JPH01186679A - Thin film semiconductor active element - Google Patents

Abstract

PURPOSE:To perform a process which makes use of rear exposure, by using an ultraviolet transmitting and visible light absorbing film as a shading film that is provided at a part which is required to avoid the radiation of light when this element is being operated. CONSTITUTION:An ultraviolet transmitting and visible light absorbing film 10 is provided at a part corresponding to the part where a gate electrode wiring (a metallic film) 26 is to be formed on a glass substrate 20 having high transmissivity to a light including a visible light and ultraviolet light. If the film 10 having a low transmissivity to the visible light and yet, a high transmissivity to the ultraviolet light is used in used in this way, it acts as a shading film to the light radiated by the visible light during operation and then, it allows rear exposure to be effected by its penetrability to the ultraviolet light during manufacturing.

Description

DETAILED DESCRIPTION OF THE INVENTION C. Industrial Application Field The present invention relates to a thin film active element formed on a substrate having high transmittance to light including visible light and ultraviolet light.

[Prior art]

Devices in which thin film active elements are provided on various glass substrates that are transparent (high transmittance) to light in a wide range of wavelengths including visible light have been widely studied. Typical examples include an active matrix type liquid crystal display (LCD) driven by a thin film active element such as a thin film transistor (TPT), and a contact type optical image sensor. Active elements used in these include diodes using amorphous silicon (a-8j),
Thin film transistor (TPT), silicon nitride (SiNx)
), etc. There are two-terminal devices using such devices.

Devices such as the above-mentioned LCD are generally used in environments where they are exposed to some kind of light irradiation.

LCDs are used under illumination light, and in recent years, they have been used with backlights illuminated from the back of the LCD to improve visibility. Furthermore, the optical image sensor converts an image into an electrical signal by receiving reflected light from the light irradiated onto the object. However, semiconductor materials such as amorphous silicon (a-8j) used in these thin film active elements have a property that their conductivity changes upon irradiation with light, that is, a property of generating a photocurrent. This property that the characteristics change depending on light, the photosensitivity, is applied to optical sensors and photosensitive drums, and is a phenomenon that cannot be ignored. but,
In active elements that drive LCDs and the like, photocurrent increases leakage current when turned off and leaks charges accumulated in display electrodes, reducing contrast and becoming a major factor in deterioration of display quality. That is, in active elements used in driving parts that do not utilize photosensitivity, the photocurrent generated by light irradiation during use is generally harmful.

For this reason, it is common to provide an independent light-shielding film made of a light-shielding material in areas where light irradiation causes an adverse effect, or to adopt an element structure in which a light-shielding constituent material is inserted into the light incidence path. This light-shielding material includes a conductive metal film and
Materials that do not transmit all wavelengths have been used, such as insulating hydrogenated amorphous gallium arsenide (a-GaAs: H) disclosed in Japanese Patent No. 219567.

On the other hand, taking advantage of the fact that the glass commonly used for the substrates of these devices has high transmittance in the ultraviolet region, a pattern formed on the substrate that does not transmit ultraviolet light is used as a light-shielding mask, and a photosensitive resin coated on the substrate is used. 2. Description of the Related Art A technique for forming a resist pattern in a self-aligned manner by exposing (resist) from the back side of a substrate, ie, a back exposure technique, has been developed and is now widely used. As an example of this, JP-A-62-
FIGS. 3A to 3F are cross-sectional views of each step in manufacturing a top-gate type a-8j-TFT using back exposure disclosed in Japanese Patent No. 30376.

FIG. 3A shows the state immediately after the source and drain electrode wirings 21 are formed on the transparent glass substrate 20.

On top of this, as shown in FIG. 3B, an a-8i film 22 that will become the active layer of TPT and a silicon nitride film that will become the gate insulating film (
A SiNx) film 23 is successively deposited. Next, as shown in FIG. 3C, a positive resist 24 is applied, and the glass substrate 21 is exposed to ultraviolet light 25 from the back side.

As a result, as shown in FIG. 3D, the source and drain electrode wiring 21 becomes a light shielding mask, and the resist 24 remains only on the source and drain electrode wiring 21 after development. On top of this, as shown in FIG. 3E, a gate electrode wiring (metal film) 26 is deposited, and as shown in FIG. 3F, a resist 24 is deposited.
At the same time, the gate electrode wiring 26 on the resist 24 is removed by lift-off, thereby completing the TPT.

In the a-8i-TFT formed by this method, the gate electrode wiring is formed in self-alignment with the source and drain electrode wiring 21, so there is an advantage that the overlap is small and the parasitic capacitance is small.

[Problem to be solved by the invention]

However, in this top gate type TPT, the third F
As can be seen from the figure, illumination light from the glass substrate 20 side directly enters the active layer (a-8i film) 22, and it is inevitable that the leakage current increases due to the photocurrent. Therefore, a-
When attempting to provide the above-mentioned light shielding film between the glass substrate 20 and the active layer 22 in order to prevent light from entering 8i,
Since the light shielding film blocks all light regardless of the wavelength, there is a fatal drawback that the process using the back exposure described above cannot be carried out.

For this reason, the T
In order to realize PT, the process itself has to be changed, and there is a problem in that the above-mentioned advantages of small overlap and small parasitic capacitance cannot be used at all.

The situation described above is a problem not only in the TPT, but also after a light shielding film is provided on the substrate.

This is a problem that arises when manufacturing thin-film active devices using a light-shielding film that blocks all light, which has been used up to now.

The present invention has been made to solve the above problems.

An object of the present invention is to provide a thin film active device that allows a process using back exposure even if a light shielding film is provided on the thin film active device.

The above and other objects and novel features of the present invention will become apparent from the description of this specification and the accompanying drawings.

[Means to solve the problem]

The outline of the invention of the present application is as follows.

A light-shielding film is provided in areas where it is desired to prevent light irradiation during use, but instead of the conventional light-shielding film that blocks light of all wavelengths, it is most important to use an ultraviolet-transmitting/visible-absorbing film. The characteristics are as follows.

[Effect]

According to the above-mentioned method, if a film with low transmittance of visible light and high transmittance of ultraviolet light is used, it becomes a light shielding film against light irradiation with visible light during use. In some cases, back exposure can be enabled.

The wavelength transmittance described above is realized as a so-called ultraviolet transmission/visible absorption filter.

Here, a film having the above characteristics is referred to as an ultraviolet transmitting/visible absorbing film.

[Embodiments of the invention]

Hereinafter, one embodiment of the present invention will be described in detail based on the drawings.

In addition, in all the figures for explaining an example.

Components having the same function are given the same reference numerals, and repeated explanations thereof will be omitted.

[Embodiment 2] FIG. 1 is a sectional view for explaining the schematic structure of Embodiment I in which the present invention is applied to a top gate type a-8i TPT.

The top gate type a-8i-TFT of this example has the third F
This is a top gate type a-8i-TFT shown in the figure to which an ultraviolet transmitting/visible absorbing film is applied.

That is, as shown in FIG. 1, ultraviolet light is transmitted to a portion of the glass substrate 20 that has a high transmittance to light including visible light and ultraviolet light, and corresponds to a portion where the gate electrode wiring (metal film) 26 is to be formed. - A visible absorbing film 10 is provided. The impurities contained in the ultraviolet transmitting/visible absorbing film 10 are deposited on the active layer (a-8i film) 22 of the thin film semiconductor active element.
It is covered with a protective film 11 that prevents the water from entering. Source and drain electrode wiring (metal film) 21 is provided at a predetermined position on this protective film 11. An active layer 22 of a thin film semiconductor active element is provided on the source and drain electrode wiring 21. A gate electrode wiring 26 is provided on this active layer 22 with a gate insulating film (SiNx film) 23 interposed therebetween.

The ultraviolet-transmitting/visible-absorbing film 10 is formed using, for example, a commercially available ultraviolet-transmitting/visible-absorbing glass filter containing nickel oxide (NIP) as a target. The protective film 11 is, for example, a silicon nitride film (SiNx film).
Use.

In this way, a portion of the glass substrate 20 that has a high transmittance for light including visible light and ultraviolet light and corresponds to a portion where the gate electrode wiring 26 is to be formed has a low transmittance for visible light and a transmittance for ultraviolet light. By providing the ultraviolet transmitting/visible absorbing film 10 with a high rate, it becomes a light shielding film against visible light irradiation during use, and its transparency to ultraviolet light enables back exposure during manufacturing. Can be done.

Next, a method of manufacturing the top gate type a-8i-TPT of this example will be explained.

FIGS. 2A and 2B are cross-sectional views at each step in manufacturing the top gate type A-8i-TFT of Example I.

First, as shown in FIG. 2A, a glass substrate 20 having a high transmittance for light including visible light and ultraviolet light is coated with an ultraviolet transmitting film containing, for example, commercially available nickel oxide (NIP).
By a sputtering method targeting a visible absorption glass filter, an ultraviolet transmitting/visible absorbing film 10 having low transmittance for visible light and high transmittance for ultraviolet light is formed, and its ultraviolet transmittance and
Etching is performed using a mask so that only the portion of the visible absorbing film 10 corresponding to the portion where the gate electrode wiring 26 is to be formed remains. Next, as shown in FIG. 2B, a protective film 11 made of a silicon nitride (SiNx) film is formed on the etched ultraviolet transmitting/visible absorbing film 16 by, for example, the CVD method.

Next, on the protective film 11, as shown in FIG. 3A, source and drain electrode wiring (metal film) 21 is formed, and on this wiring 11, as shown in FIG. 3B, a TPT active layer is formed. (e.g. a-8i film) 22 and gate insulating film (e.g. 5i film) 22
Continuously deposit Nx)23. Next, as shown in FIG. 3C, a positive resist 24 is applied, and the glass substrate 20 is exposed to ultraviolet light 25 from the back side.

As a result, as shown in FIG. 3D, the source and drain electrode wiring 21 becomes a light shielding mask, and the resist 24 remains only on the source and drain electrode wiring 21 after development. On top of this, as shown in FIG. 3E, a gate electrode wiring 26 is deposited, and as shown in FIG. 1, the gate electrode wiring 26 on the resist 24 is removed together with the resist 24 by lift-off, thereby completing the TPT. be done.

As mentioned above, the formation of a resist pattern by back exposure corresponding to FIG. - The test could be carried out without any problems as in the case without the visible absorbing film 10. When we measured the leakage current of the manufactured TPT, we found that the illumination light intensity was 10,000 lux [
The leakage current in Qxl increased only about twice as much as in the case without illumination, which had the effect of suppressing it to an extremely small level compared to the 100 times increase in the case where the ultraviolet transmitting/visible absorbing film 10 was not provided. The amount of double increase in leakage current is the amount of illumination 100 when the ultraviolet transmitting/visible absorbing film 10 is not provided.
Since it corresponds to 0 lux [Qxl], it was found that the effective amount of illumination light could be reduced to about 1710 lux by inserting the ultraviolet transmitting/visible absorbing film 10.

[Example ■] Example (2) of the present invention is the same as Example I above.

The ultraviolet transmitting/visible absorbing film according to the present invention is applied to the top gate type a-8iTPT shown in FIG. 1.

Since its structure is almost the same as that of Example 2, it will be explained using FIG. 1.

The ultraviolet-transmitting/visible-absorbing film 10 of this example This is an ultraviolet transmitting and visible absorbing film formed by (co-sputtering). This embodiment (2) is the same as FIG. 1 except that the protective film 11 made of the SiNx film is not used because the ultraviolet transmitting/visible absorbing film 10 contains few impurities. Formation of a resist pattern by back exposure corresponding to FIG. 3C is performed by irradiating the ultraviolet transmitting/visible absorbing film 10 with ultraviolet light, but it can be performed without any problems as in the case without the ultraviolet transmitting/visible absorbing film 10. The ultraviolet transmitting/visible absorbing film 10 thus obtained had sufficiently high resistance, and no abnormal current was observed between the source and drain. When the TPT was illuminated from the back of the board and the leakage current of the TPT was measured,
The leakage current at an illumination light intensity of 10,000 lux (Qxl) increases only about 5 times compared to the case without illumination, and has the effect of suppressing the increase by 100 times when the ultraviolet transmitting/visible absorbing film 10 is not provided. Ta.

As can be seen from the above description, according to Examples (1) and (2), the ultraviolet transmitting/visible absorbing film formed on the substrate with high transmittance to ultraviolet light and visible light is used as the constituent material of the thin film active element. By using it, it is possible to prevent visible light, which is the illumination light during use, from being irradiated to the active layer of the active element, and
In addition, the back exposure process can be used freely during device fabrication.

Therefore, the insertion position of the UV-transmitting/visible-absorbing film is most recommended between the substrate and the active layer, but it is not limited to this, and the UV-transmitting/visible-absorbing film can be introduced at any position. It is possible to do so.

Furthermore, it is clear that the active element is not limited to the TPT described in the embodiments, and various elements can be used without departing from the gist of the present invention.

In addition, the characteristics required for a UV-transmitting/visible-absorbing film are high transmittance for ultraviolet light that sensitizes the resist and low transmittance for visible light, but the absolute value of transmittance does not matter. . It is not necessary to completely block visible light, as long as the amount of visible light irradiation can be reduced to a range that does not deteriorate the characteristics of the device. Further, the transmittance of ultraviolet light may be as long as the resist can be exposed to light by back exposure and a resist pattern can be formed.

Here, there is a concern that the photocurrent cannot be reduced if the irradiation light includes ultraviolet light during use, but the polarizing film that is essential for LCDs generally has a low transmittance to ultraviolet light, and removes ultraviolet light from the illumination light source. It is very easy to
This does not in any way hinder the implementation of the present invention.

As the ultraviolet transmitting/visible absorbing film, glass containing nickel oxide (Nip) is exemplified in the Examples, but there is no need to be limited thereto.

If the ultraviolet transmitting/visible absorbing film is insulating as shown in the above example, it can be used as an insulating film instead of being formed independently as a light shielding film, and if it is conductive, it can also be used as a conductor. The good news is obvious.

In this case, if the ultraviolet transmitting/visible absorbing film is limited to only the active element part, the aperture ratio of the LCD etc. will be reduced in exactly the same way as a conventional light shielding film, since this is a part that has not traditionally been used as a light passage. It is clear that there is no way to do that.

The present invention has been specifically explained above based on examples, but
It goes without saying that the present invention is not limited to the embodiments described above, and can be modified in various ways without departing from the spirit thereof.

〔Effect of the invention〕

As explained above, when used in the present invention, back exposure is possible even if a light shielding film is provided, so there is an advantage that processes using back exposure developed so far can be applied without modification.

[Brief explanation of the drawing]

FIG. 1 is a sectional view for explaining the schematic structure of Embodiment I in which the present invention is applied to a top gate type a-8i TPT. FIGS. 2A and 2B are top gate type a −
3A to 3F are cross-sectional views of each process during the manufacturing of the 8i-TFT, and are intended to explain the problems of the top gate type a-8i-TFT using conventional back exposure. FIG. . In the figure, 10... UV transmitting/visible absorbing film, 11...
Protective film, 20... Glass substrate, 21... Source and drain electrode wiring, 22... Active layer, 23... Gate insulating film, 24... Positive resist, 25... Ultraviolet light, 26...Gate electrode wiring.

Claims (3)

[Claims] (1) A thin film active element in which a light shielding film is provided between a substrate having high transmittance to light including visible light and ultraviolet light and a thin film active part, the light shielding film being an ultraviolet transmitting/visible absorbing film. A thin film semiconductor active device characterized by using. (2) An ultraviolet transmitting/visible absorbing film is provided on a portion of the substrate that has high transmittance to light including visible light and ultraviolet light, corresponding to the portion where the gate electrode wiring is to be formed, and the ultraviolet transmitting/visible absorbing film is provided. Source and drain electrode wirings are provided at predetermined positions on the active film, an active layer of a thin film semiconductor active element is provided on these, and a gate electrode wiring is provided on top of the active layer with a gate insulating film interposed therebetween. Thin film semiconductor active device. (3) An ultraviolet transmitting/visible absorbing film is provided on a portion of the substrate that has high transmittance to light including visible light and ultraviolet light, corresponding to the portion where the gate electrode wiring is to be formed, and the ultraviolet transmitting/visible absorbing film is provided. covering the active film with a protective film that prevents impurities contained therein from entering the active layer of the thin film semiconductor active device;
Source and drain electrode wirings are provided at predetermined positions on the protective film, an active layer of a thin film semiconductor active element is provided thereon, and a gate electrode wiring is provided thereon via a gate insulating film. Thin film semiconductor active device.