JP2758785B2 - Electrode for thin film EL element and method for forming the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrode of a panel in a thin film EL (electroluminescence) device, and more particularly to an electrode structure, a material, and a forming method of an inverted structure EL device using an organic color filter.

[0002]

2. Description of the Related Art Thin-film EL devices currently in practical use include:
This is a thin film EL device having a double insulation structure in which a transparent electrode made of ITO (indium tin oxide), an insulating layer, a light emitting layer, an insulating layer, and a back electrode made of aluminum are sequentially stacked on a glass substrate. It is taken out through the glass substrate. However, since the emission color of the above structure is only yellow-orange, there is a strong demand for colorization.

[0003] Therefore, one of the colorization methods for a thin film EL element is described.
For example, a method of combining with a color filter made of an inorganic or organic material has been proposed. However, a color filter made of an inorganic material has problems in terms of fine workability and viewing angle dependency. For this reason, color filters made of organic materials, which are cheaper than inorganic filters, are widely used in liquid crystal displays.

However, when considering a color thin film EL device and a manufacturing method using a filter made of an organic material with the above structure, the heat resistance temperature of the color filter made of an organic material is 2.
While the temperature is about 00 ° C., the temperature in the manufacturing process of the thin-film EL element is, for example, 50%.
The substrate temperature when forming the insulating layer is as high as about 0 ° C., the substrate temperature when forming the insulating layer is about 300 ° C., and about 500 ° C. when forming the light emitting layer. Therefore, inserting a color filter of an organic material between any of a glass substrate, a transparent electrode, an insulating layer, and a light emitting layer,
This is not possible in terms of heat resistance.

Therefore, in order to manufacture a color thin film EL device using an organic filter, a thin film E which is currently in practical use is required.
A structure different from the L element, a structure in which a back electrode, an insulating layer, a light emitting layer, an insulating layer, and a transparent electrode are sequentially laminated on a glass substrate,
A structure that adopts a so-called inverted structure and finally puts an organic color filter on it has been proposed (Tsurumaki
et al., Eurodisplay '90 Digest, p212 (1990)).
The thin film EL device shown in FIG. 2 is a device having a conventional inversion structure,
On a glass substrate 1, a first electrode (back electrode) 10, a first electrode
An insulating layer 3, a light emitting layer 4 containing ZnS as a base material and adding Mn or the like, a second insulating layer 5, and a second electrode (transparent electrode) 6 are laminated. Thereafter, a filter material in which green and red pigments are dispersed in a photosensitive resin is applied on the sealing glass 9,
It is processed into a mosaic by photolithography. The same processing is performed on the red or green pigment to form the color filter 8. Finally, the glass substrate 1 and the sealing glass 9 are bonded together, and at the same time, the oil 7 is sealed between the glass substrate 1 and the sealing glass 9 to produce a color thin film EL element.

[0006]

However, there are some problems with the first electrode (back electrode) 10 when fabricating a thin film EL device having the inverted structure shown in FIG.

First, a high temperature used in the process of manufacturing a thin-film EL element, for example, a heat treatment temperature of 500 for a transparent electrode.
About 300 ° C, which is the substrate temperature at the time of forming the insulating layer,
Considering the substrate temperature of about 500 ° C. at the time of forming the light emitting layer, the material of the first electrode (back electrode) is the same as that of the related art.
It is not appropriate to use l from the viewpoint of heat resistance.

Second, after the first electrode (back electrode) 10 is subjected to post-baking of the resist at 80 ° C.
Since the etching is performed using only the F ₄ gas, the side surface becomes substantially vertical. However, this shape is not preferable, and causes electrical breakdown at the side surface, and the breakdown voltage was actually as low as 180 V or less.

Therefore, the first electrode (back electrode) is a thin film EL.
It must be made of a high melting point metal material that can withstand the high temperature used in the device fabrication process, for example, Ta, Mo, W, Ni, and the like, and the shape of the first electrode (back electrode) must be considered.

Here, when comparing Al with the high melting point metal, Al has a low specific resistance (2.74 μΩ · cm of Al), but has a low specific resistance (for example, Ta: 1) of the high melting point metal material.
3.1 μΩ · cm, Mo: 5.33 μΩ · cm, W: 5.44
μΩ · cm, Ni: 7.04 μΩ · cm) are high. Therefore,
In order to realize the same resistance value as the electrode made of Al using a high melting point metal material, a method of increasing the width of the first electrode (back electrode) and a method of increasing the film thickness are conceivable.

However, the method of increasing the width of the first electrode (back electrode) cannot cope with high definition and large display. The method of increasing the thickness of the first electrode (back electrode) is as follows.
As the film thickness increases, the material of the first insulating layer becomes less likely to adhere to the side surface of the first electrode (back electrode) in the form of a wiring, and the thin insulating layer portion becomes closer to the side surface of the first electrode (back electrode). In this case, a large amount of electrical breakdown occurs on the side surface of the first electrode (back electrode), and as a result, there is a problem that picture elements are destroyed or the color EL element is broken.

The present invention has been made in order to solve such problems, and a material which can be used for a first electrode (back electrode) for a color thin film EL element, a film of the first electrode (back electrode). It is an object of the present invention to provide a structure of a first electrode for a color thin film EL element which is highly reliable against electrical breakdown even when the thickness is increased, and a method for forming the first electrode.

[0013]

According to the present invention, there is provided a thin film EL device having an inverted structure, wherein a refractory metal material, particularly Ta, Mo, W, Ni, is used as a first electrode (back electrode) material; The electrode structure is such that the electrode side surfaces are obliquely inclined.

Also, the first electrode (back electrode) with respect to the first electrode
In order to improve the step coverage of the insulating layer, the angle formed between the side surface of the first electrode (back electrode) and the substrate (hereinafter, referred to as an inclination angle) is desirably small, particularly preferably 45 ° or less. Furthermore, in order to improve the step coverage and reduce the wiring resistance of the electrodes, the inclination angle is set to 25 °.
It is desirable that:

Further, as a material of the first electrode (back electrode),
Among the refractory metal materials, particularly, Ta, Mo, W, and Ni,
An electrode structure in which two or more different materials are selected and laminated, and the electrode side surfaces are obliquely inclined. In particular, when a glass substrate is used, it is preferable that a portion in contact with the laminated glass substrate of two or more kinds of refractory metals is Mo or Ta, and a portion in contact with the first insulating layer is W.

Further, the method is characterized in that a dry etching method using a mixed gas is used as the formation method.

In the thin film EL device having the inverted structure according to the present invention, the substrate does not need to be transparent, and is not limited to a glass substrate as long as the material is insulative and resistant to a high-temperature process. Can be used. However, since the glass substrate is relatively inexpensive and easily available, it is generally widely used, and in the present invention, the portion in contact with the laminated glass substrate of two or more kinds of refractory metals is Mo or T.
The structure in which the portion a is W in contact with the first insulating layer is particularly effective when a glass substrate is used.

[0018]

The first electrode (back electrode) is made of a high melting point metal material.
By forming, the high-temperature process of the inversion structure is facilitated, and the material of the first insulating layer is applied to the side surface of the first electrode (back electrode) by forming an oblique slope on the side surface of the first electrode (back electrode). This facilitates deposition, and prevents electrical breakdown due to an increase in the film thickness of the first electrode (back electrode).

That is, it is possible to provide an inexpensive and highly reliable color thin-film EL device by improving picture element destruction and disconnection due to electrical insulation breakdown and combining with an inexpensive organic color filter.

The first electrode (back electrode) is made of two or more different materials, that is, a material having good adhesion to the glass substrate (for example, Mo or Ta) is placed on the glass substrate side with a low resistivity, The tapered portion of the edge portion is also flat, and a material (for example, W) that is unlikely to cause dielectric breakdown is selected and laminated on the first insulating layer side, so that the electrical resistance is higher than when one kind of high melting point metal material is used. The dielectric breakdown voltage can be made higher, and furthermore, the brightness unevenness does not occur.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The electrodes for a thin film EL device and the method of forming the same according to the present invention will be described in detail below with reference to embodiments.

Embodiment 1 FIG. 1A is a structural sectional view of an embodiment of a color thin-film EL device using the electrode for a thin-film EL device according to the present invention. This color thin film EL element has a so-called inverted structure, and has a stripe-shaped first electrode (back electrode) arranged in parallel on a substrate glass 1 at a constant interval.
2, first insulating layer 3, light emitting layer 4 of ZnS: Mn, second
It has a structure in which an insulating layer 5 and a stripe-shaped second electrode (transparent electrode) 6 arranged in parallel with a certain interval in a direction perpendicular to the first electrode (back electrode) 2 are stacked.

The first electrode (back electrode) 2 has a thickness of 3500 °
The light emitting layer 4 is made of ZnS having a thickness of about 1 μm in which the base material ZnS is doped with Mn (about 0.4%) as a light emitting center.
S: Mn layer. The first insulating layer 3 has a thickness of 300 to 80
0 ° SiO ₂ film 3a and 2000-3000 ° thick S
It is composed of two layers of an i ₃ N ₄ film 3b. On the other hand, the second insulating layer 5 is composed of two layers: an Si ₃ N ₄ film 5a having a thickness of 1000 to 2000 ° and an Al ₂ O ₃ film 5b having a thickness of 300 to 500 °. The second electrode (transparent electrode) 6 has a thickness of 20 mm.
It is made of an ITO (indium tin oxide) film having a thickness of 00%.
Here, the side surface of the first electrode (back electrode) 2 has a slope as shown in FIG. 1, and θ is the angle (tilt angle) formed between the side surface of the first electrode (back electrode) and the substrate. Show.

The first electrode (back electrode) 2 is manufactured by the following steps. First, a Ta thin film 11 is formed on the substrate glass 1 by a sputtering method, processed into a predetermined wiring shape, for example, a stripe shape by a photolithography method, and the side surface of the first electrode (back electrode) 2 is inclined.

The photolithography method in which the side surface of the first electrode (back electrode) 2 is inclined comprises the following two steps.

Step (1): A step of inclining the side surface of the resist film.

Step (2): The electrode material and the resist are simultaneously etched by the mixed gas to form a first electrode (back electrode).
The process of inclining the side of the car.

FIG. 3 is a diagram for explaining the above steps (1) and (2). Positive photoresist 12 (OFPR-800, manufactured by Tokyo Ohka Kogyo Co., Ltd .; HF-2030, HF-2, manufactured by Fuji Hunt Electronics Technology Co., Ltd.)
130) is coated on the Ta thin film 11 formed on the glass substrate 1, dried, pre-baked, exposed, developed, and then subjected to post-baking, which is the step (1).

Resist 12 before post-baking
FIG. 3A shows a cross section of the Ta thin film 11. The post-baking temperature is set to a temperature higher than the normal use temperature of 80 to 120 ° C., for example, 150 ° C. or higher, and the resist 12
Is generated, and the side surface of the resist is inclined. FIG. 3B shows the state of the cross section of the resist 12 and the Ta thin film 11 after the post-baking.

Next, Ta is mixed with a mixed gas of CF ₄ and O _2.
The thin film 11 and the resist 12 are simultaneously etched, and the side surface of the first electrode (back electrode) 2 is inclined. FIG. 3C shows the cross section of the resist 12 and the Ta thin film 11 after the dry etching.

CF ₄ is the Ta thin film 11 and O ₂ is the resist 1
2 so that the mixing ratio of the etching gas is C
The etching speed of the Ta thin film 11 and the resist 12 is controlled by adjusting F ₄ : O ₂ = 70: 30, and the side surface of the first electrode (back electrode) 2 is inclined. At this time, the inclination of the side surface of the resist 12 formed in the step (1) is
This is reflected in step (2).

Thereafter, the remaining resist 12 is replaced with acetone,
Alternatively, the first electrode (back electrode) 2 of the present invention can be formed by removing with a stripper. FIG. 3D shows the state of the cross section of the first electrode (back electrode) 2 after removing the resist.

After the first electrode (back electrode) 2 is formed, the SiO ₂ film 3a and the Si ₃ N ₄ film 3 are formed by reactive sputtering.
The first insulating layer 3 is formed by depositing b, and the light emitting layer 4 is laminated on the first insulating layer 3 by an electron beam evaporation method or a CVD method. Si on the light emitting layer 4 is formed by reactive sputtering.
_A second insulating layer 5 is formed by depositing a 3N ₄ film 5a and an Al ₂ O ₃ film 5b. Next, ITO is vapor-deposited, and a stripe-shaped second electrode (transparent electrode) 6 orthogonal to the first electrode (back electrode) 2 is formed by photolithography.

A filter material in which a green or red pigment is dispersed in a photosensitive resin is applied on the seal glass 9 and then processed into a mosaic shape by photolithography.
The same processing is performed for the red and green pigments to form the color filter 8.

After the second electrode 6 is formed, a silicone resin is applied and cured by heating.
Are adhered to each other.

Alternatively, the glass substrate 1 and the sealing glass 9
And oil 7 is sealed. According to this manufacturing method, a color thin-film EL element can be easily manufactured with almost no difference from the conventional commercialization process, except for the step of etching the first electrode (back electrode) 2 and the step of forming the color filter 8.

Next, Table 1 shows an example of the result of the inclination angle of the first electrode (back electrode) prepared by combining the post-baking temperature of the resist and the mixing ratio of the etching gas under several conditions.

[0038]

[Table 1]

In Experiments B and D in Table 1, the mixed gas was used for etching, and the inclination angle was small. In addition, when the post-baking temperature is set to 150 ° C., which is higher than the normally used temperature of 80 ° C., the inclination angle can be further reduced. However, in Experiments A and C using only CF ₄ gas, the inclination angle is large.

A voltage higher than the voltage normally applied is applied between the first electrode (back electrode) and the second electrode (transparent electrode).
The breakdown was forcibly caused, and the relationship between the magnitude of the tilt angle and the electrical breakdown was determined. Optical micrographs of electrical breakdown of a typical thin film EL device are shown in FIGS. 4 and 5, respectively. First electrode (back electrode) from Experiments B and D in Table 1
2 is small, only a small dielectric breakdown portion shown in FIG. 4 is generated inside the light emitting picture element, and only a light emitting defect due to a point is seen, and the dielectric breakdown is smaller than that of the conventional structure shown in FIG. The voltage also increased to 200 to 250V.

On the other hand, when the inclination angle of the first electrode (back electrode) 10 in Experiments A and C is large, a large dielectric breakdown shown in FIG. And lower than the dielectric breakdown voltage.

As described above, the relationship between the magnitude of the inclination angle of the first electrode (back electrode) and the electrical breakdown was confirmed.

<Embodiment 2> The structure of the color thin film EL device manufactured in Embodiment 2 of the present invention is the same as that in Embodiment 1. The manufacturing method is the same except for the method of forming the first electrode (back electrode). A Mo film is formed as a first electrode (back electrode) 2 on a substrate glass 1 by a sputtering method.
As in the case of the first embodiment, a predetermined stripe shape is formed by photolithography. The mixed gas used for the etching is partly different from that of the first embodiment, and a mixed gas of CF ₄ and O ₂ is used. When the gas mixture ratio is CF ₄ : O ₂ = 30: 7
At 0, the tilt angle of the electrode side surface was 3 °. The manufactured EL element showed the dielectric breakdown shown in FIG. 4, and the dielectric breakdown voltage was as high as 250 to 300V.

In Examples 1 and 2, Ta and Mo were used as electrode materials.
A similar thin-film EL element electrode was produced.

<Embodiment 3> FIG. 1B is a structural sectional view of an embodiment of a color thin film EL device using the electrode for a thin film EL device of the present invention. The structure of the color thin-film EL device manufactured in Example 3 of the present invention is almost the same as that of Example 1, except for the structure and forming method of the first electrode (back electrode).

First electrode (back electrode) on substrate glass 1
As Example 2, a Mo film 2a was deposited at 500 ° by a sputtering method, and a W film 2b was subsequently deposited at 1000 °.
As in the case of (1), it is processed into a predetermined stripe shape by photolithography. The mixed gas used for etching is
Unlike the first embodiment, the etching rate of the Mo and W thin films and the resist is controlled by adjusting the mixing ratio of the etching gas to CF ₄ : O ₂ = 60: 40. The prepared thin film E
The L element has better adhesion to the glass substrate, and
The resistance value of the electrode was reduced, and the breakdown voltage was higher by about 100 V than in Example 1, and was 300 to 400 V.

In the third embodiment, the material Mo on the glass substrate side of the metal electrode is used to improve the adhesion between W and the glass substrate, and Ta may be used.

[0048]

By using the thin film EL device electrode according to the method of the present invention, it is possible to manufacture an EL device having an inverted structure, and to reduce the destruction of picture elements due to an increase in the film thickness of the first electrode (back electrode). Disconnection is improved, and a color EL thin film element can be provided in combination with an inexpensive organic color filter.

Further, by using a metal electrode having a multi-layer structure, the adhesion to the glass substrate is improved, and the resistance value is reduced, so that the luminance unevenness is reduced. A thin-film element can be provided.

[Brief description of the drawings]

FIG. 1 (a) is a cross-sectional view of a color thin film EL element structure according to Examples 1 and 2 of an electrode for a thin film EL element of the present invention. (B) It is sectional drawing of the color thin film EL element structure by Example 3 of the electrode for thin film EL elements of this invention.

FIG. 2 is a cross-sectional view of a color thin film EL element structure manufactured by a conventional method.

FIG. 3 is a view showing a procedure for manufacturing a first electrode (back electrode) of the present invention.

FIG. 4 is an optical microscope photograph of electrical breakdown in a color thin film EL device to which the present invention is applied.

FIG. 5 is an optical microscope photograph of electrical breakdown in a color thin film EL device manufactured by a conventional method.

[Explanation of symbols]

1 first electrode (back electrode) of the glass substrate 2 invention ... 2a first refractory metal (Mo) ... 2b second refractory metal (W) 3 first insulating layer _{... 3a SiO 2 ... 3b Si 3} N ₄ 4 Light-emitting layer 5 Second insulating layer 5a Si ₃ N ₄ 5b Al ₂ O ₃ 6 Second electrode (transparent electrode) 7 Oil 8 Color filter 9 Seal glass 10 Conventional first electrode (back electrode) 11 Metal thin film 12 Resist

Continued on the front page (72) Inventor Masaru Yoshida 22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka Inside Sharp Corporation (72) Inventor Shigeo Nakajima 22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka Inside Sharp Corporation (56 References JP-A-4-147598 (JP, A) JP-A-4-126391 (JP, A) JP-A-3-22395 (JP, A) JP-A-1-200594 (JP, A) (58) Field surveyed (Int.Cl. ⁶ , DB name) H05B 33/26 H05B 33/10

Claims (7)

(57) [Claims] 1. A thin-film EL device in which a first electrode (back electrode), a first insulating layer, a light-emitting layer, a second insulating layer, and a second electrode (transparent electrode) are sequentially laminated on a substrate. The first electrode formed is a refractory metal,
An electrode for a thin-film EL element, wherein a side surface of the first electrode (back electrode) is obliquely inclined. 2. The electrode for a thin film EL device according to claim 1, wherein an angle (inclination angle) formed between a side surface of the first electrode (back electrode) and the substrate is 45 ° or less. 3. The electrode for a thin-film EL device according to claim 1, wherein the refractory metal as a material of the first electrode (back electrode) is Ta, Mo, W, or Ni. 4. A thin-film EL device in which a first electrode (back electrode), a first insulating layer, a light emitting layer, a second insulating layer, and a second electrode (transparent electrode) are sequentially laminated on a substrate. 2. The electrode for a thin film EL device according to claim 1, wherein two or more different metal materials are selected and laminated as the high melting point metal forming the back electrode. 5. The first electrode (back electrode) formed of two or more different metal materials laminated according to claim 4, wherein a glass substrate is used as the substrate, and the high melting point metal on the side in contact with the glass substrate. Is Mo or Ta, and the refractory metal on the side in contact with the first insulating layer is W. 6. A side face of the first electrode (back electrode) is formed into an inclined surface by dry etching with a mixed gas containing a gas for etching the first electrode (back electrode) and a gas for etching a resist. 5. The method for forming an electrode for a thin-film EL device according to claim 1, comprising a step. 7. The mixed gas used for etching is a mixed gas containing at least CF ₄ as a gas for etching the first electrode (back electrode) and at least O ₂ as a gas for etching a resist. The method for forming an electrode for a thin film EL device according to claim 6.