Optical material service life evaluation method based on defect evolution driving force

Abstract

The invention provides an optical material service life evaluation method based on defect evolution driving force. The method comprises the following steps: firstly, testing the absorptivity of the optical element from an ultraviolet band to an infrared band, determining a test light source band, performing low-dose irradiation on the optical element, analyzing surface damage information influenced by pollutants, testing the transmittance change of the optical element, recording the corresponding irradiation dose, calculating the structure concentration change causing the absorption change, and calculating the structure concentration change of the optical element. Irradiating different positions of the optical element and monitoring refractive index change, determining an optical element structure evolution rate caused by irradiation according to the structure concentration change and the corresponding irradiation dose, applying a certain force to the optical element, and calculating stress borne by the optical element under different compression displacements; and internal stress and deformation resistance of the optical element under different mechanical drives are analyzed. Defect evolution research is carried out on the optical material by utilizing different damage driving forces, and damage reason analysis and service life evaluation of the optical material are realized.

Description

Technical Field

[0001] The present invention relates to the technical field of optical material quality evaluation, and particularly to a method for evaluating the lifetime of optical materials based on the driving force of defect evolution. Background Art

[0002] Due to its unique physical properties, deep ultraviolet optical materials play a crucial role in multiple key fields. In the fields of lithography processing, semiconductor chip defect detection, high-end scientific research equipment, etc., the application value of deep ultraviolet optical materials is particularly significant. It can not only achieve high-power deep ultraviolet laser output, but also has important application value in the field of optoelectronic technology, such as spectral analysis, precision manufacturing, and environmental monitoring. Therefore, the research and development of deep ultraviolet optical materials are of great significance for promoting the progress and application expansion of related technologies.

[0003] However, during the service process of deep ultraviolet optical materials, they are subjected to the actions of light, heat, force, pollutants, etc. Their damage occurs under the action of multi-coupled fields such as laser irradiation, mechanical loading, and pollutant induction. The targeted research on damage evolution is a very difficult process. The photothermal effect, photo-mechanical effect, photochemical reaction, etc. caused by irradiation or their coupling effects cause the proliferation and expansion of defects in optical materials, which is the fundamental reason for the degradation of their irradiation performance.

[0004] There are few methods for evaluating the lifetime of deep ultraviolet optical materials, and there are mainly the following difficulties: 1) The current possible lifetime evaluation method is the low-energy density irradiation method. To ensure that the photochemical damage mechanism does not transform into the photothermal damage mechanism, the energy density used is only several times that of the service state. The lifetime evaluation of components takes a long time, has many influencing factors, and is costly, making it difficult to be applied on a large scale; 2) At present, the lifetime of optical materials of other wavelength lasers is mainly affected by the photothermal damage mechanism. The increase in the laser irradiation energy density does not affect the damage mechanism, but only has an acceleration effect. Therefore, the design of lifetime evaluation is easy to achieve. The relevant research on the lifetime evaluation of optical components in other wavelength bands mainly focuses on the optimization of irradiation devices and the fine observation of damage; 3) The reasons for the damage of optical materials caused by irradiation are often not only one, and it is not clear how to judge the main reason for the damage; 4) It is difficult to reproduce the damage to verify whether the found reason is accurate.

[0005] In summary, the lifetime evaluation of optical materials has always been a huge problem faced by deep ultraviolet lasers during use, directly affecting the screening and optimization of optical materials. If the main driving force affecting the irradiation defect evolution of optical materials can be accurately found and a lifetime evaluation method based on different driving forces can be developed, the efficiency of the optimization and iteration of optical materials can be significantly improved.

[0006] In view of this, the present invention is specifically proposed. Summary of the Invention

[0007] The object of the present invention is to provide a method for evaluating the lifespan of an optical material based on the driving force of defect evolution, studying the defect evolution of the optical material using different damage driving forces, and realizing the analysis of the damage cause and lifespan evaluation of the optical material.

[0008] The present invention provides a method for evaluating the lifespan of an optical material based on the driving force of defect evolution, comprising the following steps:

[0009] S1: Test the absorption rate of the optical element in the ultraviolet to infrared band. If there is no absorption peak, select the deep ultraviolet band as the test light source band and enter step S4; if there is an absorption peak, enter step S2;

[0010] S2: If the absorption peak is in the deep ultraviolet band, it does not meet the application requirements of the deep ultraviolet band; otherwise, determine the test light source band according to the absorption peak position, analyze the absorption peak shape and enter step S3;

[0011] S3: If the full width at half maximum of all absorption peaks is significantly smaller than the absorption peak peak value, enter step S4; otherwise, perform low-dose irradiation on the optical element and analyze the surface damage information affected by pollutants;

[0012] S4: Test the transmittance change of the optical element in the test light source band and record the corresponding irradiation dose, calculate the change in the structural concentration causing this absorption change, irradiate different positions of the optical element with the test light source, monitor the refractive index change and enter step S5;

[0013] S5: If the refractive index difference at different positions is small, determine the structural evolution rate of the optical element caused by irradiation according to the change in the structural concentration and its corresponding irradiation dose; otherwise, enter step S6;

[0014] S6: Apply a certain force to the optical element, calculate the stress on the optical element under different compression displacements, and analyze the internal stress and anti-deformation ability of the optical element under different mechanical drives.

[0015] In step S1, before the test, the optical element can be cleaned by purging with an inert gas or chemical wiping. Among them, the inert gas can be nitrogen, argon, etc., the purging rate can be 2 - 6 L / min, and chemical wiping can be performed with high-purity acetone, alcohol, etc. In addition, there is no strict limit on the wavelength range of the ultraviolet to infrared band, including but not limited to 190 nm to 1000 nm.

[0016] In step S2, when determining the test light source band according to the absorption peak position, the test light source band can either adopt the peak wavelength of the absorption peak (i.e., the characteristic peak or absorption characteristic peak), or adopt a certain specific wavelength included in the characteristic peak or a light source within a certain wavelength range covered by the characteristic peak.

[0017] Before analyzing the absorption peak profile, adjust the spot size of the test light source so that its one-way size ≤ 0.5 mm, and monitor the uniformity of the test light source so that it > 98%; if the test light source does not meet the above experimental requirements, the test light source can be beam-reduced and / or homogenized, and the methods of beam reduction or homogenization include but are not limited to the lens array method, the random phase plate method, the aspherical lens group method, etc.

[0018] In step S3, if the full width at half maximum of all absorption peaks is less than 0.1 - 0.2 times the peak value of its absorption peak, then enter step S4.

[0019] When performing low-dose irradiation on the optical element, determine the test light source band corresponding to the absorption peak that does not satisfy that the full width at half maximum of the absorption peak is less than 0.1 - 0.2 times the peak value of its absorption peak, and use a test light source with an irradiation energy density of 10 - 500 mJ / cm 2 to perform low-dose irradiation on the surface of the optical element, monitor the change in the transmittance of the optical element, and record the cumulative irradiation dose received by the optical element; stop the test when the transmittance of the optical element drops by 1 - 5%, and analyze the surface damage characteristics and its rate affected by the pollutant.

[0020] In step S4, the test light source is incident on the surface of the optical element at a certain angle, and a photodetector is used to monitor the light refraction process of the optical element; control the power density of the test light source so that its refractive index basically reaches a steady state, measure the change in the transmittance of the optical element in this band, and record the corresponding irradiation dose.

[0021] Calculate the change in the structural concentration that causes the absorption change according to the following formula:

[0022]

[0023] where: c is the structural concentration (usually expressed in mol / L); R is the absorbance; ε is the molar absorptivity, which represents the absorption coefficient of 1 mole of substance in a 1-cm optical path; l is the optical path length, that is, the path length of light propagating in the solution (usually in cm).

[0024] Use a test light source with an irradiation energy density of 10 - 500 mJ / cm 2 to irradiate different positions of the optical element and monitor the change in the refractive index.

[0025] In step S5, if the refractive index difference at different positions is within 5%, then determine the structural evolution rate of the optical element caused by the irradiation effect according to the change in the structural concentration and its corresponding irradiation dose.

[0026] In step S6, apply a certain force to the optical element to generate a displacement of 0.05 - 0.2 mm / min in the compression displacement direction, load and maintain for a certain time, and then calculate the stress on the optical element under different compression displacements.

[0027] Calculate the stress on the optical element under different compression displacements according to the following formula:

[0028]

[0029] Where: σ is the stress; E is Young's modulus; Δx is the strain, that is, the ratio of the compression displacement to the original length; L0 is the original length.

[0030] According to the relationship between the refractive index of the optical element and the applied stress, analyze the internal stress and deformation resistance of the optical material under different mechanical drives. If the change in the refractive index of the optical element > 0.05 - 0.1 / MPa, then analyze the micro-area stress concentration or micro-crack propagation under mechanical drive; otherwise, go to step S7.

[0031] Step S7 includes: If the refractive index difference of the optical element > 3 - 5%, then analyze the performance degradation rate of the optical element under mechanical drive; otherwise, analyze the micro-area stress concentration or micro-crack propagation under mechanical drive. Thus, a method for evaluating the life of the optical element under stress drive is obtained.

[0032] Aiming at the problems that the damage causes of current deep ultraviolet optical elements are difficult to observe intuitively, the influencing factors are complex and diverse, difficult to reproduce, and it is difficult to effectively carry out life evaluation, the present invention aims to propose a method for evaluating the life of optical materials based on the driving force of defect evolution, so as to find out the main reasons for damage and targeted protection measures of optical materials during application, and provide a theoretical basis and experimental support for accelerating the life of optical materials.

[0033] The present invention conducts experimental research on the defect evolution of optical materials using different damage driving forces (heat, force, photochemical action), and realizes the analysis of the damage causes and life evaluation of optical materials. The method of the present invention can quickly decouple and analyze the influencing factors of damage, obtain the main reasons for the damage of the element under laser irradiation, basically determine the influence law of laser irradiation parameters on the damage, and verify the conclusions drawn; the above method can be used not only for the analysis of the damage causes of deep ultraviolet optical elements, but also for the analysis of the damage causes of other components serving in complex environments.

[0034] The implementation of the present invention has at least the following advantages:

[0035] 1. The present invention can quickly and orderly separate the various inducements that cause damage to the optical element, and can not only analyze the influence of each inducement on the damage of the optical element alone, but also analyze the influence of the coupling of several inducements on the damage of the element;

[0036] 2. The present invention can realize the quantitative analysis of the influence of each inducement on the damage of the optical element, provide direct support for the use window of laser parameters, and also provide experimental data support for the life prediction of the optical element;

[0037] 3. The present invention realizes the research of different effects in various ways, can effectively control different irradiation effects, and further improves the controllability and portability of the experiment;

[0038] 4. The present invention can directly reproduce the damage of optical elements, providing data proof for the research on the damage and protection of optical elements. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for the description of the specific embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0040] Figure 1 is a flowchart of an optical material life evaluation method based on the defect evolution driving force;

[0041] Figure 2 is the absorption rate of the optical element sample;

[0042] Figure 3 is a schematic diagram of the optical path test. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0043] It should be noted that the following detailed description is illustrative and is intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present application belongs.

[0044] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless otherwise clearly specified in the context, the singular form also includes the plural form. In addition, it should also be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0045] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts belong to the scope of protection of the present invention.

[0046] Embodiment 1

[0047] Combined with Figure 1As shown in the figure, the method for evaluating the lifespan of an optical material based on the driving force of defect evolution in this embodiment includes the following steps:

[0048] 1) Clean the surface of the optical element to be studied by purging with an inert gas such as nitrogen or argon (2 - 6 L / min) or by chemical wiping with high-purity acetone, alcohol, etc. Measure the absorbance of the optical element in the ultraviolet to infrared band using a UV-visible spectrophotometer. The test wavelengths include but are not limited to wavelengths from 190 nm to 1000 nm.

[0049] 2) Determine whether the optical element has an absorption peak. If there is no obvious absorption peak, select the deep ultraviolet band as the test light source band and proceed to step 7); if there is an absorption peak, proceed to step 3).

[0050] 3) Determine the harmful pollutants and impurities in the optical element. If the sample peak position is in the deep ultraviolet band, then the optical element does not meet the application requirements for the deep ultraviolet band; otherwise, determine the test light source band according to the position of the highest absorption characteristic peak. Among them, the test light source band can be the peak wavelength of the characteristic peak, or a specific wavelength included in the characteristic peak, or a light source within a certain wavelength range covered by the characteristic peak.

[0051] 4) Adjust the spot size of the test light source so that its single-direction size ≤ 0.5 mm, and monitor its uniformity so that it > 98%, and then proceed to step 5); otherwise, it is necessary to perform beam shrinking or homogenization on the test light source. The methods of beam shrinking or homogenization include but are not limited to the lens array method, the random phase plate method, the aspherical lens group method, etc.

[0052] 5) Place the optical element to be studied in a holder, analyze the peak shape of the absorption peak of the sample. If the full width at half maximum of all absorption peaks is less than the peak value of its absorption peak × a, where a = 0.1 - 0.2, then proceed to step 7); otherwise, determine the test light source band corresponding to the characteristic peak that does not meet this condition and proceed to step 6).

[0053] 6) Irradiate the sample surface with the test light source at a low dose. The irradiation energy density is 10 - 500 mJ / cm 2 , monitor the change in the transmittance of the optical element, record the cumulative irradiation dose received by the sample. When the transmittance of the sample drops by 1 - 5%, stop the experiment and analyze the surface damage characteristics and their rates affected by the pollutants in the optical element sample.

[0054] 7) Turn on the test light source and incident it on the surface of the optical element at a certain angle, and use a photodetector to monitor the light refraction process of the optical element.

[0055] 8) Control the power density of the detection light source so that the refractive index basically reaches a steady state, measure the change in the transmittance of the optical element sample in this band, and record the corresponding irradiation dose.

[0056] 9) Calculate the change in the structure concentration that causes this absorption change according to the following formula:

[0057]

[0058] Where: c is the structure concentration (usually expressed in mol / L); R is the absorbance; ε is the molar extinction coefficient, representing the absorption coefficient of 1 mole of substance in a 1 cm optical path length; l is the optical path length, that is, the path length of light propagation in the solution (usually in cm).

[0059] 10) Irradiate different positions of the optical element sample with a test light source having an irradiation energy density of 10 - 500 mJ / cm 2 Monitor the change in its refractive index. If the refractive index difference at different positions is within 5%, determine the structural evolution rate of the optical element caused by the irradiation effect according to the change in the concentration of the absorption structure and its corresponding irradiation dose, and realize the evaluation of the transmittance performance degradation based on laser irradiation driving; otherwise, go to step 11).

[0060] 11) Apply a certain force to the holding part of the optical element to generate a displacement of 0.05 - 0.2 mm / min in the compression displacement direction, load for 1 min and hold for 5 min, and test the change in refractive index at different positions.

[0061] 12) Calculate the pressure on the optical element under different compression displacements according to the following formula:

[0062]

[0063] Where: σ is the stress; E is the Young's modulus; Δx is the strain, that is, the ratio of the compression displacement to the original length; L0 is the original length.

[0064] 13) Analyze the internal stress and deformation resistance of the optical material under different mechanical drives according to the relationship between the refractive index of the optical element and the applied stress. If the change in the refractive index of the sample > 0.05 - 0.1 / MPa, analyze the micro-area stress concentration or micro-crack propagation caused by mechanical drive; otherwise, go to step 14).

[0065] 14) Determine the consistency of the deformation resistance performance of the sample according to the change in refractive index at different positions. If the refractive index difference of the sample > 3 - 5%, analyze the performance degradation rate of the optical element under mechanical drive; otherwise, analyze the micro-area stress concentration or micro-crack propagation caused by mechanical drive. Thus, a method for evaluating the lifetime of an optical element under stress drive is obtained.

[0066] Example 2

[0067] This example is a specific example of the method for evaluating the lifetime of an optical material based on the defect evolution driving force in Example 1. The optical material uses a certain fused silica optical element, and the specific steps are as follows:

[0068] 1) Clean the surface of the optical element to be studied by nitrogen purging (2 L / min) or wiping with high-purity alcohol. Measure the absorption rate of the optical element in the ultraviolet to infrared band using a UV-visible spectrophotometer. The test wavelength ranges from 200 nm to 1000 nm. The results are shown in Figure 2 .

[0069] 2) Determine the absorption characteristic peak with the highest peak value of the optical element. Since the sample has no obvious absorption peak, select the deep ultraviolet band as the test light source band.

[0070] 3) As Figure 3 shown, turn on the 248 nm deep ultraviolet detection light source and incident it on the surface of the optical element at a certain angle. Use a laser position tester type photodetector to monitor the displacement and power during the light refraction process of the optical element.

[0071] 4) Control the power density of the detection light source so that its refractive index basically reaches a steady state of 1.52. Test the transmittance change of the optical element sample in this band and record the corresponding irradiation dose. The results are shown in Table 1.

[0072] Table 1

[0073] Irradiation dose Transmittance before irradiation Transmittance after irradiation Change in transmittance Value 30 kJ 91％ 87％ 4％

[0074] 5) Calculate the change in hydroxyl concentration that causes this absorption change according to the following formula:

[0075]

[0076] where: R is the absorption rate, which is 4%; ε is the molar absorption coefficient, indicating the absorption coefficient of 1 mole of substance in a 1 cm optical path length. For hydroxyl, it is 77.5 ± 1.5 L / mol·cm; c is the structural concentration (i.e., the concentration of the substance, usually expressed in mol / L); l is the optical path length, that is, the path length of light propagating in the solution (usually in cm).

[0077] The change in the hydroxyl content in fused silica calculated by the above formula is 761 ppm.

[0078] 6) Irradiate different positions of the optical element sample and monitor the change in its refractive index. If the refractive index difference at different positions is within 1%, then according to the concentration change of 761 ppm of the absorption structure and its corresponding irradiation dose of 30 kJ, determine that the structural evolution rate of the optical element caused by irradiation is 2.53×10 -8 / J, and realize the evaluation of the degradation of the transmittance performance driven by laser irradiation.

[0079] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. An optical material life evaluation method based on the driving force of defect evolution, characterized in that, It includes the following steps: S1: Test the absorbance of the optical element in the ultraviolet to infrared band. If there is no absorption peak, select the deep ultraviolet band as the test light source band and go to step S4; if there is an absorption peak, go to step S2; S2: If the absorption peak is in the deep ultraviolet band, it does not meet the application requirements of the deep ultraviolet band; otherwise, determine the test light source band according to the absorption peak position, analyze the absorption peak shape and go to step S3; S3: If the full width at half maximum of all absorption peaks is significantly smaller than the peak value of its absorption peak, go to step S4; otherwise, irradiate the optical element with a low dose and analyze the surface damage information affected by pollutants; S4: Test the transmittance change of the optical element in the test light source band and record the corresponding irradiation dose, calculate the change in the structural concentration that causes this absorption change, irradiate different positions of the optical element with the test light source, monitor the refractive index change and go to step S5; S5: If the refractive index difference at different positions is small, determine the structural evolution rate of the optical element caused by irradiation according to the change in the structural concentration and its corresponding irradiation dose; otherwise, go to step S6; S6: Apply a certain force to the optical element, calculate the stress on the optical element under different compression displacements, and analyze the internal stress and anti-deformation ability of the optical element under different mechanical drives.

2. The method for evaluating the lifespan of an optical material according to claim 1, wherein In step S1, before the test, clean the optical element by purging with an inert gas or chemical wiping; the wavelength of the ultraviolet to infrared band is 190 - 1000 nm.

3. The optical material life evaluation method according to claim 1, characterized in that In step S2, before analyzing the absorption peak shape, first adjust the spot size of the test light source so that its one-way size ≤ 0.5 mm, and monitor the uniformity of the test light source so that it > 98%.

4. The optical material lifespan evaluation method according to claim 1, characterized in that, In step S3, if the full width at half maximum (FWHM) of all absorption peaks is less than 0.1 - 0.2 times the peak value of their absorption peaks, then proceed to step S4; use a test light source with an irradiation energy density of 10 - 500 mJ / cm 2 to perform low-dose irradiation on the optical element, monitor the change in the transmittance of the optical element, record the cumulative irradiation dose received by the optical element, stop the test when the transmittance of the optical element decreases by 1 - 5%, and analyze the surface damage characteristics and their rates affected by the contaminants.

5. The optical material life evaluation method according to claim 1, characterized in that In step S4, calculate the change in the structural concentration that causes the absorption change according to the following formula: Where: c is the structural concentration; R is the absorbance; ε is the molar extinction coefficient; l is the optical path length.

6. The method for evaluating the lifespan of an optical material according to claim 1, wherein In step S5, if the refractive index difference at different positions is within 5%, determine the structural evolution rate of the optical element caused by the irradiation effect according to the change in the structural concentration and its corresponding irradiation dose.

7. The method for evaluating the lifespan of an optical material according to claim 1, wherein In step S6, apply a certain force to the optical element to make it displace at a rate of 0.05 - 0.2 mm / min in the compression displacement direction, load and hold for a certain time, and then calculate the stress on the optical element under different compression displacements.

8. The method for evaluating the lifespan of an optical material according to claim 1, wherein In step S6, calculate the stress on the optical element under different compression displacements according to the following formula: Where: σ is the stress; E is the Young's modulus; Δx is the strain; L0 is the original length.

9. The optical material life evaluation method according to claim 1, characterized in that, In step S6, analyzing the internal stress and anti-deformation ability of the optical element under different mechanical drives includes: If the refractive index change of the optical element > 0.05 - 0.1 / MPa, analyze the micro-area stress concentration or micro-crack propagation under mechanical drive; otherwise, go to step S7.

10. The method for evaluating the lifetime of an optical material according to claim 9, characterized in that, Step S7 includes: testing the refractive index change at different positions of the optical element. If the refractive index difference of the optical element > 3 - 5%, analyze the performance degradation rate of the optical element under mechanical drive; otherwise, analyze the micro-area stress concentration or micro-crack propagation under mechanical drive.

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