JP2674079B2 - Original plate for mold making and optical characteristic measuring method using the original plate for mold making - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a mold making original plate used for forming an optical element such as a lens or an optical low pass filter with a transparent resin substrate. The present invention also relates to a method for measuring optical characteristics using this original plate for mold making.

[Summary of the Invention]

This invention is within the tolerance by forming a mold making original plate for forming a transparent resin substrate having a predetermined optical characteristic by using a transparent substrate capable of measuring optical characteristics. It is easy to select the mold.

Further, the present invention is an optical measuring method for a transparent resin substrate having predetermined optical characteristics, wherein a mold making original plate for forming the transparent substrate is molded with a transparent substrate having optical characteristics which can be used for making a mold. By measuring the optical characteristics of the original plate, it is possible to evaluate the optical characteristics of the transparent resin substrate after molding, making it easy to select molds that are within the allowable error and shortening the product development period. It was done.

Further, according to the present invention, it is possible to shorten the product development period by attaching the mold making original plate to the image pickup device and evaluating the optical characteristics.

[Conventional technology]

An optical low-pass filter is arranged in the optical system of the video camera to remove the pseudo color signal. In order to improve the productivity and reduce the cost, it is desired to mold an element used in an optical system of a video camera, such as an optical low pass filter, with a transparent resin.

In order to mold a precision optical element such as an optical low-pass filter with a resin, a mold for this resin molding must be made with high accuracy. There is a plating transfer method as a mold manufacturing method used when resin-molding an element which requires precision as described above.

The plating transfer method is, for example, as disclosed in Japanese Patent Laid-Open No. 61-221391, a method in which a mold making original plate is first formed and a mold is made from this mold making original plate by plating transfer. Is.

That is, in the plating transfer method, a mold is created through the following steps.

B. First, a mold making master plate is formed. This mold making master plate has the same shape as the element to be molded. As the original plate for forming a mold, one having a precision pattern formed on a silicon wafer is used.

B. A metal film for forming electrodes is formed on the surface of the original plate for mold making.

C. Metal is plated on the original plate for mold making on which the metal film is formed.

D, the plated metal is peeled off from the mold making original plate. On the plated metal, the shape corresponding to the original plate for mold making is transferred.

The outer shape of the peeled metal plating is processed to form a mold.

[Problems to be solved by the invention]

Precision optical elements such as optical low-pass filters,
Since light with a short wavelength is processed, the precision required for the mold is very high, for example, a high precision of about 100 to 200Å is required.

When a die is produced by the plating transfer method, as described above, first, a die making original plate having the same shape as the element to be formed is made. Therefore, in order to create a mold for molding a precision optical element such as an optical low-pass filter by a plating transfer method, this mold making original plate is
It must be created with a high accuracy of 100 to 200Å.

However, it is difficult to manufacture a mold making original plate with such high accuracy. Therefore, when a metal mold for molding a precision optical element such as an optical low-pass filter is formed by the plating transfer method, a large number of metal molds can be formed and an element having a desired characteristic can be formed from them. It is necessary to select molds.

When making a mold for molding precision optical elements such as optical low-pass filters by the conventional plating transfer method, from the many molds that have been created, mold the element that gives the desired characteristics. It is difficult to select molds that can be made.

That is, it is conceivable to measure the shape and size of the mold in order to select a mold capable of forming an element having desired characteristics from among a large number of created molds. However, the accuracy required for the mold is high, for example, about 100 to 200Å, and it is difficult to measure the mold with such high accuracy.

Therefore, when making a mold for molding precision optical elements such as an optical low-pass filter by the conventional plating transfer method, a mold is actually made from a large number of mold making original plates made. Then, it is necessary to resin mold an element from this created mold, test the optical characteristics using the resin molded element, and select a mold that can form an element with desired characteristics. I won't.

As described above, in order to create a mold from the mold making original plate by the plating transfer method, formation of a metal film, metal plating,
It is necessary to go through a number of processing steps such as peeling the plated metal from the original plate for mold making, external processing and the like. Further, in order to inspect the optical characteristics, the element must be resin-molded by using this completed mold.

Therefore, an object of the present invention is to provide a master plate for mold making that can easily select a mold capable of forming an element having desired characteristics.

Another object of the present invention is to provide an optical characteristic measuring method capable of evaluating the characteristics of an element produced using this mold making original plate at the stage of the mold making original plate.

Further, when developing an optical element such as an optical low-pass filter, it is necessary to repeat design, trial manufacture, and evaluation several times. That is, the optical characteristics of an optical element such as an optical low-pass filter should be evaluated by mounting a designed element on a trial basis and mounting it on an actual product to determine whether or not desired characteristics can be obtained from the prototyped element. I don't know.

As described above, in the conventional die transfer method using the plating transfer method, the die cannot be created without going through a large number of steps. Therefore, the designed element cannot be easily prototyped. Therefore, there is a problem that the development time is long.

Therefore, still another object of the present invention is to provide an optical characteristic measuring method which can reduce labor for developing an optical element and shorten development time.

[Means for solving the problem]

The present invention is a mold making original plate for forming a transparent resin substrate having predetermined optical characteristics, characterized in that the original plate is made of a transparent substrate capable of measuring optical characteristics. .

In addition, the present invention provides an optical measuring method for a transparent resin substrate having predetermined optical characteristics, in which a mold making original plate for forming the transparent substrate is molded with a transparent substrate capable of measuring optical characteristics to make a mold. This is a method for measuring the optical characteristics of a transparent resin substrate, in which the optical characteristics of the transparent resin substrate are evaluated by measuring the optical characteristics of the original plate.

This characteristic evaluation is performed by mounting the mold making master plate on the imaging device.

[Action]

A mold making original plate is molded from a transparent resin substrate. Therefore, the optical characteristics of the resin molded product can be evaluated at the stage of the mold making original plate, and the molds within the tolerance can be easily selected from the plurality of molds at the stage of the mold making original plate. In addition, the original plate for mold making can be attached to the image pickup device in the same manner as an actual product to evaluate the optical characteristics, and the product development can be shortened.

〔Example〕

Embodiments of the present invention will be described in the following order.

Optical low-pass filter configuration b. Mold making master plate c. Mold making method d. Mold making master plate selection e. Application examples a. Optical low-pass filter structure For example, it can be applied in the case of making a mold for molding an element of an optical system of a video camera such as an optical low pass filter. The optical low pass filter is
It is provided in order to prevent the black-and-white subject image from being colored.

FIG. 1 is an example of a phase noise type optical low pass filter. An example of molding such an optical low-pass filter with resin will be described. The diameter φ of this optical low-pass filter is, for example, 20 mm, and the thickness t _base is, for example, 1 mm. In this phase noise type optical low-pass filter, a plurality of stripe-shaped patterns P _t having a pitch p, a width a and a height _t are formed, as shown in the enlarged cross section of FIG. The pitch p is, for example, 0.657 mm, the width a is, for example, 0.225 mm, and the height t is, for example, 3200Å. This phase noise type optical low-pass filter has MTF (Modulation
Transfer Function) is expressed as follows.

When 0 ≦ r ≦ r _c r _c = a / λR, When r _c ≦ r ≦ 2r _c , When 2r _c ≤r≤3r _c , r: spatial frequency R: distance from pupil plane to image plane λ: wavelength of light n: refractive index of material p: pitch of pattern a: width of pattern t: height of pattern.

As can be seen from the above equation, the optical characteristics of this phase noise type optical low-pass filter are determined by the shape of the pattern P _t and its refractive index.

b. Method for making a master plate for making a mold About an example for making a master plate for making a mold when making a mold for resin molding a phase noise type optical low-pass filter as shown in FIG. explain.

In the first embodiment, a mold making original plate 21 for resin-molding such a phase noise type optical low-pass filter is used.
Is created through the following steps.

In the first embodiment, transparent glass (for example, BK7) is used as a substrate for forming the mold making master plate 21.
As shown in FIG. 3, the mask 2 is mounted on the transparent glass substrate 1. A pattern corresponding to the striped pattern P _t shown in FIG. 2 is formed on the mask 2.

In this way, with the mask 2 mounted on the transparent glass substrate 1, the transparent deposition material 3 is vacuum deposited. As the transparent vapor deposition material, for example, MgF ₂ or SiO ₂ can be used. The refractive index of MgF ₂ is (n = 1.38), SiO ₂
Has a refractive index of (n = 1.46).

By this transparent deposition material 3 is deposited on the transparent glass substrate 1, as shown in FIG. 4, Patanpu P _t of the stripe pattern P _t the same shape 'is formed on a transparent glass substrate 1 It

In the second embodiment, a mold making original plate 21 for resin-molding such a phase noise type optical low-pass filter is used.
Is created through the following steps.

In the second embodiment, transparent glass (for example, FK5) is used as a substrate for forming the mold making master plate 21.
As shown in FIG. 5, a mask 12 is mounted on this transparent glass substrate 11. A pattern corresponding to the stripe-shaped pattern P _t shown in FIG. 2 is formed on the mask 12. The refractive index of the glass of FK5 is (n = 1.49).

In this way, the transparent glass substrate 11 is etched with the mask 12 mounted on the transparent glass substrate 11. As a result, the portion without the mask 12 is removed, and as shown in FIG. 6, a striped pattern is formed on the transparent glass substrate 11.
P _t the same shape of the pattern P _t 'is formed.

c. Mold making method From the mold making original plate 21 made as described above,
A mold is created as follows.

As shown in FIG. 7, a metal film 22 made of a metal having a good mold releasability (for example, MoSi ₂ + Mo) is used as an electrode on the original plate 21 for making a mold prepared as described above as an electrode. To be done. The metal film 22 is a very thin film.
The original plate 21 for mold making has the same shape as the resin molded product 25 of the optical low-pass filter to be molded.

A master plate 21 for forming a mold, on which a metal film 22 is sputtered
Then, as shown in FIG. 8, a die metal 23 is plated. Nickel, for example, is used as the die metal 23 to be plated.

The plated metal 23 for the mold is separated from the master plate 21 for mold making.

By adjusting the outer shape of the metal 23 for the metal transferred by plating, the metal mold 24 is formed as shown in FIG.

By using this mold 24, a resin molded product 25 of an optical low pass filter is molded. The resin material used when molding the phase noise type optical low-pass filter is, for example, PMMA (polymethylmethacrylate),
The refractive index n of this material is 1.49.

d. Selection of Mold Making Master Plate As described above, in this embodiment, the mold making master plate 21 for forming the mold 24 for forming the resin molded product 25 is formed of a transparent element. That is, in the first embodiment shown in FIGS. 3 and 4, a stripe-shaped pattern P is formed on the transparent glass substrate 1 made of, for example, BK7 glass by a transparent vapor deposition material made of, for example, MgF ₂ or SiO _{2. A} master plate 21 for forming a mold is formed by forming _t ′. In the second embodiment shown in FIGS. 5 and 6, for example, a die forming substrate 21 is formed by forming a stripe pattern P _t ′ on a transparent glass substrate 11 made of FK5 glass by etching. To be done.

As described above, when the mold making substrate 21 formed of the transparent element is used, the optical element is resin-molded with the mold 24 made from the mold making original plate 21 in the state of the mold making substrate 21. At this time, it can be judged whether or not desired characteristics can be obtained from the resin molded product 25. Therefore, the molds 24 can be selected in the state of the mold making original plate 21, and the molds 24 having desired optical characteristics can be easily selected.

This will be described. As shown in the above equations to equations, the characteristics of the optical system are determined by the shape and the refractive index. When forming an optical low-pass filter as shown in FIG. 1, the optical characteristics are determined by the shape and refractive index of the stripe-shaped pattern P _t , as shown in equations (1) to (3). From becoming the same shape as the mold create master plate 21 and the resin molded product 25, and the refractive index of the pattern P _t 'that is formed in the mold create original plate 21, the pattern of the resin molded product 25 after molding P _t If the refractive index of
The optical characteristics of 21 and the resin molded product 25 molded from the mold 24 made from the mold making base plate 21 have the same optical characteristics.

In the first embodiment, MgF ₂ or SiO ₂ is vapor-deposited to form the pattern P _t ′. The refractive index of MgF ₂ (n = 1.38) is
It is different from the refractive index (n = 1.49) of PMMA resin. SiO ₂
Refractive index (n = 1.46) of PMMA resin (n = 1.46)
It is close to 9) but does not match exactly. Therefore, in this case, the shape of the mold making base plate 21 is the same as that of the formed resin molded product 25, but since the refractive index is different, the mold making base plate 21 is directly manufactured from the optical characteristics. The optical characteristics of the resin molded product 25 molded from the mold 24 made from the original plate 21 cannot be obtained.

However, in such a case, by performing an appropriate correction, from the optical characteristics of the mold making master plate 21, a resin molded product 25 molded from the mold 24 made from this mold making master plate 21. The optical characteristics of can be predicted.

This will be described. For example, it is assumed that the optical characteristic desired to be obtained from the resin molded product 25 to be molded is the characteristic indicated by the solid line k ₂ in FIG. 10, and the optical characteristic in the range indicated by the solid lines k _{1 to} k ₃ is allowed. In FIG. 8, the horizontal axis represents the spatial frequency and the vertical axis represents the MTF.

When the master plate 21 for mold making is produced, a problematic error occurs in the pattern height t, and the pattern pitch p and the pattern width a do not cause a problematic error. From this, assuming that the pattern pitch p and the pattern width a can be formed into a predetermined size,
From the formulas to formulas, it is determined whether the optical characteristics of the resin molded product 25 fall within the range indicated by the solid lines k _{1 to} k ₃ by the pattern P _{t of the} resin molded product 25.
Depends on the height of. That is, the pattern of the resin molded product 25
Of P _t the height t, tolerance t ₁ ± Δ (e.g. 3200 Å ± 200
Desired optical characteristics can be obtained by molding in Å).

The mold 24 capable of molding the height t of the pattern of the resin molded product within the tolerance t ₁ ± Δ can be selected as follows from the optical characteristics at the stage of the mold making original plate 21.

That is, the refractive index n (n = 1.49) of the material PMMA of the pattern P _t of the resin molded product 25 is set to the refractive index of MgF ₂ which is an example of the pattern P _t ′ of the mold making original plate 21 in the first embodiment. (N =
1.38), the height _{t of} the pattern P _t ′ is
When the optical characteristic MTF in the case of being within t ₁ ± Δ is calculated by the formulas-formulas, the properties shown by the one-dot chain lines l _{1 to} l ₃ in FIG. 10A are obtained. l ₁ is the pattern P _t ′ formed of MgF ₂ ,
The optical characteristic when the height _{t of the} pattern P _t ′ is (t = t ₁ + Δ), l ₂ is the optical characteristic when (t = t ₁ ), and l ₃ is (t = t ₁ −
It is the optical characteristic when Δ).

In addition, the refractive index n of the material PMMA of the pattern P _t of the resin molded product
Replacing (n = 1.49) with the refractive index (n = 1.46) of SiO ₂ which is the material of the pattern P _t ′ of the master plate 21 for mold making, the height of the pattern is within the allowable error t ₁ ± Δ. Optical characteristics MT
When F is calculated by the formulas-formulas, the characteristics shown by broken lines m _{1 to} m ₃ in FIG. 10B are obtained. m ₁ is 'in the case of forming the at SiO _2, the pattern P _t' pattern P _t height t of (t = t ₁ +
Δ) is an optical characteristic, m ₂ is an optical characteristic when (t = t ₁ ) and m ₃ is an optical characteristic when (t = t ₁ −Δ).

From this, the pattern P _t ′ of the mold making master plate 21 is changed to Mg
In the case of forming with F ₂ , when the optical characteristics of the original plate 21 for mold making are measured, if the optical characteristics are within the range of dashed-dotted lines l _{1 to} l ₃ in FIG. Master plate for mold making
Using the mold 24 made from 21, it is possible to obtain a resin molded product 25 having desired optical characteristics.

When the pattern P _t ′ of the mold making original plate 21 is formed of SiO ₂ , when the optical characteristics of the mold making original plate 21 are measured, the optical characteristics are shown by broken lines m ₁ to Within the range of m ₃ , it is possible to obtain a resin molded product 25 having desired optical characteristics by using the mold 25 made from the mold making substrate 21.

In the second embodiment, since the pattern P _t ′ can be formed with FK5 having a refractive index (n = 1.49) equal to that of PMMA resin, in this case, the optical characteristics of the master plate 21 for mold making are ,
The optical characteristics of the resin molded product 25 molded from the mold 24 made from the mold making base plate 21 are obtained. Therefore, in this case, if the optical characteristics of the mold making master plate 21 are evaluated,
The optical characteristics of the resin molded product 25 molded from the mold 24 made from the mold making original plate 21 can be directly evaluated.

e. Measurement of optical properties The pattern P _t ′ of the master plate 21 for mold making is Si having a refractive index (n = 1.46) close to that of PMMA resin (n = 1.49).
When formed by vapor deposition of O ₂ , or the refractive index of PMMA resin (n =
When a transparent glass substrate of FK5 having a refractive index (n = 1.49) equal to 1.49) is formed by etching, the optical characteristics of the master plate 21 for mold making are created from the master plate 21 for mold making. The optical characteristics of the resin molded product 25 molded from the mold 24 are almost the same. From this, for example, when arranging a resin molded product 25 of an optical low-pass filter in a video camera for commercialization, the resin molded product is processed at the stage of the master plate 21 for mold making.
25 optical characteristics can be evaluated. That is, the mold making original plate 21 corresponding to the designed optical low-pass filter is prototyped by the method as described above, and this mold making original plate 21 is attached to, for example, a video camera in the same manner as an actual product. Then, the optical characteristics of the mold making master plate 21 are measured. From the measurement results, the optical characteristics of the resin molded product 25 molded from the mold 24 made from the mold making original plate 21 are expected.

In this way, since the prototype can be evaluated at the stage of the mold making master plate 21, the product development time can be shortened.

e. Application example The present invention is not limited to the case where the optical low-pass filter is resin-molded, and the case where the optical element having a precision pattern such as the mat of the optical finder and the lenticular lens is resin-molded, or the lens is resin-molded. Can be similarly applied.

[Effect of the Invention] According to the present invention, the mold making original plate is molded from the transparent resin substrate. Therefore, by evaluating the optical characteristics of the mold making original plate, it is possible to easily select a mold having a tolerance within a plurality of molds at the stage of the mold making original plate. Further, according to the present invention, the optical characteristics of the actual resin molded product can be predicted by mounting the mold making original plate on the image pickup device in the same manner as the actual product and measuring the optical characteristics. Therefore, the optical element can be easily prototyped and the product development period can be shortened.

[Brief description of the drawings]

FIG. 1 is a plan view of an example of an optical low-pass filter and a side view thereof, FIG. 2 is an enlarged sectional view of an example of an optical low-pass filter, and FIGS. 3 and 4 show a first embodiment of the present invention. Sectional views used for the explanation, FIGS. 5 and 6 are sectional views used for explaining the second embodiment of the present invention, and FIGS. 7 to 8 are sectional views used for the explanation of die making, and FIG. Is a cross-sectional view used to explain the case of resin molding using a mold, and FIG. 10 is a characteristic diagram used to explain the evaluation of optical characteristics. Description of main symbols in the drawings 1, 11: transparent glass substrate, 2, 12: mask, 3: vapor deposition material, 21:
Master plate for mold making, 22: metal film, 24: mold, 25: resin molded product.

Claims (3)

(57) [Claims] 1. A mold making original plate for forming a transparent resin substrate having predetermined optical characteristics, wherein the mold making original plate is made of a transparent substrate capable of measuring optical characteristics. Master plate for mold making. 2. An optical measuring method for a transparent resin substrate having predetermined optical characteristics, wherein a mold making original plate for forming the transparent resin substrate is molded with a transparent substrate capable of measuring optical characteristics, By measuring the optical characteristics of the original plate for making,
A method for measuring optical characteristics of a transparent resin substrate, which is adapted to evaluate the optical characteristics of the transparent resin substrate. 3. The optical characteristic measuring method according to claim 2, wherein the mold making original plate is attached to an image pickup device to evaluate optical characteristics.