JPS6012770A - Thin film field effect transistor - Google Patents

Abstract

PURPOSE:To enable to protect the transistor made of polyimide, etc. by the guarantee of the transistor in heat insulating temperatures up to over 200 deg.C by a method wherein the electrode provided to the semiconductor thin film transistor constituting a picture display by being combined with a liquid crystal, etc. is composed of the laminated body of a heat insulating metal and a low reflectance metal. CONSTITUTION:The first metal 2 serving as the gate electrode is formed on an insulation substrate 1 of glass, etc., and an amorphous Si layer 4 is deposited over the entire surface including the metal via insulation layer 3. Next, the source electrode 7 and the drain electrode 8 opened are formed at the part opposed to the metal 2, with amorphous Si layers 9 and 10 containing phosphorus underlying the electrodes, and a polyimide 11 for transistor protection is adhered from inside the aperture to the ends of the electrodes 7 and 8. In this construction, the electrode 7 is put in a three-layer structure composed, from the substrate side, of the heat insulating metal 7a such as Cr, the low reflectance metal 7b such as Al, and the metal 7C such as Cr again, and the electrode 8 is also put in a three-layer structure of the same metals 8a, 8b, and 8c.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a thin film field effect transistor and a method for manufacturing the same, and in particular to a non-single crystal thin film field effect transistor mainly composed of silicon for constructing an image display device in combination with a liquid crystal or the like. The present invention relates to a semiconductor thin film field effect transistor (hereinafter referred to as TPT).

Non-single crystal silicon semiconductor TFT whose main component is silicon
TPT using CdSe, CdTe, etc. has better stability and also has the advantage of having a larger on-off ratio than single crystal silicon. However, when an image display device is constructed using a non-single-crystal silicon semiconductor TPT whose main component is silicon, stability increases and the image (
It is necessary to take measures to improve the contrast ratio.

Hereinafter, a TPT using an amorphous silicon semiconductor as a representative non-single crystal semiconductor mainly composed of silicon will be described in detail.

Structure of conventional example and its problems Figure 1 shows a cross-sectional view of TPT, which is one of the conventional examples.
For example, a first metal 2 serving as a gate electrode is deposited on a substrate 1 such as glass, an amorphous silicon semiconductor layer 4 is formed via an insulating layer 3, and a source and a drain are formed on the semiconductor layer. An inverted staggered TPT-type on which a second metal layer 6, 6 serving as an electrode is deposited.

An image display device is constructed by combining a substrate on which a large number of TPTs as described above are arranged and a liquid crystal, and a high-density liquid crystal image display device can be obtained by switching the liquid crystal using the TPTs.

Stability and reliability are required performances of the TPT used as a switching element for configuring such an image display device.

However, in the case of an inverted staggered TPT as shown in FIG. 1, for example, since the amorphous silicon semiconductor layer constituting the channel is exposed, moisture etc. are adsorbed to the channel part, causing the transistor characteristics to fluctuate and become unstable. This may interfere with certain movements. In order to prevent such a phenomenon, it is necessary to protect the channel portion with an organic thin film such as polyimide or an inorganic thin film such as silicon nitride or silicon oxide.

However, all of these thin films were formed at a temperature of 20
A temperature of 0C or higher is required, and a thin film formed at a temperature lower than that is inferior and has poor adhesion and cannot function as a haze barrier film.

On the other hand, the characteristics of a conventional TPT whose source and drain electrodes 6.6 are made of aluminum deteriorate when heat treatment is performed. Figure 2 shows the main elements of TPT.
S, capacitance value Cm in depletion state obtained as a result of capacitance-voltage measurement of (metal-insulating film-semiconductor) structure
When the voltage vμ (corresponds to the gate voltage value indicating the TPT off state) is reached when the average value of the capacitance value Ci in the accumulation state becomes (Dmin+Ci)/2, the depletion state shifts to the accumulation state. The results are shown in which the voltage ΔV (corresponding to the voltage required for TPT switching) required for this is plotted against each heat treatment temperature. When the metal layers 5 and 6 in FIG.
−) both changed significantly.

1 of ■w, ΔV as shown in curves I and IIl in Figure 2
The change is related to a deterioration in the rise characteristics of the TPT's train current and a decrease in the ratio of the drain current in the switched-on state and the switched-off state (on-off ratio) of the TPT. It goes without saying that the image quality of an image display device with degraded TET characteristics is poor.

To investigate the cause of this, we used Auger electron spectroscopy to measure the depth distribution of silicon and aluminum before and after heat treatment. Figure 3 shows the results. Compared to before heat treatment (solid line), after heating at 200C for 1 hour (
(dashed line), aluminum (marked with O) and silicon (marked with *)
It can be seen that they are mutually diffused. This is the source of Figure 1.

This is thought to be due to deterioration of the characteristics of TPT using aluminum for the drain electrodes 5 and 6 due to heat treatment.

As mentioned above, the conventional amorphous silicon TPT using aluminum for the source and drain electrodes 5.6 has poor heat resistance and cannot be protected by polyimide or the like, so it is stable when used to construct an image display device. This is a problem in terms of sexuality.

In order to solve this problem regarding heat resistance, the metal constituting the source and drain electrodes should be selected from aluminum and a metal other than aluminum that has excellent heat resistance (a metal that does not diffuse into the silicon during heat treatment). (meaning heat-resistant metal)
For example, patent application No. 67-17942 filed by the present applicant.
It is proposed in No. 3.

However, although it is effective to use heat-resistant metals and aluminum to lower wiring resistance and improve coverage of steps on the board, aluminum has a high light reflectance of approximately 90%, so When a TPT image display device was constructed using a layered structure for the source and drain electrodes and their bus wiring, the contrast ratio of the image deteriorated significantly.

Purpose of the Invention The present invention has been made in view of the above problems.
In order to stabilize the TPT characteristics by guaranteeing the heat resistance temperature of T to 2ooC or higher and to ensure TET by using polyamide, etc., and to maintain good image display characteristics, the source, drain electrodes and bus wiring are The present invention aims to obtain a non-single-crystal semiconductor TPT whose main component is silicon and whose reflectance is reduced.

Structure of the Invention The present invention uses a multilayer structure of a heat-resistant aluminum metal and a low reflectance metal in contact with a semiconductor layer as an electrode of an amorphous semiconductor mainly composed of silicon. That is, riften, tungsten, chromium, nichrome, tantalum, palladium, platinum, silicon-metallic compound, etc. are used as heat-resistant metals, and low reflectance metals are used.

It is desirable to use a low-reflection metal with a light reflectance of 60% or less, such as chromium, nichrome, or a silicon-metal compound.

Description of examples Hereinafter, the present invention will be explained in detail using the drawings.

As shown in FIG. 4, the structure of the present invention is such that source and drain electrodes 7 and 8 are connected to first layers 7a and 8a in contact with a semiconductor layer for improving the heat resistance of TPT, and a semiconductor layer for reducing reflection of wiring metal. The third layers 7c and 8c are located far from the second layer 7c and 8c, and the second layers 7b and 8b are mainly used to lower the wiring resistance, improve the step coverage of the wiring on the substrate, and reduce the disconnection rate at the step portion. It has a three-layer structure using aluminum. That is, in one embodiment of the present invention, as shown in FIG. 4, for example, the source and drain electrodes 7.8 are placed in the first layers 7a and 8a in contact with the semiconductor layer and in the third layer 7c located farthest from the semiconductor layer. , 8c second layer 7b, sb
The idea is to use aluminum.

Figure 6 shows the results of measuring the distribution of silicon and chromium in the depth direction before heat treatment and after heat treatment for 91 hours at 3oC using Auger Disciple spectroscopy.
It can be seen that it does not diffuse into silicon even after heat treatment at oC for 1 hour. Therefore, by using chromium in the first layers 7a and 8a, the heat resistance of TPT is improved. For example, as shown in the curves (1) and (2) in FIG. 2, VV2 (S) and ΔV (, A-L) in the capacitance-voltage measurement of the MIS structure hardly change with respect to each heat treatment temperature. Therefore, using chromium as source and drain electrodes is promising in terms of heat resistance of TPT, but because chromium has a large internal stress and cannot be deposited to a thickness of 2000 Å or more, it is necessary to form source and drain electrodes and wires using only chromium. This results in step cuts and increased wiring resistance, making it unsuitable for use as an electrode.

In order to prevent this, first layers 7a and 8 are formed as shown in FIG.
Chromium is used for a, and aluminum is used for the second/threat 7b, 8b and the bus wiring. However, in this case, since the reflectance of aluminum is high, the contrast ratio of the image display device that combines liquid crystal and TPT cannot be maintained, resulting in poor images. Therefore, on the second layer 7b, ab of the source and drain electrodes 7 and 8 in FIG.
c.

A metal such as chromium having a light reflectance of 50% or less of 8C is deposited.

Incidentally, since the reflectance of aluminum is 9a% or more, the contrast ratio of an image display device using TPT that uses aluminum for the source, drain electrodes, and bus wiring is 8% compared to that without bus wiring. However, for example, since the reflectance of chromium is about a factor of 40,
Third layer 7c.

The contrast ratio of an image display device constructed from TPT using a metal layer coated with chromium as 8C as the base, drain electrode, and bus wiring is the same as that when aluminum is used as the wiring metal. It was very effective as it was possible to obtain about 4 times the amount.

Above, we have explained the case in which the first and third layers of the source and drain electrodes in the three-layer structure are made of chrome, but the first and third layers are made of molybdenum, tantalum, tungsten, palladium, respectively. .

Effects similar to those of chromium were obtained even when nickel, chromium, nichrome, silicon, and silicon alloys were used.

In another embodiment of the present invention, as shown in FIG. 6, for example, the first layer of chromium 7a, 8a described above is deposited via amorphous silicon semiconductor layers 9, 10 containing phosphorus. First layer 7a for improving heat resistance.

Although it is difficult to obtain good ohmic contact between the metal used in 8b and silicon, interposing an amorphous silicon semiconductor layer containing impurities was effective in obtaining good ohmic contact.

In still another embodiment of the present invention, as shown in FIG. 7, after the three-layer source and drain electrodes 7 and 8 are deposited, an insulating thin film layer 11 of, for example, polyimide is deposited on the TPT channel portion at 260C. do.

The polyimide insulating thin film layer deposited with 260C has good adhesion and good film quality, and can sufficiently protect the channel part of the TPT from contaminated atmosphere, so it is useful for improving the reliability and stability of the TPT. It is valid. Of course, since the source and drain electrodes have the three-layer structure of the present invention, even after going through the 260C process, the source and drain electrodes can be made of aluminum like TPT (in the case of aluminum, two layers are used).
TPT characteristics deteriorated due to heat treatment below 00tl') TP
Needless to say, the T characteristic does not deteriorate.

In another embodiment of the present invention, for example, after the first layer of chromium 7a, 8a of the drain electrode is deposited by electron beam evaporation, the second layer of aluminum 7b, ab, including the bus wiring, and the third layer of aluminum 7a, 8a of the drain electrode are formed. Chromium 7c and sc are continuously deposited by electron beam evaporation. If the metal layer is deposited by electron beam evaporation in this way, the damage to TPT that occurs when using sputter evaporation can be avoided, and the continuous deposition makes it easier to mass-produce. Direction□
leads to the top.

Effects of the Invention As described above, in the present invention, by forming the second metal layer into a three-layer structure, even when TPT is subjected to heat treatment, the metal layer does not diffuse into silicon, and the transistor characteristics are reduced. Since the TPT does not deteriorate, the TPT can be protected by an insulating thin film layer such as polyimide, which has the effect of improving the reliability and stability of the TPT. Also sauce,
It has the effect of reducing the reflection of light from the drain and bus wiring metals, and image display devices using it exhibit very stable and good image quality. Although the amorphous silicon semiconductor has been described above as a representative example, it goes without saying that the present invention is not limited to this and can be applied to all non-single crystal semiconductors whose main component is silicon.

[Brief explanation of drawings]

Fig. 1 is a cross-sectional view of the structure of an amorphous silicon conductor thin film field effect transistor, Fig. 2 is a diagram showing changes in ΔV and V with respect to heat treatment temperature in capacitance-voltage measurement of an M4.8 structure, Fig. 31, and FIG. 6 is a diagram showing measurement results by Auger electron spectroscopy, and FIGS. 4, 6, and 7 are schematic cross-sectional views of a TPT according to an embodiment of the present invention. 1...Substrate, 2...Gate metal, 3.
...Gate insulating film, 4...Amorphous silicon, 5, 6, 7.8... Source, drain electrode, 7a, 8a, 7c. 8C...Chromium, 7b, 8b...Aluminum, 9.10...Amorphous silicon containing phosphorus, 11...Polyimide. Name of agent: Patent attorney Toshio Nakao and 1 other person 2nd
Figure 3 Suha Sogae B now 几go (Engine Figure 4?

Claims (4)

[Claims] (1) A first metal layer is selectively deposited on one main surface of the substrate, and a non-single-crystal semiconductor layer mainly composed of silicon is connected to the first metal layer via an insulating thin film layer. a second metal layer is formed so as to partially overlap the semiconductor layer, the second metal layer has a multilayer structure, and the second metal layer is formed so as to partially overlap the semiconductor layer; A multilayer structure in which the metal layer mainly consists of an aluminum layer, a heat-resistant metal layer is arranged in a region in contact with the semiconductor layer, and a low reflectance metal is arranged in a side of the aluminum layer that is not in contact with the heat-resistant metal layer. A thin film field effect transistor characterized by the following. (2) A second metal layer having a multilayer structure and a non-single-crystal semiconductor layer are deposited via a second non-single-crystal semiconductor layer whose main component is silicon containing impurities. A thin film field effect transistor according to claim 1, characterized in that: (3) The thin film field effect transistor according to claim 1, wherein part or all of the thin film field effect transistor is protected by an insulating thin film. Mi (4) The thin film field effect transistor according to claim 3, wherein the insulating thin film is made of bolyard, silicon nitride, or silicon oxide, and the insulating thin film is formed at a temperature of 200C or higher. (6) The thin film field effect transistor according to claim 1, wherein at least two metal layers of the second metal layer of the multilayer structure are successively formed by electron beam evaporation.