the pulsed beam and the grating; and Adjusting the bandwidth of the pulsed beam includes rotating the bandwidth prism through which the pulsed beam passes by an amount that cancels the magnification change caused by the rotation of the wavelength prism.

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