CN-121994357-A - Photon counting method-based vacuum ultraviolet spectrophotometry method

CN121994357ACN 121994357 ACN121994357 ACN 121994357ACN-121994357-A

Abstract

The invention belongs to the technical field of optical precision measurement and discloses a vacuum ultraviolet spectrophotometry method based on a photon counting method, which comprises the following steps of setting the polarization state of incident light according to a measurement task in a sample-free state, and collecting initial dark counts and initial baseline counts corresponding to wavelength points in a preset measurement wave band for each wavelength point; the method comprises the steps of obtaining an initial dark count and an initial baseline count, respectively calibrating the optimal working voltage of a photon counting detector under each wavelength point and a double-screening threshold value for separating noise through signal-to-noise ratio optimization, collecting the dark count and the reference count corresponding to each wavelength point based on the optimal working voltage and the double-screening threshold value corresponding to each wavelength point under the same polarization state, and effectively solving the problems of low system signal-to-noise ratio and insufficient measurement precision caused by incapability of dynamically optimizing detection parameters in a full spectrum band in vacuum ultraviolet band measurement in the prior art.

Inventors

LIU CUNDING
WANG JIAHENG
YUAN XIAO
ZHANG XIANG

Assignees

苏州大学

Dates

Publication Date: 20260508
Application Date: 20260119

Claims (8)

1. The vacuum ultraviolet spectrophotometry method based on photon counting method is matched with a photon counting detector to execute the measurement of the transmissivity or reflectivity of a sample (103), and is characterized by comprising the following steps: setting the polarization state of incident light according to a measurement task in a sample-free (103) state, and collecting initial dark counts and initial baseline counts corresponding to wavelength points in a preset measurement wave band according to the wavelength points; Based on the initial dark count and the initial baseline count, respectively calibrating the optimal working voltage of the photon counting detector at each wavelength point and a double discrimination threshold for separating noise through signal-to-noise ratio optimization; Under the same polarization state, based on the optimal working voltage and the double discrimination threshold corresponding to each wavelength point, acquiring dark counts and reference counts corresponding to the wavelength points, placing a sample (103) in a light path, and executing measurement of the sample (103) according to target measurement requirements to acquire measurement counts; Correcting the corresponding measurement count according to the dark count and the baseline count corresponding to the wavelength points, introducing a comprehensive correction coefficient based on the measurement wavelength and the environmental parameter, calculating the transmissivity or reflectivity of the sample (103) at each wavelength point, and generating the transmissivity or reflectivity spectrum of the sample (103).
2. The vacuum ultraviolet spectrophotometry based on photon counting method according to claim 1, wherein the photon counting detector comprises a first photon counting detector (104) for detecting reference light and a second photon counting detector (105) for detecting transmitted or reflected light of the sample (103).
3. The method for measuring vacuum ultraviolet spectrophotometry based on photon counting method according to claim 2, wherein for each wavelength point in a preset measurement band, an initial dark count and an initial baseline count corresponding to the wavelength point are collected, and specifically comprising the following steps: For each wavelength point, synchronously applying a step-and-scan voltage from a starting voltage to a final voltage to a first photon counting detector (104) and a second photon counting detector (105) under the state that a light source (101) is turned off, and collecting the initial dark count of the corresponding first photon counting detector (104) under each voltage point Initial dark count with a second photon count detector (105) ; Under the state that the light source (101) is started and the output is the current wavelength point, synchronously applying the same step scanning voltage to the first photon counting detector (104) and the second photon counting detector (105), and collecting the initial baseline count of the corresponding first photon counting detector (104) at each voltage point Initial baseline count with first photon count detector (104) 。
4. The method for measuring vacuum ultraviolet spectrophotometry based on photon counting method according to claim 3, wherein the method comprises the steps of calibrating the optimal working voltage of photon counting detector at each wavelength point and the double discrimination threshold for separating noise respectively through signal-to-noise ratio optimization based on the initial dark count and the initial baseline count, and specifically comprises the following steps: according to the collected initial dark counts, respectively determining initial dark count-voltage relations corresponding to the first photon count detector (104) and the second photon count detector (105); according to the acquired initial baseline counts, respectively determining initial baseline count-voltage relations corresponding to the first photon count detector (104) and the second photon count detector (105); Calculating signal-to-noise ratios of the first photon counting detector (104) and the second photon counting detector (105) at each voltage point based on the corresponding initial dark count-voltage relationship and the initial baseline count-voltage relationship; Calibrating a voltage point corresponding to the highest signal-to-noise ratio in the first photon counting detector (104) as the optimal working voltage of the first photon counting detector (104) at the current wavelength point, and calibrating a voltage point corresponding to the highest signal-to-noise ratio in the second photon counting detector (105) as the optimal working voltage of the second photon counting detector (105) at the current wavelength point; And under the calibrated optimal working voltage, respectively acquiring pulse height spectrums output by the first photon counting detector (104) and the second photon counting detector (105), and respectively setting respective low discrimination threshold and high discrimination threshold for the first photon counting detector (104) and the second photon counting detector (105) according to the corresponding pulse height spectrum distribution, wherein the low discrimination threshold and the high discrimination threshold jointly form a double discrimination threshold.
5. The photon counting method-based vacuum ultraviolet spectrophotometry of claim 4, wherein the target measurement requirement comprises an angular scanning mode or a wavelength scanning mode; And finally obtaining the transmittance or reflectance spectrum of which the transmittance or reflectance changes along with the incident angle when the angle scanning mode is adopted, and finally obtaining the transmittance or reflectance spectrum of which the transmittance or reflectance changes along with the wavelength when the wavelength scanning mode is adopted.
6. The method according to claim 5, wherein, in the same polarization state, based on the optimal operating voltage and the double discrimination threshold corresponding to each wavelength point, dark counts and reference counts corresponding to the wavelength points are collected, and the sample (103) is placed in the optical path, and according to the target measurement requirement, the measurement of the sample (103) is performed to obtain the measurement counts, and the method specifically comprises the following steps: Before a sample (103) moves into a light path, the optimal working voltage and the double discrimination threshold of a first photon counting detector (104) and a second photon counting detector (105) with calibrated wavelength points are respectively applied to the corresponding photon counting detectors, and under the condition that the light source (101) is in a closed state and the same polarization state, fixed time length is acquired Dark count of a first photon counting detector (104) in Dark count with a second photon count detector (105) ; Turning on a light source (101) to collect the light in a fixed time period Baseline count of a first photon count detector (104) Baseline count with a second photon counting detector (105) ; According to the target measurement requirement, moving the sample (103) into the optical path and setting the incident angle of the sample (103) And invoking the optimal working voltage and the double discrimination threshold of the first photon counting detector (104) and the second photon counting detector (105) with the wavelength points calibrated correspondingly to apply to the corresponding photon counting detectors respectively; under the same polarization state, collect fixed time length First photon counting detector (104) signal count in With a second photon counting detector (105) As a measurement count; Wherein the angle scanning mode is one in which the measurement wavelength is fixed and the incident angle of the sample (103) is changed in a preset angle step by step Repeatedly executing the steps of calling the optimal working voltage, the double discrimination threshold values and collecting signal counts at each angle position; Fixing the angle of incidence of the sample (103) in the wavelength scanning mode And step-scanning a preset measurement wave band by using a preset wavelength, and repeating the steps of calling, applying the optimal working voltage, the double discrimination threshold and collecting signal counting aiming at each scanning wavelength point.
7. The method of photon counting based vacuum ultraviolet spectrophotometry according to claim 6, wherein when performing reflectance spectrometry acquisition, dynamically adjusting the acceptance angle of the second photon counting detector (105) according to the law of reflection is further included in the measurement process Incidence angle of sample (103) Angle of acceptance with a second photon counting detector (105) The following are satisfied: 。
8. the method for measuring vacuum ultraviolet spectrophotometry based on photon counting method according to claim 7, wherein the corresponding measurement count is corrected, and a comprehensive correction coefficient based on the measurement wavelength and the environmental parameter is introduced, and the transmittance or reflectance of the sample (103) at each wavelength point is calculated, wherein the specific calculation formula is as follows: Wherein S represents transmittance or reflectance; Representing the integrated correction factor based on the measurement wavelength and the environmental parameters including the cavity pressure P, temperature T, and nominal optimal operating voltages of the first photon counting detector (104) and the second photon counting detector (105) at the corresponding measurement wavelengths of the enclosed environment in which the measurement is performed.

Description

Photon counting method-based vacuum ultraviolet spectrophotometry method Technical Field The invention belongs to the technical field of optical precision measurement, and particularly relates to a vacuum ultraviolet spectrophotometry method based on a photon counting method. Background Optical element transmissivity and reflectivity are key parameters for characterizing the performance of optical devices, and precise detection of the optical element transmissivity and reflectivity is critical to the development and manufacture of high-end optical systems such as photoetching machines, lasers and the like. In particular in the field of litho machines, the optical elements need to operate in the vacuum ultraviolet to deep ultraviolet band of 115nm to 500nm, which covers the critical wavelengths of the i-line, arF and F2 litho machines. However, photons in this band are strongly absorbed in the atmosphere and therefore must be measured in a vacuum or inert gas environment, whereas currently a large number of commercial devices are operated in an atmospheric environment and this full band high-precision spectral characterization cannot be achieved. Further, the optical elements of a lithographic apparatus are typically exposed to high angle incidence conditions in actual use, e.g., the range of incidence angles of the elements in 193nm immersion lithography apparatus may be up to 0 ° to over 70 °. This requires that the spectrophotometer not only be capable of operating in a vacuum environment, but also have high precision over a wide range of angles, automated angular adjustment, and signal acquisition capabilities. Although the prior art has a single vacuum ultraviolet measuring device, the prior art has obvious defects in practical application, on one hand, under the condition of weak light signals, the system has low signal-to-noise ratio, photon signals and various noises are difficult to effectively separate, and on the other hand, the prior art lacks an integrated method capable of dynamically optimizing the working parameters of a detector in a whole wave band and synchronously realizing high-precision angle scanning and real-time data processing, so that the measurement efficiency is low, the stability is poor and the angle resolution is insufficient. Therefore, in the vacuum ultraviolet band measurement in the prior art, the problems of low system signal-to-noise ratio and insufficient measurement accuracy caused by the fact that the detection parameters cannot be dynamically optimized in the whole spectrum range exist. Disclosure of Invention Aiming at the defects of the prior art, the invention aims to provide a vacuum ultraviolet spectrophotometry method based on a photon counting method, which solves the problems of low system signal-to-noise ratio and insufficient measurement precision caused by incapability of dynamically optimizing detection parameters in a full spectrum band in vacuum ultraviolet band measurement in the prior art. The aim of the invention can be achieved by the following technical scheme: A vacuum ultraviolet spectrophotometry method based on photon counting method comprises the following steps: setting the polarization state of incident light according to a measurement task in a sample-free state, and collecting initial dark counts and initial baseline counts corresponding to wavelength points in a preset measurement wave band; Based on the initial dark count and the initial baseline count, respectively calibrating the optimal working voltage of the photon counting detector at each wavelength point and a double discrimination threshold for separating noise through signal-to-noise ratio optimization; under the same polarization state, based on the optimal working voltage and the double discrimination threshold corresponding to each wavelength point, dark counts and reference counts corresponding to the wavelength points are collected, a sample is placed in a light path, and sample measurement is performed according to target measurement requirements to obtain measurement counts; correcting the corresponding measurement count according to the dark count and the baseline count corresponding to the wavelength points, introducing a comprehensive correction coefficient based on the measurement wavelength and the environmental parameter, calculating the transmissivity or reflectivity of the sample at each wavelength point, and generating the transmissivity or reflectivity spectrum of the sample. Further, the photon counting detector includes a first photon counting detector for detecting the reference light and a second photon counting detector for detecting the sample to detect the transmitted light or the reflected light of the sample. Further, for each wavelength point in a preset measurement band, an initial dark count and an initial baseline count corresponding to the wavelength point are collected, and specifically the method comprises the following steps: For each wavelength