JPH11186558A - Thin-film transistor and its manufacture method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a reflection electrode self-alignedly by a method, wherein a drain region is extended and formed into the shape of a display pixel electrode, and silver or a silver alloy is formed on at least the drain region. SOLUTION: An interlayer insulation layer 5 is deposited on a substrate 1, and an opening part 6 is formed on its gate electrode 2 and its source electrode 4. It is patterned to be an active layer 7 for depositing a silicon thin film, and a source region and a drain region 8 where impurity ions are implanted on the active layer 7, and a channel region 9 positioned in a region upward of the gate electrode 2 where impurities are not introduced are formed. A planting layer 10 consisting of silver is formed on the surface of the exposed source region and drain region 8 by a plating method. Since the plating layer 10 is formed directly on the drain region 8 formed by a semiconductor thin film 7, a reflection electrode can be formed self-alignedly.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thin film transistor as a switching element used for driving a pixel electrode of an active matrix type liquid crystal display device and the like, and a method of manufacturing the same. The present invention relates to a thin film transistor having an electrode made of a material and a method for manufacturing the same.

[0002]

2. Description of the Related Art In recent years, semiconductor devices typified by ICs and LSIs, and electronic devices or home appliances incorporating these semiconductor devices have been developed and sold in large quantities on the market. Currently, not only TV receivers, V
TRs, personal computers, and the like are also widely spread and are no longer rare. Among them, a liquid crystal display device has attracted attention as a display having advantages of being thin, lightweight and low power consumption. In particular, an active matrix type liquid crystal display device in which a switching element such as a thin film transistor (hereinafter, referred to as a TFT) is provided for each pixel so as to control each pixel can provide excellent resolution and a clear image. It has been noted for reasons.

[0003] As a conventional active element, a TFT using an amorphous silicon thin film is known.
Many active matrix type liquid crystal display devices equipped with are commercially available. At present, as an active element replacing the TFT using the amorphous silicon thin film, a pixel TFT for driving a pixel electrode and a TF for driving the pixel are used.
There is great expectation for a technique for forming a TFT using a polycrystalline silicon thin film, which has a possibility that a driving circuit for driving T can be integrally formed on one substrate.

A polycrystalline silicon thin film has higher mobility than an amorphous silicon thin film used for a conventional TFT, and it is possible to form a high-performance TFT. If the driving circuit for driving the pixel driving TFT is integrally formed on one inexpensive glass substrate, the manufacturing cost will be significantly reduced as compared with the related art.

As a technique for forming a polycrystalline silicon thin film to be an active layer of such a polycrystalline silicon TFT on a glass substrate, there is a technique of depositing an amorphous silicon thin film on a glass substrate and then forming the amorphous silicon thin film at a temperature of about 600 ° C. A solid phase growth method that heats and crystallizes for a period of time to several tens of hours, or a laser crystallization method that irradiates a pulsed laser beam such as an excimer laser and immediately melts and recrystallizes the amorphous silicon thin film in that area. Such methods have been proposed.

In this active matrix type liquid crystal display device, an ITO (Indium Tin Ox) is applied to a pixel electrode.
There are a transmission type liquid crystal display device using a transparent conductive thin film such as (ide) and a reflection type liquid crystal display device using a reflection electrode such as a metal for a pixel electrode. Originally, a liquid crystal display device is not a self-luminous display, so in the case of a transmissive liquid crystal display device, an illumination device, a so-called backlight, is arranged behind the liquid crystal display device, and display is performed by light incident from there. It is carried out. In the case of a reflective liquid crystal display device, display is performed by reflecting external incident light by a reflective electrode.

In the case of such a transmission type liquid crystal display device,
Since the display is performed using the backlight as described above, this liquid crystal has an advantage that a display having a high contrast can be performed without being greatly affected by ambient brightness or the like. When the display device is used as an electronic device, there is a problem that power consumption as a whole becomes large. At present, many such transmissive liquid crystal display devices are commercialized.

On the other hand, in the case of the reflection type liquid crystal display device, since no backlight is used, there is a problem that the brightness and contrast of the display are affected by the use environment or use conditions, that is, the brightness of the surroundings. ing. However, considering the actual working environment at work and at home, except in extreme cases, it is considered that this effect is not so serious. Such a reflective liquid crystal display device has an advantage that when used as an electronic device, the power consumption as a whole can be extremely reduced. Is underway.

A pixel electrode made of a transparent conductive thin film such as ITO or a metal as described above is made of TF.
It is connected to the drain electrode of T, and is formed so as to have a certain distance therefrom so as not to short-circuit with the adjacent gate wiring or source wiring. In recent years, in order to increase the effective area of the pixel electrode, an interlayer insulating film 51 made of a polyimide resin or an acrylic resin is formed on the entire surface of the substrate 50 including the TFT as shown in FIG. The drain electrode 52 of the TFT and the pixel electrode 55 formed on the interlayer insulating film 51 through the opened contact hole 54
The pixel electrode structure on the protective film that connects to
(Referred to as an on-passive structure).

According to this structure, the pixel electrode 55 is insulated from the gate wiring and the source wiring by the interlayer insulating film 51 made of a polyimide resin, an acrylic resin, or an inorganic insulating film. It is possible to dispose the pixel electrode 55 over the gate line and the source line, thereby increasing the effective area of the pixel electrode 55, that is, the aperture ratio. Furthermore, the interlayer insulating film 51 made of a polyimide resin or an acrylic resin can easily flatten a step caused by the TFT, the gate wiring, and the source wiring, and thus has an effect of extremely reducing the disorder of the alignment of the liquid crystal layer 56. Have.

As described above, in the transmission type liquid crystal display device, although the power consumption of the liquid crystal panel itself is very small, the power consumption of the whole device is greatly increased by using the backlight. Therefore, in order to take advantage of a liquid crystal display device which originally consumes low power, practical use of a reflection type liquid crystal display device is urgent.

Until now, in order to realize a reflective liquid crystal display device having good brightness and contrast, for example, Japanese Patent Application Laid-Open No. Hei 8-179252 discloses an aluminum thin film (hereinafter, referred to as Al) serving as a reflective electrode. A method has been proposed in which another metal film is provided below to improve the degree of orientation of Al to obtain a high reflectance.

In order to obtain a sufficient contrast ratio when performing display using a guest-host liquid crystal, for example, JP-A-56-57086 or JP-A-57-120977 has been proposed.
In Japanese Patent Application Laid-Open Publication No. H11-163, a method of forming unevenness on the surface of a reflective electrode to scatter reflected light is proposed.

Specifically, according to the method described in JP-A-56-57086, a silver thin film (hereinafter referred to as Ag) is formed on an Al thin film.
Called. ) Alternatively, an Ag alloy thin film is laminated, and Ag is deposited on the surface of Al by using the unevenness formed on the surface of Al.
Is intended to form irregularities on the surface.

In the method described in Japanese Patent Application Laid-Open No. 57-120977, for example, as shown in FIG.
The resin insulating film 51 is formed with irregularities 57 by honing, etching, or the like, and is intended to form irregularities on the surface of a metal film of Al, Ag, Ni, or the like deposited thereon.

[0016]

As described above, the reflection type liquid crystal display device can make the most of the advantage that the liquid crystal display device inherently has low power consumption. Promising applications to portable information devices and the like are promising.

However, since the display is performed by reflecting the incident light from the outside, there is a problem that the brightness and the contrast of the display are largely influenced by the brightness of the surroundings.

In order to solve such a problem, it is important to ensure a high reflectivity for incident light from the outside, and what kind of metal material is used for the reflective electrode is important for improving the reflectivity. It is one of the elements. Therefore, in many cases, a conventional reflective liquid crystal display device uses an Al thin film having high reflectance and excellent workability.

For example, Japanese Patent Application Laid-Open No. 8-179252 described above
In order to form a reflective electrode having a high reflectivity, a titanium thin film (hereinafter, referred to as Ti) or the like is formed below an Al thin film serving as a reflective electrode.
(1) The reflectance is improved by improving the degree of orientation of the thin film.

However, in such a method, it is necessary to form a two-layer metal thin film in order to form a reflective electrode, and there is a problem in that the manufacturing process becomes complicated. Also, when patterning a Ti thin film or the like formed under the Al thin film into an electrode shape,
It is conceivable that a dimensional shift occurs in any of the films due to the difference in the etching rate. For example, when the upper Al thin film shifts, a lower Ti thin film or the like is partially exposed, which has a problem that the reflection characteristics are adversely affected. Further, when the lower Ti thin film or the like shifts, the peripheral portion of the upper Al thin film is in a floating state, which causes a problem that some adverse effect occurs.

On the other hand, the methods disclosed in JP-A-56-57086 and JP-A-57-120977 described above obtain scattered reflected light using a metal material having a high reflectance. In the method disclosed in JP-A-56-57086, an Ag thin film or an A thin film is formed on an Al thin film.
The structure is such that g alloy thin films are stacked, and irregularities are formed on the surface of Ag deposited thereon by utilizing the irregularities formed on the surface of Al.

However, in such a method, it is necessary to form a two-layered metal thin film in order to form a reflective electrode, and there is a problem that the manufacturing process becomes complicated. Further, the unevenness formed on the surface of Al utilizes hillocks generated on the surface of Al by heat treatment, and it is extremely difficult to control the occurrence of unevenness. It is virtually impossible to form.

In the method disclosed in Japanese Patent Application Laid-Open No. 57-120977, the insulating film below the reflective electrode is made of a resin film such as polyimide, and the resin film is formed with irregularities by honing and etching. The surface of a metal film of Al, Ag, Ni, or the like deposited thereon has irregularities.

However, in such a method, since the unevenness is formed by honing or etching in the resin insulating film formed under the electrode, there is a problem that the manufacturing process becomes complicated. Have. In addition, since the unevenness obtained by honing or etching the resin insulating film has a size of about several μm, it is highly dependent on the angle of the incident light as it is, and sufficient scattering characteristics can be obtained. There is also a problem that it is difficult.

The above-mentioned JP-A-56-57086 and JP-A-57-120977 disclose the use of an Ag thin film or an Ag alloy thin film as a reflective electrode. In most cases, the etching method is wet etching using a nitric acid-based etchant, and fine processing techniques such as dry etching have not been established yet.

Therefore, when such Ag is used for the reflective electrode, it is necessary to set a large distance between the adjacent reflective electrodes. It is easily expected that the aperture ratio of the pixel will be reduced.

The present invention has been made in view of the above-mentioned conventional problems, and has as its object to provide a thin film transistor having a mirror-reflective electrode or a scatter-reflective electrode having a high reflectivity and a method of manufacturing the same. I do.

[0028]

According to a first aspect of the present invention, there is provided a thin film transistor having a gate electrode disposed below a semiconductor thin film, wherein the semiconductor thin film is formed on the gate electrode. And a channel region, a source region, and a drain region. The source region is connected to a source electrode, and the drain region is extended to form a display pixel electrode. Along with
Silver or a silver alloy is formed at least on a drain region formed in the shape of the display pixel electrode.

That is, according to the present invention, a reflective electrode is formed by depositing silver or a silver alloy having a high reflectivity by plating on a display pixel electrode formed by extending a drain region formed of a semiconductor thin film. Since the base electrode for plating is formed so as to extend from the drain region at the same time as forming the drain region with the semiconductor thin film, the manufacturing process of the thin film transistor can be shortened. It is.

In the thin film transistor according to a second aspect of the present invention, an interlayer insulating film having a substantially flat surface covering the source electrode is formed on the source electrode, and the semiconductor thin film is formed on the thin film transistor. It is characterized in that it is connected to the source electrode through an opening formed in the interlayer insulating film.

That is, the present invention has a structure in which a source electrode and a semiconductor thin film are connected through an opening formed in an interlayer insulating film, and this is a structure in which the semiconductor thin film is arranged on the uppermost layer. For this reason, it is not necessary to provide an opening in a display pixel electrode portion formed by a semiconductor thin film, so that there is an effect that a manufacturing process of a thin film transistor can be shortened.

Further, the thin film transistor according to a third aspect of the present invention is characterized in that the drain region extends over the source electrode via the interlayer insulating film.

That is, according to the present invention, a semiconductor thin film is deposited at least via an interlayer insulating film deposited on a source electrode, and an electrode portion formed by the semiconductor thin film can be extended to a position above the source electrode. Becomes This has the effect of increasing the area of the display pixel electrode.

The thin film transistor according to a fourth aspect of the present invention is characterized in that the surface of silver or silver alloy formed on the drain region is a mirror surface or a scattering surface.

That is, the present invention aims to maximize the reflection efficiency of light from a light source by making the surface of silver or a silver alloy a mirror surface, and is particularly applied to a projection type liquid crystal display device. In this case, a bright display can be obtained. In addition, by making the surface of silver or silver alloy a scattering surface, light from a light source is scattered efficiently to obtain a display with good visibility while maintaining brightness. When applied, it is possible to obtain a display in which the surrounding scenery and the like are not reflected on the display surface.

The thin film transistor according to a fifth aspect of the present invention is characterized in that the silver or silver alloy has a thickness of 70 nm or more.

That is, the present invention defines the thickness of silver or silver alloy as described above. If the thickness of silver or silver alloy is at least 70 nm, the wavelength is 40 nm.
In a visible light region of 0 nm to 700 nm, a reflectance higher than that of Al can be secured.

According to a sixth aspect of the present invention, in the method of manufacturing a bottom-gate thin film transistor in which a gate electrode is disposed below a semiconductor thin film, at least a substrate having an insulating surface is provided. Forming the gate electrode, forming a gate insulating film so as to cover the gate electrode, forming a source electrode on the gate insulating film, and forming the semiconductor in a region including on the gate electrode. Depositing a thin film to form a channel region, a source region, a drain region, and a display pixel electrode extended from the drain region; and a plating method on the surface of the display pixel electrode extended from the drain region. Selectively depositing silver or a silver alloy.

That is, according to the present invention, when forming a channel region, a source region, and a drain region made of a semiconductor thin film, a drain pixel region is formed by extending the drain region, and the display pixel electrode is formed on the display pixel electrode by plating. This is to deposit silver or a silver alloy, which makes it relatively easy to finely process silver or silver alloy, which is generally difficult to process, by depositing it on the surface of the lower electrode. An object of the present invention is to provide a manufacturing method capable of reflecting processing accuracy.

According to a seventh aspect of the present invention, in the method of manufacturing a bottom-gate thin film transistor in which a gate electrode is disposed below a semiconductor thin film, at least a substrate having an insulating surface is provided. Forming the gate electrode on the substrate, depositing a gate insulating film so as to cover the gate electrode, forming a source electrode on the gate insulating film, the gate electrode, the gate insulating film, and the source electrode. Is formed on the substrate,
Depositing an interlayer insulating film having a substantially flat surface by covering the step of the substrate; and forming openings in portions of the interlayer insulating film located above the gate electrode and above the source electrode, respectively. And depositing a semiconductor thin film on the interlayer insulating film including the respective openings to form a channel region, a source region, a drain region, and a display pixel electrode extending from the drain region,
Connecting the source region to the source electrode through an opening located above the source electrode; and selectively plating silver or silver on the surface of the display pixel electrode extending from the drain region by plating. And a step of precipitating an alloy.

That is, according to the present invention, when forming a channel region, a source region and a drain region comprising a semiconductor thin film, a display pixel electrode is formed by extending the drain region, and the display pixel electrode is formed on the display pixel electrode by plating. This is to deposit silver or a silver alloy, which makes it relatively easy to finely process silver or silver alloy, which is generally difficult to process, by depositing it on the surface of the lower electrode. The processing accuracy can be reflected. In addition, the source electrode and the semiconductor thin film are vertically separated via an interlayer insulating film, and the semiconductor thin film is disposed on the uppermost layer and is manufactured so as to be connected on the upper surface of the source electrode. An object of the present invention is to provide a manufacturing method capable of expanding a display pixel electrode formed by extending a region to above a source electrode.

In the method of manufacturing a thin film transistor according to the present invention, the step of selectively depositing silver or a silver alloy on a surface of the display pixel electrode extending from the drain region by plating. Before plating, a step of performing a pretreatment on the display pixel electrode extended from the drain region in order to improve the adhesion between the display pixel electrode extended from the drain region and the silver or silver alloy. It is characterized by including.

That is, according to the present invention, before depositing silver or a silver alloy on the surface of the display pixel electrode extended from the drain region, a pretreatment by strike plating of Au or the like is performed so that the display pixel electrode and the silver or silver alloy are deposited. It is intended to provide a production method for improving the adhesion to the substrate.

According to a ninth aspect of the present invention, there is provided a method of manufacturing a thin film transistor, wherein silver or a silver alloy is selectively deposited on a surface of a display pixel electrode extending from the drain region by a plating method. By controlling the thickness of the silver or silver alloy to be deposited,
The method is characterized by including a step of selecting the surface of the silver or silver alloy to an arbitrary surface state from a mirror surface to a scattering surface.

That is, the present invention relates to a method for depositing silver or a silver alloy on a surface of a display pixel electrode by a plating method and changing the surface to an arbitrary surface state from a mirror surface to a scattering surface. An object of the present invention is to provide a manufacturing method capable of easily forming a reflective electrode having a mirror surface exhibiting high reflectivity or a scattering surface having excellent scattering characteristics by controlling the thickness of silver or silver alloy to be deposited.

The thickness of the silver or silver alloy to be deposited can be controlled to change from a mirror surface to a scattering surface by gradually increasing the thickness of the silver or silver alloy. This is because the irregularities of the crystal grains are emphasized as the alloy grows. The control of the film thickness can be determined by controlling the current density and time, and a manufacturing method capable of freely changing the degree of reflection or scattering from a mirror surface to a scattering surface depending on the film thickness. It also provides.

The method of manufacturing a thin film transistor according to claim 10 of the present invention is characterized in that the silver or silver alloy has a thickness of 70 nm or more.

That is, the present invention defines the thickness of silver or silver alloy as described above. If the thickness of silver or silver alloy is at least 70 nm, the wavelength is 40 nm.
In a visible light region of 0 nm to 700 nm, a reflectance higher than that of Al can be secured.

[0049]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a sectional view showing a TFT according to the present invention, and FIG. 2 is a plan view thereof. FIG. 1 shows a cross section taken along the line AA 'in FIG.

As shown in FIG. 1, the TFT as a switching element in the present invention has the following general configuration. A metal thin film is deposited on a substrate 1 made of glass or the like, and the metal thin film is patterned into a predetermined shape to form a gate electrode 2. On this gate electrode 2, a gate insulating film 3 is deposited.
A metal thin film is deposited thereon, and the source electrode 4 is patterned into a predetermined shape.

Next, an interlayer insulating film 5 is deposited so as to cover the entire surface of the substrate 1, and an opening 6 is formed in a portion of the interlayer insulating film 5 corresponding to the portions above the gate electrode 2 and the source electrode 4. Have been.

Thereafter, a silicon thin film is deposited on the entire surface,
This silicon thin film is patterned into a predetermined shape so as to become the active layer 7 of the TFT. In the active layer 7 thus formed, the source region and the drain region 8 into which the impurity ions have been implanted, and the channel region 9 in the region above the gate electrode 2 into which the impurity ions have not been implanted.
Are formed.

Finally, a plating layer 10 made of a metal material is formed on the exposed surface of the source region and the drain region 8 by a plating method, thereby obtaining the T of the present invention.
FT is completed.

According to the present invention, a TFT called a bottom gate type or an inverted stagger type in which the gate electrode 2 is disposed under the semiconductor thin film 7 is formed, and the drain region 8 formed by the semiconductor thin film 7 is Since the plating layer 10 is formed by the direct plating method, the reflection electrode can be formed in a self-aligned manner, and there is no need to separately provide a lower electrode for forming the plating layer 10. In addition, it is possible to shorten the manufacturing process of the TFT.

Further, the TFT of the present invention is a bottom gate type TFT and is configured to be connected to the source electrode 4 through the opening 6 formed in the interlayer insulating film 5. It is possible to increase the area of the reflective electrode portion made of the semiconductor thin film 7.

Further, in the present invention, the plating layer 10
No special equipment or complicated pre-treatment is required except for the installation of plating equipment when forming, and conventional active matrix liquid crystal display devices and TFTs are used for the steps other than the plating step. It also has an advantage that it can be easily manufactured by a film forming method, an etching method, or the like used for manufacturing.

(Embodiment 1) Details of the manufacturing method according to Embodiment 1 of the present invention will be described below with reference to the drawings. 3 and 4 (a) to (e) are cross-sectional views showing the steps of manufacturing the TFT according to the first embodiment.
FIGS. 5-7 (a)-(e) show T in Embodiment 1. FIG.
It is the top view which showed the manufacturing process of FT. The sectional views and plan views of FIGS. 3 to 7 corresponding to (a) to (e) correspond to each other.

First, as shown in FIGS. 3A and 5A, a gate electrode 2 is formed on a substrate 1 such as a glass substrate. At this time, it is preferable to use a high melting point metal or the like for the gate electrode 2 in consideration of a temperature rise in a later step. Here, tantalum (hereinafter, referred to as Ta), titanium (hereinafter, referred to as Ti), molybdenum (hereinafter, referred to as Mo), niobium (hereinafter, referred to as Nb), and tungsten (hereinafter, referred to as W). .) Can be used.

Note that Al is inferior in heat resistance to the above-mentioned high melting point metals and the like, and therefore, it is not preferable to use Al alone as the gate electrode 2 because it may cause defects such as hillocks. However, the heat resistance can be expected to be improved by coating the surface with the above-described refractory metal or forming an oxide film on the surface by anodic oxidation. 2 can also be made of Al. Note that the above-described high melting point metal and the like can be formed by a known sputtering method.

Although not shown, a base coat film made of a SiO ₂ film or the like may be formed on the substrate 1 before forming the gate electrode 2 described above.

Subsequently, the SiO ₂ film or the like is formed, for example, for 200 nm by a well-known sputtering method or plasma CVD method.
The gate insulating film 3 is formed by depositing with a thickness of about m to 300 nm.

Next, as shown in FIGS. 3B and 5B, a source electrode 4 is formed on the gate insulating film 3 in a predetermined shape. Like the gate electrode 2 described above, it is preferable to use a high melting point metal or the like for the source electrode 4 in consideration of a temperature rise in a later step.

Next, as shown in FIG. 3C and FIG. 6C, an interlayer insulating film 5 is formed by depositing a SiO ₂ or SiN _x film or the like by a known sputtering method or a plasma CVD method. I do.

Subsequently, an opening 6 is formed in the interlayer insulating film 5 located on the gate electrode 2 and the source electrode 4. The opening 6 on the gate electrode 2 is for depositing a semiconductor thin film thereafter to form a channel region, and the opening 6 on the source electrode 4 is subsequently formed for the semiconductor thin film. Is deposited and connected to the source electrode 4.

At this time, the interlayer insulating film 5 can be formed by applying an acrylic resin or a polyimide resin such as Optomer SS (manufactured by Japan Synthetic Rubber Co.) if heat resistance is allowed. The use of such a resin has an advantage that the surface can be easily made extremely flat.

Next, as shown in FIGS. 4 (d) and 6 (d), a polycrystalline silicon thin film, an amorphous silicon thin film, or the like is, for example, 30 nm to 100 nm, preferably 40 nm to 100 nm.
It is deposited to a thickness of about 50 nm. If the deposited film is an amorphous silicon thin film, it is polycrystallized by irradiating a laser beam from above or annealing at about 600 ° C.

The silicon thin film thus polycrystallized is patterned into a predetermined shape to become the active layer 7 of the TFT. At this time, the silicon thin film extends to the pixel portion, and is patterned into an electrode having a continuous shape from the channel region of the TFT to the pixel region.

Next, impurity ions are implanted into the active layer 7 using a mask 11 made of an insulating film such as SiO ₂ , and thereafter, a heat treatment is performed to activate the implanted impurity ions. A source region and a drain region 8 are formed. At this time, impurity ions are similarly implanted into the electrode portion formed extending from the drain region 8 and activated. Then, a channel region 9 into which impurity ions have not been implanted is formed in a region above the gate electrode 2. Thus, the TFT according to the first embodiment is manufactured.

Here, the silicon thin film is 3 μm to 4 μm thick by wet etching or dry etching.
Fine processing of a degree is possible. Therefore, if a plating step is performed thereafter, a plating layer is formed on the silicon thin film in a self-aligned manner, so there is no need to etch silver or a silver alloy, and the fine processing accuracy of the underlying silicon thin film is reflected. Can be.

In the first embodiment, the case where the polycrystalline silicon thin film is used for the active layer has been described. However, an amorphous silicon thin film or a microcrystalline silicon thin film may be used for the active layer.

Finally, as shown in FIG. 4E and FIG. 7E, a metal film is formed on the source region and the drain region 8 by a plating method, and a plating layer 10 is formed.

Next, the plating method will be described.

Generally, the plating method often refers to an electrolytic plating method, which is a method in which a direct current is passed through an aqueous solution containing metal ions to be plated to obtain a metal film on the cathode surface. FIG. 10 shows this plating process.

The equipment prepared in this step includes a plating solution 12, a plating tank 13 for containing the plating solution 12, and a DC power supply 14. In general, an electrode made of the same material as the metal to be plated is used for the anode 15. For example, when plating Ni, a nickel electrode is used, and when plating Ag, a silver electrode is used. Further, depending on the plating solution, some heating may be required. In such a case, heating equipment for the plating tank may be provided as an accessory equipment. As the aqueous solution, for example, in the case of Ni or Ag, nickel sulfate, nickel chloride, silver cyanide, or the like is used. The metals to be plated include Cu, Ag, Au, Cr, F
e, Ni, Pt and the like can be used.

In the present invention, A having high reflectivity
g was selected. Since Ag is a material having a sufficiently low electric resistance in addition to having a high reflectance, it is considered to be suitable for use in electrodes and the like. It is also a very cheap material.

In the plating step according to the first embodiment,
For example, as a plating solution, Sylbrex 50 (Nippon Electroplating
Current density 1 A / d
The plating was performed at a plating solution temperature of 55 ° C. for about 3 minutes in m ² . At this time, as shown in FIG. 10, the respective ends of the gate electrode and the source electrode were short-circuited to apply a constant voltage to the gate electrode.

As a result, an Ag plating layer 10 of about 100 nm was formed on the source region and the drain region 8. In the first embodiment, the plating layer 10 serves as a reflective electrode.

The thickness of the plating layer 10 can be determined by controlling the current density and the time. The current density and the plating solution temperature vary depending on the type of the plating solution, and may be appropriately determined each time. Also, the plating solution could be a cyan-based Silbrex II (manufactured by Nippon Electroplating Engineers).

Next, steps before and after the plating step will be described.

Before the plating step as described above, besides washing the surface of the object to be plated, the surface may be treated with hydrochloric acid or the like, if necessary. After the plating step, the substrate is washed with warm pure water at about 70 ° C. and dried. In the first embodiment, an example of plating of a single metal has been described, but plating of an alloy may be used.

As described above, in the plating step, since the metal film can be formed in conformity with the shape of the electrode serving as the base, there is an advantage that patterning of the metal film is unnecessary. Further, since film formation is completed in about several minutes, it is possible to greatly contribute to shortening of the time required for the TFT manufacturing process.

In the first embodiment, the surface of plating layer 10 formed on source region and drain region 8 is a mirror surface. The mirror surface or the scattering surface in the first embodiment is distinguished from the mirror surface or the scattering surface by the degree of the angle dependence of the reflection intensity with respect to the incident light. For example, in the case of a mirror surface, when light is incident on the sample from a perpendicular direction and reflected light is received at a certain angle, the reflection intensity decreases as the angle increases, but in the case of one scattering surface, Shows little dependence on the angle and shows a constant reflection intensity at any angle.

That is, the mirror surface in the first embodiment is
The reflection surface has a remarkable peak value with respect to the incident light, and the scattering surface does not have a remarkable peak value with the reflection intensity.

For reference, as shown in FIG.
In order for Ag to exceed the reflectance of Al in the entire visible light region having a wavelength of 400 nm to 700 nm, it is necessary to form the film with a thickness of at least 70 nm.

Although not shown, after that, an alignment film is formed on the entire surface, the alignment film is subjected to an alignment process, and then a counter substrate on which a color filter, a counter electrode, etc. are formed is bonded. The liquid crystal display device in the first embodiment is completed by injecting a liquid crystal between the substrates.

The reflection type liquid crystal display device manufactured as described above has a high reflectance and a high light use efficiency and is bright. When a projection was formed with this reflective liquid crystal display device, the brightness was improved by about 5% as compared with a conventional reflective liquid crystal display device having a reflective electrode formed of Al.

As described above, the reflection type liquid crystal display device shown in the first embodiment has good reflection characteristics.
Therefore, in a projection type liquid crystal display device that projects the display of the liquid crystal display device on a screen or the like, since the light of the light source can be effectively used, heat generation is small, and a brighter display than in the past can be realized. It becomes possible. Such a reflection type liquid crystal display device is particularly suitable for a projection type video-related device.

(Embodiment 2) Next, details of a manufacturing method according to another embodiment of the present invention will be described with reference to the drawings. FIGS. 8A and 8B are cross-sectional views illustrating the steps of manufacturing the TFT according to the second embodiment.

The steps up to the step of depositing a silicon thin film and forming the source region and the drain region 8 are the same as those of the first embodiment, and therefore the description is omitted.

First, as shown in FIG. 8A, after completion of the TFT, cleaning was performed, and then a pretreatment for improving the adhesion was performed. In the second embodiment, for example, the Au plating layer 16 is formed by performing Au strike plating. For the Au strike plating, Aurobond TN (manufactured by Nippon Electroplating Engineers) was used as a plating solution, and a plating solution temperature of 50 ° C. and TF
This was performed for about 30 seconds while applying a voltage of 4 V to the source electrode side of T and applying a voltage of 10 V to the gate electrode side of the TFT.

In the drawing, the Au plating layer 16 is shown for convenience.
However, in practice, the Au strike plating is for improving the adhesion between the base and the plating layer, and is formed on the source region and the drain region 8 with a very small film thickness. . Therefore, the film thickness is not enough to be called a layer.

Examples of the pretreatment described above include surface treatment with an acidic chemical solution in addition to Au strike plating. This is performed by, for example, using hydrochloric acid and immersing it for several tens of seconds.

Next, as shown in FIG. 8B, a metal film is formed on the source region and the drain region 8 by a plating method, and a plating layer 10 is formed. In the plating step according to the second embodiment, for example, a non-cyan plating solution Silbrex 50 (manufactured by Japan Electroplating Engineers) is used as a plating solution.
Plating was performed at a current density of 1 A / dm ² and a plating solution temperature of 55 ° C. for about 3 minutes.

As a result, an Ag plating layer 10 of about 100 nm was formed on the source region and the drain region 8. In the second embodiment, the plating layer 10 serves as a reflective electrode.

The thickness of the plating layer 10 can be determined by controlling the current density and the time. The current density and the plating solution temperature vary depending on the type of the plating solution, and may be appropriately determined each time. Also, the plating solution could be a cyan-based Silbrex II (manufactured by Nippon Electroplating Engineers).

After the plating step, the substrate is washed with warm pure water at about 70 ° C. and dried. In addition, Embodiment 2
In the above, an example of plating of a single metal is shown, but plating of an alloy may be used.

In the second embodiment, the surface of the plating layer 10 formed on the source region and the drain region 8 has a mirror surface.

Although not shown, an alignment film is then formed on the entire surface, the alignment film is subjected to an alignment treatment, and a counter substrate on which a color filter, a counter electrode and the like are formed is bonded. The liquid crystal display device according to the second embodiment is completed by injecting a liquid crystal between the substrates.

The reflection type liquid crystal display device manufactured as described above has a high reflectance and a high light utilization efficiency and is bright. When a projection was formed with this reflective liquid crystal display device, the brightness was improved by about 5% as compared with a conventional reflective liquid crystal display device having a reflective electrode formed of Al.

As described above, the reflection type liquid crystal display device according to the second embodiment has good reflection characteristics.
Therefore, in a projection type liquid crystal display device that projects the display of the liquid crystal display device on a screen or the like, since the light of the light source can be effectively used, heat generation is small, and a brighter display than in the past can be realized. It becomes possible. Such a reflection type liquid crystal display device is particularly suitable for a projection type video-related device.

(Embodiment 3) Next, details of a manufacturing method according to another embodiment of the present invention will be described with reference to the drawings. FIG. 9 is a sectional view showing a TFT according to the third embodiment. Note that the manufacturing process and the like of the TFT according to the second embodiment are the same as those of the first embodiment, and therefore are not shown.

As shown in FIG. 9, after the TFT is completed, a metal film is formed on the source region and the drain region 8 by a plating method, and a plating layer 10 is formed.

In the plating step according to the second embodiment,
For example, as a plating solution, Sylbrex 50 (Nippon Electroplating
Current density 2A / d
The plating was performed at a plating solution temperature of 55 ° C. for about 5 minutes in m ² .

As a result, an Ag plating layer 10 of about 500 nm was formed on the source region and the drain region 8. Fine irregularities 17 are uniformly formed on the surface of the plating layer 10. And this plating layer 10
It was of a grade that could be used as a scattering reflective electrode.

An important requirement when forming the scattering reflection electrode by such a plating method is the thickness of the Ag plating layer. As schematically shown in FIG. 12, the Ag plating layer deposited on the source region and the drain region 8 subsequently increases in film thickness by crystal growth. With the growth of the Ag plating layer, very small irregularities due to Ag crystals, which were initially small, were emphasized as the crystals grew,
Eventually, it becomes uneven having the effect of scattering light. That is, the Ag plating layer gradually changes from the mirror state to the scattering state as the film thickness increases.

Specifically, the thickness of the Ag plating layer is about 70
When the thickness is at least nm, the film is in a mirror-like state, and about 100 to 200 nm is a film thickness at which a particularly good mirror-like state is obtained. Thereafter, as the film thickness increases, the scattering property gradually increases, and when the film thickness is approximately 500 nm or more, a complete scattering state is obtained. In order to use it as a good white scattering reflection electrode as in the third embodiment, it is desirable that the thickness of the Ag plating layer be 500 nm or more as described above.

Embodiment 3 thus manufactured
Have a good scattering characteristic. Therefore, in a direct-view type liquid crystal display device in which a user directly observes the display of the liquid crystal display device, the surroundings of the liquid crystal display device are not reflected in the display screen, and a brighter display than in the past is provided. It can be realized. Such a reflective liquid crystal display device is particularly suitable for portable information devices and the like.

Note that, even in the reflection type liquid crystal display device having the reflection electrode in the mirror surface state as shown in the first embodiment or the second embodiment, for example, a scattering plate having an effect of scattering light forward. It is possible to provide a liquid crystal display device suitable for direct viewing by disposing.

[0110]

As described above, according to the thin film transistor and the method of manufacturing the same of the present invention, the reflective liquid crystal display device having a high reflectivity is used because the reflective electrode in which Ag is formed on the surface of the display pixel electrode is used. It is possible to provide.

In the present invention, since the thin film transistor is a bottom gate type, it is characterized in that the number of manufacturing steps is reduced as compared with a staggered type or a coplanar type in which a gate electrode is arranged above a semiconductor thin film.

Further, in the present invention, since the semiconductor thin film is deposited via at least the interlayer insulating film deposited on the source electrode, the electrode portion formed by the semiconductor thin film is extended to above the source electrode. Becomes possible. This has the effect of increasing the area of the display pixel electrode.

Further, when Ag is formed on the surface of the display pixel electrode, Ag is deposited by a plating method to form the reflective electrode, so that patterning of the plating layer is unnecessary and Ag is formed. This has the effect of reducing the time required for film formation.

Further, according to the present invention, when a thin film transistor is formed, a display pixel electrode is formed simultaneously with a semiconductor thin film, so that there is no need to newly form a lower electrode for plating. .

As described above, according to the present invention, in manufacturing a reflection type liquid crystal display device having a high reflectance, a conventional method or manufacturing apparatus is used without using a special method or a special manufacturing apparatus. In addition, a thin film transistor can be efficiently manufactured without increasing the number of manufacturing steps, and an active matrix liquid crystal display device having good display characteristics can be efficiently manufactured using the thin film transistor manufactured as described above. This has the effect of being able to be manufactured.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a thin film transistor according to the present invention.

FIG. 2 is a plan view showing a thin film transistor according to the present invention.

FIGS. 3A to 3C are cross-sectional views illustrating a manufacturing process of the thin film transistor according to the first embodiment.

FIGS. 4D and 4E are cross-sectional views illustrating the steps of manufacturing the thin film transistor according to the first embodiment.

FIGS. 5A and 5B are plan views showing the steps of manufacturing the thin film transistor according to the first embodiment.

FIGS. 6C and 6D are plan views showing the steps of manufacturing the thin film transistor according to the first embodiment.

FIG. 7E is a plan view showing a step for manufacturing the thin film transistor according to the first embodiment.

FIGS. 8A and 8B are cross-sectional views illustrating a manufacturing process of the thin film transistor according to the second embodiment.

FIG. 9 is a cross-sectional view showing a thin film transistor according to the third embodiment.

FIG. 10 is a schematic view showing a state of a plating step in the present invention.

FIG. 11 is a diagram showing a sample (Al, Ag) deposited at room temperature by a resistance heating method at an angle (12
FIG. 4 is a drawing in which light was incident at (°) and the absolute reflectance was measured.

FIG. 12 is a cross-sectional view schematically showing crystal growth of a silver plating layer deposited on source / drain regions.

FIG. 13 is a cross-sectional view showing a thin film transistor having a pixel-on-passive structure.

FIG. 14 is a sectional view showing a conventional thin film transistor.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 2 Gate electrode 3 Gate insulating film 4 Source electrode 5 Interlayer insulating film 6 Opening 7 Active layer 8 Source and drain regions 9 Channel region 10 Plating layer 11 Mask 12 Plating solution 13 Plating bath 14 DC power supply 15 Anode 16 Au plating Layer 17 Roughness 50 Substrate 51 Interlayer insulating film 52 Drain electrode 53 Source electrode 54 Contact hole 55 Pixel electrode 56 Liquid crystal layer 57 Roughness

Continuation of the front page (51) Int.Cl. ⁶ identification code FI H01L 29/78 616K 618C

Claims (10)

[Claims] 1. A bottom gate type thin film transistor in which a gate electrode is disposed below a semiconductor thin film, wherein the semiconductor thin film is formed in a region including a portion above the gate electrode, and a channel region, a source region, and a drain The source region is connected to a source electrode, and the drain region is extended and formed in the shape of a display pixel electrode, and formed at least in the shape of the display pixel electrode. A bottom gate type thin film transistor, wherein silver or a silver alloy is formed on the formed drain region. 2. An interlayer insulating film having a substantially flat surface is formed on the source electrode so as to cover the source electrode, and the semiconductor thin film is formed through an opening formed in the interlayer insulating film. The bottom gate type thin film transistor according to claim 1, wherein the bottom gate type thin film transistor is connected to the source electrode. 3. The bottom gate type thin film transistor according to claim 1, wherein the drain region extends over a source electrode via the interlayer insulating film. 4. The bottom gate type thin film transistor according to claim 1, wherein the surface of silver or a silver alloy formed on the drain region is a mirror surface or a scattering surface. 5. The method according to claim 1, wherein said silver or silver alloy has a thickness of 70 nm.
The bottom gate type thin film transistor according to claim 1, wherein: 6. A method for manufacturing a bottom-gate thin film transistor in which a gate electrode is disposed below a semiconductor thin film, wherein the step of forming the gate electrode on a substrate having at least an insulating surface; and covering the gate electrode. Forming a gate insulating film, forming a source electrode on the gate insulating film, depositing the semiconductor thin film in a region including on the gate electrode, and forming a channel region, a source region, and a drain region. Forming a display pixel electrode extended from the drain region; and selectively depositing silver or a silver alloy by plating on the surface of the display pixel electrode extended from the drain region. A method for manufacturing a bottom-gate thin film transistor. 7. A method for manufacturing a bottom-gate thin film transistor in which a gate electrode is disposed below a semiconductor thin film, wherein the step of forming the gate electrode on at least a substrate having an insulating surface, and covering the gate electrode Depositing a gate insulating film, forming a source electrode on the gate insulating film, and covering a step on the substrate on which the gate electrode, the gate insulating film, and the source electrode are formed. Depositing an interlayer insulating film having a substantially flat surface, and forming openings in portions of the interlayer insulating film located above the gate electrode and above the source electrode, respectively. A display pixel extending from the channel region, the source region, the drain region and the drain region by depositing a semiconductor thin film on the interlayer insulating film including the opening; Forming an electrode and connecting the source region to the source electrode through an opening located above the source electrode; and plating the surface of the display pixel electrode extending from the drain region with a plating method. Selectively depositing silver or a silver alloy by the method described above. 8. In a step of selectively depositing silver or a silver alloy on a surface of a display pixel electrode extended from the drain region by a plating method, a display extended from the drain region before plating is applied. 8. The bottom according to claim 6, further comprising a step of performing a pretreatment on a display pixel electrode extended from the drain region in order to improve adhesion between the pixel electrode and the silver or silver alloy. A method for manufacturing a gate thin film transistor. 9. A method for selectively depositing silver or a silver alloy on a surface of a display pixel electrode extended from the drain region by a plating method, wherein the thickness of the deposited silver or silver alloy is controlled. 9. The method according to claim 6, further comprising the step of selecting the surface of the silver or silver alloy to an arbitrary surface state from a mirror surface to a scattering surface. 10. The film thickness of said silver or silver alloy is 70 n
10. The method of manufacturing a bottom-gate thin film transistor according to claim 6, wherein the thickness is not less than m.