CN109061781B - Method for photoetching binary harmonic diffraction Alvarez lens zoom system - Google Patents

Method for photoetching binary harmonic diffraction Alvarez lens zoom system Download PDF

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CN109061781B
CN109061781B CN201810842349.8A CN201810842349A CN109061781B CN 109061781 B CN109061781 B CN 109061781B CN 201810842349 A CN201810842349 A CN 201810842349A CN 109061781 B CN109061781 B CN 109061781B
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alvarez lens
mask
photoetching
substrate
placing
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CN109061781A (en
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侯昌伦
李泾渭
辛青
臧月
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Hangzhou Dianzi University
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    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B3/00—Simple or compound lenses
    • G02B3/02—Simple or compound lenses with non-spherical faces
    • G02B3/08—Simple or compound lenses with non-spherical faces with discontinuous faces, e.g. Fresnel lens
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B15/00—Optical objectives with means for varying the magnification
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
    • G02B27/0012—Optical design, e.g. procedures, algorithms, optimisation routines
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B5/00—Optical elements other than lenses
    • G02B5/18—Diffraction gratings
    • G02B5/1814—Diffraction gratings structurally combined with one or more further optical elements, e.g. lenses, mirrors, prisms or other diffraction gratings
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
    • G03F7/00—Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
    • G03F7/20—Exposure; Apparatus therefor

Abstract

The invention relates to a method for photoetching a binary harmonic diffraction Alvarez lens zoom system, which comprises the steps of firstly determining the surface type of a harmonic diffraction Alvarez lens, then determining the position of a first-order mask and photoetching, and finally determining the position of a high-order mask and photoetching, wherein the original characteristics of an Alvarez lens group are kept, namely, a second Alvarez lens moves along the direction vertical to an optical axis relative to a first Alvarez lens, the focal length of the Alvarez lens group can be changed, and relative to a diffraction optical element, the binary harmonic diffraction Alvarez lens zoom system has the characteristics of high precision and high efficiency; the invention has simple processing technology and higher precision than the precision of the conventional optical processing.

Description

Method for photoetching binary harmonic diffraction Alvarez lens zoom system
Technical Field
The invention belongs to the technical field of optics, relates to a binary harmonic diffraction Alvarez lens group, and particularly relates to a method for photoetching a binary harmonic diffraction Alvarez lens zoom system.
Background
DOE (diffractive Optical element) is a diffractive Optical element, which is a new Optical element with rapid development and is a research hotspot in modern optics. This is the DOE, from amplitude-type hologram to phase-type hologram to Computer Generated Hologram (CGH) and blazed phase information optical elements. Such microstructured fringe-based diffractive elements have many advantages, but their diffraction efficiency is not high, typically not more than 70%, and process factors are not easily controlled (wet processing, reconstruction, etc.), which limits the use of holographic DOEs.
BOE (binary Optical element) is a binary Optical element, which can be regarded as a kinoform (kinofom) with quantified phase values, and the size of the surface microstructure is in the wavelength order, so that the diffraction element can be manufactured by a fine process method, and BOE with high precision and high efficiency can be obtained.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides a method for photoetching a binary harmonic diffraction Alvarez lens zoom system.
The invention discloses a method for photoetching a binary harmonic diffraction Alvarez lens zoom system, which specifically comprises the following steps of:
the method comprises the following steps: taking a cuboid glass plate;
step two: determining the surface type of the harmonic diffraction Alvarez lens; wherein the surface polynomial equation of the Alvarez lens is:
Figure GDA0001856020030000021
wherein A is expressed as a polynomial coefficient;
the harmonically diffractive Alvarez lens cuts the original Alvarez lens with a phase difference of 2m pi (m > -2) according to the surface shape of the Alvarez lens, so that the phase difference between adjacent ring bands of the harmonically diffractive Alvarez lens is 2m pi, and m > -2.
Step three: determining first order mask position
Dividing the harmonic diffraction Alvarez lens into an upper half area and a lower half area at the phase position of m pi of the harmonic diffraction Alvarez lens, and if the surface shape of the harmonic diffraction Alvarez lens is on the upper half area of the harmonic diffraction Alvarez lens, placing a mask at a position corresponding to a substrate; the position corresponding to the lower half area is not provided with a mask.
Step four: lithography
The substrate is scanned with a laser, which cuts a step on the unmasked substrate by the laser, while the masked substrate is not cut by the laser.
Step five: determining high order mask position and photolithography
When a second-order mask needs to be placed, the phase positions of (1/2) m pi and (3/2) m pi of the harmonically diffractive Alvarez lens are marked, the surface profile of the harmonically diffractive Alvarez lens is higher than that of a mask placed at the corresponding substrate position of (1/2) m pi, the mask is placed at the corresponding substrate position between m pi and (3/2) m pi, the mask is not placed at the rest positions, and photoetching is carried out, wherein the photoetching depth is 1/2 times of the first photoetching depth.
When a third order mask needs to be placed, the phases of (1/4) m pi, (3/4) m pi, (5/4) m pi and (7/4) m pi of the harmonic diffractive Alvarez lens are marked. When the surface topography of the harmonically diffractive Alvarez lens is higher than the corresponding substrate position at (1/4) m pi, the mask is placed at the corresponding substrate position between (1/2) m pi to (3/4) m pi, m pi to (5/4) m pi, and (3/2) m pi to (7/4) m pi. In the photolithography, the thickness of the photolithography is 1/3 times the depth of the first photolithography.
Placing the Nth order mask, the m pi 1/2 of harmonic diffraction Alvarez lensN-1，3mπ*1/2N-1…(2N-1)mπ*1/2N-1Is marked when the surface profile of the harmonic diffractive Alvarez lens is higher than (m pi x 1/2)N-1Placing a mask at corresponding substrate positions, and placing a mask at corresponding substrate positions between (1/2) m pi to (3/4) m pi, m pi to (5/4) m pi, (3/2) m pi to (7/4) m pi, and at corresponding substrate positions between m pi/2N-1To 3m pi 1/2N-1、…(2N-1-2)mπ*1/2N-1To (2)N-1-1)mπ*1/2N-1，(2N-2)mπ*1/2N-1To (2)N-1)mπ*1/2N-1Placing a mask at the corresponding position of the substrate; n is more than 3; and (4) no mask is placed at the rest positions, and photoetching is carried out, wherein the photoetching depth is 1/N of the first photoetching depth.
Has the advantages that: according to the photoetching binary harmonic diffraction Alvarez lens zoom system, the original characteristics of the Alvarez lens group are kept, namely the second Alvarez lens moves relative to the first Alvarez lens along the direction vertical to the optical axis, the focal length of the Alvarez lens group can be changed, and relative to a diffraction optical element, the binary harmonic diffraction Alvarez lens zoom system has the characteristics of high precision and high efficiency; the invention has simple processing technology and higher precision than the precision of the conventional optical processing.
Drawings
FIG. 1 is a schematic structural diagram of an Alvarez lens group provided by an embodiment;
FIGS. 2 and 3 are schematic diagrams of a binary harmonic diffractive Alvarez lens zoom system provided by the embodiment;
FIG. 4 is a schematic illustration of example provided mask placement locations;
Detailed Description
In order to more specifically describe the present invention, the following detailed description is provided for the technical solution of the present invention with reference to the accompanying drawings and the specific embodiments.
The invention discloses a binary harmonic diffraction Alvarez lens zoom system,
the diffraction form of the binary harmonic diffractive Alvarez lens zoom system can be expressed by aberration coefficients, and the polynomial has the following formula for any wave surface phi (x, y):
Figure GDA0001856020030000041
where λ is the wavelength of the incident light, anmAre aberration optimization coefficients. The aberration optimization coefficient a can be determined by taking the general polynomial to more than 10 th ordernmAnd obtaining a sufficiently accurate phase profile. When quantization is performed using a binary modulo function, then
N＝2m(3-2)
Where m is a binary quantization level, i.e., a binary Mask (Mask) number; n-number of quantization steps.
When m is 1, i.e. a quantization level, and the phase depth is pi, the manufactured optical element is called DOE, i.e. a diffractive optical element, as shown in fig. 3, a Fresnel lens is a typical example, and other various holographic elements are DOE, but the diffraction efficiency is generally only η -40%.
When m is 2-4, it is called the level of multiple quantization and the phase depth
Figure GDA0001856020030000042
Such a multi-step optical element is called a Binary Optical Element (BOE), and as shown in fig. 3, the diffraction efficiency is:
Figure GDA0001856020030000043
when N is 8(m is 3), theoretical diffraction efficiency η is 95%, and when N is 16(m is 4), η is 99%.
The diffraction wavefront accuracy of the binary optical element reconstruction can be represented by the following formula
Figure GDA0001856020030000044
PV-peak-valley (maximum) of the wavefront error; RMS — root mean square value of the wave front error; when m is 4 and N is 16, then
Figure GDA0001856020030000045
The precision is far higher than that of the conventional optical processing; therefore, BOE is a new optical breakthrough.
Examples
FIG. 1 is a schematic structural diagram of an Alvarez lens group provided by an embodiment. Referring to fig. 1, the Alvarez lens group provided by this embodiment is composed of a first Alvarez lens and a second Alvarez lens with complementary surface shapes, the second Alvarez lens moves relative to the first Alvarez lens in a direction perpendicular to the optical axis, and the focal length of the Alvarez lens group is adjusted by adjusting the moving distance.
Fig. 2 and fig. 3 are schematic diagrams of a binary harmonic diffractive Alvarez lens zoom system provided by the embodiment. In this embodiment, a BOE process method of making N-8 (8 steps) using three masks (i.e., m-3) is used. A photoresist is coated on a substrate material (determined by a transmission wavelength), and then an etching phase depth pi (i.e. the etching depth is equal to that of the substrate material) is formed on an ion etcher by using a first Mask
Figure GDA0001856020030000051
) The microstructure of (1); then, a second mask is used to register on the same substrate for a second etching, the phase depth is
Figure GDA0001856020030000052
Obtaining BOE with 4 steps; finally, the third Mask is used to etch the phase depth
Figure GDA0001856020030000053
Thus, BOE with 8 steps of three quantization levels is completed, the theoretical diffraction efficiency is 95%, and the actual maximum can reach about 90%.
Fig. 4 is a schematic diagram of a mask placement position provided by an example. In this example, the placement of the first and second order masks is determined.

Claims (1)

1. A method for photoetching a binary harmonic diffraction Alvarez lens zoom system is characterized by comprising the following steps:
the method comprises the following steps: taking a cuboid glass plate;
step two: determining the surface shape of a harmonic diffraction Alvarez lens; wherein the surface polynomial equation of the Alvarez lens is:
Figure FDA0002369306100000011
wherein A is expressed as a polynomial coefficient;
the harmonically diffractive Alvarez lens cuts the original Alvarez lens with a phase difference of 2m pi (m > -2) according to the surface shape of the Alvarez lens, so that the phase difference between adjacent ring bands of the harmonically diffractive Alvarez lens is 2m pi, and m > -2;
step three: determining first order mask position
Dividing the harmonic diffraction Alvarez lens into an upper half area and a lower half area at the phase position of m pi of the harmonic diffraction Alvarez lens, and if the surface shape of the harmonic diffraction Alvarez lens is on the upper half area of the harmonic diffraction Alvarez lens, placing a mask at a position corresponding to a substrate; no mask is placed at the position corresponding to the lower half area;
step four: lithography
Scanning the substrate by using laser, and cutting a step on the substrate without the mask by using the laser, wherein the substrate with the mask is not cut by using the laser;
step five: determining high order mask position and photolithography
When a second-order mask needs to be placed, marking the phase positions of (1/2) m pi and (3/2) m pi of the harmonically diffractive Alvarez lens, placing the mask at the position of a substrate corresponding to the position of (1/2) m pi, wherein the surface shape of the harmonically diffractive Alvarez lens is higher than that of the substrate corresponding to the position of (1/2) m pi, placing the mask at the position of the substrate corresponding to the position between m pi and (3/2) m pi, not placing the mask at the rest positions, and performing photoetching, wherein the photoetching depth is 1/2 times of the first photoetching depth;
when a third order mask needs to be placed, the phases of (1/4) m pi, (3/4) m pi, (5/4) m pi and (7/4) m pi of the harmonic diffraction Alvarez lens are marked; placing a mask at a substrate position corresponding to a position between (1/2) m pi to (3/4) m pi, m pi to (5/4) m pi, and (3/2) m pi to (7/4) m pi when the surface profile of the harmonically diffractive Alvarez lens is higher than the corresponding substrate position at (1/4) m pi; performing photoetching, wherein the photoetching thickness is 1/3 times of the first photoetching depth;
placing the Nth order mask, the m pi 1/2 of harmonic diffraction Alvarez lensN-1，3mπ*1/2N-1…(2N-1)mπ*1/2N-1Is marked when the surface profile of the harmonic diffractive Alvarez lens is higher than (m pi x 1/2)N-1Placing a mask at corresponding substrate positions, and placing a mask at corresponding substrate positions between (1/2) m pi to (3/4) m pi, m pi to (5/4) m pi, (3/2) m pi to (7/4) m pi, and at corresponding substrate positions between m pi/2N-1To 3m pi 1/2N-1、…(2N-1-2)mπ*1/2N-1To (2)N-1-1)mπ*1/2N-1，(2N-2)mπ*1/2N-1To (2)N-1)mπ*1/2N-1Placing a mask at the corresponding position of the substrate; n is more than 3; and (4) no mask is placed at the rest positions, and photoetching is carried out, wherein the photoetching depth is 1/N of the first photoetching depth.
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