CN102732844B - Design method of coating uniformity correction baffle plate of spherical optical element on planetary rotating fixture of vacuum coating machine - Google Patents

Abstract

A method for designing a coating uniformity correction baffle for a spherical optical element on a planetary rotating jig of a vacuum coating machine. By establishing a coating model in a vacuum environment, the film thickness distribution of a plane or spherical optical element coated on a planetary rotating jig is studied. By equating the coating process of the optical elements in the planetary rotating fixture to the coating process in a simple rotating fixture, the initial shape of the coating uniformity correction baffle in the planetary rotating fixture is designed. The arc length magnification of the baffle is optimized and corrected by computer until the uniformity of the film thickness reaches the optimal result, and the actual shape of the baffle for the uniformity of the film thickness of the spherical optical element is obtained. The invention can realize the uniformity control of the thin film thickness of the spherical optical element with large aperture and large aperture/radius of curvature ratio, thereby obtaining the uniformity of the spectral characteristics of the multilayer film of the spherical optical element with large aperture and large aperture/radius of curvature ratio.

Description

A design method of a spherical optical element coating uniformity correction baffle on a planetary rotating fixture of a vacuum coating machine

technical field

The invention relates to the technical field of thin film preparation, in particular to a design method for a correction baffle used in a planetary rotating fixture of a vacuum coating machine to control the uniformity of the film thickness of a spherical optical element.

Background technique

Optical thin films are an important part of modern optical systems. On the surface of almost all optical components, the preparation of thin films with special properties by physical or chemical methods has become a necessary means to improve the optical properties of optical components. With the development of high-precision optical measuring instruments, high-resolution optical imaging technology and lithography technology, the aperture of optical elements and the ratio of aperture/radius of curvature of spherical optical elements are getting larger and larger. In order to ensure the use of large aperture, large aperture/radius of curvature ratio The optical system performance of spherical optical elements requires precise control of the uniformity of the film thickness of the optical element, thereby controlling the uniformity of transmission or reflectance and wavefront error. When physical vapor deposition is used to deposit thin films, the film deposition rate has a great relationship with the incident angle when the molecules are deposited on the surface of the optical element. The diameter of the spherical optical element in the planetary rotating fixture is smaller than that of the planetary rotating fixture, and it is placed in the center of the planetary rotating fixture. Due to the large difference in the incident angle of molecules deposited on different positions on the spherical surface, the surface of the spherical optical element with high curvature The non-uniformity of film thickness is more obvious than that of planar optical elements. The technology of controlling the uniformity of film thickness has become one of the most important research contents in the coating technology of spherical optical elements.

The existing methods to improve the uniformity of film thickness on the surface of optical components mainly include: (1) Improve the uniformity of film thickness of optical components by optimizing the movement mode of simple or planetary rotating fixtures. For example, in ion beam sputtering method coating, using a biaxial drive planetary rotation fixture system (M.Gross, S.Dligatch, and A.Chtanov, "Optimization of coating uniformity in an ion beam sputtering system using a modified planetary rotation method," Appl.Opt.50, C316-C320(2011)) can realize the uniformity of film thickness of large-scale planar optical elements. Since the operation mode of the fixture is difficult to change after the design is finalized, these methods can only be used to control the uniformity of the film thickness of flat optical elements or curved optical elements with specific shapes; (2) Correction baffles with fixed or movable installation positions To improve the uniformity of film thickness. The correction baffle achieves the purpose of correcting the uniformity of the film thickness by selectively blocking the position where the deposition rate is faster on the optical element. The use of correction baffles to improve the uniformity of film thickness has been widely used. For example, P.Kelkar et al. used correction baffles on the planetary rotating fixture to realize a series of spherical optics with different apertures and different aperture/radius of curvature ratios in the deep ultraviolet band. Control of film thickness uniformity of components (P. Kelkar, B. Tirri, R. Wilklow, D. Peterson, "Deposition and characterization of challenging DUVcoatings," Proc. SPIE7606, 706708, 706708-8 (2008)). The advantage of using the correction baffle to improve the uniformity of film thickness is that the operation mode of the fixture is fixed, and only the shape of the correction baffle needs to be changed, so it has better applicability and scalability.

The current film thickness distribution theory and the modified baffle theory design method based on it are mainly based on the following assumptions: the evaporated film material propagates in a straight line in vacuum until it is deposited on the surface of the optical element or other positions in the vacuum chamber; the deposition rate of the film material The function expression is related to the evaporation mode. For a small-area heating evaporation source, the vapor distribution function of the membrane material can be expressed by cos ⁿ ψ (F.Villa and O.Pompa, "Emission pattern of real vapor sources in high vacuum: an overview," Appl. Opt. 38, 695–703 (1999)). The modified baffle theoretical design method has been successfully used on simple rotating fixtures. For example, the modified baffle designed by B.Sassolas et al. has realized the control of the film thickness uniformity of large-aperture curved optical elements (B.Sassolas, R.Flaminio, J .Franc, C.Michel, J.-L.Montorio, N.Morgado, and L.Pinard, "Masking technique for coating thickness control on large and strongly curved aspherical optics," Appl.Opt.48, 3760-3765 (2009) ). The design of the coating uniformity correction baffle on the planetary rotating fixture is currently mainly based on the coating experience to design the initial correction baffle, and then repeatedly modify the shape of the baffle through a large number of experiments to finally achieve the expected film thickness uniformity distribution. The design process of this modified baffle is time-consuming, and usually requires several or even more than ten experiments to obtain a satisfactory result, and requires experienced designers. The method of using theory-aided design to correct the baffle has not been applied to the planetary rotation fixture, mainly because in the planetary rotation fixture, the optical element always rotates at high speed, and the position of the point on the mirror surface has no fixed relationship with the position of the correction baffle. Therefore, the mathematical expression for correcting the shape of the baffle cannot be derived directly.

Contents of the invention

The technical problem of the present invention is to overcome the deficiency of the design method of the uniformity correction baffle of the film thickness of the optical element on the planetary rotating fixture of the vacuum coating machine, and provide a method based on computer simulation to quickly and accurately design the uniformity correction of the coating thickness of the spherical optical element Baffle design method.

The principle of the technical solution of the present invention: in the process of physical vapor deposition, steam molecules propagate in a straight line in a high vacuum environment and deposit on the surface of the optical element at a certain angle. The angle of the component surface is related to the distance from the evaporation source to the deposition location. At different positions on the surface of the spherical optical element, the incident angles of molecules vary greatly, resulting in uneven distribution of film thickness after coating. After the spherical optical element placed in the center of the planetary rotating fixture is coated, the thickness of the film is symmetrically distributed. The correction baffle controls the coating time at different positions on the surface of the optical element through the shading effect, so as to realize the uniformity of the film thickness of the entire optical element. In the technical solution of the present invention, by establishing a mathematical model for the coating process, a method for calculating the thickness distribution of the spherical optical element film is obtained, wherein the vapor distribution function of the film material is determined by quantitatively comparing the theoretically calculated film thickness distribution with the experimental results. Since the film thickness distribution of the spherical optical element on the planetary rotating fixture is always approximately centrosymmetric during the coating process, from the point of view of the revolution center, the optical element can be approximated as simply rotating around the revolution center, so the design method of the baffle on the simple rotating fixture Design the initial correction baffle. In fact, due to the rotation of the planetary fixture, the correction baffle not only has a shielding effect on the position where the film thickness is relatively large on the optical element, but also has a shielding effect on the position where the thickness is the smallest. The original design of the correction baffle cannot obtain ideal The thickness uniformity of the film, but the correction baffle will block the place where the film thickness of the optical element is larger, the longer the blocking time, so it can effectively improve the uniformity of film thickness. By expanding the arc length of the corrected baffle at the same time by an appropriate multiple, the shape of the corresponding baffle when the ideal film thickness distribution is obtained by computer simulation is the corrected baffle shape required for actual coating.

The concrete realization steps of the present invention are as follows:

(1) By establishing a mathematical model for the coating process of the planetary rotating fixture in the vacuum coating machine, the film thickness distribution of the spherical optical element is obtained;

其中矢量

表示膜料分子从蒸发源到沉积位置（dS面元）的矢量，

为矢量

的长度，θ为

与光学元件表面法线之间的夹角，ψ为

与源平面法线之间的夹角，n表征膜料蒸汽分布参数；沉积速率表达式和蒸发方式相关，

θ、ψ随着行星转动夹具的运动变化。行星转动夹具平行于蒸发源平面转动时，对口径CA,曲率半径RoC的凸球面，During the vacuum coating process of physical vapor deposition, the film material forms vapor through thermal evaporation or sputtering, and the vapor molecules propagate in a straight line and deposit on the surface of the optical element. The molecular deposition rate is

where the vector

represents the vector of film material molecules from the evaporation source to the deposition position (dS bin),

as a vector

The length of , θ is

The angle between and the surface normal of the optical element, ψ is

The angle between the source plane and the normal line, n represents the vapor distribution parameter of the film material; the deposition rate expression is related to the evaporation method,

θ, ψ change with the movement of the planetary rotating fixture. When the planetary rotating fixture rotates parallel to the plane of the evaporation source, for the convex spherical surface with diameter CA and curvature radius RoC,

$\mathrm{<span\; class="notranslate">\; \&theta;</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; a</span>}\mathrm{<span\; class="notranslate">\; cos</span>}<span\; class="notranslate">\; (</span>\frac{{<span\; class="notranslate">\; |</span>\stackrel{<span\; class="notranslate">\; \&Right\; Arrow;</span>}{\mathrm{<span\; class="notranslate">\; r</span>}}<span\; class="notranslate">\; |</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; Ro</span>}{\mathrm{<span\; class="notranslate">\; C</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; r</span>}}^{{<span\; class="notranslate">\; \&prime;</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}}{\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; |</span>\stackrel{<span\; class="notranslate">\; \&Right\; Arrow;</span>}{\mathrm{<span\; class="notranslate">\; r</span>}}<span\; class="notranslate">\; |</span><span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; RoC</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ,</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}\mathrm{<span\; class="notranslate">\; a</span>}<span\; class="notranslate">\; )</span>$

For a concave spherical surface with diameter CA and radius of curvature RoC,

$\mathrm{<span\; class="notranslate">\; \&theta;</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; a</span>}\mathrm{<span\; class="notranslate">\; cos</span>}<span\; class="notranslate">\; (</span>\frac{{<span\; class="notranslate">\; |</span>\stackrel{<span\; class="notranslate">\; \&Right\; Arrow;</span>}{\mathrm{<span\; class="notranslate">\; r</span>}}<span\; class="notranslate">\; |</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; Ro</span>}{\mathrm{<span\; class="notranslate">\; C</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; r</span>}}^{{<span\; class="notranslate">\; \&prime;</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}}{\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; |</span>\stackrel{<span\; class="notranslate">\; \&Right\; Arrow;</span>}{\mathrm{<span\; class="notranslate">\; r</span>}}<span\; class="notranslate">\; |</span><span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; RoC</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}\mathrm{<span\; class="notranslate">\; b</span>}<span\; class="notranslate">\; )</span>$

$\mathrm{<span\; class="notranslate">\; \&psi;</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; arcsin</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&rho;</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; /</span><span\; class="notranslate">\; |</span>\stackrel{<span\; class="notranslate">\; \&Right\; Arrow;</span>}{\mathrm{<span\; class="notranslate">\; r</span>}}<span\; class="notranslate">\; |</span><span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$

$<span\; class="notranslate">\; |</span>\stackrel{<span\; class="notranslate">\; \&Right\; Arrow;</span>}{\mathrm{<span\; class="notranslate">\; r</span>}}<span\; class="notranslate">\; |</span><span\; class="notranslate">\; =</span>\sqrt{{\mathrm{<span\; class="notranslate">\; \&rho;</span>}}^{{<span\; class="notranslate">\; \&prime;</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; h</span>}}^{{<span\; class="notranslate">\; \&prime;</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}}$

是凸球面或凹球面所在球的中心位置与蒸发源之间的距离，h’和ρ’分别是蒸发源到面元dS的垂直和水平距离，ρ为行星转动夹具公转轨道半径，h为行星转动夹具公转平面与蒸发源平面的距离；in

is the distance between the center position of the convex sphere or the concave sphere and the evaporation source, h' and ρ' are the vertical and horizontal distances from the evaporation source to the surface element dS respectively, ρ is the orbital radius of the planetary rotating fixture, and h is the planet The distance between the revolution plane of the rotating fixture and the evaporation source plane;

By calculating the deposition rate at different times and at different positions and integrating it with time, the film thickness distribution of convex spherical or concave spherical optical elements is obtained;

(2) By comparing the theoretical simulation results and experimental results of the film thickness distribution on a large-aperture plane or spherical optical element with a diameter similar to that of the planetary rotating fixture, the film material vapor distribution parameter n is obtained;

(3) By equating the film thickness distribution of the spherical optical element in the planetary rotating fixture to the film thickness distribution of the planar optical element on the simple rotating fixture, the initial shape of the correction baffle required for the coating of the spherical optical element on the planetary rotating fixture is determined; disc, let T ₀ be the minimum film thickness on the ray L from the center of revolution to the center of the optical element, and T be the film thickness on the plane optical element at the distance R from the center of revolution on L, then the initial shape of the correction baffle is given by

$\mathrm{<span\; class="notranslate">\; l</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; R</span>}<span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}\frac{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; T</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; T</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 4</span>}<span\; class="notranslate">\; )</span>$

Determined, where l represents the arc length of the arc with the center of revolution as the center and R as the radius; for spherical optical elements, a flat disk with the same aperture is used to approximate, the film thickness distribution on the disk and the film thickness distribution on the spherical surface The same, then design the initial shape of the correction baffle according to formula (4), and the correction baffle is a flat structure;

(4) By establishing a mathematical model for the coating process after using the corrected baffle, the film thickness distribution of the spherical optical element corrected by using the baffle is obtained; the corrected baffle is installed under the optical element parallel to the planetary rotation fixture to connect the mirror elements The straight line from dS to the evaporation source, during the planetary rotation of the optical element, if the straight line intersects the correction baffle, the deposition rate on the panel dS at this moment is 0, otherwise the deposition rate is the same as when no correction baffle is used;

(5) Use the computer to optimize and correct the magnification factor κ of the arc length l of the baffle to obtain the corrected baffle shape when the uniformity of the film thickness is close to 100%, then correct the shape of the baffle

The design method is suitable for the design of the uniformity correction baffle plate of the film thickness of the central symmetric aspheric optical element.

The specific process of obtaining the film material vapor distribution parameter n in the step (2) is as follows: Calculate the film thickness distribution on the large-aperture plane or spherical optical element when the film material vapor distribution parameter n is different, and compare it with the film thickness distribution obtained by the experimental measurement , using the least squares method to determine the vapor distribution parameter corresponding to the minimum difference between the experimental and theoretical film thickness distribution is the actual vapor distribution parameter of the film material. The film thickness distribution of the spherical optical element is determined by experimentally measuring the film thickness on a small-diameter (usually 25mm or 25.4mm) test piece placed on a metal fixture with the same shape as the spherical optical element at different positions. The film thickness measurement method of the test piece mainly includes photometry method, ellipsometry, etc.

The spherical optical element is installed at the center of the fixture.

The calculation method of using computer to optimize and correct the arc length magnification of the baffle mainly includes genetic algorithm, simulated annealing algorithm, etc.;

Compared with the prior art, the present invention has the following advantages:

(1) The design efficiency of the modified baffle is high. This method uses computer optimization design to correct the shape of the baffle, and only needs to determine the steam distribution function of the membrane material through experiments. The design process of the modified baffle is completed by computer simulation, which greatly improves the design efficiency of the modified baffle.

(2) Using the computer to simulate the thickness distribution characteristics of the spherical optical element film is helpful to understand the microscopic information of the film thickness distribution after using the corrected baffle, so as to optimize the coating parameters according to the coating requirements and obtain the ideal film thickness uniformity.

Description of drawings

Figure 1 is a schematic diagram of the coating process of spherical optical elements on a planetary rotating fixture in a thermal evaporation vacuum coating machine.

Fig. 2 is the theoretical simulation and experimental results of the radial distribution of the film thickness of the planar optical element.

Fig. 3 is the radial distribution curve of film thickness of convex spherical and concave spherical optical elements before and after using the correction baffle.

Detailed ways

的长度

θ为

与光学元件表面法线之间的夹角，ψ为

与源平面法线之间的夹角，r’是凸球面或凹球面所在球的中心位置与蒸发源之间的距离，h’和ρ’分别是蒸发源到面元dS的垂直和水平距离，ρ为行星转动夹具公转轨道半径，h为行星转动夹具公转平面与蒸发源平面的距离，

是h与h’之差值，ω₁|则是行星转动夹具的转动角速率。光学元件球面所在的球中心由O标记，球面曲率半径为RoC。面元dS的位置将随光学元件行星转动而变化，在镀膜机和待镀膜光学元件参数都确定后，式（1）-（3）可表示为时间的函数。为确定t时刻沉积速率，需要确定沉积速率函数f以及蒸汽分布特征参数n。积速率函数f和蒸发方式有关，如电子枪加热蒸发MgF2材料时，沉积速率可表示为

通过数值积分计算一定时间后光学元件上不同位置的薄膜厚度，从而得到球面光学元件的薄膜厚度分布。Attached Figure 1 is a schematic diagram of the coating process of spherical optical elements on the planetary rotating fixture of the vacuum coating machine, where r represents the vector from the evaporation source to the deposition position (dS panel)

length

θ is

The angle between and the surface normal of the optical element, ψ is

The included angle with the normal of the source plane, r' is the distance between the center of the sphere where the convex or concave sphere is located and the evaporation source, h' and ρ' are the vertical and horizontal distances from the evaporation source to the panel dS, respectively , ρ is the orbital radius of the planetary rotating fixture, h is the distance between the planetary rotating fixture's revolution plane and the evaporation source plane,

is the difference between h and h', ω ₁ | is the rotational angular rate of the planetary rotating fixture. The center of the sphere where the spherical surface of the optical element is located is marked by O, and the radius of curvature of the sphere is RoC. The position of the surface element dS will change with the planetary rotation of the optical element. After the parameters of the coating machine and the optical element to be coated are determined, the formulas (1)-(3) can be expressed as a function of time. In order to determine the deposition rate at time t, it is necessary to determine the deposition rate function f and the characteristic parameter n of the vapor distribution. The product rate function f is related to the evaporation method. For example, when the electron gun heats and evaporates MgF2 material, the deposition rate can be expressed as

The film thickness at different positions on the optical element is calculated by numerical integration after a certain period of time, so as to obtain the film thickness distribution of the spherical optical element.

The vapor distribution parameter n of the film material can be obtained by comparing the theoretical simulation results and experimental measurement results of the film thickness distribution of the large-aperture plane or spherical optical element with a diameter similar to that of the planetary rotating fixture. The specific process is as follows: Calculate the film thickness distribution on the large-aperture plane or spherical optical element when the vapor distribution parameter n of the film material is different, and compare it with the film thickness distribution obtained by the experimental measurement, and use the least square method to determine when the difference between the experimental and theoretical film thickness distribution is the smallest The corresponding steam distribution parameter is the actual steam distribution parameter of the membrane material. The film thickness distribution of the spherical optical element is determined by experimentally measuring the film thickness on a small-diameter (usually 25mm or 25.4mm) test piece placed on a metal fixture with the same shape as the spherical optical element at different positions. The film thickness measurement method of the test piece mainly includes photometry method, ellipsometry, etc. The _MgF2 film material heated and evaporated by the electron gun is selected as an example here. Figure 2 shows the theoretical simulation and experimental measurement results of the film thickness distribution of the _MgF2 film material deposited on a flat disc with a diameter of 400mm. The final determination of the vapor distribution parameters of the film material is n=2.0±0.3.

The method to determine the initial shape of the corrected baffle is: the film thickness distribution of the coated spherical optical element in the planetary rotating fixture is equivalent to the film thickness distribution on the surface of the flat optical element on the simple rotating fixture, and the modified baffle is designed according to the simple rotating fixture A method for designing the initial corrected baffle shape. For a flat disk, let T ₀ be the minimum film thickness on the ray L from the center of revolution to the center of the optical element, and T be the film thickness at the distance R from the center of revolution on L, then the initial shape of the corrected baffle is determined by formula (4) . For spherical optical elements, it can be approximated by a flat disk with the same caliber. The film thickness distribution on the disk is the same as that on the spherical surface. Then, the shape of the initial correction baffle is designed according to formula (4), and the correction baffle is a flat plate structure.

After using the correction baffle, make a straight line connecting the surface element dS of the mirror surface to the evaporation source. During the planetary rotation of the optical element, if the line intersects the correction baffle, the deposition rate on the surface element dS is 0, otherwise the deposition rate is the same as It is the same when the correcting baffle is not used. According to this method, the surface film thickness non-uniformity distribution of the spherical optical element after using the correcting baffle is obtained. Using the computer to optimize the magnification κ of the arc length l of the corrected baffle, the corrected baffle shape can be obtained when the film thickness uniformity is close to 100%. The corrected baffle shape is given by Decide. The computer methods for optimizing and correcting the magnification of the arc length of the baffle mainly include genetic algorithm and simulated annealing algorithm.

Figure 3 shows the radial thickness distribution of the MgF ₂ film before and after using the correction baffle on the convex spherical surface and the concave spherical surface placed at the center of the planetary rotating fixture. The diameter of the convex spherical surface is 240mm, and the radius of curvature is 200mm; the diameter of the concave spherical surface is 160mm, and the radius of curvature is 170mm. The correction baffle is obtained according to the design method provided by the present invention. The correction baffle is installed 10mm below the optical element during coating. Before using the corrected baffle, the film thickness distribution is obtained by computer simulation, and after using the corrected baffle, the film thickness distribution is determined by measuring the film thickness on the small-caliber test piece placed at different positions on the metal fixture with the same shape as the spherical optical element. The abscissa in the image represents the ratio of the position of the test piece to the radius of the spherical optical element, and the ordinate represents the normalized thickness distribution.

In addition, the coating process on the planetary rotating fixture is equivalent to the coating process on the simple rotating fixture, and the initial shape of the correcting baffle is designed according to the design method of the correcting baffle on the simple rotating fixture, and the arc length of the corrected baffle is optimized by computer to design the corrected baffle The plate shape method can be used to control the distribution of the film thickness of the plane or spherical optical element in a specific way, which also belongs to the protection scope of this patent.

In a word, the present invention proposes a coating process on the planetary rotating jig of a vacuum coating machine equivalent to the coating process on a simple rotating jig, and the thickness uniformity of the spherical optical element is designed according to the design method of the correction baffle on the simple rotating jig Correct the initial shape of the baffle, and use the computer to optimize the arc length of the baffle to obtain the actual shape of the modified baffle. In physical vapor deposition processes such as thermal evaporation, ion beam sputtering, magnetron sputtering, and molecular layer deposition, the same method can be used for the design of the coating uniformity correction baffle on the planetary rotating fixture, and all belong to the protection scope of the present invention. Compared with the existing method for designing the coating uniformity correction baffle of the spherical optical element, the invention can more quickly and accurately realize the design of the coating uniformity correction baffle of the spherical optical element.

Parts of the present invention that are not described in detail belong to the well-known technologies in the art, such as the design principle of the uniformity correction baffle on the simple rotating fixture and the like.

Claims (5)

1. a method of design for spherical optics element plated film uniformity correcting baffle plate on vacuum plating unit planetary rotation fixture, is characterized in that performing step is as follows:

(1) by using the process of planetary rotation fixture plated film to set up mathematical model in vacuum plating unit, obtain spherical optics element film thickness and distribute

In physical vapor deposition vacuum plating process, coating materials forms steam by thermal evaporation or sputter, and steam molecule is propagated with linear fashion, and is deposited on optical element surface, and molecule deposition speed is vector wherein represent the vector of coating materials molecule from evaporation source to deposition position,

for vector

length, θ is

and the angle between optical element surface normal, ψ is

and the angle between the plane normal of source, n characterizes coating materials steam distribution parameter; Sedimentation rate expression formula is relevant with evaporation mode,

, θ, ψ be along with the motion change of planetary rotation fixture; When planetary rotation fixture is parallel to evaporation source Plane Rotation, to bore CA, the protruding sphere of radius of curvature R oC,

$\mathrm{\&theta;}=\mathrm{\&pi;}-a\cos \left(\frac{{\left|\stackrel{\&RightArrow;}{r}\right|}^2+{\mathrm{RoC}}^2-r^{\&prime;2}}{2\left|\stackrel{\&RightArrow;}{r}\right|\&times;\mathrm{RoC}}\right),---\left(1a\right)$

For bore CA, the concave spherical surface of radius of curvature R oC,

$\mathrm{\&theta;}=a\cos \left(\frac{{\left|\stackrel{\&RightArrow;}{r}\right|}^2+{\mathrm{RoC}}^2-r^{\&prime;2}}{2\left|\stackrel{\&RightArrow;}{r}\right|\&times;\mathrm{RoC}}\right)---\left(1b\right)$

$\mathrm{\&psi;}=\arcsin ({\mathrm{\&rho;}}^{\&prime;}/|\stackrel{\&RightArrow;}{r}\left|\right)---\left(2\right)$

$\left|\stackrel{\&RightArrow;}{r}\right|=\sqrt{{\mathrm{\&rho;}}^{\&prime;2}+h^{\&prime;2}}---\left(3\right)$

Wherein

protruding sphere or the central position of concave spherical surface place ball and the distance between evaporation source, h ' is respectively that evaporation source is to the vertical and horizontal throw of bin dS with ρ ', ρ is planetary rotation fixture revolution orbit radius, and h is the distance of planetary rotation fixture revolution plane and evaporation source plane;

By calculating not in the same time, the sedimentation rate of different positions to time integral, obtain protruding sphere or concave spherical surface optical element film thickness and distribute;

(2), by relatively more close with planetary rotation jig bore heavy-calibre planar or theoretical modeling result and the experimental result of spherical optics element upper film thickness distribution, obtain coating materials steam distribution parameter n;

(3) by the film thickness to planar optical elements on simple rotation fixture of equal value that spherical optics element film thickness in planetary rotation fixture is distributed, distribute, determine the original shape of the required modifying mask of spherical optics element plated film on planetary rotation fixture; To plane disc, establish T ₀for the upper minimum film thickness of the ray L from revolution center to center of optical element, T is the film thickness on the upper distance revolution center R of L place planar optical elements, modifying mask original shape by

$l=R\&times;2\mathrm{\&pi;}\left(\frac{T-T_0}{T}\right)---\left(4\right)$

Determine, wherein l representative be take revolution center as the center of circle, the arc length of the circular arc that the R of take is radius; For spherical optics element, adopt the plane disc of an identical bore approximate, the film thickness on disk distributes identical with sphere upper film thickness distribution, and then, according to formula (4) design modification baffle plate original shape, modifying mask is slab construction;

(4), by the coating process after use modifying mask is set up to mathematical model, after the correction of acquisition use baffle plate, the film thickness of spherical optics element distributes; Modifying mask is parallel to planetary rotation fixture and is arranged under optical element, do and connect minute surface bin dS to the straight line of evaporation source, in optical element planetary rotation process, if straight line and modifying mask intersect, the sedimentation rate on bin dS is 0 this moment, otherwise sedimentation rate is identical when not using modifying mask;

(5) utilize the magnification κ of computer optimization modifying mask arc length l, modifying mask shape when acquisition film gauge uniformity approaches 100%, modifying mask shape

2. the method for design of spherical optics element plated film uniformity correcting baffle plate on a kind of vacuum plating unit planetary rotation fixture according to claim 1, is characterized in that: described method of design is applicable to the design of centrosymmetry aspherical optical element film gauge uniformity modifying mask.

3. the method for design of spherical optics element plated film uniformity correcting baffle plate on a kind of vacuum plating unit planetary rotation fixture according to claim 1 and 2, it is characterized in that: the detailed process that obtains coating materials steam distribution parameter n in described step (2) is as follows: heavy-calibre planar or spherical optics element upper film thickness distribution while calculating different coating materials steam distribution parameter n, and distribute relatively with the film thickness that experiment measuring obtains, utilize method of least squares to determine experiment and the theoretical film thickness difference in distribution actual steam distribution parameter that hour corresponding steam distribution parameter is coating materials, spherical optics element film thickness distributes to measure by experiment and is placed on the small-bore of different positions on the metal fixture identical with spherical optics component shape, be that film thickness in 25mm or 25.4mm testing plate is determined, testing plate measured film thickness method adopts light-intensity method or Ellipsometric.

4. the method for design of spherical optics element plated film uniformity correcting baffle plate on a kind of vacuum plating unit planetary rotation fixture according to claim 1, is characterized in that: described spherical optics element is arranged on the central position of planetary rotation fixture.

5. the method for design of spherical optics element plated film uniformity correcting baffle plate on a kind of vacuum plating unit planetary rotation fixture according to claim 1, is characterized in that: in described step (5), utilize the method for calculation of computer optimization modifying mask arc length magnification to have genetic algorithm, simulated annealing.

Images