JPS63259067A - Production of thin zinc sulfide film - Google Patents

Abstract

PURPOSE:To produce thin ZnS films of a prescribed thickness contg. an active substance at a prescribed concn. by evaporating ZnS and the active substance from separate evaporating sources and measuring the rate of vapor deposition on a monitor substrate near substrates. CONSTITUTION:Substrates 6 and a monitor substrate 3 are heated to about 300 deg.C with heater 5. Sintered ZnS 10 and Mn 11 as an active substance are put in separate crucibles 9 and evaporated to form thin ZnS films contg. Mn on the substrates 6. When the ZnS films are produced as mentioned above, a quartz oscillator thickness gauge 8 for the active substance is set at a position at which the gauge 8 is not directly exposed to the evaporated ZnS by a shielding plate 7. The rate of evaporation of Mn is measured from the rate of vapor deposition of a vapor-deposited film on the gauge 8. The rate of vapor deposition of a vapor-deposited film on the monitor substrate 3 is measured with a thickness measuring system consisting of a light source 4, a filter 2 and a photoreceptor 1. The heating of the ZnS 10 and/or the Mn 11 is regulated in accordance with the measured results so as to keep the concn. of Mn as the active substance in vapor-deposited films on the substrates 6 at a prescribed value.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for producing a zinc sulfide thin film used in electroluminescent devices (EL devices), and particularly to a zinc sulfide thin film containing an active substance whose concentration is controlled to a predetermined concentration. The present invention relates to a method for manufacturing a zinc sulfide thin film suitable for forming a zinc sulfide thin film with a predetermined thickness.

[Prior Art] Zinc sulfide phosphor thin films containing active materials such as Mn, Cu+Ag+Tb, and Sm+CI have recently been used as light-emitting layers in electroluminescent (EL) devices.

The method for producing the phosphor thin film includes an electron beam evaporation method in which a zinc sulfide sintered body containing an active substance is irradiated with an electron beam and heated to evaporate, or a method in which zinc sulfide and the active substance are placed in separate crucibles and heated to evaporate. A two-source deposition method was used.

However, in the electron beam evaporation method, due to the difference in vapor pressure between zinc sulfide and the active material, the active material in the sintered body and the active material in the formed thin film do not have the same 20 degree angle (and the concentration gradient in the film thickness direction). Therefore, recently, zinc sulfide and the active substance were simultaneously evaporated from separate evaporation sources, and the deposition rate and deposition time were independently controlled to achieve a predetermined 715 degree concentration of the active substance. However, the 2# thin stone method, which can produce a phosphor thin film to a predetermined thickness, has come into use.At this time, in the conventional two-source Ha method, two film thickness gauges 8 are used as shown in Figure 2. , 14 are installed using a shielding plate 7 or the like so that they do not mix with each other, and the deposition rates of zinc sulfide and the active substance on the film thickness gauge 4 are measured independently. The deposition rate on the substrate was estimated from

As a film thickness meter, a quartz crystal oscillator film thickness meter with a water cooling device that calculates the thickness of the deposited film on the quartz crystal oscillator from the difference in the frequency of the quartz oscillator, or a quartz crystal oscillator film thickness meter that uses the optical interference effect in the film to calculate the thickness of the deposited film on the quartz crystal oscillator. An optical film thickness meter that calculates the film thickness from the increase in the area of the film is generally used.

[Problems to be Solved by the Invention] However, because the film thickness meter needs to measure zinc sulfide and the active substance independently, it is set at a distance from the substrate; Normally, the temperatures of the two layers are different.In such cases, to determine the actual deposition rate on the JJ root plate, the deposition rate obtained from the film thickness meter must be corrected by taking into account the adhesion coefficient of the substrate. There is a need.

However, it has been found that zinc sulfide tends to reevaporate on the substrate and the coefficient of τ depends on the substrate temperature as shown in FIG. In addition, another study has revealed that the temperature range of the substrate indicated by AA' in Figure 3 is appropriate for producing a high-brightness, long-life phosphor thin film for EL. In ZnS, a small temperature difference causes a large difference in adhesion coefficient. On the other hand, active substances such as Mr> generally have a nearly constant adhesion coefficient in the temperature range of AA'.

However, in a vacuum and with a substrate that transmits infrared rays, such as an EL glass substrate, it is difficult to maintain a constant temperature of the substrate and the reproducibility is poor. Therefore, an error in substrate temperature of about ±10° C. cannot be avoided in manufacturing. However, as mentioned earlier, this slight temperature error causes an error in the adhesion coefficient of about ±30% for zinc sulfide, and also a deposition error, which ultimately leads to large errors in the composition and thickness of the fluorescent thin film. It was the cause of. In addition, the composition of the phosphor thin film is the most important parameter that controls the luminous efficiency of EL, and the thickness of the phosphor thin film is an important parameter that affects the driving pressure of EL. Variations in composition and film thickness have been a major cause of lowering the yield in manufacturing EL phosphor thin films.

[Means for Solving the Problem] The present invention evaporates zinc sulfide and an active substance from separate evaporation sources in a vacuum apparatus, and then heats and holds the substrate in the vacuum apparatus. In the method for manufacturing a zinc sulfide thin film that forms a zinc sulfide thin film containing zinc sulfide, the evaporation rate of the evaporated film formed on the active substance film thickness gauge placed in a position where the zinc sulfide evaporated from the zinc sulfide evaporation source does not reach directly. In addition to measuring the evaporation rate of the active substance from the substrate, the formation rate of a zinc sulfide thin film containing the active substance formed on a monitoring substrate that is near the substrate and held at approximately the same temperature as the substrate or on the substrate. The deposition rate of zinc sulfide containing the active material is measured from This is a method for producing a zinc sulfide thin film characterized by maintaining the concentration at a certain level.

As described above, the adhesion coefficient in the substrate temperature range when depositing a thin film of zinc sulfide as an active substance is approximately constant, and the adhesion coefficient of zinc sulfide varies greatly. Therefore, as a method for maintaining the concentration of the active substance in the deposited film at a predetermined la degree, based on the above two measurement results of the vapor deposition rate, there is a method of: 1) changing the heating of zinc sulfide without changing the heating of the active substance; . ■A method of changing the heating of zinc sulfide by changing the heating of the active substance. ■
Possible methods include changing the heating of the active substance and zinc sulfide at the same time.

As a method for measuring the growth rate of the zinc sulfide film formed on the substrate or the monitoring substrate, there is a non-contact and accurate method of measuring the growth rate of the zinc sulfide film based on the intra-film interference effect of the zinc sulfide film. This is preferable because it allows for on-time measurement of changes in film thickness.

When measuring the zinc sulfide film formed on a monitor substrate, it is desirable that the temperature of the monitor substrate be maintained at the same temperature as the substrate used as a product, but approximately ±3°C. If the temperature difference is about , the effect of the present invention will not decrease much.

[According to the present invention, the deposition rate on the substrate can be directly adjusted according to the substrate temperature at that time. ! By controlling the temperature of the zinc sulfide evaporation source, it has become possible to correct the variation in deposition rate that conventionally occurred due to an error in the substrate temperature.

The problem with this method is that zinc sulfide is measured in a form that contains the active substance, but the amount of active substance contained in the phosphor thin film is usually less than 2 wt%. In particular, in the case of the active substance Mn, the optimum concentration is about 0.5 wt%, and such a thin film can be considered to be zinc sulfide alone when measuring the film thickness.

[Example] An example in which a ZnS phosphor thin film for EL, which contains 0.5 wt % Mn as a co-active substance and emits yellow-orange light, is deposited to a thickness of 580 nm will be described with reference to FIG.

A glass substrate (Corning 7059) on which films of ITO and silicon nitride were respectively formed was used as the deposition substrate 6. The monitor board 3 was installed immediately adjacent to the board 6, and was made of the same material and structure as the board 6. This is to make the temperatures of the monitor board 3 and the board 6 the same. Both the monitor board 3 and the board 6 are heated to 30° by the heater 5.
It was heated to about 0°C. Zinc sulfide 10 sintered in crucible 9
Then, 1 liter of molten Mn was added and heated with an electron beam to perform sufficient degassing.

The deposition rate of Mn was determined by the crystal oscillator film thickness meter 8, and the Mn
The deposition rate of zinc sulfide containing
Each was measured using an optical film thickness meter consisting of 2 filters and 1 light receiver.

In the optical film thickness meter, as the film thickness on the monitor substrate 3 increases, the transmitted light periodically increases or decreases due to the internal interference effect.

When the transmitted light is converted into monochromatic light with a wavelength of 580 nm by filter 2, the change in transmitted light in a half cycle is 1/4 of the wavelength, or 145
This corresponds to the product of the film thickness in nm and the refractive index (approximately 2°1). 58
In order to deposit 0 nm, it is sufficient to change it by about 4 cycles.

In this example, an initial electron beam power of 6 kV and 40 mA was applied to zinc sulfide with the goal of changing 580 nmv in 12 minutes, that is, one cycle in 3 minutes.

Regarding Mrl, the past average power of 8 kV and 60 mA was applied as an initial power so that Mn equivalent to 0.5 wt% of 580 nm zinc sulfide entered the film in 12 minutes. Open the substrate shutter 12, then first open the zinc sulfide crucible 7 soter 13, and after confirming that zinc sulfide begins to accumulate on the monitor substrate 3 with an optical film thickness meter, open the crucible 7 on the Mn side. I opened 13. The reason for shifting the timing of opening the crucible Yasota 13 in this way is to
This is because, unlike Mr+, zinc sulfide has a time delay of about 15 seconds to 1 minute from when the nya soter is opened until it is actually deposited on the substrate. After opening the crucible shutters 13 for both zinc sulfide and Mn and starting vapor deposition, the deposition rates of zinc sulfide and Mn are monitored every 5 seconds using the optical film thickness meter 1 and the crystal oscillator film thickness meter 8, respectively. did. After 10 seconds of vapor deposition, it was found that the deposition rate of zinc sulfide was about 8% lower than the target deposition rate, so the power of the electron beam immersed into the zinc sulfide was gradually increased until the target deposition rate was reached. The target value was reached after 30 seconds, and thereafter the target volume velocity could be stably maintained by applying constant power. Initially, the deposition rate was lower than the target value because the temperature of the substrate 6 in this batch was higher than the target value.

Regarding Mn, the target deposition rate was obtained until about 8 minutes, but after that, the deposition rate began to decrease as the number of sources in the crucible 9 decreased, so by increasing the power of the electron beam immersed in Mn. The target deposition rate was maintained.

After 12 minutes, both substrate converters 12 were closed and the electron beam power was lowered. By using such a vapor deposition method, a zinc sulfide thin film having a thickness of 580 nm and containing 0.5 wt% Mn could be manufactured with good reproducibility.

[Effects of the Invention] According to the present invention, when producing a phosphor thin film made of zinc sulfide and an active substance by a two-source vapor deposition method, which was previously impossible,
It has become possible to accurately control the composition and thickness of the thin film, greatly increasing the yield when manufacturing EL phosphor thin films, and making it possible to manufacture EL phosphor thin films at low cost. Become.

[Brief explanation of drawings]

The first bacterium is a schematic diagram showing the outline of the ZnS thin film manufacturing apparatus used in the examples, and FIG. 2 is a conventionally known ZnS
FIG. 3 is a schematic diagram showing the outline of the thin film manufacturing apparatus, and is a diagram showing the dependence of the adhesion coefficient of zinc sulfide on the substrate temperature. Figure 1

Claims (2)

[Claims] (1) Production of a zinc sulfide thin film by evaporating zinc sulfide and an active substance from separate evaporation sources in a vacuum apparatus to form a zinc sulfide thin film containing the active substance on a substrate heated and maintained in the vacuum apparatus. In the method, the evaporation rate of the active substance is measured from the evaporation rate of a deposited film formed on a film thickness gauge for the active substance placed in a position where the zinc sulfide evaporated from the evaporation source for zinc sulfide does not directly reach the substrate. Determining the deposition rate of zinc sulfide containing the active substance from the formation rate of a thin film of zinc sulfide containing the active substance formed on a monitoring substrate that is nearby and held at approximately the same temperature as the substrate or on the substrate. A method for producing a zinc sulfide thin film, comprising: changing the heating of the active substance and/or the evaporation source for zinc sulfide based on the measurement results to maintain the concentration of the active substance in the deposited film at a predetermined concentration. (2) Claim 1, wherein the temperature of the monitor substrate is maintained within a temperature difference of 3° C. with respect to the temperature of the substrate.
A method for producing a zinc sulfide thin film as described in .