JPH0161250B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of manufacturing a surface acoustic wave transducer.

The interdigital transducer is an indispensable component for realizing a surface acoustic wave device such as a filter or delay line using a piezoelectric substrate, and largely determines the performance of the surface acoustic wave device.

The interdigital transducer can be realized by simply forming a desired pattern of electrodes on a substrate using IC technology, so surface acoustic wave devices using this transducer can be miniaturized and
In recent years, efforts have been made to put it into practical use as a new telecommunications circuit element that can be easily integrated into ICs and without adjustment.

A filter will be described below as an example of a typical surface acoustic wave element. As is well known, the basic interdigital interdigital electrode is as shown in FIG. Reference numerals 1 and 2 are pad parts for external extraction, 3 is a cross electrode part, and 4 is a mating part. P is the repetition period of the crossed electrodes, l is the electrode width, S is the electrode gap width, and approximately l=S.
The repetition period P of this crossed electrode determines the center frequency of the filter.

Incidentally, in recent years, as telecommunication circuits and devices have become increasingly high-frequency, high-frequency surface acoustic waves of 1 GHz or higher have been required. The interdigital electrodes of such high-frequency surface acoustic wave filters must have a repetition period of 1 μm, and the electrode width and electrode gap width must be
The fine dimensions are 0.5μm or less.

The lift-off method is usually used to manufacture such fine interdigital electrodes. FIG. 2 is a cross-sectional view of a typical manufacturing process for fine interdigital electrodes.

(1) A resist 22 is applied onto the piezoelectric substrate 21 and exposed 23 is performed.

(2) By developing the resist 22, the opening 24 is
form. At this time, the walls of the opening are made to have a reverse slope as shown in 25.

(3) Apply electrode material 26 to the entire surface of the sample.

(4) By dissolving and removing the resist 22, unnecessary electrode material on the resist is removed and the electrode 27 is formed.

In step (2), forming the reverse slope 25 of the resist wall is important. If the wall does not have a reverse slope, the electrode material deposited on the entire surface will be continuous between the top of the resist and the piezoelectric substrate part of the opening, so even if the resist is melted, it will not be deposited on the resist. Unwanted electrode material cannot be removed. Therefore, as shown in FIG. 2 and 3, it is necessary to make the width b of the opening at the substrate surface larger than the width l of the opening at the upper part of the resist. This requirement requires that the width c of the lower part of the resist be smaller than the width l of the opening, and if the repetition period P becomes small, it will be difficult to form a resist pattern in the shape of an inverted trapezoid with such a small bottom surface. Become.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for easily manufacturing interdigital transducers with fine dimensions.

The present invention comprises a step of depositing an electrode material on a piezoelectric substrate, a step of depositing an auxiliary layer made of an organic material thereon, a step of depositing a resist thereon, and a step of patterning the resist. The method is characterized by diagonally depositing an inorganic material on the patterned resist, etching the auxiliary layer using the inorganic material as a mask to form an opening, and then anodizing the electrode material through the opening. There is.

Next, the present invention will be explained in detail using the drawings.

FIG. 3 is a process sectional view showing an embodiment of the present invention.

(1) Aluminum (Al) 30 is deposited on the piezoelectric substrate 21 as an electrode material to a thickness of 700 Å. Next, AZ-1350 (manufactured by Shippley, USA) 31 was deposited as an auxiliary layer thereon to a thickness of 1900 Å. Furthermore, an electron beam resist PMMA32 is deposited thereon. This resist 32 is subjected to electron beam exposure 33.

(2) Openings 34 are formed by developing the resist 32 with a mixed solution of methyl isobutyl ketone and isopropyl alcohol. At this time, the walls of the opening do not need to have the opposite slope required by the lift-off method;
You can also draw the hem like 35.

(3) As shown at 36, titanium (Ti) is vapor-deposited from an oblique direction. Ti is deposited on the top of the resist 32 as shown in 37 due to the unevenness of the resist 32. The film thickness was approximately 200 Å.

(4) Oxygen ion beam 38 from the vertical direction
The auxiliary layer 31 is etched using the pattern 37 as a mask to form an opening 39.

(5) Aluminum in the opening 39 is anodized to form an insulator pattern 40. Next, by peeling off the resist,
Remove the Ti and then peel off the auxiliary layer.

(6) A resist 41 is deposited thereon, and exposure 42 is performed.

(7) Develop the resist 41 to form an opening 43.

(8) By etching the electrode material in the opening 43, the electrode in the pad part is formed, and unnecessary electrode material on the scribe line 44 between the chips is removed.

Here, the inclination angle of the oblique vapor deposition 36 in step (3) is determined as follows.

FIG. 4 1 is a plan view of the crossed electrode section immediately before the oblique vapor deposition process. 51 is a resist line portion, 52 is a space portion, and 53 is a matching portion. When the width of the resist line portion is l and the width of the space portion is S, the repetition period P of the crossed electrodes is the sum of l and S. The cross section 55-56 is as shown in FIG. 42. 57 is an auxiliary layer. The cross section 58-59 passing through the abutting portion 53 in FIG. 41 is shown in FIG.
The gap between the resist line portions 51 is P
+S. Therefore, the inclination angle a of oblique vapor deposition, where t is the thickness of the resist, needs to be equal to or greater than tan ^-1 (P+S/t). In this example, P=0.25μm, S=
Since 0.15 μm and t=0.45 μm, a=42 degrees or more is required, and a=60 degrees was used here.

In step (4), the auxiliary layer 31 is made of an organic material, and since organic materials have an order of magnitude higher etching rate than inorganic materials such as Ti when it comes to oxygen ion beam etching, the openings 39 are deep. Can be clearly formed. pattern 37
It is clear that the inorganic material forming the auxiliary layer 31 and the organic material of the auxiliary layer 31 are appropriately selected in order to carry out this process efficiently, and are not limited to the examples shown.

The area to be anodized in step (5) is the area other than the electrodes of the cross electrode portion, as shown at 60 in FIG. This area to be anodized is not surrounded in any part by an anodized area. Further, the width of the area to be anodized is almost constant and has minute dimensions. Therefore, the cross electrodes can be easily formed by anodic oxidation.

As explained above, according to the manufacturing method according to the present invention, when patterning a resist, it is not necessary for the cross-sectional wall of the resist to have a reverse slope. High frequency surface acoustic wave interdigital transducers can be easily manufactured because masks can be easily formed and fine-sized electrodes can be easily manufactured using anodic oxidation.

[Brief explanation of drawings]

FIG. 1 is a plan view showing the basic shape of the interdigital electrode. Figure 2 is a diagram for explaining the conventional process for manufacturing fine interdigital electrodes, 1 is a state in which the resist is exposed, 2 is a state in which the resist is developed, and 3 is a state in which the electrode material is applied. , 4 shows the state in which electrodes are formed. FIG. 3 is a process sectional view of an embodiment of the present invention, in which 1 shows a state in which an electrode material, an auxiliary layer, and a resist are deposited on a piezoelectric substrate, and then the resist is exposed, 2 shows a state in which the resist is developed, 3 is a state in which an inorganic material is obliquely deposited, 4 is a state in which an auxiliary layer is etched, 5 is a state in which the upper mask is removed after anodizing the electrode material, 6 is a state in which a resist is applied and exposed, and 7 is a state in which a resist is applied and exposed. 8 shows a state in which the resist has been developed, and 8 shows a state in which the resist is removed after removing unnecessary electrode material. FIG. 4 is a diagram for determining the oblique deposition angle in FIG. It is. FIG. 5 is a plan view showing the area to be anodized. In the figure, 1 and 2 are pad parts for external extraction, 3 is a cross electrode part, 4 and 53 are mating parts, 21 is a piezoelectric substrate, 22, 32, and 41 are resists, and 23, 33, and 42 are exposure parts. ,24,34,3
9, 43 are openings, 25 are reversely inclined walls, 26, 30
is an electrode material, 27 is an electrode, 31 is an auxiliary layer, 35 is a resist wall, 36 is an oblique evaporation, 37 is an inorganic material, 38 is an etching, 40 is an oxide, 44 is a scribe line part, 60 is to be anodized Represents an area.

Claims (1)

[Claims] 1. A step of depositing an electrode material on a piezoelectric substrate, a step of depositing an auxiliary layer made of an organic material thereon, and a step of depositing a resist thereon,
A step of patterning the resist, diagonally depositing an inorganic material on the patterned resist, etching the auxiliary layer using it as a mask to form an opening, and then applying the electrode material to the anode through the opening. A method for manufacturing a surface acoustic wave transducer characterized by oxidation.