JPH0322605A - Manufacture of surface acoustic wave element - Google Patents

Abstract

PURPOSE:To reduce number of man-hour and to simplify the process in comparison with the etching method by the development liquid or a conventional three- layer resist lift-off method by etching a metallic layer on an Li2B4O7 substrate through the use of a specific alkali water solution. CONSTITUTION:At first an Al layer 22 being an electrode is formed on an Li2B4O7 substrate 21 with a prescribed film thickness and a resist layer 23 is formed on the Al layer 22. Then the resist layer 22 is exposed and developed by using a photo resist mask with a prescribed pattern such as a general positive resist mask to form the pattern of the resist layer on the substrate 21. Then the Al layer 22 of the prescribed part is etched with alkali development liquid. In this case, a mixed water solution of KOH and K3[Fe(CN)6] adjusted to pH11-pH13 is used at a temperature of 10-50 deg.C as an etchant of the Al layer. Then the resist layer 23 is removed finally to form the Al electrode.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention provides Ll2B40? The present invention relates to a method of manufacturing a surface acoustic wave device using.

(Prior Art) Conventionally, piezoelectric substrate materials used in surface acoustic wave devices include quartz, LITaO 3 , LINbO 3 , L
12B407 etc. Among these materials, L12B4
0? has attracted attention in recent years because of its good temperature characteristics and coupling coefficient.

However, Li2B*Oy is crystal, LITaO z,
Compared to LiNb03, it is weak against acids and dissolves in pure water. Therefore, when forming an Ai electrode, it is not possible to use the conventional wet etching process using acid, and a three-layer lift-off process or a developer solution is required. An etching process is used.

In the three-layer lift-off process, as shown in FIG. 9, first, a lower resist film 2 is formed on a Li2B407 substrate 1 (FIG. 9(a)), and an intermediate layer 3 is formed on this (FIG. 9(a)). (FIG. 9(b)), and further an upper resist layer 4 is formed (FIG. 9(C)). Then, the upper resist layer 4 is exposed and developed based on a predetermined pattern (FIG. 9(d)).
,,11 After etching the intermediate layer 3 (Fig. 9(e)
)) The lower resist layer 2 is exposed and developed, and the upper resist layer 4 and the lower resist layer 2 are removed (FIG. 9(f)).
.

In this way, an overhang structure 5, which is a negative electrode pattern, is formed on the substrate 1. After this, an AJ2 layer 6 that will become an electrode is formed on the substrate (FIG. 9(g)),
Finally, the overhang structure 5 is removed to form the l electrode (FIG. 9(h)).

On the other hand, in the etching process using a developer, as shown in FIG. 0. An AJ layer 12 serving as an electrode is formed on the substrate 11 (FIG. 10<8)), and a resist layer 13 is formed thereon (FIG. 10(b)). Then, the resist layer 13 is exposed and exposed based on a predetermined pattern.
A pattern is formed on the substrate 11 (see FIG. 10).
C)).

Thereafter, a predetermined portion of the AI2 layer 12 is etched using a developer (FIG. 10(d)). At this time, the developer for forming the pattern and the developer for etching are the same. Finally, the resist layer 13 is removed to form an Ai electrode (FIG. 10(e)).

(Problems to be Solved by the Invention) However, the above-described three-layer lift-off process has an increased number of steps and is more complicated than the conventional wet etching process using an acid, which has caused a decrease in yield.

Furthermore, in the etching process using a developer, the resist pattern is dissolved in the developer, resulting in a decrease in the resist film, making it difficult to accurately control the line width of the pattern. Furthermore, since the developer is not the original AJ2 etching solution, there is a large amount of residue, which deteriorates the etching performance.As a result, the variation in the excitation frequency of the surface acoustic wave device becomes large, which is a cause of a reduction in yield.

The present invention has been made to solve the above-mentioned conventional problems. O? In the process of forming an electrode pattern on the substrate surface, an etchant different from the developer, i.e., a mixed aqueous solution of KOH and K 3 [Fe(CN) s ] prepared at pH 13, is heated to 10°C.
By using it as an alkaline etching solution at ~50°C, the number of steps and process time are significantly reduced compared to the conventional three-layer lift-off process, simplifying the process.
It is an object of the present invention to provide a method for manufacturing a surface acoustic wave device that can reduce variations in frequency characteristics of the surface acoustic wave device compared to an etching process using a developer.

[Structure of the Invention] (Means for Solving the Problems) The method for manufacturing a surface wave element of the present invention is based on LI2B. 07
A step of forming a metal layer on the surface of the substrate, a step of forming a resist layer on the metal layer, exposing and developing the resist layer based on a predetermined pattern, and a step of forming a predetermined portion of the metal layer. , consisting of a mixed solution of KOI+ and K 3 [Pe(CN) s ], pH 11 to pH 13, temperature 10°C to 5.
The method is characterized by comprising an etching step using an alkaline aqueous solution at 0°C.

(Function) The present invention uses KOH and K 3 [Pe(CN) s when etching the metal layer on the L12B40 substrate.
], pH 11~pnia, temperature 10℃
By using an alkaline aqueous solution at ~50°C, the number of steps can be shortened and simplified compared to the conventional three-layer resist lift-off method or etching method using a developer. It becomes possible to suppress frequency variations in surface wave elements to a small level and significantly improve yield.

(Example) Hereinafter, an example of the method of the present invention will be described with reference to the drawings.

FIG. 1 is a diagram showing the etching method of the example.
An A°C layer 22 which will become an electrode is formed on the Li2B<Or substrate 21 to a predetermined thickness, e.g.
1(a)), a resist layer 2 is placed on this AJ2 layer 22.
3 (Fig. 1(b)).

Then, the resist layer 22 is exposed and developed using a photoresist mask with a predetermined pattern, such as a general positive resist mask, to form a pattern of the resist layer on the substrate 2l (FIG. 1(C)).

Thereafter, a predetermined portion of the Ag layer 22 is etched using an alkaline developer (FIG. 1(d)). At this time, as an etchant for the Al layer 22, a mixed aqueous solution of KOJI and K 3 [Pe(CN) s ] prepared at pHll-allll3 was used at lO<0>C to 50<0>C.

Finally, the resist layer 23 is removed to form an A.degree. C. electrode (FIG. 1(e)).

In the method of this embodiment, the AJ2 layer 22 was formed by vapor deposition, sputtering, or the like, and the substrate heating temperature at that time was 150° C. or lower.

Here, as the etchant for the Al layer 22, an alkaline aqueous solution satisfying the conditions (1) to (4) shown below is used.

■It must be a mixed aqueous solution consisting of KOH and K 3 [Pe(CN) s ].

KOH is generally used as an alkaline etching solution for oil.
(potassium hydroxide), NaOH (sodium hydroxide), and the like. In general, these etching rates are much slower than acid etching rates, and are not suitable for etching at A° C. for mass production.

However, when K 3 [Pe(CN) a ] is added to KOH, the etching rate improves in proportion to the amount of K 3 [Fe(CN) s ], and it is difficult to obtain an etching rate sufficient for mass production. I can do it. An experimental example will be described below.

K01! The amount of K 3 [Pe(CN) a
] Figure 2 shows the change in the A,9 etching rate as the amount was increased. From the same figure, K 3 [Pe(C
It can be seen that the etching rate of f:k and Ab are proportional.

(I) I1 of the alkaline aqueous solution should be 11-13.

The relationship between the etching rate of the L12B407 substrate and the etchant pl1 is shown in FIG. From this figure, it can be seen that the etching rate and the etchant 911 are proportional.

By the way, the pH of conventionally used developers is about 13. That is, when an etchant with a pH of 13 or higher is used, even the unexposed portions of the resist may be slightly dissolved, making it difficult to accurately control the line width of the pattern.

Conversely, if an etchant with a pH below 11 is used, etch pits will occur, and especially in the case of thin films, the influence of frequency is significant. For these reasons, it is desirable that the alkaline etchant has a pl+ of 11 to 13.

■Alkaline aqueous solutions should be used at 10°C to 50°C.

FIG. 4 shows the relationship between the etching rate in A° C. and the etchant liquid temperature. From the same figure, the etching rate of AJ2 and the etchant liquid temperature are almost proportional, and the liquid temperature is 10
When the temperature is below 0.degree. C., the etching rate is too slow to be used in mass production.

Furthermore, as the temperature of the solution increases, the etching rate also increases, but when the temperature rises above 50° C., the alkaline etchant soaked from the interface between A and the resist ends up etching the A at the edge of the pattern.

This state is shown in FIG. For these reasons, it is desirable to use the alkaline etchant at a liquid temperature of lO<0>C to 50<0>C.

Based on the above, an alkaline etching solution that satisfies the conditions (1) to (2) above is used.

Using the above etchant, a 280M}Iz band pager filter was actually produced as a prototype.

FIG. 6 shows a SEX photograph of the AI electrode pattern formed at this time. As shown in the figure, the edges of the electrodes were formed sharply.

FIG. 7 shows the frequency characteristic distributions of the filter manufactured by the method of this embodiment and the filter manufactured using the conventional three-layer resist lift-off method. From this result, the filter manufactured by the alkaline etching process of the method of this example (Fig. 7 (a)) has the same frequency characteristics as the filter manufactured by the conventional three-layer resist lift-off method (Fig. 7 (b)). It was confirmed that it was possible to obtain

In this way, according to the above embodiment method, L12B407
It was confirmed that it is effective to use an alkali etching process when forming a 280 MIIz band pager filter (film thickness of approximately 1000 mm) on a substrate.

In addition, by forming the Al layer by vapor deposition or sputtering, etc., and by heating the substrate at a temperature of 150°C or less, it is possible to prevent etching from proceeding from the vapor-deposited Al grain boundaries. Improved adhesion and chemical resistance.

In the method of the above embodiment, an example was explained in which the method of the present invention was applied to etching a thin film of AJ2 (film thickness of about 1000 mm), but the method of the present invention can also be applied to etching a thick film.

In this case, the alkaline etching rate of Ai is much lower than the acid etching rate of A°C, so alkaline etching is effective when etching thin films (film thickness approximately 1000 μm), but it is not suitable for the mass production process of thick film etching. It is not suitable as such.

Therefore, in the case of thick film etching, a method as shown in FIG. 8 is used. That is, first, an Ai thick film 32 that will become an electrode is formed on a Li2B407 substrate 31 (FIG. 8(a)).
, a resist layer 33 is formed on this eight layer 32 (eighth layer 33).
Figure (b)). Then, the resist layer 33 is exposed and developed based on a predetermined pattern, and the resist layer 33 is placed on the substrate 31.
A pattern is formed (FIG. 8(C)). After this, A
After etching about 90% of the thick film 32 with acid (FIG. 8(d)) and etching the last thin Ai layer 32a with alkali (FIG. 8(e)), the resist layer 32 is removed (FIG. 8(d)).
Figure (f)).

By using this method, the etching time can be made sufficiently suitable for mass production, and a thick-film Yabu electrode can be formed without damaging the L12B407 substrate 31. This is an effective method for forming a film.

[Effects of the Invention] As explained above, according to the method for manufacturing a surface acoustic wave device of the present invention, L12B. By forming an Ai electrode on the 07 substrate, the number of steps can be shortened and simplified compared to the conventional three-layer resist lift-off method or etching method using a developer. It becomes possible to suppress the frequency variations of the elements and significantly improve the yield.

[Brief explanation of the drawing]

FIG. 1 is a diagram for explaining the alkali etching process according to the method of this embodiment, and FIG.
) s ] A diagram showing the relationship between m and AJ2 etching rate, Figure 3 is a diagram showing the relationship between L1zBsOrM plate etching rate and etchant pl1, and Figure 4 is a diagram showing the relationship between Ab etching rate and etchant liquid temperature. figure,
Figure 5 is a diagram showing an Ai electrode manufactured using the conventional high-temperature alkali etching method, Figure 6 is a diagram showing the AJ2 electrode of a 2JIO MHz odd pager filter manufactured using the method of the example, and Figure 7 is a diagram showing the AJ2 electrode of a 2JIO MHz odd pager filter manufactured using the method of the example. A diagram showing the frequency characteristics of 280 MHz band pager filters manufactured using the conventional method, FIG. 8 is a diagram for explaining the alkaline etching process of AJ2 thick film according to another example method, and FIG. 9 is a diagram showing the conventional three-layer filter. FIG. 10 is a diagram for explaining the lift-off process, and FIG. 10 is a diagram for explaining the etching process using a conventional developer. 21... Ll2I3407 board 22...
......A layer 23...Resist layer 32...An thick film 32a...A thin film (e) 1st Figure 4 Figure 5 Figure 8 Figure 10 (a) Figure 10

Claims (1)

[Claims] A step of forming a metal layer on the surface of the Li_2B_4O_7 substrate, a step of forming a resist layer on this metal layer, exposing and developing this resist layer based on a predetermined pattern, and a step of forming a predetermined portion of the metal layer with KOH. and K_3[Fe(
A method for manufacturing a surface acoustic wave device, comprising the step of etching using an alkaline aqueous solution consisting of a mixed solution of CN)_6] with a pH of 11 to 13 and a temperature of 10 to 50C.