Patent Application
20100220270
The present application contains subject matter related to that disclosed in Japanese Priority Patent Application JP 2009-046626 filed in the Japan Patent Office on Feb. 27, 2009, the entire content of which is hereby incorporated by reference.
The present application relates to a method for forming a reflection electrode used for a display device, such as a liquid crystal display device, and to a drive substrate and a display device, each of which includes the reflection electrode.
In the present days, in a reflection type liquid crystal device used for a mobile apparatus or the like, unlike a transmissive liquid crystal device including a so-called backlight, a display is performed using light incident from the surrounding environment. Accordingly, it is necessary to reflect light incident from the surrounding environment to an observer side while the loss of the light is decreased as low as possible.
As a reflection layer used in the reflection type liquid crystal device, for example, an intra-LCC (liquid crystal cell) diffuse reflection plate method, an extra-LCC reflection plate method, and a forward scattering reflection plate method have been used, and among those mentioned above, the intra-LCC diffuse reflection plate method has been frequently used because of its significantly superior display characteristics.
A reflection electrode used in this intra-LCC diffuse reflection plate method can be obtained when a metal thin film of aluminum (Al), silver (Ag), or the like, which is used as a pixel electrode, is formed to have a concave-convex surface. In particular, the following method may be mentioned. That is, for example, after thin film transistors (TFTs) are formed on a substrate, an interlayer insulating film is formed on the TFTs, and after the surface of this interlayer insulating film is patterned by a photolithographic method, a concave-convex shape is formed by performing a heat treatment. Subsequently, a metal thin film to be formed into reflection electrodes is formed over the entire surface of the substrate by vacuum film formation and is then patterned by a photolithographic method (see Japanese Patent Nos. 3895059 and 3866522). In addition, the following method may also be used. In this method, after TFTs are formed on a substrate, a resin film is formed on the TFTs with an interlayer insulating film interposed therebetween, the resin film thus formed is patterned into a stripe shape by a photolithographic method, and a heat treatment is performed to deform the resin film thus patterned. Subsequently, after a resin is further applied on the deformed resin film to form a smooth concave-convex surface, a metal thin film to be formed into reflection electrodes is formed over the entire surface of the substrate by vacuum deposition, and this metal thin film is patterned by a photolithographic method (Japanese Unexamined Patent Application Publication No. 2002-229060).
Compared to a method in which an electrode surface is directly roughened by a sandblast method or the like and to a method in which after silicon dioxide (SiO2) or the like is taper-etched, a metal thin film is formed, the methods described above each have an advantage in that no process damage is done to the elements. In addition, since a smooth concave-convex shape can be easily controlled, the methods described above have been widely used.
However, according to the methods described above, a photolithographic method using a resist (photosensitive resin) material is necessarily used in order to control the shape of the interlayer insulating film and to pattern the metal film after the formation thereof, and as a result, the number of steps is disadvantageously increased in the methods described above.
The present application has been conceived in consideration of the problem described above, and it is desirable to provide a method for forming a reflection electrode by a simple process, and a drive substrate and a display device, each of which uses the reflection electrode described above.
In accordance with an embodiment of the present application, there is provided a method for forming a reflection electrode which includes the following steps (A1) to (D1). That is, the method includes a step (A1) of forming a first catalytic layer in a first region of an electrode forming region of a substrate; a step (B1) of forming a first plating layer on the first catalytic layer by performing a first electroless plating treatment; a step (C1) of forming a second catalytic layer at least in a region (second region) of the electrode forming region other than the first region; and a step (D1) of forming a second plating layer on the second catalytic layer by performing a second electroless plating treatment, so that the reflection electrode is formed to have a concave-convex surface.
In accordance with an embodiment of the present application, there is provided a drive substrate including a substrate which has a reflection electrode having a concave-convex surface in an electrode forming region, and the reflection electrode has a first catalytic layer (A2) provided in a first region of the electrode forming region; a first plating layer (B2) provided on the first catalytic layer; a second catalytic layer (C2) provided at least in a region (second region) of the electrode forming region other than the first region; and a second plating layer (D2) provided on the second catalytic layer.
In accordance with an embodiment of the present application, there is provided a display device which includes a drive substrate having reflection electrodes provided in electrode forming regions; and a display portion which performs a display using incident light reflected by the reflection electrodes.
In the display device described above, light incident from the outside is efficiently reflected by concave-convex portions of the reflection electrodes each formed of the first and the second plating layers and is then sent to a side of the display portion, such as a liquid crystal layer; hence, a display is performed.
In the method for forming a reflection electrode according to an embodiment of the present application, after the first plating layer is formed by selectively performing the first electroless plating treatment on the first region of the electrode forming region on the substrate, the second electroless plating treatment is performed on the remaining second region; hence, a reflection electrode having a concave-convex shape can be formed in a desired region. Accordingly, compared to a related case in which a photolithographic method is used, the reflection electrode can be formed by simple steps. In addition, the usage amount of a photosensitive resin can be reduced, and hence cost can be reduced. As a result, by using the method described above, an inexpensive drive substrate and an inexpensive display device can be realized.
Additional features and advantages are described herein, and will be apparent from the following Detailed Description and the figures.
The present application will be described with reference to the drawings according to an embodiment.
1. First embodiment
(1) Whole structure of a liquid crystal display device.
(2) Formation method 1 of a reflection electrode (an example in which a second catalytic layer is provided between a first plating layer and a second plating layer.)
2. Second embodiment (an example in which a second catalytic layer is not provided between a first plating layer and a second plating layer.)
3. Third embodiment (an example in which a third plating layer (Ag layer) is provided.)
4. Fourth embodiment (the same as that of the third embodiment.)
In more particular, a gate electrode 11, a gate insulating film 12, a semiconductor layer (channel) 13, source/drain electrodes 14 are formed on the substrate 10 in that order, and a protective film 15 and an interlayer insulating film 16 are formed on the source/drain electrodes 14. A contact hole 16A is formed in the interlayer insulating film 16, and each reflection electrode 5 is formed in the contact hole 16A (the bottom portion and sidewall thereof) and on the interlayer insulating film 16 with an adhesive layer 17 interposed therebetween. In this embodiment, the reflection electrode 5 is formed by using an electroless plating method as described below and includes a first catalytic layer 18, a first plating layer 19, a second catalytic layer 20, and a second plating layer 21.
The substrate 10 is formed, for example, from silicon, synthetic quartz, glass, metal, resin, or a resin film. The gate electrode 11 is formed from chromium (Cr), molybdenum (Mo), or the like, and the gate insulating film 12 is formed from silicon oxide (SiOx), silicon nitride (SiNx), or the like. The semiconductor layer 13 is formed from a semiconductor material such as amorphous silicon (a-Si), and the source/drain electrodes 14 are formed from a metal material, such as aluminum (Al). The protective film 15 is formed from an insulating material such as silicon nitride (SiNx). Although the interlayer insulating film 16 is formed from SiNx or the like as in the case of the gate insulating film 12, any material may also be used as long as it has, for example, a low dielectric constant, heat resistance, a mechanical strength, and an effect of preventing diffusion of a wire metal.
The adhesive layer 17 is a layer to enhance the adhesion of the first catalytic layer 18 and the second catalytic layer 20 to the interlayer insulating film 16. As a material forming this adhesive layer 17, for example, there may be mentioned a silane coupling agent containing at least one selected from an amino-based silane compound, a mercapto-based silane compound, a phenyl-based silane compound, an alkyl-based silane compound, and the like. As the adhesive layer 17, an appropriate compound may be selected in accordance with materials forming the first catalytic layer 18, the second catalytic layer 20, and the interlayer insulating film 16. In addition, as the silane coupling agent, in particular, for example, KBM-603 (trade name) (N-2(aminoethyl)-3-aminopropyltrimethoxysilane) manufactured by Shin-Etsu Chemical Co., Ltd. may be used.
In this embodiment, the surface of the interlayer insulating film 16 and an inside area of the contact hole 16A are used as an electrode forming region, and in this electrode forming region, the reflection electrode 5 having a concave-convex surface is formed. The first catalytic layer 18 of the reflection electrode 5 is provided on the interlayer insulating film 16 to form a predetermined pattern. Although the cross-sectional shape of this first catalytic layer 18 is divided into a plurality of segments, the plan shape has, for example, a mesh pattern as shown in
The thickness of the first catalytic layer 18 is, for example, approximately several to ten nanometers. When the patterning accuracy, the adhesion to the adhesive layer 17, and the usage amount of the material are taken into consideration, the thickness of the first catalytic layer 18 is preferably decreased as long as it functions as an electroless plating catalyst. The second catalytic layer 20 is formed on the first plating layer 19 provided on the interlayer insulating film 16 and on the adhesive layer 17 in the region (second region) other than the first region of the first catalytic layer 18 as in the case of the first catalytic layer 18. The first catalytic layer 18 and the second catalytic layer 20 each include at least one catalytic material selected from palladium (Pd), gold (Au), platinum (Pt), silver (Ag), and the like, used for an electroless plating treatment which will be describe later.
The first plating layer 19 is a layer grown on the patterned first catalytic layer 18 and has a thickness, for example, of approximately several tens to several hundreds of nanometers. The second plating layer 21 is formed so as to cover the first plating layer 19 formed on the first catalytic layer 18 and the second catalytic layer 20 and has a thickness, for example, of several hundreds of nanometers. The first plating layer 19 and the second plating layer 21 are plating layers each deposited by the electroless plating treatment which will be described later.
As an electroless plating material forming the first plating layer 19 and the second plating layer 21 described above, for example, a single metal, such as nickel (Ni), copper (Cu), gold (Au), silver (Ag), palladium (Pd), cobalt (Co), platinum (Pt), indium (In), tin (Sn), or rhodium (Rd), may be used. In addition, a metal which can generate a eutectic form with the metal mentioned above, such as phosphorous (P), boron (B), chromium (Cr), manganese (Mg), iron (Fe), zinc (Zn), molybdenum (Mo), cadmium (Cd), tungsten (W), rhenium (Re), titanium (Ti), sulfur (S), or vanadium (V), may also be used.
However, materials forming the first plating layer 19 and the second plating layer 21 are appropriately selected in association with materials forming the first catalytic layer 18 and the second catalytic layer 20, each of which functions as a catalyst of the electroless plating treatment.
In addition, the structure of the reflection electrode 5 as described above can be easily identified by one of the following methods (1) to (5).
(1) A cross-sectional shape of the reflection electrode 5 is observed, for example, by a scanning electron microscope (SEM).
(2) A cross section of the reflection electrode 5 is observed, for example, by a transmission electron microscope (TEM) to detect a catalytic material (the first catalytic layer 18 and the second catalytic layer 20) of the electroless plating treatment.
(3) Whether a metal capable of generating a eutectic form is included in the reflection electrode 5 or not is detected, for example, by secondary ion-microprobe mass spectrometry (SIMS) or x-ray photoelectron spectroscopy (XPS). For example, when the first plating layer 19 and the second plating layer 21 are formed to include nickel, it is also detected whether boron and/or phosphorous is contained or not.
(4) Whether an additive, such as an organic compound, used for the electroless plating treatment is included in the reflection electrode 5 or not is detected, for example, by SIMS.
(5) The roughness of the surface is observed, for example, by an atomic force microscope (AFM) or a stylus meter. However, when any type of surface treatment is performed after the electroless plating treatment, the evaluation is difficult to perform.
For example,
The counter substrate 2 includes, for example, a polarizer 23, a retardation film 24, a color filter 25, and a transparent electrode (common electrode) 26 on a glass substrate 22.
[Manufacturing Method]
Next, a method for manufacturing the drive substrate 1 including the reflection electrode 5 will be described with reference to
(1. Formation of a TFT)
First, as shown in
Subsequently, as shown in
(2. Formation of the Interlayer Insulating Film 16 and the Adhesive Layer 17)
Next, as shown in
(3. Formation of the Reflection Electrode 5)
Next, as shown in
Finally, as shown in
After the drive substrate 1 including the reflection electrodes 5 is placed to face the counter substrate 2 and is sealed thereto which is additionally formed, the liquid crystal layer 3 is formed by injecting a liquid crystal between the drive substrate 1 and the counter substrate 2. As a result, the liquid crystal display device shown in
In this liquid crystal display device, light incident from the outside (surrounding environment) is efficiently reflected (diffuse-reflected) to a side of the liquid crystal layer 3 by the concave-convex portion of the reflection electrode 5 formed by the first plating layer 19 and the second plating layer 21, and as a result, a display can be performed.
(Another Structural Example of the Reflection Electrode 5)
In the first embodiment described above, since the second catalytic layer 20 is formed on the first plating layer 19, depending on the thickness of the second catalytic layer 20, the type of electroless plating solution to be used, and the process conditions, the adhesion between the first plating layer 19 and the second plating layer 21 may be degraded in some cases.
In this embodiment, it is attempted to improve the adhesion between the first plating layer 19 and the second plating layer 21. Since the steps shown in
When the pattern shape of the first catalytic layer 18 and that of the second catalytic layer 20 are controlled, and the film forming time of the first plating layer 19 and that of the second plating layer 21 are also controlled, the cross section of the reflection electrode 5 can be formed to have a desired shape. In addition, when a heat treatment is performed in a vacuum atmosphere, for example, at 200° C. after the second plating layer 21 is formed, the resistance thereof is decreased, and hence it can be used as an electrode. Furthermore, the second plating layer 21 is a so-called autocatalytic plating layer which is deposited using the first plating layer 19 as a catalyst.
Next, the operation and effect by the reflection electrode 5 and the formation method thereof will be described with reference to Comparative Examples 1 and 2.
In Comparative Example 1, as shown in
In Comparative Example 2, patterning of the interlayer insulating film 16 is performed by a photolithographic method using a half tone mask (or a two-stage exposure) as shown in
In the formation method of the reflection electrode 100 according to Comparative Examples 1 and 2, a step, such as etching, using a photoresist is necessarily performed two to three times, and hence the number of steps is unfavorably increased. In addition, since the photoresist is consumed in each photolithographic step, cost is disadvantageously increased.
On the other hand, in this embodiment, the first catalytic layer 18 is first formed in a predetermined region (first region) on the drive substrate 1 to form a plating layer, and a first electroless plating treatment is performed on this first catalytic layer 18, so that the first plating layer 19 is formed. Subsequently, the second catalytic layer 20 is formed at least in the region (second regions) other than the first region of the first catalytic layer 18, and a second electroless plating treatment is performed on the second catalytic layer 20, so that the second plating layer 21 is formed. As a result, the reflection electrode 5 having concave-convex surface can be formed in a desired region.
That is, in this embodiment, by the two-stage electroless plating treatment, the concave-convex shape of the reflection electrode 5 is formed without using an etching step or the like. Hence, compared to the case in which a photolithographic method is used as in Comparative Examples 1 and 2, a patterning step performed after the film formation is not necessary, and a reflection electrode having a concave-convex shape can be formed by simple steps. In addition, since the usage amount of a photosensitive resin (resist) can be reduced, cost can be reduced, and in addition, since an etching solution or an etching gas is not used, an environmental load can also be reduced.
In addition, in this embodiment, for example, when the thicknesses of the first catalytic layer 18, the second catalytic layer 20, the first plating layer 19, and the second plating layer 21 are appropriately selected, the reflection electrode 5 can be easily formed to have a desired concave-convex shape.
In this embodiment, although the Ni—B layers are formed as the first plating layer 19 and the second plating layer 21, when a metal layer, such as a Ag layer, having a higher optical reflectance is formed on the surface of the Ni—B layer, the reflectance of the reflection electrode 5 can be improved. Hereinafter, examples of the above case will be described.
In this embodiment, as shown in
In this embodiment, as shown in
Hereinafter, a particular example will be described.
First, a film of a metal (Cr) to be formed into the gate electrode 11 was formed on the substrate 10 by a sputtering method, and the gate electrode 11 was formed by patterning using a photolithographic method. Next, a film of a material (SiNx) to be formed into the gate insulating film 12 was formed, and as the semiconductor layer 13, an a-Si layer (channel) and an n+ a-Si layer to be formed into the contact layers (not shown) to be contact with the source/drain electrodes 14 were sequentially formed. Next, the semiconductor layer 13 thus formed was patterned by etching using a resist mask so as to have an island shape. Subsequently, a film of a metal (such as Al) to be formed into the source/drain electrodes 14 was formed by a vacuum process and was then patterned into a desired shape by etching using a resist mask, so that the source/drain electrodes 14 were formed. Next, after the n+ a-Si layer (not shown) formed on the a-Si layer was etched, the protective film 15 (SiNx) was formed, and the interlayer insulating film 16 was then formed thereon.
Next, after the interlayer insulating film 16 was patterned by a photolithographic method to form a concave portion at a place at which the contact hole 16A for a TFT was to be formed, a surface treatment was performed on the surface of the interlayer insulating film 16 by a spin coating method using a silane coupling agent of the aforementioned material, so that the adhesive layer 17 was formed. In this step, the silane coupling agent diluted by a solvent was used, and after the treatment was performed, heating was performed at 120° C. for 5 minutes or more. As an amino-based silane coupling agent to be formed into the adhesive layer 17, KBM-603 (trade name) manufactured by Shin-Etsu Chemical Co., Ltd. was used. In addition, after the silane compound layer was formed on the substrate by a vapor phase method, in order to remove an excess silane compound, ultrasonic washing was performed using a solvent, such as ethanol or isopropyl alcohol (IPA), followed by drying.
Next, the first catalytic layer 18 was formed from palladium fine particles used as a catalyst by patterning using an inversion offset method, and the substrate was then immersed in an electroless plating solution, so that the first plating layer 19 was formed. As the plating solution, a Ni—B film forming plating solution, BEL-801 (trade name), manufactured by C. Uyemura Co., Ltd. was used. When the temperature of the plating bath was set to 60° C., and the immersion was performed for 3 minutes, a Ni—B plating layer having a thickness of approximately 450 nm was formed. Subsequently, the second plating layer 21 was formed. First, as in the case of the first catalytic layer 18 described above, the second catalytic layer 20 is first formed on the first plating layer 19 and the adhesive layer 17 by an inversion offset method, and the substrate was then immersed in an electroless plating solution for 2 minutes, so that the second plating layer 21 having a thickness of approximately 200 nm was formed in a necessary region. By this process, the reflection electrode 5 was formed to have a step of approximately 450 nm between a concave and a convex portion. In addition, after the first plating layer 19 was formed, a heat treatment was performed at 200° C. in a vacuum atmosphere, so that the resistance of the first plating layer 19 was decreased.
Heretofore, although the present application has been described with reference to the first to the fourth embodiments and the example, the present application is not limited to those embodiments and the like and may also be variously modified. For example, when the contact characteristics with the source/drain electrodes 14 may cause a problem, without forming the adhesive layer 17, the plating layer may be directly formed on the interlayer insulating film 16.
In addition, in this embodiment, although the first plating layer 19 and the second plating layer 21 are formed from the same type of metal (such as Ni—B), they may be formed from metal materials different from each other. For example, the second plating layer 21 may be formed from Ag, and the first plating layer 19 may be formed from another metal (such as Ni).
In addition, in the above embodiments and the like, although the reflection type liquid crystal display device is described by way of example which performs a display using light reflected by the reflection electrode instead of illumination light emitted from a backlight, the display device according to an embodiment of the present application is not limited thereto. For example, the present application may also be applied to a so-called semi-transmissive liquid crystal display device which performs a display using both reflection light of outside light and illumination light emitted from a backlight, the backlight being provided at a rear side of a liquid crystal panel as well as reflection electrodes provided only in some regions of an effective display region.
Furthermore, the material and the thickness of each constituent element, and the film forming method and the conditions thereof, which are described in the above embodiments and the like, are not particularly limited; hence, another material and another thickness may also be selected, and another film forming method and other film forming conditions may also used.
It should be understood that various changes and modifications to the presently preferred embodiments described herein will be apparent to those skilled in the art. Such changes and modifications can be made without departing from the spirit and scope and without diminishing its intended advantages. It is therefore intended that such changes and modifications be covered by the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| P2009-046626 | Feb 2009 | JP | national |
