JPH02237161A - Thin-film transistor and its manufacture - Google Patents

Abstract

PURPOSE:To control an active semiconductor layer to a desired thickness and to reduce a photocurrent by a method wherein a channel-protective film is formed of a semiconductor oxide film including an oxide film obtained by oxidizing the surface of the active semiconductor layer by means of a plasma. CONSTITUTION:A channel-protective film 5 is formed of a semiconductor oxide film formed by oxidizing a semiconductor layer by means of a plasma oxidation method. The semiconductor layer as a base material of this oxide film may be formed of only an active semiconductor layer 4 or of both the active semiconductor layer 4 and a contact layer 8 formed on it. Accordingly, an excess thickness part of the active semiconductor layer 4 can be reduced to a required minimum. Since the thickness of the active semiconductor layer 4 is made thin, a photocurrent generated when light is incident is reduced remarkably.

Description

[Detailed Description of the Invention] [Summary] This invention relates to a thin film transistor matrix used for driving liquid crystal display devices, electroluminescence, etc., and a method for manufacturing the same, which allows controlling an active semiconductor layer to a desired thickness without complicating the manufacturing process. A gate electrode is provided on one of the two opposing main surfaces of the active semiconductor layer via a gate insulating film, and a channel is provided on the other side in a portion opposite to the gate electrode. In the structure of the thin film L-transistor provided with a protective film, the channel protective film is a semiconductor oxide film including an oxide film obtained by plasma oxidizing the surface of the active semiconductor layer.

(Industrial Application Field) The present invention is applicable to liquid crystal display devices and electroluminescence (
The present invention relates to a thin film transistor (TPT) matrix used for driving an EL device, etc., and a method for manufacturing the same.

In a TPT matrix, it is important to minimize the photocurrent caused by light incident on the active semiconductor layer in order to improve device characteristics.

[Conventional technology]

Motion half m Amorphous silicon (a-S
FIG. 4 shows the conventional structure and manufacturing process of a self-aligned TPT matrix using i).

First, a gate electrode 2 made of a Ti film is formed on a glass substrate 1 [see FIG. 3(a)].

On this gate electrode 2, a gate insulating film 3 made of a SiN film, an a-St film 4 as an active semiconductor layer, and a Sin. A film 5 and an a-Si film 6 as an adhesion layer are successively formed by plasma chemical vapor deposition (P-CVD) [see FIG. 13(b)].

Next, a photoresist is coated on the a-Si[6], and this resist film is irradiated with ultraviolet rays from the back surface of the glass substrate 1 using the gate electrode 2 as a mask, thereby forming a resist pattern 7 that is self-aligned with the gate. Form〔
See figure (C)].

Next, using the resist film 7 as a mask, the uppermost a-Si film 6 and the lower StOz film 5 are etched using a hydrofluoric acid etching solution by reactive ion etching to remove these exposed portions. (See figure (d)).

Next, n″a was formed as a contact layer by P-CVD method.
- A Si film 8 is formed, and a Ti film 9 is formed thereon as a conductive film.
are laminated using a vacuum evaporation method [see figure (e)].

Next, the resist film 7 used as the mask is removed with acetone, and the n''a-SiM 8 and Ti film 9 thereon are lifted off [see FIG. 3(f)].

Next, a resist pattern (not shown) for forming the source electrode S and drain electrode D is formed, and plasma etching is performed using this as a mask to form the Ti film 9,n''.
Unnecessary portions of the a-St film 8 and the a-Si film 4 are removed by etching. Note that the SiN film 3 remains even after the wood processing is performed [see figure (■)].

Next, in order to commonly connect the drain electrodes D on the same line, a drain bus 10 made of a laminated film of a Cr film and an Al film is formed (see the same figure).

Although not shown, the intersection between the drain bus 10 and the gate bus is insulated between the eyebrows with a polyimide film.

Next, a pixel electrode 11 made of an IT◯ film is formed so that one end of the pixel electrode 11 overlaps the end of the source electrode S [see FIG. 12(i)].

[Problem to be solved by the invention]

In the above conventional structure, since the channel protective film 5 and the adhesive layer 6 covering the channel portion transmit light, the active semiconductor layer 4
Light enters inside and a photocurrent is generated. The magnitude of this photocurrent increases as the active semiconductor layer 4 becomes thicker.

In the conventional TPT structure, due to constraints in the manufacturing process, the thickness of the active semiconductor layer 4 has to be made thicker than necessary compared to the thickness necessary for the operation of the TPT, which also increases the photocurrent. The current value in the OFF state of TPT is 2
There was a problem in that the amount increased by ~3 orders of magnitude, deteriorating the device characteristics.

An object of the present invention is to make it possible to control an active semiconductor layer to a desired thickness without complicating the manufacturing process, thereby reducing photocurrent.

[Means to solve the problem]

The configuration of the present invention is shown in FIG.

In the present invention, the channel protective film 5 is a semiconductor oxide film formed by oxidizing a semiconductor layer using a plasma oxidation method. Note that the semiconductor layer serving as the base material of this oxide film may be only the active semiconductor layer 4, or may be both the active semiconductor layer 4 and the contact layer 8 formed thereon.

In the above structure, a gate electrode 2 is formed on an insulating substrate 1, a gate insulating film 3 covering the gate electrode 2, at least an active semiconductor layer 4 is formed on the gate electrode 2, and a contact layer 8 is formed on the active semiconductor layer.
and a conductive film 9, at least the conductive film 9 is connected to the gate electrode 2.
A channel protection film 5 made of a semiconductor oxide film is formed on the active semiconductor layer 4 directly above the gate electrode 2 by forming a shape having an opening directly above and performing plasma oxidation using the conductive film 9 as a mask. At the same time, the semiconductor layer 4 can be manufactured by controlling the thickness of the active semiconductor layer 4 in this portion to a desired thickness.

[For production]

With the above structure, the final thickness of the active semiconductor layer 4 can be reduced to the necessary minimum by oxidizing all the excess thickness of the active semiconductor layer to form the channel protection film 5. By reducing the thickness of the active semiconductor layer 4 in this way, the photocurrent generated by the incidence of light is significantly reduced.

- When the semiconductor layer to be oxidized to form the channel protective film 5 is only the active semiconductor layer 4, and when both the active semiconductor layer 4 and the contact layer 8 are used,
This will be explained in detail in the section describing the embodiments.

As described above, according to the present invention, it is possible to control the film thickness of the active semiconductor layer, and not only can the TPT characteristics be improved, but also the oxidation of the semiconductor layer progresses in the lateral direction, so that the channel protective film 5 can be It has a shape that goes under the end of the source/drain electrode. Therefore, it also leads to dispersion of stress acting on the side edges of the contact layer, and it is also possible to eliminate the occurrence of cictic. Furthermore, the etching step of the channel protective film in the conventional manufacturing process is no longer necessary, and the manufacturing process can be simplified.

〔Example〕

First and second embodiments of the present invention will be described below with reference to the drawings.

A first embodiment of the present invention is shown in FIGS. 2(a) to 2(i).

In this example, a-SilpJ4 was used as the active semiconductor layer, and the channel protection film 5 was formed by oxidizing this a-Si film 4.

A gate electrode 2 made of a Ti film is formed on a glass substrate 1 (see figure (a)), and a SiN film 3 as a gate insulating film and an a-Si film 4 as an active semiconductor layer are deposited thereon.
-Continuous film formation by CVD method. In this example, unlike the conventional method, a channel protective film is not formed on this (see figure (b)).
reference〕.

Although it is desirable for the thickness of the a-St film 4 to be about 50 in terms of design, it is extremely difficult to form such a thin film uniformly and without defects. Practically speaking, it is almost impossible. Therefore, in this example,
A=Si film 4 was deposited to an initial thickness of about 300 mm.

Next, a photoresist is applied and exposed to ultraviolet light from the back surface of the glass substrate 1 using the gate electrode 2 as a mask to form a resist 1/pattern 7 that is self-aligned with the gate electrode 2 [see FIG. 3(C)].

? Approximately 50% of the contact layer was
An n''a-Si film 8 having a thickness of 0.04 cm is formed, and a Ti film 9 is further formed thereon as a conductive film for the source/drain electrodes by vacuum evaporation [see FIG. 4(d)].

Next, the resist film 7 is removed with acetone, and the -F
The n'' a-Si film 8 and Ti film 9 are lifted off to expose the channel portion, that is, the a-St film 4 directly above the gate electrode 2 [see FIG. 2(e)].

Next, using the Ti film 9 as a mask, for example, the RF power is 300 W, the substrate temperature is 250°C, and the reaction chamber pressure is ITo.
Plasma oxidation is performed under the conditions of r r and a bias voltage of 200 mm to oxidize the exposed portion of the active semiconductor layer 4, leaving a thickness of approximately 50 mm, thereby forming an SiO2 film 5 that will serve as a channel protective film. The oxidation rate under the above conditions is approximately 100
person/time [see figure (e)].

Although it is not necessary to specifically limit the thickness of the SiO film 5 formed in this step, the thickness of the final a-Si film 4 should be set to the minimum thickness necessary to obtain the desired characteristics as described above. By reducing the thickness of the a-Si film 4 in this way, it is possible to reduce the photo force flux without deteriorating various characteristics, and it is possible to reduce the OFF current. becomes.

As described above, in this embodiment, the channel protection film 5 is formed by plasma oxidation of the surface portion of the a-Si film 4, which is the active semiconductor layer, so the a-Si film 4 is formed thickly during film formation. The unnecessary part of this is converted into a channel protective film 5, and a
-Si[4 can be controlled to have a thin thickness as described above.

Next, the oxide film formed on the top of the Ti film 9 is slide-etched, and a resist film (not shown) is used as 7 masks to remove unnecessary parts of the Ti film 9, n''a-Si film 8, 6-Si film 4. is removed by plasma etching to form a source electrode S and a drain electrode D. [See the same figure (see powder)].

The subsequent steps may proceed in the same manner as before. That is, in order to connect the drain electrodes D on the same line in common, a drain bus 10 made of a laminated film of a Cr film and an A2 film is formed [see FIG. 4(h)]. Although not shown, the intersection between the drain bus 10 and the gate bus is insulated between the eyebrows with a polyimide film.

Next, one end of the pixel electrode 1l made of ITO film is .
It is formed so as to overlap the end of the source electrode S (see figure (i)).

In manufacturing this embodiment as described above, the plasma oxidation process for oxidizing the active semiconductor layer is increased compared to the conventional method, but the etching process for the channel protective film is not required, so the increase or decrease in the number of processes is do not have. Furthermore, since the thickness of the active semiconductor layer 4 can be reduced to the necessary minimum, photocurrent is reduced.

Next, a second embodiment of the present invention will be described with reference to FIGS. 3(a) to (i). This example is an example in which the channel protective film 5 is formed using the active semiconductor layer 4 and the contact N8 as base materials.

In this second embodiment, unlike the first embodiment described above,
A gate electrode 2 made of Ti is formed on a glass substrate 1 [see figure (a)], and a SiN film 3 is coated thereon.
a-Si film 4 and further n″″a- as a contact layer.
A Si film 8 is continuously formed by the P-CVD method (see the same figure at 0C).

The initial thicknesses of the a-St film 4 and n''a-Si film 8 are as follows:
As in the first embodiment, about 300 people and about 500 people
As a person.

Next, a resist pattern 7 that is self-aligned with the gate electrode 2 is formed thereon [see figure (C)], and then a source pattern 7 is formed.
A Ti film 9 is formed as a conductive film for drain electrode scraping by a vacuum evaporation method [see figure (d)], and then the resist film 7 and the Ti film 9 thereon are removed by a lift-off method.
See figure (e)].

At the end of this process, the na-Si directly above the gate electrode 2 is
Membrane 8 is exposed. Therefore, using the Ti film 9 as a mask, plasma oxidation is performed to oxidize the entire thickness of the n'''a-Si film 8 and the first layer of the underlying a-Si film 4, thereby forming a SiOzWi. A channel protective film 5 is formed [see the same figure].

In this example, the thickness is the minimum thickness that is desirable in terms of characteristics. That is, the plasma oxidation is performed to the extent that the a-Si film 4 with a thickness of approximately 50 mm remains. Therefore, in this example, approximately 50
The entirety of the n'' a-Si film 8 having a thickness of 0 and about 250 from above the a-St film 4 is converted into a channel protective film 5.

As described above, in this embodiment, the final thickness of the a-Si film 4 is made extremely thin by approximately 50 mm, which is the desired thickness, so that the photovoltage is significantly reduced compared to the conventional method, and the effect is the same as the first one described above. There is no difference from the embodiment.

The subsequent steps may be carried out in the same manner as in the first embodiment, and as shown in FIGS. ” a-Si film 3
, remove unnecessary parts of the a-Si film 4, form a drain bus 10 that commonly connects the drain electrodes G on the same line, and then form a pixel electrode E made of ITO whose end is connected to the source electrode S. 7, this embodiment is completed.

In the second embodiment described above, as in the first embodiment, the thickness of the active semiconductor layer can be controlled arbitrarily without increasing the number of manufacturing steps, so the photocurrent is reduced. , the device characteristics of TPT are improved. Also,
Since the channel protective film 5 overlaps the lower part of the edge of the Ti film 9, which is the conductive film of the source/drain electrode, stress that gathers at the edge of the source/drain electrode can be dispersed, and the generation of oxidation can be prevented.

In addition, in the first and second embodiments described above, an example was explained in which an a-Si film was used as the semiconductor layer, but the present invention is not limited to this. S
t, etc., are not particularly limited.

Further, it goes without saying that the initial thickness of the active semiconductor layer and the contact layer and the final thickness of the active semiconductor layer are not limited to those of the first and second embodiments.

〔Effect of the invention〕

As explained above, according to the present invention, the thickness of the active semiconductor layer can be controlled arbitrarily, photocurrent can be suppressed and the device characteristics of TPT can be improved, and therefore the manufacturing yield can be improved. , it is possible to reduce manufacturing costs. Furthermore, the stress that collects at the edges of the source/drain electrodes can be dispersed, and the occurrence of cracks can be eliminated.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram of the configuration of the present invention, Fig. 2 (a) to (i) is an explanatory diagram of the first embodiment of the present invention, and Fig. 3 (a) to (i) is an explanatory diagram of the second embodiment of the present invention. Explanatory diagram, 4th
Figures (a) to (i) are explanatory diagrams of conventional TPT manufacturing steps. In the figure, 1 is an insulating substrate (glass substrate), 2 is a gate electrode, 3 is a gate insulating film (SiN film), 4 is an active semiconductor layer (a-St film), 5 is a channel protection film (Sing film), 7 is a resist pattern, 8 is a contact layer (n'a
-Si film), 9 is a conductive film (Tt film), S and D are source electrodes and 70-7z...

Claims (2)

[Claims] (1) A gate electrode (2) is connected to one of the two opposing main surfaces of the operational semiconductor layer (4) via a gate insulating film (3).
On the other hand, in the structure of a thin film transistor in which a channel protective film (5) is disposed at a portion facing the gate electrode (2), the channel protective film (5) is arranged on the active semiconductor layer (4).
A thin film transistor characterized in that it is a semiconductor oxide film including an oxide film whose surface is plasma oxidized. (2) A gate electrode (2), a gate insulating film (3), and an active semiconductor layer (4) are formed on an insulating substrate (1), and a contact layer (8) and a conductive film (9) are formed thereon. After the conductive film is formed in a shape having at least an opening directly above the gate electrode (2), a plasma oxidation method is performed using the conductive film (9) as a mask, and the gate electrode of the active semiconductor layer (4) is (2) Manufacturing a thin film transistor characterized by including a step of forming a channel protective film (5) made of a semiconductor oxide film directly above the film and controlling the active semiconductor layer (4) in the corresponding part to a desired thickness. Method.