JP2647069B2 - Active matrix panel manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a thin film transistor.
To a method of manufacturing an active matrix panel having
You.

[0002]

2. Description of the Related Art In recent years, research and development of thin film transistors using silicon thin films have been actively conducted. This technology is expected to be applied to many applications such as an active matrix panel for realizing a thin display using an inexpensive insulating substrate or an inexpensive and high-performance image sensor. In many cases, In _{2 is used} as a conductor for wiring or the like in order to improve optical characteristics using a transparent substrate.
O ₃ , SnO ₂ , ITO (Indium Tin Ox)
ide) and the like. Hereinafter, a case where a thin film transistor is applied to an active matrix panel will be described as an example, but the present invention can be similarly applied to a case where a thin film transistor is applied to another. This is because the gist of the present invention relates to improvement of essential characteristics of a thin film transistor using a silicon thin film.

A liquid crystal display device in which a thin film transistor is applied to an active matrix panel is generally composed of an upper glass substrate, a lower thin film transistor substrate, and a liquid crystal sealed therebetween. A liquid crystal driving element arranged in a matrix is selected by an external selection circuit, and a voltage is applied to a liquid crystal driving electrode connected to the liquid crystal driving element to display an arbitrary character, graphic, or image. is there.

FIG. 1 shows a general circuit diagram of the thin film transistor substrate.

FIG. 1A is a matrix layout of liquid crystal driving elements on a thin film transistor substrate. An area surrounded by l in the figure is a display area, in which the liquid crystal driving element 2 is disposed.
Are arranged in a matrix.

Reference numeral 3 denotes a data signal line to the liquid crystal driving element 2, and reference numeral 4 denotes a timing signal line to the liquid crystal driving element 2. FIG. 1B shows a circuit diagram of the liquid crystal driving element 2.

Reference numeral 5 denotes a thin film transistor, which performs data switching. Reference numeral 6 denotes a capacitor used for holding a data signal. The capacity of this capacitor includes the capacity of the liquid crystal itself and the capacity of a capacitor provided intentionally. However, in some cases, the capacity of the capacitor may include only the capacity of the liquid crystal. Reference numeral 7 denotes a liquid crystal panel, reference numeral 711 denotes a liquid crystal drive electrode formed corresponding to each liquid crystal drive element, and reference numeral 7-2 denotes an upper glass panel.

As can be seen from the above description, the thin film transistor is used for switching the data of the voltage applied to the liquid crystal. Since the display of the liquid crystal is determined by the potential of the capacitor, the thin film transistor must be able to pass a sufficiently large current when in the ON state so that data can be written in a short time.
The current at this time (hereinafter referred to as ON current) is determined by the capacity of the capacitor and the required writing time, and a thin film transistor must be manufactured so that the ON current can be cleared. The ON current that can flow through the thin film transistor greatly depends on the size (channel length and channel width), structure, manufacturing process gate voltage, drain voltage, and the like of the transistor.

When the thin film transistor is applied to an active matrix panel, an image sensor, or the like, it is obvious that it is more cost effective to integrate peripheral driving circuits such as a shift register at the same time. In this case, the thin film transistor is required to operate at a very high frequency of several MHz. Therefore, an extremely large ON current is required.

Hereinafter, a conventional method for manufacturing a thin film transistor and its characteristics will be described with reference to the drawings.

FIGS. 2A to 2D are views showing an example of a conventional method for manufacturing a thin film transistor. First, FIG.
The silicon thin film 9 is formed on the insulating substrate 8 as described above. For this, a plasma CVD method, a low pressure CVD method, a sputter method or the like is usually used. Next, as shown in FIG. 2B, after forming the gate insulating film 10 and the gate electrode 11, the source region 12 and the drain region 13 are formed by doping impurities by an ion implantation method, a thermal diffusion method or the like. Next, as shown in FIG. 2C, after depositing an interlayer insulating film 14,
The contact hole 15 is opened. Finally, as shown in FIG. 2D, a transparent conductive film such as In ₂ O ₃ , SnO ₂ , ITO is deposited, and the source electrode 16 and the drain electrode 17 are deposited.
To form

[0012]

FIG. 3 is a graph showing one example of the characteristics of the thin film transistor thus manufactured. It has a channel length of 30 μm and a channel width of 10 μm.
This is a result obtained by measuring the characteristics of the N-channel thin film transistor by the present applicant under the conditions of m and drain voltage 4V. The vertical axis is the drain current ID, and the horizontal axis is the gate voltage VGS
It is. As can be seen from this figure, although relatively good characteristics are generally obtained, the threshold voltage (hereinafter referred to as Vth) is obtained.
It is written. ) Is high, and the change from the OFF state to the ON state is slow. For this reason, the ON current is reduced. With such a characteristic, it is impossible to achieve various applications. In particular, the characteristic is completely insufficient for configuring a peripheral driving circuit of an active matrix panel or an image sensor. In order to apply the thin film transistor to such various fields, it is necessary to reduce Vth, increase mobility, and increase the ON current by one digit or more.

An object of the present invention is to remove the bristle point of such a conventional thin film transistor. The purpose of the present invention is to reduce Vth and increase mobility, and to reduce ON.
An electrode with a thin-film transistor that greatly increases the current
By providing active matrix panel manufacturing methods
is there.

[0014]

According to a method of manufacturing a liquid crystal device of the present invention, there is provided a method of manufacturing an active matrix panel having a thin film transistor, comprising the steps of: forming a silicon thin film of the thin film transistor on a substrate; Forming a gate insulating film, hydrogen after forming the silicon thin film and the gate insulating film,
Alternatively, the method includes a step of performing plasma treatment in an atmosphere containing hydrogen and nitrogen as main components, and a step of forming a transparent conductive film including a metal oxide after the plasma treatment. The method for manufacturing a liquid crystal device according to the present invention is a method for manufacturing an active matrix panel having a thin film transistor, comprising: forming a silicon thin film of the thin film transistor on a substrate; and forming a gate insulating film of the thin film transistor on the substrate. A step of performing plasma processing in an atmosphere containing hydrogen or hydrogen and nitrogen as main components after forming the silicon thin film and the gate insulating film, and a step of forming a transparent conductive film made of a metal oxide after the plasma processing. Wherein the step after the plasma treatment is performed at 350 ° C. or lower.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings.

FIGS. 4A to 4E show an accelerator according to the present invention.
It is a figure showing an example of the manufacturing method of the active matrix panel . First, a silicon thin film 19 is formed on an insulating substrate 18 as shown in FIG. Next, as shown in FIG. 4B, after a gate insulating film 20 and a gate electrode 21 are formed, a source region 22 and a drain region 23 are formed. Next, FIG.
As shown in (c), an interlayer insulating film 24 is deposited. The above manufacturing method is the same as the conventional one. Next, as shown in FIG. 4D, plasma processing is performed in an atmosphere containing hydrogen or hydrogen and nitrogen as main components. Reference numeral 25 denotes generated hydrogen plasma. As will be described later, the characteristics of the thin film transistor, particularly the ON current, are greatly improved by this plasma treatment. Finally, as shown in FIG. 4E, a transparent conductive film is deposited after opening a contact hole, and a source electrode 26 and a drain electrode 27 are formed. Thus, a thin film transistor is completed.

As is well known, various structures and manufacturing methods are known for thin film transistors, and the manufacturing method shown in FIG. 4 is only one example. Therefore, the present invention is similarly applied if the contents described in the claims are applicable.

FIG. 5 is a graph showing one example of the characteristics of the thin film transistor according to the present invention thus manufactured.
The solid line (A) shows the characteristics of the thin film transistor according to the present invention. The broken line (B) shows the characteristics of the conventional thin film transistor, which is the same as the characteristics shown in FIG. The parameters such as the transistor size and the drain voltage of the two completely match. As apparent from this graph, the thin film transistor manufactured according to the present invention has an extremely large ON current, and the characteristics are greatly improved. That is, not only is Vth reduced, but also the mobility is increased. As a result, the ON current is increased by 1.5 to 2 digits as compared with the conventional case. In addition, accompanying this, from OFF state to O
The change to the N state is also very steep.

The thin film transistor manufactured according to the present invention can be sufficiently applied to applications requiring high-speed operation of several MHz, such as peripheral driving circuits such as an active matrix panel and an image sensor. Can be expanded.

The reason why the characteristics are greatly improved by the present invention is as follows. Generally, a silicon thin film cannot be formed as a single crystal thin film, but is in a polycrystalline state or an amorphous state. For this reason, it has many irregularities in the arrangement of silicon atoms, and as a result, contains many dangling bonds. Such a dangling bond forms a level in the forbidden band of silicon, and not only has a function of trapping carriers, but also forms a space charge by being charged. That is, the mobility of carriers is reduced by the trapping of carriers, and Vt is formed by forming space charges.
h rises. The plasma treatment of the present invention reduces the density of the dangling bonds by filling the dangling bonds with hydrogen atoms. as a result,
The mobility increases, Vth decreases, and a thin film transistor having an extremely large ON current is realized.

In the present invention, the reason why the atmosphere of the plasma processing is allowed to contain nitrogen is to facilitate generation of hydrogen plasma. In general, hydrogen is hard to be in a plasma state, but this problem can be easily solved by mixing nitrogen. In addition, the present investigator has confirmed through experiments that there is no adverse effect of mixing nitrogen.

Also, in the active matrix panel,
As described above, a transparent conductive film is often used as the wiring / electrode material, but the present invention provides a manufacturing method for performing the plasma treatment before forming the transparent conductive film. Generally, In ₂ O ₃ ,
A metal oxide such as SnO ₂ or ITO is used. However, if the above-described plasma treatment is performed after forming such a transparent conductive film, the metal oxide is reduced to exhibit metallic properties. In severe cases, it may even appear to be more scattered than fine metal grains. Under such circumstances, the transparent conductive film can no longer maintain its original characteristics. Therefore, according to the present invention, as shown in FIG. 4, there is provided a manufacturing method for performing the plasma treatment before forming a transparent conductive film. This makes it possible to significantly improve the transistor characteristics even for the use of a thin film transistor using a transparent conductive film. In the example shown in FIG. 4, after the interlayer insulating film 24 is formed, the plasma processing is performed, and thereafter, a contact hole is opened to form a transparent conductive film. However, the same process as that described above is always required. There is no. For example, the plasma treatment may be performed after opening a contact hole, immediately after forming a silicon thin film, or immediately after forming a gate insulating film. That is, after forming a silicon thin film,
The plasma treatment may be performed at any stage before the formation of the transparent conductive film.

Further, the present invention provides a method for manufacturing a thin film transistor in which the manufacturing process after the plasma treatment is performed at 350 ° C. or lower. This will be described below with reference to the drawings.

FIG. 6 is a graph showing the dependence of the effect of the plasma treatment on the heat treatment. As an indicator of the effect of the plasma processing, Vth is plotted on the vertical axis. Vth
Is defined as a gate voltage necessary for flowing a drain current of 10 nA with a drain voltage of 4 V. As is apparent from the figure, by performing the plasma treatment, Vt
h dropped from 9V to 3.7V, 200 ° C, 250 ° C.
Even if heat treatment at 300 ° C. is sequentially applied, the value does not change at all. The heat treatment at 350 ° C. shows a slight increase in Vth, but only a slight change. However, when a heat treatment of 400 ° C. or more is applied, Vth increases sharply,
In the case of ° C., the values are almost the same at the beginning. in this way,
The effect of the plasma treatment is almost completely maintained by the heat treatment at 350 ° C. or lower, but rapidly deteriorates at 400 ° C. or higher. Therefore, after performing the plasma treatment, the effect is exhibited only by keeping all the manufacturing steps at 350 ° C. or lower.

For example, in FIG. 4, if high-temperature annealing is required for the purpose of activating impurities in the source / drain regions, the plasma processing must be performed after the annealing. . The reason why the characteristics are degraded again by the heat treatment after the plasma treatment is considered as follows. In other words, hydrogen introduced by plasma treatment bonds with silicon atoms to eliminate dangling bonds, but the bond is maintained by a finite binding energy, and the bonding is easily performed by external heat energy. Unleashed. The magnitude of the thermal energy exponentially contributes to the degree of dissociation, and therefore, the dissociation of silicon and hydrogen proceeds rapidly from a certain temperature.

[0026]

As described above, according to the present invention, the characteristics of the thin film transistor, particularly the characteristics in the ON state, can be remarkably improved. Moreover, since the transparent conductive film is formed after the plasma treatment, problems such as reduction of the transparent conductive film due to the plasma treatment can be prevented. In addition, since the plasma treatment is performed after the formation of the silicon thin film and the gate insulating film, a thin film transistor having a clean interface can be provided. Accordingly, the present invention provides a method of manufacturing an active matrix panel having excellent effects, which can improve the characteristics of a thin film transistor and maintain the characteristics of a transparent conductive film.

[Brief description of the drawings]

FIGS. 1A and 1B are general circuit diagrams of an active matrix substrate using a thin film transistor.

FIGS. 2A to 2D are views showing one example of a conventional method for manufacturing a thin film transistor.

FIG. 3 is a graph showing an example of characteristics of a thin film transistor manufactured by a conventional method.

FIGS. 4A to 4E are diagrams illustrating an example of a method for manufacturing an active matrix panel having a thin film transistor according to the present invention.

FIG. 5 is a graph showing an example of characteristics of a thin film transistor manufactured by the method of the present invention.

FIG. 6 is a graph showing how the characteristics of a thin film transistor manufactured by the method of the present invention change with heat treatment.

Claims (2)

(57) [Claims] 1. A method of manufacturing an active matrix panel having a thin film transistor, comprising: forming a silicon thin film of the thin film transistor on a substrate; forming a gate insulating film of the thin film transistor on the substrate; A step of performing a plasma treatment in an atmosphere containing hydrogen or hydrogen and nitrogen as main components after forming the gate insulating film; and a step of forming a transparent conductive film made of a metal oxide after the plasma treatment. A method of manufacturing an active matrix panel. 2. A method for manufacturing an active matrix panel having a thin film transistor, comprising: forming a silicon thin film of the thin film transistor on a substrate; forming a gate insulating film of the thin film transistor on the substrate; A step of performing plasma treatment in an atmosphere containing hydrogen or hydrogen and nitrogen as main components after forming the gate insulating film, and a step of forming a transparent conductive film made of a metal oxide after the plasma treatment, A method for manufacturing an active matrix panel, wherein the step after the plasma treatment is performed at 350 ° C. or lower.