JPH08187791A - Production of optical element - Google Patents

Abstract

PURPOSE: To reduce the irregulality of difference in level due to the position within the plane of a substrate to the utmost and to make an element shape fine. CONSTITUTION: A stepped master layer 24 having two or more steps at least a part of which is composed of a non-photosensitive material 21 is formed on a substrate. The surface of the substrate 10 is processed into an undulated surface S corresponding to element function by anisotropic etching using the master layer as an etching mask.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a micro optical element such as a microlens or a microdiffraction grating, which is used as a device for a display device, a communication device, or a computer.

In the field of display devices, for example, as a simple optical element (optical functional element), a so-called binary optical element that approximates an ideally curved optical functional surface (such as the outer surface of a lens) with a staircase surface is used. Is widely used.

[0003]

2. Description of the Related Art As a method of manufacturing a microlens or a microlens array, there is a method of forming a lens prototype on a substrate and processing the substrate into a lens shape.

For example, a resist layer having a circular planar shape is formed on a substrate, which is heated to soften it and deformed into a hemispherical shape by utilizing the surface tension of the resist material, followed by ion milling or RIE (reaction). The substrate is ground using a hemispherical resist layer as a mask by using an anisotropic etching technique such as (ionic ion etching). As a result, the surface of the substrate is processed into an undulating surface (hemispherical surface) corresponding to the thickness of the resist layer.

In some cases, an electron beam exposure method is used to form a resist layer as a prototype. In that case, the exposure amount (beam intensity or drawing speed) is changed during beam scanning to adjust the exposure depth, and the thickness of the resist layer after development is smoothly changed.

According to these methods, it is possible to obtain an element having an ideal shape having a smooth curved surface. However, the method of forming a prototype by heating has a problem in reproducibility, and it is difficult to manufacture an element whose planar shape is not circular. The method using the electron beam exposure method requires a long time for exposure and is not suitable for practical use in terms of mass productivity.

On the other hand, conventionally, a binary optical element having a stepwise pseudo curved surface has been formed by a manufacturing method in which a series of lithographic steps are carried out for each stage of curved surface approximation.

That is, in the case of the conventional manufacturing method,
The number of exposure masks corresponding to the approximate number of steps is prepared in advance. First, the resist material is applied on the substrate that will be the base of the optical element, and pattern exposure is performed using the first exposure mask. The substrate is etched to a certain depth using the obtained resist layer as a mask, and the resist layer is once removed. Next, the resist material is applied again, pattern exposure is performed using the second exposure mask, the substrate is etched, and then the resist layer is removed. Then, after that, resist application, exposure, etching, and resist removal are repeated. At that time, use a different exposure mask each time,
The etching conditions (time or rate) are changed as necessary according to the order of use.

[0009]

In the conventional method for producing a binary optical element, since the etching target region of the substrate is exposed to perform the etching, the etching method, the etching apparatus, the position of the substrate arranged in the apparatus, and the like are etched. The variation in the etching rate in the surface of the substrate depending on the processing conditions (hereinafter referred to as in-plane distribution) directly appears as the variation in the step of each part of the optical element. For example, in RIE, the etching of the peripheral portion is usually faster than that of the central portion of the substrate, and the step of the peripheral portion is larger than that of the central portion. Therefore, there is a problem in that the optical characteristics differ depending on the part in the substrate.

Further, in the second and subsequent lithography, as the height difference of the substrate surface increases, the top and bottom of the resist layer coated on the substrate becomes more prominent. Therefore, there is also a problem that the exposure conditions become unstable, especially in a fine pattern close to the resolution limit of the exposure apparatus, and patterning defects easily occur. That is, it is difficult to miniaturize the optical element.

The present invention has been made in view of the above problems, and an object of the present invention is to minimize the variation in steps due to the position within the substrate surface and to miniaturize the element shape.

[0012]

As shown in FIG. 1, the manufacturing method of the invention of claim 1 forms a non-photosensitive material layer covering the surface of a substrate, and uses the photosensitive material to form the non-photosensitive material. By repeating the patterning for removing a part of the material layer, a stepwise prototype layer having two or more steps is formed on the substrate, and the substrate is formed by anisotropic etching using the prototype layer as an etching mask. This is a method of processing the surface layer of (1) into an undulating surface according to the device function.

According to a second aspect of the present invention, as the photosensitive material, a photoresist having a non-linear residual film rate characteristic is used. According to a third aspect of the present invention, in the manufacturing method of the present invention, a stepwise prototype layer having a non-photosensitive material layer and a photosensitive material layer and having two or more steps is formed on the substrate, and the prototype layer is used as an etching mask. This is a method of processing the surface layer surface of the substrate into an undulating surface according to the device function by anisotropic etching.

According to the manufacturing method of the invention of claim 4, a stepwise prototype layer having a step number of 3 or more, which comprises a non-photosensitive material layer and a photosensitive material layer having a step on the upper surface, is formed on a substrate. In this method, the surface layer surface of the substrate is processed into an undulating surface according to the device function by anisotropic etching using the prototype layer as an etching mask.

According to a fifth aspect of the present invention, a method of forming a photosensitive material layer having a step on its upper surface by performing multiple exposures of different patterns on a photoresist and then performing development processing. Is.

According to a sixth aspect of the present invention, there is provided a second optical system which is a duplicate of the optical element produced by producing a mold having a surface layer surface having the same shape as that of the undulating surface and molding the mold using the mold. A device is manufactured.

[0017]

When a plurality of layers of different materials are etched, even if there is a difference in the etching rate (etching rate) between the layers, the tendency of the in-plane distribution of the etching rate is almost the same regardless of the material of each layer. It is the same. That is, the ratio of the etching rates of the respective layers is substantially constant regardless of the position within the etching surface.

Therefore, by providing a prototype layer on the substrate, etching the substrate together with the prototype layer, and processing the substrate into an undulating surface that reflects the prototype layer, variations in steps due to the in-plane distribution of the etching rate are reduced. can do.

If the prototype layer is made of a non-photosensitive material, the prototype layer can be formed using a photoresist having a non-linear residual film rate characteristic. When the residual film rate characteristic is non-linear, a resist layer having a pattern faithful to the exposure mask can be obtained as compared with the case where the characteristic is linear, so that finer substrate processing can be performed.

On the other hand, if a part of the prototype layer is made of a photosensitive material, the photosensitive material can be subjected to pattern exposure to form a desired step, so that it is separately exposed for lithography. Since it is not necessary to apply a conductive material to provide an etching mask, the number of manufacturing steps of the prototype layer can be reduced.

When multiple exposure is performed on a photosensitive material that is a constituent member of the prototype layer, if a photoresist having a linear residual film rate characteristic is used as the photosensitive material, an exposure amount for obtaining a desired step difference is obtained. Control becomes easier.

[0022]

FIG. 1 is a diagram showing a first embodiment of the present invention.
In addition, in FIGS. 1A to 1H, the same reference numerals are attached to the constituent elements made of the same member except for a part, regardless of the processing state. The same applies to each figure described later.

In the example of FIG. 1, the method of the present invention is applied to the manufacture of the Fresnel type microlens 1 shown in FIG. The microlens 1 is a binary optical element having a pseudo curved surface S composed of four steps of contour surfaces.

In manufacturing the microlens 1, first, a chromium layer 21 that uniformly covers the surface of the silicon dioxide wafer 10 as a substrate is formed by vapor deposition. Then, photoresist coating, pattern exposure, development, and post-baking are sequentially performed to provide a resist layer 31 having a predetermined pattern on the chrome layer 21 [FIG. 1 (A)]. At this time,
A resist layer corresponding to a mark for later mask alignment is also provided at the same time.

For pattern exposure, a stepper that radiates ultraviolet rays (i-rays) is used, and therefore a reticle having a predetermined pattern is prepared in advance. As the photoresist, an i-line resist having a non-linear residual film rate characteristic is used.

Next, the chromium layer 21 is patterned by RIE using a Cl-based gas to remove the resist layer 31 [FIG. 1 (B)]. Then, the silicon dioxide wafer 10
Chromium is vapor-deposited on the surface of. As a result, a chromium layer 22 having undulations corresponding to the step between the patterned chromium layer 21 and the silicon dioxide wafer 10 is obtained [FIG.
(C)]. However, the thickness of chromium deposited at this time is larger than that of the lower chromium layer 21.

Then, a second resist layer 32 is provided on the chromium layer 22 using the same photoresist as before (FIG. 1D). Using the second resist layer 32 as a mask, a part of the chromium layer 22 is etched by a predetermined thickness [FIG. 1 (E)]. In the illustrated example, the silicon dioxide wafer 10
However, the silicon dioxide wafer 10 does not necessarily have to be exposed. By removing the second resist layer 32, a prototype layer 23 having a stepwise changing thickness is obtained [FIG. 1 (F)].

As is apparent from the above description, in the example of FIG. 1, the formation of the chromium layers 21 and 22 which are the non-photosensitive material layers and the patterning thereof are performed twice, and the exposure pattern is appropriately set at that time. By overlapping with each other, a three-step staircase-shaped prototype layer 23 is formed.

The lift-off method can be used for patterning one or both of the chromium layers 21, 22.
In that case, after providing the resist layer 31, the chromium layer 21
, The patterning of photoresist and the formation of layers are interchanged. However, chrome layer 2
After forming 1 and 22, some of them are still removed (patterned).

After forming the prototype layer 23 as described above, C
Using a mixed gas composed of an l-based component and a CF-based component, R
The silicon dioxide wafer 10 is etched by IE [FIG. 1 (G)]. Since the progress of etching is faster as the prototype layer 23 is thinner, the surface layer surface of the silicon dioxide wafer 10 is processed into an uneven surface reflecting the thickness of the prototype layer 23.

At the time when the surface layer surface of the silicon dioxide wafer 10 becomes an undulating surface corresponding to the desired lens function, the etching is finished to complete the microlens 1 [FIG. 1 (H)]. The etching rate can be easily adjusted by changing the mixing ratio of the etching gas. Therefore, if a preliminary experiment is performed to obtain the etching rate ratio between chromium and silicon dioxide and the thickness of each stage of the prototype layer 23 is appropriately set, the microlens 1 having a desired shape can be obtained. .

FIG. 2 is a diagram showing a second embodiment of the present invention. Note that, in FIG. 2, constituent elements corresponding to the example of FIG. 1 are denoted by the same reference numerals regardless of the shape or the material. The same applies to the following figures.

First, chromium is vapor-deposited on the surface of the silicon dioxide wafer 10 and a chromium layer 21 having a predetermined pattern is provided by a photolithography method [FIG. 2 (A)]. Then, a photoresist 33a is uniformly applied to the surface of the silicon dioxide wafer 10 including the chromium layer 21 [FIG. 2 (B)].

Next, pattern exposure is performed on the photoresist 33a by using the exposure mask M2 having a pattern different from that used for patterning the chromium layer 21 [FIG. 2 (C)].
Note that in order to prevent uneven exposure, chromium may be thinly vapor-deposited on the surface of the silicon dioxide wafer 10 prior to applying the photoresist 33a to make the reflectance uniform.

After the exposure, the photoresist 33a is developed and post-baked to obtain a prototype layer 24 composed of the chromium layer 21 and the resist layer (insolubilized photoresist) 33 [FIG. 2 (D)]. The prototype layer 24 has a two-step staircase shape. However, although the resist layer 33 in the prototype layer 24 has a flat upper surface, it has a portion that does not overlap the chromium layer 21, and the thickness thereof differs between the upper portion of the chromium layer 21 and other portions.

After that, the silicon dioxide wafer 10 is etched by RIE [FIG. 2 (E)]. As a result, since the thickness of the resist layer 33 of the prototype layer 24 is different as described above, by appropriately setting the etching rate ratio of each material, the microlens 2 having the four-step pseudo curved surface S can be obtained. It can be obtained [FIG. 2 (F)].

FIG. 3 is a diagram showing a third embodiment of the present invention. First, a chromium layer 21 having a predetermined pattern is provided on the silicon dioxide wafer 10 [FIG. 3 (A)]. Then, for example, a photoresist 34a having a linear residual film rate characteristic is uniformly applied to the surface of the silicon dioxide wafer 10 including the chromium layer 21. If the residual film rate characteristic is linear, it is easy to control the multiple exposure in the next step.

Next, the photoresist 34a is subjected to the first pattern exposure using the exposure mask M2 having a pattern different from that used when patterning the chromium layer 21, for example (FIG. 3B).

Subsequently, for example, the second pattern exposure is performed on the photoresist 34a by using the exposure mask M1 having the same pattern as the patterning of the chromium layer 21 [FIG. 3 (C)]. However, the exposure time of the second pattern exposure is shorter than the exposure time of the first time. The order of using the exposure masks M2 and M1 may be exchanged.

When the photoresist 34a is developed and post-baked after two exposures, a three-step prototype layer 25 including the chromium layer 21 and the resist layer 34 having a step on the upper surface is obtained [FIG. 3]. (D)].

After that, the silicon dioxide wafer 10 is etched by RIE [FIG. 3 (E)]. As a result, since the thickness of the resist layer 34 of the prototype layer 25 is different as described above, by appropriately setting the etching rate ratio of each material, the microlens 3 having the four-step pseudo curved surface S can be obtained. It can be obtained [FIG. 3 (F)].

FIG. 4 is a diagram showing a fourth embodiment of the present invention. The example of FIG. 4 is a modification of the pattern, and the manufacturing procedure is the same as the example of FIG. First, a chromium layer 21 having a predetermined pattern is provided on the silicon dioxide wafer 10 [FIG.
(A)]. Then, the photoresist 35a is uniformly applied to the surface of the silicon dioxide wafer 10 including the chromium layer 21.

Next, the photoresist 35a is subjected to the first pattern exposure using the exposure mask M3 [FIG.
(B)], and subsequently, a second pattern exposure is performed on the photoresist 35a using the exposure mask M4 [FIG.
(C)]. The exposure time for the second pattern exposure is shorter than the exposure time for the first exposure.

When the photoresist 35a is developed and post-baked, a three-step prototype layer 26 composed of the chromium layer 21 and the resist layer 35 having a step on the upper surface is obtained [FIG. 4 (D)].

Then, the silicon dioxide wafer 10 is etched by RIE [FIG. 4 (E)]. This gives 4
The microlens 4 having the stepped pseudo curved surface S can be obtained [FIG. 4 (F)].

On the surfaces of the microlenses 1 to 4 obtained by the above manufacturing method, a thin film of nickel or silver, for example, is provided, and nickel plating is further applied to the thin film to produce a mold of the pseudo curved surface S. be able to. Then, if resin molding is performed using the mold, it is possible to mass-produce resinous microlenses that are replicas of the microlenses 1 to 4.

According to the above-mentioned embodiment, by using the exposure masks M1 to 4 which are manufactured so that the translucent patterns partially overlap with each other, the number of masks (the number of partial exposures) n squared (n ² ). It is possible to form a pseudo curved surface S having
It is possible to efficiently manufacture the microlenses 1 to 4 having an ideal shape.

According to the embodiment shown in FIG. 1, since the prototype layer 23 is made of metal (chromium) which is a non-photosensitive material,
An optical element having a fine structure can be easily produced by using a photoresist having a non-linear residual film rate characteristic suitable for fine processing.

According to the embodiment shown in FIG. 2, since part of the prototype layer 24 is formed by using the photoresist 33a, compared with the case where the prototype layer 24 is formed by using only the non-photosensitive material, the optical element is formed. It is possible to reduce the number of manufacturing steps.

According to the embodiments of FIGS. 3 and 4, the prototype layers 25 and 2 are formed by multiple exposures with different patterns and different exposure times.
Since No. 6 is formed, the number of man-hours for manufacturing the optical element can be significantly reduced because the number of times of applying and developing the photoresist is reduced.

In the above-mentioned embodiment, if the etching conditions are selected so that the etching rate of the prototype layer is higher than the etching rate of the substrate, the step of the prototype layer may be made smaller than the step of the optical element. The patterning accuracy in forming the prototype layer can be improved.

In the above-mentioned embodiment, the shape of the optical element can be variously selected according to the application. For example, a Fresnel shape of third order or higher may be used. Further, the number of steps of the pseudo curved surface S is not limited to the illustrated value. The prototype layers 23 to 26 are made of titanium,
It can be formed using a material other than chromium, such as a metal such as tantalum or a semiconductor typified by silicon. Also,
The substrate material may be silicon.

[0053]

According to the inventions of claims 1 to 6,
It is possible to minimize the variation of the step due to the position on the substrate surface, and to miniaturize the element.

According to the invention of claim 2, a finer optical element can be manufactured. According to the invention of claim 3, the number of manufacturing steps can be reduced. According to the inventions of claims 4 and 5, the number of manufacturing steps can be significantly reduced.

[Brief description of drawings]

FIG. 1 is a diagram showing a first embodiment of the present invention.

FIG. 2 is a diagram showing a second embodiment of the present invention.

FIG. 3 is a diagram showing a third embodiment of the present invention.

FIG. 4 is a diagram showing a fourth embodiment of the present invention.

[Explanation of symbols]

 1-4 Microlens (optical element) 10 Silicon dioxide wafer (substrate) 21,22 Chrome layer (non-photosensitive material layer) 23-26 Prototype layer 31,32 Resist layer (photosensitive material) 33-35 Resist layer (photosensitive) Material layer) S Pseudo curved surface (relief surface)

Claims (6)

[Claims] 1. A step number is formed on the substrate by repeating formation of a non-photosensitive material layer covering the surface of the substrate and patterning for removing a part of the non-photosensitive material layer using a photosensitive material. Is formed into two or more stepwise prototype layers, and the surface layer surface of the substrate is processed into an undulating surface according to the element function by anisotropic etching using the prototype layer as an etching mask. Of manufacturing. 2. A photoresist having a non-linear residual film ratio characteristic is used as the photosensitive material.
A method for producing the optical element described. 3. A stepwise prototype layer having a step number of 2 or more consisting of a non-photosensitive material layer and a photosensitive material layer is formed on a substrate, and anisotropic etching is performed using the prototype layer as an etching mask. A method for manufacturing an optical element, characterized in that the surface layer of the substrate is processed into an undulating surface according to the element function. 4. A stepwise prototype layer having a step number of 3 or more, comprising a non-photosensitive material layer and a photosensitive material layer having a step on the upper surface, is formed on a substrate, and the prototype layer is used as an etching mask. 4. The method for producing an optical element according to claim 3, wherein the surface layer surface of the substrate is processed into an undulating surface according to the element function by anisotropic etching. 5. The photosensitive material layer having a step on the upper surface is formed by performing multiple exposure of different patterns on a photoresist and then performing a developing process. Method of manufacturing optical element of. 6. A mold having a surface layer surface having the same shape as the undulating surface is manufactured by using the optical element obtained by the method for manufacturing an optical element according to claim 1. A method for producing an optical element, comprising producing a second optical element that is a duplicate of the optical element by molding using the mold.