JPS6074708A - Manufacture for surface acoustic wave device - Google Patents

Abstract

PURPOSE:To obtain a surface acoustic wave device incorporated with monolithic structure and having excellent characteristic by forming an electrode for surface acoustic wave excitation and the then forming a wiring part of a semiconductor circuit so as to keep properly the film thickness and line width of said electrode. CONSTITUTION:For example, gallium arsenide GaAs is used for a semiconductor substrate 1. Since this substrate 1 has piezoelectricity in a specific cut direction, the electroacoustic surface wave conversion is attained by forming a comb line electrode 2 made of a thin metallic film such as aluminum and a reed screen electrode 3 on the surface as the electrode for surface acoustic wave excitation. In this case, the surface acoustic wave device having a desired characteristic is realized by designing properly the shape of the electrodes 2, 3. An oscillating circuit section as a semiconductor circuit 4 is formed further on the substrate 1 and said semiconductor circuit 4 and the electrodes 2, 3 are connected by a wiring metallic film 5.

Description

Detailed Description of the Invention [Technical Field of the Invention] The present invention relates to a method of manufacturing a surface acoustic wave device in which a surface acoustic wave device and a semiconductor circuit are integrated in a monolithic structure.

[Technical background of the invention and its problems] Generally, in a device that combines a surface acoustic wave device and a semiconductor circuit, such as a surface acoustic wave oscillator, the surface acoustic wave device and the semiconductor circuit are housed in separate packages. They were constructed by being connected to each other by printed wiring or the like.

However, such a configuration is difficult to miniaturize and has problems such as reduced reliability due to exposed wiring, so it is being considered to replace it with a hybrid configuration. In other words, a wiring board with metal thin film wiring on alumina or the like is used, and a surface acoustic wave device and a chip-shaped semiconductor circuit are bonded and wired onto this board.

On the other hand, in addition to this hybrid surface acoustic wave device, in order to further reduce the size, improve reliability, and reduce manufacturing costs, a surface acoustic wave device and a semiconductor circuit are integrated on a single semiconductor substrate. , surface acoustic wave devices with a so-called monolithic structure are also being considered. However, a surface acoustic wave device with a monolithic structure has not yet been realized. There are various possible reasons for this, one of which is that the electrode structure suitable for surface acoustic wave devices is significantly different from the electrode structure in semiconductor circuits. In particular, the characteristics of surface acoustic wave devices are greatly affected by the surface condition of the substrate, so the electrode film thickness must be controlled to a value determined by the frequency band in use, such as the center frequency of the surface acoustic wave device. 0.2
The film thickness is less than μmn. On the other hand, in semiconductor circuits, wiring made of aluminum and ohmic electrodes made of alloys of platinum, gold, and germanium are formed, but the film thickness of these electrodes is generally about 1 μm.

Furthermore, high-temperature processes exceeding 400 degrees Celsius are used for VB construction of semiconductor circuit parts, which has a negative effect on surface acoustic wave devices. That is, the surface acoustic wave excitation electrode in a surface acoustic wave device generally consists of electrode fingers in a 1M thin pattern with a width of about 1 μm, and the electrode fingers become thin when subjected to a high temperature process during the manufacture of a semiconductor circuit section. As a result, there is a problem that a shift in the center frequency of the surface acoustic wave device causes deterioration of frequency characteristics.

[Objective of the Invention] The object of the invention is to properly maintain the film thickness and line width of the surface acoustic wave excitation electrode so that the surface acoustic wave device and the semiconductor circuit are integrated into a monolithic structure with good characteristics. An object of the present invention is to provide a method for manufacturing a surface acoustic wave device.

[Summary of the Invention] The present invention provides a method for forming surface acoustic wave excitation electrodes after completing the manufacturing process for all parts of the semiconductor circuit except for the wiring parts, and then forming the wiring parts of the semiconductor circuit. It is characterized by

[Effects of the Invention] According to the present invention, the electrodes for surface acoustic wave excitation in the surface acoustic wave device are not exposed to the hot water temperature during the semiconductor circuit manufacturing process, so that the electrode fingers do not become thin. Since there is no possibility of breakage or the like occurring at connection parts with relatively thick wiring parts of the semiconductor circuit, desired characteristics can be stably obtained.

Therefore, it is possible to easily mass-produce surface acoustic wave devices such as one-chip ultra-small oscillators in which a surface acoustic wave device and an oscillation circuit section consisting of a semiconductor circuit are monolithically configured without problems such as variations in characteristics. This makes it possible to provide this type of device at low cost.

[Embodiments of the Invention] FIG. 1 shows a schematic configuration of a monolithic surface acoustic wave oscillator as a surface acoustic wave device according to an embodiment of Yoriaki's invention.

In the figure, 1 is a semiconductor substrate, for example, gallium arsenide (GaAS) is used. Since this substrate has piezoelectricity in a specific cutting direction, it is possible to generate electro-surface acoustic wave conversion can be performed. In this case, by appropriately grading 81 the shape of these surface acoustic wave devices IM2.3, a surface acoustic wave device having desired characteristics can be realized.

On the other hand, an oscillation circuit section is further formed as a semiconductor circuit 4 on the semiconductor substrate 1, and this semiconductor circuit 4 and the surface acoustic wave excitation electrodes 2 and 3 are connected by a wiring metal film 5. When a DC voltage is applied to the power supply input terminal 6, an excitation output of a frequency determined by the shape and dimensions of the surface acoustic wave excitation electrode 2.degree.3 is obtained from the output terminal 7. For example, when it is desired to obtain I G l-1z as the oscillation frequency, the line width of the interdigitated electrodes 2 should be 0.7 μm and the pitch should be 1.4 μm.

FIG. 2 is a tlIi plan view showing an enlarged view of the peripheral structure of the semiconductor circuit 4 in FIG.
9 is gold j [I! ! , 10 are insulators for passivation. In this invention, as mentioned above, all of these 8-karat gold! 8.9 and the insulating film 1o are first formed, and then the surface acoustic wave excitation electrode 2 is formed.
．． 3 is formed, and then a wiring metal film 5 is formed.

Hereinafter, the manufacturing process of this surface acoustic wave oscillator will be explained using FIG. 3.

First, as shown in FIG. 3(a), semi-insulating GaAs1!
After forming the S I O2H12 on the plate 11, the same figure (b
) A photoresist 13 is applied and developed as shown in FIG.

Then, as shown in FIG. 5C, the portions of the 5iQ2 film 12 without the photoresist 13 are removed by etching, and ions are implanted as shown by the arrows using the photoresist 13.5i02 layer 12 as a mask. And Figure 3 (a
) to (C) in the same figure (d), (e) and (
f), (l) By repeatedly selectively implanting ions into the substrate 11, the N+ layer 14, the active layer 15 .
A resistive layer 16 is formed. After ion implantation, 5i is applied to the entire surface again.
Ozlli 17 is formed and annealed at high temperature using this as a protective film to activate each layer. As a result, a semiconductor channel is formed as shown in FIG. 3(h).

Next, as shown in FIG. 3(i), the SiO2 film 17 is selectively etched using the photoresist 18 as a mask.
As shown in the figure (j), Pt/Au/Ge11 is formed as the metal film 19 for the ohmic electrode, and then, as shown in the figure (k).
As shown in FIG. 2, unnecessary portions of this metal film 19 are removed by lift-off.

Thereafter, the metal film 19 is alloyed by temperature treatment to form an ohmic electrode.

Next, as shown in FIG. 3(1), 5iO21117 is further etched using a photoresist 20, and then an aluminum film is formed as a Schottky electrode metal film 21 as shown in FIG. 3(m). As shown in figure (n), this money ff1N! An unnecessary portion of 21 is removed by lift-off to form a Schottky electrode. And Figure 3 (
0), by forming 5IO21!122 on the entire surface as a passivation insulating film, all manufacturing steps of the semiconductor circuit except for the wiring portion are completed.

Next, as shown in FIG. 3(p), after forming a photoresist 23 on the entire surface, the photoresist 23 is exposed to light so that the portion where the surface acoustic wave excitation electrode is to be formed is removed.
develop. Next, this F7It-L cyst 23 is retained.
! Isotropically etching the rs + 02 film 22 as a film,
Thereafter, as shown in FIG. 3(Q), a metal film 24 that becomes an electrode for excitation of surface acoustic waves is formed, for example, with a film thickness of 0.1 to 0.2 μm.
Forms an aluminum film of approximately And 5iO21122
, photoresist 23, and remove unnecessary portions of gold 111124 by lift-off.

This state is shown in FIG. 3(r), where the metal film 24
A surface acoustic wave excitation electrode is formed.

Next, as shown in FIG. 3(S), a photoresist 25 is applied and developed, and then as shown in FIG. 5i02122 for passivation on parts
is removed by etching. Next, a resist 2G shown in FIG. 3(U) is applied, and exposed and developed so that the photoresist 26 remains in areas other than the areas where the wiring portion of the semiconductor circuit is to be formed. Let's do it.

Then, as shown in FIG. 3(V), the wiring metal I! 27
For example, after forming Au/Pt/Ti1l on the entire surface, by removing 26 from the photoresist 1, Au/Pt/Ti1l is formed on the entire surface.
Unnecessary portions of the Pt/Ti film are removed by lift-off to form wiring portions of the semiconductor circuit.

In this way, a surface acoustic wave oscillator with a monolithic structure as shown in FIG. 3(W) is completed.

According to the manufacturing process of the surface acoustic wave device based on the present invention described above, after the semiconductor circuit forming process including the high temperature process shown in FIGS. 3(a) to 3(0), the steps shown in FIGS.
Since the electrode for surface acoustic wave excitation was formed in (r), and the wiring part of the semiconductor circuit was then formed in (S) to (W) of the same figure, the electrode finger of the electrode for surface acoustic wave excitation was formed. The film will not become blocked due to exposure to high temperatures, and breakage will not occur at the connection with the wiring of a relatively thick semiconductor circuit. Therefore, desired characteristics (center frequency 1 frequency characteristics, etc.) as a surface acoustic wave oscillator can be easily obtained.

In addition, in the above embodiment, the electrode for surface acoustic wave excitation is formed by using the insulating film for the semiconductor circuit as a lift-off film, so the fine shape of the electrode is determined by the electrode formed thereon. The resist film becomes
It is possible to form electrodes with extremely high precision.

This invention can be implemented with various other modifications. For example, as shown in FIG. 10, it is possible to reduce the stray capacitance of the wiring between the semiconductor circuit 4 and the surface acoustic wave device. This is passivation insulation II!
The reason for this is that the dielectric constant of the SiO2 film as 10 is smaller than that of the QaAs substrate, which is the semiconductor substrate 1, at about 115.

In addition, the materials of each part are not limited to those listed in the examples,
For example, the passivation insulating film may be another dielectric film such as SiN. Any metal material for each electrode may be used as long as it fulfills its original function; for example, 3i
Also, aluminum doped with Cu can be used as the electrode material.

In addition, regarding semiconductor substrates other than GaAS substrates,
For example, a Si substrate can be used, and a piezoelectric thin film may be formed on the surface acoustic wave device forming portion to improve piezoelectricity.

[Brief explanation of drawings]

FIG. 1 is a perspective view showing a schematic configuration of a surface acoustic wave oscillator as an example of a surface acoustic wave device according to an embodiment of the present invention, FIG. 2 is a view showing a cross-sectional structure of a main part thereof, and FIG. FIG. 4 is a perspective view of a surface acoustic wave device according to another embodiment of the invention. 1.11... Semiconductor substrate, 2, 3... Electrode for surface acoustic wave excitation, 4... Semiconductor circuit, 5, 27... Metal film for wiring, 6...''RWA input terminal, 7 ...Output terminal, 8.19...Metal film for ohmic electrode, 9,20.
...Shop Figure 3 Figure 3 Figure 8 Figure 3 4m

Claims (3)

[Claims] (1) When manufacturing a surface acoustic wave device in which a surface acoustic wave excitation electrode and a semiconductor circuit electrically connected to this N pole are formed on a common substrate having piezoelectricity, one of the semiconductor circuits is A method for manufacturing a surface acoustic wave device, comprising forming the surface acoustic wave excitation electrode after completing the manufacturing process for all parts except the wiring part, and then forming the wiring part of the semiconductor circuit. . (2) A method for manufacturing a surface acoustic wave device according to claim 1, characterized in that the surface acoustic wave excitation electrode is formed by performing lift-off using an insulating film for passivation in a semiconductor circuit. . (3) Manufacture of the surface acoustic wave device according to claim 1, wherein the insulating film for passivation of the semiconductor circuit is left below the wiring part between the semiconductor circuit and the surface acoustic wave excitation electrode. Method.