JPS5839794B2 - 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 one of the simplest sputtering methods, but unless the specific resistance of the zinc oxide porcelain target is lowered, 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.

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

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 firing density was less than 80% of the theoretical density, which was also unsuitable 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
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 discovered that porcelain obtained by adding lithium phosphate to zinc oxide has a high resistivity, high density, and a target with little difference in density distribution throughout the porcelain. It is.

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

Examples Using powders of ZnO and Li3PO4 as raw materials, they were mixed to obtain porcelain with the ratio shown in Table 1, and wet-processed.
Mixed.

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

Next, it was ground and mixed with an organic binder in a wet mill, further dehydrated, dried, and then sized.

After this, the powder was pressurized at a pressure of 1000 kg/cm,
Diameter 100++m.

It was molded into a disc with a thickness of 5 cm.

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

Incidentally, the firing temperature of Sample No. 1.2, which is a reference example in Table 1, is 1250°C.

When the specific resistance of the obtained target and the percentage of the fired density to the theoretical density (fired density/theoretical density x 100) were measured, the results shown in Table 1 were obtained.

Here, the theoretical density of zinc oxide is 5.67? /-.

In Table 1, sample number 1.2 is a conventional sample in which lithium phosphate is not added, and the others are samples according to the present invention.

Next, in order to investigate the density distribution of the target, as shown in Figure 1, from the center of the target
Square plates were cut out at intervals of about 10 x 10 squares on each side and 3 to 4 inches thick.

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

The density was measured using hexachlor-1,3-butadiene (2
The process was carried out by the Archimedes method using the immersion liquid having a density of 1.682 ff/crit at 0°C.

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

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

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 two-pole sputtering method among the 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 carry out high-frequency sputtering, the airtight container 1 is sealed and then evacuated from the exhaust hole 7 to a degree of vacuum of 1X10-6 ton- or more.

Next, argon, oxygen or a mixed gas of oxygen and argon is introduced from the gas inlet 8 until the gas pressure reaches I x 10-'
~lXl0”torr.

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

2 to 10 W/cr per unit area for target sample 4
A high frequency power is supplied.

A zinc oxide pressure crystal film was actually created under the following sputtering conditions.

Mixed gas ratio: Argon: Oxygen - 90% by volume: 10% by volume Pressure: 2X10-3torr Frequency of high frequency power supply: 13.56 MHz Power of high frequency power supply: 6W/c Temperature of glass substrate on adhesion surface: 350°C Above Sputtering was carried out under these conditions, and the film quality of the piezoelectric crystal film was examined, with the results shown in Table 1.

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

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 addition, in this invention, the range in which lithium phosphate is contained in zinc oxide is 0.01 to 0.01 in terms of atomic percent of lithium.
It is sufficient if it is 20.0 atomic %.

In other words, if it is less than 0.01 atom%, the sintered density and resistivity will not increase, and if it exceeds 20.0 atom%, the porcelain grains will become thicker (grow), resulting in lower density and lower resistance. Become.

As described above, according to the present invention, the sintered density is lower than that of conventional targets, and the variation in density is reduced by 1 at high densities.
You can get something small within the 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. As a target for high frequency sputtering,
Zinc oxide-based porcelain for high-frequency sputtering, characterized by containing lithium phosphate in zinc oxide.