JPH11119255A - Reflection type liquid crystal display device and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a reflection type liquid crystal display device having a high reflection factor and high contrast. SOLUTION: The liquid crystal display device includes a liquid crystal layer 110 held between a 1st substrate capable of transmitting visible light and including electrodes and a 2nd substrate 101 forming a flat insulating layer 107 having pixel switching elements, scanning lines, signal lines, and contact holes and covering the pixel switching elements and an active matrix array including contact hole metals 108 filled with contact holes and reflection electrodes 109 allowed to be driven by the pixel switching elements, arranged like a matrix and capable of reflecting visible light on its surface. In the device, each pixel switching element, each contact hole metal 108 and each reflection electrode 109 are electrically connected to each other and the metal 108 and the electrode 109 are formed by respectively different materials.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reflection type liquid crystal display device for displaying television images, computer screens and the like, and a method of manufacturing the same.

[0002]

2. Description of the Related Art In recent years, liquid crystal displays have been used as display devices instead of conventional CRTs. In the field of video projectors, the conventional C
Among those using RT, those using a liquid crystal display device as a light valve have begun to be widely used in terms of high brightness and compactness.

In recent years, high-resolution displays, such as TVs, require high-definition televisions, and computer monitors require XGA and SXGA standards. However, conventional transmissive liquid crystal displays require transmittance such as wiring and pixel switch elements. Is increased (the aperture ratio is reduced), making it difficult to achieve high luminance. Therefore, a reflective liquid crystal display device in which wirings and pixel switch elements are formed below a reflective electrode has been proposed.

FIG. 5 shows a cross section of an image display section of a conventional reflection type liquid crystal display device. In the figure, 501 is a silicon substrate, 50
2 is an ion doping layer; 503 is a gate insulating layer;
4 is a gate electrode, 505 is a signal line, 506 is a source electrode, 507 is a planarization insulating layer, 508 is a reflective electrode, and 509
Is a liquid crystal layer, 510 is an alignment film, 511 is a transparent electrode, 512
Is a transparent substrate. The gate electrode and the gate immediately below the gate electrode
A pixel switch element is formed by a gate insulating film, a silicon substrate thereunder, an ion doping layer, a source electrode, and a part of a signal line, and the gate electrode also serves as a scanning line.

In a conventional liquid crystal display device, a twisted nematic (hereinafter abbreviated as TN) liquid crystal mode is mainly used for a liquid crystal layer 509. Particularly, in the case of a liquid crystal display device driven by an active matrix as shown, the twist angle of TN is 45 to 60 degrees, and the dielectric anisotropy of the liquid crystal often has a positive value. The thickness of the liquid crystal layer is 4 to
6 μm.

The basic operation of the liquid crystal display will be described. When polarized light made of a polarizing plate or the like is incident on the reflective liquid crystal display device, the polarization state is modulated while passing through the liquid crystal layer 509. The degree can be controlled by a voltage difference (electric field) applied between the transparent electrode 511 and the reflective electrode 508. The potential of the reflective electrode is generated when the pixel switch element selected by the scanning line is activated and charges are given from the signal line. Further, the output modulated light reflected from the reflection electrode can be converted into a light output amount by passing the modulated light through a polarizing plate or the like.

The manufacturing method will be described. First, a gate insulating layer, an ion doping layer, a gate electrode, a source electrode, and a signal line on a silicon substrate are formed. Thereafter, a planarizing insulating layer is formed, and a contact hole leading to the source electrode is formed by photolithography and etching.

Next, a reflective electrode is formed, and the reflective electrode is separated by photolithography and etching so as to have a predetermined size and arrangement. As a result, the source electrode and the reflection electrode are electrically connected, but a step corresponding to the thickness of the planarizing insulating layer exists in the contact hole.

An alignment film is formed on the substrate and a predetermined alignment process is performed. Separately, a transparent substrate including a transparent electrode is prepared, an alignment film is formed on the transparent electrode, a predetermined alignment process is performed, and the liquid crystal is arranged so as to face the substrate on which the reflective electrode is formed. Form a layer.

[0010]

However, in the conventional structure as described above, a step corresponding to the thickness of the planarization insulating layer exists in the contact hole in the reflective electrode. The light incident on the step portion is irregularly reflected, receives abnormal modulation, and is reflected. That is, the output modulated light of the reflection type liquid crystal display device having this structure is the sum of the modulation by the normal liquid crystal and the abnormally modulated light by the irregular reflection of the contact hole.

A particular problem arises when a black screen is created. In the modulation by the liquid crystal, the modulation direction of the output light is controlled so as to be perpendicular to the polarization direction of a polarizing plate or the like on the output side. In the control section, normal modulation control cannot be performed, and the corresponding light passes through the output side polarizing plate. This causes the black level to float in black display, and lowers the contrast (contrast = brightness in white display / brightness in black display), which is one of the important display performances of the display element.

In other words, in order to obtain a reflective display element with good contrast, all reflective electrodes need to be flat.

From the demand for flatness, a method is used in which a material for the reflective electrode 508 is formed at one end, a thickness greater than the thickness of the planarizing insulating layer 507 is formed, the surface thereof is mechanically polished and planarized, and then the reflective electrode is separated. Although aluminum, which is a high-reflectance material, is generally used for the reflective electrode, aluminum is too soft to be easily scratched and difficult to polish, and a considerable film thickness is required to fill the steps. However, the film was not practical due to film peeling and uneven polishing due to mechanical stress during polishing.

[0014]

In order to solve this problem, the present invention provides a method of forming a contact hole metal on an insulating layer under a reflective electrode by first filling only the contact hole with a contact hole metal. Then, the insulating layer is flattened including the contact hole, and a reflective electrode is formed. As a result, different materials can be used as the material for filling the contact hole and the reflective electrode material as long as electrical connection can be made.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS.

(Embodiment 1) FIG. 1 shows a cross section of an image display section of a reflection type liquid crystal display device according to Embodiment 1 of the present invention.
In FIG. 1, 101 is a silicon substrate, 102 is an ion doping layer, 103 is a gate insulating layer, 104 is a gate electrode, 105 is a signal line, 106 is a source electrode, 107 is a planarizing insulating layer, 108 is a contact hole metal, 109
Is a reflective electrode, 110 is a liquid crystal layer, 111 is an alignment film, 112
Is a transparent electrode, and 113 is a transparent substrate.

A pixel switch element is formed by a gate electrode, a gate insulating film immediately below the gate electrode, a silicon substrate thereunder, an ion doping layer, a source electrode, and a part of the signal line. In addition, the gate electrode also serves as a scanning line.

A method of manufacturing the reflection type liquid crystal display device according to the first embodiment of the present invention will be described with reference to FIG. FIG. 2 (a)
(G) is a cross-sectional view of the image display unit during the manufacturing process.

In FIG. 2, reference numeral 201 denotes a silicon substrate;
02 is an ion doping layer, 203 is a gate insulating layer, 2
04 is a gate electrode, 205 is a signal line, 206 is a source electrode, 207 is a planarization insulating layer, 208 is a contact hole metal, 209 is a reflective electrode, 210 is a liquid crystal layer, 211 is an alignment film, 212 Is a transparent electrode, and 213 is a transparent substrate.

First, a gate insulating layer 203, an ion doping layer 202, and a gate electrode 204 on a silicon substrate 201
Then, a source electrode 206 and a signal line 205 are formed (a).

Thereafter, an insulating layer (for example, a silicon oxide layer)
Is formed, the upper portion of the insulating layer is flattened by, for example, chemical mechanical polishing.

Next, a contact hole leading to the source electrode is formed on the flattening insulating layer 207 by photolithography and dry etching (FIG. 2B). Next, a blanket tungsten filling this contact hole is formed (c). As a result, the surface of the display section is substantially flattened by the flattening insulating layer 207 and blanket tungsten.

Further, the reflective electrode 209 is formed into a film, and the reflective electrode 209 is separated by photolithography and etching so as to have a predetermined size and arrangement (d). As a result, the source electrode 206 and the reflective electrode 209 are electrically connected, but there is no step in the contact hole. An alignment film 211 is formed on the substrate, and a predetermined alignment process is performed (e).

Further, a transparent substrate 213 including a transparent electrode 212 is prepared, and an alignment film 211 is formed on the transparent electrode 213.
Is formed, a predetermined alignment process is performed, and the reflection electrode 20 is formed.
(F) so as to face the substrate on which the substrate 9 is formed;
A liquid crystal layer 210 is formed in the gap (g).

(Embodiment 2) FIG. 3 shows a cross section of an image display section of a reflection type liquid crystal display device according to Embodiment 2 of the present invention.
3, reference numeral 301 denotes a silicon substrate, 302 denotes an ion doping layer, 303 denotes a gate insulating layer, 304 denotes a gate electrode, 305 denotes a signal line, and 306 denotes source electrodes 1 and 307.
Is an intermediate insulating layer, 308 is a source electrode 2, 309 is a light shielding layer, 310 is a flattening insulating layer, 311 is a contact hole metal, 312 is a reflective electrode, 313 is a liquid crystal layer, 314 is an alignment film, and 315 is an alignment film. The transparent electrode 316 is a transparent substrate.

A pixel switch element is formed by a gate electrode, a gate insulating film immediately below the gate electrode, a silicon substrate thereunder, an ion doping layer, a source electrode 1 and a part of a signal line. The gate electrode also serves as a scanning line.

A method of manufacturing the reflection type liquid crystal display device according to the second embodiment of the present invention will be described with reference to FIG. FIG. 4 (a)
(G) is a cross-sectional view of the image display unit during the manufacturing process.

In the figure, 401 is a silicon substrate, 402 is an ion doping layer, 403 is a gate insulating layer, and 404 is a gate insulating layer.
405 is a signal line, 406 is a source electrode 1, 40
7 is an intermediate insulating layer, 408 is a source electrode 2, 409 is a light shielding layer, 410 is a flattening insulating layer, 411 is a contact hole metal, 412 is a reflective electrode, 413 is a liquid crystal layer, 414 is an alignment film, 415 Is a transparent electrode, and 416 is a transparent substrate.

First, on a silicon substrate 401, a gate insulating layer 403, an ion doping layer 402 and a gate electrode 4
04, source electrode 1 (496) and signal line 405 are formed (a). Then, after forming an intermediate insulating layer (for example, a silicon oxide layer) 407, a contact hole leading to the source electrode 1 is formed by photolithography and dry etching (b).

Next, a conductive material is deposited and separated into a predetermined shape to form the source electrode 2 and the light-shielding layer 409 (c). At this time, the source electrode 1 and the source electrode 2 are electrically connected.

Next, after forming an insulating layer (for example, a silicon oxide layer), the upper portion of the insulating layer is flattened by, for example, chemical mechanical polishing. Next, the flattening insulating layer 410 is subjected to photolithography and dry etching to form a source.
A contact hole leading to the contact electrode 2 is formed (d).

Next, blanket tungsten for filling the contact hole is formed (e). As a result, the surface of the display section is substantially planarized by the planarization insulating layer 410 and blanket tungsten.

Further, the reflective electrode 412 is formed into a film, and the reflective electrode 412 is separated by photolithography and etching so as to have a predetermined size and arrangement (f). As a result, the source electrode and the reflection electrode 412 are electrically connected.
There is no step in the contact hole.

An alignment film 414 is formed on this substrate, and a predetermined alignment process is performed. Further, a transparent substrate 416 including a transparent electrode 415 is prepared, an alignment film 414 is formed on the transparent electrode 415, subjected to a predetermined alignment treatment, and further disposed so as to face the substrate on which the reflective electrode 412 is formed. ,
A liquid crystal layer 413 is formed in the gap (g).

The present embodiment is used when handling strong light as compared with the first embodiment. The reflection type liquid crystal display device reflects most of the light, but light incident on the gap between the reflection electrodes enters the device as it is. When this light is strong and reaches the semiconductor portion of the pixel switch element, the pixel switch element malfunctions. Therefore, in this embodiment, a light-blocking layer is provided in the middle of the insulating layer. The source electrode 2 also serves as a light shield.

According to the present embodiment, light that has entered the interior through a slight gap between the reflective electrodes is further shielded by the light-shielding layer and the source electrode 2 and is less likely to reach the semiconductor layer.

In the device having the structure of the first embodiment, a decrease in contrast was observed when light of 500,000 lux or more was applied, but in the second embodiment, a decrease in contrast was observed up to 4 million lux. Did not.

The description common to the first and second embodiments will be described below. In this embodiment mode, the planarization insulating layer needs to be planarized. However, any material can be used for the planarization insulating layer as long as it is an insulating material, and a material that can be easily planarized can be selected.

For example, chemical and chemical polishing of silicon oxide is so common that it has already been adopted as a standard process for producing high-density semiconductors. In particular, in the case of a reflective liquid crystal display device fabricated on a silicon substrate, the steps up to the fabrication of the reflective electrode are exactly the same as those of semiconductor processes such as DRAM and LSI. Is good. Similarly, blanket tungsten is also widely used as an electrical connection means between layers in semiconductor processes such as DRAM and LSI.

The means for filling the contact hole is
It is not necessary to separately limit, for example, a sputtering method or a CVD method.
It is also possible to selectively form a film only on the contact hole by a plating method or a plating method, or to remove a portion other than the contact hole by etching or polishing after forming a film once on the insulating layer including the contact hole. The material is not limited to tungsten, but may be copper, gold, cobalt, nickel, chromium, or an alloy thereof as necessary.

The flattening insulating layer may be made of an organic material (for example, a UV curable resin). In particular, in the case of a UV curable resin, flatness of the surface can be ensured only by forming a film, and a contact hole can be formed by UV exposure and development using a photomask, which is very simple.

The intermediate insulating layer and the planarizing insulating layer may be opaque to visible light. Also, for the reflective electrode,
High reflectivity materials such as aluminum are desirable. However, pure aluminum is very sensitive to heat and will lose its surface if exposed to even a small amount of heat. Therefore, if a small amount of impurities such as titanium, silicon, and copper are added, they become very resistant to heat. However, the addition of impurities causes a slight decrease in reflectance, so that whether to use pure aluminum or to add impurities is optimally selected depending on the subsequent temperature process.

Further, a protective layer or a dielectric mirror layer may be provided on the surface of the reflective electrode. As described above, pure aluminum is thermally weak. However, if an aluminum oxide layer having a thickness of several Å to several thousand Å is formed on the surface, heat resistance is improved. Aluminum oxide is almost transparent to visible light.

If silicon oxide or titanium oxide is laminated on aluminum with an appropriate thickness, the reflectivity is further improved. With aluminum alone, the reflectivity of the reflective electrode is 90
%, But about 95% if two or three layers of silicon oxide or titanium oxide are laminated on aluminum at an appropriate thickness. Furthermore, if about 10 layers of silicon oxide or titanium oxide are laminated with an appropriate thickness regardless of the reflectivity of the reflection electrode, a dielectric mirror can be formed only by this laminated film, and 99%
Such a high reflectance is also possible.

The liquid crystal mode of the liquid crystal layer is not particularly limited. Conventionally, the TN mode has been the mainstream, but the TN mode is not optimal for the reflection type liquid crystal display device. For example, the TN mode has a negative dielectric anisotropy, A vertical alignment mode (VA mode) in which liquid crystal molecules are aligned in a direction substantially perpendicular to the substrate in the absence of an electric field is more suitable for a reflective liquid crystal display device. For example, a 45 degree twisted TN
The contrast of the reflective LCD device of the mode is about 100, while the contrast of the VA mode exceeds 800.

In this embodiment, the alignment film is used to align the liquid crystal. However, it is not necessary depending on the liquid crystal mode which is not always necessary. A bead may be used to obtain the thickness of the liquid crystal layer. Further, a polarizing plate or a retardation plate may be attached to the reflection type liquid crystal display device.

[0047]

As described above, according to the present invention, it is possible to provide a reflective liquid crystal display device having a high reflectance and a high contrast.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of an image display unit of a reflective liquid crystal display device according to a first embodiment of the present invention.

FIGS. 2A to 2G are cross-sectional views of an image display unit during a manufacturing process of the reflective liquid crystal display device according to the first embodiment of the present invention;

FIG. 3 is a cross-sectional view of an image display section of a reflective liquid crystal display device according to a second embodiment of the present invention.

FIGS. 4A to 4G are cross-sectional views of an image display unit in a manufacturing process of the reflective liquid crystal display device according to the second embodiment of the present invention.

FIG. 5 is a cross-sectional view of an image display unit of a conventional liquid crystal display device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 101 Silicon substrate 102 Ion doping layer 103 Gate insulating layer 104 Gate electrode 105 Signal line 106 Source electrode 107 Planarization insulating layer 108 Contact hole metal 109 Reflection electrode 110 Liquid crystal layer 111 Alignment film 112 Transparent electrode 113 Transparent substrate 201 Silicon substrate 202 Ion doping layer 203 Gate insulating layer 204 Gate electrode 205 Signal line 206 Source electrode 207 Flattening insulating layer 208 Contact hole metal 209 Reflecting electrode 210 Liquid crystal layer 211 Alignment film 212 Transparent electrode 213 Transparent substrate 301 Silicon substrate 302 Ion doping layer 303 Gate insulating layer 304 Gate electrode 305 Signal line 306 Source electrode 1 307 Intermediate insulating layer 308 Source electrode 2 309 Light shielding layer 310 Flattened Insulation layer 311 Contact hole Metal 312 reflective electrode 313 liquid crystal layer 314 alignment film 315 transparent electrode 316 transparent substrate 401 silicon substrate 402 ion doping layer 403 gate insulating layer 404 gate electrode 405 signal line 406 source electrode 1 407 intermediate insulating layer 408 Source electrode 2 409 Light shielding layer 410 Flattening insulating layer 411 Contact hole metal 412 Reflecting electrode 413 Liquid crystal layer 414 Alignment film 415 Transparent electrode 416 Transparent substrate

Continuation of the front page (51) Int.Cl. ⁶ Identification code FI H01L 27/092 H01L 29/78 301X 29/78 (72) Inventor Kazuhiro Nishiyama 1006 Kazuma Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (9)

[Claims] 1. A first substrate that transmits visible light and includes an electrode,
An insulating layer having a pixel switch element, a scanning line, a signal line, and a contact hole, covering the pixel switch element, a contact hole metal filling the contact hole of the insulating layer, and being driven by the pixel switch element A second substrate on which an active matrix array including a reflective pixel electrode that reflects visible light and is arranged in a matrix is formed, and the polarization state of incident light is modulated by being sandwiched between the first and second substrates. Reflective liquid crystal display device including a liquid crystal layer, wherein the pixel switch element, the contact hole metal and the reflective pixel electrode are electrically connected, and the contact hole metal and the reflective pixel A reflective liquid crystal display device, wherein the electrodes are made of different materials. 2. A first substrate that transmits visible light and includes an electrode,
An intermediate insulating layer having a pixel switch element, a scanning line, a signal line, and a contact hole and covering the pixel switch element; and an intermediate electrode located on the intermediate insulating layer and electrically connected through the contact hole. And an insulating layer having a contact hole and covering the intermediate electrode, a contact hole metal filling the contact hole of the insulating layer, and a visible light arranged in a matrix driven by the pixel switch element. A reflective liquid crystal display including a second substrate on which an active matrix array including a reflective pixel electrode for reflecting light is formed, and a liquid crystal layer sandwiched between the first and second substrates for modulating a polarization state of incident light. The device, wherein the pixel switch element, the intermediate electrode, the contact hole metal, and the reflective pixel electrode are electrically connected, and the contact hole metal and the reflective pixel electrode are electrically connected to each other. A reflective liquid crystal display device, wherein the reflective pixel electrodes are made of different materials. 3. The reflection type liquid crystal display device according to claim 1, wherein the pixel switch element is a semiconductor element using any one of single crystal silicon, polysilicon, and amorphous silicon. 4. The reflection type according to claim 1, wherein the contact hole metal is mainly composed of tungsten or one of nickel, copper, gold, cobalt and chromium. Liquid crystal display. 5. The liquid crystal layer according to claim 1, wherein the liquid crystal layer has a negative dielectric anisotropy, and the liquid crystal molecules of the liquid crystal in the liquid crystal layer are oriented in a direction substantially perpendicular to the substrate in the absence of an electric field. 5. The reflective liquid crystal display device according to any one of items 1 to 4. 6. A step of forming an insulating layer having a contact hole on at least a substrate including a pixel switch element, a scanning line and a signal line and covering the pixel switch element; and forming the contact hole of the insulating layer. Forming a contact hole metal for filling the pixel, forming a reflective pixel electrode arranged in a matrix driven by the pixel switch element and reflecting visible light, and transmitting the visible light through the substrate. A method for manufacturing a reflection type liquid crystal display device, comprising a step of forming a liquid crystal layer for modulating the polarization state of incident light by sandwiching the first substrate including electrodes between the two substrates. 7. A step of forming an intermediate insulating layer having a contact hole on at least a substrate including a pixel switch element, a scanning line, and a signal line and covering the pixel switch element; Forming an intermediate electrode positioned and electrically connected through the contact hole; forming an insulating layer having the contact hole and covering the intermediate electrode; and forming the contact hole of the insulating layer. Forming a contact hole metal for filling the pixel, forming a reflective pixel electrode arranged in a matrix driven by the pixel switch element and reflecting visible light, and transmitting the visible light through the substrate. A method for manufacturing a reflection type liquid crystal display device, comprising a step of forming a liquid crystal layer for modulating the polarization state of incident light by sandwiching the first substrate including electrodes between the two substrates. 8. The step of forming an insulating layer having a contact hole and covering a pixel switch element or an intermediate electrode includes the steps of forming an insulating layer, flattening the insulating film, and contacting the insulating film. 8. The method according to claim 6, further comprising the step of forming a hole. 9. A contact hole metal formed by sputtering or C
The method of manufacturing a reflective liquid crystal display device according to any one of claims 6 to 8, wherein the reflective liquid crystal display device is formed by any one of a VD method, a plating method, and a high vacuum evaporation method.