JP2659008B2 - Liquid crystal panel manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a liquid crystal panel having a thin-film silicon transistor of polycrystalline silicon or amorphous silicon on a transparent substrate such as a quartz plate, soda glass, or borosilicate glass.

[0002]

2. Description of the Related Art In recent years, in the information-oriented society, there has been remarkable progress in the development of computer-related equipment, and with this, display devices have also been actively developed as a substitute for conventional CRTs. I have.

In particular, a flat panel display using liquid crystal has been widely used not only as a timepiece calculator but also as a panel for home appliances and automobiles in terms of low power, low voltage, and ease of viewing as a light receiving type. In addition, a method of driving a liquid crystal by the active matrix of a thin film transistor has been studied as one of the inexpensive flat displays that are currently replacing the CRT.

This is a display panel for image display in which a switching thin film transistor circuit is formed in a matrix on a transparent substrate and liquid crystal is sealed between the substrate and another transparent glass plate.

The structure of a general thin film silicon transistor which has been reported in the prior art is as shown in FIG. 1. First, a thin film silicon 2 such as polycrystalline silicon or amorphous silicon is formed on a transparent substrate 1 and then only the transistor forming portion is formed by photoetching. The remaining thin film silicon is removed.

Next, an oxide film 3 is formed on the surface of the thin film silicon by a thermal oxidation method or a CVD method, thin film silicon for a gate electrode is deposited on the oxide film, and a gate electrode is formed by photoetching. For the gate electrode, a method of directly depositing thin film silicon containing impurities or a method of lowering wiring resistance by thermally diffusing impurities after depositing the thin film silicon.

Next, ion implantation is performed using the gate electrode as a mask to form a source and a drain, and an insulating film 4 is deposited on the main surface of the substrate.

Next, after a contact hole is formed by photoetching, a metal wiring 5 is formed.

As described above, in the conventional general method of manufacturing a thin film silicon transistor, thin film silicon for forming a transistor is directly formed on the main surface of the substrate because the transparent substrate uses an insulating substrate such as a quartz plate or glass.

[0010]

However, on the surface of these transparent substrates, an abrasive such as alumina powder or cerium oxide used for surface polishing adheres to the surface irregularities such as polishing flaws. Other glass substrates contain various mobile ions including sodium ions and metal ions such as iron ions and copper ions, so that even if the transparent substrate surface is subjected to general cleaning, the contaminants and the like are removed. It is impossible to remove them completely.

Therefore, during many heat treatment steps applied when forming a thin film transistor on a transparent substrate, these impurities penetrate into the thin film silicon and adversely affect the TFT characteristics, resulting in an initial yield such as a decrease in ON current or an abnormal increase in OFF current. Of course, there is a problem in terms of long-term reliability.

Moreover, in the case of a transparent substrate having low purity, surface leakage of the substrate due to impurities is also regarded as a problem.

[0013]

According to the present invention, there is provided a method of manufacturing a liquid crystal panel having a thin film transistor on a transparent glass substrate, wherein the step of cleaning the surface of the glass substrate and the step of removing the surface of the cleaned glass substrate by etching. Forming an insulating film having a composition different from that of the glass substrate on the glass substrate whose surface is removed by etching, and forming a silicon thin film to be a source / drain region of a thin film transistor on the insulating film. And a step of forming a transparent conductive film electrically connected to one of the source / drain regions on the insulating film.

[0014]

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiment 1 FIG. 2 shows a thin film silicon transistor formed on a transparent substrate according to the present invention via an insulating film 6.

First, a transparent substrate (using soda glass) 7
After washing thoroughly, the surface was diluted with hydrofluoric acid to about 1000
ÅRemove. Then, the oxide film 6 is formed to a thickness of 5000
Form. Then, a polycrystalline silicon film 8 is formed on this CVD oxide film 6 at 3000.degree.

Then, a gate oxide film 9 is deposited on the polycrystalline silicon film by 2,000 .ANG. By CVD, phosphorus-doped polycrystalline silicon for a gate electrode is deposited, and a gate electrode is formed by photoetching.

Next, phosphorus is ion-implanted at a high concentration using the gate electrode as a mask.

An oxide film is formed on the main surface of the transparent substrate including the transistor portion where the source and drain are formed by a CVD method.
After depositing 0 °, a contact in the source / drain portion is opened by photoetching.

Next, an aluminum silicon alloy is sputtered on the main surface of the substrate as a metal wiring material, and then a metal wiring 10 is formed by photoetching.

As described above, according to the present invention, when a thin film silicon transistor is formed on a transparent substrate, the surface layer of the transparent substrate is first removed by a slight etching and then a thin film is formed via a CVD oxide film having a high purity and a composition different from that of the transparent substrate. Since a silicon transistor is formed, intrusion of contaminants into the substrate and prevention of surface leakage due to impurities on the substrate surface have been particularly effective in stabilizing initial TFT characteristics.

In addition to the above-described soda glass substrate, even when a thin film silicon transistor (polycrystalline silicon and amorphous silicon transistor) is formed on a borosilicate glass or another transparent glass substrate in the same manner as in the first embodiment. Similar confirmation of characteristic stabilization has been obtained.

Example 2 After the transparent substrate 7 'was sufficiently washed, the surface layer was removed by etching with a diluted solution of hydrofluoric acid at 1000.degree. And a polycrystalline silicon film 8 'is further formed at 3000.degree. The following steps are performed in Example 1.
Is the same as

By using phosphorus silicate glass as the insulating film, the effect as a passivation film is greater than that of the first embodiment due to the getter function of phosphorus, and not only the stability of the initial TFT characteristics but also the stability at a long time is great. The effect was obtained.

Example 3 First, the transparent substrate 7 ″ was thoroughly washed, and then the substrate surface was removed by etching with a diluted solution of hydrofluoric acid by about 1000 °. Thereafter, an argon-based 1% monosilane gas and N _{Using a two-} gas method, a titanium film was deposited at a temperature of about 350 ° C. at 2000 ° C., and a polycrystalline silicon film 8 ″ was formed. Thereafter, a thin film transistor was formed in the same process as in Example 1.

The present ticker film is formed by using a monosilane gas in plasma, and can form a dense film peculiar to the ticker film at a low temperature, so that it is very effective for preventing invasion of contaminants. Therefore, the same or better effects as in the first and second embodiments can be obtained.

In addition to Examples 1, 2, and 3, an insulating film formed on a transparent substrate is spin-coated using a liquid coating material known as a silica diffusion coating material, and then heated at a temperature of about 400 ° C. for insulation. Attempts have also been made on a method for forming a film or a method for forming an insulating film by spin coating a liquid polyimide resin, but the effect of stabilizing the durability is observed.

Embodiment 4 An example in which an active matrix is formed by using a thin film silicon transistor according to the present invention will be described.

As shown in FIG. 3, the surface of the transparent substrate 11 is etched by about 1000.degree. With a diluted solution of hydrofluoric acid, an oxide film 12 is deposited by a CVD method, a polycrystalline silicon film 13 is deposited, and a transistor is formed by photoetching. Except for removing other polycrystalline silicon films.

Next, CVD is applied on the polycrystalline silicon film.
A gate oxide film 14 is formed by a method, a phosphorus-doped polycrystalline silicon film 15 for a gate electrode is formed, and then a gate wiring portion is formed by photoetching.

Next, high concentration phosphorus is ion-implanted to form a source / drain portion.

Next, an oxide film 16 is formed on the main surface of the substrate by CVD.
After depositing, contact holes are opened by photoetching.

Next, the transparent conductive film is sputtered at about 500 ° and photo-etched to form a transparent electrode 17.

Next, after aluminum alloy for metal wiring is sputtered, photoetching is performed to form metal wiring 18 only on the source line.

[0035]

According to the invention of the present application, by satisfying the above constitutional requirements, the following remarkable effects can be obtained. (A) Since the thin film transistor is formed on the glass substrate after the surface of the transparent substrate is cleaned and the surface of the cleaned glass substrate is etched, the contamination on the substrate surface is formed in a later process. Can be prevented from entering.

(B) Preventing Na ions or metal ions such as Fe and Cu diffused from inside the transparent substrate from being diffused into the liquid crystal together with the inside of the transistor by using an insulating film formed on the substrate surface in advance. Can be.

In the active matrix substrate using the thin film silicon transistor formed by the above method, the TFT characteristics of the thin film silicon transistor were stable and the ON / OFF ratio of the signal current was as good as 10 ⁴ or more. . In addition, the liquid crystal panel using an active matrix substrate has a good display retention, no surface leakage compared to liquid crystal panels manufactured by the conventional method, and uneven brightness or darkness of each pixel, or the location of the screen. The present invention greatly contributes to the stabilization of the characteristics of the thin film silicon transistor and the improvement of long-term reliability, because remarkable differences are observed in display unevenness and the occurrence of defects due to the above.

In the embodiment, the insulating film formed on the transparent substrate is all used as a single layer. For example, a non-doped oxide film is formed continuously after forming a phosphor silicate glass, rather than using an oxide film formed by a CVD method as a single layer. Needless to say, the effect of the impurity passivation can be obtained more effectively with the two-layer insulating film having the film formed thereon, and furthermore, the non-doped oxide film sandwiches the phosphor silicate glass from both sides, and the three-layer method further increases the effect. It has also been confirmed to be effective.

Further, with respect to the etching of the surface of the transparent substrate, it is necessary to increase or decrease the amount to be removed depending on the polishing state of the substrate.

[Brief description of the drawings]

FIG. 1 is a cross-sectional structure of a thin film silicon transistor formed on a transparent substrate by a conventional manufacturing method.

FIG. 2 is a cross-sectional structure of a thin-film silicon transistor formed on a transparent substrate according to the present invention.

FIG. 3 is a partial cross-sectional structure of an active matrix substrate in which thin film transistors according to the present invention are arranged in a matrix on a transparent substrate.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Transparent substrate 2 ... Thin film silicon 3 ... Oxide film 4 ... Insulating film 5 ... Metal wiring 6 ... Insulating film (oxide film) 7,7 ', 7 "... Transparent substrate 8,8', 8" ... Polycrystalline silicon film 9 ... Gate oxidation Film 1o ... metal wiring 11 ... Transparent substrate 12 ... Oxide film 13 ... Polycrystalline silicon film 14 ... Gate oxide film 15 ... Polycrystalline silicon film 16 ... Oxide film 17 ... Transparent electrode 18 ... Metal wiring

Claims (1)

(57) [Claims] In a method for manufacturing a liquid crystal panel having a thin film transistor on a transparent glass substrate, a step of cleaning the surface of the glass substrate, a step of etching and removing the surface of the cleaned glass substrate, and a step of etching and removing the surface Forming an insulating film having a composition different from that of the glass substrate on the formed glass substrate; forming a silicon thin film to be a source / drain region of a thin film transistor on the insulating film; Forming a transparent conductive film electrically connected to one of the insulating films on the insulating film.