JPS5946443B2 - Manufacturing method of surface acoustic wave wafer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of manufacturing a surface acoustic wave wafer that can improve the group delay time temperature characteristics of a surface acoustic wave element and increase the electromechanical coupling coefficient.

Surface acoustic wave elements are required to have good group delay time-temperature characteristics, that is, to have little change in group delay time over a wide range of temperature changes, and to have a large electromechanical coefficient.

Although there are those using an ST-cut quartz crystal plate that have good group delay characteristics, the electromechanical coupling coefficient is very small and they are not suitable for practical use at all.

For this reason, LiNbO3 single crystal or LiTaO3
Although a 1jlL crystal is used as a substrate, it has the drawback that group delay characteristics are not very good.

In order to improve group delay characteristics, for example, as detailed in U.S. Pat. No. 3,965,444, a surface acoustic wave substrate has been provided with a material different from that of the surface acoustic wave substrate. There is.

This is a LiTaO5 single-crystal substrate with Y-cut and Z-direction surface wave propagation, on which SiO2 is mounted by high-frequency sputtering using fused silica as a target.

However, in the manufacturing process of the above structure, it takes a long time (approximately 40 to 80 hours) to attach SiO□ by high-frequency sputtering, and the high-frequency sputtering is generally 10-8).
Since the process is carried out by sealing oxygen in a vacuum furnace of about 100 lbs., the problem is that the work is very complicated.

Because of this, productivity was low and mass production was not possible.

The present invention has been made in consideration of these circumstances, and its purpose is to provide a surface acoustic wave element, that is, a surface acoustic wave wafer, which has a high electromechanical coupling coefficient and good group delay time temperature characteristics. An object of the present invention is to provide a method for manufacturing a surface acoustic wave wafer that can be manufactured easily and in a short time.

An embodiment of the manufacturing method according to the present invention will be described below with reference to the drawings.

Figures 1a and 1g schematically show an exploded view of the manufacturing process of the same example.

A surface acoustic wave substrate 1, which is cut out from a lithium tantalate (LiTa03) single crystal by X-cutting and 112° Y-direction surface wave propagation, has its upper surface mirror-polished as shown in FIG. 1a.

As shown in FIG. 1, aluminum 2 is formed to a thickness of about 1 μm on the mirror-polished upper surface of the substrate 1 by vacuum evaporation.

After that, the aluminum 2 is formed into a predetermined comb-like pattern, for example by PEP (Photo
Etching Process)
Interdigital electrodes 3 are formed as shown in Figure C.

As a result, a surface acoustic wave element having a conventional general structure is formed.

By the way, in this method, a chemical vapor deposition method (CVD: C
chemical vapor deposition
), silicon dioxide (5102) 4 containing phosphorus (b) is deposited to a thickness of about 2 μm as shown in FIG. 1d.

This deposition of SiO□4 by CVD is performed by a thermochemical reaction on the surface of the substrate 1 at high temperatures. For example, silane (SiH4) is mixed with a small amount of phosphine (PH3), and oxygen (0□) and thermochemical PSG (phosphorus,
phosphorus (silicerate glass) and water.
This is accomplished by forming a silicon dioxide film containing P).

After that, a resist (Az-13
50J) 5 is applied, and the resist 5 located above the circuit connection electrode portion is removed as shown in FIG. 1e, and a window is opened.

If the S i O 24 is subjected to the corrosion removal process, only the 5 iO 24 in the area not covered with the resist 5 is removed, and only the direction connection electrode 3a is exposed, as shown in FIG. 1f.

Thereafter, as shown in FIG. 1g, the resist 5 is removed.
A surface acoustic wave wafer is formed by cleaning,
A lead wire (not shown) is connected to the electrode 3a by bonding etc.
A surface acoustic wave element is manufactured by arranging the above elements as shown in the partially cutaway perspective view of FIG. 2.

In the past, ′ □S
A silicon dioxide film was formed by a thermochemical reaction: iH4+202-8iO□+2H20.

However, due to the nature of silicon dioxide film, it is prone to peeling and cracking, so it is very difficult to obtain a sufficient thickness to secure surface acoustic wave I4 sand, and the surface is rough, ff, -. Since it does not have a dense structure, its surface wave characteristics are not very good.However, by forming PSG as described above, it becomes possible to solve the problems associated with silicon dioxide films.

Because SP Sa itself has a dense structure and a smooth surface, it has excellent surface wave characteristics, and since peeling and cracking are less likely to occur, it can be easily formed to a desired thickness.

Therefore, it is possible to easily obtain better characteristics than conventional ones.

Specifically, the above manufacturing method is carried out, for example, as follows.

In this example, a CVD apparatus manufactured by Tokyo Shibaura Electric Co., Ltd., Model VG-I4 is used.

First, the surface acoustic wave substrates 1 on which the interdigital electrodes 3 are formed are boiled in trichlorethylene for about 5 minutes, and after cleaning the surface, they are placed side by side on the base of a CVD apparatus.

Then, the base is heated to 450° C. at a temperature increase rate of about 10° C./minute, and the surface acoustic wave substrate 1 is heated to a high temperature.

In this state, silane (SiH,) with a concentration of 3% was applied at 300 cc per minute, and phosphine (PH3) was applied at 1 minute per minute.
．． 5cc and at the same time oxygen (02) at 300c per minute
5i024 is deposited on the substrate 1 by CVD.

This deposition process CVD continues for 30 minutes.

Then the above SiH4. Stop the supply of PH3,0□, and
Return the inside of the VD device to room temperature at a rate of about 10℃/1 minute,
The substrate 1 with the 5i02 deposited on its surface is taken out.

Note that during the above operation, nitrogen gas is constantly flowing at about 10 A/minute as a carrier gas.

゛ The surface acoustic wave wafer substrate 1 manufactured in this manner is coated with PSG (phosphorus silicate glass).

In other words, the surface acoustic wave wafer has its surface covered with the phosphine (
It is covered with SiO□ doped with phosphorus (PH3).

Therefore, the temperature characteristics of the group delay time of the surface acoustic wave substrate 1 and the temperature characteristics of the group delay time of the doped 5i024 cancel each other out, thereby improving the group delay time temperature characteristics.

In this respect, the above effects cannot be expected at all with conventional silicon dioxide films.

For example, the temperature customization of the group delay time of the product manufactured in the above embodiment is about 5/'C, and the conventional temperature is 20 ppm.
/ 'C exhibits much better characteristics.

Moreover, at the electromechanical coupling coefficient method measurement frequency of 100 MHz, it was 1.4 and 0.8 without installing 5i024.
%.

It is also possible to simultaneously improve the switching electromechanical coupling coefficient.

Additionally, as a secondary benefit, the warpage of surface acoustic wave wafers can be reduced by approximately 20% compared to those manufactured using conventional methods, making it possible to mass-produce uniform wafers with less warpage. .

Further, since high frequency sputtering is not used and the phosphorus-doped 5i02' coating is applied at the same time, the surface becomes very smooth, and unexpected situations such as so-called θ cracking and peeling of the Sio2 film do not occur.

This is because the surface becomes porous when only coated with 5iQ2, but smoothness occurs due to single-term doping.

Furthermore, the most characteristic feature of this method is that the manufacturing processing time is extremely short.

That is, it takes 40 to 80 hours to form a 5i02 film to a thickness of about 2 μm using conventional high-frequency sputtering.

On the other hand, with CVD, a PSG film with a thickness of about 2 μm can be formed in about 2 hours.

This is because PSG is easily deposited on the surface of the substrate 1 together with the heating of the surface of the substrate 10.

Therefore, the manufacturing process can be completed in a short time, mass productivity can be improved, and since the growth rate of the thin PSG is fast and its control is simple, it is easy to handle.

As explained above, according to the present invention, surface acoustic wave wafers, which have advantages such as improved group delay time temperature characteristics and increased electromechanical coupling coefficient, can be easily controlled by effectively utilizing the CVD method. Furthermore, it exhibits the excellent effect of being able to be manufactured in a short time, and has advantages such as being excellent in mass productivity.

Please note that the present invention is not limited only to the above embodiments.
,) For example, the processing time required for each step may be determined according to the design specifications, that is, the thickness of the electrode, the thickness of the PSG film, etc. may be determined as appropriate, for example, about 2 to 10 μm.

It goes without saying that conditions for CVD may also be determined as appropriate.

Furthermore, a piezoelectric material may be used as the substrate 1, and Li
It can be similarly applied to NbO3 single crystals and the like.

In short, the method of the present invention can be implemented with various modifications without departing from the gist thereof.

[Brief explanation of drawings]

Figures 1a and 1g are diagrams schematically showing a manufacturing structure showing an embodiment of the method of the present invention, and Figure 2 is a partially cutaway cross-sectional perspective view of a surface acoustic wave quencher manufactured by the method of the present invention. It is a diagram. 1... Surface acoustic wave substrate, 2... Aluminum (for electrode), 3... Electrode, 4... 5iO2 (PSG), 5
...Resist.

Claims (1)

[Claims] 1 Silane (SiH, ) and oxygen (0
1. A method for manufacturing a surface acoustic wave wafer, characterized in that silicon dioxide containing phosphorus (0), which is a thermochemical reaction product whose main component is a reaction product with phosphorus (0), is attached by a chemical vapor deposition method.