CN111235527B - Method for manufacturing optical thin film, film system structure, film coating method and laser reflector - Google Patents

Method for manufacturing optical thin film, film system structure, film coating method and laser reflector Download PDF

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Publication number
CN111235527B
CN111235527B CN202010164265.0A CN202010164265A CN111235527B CN 111235527 B CN111235527 B CN 111235527B CN 202010164265 A CN202010164265 A CN 202010164265A CN 111235527 B CN111235527 B CN 111235527B
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film
index
stack
substrate
manufacturing
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CN111235527A (en
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卫耀伟
王震
张飞
李树刚
唐明
吴倩
潘峰
罗晋
罗振飞
刘民才
张清华
王健
许乔
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Laser Fusion Research Center China Academy of Engineering Physics
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Laser Fusion Research Center China Academy of Engineering Physics
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    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C14/00—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material
    • C23C14/06—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material characterised by the coating material
    • C23C14/10—Glass or silica
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C14/00—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material
    • C23C14/06—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material characterised by the coating material
    • C23C14/08—Oxides
    • C23C14/083—Oxides of refractory metals or yttrium
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C14/00—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material
    • C23C14/22—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material characterised by the process of coating
    • C23C14/34—Sputtering
    • C23C14/46—Sputtering by ion beam produced by an external ion source
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C14/00—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material
    • C23C14/22—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material characterised by the process of coating
    • C23C14/54—Controlling or regulating the coating process
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B1/00—Optical elements characterised by the material of which they are made; Optical coatings for optical elements
    • G02B1/10—Optical coatings produced by application to, or surface treatment of, optical elements
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B5/00—Optical elements other than lenses
    • G02B5/08—Mirrors
    • G02B5/0816—Multilayer mirrors, i.e. having two or more reflecting layers

Abstract

A method for manufacturing an optical film, a film system structure, a film coating method and a laser mirror belong to the field of optical equipment. The method comprises the following steps: manufacturing a first film stack meeting the spectral index on a substrate; manufacturing a second film stack meeting the surface shape index on the first film stack; and manufacturing a third film stack meeting the damage index on the second film stack. The optical film obtained by the method can realize the high-yield preparation of the laser reflecting film with high comprehensive index.

Description

Method for manufacturing optical thin film, film system structure, film coating method and laser reflector
Technical Field
The application relates to the field of optical equipment, in particular to a method for manufacturing an optical thin film, a film system structure, a film coating method and a laser reflector.
Background
With the continuous progress of laser technology, the index requirements of various laser devices on laser mirrors are higher and higher. Laser mirrors generally have higher quality requirements than conventional optical mirrors.
For laser mirrors, there is a comprehensive specification requirement, which generally includes: surface shape index, damage threshold index and spectrum index. In the manufacturing process, each main process parameter influences each index mutually, and the simultaneous reaching of multiple indexes is difficult to realize through a single process factor.
Therefore, the comprehensive index requirement is a great challenge to the coating process, and the index level and the qualification rate are easily reduced greatly.
Disclosure of Invention
The application provides a method for manufacturing an optical thin film, a film system structure, a film coating method and a laser reflector so as to realize the manufacturing of a high-quality optical device.
The application is realized as follows:
in a first aspect, embodiments of the present application provide a method of making an optical film. The method takes comprehensive indexes including a spectrum index, a surface shape index and a damage index as a reference to prepare the film on the substrate. The method comprises the following steps: manufacturing a first film stack meeting the spectral index on a substrate; manufacturing a second film stack meeting the surface shape index on the first film stack; and manufacturing a third film stack meeting the damage index on the second film stack.
In some optional examples of the first aspect, the first film stack, the second film stack and the third film stack are respectively deposited and coated by different coating parameters.
In some optional examples of the first aspect, in the step of fabricating the first film stack, the second film stack, and the third film stack, the plating parameters include a deposition rate, an ion source energy, and a vacuum degree.
In a second aspect, embodiments of the present application provide a film-based structure belonging to an untuned multilayer film system, the film-based structure having a total thickness of 8 microns having 38 layers and represented by the following form:
G/(19.8H)(59.04L)(60.7H40.04L)2(202.8H)(173.4L)(173.6H199.2L)4(173.6H199.2L)7(173.6H 199.2L)3(120.4H)(140.3L)/AIR；
wherein G represents a substrate, Air represents Air, H represents hafnium oxide as a high refractive index material, and L represents silicon dioxide as a low refractive index material;
19.8H represents a thickness of 19.8 nm for hafnium oxide, 59.04L represents a thickness of 59.04 nm for silicon dioxide, and so on;
the first membrane stack is:
(19.8H)(59.04L)(60.7H40.04L)2(202.8H)(173.4L)(173.6H199.2L)4；
the second membrane stack is: (173.6H199.2L)7；
The third membrane stack is: (173.6H199.2L)3(120.4H)(140.3L)。
In some optional examples of the second aspect, the first membrane stack is a non-regular membrane and/or the second membrane stack is a regular membrane.
In some optional examples of the second aspect, the film-system structure has a surface shape accuracy peak-to-valley value of 350 nm or less.
In some optional examples of the second aspect, the damage threshold of the film-system structure at 1053nm is equal to or greater than 40J/cm2。
In some alternative examples of the second aspect, the reflectance of the film-system structure has the following characteristics:
the P polarized reflectivity at 1053nm is more than or equal to 99.5%;
a reflectance between 450 nm and 700 nm of greater than 50%;
the reflectance at 351 nanometers is greater than 50% and less than 70%.
In a third aspect, embodiments of the present application provide a film plating method for manufacturing the above film-based structure. The coating method comprises the following steps:
providing a coating environment having a container with a background vacuum degree of 1.5 × 10, and a substrate retained in the container-4Pa, keeping the temperature at 80 ℃ for 6 hours;
a first film stack was formed at a deposition rate of 0.12nm/s, 800V and 400mA, and a degree of vacuum of 2.7X 10-4Preparing hafnium oxide under Pa conditions, with deposition rate of 0.5nm/s, 350V and 350mA, and vacuum degree of 2.1 × 10-4Manufacturing silicon dioxide under the condition of Pa;
making a second film stack with a deposition rate of 0.5nm/s, 1000V and 400mA, and a vacuum degree of 2.9 × 10-4Preparing hafnium oxide under Pa conditions, with deposition rate of 0.8nm/s, 400V and 400mA, and vacuum degree of 2.0 × 10-4Manufacturing silicon dioxide under the condition of Pa;
making a third film stack with a deposition rate of 0.1nm/s, 1000V and 400mA, and a vacuum degree of 2.7 × 10-4Preparing hafnium oxide under Pa conditions, with deposition rate of 0.4nm/s, 400V and 400mA, and vacuum degree of 2.1 × 10-4Silica was produced under Pa.
In a fourth aspect, embodiments of the present application provide a laser mirror having a substrate and a film system structure as described above.
In the implementation process, the optical film manufacturing method provided by the embodiment of the application combines the characteristics of the laser reflector with the influence factors of a single index, adopts the idea of realizing the target by steps, and realizes the high-qualification rate preparation of the laser reflector with high comprehensive index.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings that are required to be used in the embodiments will be briefly described below, it should be understood that the following drawings only illustrate some embodiments of the present application and therefore should not be considered as limiting the scope, and for those skilled in the art, other related drawings can be obtained from the drawings without inventive effort.
FIG. 1 is a schematic diagram showing the correlation between laser mirror performance and process parameters;
fig. 2 shows a graph of the relation between the oxygenation pressure and the accuracy of the surface shape;
FIG. 3 is a graph showing the relationship between ion beam current and residual stress at a determined ion beam pressure;
FIG. 4 is a graph showing the relationship between ion beam current, beam pressure and residual stress;
FIG. 5 is a graph showing the relationship between ion beam current, beam pressure and refractive index;
FIG. 6 shows a graph of different ion source energies versus surface shape accuracy;
FIG. 7 is a graph showing the correspondence between process selection and performance criteria for producing a coating on a substrate in an example of the present application;
FIG. 8 is a surface diagram of a plated surface in an example of the present application;
FIG. 9 shows a reflectance spectrum of a laser mirror in an example of the present application at a wavelength between 300nm and 1300 nm;
fig. 10 shows a schematic structural view of a laser mirror in an example of the present application.
Icon: 100-laser mirror; 101-a substrate; 102-a first membrane stack; 103-a second membrane stack; 104-third membrane stack.
Detailed Description
In the present application, all the embodiments, implementations, and features of the present application may be combined with each other without contradiction or conflict. In the present application, conventional equipment, devices, components, etc. are either commercially available or self-made in accordance with the present disclosure. In this application, some conventional operations and devices, apparatuses, components are omitted or only briefly described in order to highlight the importance of the present application.
Laser Mirrors (LM) are a type of high quality/high quality mirror used in Laser resonators and other optical devices.
Generally, LM is expected to have some of the following basic features (mainly referring to the reflective film layer/coating/plating of the laser mirror):
1. small reflection losses (especially for highly reflective mirrors) or a specified transmission in a given wavelength range (for output couplers).
2. The surface is optically high in quality (e.g., very flat over a large range) so that wavefront distortion is avoided and beam quality is maintained.
3. Can resist high light intensities without laser induced damage (for Q-switched lasers, where Q represents a quality factor), i.e. with a high damage threshold.
Due to the high quality requirement of LM, the manufacturing difficulty is large. The quality of the finished product is also not stable. For example, even highly reflective mirrors have residual transmitted light, which results in output light that is mixed with a significant amount of stray light during use. Also, the non-uniformity distribution of the residual transmission causes more significant problems.
Wherein, the reflecting film layer can be selected as a dielectric material and is a transparent film structure which is attached on the substrate. The reflective film layer may be one or more layers, and typically has a thickness in the sub-micron (100nm-1000nm) or nano-scale. For a multilayer reflective film layer, each layer may have a coating of a different refractive index, or may be a graded refractive index coating. The difference in refractive index may be obtained by the choice of materials of construction (typically two materials), such as the difference in composition.
The reflective film layer is used to change the light reflectance properties of the surface by interference effects of reflected light at the optical interface with the substrate or at each optical interface between adjacent layers in the multilayer. The laser reflector has specific functions by forming the reflecting film layer by selecting a multi-layer combination mode. For example, the bandwidth of the reflection band is wider; the reflectance values of different bands can be modulated to be different in all wavelength ranges; producing a specified polarization characteristic for the incident light.
From the structure of LM, it mainly includes a substrate (or base plate, base) and a film layer (mirror coating) on the substrate. In general, a glass substrate (e.g., quartz) is used as the laser mirror, and it generally has high transparency, few defects such as bubbles, smooth surface, and hardness. In other examples, the laser mirror may also use a laser crystal as the substrate. Wherein, the substrate can be circular, oval or any other optional shape, and the size is freely selected according to the design requirement without special limitation. For example, a circular substrate having a diameter of 25mm or 12mm and a thickness of 6 mm.
Although the reflective coating of a laser mirror plays a major role and influence on its performance, the properties of the substrate need to be considered specifically. For example, it is desirable that the surface of the substrate be of high quality (flatness), high rigidity, low coefficient of thermal expansion, high thermal conductivity (to avoid thermal expansion that may occur), optically uniform (to avoid beam distortion of transmitted light), low absorption and scattering losses, and so forth.
It should be noted that the process proposed in the examples of the present application is described by way of example with reference to a laser mirror, but other types and applications of optical elements can be produced according to this process. Exemplary optical elements include, but are not limited to, output couplers with partially transmissive properties, optical dichroic mirrors, anti-mirrors, optical filters (to attenuate light in a particular wavelength region), beam splitters, solar cell covers, and polarizers.
The performance of a laser mirror is related to the substrate and the reflective coating formed thereon, with it being more critical that the performance of the reflective coating plays a major role. The properties of the reflective coating are related to the preparation method and specific process parameters.
The reflective coating may be formed in any suitable manner, and for example, some of the processes described below.
1. And (4) electron beam deposition.
The crucible is heated by an electron beam emitted from a hot wire to evaporate the material in the crucible, and then converged on the surface of the substrate by a magnetic field. The heated substrate is used in the deposition process, so that the coating quality is improved.
Similarly, heating the material in the crucible by a resistance wire may be selected.
2. Ion assisted deposition.
The growing surface is bombarded with additional ion beams simultaneously with the electron beam deposition to improve the quality of the coating. The additional ion beam used is incident on the substrate and can reorder the deposited material, improving its density, etc. The method can be used to make oxygen-containing coatings (e.g., silicon dioxide or titanium dioxide).
3. Ion beam sputtering.
A second filament is used to neutralize the ions. The ion source generates high-energy ion beams to bombard a target (metal or metal oxide) in vacuum, so that atoms of the target are sputtered out to deposit on a substrate in a film forming process. By the method, uniform and non-porous coating with low surface roughness can be obtained, and the adhesion between the coating and the substrate is stable.
4. And (3) performing plasma reactive sputtering.
A film is sputtered in advance and then locally reacted by a plasma.
The above-mentioned various reflective coating forming processes have advantages and disadvantages, and can be selected according to practical situations, for example, when selecting the preparation method, the following considerations need to be taken into account: the applicable category of the coating material; the thickness, uniformity and precision of the plating layer; optical quality (e.g., stability and consistency of refractive index); light damage resistance; a substrate temperature; and (5) coating growth time.
In the application example, the laser mirror is manufactured by using an ion-assisted electron beam evaporation coating technology. Through research, the inventor thinks that:
for the above technology, there are three steps and seven main process parameters mainly affecting the performance of the laser mirror, and the relationship between each main process parameter and each index of the mirror is shown in fig. 1. Wherein, three process steps are as follows: substrate processing, preparation parameters, and post-processing. The seven main process parameters refer to: cleaning, ion bombardment, temperature, speed, vacuum degree, particle source parameters and laser pretreatment. The seven main parameters can correspond to three indexes of the laser reflector, namely a spectrum index, a surface shape index and a damage index.
The process meeting the comprehensive indexes comprising the three indexes is selected for guiding the high-quality manufacturing of the laser reflector.
Considering the complexity of realizing the specific performance of the laser reflector, the inventor selects a method different from the traditional simulation or algorithm design, analyzes the influence factors of a single selected concerned index, combines the characteristics of the laser reflector, and adopts the idea of realizing the target by steps so as to realize the high-yield preparation of the laser reflector with high comprehensive index, as described below.
1. Key influence factor analysis of single index
1.1. Surface shape index
For a laser mirror, the profile index refers to the reflected wavefront (wavefront) index. For thin film components, the reflected wavefront is typically influenced by the clamping regime and process factors (oxygen charge, ion source energy).
1.2. Spectral index
For the laser reflector, the spectral index means that high reflection of laser with selected wavelength (which may be one band or multiple bands) is realized, and stray light in a light path is eliminated to a certain extent. In the process of spectrum design, high reflection of laser light in a specific wavelength range can be realized through a structured film system. The bandwidth of the structured film system is determined by the ratio of the refractive indices of the high refractive index material and the low refractive index material. The elimination of stray light in a certain broadband range (300-400 nm) is difficult to realize by a general regular film system, and must be realized by a non-regular optimized film system, and the non-regular film system can bring partial ultrathin layer (10 nm).
In summary, the main reflection band in the spectral index is mainly affected by the ratio of the refractive indexes of the film materials, and the stray light reflection band is mainly affected by the ultrathin layer. From a process perspective, the refractive index is primarily affected by the ion source energy, while the ultra-thin layer is primarily affected by the deposition rate. Thus, spectral indices are mainly affected by ion source energy and deposition rate.
1.3. Index of damage
The damage index refers to the laser damage resistance threshold of the mirror. The damage of the thin film element is mainly affected by the defect of the substrate or the defect generated in the coating process. The main factors influencing this are the oxygen charge (which determines the degree of oxidation of the coating material) and the ion source energy (which determines the film defects).
Through the above analysis, the association between each index of interest and the process factor can be confirmed.
2. Law of influence between key process factors and single index
2.1. Influence law of surface shape index
The surface shape index is mainly influenced by oxygen charging amount and ion source energy.
The relationship between the surface shape index and the oxygen charging amount is shown in FIG. 2. Fig. 2 discloses the following rule that as the oxygen pressure increases (the oxygen charging amount increases), the surface shape of the film shows the change trend of the transition of tensile stress-compressive stress-tensile stress, namely, the film as a whole shows the change trend of the concave-convex-concave surface topography.
The regular relationship between the surface shape index and the ion source energy is shown in fig. 3 and 4. FIG. 3 shows SiO2The residual stress of the single-layer film is related to the change of the ion source beam. Fig. 3 shows that when the (ion) beam pressure is fixed at 1000V and the beam current changes from 200mA to 600mA, the silicon dioxide single-layer film shows compressive stress and shows a gradually increasing trend along with the increase of the beam current, a larger jump exists in the range of 500mA to 600mA, and the change rule is mutually matched with the change rule of the refractive index of the silicon dioxide single-layer film.
FIG. 4 shows HfO2The residual stress of the single-layer film is related to the change of the ion source beam pressure (A) and the ion source beam current (B). Fig. 4 shows that when the (ion) beam current is fixed at 400mA and the beam pressure is varied in the range of 200V to 1000V, the single-layer film of hafnium oxide gradually transits from tensile stress to compressive stress as the beam pressure increases. When the beam pressure is fixed to be 1000V, and the beam current is changed in the range of 200 mA-600 mA. Along with the rise of the beam current, the hafnium oxide single-layer film shows the compressive stress and shows the trend of gradually strengthening along with the increase of the beam current. In addition, the hafnium oxide single-layer film is monotonous in variation with beam current and beam voltage.
2.2. Law of influence of spectral indexes
Fig. 5 shows the relationship between beam current (a), beam voltage (B) and film refractive index of the ion source energy. For the part A in FIG. 5, when the fixed beam voltage is 1000V and the beam current changes in the range of 300-600 mA, the refractive index first increases and then decreases with the increase of the beam current. The beam size of the neutralizer and the beam size of the main source are set to be in a certain proportional relation so as to ensure the stable work of the ion source, and therefore the beam size of the neutralizer has certain influence on the refractive index of the hafnium oxide film layer. For the part B in FIG. 5, when the fixed beam current is 400mA, and the beam pressure changes within the range of 250-1000V, the beam current of the neutralizer is basically unchanged, the refractive index of the hafnium oxide film layer gradually increases with the increase of the beam pressure, and then the refractive index also obviously decreases with the 1000V beam pressure.
2.3. Law of influence of damage threshold
FIG. 6 shows SEM topographies of film surfaces at different ion source energies. In fig. 6 the following is disclosed: as the ion source energy increases, the film surface defects increase (defects in part B of fig. 6 increase compared to defects in part a of fig. 6), and the increase in defects means a decrease in the damage threshold of the plating film. That is, part a indicates a smooth surface, no defects, and a corresponding damage threshold is high; the surface B has more defects and a damage threshold value is low. Therefore, in order to effectively suppress defects to ensure a laser damage threshold, the ion source energy should be controlled within a reasonable range.
Based on the above analysis, the comprehensive indexes including the spectrum index, the surface shape index and the damage index need to be considered at the same time, and the quality of the laser mirror is controlled corresponding to the selection process, as shown in fig. 7. In the excitation mirror, the outermost layer on the air side tends to have a strong electric field distribution due to electric field modulation, and therefore, damage often occurs in the outer layer. Therefore, according to the regular relation between the defects and the main process parameters, the process 3 (low deposition rate and ultra-low absorption) is adopted for the outermost layer to obtain a low-defect process, and the process is used for preparing the damage-resistant layer to achieve the standard of the damage index. The surface shape index realizes the effect of ultra-low stress and high surface shape index through the stress matching layer prepared by the process 2. Meanwhile, in order to realize the optimal spectrum effect, a process 1 (ultra-low deposition rate) is adopted to prepare an irregular film system with an ultra-thin layer, so as to meet the spectrum purpose of eliminating stray light. By the process selection of the coating with the multilayer structure, the spectrum index, the surface shape index and the damage index of the obtained laser mirror can reach the standard at the same time.
Thus, methods of making optical films can be given in the examples of this application. The method can be used for optimizing the manufacturing process of the film, so that the optical film with high quality (meeting the requirements of spectral indexes, surface shape indexes and damage indexes) can be obtained. Generally, the method prepares a thin film on a substrate based on a global index.
Specifically, in an example, the foregoing method includes: a first film stack satisfying a spectral index is fabricated on a substrate. And manufacturing a second film stack meeting the surface shape index on the first film stack. And manufacturing a third film stack meeting the damage index on the second film stack. Accordingly, when the first film stack is manufactured, the process is selected as the process 1; when the second film stack is manufactured, the process is selected as the process 2; in fabricating the third stack, the process is selected as the process 2 described above. In some examples, the process selection may achieve a yield of finished products that may be greater than 90% and the performance indicators described below.
Surface shape index: the surface shape precision peak-valley value (PV value) is less than or equal to 350 nanometers.
Damage index: the damage threshold value at 1053nm is more than or equal to 40J/cm2。
The spectral indexes are as follows: p-polarized reflectance (R) at 1053nmp) Greater than or equal to 99.5 percent. The reflectance (R) between 450 nm and 700 nm is greater than 50%. The reflectance (R) at 351 nanometers is greater than 50% and less than 70%. The above-described reflectivity characteristics of the film-system structure can be selected based on the functional or performance requirements of the final product, and different reflection characteristics can exist for different performance requirements. For example, in some examples, the dominant wavelength band used by the product is 1053nm, which therefore has a limit to polarized light, while other wavelength bands are primarily limited to eliminating stray light in the optical path.
In the actual manufacturing process, the film is manufactured in an ion beam sputtering mode, and the first film stack, the second film stack and the third film stack are respectively subjected to deposition coating through different coating parameters. In the present example, the coating parameters include deposition rate, ion source energy, and vacuum. Wherein, three membrane piles are all formed by stacking a plurality of membrane layers. The number of the film layers of the three film stacks can be the same or different, and is selected according to the performance design requirement of the optical element.
In an alternative example, based on the above process selection, the present application provides a coating method for fabricating a selected film structure on a substrate, so that a laser mirror 100 as shown in fig. 10 can be obtained, which includes a substrate 101 and a first film stack 102, a second film stack 103 and a third film stack 104. The relative positions of the layers and stacks of films are shown in fig. 8, and the thickness of the layers and substrates is not shown as a limitation.
The film coating method comprises the following steps:
step S101, providing a coating environment, wherein the coating environment comprises a container and a substrate retained in the container, and the background vacuum degree of the container is 1.5 multiplied by 10-4Pa, and keeping the temperature at 80 ℃ for 6 hours.
Step S102, manufacturing a first film stack, wherein the deposition speed is 0.12nm/S, the deposition speed is 800V and 400mA, and the vacuum degree is 2.7 multiplied by 10-4Hafnium oxide under Pa, deposition rate of 0.5nm/s, 350V and 350mA, degree of vacuum of 2.1X 10-4Silica was produced under Pa.
Step S103, manufacturing a second film stack, wherein the deposition speed is 0.5nm/S, the deposition speed is 1000V and 400mA, and the vacuum degree is 2.9 multiplied by 10-4Hafnium oxide under Pa, deposition rate of 0.8nm/s, 400V and 400mA, degree of vacuum of 2.0X 10-4Silica was produced under Pa.
Step S104, making a third film stack with a deposition rate of 0.1nm/S, 1000V and 400mA, and a vacuum degree of 2.7 × 10-4Hafnium oxide under Pa, deposition rate of 0.4nm/s, 400V and 400mA, degree of vacuum of 2.1X 10-4Silica was produced under Pa.
In an example, the three film stacks are each formed by alternating a given number of layers of two materials, hafnium oxide and silicon dioxide.
The above coating method can be carried out in an uncoordinated multilayer film system with a total thickness of 8 μm and 38 layers. The film structure of the film system is represented by the following form:
G/(19.8H)(59.04L)(60.7H40.04L)2(202.8H)(173.4L)(173.6H199.2L)4(173.6H199.2L)7(173.6H 199.2L)3(120.4H)(140.3L)/AIR。
the above expression describes the stacking sequence of the 38 film layers formed over the substrate, and their respective thicknesses.
Wherein G represents a substrate, Air represents Air, H represents hafnium oxide as a high refractive index material, and L represents silicon dioxide as a low refractive index material.
19.8H indicates a thickness of 19.8 nm for hafnium oxide, 59.04L indicates a thickness of 59.04 nm for silicon dioxide, and so on. The thickness of the hafnium oxide is 60.7 nm as indicated by 60.7H, and so on. Wherein thickness refers to its physical thickness.
The power exponent indicates the number of cycles of the repeating unit. For example, (60.7H40.04L)2Showing a stacked structure in two layers of film-the cell-has two, i.e. it shows a stack of four layers of film. Therefore, (60.7H40.04L)2Also denoted as (60.7 H40.04L60.7H40.04L).
The first film stack is a non-structured film comprising 16 layers and is represented by the expression:
(19.8H)(59.04L)(60.7H40.04L)2(202.8H)(173.4L)(173.6H199.2L)4。
the second film stack was a regular film comprising 14 layers and was expressed by the following expression: (173.6H199.2L)7. The structured film system is formed by the optical thickness of each film layer being 1/4 of the design wavelength (central wavelength), that is
Figure BDA0002406060420000131
Optical thickness is the product of the geometric thickness (physical thickness) of the film and the refractive index of the film.
The third stack comprises 8 layers and is expressed by the following expression:
(173.6H 199.2L)3(120.4H)(140.3L)。
corresponding to the film system structure, the Pv value in the surface shape index can reach 157 nm; the damage threshold value in the damage index can reach 55.7J/cm2@1053nm, as shown in FIG. 8; the reflectance in the spectral index is shown in FIG. 9, and the reflectance curves of 5 samples (2-0, 2-1', 2-2') are highly coincident, indicating that the process can achieve high stability performance.
It should be noted that the foregoing process description for each film stack (first film stack, second film stack, and third film stack) is also a process description for the corresponding film layers in each film stack. For example, for the above-mentioned first film stack having 16 film layers, each of the silicon dioxide layer and the hafnium dioxide layer is respectively applied by the corresponding method in step S102 of the foregoing plating method, each of the silicon dioxide layer and the hafnium dioxide layer in the second film stack is respectively applied by the corresponding method in step S103 of the foregoing plating method, and each of the silicon dioxide layer and the hafnium dioxide layer in the third film stack is respectively applied by the corresponding method in step S104 of the foregoing plating method.
The above description is only a preferred embodiment of the present application and is not intended to limit the present application, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, improvement and the like made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims (10)

1. A film-based structure belonging to an untuned multilayer film system, wherein the film-based structure having a total thickness of 8 μm has 38 layers and is represented by the following form:
G/(19.8H)(59.04L)(60.7H40.04L)2(202.8H)(173.4L)(173.6H199.2L)4(173.6H199.2L)7(173.6H 199.2L)3(120.4H)(140.3L)/AIR；
wherein G represents a substrate, Air represents Air, H represents hafnium oxide as a high refractive index material, and L represents silicon dioxide as a low refractive index material;
19.8H represents a thickness of 19.8 nm for hafnium oxide, 59.04L represents a thickness of 59.04 nm for silicon dioxide, and so on;
the first membrane stack is:
(19.8H)(59.04L)(60.7H40.04L)2(202.8H)(173.4L)(173.6H199.2L)4；
the second membrane stack is: (173.6H199.2L)7；
The third membrane stack is: (173.6H199.2L)3(120.4H)(140.3L)。
2. The film system structure of claim 1, wherein the first film stack is a non-regular film and/or the second film stack is a regular film.
3. The film-based structure of claim 1, wherein the film-based structure has a surface profile precision peak-to-valley value of 350 nm or less.
4. The film-based structure of claim 1, wherein the damage threshold of the film-based structure at 1053nm is equal to or greater than 40J/cm2。
5. The film-based structure of claim 1, wherein the film-based structure has a reflectivity having the following characteristics:
the P polarized reflectivity at 1053nm is more than or equal to 99.5%;
a reflectance between 450 nm and 700 nm of greater than 50%;
the reflectance at 351 nanometers is greater than 50% and less than 70%.
6. A coating method for producing the film system structure according to any one of claims 1 to 5, comprising:
providing a coating environment having a container, a substrate retained in the container, and a background vacuum degree of the container of 1.5 × 10-4Pa, at a temperature of 80 DEG CWarming for 6 hours;
a first film stack was formed at a deposition rate of 0.12nm/s, 800V and 400mA, and a degree of vacuum of 2.7X 10-4Preparing hafnium oxide under Pa conditions, with deposition rate of 0.5nm/s, 350V and 350mA, and vacuum degree of 2.1 × 10-4Manufacturing silicon dioxide under the condition of Pa;
making a second film stack with a deposition rate of 0.5nm/s, 1000V and 400mA, and a vacuum degree of 2.9 × 10-4Preparing hafnium oxide under Pa conditions, with deposition rate of 0.8nm/s, 400V and 400mA, and vacuum degree of 2.0 × 10-4Manufacturing silicon dioxide under the condition of Pa;
making a third film stack with a deposition rate of 0.1nm/s, 1000V and 400mA, and a vacuum degree of 2.7 × 10-4Preparing hafnium oxide under Pa conditions, with deposition rate of 0.4nm/s, 400V and 400mA, and vacuum degree of 2.1 × 10-4Silica was produced under Pa.
7. A method for producing an optical film having a film system structure according to any one of claims 1 to 5, the method producing a film on a substrate based on a composite index including a spectral index, a profile index, and a damage index, the method comprising:
manufacturing a first film stack meeting the spectral index on a substrate;
manufacturing a second film stack meeting the surface shape index on the first film stack;
and manufacturing a third film stack meeting the damage index on the second film stack.
8. The method of claim 7, wherein the first, second, and third film stacks are each deposited by different deposition parameters.
9. The method of claim 8, wherein the coating parameters include deposition rate, ion source energy, and vacuum during the steps of forming the first, second, and third stacks.
10. A laser mirror characterized by a substrate and having a film system structure according to any one of claims 1 to 5.
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