A method for detecting the photochemical activity of photoresist based on laser-induced breakdown spectroscopy

Abstract

A method for detecting the photochemical activity of photoresists based on laser-induced breakdown spectroscopy belongs to the field of semiconductor photoresist detection and ultrafast spectroscopy applications. This method induces multiphoton ionization of the photoresist using a femtosecond laser, captures the characteristic radiation of transient products using a spectral detection system, and tracks the sequence of product appearance at the picosecond level using a spectrometer. This method can accurately reconstruct the sequence of chemical bond breaking and reaction pathways in the initial stage of photoresist excitation through dual-dimensional analysis of "energy threshold" and "temporal distribution." It has advantages such as high temporal resolution, high sensitivity, and strong anti-interference ability, providing a new experimental means for in-depth analysis of the exposure mechanism of novel metal cluster photoresists and optimization of material formulations.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor photoresist detection and ultrafast spectroscopy application technology, specifically relating to a photoresist photochemical activity detection method based on laser-induced breakdown spectroscopy, and a detection system for implementing this method. Background Technology

[0002] As extreme ultraviolet (EUVL) lithography technology advances to 5nm and more advanced process nodes, the demand for high-resolution, high-sensitivity photoresists is becoming increasingly urgent. Metal-oxygen cluster photoresists (such as tin-oxygen clusters) have become the most promising candidate materials due to their high absorption cross-section for EUV photons and extremely small molecular size. However, the extremely high energy of EUV photons leads to complex photochemical reactions in the photoresist. The key factors determining the final solubility change and patterning performance of the photoresist lie in the sequence of chemical bond breaking during exposure, free radical generation, and subsequent reaction pathways. Understanding the chemical bond breaking sequence of the photoresist during exposure is crucial for optimizing photoresist formulations. Traditional steady-state spectroscopy techniques lack ultrafast temporal resolution, making it difficult to track the non-thermal bond breaking sequence and transient species evolution in the early stages of photolithography molecule excitation. Therefore, developing a photochemical detection method that simultaneously possesses ultrafast temporal resolution and high-sensitivity component recognition, thereby elucidating the complete evolution process of the photoresist from initial bond breaking to secondary chemical reactions, is a key research direction for current photoresist materials. Summary of the Invention

[0003] The purpose of this invention is to provide a method for detecting the photochemical activity of photoresist based on laser-induced breakdown spectroscopy. This method aims to accurately deduce the bond-breaking sequence of the photoresist by tracking key intermediate substances generated during the exposure process, thus solving the problem of existing technologies' difficulty in tracking the very early bond-breaking sequence of photoresist. This invention is achieved through the following technical solution:

[0004] First, this invention provides a photoresist photochemical activity detection system based on laser-induced breakdown spectroscopy, comprising: an excitation optical path, a sample detection area, and a signal detection and control system. The excitation optical path includes a laser, a collimating lens, an energy regulator for adjusting energy density, an electronic shutter for controlling exposure time, and a first focusing lens. The sample detection area includes a photoresist sample and a vacuum sample cell. The signal detection and control system includes a signal delay system for synchronous triggering, a second lens, and a spectrometer. The laser emits laser pulses, which are converted into parallel light by the collimating lens. After the energy regulator and electronic shutter adjust the input energy and exposure time, the light is focused by the first lens and irradiates the photoresist sample in the vacuum sample cell. The photoresist sample undergoes a photochemical bond-breaking reaction, generating transient fluorescence and plasma radiation. The generated transient fluorescence and plasma radiation signals are collected by the second lens. The second lens focuses and couples the signals to the spectrometer for detection and analysis of emission spectral characteristic components and detection of time-resolved dynamics. The signal delay system is connected to the laser and the spectrometer respectively, used to synchronously trigger and control the delay time between the systems, and to control the detector gate opening time to achieve stable measurement of the fluorescence spectral signal.

[0005] Furthermore, the laser is a femtosecond or nanosecond pulsed laser with a pulse width on the order of femtoseconds and a pulse duration shorter than the electron-phonon coupling time, used to induce multiphoton ionization and nonthermal photochemical bond breaking in the photoresist sample.

[0006] Furthermore, the spectrometer has a time resolution of less than nanoseconds, which is used to capture the plasma emission spectrum generated by the photoresist sample under stimulation and to detect the transient fluorescence emission time and lifetime distribution generated by specific characteristic products.

[0007] Furthermore, the photoresist sample is an organic or inorganic cluster photoresist containing metal atoms. After being pressed into a wafer, the sample is fixed on a vacuum sample cell to avoid interference from air on the emission spectrum of characteristic transient products.

[0008] The present invention also provides a photoresist photochemical detection method based on the above system, comprising the following steps: Step 1, spectral acquisition and peak assignment: The energy of the incident laser pulse is adjusted by an energy regulator, and the emission spectrum of the photoresist sample under different excitation energies is acquired by a spectrometer and the characteristic product peaks are assigned.

[0009] The second step is to determine the energy threshold: statistically analyze the curves of signal intensity of different characteristic products as a function of energy to determine the minimum energy threshold for the appearance of intermediate products of free radicals.

[0010] The third step is time-resolved kinetic detection: Under the excitation energy threshold conditions corresponding to each free radical, the time sequence of fluorescence signals emitted by each characteristic product is recorded using the time-resolved function of the spectrometer.

[0011] The fourth step is to deduce the chemical reaction pathway: by combining the order of energy thresholds with the order of time sequence, the logic of the breakage of different chemical bonds in the photoresist molecules is determined, thereby revealing the exposure mechanism.

[0012] Furthermore, in the method of the present invention, the relative concentrations of each free radical at different energies are analyzed by spectral signal intensity to infer the main reaction components under low-energy conditions.

[0013] Furthermore, in the method of the present invention, the appearance time of the corresponding intermediate product is determined by observing the rising edge of the fluorescence signal, and the reaction sequence is explained in conjunction with its position in the photoresist structure.

[0014] The present invention has the following technical effects:

[0015] This invention combines femtosecond laser-induced breakdown spectroscopy with time-resolved technology, achieving precise identification of multiple species while possessing ultra-high temporal resolution ranging from hundreds of picoseconds to nanoseconds, directly enabling real-time tracking of the initial bond-breaking sequence of the photolithography reaction. By configuring a vacuum sample cell and combining it with a signal delay control system, this invention effectively suppresses interference from the external environment and atmospheric background radiation, significantly improving the signal-to-noise ratio of weak feature signals and ensuring the accuracy of detecting transient products under multiphoton ionization mechanisms. Furthermore, this invention constructs a dual-dimensional analysis method of "energy threshold-time resolution," which can clearly define the relationship between the breaking energy and kinetics of different chemical bonds within the photoresist, providing crucial experimental means and technical support for the exposure mechanism of novel metal cluster photoresists. Attached Figure Description

[0016] Figure 1 This is a flowchart of the method of the present invention.

[0017] Figure 2 This is a schematic diagram of the optical path structure of the method of the present invention.

[0018] Figure 3 This is the structure of the tin-oxygen cluster photoresist material used in the embodiments of the present invention, which is composed of a tin-oxygen metal framework combined with two ligands: cyclotannin-3-acetic acid and dibutyltin oxide. In the structure, gray represents C, purple represents Sn, yellow represents S, red represents O, and blue represents N.

[0019] Figure 4 This is the energy-dependent spectrum of the cluster photoresist measured in an embodiment of the present invention.

[0020] Figure 5 This is a time-resolved fluorescence spectrum of cluster photoresist measured in an embodiment of the present invention.

[0021] Figure 6 This is the photochemical reaction pathway of the cluster photoresist measured in an embodiment of the present invention.

[0022] In the figure: 1 is the laser; 2 is the collimating lens; 3 is the energy regulator; 4 is the electronic shutter; 5 is the first lens; 6 is the photoresist sample; 7 is the vacuum sample cell; 8 is the signal delay system; 9 is the second lens; 10 is the spectrometer. Detailed Implementation

[0023] To more clearly and comprehensively describe the objectives, technical approach, and advantages of this invention, the following detailed description will refer to the accompanying drawings and provide embodiments. Obviously, the described embodiments are merely some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without inventive effort are within the scope of protection of this invention.

[0024] Appendix Figure 1 A flowchart of the detection method of the present invention is provided, attached. Figure 2 A schematic diagram of the optical path structure for implementing the detection method of this invention is provided. (See attached diagram.) Figure 2 As can be seen, the detection system based on laser-induced breakdown spectroscopy of the present invention includes a fluorescence excitation optical path, a sample detection area, and a signal detection and control system. The fluorescence excitation optical path includes a laser 1, a collimating lens 2, an energy regulator 3, an electronic shutter 4, and a first lens 5. The sample detection area includes a vacuum sample cell 7 and a photoresist sample 6 within the vacuum sample cell 7. The signal detection and control system includes a signal delay system 8 for synchronous triggering, a second lens 9, and a spectrometer 10. The signal delay system 8 is connected to both the laser 1 and the spectrometer 10, and is used to synchronously trigger and control the delay time between the systems. To achieve precise control of the detector gate opening time and thus stable measurement of fluorescence spectral signals, this invention utilizes a laser 1 to generate pulsed laser light, which is converted into parallel light by a collimating lens 2. This light is then focused by a first lens 5 after passing through an energy regulator 3 and an electronic shutter 4, exciting a photoresist sample 6 in a vacuum sample cell 7. Under excitation, the photoresist sample 6 undergoes a photochemical bond-breaking reaction, generating transient fluorescence and plasma radiation. This radiation signal is collected by a second lens 9, which focuses and couples the signal to a spectrometer 10 for detection and analysis of emission spectral characteristic components and for the detection, calculation, and analysis of time-resolved dynamics.

[0025] In some embodiments of the present invention, the laser 1 is a femtosecond pulsed laser, the pulse duration of which is shorter than the electron-phonon coupling time, and it can achieve non-thermal induced bond breaking in the photoresist through multiphoton ionization. The wavelength of the pump light is selected by the multiphoton characteristics of the photoresist reaction.

[0026] In some embodiments of the present invention, the second lens 9 of the spectral collection optical path and the probe of the spectrometer 10 should be located on the side of the photoresist sample to avoid direct exposure to the excitation light and improve the signal-to-noise ratio of the spectrum.

[0027] In some embodiments of the present invention, the photoresist sample 6 is an organic or inorganic cluster photoresist containing metal atoms. After being pressed, the sample is fixed on a vacuum sample cell 7 on a three-dimensional displacement stage to avoid interference from air on the emission spectrum of characteristic transient products.

[0028] In some embodiments of the present invention, the spectrometer 10 is a high-resolution spectrometer used to capture the plasma emission spectrum generated by the photoresist sample under stimulation and to detect the transient fluorescence emission time and lifetime distribution generated by specific characteristic products.

[0029] Based on the above system, the photoresist photochemical activity detection method based on laser-induced breakdown spectroscopy provided by this invention includes the following steps:

[0030] Step 1: Collect emission spectra at different energies; use an energy regulator to adjust the incident laser pulse energy, collect the emission spectra of the photoresist sample at different excitation energies using a spectrometer, and assign the peak values ​​of characteristic products;

[0031] Step 2: Collect the relative times of fluorescence appearance for different substances;

[0032] Step 3: Observe the spectral changes at different energies and assign peak values ​​to find characteristic peaks;

[0033] Step 4: Find the lowest excitation energy and calculate the intensity of different characteristic peaks and the self-reference change;

[0034] Step 5: Observe the relative time of appearance of fluorescence signals of different characteristic peaks at the threshold energy;

[0035] Step 6: Infer the dominant structural changes in the photoresist chemical reaction.

[0036] In some embodiments of the method of the present invention, the energy of the incident laser pulse is adjusted by an energy regulator, and the emission spectrum of the photoresist sample at different excitation energies is collected by a spectrometer and assigned to the characteristic product peak.

[0037] In some embodiments of the method of the present invention, the minimum energy threshold for the appearance of intermediate products such as free radicals is determined by statistically analyzing the curves of the signal intensity of different characteristic products with energy; under the minimum energy condition, the time sequence of fluorescence signals emitted by each characteristic product is recorded using a spectrometer.

[0038] In some embodiments of the method of the present invention, the order of breaking of different chemical bonds in photoresist molecules is determined by combining the high and low order of energy thresholds with the order of time sequence, thereby revealing the exposure mechanism.

[0039] The following examples further illustrate this point. The sample used in the examples is a tin oxide cluster photoresist material, which has the following characteristics: Figure 3 The structure shown.

[0040] Example 1:

[0041] The photoresist photochemical activity detection method based on laser-induced breakdown spectroscopy in this embodiment includes the following steps:

[0042] (1) Collection of fluorescence spectral signals and peak assignment. The laser and spectrometer were turned on. The laser was focused by the lens and acted on the sample surface. The fluorescence spectrum was collected from the side using the spectrometer. The experiment accurately captured the characteristic spectral lines of Sn (381 / 452nm), C2 (437 / 469 / 516nm), CH (431nm), CN (359 / 386 / 388nm) and H (656nm).

[0043] (2) Energy threshold analysis for different signals. (See attached diagram) Figure 4 As shown, a C2 signal was observed in the spectrum below 11 mW, and a CH signal was observed below 14 mW, indicating that the detachment of light side-chain groups can be induced at lower energies (below 14 mW). At 16 mW, a Sn signal appeared, indicating that the Sn-C bonds in the core region began to break extensively, leading to scaffold collapse in the photoresist. Above 20 mW, a CN signal appeared, corresponding to the decomposition of the tannin ligand. Energy-dependent analysis suggests that the reaction pathway of this photoresist begins with the reaction of the dibutyltin oxide ligand portion, where the Sn-C bond breaks, causing the butyl ligand to detach. Subsequently, the butyl ligand reacts to produce H and CH fragments. With increasing energy, the metal scaffold undergoes cleavage, with Sn-O bonds breaking to generate Sn atoms. Finally, a reaction occurs around the tannin ligand to produce CN fragments.

[0044] (3) Time-resolved spectral analysis. (See attached image) Figure 5As shown, under low-energy conditions, the temporal sequence exhibited by the cluster photoresist is as follows: H is excited first, followed by CH and Sn signals approximately 20 ns later, C2 signal after 68 ns, CN signal after 70 ns, and finally C signal. The time-resolved results are consistent with the conclusions at different energies, namely, the dibutyltin oxide ligand is excited first, the H and CH signals originate from the cleavage of the butyl chain, corresponding to the breakage of CH and C-C bonds respectively, the appearance of the Sn signal represents the cleavage of the tin-oxygen framework, and the appearance of CN indicates that the remaining tannin ligands underwent a ring-opening reaction. Based on the above signal activity analysis, the approximate reaction pathway of the tin-oxygen cluster photoresist analyzed in this example can be deduced, as shown in the attached figure. Figure 6 As shown.

[0045] Based on the above embodiments, the method provided by the present invention can accurately reconstruct the reaction path of metal cluster photoresist during photoexcitation by considering the time difference and energy dependence characteristics of different free radicals and characteristic fragments. It first observes which part of the ligands reacts first, and then infers the reaction process in the ligands through free radical signals, thereby predicting the structural evolution law that plays a dominant role in extreme ultraviolet exposure performance.

Claims

1. A photoresist photochemical activity detection system based on laser-induced breakdown spectroscopy, characterized in that, The system includes a fluorescence excitation optical path, a sample detection area, and a signal detection and control system. The fluorescence excitation optical path includes a laser (1), a collimating lens (2), an energy regulator (3), an electronic shutter (4), and a first lens (5). The sample detection area includes a vacuum sample cell (7) and a photoresist sample (6). The signal detection and control system includes a signal delay system (8) for synchronous triggering, a second lens (9), and a spectrometer (10). The laser (1) generates pulsed laser light, which is converted into parallel light by the collimating lens (2). The input energy and exposure are adjusted by the energy regulator (3) and the electronic shutter (4). After a certain time, the photoresist sample (6) in the vacuum sample cell (7) is focused by the first lens (5); the photoresist sample (6) undergoes a photochemical bond breaking reaction and generates transient fluorescence and plasma radiation; the generated transient fluorescence and plasma radiation signals are collected by the second lens (9); the second lens (9) focuses and couples the signal to the spectrometer (10) to detect and analyze the emission spectrum characteristic components and detect the time-resolved dynamics; the signal delay system (8) is connected to the laser (1) and the spectrometer (10) respectively, and is used to synchronously trigger and control the delay time between the systems and control the opening time of the detector gate.

2. The system according to claim 1, characterized in that: The laser (1) is a femtosecond or nanosecond pulsed laser with a pulse width on the order of femtoseconds, used to induce multiphoton ionization and nonthermal photochemical bond breaking in the photoresist sample (6).

3. The system according to claim 1, characterized in that: The spectrometer (10) has a time resolution of less than ns and is used to capture the plasma emission spectrum generated by the photoresist sample under stimulation and to detect the transient fluorescence emission time and lifetime distribution generated by specific characteristic products.

4. The system according to claim 1, characterized in that: The photoresist sample (6) is an organic or inorganic cluster photoresist containing metal atoms. The sample is fixed on a vacuum sample cell (7) after being pressed.

5. A photochemical detection method for photoresist, characterized in that, The system described in any one of claims 1-4 is implemented by comprising the following steps: Step 1, Spectral Acquisition and Peak Assignment: The energy of the incident laser pulse is adjusted by the energy regulator (3), and the emission spectrum of the photoresist sample (6) under different excitation energies is acquired by the spectrometer (10), and the characteristic product peaks are assigned. The second step is to determine the energy threshold: statistically analyze the curves of signal intensity of different characteristic products as a function of energy to determine the energy threshold for the appearance of intermediate products of free radicals. The third step is time-resolved kinetic detection: under the energy threshold conditions corresponding to each intermediate product, the time sequence of fluorescence signals emitted by each characteristic product is recorded using a spectrometer (10); The fourth step is to deduce the chemical reaction pathway: by combining the order of energy thresholds with the order of time sequence, the logic of the breakage of different chemical bonds in the photoresist molecules is determined, thereby revealing the exposure mechanism.

6. The method according to claim 5, characterized in that: The relative concentrations of free radicals at different energies were analyzed by spectral signal intensity.

7. The method according to claim 5, characterized in that: The occurrence time of the corresponding intermediate product is determined by observing the rising edge of the fluorescence signal.

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