JPH06132533A - Manufacture of tft array substrate - Google Patents

Abstract

PURPOSE:To perform highly-selective etching with a low resistance semiconductor protective film and a semiconductor layer by, in the process where the low resistance semiconductor layer of a channel area is dry-etched, using such a mixture gas as the gas that forms chlorine radicals, inactive gas, etc. CONSTITUTION:A molybdenum tantalum alloy film is formed on a glass substrate 1, and a gate electrode 2 is formed an a glass substrate 1, and a gate electrode 2 is formed after a resist is applied. After a gate insulation film 3 and a semiconductor film 4 are sequentially deposited, a law resistance semiconductor film 5 is formed, further, the semiconductor film 4 and the low resistance semiconductor film 5 are formed at the same time, then, a pixel electrode 6 is formed. After a conductive film mode of molybdenum and is deposited, a drain electrode 7 and a source electrode 8 are formed at the same time. With a resist, an the drain electrode 7 and the source electrode 8, used as a mask, plasma etching is performed with the low resistance semiconductor film 5, to be served as a channel area. The gas used is the mixture gas of Cl2 gas and argon gas, with the mixture ratio of argon gas 30% with respect to the Cl2 gas flow rate.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a TFT array substrate, and more particularly to a method of manufacturing a thin film transistor for an active matrix type liquid crystal display device using this technique.

[0002]

2. Description of the Related Art In recent years, liquid crystal display devices have the great advantages of thinness, light weight, and low power consumption.
It is widely used for display devices of equipment A, and at the same time, improvement in manufacturing technology and productivity of liquid crystal display elements is strongly desired. In particular, an active matrix type liquid crystal display device in which a three-terminal device such as a thin film transistor (hereinafter referred to as a TFT) is connected to each of the display pixels as a switch is easy to obtain a large screen, It is drawing attention because it can be applied to semiconductor manufacturing technology.
Research and development of the TFTs used are also being actively conducted. For example, a liquid crystal display element using a glass substrate on which a TFT is formed as one substrate is already known (IEEE
Trans.on Electron Devices, 995-1001, [20], 1973).

The structure and manufacturing method of a liquid crystal display device using such a conventional TFT will be described with reference to FIG. FIG. 2 is an example of a cross-sectional view of a display pixel portion of a liquid crystal display element using a TFT. An insulating substrate made of glass or the like is used as a front glass substrate 1, a scanning electrode line (not shown) and a gate electrode 2 are simultaneously formed thereon, and a gate insulating film 3 and a semiconductor film 4 are sequentially formed. Next, the low resistance semiconductor film 5 is formed and patterned simultaneously with the semiconductor film 4.
After that, the pixel electrode 6 is formed, the gate insulating film on the electrode pad is removed, and the signal electrode (not shown), the source electrode 8, and the drain electrode 7 are formed. In this state, the source electrode 8 and the drain electrode 7 are short-circuited by the low resistance semiconductor film 5. Therefore, the low-resistance semiconductor film 5 in the channel region is removed by using the resist on the source electrode 8 and the drain electrode 7 as a mask. Finally, an insulating film 9 is formed to protect the TFT array substrate.

On the surface of the TFT array substrate thus manufactured, the light-shielding film 11, the counter electrode 12 and the alignment film 13 are formed.
The rear glass substrate 10 on which the layers are sequentially formed face each other with the alignment films facing each other, and the liquid crystal composition 14 is sealed in the gaps to manufacture a liquid crystal cell. Further, an external circuit is connected to such a liquid crystal cell and housed in a case to manufacture a liquid crystal display element using a TFT (hereinafter referred to as TFT-LCD).

In the above-mentioned TFT-LCD manufacturing process, particularly in manufacturing the TFT array substrate, the low resistance semiconductor film 5 must be selectively etched without impairing the performance of the lower semiconductor film 4, so that the channel region is not etched. The process of removing the low resistance semiconductor film 5 has a great influence on the characteristics of the TFT array substrate. This low resistance semiconductor film 5
Are phosphorus-doped n-type semiconductors and boron-doped p
The type semiconductor is made of polycrystalline silicon (poly-Si), amorphous silicon (a-Si), or the like used as the silicon base material for the semiconductor film 4. A plasma etching technique is used as these etching methods. For example, a TFT-L using n ⁺ type a-Si as the low resistance semiconductor film 5
In the case of CD, CF ₄ and O ₂ are used for etching the n ⁺ type a-Si film.
It is known to use a mixed gas consisting of

[0006]

However, since the selection ratio of the semiconductor film 4 and the low resistance semiconductor film 5 in plasma etching is almost equal to 1, the etching rate, the unevenness of the film thickness, the thin film formation and the pattern forming process are Normally occurring fluctuation directly affects the film thickness of the semiconductor film, and there is a problem that it is difficult to maintain the film thickness within a predetermined thickness range.

In order to deal with this problem, the thickness of the semiconductor film should be made sufficiently thick, or the apparatus for the thin film forming process should be strictly controlled in order to improve the uniformity in the thin film forming process and the pattern forming process. However, there is a problem that it is not enough.

Further, as the size of the TFT-LCD is increased, the size of the substrate used is also increased. Therefore, there is an increasing need to obtain a process margin in consideration of mass productivity.

The present invention has been made to solve the above problems, and performs high selective etching of a low resistance semiconductor protective film and a semiconductor film in a manufacturing process of a TFT-LCD, particularly in a manufacturing method of a TFT array substrate. It is an object of the present invention to provide a manufacturing method capable of manufacturing.

[0010]

A method of manufacturing a TFT array substrate according to the present invention includes a substrate, a semiconductor layer made of silicon as a base material and a low resistance via a predetermined electrode and an insulating layer formed on the substrate. A step of sequentially forming the semiconductor layers, a step of forming a source electrode and a drain electrode on the semiconductor layer and the low-resistance semiconductor layer by forming a channel region, and a step of forming the low-resistance semiconductor layer in the channel region using a mixed gas plasma In the method for manufacturing a TFT array substrate, which comprises a step of dry etching, a mixed gas is a gas that forms chlorine ions or chlorine radicals in plasma, a gas that forms fluorine ions or fluorine radicals in plasma, or an inert gas. It is characterized by being composed of a mixed gas with at least one gas.

Gases that form chlorine ions or chlorine radicals in the plasma according to the present invention include HCl and Cl ₂
For example, a gas containing a chlorine atom in its molecule can be used.

Gases that form fluorine ions or fluorine radicals in the plasma according to the present invention are CF ₄ , C ₂ F ₆ ,
Fluorocarbon gases such as C ₃ F ₈ and CHF ₃ and SF
₆ gases can be used. In addition, as the inert gas,
Helium, neon, argon, krypton, xenon,
Nitrogen gas or the like can be used.

The mixing ratio of the gas that forms chlorine ions or chlorine radicals in the plasma and the gas that forms fluorine ions or fluorine radicals in the plasma or at least one of the inert gases in the plasma is Although it varies depending on the gas pressure, the type of gas, the gas concentration, etc., it is preferable that the mixing ratio is such that the etching rate selectivity ratio between the low resistance semiconductor layer and the semiconductor layer is at least 2 or more.

Examples of the dry etching method according to the present invention include excitation gas etching, plasma etching, reactive ion etching, sputter etching, reactive ion beam etching, and ion beam etching.

A step of sequentially forming a semiconductor layer containing silicon as a base material and a low resistance semiconductor layer through a predetermined electrode and an insulating layer formed on a substrate according to the present invention,
In the step of forming the source electrode and the drain electrode on the semiconductor layer and the low resistance semiconductor layer by providing the channel region, a known method such as a sputtering method or a photolithography method used for a TFT can be used. it can. Further, it is preferable to have a step of forming a gate electrode and an insulating film above or below the channel region before and after the above steps.

[0016]

[Operation] The operation when etching is carried out using a mixed gas of Cl ₂ gas as a gas forming chlorine ions or chlorine radicals in plasma and argon gas as an inert gas will be described. The device used was a capacitively coupled device with parallel plate electrodes, and the cathode electrode was
A high frequency voltage of 13.56 MH was applied. The substrate to be etched is held on the cathode electrode side. When argon gas was mixed at about 30% with Cl ₂ gas flow rate, the etching rate of low resistance semiconductor film was 710 Å / mi.
At n., the etching rate of the semiconductor film was 230 Å / min., and a selectivity of 3.1 was obtained. In addition, Cl ₂ gas pressure,
By changing the flow rate, the etching rate of the low resistance semiconductor film is 700 to 2100 angstroms / min., And the etching rate of the semiconductor film is 200 to 1000 angstroms / min.
It changed to min. and the selection ratio obtained the value of 2.5-3.1.

Further, CF ₄ gas is added to the Cl ₂ gas flow rate of 2
When mixed at 5%, the etching rate of the low resistance semiconductor film was 1080 Å / min. And the etching rate of the semiconductor film was 370 Å / min. Furthermore, 150% of CF ₄ gas against Cl ₂ gas flow rate
When the amount is increased, the etching rate of the low resistance semiconductor film becomes 113
At 0 angstrom / min., The etching rate of the semiconductor film was 430 angstrom / min., And a selectivity ratio of 2.6 was obtained. In each case, a selectivity of 2 to 5 was obtained. This is a significant improvement over the selection ratio of approximately 1 in plasma etching using a conventional mixed gas of CF ₄ and O ₂ .

[0018]

The present invention will be described in detail below with reference to the drawings. FIG. 1 shows a part of a schematic cross section of a display pixel part of a TFT array substrate, and FIG. 2 shows a part of a schematic cross section of a display pixel part of a TFT liquid crystal display element.

Example 1 A molybdenum-tantalum alloy thin film was formed on the front glass substrate 1 to a thickness of about 0.2 μm by a sputtering method, a resist was applied thereto, and then a stripe-shaped scanning electrode line and this scanning electrode were electrically applied by a photolithography method. Gate electrode 2 connected to
Pattern is formed by plasma etching. Next, the gate insulating film 3 is formed by the plasma CVD method.
0.3 μm silicon nitride (SiN _x ) and semiconductor film 4
0.3 μm of amorphous silicon (a-Si) is continuously deposited. Next, a low resistance semiconductor film 5 (n ⁺ a-Si) doped with about 10 ²⁰ phosphorus / mol of phosphorus was added to 0.05 by plasma CVD.
Then, the semiconductor film 4 and the low resistance semiconductor film 5 are simultaneously formed by photolithography. After that, the portion that needs to be electrically connected to the outside, for example, the gate insulating film 3 on the electrode pad is removed by photolithography. Next, the indium / tin oxide film (IT
An O film) is deposited to a thickness of about 0.1 μm to form the pixel electrode 6 by the photolithography method. Further, a conductive film made of molybdenum (0.05 μm) and aluminum (1.0 μm) is deposited by the sputtering method, and the signal electrode line and the drain electrode 7 and the source electrode 8 electrically connected to the signal electrode line are plasma-processed by the photolithography method. Simultaneous molding by etching method.

Next, plasma etching of the low resistance semiconductor film 5 to be the channel region is performed using the resist on the drain electrode 7 and the source electrode 8 as a mask. The gas used is a mixed gas of Cl ₂ gas and argon gas,
The mixing ratio is 30% argon gas to Cl ₂ gas flow rate.
And At this time, the etching rate of the low resistance semiconductor film 5 is
710 Å / min. Was obtained. In addition, the semiconductor film 4 prepared separately for comparison gave 230 angstrom / min. And a selectivity ratio of 3.1.

Finally, next, an insulating film 9 such as silicon nitride (SiN _x ) is deposited on the glass substrate 1 at a thickness of about 0.1 μm to 1.0 μm.
Then, the insulating film 9 in a portion that needs to be electrically connected is removed by the photolithography method, and the alignment film 13 is formed to produce a TFT array substrate. As a result of measuring the characteristics of the TFT array substrate manufactured in this way, the dark current becomes smaller than that of the conventional TFT array substrate, and the characteristic variation at each site within the same large-sized substrate is greatly reduced, and good characteristics are reproduced. I showed it well.

Further, as shown in FIG. 2, this TFT array substrate is used as a front glass substrate 1, and a light-shielding called a black matrix for shielding the light transmitted from the non-pixel electrode portion and the light incident on the TFT on the surface. The glass substrate on which the transparent counter electrode 12 including the film 11 and the indium tin oxide film (ITO film) is formed is the rear glass substrate 10.
As a liquid crystal alignment film 1 on the TFT formation side of the front glass substrate 1 and on the counter electrode 12 formation side of the rear glass substrate 10, respectively.
3 is formed, and after the alignment treatment is performed, the front surface glass substrate 1 and the rear surface glass substrate 10 are about 10 μm with the alignment treatment surface inside.
The liquid crystal composition 14 is sealed in parallel with each other at a distance of m to oppose each other, and a liquid crystal cell is formed. Further, an external circuit is connected to such a liquid crystal cell and housed in a case to manufacture a liquid crystal display element using a TFT (hereinafter referred to as TFT-LCD).

When a predetermined voltage was applied to the signal line and the scanning electrode line of this TFT-LCD and the liquid crystal screen was evaluated, a good screen without unevenness was obtained.

Example 2 A mixed gas ratio of CF ₄ gas was 25% with respect to Cl ₂ gas flow rate.
The same material and process as in Example 1 except that they were mixed
An array substrate is produced. In this case, the etching rate of the low resistance semiconductor film was 1080 angstrom / min. And the etching rate of the semiconductor film was 370 angstrom / min. In addition, CF _{4 with} respect to Cl ₂ gas flow rate
When the amount of gas was increased to 150%, the etching rate of the low resistance semiconductor film was 1130 angstroms / min. And the etching rate of the semiconductor film was 430 angstroms / min. In addition, a TFT array substrate and TF
The same results as in Example 1 were obtained in the characteristic evaluation of the T-LCD.

[0025]

According to the method of manufacturing the TFT array substrate of the present invention, in the step of dry etching the low resistance semiconductor layer in the channel region, the mixed gas forms a chlorine ion or a chlorine radical in the plasma and the gas in the plasma. Since it is made of a mixed gas with a gas that forms fluorine ions or fluorine radicals or a gas that is at least one of an inert gas, selective etching of the low resistance semiconductor layer and the semiconductor layer thereunder can be easily performed. As a result, good TFT-LCD characteristics can be obtained with good reproducibility, and can be obtained over the entire surface of a large substrate without variation. with this,
It is possible to obtain a good screen with excellent even contrast. Further, since the semiconductor layer can be made thinner, the process margin is improved.

[Brief description of drawings]

FIG. 1 is a diagram showing a schematic cross section of a display pixel portion of a TFT array substrate.

FIG. 2 is a diagram showing a schematic cross section of a display pixel portion of a liquid crystal display element using a TFT.

[Explanation of symbols]

1 ... Front glass substrate, 2 ... Gate electrode, 3 ...
... gate insulating film, 4 ... semiconductor film, 5 low resistance semiconductor film, 6 pixel electrode, 7 drain electrode, 8
………… Source electrode, 9 ………… Insulating film, 10 ………… Rear glass substrate, 11 ………… Light-shielding film, 12 ………… Counter electrode, 1
3 ... Liquid crystal alignment film, 14 ... Liquid crystal composition.

Claims (1)

[Claims] 1. A substrate, a step of sequentially forming a semiconductor layer containing silicon as a base material and a low resistance semiconductor layer through a predetermined electrode and an insulating layer formed on the substrate, the semiconductor layer and the low resistance. Forming a source electrode and a drain electrode on the semiconductor layer by providing a channel region;
Dry etching the low resistance semiconductor layer in the channel region using plasma of a mixed gas.
In the method of manufacturing an FT array substrate, the mixed gas is at least one of a gas that forms chlorine ions or chlorine radicals in plasma and a gas that forms fluorine ions or fluorine radicals in plasma or an inert gas. A method of manufacturing a TFT array substrate, which comprises a mixed gas of