CN110082845B - Method for preparing micro lens - Google Patents

Method for preparing micro lens Download PDF

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Publication number
CN110082845B
CN110082845B CN201910316865.1A CN201910316865A CN110082845B CN 110082845 B CN110082845 B CN 110082845B CN 201910316865 A CN201910316865 A CN 201910316865A CN 110082845 B CN110082845 B CN 110082845B
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photoresist
micro
substrate
microlens
lens
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CN110082845A (en
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王亮
张博健
罗慧雯
何伟
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University of Science and Technology of China USTC
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University of Science and Technology of China USTC
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    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B3/00—Simple or compound lenses
    • G02B3/0006—Arrays
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B3/00—Simple or compound lenses
    • G02B3/0006—Arrays
    • G02B3/0012—Arrays characterised by the manufacturing method
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B3/00—Simple or compound lenses
    • G02B2003/0093—Simple or compound lenses characterised by the shape

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  • General Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
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Abstract

A method of making a microlens comprising: step 1, designing a curved surface equation and top and bottom heights of a micro lens; step 2, processing the photoresist on the substrate to form a spherical crown type photoresist, wherein the diameter of the bottom surface of the spherical crown type photoresist is the same as that of the designed micro-lens; step 3, determining the etching selection ratio of the substrate and the spherical cap type photoresist according to the top-bottom height of the spherical cap type photoresist and the designed top-bottom height; step 4, etching the substrate and the spherical crown type photoresist to ensure that the top-bottom height and the bottom diameter of the etched substrate are respectively the same as the designed top-bottom height and bottom diameter; and 5, evaporating a medium antireflection film on the outer part of the etched substrate. The spherical crown type photoresist micro-lens prepared by the photoresist hot melting method is subjected to dry etching, so that the pre-designed paraboloidal type micro-lens is transferred to the substrate, and the dielectric antireflection film is evaporated on the substrate, thereby enlarging the diameter of the bottom surface of the micro-lens, increasing the durability of the micro-lens and improving the optical coupling rate.

Description

Method for preparing micro lens
Technical Field
The disclosure relates to the field of photodetectors and microlenses, and in particular relates to a method for manufacturing a microlens.
Background
The short-wave near-infrared photoelectric detector is a photoelectric detector chip with wide application, is often made based on III-V semiconductor materials, and can be divided into single-die chips and array products of the chips. No matter the single-die chip or the arrayed product of the chips, the larger the active area is, the larger the corresponding direct photosensitive surface is, which means that the larger the junction capacitance is, and the larger the RC constant of the device is. Under the restriction of RC constant, the diameter of the active area of the chip is often less than tens of microns and far less than the actual size (hundreds of microns) of the detector chip, so that the actual photoelectric detection effective area of the chip is very small. The introduction of microlenses and microlens arrays effectively solves this problem, greatly reduces the volume compared to conventional lenses, and is easier to integrate and mass produce.
At present, a photoresist hot-melting method is widely used for preparing a micro lens and a micro lens array, the prepared micro lens is a spherical crown type photoresist with a certain contact angle, the formed spherical crown type micro lens has single function and has reflection, the problems of insufficient focusing light spot and longer focal depth caused by aberration and chromatic aberration exist, and the durability and the stability of the photoresist material serving as the micro lens cannot meet the requirements of a photoelectric detector chip.
Disclosure of Invention
Technical problem to be solved
On the basis of not influencing the photoelectric characteristics of the photodiode, the mass production can be conveniently carried out, the micro-lens process is optimized, and the effective photosensitive surface area of the photoelectric detector, the focusing effect, the durability, the stability and the anti-reflection performance of the micro-lens are effectively improved.
(II) technical scheme
The present disclosure provides a method for manufacturing a microlens, comprising: step 1, designing a curved surface equation and top and bottom heights of the micro lens; step 2, processing the photoresist on the substrate to form a spherical crown type photoresist, wherein the diameter of the bottom surface of the spherical crown type photoresist is the same as that of the designed micro-lens; step 3, determining the etching selection ratio of the substrate and the spherical cap type photoresist according to the top-bottom height of the spherical cap type photoresist and the designed top-bottom height; step 4, etching the substrate and the spherical crown type photoresist to ensure that the top-bottom height and the bottom diameter of the etched substrate are respectively the same as the designed top-bottom height and bottom diameter; and 5, evaporating a medium antireflection film outside the etched substrate.
Optionally, the processing the photoresist on the substrate includes: selecting a photoresist according to the designed microlens; and processing the photoresist on the back of the substrate by using a photoresist hot melting method.
Optionally, the etching selection ratio is equal to a ratio between a top-bottom height of the design and a top-bottom height of the spherical cap type photoresist.
Optionally, the etching the spherical cap type photoresist and the substrate includes: adjusting the etching selection ratio of the dry etching to be equal to the ratio; and etching the substrate and the spherical crown type photoresist by using dry etching.
Optionally, the curved surface equation of the designed microlens is a paraboloid equation.
Optionally, the microlenses are disposed in a chip, and the microlenses in the chip are a single microlens or a microlens array.
Optionally, when the micro lenses in the chip are single micro lenses, the diameter of the bottom surface of each micro lens is 80-400 μm, the size distance difference between each micro lens and the chip is 10-100 μm, and the size of the cutting path between the chips is 5-20 μm.
Optionally, when the microlenses in the chip are microlens arrays, the diameter of the bottom surfaces of the microlenses is 100-360 μm, and the size distance difference between the microlenses is 20-60 μm.
(III) advantageous effects
The preparation method of the micro lens provided by the disclosure has the following beneficial effects:
(1) the size of the micro lens required by a target is designed by using optical software, and the diameter of the bottom surface of the micro lens can be enlarged to the maximum extent by combining a photoresist hot melting method and dry etching with adjustable etching selection ratio, so that the effective photosensitive area of a chip is enlarged;
(2) by transferring the microlenses to the substrate, the durability of the microlenses is increased;
(3) the optical loss is reduced and the optical coupling rate is improved by evaporating the medium transparent enhancement film;
(4) through the design of the paraboloid type micro lens, the aberration and chromatic aberration of the lens are reduced, and the size of a focusing light spot and the size of the focal depth are reduced.
Drawings
Fig. 1 schematically shows a flowchart of a method for manufacturing a microlens provided by an embodiment of the present disclosure.
Fig. 2 schematically shows a side structure schematic diagram of a back-incident III-V semiconductor photodiode of a microlens provided by an embodiment of the present disclosure.
Fig. 3A schematically illustrates a back side structure view of a single-tube device wafer of a back-incident III-V semiconductor photodiode provided by an embodiment of the present disclosure.
Fig. 3B schematically illustrates a backside structure diagram of a wafer of a back-incident III-V semiconductor photodiode array device provided by an embodiment of the disclosure.
Detailed Description
For the purpose of promoting a better understanding of the objects, aspects and advantages of the present disclosure, reference is made to the following detailed description taken in conjunction with the accompanying drawings.
Fig. 1 schematically shows a flowchart of a method for manufacturing a microlens provided by an embodiment of the present disclosure. Referring to fig. 1, the preparation method shown in fig. 1 will be described in detail with reference to fig. 2, 3A and 3B.
The microlens in this embodiment is a back-incident type design on the basis of a III-V group semiconductor photodiode chip, and the microlens is prepared before a tape-out process of the chip and scribing and breaking after thinning and polishing are completed, the preparation method including:
step 1, designing a curved surface equation and top and bottom heights of the micro lens.
The size of the micro lens required by a target is designed through optical software, the detection application of the photodiode chip is different, and the required size of the micro lens is different. Specifically, the basic size parameters of the microlens, such as the bottom surface diameter D, are determined by combining the size of a semiconductor photodiode chip (the side length is generally between 300-500 μm), and the size of an active region generated by diffusion of a device dopant, the target focal length and the focusing depth range are determined by combining an epitaxial wafer structure in the chip, and other size parameters of the microlens, such as the top-bottom height h and the curve equation of the rotation of the microlens around the central axis, are designed based on the ray tracing principle, so that the curve equation of the microlens can be obtained according to the curve equation.
The shape of the micro lens is a paraboloid, and compared with a spherical crown lens, the paraboloid lens has smaller aberration and chromatic aberration, namely, smaller focusing light spot and smaller focal depth.
In the operation, all size parameters of the micro lens can be calculated according to the curved surface equation and the top-bottom height h only by determining the curved surface equation and the top-bottom height h of the micro lens; or all the size parameters of the micro lens can be calculated according to the curved surface equation and the bottom surface diameter D only by determining the curved surface equation and the bottom surface diameter D of the micro lens.
The microlenses are disposed in a chip, wherein the microlenses in the chip are single microlenses (i.e., the chip is a single die chip) or a microlens array (i.e., the chip is an arrayed device). When the chip is a single die chip, the size of the microlens corresponds to the single device in fig. 3A, and at this time, the diameter D of the bottom surface of the microlens is 80 to 400 μm, the size pitch difference W between the microlens and the chip is 10 to 100 μm, and the dicing street size W0 is 5 to 20 μm; when the chip is an arrayed device, the size of the micro-lenses corresponds to the arrayed device in FIG. 3B, and at this time, the diameter D of the bottom surface of each micro-lens is 100-360 μm, and the size distance difference W between the micro-lenses is 20-60 μm.
And 2, processing the photoresist on the substrate to form a spherical cap type photoresist, wherein the diameter of the bottom surface of the spherical cap type photoresist is the same as that of the designed micro lens.
And selecting the photoresist according to the size requirement of the designed micro lens and the photoresist hot melting parameters, and processing the photoresist on the back of the substrate by using a photoresist hot melting method. Specifically, the photoresist is subjected to ultraviolet exposure under a circular array mask, a cylindrical array photoresist structure is obtained after development, the photoresist is heated to a molten state, and the cylindrical structure is converted into a smooth spherical crown structure through the surface tension of the photoresist, so that the spherical crown type photoresist is formed.
In the operation, the shape of the spherical cap type photoresist can be controlled by adjusting the thickness of the spin-on photoresist and the hot melting temperature, so that the diameter of the bottom surface of the formed spherical cap type photoresist meets the size requirement designed in advance. This is because the size of the bottom surface diameter of the microlens transferred on the substrate cannot be modified by dry etching, so the bottom surface diameter of the photoresist of the spherical cap type formed by the photoresist hot-melt method should be the same as the bottom surface diameter of the microlens designed in advance.
And 3, determining the etching selection ratio of the substrate and the spherical cap type photoresist according to the top-bottom height of the spherical cap type photoresist and the designed top-bottom height.
The top-bottom height of the spherical cap type photoresist is measured, so that the etching selection ratio of the substrate to the spherical cap type photoresist (namely the substrate etching rate: the photoresist etching rate) can be calculated to be equal to the ratio of the top-bottom height of the spherical cap type photoresist to the top-bottom height of the designed micro lens.
And 4, etching the substrate and the spherical cap type photoresist to ensure that the top-bottom height and the bottom diameter of the etched substrate are respectively the same as the designed top-bottom height and bottom diameter.
Firstly, the formula of dry etching is adjusted until the etching selection ratio is equal to the ratio of the top-bottom height of the spherical crown type photoresist to the top-bottom height of the designed micro-lens.
And then, etching the spherical cap photoresist and the substrate by using dry etching of the etching selection ratio until the spherical cap photoresist is completely etched, so that the designed appearance of the micro lens is transferred to the substrate, wherein the etched substrate is parabolic, and each size parameter (such as top and bottom height, bottom diameter and slope of a micro lens curved surface at the ground) of the etched substrate is the same as the size parameter of the pre-designed micro lens.
And 5, evaporating a medium antireflection film on the outer part of the etched substrate.
Depositing a dielectric antireflection film, such as SiN, on the back of the etched substrate by Plasma Enhanced Chemical Vapor Deposition (PECVD)x(silicon nitride), etc., thereby improving the optical coupling efficiency of the microlens.
Taking a single device structure as an example, the lateral cross section of the finally formed single device structure is shown in fig. 2, wherein the microlens is composed of a substrate and a dielectric antireflection film which meet the design requirements.
The method for manufacturing the microlens in the present disclosure is described in detail, and the method combines optical software simulation, a photoresist hot melting method and dry etching, designs different microlens size requirements according to different requirements, forms a spherical cap type photoresist with a bottom diameter meeting the requirements through the photoresist hot melting method, transfers the microlens meeting the target requirements to a substrate through the dry etching with a set etching selection ratio, and evaporates a medium antireflection film on the substrate to form a parabolic target microlens. On the basis of not influencing the photoelectric characteristics of the photodiode, the mass production can be conveniently carried out, the micro-lens process is optimized, and the effective photosensitive area of the photoelectric detector and the focusing effect and the anti-reflection performance of the micro-lens are effectively improved.
The above-mentioned embodiments are intended to illustrate the objects, aspects and advantages of the present disclosure in further detail, and it should be understood that the above-mentioned embodiments are only illustrative of the present disclosure and are not intended to limit the present disclosure, and any modifications, equivalents, improvements and the like made within the spirit and principle of the present disclosure should be included in the scope of the present disclosure.

Claims (6)

1. A method of making a microlens comprising:
step 1, designing a curved surface equation and a top-bottom height of a micro lens through optical software by utilizing a ray tracing principle according to the size of a chip, the size of an active area, a target focal length and a focusing depth range determined by an epitaxial wafer structure in the chip and the thickness of a medium antireflection film, wherein the curved surface equation is a paraboloid equation;
step 2, processing the photoresist on the substrate to form a spherical crown type photoresist, wherein the diameter of the bottom surface of the spherical crown type photoresist is the same as that of the designed microlens;
step 3, determining an etching selection ratio of the substrate and the spherical cap type photoresist according to the top-bottom height of the spherical cap type photoresist and the designed top-bottom height of the micro lens, wherein the etching selection ratio is equal to the ratio of the designed top-bottom height of the micro lens to the designed top-bottom height of the spherical cap type photoresist;
step 4, etching the substrate and the spherical cap type photoresist to enable the top-bottom height and the bottom diameter of the etched substrate to be the same as the top-bottom height and the bottom diameter of the designed micro lens respectively;
and 5, evaporating a medium antireflection film outside the etched substrate.
2. The method of claim 1, wherein the processing the photoresist on the substrate comprises:
selecting a photoresist according to the designed microlens;
and processing the photoresist on the back of the substrate by using a photoresist hot melting method.
3. The method of claim 1, wherein the etching the spherical cap photoresist and the substrate comprises:
adjusting the etching selection ratio of the dry etching to be equal to the ratio;
and etching the substrate and the spherical crown type photoresist by using dry etching.
4. The method of claim 1, wherein the microlenses are provided in a chip, and the microlenses in the chip are a single microlens or a microlens array.
5. The method for manufacturing a microlens as claimed in claim 4, wherein, when the microlens in the chip is a single microlens, the diameter of the bottom surface of the microlens is 80-400 μm, the shortest distance between the edge of the microlens and the edge of the chip is 10-100 μm, and the size of the scribe line between the chips is 5-20 μm.
6. The method as claimed in claim 4, wherein when the micro-lenses in the chip are micro-lens arrays, the diameter of the bottom surface of each micro-lens in the micro-lens array is 100-360 μm, and the shortest distance between the edges of two micro-lenses in the micro-lens array is 20-60 μm.
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CN112034541B (en) * 2020-10-15 2022-08-16 苏州苏纳光电有限公司 Method and system for preparing silicon microlens product by photoresist hot melting method
CN112909106A (en) * 2021-01-13 2021-06-04 湖北光安伦芯片有限公司 Manufacturing method of substrate back micro lens, photoelectric detector and manufacturing method of photoelectric detector
CN113900179A (en) * 2021-10-19 2022-01-07 河南仕佳光子科技股份有限公司 Array waveguide grating demultiplexer chip of cladding integrated micro-lens and preparation method thereof
CN115437043A (en) * 2022-07-29 2022-12-06 深圳通感微电子有限公司 Method for preparing micro lens by using semi-molten photoresist and micro lens

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CN1517723A (en) * 2003-01-27 2004-08-04 ���ǵ�����ʽ���� Method for manufacturing microlens array
CN105372726A (en) * 2015-12-14 2016-03-02 中山大学 Diamond micro lens array and preparation method thereof

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US5286338A (en) * 1993-03-01 1994-02-15 At&T Bell Laboratories Methods for making microlens arrays
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CN105372726A (en) * 2015-12-14 2016-03-02 中山大学 Diamond micro lens array and preparation method thereof

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