JPH11220351A - Surface acoustic wave device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an SAW(surface acoustic wave) device which has such a layout of electrodes that can prevent the resist falling to the utmost when the SAW device is produced. SOLUTION: This SAW device S includes one or more pieces of drive electrodes 5 which are provided on a piezoelectric substrate 1. Every electrode 5 consists of an exciting electrode 2 and the reflector electrodes 3 and 4 whose fingers 2c and 3c are connected to two rows of bus bars 2a and 2b which are formed with a prescribed space secured between them. Then one or more opening parts or discontinuous parts having a >=80% electrode loading factor in a circle of a diameter equal to the bus bar width are formed on at least one of both bus bars of the electrode 5.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface acoustic wave device such as a surface acoustic wave (SAW) filter or a resonator having an excitation electrode provided on a piezoelectric substrate, and more particularly, to miniaturization, improvement of characteristics, and high yield. It relates to a possible and excellent surface acoustic wave device.

[0002]

2. Description of the Related Art In general, a surface acoustic wave device comprises a comb-shaped electrode or a driving electrode comprising a comb-shaped electrode and a reflector on a piezoelectric substrate, a routing electrode connected to such a driving electrode, and the like. Of the surface acoustic wave device.

[0003] The drive electrodes are usually manufactured by either a lift-off method or an etching method. Here, the etching method includes a dry etching method and a wet etching method. In the case of the dry etching method, corrosion of Al (aluminum) used as an electrode material or Al-Cu (aluminum-copper) alloy is induced. There is. Further, the wet etching method is not practical because the precision of patterning is deteriorated, and it is difficult to produce a comb-shaped electrode having a designed shape. Therefore, in order to produce a surface acoustic wave device with high precision and no electrode corrosion,
The lift-off method is suitably performed.

FIGS. 4A to 4E show an example of a process for manufacturing a surface acoustic wave device by a lift-off method. First, FIG.
A piezoelectric substrate 51 is prepared as shown in FIG. Next, as shown in FIG. 4B, a positive photoresist layer 52 is applied on the piezoelectric substrate 51. Next, in the state shown in FIG. 4B, exposure is performed while covering the piezoelectric substrate 51 with a photomask (not shown), and further, exposure is performed from the back surface of the piezoelectric substrate 51. Here, the exposure from the back surface of the piezoelectric substrate 51 is as follows.
From the surface of the photoresist layer 52, the photoresist layer 52
By increasing the exposure intensity on the side of the piezoelectric substrate 51, the cross-sectional shape of the photoresist layer 52 is formed to have a reverse tapered shape as shown in FIG.

Next, the piezoelectric substrate 51 on which the photoresist layer 52 is formed is immersed in a predetermined developing solution. At this time, since the photoresist layer 52 is of a positive type, the photoresist layer in the exposed area is dissolved in a developing solution, and FIG.
As shown in (c), only the photoresist layer in the unexposed area remains. By the exposure from the back surface described above, the exposure intensity of the photoresist layer on the piezoelectric substrate 51 side is higher than that of the surface of the photoresist layer. It becomes.

Next, as shown in FIG. 4D, an electrode material such as Al is formed on the wafer by a thin film forming method such as a vacuum evaporation method. Here, the particles of the electrode material are perpendicularly incident on the wafer, and the electrode film 5 is formed on the photoresist layer 52.
3, the electrode film 53 becomes discontinuous at the reverse tapered portion of the photoresist layer 52. Thereafter, the wafer is immersed in a predetermined stripping solution to remove the photoresist layer and the electrode film 53 formed thereon, and the patterning of the electrode film 53 is completed as shown in FIG.

In such a lift-off method, it is necessary to ensure a reverse taper necessary for the electrode film 53 to be discontinuous in order to perform patterning with high precision. Must be thicker.

[0008]

In recent years, in order to cope with the miniaturization required for the surface acoustic wave device, a device has been devised in which the comb-shaped electrode and the routing electrode are densely arranged in a smaller area. For this reason, the comb-shaped electrode and the routing electrode are arranged without any gap. However, at this time, a so-called resist falling defect occurs in which the photoresist layer at the comb-shaped electrode portion is not properly patterned and falls.

This means that the center frequency is 900 MHz, for example.
In this case, the electrode line width of the comb-shaped electrode of the surface acoustic wave filter is about 1 μm, and thus occurs when the interval between the comb-shaped electrode and the lead-out electrode is small. When this phenomenon occurs, the periodic structure of the comb-shaped electrode is broken, and the surface acoustic wave cannot be confined in the comb-shaped electrode, so that the characteristics of the resonator and the filter deteriorate.

Further, when the degree of resist fall is worse, the opposing electrodes of the comb electrodes are short-circuited, so that characteristics such as a resonator and a filter cannot be obtained at all. If such a defect occurs, the characteristics of the surface acoustic wave device cannot be obtained. Therefore, in order to produce a small and good surface acoustic wave device with high yield, it is necessary to prevent the resist from falling down. .

SUMMARY OF THE INVENTION It is an object of the present invention to provide a surface acoustic wave device having an electrode arrangement capable of preventing a resist from falling down as much as possible when manufacturing the surface acoustic wave device.

[0012]

According to a surface acoustic wave device of the present invention for solving the above-mentioned problems, a plurality of electrode fingers are connected to two rows of bus bars formed at a predetermined distance on a piezoelectric substrate. One or more drive electrodes each comprising an excitation electrode and a reflector electrode, wherein at least one bus bar of the drive electrodes has an opening having an electrode loading ratio of 80% or less in a circle having a bus bar width in diameter. It is characterized in that one or more portions or discontinuous portions are formed.

The electrode loading ratio is a metallization ratio.

[0014]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a plan view showing an example of a surface acoustic wave device according to the present invention. This surface acoustic wave device S is formed in two rows on a piezoelectric substrate 1 at a predetermined distance. And at least one drive electrode 5 composed of an excitation electrode 2 and reflector electrodes 3 and 4 having a plurality of electrode fingers 2c and 3c connected to each of the bus bars 2a and 2b. In the bus bar (2a in this case), one or more openings or discontinuous portions (hereinafter, also referred to as electrode non-loaded portions) having an electrode loading rate of 80% or less in a circle having a diameter of the bus bar are formed. Things.

In this manner, by providing the electrode non-loaded portion on the bus bar 2a, the photoresist is not collapsed even if the drive electrode is patterned by the lift-off method using the positive type photoresist. This principle can be explained as follows.

FIG. 6 shows an optical path and an exposure state at the time of exposure when there is no electrode-unloaded portion on the bus bar of the conventional drive electrode. M is a photomask, and M1 and M2
Is a mask area. When the lift-off is performed, the photoresist layer 52 serving as the electrode loading section is removed by development. When a positive resist is used, the electrode loading section is exposed. At this time, the light L reflected on the back surface of the piezoelectric substrate 51,
The non-exposed portion where L is irregularly reflected and the electrode is not loaded is exposed from the back surface by the reflected light. As a result, during development, the photoresist layer is developed on the substrate 51 side, and the remaining photoresist layer becomes thinner, and as a result, a phenomenon that the photoresist falls (resist collapse) occurs.

Here, by optimizing the total exposure such as the exposure time by increasing or decreasing the amount of exposure, it is possible to prevent the photoresist from falling down to some extent. In the region where the amount of exposure locally increases from the back surface of the piezoelectric substrate 51 as shown in FIG. 6, excessive exposure cannot be avoided.

In this phenomenon, particularly in the gap portion of the bus bar in the surface acoustic wave electrode pattern, the overexposure locally occurs, and the resist easily collapses. this is,
This is because the gap of the bus bar becomes the above-mentioned local overexposure region because the Al electrode is spread on both sides. When the width of the bus bar is narrow, the resist does not fall down. That is, in the case of a pattern having a wide bus bar, the resist is likely to fall in the gap portion of the bus bar.

On the other hand, in the surface acoustic wave S of the present invention, at least one of the bus bars (in this case, 2a) of the drive electrode 5 is loaded with an electrode in a circle C having a diameter of the bus bar width shown in FIG. Since one or more electrode non-loaded portions (openings 2d and 3d in this case) having a ratio of 80% or less are formed, the above-described photoresist collapse does not occur.

The electrode loading ratio of 80% or less is determined as follows. For example, when the width of the bus bar is 20 μm or less, the resist does not collapse in the gap portion, but when the width of the bus bar is 30 μm or more. That is, when the width of the bus bar is 30 μm,
When the electrode loading ratio is 100%, the resist collapses, and in other words, it does not occur when the electrode loading ratio is 80% or less (the electrode loading ratio when a 20 μm bus bar is arranged in a 30 μm diameter circle). So this ratio is
In the case where the width of the bus bar is 30 μm or more, if the ratio is not more than the same, it is expected that no resist collapse will occur.

The above-mentioned electrode non-loading portion is shown in FIGS.
As shown in (1), a notch may be formed to form a discontinuous portion. That is, as shown in FIG. 3 (a), cutouts 12d, 13d cut linearly are formed on the excitation electrode 12 side and / or the reflector electrode 13 side within the circle C1 of the width of the bus bar, and the electrode loading is performed. The ratio may be set to 80% or less, or, as shown in FIG.
Notches 22d, 23d cut stepwise on the side and / or the reflector electrode 23 side may be formed so that the electrode loading ratio is 80% or less, or as shown in FIG. 3 (b). In the circle C3 having the width of the bus bar, the excitation electrode 32
Even if notches 32d and 33d cut in a U-shape are formed on the side of the reflector electrode 33 and / or the reflector electrode 33, the same effect as described above can be obtained even if the electrode loading ratio is 80% or less.

[0023]

[Example 1] 3 inches in diameter and 0.35 m in thickness
m, a positive resist was applied to a thickness of 0.9 μm by spin coating on a 36 ° YX lithium tantalate single crystal substrate whose front surface was mirror-finished and whose back surface was polished with GC # 1000.

With an exposure machine using Deep-UV light,
Surface exposure 10.0 mJ / cm ² , back exposure 1.3 mJ / cm 2
After developing, a comb-shaped electrode having a minimum line width of 1.0 .mu.m was patterned in such a manner as shown in FIG.

Here, an electrode non-loading portion having a length of 50 μm and having an electrode loading rate of 50% was arranged between the comb-shaped electrode, the routing electrode for connecting the comb-shaped electrode and the wire bonding pad, and the comb-shaped electrode. By providing such an electrode non-loaded portion, resist collapse did not occur during patterning of the electrode.

After that, an Al electrode is vapor-deposited by electron beam with a film thickness of 4000.degree., Immersed in a resist stripping solution heated to 80.degree. C., and further subjected to ultrasonic waves to completely strip unnecessary resist and electrode material to complete patterning. did.

Thereafter, the patterned wafer was cut by dicing, bonded and cured in an SMD package with epoxy resin. After bonding a 35 μφ Al wire on the pad portion of the SMD package and the Al pad on the chip by ultrasonic bonding, the package lid was sealed and completed.

The characteristics were measured using a network analyzer, and it was confirmed that the filter satisfies the specifications. From the characteristics, it was also confirmed from the characteristics that the failure due to the falling of the resist did not occur.

[Example 2] A photomask having an electrode-unloaded portion on a comb-shaped electrode and a bus bar of a reflector was prepared, and a resist was applied to the same type of substrate as in Example 1 using this photomask.

With an exposure machine using Deep-UV light,
Surface exposure 11.6 mJ / cm ² , back exposure 1.3 mJ / cm
After exposure in step ² , development was performed, and the electrodes of a ladder-type filter in which four comb electrodes having a minimum line width of 1.0 μm were arranged in series and three in parallel as shown in FIG. Patterned. Here, an electrode non-loading pattern having the same shape as the photomask was formed on the comb-shaped electrode and the bus bar of the reflector, and the resist pattern between the comb-shaped electrode and the reflector was normally patterned.

Thereafter, the electrodes were deposited by an electron beam, and the unnecessary resist was stripped to complete the patterning. Since the resist pattern between the comb electrode and the reflector was normally patterned, the opposing electrodes of the comb electrode were not short-circuited via the reflector. Thereafter, assembling was performed in the same manner as in Example 1, and the characteristics were evaluated. As a result, it was confirmed that the products were also good in characteristics.

[0032]

As described above in detail, according to the electrode arrangement of the surface acoustic wave device of the present invention, when patterning a photoresist by the lift-off method, the localization of the exposure amount due to irregular reflection from the back surface of the piezoelectric substrate is performed. This prevents the resist pattern from falling down during development, thereby preventing the periodic structure of the drive electrodes from being disturbed, and electrically short-circuiting between the electrodes to reduce the characteristics as a resonator or filter. There is no defect that cannot be obtained.

Further, it is possible to arrange the drive electrodes and the routing electrodes in a dense manner, and it is possible to provide a small and highly reliable surface acoustic wave device.

[Brief description of the drawings]

FIG. 1 is a plan view illustrating an example of a surface acoustic wave device according to the present invention.

FIG. 2 is an enlarged plan view of a portion B in FIG. 1;

FIGS. 3A to 3C are partial plan views each illustrating an example of another surface acoustic wave device according to the present invention.

FIGS. 4A to 4E are schematic cross-sectional views illustrating steps of manufacturing a drive electrode of a surface acoustic wave device.

FIG. 5 is a cross-sectional view illustrating a photoresist after lift-off.

FIG. 6 is a schematic cross-sectional view illustrating a state in which a photoresist is exposed.

FIG. 7 is a plan view illustrating a conventional drive electrode.

[Explanation of symbols]

1: piezoelectric substrate 2: excitation electrode 3, 4: reflector electrode 5: drive electrode 2d, 3d, 12d, 13d, 22d, 23d, 32
d, 33d: Opening (or discontinuous part) 2a, 2b, 3a: Bus bar S: Surface acoustic wave device

Claims (1)

[Claims] 1. An elastic structure in which one or more drive electrodes comprising an excitation electrode and a reflector electrode each having a plurality of electrode fingers connected to two rows of busbars formed at a predetermined distance on a piezoelectric substrate. In a surface acoustic wave device, at least one opening or discontinuous portion having an electrode loading rate of 80% or less in a circle having a bus bar width is formed in at least one side of the drive electrode. Surface acoustic wave device.