JPH064597Y2 - Thin film transistor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a thin film transistor.

[Conventional technology]

For example, a thin film transistor for driving a pixel electrode, which is arranged on a pixel electrode forming substrate of an active matrix type liquid crystal display device so as to correspond to each pixel electrode thereof, is generally of an inverted stagger type.

FIG. 2 shows a conventional pixel electrode driving thin film transistor. The thin film transistor includes a gate electrode G formed on a surface of a substrate 1, a gate insulating film 2 covering the gate electrode G, and a gate insulating film 2 on the gate insulating film 2. And an a-Si semiconductor layer 3 formed to face the gate electrode G, and a source electrode S and a drain electrode D formed on the semiconductor layer 3. The a-Si semiconductor layer 3 is i
-A-Si layer 3a and n ^<+>- a formed as a contact layer with the source electrode S and the drain electrode D on it.
-Si layer 3b, and n ⁺ -a-Si layer 3b
Are separated in the channel region between the source electrode S and the drain electrode D. In addition, the gate electrode G is connected to a gate line formed integrally therewith,
One of the source and drain electrodes, for example, the drain electrode D is connected to a data line integrated with the source electrode, and the other source electrode S is connected to the transparent pixel electrode a formed on the gate insulating film 2.

By the way, the gate electrode G and the gate line and the source and drain electrodes S and D and the data line of the thin film transistor are conventionally formed of metal such as Mo, Cr and Ta or ITO which is a transparent conductive material. Since the material (1) has a relatively high resistivity, if the transistors are made small and the gate lines and data lines are made thin in order to increase the arrangement density of the pixel electrodes, the electrodes G, S, D and the gate lines of the transistors and The resistance value of the data line becomes considerably high, which affects the operation of the transistor. Therefore, in the thin film transistor,
As the width of each electrode G, S, D and the gate line and the data line is reduced, the film thickness is increased,
Its resistance is being lowered. However, the above Mo, Cr, T
Metals such as a and ITO have large stress in the film,
When the film thicknesses of the source and drain electrodes S and D and the data line formed on the stepped surface from the semiconductor layer 3 to the gate insulating film 2 on the surface of the substrate 1 are increased, the electrodes S and D and the data line are formed. In addition, cracks and peeling may occur due to the stress of the film.

On the other hand, Al or Al alloy is mainly used as a wiring material such as LSI using a single crystal semiconductor. Since this Al or Al alloy has a small resistivity and a small film stress, the Al or Al alloy is Alternatively, if the source / drain electrodes S and D and the data line of the thin film transistor are formed of Al alloy, the above-mentioned problem can be solved.

[Problems to be solved by the device]

However, since the source and drain electrodes S and D of the thin film transistor are made of Al or Al alloy,
The interface between the Al or Al alloy and the a-Si semiconductor layer 3 (n
^Since a high-resistance alloy layer is formed on the ⁺ -a-Si layer 3b), good ohmic characteristics between the source / drain electrodes S and D and the semiconductor layer 3 cannot be obtained. There's a problem. Further, etching for patterning Al or an Al film into a predetermined electrode shape is generally C
l _2, is carried out by _CCl 4, a dry etching method using a chlorine gas containing the SiCl ₄ or the like, for these gases, which would also etched Si, the source of the thin-film transistor, the drain electrode S, a D Al or A
When the Al or Al alloy film is patterned into the shape of the source and drain electrodes S and D by the dry etching method, the channel region (ia-Si) of the a-Si semiconductor layer 3 is formed. There is also a problem that the layer 3a) is damaged, which affects the characteristics of the transistor.

According to the present invention, the resistance value of the source / drain electrode can be reduced, and good ohmic characteristics between the source / drain electrode and the a-Si semiconductor layer can be obtained. An object of the present invention is to provide a thin film transistor capable of forming a semiconductor layer that is not damaged by patterning a drain electrode.

[Means for Solving the Problems]

In order to achieve the above object, the present invention provides a source electrode and a drain electrode formed on an a-Si semiconductor layer, in order from the semiconductor layer side, an extremely thin Ti film, an extremely thin Cr film, and a film thickness. And a thick Al or Al alloy film are laminated to form a three-layer structure.

[Action]

According to the thin film transistor of the present invention, the upper layer film of the source electrode and the drain electrode is a thick film of Al or Al alloy having a low resistivity, and the lower layer and the intermediate layer of the Ti film and the C layer.
Since the r film is an extremely thin film and has a small resistance to a current flowing between the a-Si semiconductor layer and the source and drain electrodes in the electrode thickness direction, the resistance value of the entire source and drain electrodes should be lowered. You can Also, a
Although the resistivity of Ti of the lower layer film in contact with the -Si semiconductor layer is large, the resistance value of the alloy layer formed at the interface between the Ti film and the a-Si semiconductor layer is small, so that the source / drain electrodes and a- Good ohmic characteristics with the Si semiconductor layer can be obtained. Further, the source and drain electrodes are formed by stacking a Ti film, a Cr film, and an Al or Al alloy film and then patterning these films sequentially by a dry etching method. Since the etching selection ratio of Ti can be quite large, when etching a thick Al or Al alloy film, Ti
The Cr film can prevent the film and the underlying a-Si semiconductor layer from being etched.
Since the etching selectivity between the film and the Ti film and the a-Si semiconductor layer can be sufficiently large, C
The r film and the Ti film can also be etched without damaging the a-Si semiconductor layer.
The semiconductor layer can also be a semiconductor layer that is not damaged by patterning the source and drain electrodes.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG.
Incidentally, in FIG. 1, the same components as those shown in FIG. 2 are designated by the same reference numerals and the description thereof will be omitted.

This thin film transistor has a source electrode S and a drain electrode D formed on an a-Si semiconductor layer 3, and a three-layer electrode in which a Ti film 4, a Cr film 5, and an Al film 6 are laminated in this order from the semiconductor layer 3 side. Each of the Ti film 4 and the Cr film 5 is an ultrathin film having a thickness of several hundred Å, and the Al film 6
Is a thick film with a thickness of 1000Å or more. Further, the drain electrode D is connected to a data line (not shown) integrated therewith, and this data line also has the above-mentioned three-layer structure.

In the thin film transistor, however, the source electrode S and the drain electrode D have the three-layer structure as described above instead of the conventional single-layer electrode. Therefore, the resistance values of the source and drain electrodes S and D are Can be lowered. That is, the source and drain electrodes S and D
Is a thick film of Al whose upper layer film 6 has a low resistivity,
Further, the Ti film 4 and the Cr film 5 of the lower layer and the intermediate layer are extremely thin films, and the resistance to the current flowing between the a-Si semiconductor layer 3 and the source electrode S and the drain electrode D in the electrode thickness direction is small, The resistance value of the entire source electrode S and drain electrode D can be reduced. Further, in the data line, most of the current flows through the upper layer Al6 having a large film thickness and a small resistivity, so that the resistance value of this data line can be made sufficiently small.

The table below shows the resistivity of various conductive materials.

As can be seen from this table, the resistivity of Al is about 1/17 of Ti and about 1/2 of that of Mo.
The resistance values of the source and drain electrodes S and D and the data line, which mainly include the I film 6, are sufficiently small.

In the thin film transistor, the a-Si semiconductor layer 3
Although the resistivity of Ti of the lower layer film in contact with is large, the resistance value of the alloy layer generated at the interface between the Ti film 4 and the a-Si semiconductor layer 3 (interface between the n ⁺ -a-Si layer 3b). Is small, a good ohmic characteristic between the source / drain electrodes S and D and the a-Si semiconductor layer 3 can be obtained.

Further, the source / drain electrodes S and D and the data line are formed by laminating the Ti film 4, the Cr film 5 and the Al film 6 on the entire substrate and then patterning these films sequentially by the dry etching method. Since the etching selection ratio between the Al film 6 and the Cr film 5 can be made considerably large, the Al film 6 having a large film thickness can be etched by using the Cr film 5 thereunder as an etching stopper. The etching of the Ti film 4 and the a-Si semiconductor layer 3 thereunder can be prevented by the Cr film 5, and the etching selection ratio between the Cr film 5 and the Ti film 4 and the Ti film 4 can be prevented. Since the etching selectivity between the a-Si semiconductor layer 3 and the a-Si semiconductor layer 3 can be sufficiently large, the Cr film 5 and the Ti film 4 are also etched without damaging the a-Si semiconductor layer 3. It can be grayed. Also, Ti
An alloy layer, that is, a Ti silicide layer (not shown) is formed at the interface between the film 4 and the a-Si semiconductor layer 3, and the Ti silicide layer is an alloy layer of Cr and Si (Cr silicide layer). It can be etched much more easily than Therefore, according to the above thin film transistor, the a-Si semiconductor layer 3 also has the source and drain electrodes S and D.
It is possible to obtain a semiconductor layer which is not damaged by the patterning. The etching of the Al film 6 is performed by BC
The Cr film 5 is etched under the condition that the Cr film 5 is not etched using a gas such as l ₃ , CCl ₄ or He, and the etching of the Cr film 5 is performed under the condition that the Ti film 4 is not etched using the gas such as CCl ₄ , O ₂ The etching of the Ti film 4 is performed by using a gas such as CCl ₄ , CF ₄ , SF ₆ or the like a-.
It may be performed under the condition that the Si semiconductor layer 3 is not etched.

Although the upper layer film 6 of the source / drain electrodes S and D is an Al film in the above embodiment, the upper film 6 may be an Al alloy film, and in that case, the same effect as that of the above embodiment can be obtained. You can

[Effect of device]

According to the thin film transistor of the present invention, the source electrode and the drain electrode formed on the a-Si semiconductor layer are formed in order from the semiconductor layer side to an extremely thin Ti film, an extremely thin Cr film, and a thick Al film. Alternatively, since it has a three-layer structure in which an Al alloy film is laminated, the resistance value of the source and drain electrodes can be lowered, and the source and drain electrodes and aS
Good ohmic characteristics between the i-semiconductor layer and the i-semiconductor layer can be obtained, and the a-Si semiconductor layer can be a semiconductor layer that is not damaged by patterning the source and drain electrodes.

[Brief description of drawings]

FIG. 1 is a sectional view of a thin film transistor showing an embodiment of the present invention, and FIG. 2 is a sectional view of a conventional thin film transistor. 1 ... Substrate, G ... Gate electrode, 2 ... Gate insulating film, 3 ... a
-Si semiconductor layer, 3a ... ia-Si layer, n ^<+> -a-S
i layer, S ... Source electrode, D ... Drain electrode, 4 ... Ti
Film, 5 ... Cr film, 6 ... Al film.

Claims (1)

[Scope of utility model registration request] 1. A gate electrode formed on a substrate surface, a gate insulating film covering the gate electrode, an a-Si semiconductor layer formed on the gate insulating film so as to face the gate electrode, and the semiconductor layer. In a thin film transistor including a source electrode and a drain electrode formed on the top surface of the thin film transistor, the source electrode and the drain electrode are formed in order from the semiconductor layer side by an extremely thin Ti film, an extremely thin Cr film, and a thick Al film.
Alternatively, a thin film transistor having a three-layer structure in which an Al alloy film is laminated.