JP2888158B2 - Manufacturing method of surface acoustic wave device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a process for manufacturing a surface acoustic wave device, and more particularly to manufacturing an electrode film.

[0002]

2. Description of the Related Art Surface acoustic wave devices (hereinafter abbreviated as SAW devices) which are frequently used as mobile communication devices.
Generally uses LiNbO ₃ (hereinafter, referred to as “piezoelectric material”) as its piezoelectric material.
An LN) or LiTaO ₃ (hereinafter abbreviated as LT) single crystal substrate is used, and the electrode film is made of Al or Al.
System alloy film is used. It is known that when a high power signal is input to a SAW device, a large stress is applied to an Al electrode by a surface acoustic wave generated on a piezoelectric substrate, and Al atoms move, that is, so-called stress migration occurs. . When this failure occurs, the transmission characteristics of the SAW filter deteriorate (the insertion loss increases and the Q value decreases).

Conventionally, Al-based alloys containing a small amount of Cu, Si, Ti or the like have been used as electrode materials in order to increase the stress migration resistance of electrodes of SAW devices, that is, the power durability. However, although the power resistance of the electrode improves as the concentration of the added element increases, problems such as increased insertion loss and etching residue during electrode processing occur. There was a problem that high-concentration addition that satisfies the power property cannot be performed.

[0004] As a new countermeasure against stress migration, Japanese Journal Applied Physics (Jpn. J. Appl. Phys.) No. 33
Volume 3015 page (1994), 36 degree rotation Y cut LT
When the substrate is etched with hydrofluoric acid and an Al film is formed by an ion beam sputtering method, a (111) -oriented single-crystal Al film is obtained. A SAW filter using this film as an electrode is a conventional polycrystalline Al film. It is reported that they have extremely excellent power durability compared to electrodes.

[0005] In general, LT and LN crystal substrates are liable to undergo composition fluctuations due to the escape of Li and oxygen at their surface portions, and a compositionally modified layer or a degraded layer is formed within a range of several tens of nanometers (nm) on the surface layer. Therefore, it is known that this is a major obstacle to epitaxially growing an Al film on the substrate surface. Conventionally, as a countermeasure against the metamorphic layer or the deteriorated layer, etching removal from the substrate surface has been performed by the above-described chemical etching method.

[0006]

However, if the etching treatment is performed only with hydrofluoric acid as in the method of manufacturing a single-crystal Al film described in the above-mentioned article, the surface of the LT or LN crystal having a normal crystal structure can be obtained. It was difficult to obtain a single crystal Al film uniformly over the entire substrate surface, and as a result, it was found that the production yield of the SAW device was low.

An object of the present invention is to provide a method for manufacturing a surface acoustic wave device having excellent power durability using an LN or LT single crystal substrate. It is in.

[0008]

According to the present invention, there is provided a method of manufacturing a surface acoustic wave device, comprising forming a single crystal Al or Al-based alloy electrode on a lithium niobate and lithium tantalate single crystal substrate. In the method of manufacturing a wave device, a step of removing a surface altered layer of the single crystal substrate, which comprises sequentially performing an ion implantation step, a chemical etching step, and an oxidation treatment step before forming a single crystal Al or Al-based alloy electrode. It is characterized by having. Here, an inert gas or nitrogen (other than that is undesirable because it affects the SAW characteristics) is used in the ion implantation step, and a hydrofluoric acid-based solution or an alkali solution (the substrate is
Other than insoluble), the oxidation treatment step is hydrogen peroxide solution,
It is preferable to use a strong oxidizing agent such as ozone, oxygen plasma or oxygen radical beam.

[0009]

The single-crystal piezoelectric substrates LN and LT used in a surface acoustic wave device such as a SAW filter are materials that cannot be easily etched by an acid or alkali solution.
Further, even if the etching progresses, a deteriorated layer is easily left on the etched surface, and it is difficult to obtain a proper normal surface of the crystal substrate. However, if ion implantation treatment with an inert gas or nitrogen is performed before etching the substrate surface layer of LN and LT with an acid or alkali, the subsequent etching with an acid or alkali solution easily proceeds, In addition, it was found that the etching was finished in a state where no altered layer remained on the etched surface. The effect of this ion implantation is that, since the substrate surface is damaged by ions, the etching resistance due to acid or alkali is reduced, and the etching is facilitated. Further, by performing an oxidation treatment as a post-treatment after the chemical etching, a more normal crystal plane could be obtained. This is because, by supplementing oxygen that easily escapes from the substrate surface with an oxygen radical beam, a compositionally modified layer that is slightly present in the substrate surface layer can be reduced, and the original crystal plane of the substrate can appear.

[0010] By performing the above etching process, L
In N and LT, since a crystal plane without an altered layer appears uniformly over the entire surface of the substrate,
A single crystal Al film having excellent power durability can be easily and uniformly grown, and as a result, SA having excellent power durability can be obtained.
A W device can be manufactured with high yield.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.

For LN and LT, the following methods (1) and (2) are used as comparative examples, and the following method (3) is used as an example.
Surface treatment is performed on ten substrates according to the method described in above, and an Al film is deposited by ion beam sputtering,
The single crystallinity was examined by reflection high-energy electron diffraction (RHEED), and the frequency of obtaining a single-crystal Al film was measured. (1) Only chemical etching (2) Inert gas ions (He ⁺ , Ar ⁺ , Kr ⁺ , X
e ⁺ ) or nitrogen ions (N ⁺ ) at an ion energy of 100 keV and a dose of 1 × 10 ¹⁵ to 1 × 10 ¹⁷ / cm.
After ion implantation to the substrate surface layer in the ^second range, from the through ion implantation, chemical etching of (1) performing a chemical etching (3) (2), hydrogen peroxide, ozone, oxygen plasma And an oxidation treatment using an oxygen radical beam or the like.

FIG. 1 shows a process flow showing the surface treatment step (3).

When hydrofluoric acid (HF) at a temperature of 100 ° C. is used as an etchant in Table 1, a mixed solution having a volume ratio of hydrofluoric acid (HF): nitric acid (HNO ₃ ) = 1: 2 at a temperature of 200 ° C. is shown in Table 2. Table 3 shows the temperature of 200 ° C.
The results obtained when performing a chemical etching using a mixed solution consisting of hydrofluoric acid: phosphoric acid = 2: 1 as an etchant. It can be seen that the frequency of obtaining a single crystal Al film is highest on any of the substrates subjected to ion implantation, chemical etching, and oxidation. A, B, in the oxidation treatment step in the table,
C and D indicate that the oxidation treatment was performed using a hydrogen peroxide solution, ozone, oxygen plasma, and an oxygen radical beam, respectively. In addition, it was confirmed that the irradiation with the oxygen radical beam had peaks at wavelengths of 615.8 nm and 777.4 nm.

[0015]

[Table 1]

[0016]

[Table 2]

[0017]

[Table 3]

The etchant is heated at a temperature of 5 in the same manner.
Almost the same results as in Tables 1 to 3 were obtained even when using an alkaline solution such as caustic soda or potassium hydroxide at 0 to 100 ° C.

Further, in the substrate pretreatment in which the order of the respective steps was changed, almost no single-crystal Al film could be obtained.

[0020]

As described above, according to the present invention, L
The surface treatment of the N and LT substrates can be effectively performed. As a result, a single crystal Al film can be surely grown, and a surface acoustic wave device excellent in power durability can be manufactured at a high yield. You can do it.

[Brief description of the drawings]

FIG. 1 is a surface treatment process diagram for explaining the method of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 2 Altered layer 2a Ion plantation layer 2b Oxygen deficiency layer 3 Ions 4 Etchant 5 Oxygen radical

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-5-199062 (JP, A) JP-A-5-82502 (JP, A) JP-A-3-22605 (JP, A) JP-A 52-1990 119849 (JP, A) JP-A-6-112488 (JP, A) JP-A-4-167431 (JP, A) JP-A-4-94539 (JP, A) JP-A-2-103935 (JP, A) JP-B2-47885 (JP, B2) (58) Fields investigated (Int. Cl. ⁶ , DB name) H03H 3/08-3/10 H01L 21/308

Claims (4)

(57) [Claims] 1. A method for manufacturing a surface acoustic wave device comprising forming a single-crystal Al or Al-based alloy electrode on a lithium niobate and lithium tantalate single-crystal substrate. Forming a surface-altered layer of the single crystal substrate by sequentially performing an ion implantation step, a chemical etching step, and an oxidation treatment step before forming the surface acoustic wave device. 2. The method for manufacturing a surface acoustic wave device according to claim 1, wherein ion implantation is performed with an inert gas or nitrogen. 3. The method for manufacturing a surface acoustic wave device according to claim 1, wherein chemical etching is performed using a hydrofluoric acid-based solution or an alkaline solution. 4. The method for manufacturing a surface acoustic wave device according to claim 1, wherein an oxidizing treatment is performed by using a hydrogen peroxide solution, ozone, oxygen plasma, and oxygen radicals.