JPH08108475A - Manufacture of optical element - Google Patents

Abstract

PURPOSE: To provide a method for manufacturing an optical element capable of easily manufacturing an optical element having high diffraction efficiency, converging efficiency, and an ideal shape. CONSTITUTION: A work layer 2 is formed on a base plate 1 and the work layer 2 is worked into a shape having a desired depth distribution. By changing a selection ratio to be expressed by ratio of etching rate of the base plate 1 and the work layer 2, the work layer 2 and the base plate 1 are worked by anisotropic etching, and the work layer 2 is transferred to the base plate 1 by changing the shape of the work layer so as to obtain a desired optical element.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an optical element having a predetermined structure on the surface such as a relief type grating.

[0002]

2. Description of the Related Art In recent years, diffractive optical elements and Fresnel lenses have attracted attention due to demands for higher performance and smaller size and lighter weight of optical systems. It is known that in a diffractive optical element having a relief type grating structure, high diffraction efficiency can be obtained by blazing the groove cross-sectional shape.

Conventionally, as one of the methods for manufacturing such a diffractive optical element, there is a method of directly processing a substrate into a desired shape by using a diamond tool or the like. However, in this method, when the substrate is a hard material such as glass, the wear of the tool is significant and the processing efficiency is poor,
It is difficult to manufacture a diffractive optical element having a practical area. Therefore, in such a manufacturing method, there is a problem that the material of the substrate is substantially limited to a material having good workability such as metal.

In order to solve such a problem, for example, in Japanese Patent Laid-Open No. 60-103311, a resist is coated on a substrate and then exposed and developed to form a predetermined pattern on the resist. After that, a method of transferring the resist pattern shape to the substrate by dry etching is disclosed.

According to this manufacturing method, the diffractive optical element can be manufactured without directly processing the substrate.
There is an advantage that a hard material such as glass can be used as the substrate. However, on the other hand, since the resist has a property that the remaining film thickness does not change linearly with the exposure amount, for example, a blazed diffraction lens shape is formed on the resist surface by electron beam exposure. In this case, the exposure dose must be precisely controlled according to the characteristics of the resist, and therefore, in the electron beam exposure apparatus, it is necessary to precisely control the electron beam intensity or line width.
There is a problem that the device becomes complicated and expensive, and drawing of a large area becomes difficult.

In order to solve such a problem, the applicant of the present invention, for example, in Japanese Patent Application No. 5-331153, forms a processing layer on a substrate, machines the processing layer into a desired shape, and then forms the shape. We have proposed a method for manufacturing an optical element by transferring the above to the substrate by anisotropic etching. According to such a manufacturing method, since the processing layer can be cut by a numerical control type cutting machine or the like, a desired shape can be formed more easily than the method by exposure and development, and the diffractive optical element can be easily manufactured. can do.

On the other hand, a spectral grating, which is a type of diffractive optical element, is often blaze because of the need for high diffraction efficiency. However, it is difficult to cover a wide wavelength range with a conventional diffraction grating that is blazed for one wavelength. As means for solving this problem, “Optical” 12 , p. 201 (1983) proposes a blazed diffraction grating for two wavelengths.
This diffraction grating has a cross-sectional shape as shown in FIG. 6, and is effective not only for widening the wavelength range used, but also for reducing the anomaly of diffracted light intensity.

[0008]

However, as a result of various studies by the present inventors, it was found that the above-mentioned manufacturing method proposed by the present applicant has points to be improved as described below. did. For example, in the case of a diffractive lens, the groove cross-sectional shape for obtaining the maximum diffraction efficiency is a shape that reflects the phase distribution function of the diffractive lens. In this case, the hypotenuse of the groove is generally a curved line rather than a straight line. Therefore, the ideal shape to be formed in the processed layer is, for example, as shown in FIG.
It becomes a shape like A. In order to obtain this shape by cutting with a cutting tool, it is necessary to perform point cutting, for example, diamond point turning. However, the point cutting requires a large amount of processing data and requires a long time for processing. There is also a problem that roughness remains on the processed surface. In addition,
In the case of line cutting, as shown by the solid line in FIG. 5B, the oblique side of the groove shape is a straight line, so maximum diffraction efficiency cannot be obtained,
In particular, when the number of grooves to be formed is small, the decrease in diffraction efficiency due to making the oblique side of the groove a straight line becomes a problem in practical use.

On the other hand, in the case of a diffraction grating blazed into two wavelengths, it can be manufactured into a cross-sectional shape shown in FIG. 6 by cutting twice using two kinds of cutters according to the blaze angle. However, when performing cutting twice using two types of cutters as described above, there is a problem that the relative position interval of the cutters must be controlled with high accuracy, and since the cutting is performed twice, manufacturing is difficult. Another problem is that it takes time. Further, when the material of the diffraction grating is hard, it is difficult to process and there is a problem that the processing takes time.

By the way, if the processed layer is formed of a photosensitive material,
By performing exposure and development, an ideal shape as shown in FIG. 5A or a shape as shown in FIG. 6 can be formed in the processed layer. But, as I already explained,
In this case, the exposure amount must be precisely controlled according to the characteristics of the resist, so that the apparatus becomes complicated and expensive, and it is difficult to draw a large area. In addition, if the shape formed on the processed layer deviates from the ideal shape, the shape of the processed layer is transferred in a similar manner, so that the shape of the manufactured optical element also deviates from the ideal shape, and the diffraction efficiency decreases. There are also problems.

The present invention has been made in view of the above problems, and an object thereof is to provide an optical element manufacturing method capable of easily manufacturing an optical element having an ideal shape with high diffraction efficiency and light collection efficiency. And

[0012]

In order to achieve the above object, a method of manufacturing an optical element according to the present invention comprises a step of forming a processing layer on a substrate and forming the processing layer into a shape having a desired depth distribution. Anisotropic etching is performed on the processing layer and the substrate to change the shape of the processing layer on the substrate while changing the selectivity of the processing step and the etching rate of the substrate and the processing layer. And a transfer step.

The processing of the processing layer is preferably mechanical processing in terms of processing accuracy.

The anisotropic etching is preferably performed using reactive gas plasma from the viewpoint of controlling the selection ratio.

[0015]

According to the present invention, as shown in FIG. 1A, a processing layer 2 is formed on a substrate 1, and the processing layer 2 is processed into a shape having a desired depth distribution, and then the selection ratio is changed. While anisotropically etching the processing layer 2 and the substrate 1, the shape of the processing layer 2 is changed and transferred to the substrate 1 as shown in FIG. 1D. Here, the selection ratio is defined as follows.

[Equation 1]

When the selection ratio is gradually reduced, for example, 1
From 3 to 0.6 and 0.2 in 3 steps, the shape of the processed layer 2 is transferred to the substrate 1 as shown in FIG. 1D through FIGS. 1B and 1C. Here, for simplicity, the etching rate of the processed layer 2 is kept constant, and
The etching time is made equal at each selection ratio. As described above, when anisotropic etching is performed by changing the selection ratio, the shape of the substrate 1 changes to the shape of the processed layer 2.

Further, when the processing layer is processed by machining, it can be processed by a numerical control processing machine based on the processing data of the optical element to be manufactured. here,
Since the numerical control processing machine of recent years has a processing accuracy of submicron, it is possible to obtain a desired shape with extremely high accuracy.

When the anisotropic etching is an etching using a reactive gas plasma, the etching gas in the plasma or the molecules formed by the dissociation of the etching gas and the surface of the processing layer 2 or the substrate 1 are formed. The chemical reaction occurs, the reaction product is released from the surface, and the processed layer 2 and the substrate 1 are etched. This phenomenon in the reactive gas plasma is caused by changes in various conditions such as the composition of the discharge gas, the discharge power density, the discharge gas pressure, the frequency of the applied voltage, the flow rate of the discharge gas, the electrode temperature and the gas temperature. Since it is sensitive to the changes, the desired selection ratio can be obtained by changing the conditions.

[0019]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 2 is a diagram for explaining a sequential process according to the first embodiment of the present invention. This example is
In order to manufacture a transmission type diffractive optical element having a function of a convex lens, as shown in FIG. 2A, first, as shown in FIG. 2A, a processing layer 2 having a predetermined thickness t is formed on one surface of a substrate 1 transparent to light having a predetermined wavelength range.
Formed. Here, the predetermined wavelength range is a wavelength range when the manufactured optical element is used, and transparent means that a required transmittance is sufficiently obtained in the wavelength range. In addition, the value of the thickness t is as shown in FIG.
In the machining shown in C, even if there is some error in the movement of the cutting tool 3, it is made larger than the maximum processing depth d in order to prevent the cutting tool 3 from coming into contact with the substrate 1.

Next, as shown in FIG. 2B or FIG. 2C, machining is performed to form a shape having a desired depth distribution in the processed layer 2 as shown in FIG. 2D. After that, while changing the selection ratio as shown in FIG. 2E, in this case, the anisotropic etching process is performed while gradually decreasing the selection ratio, thereby changing the shape of the processing layer 2 and transferring it to the substrate 1. Then, an optical element as shown in FIG. 2F is obtained.

FIG. 3 is a diagram for explaining the steps of the main part of the second embodiment of the present invention, in which a transmission type diffractive optical element having the function of a concave lens is manufactured. Therefore, in this embodiment, the processing layer 2 formed on the substrate 1 in FIG. 2A is machined into a shape as shown in FIG. 3A. After that, by performing an etching process while gradually increasing the selection ratio, the shape of the processed layer 2 is changed and transferred to the substrate 1 to obtain an optical element as shown in FIG. 3B.

FIG. 4 is a diagram for explaining the steps of the main part of the third embodiment of the present invention, which is for manufacturing a transmission diffraction grating blaze into two wavelengths. Therefore, in this embodiment, the processing layer 2 formed on the substrate 1 in FIG.
Are processed into the shape of the blazed diffraction grating as shown in FIG. 4A. Then, the selection ratio is changed in two steps, for example, etching is initially performed with a large selection ratio, and etching is performed with a small selection ratio in the middle to obtain a diffraction grating having a shape as shown in FIG. 4B.

According to each of the above-mentioned embodiments, the processing layer 2 is formed on the substrate 1, the processing layer 2 is machined into a desired shape, and then anisotropic etching is performed while changing the selection ratio.
Since the shape of the processed layer 2 is changed and transferred to the substrate 1, it is possible to easily manufacture an optical element having an ideal shape and high diffraction efficiency. Further, since the processing layer 2 is cut, it can be easily manufactured regardless of the workability of the material of the diffraction grating, and when the processing layer 2 is processed by the bite, it may be line cutting instead of point cutting. Therefore, it is also preferable in terms of surface roughness during processing. Furthermore, in the third embodiment, since the shape of the blazed diffraction grating shown in FIG. 4A can be formed by one cutting process using one type of cutting tool, a desired diffraction grating can be manufactured easily and highly accurately. can do.

Next, each step in each of the above embodiments will be described in more detail. First, the processing layer 2 is formed on the substrate 1.
The process of forming the will be described. As the material of the substrate 1, a material having a necessary and sufficient transmittance in the wavelength range of light used when used as an optical element is used. For example, when it is used in the ultraviolet region, quartz, synthetic quartz, SiO ₂ glass, LiF, MgF ₂ , CaF ₂ , BaF ₂ , sapphire, KBr, KI, etc. can be used. From the viewpoint of environmental resistance, it is preferable to use synthetic quartz, SiO ₂ glass, or CaF ₂ .

As the material of the processing layer 2, a material that is easier to machine than the substrate 1 can be used, for example, a resin or a metal that can be easily machined. Examples of metals that can be easily machined include A1 and P-Ni (electroless nickel). This processed layer 2 is made of resin,
It can be formed using a spin coater or the like, and by selecting the baking conditions at that time, the hardness can be made suitable for the subsequent steps. When the processed layer 2 is made of metal, it can be formed by vacuum vapor deposition, sputtering, plating or the like.

Next, the process of machining the processed layer 2 into a shape having a desired depth distribution, for example, a blaze shape will be described. In the first and second embodiments, when manufacturing a diffractive lens having a ring pattern, for example, as shown in FIG. 2B, a cutting machine, for example, a numerically controlled lathe machine (not shown) The substrate 1 on which the processed layer 2 is formed is attached as. Then, while rotating the workpiece, the cutting tool 3 is moved based on the design data of the lens to be manufactured, and the processing layer 2 is cut into a desired shape.
In this way, by processing only the processing layer 2 without directly processing the substrate 1, it is possible to perform cutting processing easily and at high speed regardless of the workability of the substrate 1.

In the first and third embodiments, when manufacturing an optical element having a linear pattern, for example, a diffractive cylindrical lens or a diffraction grating blazed to two wavelengths, a cutting machine, for example, a numerical control milling machine type. Using a processing machine, a ruling engine type processing machine, etc., for example, as shown in FIG. 2C, the tool 3 is fixed and the work is moved vertically and horizontally, or the work is fixed and the tool 3 is moved vertically and horizontally. The processing layer 2 is cut into a desired shape. Also in this case, since only the processing layer 2 is processed without directly processing the substrate 1, regardless of the workability of the substrate 1,
Can be cut easily and at high speed.

By cutting the working layer 2 in this manner, a shape having a desired depth distribution can be easily obtained. Further, recent numerical control processing machines have a processing accuracy of submicron, and can obtain a desired shape with extremely high accuracy. Furthermore, by changing the processing data, it is possible to easily obtain shapes corresponding to optical elements of various shapes, such as Fresnel lenses and diffraction gratings having a condensing function, without being limited to the above example. Also, for example,
Since the lathe type processing machine, the milling machine type processing machine, and the ruling engine type processing machine are versatile and the same processing machine can be used for various purposes, the cost for manufacturing the optical element can be suppressed.

Next, a process of anisotropically etching the shape formed on the processed layer 2 while changing the selection ratio and transferring it to the substrate 1 will be described. As the anisotropic etching, for example, etching using reactive gas plasma is suitable in terms of controllability of selection ratio and anisotropy. As the reactive gas plasma, for example, reactive ion etching, plasma etching, reactive ion beam etching, ion beam milling, sputter etching,
There are microwave plasma etching and the like.

In this transfer step, etching is performed with an etching gas 4 as shown in FIG. 2E, for example, while changing the etching selection ratio between the substrate 1 and the processed layer 2 based on the design data of the optical element. Here, when manufacturing a diffractive lens having a function of a convex lens as in the first embodiment, the processing layer 2 is processed into a blaze shape as shown in FIG. 2D, and an etching treatment is performed while reducing the selection ratio. To do. Note that, in FIG. 1, for simplification, the processing layer 2 in which the hypotenuse portion is processed into a linear shape is transferred to a shape having two bent portions, but it is possible to continuously change the selection ratio. Thereby, as shown in FIG. 2F, the hypotenuse part can be formed into a curved shape.

When manufacturing a diffractive lens having the function of a concave lens as in the second embodiment, the processing layer 2 is processed into a blaze shape as shown in FIG. 3A, and etching is performed while increasing the selection ratio. do. In this way, the shape of the processed layer 2 is transferred to the substrate 1 while changing its shape, so that an optical element as shown in FIG. 3B can be obtained. Further, in the case of manufacturing a blazed diffraction grating with two wavelengths as in the third embodiment, the processing layer 2 is processed into a blazed shape as shown in FIG. 4A, and the selection ratio is large at the beginning, for example. By performing etching in two steps so as to reduce the size in the middle, a diffraction grating as shown in FIG. 4B can be obtained.

As described above, by etching while changing the selection ratio, the blazed shape formed on the processed layer 2 can be transferred to an ideal shape as shown in FIG. 2F, FIG. 3B or FIG. 4B. A diffractive optical element having high diffraction efficiency can be easily manufactured. Further, by changing the method of changing the selection ratio, it is possible to manufacture optical elements having different shapes even if the shapes formed on the processed layer 2 are the same. For example, even when the shape as shown in FIG. 4A is formed on the processed layer 2, if the selection ratio is changed in two steps, an optical element having the shape as shown in FIG. 4B can be manufactured, and the selection ratio is continuous. In other words, it is possible to manufacture an optical element having a shape as shown in FIG. 4C.

Although the case of manufacturing the transmissive diffractive optical element has been described above, the present invention can be effectively applied to the case of manufacturing a reflective diffractive optical element. In this case, the substrate 1 need not be transparent.

In each of the above embodiments, the working layer 2 is machined by a cutting machine, but the working layer 2 can also be formed by pressing a die having a desired shape, such as a die. Can be formed into a desired shape. On this occasion,
Since the desired shape can be formed simply by pressing the mold, the desired shape can be obtained easily and quickly, and mass production becomes possible. In addition, a desired shape can be obtained with good accuracy and reproducibility of the mold.

The processed layer 2 may be formed into a desired shape by exposure and development. In this case, the processing layer 2
Is formed of a photosensitive material such as photoresist.
The processing layer 2 can be formed by using a spin coater or the like as in the case where the processing layer 2 is made of resin. It is difficult to form the processed layer 2 into an ideal shape only by exposure and development from the viewpoints of controlling the exposure amount and characteristics of the photosensitive material. However, since it is possible to form an approximate shape by exposure and development, it is possible to correct the shape of the processed layer 2 by etching the processed layer 2 formed in an approximate shape while changing the selection ratio. The substrate 1 can have a desired ideal shape. In this case, if the shape to be formed on the processed layer 2 is, for example, a blazed shape, exposure and development will be easier, so that an optical element having an ideal shape can be manufactured more easily. In addition, by changing the data for exposure, various shapes can be easily formed, and thus optical elements having various shapes can be easily manufactured as in the case of machining.

Here, the processed layer 2 is exposed and developed.
There are various methods of forming the processed layer 2 into a desired shape. For example, the processed layer 2 can be formed into a desired shape by irradiating the processed layer 2 with exposure light through a transmittance modulation type photomask. In this case, the processed layer 2 can be formed into a desired shape by one exposure, so that the predetermined shape can be quickly obtained with the accuracy of the photomask, and mass production becomes possible. Further, by changing the photomask used, the processing layer 2 can be processed into various shapes, and optical elements with various shapes can be easily manufactured.

The working layer 2 can also be irradiated by irradiating the working layer 2 while modulating the dose of the laser beam or the electron beam.
Can be formed into a desired shape. In this case, by changing the dose control or scanning data, the processing layer 2
Can be easily formed into various shapes, and optical elements with various shapes can be easily manufactured.

Further, it is possible to form the processed layer 2 into a desired shape by using the two-beam interference exposure. In this case, for example, when the processing layer 2 is processed into a sinusoidal shape,
It is also possible to form the shape of the lenticular lens on the substrate 1 by increasing the selection ratio at the beginning and performing etching while gradually decreasing it to change the shape of the processing layer 2 and transfer it to the substrate 1. . Lenticular lenses of various shapes can be obtained by changing the control data and dose of the two light fluxes. In addition to the shape of the lenticular lens, various shapes can be obtained by changing the method of changing the selection ratio.

Next, a method for changing the anisotropic etching selection ratio in each of the above-described embodiments and modifications will be described in detail. In the case of reactive ion etching, for example, the above selection ratio can be changed by changing the composition of gas in plasma, discharge power density, pressure of discharge gas, frequency of applied voltage, and the like.

For example, when the composition of the gas in the plasma is changed, the types and proportions of the reactive species and neutral species, the energy of the ions, etc. are changed, and the reaction on the surface and the speed thereof are changed. Further, since the degree of etching is changed physically or chemically, it is possible to change the selection ratio.
This phenomenon is common not only to reactive ion etching but also to plasma, and in etching using plasma, the selection ratio can be similarly changed.

According to this method, the selection ratio can be changed relatively large, and the gas flow rate can be precisely controlled by a mass flow controller or the like, so that the selection ratio can be precisely controlled. For example, when the working layer is resist, the resist is an organic material, since it is removed by oxidation by O _2, be added to the O ₂ gas as an etching gas, the etching rate of the resist is increased,
The selection ratio changes. When H ₂ gas is added to the etching gas, a polymer film is formed on the surface, the etching rate changes, and the selection ratio changes. The present inventors have confirmed by experiments that in reactive ion etching, the selection ratio can be changed by adding O ₂ gas to CF ₄ gas and changing the addition amount.

Further, when the discharge power density is changed, the types and densities, energies, etc. of the reactive species and neutral species are changed, and the energy of the ions is also changed. Therefore, the selection ratio is changed as in the case of changing the gas composition. Can be changed. This phenomenon also
This is common not only to reactive ion etching but also to plasma, and it is possible to change the selection ratio similarly in etching using plasma.

In the case of this discharge power density, the selection ratio can be delicately changed, so that it is particularly effective when the selection ratio is slightly changed. The present inventors have also confirmed by experiments that in reactive ion etching, the selection ratio can be changed by changing the discharge power density.

When the pressure of the discharge gas or the frequency of the applied voltage is changed, the energy of ions and the average energy of electrons are changed, so that the selection ratio can be changed in the same manner as in the above case. This phenomenon is common to etching in which an ion assist reaction occurs, and the selection ratio can be changed by plasma etching, reactive ion beam etching, microwave plasma etching, ion beam milling, etc., in addition to reactive ion etching.

On the other hand, as the etching gas to be used, for example, in the case of quartz glass used in the visible region or the ultraviolet region, a fluorine-based gas such as CF ₄ gas or CHF ₃ gas can be used. Further, for example, in the case of Si used in the infrared region, a fluorine-based gas such as CF ₄ gas, SF ₆ gas, NF ₃ gas or a chlorine-based gas such as Cl ₂ gas or CCl ₄ gas should be used. You can

By using the above method, the selection ratio can be easily changed. Particularly, by using the method of controlling the composition of the gas in the plasma and the discharge power density, the selection ratio can be changed over a wide range with high accuracy. be able to.

[0047]

As described above, according to the present invention, a processing layer is formed on a substrate, the processing layer is processed into a desired shape, and then anisotropically etched while changing the selection ratio. Since the shape is transferred to the substrate, the shape of the processed layer can be deformed and transferred to the substrate. Therefore,
Even if the processing layer is formed with a shape that is easy to process, for example, a blazed shape, the substrate can be formed into a desired shape, and an optical element having high diffraction efficiency and light collection efficiency can be easily manufactured.

Further, by changing the processing method, the processing data, and the method of changing the selection ratio, optical elements of various shapes can be easily manufactured. Furthermore, since the substrate is not directly processed, the optical element can be easily manufactured regardless of the workability of the substrate, and various materials can be used as the material of the optical element.

Further, the machining of the machining layer makes it possible to easily manufacture a high-performance optical element with high precision. Further, the optical element can be manufactured at a higher speed than in the case of using dose modulation exposure or the like. Further, since the processing device has versatility, the optical element can be manufactured at low cost.

Further, the anisotropic etching is performed by using a reactive gas plasma, so that the selective ratio can be changed according to various parameters such as the composition of the discharge gas, the discharge power density, the pressure of the discharge gas and the frequency of the applied voltage. Can be changed, and the degree of freedom in changing the selection ratio can be increased.

[Brief description of drawings]

FIG. 1 is a diagram for explaining the operation of the present invention.

FIG. 2 is a diagram for explaining a sequential process of the first embodiment of the present invention.

FIG. 3 is likewise a view for explaining the process of the main part of the second embodiment.

FIG. 4 is also a diagram for explaining the process of the main part of the third embodiment.

FIG. 5 is a diagram for explaining a conventional technique.

FIG. 6 is likewise a diagram for explaining a conventional technique.

[Explanation of symbols]

 1 substrate 2 processing layer 3 bytes 4 etching gas

Claims (3)

[Claims] 1. A step of forming a processed layer on a substrate, and a step of processing the processed layer into a shape having a desired depth distribution,
A step of anisotropically etching the processing layer and the substrate while changing the selection ratio represented by the etching rate ratio of the substrate and the processing layer, and changing and transferring the shape of the processing layer to the substrate; A method for manufacturing an optical element, comprising: 2. The method of manufacturing an optical element according to claim 1, wherein the processing of the processing layer is mechanical processing. 3. The method of manufacturing an optical element according to claim 1, wherein the anisotropic etching is etching using a reactive gas plasma.