JP5032188B2 - Liquid crystal display device and manufacturing method thereof - Google Patents

Description

  The present invention relates to a liquid crystal display device and a manufacturing method thereof, and more particularly to a reflective liquid crystal display device or a transflective liquid crystal display device and a manufacturing method thereof.

  With the recent progress of the advanced information society and the rapid spread of multimedia systems, the importance of liquid crystal display (LCD) devices and organic EL (ElectroLuminescence) display devices is increasing. One of the driving methods of these display devices is an active matrix type using a switching element, which is currently mainstream. In the active matrix type, for example, a TFT array substrate in which TFTs (Thin Film Transistors) as switching elements are electrically connected to each pixel electrode and arranged in an array is used.

  On the other hand, the liquid crystal display device includes a transmissive liquid crystal display device that requires a backlight, a reflective liquid crystal display device that does not require a backlight and uses reflected light from the outside, and a transflective liquid crystal device that combines both of them. There are roughly three types of display devices. Conventionally, transmissive liquid crystal display devices have been the mainstream, but the development of reflective and transflective liquid crystal display devices has been promoted due to the demand for low power consumption.

In the TFT array substrate in the reflective type and transflective type liquid crystal display devices, in order to improve the visibility, irregularities are formed on the surface of the reflective electrode electrically connected to each pixel electrode. Such an uneven shape is obtained, for example, by forming unevenness on the surface of the organic flattening film formed on the TFT channel portion and forming a reflective electrode on the organic flattening film (see Patent Document 1). .
JP 2000-347219 A

  However, in the liquid crystal display device described in Patent Document 1, it is not only necessary to form an organic planarization film, but also a reflection hole formed on the organic planarization film by forming a contact hole in the organic planarization film. It was necessary to electrically connect the electrode and the drain electrode formed under the organic flat film. For this reason, there existed a problem that the number of manufacturing processes and manufacturing cost increased, and it was inferior to productivity.

  The present invention has been made in view of such problems, and an object of the present invention is to provide a liquid crystal display device excellent in visibility and productivity and a manufacturing method thereof.

  A liquid crystal display device according to the present invention includes a gate electrode formed on a transparent insulating substrate, a gate insulating film covering the gate electrode, a semiconductor layer formed on the gate insulating film, and formed on the semiconductor layer A liquid crystal display device comprising a source electrode and a drain electrode, and a reflective electrode formed on the gate insulating film, wherein an uneven shape is formed on a surface of the gate insulating film below the reflective electrode. Is.

  The method of manufacturing a liquid crystal display device according to the present invention includes a step of forming a first metal film on a transparent insulating substrate, patterning the first metal film to form a gate electrode, and a gate covering the gate electrode. After sequentially forming the insulating film and the semiconductor layer, patterning the semiconductor layer, forming a concavo-convex shape on the gate insulating film, and forming a second metal film on the semiconductor layer and the gate insulating film And patterning the second metal film to form a source electrode and a drain electrode on the semiconductor layer, and forming a reflective electrode on the gate insulating film having the concavo-convex shape.

  ADVANTAGE OF THE INVENTION According to this invention, the liquid crystal display device excellent in visibility and productivity and its manufacturing method can be provided.

  Hereinafter, embodiments of the liquid crystal display device according to the present invention will be described. However, the present invention is not limited to the following embodiment. Further, in order to clarify the explanation, the following description and drawings are appropriately omitted and simplified.

Embodiment 1 FIG.
The structure of the transflective liquid crystal display device according to this embodiment will be described with reference to FIGS. FIG. 1 is a plan view showing a configuration of one pixel of a TFT array substrate of a transflective liquid crystal display device according to the present embodiment. 2 is a cross-sectional view taken along the line XX ′ of FIG.

  As shown in FIG. 2, the active matrix TFT array substrate according to this embodiment includes a transparent insulating substrate 1, a gate electrode / wiring 2, a gate insulating film 3, a semiconductor active film 4, an ohmic contact film 5, and a source wiring 6a. Source electrode 6b, drain electrode 7a, reflective electrode 7b, passivation film 8, pixel electrode 9, and contact hole 10. In FIG. 1, the passivation film 8 is omitted for clarity.

  As the transparent insulating substrate 1, a transparent insulating substrate such as a glass substrate or quartz glass can be used. Although the thickness of the insulating substrate 1 may be arbitrary, in order to reduce the thickness of the liquid crystal display device, a thickness of 1.1 mm or less is preferable. If the insulating substrate 1 is too thin, the substrate is distorted due to the thermal history of the process, so that the patterning accuracy is lowered. Therefore, it is necessary to select the thickness of the insulating substrate 1 in consideration of the process to be used. Further, when the insulating substrate 1 is made of a brittle material such as glass, it is preferable to chamfer the end surface of the substrate in order to prevent foreign matter from being mixed due to chipping from the end surface. Furthermore, in order to specify the direction of substrate processing in each process, it is preferable in terms of process management to provide a notch in a part of the transparent insulating substrate 1.

  The gate electrode / wiring 2 is formed on the transparent insulating substrate 1. As the gate electrode / wiring 2, a metal film mainly composed of Al, Mo, Cr, Ta, Ti, Cu or the like having a thickness of about 100 to 500 nm can be used.

The gate insulating film 3 is formed so as to cover the gate electrode / wiring 2 on the transparent insulating substrate 1. As the gate insulating film 3, a silicon nitride film (SiN _x ), a silicon oxide film (SiO _x ), a silicon oxynitride film (SiO _x N _y ), or a laminated film thereof having a thickness of about 300 to 600 nm can be used. . When the film thickness is small, a short circuit is likely to occur at the intersection of the gate electrode / wiring 2 and the source wiring 6a. On the other hand, when the film thickness is large, the ON current of the TFT becomes small and the display characteristics deteriorate.

  The semiconductor active film 4 is formed on the gate insulating film 3. As the semiconductor active film 4, an amorphous silicon (a-Si) film or a polycrystalline silicon (p-Si) film having a thickness of about 100 to 300 nm can be used. When the film is thin, the loss tends to occur during dry etching of the ohmic contact film 5 described later. On the other hand, when the film is thick, the ON current of the TFT becomes small.

When an a-Si film is used as the semiconductor active film 4, the interface between the gate insulating film 3 and the a-Si film may be SiN _x or SiO _x N _y , so that the TFT becomes conductive. From the viewpoint of controllability and reliability of the threshold voltage (V _th ) of the TFT, which is a voltage. On the other hand, in the case of using a p-Si film as the semiconductor active film 4, the interface control and reliability of _{V th} of TFT be SiO _x or _SiO x _{N y} with p-Si film of the gate insulating film 3 From the viewpoint of sex.

  The ohmic contact film 5 is formed on the semiconductor active film 4. As the ohmic contact film 5, an n-type a-Si film or an n-type p-Si film obtained by doping a small amount of P into a-Si or p-Si having a thickness of about 20 to 70 nm can be used. In the channel portion of the TFT, the ohmic contact film 5 on the semiconductor active film 4 is removed. That is, the ohmic contact film 5 is formed on one semiconductor active film 4 so as to be divided into two regions on the source side and the drain side.

  The source electrode 6b and the drain electrode 7a are formed on the ohmic contact film 5, and are connected to the semiconductor active film 4 through each of them. Further, as shown in FIG. 1, the source electrode 6b is branched from the source line 6a in a region where the source line 6a and the gate line 2 intersect in a plane. The source wiring 6 a extends to a source terminal (not shown) so as to be substantially perpendicular to the gate electrode / wiring 2.

  On the other hand, the drain electrode 7a is formed integrally with the reflective electrode 7b. Here, the reflective electrode 7 b is formed on the gate insulating film 3. As shown in FIGS. 1 and 2, since the gate insulating film 3 has a plurality of convex portions, the reflective electrode 7 b also includes a plurality of convex portions 11. That is, the surface of the reflective electrode 7b has an uneven shape. Thereby, the liquid crystal display device excellent in visibility is obtained. Further, in the liquid crystal display device according to the present invention, the drain electrode 7a and the reflective electrode 7b are integrally formed, and an organic planarizing film is unnecessary. Therefore, the manufacturing process can be simplified and the productivity is excellent.

  The source wiring 6a, the source electrode 6b, the drain electrode 7a, and the reflective electrode 7b are made of the same metal film. As this metal film, a metal film mainly composed of Cr, Al, Ag or the like having a thickness of about 100 to 500 nm can be used.

  The passivation film 8 is formed on the source wiring 6a, the source electrode 6b, the drain electrode 7a, and the reflective electrode 7b. As the passivation film 8, the same material as that of the gate insulating film 3 can be used.

  The pixel electrode 9 is formed on the passivation film 8. The pixel electrode 9 is electrically connected to the reflective electrode 7 b through a contact hole 10 formed in the passivation film 8. As the pixel electrode 9, a transparent conductive film typified by ITO can be used.

  Next, a method for manufacturing the active matrix TFT array substrate according to the first embodiment will be described with reference to FIGS. Note that the examples described below are typical, and it goes without saying that other manufacturing methods can be adopted as long as they meet the spirit of the present invention.

  As shown in FIG. 3A, a gate electrode / wiring 2 is formed on an insulating substrate 1. Specifically, first, a first metal film for forming the gate electrode / wiring 2 is formed on the insulating substrate 1 having a cleaned surface by a method such as sputtering or vacuum deposition. As a preferred embodiment, a Cr film having a thickness of 200 nm is formed by sputtering.

  Then, the first metal film is patterned by a first photolithography process (photographic process) to form gate electrodes / wirings 2. The photolithography process is as follows. After cleaning the active matrix TFT array substrate, a photosensitive resist is applied and dried. Next, it exposes through the mask pattern in which the predetermined pattern was formed, and develops, and forms the resist which transferred the mask pattern on the board | substrate photographic-enhancedly. Etching is performed after the photosensitive resist is cured by heating, and the photosensitive resist is peeled off.

  The first metal film can be etched with an etchant. For example, in the case of a Cr film, a ceric ammonium nitrate aqueous solution may be used as an etching solution. In addition, it is preferable to etch the first metal film so that the pattern edge has a tapered shape in order to prevent a short circuit at a step with another wiring. Here, the taper shape means that the pattern edge is etched so that the cross section has a trapezoidal shape.

Next, as shown in FIG. 3B, a gate insulating film 3 made of SiN _x , SiO _x , SiO _x N _y or the like, a semiconductor active film 4 made of a-Si or p-Si, n-type a-Si Alternatively, a thin film for forming the ohmic contact film 5 made of n-type p-Si is continuously formed by a plasma CVD (Chemical Vapor Deposition) method. As a preferred embodiment, an SiN _x film having a thickness of 400 nm, an a-Si film having a thickness of 200 nm, and an n-type a-Si film having a thickness of 50 nm are continuously formed. When an a-Si film is used as the semiconductor active film 4, mobility is reduced in a short film formation time by reducing the film formation rate near the interface of the gate insulating film 3 and increasing the film formation rate of the upper layer portion. A TFT with a large leakage current at the time of OFF can be obtained.

In the second photolithography process, the resist pattern 12 is formed on the region where the TFT portion is to be formed, and at the same time, the resist pattern 12 is thinner than the resist pattern 12 at a position corresponding to the convex portion 11 of the reflective electrode 7b formed in the subsequent process. A plurality of resist patterns 12a are formed. Then, the semiconductor active film 4 and the ohmic contact film 5 are patterned. The semiconductor active film 4 and the ohmic contact film 5 can be dry-etched with a known gas composition (for example, a mixed gas of SF ₆ and HCl).

  The etching process of the semiconductor active film 4 and the ohmic contact film 5 will be described in detail. First, as shown in FIG. 3C, the semiconductor active film 4 and the ohmic contact film 5 in a region where the resist patterns 12 and 12a are not formed are etched. When the etching proceeds to some extent, the thin resist pattern 12a disappears, and the underlying semiconductor active film 4 and ohmic contact film 5 begin to be etched. Accordingly, the etching proceeds in a state in which the portion where the thin resist pattern 12a has been formed forms a convex portion. In order to completely remove the semiconductor active film 4 and the ohmic contact film 5 to be removed, over etching is performed up to the gate insulating film 3. As a result, as shown in FIG. 4D, a convex portion is formed in the gate insulating film 3 when the etching is completed. That is, the surface of the gate insulating film 3 has an uneven shape. Here, this uneven shape does not reflect the uneven shape formed in the lower layer of the gate insulating film 3, but is formed on the surface of the gate insulating film 3 itself, so that precise shape control is possible. It is. Note that an ashing step may be provided in the etching process in order to surely erase the thin resist pattern 12a. Further, the height of the convex portion can be changed depending on the thickness of the resist pattern 12a. Further, it can be changed by the selection ratio of the etching rate between the semiconductor active film 4 and the gate insulating film 3.

  Next, as shown in FIG. 4E, after forming the second metal film 13 for forming the source wiring 6a, the source electrode 6b, the drain electrode 7a, and the reflective electrode 7b by a method such as sputtering, By a third photolithography process, a resist pattern 14 is formed on a region where the source wiring 6a, the source electrode 6b, the drain electrode 7a, and the reflective electrode 7b are formed from the second metal film. As a preferred embodiment, a Cr film having a thickness of 200 nm is formed by sputtering. Here, since the second metal film 13 in the region to be the reflective electrode 7b is formed on the gate insulating film 3 having the convex portion, the second metal film 13 in the region of the reflective electrode 7b is also the convex portion 11. Have As the etching method for the second metal film 13, wet etching is used. For example, when the second metal film 13 is made of Cr, a cerium ammonium nitrate aqueous solution may be used. Note that if at least the surface of the second metal film is made of Al or an Al alloy, the reflection characteristics can be further improved.

  Next, as shown in FIG. 4F, the ohmic contact film 5 in the channel portion of the TFT portion is removed by etching. Thereby, the semiconductor active film 4 is exposed in the TFT portion channel portion. The ohmic contact film 5 can be dry etched using, for example, HCl.

Next, a film for forming a passivation film 8 made of SiN _x , SiO _x , SiO _x N _y or the like is formed by a plasma CVD method. As a preferred embodiment, an SiN _x film having a thickness of 300 nm is formed. A passivation film 8 is formed from this film by a fourth photolithography process. Exposure is performed uniformly using a light shielding mask (not shown) having an opening corresponding to the contact hole 10 as shown in FIG. After the exposure step, development is performed using a developer. Thereafter, in the region corresponding to the contact hole 10, an opening is formed by the etching process, and the reflective electrode 7b is exposed.

  Next, a transparent conductive film for forming the pixel electrode 9 is formed by a sputtering method, a vacuum evaporation method, a coating method, or the like. The pixel electrode 9 is formed from the transparent conductive film by a fifth photolithography process. For example, in the case of ITO, an oxalic acid-based etching solution may be used. As a result, the active matrix TFT array substrate shown in FIG. 2 is obtained.

  The active matrix TFT array substrate manufactured as described above is bonded as a pair of substrates via a counter substrate (not shown) having a color filter and a counter electrode and a spacer, and liquid crystal is injected into the gap. A transflective liquid crystal display device is manufactured by attaching the liquid crystal panel sandwiched with the liquid crystal layer to the backlight unit. The present invention can also be applied to a reflective liquid crystal display device. In the case of a reflective type, a backlight unit is not necessary.

Embodiment 2
Next, an embodiment different from the TFT array substrate according to Embodiment 1 will be described. In the following description, the same components as those in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted as appropriate. The TFT array substrate according to the first embodiment and the TFT array substrate according to the second embodiment have the same basic configuration, but are different in the method of forming the convex portion 11 of the reflective electrode 7b. Specifically, the method of forming the convex portion of the gate insulating film 3 is different.

A method for manufacturing an active matrix TFT array substrate according to the second embodiment will be described with reference to FIG. After forming the gate electrode 2, the gate insulating film 3 made of SiN _x , SiO _x , SiO _x N _y or the like, the semiconductor active film 4 made of a-Si or p-Si, n-type a-Si or n-type p-Si The process is the same as in the first embodiment until the thin film for forming the ohmic contact film 5 is continuously formed by plasma CVD (Chemical Vapor Deposition).

  Next, as shown in FIG. 5A, in the second photolithography process, a resist pattern 12 is formed on the region where the TFT portion is to be formed, and at the same time, the convex portion of the reflective electrode 7b formed in a later step. A plurality of resist patterns 12 b are formed at positions corresponding to 11. Here, in the first embodiment, the resist pattern 12a is thinner than the resist pattern 12, but in the second embodiment, the resist pattern 12b and the resist pattern 12 may have the same thickness. Then, the semiconductor active film 4 and the ohmic contact film 5 are patterned. Here, the semiconductor active film 4 and the ohmic contact film 5 are wet-etched with a hydrofluoric acid-based etchant instead of dry etching.

  The etching process of the semiconductor active film 4 and the ohmic contact film 5 will be described in detail. First, as shown in FIG. 5B, the semiconductor active film 4 and the ohmic contact film 5 in the region where the resist patterns 12 and 12b are not formed are etched. When the etching proceeds to some extent, the resist pattern 12b is lifted off by side etching the semiconductor active film 4 and the ohmic contact film 5 therebelow. Therefore, the underlying semiconductor active film 4 and ohmic contact film 5 begin to be etched from the surface. Accordingly, the etching proceeds in a state where the portion where the resist pattern 12b is formed forms a trapezoidal convex portion. In order to completely remove the semiconductor active film 4 and the ohmic contact film 5 to be removed, over etching is performed up to the gate insulating film 3. As a result, as shown in FIG. 5C, a convex portion is formed in the gate insulating film 3 when the etching is completed. That is, the surface of the gate insulating film 3 has an uneven shape. The subsequent manufacturing steps are the same as those in the first embodiment.

  A plurality of convex portions are also formed on the gate insulating film 3 of the liquid crystal display device according to the second embodiment, and the reflective electrode 7 b formed thereon has the plurality of convex portions 11. That is, the surface of the reflective electrode 7b has an uneven shape. Thereby, the liquid crystal display device excellent in visibility is obtained. The drain electrode 7a and the reflective electrode 7b are integrally formed, and an organic planarizing film is unnecessary. Therefore, the manufacturing process can be simplified and the productivity is excellent.

Embodiment 3
Next, an embodiment different from the TFT array substrate according to the first and second embodiments will be described. In the following description, the same components as those in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted as appropriate. The TFT array substrate according to the first embodiment and the TFT array substrate according to the third embodiment have the same basic configuration, but are different in the method of forming the convex portion 11 of the reflective electrode 7b. Specifically, the method of forming the convex portion of the gate insulating film 3 is different.

A method for manufacturing an active matrix TFT array substrate according to the third embodiment will be described with reference to FIG. After forming the gate electrode 2, the gate insulating film 3 made of SiN _x , SiO _x , SiO _x N _y or the like, the semiconductor active film 4 made of a-Si or p-Si, n-type a-Si or n-type p-Si The process is the same as in the first embodiment until the thin film for forming the ohmic contact film 5 is continuously formed by plasma CVD (Chemical Vapor Deposition).

  Next, as shown in FIG. 6A, a transparent conductive film 14 containing indium oxide is formed on the ohmic contact film 5. The film thickness is preferably about 80 nm. When forming the transparent conductive film 14, the transparent insulating substrate 1 is preheated in a temperature range of 100 to 175 ° C., or after the transparent conductive film 14 is formed, it is heated in the above temperature range.

  Next, the transparent conductive film 14 is wet-etched using oxalic acid, whereby indium crystals 15 remain on the ohmic contact film 5 as shown in FIG. 6B.

Next, as shown in FIG. 6C, a resist pattern 12 is formed on the region for forming the TFT portion by the second photolithography process. Then, the semiconductor active film 4 and the ohmic contact film 5 are dry-etched with, for example, a mixed gas of SF ₆ and HCl. Here, the indium crystal 15 functions as a mask. Therefore, first, the semiconductor active film 4 and the ohmic contact film 5 in the region where the resist pattern 12 and the crystal 15 are not formed are etched. When the etching proceeds to some extent, the indium crystal 15 disappears, and the semiconductor active film 4 and the ohmic contact film 5 therebelow start to be etched. Therefore, the etching proceeds in a state where the portion where the crystal 15 is formed forms a fine convex portion. In order to completely remove the semiconductor active film 4 and the ohmic contact film 5 to be removed, over etching is performed up to the gate insulating film 3. Thereby, as shown in FIG. 6D, a convex portion is formed in the gate insulating film 3 when the etching is completed. That is, the surface of the gate insulating film 3 has an uneven shape. The subsequent manufacturing steps are the same as those in the first embodiment.

  A plurality of convex portions are also formed on the gate insulating film 3 of the liquid crystal display device according to the third embodiment, and the reflective electrode 7 b formed thereon has the plurality of convex portions 11. That is, the surface of the reflective electrode 7b has an uneven shape. Thereby, the liquid crystal display device excellent in visibility is obtained. The drain electrode 7a and the reflective electrode 7b are integrally formed, and an organic planarizing film is unnecessary. Therefore, the manufacturing process can be simplified and the productivity is excellent.

It is a top view which shows the structure of the TFT array substrate which concerns on embodiment of this invention. It is XX 'sectional drawing of FIG. FIG. 6 is a cross-sectional view showing a manufacturing process of the TFT array substrate according to the first embodiment. FIG. 6 is a cross-sectional view showing a manufacturing process of the TFT array substrate according to the first embodiment. 11 is a cross-sectional view showing a manufacturing process of the TFT array substrate according to the second embodiment. FIG. 12 is a cross-sectional view showing a manufacturing process of the TFT array substrate according to the third embodiment. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Transparent insulating substrate 2 Gate electrode and wiring 3 Gate insulating film 4 Semiconductor active film 5 Ohmic contact film 6a Source wiring 6b Source electrode 7a Drain electrode 7b Reflective electrode 8 Passivation film 9 Pixel electrode 10 Contact hole 11 Convex parts 12, 12a, 12b , 14 Resist pattern 13 Second metal film 14 Transparent conductive film 15 Indium crystal

Claims (10)

A gate electrode formed on a transparent insulating substrate having a flat surface ;
A gate insulating film formed on the transparent insulating substrate so as to cover the gate electrode;
A semiconductor layer formed on the gate insulating film;
A source electrode and a drain electrode formed on the semiconductor layer;
A liquid crystal display device comprising a reflective electrode formed on the gate insulating film,
Under the reflective electrode, with the back surface of the gate insulating film is flat, the surface is a liquid crystal display device having an uneven shape.   The liquid crystal display device according to claim 1, wherein the drain electrode and the reflective electrode are integrally formed.   The liquid crystal display device according to claim 1, wherein the semiconductor layer includes a semiconductor active film and an ohmic contact film. Forming a first metal film on the transparent insulating substrate and patterning the first metal film to form a gate electrode;
Sequentially forming a gate insulating film and a semiconductor layer covering the gate electrode, patterning the semiconductor layer, and forming an uneven shape on the gate insulating film;
Forming a second metal film on the semiconductor layer and the gate insulating film; patterning the second metal film to form a source electrode and a drain electrode on the semiconductor layer; And a step of forming a reflective electrode on the film.   5. The method of manufacturing a liquid crystal display device according to claim 4, wherein a resist pattern is formed on the TFT formation region and the concavo-convex shape formation region in the semiconductor layer, and the semiconductor layer is patterned.   6. The method of manufacturing a liquid crystal display device according to claim 5, wherein the resist pattern on the uneven shape forming region disappears in the etching process of the semiconductor layer.   6. The method of manufacturing a liquid crystal display device according to claim 5, wherein the resist pattern on the uneven shape forming region is lifted off in the etching process of the semiconductor layer. Before patterning the semiconductor layer, a transparent conductive film containing indium oxide is formed on the semiconductor layer, the transparent conductive film is etched using an oxalic acid-based etching solution, and then the semiconductor layer is patterned. The method of manufacturing a liquid crystal display device according to claim 4. The method according to any one of claims 4-8, characterized in that integrally formed with the reflective electrode and the drain electrode. The semiconductor layer manufacturing method of the liquid crystal display device according to any one of claims 4-9, characterized in that it comprises a semiconductor active film and an ohmic contact film.

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