JPH09256139A - Method for producing zinc oxide film - Google Patents

Abstract

(57) Abstract: A ZnO (zinc oxide) film having good crystallinity, which is used in a SAW device such as a SAW (surface acoustic wave) filter, is formed in a short time. SOLUTION: The film formation is divided into two steps. In the first step, a thin buffer layer having good crystallinity is formed, and in the second step, the growth rate is increased to form a growth layer. The first step is
Film formation rate as low as 0.4 μm / h or less, or 150
At a high temperature of ℃ to 300 ℃, the full width at half maximum of the rocking curve of the X-ray diffraction line is set to 9 degrees or less, and 0.05 to 0.1 µ.
A method of forming a buffer layer of m is effective.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a zinc oxide film (hereinafter referred to as Z
The present invention is applied to a method for producing a thin film for a SAW device using a surface acoustic wave (hereinafter referred to as SAW), particularly to a method for producing an nO film).

[0002]

2. Description of the Related Art There are many crystals exhibiting piezoelectricity,
There are not many substances that exhibit piezoelectricity in the thin film state. Zinc oxide (Zn oxide) is a substance that exhibits piezoelectricity in a thin film state.
O) and aluminum nitride. Since these crystals have a hexagonal wurtzite crystal structure, it is necessary to orient the c-axis of the microcrystals in the film perpendicular to the substrate in order to have good piezoelectricity. ZnO is industrially used as a thin film for SAW devices such as SAW filters and SAW convolvers, because a c-axis oriented film can be easily formed on a glass substrate or a silicon substrate.

As a film forming method for producing a thin film,
There are various sputtering methods such as a high frequency magnetron sputtering method and an ECR sputtering method. Either metal zinc (Zn) or zinc oxide (ZnO) is often used as the target.

[0004]

The propagation of SAW is ZnO.
It depends on the c-axis orientation of the film. As a method for evaluating the c-axis orientation, the half-width of the rocking curve of the X-ray due to the (002) plane can be mentioned. If this value is 7 degrees or less, the propagation of SAW equivalent to that of a single crystal is shown. Has been done. On the other hand, Z
Since the nO film needs to have a film thickness on the order of μm for the application of a SAW device, it is industrially desirable to increase the film forming speed.

FIG. 4 is a diagram showing the relationship between the film forming rate and the half-width of the rocking curve. For example, in a high-frequency magnetron sputtering apparatus, if the other conditions are kept constant and only the film formation rate is increased from 0.42 μm / h to 0.57 μm / h, the X-ray diffraction line of the (002) plane of the ZnO film is The full width at half maximum of the rocking curve was 7.1 degrees to 11.5 degrees, and the crystallinity of the thin film was poor. As described above, in the film formation of ZnO, if the film formation rate is increased, the half width of the rocking curve of the X-ray diffraction line becomes large. That is, the crystallinity of the thin film deteriorates. In order to reduce the full width at half maximum of the diffracted X-rays to 7 degrees or less, the film forming rate must be 0.4 μm / h or less. In order to obtain a better quality thin film, the film must be formed at a slower film forming speed, which requires a long time, which is extremely inefficient.

FIG. 5 shows the relationship between the optimum substrate temperature when forming a ZnO film and the film forming rate. From this figure, it can be seen that the higher the substrate temperature is, the higher the film formation rate can be. However, in order to obtain the film formation rate close to 1 μm / h, the substrate temperature must be 400 ° C. or higher. This is the temperature at which the handling of the substrate is quite difficult, especially for ordinary hard glass, its maximum operating temperature (380 ° C)
Beyond.

It is generally well known that the crystallinity of a thin film strongly depends on the substrate on which the film is deposited, in addition to the film formation rate and the substrate temperature. When a ZnO film is formed, if a ZnO film is deposited on a sapphire substrate instead of a glass substrate or a silicon substrate, a film having better crystallinity than other substrates is obtained,
Depending on the conditions, epitaxial growth can also be performed. The influence of such a sapphire substrate is due to the fact that the lattice constant of sapphire is close to that of ZnO. However, since sapphire is expensive, it can only be used as a substrate for a very special purpose.

In view of the above problems, it is an object of the present invention to provide a ZnO film having a good crystallinity which raises the film formation rate at a low temperature at which glass can be used and has no problem in SAW propagation. It is to provide a manufacturing method.

[0009]

In order to solve the above-mentioned problems, the present invention deposits a thin buffer layer having good crystallinity on a substrate, and then forms a growth layer thicker than the buffer layer on the substrate under conditions of a high film formation rate. Shall be deposited. In particular, the buffer layer having a half-width of the rocking curve of the X-ray diffraction peak of 9 degrees or less is set to 0.
It is assumed that a growth layer is deposited at a rate of 1 μm / h or more after forming a film having a thickness of 05 to 0.1 μm.

By doing so, a growth layer in which the number of nuclei of crystals starts is small and the good crystallinity of the buffer layer is succeeded, and the full width at half maximum of the rocking curve of the X-ray diffraction peak of the growth layer becomes 7 degrees or less. . With the buffer layer having such a thickness, the film formation time can be shortened. And 0.4 μm / h
Deposit the buffer layer at the following deposition rate, or
The buffer layer is preferably deposited at a substrate temperature of 0 to 300 ° C.

By doing so, the half-width of the rocking curve of the X-ray diffraction peak of the buffer layer becomes 9 degrees or less, and the half-width of the rocking curve of the X-ray diffraction peak of the growth layer on it becomes 7 degrees or less. .

[0012]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 3 is a schematic sectional view of the ECR sputtering apparatus used in the experiment for the present invention. The silicon substrate 4 is placed on the stage 3 in the reaction chamber 1 whose pressure is reduced by the vacuum pump 2. 2.45 GHz microwaves are transmitted from the microwave power source 6 above the reaction chamber 1, and the electrons cause cyclotron resonance due to the microwaves and the magnetic field of the solenoid coil 7 around the upper portion of the reaction chamber 1, causing violent movement and reaction. The gas in the chamber 1 is turned into plasma 10.
Plasma is generated even at a higher degree of vacuum than plasma due to other glow discharges, and the film quality is good. In this case, argon ions generated by ECR plasma sputter the Zn target 5 to deposit a ZnO film on the silicon substrate 1 to form a film. At this time, oxygen is supplied by mixing oxygen into argon from the gas inlet 9. The film formation rate and film quality of ZnO to be formed can be controlled by the pressure in the reaction chamber, the gas composition, the microwave power, the power from the bias power source 8, the substrate temperature, the target-silicon substrate distance, and the like. For example, if the pressure is low, the amount of argon is high, the bias power is high, and the distance between the target and the silicon substrate is short, the deposition rate increases.

[Experiment 1] First, the substrate temperature was 100 ° C. and the ZnO film formation rate was 0.07 μm / h at 0.07 μm / h.
When a μm buffer layer (hereinafter, the film formed in the first step is referred to as a buffer layer) is formed, (002) of the ZnO film is formed.
As for the rocking curve of the X-ray diffraction peak of the plane, the full width at half maximum was less than 1 degree, that is, a film with good crystallinity could be produced.
Then, a film thickness of 5 μm was formed on this film at a film formation rate of 1 μm / h.
When the growth layer of 1 was formed, a film having good crystallinity, in which the half-width of the rocking curve of the X-ray diffraction peak of the (002) plane was smaller than 1 degree, could be produced. Similarly, after forming various crystalline buffer layers, a growth layer having a thickness of 5 μm was formed thereon at a film forming rate of 1 μm / h, and the crystallinity of the film was examined by X-ray. In addition, when there is no buffer layer and only the growth layer having a film formation rate of 1 μm / h is formed, the half-width of the rocking curve is 1
It will be 3 times.

FIG. 1 shows the influence of the buffer layer on the quality of the grown layer. The horizontal axis is the buffer layer (0.07 μm)
Is the half-width of the rocking curve of the X-ray diffraction peak, and the vertical axis is the half-width of the entire growth layer (5 μm) deposited thereon. From this, it can be seen that if a growth layer is formed after forming a buffer layer having a certain degree of crystallinity, a practical film can be obtained even if the growth layer is formed under the condition of a high film formation rate. Further, the better the crystallinity of the buffer layer, the better the crystallinity of the growth layer, and the fact that the crystallinity of the growth layer is a practical limit is that the half-width of the rocking curve is 7 degrees or less. The full width at half maximum of the rocking curve of the buffer layer must be 9 degrees or less. From this figure and FIG. 4, it can be seen that the film formation rate of the buffer layer may be 0.4 μm / h or less.

The thickness of the buffer layer is 0.05.
It has been experimentally confirmed that a range of 0.1 μm is preferable. The crystallinity of the growth layer deteriorated both when the thickness was made thinner than 0.05 μm and when it was thicker than 0.1 μm. It is considered that the buffer layer in this range has an appropriate number of crystal nuclei in the growth layer. By electron microscope observation of the cross section of the film produced by the method of the present invention, it was observed that the grain size was grown from the surface to the substrate interface.

Similar effects could be confirmed by other sputtering apparatus such as RF sputtering in addition to ECR sputtering. [Experiment 2] The deposition rate of the buffer layer was kept at 100 to 300 at a constant condition of 0.8 μm / h, which was 10 times that of Experiment 1.
The temperature was changed to ℃ and deposited.

FIG. 2 shows the relationship between the film formation temperature and the full width at half maximum of the rocking curve of the buffer layer. The horizontal axis represents the film forming temperature of the buffer layer, and the vertical axis represents the half-width of the rocking curve.
From this figure, it is understood that the higher the film forming temperature of the buffer layer, the higher the crystallinity. It is considered that the substrate temperature increases the kinetic energy of the atoms deposited on the film and acts to put the atoms into the optimum sites.

When a growth layer was deposited thereon by high-speed film formation similar to that in Experiment 1, it was confirmed that, as in Experiment 1, the better the crystallinity of the buffer layer, the better the crystallinity of the growth layer. . It was found that the film-forming temperature must be 150 ° C. or higher in order that the half-width of the rocking curve of the buffer layer is 9 degrees or less for the crystallinity of the growth layer to be stacked thereon being practical.

Further experiments were conducted using a glass substrate, and similar results were obtained.

[0020]

As described above, the present invention shows, as a method for forming a ZnO thin film, a method for obtaining a thin film having high crystallinity on a glass substrate or a silicon substrate at a high film forming rate. That is, the film formation is divided into two steps, and in the first step, a thin buffer layer having good crystallinity is deposited,
The second stage is a method of growing a film thicker than the buffer layer at a high film formation rate.

As the first step, there is a method of slowing the deposition rate or raising the temperature to generate a small number of good quality nuclei. By the method of the present invention, the film formation rate as a whole is increased, and a ZnO thin film having high crystallinity can be obtained in a short time. Therefore, the present invention provides a SAW using a ZnO thin film.
It contributes to cost reduction, spread, and development of devices and the like.

[Brief description of drawings]

FIG. 1 is a diagram showing the relationship between the full width at half maximum of the rocking curve of the X-ray diffraction peak of the buffer layer and that of the entire film.

FIG. 2 is a diagram showing a relationship between a full width at half maximum of an X-ray of a buffer layer and a film forming temperature.

FIG. 3 is a schematic sectional view of an ECR sputtering device.

FIG. 4 is a diagram showing a relationship between a film formation rate of a buffer layer and a half width of a rocking curve of an X-ray diffraction peak.

FIG. 5 is a diagram showing a relationship between a film formation temperature and a film formation rate of a film having good crystallinity.

[Explanation of symbols]

 1 Reaction Chamber 2 Vacuum Pump 3 Stage 4 Silicon Substrate 5 Zn Target 6 Microwave Power Supply 7 Solenoid Coil 8 Bias Power Supply 9 Gas Inlet 10 Plasma

Claims (5)

[Claims] 1. A method for producing a zinc oxide film, which comprises depositing a thin buffer layer having good crystallinity on a substrate and then depositing a growth layer thicker than the buffer layer on the substrate under conditions of a high film formation rate. . 2. A buffer layer in which the rocking curve of the X-ray diffraction peak has a half value width of 9 degrees or less on a silicon substrate in an amount of 0.05 to 0.05.
The method for producing a zinc oxide film according to claim 1, wherein a growth layer is deposited at a rate of 1 μm / h or more after forming a film having a thickness of 0.1 μm. 3. A buffer layer having a rocking curve of an X-ray diffraction peak with a full width at half maximum of 9 degrees or less on a glass substrate in an amount of 0.05 to 0.05.
The method for producing a zinc oxide film according to claim 1, wherein a growth layer is deposited at a rate of 1 μm / h or more after forming a film having a thickness of 0.1 μm. 4. The method for producing a zinc oxide film according to claim 1, wherein the buffer layer is deposited at a film forming rate of 0.4 μm / h or less. 5. The method for producing a zinc oxide film according to claim 1, wherein the buffer layer is deposited at a substrate temperature of 150 to 300 ° C.