KR20020016113A - Method of manufacturing for micro-lens - Google Patents

Abstract

PURPOSE: A method for fabricating a micro lens is provided, which fabricates the micro lens easily with a stable operation and reduces a size of the micro lens with a low cost and a high controllability. CONSTITUTION: According to the method, a photo resist(2) is projected on an upper surface of a charged coupled device(1). Then, the upper surface of the charged coupled device is reflowed to form a photo resist(2a) having a curvature through a reflow process. And a metallic insert(4) is electrically cast on an upper part of the photo resist of the charge coupled device through an electrical casting process, and a seed metal layer(3) is formed along a boundary between the photo resist and the metallic insert. Then, a micro lens(5) is formed through the metallic insert in a micro lens molding process.

Description

Method of manufacturing for micro-lens

The present invention relates to a method for manufacturing a microlens, and in particular, a lens-shaped master having an arbitrary curvature is manufactured by using a property such that a material such as plastic has a curved surface due to surface tension above a glass transition temperature. After manufacturing a mold having a lens surface through electroforming on the master surface to enable injection and compression molding of the microlens.

Micro lenses are used in various applications such as internal fiber connections in liquid crystal displays, optical receivers, and optical communication systems.

There are many difficulties in relying on the machining of micro lenses, but new processing techniques have been tried to overcome these problems. However, there are limitations in reducing dimensional deviation between products and high price.

In the microlens manufacturing method using the ion exchange method, the refractive index increases at a plurality of places of the multi-component glass substrate by using the ion exchange method. Thus, a plurality of lenses are formed at high refractive index locations. However, in this method, the diameter of the lens cannot be large compared to the distance between the lenses. Therefore, it is difficult to design a lens having a large numerical aperture (NA). In addition, in order to produce such a microlens array, a large-scale manufacturing apparatus such as an ion diffusion device is required, and therefore it is difficult to manufacture a microlens array having a large area. In addition, an ion exchange process is required for each glass as opposed to a molding method using a mold.

Therefore, unless the management of manufacturing conditions in the manufacturing apparatus is carefully carried out, a change in the quality of the lens, such as the focal length, is likely to increase between the lots. In addition, the cost of using this method is relatively high compared to the method using a mold.

Moreover, in the ion exchange method, since alkaline ions for ion exchange are indispensable for a glass substrate on a glass substrate, a substrate material is limited to alkali glass. However, alkali glass is not suitable for semiconductor-based devices that must be free of alkali ions.

Moreover, the coefficient of thermal expansion of the glass substrate is significantly different from that of light irradiation or the receiving element substrate, so that the misalignment between the microlens array and the elements occurs due to the mismatch between the coefficients of thermal expansion as the integration density of the elements increases. easy to do.

In addition, compression strain is inherent on the glass surface treated by the ion exchange method. Therefore, the glass tends to be twisted, so that as the size of the microlens array increases, bonding or bonding between the glass and the light irradiation or receiving element becomes difficult.

In another conventional microlens array manufacturing method using a resist reflow (or dissolution) method, a resin formed on a substrate is patterned in a cylindrical shape by using photolithography technology as shown in FIG. S11), the resin is heated and reflowed (S12) to produce a microlens array (S13).

By using the resist reflow method, various types of lenses can be manufactured at low cost. In addition, this method does not have problems such as thermal expansion coefficient and torsion in contrast to the ion exchange method. However, in the resist reflow method, the profile of the microlens depends greatly on the thickness of the resin, the wet conditions between the substrate and the resin, and the thermal temperature. Therefore, while the refresh rate per single substrate surface is high, variations between lots are likely to occur.

In addition, when adjacent lenses are brought into contact with each other due to reflow, the desired lens profile cannot be obtained due to the surface tension. Therefore, it is difficult to achieve high light collecting rate in a manner of contacting adjacent lenses and reducing the unused area between the lenses. In addition, where a lens diameter of 20 or 30 microns to 200 or 300 microns is desired, the thickness of the deposited resin should be large enough to obtain a spherical surface by reflow. However, it is difficult to deposit a resin material having desired optical properties such as refractive index and light transmittance uniformly and thickly. Thus, it is difficult to produce microlenses having a large curvature and a relatively large diameter.

In another conventional method, an original plate of microlenses is manufactured, and the lens material is deposited on the original plate, and then the deposited lens material is separated. One plate or mold is manufactured by the electron beam lithography method or the wet etching method. However, in the ion beam lithography method, since the ion beam lithography apparatus is expensive, a large investment is required. In addition, it is difficult to manufacture a mold having a large area because the electron beam impact area is limited.

In addition, in the wet etching method, since isotropic etching using a chemical reaction is used in principle, even if the composition and crystal structure of the metal plate change only a little, the etching will continue unless the plate is cleaned.

In the case of forming the micromicrolens, a shape may deviate from the desired due to the etching that lasts for a period from the time at which the desired profile is obtained to the time at which the microlens is obtained. However, it is difficult to accurately form microlenses having a radius of curvature of less than 200 μm in diameters of several hundred microns and the best spherical portions with conventional lens manufacturing techniques. Also, most of the prior arts are limited in their use as they are made with the lens attached to the substrate on which it is to be placed.

Accordingly, it is an object of the present invention to provide a manufacturing method suitable for manufacturing a microlens which can be easily manufactured and also stably operate the microlens while providing flexibility in the application of the method of manufacturing the microlens. .

Another object of the present invention is to easily reduce the size of the microlenses, to be easily manufactured at a relatively low cost and high control rate, and to provide a mold or a microlens array for a microlens having a desired curvature or a large numerical aperture. It is.

Microlens manufacturing method of the present invention for achieving this object,

Preforming a preliminary plastic product having a microstructured microstructure;

When the preforming of the plastic product is completed from the molding process, manufacturing the product as a master having a lens shape having a curvature by a reflow method;

Performing electroforming on an upper surface of the master having a lens shape through the reflow process;

Manufacturing a molding insert having an opposite shape of a lens through the electroforming;

Injection and compression molding the microlens based on the molding insert is characterized in that.

1 is a resist reflow method for microlens molding

2 is a molding flow chart of the microlens according to the present invention.

3 is a diagram schematically illustrating a molding process of a mold insert structure according to the present invention.

4 is a flow chart showing an example of compression molding of a microlens according to the present invention.

* Description of the symbols for the main parts of the drawings *

1: solid-state image pickup device 2: photoresist

2a: resist 3: seed metal layer

4: electro-molded mold 4a: electro-molded mold

5: microlens

Hereinafter, the present invention will be described with reference to the drawings.

FIG. 2 is a block diagram of a microlens according to the present invention, and FIG. 3 schematically illustrates a molding process of a mold insert structure according to the present invention, and FIG. 4 illustrates a method of molding a microlens according to the present invention.

In the present invention, a lens-shaped master having an arbitrary curvature is produced by using a property such as plastic to have a curved surface by surface tension above the glass transition temperature, and the lens surface is formed by electroforming on the master surface. After manufacturing a mold having a microlens aims to mass production through injection molding and compression molding.

2 is a manufacturing flowchart of a compression molding for manufacturing a microlens for processing a microlens according to an embodiment of the present invention.

First, preliminary molding of a preliminary plastic product having a microstructure of micro units (S20).

When the preforming of the plastic product is completed from the molding process, the product is manufactured in a master having a lens shape by a reflow method (S21).

When the manufacturing of the master having a lens shape is completed through the reflow process, electroforming is performed on the upper surface (S22).

Through the electroforming to produce a molding insert having the opposite shape of the lens to mold the fine lens (S23).

FIG. 3 schematically shows a structure made according to the steps S20 to S23 of FIG. 2.

In the preforming step S20, the photoresist 2 protrudes from the top surface of the solid state image pickup device 1.

Through the reflow process of S21, the top surface of the solid state image pickup device 1 is reflowed to form a photoresist 2a having a curvature.

The mold insert 4 is electroformed at the upper portion of the photoresist 2a of the solid state imaging device 1 through the electroforming of S22, and seeded along the interface between the photoresist 2a and the mold insert 4 electroformed. The metal layer 3 is formed.

In the microlens molding of S23, the microlens 5 is formed through the electroformed mold insert 4a.

A method of molding a microlens through a mold for molding the microlens as shown in FIG. 2 and a mold insert prepared for molding the microlens as shown in FIG. 3 is as follows.

First, a substrate made of the solid state image pickup device 1 having the convex photoresist 2 close to the lens shape is prepared. The material used is a material having fluidity when heated, and thermoplastic resin or PR is typical. The processing method can be manufactured by traditional CNC machining or photo-processing after spin coating the PR onto the substrate.

In this way, the preliminary master is locally heated by the laser to the unevenness of the glass transition temperature, and the unevenness becomes viscous. Form.

The current technology is to use the manufactured lens as it is. This method has problems in terms of mass production, probability, material limitation, and the like.

The seed metal layer 3 is covered on the lenticular master thus formed, and a mold insert 4a which is excavated into a lens shape through electroforming is manufactured to mold the microlens. In other words, if only one well-made lens master (mold insert) is made, a mold insert that can be mass-produced can be manufactured and molded without material constraints.

An example of the microlens processing method using the compression molding mold according to the present invention is similar to the general microcompression molding or injection molding method as shown in FIG. 4.

When the mold insert 4a is prepared through the manufacturing method as shown in FIGS. 2 and 3, the mold insert 4a is mounted (S30), and the base material, which is a microlens, is placed in the cavity of the mold mounted on the compression molding machine (S31). Thereafter, the upper and lower plates for compression molding are closed and preloaded (S32). The preload here is not the pressure for shaping, but the contact with the heated mold in order to reach the material quickly to the processing temperature. The mold heats the upper and lower plates by installing an electric resistance heating element uniformly, and compresses the upper and lower plates by applying pressure to the upper and lower plates when the temperature rises to a predetermined temperature (more than 100 ° C. to 300 ° C. above the glass transition temperature of the plastic or the binder) (S33). Depending on the mechanical properties (compressive strength, fracture strength, shear strength) of the microstructure of the mold insert, the use of compression pressure is restricted, but generally has sufficient moldability with a compressive stress of 30 MPa or less. After applying the compression pressure, the heating of the mold is finished (S34), and enters the cooling and holding step (S35). Cooling is performed through a cooling line installed in the mold. During this process, pressure is maintained by keeping the pressure free to prevent dimensional changes due to shrinkage of the product. When the mold is cooled below the predetermined temperature, the pressure is gradually lowered (S36). After further cooling proceeds (S37), taking out while inducing the separation of the product (microlens) with the mold wall surface (S38).

The micro-compression molding mold used is a method of forming a product having a structure of micro size or less, heating the material in contact with the mold to make the material flowable above the glass transition temperature, and applying pressure to the mold to make the material have a microstructure. It is the way to carry it. Here, the mold is used in a broad sense including a mold and a mold insert, and the material may be a material such as silicon in addition to the metal material.

The mold proposed in the present invention is a mold designed to be suitable for molding a fine molded product, and post-processing of a product of several mm or less is performed in the mold. Micromolded inserts used for microforming can be used by replicating microstructures made by LIGA or silicon micro-machining by dry or wet etching through electroplating (electroforming, electroplating, electroplating), dry, Silicon substrates with microstructures produced by wet etching are used. Micro-compression molding suitable for mass production of micro components can use silicon substrates as mold inserts sufficiently because they can be molded at a lower pressure than in injection molding. It is also possible to deposit and use a metal structure on a silicon substrate. The molding materials that can be used are powders of plastics, metals, ceramics, and the like, as well as the use of binders if necessary.

According to the compression molding process of the microlenses, it is a simple process and a mass production is possible as compared to the existing microparts production process.

Through this method, it is possible to manufacture microlenses such as hemispherical lenses, fly-eye lenses, and lens lenses, and optical pickup lenses.

It is possible to reduce the dimensional deviation between products and to manufacture at low cost. It is also possible to design a lens having a large numerical aperture (NA) by increasing the diameter of the lens as compared with the distance between the lenses. A large area microlens array can be manufactured without a large manufacturing apparatus.

The change in the quality of the lens such as the focal length is small and the manufacturing cost is relatively lower than the ion exchange method or the resist reflow method.

According to the present invention, the microlenses can be molded and reproduced, so that the microlenses can be manufactured at a low unit cost, and in contrast to the ion exchange method, the problem of alignment error and torsion due to the difference in thermal expansion coefficient can be solved.

In addition, microlenses with a radius of curvature of less than 200 μm or more at diameters of several hundred microns and at the best spherical portions can be accurately molded and their reliability is increased.

In addition, it is possible to manufacture individual units through molding, so the application range is wide for many devices.

Claims (3)

In the manufacturing method of a microlens, Preforming a preliminary plastic product having a microstructured microstructure; When the preforming of the plastic product is completed from the molding process, manufacturing the product as a master having a lens shape having a curvature by a reflow method; Performing electroforming on an upper surface of the master having a lens shape through the reflow process; Manufacturing a molding insert having an opposite shape of a lens through the electroforming; Microlens manufacturing method comprising the step of injection and compression molding the microlens based on the molding insert. The method of claim 1, The plastic microstructure molded in the preforming step is a microlens manufacturing method, characterized in that the photoresist is protruded on the upper surface of the solid-state imaging device. The method of claim 1, In the electroforming step, the mold insert is electroformed on the photoresist of the solid state image pickup device, and a seed metal layer is formed along the interface between the photoresist and the electroformed mold insert to form the mold insert. Way.