JPH03242012A - Manufacture of surface acoustic wave device - Google Patents

Abstract

PURPOSE:To execute the film thickness control of an electrode and to attain fine adjustment of the center frequency of a surface acoustic wave device by providing a film thickness measurement process, a film thickness discrimination process and an etching process after an electrode forming process. CONSTITUTION:A film thickness measuring process 28 measures the film thickness of an electrode formed on a piezoelectric substrate, and a film thickness discrimination process 29 decides whether or not the film thickness of the electrode on the piezoelectric substrate is equal to the setting film thickness depending whether difference between the film thickness of the electrode and the setting film thickness is equal to zero. An etching process 30 applies the etching in response to the difference from the film thickness to the electrode when the difference from the film thickness is not zero, and the film thickness is measured at the film thickness measuring process 28. The film thickness measuring process 28, the film thickness decision process 29 and the etching process 30 are repeated till the difference from the film thickness is decided to be zero by the film thickness decision process 29. Thus, the film thickness control of the electrode being a decisive factor of the center frequency is facilitated.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention relates to a method for manufacturing a surface acoustic wave device using surface acoustic waves propagating through a piezoelectric substrate, and particularly a method for manufacturing a surface acoustic wave device using a surface acoustic wave propagating through a piezoelectric substrate. This relates to a manufacturing method.

(Prior Art) Conventionally, there have been technologies in this field, such as those shown in FIGS. 2 and 3, for example. The configuration will be explained below using figures.

FIG. 2 shows a configuration example of a conventional method for manufacturing a surface acoustic wave device, and is a flowchart when a lift-off method is used to form electrodes. A process diagram is shown in FIG.

Hereinafter, with reference to FIG. 3, by the manufacturing method shown in FIG. 2,
For example, a case will be described in which a surface acoustic wave filter, which is a surface acoustic wave device, is manufactured.

(I>Substrate Cleaning Step 1 The piezoelectric substrate 11 made of a piezoelectric material shown in FIG. 3(a) is cleaned using an organic solvent or the like to remove contaminants adhering to its surface.

(II) Resist film forming step 2 On the top surface of the piezoelectric substrate 11 cleaned in the step (1) above,
As shown in FIG. 3(b), a resist is applied to form a resist film ↓2.

(III) Resistance 1 - Pattern Formation Step 3 An electrode pattern is transferred to the resist film 12 formed in the above (old process) as shown in FIG. The resist pattern 13 is formed by developing the pattern.

(IV) Metal film deposition step 4 In the step (DI>), the substrate 11 on which the Lugis pattern 13 was formed is set in a metal film deposition apparatus 14 as shown in FIG. 3(d).

The metal film deposition device 4 is, for example, an electronic film deposition device 1, a vapor deposition device, a crucible 14a filled with aluminum (A, which is an evaporation source), and a crucible A in a crucible 14a. It has an electron gun 4b for irradiating the deuteron beam e.Furthermore, the metal film deposition device 14 includes a substrate holder 14c.
and, for example, a film thickness monitor device 1 equipped with a crystal oscillator sensor.
4d is provided.

First, the substrate 11 is attached to the substrate holder '14C of the metal film deposition apparatus 14, and the inside of the apparatus is evacuated.

Next, the electron beam e is emitted from the electron gun 14b, and the electron beam e is irradiated onto Ai in the crucible L4a.
i is evaporated to form AJ! on the surface of the substrate 11. A hairy metal film 15 is formed.

(X') Resist pattern removal step 5 After forming the metal film 15 in the step (IV), the resist pattern 13 and unnecessary portions of the metal film 15 are removed, as shown in FIG. 3(e). Multiple interdigital electrode fingers 1
An electrode 16 with 6a is formed. After that, see Figure 3 (
As shown in f), a surface acoustic wave filter 19 is formed by providing an input terminal 17, a neutral force terminal 18, etc. using metal such as gold (Au), and the present manufacturing process is completed.

In one surface acoustic wave filter manufactured as described above, when an electric signal S1 is input to the input terminal 17, the electric signal SL is transmitted to the surface of the piezoelectric substrate 11 at the interdigital electrode finger ↓6a on the input terminal 17 side. is converted into a surface acoustic wave W1 excited by the surface acoustic wave W1, and the surface acoustic wave W1 further propagates through the piezoelectric substrate 11,
The surface acoustic wave W1 is converted into an electric signal S2 by the interdigital electrode end 16a on the output terminal 18 side, and is output to the output terminal 18. From this, the electrical signal S1 is filtered to become an electrical signal S2 of a predetermined bandwidth and a desired center frequency f.Here, the center frequency f of the surface acoustic wave filter 19 is It can be expressed as follows by the propagation speed (■) of the wave Wl and the wavelength λ (that is, the pitch of the interdigital electrode fingers 16a).

(In formula 1, wavelength λ is a value that cannot be changed once the interdigital electrode finger ↓6a is formed.
Propagation speed■. is a value that changes depending on the state of the surface of the piezoelectric substrate 11, that is, the presence or absence of the interdigital electrode fingers 16a. By forming the interdigital electrode fingers 16a, the propagation velocity 0 becomes smaller due to its weight, but it is not possible to calculate how much it becomes smaller. Therefore, the thickness of the metal film 15 forming the interdigital electrode fingers 16a is varied in advance to change its weight, and the center frequency f is determined. The film thickness (set film thickness) of the electrode 6 is determined based on the data.

In the manufacturing process shown in FIG. 3, the electrode 16 is
This has the advantage that the planar shape of the electrode 16 can be miniaturized.

(Problems to be Solved by the Invention) However, the method for manufacturing the surface acoustic wave device having the above configuration has the following problems.

When forming the electrode 16 in the metal film deposition step 4, it is difficult to control the film thickness of the electrode 6, and fluctuations in the center frequency fo are unavoidable. Normally, the metal film deposition device 14 and the like are provided with a film thickness monitor device 14d, which includes, for example, a crystal resonator sensor, in order to measure the thickness of the metal film 15 to be deposited.

The film thickness monitor device 14d indirectly determines the film thickness of the metal film 15 that would have been deposited on the piezoelectric substrate 11 based on the film thickness of the metal film that was deposited on the film thickness monitor device 14d. Therefore, for example, the film thickness monitor device 14d and the piezoelectric substrate 1
Due to the non-uniformity of the adhesion state of A and f7 due to the positional difference in 1, it is difficult to accurately measure the thickness of metal film 5, and the thickness measurement usually takes about ±10%. This error causes an error in the center frequency f of one surface acoustic wave filter. is displaced. This center frequency f. This displacement can be covered by widening the bandwidth when the surface acoustic wave filter 19 is used as a broadband filter, but is a fatal defect when used as a narrowband filter.

In order to solve this problem, for example, it is possible to take one end of the piezoelectric substrate 11 out of the metal film deposition device 14 and directly measure the film thickness on the metal film 5 using an external film thickness measuring device or the like. Conceivable.

However, in this case, it is necessary to take the piezoelectric substrate 11 out of the metal deposition apparatus 1-4, which is maintained in a vacuum state, which causes the surface of the metal film 1-5 to oxidize, etc. AJ! on the top surface of the metal film 15! Even if the metal film is deposited again, peeling or the like is likely to occur at the interface between the metal film deposited again and the metal plate 1-5, resulting in deterioration of the reliability of the electrode 16. Furthermore, when measuring the thickness of the metal film 15 using the film thickness measuring device, it becomes necessary to remove the resist pattern 13 in order to accurately measure the thickness.

As described above, even if a method of directly measuring the film thickness of metal [15] was used, the problems of the prior art described above could not be satisfactorily solved.

The present invention provides a method of manufacturing a surface acoustic wave device that solves the problem of the prior art, which is that it is difficult to control the thickness of the electrode, which is a determining factor of the center frequency.

(Means for Solving the Problems) In order to solve the above-mentioned problems, the present invention provides a method for manufacturing a surface acoustic wave device, in which a metal film is deposited on a piezoelectric substrate to a thickness greater than a predetermined film thickness. An electrode forming step of selectively forming an electrode, and a film thickness of the electrode formed on the piezoelectric substrate,
A film thickness measurement step of measuring using a film thickness measurement device, determining a film thickness difference between the measured value in the film thickness measurement step and the set film thickness, and determining whether or not the film thickness difference is zero; When the judgment result is zero, there is a film thickness judgment step in which the manufacturing process is terminated, and when the judgment result is not zero, the electrode is etched with an etching sheet according to the film thickness difference, and the film thickness measurement step is performed. The etching process is sequentially performed.

(Function) According to the present invention, since the method for manufacturing a surface acoustic wave device is configured as described above, the electrode forming step is performed by attaching an electrode having a film thickness thicker than a desired predetermined film thickness to a piezoelectric substrate. The film thickness measurement step works to measure the film thickness of the electrode formed on the piezoelectric substrate.The film thickness determination step determines whether the film thickness difference is zero or not. The etching process works to determine whether or not the film thickness of the electrode on the piezoelectric substrate is equal to the set film thickness.If the film thickness difference is not zero, the etching process is performed at an intensity and time according to the film thickness difference. The film thickness of the electrode etched in this etching step is further measured in the film thickness measuring step. The thickness determination step and the etching step are repeated until the film thickness difference is determined to be zero in the film thickness determination step, and when the film thickness difference is determined to be zero, the present manufacturing process ends.

Therefore, the above problem can be solved.

(Example) Figure 1 shows a method for manufacturing a surface acoustic wave device according to an example of the present invention, and is a schematic flowchart when a lift-off method is used to form electrodes. An example of a specific manufacturing process diagram is shown in FIG. 4. In FIG. 1, the electrode forming step 20 and the film thickness measuring step 28 are connected by a connector A.

The manufacturing method shown in FIG. 1 will be described below with reference to FIG. 4. In this case, the manufacturing method shown in FIG. 1 is used to manufacture, for example, a surface acoustic wave filter as shown in FIG. 3 (f>).

(i) Electrode formation step 20 ■Substrate cleaning step 21 Lithium tantalate (1-
A piezoelectric substrate 31 made of a piezoelectric material such as iTa03> is cleaned with an organic solvent or the like to remove contaminants on the surface of the substrate.

: Axel resist film forming step 22 For example, a negative type resist is applied onto the piezoelectric substrate 3L cleaned in the step ('i1') to form a resist film 32 as shown in FIG. 4(b). 4-electrode pattern transfer step 23 The resist film 32 formed in the step (2) above is exposed to light using the mask pattern 33 for electrode formation as a mask, for example, as shown in FIG. [Translated to 32.

■Developing step 24 Resist film 3 to which the electrode pattern was transferred in the step (■)
2 is developed.

(2)02 plasma associating step 25 If the resist film 32 developed in the step (2) is subjected to 02 plasma athering to remove unnecessary residues of the resist film 32, the photolithography technique shown in FIG.
) A resist pattern 34 for forming electrodes is formed.

■Metal film deposition step 26 Using the resist pattern 34 formed in the step (■) as a mask, a metal film 35 such as Al is deposited on the piezoelectric substrate 31 as shown in FIG. 4(e). .

Here, the metal film 35 is deposited in the following manner using, for example, the same metal film deposition apparatus 1-4 used in the metal film deposition step 4 in FIG.

First, the desired center frequency f. The set film thickness of the electrode required to obtain T1. That is, the set thickness T1 of the metal film 35 is checked in advance. The film thickness and center frequency f of the electrode. An example of this relationship is shown in FIG.

FIG. 5 is a correlation diagram between the film thickness of the electrode and the center frequency.

As can be seen from this figure, for example, the center frequency f. -2,
If 48 GHz is desired, the set thickness of the electrode, that is, the set thickness of the metal film 3'' must be about 30A.

Next, the metal film 35 is deposited so as to be thicker than the desired set film thickness Tl (=530 people), but if the film thickness of the metal film 35 at this time is T2 (-T1-7-ΔT>) ,
Considering the error of the film thickness monitor device 14d, the film thickness T2 is calculated as 6 by the indicated value of the crystal oscillator sensor of the film thickness monitor device 14d.
Set it to about 00A.

Thereafter, the metal film 35 is deposited on the piezoelectric substrate 31 by irradiating Al in the crucible 14a with the electron beam e from the electron t14b while monitoring the film thickness with the film thickness monitor device 14d.

■Resist pattern removal step 27 After the step (■) above, if the resist pattern 34 and unnecessary parts of the metal film 35, etc. are removed, as shown in FIG. 4(f), almost the same as FIG. Electrode 3 having a planar shape
6 is formed.

Here, the resist pattern 34 is removed by, for example, immersing it in a solvent and applying ultrasonic waves, as well as removing the unnecessary metal film 35 on the resist pattern 34. As a result, an electrode 36 having a film thickness T2=6008 is formed.

(ii) M Thickness Measuring Step 28 The wA thickness of the electrode 36 formed in the step (i) is measured using, for example, a contact type film thickness measuring device 37 as shown in FIG. 4 (g). This film thickness measuring device 37 includes a probe 37a made of, for example, a diamond needle, and a control section 37b composed of a sensor (not shown) that detects the deflection of the probe 37a, a recorder that records the sensing results, etc. Under the control of the control section 37b, the probe 37a traces the surface of the piezoelectric substrate 31, thereby measuring the film thickness T2 of the electrode 36.

(iii) Film thickness determination step 29 After measuring the film thickness T2 in the step (ii) above, the 6 film thickness differences between the film thickness T2 and the set film thickness T1 are determined, and the 6 film thickness differences are zero. In this case, the main manufacturing process is ended.

(iv) Etching step 30 If the film thickness difference obtained in step (iii) is not zero, then the film thickness is Etching is applied to the electrode 36 so that the difference becomes zero.Etching at this time includes, for example, '2 ricic acid, acetic acid,
The entire surface of the web is etched for several seconds by etching the web 1 using a mixture of 1 part nitric acid and 1 part water. As a result, the film thickness of the electrode 36 changes from T2 to T3.

(V) Film Thickness Determination Step 29 The film thickness T3 of the electrode 36 formed in the step (IV) is measured again using, for example, a film thickness measuring device 37.

Measure the film thickness T3 and find it 7'? After that, the film thickness T3 and the set film thickness T
The film thickness difference ΔT from 1 is determined.

Thereafter, if the film thickness difference 6 is not zero, the etching step 30, film thickness measurement step 28, and film thickness determination step 29 are repeated until the film thickness difference ΔT becomes zero.

When the film thickness difference ΔT becomes zero, the desired set film thickness T
1 is formed, and then the piezoelectric substrate 31
If input terminals, output terminals, etc. (not shown) are provided on the surface acoustic wave filter 38 as in the single surface acoustic wave filter shown in FIG. 3, the surface acoustic wave filter 38 is formed, and the present manufacturing process is completed.

This embodiment has the following advantages.

In this example, in addition to the electrode forming step 20, a film thickness measuring step 28, a film thickness f determining step 29, and an etching step 30 are performed.
has been established. Therefore, the film thickness of the electrode 36 can be controlled accurately.
and can be easily performed, and the center frequency f of the surface acoustic wave filter 38. It is possible to make fine adjustments. For example, in the manufacturing method shown in FIG. 2, the thickness of the electrode 6 of the surface acoustic wave filter 19 varied by about 50A, but in the manufacturing method shown in FIG. The variation in thickness is about ±IOA. Therefore, the center frequency f. The variation in IO is reduced from several MHz to about 1 to 2 MHz. As a result, especially the surface acoustic wave filter 3
8 as a narrowband filter, the center frequency f.

Since the setting accuracy of is increased, its frequency characteristics are significantly improved.

Note that the present invention is not limited to the illustrated embodiment, and various modifications are possible. Examples of variations include the following:

(A> The flowchart shown in FIG. 1 schematically shows one configuration example of the manufacturing method of the present invention, and the configuration can be modified. For example, in FIG. 1, the electrode formation step Although the electrode forming step 20 is configured using a lift-off method, it is also possible to configure the electrode forming step 20 using a method other than the lift-off method. In that case, each step 21 to 27 in FIG. 1 is changed. For example, A metal film 3 is formed on the entire surface of the piezoelectric substrate 31.
5, a resist pattern '34 is formed on the metal wA35, and the electrode 36 is formed by etching the metal film 35 using the resist pattern '34 as a mask. Good too. Also,
In the manufacturing method shown in FIG. 1, the electrode forming step 20. It is also possible to add other steps to the film thickness measurement step 28, the film thickness determination step 29, and the etching step 30, such as a final cleaning step after the electrode 36 is formed.

(B) The manufacturing techniques used in each step of FIG. 4<a) to (i) are shown as examples, and may be changed. For example, in the electrode pattern transfer step 23, the resist 32 is made of a negative type and a corresponding mask pattern 33 is used. It's okay.

The metal film deposition device 14 used to deposit the metal film 35 in the metal film deposition step 26 may be configured with a device other than the electron beam evaporation device. The film thickness measuring device 37 used in the film thickness measuring step 28 may be configured not only as a contact type device but also as a non-contact type device, for example. Etching process 30
The etching applied to the electrode 36 may be wet etching using another etchant or dry etching depending on the constituent material of the metal film 35. Furthermore, depending on the material selectivity of the etching applied to the electrode 36, the piezoelectric substrate 3 may be etched during the etching.
For example, an etching mask may be provided on the top of the substrate 1.

(C) The constituent material, shape, etc. of the surface acoustic wave filter 38 can be changed. For example, the piezoelectric substrate 31 is
In addition to iTa0, it may also be composed of L iN b 03, crystal, or the like. The metal film 35, that is, the electrode 36 is made of not only Ai but also, for example, AJ! It may also be formed using an A, R-based alloy, etc. in which impurities are added in a 1-1 range.

(D> The present invention can be widely applied to surface acoustic wave devices other than surface acoustic wave filters.

(Effects of the Invention) As described above in detail, according to the present invention, a film thickness measurement process, a film thickness determination process, and an etching process are provided after the electrode formation process. Therefore, the film thickness of the electrode can be controlled with high accuracy, and the center frequency of the surface acoustic wave device can be finely adjusted, and the desired center frequency can be set accurately and easily.

Therefore, a surface acoustic wave device having a frequency characteristic of /fh can be manufactured easily and at low cost.

[Brief explanation of drawings]

FIG. 1 is a flowchart showing a method for manufacturing a surface acoustic wave device according to an embodiment of the present invention, FIG. 2 is a flowchart showing a method for manufacturing a conventional surface acoustic wave device, and FIG. 3 is similar to the flowchart in FIG. FIG. 4 is a diagram showing a specific manufacturing process corresponding to the flowchart in FIG. 1, and FIG. 5 is a diagram showing the correlation between the film thickness of the electrode and the center frequency. 20... Electrode formation step, 31... Piezoelectric substrate, 35.
...metal film, 36...electrode, 37...film thickness measuring device, three...surface acoustic wave device.

Claims (1)

[Claims] An electrode forming step of selectively forming an electrode thicker than a predetermined film thickness by depositing a metal film on a piezoelectric substrate; and an electrode film formed on the piezoelectric substrate. A film thickness measuring step of measuring the thickness using a film thickness measuring device, determining a film thickness difference between the measured value in the film thickness measuring step and the set film thickness, and determining whether or not the film thickness difference is zero. and when the judgment result is zero, the manufacturing process is terminated; and when the judgment result is not zero, the electrode is etched at an etching rate according to the film thickness difference, and the film thickness measurement step is performed. 1. A method for manufacturing a surface acoustic wave device, characterized in that a step of returning and etching is sequentially performed.