JPS6235496A - Formation of electroluminescence thin film - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a method for forming an electroluminescent thin film forming a light emitting layer in an electroluminescent device or the like.

"Prior Art and its Problems" An electroluminescent thin film (hereinafter referred to as EL thin film) having zinc sulfide as a base material is used as a light emitting layer of an electroluminescent element (hereinafter referred to as EL element).

Conventionally, as a method for forming such an EL thin film, a method of vacuum-depositing a zinc sulfide sintered body to which an active substance is added has generally been adopted. In this case, a resistance heating method or an electron beam heating method is employed as a heating method for the zinc sulfide sintered body.

However, in the case of the vacuum deposition method using resistance heating, there is a difference between the vapor pressure of the active substance and the vapor pressure of zinc sulfide at a constant temperature, so their evaporation rates are different, and the concentration of the active substance in the formed thin film is For example, when zinc sulfide with manganese added as an active substance is vacuum-deposited using a resistance heating method, the concentration of manganese sulfide vapor differs from that in the zinc sulfide sintered body, which is the raw material for vapor deposition. Because the pressure is low, the concentration of manganese in the thin film is lower than the concentration of manganese in the manganese-activated zinc sulfide sintered body, which is the raw material for vapor deposition. There was a problem in that the manganese concentration was higher in some parts.

On the other hand, in the case of the vacuum evaporation method using electron beam heating, the concentration change and concentration gradient of the active substance in the formed thin film are greatly improved compared to the vacuum evaporation method using resistance heating. However, a zinc sulfide thin film containing an active substance formed by vapor deposition using an electron beam heating method often contains pinholes and fine particles with a diameter of several microns or less. The reason for this is thought to be that since zinc sulfide is insulating and sublimable, it is charged by irradiation with an electron beam of several kV, and the fine particles are repelled by Coulomb force and adhere to the substrate. EL containing such pinholes and microparticles
When a thin film EL element is formed using a thin film, there is a problem that dielectric breakdown and peeling tend to occur.

In addition to the vacuum evaporation method described above, an RF sputtering method is also used as a method for forming the EL thin film. That is, this method uses as a target zinc sulfide with an active substance added thereto and molded, or zinc sulfide with an appropriate amount of small pieces of the active substance arranged thereon, and sputters using argon gas. This method is improved over the vacuum evaporation method described above in terms of adhesion of microparticles onto the substrate.

However, this method has the problem that the crystal grain size of the formed zinc sulfide thin film is small, the crystal distortion is large, and the luminance is lower than that of the vacuum evaporation method.

[Object of the Invention] An object of the present invention is to solve the problems of the prior art described above and to provide a method for forming an EL9 film with excellent film quality.

"Structure of the Invention" The method for forming an EL thin film according to the present invention is characterized by performing sputtering using zinc sulfide and an active substance as targets in a mixed gas atmosphere of argon and hydrogen.

In the present invention, by performing sputtering in a mixed gas atmosphere of argon and hydrogen, it is possible to obtain an EL thin film with a larger crystal grain size and higher emission brightness than in the case of conventional RF sputtering. The reason for this is not clear at present, but hydrogen suppresses the effects of oxygen generated by the decomposition of residual gas and water in the sputtering equipment, and hydrogen mixes into the EL thin film and causes defects. Improvements can be made.

In the present invention, a target formed by adding an active substance to zinc sulfide, or a target formed by adding an active substance to zinc sulfide, or a target formed by disposing an appropriate amount of small pieces of an active substance to zinc sulfide, is used. Here, the active substance is Mn.

Transition metals such as Cu, rare earth elements such as S and Tb, or compounds thereof such as halogens, oxides, and T&oxides are used.

Further, the mixing ratio of the sputtering gases is not particularly limited, but it is preferable that the mixing ratio be argon gas: 80 to 100 SCCM, and hydrogen gas = 0.5 to 8.0 SCCM. If the mixing ratio of the sputtering gas deviates from the above range, the brightness of the EL thin film tends to decrease. Furthermore, other conditions include sputtering pressure of 0.5
X 10-2w 1.8
Human sputtering power 1.6-3.2 w/cm
Approximately 2 is appropriate.

``Example of the invention'' (Target adjustment) ■0.0 l-fat% of active substance is added to high purity zinc sulfide (99,9999% or more), molded into a predetermined shape by hot isostatic pressing, and then The target was sintered at 900°C for 2 hours. In this case, the active substance is Mn
, Cu, Sta, Tb, or their halides (eg, fluorides) and sulfides were used.

■An appropriate amount of active material chips were placed on high purity zinc sulfide (9L99!89% or more) to serve as a target. As the active substance, the same one as above was used.

(Sputtering conditions) Using high purity argon gas (99,99139% or more) and high purity hydrogen gas (99J99% or more), use a mass flow controller to adjust the argon gas to 80 to 1008 CCH.
range, hydrogen gas is 0.5 to 8. The two gases were introduced into the apparatus while being controlled to be within the O5CGH range, and the two gases were mixed within the apparatus.

Also, the sputtering pressure is 0.5 x 10-2~!
, 8 X 1O-2Torr, substrate temperature 100-20
The temperature was 0° C., the film formation rate was 6000 to 10000 people, and the sputtering power was 1.6 to 3.2 w/cm 2 .

(Sputtering device) As shown in Fig. 1, a pair of electrodes 2 and 3 are installed in the device body 1.
is installed. For one electrode 2.

A substrate holder 4 is attached, and a substrate 5 is placed thereon. Further, a heater 8 for heating the substrate is attached to the substrate 5. Further, a target 7 is attached to the other electrode 3. A shutter 8 that can be opened and closed is arranged between the electrodes 2.3. Inside the device main body 1, there is a hydrogen introduction pipe S.
and an argon introduction pipe 10 are connected.

Using this apparatus, a substrate 5 is heated by a substrate heating heater 4, hydrogen and argon are introduced from a hydrogen introduction tube 9 and an argon introduction tube 10, and a high frequency voltage is applied between electrodes 2.3. When pressure is applied, a discharge occurs, and the argon gas is ionized into Ar, which collides with the target and releases zinc and sulfur in the target, which are deposited on the substrate 5 to form an EL thin film. .

It has been found that the EL thin film obtained in this way has significantly fewer fine particles than an EL thin film formed by conventional vacuum evaporation, and has a larger crystal grain size than an EL thin film formed by conventional sputtering.

(Manufacture of thin film EL device) As shown in FIG. 2, a transparent electrode 12 made of indium oxide-tin oxide is formed on a glass substrate 11, an insulating layer 13 made of tantalum pentoxide is roughly formed, and By forming a KL thin film 14 thereon, further forming an insulating layer 5, and finally forming an aluminum electrode 16, the Fl
A membrane EL device was manufactured.

The EL thin film 14 has a diameter of 5 inches as a target.

A Mn chip was placed on a zinc sulfide plate formed to a thickness of 5 mm, and sputtering was performed in an atmosphere of a mixed gas of argon and hydrogen as described above. For comparison, an EL element was also manufactured in which the EL thin film 14 was formed by sputtering in an atmosphere containing only argon gas.

The relationship between the applied voltage and luminance of the thin film EL device obtained in this way is shown in FIG. 3. In FIG. As is clear from FIG. 3, the brightness of the thin film EL device obtained by the method according to the present invention is increased by about one order of magnitude, and the threshold voltage is increased by several orders of magnitude compared to the thin film EL device obtained by the comparative example. It can be seen that the voltage is about 10V lower.

"Effects of the Invention" As explained above, according to the present invention, since sputtering is performed in a mixed gas atmosphere of argon and hydrogen using zinc sulfide and an active substance as targets, there are very few fine particles. It is possible to form an EL thin film with excellent transparency and crystallinity, and with a large crystal grain size. Therefore, if the method according to the present invention is applied to the production of thin film EL devices, devices with high luminance and low threshold voltage can be obtained, and power consumption can be reduced.

[Brief explanation of the drawing]

FIG. 1 is a schematic explanatory diagram showing an example of a sputtering apparatus for implementing the present invention, FIG. 2 is a sectional view showing an example of a thin film EL element manufactured by applying the present invention, and FIG. 2 is a chart showing the voltage-luminance characteristics of a thin film EL device manufactured by applying the method and a W1 film EL device manufactured by a conventional method. In the diagram! is the sputtering equipment main body, 2.3 is the electrode, 4
is a substrate holder, 5 is a substrate, 6 is a heater for heating the substrate, 7 is a target, 9 is a hydrogen introduction tube, 10 is an argon introduction tube,
14 is an EL thin film.

Claims (1)

[Claims] A method for forming an electroluminescent thin film, which is characterized by sputtering using zinc sulfide and an active substance as targets in a mixed gas atmosphere of argon and hydrogen.