JPH04299572A - Thin film transistor and its manufacturing method - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

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 and a method for manufacturing the same.

0002

2. Description of the Related Art A method of manufacturing a thin film transistor used in a conventional active matrix liquid crystal display device is shown in FIG. In the thin film transistors used in active matrix liquid crystal display devices, there are two types in which the transparent conductive film serving as the pixel electrode is located above the transistor and another type in which the transparent conductive film is located below the transistor, as shown in Figure 2. A thin film transistor is a type in which a transparent conductive film is located below the transistor.

First, as shown in FIG. 2A, an indium tin oxide (ITO) layer 22 that will become a pixel electrode and a chromium (ITO) layer that will become a gate electrode are placed on an insulating substrate 21 made of glass or the like.
A chromium (Cr) layer 23 is formed by a vacuum evaporation method, a sputtering method, or the like, and a chromium (Cr) layer 23 is formed into a predetermined pattern by an etching method or the like.

Next, as shown in FIG. 2B, an indium tin oxide (ITO) layer 22 is formed into a predetermined pattern by etching or the like.

Next, as shown in FIG. 2(c), a tantalum oxide (TaOx) layer 24 and a silicon nitride (SiNx) layer 25, which will become a gate insulating film, an i-type amorphous silicon layer 26, which will become a channel region, and an etching process. A silicon nitride film 27 is formed which acts as a stopper.

Next, as shown in FIG. 2D, a silicon nitride film 27 is formed into a predetermined pattern by etching or the like so that it remains only on the gate electrode 23.

Next, as shown in FIG.
n+ type amorphous silicon layer 2 serving as a drain region
8 is formed by, for example, a plasma CVD method.

Next, as shown in FIG. 2F, a contact hole 29 is formed on the side of the transistor by, for example, an etching method.

Next, as shown in the same figure (g), the source
Molybdenum silicide (MoSi) layer 30 serving as a drain electrode
and an aluminum layer 31 are formed by vacuum evaporation or sputtering.

Next, as shown in FIG.
The Si) layer 30 and the n+ type amorphous silicon layer 28 are removed and separated by an etching method using an aqueous solution of hydrogen fluoride and nitric acid, thereby forming a source region portion and a drain region portion. During this etching,
The silicon nitride film 27 serves as an etching stopper. Finally, a passivation film 32 made of silicon nitride etc.
Form and complete.

[0011] In the above-mentioned method for manufacturing a thin film transistor,
Since etching is performed in each step of (a), (b), (d), (f), and (h) in Figure 2, five photomasks are required.

FIG. 3 shows a method for manufacturing a thin film transistor in which a transparent conductive film is located above the transistor.

First, as shown in FIG. 5A, a tantalum (Ta) film 52 that will become a gate electrode is formed on an insulating substrate 51 made of glass or the like, and then formed into a predetermined pattern by etching or the like.

Next, as shown in FIG. 5B, the surface of the tantalum (Ta) film 52 is anodized to form tantalum oxide (
A TaOx) film 53 is formed.

Next, as shown in FIG. 5C, a first insulating film 54 made of silicon nitride or the like is formed to become a gate insulating film.
, an i-type amorphous silicon layer 55 which becomes a channel region.
, and a second insulating film 56 made of silicon nitride or the like which acts as an etching stopper.

Next, as shown in FIG. 5D, most of the second insulating film 56 is removed by etching so that the second insulating film 56 remains only on the gate electrode 53.

Next, as shown in FIG. 3(e), an n+ type amorphous silicon layer 57 is formed.

Next, as shown in FIG. 5F, the peripheral portions of the n+ type amorphous silicon layer 57 and the i type amorphous silicon layer 55 are removed by etching or the like.

Next, as shown in the same figure (g), the source
A metal film 58 made of titanium (Ti) or the like, which will serve as a drain electrode, is formed and patterned by etching or the like. Note that in this step, in order to prevent the transparent conductive film 59 made of indium tin oxide (ITO) described later from coming into contact with the amorphous silicon layers 55 and 57,
The metal film 58 is made of titanium so that the peripheral parts of the amorphous silicon layers 55 and 57 are completely covered with the metal film 58 made of titanium.
pattern. That is, since ITO is unstable, contact resistance changes over time when it comes into contact with the n+ type amorphous silicon layer 57. To prevent this, the n+ type amorphous silicon layer 57 and the ITO
It is necessary to create a structure that prevents contact between the two.

Next, as shown in FIG. 6(h), a transparent conductive film 59 made of ITO or the like is formed to serve as a pixel electrode.
Patterning is performed using an etching method or the like.

Finally, as shown in FIG. 5(i), a passivation film 60 made of a silicon nitride film or the like is formed to complete the process.

In the method for forming a thin film transistor described above,
A photomask is required in each step of (a), (d), (f), (g), and (h) in FIG.

As described above, the conventional thin film transistor manufacturing method uses a large number of photomasks, so the photo process takes time and has a problem of poor mass productivity. In addition, when the transparent conductive film is placed on top of the transistor,
Since the transparent conductive film 59 is partially etched to form holes during the process, there is also the problem that pinholes in the resist and the like cause a decrease in yield.

[0024]

SUMMARY OF THE INVENTION The invention according to this application has been made to solve such problems, and according to the first invention, a gate electrode, a gate insulating film, and a channel region are formed on an insulating substrate. In a thin film transistor in which a source region and a source electrode, and a drain region and a drain electrode are separately formed on a channel region, the channel region is formed of an i-type amorphous film containing a carbon element. A thin film transistor characterized in that it is formed of a silicon layer is provided.

According to the second invention, a gate electrode, a gate insulating film, and a semiconductor film to be a channel region are sequentially formed on an insulating substrate, and on the channel region,
A thin film transistor in which a source region and a source electrode, and a drain region and a drain electrode are respectively formed by dividing the thin film transistor, wherein the upper layer side of the source electrode and the drain electrode is formed of a transparent conductive film made of tin oxide. is provided.

Furthermore, according to the third invention, (a) forming a first metal film to serve as a gate electrode on a predetermined portion of the insulating substrate; and (b) forming a gate insulating film on the metal film. A process of sequentially laminating an insulating film to become a film, an i-type amorphous silicon layer containing carbon element to become a channel region, an n+ type amorphous silicon layer to become a source/drain region, and a second metal film to become a source/drain electrode. ,(
c) the second metal film on the peripheral part of the first metal film, n
(d) removing the + type amorphous silicon layer and the i type amorphous silicon layer containing carbon element;
forming a transparent conductive film made of tin oxide from above the layer to the periphery; (e) removing the transparent conductive film on the first metal film, the second metal film, and the n+ type amorphous silicon layer; and (f) forming a protective film on the layer.

[0027]

[Function] According to the first invention, since the i-type amorphous silicon layer contains a carbon element, the i-type amorphous silicon layer acts as a stopper layer during etching. There is no need for special provision, and a thin film transistor with a simplified photo process can be provided.

According to the second invention, since the transparent conductive film serving as the pixel electrode is composed of tin oxide, contact with the n+ type amorphous silicon film is not a problem, and thus the transparent conductive film and the amorphous silicon film are There is no need for a special manufacturing process to avoid contact with the thin film transistor, and a thin film transistor with a simplified manufacturing process can be provided.

According to the third invention, it is possible to provide a method for manufacturing a thin film transistor in which the photoprocessing step is simplified.

[0030]

[Example] The invention according to the present application will be explained in detail below. FIG. 1 is a diagram showing a manufacturing process for explaining the invention related to the present application, and 1 is an insulating substrate made of glass or the like.

First, as shown in FIG. 5A, a metal film 2 that will become a gate electrode is formed to a thickness of about 2000 Å by vacuum evaporation or sputtering, and then patterned by etching or the like. As this metal film 2, aluminum (Al), chromium (Cr), tantalum (Ta), etc. are suitably used. Further, as the etching solution, phosphoric acid is suitably used when etching aluminum, a ceric ammonium nitrate aqueous solution is suitably used when etching chromium, and hydrofluoronitric acid is suitably used when etching tantalum.

Next, as shown in FIG. 3(b), a tantalum oxide film (TaOx) 3, a silicon nitride film (SiNx) 4 that will become a gate insulating film, an i-type amorphous silicon layer 5 that will become a channel region, and a source and n+ which becomes the drain region
A type amorphous silicon layer 6 and a metal layer 7 made of titanium (Ti) or the like which will become source/drain electrodes are successively laminated. The tantalum oxide film 3 is formed to a thickness of about 2000 Å by, for example, an anodic oxidation method, and the silicon nitride film 6 is formed to a thickness of about 2000 Å by, for example, a plasma CVD method.
The i-type amorphous silicon layer 5 is formed to a thickness of about 500 Å by, for example, a plasma CVD method, and the n+ type amorphous silicon layer 6 is formed to a thickness of about 1000 Å by, for example, a plasma CVD method. 7 is formed to a thickness of about 4000 Å by vacuum evaporation or the like. In the present invention, it is important to mix a carbon element into the i-type amorphous silicon layer 5. That is, by mixing a carbon element into this i-type amorphous silicon layer 5, it can function as a stopper layer when etching the source/drain electrode layer 7 and the n+ type amorphous silicon layer 6, and it can be made to function as a stopper layer when etching the source/drain electrode layer 7 and the n+ type amorphous silicon layer 6. There is no need to provide a special stopper layer. The amount of carbon element added depends on the substrate temperature and n
Although it varies depending on the film quality of the + type amorphous silicon layer 6, basically, the etching rate for the etching solution is such that the n+ type amorphous silicon layer 6>i
Type amorphous silicon layer 5>gate insulating film 4,
Further, the carbon element may be added so that the energy band gap of the i-type amorphous silicon layer 5 is 2.5 eV or less, preferably 2.0 eV or less. Note that the channel region and the amorphous silicon layer 5 are not limited to being composed of a single layer containing carbon element, but may be composed of two layers: an i-type amorphous silicon layer that does not contain carbon element and an amorphous silicon layer containing carbon element. It may also be a structure. In order to contain carbon element in the amorphous silicon layer,
For example, methane gas, ethane gas, or the like may be used as the deposition gas.

Next, as shown in FIG. 2C, the metal layer 7, the n + -type amorphous silicon layer 6, and the i-type amorphous silicon layer 5 around the upper part of the gate electrode 2 are removed by etching. In this case, an etching solution such as fluoronitric acid is used.

Next, as shown in FIG. 3(d), a transparent conductive film 8 made of tin oxide is deposited to a thickness of 10 mm by sputtering.
It is formed to a thickness of about 00 Å. In this way, when the transparent conductive film 8 is formed of tin oxide, there is almost no change in contact resistance with the n+ type amorphous silicon layer 6 over time, and there is no need for special patterning of the source/drain electrodes as in the conventional method. .

Next, as shown in FIG. 2(e), in order to separately form a source region and a drain region, the transparent conductive film 8, the metal layer 7, and the n+ type amorphous silicon layer on the gate electrode 2 are separated. 6 is removed by etching. For the transparent conductive film 8, for example, a salt-nitric acid based etching solution using zinc as a catalyst may be used, and for the metal layer 7 and the n+ type amorphous silicon layer 6, for example, an etching solution prepared by adding water to fluoronitric acid may be used.

Finally, as shown in FIG. 3(e), a passivation film 10 made of a silicon nitride film or the like is formed to complete the thin film transistor.

[0037]

[Effect of the invention] As described above, according to the first invention, i
Since the i-type amorphous silicon layer contains a carbon element, this i-type amorphous silicon layer acts as a stopper layer during etching, eliminating the need to provide a special stopper layer during etching, simplifying the photoprocessing process. It is possible to provide thin film transistors that are

Further, according to the second invention, since the transparent conductive film serving as the pixel electrode is made of tin oxide, there is little change in contact resistance over time due to contact with the n+ type aluminous silicon film. This eliminates the need for a special manufacturing process to avoid contact between the transparent conductive film and the amorphous silicon film, making it possible to provide a thin film transistor with a simplified manufacturing process.

Furthermore, according to the third invention, after forming the gate electrode, the film is continuously formed up to the source and drain electrodes, so that the manufacturing yield is significantly improved and three photomasks are used. With this technology alone, thin film transistors can be manufactured, and mass productivity will be significantly improved.

[Brief explanation of the drawing]

[Fig. 1] Diagram for explaining the method for manufacturing a thin film transistor according to the present application

[Figure 2] Diagram for explaining the conventional manufacturing method of thin film transistors

[Figure 3] Diagram for explaining another conventional thin film transistor manufacturing method

[Explanation of symbols]

1: Insulating substrate 2: Gate electrode 4: Gate insulating film 5: Channel area 6: Source/drain region 7: Source/drain electrode 8: Transparent conductive film

Claims (3)

[Claims] 1. A gate electrode, a gate insulating film, and a semiconductor film serving as a channel region are sequentially formed on an insulating substrate, and a source region and a source electrode, and a drain region and a drain electrode are respectively divided on the channel region. 1. A thin film transistor formed by using a thin film transistor, characterized in that the channel region is formed of an i-type amorphous silicon layer containing a carbon element. 2. A gate electrode, a gate insulating film, and a semiconductor film serving as a channel region are sequentially formed on an insulating substrate, and a source region and a source electrode, and a drain region and a drain electrode are respectively divided on the channel region. 1. A thin film transistor formed by the above method, wherein a transparent conductive film made of tin oxide is formed from the upper part of the source electrode and the drain electrode to the peripheral part thereof. 3. (a) forming a first metal film that will become a gate electrode on a predetermined portion on an insulating substrate; (b) forming an insulating film that will become a gate insulating film and a channel region on the metal film; an i-type amorphous silicon layer containing a carbon element,
a step of sequentially laminating an n+ type amorphous silicon layer that will become a source/drain region and a second metal film that will become a source/drain electrode; (c) a step of laminating the second metal film in a peripheral area above the first metal film , a step of removing an n+ type amorphous silicon layer and an i-type amorphous silicon layer containing a carbon element; (d) a step of forming a transparent conductive film made of tin oxide from above the layer to the peripheral portion; (e) a step of removing the transparent conductive film, the second metal film, and the n+ type amorphous silicon layer on the first metal film;
f) A method for manufacturing a thin film transistor, comprising the step of forming a protective film on the layer.