JPH07153959A - Thin-film transistor and manufacture thereof - Google Patents

Abstract

PURPOSE:To provide a TFT, in which the dispersions of capacitance CGS between a gate and a source and capacitance CGS between the gate and a drain are minimized with a small area, and manufacture thereof. CONSTITUTION:A gate electrode 2, a gate insulating film 9, a semiconductor layer 3 and a transparent electrode layer 13 are formed successively onto a transparent substrate 1, a photo-resist layer 11 covering the transparent electrode layer 13 is formed, the transparent substrate 1 side is exposed using the gate electrode 2 as a mask, the photo-resist layer 11 in the upper section of the gate electrode 2 is removed through etching, and the transparent electrode layer 13 is patterned. Accordingly, a first source electrode 8a, a first drain electrode 7a and a picture element electrode 6 are shaped, and a second source electrode 8b and a second drain electrode 7b are formed onto the first source electrode 8a and the first drain electrode 7a.

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 its manufacturing method. More specifically, the present invention relates to a thin film transistor in which a gate electrode and a source electrode and a drain electrode are formed in a self-aligned manner and a manufacturing method thereof.

[0002]

2. Description of the Related Art An active matrix type liquid crystal display device is one in which pixel electrodes are arranged in a matrix to display an image, and a thin film transistor for switching pixels is provided in the vicinity of each pixel electrode on one transparent substrate. (Hereinafter referred to as TFT) is arranged.

In a conventional TFT called an inverted stagger type NSI structure, a gate electrode and a semiconductor layer are provided on a transparent substrate 1 made of glass or the like, and (upper) source region and drain region are provided on the surface side of the semiconductor layer. , The drain electrode is provided so as to be connected to both the pixel electrode and the drain region. According to this type of conventional TFT manufacturing method, a gate electrode made of aluminum or the like, a gate insulating film made of silicon nitride, a semiconductor layer made of amorphous silicon, a source region and a drain region for obtaining ohmic contact are provided. The layers are sequentially formed by photolithography. Next, a pixel electrode made of ITO or the like is provided at a required position, and then a source electrode and a drain electrode are formed respectively.

[0004]

In the TFT having the inverted stagger type NSI structure as described above, the gate electrode, the source electrode, and the drain electrode are formed by separate masks, so that there is a sufficient margin in consideration of the mask alignment deviation. Therefore, there is a problem that the size of the TFT becomes large.

Further, due to the misalignment, the overlapping portion of the source electrode 8 and the drain electrode with respect to the gate electrode is different, so that the gate-source capacitance C _GS and the gate-drain capacitance C _GD are different, which results in good switching of the TFT. There is a problem that the characteristics cannot be obtained.

Therefore, the present invention solves the above-mentioned problem and allows the capacitances C _GS and C _GD to be increased without increasing the number of masks.
It is an object of the present invention to provide a TFT that can be formed with a minimum design rule and a manufacturing method thereof, in which the variation of the above can be minimized.

[0007]

A TFT of the present invention comprises a transparent substrate, a gate electrode formed on the transparent substrate, a semiconductor layer formed on the gate electrode, and the gate formed on the semiconductor layer. The transparent electrode layer is formed symmetrically with respect to the electrodes, and the source electrode and the drain electrode are respectively formed on the transparent electrode layer.

In the method of manufacturing a TFT of the present invention, (a) a gate electrode is formed on a transparent substrate, (b) an insulating film is formed so as to cover the gate electrode, and (c) the gate electrode is formed. A semiconductor layer is laminated and patterned on the insulating film above, (d) a transparent electrode layer is provided on the insulating film and the semiconductor layer, and (e) the transparent electrode layer is patterned using the gate electrode as a mask. Thus, the end portions of the source electrode and the drain electrode are defined.

Further, in the liquid crystal display device of the present invention, the liquid crystal layer is held by two transparent substrates, pixel electrodes are formed in a matrix on at least one transparent substrate, and an active element having a switching element for each pixel is provided. A matrix type liquid crystal display device in which the TFT is used as a switching element.

[0010]

In the TFT of the present invention, since at least the end portions of the source electrode and the drain electrode on the side of the gate electrode are formed of the transparent electrode layer, the back surface side can be exposed by using the gate electrode as a mask. Therefore, the photoresist layer is exposed to a little inside along the gate insulating film and the gate wiring due to the diffraction phenomenon of light. That is, the source electrode and the drain electrode can be separated by self-alignment with the drain electrode, and it is not necessary to consider the alignment margin. Therefore, a TFT having a small size can be formed with the minimum design rule.

Further, as a result of the end portions of the source electrode and the drain electrode being formed by self-alignment, they are formed symmetrically with respect to the gate electrode, and the overlapping portion of the gate electrode and the source electrode / drain electrode is formed by the The width is determined by the diffraction phenomenon, and the widths are almost the same. Therefore, the capacitances C _GS and C
_GD has almost the same value because it is formed in the overlapping portion of the gate electrode, the source electrode and the drain electrode.

[0012]

EXAMPLES Next, the TFT of the present invention will be described with reference to the drawings.
An example of the manufacturing method will be described. FIG. 1 is a cross-sectional explanatory view for explaining the manufacturing process of the manufacturing method of the TFT of the present invention, and FIGS.
FIG. 6A is a plan view for explaining one transparent substrate manufacturing process for manufacturing a liquid crystal display device using the TFT of the present invention.

As shown in the sectional view of FIG. 1, the TFT of the present invention has a gate electrode 2 on a transparent substrate 1 and a gate insulating film 9 formed on the substrate 1 so as to cover the gate electrode 2.
And a semiconductor layer 3 formed in the gate-electrically-operated portion on the gate insulating film 9, and a transparent electrode layer (first source electrode 8a, first drain electrode 7a,) formed at a required position with respect to the gate electrode 2. The pixel electrode 6), the second source electrode 8b and the second drain electrode 7b formed on the transparent electrode layer, and the passivation film 10 as a protective film. The first source electrode 8a and the second source electrode 8
The source electrode 8 is composed of b, and the drain electrode 7 is composed of the first drain electrode 7a and the second drain electrode 7b. The TFT of the present invention is characterized in that the first source electrode 8a and the first drain electrode 7a are formed by self-alignment with the gate electrode 2 by exposing from the back surface side as described in the manufacturing method described later. , The first source electrode 8a and the first drain electrode 7a are formed of transparent layers, both electrode end portions are formed at substantially the same position with respect to the gate electrode, and the gate electrode has a small size and is symmetrical. The structure is such that the semiconductor layer 3 extends outside the gate electrode 2 and sufficient ohmic contact with the semiconductor layer 3 is obtained.

Next, the manufacturing method will be described. First,
After forming a conductor film such as aluminum on the transparent substrate 1 such as glass by a sputtering method or the like, a photoresist layer 11 is patterned and formed by a photolithography technique,
The gate electrode 2 and the gate wiring 12 connected to the gate electrode 2 are simultaneously formed between the pixels in the TFT formation portion of each pixel by etching (see FIG. 2A). After that, the gate insulating film 9 made of silicon nitride or the like is entirely provided by the plasma CVD method or the like, and the semiconductor layer 3 made of amorphous silicon is further deposited on the surface by the CVD method or the like.
It is formed so as to protrude from the gate electrode 2 (FIG. 2B).
reference).

Next, a transparent electrode layer 13 made of a polysilicon film doped with impurities is formed, and the transparent electrode layer 13 is covered with a photoresist layer 11. Then, from the back side of the substrate, the gate electrode 2 is used as a mask for the photoresist. The layer 11 is exposed (see FIG. 1 (a)). Thereby, the photoresist layer 1
1 is exposed to a little inside the gate electrode 2 due to the diffraction phenomenon of light. Next, the exposed photoresist layer 11 is developed, and then the transparent electrode layer 13 is etched from the surface side of the substrate by a reactive ion etching (RIE) method or the like (see FIGS. 1B and 2C). , The first source electrode 8a, the first drain electrode 7a, and the pixel electrode 6 (see FIGS. 1C and 3D). The ohmic contact between the transparent electrode layer 13 and the semiconductor layer 3 is achieved by diffusion from the transparent electrode layer 13 after patterning to the semiconductor layer 3. Source electrode 8 for gate electrode 2
Since the widths W ₁ and W ₂ of the overlapping portions of the drain electrode 7 and the drain electrode 7 are determined by the diffraction phenomenon of light during exposure, they have almost the same width. Therefore, the gate-source capacitance C _GS and the gate-drain capacitance C _GD are almost the same. Since the pixel electrode 6 and the first drain electrode 7a are both made of the transparent electrode layer 13, they are continuous.

Next, a metal film made of chromium or aluminum is formed, and the second drain electrode 7b and the second drain electrode 7b are formed on the first drain electrode 7a, the first source electrode 8a and the source wiring 15 by the photolithography technique. The second source electrode 8b and the second source wiring 16 continuous with the source electrode 8 are formed by patterning (see FIG. 3E). With such a multilayer structure, the resistance of each electrode and wiring can be reduced, and a TFT having good characteristics can be obtained. Further, the source wiring 15 is interrupted at the intersection with the gate wiring 12, but the second source wiring 1
6 are stacked and connected. The source wiring 15 and the second source wiring 16 are formed between pixels.

Next, after forming a passivation film made of silicon nitride or the like on the entire surface, the pixel electrode portion is opened by the photolithography technique (see FIG. 3E).

In this way, the transparent substrate on one side of the liquid crystal display device is formed. Although polysilicon doped with impurities is used as the transparent electrode layer 13 in the above-described embodiment, ITO, SnO ₂ , In ₂ may be used in addition to polysilicon.
O ₃ or the like can also be used. In this case, the contact portion of the surface of the semiconductor layer 3 with the transparent electrode layer 13 is doped with impurities so that ohmic contact can be obtained.

Further, a counter electrode corresponding to the pixel electrode is formed on another transparent substrate, both transparent substrates are made to face each other so that the pixel electrode and the counter electrode face each other, and spacers are interspersed therein to maintain a constant gap. A liquid crystal display device is formed by sealing the peripheral edges of both transparent substrates with a sealant layer and enclosing a liquid crystal material in the gap.

[0020]

According to the manufacturing method of the TFT of the present invention, the source electrode and the drain electrode can be determined by self-alignment, and it is not necessary to consider the alignment margin. This makes it possible to use small TFTs with the smallest design rules.
Therefore, a pixel electrode can be formed large accordingly, and a flat panel display device such as a liquid crystal display device having a large aperture ratio can be obtained.

According to the manufacturing method of the TFT of the present invention, the gate-source capacitance C _GS and the gate-drain capacitance C
_{Since GD} has almost the same value, a TFT having improved switching characteristics can be obtained, and the display characteristics of a flat panel type display device using this TFT are improved.

[Brief description of drawings]

FIG. 1 is a cross-sectional explanatory diagram illustrating a manufacturing process of a method for manufacturing one transparent substrate of a liquid crystal display device of the present invention.

FIG. 2 is an explanatory plan view for explaining the manufacturing process of the method for manufacturing one transparent substrate of the liquid crystal display device of the present invention.

FIG. 3 is an explanatory plan view for explaining the manufacturing process of the method for manufacturing one transparent substrate of the liquid crystal display device of the present invention.

[Explanation of symbols]

 1 transparent substrate 2 gate electrode 3 semiconductor layer 6 pixel electrode 7 drain electrode 8 source electrode 9 gate insulating film 13 transparent electrode layer

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Makoto Takamura, 21 Mizozaki-cho, Saiin, Ukyo-ku, Kyoto ROHM Co., Ltd.

Claims (3)

[Claims] 1. A transparent substrate, a gate electrode formed on the transparent substrate, a semiconductor layer formed on the gate electrode, and formed on the semiconductor layer symmetrically with respect to the gate electrode. A thin film transistor comprising a transparent electrode layer and a source electrode and a drain electrode respectively formed on the transparent electrode layer. 2. (a) A gate electrode is formed on a transparent substrate, (b) an insulating film is formed so as to cover the gate electrode, and (c) a semiconductor is formed on the insulating film above the gate electrode. Source and drain electrodes by stacking and patterning layers, (d) providing a transparent electrode layer on the insulating film and the semiconductor layer, and (e) patterning the transparent electrode layer using the gate electrode as a mask. Forming a thin film transistor. 3. An active matrix type liquid crystal display device in which a liquid crystal layer is sandwiched between two transparent substrates, pixel electrodes are formed in a matrix on at least one transparent substrate, and a switching element is provided for each pixel. ,
A liquid crystal display device, wherein the switching element is the thin film transistor according to claim 1.