Photo-etching system and photo-etching method

Abstract

An optical lithography system for controlling a plasma location in an extreme ultraviolet lithography light source can include a vacuum chamber; a droplet generator to dispense a stream of droplets into the vacuum chamber, wherein the droplets are formed of a metallic material; a laser light source to emit a plurality of laser pulses including at least a first pulse and a second pulse into the vacuum chamber; a sensor to detect an observed plasma location within the chamber, wherein the observed plasma location includes a location at which the plurality of laser pulses vaporize a droplet of the stream of droplets to generate a plasma that emits extreme ultraviolet light radiation; and a first feedback loop connecting the sensor to the laser light source, wherein the first feedback loop adjusts a time delay between the first and second pulses to minimize a difference between the observed plasma location and a target plasma location.

Description

Technical Field

[0001] This disclosure relates to a photoetching system and a photoetching method. Background Technology

[0002] Extreme ultraviolet (EUV) lithography is an optical lithography technique in which a scanner uses light in the extreme ultraviolet region (e.g., across wavelengths of approximately one to one hundred nanometers). A particular type of EUV lithography (called laser-produced plasma (LPP) EUV lithography) uses a light source to convert molten metal, such as tin, into a highly ionized plasma that emits EUV radiation. An LPP EUV light source generally includes a vacuum chamber, a laser power source (e.g., a carbon dioxide laser), and a droplet generator. The droplet generator dispenses droplets of molten metal into the vacuum chamber, and when a droplet reaches a predefined position within the vacuum chamber, the laser power source fires a series of laser pulses into the vacuum chamber. When the laser pulses strike the droplet, the droplet is vaporized into plasma, which emits EUV radiation.

[0003] A series of optical elements (e.g., including multilayer mirrors) are then used to guide the EUV radiation into a scanner, which is then used to project a pattern (etched into a photomask) onto a silicon wafer. The EUV process can be used to create high-resolution line patterns on silicon wafers, with a potential scale of seven nanometers or larger. Summary of the Invention

[0004] An optical etching system includes a vacuum chamber, a droplet generator, a laser source, a sensor, and a first feedback loop. The droplet generator distributes a droplet stream into the vacuum chamber. The droplets are formed of a metallic material. The laser source emits multiple laser pulses, including at least one pre-pulse and a main pulse, into the vacuum chamber. The sensor detects observed plasma locations within the vacuum chamber and captures a first image of the returning beam of the pre-pulse from the droplets when the pre-pulse strikes the droplets and before the main pulse strikes the droplets. The observed plasma locations include the locations where the laser pulse vaporizes the droplets to generate plasma emitting extreme ultraviolet radiation. The first feedback loop connects the sensor to the laser source. The first feedback loop adjusts the time delay between the pre-pulse and a second pulse to minimize the difference between the observed plasma locations and the target plasma locations.

[0005] A photolithography system includes a vacuum chamber, a droplet trap, a droplet generator, a laser source, a sensor, a feedback loop, and a droplet generator meter. The droplet trap is located within the vacuum chamber. The droplet generator distributes a droplet stream into the vacuum chamber and to the droplet trap. The droplets are formed from a metallic material. The laser source emits multiple laser pulses, including at least a first pulse and a second pulse, into the vacuum chamber. The sensor detects an observed plasma location within the vacuum chamber. The observed plasma location includes the location where the laser pulse vaporizes the droplets in the droplet stream to generate plasma emitting extreme ultraviolet radiation. The feedback loop connects the sensor to the laser source. The feedback loop adjusts the trajectory of the laser pulses to minimize the difference between the observed plasma location and the target plasma location. The droplet generator meter is connected to the droplet generator to provide feedback.

[0006] An optical etching method includes: distributing a droplet stream into a vacuum chamber, wherein the droplets are formed of a metallic material; emitting a plurality of laser pulses on the droplet stream using a laser source, wherein when a laser pulse strikes a droplet, the droplet vaporizes into a plasma emitting extreme ultraviolet radiation, the laser pulses including a pre-pulse and a main pulse, and when the pre-pulse strikes a droplet, the shape of the droplet changes from a spherical shape to a flattened, thin sheet shape; and capturing a first image of the return beam of the pre-pulse from one of the droplets while the pre-pulse strikes one of the droplets and before the main pulse strikes said one of the droplets.

[0007] An optical etching method includes: dispensing a droplet into a vacuum chamber; emitting a pre-pulse laser to the droplet; sensing a first image of the return beam of the pre-pulse laser from the droplet; emitting a main pulse laser to the droplet after emitting the pre-pulse laser, wherein the droplet vaporizes into plasma emitting extreme ultraviolet radiation when the main pulse laser strikes the droplet; sensing a second image of the return beam of the main pulse laser from the droplet after sensing the first image and emitting the main pulse laser; and adjusting the position of the plasma within the vacuum chamber based at least on the second image.

[0008] An optical etching method includes: providing a droplet from a droplet generator toward a droplet trap of an extreme ultraviolet (EUV) lithography source; emitting a master pulse laser to strike the droplet and forming a plasma emitting EUV radiation in a vacuum chamber of the EUV lithography source; detecting a first image of the droplet when the master pulse laser strikes the droplet; filtering the master pulse laser from the first image to extract the return beam of the master pulse laser; and determining the x, y, z coordinates of the plasma based on the return beam of the master pulse laser.

[0009] An optical etching method includes: distributing a plurality of droplets from a droplet generator toward a droplet trap of an extreme ultraviolet (EUV) lithography light source; emitting a master pulse laser to strike one of the droplets to form a plasma emitting EUV radiation in a vacuum chamber of the EUV lithography light source; and detecting the position of the plasma when the master pulse laser strikes said one of the droplets. Attached Figure Description

[0010] The best understanding of this disclosure can be obtained by reading it in conjunction with the accompanying figures, as described in the following detailed description. It should be noted that, according to industry standard practice, the various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or decreased for clarity of explanation.

[0011] Figure 1 A schematic diagram illustrating one example of an extreme ultraviolet lithography source according to an example of this disclosure;

[0012] Figure 2 For illustration Figure 1 A schematic diagram of an example of a first feedback generator;

[0013] Figure 3 A flowchart illustrating a method for controlling the position of plasma in an extreme ultraviolet lithography source according to an example of this disclosure is provided.

[0014] Figure 4 A flowchart illustrating a method for controlling the position of plasma in an extreme ultraviolet lithography source according to another example of this disclosure is provided.

[0015] [Symbol Explanation]

[0016] 100: Extreme Ultraviolet Light Micro-Lithograph Source

[0017] 102: Vacuum Chamber

[0018] 104: Laser power source

[0019] 106: Droplet generator

[0020] 108: Seed Laser

[0021] 110: Power Amplifier

[0022] 112: Beam Transport System (BTS)

[0023] 114: Sensor

[0024] 116: First Feedback Generator (FG)

[0025] 118: Controller

[0026] 120: Droplet

[0027] 122: Flat, round thin sheet

[0028] 124: Second Feedback Generator

[0029] 126: Controller

[0030] 128: Droplet Generator (DG) Meter

[0031] 200: Filter

[0032] 202: Amplifier

[0033] 204: Position-Sensitive Detector

[0034] 300, 400: Method

[0035] 302,304,306,308,402,404,406,408,410,412,414,416,418,420: Steps Detailed Implementation

[0036] The following disclosure provides numerous different embodiments or instances for implementing various features of the provided subject matter. Specific examples of components and arrangements are described below to simplify this disclosure. These are, of course, merely examples and are not intended to be limiting. For instance, in the following description, the formation of a first feature on or on a second feature may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed between the first and second features such that the first and second features are not in direct contact. Furthermore, element symbols and / or letters may be repeated in various instances in this disclosure. This repetition is for simplicity and clarity and does not in itself represent a relationship between the various embodiments and / or configurations discussed.

[0037] Additionally, for simplicity, spatial relative terms such as “below,” “under,” “lower,” “above,” “upper,” and similar terms are used herein to describe the relationship between one element or feature and another (other) element or feature, as illustrated in the figures. These spatial relative terms are intended to cover different orientations of elements in use or operation, in addition to those depicted in the figures. Devices may be oriented in other ways (rotated 90 degrees or otherwise), and the spatial relative descriptive terms used herein shall be interpreted accordingly.

[0038] In one example, this disclosure provides plasma position control for an extreme ultraviolet (EUV) light source. As described above, the EUV light source may generally include a vacuum chamber, a laser power source, and a droplet generator. The droplet generator dispenses droplets of molten metal (e.g., tin) into the vacuum chamber, and when the droplets reach a predefined position within the vacuum chamber, the laser power source emits a series of laser pulses into the vacuum chamber. When the first pulse (also referred to as the “pre-pulse”) strikes the droplet, the generally spherical droplet takes on a flattened, oval-like sheet shape. When the second pulse (also referred to as the “main pulse”) strikes this oval sheet, the oval sheet is vaporized into plasma emitting EUV radiation. The EUV radiation can then be used to project a pattern formed in a photomask onto a silicon wafer, and this pattern can be etched into the wafer.

[0039] The precision of laser impact on droplets is a major determinant of the conversion efficiency (i.e., how much laser power is converted into EUV radiation) of an EUV light source. Current-stage LPP (Laser-to-Plasma) light sources have been shown to exhibit conversion efficiencies of less than 10 percent. Therefore, these sources consume a large amount of energy but manage to produce a relatively small amount of light for that power. Conventional LPP light sources include a control system to fix the droplet position and the laser position relative to the droplets individually, but do not allow fixing the plasma position (e.g., the position of the master pulse impacting a flat, cylindrical sheet in a vacuum chamber to generate plasma). Therefore, over time, conditions such as laser beam drift or changes in plasma position can affect the precision of laser impact on droplets and thus reduce the conversion efficiency of the light source.

[0040] This disclosure provides examples of feedback control to fix the plasma position within the vacuum chamber of an EUV light source. In one example, in addition to calculating the droplet position from the return beam of the prepulse (i.e., the first laser pulse impacting the spherical droplet) in a conventional manner, this disclosure also calculates the droplet position from the return beam of the autopulse (i.e., the second laser pulse impacting the flattened disc). The x, y, and z coordinates extracted from the return beam can be used to control the feedback of the laser power source. For example, the x-coordinate (i.e., the position along a line parallel to the droplet flow direction) can be used to adjust the time delay between the prepulse and the laser pulse, thus adjusting the position where the flattened disc vaporizes into plasma (e.g., by allowing the flattened disc to fall a shorter or longer distance before vaporization). Additionally, the y and z coordinates can be used to adjust optical elements (e.g., mirrors) that guide the laser pulse beam relative to the droplet and the flattened disc. Adjustments to the time delay and beam-guiding optics based on the observed plasma position within the vacuum chamber allow the plasma position to remain fixed at a target location. In other words, these adjustments can be used to continuously minimize the increment or difference between the observed plasma position and the target plasma position, so that the plasma position remains fixed and does not drift.

[0041] In the context of this disclosure, the term "droplet" is understood to represent molten metal (e.g., tin) dispensed into the vacuum chamber of an EUV light source before being struck by a laser pulse. The term "flat oval sheet" is understood to represent molten metal after being struck by a first laser pulse but before it transforms into plasma (e.g., after being struck by a pre-pulse but before being struck by a main pulse). Furthermore, the term "observed plasma location" is understood to represent the location where laser strikes on the flat oval sheet are observed (e.g., by a camera or other sensor). The term "target plasma location" is a predefined location where laser strikes on the flat oval sheet are desired. Examples of this disclosure may attempt to maintain a fixed plasma location by continuously monitoring the observed plasma location and adjusting the EUV light source as needed to ensure the plasma location is as close as possible to the target plasma location.

[0042] Figure 1 A schematic diagram illustrating one example of an extreme ultraviolet lithography source 100 according to an example of this disclosure. Figure 1 The discussion refers to the positions in the x, y, z coordinate plane. In one example, the x-axis of the coordinate plane is defined by a line parallel to the direction of droplet propagation (or perpendicular to the direction of laser pulse propagation). The z-axis of the coordinate plane is defined by a line parallel to the direction of laser pulse propagation (or perpendicular to the direction of droplet propagation). The y-axis of the coordinate system is defined by a line perpendicular to both the x-axis and z-axis.

[0043] As described above, the system 100 generally includes a vacuum chamber 102, a laser power source 104, and a droplet generator 106.

[0044] The droplet generator 106 includes a container for distributing a continuous flow of microscopic droplets, wherein the droplets are formed from a metallic material in liquid or solid form. For example, in one instance, the droplets are formed from molten tin. However, in other instances, the droplets may be formed from other materials, such as tin-containing liquid materials (e.g., eutectic alloys containing tin, lithium, and xenon).

[0045] In one example, the droplet generator 106 may include a gas supply or other system (not shown) for pumping gas that forces droplets away from the droplet generator 106 (e.g., via a nozzle). In this case, the flow rate of the continuous flow of droplets may be a function of the pressure of the pumped gas. For example, the flow rate may be faster when the gas pressure increases, and slower when the gas pressure decreases.

[0046] In one instance, each droplet may have a diameter of approximately 25 to 30 micrometers, and the droplet generator 106 may dispense these droplets at a rate of approximately 50,000 droplets per second or 50 kilohertz.

[0047] Droplet generator 106 is coupled to vacuum chamber 102. Vacuum chamber 102 includes an internal volume maintained in a vacuum environment. Droplet generator 106 can distribute a continuous flow of droplets into the vacuum environment of vacuum chamber 102. For example, droplet generator 106 may be located at an inlet near the top of vacuum chamber 102 and can distribute droplets into vacuum chamber 102 such that the droplets fall towards the bottom of vacuum chamber 102. As described above, as indicated by droplet 120, the droplets distributed by droplet generator 106 may have a generally spherical shape.

[0048] Laser power source 104 is also coupled to vacuum chamber 102. In one example, laser power source 104 generally includes a seed laser 108, a set of power amplifiers 110, and a beam transport system (BTS) 112. In one example, seed laser 108 is a 20-30 kW carbon dioxide (CO2) laser source. However, in other examples, seed laser 108 may include another type of laser source, such as a neodymium-doped yttrium aluminum garnet (Nd:YAG) laser source. Seed laser 108 may include a single laser or multiple lasers. Seed laser 108 is used to generate multiple laser pulses, including pre-pulses and main pulses. Laser pulses may have a specific spot size (e.g., approximately 100 to 300 micrometers). In one example, laser pulses are generated by seed laser 108 at the same rate as the droplets dispensed by droplet generator 106. However, as discussed in more detail below, the rate of laser pulse generation can be adjusted to maintain a fixed plasma position within vacuum chamber 102. In another example, the seed laser 108 may include a preamplifier (e.g., a high-gain carbon dioxide amplifier) ​​that performs initial amplification of the laser pulse (e.g., up to approximately 100 watts).

[0049] In one example, this group of power amplifiers 110 includes multiple amplifiers that amplify the laser pulses generated by the seed laser 108 in multiple stages. In one example, the laser pulses can be amplified to an average pulse power of up to tens of kilowatts and a peak pulse power of millions of kilowatts. Therefore, this group of power amplifiers 110 can provide most of the amplification required to reach a power level high enough to generate EUV radiation in the vacuum chamber 102.

[0050] In one example, BTS 112 includes a set of optical elements (e.g., periscopes and / or mirrors, including M120 and / or M150 mirrors, which may be coated to minimize absorption of light from the laser) for extending the laser pulse beam and guiding the beam to a specific, predefined position (e.g., toward the droplet flow) within the vacuum chamber 102. In one example, BTS 112 can deliver the beam up to thirty meters in the direction of the vacuum chamber 102. Thus, the laser pulse beam is guided or controlled to maximize the generation of EUV radiation. In one example, as discussed in more detail below, BTS 112 may also include a second feedback generator 124 that adjusts BTS 112 (e.g., adjusts the angle and / or direction of the guided beam) in an effort to maintain a fixed plasma position within the vacuum chamber.

[0051] In one example, the laser power source 104 may further include a controller 126. The controller 126 may adjust the power of the laser source 104 in response to the intensity of photons emitted by the plasma in the vacuum chamber 102 (e.g., by adjusting the output of this set of power amplifiers 110). For example, the controller 126 may adjust the amplifiers to increase or decrease the amplification of the laser pulses emitted by the seed laser 108.

[0052] As described above, the vacuum chamber 102 includes a container or volume therein that generates EUV radiation. The vacuum chamber 102 may include one or more sensors 114. In one example, the sensors 114 may include multiple cameras located at different locations within the vacuum chamber 102. In this case, the multiple cameras may include multiple different types of cameras used and positioned to capture different types of information. For example, the vacuum chamber may include a coarse droplet source camera (CDSC) for capturing images of the droplet positions within the vacuum chamber 102, a fine droplet source camera (FDSC) for capturing images of the flattened disc within the vacuum chamber 102, and one or more other types of cameras. In one example, the sensors 114 are positioned to monitor the positions of the pre-pulse and main pulse in the vacuum chamber, i.e., where the pre-pulse impacts the droplet 120 and where the main pulse impacts the flattened disc 122. For example, if sensor 114 includes a camera, the camera can capture images of the pre-pulse and the main pulse when the pre-pulse and the main pulse strike the droplet 120 and the flat oval sheet 122, respectively.

[0053] System 100 includes other elements that assist in controlling the plasma position within vacuum chamber 102 (i.e., the position where the flat, round sheet 122 vaporizes). In one example, these other elements include a first feedback generator (FG) 116 and a controller 118.

[0054] Figure 2 For illustration Figure 1 A schematic diagram of an example of a first feedback generator 116. In one example, the first feedback generator 116 includes a filter 200, an amplifier 202, and a position-sensitive detector 204. The filter 200 can be used to extract the return beam from the flattened disc 122 from an image provided by the sensor 114. In one example, the return beam from the flattened disc 122 includes laser light reflected by the flattened disc 122 when the main pulse strikes it. In one example, the filter 200 can extract the return beam from the image by filtering light from the laser pre-pulse and light from the laser main pulse. In one example, the filter 200 may include a coated mirror, such as a bipolar mirror. Once the pre-pulse light and the main pulse light have been filtered from the image, the image can be transmitted to the amplifier 202, which amplifies the return beam in the image. The position-sensitive detector 204 receives the amplified and filtered image and determines the x, y, z coordinates of the observed plasma position in the vacuum chamber 102 based on the beam deflection in the image. In one example, the position-sensitive detector 204 is a four-unit optical detector array.

[0055] Return to reference Figure 1 The position-sensitive detector 204 can provide the controller 118 with the x-coordinate of the observed plasma position. The controller 118 can then adjust the time delay between the pre-pulse and the main pulse based on the position of the observed plasma position's x-coordinate relative to the target plasma position's x-coordinate. For example, if the observed plasma position's x-coordinate is the same as the target plasma position's x-coordinate (or within a certain acceptable predefined tolerance), the controller 118 can keep the time delay unchanged. However, if the observed plasma position's x-coordinate is not the same as the target plasma position's x-coordinate (or is not within its acceptable predefined tolerance), the controller 118 can shorten or lengthen the time delay as needed until the observed plasma position's x-coordinate is the same as the target plasma position's x-coordinate (or within its acceptable predefined tolerance).

[0056] Adjusting the time delay can thus adjust the position of the flat disc relative to the plasma (i.e., at least the x-position). Therefore, the position where the main pulse strikes the flat disc (i.e., the plasma position) can be easily adjusted by controlling the timing of the main pulse emission relative to the pre-pulse (which allows the flat disc to fall a slightly shorter or slightly longer distance before vaporizing). Therefore, the position-sensitive detector 204 and controller 118 may include a first feedback loop that allows adjustment of the plasma position without adjusting the position of the laser power source 104 or the droplet generator 106. In one example, controller 118 may include a four-unit timing loop.

[0057] The position-sensitive detector 204 can also provide the y and z coordinates of the observed plasma position to the BTS 112 in a second feedback loop. The second feedback generator 124 of the BTS 112 can adjust the BTS 112 in response to the observed y and z coordinates of the plasma position (e.g., by adjusting the angle and / or position of one or more mirrors used to guide the beam, such as the M120 and / or M150 mirrors of the BTS 112). For example, if the observed y and z coordinates of the plasma position are the same as (or within) the y and z coordinates of the target plasma position, the BTS 112 may not be adjusted. However, if the observed y and z coordinates of the plasma position are not the same as (or not within) the y and z coordinates of the target plasma position, the second feedback generator 124 of the BTS 112 can adjust the BTS 112 on the y and / or z axes so that the beam transmitted from the BTS 112 to the vacuum chamber 102 impacts the flattened disc at the target plasma position. Therefore, the plasma position can be further fixed by adjusting the position of the laser beam relative to the droplet and the flattened disc on the y and z axes.

[0058] However, adjusting the y and / or z position of the laser beam can alter the falling position of the unvaporized droplet portion. That is, as the droplet flows into the vacuum chamber 102 and is vaporized by the laser pulse, some portions of the droplet may fail to vaporize (e.g., despite maximum effort to precisely control the plasma position, the laser pulse may still miss all or part of the droplet). The unvaporized portions of the droplet may fall to the bottom of the vacuum chamber 102, where they may be captured by a droplet trap (not shown). The droplet trap collects the unvaporized portions, preventing them from accumulating on the inner surface of the vacuum chamber 102. Accumulation of molten metal on the inner surface of the vacuum chamber 102 can degrade the performance of the system 100 and reduce its conversion efficiency.

[0059] In one example, the vacuum chamber 102 may further include a droplet generator (DG) meter 128. The droplet generator meter 128 can monitor the metering of droplets (e.g., droplet 120 and the like) dispensed by the droplet generator 106. More specifically, the droplet generator meter 128 can monitor the y and z positions of the droplets and can control the position of the droplet generator 106 to ensure that droplets are not dispensed to any location where any unvaporized portion of the droplet might fall outside the droplet trap. Therefore, the droplet generator meter 128 can provide feedback to the droplet generator 106 in a third feedback loop to ensure that any adjustments made to the BTS 112 do not result in excessive droplet buildup outside the droplet trap.

[0060] Will understand, Figure 1 This represents a simplified form of the EUV light source 100. In some instances, the EUV light source 100 may include additional components not shown, such as a collector and a droplet trap. The collector may include a multi-layered mirror on which photons from EUV radiation are reflected and directed through an intermediate focusing unit located outside the vacuum chamber 102. The droplet collector may be positioned to collect the portion of droplets that have not been vaporized by the laser pulse and have fallen to the bottom of the vacuum chamber 102.

[0061] Figure 3 A flowchart illustrating a method 300 for controlling the position of plasma in an extreme ultraviolet (EUV) lithography source according to an example of this disclosure is provided. Method 300 can be performed using one or more different components of a laser-generated EUV plasma source under the control of a controller or processor.

[0062] Method 300 begins in step 302. In step 304, a continuous flow of molten metal droplets is dispensed into a vacuum chamber. As described above, these droplets may be spherical in shape and may have a diameter of approximately 25 to 30 micrometers. The droplets may be dispensed at a rate of approximately 50,000 droplets per second or 50 kHz. The droplets may include tin or tin-containing liquid materials (e.g., eutectic alloys containing tin, lithium, and xenon) in liquid or solid form.

[0063] In step 306, multiple laser pulses (including at least a first and a second pulse) may be emitted into the vacuum chamber. As described above, the multiple laser pulses may be generated from a 20-30 kW carbon dioxide (CO2) laser source and may be amplified before entering the vacuum chamber. The multiple laser pulses may have a specific spot size (e.g., approximately 100 to 300 micrometers). When the first laser pulse strikes a droplet in the vacuum chamber, the previously spherical droplet morphs into a flattened, oval-like sheet. When the second laser pulse strikes this flattened sheet, it vaporizes into a highly ionized plasma emitting EUV radiation.

[0064] In step 308, the laser source can be adjusted to maintain the plasma position within the vacuum chamber at a fixed location during subsequent dispensing and emission operations. As described above, the plasma position is the location within the vacuum chamber where droplets are vaporized to form plasma.

[0065] Method 300 can then return to step 304 and continue as described above. Therefore, method 300 can continuously cycle through steps 304 to 308 during the EUV lithography process to ensure that the plasma position remains fixed throughout the EUV lithography process.

[0066] Figure 4 A flowchart illustrating a method 400 for controlling the position of plasma in an extreme ultraviolet (EUV) lithography source according to another embodiment of this disclosure is provided. Method 400 can be considered a more detailed version of method 300 as described above. Therefore, method 400 can be performed using one or more different components of a laser-generated plasma EUV source under the control of a controller or processor.

[0067] Method 400 begins in step 402. In step 404, a continuous flow of molten metal droplets is dispensed into a vacuum chamber. As described above, these droplets may be spherical in shape and may have a diameter of approximately 25 to 30 micrometers. The droplets may be dispensed at a rate of approximately 50,000 droplets per second or 50 kHz. The droplets may include tin or tin-containing liquid materials (e.g., eutectic alloys containing tin, lithium, and xenon) in liquid or solid form.

[0068] In step 406, a first laser pulse (e.g., a pre-pulse) may be emitted into the vacuum chamber. As described above, the first laser pulse may be generated from a 20-30 kW carbon dioxide (CO2) laser source and may be amplified before entering the vacuum chamber. The first laser pulse may have a specific spot size (e.g., approximately 100 to 300 micrometers). When the first laser pulse strikes a droplet in the vacuum chamber, the previously spherical droplet transforms into a flattened, thin sheet shape.

[0069] In step 408, a first image of the reflected beam from the droplet (e.g., a portion of the laser light from a first laser pulse reflected after colliding with the droplet) may be captured. In one example, the first image may be captured by a camera located within a vacuum chamber (such as a coarse droplet source camera).

[0070] In step 410, after a delay (where this delay defines the time difference between the first and second laser pulses), the second laser pulse (e.g., the master pulse) can be emitted into the vacuum chamber. Like the first laser pulse, the second laser pulse can be generated from a 20-30 kW carbon dioxide (CO2) laser source and can be amplified before entering the vacuum chamber. The second laser pulse can have a specific spot size (e.g., approximately 100 to 300 micrometers). When the second laser pulse strikes the flat, oval sheet, the sheet vaporizes into a highly ionized plasma emitting EUV radiation.

[0071] In step 412, a second image of the reflected beam from the flat, cylindrical sheet (e.g., a portion of the laser from the first and / or second laser pulses reflected after colliding with the flat, cylindrical sheet) can be captured. Thus, the second image can depict the observed plasma location within the vacuum chamber. In one example, the second image can be captured by a camera located within the vacuum chamber (such as a fine droplet source camera).

[0072] In step 414, the x, y, and z coordinates of the observed plasma position can be determined based on analysis of at least the second image. For example, in one instance, the second image can be processed to remove light from the first and second laser pulses and amplify the returning beam from the flat, round sheet. The x, y, and z coordinates of the observed plasma position can then be determined based on beam deflection. The x-coordinate can represent the position of the observed plasma position along a line parallel to the direction of droplet flow. The z-coordinate can represent the position of the observed plasma position along a line parallel to the propagation of the laser pulse. The y-coordinate can represent the position of the observed plasma position along a line perpendicular to both the x-axis and z-axis.

[0073] In step 416, a first adjustment to the delay between the first laser pulse and the second laser pulse may be calculated, wherein this first adjustment minimizes the difference at the x-position between the observed plasma position and the target plasma position. In one instance, where the difference at the x-position is zero or within a predefined tolerance, the first adjustment may not be necessary.

[0074] In step 418, a second adjustment to the beam delivery system guiding the first and second laser pulses may be calculated, wherein the second adjustment minimizes the difference in y, z positions between the observed plasma position and the target plasma position. In one instance, the second adjustment may involve adjusting the position and / or angle of one or more mirrors (e.g., M120 and / or M150 mirrors) of the beam delivery system. In one instance, where the difference in y, z positions is zero or within a predefined tolerance, the second adjustment may not be necessary.

[0075] In step 420, at least one of the first adjustment and the second adjustment is applied to the EUV light source. For example, the application of the first adjustment may cause a change in the time delay between the emission of the first laser pulse and the second laser pulse (e.g., making the time delay shorter or longer). The application of the second adjustment may cause the beams of the first laser pulse and the second laser pulse to be guided into the vacuum chamber at an angle and / or direction. As mentioned above, one or both of the first and second adjustments may be unnecessary at any given time.

[0076] Method 400 can then return to step 404 and continue as described above. Therefore, method 400 can continuously cycle through steps 404 to 420 during the EUV lithography process to ensure the plasma position remains fixed at the target plasma position throughout the EUV lithography process. As described above, some iterations of method 400 may result in no adjustment to the EUV light source. For example, a first adjustment may be determined to be necessary, while a second adjustment may be determined to be unnecessary, or vice versa. Alternatively, if the plasma position has not changed (or has changed within a predefined tolerance), both the first and second adjustments may be determined to be unnecessary. However, by continuously monitoring the observed plasma position, it is possible to quickly determine when any adjustment is necessary and to make timely adjustments to maintain a fixed plasma position.

[0077] It should be noted that methods 300 and 400 can be extended to include additional steps, or modified to include additional operations related to the steps outlined above. Furthermore, although not explicitly specified, one or more steps, functions, or operations of methods 300 and 400 may include storage, display, and / or output steps as required by a particular application. In other words, as required by a particular application, any data, records, fields, and / or intermediate results discussed in methods 300 and 400 may be stored, displayed, and / or output on the device performing the method or another device. Additionally, without departing from the instance of this disclosure, the steps, blocks, functions, or operations of methods 300 and 400 may be combined, separated, and / or performed in an order different from that described above.

[0078] Therefore, examples of this disclosure provide plasma position control for EUV light sources. The aforementioned control techniques can be implemented to maintain the plasma position (e.g., the position where the main pulse strikes the flat, cylindrical sheet to generate plasma) at a fixed location within the vacuum chamber. By maintaining this fixed position, the effects of conditions that may reduce the conversion efficiency of the light source (such as laser beam drift or changes in plasma position) can be minimized.

[0079] In one example, this disclosure provides a photolithography system including a vacuum chamber, a droplet generator, a laser source, a sensor, and a first feedback loop. The droplet generator distributes a droplet stream into the vacuum chamber, wherein the droplets may be formed from a metallic material. The laser source emits multiple laser pulses, including at least a first pulse and a second pulse, into the vacuum chamber. The sensor detects an observed plasma location within the chamber, wherein the observed plasma location is the location where the multiple laser pulses vaporize the droplets in the droplet stream to generate plasma. The plasma emits extreme ultraviolet (EUV) radiation, which can be used to etch a semiconductor wafer. The first feedback loop connects the sensor to the laser source and adjusts the time delay between the first and second pulses. Adjusting the time delay minimizes the difference between the observed plasma location and the target plasma location.

[0080] In another example, this disclosure provides a photolithography system including a vacuum chamber, a droplet generator, a laser source, a sensor, and a first feedback loop. The droplet generator distributes a droplet stream into the vacuum chamber, wherein the droplets may be formed from a metallic material. The laser source emits multiple laser pulses, including at least a first pulse and a second pulse, into the vacuum chamber. The sensor detects an observed plasma location within the chamber, wherein the observed plasma location is the location where the multiple laser pulses vaporize the droplets in the droplet stream to generate plasma. The plasma emits extreme ultraviolet (EUV) radiation, which can be used to etch a semiconductor wafer. The first loop connects the sensor to the laser source and allows adjustment of the trajectory of the multiple laser pulses. Adjustment of the trajectory minimizes the difference between the observed plasma location and the target plasma location.

[0081] In another example, a droplet stream is distributed into a vacuum chamber. The droplets are formed from a metallic material. Multiple laser pulses are emitted from a laser source at the droplet stream. When the laser pulses strike the droplets, the droplets vaporize into plasma that emits extreme ultraviolet radiation. The laser source is adjusted to maintain a fixed plasma position within the vacuum chamber. This plasma position is the location within the vacuum chamber where the droplets vaporize.

[0082] The advanced lithography processes, methods, and materials described in this disclosure can be used in many applications, including fin-type field-effect transistors (FinFETs). For example, fins can be patterned to create relatively tight spacing between features, and the above disclosure is well-suited for this purpose. Furthermore, the spacers used to form the fins of FinFETs can be processed according to the above disclosure.

[0083] An optical etching system includes a vacuum chamber, a droplet generator, a laser source, a sensor, and a first feedback loop. The droplet generator distributes a droplet stream into the vacuum chamber. The droplets are formed of a metallic material. The laser source emits a plurality of laser pulses, including at least a first pulse and a second pulse, into the vacuum chamber. The sensor detects an observed plasma location within the vacuum chamber. The observed plasma location includes the location where the laser pulses vaporize the droplets in the droplet stream to generate plasma emitting extreme ultraviolet radiation. The first feedback loop connects the sensor to the laser source. The first feedback loop adjusts the time delay between the first and second pulses to minimize the difference between the observed plasma location and the target plasma location. In some embodiments, the metallic material includes tin. In some embodiments, the laser source includes a carbon dioxide seed laser. In some embodiments, the first feedback loop includes: a first feedback generator for extracting the x, y, z coordinates of an observed plasma location from an image captured by a sensor, wherein the image depicts portions of a first pulse and a second pulse reflected at the observed plasma location; and a controller for calculating adjustments to the time delay based on the x-components of the x, y, z coordinates. In some embodiments, the x-components are defined along a line parallel to the direction of travel of the droplet flow. In some embodiments, the laser source further includes a beam delivery system for guiding laser pulses toward the droplet flow. In some embodiments, the photoetching system further includes a second feedback loop connecting the sensor to the beam delivery system, wherein the second feedback loop adjusts the trajectory of the laser pulses to minimize the difference between the observed plasma location and the target plasma location. The second feedback loop includes: a first feedback generator and a second feedback generator, the second feedback generator being in the beam delivery system for calculating adjustments to a mirror of the beam delivery system based on the y and z coordinates of the x, y, z coordinates. In some embodiments, the mirror is an M150 mirror. In some embodiments, the z-component is defined along a line parallel to the direction of propagation of the laser pulse.

[0084] A photolithography system includes a vacuum chamber, a droplet generator, a laser source, a sensor, and a feedback loop. The droplet generator distributes a stream of droplets into the vacuum chamber. The droplets are formed from a metallic material. The laser source emits multiple laser pulses, including at least a first pulse and a second pulse, into the vacuum chamber. The sensor detects observed plasma locations within the vacuum chamber. The observed plasma locations include the locations where the laser pulses vaporize the droplets in the droplet stream to generate plasma emitting extreme ultraviolet radiation. The feedback loop connects the sensor to the laser source. The feedback loop adjusts the trajectory of the laser pulses to minimize the difference between the observed plasma locations and the target plasma locations.

[0085] A method for controlling a photolithography system includes: distributing a droplet stream into a vacuum chamber, wherein the droplets are formed of a metallic material; emitting multiple laser pulses from a laser source onto the droplet stream, wherein when the laser pulses strike the droplets, the droplets vaporize into plasma emitting extreme ultraviolet radiation; and adjusting the laser source to maintain a fixed plasma position within the vacuum chamber, wherein the plasma position is the location within the vacuum chamber where the droplets vaporize. In some embodiments, the adjustment includes: determining the x, y, z coordinates of an observed plasma position, wherein the observed plasma position includes the location within the vacuum chamber where the observed laser pulses vaporize the droplets in the droplet stream; and adjusting the time delay between a first pulse and a second pulse in the pulses based on the x-component of the x, y, z coordinates, wherein the adjusted time delay minimizes the difference between the observed plasma position and the fixed plasma position. In some embodiments, when the first pulse strikes the droplet, the droplet shape changes from a spherical shape to a flattened oval shape, and wherein when the second pulse strikes the flattened oval shape, the flattened oval shape is vaporized. In some embodiments, the x-component is defined along a line parallel to the direction of droplet flow. In some embodiments, the method of controlling the photoetching system further includes adjusting the trajectory of the laser pulse to further minimize the difference between the observed plasma position and the fixed plasma position. In some embodiments, adjusting the trajectory includes adjusting a mirror of the beam delivery system of the laser source. In some embodiments, the adjustment adjusts the trajectory along a line parallel to the direction of laser pulse propagation. In some embodiments, the metallic material includes tin. In some embodiments, the laser source includes a carbon dioxide seed laser.

[0086] The foregoing outlines features of several embodiments to enable those skilled in the art to better understand the nature of this disclosure. Those skilled in the art should understand that they can readily use this disclosure as a basis for designing or modifying other processes and structures to achieve the same purpose and / or attain the same advantages of the embodiments described herein. Those skilled in the art should also recognize that these equivalent constructions do not depart from the spirit and scope of this disclosure, and that various changes, substitutions, and replacements can be made herein without departing from the spirit and scope of this disclosure.

Claims

1. An extreme ultraviolet light source, characterized in that, include: A vacuum chamber; A droplet generator for distributing a droplet stream into the vacuum chamber, wherein the droplet stream is formed from a metallic material; A laser source for emitting multiple laser pulses, including at least one pre-pulse and one main pulse, into the vacuum chamber; A sensor for detecting an observed plasma position within the vacuum chamber, wherein the sensor is used to capture a first image from a return beam of the droplet from the prepulse impacting the droplet stream and before the main pulse impacts the droplet; the sensor is used to capture a second image from the return beam of the main pulse impacting the droplet; the sensor is used to determine the observed plasma position based on the second image, wherein the plurality of laser pulses vaporize the droplet in the droplet stream to generate a plasma emitting extreme ultraviolet radiation; wherein when the prepulse laser impacts the droplet, the shape of the droplet changes from a spherical shape to a flattened, thin, oval shape; and A first feedback loop connects the sensor to the laser source, wherein the first feedback loop adjusts the observed plasma position by adjusting a time delay between the prepulse and the main pulse based at least on the second image, so as to minimize a difference between the observed plasma position and a target plasma position.

2. The extreme ultraviolet light source as described in claim 1, characterized in that, The metallic material includes tin.

3. The extreme ultraviolet light source as described in claim 1, characterized in that, The laser source includes a carbon dioxide seed laser.

4. The extreme ultraviolet light source as described in claim 1, characterized in that, The first feedback loop includes: A first feedback generator is used to extract the x, y, z coordinates of the observed plasma location from the second image captured by the sensor, wherein the second image depicts a portion of the main pulse reflected at the observed plasma location; and A controller is used to calculate an adjustment to the time delay based on an x-component of the x, y, z coordinates, wherein the x-component is defined along a line parallel to a direction of travel of the droplet flow.

5. The extreme ultraviolet light source as described in claim 4, characterized in that, The laser source further includes: A beam delivery system is used to guide the multiple laser pulses toward the droplet flow.

6. The extreme ultraviolet light source as described in claim 5, characterized in that, Further includes: A second feedback loop connects the sensor to the beam delivery system, wherein the second feedback loop adjusts a track of the plurality of laser pulses to minimize the difference between the observed plasma position and the target plasma position.

7. The extreme ultraviolet light source as described in claim 6, characterized in that, The second feedback loop includes: The first feedback generator; and A second feedback generator in the beam delivery system is used to calculate an adjustment of a mirror of the beam delivery system based on a y-coordinate and a z-coordinate of the x, y, z coordinates.

8. The extreme ultraviolet light source as described in claim 7, characterized in that, The z-component is defined along a line parallel to a propagation direction of the plurality of laser pulses.

9. An extreme ultraviolet light source, characterized in that, include: A vacuum chamber; A droplet trap is located in the vacuum chamber. A droplet generator for distributing a droplet stream to the vacuum chamber and to the droplet trap, wherein the droplet is formed of a metallic material; A laser source for emitting a plurality of laser pulses, including at least a first pulse and a second pulse, into the vacuum chamber; A sensor for detecting an observed plasma location within the vacuum chamber, wherein the observed plasma location includes a location where the plurality of laser pulses vaporize a droplet of the droplet stream to generate a plasma emitting extreme ultraviolet radiation; A feedback loop connects the sensor to the laser source, wherein the feedback loop adjusts the trajectory of the plurality of laser pulses to minimize a difference between the observed plasma position and a target plasma position; and A droplet generator meter is connected to the droplet generator to provide feedback, wherein the droplet generator meter is used to observe the droplet flow distributed by the droplet generator and to control a position of the droplet generator to ensure that the droplet flow falls into the droplet trap.

10. A method for controlling an extreme ultraviolet light source, characterized in that, include: A droplet is distributed into a vacuum chamber, wherein the droplet is formed of a metallic material; A laser light source is used to emit multiple laser pulses at the droplet flow. When the multiple laser pulses strike the droplet, the droplet vaporizes into a plasma that emits extreme ultraviolet radiation. The multiple laser pulses include a pre-pulse and a main pulse. When the pre-pulse strikes the droplet, the shape of the droplet changes from a spherical shape to a flat, thin, oval shape. As the prepulse strikes one of the droplets and before the main pulse strikes the one of the droplets, a first image of a return beam of the prepulse is captured by the one of the droplets; After capturing the first image and emitting the main pulse, a second image of a returning beam of the main pulse is sensed by the droplet; and The laser source is adjusted based at least on the second image to maintain a position within the vacuum chamber where the droplets vaporize as a fixed target plasma position within the vacuum chamber.

11. The control method as described in claim 10, characterized in that, The adjustments include: Determine the x, y, z coordinates of an observed plasma location, wherein an observed plasma location includes a location within the vacuum chamber where the plurality of laser pulses are observed to vaporize a droplet from the droplet stream; and Based on the first image and an x-component of the plurality of x, y, z coordinates, a time delay between the pre-pulse and the main pulse in the plurality of pulses is adjusted, wherein the time delay is adjusted to minimize a difference between the observed plasma position and the fixed target plasma position, the x-component being defined along a line parallel to the direction of travel of the droplet flow.

12. The control method as described in claim 11, characterized in that, When the main pulse strikes the flat, round sheet, the flat, round sheet is vaporized.

13. The control method as described in claim 11, characterized in that, Further includes: The trajectory of the plurality of laser pulses is adjusted to further minimize the difference between the observed plasma position and the fixed target plasma position.

14. The control method as described in claim 13, characterized in that, Adjusting the track involves adjusting a reflector of the beam delivery system of the laser source.

15. The control method as described in claim 13, characterized in that, This adjustment will adjust the trajectory along a line parallel to the direction in which the plurality of laser pulses propagate.

16. The control method as described in claim 10, characterized in that, The metallic material includes tin.

17. The control method as described in claim 10, characterized in that, The laser source includes a carbon dioxide seed laser.

18. A method for controlling an extreme ultraviolet light source, characterized in that, include: Dispensing a droplet into a vacuum chamber; A pre-pulse laser is emitted towards the droplet; A first image of a returning beam of the pre-pulsed laser is sensed by the droplet; After the pre-pulse laser is emitted, a main pulse laser is emitted to the droplet, wherein when the main pulse laser strikes the droplet, the droplet vaporizes into a plasma that emits extreme ultraviolet radiation; After sensing the first image and emitting the main pulse laser, a second image of a returning beam of the main pulse laser is sensed by the droplet; and At least one plasma position within the vacuum chamber is adjusted based on the second image to minimize a difference between the plasma position within the vacuum chamber and a target plasma position.

19. The control method as described in claim 18, characterized in that, When the pre-pulse laser strikes the droplet, the droplet's shape changes from a spherical shape to a flat, thin, oval shape.

20. The control method as described in claim 18, characterized in that, Adjusting the plasma position within the vacuum chamber includes adjusting a time delay between the pre-pulse laser and the main pulse laser.

21. The control method as described in claim 18, characterized in that, Adjusting the position of the plasma within the vacuum chamber includes adjusting the optical elements used to guide the master pulse laser relative to the droplet.

22. The control method as described in claim 18, characterized in that, Further includes: Amplify the power of the pre-pulse laser.

23. The control method as described in claim 18, characterized in that, Further includes: Amplify the power of the main pulse laser.

24. The control method as described in claim 18, characterized in that, The spot size of the pre-pulsed laser is 100 to 300 micrometers.

25. A method for controlling an extreme ultraviolet light source, characterized in that, include: A droplet is supplied from a droplet generator toward a droplet trap that is an extreme ultraviolet light lithography source; A master pulse laser is emitted to strike the droplet, and a plasma emitting extreme ultraviolet radiation is formed in a vacuum chamber of the extreme ultraviolet lithography light source. A first image of the droplet is detected when the main pulse laser strikes the droplet; The main pulse laser is filtered from the first image to extract a return beam of the main pulse laser; The x, y, z coordinates of the plasma are determined based on the returned beam of the main pulse laser. Based on the x, y, z coordinates of the plasma, a laser source of the droplet generator is adjusted to minimize a difference between an observed plasma position and a target plasma position; and Before emitting the main pulse laser, a pre-pulse laser is emitted to strike the droplet.

26. The control method as described in claim 25, characterized in that, The main pulse laser is filtered from the first image to extract a return beam of the main pulse laser.

27. The control method as described in claim 25, characterized in that, The determination of the x, y, z coordinates of the plasma is performed after the main pulse laser is filtered from the first image.

28. The control method as described in claim 25, characterized in that, The method further includes, after determining a y-component of the x, y, z coordinates of the plasma, adjusting the optical elements used to guide the master pulse laser relative to the droplet, wherein the y-component is defined along a line perpendicular to a direction of travel of the droplet flow.

29. The control method as described in claim 25, characterized in that, The method further includes adjusting the timing of the main pulse laser impacting the droplet after determining an x-component of the x, y, z coordinates of the plasma, wherein the x-component is defined along a line parallel to a direction of travel of the droplet flow.

30. The control method as described in claim 25, characterized in that, Further includes: Before detecting the first image of the droplet, a second image of the droplet is detected when the pre-pulsed laser strikes the droplet.

31. A method for controlling an extreme ultraviolet light source, characterized in that, include: Multiple droplets are distributed from a droplet generator toward a droplet trap that is an extreme ultraviolet light lithography source; A master pulse laser is emitted to strike one of the plurality of droplets to form a plasma that emits extreme ultraviolet radiation in a vacuum chamber of the extreme ultraviolet lithography light source; A position of the plasma is detected when the main pulse laser strikes one of the plurality of droplets; When the main pulse laser strikes one of the plurality of droplets, the positions of the plurality of unvaporized droplets among the plurality of droplets are detected; Adjust the position of the droplet generator to ensure that the plurality of unvaporized droplets fall within the droplet trap; and Before emitting the main pulse laser, a pre-pulse laser is emitted to strike one of the plurality of droplets.

32. The control method as described in claim 31, characterized in that, Further includes: Before detecting the location of the plasma, the location of one of the plurality of droplets is detected when the pre-pulse laser strikes one of the plurality of droplets.

33. The control method as described in claim 31, characterized in that, Further includes: The timing of emitting the main pulse laser is adjusted based on the location where the plasma is detected.

34. The control method as described in claim 31, characterized in that, Further includes: Amplify the power of the main pulse laser.

35. The control method as described in claim 31, characterized in that, Adjusting the position of the plasma includes adjusting the optical elements used to guide the main pulse laser relative to the plurality of droplets.

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