JP2003258592A - Surface acoustic wave element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a highly reliable surface acoustic wave element using a piezoelectric substrate made of lithium tetraborate and suppressing deterioration in the adhesive strength between the piezoelectric substrate 1 and an electrode pad 5. <P>SOLUTION: A plurality of electrode patterns 2 and electrode pads 5 are formed on the lithium tetraborate single crystal substrate 1, and an insulation film 3 is formed to expose part of the electrode pads 5 in the configuration of the surface acoustic wave element. <P>COPYRIGHT: (C)2003,JPO

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface acoustic wave device using a lithium tetraborate single crystal substrate, and more particularly to a surface acoustic wave device having an electrode pad which is optimal for wire bonding. It relates to a wave element. 2. Description of the Related Art Conventionally, surface acoustic wave elements have been used as high-frequency filters applied to mobile communication and the like.
As a material of a piezoelectric substrate constituting the surface acoustic wave element, a single crystal such as lithium niobate (LiNbO ₃ ) or lithium tantalate (LiTaO ₃ ) is widely used. But,
Since these materials do not sufficiently satisfy both the insertion loss and the temperature characteristics when used as a filter, recently the lithium-tetraborate having an electro-mechanical coupling coefficient about 10 times larger than that of quartz and having a zero-temperature coefficient is used. (Li ₂ B ₄ O ₇ ) single crystal substrates are attracting attention. However, since this piezoelectric substrate has a property of dissolving in acid or water, it is required to manufacture a surface acoustic wave element.
It is impossible to form an IDT electrode, a reflector and an electrode pad on the piezoelectric substrate by using an etching solution using acid or water. Therefore, conventionally, a method of forming an electrode pattern on a piezoelectric substrate by a lift-off method that does not require acid or water has been proposed. In the conventional lift-off process, first, a resist pattern is formed on a piezoelectric substrate, and an IDT electrode, a reflector and an electrode pad of an aluminum thin film are formed thereon, and then the resist is removed to remove the aluminum. A thin film is deposited on a piezoelectric substrate. However, when patterning a resist on a piezoelectric substrate, it is necessary to form an overhang shape. However, when the piezoelectric substrate is heated, its shape is deformed. The piezoelectric substrate could not be heated to a high temperature to adhere to the resist stripping surface. Therefore, the adhesion strength of the aluminum thin film to the piezoelectric substrate is reduced, and a dicing tape for dicing is attached to the surface of the piezoelectric substrate on which a pattern such as an IDT electrode is formed in order to separate the wafer of the piezoelectric substrate into chips.
When cut from above, there is a problem that the cutting water used for dicing melts the surface of the lithium tetraborate single crystal substrate, and the adhesion strength between the piezoelectric substrate and the aluminum thin film is further deteriorated. On the other hand, in order to strengthen the adhesion strength between the piezoelectric substrate and the aluminum thin film, an insulating film (for example, Si-based) is formed on the aluminum thin film, and the insulating film on the electrode pads is removed to form the insulating film. A technique has been proposed. Hereinafter, this technique will be described with reference to FIGS. First, the wafer 101 serving as a lithium tetraborate piezoelectric substrate is washed, and an IDT electrode, an electrode pattern 102 of a reflector, and an electrode pad 105 are formed thereon by a lift-off method using an aluminum thin film (FIG. 3).
(A)). Next, the electrode pattern 102, the electrode pad 1
An insulating film 103 is formed on the substrate 05 by sputtering.
(B)) Further, a resist 104 is applied and formed on the insulating film 103 (FIG. 3C). Then, the electrode pad 10
The resist 104 on the substrate 5 is exposed to change its quality, and only the exposed portion is removed by a solvent in a developing step (FIG. 3).
(D)). Next, the portion of the insulating film 103 from which the resist 104 has been removed is removed by a reactive ion etching method (FIG. 3E). Thereby, the electrode pad 105 is exposed. After that, the resist 104 is peeled to form the insulating film 103. (FIG. 3 (f)). After that, the wafer 101 is cut by dicing to form a piezoelectric substrate. However, FIGS. 3 (d), (e),
As shown in FIG. 3F, when the resist 104 on the electrode pad 105 is removed by the developing process of FIG.
In (e) and (f), not only the electrode pad 105 but also the upper surface of the wafer 101 is exposed. Therefore,
When the wafer 101 is cut into chips, the surface of the wafer 101, which is lithium tetraborate, is melted by the cutting water used for dicing, and as shown in FIG. Adhesion strength deteriorates,
For example, when wire bonding is performed on the electrode pad 105, there is a problem that the aluminum thin film is peeled off from the interface between the wafer 101 and the electrode pad 105 and the wire does not stick to the electrode pad. The present invention has been devised in view of the above problems, and has as its object to form an insulating film without exposing an interface between an electrode pad and a wafer. An object of the present invention is to solve the problem that an aluminum thin film is peeled off and to provide a surface acoustic wave device having an electrode pad that is optimal for wire bonding. In order to solve the above problems, a surface acoustic wave device according to the present invention comprises a plurality of IDT electrodes and electrode pads formed on a lithium tetraborate single crystal substrate, A surface acoustic wave device wherein an insulating film is formed on the lithium tetraborate single crystal substrate so that a part of the electrode pad is exposed. According to the structure of the present invention, lithium tetraborate is provided. Since the insulating film is formed on a wafer made of a single crystal substrate so that a part of the electrode pad is exposed, when cutting the wafer into chips, water for cutting used for dicing is applied to the piezoelectric substrate and the electrode pad. And the piezoelectric substrate is not dissolved by water or acid and deteriorates, whereby the adhesion between the piezoelectric substrate and the electrode pad can be maintained. Performance can be improved. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A method for manufacturing a surface acoustic wave device according to the present invention will be described below in detail with reference to the drawings. FIG. 1 is a diagram showing a surface acoustic wave device of the present invention, (a) is a perspective view thereof,
(B) is an enlarged explanatory view of a dotted line portion. FIG.
The surface acoustic wave element shown in (a) is one in which longitudinally coupled resonator type surface acoustic wave filters are connected in two stages. In the surface acoustic wave device A of the present invention, an electrode pattern 2 made of an aluminum thin film and an electrode pad 5 are formed on a piezoelectric substrate 1, and an insulating film 3 is formed thereon. As the piezoelectric substrate 1, a lithium tetraborate single crystal is used. An electrode pattern 2 formed on the piezoelectric substrate 1
Consists of an IDT electrode and a reflector. The electrode pad 5 is formed so as to extend from a part of the IDT electrode of the electrode pattern 2 toward the outer peripheral side of the piezoelectric substrate 1 so that a bonding wire connecting the electrode pad 5 to an external electrode can be connected. Has become. Assuming that the thickness of the electrode pattern 2 and the electrode pad 5 is t1, t1 ≧ 2000 ° is preferable. That is,
When t1 is less than 2000 °, the aluminum thin film becomes thin, so that the adhesion between the electrode pad 5 and the wafer deteriorates, and when the bonding wire is connected to the electrode pad 5, the electrode pad 5 is peeled off or the aluminum thin film penetrates. This is because water and the like pass through the wafer surface and the substrate surface is melted, which is not preferable. As shown in FIG. 1B, the electrode pad 5 includes an exposed portion 5a exposed from the insulating film 3 and a covering portion 5b covered by the insulating film 3. It is preferable that the exposed portion 5a be formed at the center as shown in the figure, because the covering portion 5b completely covers the outer periphery of the electrode pad 5. More preferably, when the width of the coating portion 5b is W, W ≧ 100000Å (10 μm)
It is good to form with the value of m). If the temperature is less than 100,000 °, the surface of the wafer is liable to be eroded by the infiltration of moisture or the like from the interface between the electrode pad 5 and the wafer, and the wafer is liable to be melted. However, the present invention is not limited to this, and the effects of the present invention can be obtained even when a part of the electrode pad 5a is exposed. The insulating film 3 is formed for the purpose of protecting the lithium tetraborate single crystal substrate from water, acid, and the like during the manufacturing process, and preventing the electrode pattern 2 from being oxidized. As a material to be used, a Si-based material, specifically, SiO ₂ or Si ₃ N ₄ is used. This insulating film 3
Is 100 ° when the thickness of the insulating film is t2.
It is preferable that ≦ t2 ≦ 300 °. t2 is 100Å
If the thickness is less than the above, the electrode pattern 2 does not function as an insulating film, and the electrode pattern 2 is easily affected by a change in characteristics due to short-circuiting of the electrodes. In this case, the deterioration of insertion loss becomes a major problem. Next, a method of manufacturing the surface acoustic wave device A according to the present invention will be described with reference to FIG. FIG. 2 is a sectional view taken along line XX of FIG. First, a wafer 10 made of a lithium tetraborate single crystal substrate is washed, and an electrode pattern 2 of an aluminum thin film is formed on the wafer 10 by a lift-off method.
And an electrode pad 5 (FIG. 2A). Next, an insulating film 3 serving as a protective film is formed on the electrode pattern 2 and the electrode pad 5 by sputtering.
(B)) Further, a resist 4 is applied and formed on the insulating film 3 (FIG. 3C). The resist 4 has a thickness of about 1.5 μm by spin coating so as to cover the entire surface of the insulating film 3.
The positive resist of novolak resin is used as the material. Next, the resist 4 on the electrode pad 5
Exposure to change the quality. In this case, a photomask (not shown) is adjusted so that only the portion of the resist 4 on the exposed portion 5a of the electrode pad 5 is selectively exposed. next,
In the developing step, only the exposed portion is removed with a solvent (FIG. 2D). Thereby, a part of the insulating film 3 corresponding to the exposed portion 5a is exposed. Note that an organic alkali-based developer is used as the solvent. afterwards,
The insulating coating 3 exposed after the portion where the resist 4 has been removed is removed by a reactive ion etching method (FIG. 2).
(E)). As a result, the exposed portion 5a of the electrode pad 5 is formed. Then, the insulating film 3 is formed by removing the resist 4. (FIG. 2 (f)). Then, the piezoelectric substrate 1 is formed by cutting the wafer 10 by dicing. Here, the feature of the present invention is shown in FIG.
In the developing step (d), selective exposure is performed using a photomask.
The resist 4 is deteriorated by irradiating light so as to be narrower than the plane area of the electrode pad 5. Thereby, in the step of developing the resist 4, the removed resist becomes smaller than the area of the electrode pad 5, and the region of the insulating film 3 corresponding to the removed region of the resist 4 can be removed by reactive ion etching. It is. In this way, as shown in FIG. 2F, a part of the electrode pad 5 can be covered with the insulating film 3 after the removal of the resist 4. Thus, according to the structure of the present invention, it is possible to prevent water or the like from entering between the electrode pad 5 and the piezoelectric substrate 1, and to reduce the bonding strength between the electrode pad 5 and the piezoelectric substrate 1, Further, since the insulating film can be formed without exposing the interface between the electrode pad 5 and the wafer 10, the problem that the aluminum thin film is peeled off from the interface between the electrode pad 5 and the wafer 10 is solved, and the electrode pad optimal for wire bonding is solved. And a surface acoustic wave element having the following. Further, in the exposure, the exposed portion 5a can be formed only by changing the photomask, so that no additional steps are required, the cost is not increased, and the highly reliable surface acoustic wave element A can be formed very easily. Can be manufactured. As described above, according to the structure of the present invention, the exposure between the lithium tetraborate single crystal substrate and the electrode pad as in the conventional case can be suppressed. The adhesion strength between the lithium tetraborate single crystal substrate and the electrode pad due to the peeling of the electrode pad can be suppressed without melting the lithium oxide single crystal substrate. As a result, the occurrence of wire bonding defects does not occur, the reliability is improved, the number of inspection steps can be reduced, and the number of inspection steps in the steps can be simplified.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 (a) is a perspective view of a surface acoustic wave device of the present invention,
(B) is an enlarged explanatory view of a dotted line. FIGS. 2A to 2F are views for explaining a manufacturing process of the surface acoustic wave device of the present invention. 3 (a) to 3 (g) are views for explaining a manufacturing process of a conventional surface acoustic wave device. [Description of Signs] 1: Piezoelectric substrate (lithium tetraborate single crystal substrate) 2: Electrode pattern 3: Insulating film 4: Resist 5: Electrode pad 5a: Exposed portion 5b: Covered portion

   ────────────────────────────────────────────────── ─── Continuation of front page    F term (reference) 5J097 AA24 AA32 DD25 DD29 FF01                       HA03 KK09

Claims (1)

Claims: 1. A method for manufacturing a semiconductor device comprising the steps of: forming a plurality of I on a lithium tetraborate single crystal substrate;
A surface acoustic wave device comprising: a DT electrode and an electrode pad; and an insulating film formed on the lithium tetraborate single crystal substrate so that a part of the electrode pad is exposed.