JPS5936409A - Measuring method of electrode width of surface acoustic wave filter - Google Patents

Abstract

PURPOSE:To discriminate indefectible goods, by measuring the resistance value of a checking electrode stuck into a pattern constituting a filter after the electrode etching process and obtaining the width of crossing finger electrodes on a basis of the measured result. CONSTITUTION:In a filter element using surface acoustic waves which are excited by crossing electrodes of a thin film conductor provided on a piezoelectric substrate, a pattern 5 for maesurement of parallel resistance consisting of plural conductor stripes which have the same width and pitch as crossing finger electrodes and a pattern 6 for measurement of resistance consisting of one conductor stripe whose electrode width W is equal to the total sum of electrode widths of said plural stripes are added to the electrode pattern constituting the filter. Resistance values of checking electrodes 5 and 6 are measured after the electrode etching process, and the width of crossing finger electrodes is obtained on a basis of measured results.

Description

[Detailed Description of the Invention] Object of the Invention] The present invention relates to a surface acoustic wave filter (“surface acoustic wave filter”).
Also called. ), and particularly relates to a method for measuring the interdigital electrode width, which affects the center frequency of filter response characteristics.

Prior Art] A surface acoustic wave filter is composed of thin film electrodes provided on a piezoelectric substrate. A basic configuration example of a resonant filter aimed at reducing loss is a two-pronged filter consisting of an interdigital transducer 1.2 and conductor strips 2 and reflectors 3, 4 as shown in Figure 1. It is a resonator. The center frequency of the filter is determined by the sound velocity of the piezoelectric substrate and the electrode pitch of the interdigital electrodes.
In the ao336°YX plate, when the center frequency is IGH2, the wavelength λ is approximately 4 μm, and the electrode width (/l/4) is 1i.
It is tm.

However, since the propagation speed of surface waves differs between the free surface and the conductor film surface, if the width of the side etching stain changes during the electrode etching process of device fabrication, the wave propagation speed will be affected and the center frequency of the filter will also change. do. FIG. 2 shows the relationship between the electrode width ratio (the ratio of the conductor part width to the free surface part width) and the center frequency.

In FIG. 2, W is the width of the electrode part p and the free surface part F,
ΔW is the amount of side etching.

The amount of side etching varies depending on the film thickness of the electrode, photoresist process, etching conditions, etc. For this reason, a problem arose in that the center frequency of the filter element varied between substrates or within a substrate.

Conventionally, there was no suitable inspection method and judgment was made based on the response characteristics after the device fabrication was completed, which had the disadvantage that substrates that did not meet the specifications due to frequency fluctuations were sent to the final process, resulting in a significant drop in device yield. there were.

(Object of the Invention) The present invention was made in view of the above circumstances, and its purpose is to eliminate the above-mentioned drawbacks in the inspection of conventional surface acoustic wave filters, and to improve the electrode width immediately after the etching process. An object of the present invention is to provide a method for measuring the electrode width of a surface acoustic wave filter, which makes it possible to determine whether the product is non-defective through measurement.

[Detailed description of the invention]

The above object of the present invention is to provide a filter element using surface acoustic waves excited by interdigital electrodes of a thin film conductor provided on a piezoelectric substrate, in which an electrode pattern constituting the filter has a width and pitch equal to that of the interdigital electrodes. By adding a test electrode pattern that can measure the parallel resistance of multiple conductor stripes and the resistance of one conductor stripe having an electrode width equal to the sum of the electrode widths of the multiple stripes, the electrode etching process This is achieved by a method for measuring the electrode width of a surface acoustic wave filter, which is characterized in that the resistance value of the test electrode is later measured and the width of the interdigital electrode is determined from the result.

Embodiments of the Invention] Hereinafter, embodiments of the present invention will be described in detail based on the drawings.

FIG. 3(a), Φ) is a pattern for electrode width measurement showing an embodiment of the present invention. , (a) interdigital electrode and 'PM
Parallel resistance measurement pattern 5 of multiple (one) kt conductor stripe rows with the same pitch (each λ/4.λ/2), (b) has a width W (equal to the sum of the stripe widths in (a)) λ/4xn) shows a resistance measurement pattern 6 of one At conductor strip. Note that the lengths of the stripes are the same in (a) and υ. Since it can be considered that the resistivity and film thickness of the measurement patterns 5 and 6 and the At electrode film are the same, the resistance value differs only depending on the side etching amount ΔW. By placing such a measurement pattern near the filter pattern, it becomes possible to perform measurements under the same At film and etching conditions as the filter element.

The amount of reduction in electrode width due to the side etching amount ΔW is (
In a), it is 2·Δw−n, and in Φ), it is 2·ΔW.

When the measured resistance value in (a) is R1 (Ω) and the measured value in (b) is R2 (Ω), ΔW under the above conditions is ΔW= (R1-R2)W/2 (R1-R2)
...(1). Therefore, the relationship between the increase in resistance value and the amount of side etching can be obtained.

The line width after etching is L=λ/4−ΔW (2). Further, since the relationship between the electrode width and the center frequency of the filter can be obtained from FIG. 2 as described above, it is possible to determine the quality of the product by considering the specifications of the filter.

In order to know the degree of variation in electrode width within a substrate, it is sufficient to distribute the above measurement pattern within a photomask. As a practical example, as shown in Figure 4, a measurement pattern 7 is placed on a part of the wire bonding pad of the filter pattern.
．． There is a method of inserting 8 and repeating it in the photomask together with the filter pattern. Particularly in high frequency bands, the electrode pitch becomes smaller and the ratio occupied by the interdigital electrode portion becomes smaller, so there is an advantage that adding a test pattern does not particularly affect the chip size.

It goes without saying that the measurement method of this embodiment can also be applied to filters with structures other than those illustrated.

As described above, according to this embodiment, by performing the element evaluation of the surface acoustic wave filter immediately after the At etching process, there is an effect that only the substrates determined to be good can be sent to the subsequent process.

〔Effect of the invention〕

As described above, according to the present invention, in a filter element that uses surface acoustic waves excited by interdigital electrodes of a thin film conductor provided on a piezoelectric substrate, the interdigital electrodes and the width A testing electrode pattern is added that can measure the parallel resistance of a plurality of conductor stripes with the same pitch and the resistance of one conductor stripe having an electrode width equal to the sum of the electrode widths of the plurality of stripes. After the etching process, the resistance value of the test electrode is measured, and the width of the interdigital electrode is determined from this result. This allows element evaluation to be performed at an intermediate stage of the manufacturing process, allowing only non-defective products to be processed later. This makes it possible to send it to the process, which has a large economic effect.

[Brief explanation of drawings]

Fig. 1 is a diagram of the electrode structure of a resonant filter, Fig. 2 is a diagram showing the relationship between side etching amount and center frequency variation, Fig. 3 is a diagram showing a pattern for measuring electrode width according to the present invention, and Fig. 4 FIG. 2 is a diagram showing an example in which a filter pattern and a measurement pattern are integrated. 5 to 8... Resistance measurement pattern for inspection. Figure 1 Figure 2 Figure 1 σ・2 zu・／ρ ρ／ρ・2 434
'%AY 3rd part 4- Figure 7

Claims (1)

[Claims] In a filter element using surface acoustic waves excited by interdigital electrodes of a thin film conductor provided on a piezoelectric substrate, a plurality of conductor stripes having the same width and pitch as the interdigital electrodes are arranged in parallel in an electrode pattern constituting the filter. A test electrode pattern is added that can measure the resistance and the resistance of one conductor stripe having an electrode width equal to the sum of the electrode widths of the plurality of stripes, and after the electrode etching process, the resistance value of the test electrode is measured. A method for measuring the electrode width of a surface acoustic wave filter, characterized in that the width of the interdigital electrode is determined from the result.