JPS5823342B2 - Zinc oxide porcelain for high frequency sputtering - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to zinc oxide ceramic used as a target for high frequency sputtering.

Methods for producing piezoelectric crystal films of zinc oxide include vacuum evaporation, gas phase reaction, and sputtering.

Among these sputtering methods, there are two types of sputtering methods: a DC two-pole type, a DC three-pole type, and a high-frequency sputtering method.

The DC bipolar type is the simplest of the sputtering methods, but unless the resistivity of the zinc oxide porcelain target is low, positive charges will accumulate on the surface of the target exposed to ions, resulting in poor sputtering. I can't do it efficiently,
Stable discharge could not be maintained.

Furthermore, since a target with a low specific resistance is used, the specific resistance of the obtained film also tends to be low.

Although these films can be used at high frequencies due to the dielectric relaxation phenomenon, they have not been able to be used over a wide range of low frequencies.

Further, in such a sputtering method, an active gas such as oxygen, an inert gas such as argon, or a mixture thereof is generally used as the atmospheric gas.

One method of increasing the specific resistance of a crystal film is to increase the amount of oxygen in the atmospheric gas, but this method has the drawback of slowing down the growth rate of the crystal film.

On the other hand, the high-frequency sputtering method has the advantage of being able to use targets with either low resistance or high resistance, but it is necessary to increase the growth rate of the film in order to industrially mass-produce crystal films.

For this purpose, a high-density target is required.

In other words, if the density is high, the power applied per unit area of the target (power density) can be increased.
This is because the growth rate of the film increases.

Furthermore, as mentioned above, if a piezoelectric crystal film of zinc oxide is to be used in a wide range from low frequency range to high frequency range, it is necessary to increase the specific resistance of the crystal film, and a high resistance target is required. .

Conventionally, high-purity zinc oxide porcelain was used as a target, but when the pre-fired molded product is fired at a high temperature of 1300℃ or higher, the sintered density becomes over 90% of the theoretical density, but the resistivity is low. Therefore, it is unsuitable as a target for high frequency sputtering.

On the other hand, when fired at less than 1300℃, the specific resistance increases, but
The sintered density was less than 80% of the theoretical density, which was also inappropriate as a target, and in all cases, high resistance and high density could not be obtained with high purity zinc oxide porcelain.

For example, a low density target (sintered density/theoretical density
When high frequency sputtering is performed at 100% (90%), the surface of the obtained piezoelectric crystal film becomes uneven.

This is presumably due to the fact that the zinc oxide clusters were dispersed unevenly.

As a result of various studies on the above-mentioned problems, we found that porcelain made by adding vanadium to zinc oxide has a specific resistance.

They discovered that it is possible to obtain a target with a high density and a small difference in density distribution throughout the porcelain.

This invention will be described in detail below according to examples.

EXAMPLE Using ZnO and V2O5 powders as raw materials, they were prepared and wet-mixed so as to obtain porcelain having the ratios shown in Table 1.

After dehydrating these, they were calcined at 600 to 800°C for 2 hours.

Next, it was ground and mixed with organic pine*kuda in a wet mill, further dehydrated, dried, and then sized.

After this, the powder was pressurized at a pressure of 1000 kg/clr,
It was molded into a disk with a diameter of 100m7M and a thickness of 57n11.

Furthermore, the molded disk was fired at 1200° C. for 2 hours to create a target sample containing vanadium.

In addition, the firing temperature of sample number 1, which is a reference example in Table 1, is 1
The temperature is 250°C.

When the resistivity of the obtained target and the percentage of the sintered density with respect to the theoretical density (sintered density/theoretical density X100) were measured, the results shown in Table 1 were obtained.

Here, the theoretical density of zinc oxide is 5.67? /cr; was set to 1.

In Table 1, sample number 1 is a conventional sample that does not contain vanadium, and the others are samples according to the present invention.

Next, in order to investigate the density distribution of the target, as shown in Fig.
Square plates with a side of 110×10i and a thickness of 3 to 4 mm were cut out at m intervals.

Both sides and the surrounding area of the cut porcelain were polished, a thin wax layer was attached on the surface, and this was used as a sample for measuring the sintered density.

The density was measured using hexachlor-1,3-butadiene (2
The density at 0° C. was 1.682 g/crd) and the Archimedes method was used.

Table 2 shows the sintered density at each measurement position and its standard deviation (
a').

From Table 2, it can be seen that the density variation at each position of the sintered porcelain according to the present invention, that is, the density variation, σ, is greatly improved.

Next, a piezoelectric crystal film of zinc oxide was created by high-frequency sputtering using the target described above.

FIG. 2 shows an apparatus for implementing a high frequency bipolar sputtering method among high frequency sputtering methods.

Reference numeral 1 denotes an airtight container (bell jar), and a pair of parallel plate-shaped cathode 2 and anode 3 are arranged in this airtight container 1.

Each target sample 4 described above is fixed on the cathode 2 .

5 is a shutter. The anode 3 has glass as a deposit,
A substrate 6 made of metal or the like is fixed, and this substrate 6 is heated in the range of 200 to 500° C. during sputtering.

7 is an exhaust hole, and 8 is a gas inlet.

To perform high frequency sputtering, the airtight container 1 is sealed and then evacuated from the exhaust hole 7 to a degree of vacuum of I.times.10@-6 Torr or higher.

Next is the gas inlet. Introduce argon, oxygen, or a mixed gas of oxygen and argon from 8 until the gas pressure reaches lXl0-1~
Set it to 1X1O-3 Torr.

A high frequency voltage is applied to the cathode 2 by a high frequency power source 9.

2 to 10 W/c per unit area for target sample 4
Supplies rA high frequency power.

A zinc oxide piezoelectric crystal film was actually sputtered under the following sputtering conditions.

Mixed gas ratio: Argon: Oxygen = 90% by volume: 10% by volume Pressure Crab 2X10-3 Torr Frequency of high frequency power supply: 13.56 MHz High frequency power supply electric crab 6 W/cr/L Temperature of glass substrate on adhesion surface; 350° C Sputtering was performed under the above conditions, and the film quality of the piezoelectric crystal film was examined, and the results were as shown in Table 1.

From Table 1, piezoelectric crystal films with good film quality were obtained by containing vanadium.

Furthermore, when the relationship between the maximum input power that can be applied to each target sample and the sintered density was measured, the results shown in FIG. 3 were obtained.

The average value of 20 target samples is shown in FIG. 3, and the variation thereof is also shown in FIG.

As can be seen from FIG. 3, the device according to the present invention has the effect that the maximum input power is more than twice that of the conventional device, the crystal film formation speed can be more than doubled, and mass productivity can be improved.

In the present invention, vanadium may be contained in zinc oxide within a range of 0.001 atomic % or more to 20 atomic % or less.

In other words, if the vanadium content is less than \0.001 atomic%, the sintered density and resistivity will not increase, and if it exceeds 20 atomic%, the porcelain grains will grow larger, resulting in a lower density and lower resistance. turn into.

Similar effects can also be obtained by using vanadium with compounds such as metals and oxides as additives.

As described above, according to the present invention, it is possible to obtain a target that has a higher sintered density than conventional targets and has small variations in the density within one target.

Further, it has the effect that a large maximum input power can be obtained, and a crystal film of good quality can be obtained with good mass production.

[Brief explanation of the drawing]

Figure 1 is an explanatory diagram for cutting out a sample for measuring sintered density from a target sample, Figure 2 is a high-frequency two-pole sputtering device, and Figure 3 is an illustration of the maximum input power that can be applied to the target sample and the sintered density. It is a figure showing a relationship. 1... Airtight container, 2... Cathode, 3...
...Anode, 4...Target, 6...
··substrate.

Claims (1)

[Claims] 1. Zinc oxide-based porcelain for high-frequency sputtering, which is characterized by containing vanadium in zinc oxide, which is used as a target for high-frequency sputtering.