Technical Field
The human body obtains 70% of external information from vision, and with the development of scientific technology, a display becomes an important tool for information transmission and man-machine communication. The most mature Display technology in the contemporary generation, the most popular Thin Film Transistor Liquid Crystal Display (TFT-LCD) with the highest market share. The TFT-LCD operates on the principle that the arrangement of the liquid crystal molecules inside the TFT-LCD changes under the action of an electric field, which is called the electro-optic effect. The change of the liquid crystal molecular structure influences the change of light passing through the liquid crystal molecular structure, then the light and shade change can be shown under the action of the polarizer, and then the gray level and the brightness change of the light can be finally controlled by controlling an electric field by matching with a Color Filter (CF), so that the aim of displaying images is fulfilled. In the TFT-LCD device, in order to improve the response speed, it is necessary to align the liquid crystal molecules at the electrode interface and form a certain pretilt angle, so that the alignment operation of the alignment films on the surfaces of the TFT substrate and the CF substrate is required in the production process. The current alignment technology is divided into rubbing alignment and photo-alignment, wherein the photo-alignment technology mainly uses an alignment material with high ultraviolet light sensitivity and good stability for light alignment. Compared with the rubbing alignment technology, the photo-alignment technology has the advantages of non-contact, no pollution, no static electricity, realization of multi-domain alignment and the like, thereby being widely applied.
The ultraviolet light vertical alignment technology (UV2A) is a novel photo-alignment technology for precisely controlling the molecular deflection of an alignment film by polarized ultraviolet light. The liquid crystal panel produced by using the UV2A technology has the characteristics of high aperture, high contrast ratio, fast response and the like, which makes the UV2A a very competitive optical alignment technology. In the photo-alignment process, after the polymerized high molecules in the alignment film are irradiated by polarized ultraviolet light, the polymerized high molecules can deviate towards the light irradiation direction due to the existence of the phototaxis monomer in the high molecules, so that the orientation angle of liquid crystal molecules is formed. In order to achieve the wide viewing angle display effect of the liquid crystal panel, the UV2A process needs to use polarized ultraviolet light with a certain inclination angle as a light source to perform two-way irradiation twice or more on the sub-pixels on the surface of the TFT substrate or the CF substrate, so as to form the alignment effect of 4Domian and 8 Domian.
The key component for realizing bidirectional light irradiation by the UV2A process is a mask plate, and the currently used mask plate is designed to be semi-transparent and semi-opaque. In the photo-alignment process, a light shielding part on a mask plate firstly shields one half of sub-pixels, and a light transmission part on the mask plate is used for photo-alignment on the other half of sub-pixels; and then, rotating the substrate by 180 degrees, shielding the half sub-pixel subjected to the illumination alignment before by using a mask plate, and performing the illumination alignment on the unexposed half sub-pixel, thereby achieving the purpose of full-pixel bidirectional illumination.
However, the current mask used in the UV2A process adopts a half-shading and half-transmitting design, and the utilization rate of ultraviolet light is low. In order to achieve the purpose of full-pixel bidirectional illumination, each pixel is subjected to unidirectional illumination at least twice, and the substrate is rotated for at least 180 degrees once, so that the process time of optical alignment is prolonged, the design of an equipment illumination unit is repeated, the manufacturing cost of a machine table is high, and the requirement of economic production is not met.
Disclosure of Invention
In order to solve the technical problems, the invention provides a mask plate for substrate photo-alignment and a photo-alignment method, wherein the mask plate is provided with a light transmitting area and a reflecting area which are alternately arranged, so that each sub-pixel is simultaneously subjected to bidirectional exposure, the utilization rate of ultraviolet light is doubled, and the energy consumption is greatly reduced. Meanwhile, the whole structural unit of the equipment is halved, so that the production cost is greatly saved, and the production efficiency is greatly improved.
The technical scheme provided by the invention is as follows:
the invention provides a mask for substrate photo-alignment, which comprises a light-transmitting area and a reflecting area which are repeatedly and alternately arranged, wherein the reflecting area comprises at least one reflector which is vertically arranged, light passing through the light-transmitting area reaches the surface of a substrate in the original incident angle direction, and the light passing through the reflecting area reaches the surface of the substrate after being reflected by the reflector.
Preferably, the widths of the light-transmitting area and the reflecting area are equal, and the direction of the light reaching the substrate surface from the light-transmitting area and the direction of the light reaching the substrate surface from the reflecting area are mirror symmetry.
Preferably, the mirror includes a reflective layer, a base layer, and an absorption layer, wherein the reflective layer faces a light incident direction.
Preferably, the distance between the surface of the absorbing layer of one reflector and the surface of the reflecting layer of the adjacent reflector is D, and D is not more than H × tan θ, where H is the height of the reflector and θ is the included angle between the incident light and the reflector.
Preferably, the light-transmitting region further includes a blocking portion located at a light-emitting side.
Preferably, the blocking portion and the reflecting mirror are arranged in parallel.
The invention also provides a method for carrying out optical alignment on the substrate, which adopts a mask plate with a light-transmitting area and a reflecting area which are repeatedly and alternately arranged, wherein the reflecting area comprises at least one reflector which is vertically arranged, the light passing through the light-transmitting area reaches the surface of the substrate in the original incident angle direction, and the light passing through the reflecting area reaches the surface of the substrate after being reflected by the mirror surface of the reflector.
Preferably, the mirrors absorb part of the light reflected by adjacent mirrors.
Preferably, the light-transmitting region blocks a portion of light from passing therethrough.
Preferably, the light passing through the light-transmitting area and the light passing through the reflecting area are symmetrical in direction and equal in quantity.
Compared with the prior art, the mask and the photo-alignment method can provide a bidirectional light path for photo-alignment of the substrate, improve the utilization rate of ultraviolet light, reduce equipment illumination units, shorten the photo-alignment processing time, greatly improve the production efficiency and greatly reduce the production cost.
Detailed Description
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following description will be made with reference to the accompanying drawings. It is obvious that the drawings in the following description are only some examples of the invention, and that for a person skilled in the art, other drawings and embodiments can be derived from them without inventive effort.
For the sake of simplicity, the drawings only schematically show the parts relevant to the present invention, and they do not represent the actual structure as a product. In addition, in order to make the drawings concise and understandable, components having the same structure or function in some of the drawings are only schematically illustrated or only labeled. In this document, "one" means not only "only one" but also a case of "more than one".
As shown in fig. 1, a mask 10, which is used for a photo-alignment process of a substrate, is made of transparent quartz glass or transparent resin, has a thickness of preferably 3 mm, and includes a transparent region 1 and a reflective region 2 alternately arranged repeatedly, wherein each of the transparent region 1 and the reflective region 2 has the same width, and preferably, the widths of the transparent region 1 and the reflective region 2 are both 300 to 400 μm. Each reflection area 2 includes at least one mirror 3 arranged in a vertical direction, the mirrors 3 are embedded inside the reflection area 2, and the mirrors 3 are arranged at equal intervals in a column direction. Incident light irradiates the mask at a certain angle (0-90 degrees), and the arrow direction in fig. 1 represents the emergent direction of ultraviolet light.
As shown in fig. 2, the mirror 3 includes three parts, a reflective layer 31, a base layer 32, and an absorption layer 33. The reflective layer 31 faces the incident direction of the ultraviolet light for reflecting the ultraviolet light, the absorption layer 33 absorbs the ultraviolet light, and the base layer 3 is located between the reflective layer 31 and the absorption layer 33.
For the structure of the reflector 3, firstly, the laser engraving technology is used to engrave the substrate layer 32 at a certain distance in the reflective region 2, and the substrate layer 32 is made of ultraviolet-resistant material. And then, plating an ultraviolet reflecting film on one side of the base layer 32 facing the incident direction of the ultraviolet 4 by using an evaporation technology to form the reflecting layer 31, wherein the reflecting layer 31 can adopt a composite film formed by combining multiple layers of high-refractive-index materials, and preferably, the reflecting layer 31 is a base layer/HfO 2/UV-SiO2/MgF2 film. Finally, a magnetron sputtering coating technology is used for coating an ultraviolet light absorption film on one side of the substrate layer 32 opposite to the incident direction of the ultraviolet light 4 so as to form the absorption layer 33, a semiconductor material film with a high forbidden band width can be used for the absorption layer 33, and preferably, the absorption layer 33 is a TiO2 film.
In order to prevent light from directly emitting out of the mirror unit region without reflection, the distance between two adjacent mirrors 3 is also controlled. As shown in fig. 3, in the reflection area 2, the height of the reflector 3 is the same as the thickness of the mask, and both are the height H, the angle between the incident light and the reflection layer 31 on the surface of the reflector 3 is θ, and for two adjacent reflectors 3, the linear distance from the surface of the absorption layer 33 of one reflector to the surface of the reflection layer 31 of the other adjacent reflector is D.
Wherein the relationship between distance D, height H, and angle θ is:
as shown in fig. 4(a), when D < H × tan θ, there are two light losses of the incident light, namely, light 42 passing through the end face of the mirror 3 and light 41 secondarily reflected by the back face of the adjacent mirror 3. Secondary reflections of the light 41 may cause parasitic light generation.
As shown in fig. 4(b), when D ═ H × tan θ, which is the optimum state, there is only one light loss of the incident light, that is, the light 42 passing through the end face of the mirror 3 is lost.
As shown in fig. 4(c), when D > H × tan θ, some incident light 43 directly reaches the substrate surface without passing through the reflector 3, and stray light is generated, and at this time, the alignment process cannot be performed using the mask.
Since the absorption layer 33 is disposed on the back surface of the reflector 3 of the present invention, the absorption layer 33 can prevent the light 41 from forming stray light through secondary reflection, thereby avoiding the influence on the emergent light direction. Therefore, the relationship between the distance D, the height H and the angle θ should be D ≦ H tan θ, preferably D ≦ H tan θ.
Specifically, in the photo-alignment process of the substrate, the angle between the incident direction of the ultraviolet light 4 and the surface of the reticle 10 is 30 °, and since the reflector 3 is vertically disposed, the angle θ between the incident direction of the ultraviolet light 4 and the reflective layer 31 on the surface of the reflector 3 is 60 °. Since the thickness of the mask is 3 mm and the height H of the reflecting mirror 3 is 3 mm, the distance D between two reflecting mirrors 3 is 3 × tan60 °, and preferably, in consideration of the actual process error, the linear distance D between the surface of the absorbing layer 33 of the previous reflecting mirror and the surface of the reflecting layer 31 of the next adjacent reflecting mirror is 5.19 ± 0.005 mm.
As shown in fig. 3 and fig. 5, since the material of the transparent region 2 is transparent quartz glass or transparent resin, in order to ensure that the light energy of the emergent light of the transparent region 1 is equal to that of the reflective region 2, some process adjustment needs to be performed on the light transmission amount of the transparent region 1, measures for weakening the light amount need to be added, and optionally, the transparency of the transparent region may be reduced, or a partial light shielding region may be provided. As a preferred embodiment, in order to make the amount of light transmitted by the light transmitting area 1 equal to the amount of light reflected by the reflecting area 2, a blocking portion is provided on the light exit side of the light transmitting area 1, and preferably, an ultraviolet light blocking film is provided on the ultraviolet light exit surface of the light transmitting area 1 to form the blocking layer 5. The shielding layers 5 are also arranged at equal intervals, the shielding layers 5 correspond to the reflecting mirror 3 and are arranged in parallel, and the light shielding area of the shielding layers 5 is equal to the cross-sectional area of the reflecting mirror 3, as shown in fig. 5. The shielding layer 5 may be made of a light shielding material of a metal or metal oxide material resistant to ultraviolet light, and preferably, the shielding layer 5 is a Cr film. Although the size of the cross section of the shielding layer 5 of the light-transmitting region 1 is the same as that of the mirror 3, the exposure amounts of the light-transmitting region 1 and the reflective region 2 are not completely the same, but are within an allowable error range, and therefore, the actual exposure quality is not affected. If the exposure is guaranteed to be completely consistent, the shielding layer 5 needs to be expanded slightly, the width needs to be expanded 5.1961 (3 × tan60 °) -5.19 to 0.0061mm, and the value can be ignored in consideration of process errors.
In the process of carrying out optical alignment on the substrate by using the mask 10, when ultraviolet light 4 enters the light-transmitting area 1 of the mask 10, the light directly transmits from the transparent part of the light-transmitting area 1 to reach the surface of the substrate, the direction of the light is kept unchanged, the light reaches the surface of the substrate in the original incident angle direction, and meanwhile, part of the ultraviolet light 4 is blocked by the shielding layer 5 of the light-transmitting area 1 and cannot reach the surface of the substrate; when ultraviolet light 4 enters the reflecting area 2 of the mask plate 10, the ultraviolet light 4 passing through the space between two adjacent reflectors 3 reaches the surface of the substrate after being reflected by the reflecting layers 31 of the reflectors 3, the direction of the reflected light is mirror symmetry with the incident direction of the ultraviolet light 4, meanwhile, part of the ultraviolet light 4 is reflected by the reflectors 3, is absorbed by the absorbing layers 33 of the adjacent reflectors 3 and cannot reach the surface of the substrate, and therefore the consistency of the emergent light direction is guaranteed. As shown in fig. 4, the arrows represent the light direction, and the light direction of the ultraviolet light 4 passing through the light-transmitting region 1 and the light direction of the ultraviolet light 4 passing through the reflecting region 2 are mirror-symmetric, so as to achieve the purpose of bidirectional photoalignment.
In this embodiment, by providing the light-transmitting region 1 and the reflective region 2, the bidirectional photoalignment can be performed simultaneously using one mask 10, and the exposure energy of the bidirectional photoalignment is kept uniform due to the shielding layer 5.
In another embodiment, in order to ensure that the light energy of the emergent light of the transparent region 1 and the reflective region 2 is equal, the transparency of the transparent region 1 can be reduced, and the shielding layer 5 is not required. The light transmission area 1 reduces the light throughput of the ultraviolet light 4 by reducing the transparency, and can ensure that the light quantity passing through the light transmission area 1 and the reflection area 2 is equal.
In another embodiment, in order to ensure that the light energy of the outgoing light from the transmissive region 1 and the reflective region 2 is equal, the transparency of the transmissive region 1 can be reduced, and the shielding layer 5 is also provided.
The invention uses one mask plate to provide a bidirectional light path to carry out optical alignment on the substrate, thereby improving the utilization rate of ultraviolet light, reducing equipment illumination units, shortening the processing time of optical alignment, greatly improving the production efficiency and greatly reducing the production cost.
It should be noted that the above mentioned embodiments are only preferred embodiments of the present invention, but the present invention is not limited to the details of the above embodiments, and it should be noted that, for those skilled in the art, it is possible to make various modifications and amendments within the technical concept of the present invention without departing from the principle of the present invention, and various modifications, amendments and equivalents of the technical solution of the present invention should be regarded as the protection scope of the present invention.