JPH05144570A - Electroluminescence element - Google Patents

Abstract

PURPOSE:To achieve high brightness characteristics by using diamond crystals formed by vapor phase synthesis for a light emission layer, and setting a crystal defect density to be a specified value or less. CONSTITUTION:A transparent conductive film 2 is formed on a transparent substrate 1 of glass, quartz or the like, and an insulation layer 3 of SiO2, Y2O3 or the like is formed on it. A light emission layer 4 comprising diamond thin film is then formed on it by microwave plasma CVD or the like. Its thickness is 0.1-10/10mum. A crystal defect density in diamond crystals is set to be 10<8>/cm<2> or less. Oxygen-including gas such as O2, H2O, N2O, is added to material gas (carbon-including gas such as methane, ethane) for this purpose. An electrode 6 is formed thereon through the insulation layer 5.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electroluminescent device, and more particularly to an electroluminescent device having a diamond crystal as a light emitting layer.

[0002]

2. Description of the Related Art An electroluminescent device (hereinafter referred to as an EL device) using a vapor phase synthetic diamond crystal as a light emitting layer is, for example, Japanese Journal of Applied Applied Physics, Vol. 28, No. 10, L1848 to L1850. (1989) EL element of double insulating layer structure and Schottky type light emitting diode (Nishibayashi et al., Proceedings of the 36th Joint Lecture on Applied Physics 2a-N-8, page 481, 1989). It has been reported.

[0003]

However, among the above-mentioned conventional examples, the Schottky type light emitting diode uses homoepitaxial on a diamond single crystal substrate (high-voltage synthesized product), which is costly and not practical. Further, the EL element reported by the present inventors uses polycrystalline diamond formed on a normal silicon wafer, and has a configuration capable of cost reduction due to mass production, but further increase in emission intensity is desired. ing.

[0004]

The present invention has been made in view of the above problems, and an electroluminescent element of the present invention is an electroluminescent element having a diamond crystal formed by vapor phase synthesis as a light emitting layer, It is characterized in that the diamond crystal has a crystal defect density of 10 ⁸ defects / cm ² or less.

[0005]

The function of the present invention will be described below together with the findings obtained in making the present invention.

Diamond crystals are generally precipitated as polyhedral grains having {100} faces and {111} faces, and coalescing these grains gives a film diamond. This {1
There is a difference in light emission between the {00} plane and the {111} plane. For example, blue emission near 430 nm has a large emission intensity on the {100} plane, but the emission intensity is very weak on the {111} plane. The details of this reason are unknown, but {10
It is considered that the crystal growth mechanism is different between the 0} plane and the {111} plane, and there are differences in the incorporation of impurities, the amount of dislocations / defects, and the crystallinity. Report by the present inventors (Japanese-
Journal-of-Applied-Physics 29 volumes,
No. 10, pp. L1901 to L1903, 1990)
According to, the {111} plane grows in a polynuclear growth mode,
The {100} plane is growing in a single nucleus growth mode. Due to this multi-nucleus growth mode of the {111} plane, a large amount of dislocations / defects of 10 ¹⁰ / cm ² or more are formed in the {111} plane. The present inventors assumed that the presence of a large amount of dislocations / defects would hinder the acceleration of electrons in the crystal, which would cause a decrease in the emission brightness of the EL element. The inventors have found that the luminous efficiency of the EL device can be increased by setting the crystal defect density of the {111} plane to be 10 ⁸ defects / cm ² or less, and have reached the present invention. The desirable crystal defect density of the present invention is 10 ⁸ defects / cm ^2.
Hereafter, it is more preferably 5 × 10 ⁷ pieces / cm ² or less.

The decrease in the crystal defect density of the {111} plane is caused by adding oxygen to the raw material gas at the time of diamond crystal formation,
This is achieved by changing the nuclear growth mode of the {111} plane from the multi-nuclear growth mode to the single-nuclear growth mode. Due to the change from the multi-nucleus growth mode to the single-nucleus growth mode, the crystallinity of the {111} plane is improved and the dislocation / defect amount is significantly reduced. Although there are many unclear points about the details of this reason, it is considered that the addition of oxygen, which has a large etching effect, reduces the supersaturation degree and the nucleation rate.

The method of reducing dislocations and defects may be a method of adding an oxygen-containing gas to the source gas, or a method of adding another etching gas, for example, a gas containing fluorine or chlorine.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Next, the present invention will be described in more detail with reference to preferred embodiments.

1 and 2 are cross-sectional views of an embodiment of the EL device of the present invention. In the figure, 1 is the substrate of the EL element,
Transparent materials such as glass and quartz, Si, W, Au, C
It is a bulk or film of a high melting point metal such as r, Ta, Mo or a semiconductor. This substrate must be able to exist stably at a temperature at which a diamond thin film is formed, for example, at a temperature of 500 ° C to 900 ° C. In the case of a metal or a semiconductor, it serves as a reflective layer for EL emission and an electrode layer of an EL element.
In FIG. 1, 2 is a transparent conductive film such as ITO, SnO ₂ and Zn.
O, SnO ₂ —Sb, Cd ₂ SnO _{4 and the} like, SnO ₂ is suitable for satisfying the above temperature conditions. The transparent conductive film 2 is formed to a thickness of about 500Å to 1500Å by a vacuum vapor deposition method, an ion plating method, a sputtering method, a spray method, a CVD method or the like. Figure 1
Medium 3 is an insulating layer, and a material that is transparent in the visible region, has a high withstand voltage, and has a large dielectric constant is suitable. Examples of such materials include SiO ₂ , Y ₂ O ₃ , HfO ₂ , Si ₃ N ₄ , and A.
l ₂ O ₃ , Ta ₂ O ₅ , PbTiO ₃ , BaTa ₂ O
₆ , dielectrics such as SrTiO ₃ may be used. These materials are also formed in a thickness range of 500Å to 5000Å by any of the methods for forming the transparent conductive film 2 described above. In FIG. 1, 4 is a light emitting layer made of a diamond thin film,
Microwave plasma CVD method, hot filament CVD
Method, DC plasma jet method, ECR plasma CVD
Method, the combustion flame method, etc., and the thickness thereof is in the range of 0.1 to 10 μm. The gas used at this time is a carbon-containing gas such as methane, ethane, propane, ethylene, benzene, acetylene, and other hydrocarbons, methylene chloride, carbon tetrachloride, chloroform, trichloroethane, and other halogenated carbons, methyl alcohol, and ethyl alcohol. Alcohols such as CO ₂ , gases such as CO and N ₂ , H ₂ , O ₂ ,
It is an additive gas or a diluent gas such as H ₂ O and Ar (argon).

In order to reduce the dislocation / defect density to 10 ⁸ / cm ² or less, oxygen-containing gas such as O ₂ , H ₂ O, N ₂ O is added to the raw material gas. The amount added is such that the ratio of oxygen to carbon (O / C) in the raw material gas is 0.2 ≦ O / C ≦
2, preferably 0.5 ≦ O / C ≦ 1. If it is less than 0.2, there is no effect of oxygen addition and diamond crystals with few dislocations / defects are not formed, and if it is 2 or more, a practically usable diamond formation rate cannot be obtained due to the etching effect of oxygen. Is.

More detailed conditions for synthesizing diamond crystals include, for example, oxygen and carbon ratio (O / C) in the raw material gas.
In the atmosphere gas having the above range of 1 to 1000
As the Torr, a diamond crystal is synthesized by a known microwave plasma CVD method, a hot filament CVD method, or a combustion flame method, and further, a known magnetic field microwave plasma CVD method is used within a pressure range of 0.01 to 10 Torr. , And so on. The diamond crystal does not necessarily have to be formed on the entire surface of the substrate, and may be formed only on a desired portion by the selective deposition method of diamond based on, for example, JP-A-2-30697 of the present inventors. Further, based on the above-mentioned JP-A-2-30697, a diamond crystal having a single nucleus may be used by sufficiently reducing the nucleation site to 10 μm ² or less. However, in the case of forming a diamond crystal consisting of a single nucleus in the combustion flame method, the nucleus generation density is generally low, and if the nucleation site is 10 μm ² or less, precipitation is likely to occur, so the nucleation site is 100 μm ²
It is desirable that the value be less than or equal to 10 μm ²

Of the above diamond crystal synthesizing methods,
The combustion flame method uses an oxygen-acetylene flame, and 0.85 ≦ O.
_By setting ₂ / C ₂ H ₂ ≦ 0.98, particularly high quality (crystal defect density of about 1 × 10 ⁷ pieces / cm ² ) diamond can be formed, and a relatively high formation rate (tens of μm / cm ² ). h
r) can be obtained. Further, since the magnetic field microwave plasma CVD method can synthesize under relatively low pressure as compared with other methods, uniform film formation on a large area (for example, film thickness unevenness of about ± 10% on a φ5-inch wafer) is possible. It is possible.

As a selective deposition method of diamond, there is a method of forming a pattern of scratched portions on a substrate by using diamond abrasive grains, which is disclosed in, for example, JP-A-2-30697 of the present inventors. However, the method is not particularly limited to such a method.

In the method disclosed in Japanese Patent Laid-Open No. 2-30697, after the surface of the substrate is scratched, a mask is formed in a pattern on the substrate, etching is performed, and the mask is removed to perform the scratching. This is a method of forming the parts in a pattern. Alternatively, a method may be used in which a mask member is provided in a pattern on the substrate, the surface of the substrate is scratched, and the mask member formed in a pattern by etching is removed to form the scratched portion in a pattern. Alternatively, after the surface of the substrate is scratched, a mask member having heat resistance may be formed in a pattern to form the scratched portion in a pattern.

The method of the scratch treatment using the diamond abrasive grains is not limited to a specific method, and for example, there are methods such as polishing using the diamond abrasive grains, ultrasonic treatment, or sandblasting. .. For example, 1μ
When the Si single crystal substrate is scratched by using a diamond abrasive grain of m or less and a horizontal polisher, a nucleus generation density of 10 ⁷ / cm ² or more is obtained. Also, the method of ultrasonic treatment is
Particle size 1 μm to 50 μ at a rate of 0.1 to 1 g / 10 ml
The substrate is placed in a liquid in which m abrasive particles are dispersed for 5 minutes to 4
It is carried out by applying ultrasonic waves with an ultrasonic cleaner or the like for a time, preferably about 10 minutes to 2 hours. By this ultrasonic treatment method, it is possible to obtain a nucleus generation density of 10 ⁷ / cm ² or more.

An example of a method of selectively depositing diamond by forming a pattern of scratched portions on a substrate using diamond abrasive grains will be described with reference to the schematic diagrams of FIGS. 7A to 7E. Is evenly scratched using diamond abrasive grains (Fig. 7).
A). A mask 39 is formed on the surface of the base (FIG. 7).
B). The mask may be made of any material, and examples thereof include a resist formed in a pattern using a photolithography method (optical drawing method).

Next, the substrate 38 is etched through the mask 39 to form a scratched portion in a pattern (FIG. 7C). The etching may be dry etching or wet etching. In the case of wet etching, for example, etching with a mixed solution of hydrofluoric acid and nitric acid can be given. In the case of dry etching, plasma etching, ion beam etching, or the like can be given. As the etching gas for plasma etching, CF ₄ gas and CF ₄ gas to which a gas such as oxygen or argon is added can be used. As the etching gas for the ion beam etching, rare gas such as Ar, He, Ne, oxygen, fluorine,
A gas such as hydrogen or CF ₄ is also possible. The etching depth is 100 Å or more, preferably 500 to 10000 Å, most preferably 800 to 2000 Å. Next, when the mask 39 is removed (FIG. 7D) and diamond is formed using the vapor phase synthesis method, the diamond 40 is selectively formed in the scratched portion (FIG. 7E).

FIG. 8 shows a schematic diagram of a method for synthesizing diamond by the combustion flame method. 41 is a burner, 42 is a base, 4
3 is an inner flame, 44 is an outer flame, and 45 is a substrate holder, which cools the base body 42 by water cooling. The raw material gas is oxygen and acetylene, and hydrogen gas, other hydrocarbon gas (methane, ethylene, etc.) and doping gas (containing gas such as boron, phosphorus, nitrogen, etc.) may be added thereto. Although the gas flow rate varies depending on the size of the burner, it is generally preferably about 1 liter / min to 10 liter / min. In the present invention, the flow rate ratio of oxygen and acetylene is 0.2 ≦.
O ₂ / C ₂ H ₂ ≦ 2, preferably 0.85 ≦ O ₂ / C ₂
H ₂ ≦ 0.98, more preferably 0.90 ≦ O ₂ / C
₂ H ₂ ≦ 0.95 is preferred.

Further, when the above O ₂ / C ₂ H ₂ ratio is within a desirable range (0.85 to 0.98), the difference in nucleation density between the scratched and unscratched portions tends to be large (Fig. 9). In order to carry out the selective deposition method, it is generally desirable to create regions having different nucleation densities of three digits or more, but in the combustion flame method, it is within the above range (0.85 ≦ O ₂
/ C ₂ H ₂ ≦ 0.98), a nucleation density difference of 3 digits or more occurs. Therefore, when an electroluminescent element using selectively deposited diamond by the combustion flame method is produced, it is desirable to perform it within the above gas flow rate range. The substrate temperature is 5
00 ° C to 1200 ° C, preferably 600 to 800 ° C is preferable.

Further, by mixing a trace amount of element which becomes an emission center into the diamond layer, an emission color peculiar to the emission center can be obtained. This emission center material is B, T on the short wavelength side (blue to purple or ultraviolet region).
e, As, Au, Mg, P, Sb, Si, Ta, Cu,
N, long wavelength (from red to infrared region) side, Tl, B
a, Li, Cd, Cs, In, Ra, S, Sr, Ti,
Zn, Ca, Ce, Co, Cr, Fe, Ga, K, M
n, Nb, Os, Pb, Rb, Rh, Sc, Th, V,
W, Y, or A for these two intermediate wavelength regions
g, Be, Bi, Cu, Ge, Hg, Pt, Re, Z
Examples thereof include r, Al, Ir, Ni, Ru, Sn, Tb and O. Further, it may be a halide, sulfide or oxide of these elements. As a method of adding these trace elements, a method of adding these trace element-containing gases to the raw material gas, an ion implantation method, or the like can be used.

Even if a trace element is not added, light emission is recognized around 430 nm, for example, due to a very small amount of dislocations and defects in the crystal.

In FIG. 1, reference numeral 5 denotes an insulating layer, which is similar to the insulating layer 3. In FIG. 1, 6 is an electrode, which is made of Al, Au, Ag,
Metals such as Pt, W, Cu, Ti and Ni. The electrode 6 has a thickness of 500 to 150 by a vacuum deposition method, an ion plating method, a sputtering method, a CVD method, a plating method, or the like.
It is formed with a thickness of 0Å. As a result, when an AC voltage is applied between the electrodes, EL light emission can be obtained from the glass 1 side.

On the other hand, in FIG. 2, 7 is an electrode, which is a metal or semiconductor which is stable at the diamond forming temperature. Reference numeral 8 denotes an insulating layer, which is similar to the insulating layer 3 in FIG. Reference numeral 9 is a light emitting layer.
1 is the same as the light emitting layer 4 of FIG.
Is the same as. A transparent conductive film 11 is a transparent conductive film 2 of FIG.
Is the same as. Therefore, according to the configuration of FIG. 2, EL light emission can be obtained from the upper surface in the figure.

Further, depending on the direction of the emitted light of the EL element, the constitution is as follows: substrate (glass) / transparent conductive film layer / insulating layer / light emitting layer / insulating layer / metal electrode (also serving as a reflecting layer) / substrate / metal electrode. Layer (reflection layer) / insulating layer / light emitting layer / insulating layer /
Two substrate configurations of transparent conductive film layer are possible. That is, one of the electrodes of the EL element may be a transparent conductive film, and the other may be an opaque metal or semiconductor electrode, and the configuration position changes depending on the emission extraction direction.

[0026]

Embodiments of the present invention will now be described in detail with reference to the drawings. (Embodiment 1) FIG. 3 is a sectional view of an EL device of this embodiment.

First, the SnO ₂ film 1 is formed on the quartz substrate 12 in the figure.
3 is formed to a thickness of 1000 Å by the ion plating method. The HfO ₂ layer 14 is formed on this by a reactive vapor deposition method to a thickness of 2000 Å. Next, the particle size is 15 μm
The substrate is put in a solution prepared by dispersing diamond abrasive grains in alcohol, and the HfO ₂ layer surface alone is scratched by ultrasonic cleaning. After thoroughly cleaning this substrate, it is placed in the microwave plasma CVD apparatus shown in FIG. 4 and exhausted to 1 × 10 ⁻⁷ Torr by the exhaust system 18. From gas supply system 19 CH ₄ : 1.5 SCCM, H ₂ : 200 SCCM, O
₂ : It was introduced into the reaction chamber 20 at a flow rate of 0.5 SCCM, the internal pressure of the apparatus was set to 40 Torr, microwave discharge was generated by the microwave 21 of 2.45 GHz, and the polycrystalline diamond layer 15 of about 2 μm was formed. At this time, the temperature of the substrate 22 was 850 ° C. Next, the HfO ₂ layer 16 is formed to a thickness of 2000 Å by the reactive vapor deposition method, and the Al electrode 17 having a size of φ5 mm is formed thereon by the vacuum vapor deposition method.
It was formed with a thickness of 0Å. When an AC electric field having a frequency of 1 kHz is applied between the electrode 13 and the electrode 17 of this EL element,
Light emission starts from about 90 V and the center wavelength of the light emission is 43
It was 0 nm.

The brightness at this time was significantly increased to 8 times that of an element similar to the above electroluminescent element except that the diamond layer was formed without adding oxygen. Further, when the crystal defect density of the diamond crystal formed under the same conditions as in this example was measured by using a transmission electron microscope (TEM), it was confirmed to be 5 × 10 ⁷ defects / cm ² . (Examples 2 to 6, Comparative Examples 1 and 2) An EL device was prepared in the same manner as in Example 1 except that the amounts of oxygen and methane during the diamond layer formation were changed, and the brightness thereof was measured. Table 1 shows the comparison of the conditions at this time and the brightness of the element to which oxygen was not added at the time of diamond formation, and the defect density of the diamond crystal formed under the same conditions. The crystal defect density was measured in the same manner as in Example 1.

It can be seen that good luminous efficiency is obtained in Examples 2 to 6.

[0030]

[Table 1] * Luminous efficiency with respect to a sample (Comparative Example 1) in which oxygen is not added at the time of forming a diamond layer (Example 7) This example shows an electroluminescent device in which a diamond crystal having a single nucleus is formed by a selective deposition method. FIG. 5 shows a cross-sectional view thereof.

First, the SnO ₂ film 2 is formed on the quartz substrate 23 in the figure.
4 is formed to a thickness of 1000Å by the ion plating method. An HfO ₂ layer 25 was formed thereon by a reactive vapor deposition method to a thickness of 2500 Å. Next, this substrate was placed in alcohol in which diamond particles having an average particle size of 15 μm were diffused, and a scratch treatment was performed using an ultrasonic cleaner. Then, using a mask aligner (PLA500 manufactured by Canon Inc.) on this substrate, a PMM with a diameter of 8 μm is formed.
An A type resist pattern was formed. This substrate was etched to a depth of 1000Å using an Ar ion beam etching device. The etching conditions at that time were an accelerating voltage of 1 kV and an etching time of 10 minutes. Next, the resist was removed using an organic solvent, and diamond was formed using a combustion flame method. The conditions at this time were O ₂ : 1.90 liter / min, C ₂ H
₂ : 2 liter / min, substrate temperature: 700 ° C., synthesis time: 10 minutes. As a result of this diamond formation, diamond particles 26 consisting of a single nucleus of about 8 μm were selectively formed only on the portion (resist pattern forming portion) where the scratching treatment remained.

Next, the HfO ₂ layer 27 was formed to a thickness of 2000 Å by the reactive evaporation method, and the Al electrode 28 was formed thereon to a thickness of 1000 Å by the vacuum evaporation method. This E
When an alternating electric field having a frequency of 1 kHz was applied between the electrode 24 and the electrode 28 of the L element, light emission started from about 80 V and the emission center wavelength was 430 nm.

The brightness at this time was about four times as large as that of the device of Example 1, and was greatly increased. The defect density of the diamond crystal formed in the same manner as in this example was measured by using a TEM and found to be 1 × 10 ⁷ defects / cm ² . (Embodiment 8) This embodiment shows an electroluminescent device having a diamond layer formed by using the magnetic field microwave plasma CVD apparatus shown in FIG.

In the figure, 29 is a cavity resonator, 30 is an electromagnet, and 31 is a microwave waveguide, which is connected to a microwave oscillator (not shown). Reference numeral 32 is a microwave introduction window made of quartz glass, and 33 is a gas introduction port, which is connected to a gas cylinder and a gas flow rate regulator (not shown). Reference numeral 34 is a substrate, 35 is a substrate holder containing a heater capable of heating up to 1000 ° C., 36 is a sample chamber, 37 is an exhaust port, and a pressure adjusting valve and a vacuum pump (not shown) are connected to a turbo molecular pump to which a rotary pump is connected. X10 ^-7 Torr can be evacuated) is connected.

The element is formed by forming a diamond layer as shown in FIG.
Except that the magnetic field microwave plasma CVD method of
The same procedure as in Example 1 was performed.

The diamond layer was formed under the following conditions.

The source gas is O ₂ : 92 SCCM, C ₂ H
₂ : 100 SCCM each was introduced. The pressure is 0.
1 Torr, the magnetic field strength is 2 near the microwave introduction window 32
000 Gauss, and the vicinity of the substrate was adjusted to 900 Gauss. The substrate temperature was 720 ° C. and the microwave output was 1.0 kW.

The EL element formed as described above is the first embodiment.
The device showed almost the same emission luminance as that of the device. The crystal defect density of the diamond crystal formed in the same manner as in this example was measured by using a TEM. As a result, it was 6 × 10 ⁷ pieces / cm 2.
Turned out to be ² .

[0039]

As described above, according to the electroluminescent device of the present invention, an electroluminescent device with higher brightness can be obtained.

[Brief description of drawings]

FIG. 1 is a sectional view of an embodiment of an EL device of the present invention.

FIG. 2 is a sectional view of an embodiment of an EL device of the present invention.

FIG. 3 is a sectional view of an EL device of Example 1 of the present invention.

FIG. 4 is a schematic view of a film forming apparatus used for forming a diamond thin film in the present invention.

FIG. 5 is a sectional view of an EL device of Example 7 of the present invention.

FIG. 6 is a schematic view of another film forming apparatus used for forming a diamond thin film in the present invention.

FIG. 7A is a schematic diagram of a selective deposition method.

FIG. 7B is a schematic diagram of a selective deposition method.

FIG. 7C is a schematic diagram of a selective deposition method.

FIG. 7D is a schematic diagram of a selective deposition method.

FIG. 7E is a schematic view of a selective deposition method.

FIG. 8 is a schematic view of a combustion flame method used for diamond formation in the present invention.

FIG. 9 is a characteristic diagram showing a nucleus generation density by a combustion flame method.

[Explanation of symbols]

1 substrate, 2 transparent conductive film, 3 insulating layer, 4 light emitting layer, 5 insulating layer, 6 electrode, 7 electrode, 8 insulating layer, 9 light emitting layer, 10 insulating layer, 11 transparent conductive film, 12 substrate (quartz), 13 SnO ₂ layer, 1
4 HfO ₂ layer, 15 light emitting layer, 16 HfO ₂
Layer, 17 Al electrode, 18 exhaust system, 19 gas supply system, 20 reaction chamber, 21 microwave oscillator and waveguide, 22 substrate, 23 substrate (quartz), 24
SnO ₂ layer, 25 HfO ₂ layer, 27 HfO ₂
Layer, 26 diamond crystal, 28 Al electrode, 2
9 cavity resonator, 30 electromagnet, 31 microwave waveguide, 32 microwave introduction window, 33 gas introduction port, 34 substrate, 35 substrate holder, 36 sample chamber, 37 exhaust port, 38 substrate, 39 resist pattern, 40 diamond crystal , 41 burner, 42 base, 43 internal flame, 44 external flame, 45
Substrate holder.

Claims (1)

[Claims] 1. An electroluminescent device using a diamond crystal formed by vapor phase synthesis as a light emitting layer, wherein the diamond crystal has a crystal defect density of 10 ⁸ / cm 2.
^An electroluminescent device characterized by being ² or less.