JP3345779B2 - SAW chip and method of manufacturing SAW device using the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a surface acoustic wave (SA)
W) using SAW (Surface Acoustic)
c Wave) chip and an improvement in a method of manufacturing a SAW device using the SAW chip.

[0002]

2. Description of the Related Art In various electronic devices such as communication devices, computers and watches, SAWs (Surface Acoustic Wave) are used as electronic components such as resonators and filters.
e) SAW devices using chips are used. In this SAW chip, a quartz crystal having a good temperature characteristic and capable of easily performing shape processing such as etching and mechanical processing is used as a piezoelectric material.

FIG. 9 is a process chart showing an example of a method of manufacturing such a SAW chip, and FIG. 10 is a process chart showing an example of a method of manufacturing a SAW device from the manufactured SAW chip.

In FIG. 9A, the surface of a quartz wafer 2 is cleaned, and in FIG. 9B, an electrode film 3 made of, for example, aluminum or an aluminum alloy is formed on the quartz wafer 2. Next, as shown in FIG. 9C, for example, a photoresist 4 corresponding to a predetermined electrode pattern is arranged on the electrode film 3. And, for the reasons described below, by dry etching technology such as reactive ion etching and microwave plasma etching,
For example, the electrode film 3 is etched using chlorine gas. When the electrode film 3 is etched as shown in FIG. 9D and the photoresist 4 is removed, for example, interdigital electrodes, reflectors, wiring patterns and the like are formed on the quartz wafer 2. Become.

[0005] Thereafter, as shown in FIG.
The electrode film 3 of the SAW chip 1 is etched to adjust, for example, the resonance frequency and the filtering characteristics of the chip 1. Here, since the electrode film 3 is etched, the adjustment is performed while increasing the resonance frequency of the SAW chip 1.

Thereafter, the crystal wafer 2 is diced (cut) (not shown) so as to be each of the SAW chips 1, and the characteristics and appearance of each of the SAW chips 1 are inspected.

Next, a base 1 as shown in FIG.
0 is prepared, and as shown in FIG. 10B, the SAW chip 1 which is a quartz chip is fixed to the package base 10 by, for example, an adhesive 11. Then, FIG.
0 (C), wire bonding is performed with the base 10 side, and the SAW chip 1 and the base 1 are bonded by a bonding wire 12 made of, for example, aluminum wire.
0 is electrically connected. Here, when a drive voltage is applied to the SAW chip 1 via the bonding wire 12,
The frequency characteristic is set to be slightly higher than desired.

[0010] Then, as shown in FIG. 10 (D), the SAW chip 1 uses, for example, C
Plasma etched using F4 gas, SAW
The chip 1 is adjusted to lower the frequency. here,
The reason why CF4 gas is used is that aluminum is not etched and only quartz is etched. For this reason, as a result, the frequency of the SAW chip 1 is adjusted in a lowering direction.

Thereafter, as shown in FIG. 10E, the cap 13 is seam-welded to the base 10, for example, to seal the SAW chip 1 in a nitrogen atmosphere, for example. Then, the SAW chip 1 is heat-treated after sealing,
The characteristics and leak test of the SAW chip 1 are performed, and the SAW chip 1 is tested.
The device 1A is completed.

[0010]

As described above, an electrode forming step of forming a comb-shaped electrode or the like on a quartz substrate for forming the SAW chip 1 (see FIGS. 9C and 9C).
In (D)), a dry etching technique is used.

This is for the following reason.

In a SAW device, the higher the frequency of the vibration output, the smaller the width of the electrode pattern formed on the quartz substrate 2 and the higher the electrode processing accuracy. For example, in the case of a 433 MHz SAW resonator, the width of the comb-shaped electrode is 1.8 μm. For example, in the case of a 868 MHz SAW resonator, the width of the comb-shaped electrode is 0.9 μm. For this reason, when a wet etching method using phosphoric acid is used to form an electrode as in the past, the etchant penetrates the interface between the resist 4 and the electrode 3 to process an electrode having a fine width. Cannot be performed with high accuracy.

Therefore, when the dry etching method as described with reference to FIG. 9 is used, a new problem that abnormal frequency fluctuation occurs in the process after the description with reference to FIG. 10 occurs. SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to provide a highly reliable SAW chip and a method of manufacturing a SAW device using the same without causing abnormal frequency fluctuation even in a process of incorporating the SAW chip into a base. And

[0014]

According to the first aspect of the present invention, there is provided a method of manufacturing a SAW chip for forming an electrode pattern on a piezoelectric substrate by dry etching.
An electrode film forming step of forming an electrode film of aluminum or an aluminum alloy on the piezoelectric substrate, and a dry etching step of performing dry etching until the surface of the piezoelectric substrate is exposed so that the electrode film has a predetermined electrode pattern; A cleaning step using phosphoric acid as a cleaning liquid for removing residual aluminum on the exposed piezoelectric substrate surface.

According to the configuration of the first aspect, the following operations are provided. According to the study of the present inventors, in the processing step after forming electrodes on the piezoelectric substrate, the cause of the abnormal frequency fluctuation is that aluminum cut by plasma or the like in the step of forming electrodes by dry etching. It remains on the surface of the piezoelectric substrate.

A SAW chip in which such aluminum remains on the surface of the piezoelectric substrate is incorporated into a package base, and the frequency is adjusted by plasma etching using, for example, a commonly used fluorine-based gas such as CF4 gas. When it is performed, first, aluminum fluoride is generated by a chemical reaction, and this aluminum fluoride further reacts with oxygen in the air, and Al2O3 is gradually formed. That is, it has been clarified by the present inventors that if such a change occurs on the surface of the piezoelectric substrate, the propagation characteristic of the surface acoustic wave changes and the frequency fluctuates abnormally.

Therefore, when forming a SAW device, prior to incorporating the SAW chip into the base and adjusting the frequency, in the step of forming the SAW chip, if the electrode film made of aluminum or an aluminum alloy is formed by dry etching, First, dry etching is performed until the surface of the piezoelectric substrate is exposed, and the exposed surface of the piezoelectric substrate is cleaned to remove residual aluminum. As a result, since the SAW chip is incorporated into the base and the frequency is adjusted without aluminum remaining on the surface of the piezoelectric substrate, even if a fluorine-based gas is used in the frequency adjustment,
Due to chemical reaction, residual aluminum is converted to fluorine in air,
Further, Al2O3 is not formed due to the combination with oxygen, and the change in the propagation characteristics of the surface acoustic wave due to the formation of Al2O3 can be prevented.

[0018]

According to a second aspect of the present invention, in the configuration of the first aspect, after the cleaning step, an anodic oxide film forming step of forming an anodic oxide film on the surface of the electrode pattern is provided.

According to the second aspect , if the anodic oxide film is formed on the surface of the electrode pattern, the surface of the electrode pattern is protected by the hard oxide film. Therefore, even if plasma etching using a fluorine-based gas is performed in the subsequent frequency adjustment step, the electrode pattern surface is not affected by reactive fluorine such as fluorine radicals generated thereby.

According to a third aspect of the present invention, there is provided a method of manufacturing a SAW device using a SAW chip in which an electrode pattern is formed on a piezoelectric substrate by dry etching. An electrode film forming step of forming a film, a dry etching step of performing dry etching until the piezoelectric substrate surface is exposed so that the electrode film has a predetermined electrode pattern, and a residual aluminum on the exposed piezoelectric substrate surface. A cleaning step for removing, an anodic oxide film forming step of forming an anodic oxide film on the surface of the electrode pattern after the cleaning step, and a SAW chip having the anodic oxide film formed on a base of a predetermined package. Using a fluorine-based gas for the fixing step and the SAW chip fixed to the base or the SAW chip before fixing. Plasma and a step of frequency adjustment by etching, by the manufacturing method of the SAW device is achieved.

According to a fourth aspect of the present invention, in the third aspect , phosphoric acid is used as a cleaning solution in the cleaning step .

[0023]

Preferred embodiments of the present invention will be described below in detail with reference to the accompanying drawings.

FIG. 1 is a perspective view showing a preferred embodiment of the SAW chip of the present invention. First, referring to FIG.
The W device 100 will be described. The SAW device 100 in FIG. 1 is, for example, a SAW resonator, and includes a SAW chip 110, a base 120, a cap 130, and the like.

The SAW chip 110 includes a piezoelectric substrate 111,
IDT (International IDT)
digital Transducer ") 11
2. It has a reflector 113 and the like.

The piezoelectric substrate 111 is made of, for example, quartz, LiT
This is a substrate formed of a piezoelectric material such as aO3 or LiNbO3. In this embodiment, a quartz substrate 111 is used.

The IDT 112 and the reflector 113 are
For example, the piezoelectric substrate 111 is made of aluminum or an alloy of aluminum and copper, and is formed on the piezoelectric substrate 111 by a dry etching process described later.

That is, the SAW resonator 10 of the present embodiment
0 is a frequency whose output frequency is high, for example, 868 MHz or more. Therefore, in the SAW resonator 100,
The electrodes forming the interdigital transducer 112 and the reflector 113 are thin and have a width of about 0.9 μm. A dry etching technique has been adopted in response to the process of forming such a thin electrode.

The IDT 112 has a function of exciting a surface acoustic wave by, for example, supplying a driving voltage and outputting a vibration of a predetermined frequency. The reflectors 113, 113 are I
The IDT 112 is formed so as to sandwich the DT 112.
Reflects the surface acoustic wave excited by the
The surface acoustic waves are confined in the reference numerals 3 and 113. The base 120 is, for example, a ceramic box having a hollow portion 121 formed in a central portion thereof. The SAW chip 110 is fixed to the hollow portion 121 by, for example, an adhesive. Further, the base 120 has a wiring portion (not shown) formed from the hollow portion 121 to the outer peripheral bottom surface 122 so that the SAW chip 110 can be electrically connected to the outside. The electrode portion of the base 120 is bonded to the IDT by bonding wires 140 and 140.
112 and is electrically connected. The cap 130
The lid is a plate-like lid, and is fixed to an upper portion of the base 120 by, for example, seam welding or the like in order to seal the SAW chip 110 in a vacuum or in a nitrogen atmosphere. Note that a package is constituted by the base 120 and the cap 130.

Here, when manufacturing the SAW device 100 as shown in FIG. 1, the final adjustment of the frequency of the SAW chip 110 is performed, for example, as described later.
After the bonding wires 140, 140 are connected to 10 and before sealing with the cap 130, the etching is performed by plasma etching using a fluorine-based gas.

FIG. 2 shows such a SAW device 100.
FIG. 3 is a flowchart schematically illustrating a manufacturing process for manufacturing the SAW device.
FIG. 3 is a process chart illustrating an example of a method for manufacturing an AW chip 110.

Referring to FIG. 2, first, an electrode film made of aluminum is formed on the quartz surface (ST1). This step is shown in FIGS. 3A and 3B.

That is, in the step of forming the electrode pattern, as shown in FIG. 3A, the surface of the quartz wafer 22 is washed with pure water, and in FIG.
An electrode film 23 made of, for example, aluminum or an aluminum alloy is formed thereon by a vapor deposition method or a sputtering method.

Next, in ST2, the electrode film 23 is etched to form an electrode pattern 26. To perform this step, first, as shown in FIG. 3C, for example, a photoresist 24 corresponding to a predetermined electrode pattern is disposed on the electrode film 23, for example.

Next, the electrode film 23 is dry-etched by reactive ion etching with a parallel plate type apparatus using, for example, a chlorine (Cl) gas, for example, a mixed gas of BCl 3, Cl 2 and N 2.

That is, as described above, the SAW device 100 of this embodiment has a very narrow electrode pattern, a line width of about 0.9 μm, and a film thickness of about 0.1 μm. For this reason, when the wet etching method using phosphoric acid is used as conventionally performed, the etching solution permeates the interface between the resist 24 and the electrode film 23, and the electrode with a fine width is processed with high precision. Therefore, this dry etching step is performed. Then, after the electrode film 23 is etched until the surface of the quartz substrate 22 is exposed, Al removal cleaning in ST3 of FIG. 2 is performed (ST3).

This ST3 is performed before the resist 24 is still removed as shown in FIG. That is, in this state, the quartz substrate 22 is carried into the processing tank and is immersed in a predetermined cleaning liquid, for example, phosphoric acid, so that A
1 Removal washing is performed. The conditions for this Al removal cleaning are as follows: the substrate is washed in a 5% aqueous solution of ammonium hydrogen phosphate for 3 minutes at a temperature of 25 ° C., rinsed with pure water for 10 minutes, and then dried by spinning. . Not only phosphoric acid but also KOH, NaOH,
An aqueous solution of LiOH, tetramethylammonium hydroxide, ammonia or the like, or an aqueous solution having a chloric acid-based etching ability may be used.

As a result, the residual Al adhered to the surface of the quartz substrate 22 during the dry etching is removed by washing away with phosphoric acid. Next, the resist 24 is removed, and as shown in FIG. 3D, for example, the interdigital electrode 112, the reflector 113, and the electrode pattern 26 forming the wiring pattern and the like are formed on the quartz substrate 22. Become.

Here, the above-mentioned Al removal cleaning is performed by using the resist 2
4 can be performed after the removal. The washing conditions in this case include, for example, washing with 85% by weight of phosphoric acid at a temperature of 35 ° C. for 1 minute, rinsing with pure water for 10 minutes, and then spinning and drying. To

Next, at ST4 of FIG.
An anodic oxide film 25 is coated on 6 by an electrochemical surface reaction or the like. This state is shown in FIG.

Next, the process proceeds to ST5 in FIG. 2 to perform frequency adjustment. That is, in the state up to FIG. 3E, when a driving voltage is applied to the SAW chip 110, the frequency characteristics thereof are set to be slightly higher than desired.

Therefore, in step ST5, the SAW chip 110
Plasma-etched using a fluorine-based gas, SA
The W chip 110 is adjusted to lower the frequency. Here, the reason why the fluorine-based gas is used is that when it is used, aluminum is not etched and only quartz is etched. Therefore, as a result, the SAW chip 1
The frequency is adjusted so as to lower the frequency of No. 10.

The fluorine-based gas used for this frequency adjustment is CHF3, F2, NF in addition to CF4 described above.
3 CCIF3, C2F6, CBrF3, CH
2F2, CHClF2, C3 F8, CC12
F2, C4 F8, CHCl2 F2, C4 F
A material containing at least one of 8 CHCl2 F, CBr2 F2 and CC13F is used. The frequency adjustment may be performed after the Al removal cleaning and before the fixing of the SAW chip 110 to the base described with reference to FIG. 4, or, as described later, the fixing of the SAW chip 110 to the base. It may be done later. If the oxide film 25 is formed on the electrode film 23 as described above, even if the plasma etching using a fluorine-based gas is performed in this frequency adjustment step (ST5), the fluorine radicals generated by the plasma etching are generated. The electrode pattern surface is not affected by reactive fluorine such as.

After the anodic oxide film 25 is coated on the electrode pattern 26 as shown in FIG.
As shown in (F), dicing (cutting) is performed at the position of C, so that each SAW chip 110 is cut.

The completed SAW chip 110 is mounted on a base 120 as shown in FIG.

First, the base 12 as shown in FIG.
0 is prepared, and the SAW chip 110 is fixed to the base 120 by, for example, the adhesive 11 as shown in FIG. Thereafter, as shown in FIG.
Wire bonding is performed on the side, and SAW chip 110 and base 120 are electrically connected by bonding wire 140 made of, for example, aluminum wire.

After the removal of the resist 24 described with reference to FIG. 3, if the frequency adjustment is not performed before the SAW chip 110 is incorporated into the base 120, the SAW chip 110 is connected to the SAW chip 110 via the bonding wire 140 at this stage. When a drive voltage is applied, the frequency characteristics are set to be slightly higher than desired.

For this reason, as shown in FIG. 4D, the SAW chip 110 is plasma-etched with a fluorine-based gas using a predetermined frequency adjusting device, and is adjusted to lower the frequency. The type of the fluorine-based gas in this frequency adjustment is the same as the condition described above.

Thereafter, as shown in FIG. 4E, the cap 130 is seam-welded to the base 120 to seal the SAW chip 110 in, for example, a nitrogen atmosphere.

This embodiment is configured as described above, and has the following advantages.

First, since the electrodes of the SAW chip 110 are formed by dry etching, fine processing is possible, which is suitable for producing a high-frequency, high-performance SAW device 100.

Since a trace amount of the Al component on the quartz surface after the dry etching is removed in the Al cleaning step, the residual Al component may react and change on the quartz surface of the SAW chip 110. Therefore, it is possible to prevent the propagation characteristics of the surface acoustic wave from being adversely affected, thereby effectively preventing abnormal changes in the frequency characteristics of the product, and preventing the occurrence of defective products, thereby improving the product yield. be able to.

FIG. 5 is a graph in which the horizontal axis represents the processing step and the vertical axis represents the frequency change with reference to the frequency after frequency adjustment. As shown in the upper part, in a conventional SAW device in which only dry etching is used for forming an electrode, after a processing step A (for example, a sealing step), or after a processing step B (for example, an annealing treatment) of a later step. The variation and the shift are large with respect to the frequency after the frequency adjustment. On the other hand, in the SAW device in which Al cleaning is performed according to the embodiment of the lower stage, the variation and the frequency shift are extremely reduced even when the time elapses or the processing history is added.

Further, before the frequency adjustment, the SAW chip 11
If an anodic oxide film is formed on the electrode surface of No. 0, the electrode surface is prevented from being attacked by the reactive fluorine component of the fluorine-based gas used at the time of frequency adjustment.

FIG. 6 shows the results of the composition analysis on the electrode surface. The horizontal axis represents the depth of the electrode film 23 corresponding to the SiO2 sputter etching rate conversion, and the vertical axis represents the component content (atomic percent). I have. FIG. 6 shows the electrode film 23 after frequency adjustment by plasma etching with a fluorine-based gas without forming the anodic oxide film 25 on the surface of the electrode 23.
FIG. 7 shows the component state corresponding to the depth from the surface (in terms of the SiO2 sputter etching rate).
3 shows a state in which the frequency is adjusted by plasma etching using a fluorine-based gas after forming the anodic oxide film 25 on the three surfaces.

As can be seen by comparing FIGS. 6 and 7,
When the anodic oxide film 25 is formed on the surface of the electrode 23, the content of fluorine (F) near the surface of the electrode 23 is small.

For this reason, as shown in FIG. 8, after the anodic oxide film 25 is formed on the surface of the electrode 23, the frequency is adjusted by plasma etching using a fluorine-based gas.
In the case where the anodic oxide film 25 is not formed on the surface of the electrode 23 and the frequency is adjusted by plasma etching with a fluorine-based gas, the amount of frequency shift according to the standing time after the frequency adjustment is smaller compared to D, and the performance Is stable.

[0058]

As described above, according to the present invention,
It is possible to provide a highly reliable SAW chip and a method for manufacturing a SAW device using the same without causing abnormal frequency fluctuation even in a process of incorporating the SAW chip into a base.

[Brief description of the drawings]

FIG. 1 is a schematic perspective view showing a preferred embodiment of a SAW device of the present invention.

FIG. 2 is a flowchart simply showing a manufacturing process of a SAW chip used for the SAW device of FIG. 1;

FIG. 3 is a schematic process diagram simply showing a manufacturing process of a SAW chip used for the SAW device of FIG. 1;

FIG. 4 is a schematic process diagram simply showing a process of fixing a SAW chip used in the SAW device of FIG. 1 to a base.

FIG. 5 is a view for explaining a state of frequency change corresponding to a processing step in the SAW device of FIG. 1 and a conventional SAW device.

FIG. 6 is a view showing a fluorine-containing state of an electrode film when an anodic oxide film is not formed on an electrode surface of a SAW chip.

FIG. 7 is a diagram showing a fluorine-containing state of the electrode film when an anodic oxide film is formed on the electrode surface of the SAW chip of the embodiment.

FIG. 8 is a diagram showing a comparison of frequency shift between the SAW device of FIG. 1 and a conventional SAW device.

FIG. 9 is a schematic process diagram simply showing a manufacturing process of a SAW chip used for a conventional SAW device.

10 is a schematic process diagram simply showing a process of fixing a SAW chip used in the SAW device of FIG. 9 to a base.

[Explanation of symbols]

 100 SAW device 110 SAW chip 111 Piezoelectric substrate (quartz substrate) 112 Electrode 120 Base 130 Cap 140 Bonding wire

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-2-94911 (JP, A) JP-A-10-135759 (JP, A) JP-A-62-285011 (JP, A) 283970 (JP, A) JP-A-11-36086 (JP, A) JP-A-8-46474 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H03H 3/10 H01L 21 / 304 647 H01L 21/3065 H03H 9/145

Claims (4)

(57) [Claims] 1. A method for manufacturing a SAW chip, wherein an electrode pattern is formed on a piezoelectric substrate by dry etching, comprising: an electrode film forming step of forming an electrode film of aluminum or an aluminum alloy on the piezoelectric substrate; A dry etching step of performing dry etching until the surface of the piezoelectric substrate is exposed, and a cleaning step of using phosphoric acid as a cleaning liquid for removing residual aluminum on the exposed surface of the piezoelectric substrate so that the electrode pattern is formed. A method for manufacturing a SAW chip, comprising: 2. The method according to claim 1, further comprising an anodic oxide film forming step of forming an anodic oxide film on the surface of the electrode pattern after the cleaning step. 3. A method for manufacturing a SAW device using a SAW chip for forming an electrode pattern on a piezoelectric substrate by dry etching, comprising: an electrode film forming step of forming an electrode film of aluminum on a piezoelectric substrate; A dry etching step of performing dry etching until the surface of the piezoelectric substrate is exposed so as to form a predetermined electrode pattern; a cleaning step of removing residual aluminum on the exposed surface of the piezoelectric substrate; An anodic oxide film forming step of forming an anodic oxide film on the surface of the electrode pattern; a step of fixing the SAW chip having the anodic oxide film formed thereon to a base of a predetermined package; SAW before fixation
Adjusting the frequency of the chip by performing plasma etching using a fluorine-based gas on the chip. The method according to claim 4, wherein said cleaning step, characterized by the use of phosphoric acid as a cleaning liquid, a SAW device manufacturing method according to claim 3.