JP2620945B2 - Manufacturing method of thin film array ultrasonic transducer - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic transducer, and more particularly to a thin-film array ultrasonic transducer suitable for non-destructively observing a fine structure.

[Conventional technology]

2. Description of the Related Art Conventionally, an array sensor that transmits and receives ultrasonic waves having a frequency of 1 to 10 MHz is used in an ultrasonic tomography apparatus. However, recently, such as semiconductor package inspection and material defect inspection,
It is necessary to see finer structures, and for that purpose, it is necessary to improve the resolution by using high-frequency ultrasonic waves having a frequency of 50 to 100 MHz. Since the piezoelectric body that transmits and receives ultrasonic waves in this region has a pressure of 50 μm or less, a piezoelectric body formed as a thin film is used.

Conventionally, the thin-film ultrasonic transducer is formed as a single transducer and mechanically scans in a plane to obtain information and form an image. An ultrasonic microscope using this method is discussed in "Solid State Physics" 17 (1982), pp. 51-57.

[Problems to be solved by the invention]

In the above prior art, the substrate on which the piezoelectric thin film is formed is used as a lens, and the ultrasonic waves are radiated through the lens, and usually, no acoustic matching layer is provided. On the other hand, in the case of an array converter, it is considered to be advantageous to use a system in which an array of piezoelectric thin films or direct sound is emitted in order to improve the electrical and mechanical separation of each element. In that case, an acoustic matching layer for matching the piezoelectric thin film with the ultrasonic wave propagation medium (for example, water) is required.

In the ultrasonic array converter in the several MHz band, the above-mentioned acoustic matching layer is formed usually after polishing and cutting ceramic to a desired thickness and width. This acoustic matching layer may be used without being cut, but it is better to separate it in order to improve the separation between elements. In addition, in the case of an array transducer that transmits and receives ultrasonic waves of several tens of MHz or more, the width of one element becomes small, and the separation of the matching layer is indispensable.

However, according to the conventional method, the thin film piezoelectric material is divided by etching, then the acoustic matching layer is formed, and then the etching is performed to divide the thin film piezoelectric material, which requires high pattern matching accuracy and requires many steps. Become. Heretofore, there has been no specific report on a thin-film array transducer utilizing thickness longitudinal vibration, and no consideration has been given to the problems in configuring a transducer including an acoustic matching layer.

An object of the present invention is to provide a method of manufacturing a thin film array converter that can be formed in a small number of steps.

[Means for solving the problem]

The above object is to provide a piezoelectric thin film formed on a substrate, and an ultrasonic transducer including an upper electrode formed thereon,
After forming the acoustic matching layer first, the acoustic matching layer, upper electrode,
This is achieved by sequentially etching the piezoelectric thin film.

(Operation)

In order to produce a thin film array ultrasonic transducer, it is necessary to divide uniformly formed piezoelectric thin films, electrodes, and acoustic matching layers. However, since the size of each converter is on the order of 10 μm, photolithography and etching are required to perform division. When etching the piezoelectric thin film, the electrode, and the acoustic matching layer constituting the ultrasonic transducer, it is necessary to select an appropriate etchant, and at the same time, form a mask with a material having resistance to the etchant.

The thin-film array ultrasonic transducer according to the present invention is characterized in that after forming up to the acoustic matching layer, etching is sequentially performed using the layer provided thereon as a mask.
First, the acoustic matching layer is etched using a resist pattern formed by photolithography as a mask, and the next electrode layer and piezoelectric thin film are etched using the patterned acoustic matching layer as a mask. Thus, patterning by photolithography is performed only once, and the number of steps can be reduced.

〔Example〕

Hereinafter, a first embodiment of the present invention will be described with reference to FIG.

FIG. 1 shows a thin-film array ultrasonic transducer according to the present invention, wherein a is a plan view and b is a cross-sectional view. In the figure, 1 is a quartz glass substrate, 2 is a chromium (Cr) / gold (Au) electrode, 3 and 3-1 to 3-n are zinc oxide (ZnO) thin films,
And 4-1 to 4-n is an aluminum (Al) electrode, 5 and 5-1 to 5-n is an acoustic matching layer made of SiO _2.

The procedure for producing the ultrasonic transducer shown in FIG. 1 will be described with reference to FIG. First, chromium (Cr) and gold (Au) are vapor-deposited on a quartz glass substrate 11 at 220 ° C. to form a lower electrode 12 (FIG. 1A). Next, a zinc oxide thin film 13 having a thickness of 30 μm is formed by a high-frequency magnetron sputtering method (FIG. 2B). The sputtering conditions were as follows: a power of 75 W, a substrate temperature of 220 ° C., and a gas pressure of argon (Ar) -oxygen (O ₂ ) (50% to 50%) introduced gas of 3 Pa (Pascal).

Aluminum (Al) is deposited on the thin film 13 at room temperature to form an upper electrode 14 (FIG. 3c). Further, a silicon oxide (SiO ₂ ) film having a thickness of about 15 μm is formed as the acoustic matching layer 15 by a high-frequency magnetron sputtering method (FIG. 4D). The sputtering conditions were 200W power, 200 ° C substrate temperature,
The gas pressure of the argon (Ar) -oxygen (90% -10%) introduction gas was 5 Pa. Under these conditions, the sputtering time is 7 hours.

In order to process the above uniform multilayer film into an array converter,
Etching is performed as follows. First, using photolithography technology, pitch 60μm, element width 50μ
Then, resist patterns 16-1 to 16-n having a width of 10 μm, a groove width of 10 μm, and a length of 1 mm in the minor axis direction are formed (FIG. 3E). Using this resist pattern as a mask, etching is performed for 1 hour in a mixed solution of hydrofluoric acid (HF) and ammonium fluoride (NH ₃ F) (mixing ratio 1: 6), and the silicon oxide film 15 is patterned.
After the resist is removed (f in FIG. 4), the patterned silicon oxide film 15 is used as a mask in an aluminum etching solution (mixed solution of phosphoric acid, nitric acid, glacial acetic acid, water = 75: 5: 15: 5). Then, the aluminum film 14 is patterned by etching for a minute (FIG. 9G). Further, etching is performed in a 2% hydrochloric acid aqueous solution for 5 minutes to pattern the zinc oxide thin film 13 (h in the figure). Finally, in order to expose a part of the upper electrodes 14-1, 2,..., N serving as lead wire lead-out portions from each element, the matching layer thereon is removed.

As described above, the thin film array converter shown in FIG. 1 is configured. In this method, formation of a fine pattern is 1
Since only one round is required, the precision of mask alignment is not required. Lead wires are drawn out from the lower and upper electrodes 4-1 to 4-n of this converter by wire bonding.

In this state, the lower electrode, the zinc oxide thin film 3-1 to
3-n, upper electrodes 4-1 to 4-n, acoustic matching layers 5-1 to
The n elements of 5-n were grouped into groups, each of which was driven with a phase difference delayed toward the center to emit a sound wave, and the beam was measured. The beam shape became sharp. Further, it was confirmed that the beam can be scanned by sequentially switching and driving the plurality of groups. This is because each element is separated by etching and can operate independently.

FIG. 3 is a diagram showing a plane and a cross section of a thin film array converter according to a second embodiment of the present invention. In FIG.
21 is a substrate, 22-1 to 22-n are lower electrodes 23-1 to 23n are zinc oxide (ZnO) thin films, and 24-1 to 24-n are aluminum (A
l) film, 25 is a gold film, 26-1 to 26-n are fused quartz (SiO ₂ )
It is a membrane.

The manufacture of this array converter is performed in substantially the same manner as in the first embodiment. However, in the second embodiment, the difference is that the lower electrode is an electrode separating the elements, and the upper electrode is a common electrode. First, an electrode 22 made of chromium (Cr) and gold (Au) is formed on a quartz glass substrate 2, and a portion 22- having a width equal to or wider than the element width is formed.
1 to 22-n. On this, a zinc oxide (ZnO) thin film 23 and an aluminum (Al) electrode 24 are formed. Further, a part thereof is covered with a gold (Au) film 25. This gold film functions as a mask when etching aluminum. Further, a fused quartz (SiO ₂ ) film 26 is formed on the aluminum film, and is aligned with the lower electrodes 22-1 to 22-n.
A linear resist pattern having a pitch of 60 μm, a width of 50 μm, and a length of 1 mm may be formed, and etching may be performed sequentially in the same manner as in the first embodiment. In this method, unlike the first embodiment, it is not necessary to etch the fused quartz film 26 twice. Further, there is an advantage that the lower electrode formed on the substrate serves as a bonding pad when a lead wire is drawn out, and sufficient strength can be obtained.

〔The invention's effect〕

As described above, according to the present invention, the acoustic matching layer,
Since each layer of the electrode and the piezoelectric thin film is uniformly formed, each layer is sequentially etched, so that a fine pattern is formed only once by photolithography, and the number of steps for forming an array converter can be reduced. is there.

[Brief description of the drawings]

FIG. 1 is a plan view (a) and a cross-sectional view (b) of an ultrasonic thin film array converter according to an embodiment of the present invention, and FIG. 2 is a sectional view of a processing step showing a procedure for manufacturing the ultrasonic converter of the present invention. FIG. 3 is a plan view (a) and a sectional view (b) of an ultrasonic thin film array converter according to another embodiment of the present invention. 1,11,21 …… Substrate, 2,12,22 …… Lower electrode, 3,13,23 ……
Zinc oxide thin film, 4,14 ... upper electrode, 5, 15, 26 ... acoustic matching layer, 24 ... aluminum film, 25 ... gold film.

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Kiyoshi Ishikawa 1-280 Higashi Koikebo, Kokubunji-shi, Tokyo Inside Central Research Laboratory, Hitachi, Ltd. (56) References JP-A-57-113700 (JP, A) JP-A-61 -15500 (JP, A) JP-A-60-128768 (JP, A)

Claims (5)

(57) [Claims] A step of forming a first electrode on the substrate; a step of forming a thin film made of a piezoelectric material on the first electrode; and a step of forming a second electrode on the thin film. Forming an acoustic matching layer on the second electrode; arranging a mask having a plurality of openings with predetermined dimensions on the acoustic matching layer; 2 electrodes, each layer of the thin film,
A method of sequentially etching elements using etching solutions having different compositions to form elements arranged independently of each other, the method for manufacturing a thin film array ultrasonic transducer. 2. The method according to claim 1, wherein said piezoelectric body is zinc oxide (ZnO). 3. The method for manufacturing a thin film array ultrasonic transducer according to claim 1, wherein said acoustic matching layer is made of fused silica (SiO ₂ ). 4. The method for manufacturing a thin film array ultrasonic transducer according to claim 1, wherein said substrate is fused quartz (SiO ₂ ). 5. The method according to claim 1, wherein said substrate is made of Al ₂ O ₃ .