JPH1083887A - Manufacture of thin-film electroluminescent element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent troubles during processes resulting from gaps in a second insulating layer on a luminescent layer and to also prevent dielectric breakdown of the second insulating layer in a thin-film electroluminescent element in which at least a first electrode, a first insulating layer, the luminescent layer, a second insulating layer, and a second electrode are deposited on an insulating substrate. SOLUTION: After a luminescent layer 5 has been formed, a bias sputtering method is effected for 120 minutes, in which silicon is used as a target and power of 100W is applied to the target 14 and 500W to an electroluminescent element 1 inside mixed gases of Ar and N2 to deposit a film of Si3 N4 that is 200nm thick. By this bias sputtering, a second insulating layer formed almost completely covers indentations in the surface of the luminescent layer, thus preventing the trouble of infiltration of water into the luminescent layer 5 during wet processes and dielectric breakdown during voltage application. A complex film may be formed by simultaneous sputtering using a plurality of targets.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to
The present invention relates to a method of manufacturing a thin-film electroluminescent element (hereinafter, referred to as a thin-film EL element) which exhibits electroluminescence and is used for display or the like, and particularly to a method of forming an insulating layer.

[0002]

2. Description of the Related Art A thin-film EL element exhibiting electroluminescence by applying a voltage has high luminance emission, high-speed response,
Since it has many excellent features such as a wide viewing angle and high resolution, it has attracted attention as a thin display device. FIG. 4 (a)
1 shows a cross-sectional view of the thin-film EL element 1. A first electrode 3, a first insulating layer 4, a light emitting layer 5, a second insulating layer 6, and a second electrode 7 are sequentially laminated on a light transmitting substrate 2 such as glass.

The first electrode 3 is, for example, a transparent electrode of indium tin oxide (ITO), and the first and second insulating layers 4, 6
As a silicon oxide film (hereinafter referred to as SiO ₂ film)
And a silicon nitride film (hereinafter referred to as a Si ₃ N ₄ film) are known as typical examples. As the light emitting layer 5, for example, zinc sulfide (ZnS: Mn) doped with manganese (Mn) as an active substance, strontium sulfide (SrS: Ce) added with cerium (Ce), or a laminated film thereof is used. The second electrode 7 is made of molybdenum (Mo)
And the like. By applying an AC voltage from the power supply 8 between the first electrode 3 and the second electrode 7, electroluminescence is obtained.

[0004] Such a thin-film electroluminescent device is usually manufactured as follows. An ITO film is formed on the glass substrate 2 by a sputtering method, and is patterned by photolithography to form a striped first electrode 3. next,
The first insulating layer 4 is formed by a sputtering method. in addition,
SrS: Ce and ZnS: Mn by electron beam evaporation
Is formed. Further, after the second insulating layer 6 is formed by the sputtering method, the second electrode 7 is formed by the sputtering method, and is patterned into a stripe by photolithography.

Here, in order to explain the details of the patterning step of the metal film to be the second electrode in the above manufacturing steps, cross-sectional views of the main steps are shown in FIGS. 5 (a) to 5 (d). First, after forming the Mo film 7a to be the second electrode, a resist 9a is applied [FIG. 5 (a)]. Thereafter, the film is baked to improve the adhesion between the resist and the Mo film, exposed to ultraviolet (UV) light using a mask, and developed with a developer to form a resist pattern 9 (FIG. 9B). .

After baking again, the portion of the Mo film 7a where the resist has been removed is etched [FIG. Finally, the resist is completely removed to remove the second electrode 7
The patterning step of FIG. During this time, after development, etching, and after removing the resist, a process of washing with pure water for 10 to 20 minutes and drying the film is included.

[0007]

FIG. 4B is an enlarged sectional view of the light emitting layer 5 and the second insulating layer 6 part. Light emitting layer 5
Is a method in which a first electrode 3 of ITO and a first insulating layer 4 of a silicon oxynitride film (hereinafter referred to as SiON) are deposited on a glass substrate 2 by a sputtering method, and then deposited by an electron beam evaporation method.
It is formed by laminating about 1 μm of rS: Ce and 0.1 μm of ZnS: Mn. Furthermore, Si as a second insulating layer 6 is formed thereon.
_{A 3} N ₄ film is deposited at a thickness of 0.2 μm.

As can be seen from the figure, SrS of the light emitting layer 5 formed by the above-described process has columnar crystals having a diameter of 40 to 80 nm grown side by side. Then, a ZnS film is formed thereon, and the protrusions are preferentially deposited to form hemispherically raised mounds, and the surface has irregularities of about 100 nm. Further, a mound 10 in which the second insulating layer is preferentially deposited on the convex portion is formed, and a gap 11 is generated at a boundary with another portion. That is, although the film formation conditions of the second insulating layer 6 are optimized so as to cover the unevenness of the light emitting layer 5, if there are large unevenness on the surface of the light emitting layer 5, the second insulating layer 6 The layer 6 may not be completely covered.

As described above, in the pattern formation process of the second electrode 7, after development, etching, and after removal of the resist, processes of pure water cleaning and drying are included, respectively. Of water from the environment occurs through the gap 11 of the second insulating layer 6. SrS, which is necessary for colorization of the thin film EL element, is an extremely sensitive material, and if there is a gap 11 in the second insulating layer 6, there is a problem that the light emitting layer is hydrolyzed during washing with water. Hydrolysis also occurs to varying degrees with ZnS and the like.

If a dry process such as dry etching is performed as a patterning method for the second electrode 6, the problem of hydrolysis can be avoided, but on the other hand, the equipment is expensive, which leads to an increase in cost and is not suitable for mass production. . Further, when the coverage of the second insulating layer 6 is reduced, there is also a problem that an electric field is concentrated on the portion and dielectric breakdown occurs. Due to these problems, in particular, the thin film E having a light emitting layer containing SrS as a base material is used.
The L element has been difficult to realize.

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and an object of the present invention is to eliminate a gap in a second insulating layer which causes flooding of an emission layer and concentration of an electric field, thereby avoiding such problems and providing a high withstand voltage thin film. An object of the present invention is to provide a method for manufacturing an EL element.

[0012]

According to the present invention, at least a first electrode, a first insulating layer, a light emitting layer which is a group II metal chalcogenide, and a second insulating layer are provided on an insulating substrate. In the method for manufacturing a thin-film EL element in which the second electrode is stacked, the second insulating layer is formed by a bias sputtering method.

According to the bias sputtering method, the adhered substance which has been etched from the target by Ar ions or the like and deposited on the substrate is etched again by Ar ions or the like to bury minute holes and flatten the deposited film. This is known as a semiconductor microfabrication technology (for example, Tokuyama and Hashimoto, MOS LSI manufacturing technology, page 135, Nikkei McGraw-Hill, 1985). It was also confirmed that the present invention can be used to improve the coverage of the second insulating layer that covers the unevenness of the light emitting layer surface.

In particular, the second insulating layer may be any of a Si ₃ N ₄ film, a silicon oxide film (hereinafter referred to as SiO ₂ film), a SiON film, and an aluminum oxide film (hereinafter referred to as Al ₂ O ₃ film). I do. These films, which are compounds of silicon or aluminum, are stable insulating films widely used in semiconductor devices, and can be formed by a reactive sputtering method using silicon or aluminum as a target, which is easily available.

Further, a composite film can be formed by performing bias sputtering simultaneously and multiple times using a plurality of targets. With such a method, the film characteristics can be controlled by combining films having different characteristics. For example, an Al ₂ O ₃ film and a titanium oxide film (hereinafter T)
iO ₂ film) is alternately laminated to form an aluminum titanium oxide film (hereinafter, referred to as an ATO film).

The dielectric constant and the dielectric strength of the ATO film can be controlled by changing the ratio between the TiO ₂ film having a large dielectric constant and the Al ₂ O ₃ film having a large dielectric strength.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 2 shows a thin film EL according to the present invention.
It is sectional drawing to which the light emitting layer and the 2nd insulating layer part of the element were expanded. In the thin film EL device of this embodiment, the first electrode 3, the first insulating layer 4, the light emitting layer 4, the second insulating layer 5, and the second electrode 6 are sequentially laminated on the glass substrate 2 as shown in FIG.
Is the same as the conventional example. However, in this enlarged view, there is a hemispherical mound of about 100 nm on the surface of the light emitting layer 5 that is a columnar crystal, but the surface of the second insulating layer 5 that covers the unevenness on the surface of the light emitting layer 4 is , And no gap is seen in the second insulating layer 6 as in the example of FIG.

Such a thin-film electroluminescent device is manufactured as follows. An ITO film having a thickness of 180 nm is formed on a glass substrate 1 by a sputtering method, and is patterned by photolithography to form a stripe-shaped transparent electrode 2. Next, 200 nm thick SiO 2 was formed by sputtering.
The first insulating layer 3 of a composite film of the _two films and the SiON film is formed. On top of that, a 1 μm thick S was deposited by electron beam evaporation.
Luminescent layer 5 of rS: Ce and 100 nm ZnS: Mn
Is selectively formed using a mask.

Next, a nitride film to be the second insulating film 6 is formed. First, FIG. 1 is a conceptual diagram of a bias sputtering apparatus used in the manufacturing method of the present invention. The substrate holder 13 and the target 14 are independently connected to a high-frequency power supply 15. Since the high-frequency power supplies 15 cannot be individually matched at the same frequency, it is necessary to slightly shift one of the frequencies. In the present invention, the high frequency power supply 15a connected to the target 14 is modulated to 13.54 MHz and used. 16 is an infrared lamp for heating the substrate, 17 is a sputtering gas, and 18 is a vacuum pump. To deposit an insulating film as in this embodiment, high frequency sputtering is better than DC sputtering.

First electrode 3, first insulating layer 4, EL light emitting layer 5
The glass substrate 2 on which is formed is set on the substrate holder 13. Silicon (hereinafter referred to as Si) was used for the target 14. After evacuating the vacuum chamber 12 with a vacuum pump 18, argon (hereinafter referred to as Ar) and nitrogen (hereinafter referred to as N ₂
) Was introduced at a pressure of about 1 Pa. Sputtering target 1
A power of 100 W was applied to the glass substrate 2 side and a power of 500 W was applied to the glass substrate 2 side for 120 minutes. The power applied to the target side and the substrate side is determined in consideration of the desired film thickness. During sputtering, the temperature is maintained at 300 ° C. by the heater 16. Temperature adjustment during film formation affects the film coverage, so it is necessary to keep the temperature from fluctuating so much. Sputter gas 1
By a reactive sputtering method between the target 7 and the target 14, a Si ₃ N ₄ film having a thickness of about 200 nm to be a second insulating layer was obtained. This film thickness is determined in consideration of the withstand voltage and capacitance of the insulating layer, and a film having a withstand voltage may be, for example, a 50-nm-thick film.

After patterning the second insulating layer by photolithography, a Mo film having a thickness of 180 nm is formed by a sputtering method, and patterned into a stripe shape by photolithography to form a second electrode. By employing such a manufacturing method, a thin-film EL device in which the light emitting layer 5 is completely covered with the second insulating layer 6 as shown in the cross section in FIG. 2 can be obtained.

When a test element of 10 mm square was tentatively manufactured and subjected to an immersion test, the defect rate of the comparative example in which no bias sputtering was performed was 1%, whereas the test element according to the manufacturing method of the present invention was 0%. 0.05%. Also, in the dielectric strength between the first and second electrodes, the test element according to the manufacturing method of the present invention improved the average by about 40 V from the comparative example.

In each case, the second insulating layer 6 almost completely covers the light emitting layer 5 by the bias sputtering method. When a metal is used as a target as described above, an insulating film formed by a gas can be changed. For example, if an SiO ₂ film is required, a mixed gas of Ar and oxygen (hereinafter referred to as O ₂ ) may be used as the sputtering gas 17. In addition, Ar, N ₂ , O
_If a mixed gas of ₂ is used, a SiON film can also be formed. Of course, a Si ₃ N ₄ target or a SiO ₂ target may be used.

If an Al ₂ O ₃ film is required, a sputtering gas of Ar and O
_What is necessary is just to make it the mixed gas with ₂ . Alternatively, an Al ₂ O ₃ target may be used. FIG. 3 is a conceptual diagram of another bias sputtering apparatus used in the manufacturing method of the present invention. This device has two targets. Target 1
4, aluminum or Al ₂ O ₃ , titanium or TiO ₂ for the target 19, and a mixed gas of Ar and O ₂ for the sputtering gas 17. By rotating the substrate holder 13 during sputtering, the thin film EL element 1
On the surface of the light emitting layer 5, an Al ₂ O ₃ film and a TiO ₂ film are alternately laminated to form an ATO film which is a composite film of the Al ₂ O ₃ film and the TiO ₂ film. Two targets 14, 1
By changing the power applied to the high-frequency power supply 15 connected to the power supply 9, it is possible to easily control the abundance ratio of Al and Ti in the film and the film pressure.

As described above, by performing multiple simultaneous bias sputtering in an apparatus having a plurality of targets, a second insulating layer having a complicated composition or thickness can be formed. In addition, since the bias sputtering method is used, the light emitting layer is sufficiently covered. In the above embodiment, the example in which the transparent electrode of ITO is provided on the first electrode on the glass substrate side, but the first electrode on the glass substrate side may be a metal electrode.

Further, as the phosphor forming the light emitting layer,
In addition to the above-mentioned ZnS and SrS, sulfides of calcium and barium, selenides and tellurides of zinc, calcium, strontium and barium, or mixed crystals thereof can also be used. As the luminescent center, in addition to the above-mentioned manganese and cerium (Ce), rare earth europium (Eu), praseodymium (Pr), terbium (Tb)
One or more of these are used. As a method for forming the light emitting layer, in addition to the electron beam evaporation method, a resistance heating evaporation method, a sputter evaporation method, and an organic metal CVD (MOCVD)
Or an atomic layer epitaxy (ALE) method.

[0027]

As described above, according to the present invention, after forming a light emitting layer, a second insulating layer is formed thereon by a bias sputtering method so that the second insulating layer completely covers the light emitting layer. As a result, almost no trouble of water infiltration at the time of the subsequent patterning process and dielectric breakdown of the element at the time of applying a voltage were almost eliminated.

As a result, not only the improvement in the withstand voltage described with reference to the light of the embodiment but also a remarkable improvement in the yield was observed. That is, the present invention greatly contributes to quality improvement and cost reduction of the thin film EL element.

[Brief description of the drawings]

FIG. 1 is a structural diagram of a bias sputtering apparatus embodying the present invention.

FIG. 2 is a sectional view of a thin film EL element.

FIG. 3 is a structural view of another bias sputtering apparatus for implementing the present invention.

FIG. 4 is a cross-sectional view of a conventional thin film EL device.

FIG. 5 is a cross-sectional view showing main steps of a conventional thin-film EL element.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Thin-film EL element 2 Glass substrate 3 First electrode 4 First insulating layer 5 Light emitting layer 6 Second insulating layer 7 Second electrode 7a Mo film 8 AC power supply 9 Photoresist pattern 9a Photoresist film 10 Mound 11 Gap 12 Vacuum chamber 13 Substrate holder 14 Target 15 High frequency power supply 16 Heater 17 Sputter gas 18 Vacuum pump 19 Target

Claims (4)

[Claims] 1. An insulating substrate comprising at least a first electrode, a first insulating layer, a light emitting layer of a group II metal chalcogenide,
A method for manufacturing a thin-film EL device in which a second insulating layer and a second electrode are stacked, wherein the second insulating layer is formed by a bias sputtering method. 2. The method according to claim 1, wherein the second insulating layer is any one of a silicon nitride film, a silicon oxide film, a silicon oxynitride film, and an aluminum oxide film. 3. The method for manufacturing a thin film EL device according to claim 1, wherein a composite oxide film as a second insulating layer is formed by performing bias sputtering simultaneously and multiple times using a plurality of targets. . 4. The method according to claim 3, wherein an aluminum oxide film and a titanium oxide film are alternately laminated to form an aluminum titanium oxide film.