JPS5823341B2 - Zinc oxide porcelain for high frequency sputtering - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION This invention relates to acid (ES zinc-based porcelain) piezoelectric crystal films of zinc monoxide used as targets for high-frequency sputtering. There are laws, etc.

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 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 zinc oxide piezoelectric crystal film is to be used in a wide range from the low harmonic region to the high frequency region, it is necessary to increase the specific resistance of the crystal film, and a target with high resistance 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 temperatures below 1300°C, the specific resistance increases, but the sintered density is less than 80% of the theoretical density, which is also unsuitable as a target.In either case, high-purity zinc oxide porcelain has high resistance. No high density was obtained.

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 phosphorus to zinc oxide has a high resistivity.

They discovered that a target with high density and little difference in density distribution throughout the porcelain could be obtained.

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

Example j Four powders of 0,203 (PO4)2 and 4H20 were used as raw materials, and 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 is ground and mixed with an organic binder in a wet mill*.

It was threaded, further dehydrated, dried, and then sized.

Thereafter, the powder was pressed at a pressure of 1000 kg/cA and molded into a disk with a diameter of 100 mIIL and a thickness of 5 mm.

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

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'? /crd.

In Table 1, sample number 1 is a conventional sample to which no phosphorus is 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 Fig.
Approximately 10 x 10101n on one side with m spacing, thickness 3 to 41nII
I cut out an L square plate.

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
Density of 08C is 1.682? /c shoulder) was used as the immersion liquid by the Archimedes method.

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 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 torn or more.

Next is the gas inlet. Introduce argon, oxygen, or a mixture of oxygen and argon gas from No. 8 until the gas pressure reaches 0-1~l.
Make it so that Xl0-”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
m high frequency power is supplied.

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: 2X 10-5 torr Frequency of high frequency power supply: 13.56MHz Power of high frequency power supply: 6 W/crrL Temperature of substrate to be adhered to: 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 incorporating phosphorus.

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.

In addition, 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 phosphorus is contained in zinc oxide may be 0.01 to 20 at %.

In other words, if it is less than 0.01 atom%, it has no effect on sinterability;
If it exceeds 20 atom %, grain growth will occur again, leading to a decrease in sinterability.

Further, similar effects can be obtained by using phosphorus alone or a compound such as an oxide as an additive.

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, characterized in that the target used for high-frequency sputtering and 2 is Kokichi, which is made by adding phosphorus to zinc oxide.