JP6820747B2 - Calibration of photoelectromagnetic sensor in laser light source - Google Patents

Description

[1] The present application relates generally to laser systems, and more specifically to the calibration of photoelectromagnetic sensors in laser light sources of laser-generated plasma (LPP) extreme ultraviolet (EUV) systems.

[2] In the semiconductor industry, the development of lithography technology that enables printing of even smaller integrated circuit dimensions continues. Extreme ultraviolet (“EUV”) light (sometimes referred to as soft x-rays) is commonly defined as electromagnetic radiation with wavelengths between 10 nm and 102 nm. EUV lithography is currently generally considered to contain EUV light with wavelengths in the range of 10-14 nm and is used to generate very small features (eg, features of 32 nm or less) on substrates such as silicon wafers. These systems must be extremely reliable and must provide cost-effective throughput and reasonable process tolerance.

[3] Methods for producing EUV light are not necessarily limited, but one or more elements having one or more emission lines in the EUV range, such as xenon, lithium, tin, indium, antimony, Includes converting materials with telluride, aluminum, etc. into plasma states. In one such method, often referred to as laser-generated plasma (“LPP”), the required plasma is a droplet, stream, or flow of material with the desired ray emitting element within the LPP EUV light source plasma chamber. It can be generated by irradiating a target material such as a cluster with a laser beam at an irradiation site.

[4] FIG. 1 shows some of the components of the prior art LPP EUV system 100. A laser light source 101, such as a CO ₂ laser, produces a laser beam 102 that passes through a beam delivery system 103 and a focusing optical system 104 (including a lens and a steering mirror). The focusing optical system 104 has a first focus 105 at an irradiation site in the LPP EUV light source plasma chamber 110. The droplet generator 106 produces a droplet 107 of a suitable target material that, when hit by the laser beam 102 at the first focal point 105, produces a plasma that irradiates EUV light. The elliptical mirror (“collector”) 108 focuses the EUV light from the plasma at the focal spot 109 (also referred to as the intermediate focal position) in order to send the generated EUV light to, for example, a lithography scanner system (not shown). .. The focal spot 109 is typically in a scanner (not shown) containing a wafer exposed to EUV light. In some embodiments, there may be multiple laser light sources 101 in which all of the beams are concentrated in the focusing optics 104. One type of LPP EUV light source uses a CO ₂ laser and a zinc selenide (ZnSe) lens with an antireflection coating and an aperture of about 6 to 8 inches (about 15.24 cm to 20.32 cm). It may be a thing.

[5] The laser light source 101 can be generated in burst mode, where several light pulses are generated in bursts with some time between bursts. The laser light source 101 can include several lasers that generate a pulsed laser beam with well-defined characteristics such as wavelength and / or pulse length. In the laser light source 101, the beam delivery system 103, and the focusing optical system 104, different laser beams can be combined, divided, or otherwise manipulated.

[6] Before the laser beam 102 reaches the LPP EUV light source plasma chamber 110, the beam 102 is measured at various points within the laser light source 101, the beam delivery system 103, and / or the focusing optics 104. .. Measurements are made using various instruments that measure one or more aspects of the laser beam 102. In some instances, the laser beam 102 can be measured before or after being combined with other generated beams.

[6] However, the instrument may not directly measure certain characteristics of the laser beam 102, or may not be calibrated in such a way as to measure the characteristics of the laser beam 102.

[7] According to an embodiment, the system is configured to measure a laser beam with a pre-pulse and a main pulse divided by length of time within a laser-generated plasma (LPP) extreme ultraviolet (EUV) system. An energy monitor, a power meter configured to sense the average power of a series of laser pulses over a defined time period, and a part of the defined time period from the first main pulse to time. An energy monitor with a photoelectromagnetic (PEM) detector configured to provide a voltage signal indicating a temporal profile of the first prepulse, divided by length; the main pulse calibration coefficient and the first main pulse. Determines the power of the first prepulse based on the average power and the power of the first main pulse, just as it determines the power of the first main pulse based on the pulse integration of some of the voltage signals corresponding to A calibration module configured to determine the pre-pulse calibration coefficient based on the power of the first pre-pulse and the integral of a portion of the voltage signal corresponding to the first pre-pulse; And, based on the pulse integration of part of the second voltage signal provided by the PEM detector corresponding to the second prepulse, and to determine the energy of the second prepulse, as well as the main pulse calibration. A single pulse energy calculation (SPEC) module configured to determine the energy of the second main pulse based on the coefficients and the pulse integration of a portion of the second voltage signal to the second main pulse. , Equipped with.

[8] The system is configured to calculate the energy of the laser beam over a second defined time period based on the second voltage signal provided by the PEM, with the calculated energy of the laser beam. It is configured to compare with the average power perceived by the wattmeter over a second defined time period, and to instruct the calibration module to update the prepulse calibration coefficient based on this comparison. A recalibration module can be further provided.

[9] According to an embodiment, the method is to receive measurements of a laser beam with pre-pulse and main pulse using an energy monitor within a laser-generated plasma (LPP) extreme ultraviolet (EUV) system. The beam measurements are the average power of a series of laser pulses over a defined time period measured using a power meter and the pre-pulse, which is divided by the length of time from the first main pulse of the main pulses. The first voltage signal, including a first voltage signal indicating the temporal profile of the first prepulse, is provided by a photoelectromagnetic (PEM) detector; to the main pulse calibration coefficient and the first main pulse. Determining the power of the first main pulse based on the integration of a portion of the corresponding first voltage signal; the power of the first prepulse based on the average power and the power of the first main pulse. To determine the pre-pulse calibration coefficient based on the power of the first pre-pulse and the integration of a portion of the first voltage signal corresponding to the first pre-pulse; the pre-pulse calibration coefficient and the first. Determining the energy of the second prepulse based on the integration of a portion of the second voltage signal provided by the PEM detector corresponding to the two prepulses; as well as the main pulse calibration coefficient and the second Includes determining the energy of the second main pulse based on the integration of a portion of the second voltage signal corresponding to the main pulse.

[10] According to an embodiment, the non-temporary computer-readable medium has instructions embodied on it, the instructions using an energy monitor within a laser-generated plasma (LPP) extreme ultraviolet (EUV) system. Receiving a measurement of a laser beam with a pre-pulse and a main pulse, the measurement of the laser beam is the average power of a series of laser pulses over a defined time period measured using a power meter and the main pulse. The first voltage signal includes a first voltage signal indicating the temporal profile of the first prepulse of the prepulses divided by the length of time from the first main pulse, and the first voltage signal is photoelectromagnetic (PEM). Provided by the detector; determining the power of the first main pulse based on the main pulse calibration coefficient and the integration of a portion of the first voltage signal corresponding to the first main pulse; average power And the power of the first main pulse to determine the power of the first prepulse; with the power of the first prepulse and the integration of a portion of the first voltage signal corresponding to the first prepulse. To determine the pre-pulse calibration coefficient based on; the second, based on the pre-pulse calibration coefficient and the integral of a portion of the second voltage signal provided by the PEM detector corresponding to the second pre-pulse. Determine the energy of the pre-pulse of; and determine the energy of the second main pulse based on the main pulse calibration coefficient and the integration of a portion of the second voltage signal corresponding to the second main pulse. It can be performed by one or more processors to perform operations that include doing.

[11] According to embodiments, the system is configured to measure laser pulses that have the same wavelength and occur within a burst within the laser source of a laser-generated plasma (LPP) extreme ultraviolet (EUV) system. An energy monitor that shows a power meter configured to measure the average power of a laser pulse over a defined time period and a temporal profile of the burst of the laser pulse over at least a portion of the defined time period. An energy monitor comprising a photoelectromagnetic (PEM) detector configured to provide a first voltage signal; configured to determine a calibration coefficient based on an average power and a first voltage signal. A calibration module, in which the calibration coefficient is the ratio of the energy of the burst of laser pulses determined from the average power to the integration of the first voltage signal; as well as the calibration coefficient and the temporal of subsequent pulses. Single pulse energy calculation (SPEC) configured to determine the energy of subsequent pulses of a series of laser pulses based on the pulse integration of a second voltage signal provided by a profiled PEM detector. It has a module.

[12] The system is to calculate the energy of the second burst based on a third voltage signal indicating the second temporal profile of the second burst, and wattmeter the energy of the second burst. It further comprises a recalibration module configured to compare with the second average power sensed by and to instruct the comparison module to update the calibration coefficient based on this comparison.

[13] According to an embodiment, the method measures laser pulses that have the same wavelength and occur in a burst using an energy monitor within the laser source of a laser-generated plasma (LPP) extreme ultraviolet (EUV) system. That is, receiving the average power of the laser pulse measured over a defined time period from the power meter, and the time of the burst of laser pulse sensed during at least a portion of the defined time period. Including receiving a first voltage signal indicating a profile from a photoelectromagnetic (PEM) detector; determining the calibration coefficient based on the average power and the first voltage signal, the calibration coefficient is , The ratio of the burst energy of the laser pulse determined from the average power to the integration of the first voltage signal; as well as the calibration coefficient and the number provided by the PEM detector showing the temporal profile of the subsequent pulse. Includes determining the energy of subsequent pulses of a series of laser pulses based on the integration of the voltage signals of 2.

[14] According to an embodiment, the non-temporary computer-readable medium has an embodied instruction on it, which produces a laser pulse having the same wavelength and generated in a burst, laser-generated plasma (LPP). ) Measuring with an energy monitor in the laser source of an extreme ultraviolet (EUV) system, receiving and defining the average power of the laser pulse measured over a defined time period from the power meter. Includes receiving a first voltage signal from the photoelectromagnetic (PEM) detector, which indicates the temporal profile of the burst of laser pulses sensed during at least a portion of the time period; average power and first. The calibration coefficient is to be determined based on the voltage signal of, which is the ratio of the burst energy of the laser pulse determined from the average power to the integration of the first voltage signal; and the calibration. Performs an operation that includes determining the energy of the subsequent pulse of a series of laser pulses based on the coefficients and the integration of a second voltage signal provided by the PEM detector that indicates the temporal profile of the subsequent pulse. It can be run by one or more processors.

[1] It is a figure which shows a part of the LPP EUV system according to the prior art. [2] It is a figure which shows the energy monitor according to an exemplary embodiment. [3] It is a figure which shows the burst mode of a laser light source according to an exemplary embodiment. [4] FIG. 6 shows a graph output by a PEM detector showing the temporal profile of a burst with a main pulse. [5] FIG. 5 shows a graph output by a PEM detector showing a temporal profile of a single main pulse. [6] FIG. 6 shows a graph output by a PEM detector showing a temporal profile of a burst with prepulses. [7] FIG. 6 shows a graph output by a PEM detector showing a temporal profile of a single prepulse. [8] It is a figure which shows the example of the graph output by a PEM detector which shows the time profile of the pre-pulse and the main pulse divided by the length of time. [9] FIG. 6 is a block diagram showing a system for measuring pulse energy according to an exemplary embodiment. [10] FIG. 6 is a flow chart illustrating an exemplary method of measuring pulse energy according to an exemplary embodiment. [11] FIG. 6 is a flow chart illustrating an exemplary method of calibrating a photoelectromagnetic (PEM) detector with a wattmeter for a unitary laser beam. [12] FIG. 6 is a flow chart illustrating an exemplary method of calibrating a PEM detector with a wattmeter for a combined laser beam.

[13] In the LPP EUV system, the energy of the laser pulse is calculated at various locations in the laser source, beam delivery system, and / or focusing optics. The sensors used to measure the laser beam within the LPP EUV system do not directly measure the energy of the laser beam pulses. The sensor includes a wattmeter that provides a measurement of the average power of the pulses generated over a defined time period. The sensor further includes a photoelectromagnetic (PEM) detector that outputs a voltage signal based on infrared (IR) light detected over a limited time period. The voltage signal provides a temporal profile of the individual laser pulses. The data collected by the sensor is used to calculate the calibration factor for calibrating the PEM detector against the wattmeter. After calibration, the energy of the pulse can be calculated from the voltage signal provided by the PEM detector.

[14] The laser beam to be measured can include pulses of light of the same wavelength called a unitary laser beam. The unitary laser beam can include either a pre-pulse of the first wavelength or a main pulse of the second wavelength. To determine the energy of the pulse of light in the unitary laser beam, the PEM detector is calibrated to the wattmeter by calculating the calibration coefficient for the unitary laser beam. For unitary laser beams, the calibration factor is a percentage based on the voltage signal provided by the PEM detector via the measurements and bursts received from the wattmeter. After calibration, the energy of the pulse in the unitary laser beam is calculated using the calibration factor and the voltage signal provided by the PEM detector.

[15] In an LPP EUV system, when two unitary laser beams of different wavelengths are combined, the resulting combined laser beams have pulses of alternating wavelengths that are separated within the time domain. In the embodiments described herein, the pulses in the combined laser beam alternate between pre-pulses of the first wavelength and main pulses of the second wavelength. When calculating the energy of the main pulse in the combined laser beam, the calibration factor calculated from the unitary laser beam of the main pulse is used. The different effects of the optical components in the LPP EUV system between the pre-pulse and the main pulse in the combined laser beam calculate different calibration factors for the pre-pulse in the combined laser beam. The pre-pulse calibration coefficient is determined based on the difference between the power measured by the wattmeter and the power due to the main pulse in the combined laser beam. After calibration, the calibration coefficients and the voltage signal provided by the PEM detector are used to calculate the respective energies of the pre-pulse and main pulse in the combined laser beam.

[16] FIG. 2 is a diagram of an energy monitor 200 according to an exemplary embodiment, comprising a power meter 202 and a PEM detector 208. The energy monitor 200 can receive the laser beam 102 from another component in the laser light source 101, for example using a beam splitter. As will be apparent to those skilled in the art, the laser beam 102 has one or more optical components to pick off a portion of the laser beam 102 for measurement before reaching the energy monitor 200. Pass through. These optical components can include a diamond window, a partial reflector, or a zinc selenide window. An example of a laser seed module that can include an energy monitor 200 is discussed in US Patent Application 2013/0321926, published December 5, 2013, assigned to the assignee of the present application. ing.

[17] The energy monitor 200 is arranged to measure the laser beam 102 at a specific location within the laser light source 101, the beam delivery system 103, or the focusing optical system 104. In some embodiments described herein, by arranging an energy monitor 200, the energy monitor 200 measures a unitary laser beam 102 that includes a laser pulse of light of the same wavelength (eg, a pre-pulse or a main pulse). Will let you. Laser pulses of light are generated by a single light source, but can be generated by multiple light sources in other systems. In another embodiment described herein, arranging the energy monitor 200 causes the energy monitor to measure the combined laser beam 102 produced by two laser light sources with different wavelengths. The laser light source 101, the beam delivery system 103, and the focusing optical system 104 can include one or more energy monitors 200.

[18] The laser beam 102 follows an optical path through the energy monitor 200. The laser beam 102 is split by a beam splitter 204 such that the first portion of the laser beam 102 continues along the optical path, while the rest of the laser beam 102 is directed towards the reflector 206. The reflector 206 then sends the rest of the laser beam 102 toward the power meter 202.

[19] The power meter 202 is configured to measure the average power of the laser beam 102 over a defined time period. The measurement can extend to several bursts of laser beam 102. In some instances, the measurements can extend to 5, 10, or 20 bursts of laser beam 102. The defined time period can be a fraction of a second or a few seconds. In some instances, the defined time period is 1 second.

[20] A portion of the laser beam 102 that is not directed at the wattmeter 202 is directed at yet another beam splitter 204. From the beam splitter 204, a first portion of the laser beam is directed, for example, to yet another sensor or other optical component (not shown). The rest of the laser beam 102 is directed towards the PEM detector 208.

[21] The PEM detector 208 provides a voltage signal indicating the temporal profile of the laser beam 102. The temporal profile covers at least a portion of the defined time period used by the power meter 202. The temporal profile can extend to at least one burst of laser beams 102. The temporal profile extends to the pre-pulse and main pulse to calculate the energy of the pulse in the combined laser beam.

[22] Although only one PEM detector 208 is shown in FIG. 2, additional PEM detectors (not shown) can be included in the energy monitor 200. In addition, the laser beam 102 can be modified prior to measurement by the PEM detector 208, for example using a lens (not shown) or a diffuser set (not shown). The energy monitor 200 can be enclosed by a casing and attached to a part of the laser light source 101, or can be enclosed inside the laser light source 101.

[23] FIG. 9 is a block diagram of a system 900 for measuring pulse energy according to an exemplary embodiment. The system 900 includes an energy monitor 902, a calibration module 904, a single pulse energy calculation (SPEC) module 906, and an optional recalibration module 908. The system 900 can be implemented in a variety of ways known to those of skill in the art, including, but not limited to, a computing device having a processor with access to memory capable of storing executable instructions. is there. A computing device can include one or more input and output components, including components for communicating with other computing devices via a network or other form of communication. The system 900 comprises one or more modules embodied in computing logic or executable code.

[24] The energy monitor 902 is configured to receive data about the laser pulse of the laser beam 102. The energy monitor 902 comprises or electronically communicates with a power meter and a PEM detector. In some instances, the energy monitor 902 is an energy monitor 200 with a power meter 202 and a PEM detector 208. The wattmeter is configured to measure the average power of a laser pulse over a defined time period. The defined time period can be, for example, 1 second. The PEM detector is configured to provide a voltage signal indicating the temporal profile of the laser pulse over at least a portion of the defined time period.

[25] When the energy monitor 200 or 902 is placed in the LPP EUV system 100 to receive the unitary laser beam 102, the calibration module 904 may include a power meter (eg, power meter 202) and a PEM detector (eg, eg). It is configured to determine the calibration coefficient based on the data collected by the PEM detector 208). The calibration factor is calculated for each unitary laser beam. The calibration factor is used to calculate the energy of a single pulse (eg, single main pulse 502 or single prepulse 702) based on the PEM detector data collected later. The calibration factor is a percentage determined from the integral of the average power and voltage signals.

[26] A burst of pulses is analyzed to determine the calibration factor at the unitary laser beam 102. FIG. 3 is an example 300 of two bursts 302 of laser pulses according to an exemplary embodiment. Example 300 is an outline of the temporal profile provided by the PEM detector 208, shown as a voltage that changes as a function of time (measured in milliseconds (ms)).

[27] Each burst 302 is shown in Example 300 as a curve having a rising edge 310, a peaking 312, and then maintaining a voltage level 314 below the peak level by the length of time to end at the falling edge 316. Is done. The burst 302 has a burst length 304 starting at the rising edge 310 and ending at the falling edge 316. As described elsewhere herein, when calculating the energy of the burst 302 to calculate the calibration factor, the PEM detector 208 has a scope window 306 that includes at least a burst length 304. The scope window 306 can be extended to capture the time between bursts 302, or shortened to capture only one or two pulses within burst 302.

[28] The burst period 308 is measured from the rising edge 310 of the first burst 302 to the rising edge 310 of the second burst 302. The burst period 308 can be determined from the repeat rate or "rep rate" of burst 302, which indicates the number of bursts over a defined time period (eg, 1 second). The burst rep rate can be expressed as a frequency such as 5 hertz (Hz), 10 Hz, or 20 Hz.

[29] FIG. 4 is a graph 400 showing a temporal profile provided by the output of the PEM detector 208 of the burst 402 of the unitary laser beam 102 with the main pulse. Graph 400 is an actual example of the output shown in FIG. The unitary laser beam 102 is generated by a single light source. In an embodiment, the main pulse has a waveform of 10.59 microns. As shown in the figure, the burst 402 lasts approximately 3.5 ms and comprises a predetermined number of laser pulses. According to various embodiments, the burst 402 can include a different number of laser pulses based on the burst length. The laser pulse has a width (measured as the length of time) and an amplitude. As part of the calculation of the calibration factor, the calibration module 904 can integrate the pulses of the burst 402 over the length of time shown in graph 400.

[30] FIG. 6 is a graph 600 output by PEM detector 208 showing the temporal profile of burst 602 of unitary laser beam 102 with prepulse. Graph 600 is an actual example of the output shown in FIG. The unitary laser beam 102 is generated by a single light source, but can be generated by multiple light sources in other systems. In embodiments, the prepulse has a wavelength of 10.26 microns. As shown in the figure, the burst 602 has a duration of approximately 3.5 ms and comprises a predetermined number of laser pulses. According to various embodiments, the burst 602 can include a different number of laser pulses based on the burst length. The laser pulse has a width (measured as the length of time) and an amplitude. As part of the calculation of the calibration factor, the calibration module 904 can integrate the pulses of the burst 602 over the length of time shown in Graph 600.

[31] The calibration factor for the unitary laser beam 102 is similarly calculated for both the unitary beam with the main pulse and the unitary beam with the prepulse. First, the calibration module 904 determines the energy of the burst of laser pulses from the average power. The energy generated during the defined time period, for which power was measured over that period, is determined as follows.
In the above equation, E _total is the energy of the laser beam 102 over a defined time period, P _metered is the power measurement made by the power meter 202, and T _period is the defined time _period of the power meter 202 (eg). 1 second). From the E _total , the amount of energy in the burst is calculated using the burst rep rate as follows.
In the above equation, E _burst is the energy of the burst, E _total is the energy of the unitary laser beam 102 over a defined time period (eg, 1 second), and f _burst is the burst rep rate.

[32] The following equation is used to determine the calibration factor K _p .
Therefore,
Is. In the above equation, K _p is the calibration coefficient and V is the PEM detector such that the integral ∫Vdt is the region below the curve of the voltage signal provided by the PEM detector 208 over the length of the burst time. A voltage signal received from 208, the _Eburst is the burst energy determined from the average power data received from the wattmeter 202. The calibration factor K _p has a unit of wattage per volt.

[33] The SPEC module 906 is configured to calculate the energy of a single pulse using the calibration factors calculated by the calibration module 904. The SPEC module 906 receives voltage data from the PEM detector 208 with a temporal profile of a single pulse (eg, single main pulse 502 or single prepulse 702) in the unitary laser beam.

[34] FIG. 5 is a graph 500 output by the PEM detector 208 showing the temporal profile of a single main pulse 502 at the unitary laser beam 102. The single main pulse 502 can be a pulse within the burst 402 or a pulse within the subsequent burst. The single main pulse 502 is captured by reducing the scope window 306 of the PEM detector 208. The main pulse 502 has amplitude and width (measured as the length of time). As part of the energy calculation for pulse 502, the SPEC module 906 can integrate the main pulse 502.

[35] FIG. 7 is a graph 700 output by a PEM detector showing the temporal profile of a single prepulse 702 at the unitary laser beam 102. The single prepulse 702 is captured by reducing the length of time that the PEM detector 208 measures the laser beam 102 over its length. The prepulse 702 has an amplitude and width (measured as the length of time). As part of the energy calculation for the prepulse 702, the SPEC module 906 can integrate the prepulse 702.

[36] Using the single pulse temporal profile, the single pulse energy is calculated according to the following formula:
In the above equation, E _pulse is the energy of the pulse, K _p is the calibration coefficient for the pulse of the measured pulse wavelength, and V is the integral ∫Vdt by the PEM detector 208 over the length of the pulse time. A voltage signal received from the PEM detector 208 that indicates the temporal profile of the pulse being measured, such as the region below the curve of the voltage signal provided.

[37] The optional recalibration module 908 is configured to determine whether to reconfigure the PEM detector 208. The calibration factor may lose accuracy over time, for example due to instrument drift, equipment degradation, or poor quality of the beam splitter that receives the laser beam. In a unitary laser beam, during a subsequent burst of laser pulses (eg, burst 402 or burst 602), the recalibration module 908 calculates the laser beam 102 using the measurements of the wattmeter 202 and the data provided by the PEM detector 208. It is configured to compare with the power generated. As described herein, this comparison is made using a time period of 1 second. Other time periods may also be used, such as burst length 304 or burst period 308, or some burst periods, as will be apparent to those skilled in the art based on the following description.

[38] To calculate the power of the pulse of the laser beam 102 over a 1 second engine, the calibration factor is used to determine the energy of the pulse over the burst (eg, burst 402 or 602) as follows.
In the above equation, K _p is the calibration factor and V is the PEM detector such that the integral ∫Vdt is the region below the curve of the voltage signal provided by the PEM detector 208 over the length of the burst time. The voltage signal received from 208, _Eburst is the calculated energy of the burst. The sum of the laser pulse energies is used to determine the total energy of the laser beam 102 over time, as follows:
In the above equation, E _burst is the energy of the burst, E _total is the calculated energy of the laser beam 102 over a defined time period (eg, 1 second), and ΣE _burst is the laser pulse over a defined time period. It is the total energy. To determine the power of the pulse, the total energy is divided by the time period (eg, 1 second) as follows.
In the above equation, E _total is the calculated energy of the laser beam 102 over a defined time period, P _calculated is the power value calculated from the voltage signal received from the PEM detector 208, and T _period is defined. The time period (eg, 1 second).

[39] To determine whether to instruct the calibration module 904 to recalculate the calibration coefficient, the recalibration module 908 can calculate the difference between the calculated power and the measured power. This difference can be expressed as a percentage. To determine whether to recalibrate, the recalibration module 908 can compare this difference with the threshold. In some instances, if the two power values are separated by more than 15%, the recalibration module 908 orders the calibration module 904 to recalculate the calibration factor. Based on this comparison, the recalibration manager 908 can instruct the calibration module 904 to update the calibration factor by recalculating the calibration factor during the subsequent burst of pulses of the laser beam 102.

[40] When the energy monitor 200 or 902 is placed in the LPP EUV system 100 to receive the combined laser beam 102, the system 900 in FIG. 9 transfers the energy of the prepulses in the combined laser beam 102. It is further configured to determine the calibration factor used to determine. The energy monitor 902 is placed in the LPP EUV system 100 to measure the combined laser beam 102.

[41] To calculate the calibration factors for the prepulses in the combined laser beam 102, the calibration module 904 uses a different set of calculations than that used to calibrate the unitary laser beam. These calculations use the calibration coefficients calculated for the unitary laser beam 102 of the main pulse to determine part of the power measured by the wattmeter 202 due to the main pulse and then the rest of the power. Use to determine the calibration factor for the prepulse in the combined laser beam.

[42] FIG. 8 is an exemplary temporal profile 800 of a voltage signal output by a combined pulse PEM detector 208, comprising a pre-pulse and a main pulse separated by length of time. The combined laser beam 102 is generated by combining the unitary laser beam 102 with a single laser beam, and within the resulting burst of the combined laser beam 102, the pre-pulse of burst 602 and the main pulse of burst 402 alternate. Will occur in. As shown in FIG. 8, the pre-pulse 802 precedes the main pulse 804 by 15 microseconds. The laser pulse has a width (measured as the length of time) and an amplitude. Over the length of time shown in Graph 800, the calibration module 904 and the SPEC module 906 can integrate the prepulse 802 separately from the main pulse 804. This integral is used to determine the calibration factor for calculating the energy of the prepulse and to calculate the energy of the subsequent prepulse in the combined laser beam.

[43] The calibration module 904 calculates the power of the main pulse of the combined beam based on a portion of the voltage signal provided by the PEM detector 208 that indicates the temporal profile of the main pulse within the combined pulse. To do. Using this temporal profile, the energy of the main pulse is calculated according to the following equation.
In the above equation, E _{mine pulse} is the energy of the main pulse, K _mp is the calibration coefficient for the main pulse calculated for the unitary laser beam 102, and V is the integral ∫Vdt over the length of the main pulse time. A voltage signal received from the PEM detector 208 that indicates the temporal profile of the main pulse being measured, such as the region below the curve of the voltage signal provided by the PEM detector 208.

[44] The average power of the combined pulses is measured by the wattmeter 202 over a defined time period (eg, 1 second). Based on the energy of the main pulse, the power resulting from the main pulse over a defined time period is calculated as follows.
In the above equation, E _{main pulse} is the energy of the _{main pulse} , P _{main pulse} is the calculated power of the main pulse, T _period is the defined time period used by the wattmeter 202, and ΣE _{main pulses} is. , The sum of the energies of the main pulse generated over the defined time period used by the power meter 202. To determine a portion of the power measured by the wattmeter 202 due to the prepulse, the calibration module 904 determines the difference as follows:
In the above equation, P _pre-pulse is part of the power measured by the wattmeter due to the _pre-pulse of the combined pulse over a defined time period, and P _measured is the combination measured by the wattmeter 202. It is the power of the pulse, and the P _{mine pulse} is the calculated power of the main pulse.

[45] Using the power resulting from the prepulse, the energy resulting from the prepulse is determined by:
In the above equation, E _pre-pulse is the total energy of the _pre-pulse over the defined time period used by the wattmeter 202, and P _pre-pulse is the power resulting from the _pre-pulse of the combined pulse over the defined time period. Part of the power measured by the meter, the _Pulse is the defined time period (eg, 1 second) of the power meter 202.

[46] The following equation is used to determine the calibration factor of the prepulse in the combined laser beam.
In the above equation, K _pp is the calibration coefficient of the prepulse in the combined laser beam and V is the curve of the voltage signal provided by the PEM detector 208 over at least a portion of the time period in which the integral ∫Vdt is defined. As in the lower region, it is the voltage signal received from the PEM detector 208, where the _Epre-pulse is the total energy of the prepulse over the defined time period used by the wattmeter 202. The calibration factor K _pp has a unit of wattage per volt.

[47] Once the calibration factors for the pre-pulses in the combined laser beam have been determined, the SPEC module 906 comprises a temporal profile of the pre-pulse and main pulse pair in the combined laser beam from the PEM detector 208. Receive the voltage data of. The SPEC module 906 can then determine the energy of the subsequent prepulse using the following equation.
In the above equation, E _pre-pulse is the energy of a single _pre-pulse , K _pp is the calibration coefficient for the _{pre-pulse pulse} in the combined laser beam 102, V is the integral ∫Vdt is the length of the pre-pulse time. A voltage signal received from the PEM detector 208 that indicates the temporal profile of the prepulse being measured, such as the area below the curve of the voltage signal provided by the PEM detector 208.

[48] The optional recalibration module 908 may further determine whether to recalibrate the PEM detector 208 with a power meter 202 for the prepulse in the combined laser beam 102, as described above. it can. For the combined laser beam, the recalibration module 908 determines the power of the pulse by summing the energies of the pulses in the combined laser beam over a defined time period corresponding to the wattmeter 202. The recalibration module 908 then compares the power calculated from the sum with the power measured by the wattmeter 202, as described above.

[49] FIG. 10 is a flow chart of an exemplary method 1000 for calculating pulse energy according to an exemplary embodiment. Method 1000 can be performed by system 900.

[50] In operation 1002, the PEM detector is calibrated with a wattmeter for the beam of the first laser. The first laser can generate a main pulse or a pre-pulse in the unitary laser beam as described above. FIG. 11 is a flow chart of exemplary method 1100 for calibrating a PEM detector with a wattmeter to determine the energy of a pulse within a unitary laser beam. Method 1100 can be performed, for example, by the energy monitor 200 or 902 of system 900 and the calibration module 904 as part of operation 1002.

[51] In operation 1102, a power measurement is received from a power meter (eg, power meter 202). The power measurement shows the average power of the pulses of the unitary laser beam 102 over a period of time.

[52] In operation 1104, a voltage signal over a length of time is received from the PEM detector (eg, PEM detector 208). This voltage signal is the temporal profile of the pulse burst of the unitary laser beam 102. The length of time the data is collected by the PEM detector 208 is at least one burst within the time period of the power meter 202.

[53] In operation 1106, the calibration factor of the laser beam 102 is calculated. The calibration factor is calculated as described in connection with the calibration module 904. The calibration factor can be calculated by the calibration module 904.

[54] When the energy monitor 200 is measuring the unitary laser beam, the method 1000 skips the operation 1004 and proceeds to the operation 1006. In operation 1006, the energy of the pulse is calculated. The energy of the pulse is calculated, for example, as described in connection with the SPEC module 906 elsewhere herein. In some instances, the SPEC module 906 performs operation 1006.

[55] In the optional operation 1008, for example, the recalibration module 908 determines whether to recalibrate the PEM detector. This determination is made by comparing the power calculated from the voltage signal provided by the PEM detector with the power measured by the wattmeter. If it is decided to recalibrate, method 1000 returns to operation 1002 or, in some instances, to operation 1004. If it is decided not to recalibrate, method 1000 returns to operation 1006.

[56] When the laser beam measured by the energy monitor 200 is a combined laser beam, method 1000 proceeds from operation 1002 to operation 1004. The PEM detector is calibrated for the combined beam to determine the energy of the prepulse within the combined beam. The second laser is capable of generating pre-pulses in the burst, as described above, and is combined with the main pulse in the combined laser beam 102. In operation 1004, a calibration factor is determined for the prepulse in the combined laser beam 102. The combined lasers because the optical components of the LPP EUV system 100 affect the relationship between the temporal profile of the prepulse and the power measured by the wattmeter 202 after the unitary laser beam 102 is combined. The calibration coefficient for the prepulse in the beam 102 is determined separately from the calibration coefficient for the prepulse in the unitary laser beam 102. The pre-pulse calibration coefficient is determined based on the difference between the power measured by the wattmeter and the power due to the main pulse in the laser beam combined.

[57] FIG. 12 is an exemplary method of calibrating a PEM detector (eg, PEM detector 208) using a power meter (eg, power meter 202) with a combined laser beam having a pre-pulse and a main pulse. It is a flowchart of 1200. Method 1200 is an exemplary method of performing operation 1004 of method 1000 when the laser beam measured by the energy monitor 200 is a combined laser beam. The method 1200 can be performed, for example, by the calibration module 904 of the system 900.

[58] In operation 1202, voltage data is received from the PEM detector 208 in the energy monitor 200 or 902. The voltage data is a temporal profile of the combined laser beams 102, as shown in FIG. The length of time the data is collected by the PEM detector 208 is at least part of the time period of the power meter 202.

[59] In operation 1204, the power due to the main pulse is determined. The power of the main pulse is determined as described in connection with the calibration module 904 and the SPEC module 906.

[60] In operation 1206, power data is received from the power meter 202. The power data shows the average power of the pulses of the combined laser beam 102 over a time period.

[61] In operation 1208, the power due to the prepulse in the combined laser beam 102 is determined. The power of the prepulse is determined as described in connection with the calibration module 904 and the SPEC module 906.

[62] In operation 1210, the calibration factor of the prepulse in the combined laser beam 102 is calculated. The calibration factor is calculated as described in connection with the calibration module 904.

[63] Proceeding to operation 1006, when the laser beam measured by the energy monitor 200 is a combined laser beam, the respective energies of the main pulse and prepulse in the combined laser beam are described above for operation 1006. It is calculated as you did. The energy of the main pulse in the combined laser beam is calculated using the calibration factors of operation 1002 calculated for the unitary beam of the main pulse. The calibration factor of operation 1004 is used to calculate the energy of the prepulse in the combined laser beam. When the laser beam measured by the energy monitor 200 is a combined laser beam, the method 1000 can proceed to the optional operation 1008 as described above.

[64] The disclosed methods and devices have been described above with reference to some embodiments. Those skilled in the art will appreciate other embodiments in view of the present disclosure. Certain aspects of the methods and devices described can be readily implemented using configurations other than those described in the above embodiments, or with elements other than those described above. For example, it is possible to use different algorithms and / or logic circuits, and in some cases different types of laser beam generation systems, which are probably more complex than those described herein.

[65] It will also be appreciated that the methods and equipment described can be implemented in a number of ways, such as as a process, as a device, or as a system. The methods described herein can be implemented to some extent by program instructions for instructing the processor to execute such methods. Such instructions are recorded on optical discs such as hard disk drives, floppy disks, compact discs (CDs) or digital versatile discs (DVDs), and computer-readable storage media such as flash memory. In certain embodiments, program instructions may be stored remotely and transmitted over a network via an optical or electronic communication link. It should be noted that the order of the steps of the methods described herein can be changed and may still be within the scope of this disclosure.

[66] It will be appreciated that the given illustrations are for illustration purposes only and can be extended to other implementations and embodiments using different conventions and techniques. Although some embodiments have been described, it is not intended to limit the disclosure to the embodiments disclosed herein. In contrast, it is intended to cover all alternatives, modifications, and equivalents apparent to those skilled in the art.

[67] Although the invention has been described above with reference to specific embodiments, those skilled in the art will appreciate that the invention is not limited thereto. The various features and aspects of the invention described above can be used individually or jointly. Furthermore, the present invention can be used in any number of environments and scopes beyond those described herein, without departing from the broader intent and scope of the specification. Therefore, the specification and drawings are considered to be exemplary rather than restrictive. It will be appreciated that the terms "prepare,""include," and "have" as used herein are intended to be read specifically as open-ended terms in the art.

Claims (10)

Laser-generated plasma An energy monitor configured to measure a laser beam with a pre-pulse and a main pulse divided by the length of time in an extreme ultraviolet system, averaging a series of laser pulses over a defined time period. A power meter configured to sense power and a voltage indicating the temporal profile of the first prepulse divided by the length of time from the first main pulse during a portion of the defined time period. An energy monitor with a photoelectromagnetic detector configured to provide a signal,
The average power and the first main so as to determine the power of the first main pulse based on the main pulse calibration coefficient and the pulse integration of a portion of the voltage signal corresponding to the first main pulse. To determine the power of the first prepulse based on the power of the pulse, and to integrate the power of the first prepulse with a portion of the voltage signal corresponding to the first prepulse. With a calibration module configured to determine the pre-pulse calibration coefficient based on
By the length of time from the second main pulse, based on the pre-pulse calibration coefficient and the pulse integration of a portion of the second voltage signal provided by the photoelectromagnetic detector corresponding to the second pre-pulse. The second, as to determine the energy of the second prepulse to be divided, and based on the main pulse calibration coefficient and the pulse integration of a portion of the second voltage signal into the second main pulse. Equipped with a single pulse energy calculation module, which is configured to determine the energy of two main pulses,
The system in which the second pre-pulse and the second main pulse follow the first pre-pulse and the first main pulse. Further comprising a recalibration module instructing the calibration module to update the prepulse calibration module, the recalibration module is based on the second voltage signal provided by the photoelectromagnetic detector. The system of claim 1, configured to calculate the energy of the laser beam over a defined time period. The recalibration module is to compare the calculated energy of the laser beam with the average power sensed by the wattmeter over the second defined time period, and to the comparison. The system of claim 2, further configured to instruct the calibration module to update the prepulse calibration coefficient based on. The system of claim 3, wherein the recalibration module is configured to instruct the calibration module to update the calibration factor of the prepulse if the comparison exceeds a threshold. The calibration module is intended to determine the power of the first prepulse by subtracting the power resulting from the main pulse during the defined time period from the average power over the defined time period. The system according to claim 1, which is configured in 1. Laser Generation Plasma Receiving a laser beam measurement with a pre-pulse and a main pulse using an energy monitor within an extreme ultraviolet system, said measurement of the laser beam being defined using a power meter. A first voltage that indicates the average power of a series of laser pulses over a time period and the temporal profile of the first prepulse of the prepulses divided by the length of time from the first main pulse of the main pulses. The first voltage signal, including the signal, is provided by the photoelectromagnetic detector.
Determining the power of the first main pulse based on the main pulse calibration factor and the integral of a portion of the first voltage signal corresponding to the first main pulse.
Determining the power of the first prepulse based on the average power and the power of the first main pulse.
Determining the prepulse calibration coefficient based on the power of the first prepulse and the integral of a portion of the first voltage signal corresponding to the first prepulse.
By the length of time from the second main pulse, based on the pre-pulse calibration factor and the integral of a portion of the second voltage signal provided by the photoelectromagnetic detector corresponding to the second pre-pulse. Determining the energy of the second prepulse to be divided,
Determining the energy of the second main pulse based on the main pulse calibration coefficient and the integral of a portion of the second voltage signal corresponding to the second main pulse.
Including
A method in which the second pre-pulse and the second main pulse follow the first pre-pulse and the first main pulse. The method of claim 6, further comprising calculating the energy of the laser beam over a second defined time period based on the second voltage signal provided by the photoelectromagnetic detector. Comparing the calculated energy of the laser beam with the average power over the second defined time period.
To update the calibration coefficient of the prepulse based on the comparison,
7. The method of claim 7, further comprising. The method of claim 8, wherein updating the calibration factor of the prepulse is based on the comparison exceeding a threshold. Determining the power of the first prepulse is performed by subtracting the power resulting from the main pulse during the defined time period from the average power over the defined time period. The method according to claim 6.