JP3221420B2 - Semiconductor high frequency integrated circuit and method of manufacturing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor high-frequency integrated circuit and a method of manufacturing the same, and more particularly, to an MMIC (Microwatt).
ave Monolithic Integrated Circuit) and a method of manufacturing the same.

[0002]

2. Description of the Related Art Conventionally, as a switch for turning on / off a high frequency (microwave, millimeter wave region, etc.) used in a radio frequency, an FET (Field Effect Transistor) or a PIN has been used.
Electronically controlled devices such as diodes, so-called semiconductor switches, have been used.

FIG. 9 is a block diagram showing a transmitting / receiving unit in a conventional wireless communication device. As shown in the figure, the circuits of the transmission system and the reception system are each called IMIC called MMIC.
It is integrated on a C chip. Here, the transmission system and the reception system are respectively formed on separate chips, but both may be integrated on the same chip.

[0004] In the transmitting MMIC 31, at least an amplifier 31a and a PIN diode 31c, which is a switch for switching a signal path, are integrated.
Similarly, the MMIC 32 of the receiving system integrates at least an amplifier 32a and a PIN diode 32c for switching a signal path.

Of course, the actual MMICs 31 and 32 also integrate circuits such as a phase shifter, an attenuator, a frequency converter, and a modulator / demodulator in addition to the above-described configuration. The PIN diodes 31c and 32c each include a DC bias circuit and the like. Although they are connected, their description is omitted here. As described above, each PIN diode is switched on / off in accordance with the voltage applied to the control terminals 34 and 35, and one of a transmission system and a reception system is connected to the antenna 33.

That is, at the time of transmission, the signal input to the terminal 36 is amplified by the amplifier 31a,
The signal is input to the antenna 33 through the PIN diode 31c. At the time of reception, the signal received by the antenna 33 is a PIN diode 32c and an amplifier 32a.
Through the terminal 37.

However, such a semiconductor switch such as a PIN diode has problems such as insertion loss, isolation deterioration, signal passing loss, etc. due to the resistance and parasitic capacitance of the semiconductor, and is not satisfactory. Absent. In particular, the higher the frequency of a signal to be handled, the more serious such a problem becomes. The optimized pass loss of the switch due to the PIN diode as an individual component is, for example, about 0.8 dB at 30 GHz.

On the other hand, when it is attempted to integrate each circuit of the transmitting and receiving unit and a PIN diode for switching a signal path by MMIC, the optimum conditions in the active layer of the active element such as an FET and the PIN diode are respectively different from each other. Because of the differences, it can be said that it is difficult to monolithically integrate them on the same substrate.

On the other hand, it is not conceivable to use an FET instead of a PIN diode. However, the use of an FET further increases the passage loss (for example, 30%).
(1.1-1.5 dB at GHz) Not very satisfactory. Therefore, it can be said that there is a limit in using a semiconductor switch in a semiconductor high-frequency integrated circuit such as an MMIC.

In recent years, there has been a movement to employ a micro switch (hereinafter, referred to as a micro machine switch) for mechanically performing on / off control in order to solve such a problem. For example, Japanese Patent Application Laid-Open No. 9-17300 discloses a device in which a minute micromachine switch is formed on a GaAs substrate. However, although such a micromachine switch is excellent in high-frequency characteristics, it actually has various problems when actually integrated in an MMIC or the like.

Here, a conventional micromachine switch will be described with reference to the drawings. FIG.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1A is a plan view showing a micromachine switch disclosed in Japanese Patent Application Laid-Open No. 7300, and FIG. As shown in FIGS. 3A and 3B, the GaAs substrate 4
A signal line 44 is provided on 1 with a predetermined gap therebetween, so that the signal line 44 constitutes an open circuit. An anchor structure 42 is provided on the GaAs substrate 41 near the signal line 44, and a cantilever arm 45 made of silicon oxide is provided thereon.

The cantilever arm 45 can bend in the direction of the arrow 48 with its tip extending over the gap of the signal line 44. In addition, a contact portion 47 made of a conductive member is formed on the lower surface of the distal end portion so as to cover both ends of the signal line 44. Therefore, the cantilever arm 45
Is bent toward the substrate surface, so that the contact portion 47 contacts both ends of the signal line 44, and the signal line 44 forms a closed circuit.

An upper electrode 46 is formed on the upper surface of the cantilever arm 45, and a control electrode 43 is formed on the GaAs substrate 41 so as to face the upper electrode 46. That is, when a voltage is applied between the upper electrode 46 and the control electrode 43, an electrostatic force is generated between these electrodes, and the cantilever arm 45 bends toward the substrate to form a closed circuit as described above. You. Thereafter, when the application of the voltage is released, the generation of the electrostatic force is stopped, and the cantilever arm 45 returns to its original shape to form an open circuit.

[0014]

However, FIG.
As apparent from the description, the anchor structure 42 supporting the cantilever arm 45, which is a movable portion, is formed directly on the GaAs substrate 41 in the conventional micromachine switch, so that the contact portion 47 is transmitted from the signal line 44. It can be said that a part of the high-frequency signal leaks to the upper electrode 46 and the anchor structure 42 along the cantilever arm 45. Therefore,
The high-frequency energy that should be transmitted to the signal line 44 is attenuated, and it is difficult to realize a low-loss switch with such a conventional structure. Incidentally, the insertion loss in this structure is 2 to 3 dB at 30 GHz.

Further, in the above-described conventional example, after forming the signal line 44 on the substrate 41, it is necessary to add a new process for forming the anchor structure 42 and the cantilever arm 45 made of silicon oxide. Therefore, the conventional MMI
Such a structure cannot be produced only by the manufacturing process of C.

Furthermore, the above-mentioned conventional example discloses that the film forming temperature of the SiO ₂ film, which is the material of the cantilever arm 45, is set to about 250 ° C. or less so that the micro machine switch and the MMIC can be monolithically integrated. ing.
Specifically, it is disclosed that this SiO ₂ film is formed using plasma CVD.

However, as is well known, the mechanical properties (eg, strain, stiffness, reliability, etc.) and the electrical properties (eg, dielectric constant, maximum breakdown voltage, etc.) of a material are improved by optimizing temperature conditions. You. Therefore, in the manufacturing process, it is necessary to appropriately change the temperature conditions in order to improve these characteristics, but this cannot be performed in the conventional example. As described above, the restriction on the temperature condition is a major obstacle in realizing a high-performance micromachine switch and an integrated circuit.

SUMMARY OF THE INVENTION The present invention has been made to solve such a problem, and it is possible to eliminate leakage of a signal flowing through a signal line and to easily manufacture a semiconductor high-frequency integrated circuit by a conventional MMIC manufacturing process. It is an object to provide a circuit and a method for manufacturing the circuit.

[0019]

In order to achieve the above object, one embodiment of the semiconductor high frequency integrated circuit of the present invention is:
A semiconductor substrate having an integrated circuit including an active element and a passive element; an interlayer insulating film covering a main surface of the semiconductor substrate; a first signal line provided on the interlayer insulating film and connected to the integrated circuit; A second signal line provided on the interlayer insulating film and having an end at a predetermined distance from an end of the first signal line; and a second signal line between the first and second signal lines. In a semiconductor integrated circuit having switch means for controlling conduction / non-conduction, the switch means is provided at one of ends of the first or second signal line and comprises a support member made of a conductive member; A cantilever arm provided on the support member and extending above the other signal line and made of a conductive member;
And a control electrode provided immediately below the cantilever arm between the ends of the signal lines.

In another aspect of the semiconductor high-frequency integrated circuit of the present invention, the semiconductor substrate is a silicon substrate or a compound semiconductor substrate. The integrated circuit includes a phase shifter, a transmission / reception switch, a variable attenuator, a frequency converter, a frequency multiplier, a frequency filter, an oscillator, a modulator,
At least one of a demodulator and an amplifier is included. Further, the first and second signal lines are any of a microstrip line, a coplanar line, and a slot line.

According to another aspect of the method of manufacturing a semiconductor high-frequency integrated circuit of the present invention, a step of forming an integrated circuit including an active element and a passive element on a semiconductor substrate, and forming an interlayer insulating film on a main surface of the semiconductor substrate. Forming, forming a first signal line connected to the integrated circuit on the interlayer insulating film, and having an end at a position separated by a predetermined distance from an end of the first signal line A step of forming a second signal line, a step of forming a sacrificial film on the interlayer insulating film with a thickness covering the first and second signal lines, and a step of forming the first or second signal line. Opening a through hole in the sacrificial film on one end, forming a support member on the one end by filling a conductive member in the through hole, Extend to the other signal line and Forming a cantilever arm consisting of sexual member, in which a step of removing the sacrificial layer.

In another aspect of the method for manufacturing a semiconductor high-frequency integrated circuit of the present invention, the semiconductor substrate
It is a silicon substrate or a compound semiconductor substrate. Further, the integrated circuit includes at least one of a phase shifter, a transmission / reception switch, a variable attenuator, a frequency converter, a frequency multiplier, a frequency filter, an oscillator, a modulator, a demodulator, and an amplifier. Further, the first and second signal lines are any one of a microstrip line, a coplanar line, and a slot line.

With such a configuration, the present invention provides
An MMIC including a micromachine switch can be configured by using a conventional MMIC through process having an air bridge structure without any change. Therefore, a high-performance micromachine switch can be manufactured on the MMIC at low cost.

[0024]

Next, one embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a plan view showing one embodiment of the present invention. Here, an example is shown in which a field effect transistor (hereinafter, referred to as an FET) as an amplifying element and a micromachine switch are mounted on a compound semiconductor substrate. The description of the DC bias circuit and the impedance matching circuit of the FET is omitted.

As shown in FIG. 1, an FET 25 and a micro-machine switch 24 connected to the FET 25 are mounted on a substrate 1 made of a compound semiconductor such as GaAs, and an equivalent circuit thereof is shown in FIG. Become.

That is, the electrode 21 on the input side is connected to the FET 2
The FET 25 has a source connected to a ground (earth) outside the chip via a ground electrode 26 and a bonding wire connected thereto, and a drain connected to one end of the micromachine switch 24. ing. The other end of the micromachine switch 24 is connected to the output-side electrode pad 22. The on / off control of the micromachine switch 24 is performed by the electrostatic force generated by the voltage applied to the control electrode pad 23. Thus, the high-frequency signal input from the electrode pad 21 is amplified by the FET 25,
The power is transmitted to the electrode pad 22 on the output side in accordance with on / off control by the electrode pad 23.

Now, the detailed structure of the micromachine switch will be described with reference to FIG. FIG.
(A), (b) and (c) are respectively AA ′ in FIG.
FIG. 3 is a cross-sectional view taken along line BB ′ and line CC ′. As shown in FIG. 1C, an active layer 2 is formed on a substrate 1 and a gate electrode 3 is formed on a region to be a gate.
g is formed, an ohmic electrode 4s is formed on a region serving as a source, and an ohmic electrode 4d is formed on a region serving as a drain.

The surface of the substrate 1 on which the gate electrode 3g and the ohmic electrodes 4s, 4d are formed is covered with an interlayer insulating film 5. Then, as shown in FIG. 1A and FIG. 1, the two gate electrodes 3g are drawn out in the horizontal direction with respect to the substrate 1 and the electrode pads 2 are formed through the electrodes 6g.
1 is connected.

Similarly, an electrode 6s is formed on the ohmic electrode 4s, a source electrode 7s and an electrode 8s are formed thereon, and the two electrodes 8s are short-circuited via the air bridge wiring 9b. . In addition, ohmic electrode 4
An electrode 6d is formed on d, and a drain electrode 7d is formed thereon.

The drain electrode 7d extends to a region outside the FET and functions as a signal line. That is, by appropriately adjusting the thickness of the interlayer insulating film 5 in advance, the interlayer insulating film 5 and the substrate 1 are used as dielectrics, and a metal surface provided on the back surface of the substrate 1 or a package holding and fixing the substrate 1 is provided. A microstrip line is formed by using a metal part such as a ground electrode. Therefore, by adopting such a structure, it can be used for high-frequency transmission. Of course, it can also be used for transmitting DC signals. Further, instead of the microstrip line, a coplanar line, a slot line, or the like can be formed.

On the other hand, as shown in FIG. 2B, a signal line 7sw is provided on the interlayer insulating film 5 at a predetermined distance from an end of the drain electrode 7d. Are electrode pads 22. And the signal line s
An electrode 8sw is formed on the end of w, and a cantilever arm 9sw is formed thereon. A control electrode 3c is formed on the substrate 1 directly below the cantilever arm 9sw, and one end of the control electrode 3c is connected to the electrode 6 in FIG.
It is connected to the electrode pad 23 via c.

As described above, the voltage applied to the control electrode 3c via the electrode pad 23 causes the (control electrode 3c)-
The Coulomb force acts between the (cantilever arm 9sw), the cantilever arm 9sw is bent toward the substrate side and comes into contact with the drain electrode 7d to close the circuit. As a result, the high-frequency signal input from the electrode 21 is amplified by the FET 25 and then transmitted through the drain electrode 7d and the cantilever arm 9sw.
Is output to Conversely, by stopping the application of the control voltage to the control electrode 3c and connecting it to a ground potential (not shown), the Coulomb force does not work and the circuit is opened. Therefore, the high-frequency signal input from the electrode pad 21 is cut off by the micromachine switch 24 and is not output from the electrode 22. In this embodiment, since a structure for supporting the cantilever arm is provided on the transmission line, signal leakage to the outside of the transmission line is small, and 30 GHz
Thus, the loss can be suppressed to 0.5 dB or less.

In the above description, the material of the substrate 1 is Ga
Although the use of a compound semiconductor such as As has been described, the present invention is not limited to this. For example, similar micromachine switches and semiconductor integrated circuits can be manufactured using a silicon substrate. FIG. 3 shows an example in which the control electrode 3c is provided directly on the substrate 1, but when the wiring layer has a multilayer structure, it is not always necessary to provide the control electrode 3c in the same layer as the gate electrode 3g. Therefore, a control electrode may be provided in an intermediate layer between the layer where the gate electrode 3g is formed and the layer where the drain electrode 7d is formed.

Here, the manufacturing process of the micromachine switch and the semiconductor integrated circuit shown in FIGS. 1 to 3 will be described with reference to the drawings.

FIGS. 4 to 7 are cross-sectional views showing steps of manufacturing the micromachine switch and the like according to FIGS. 4 to 6 show cross-sectional views taken along line CC ′, and FIG.
FIG. 4 shows a cross-sectional view taken along line B ′. First, as shown in FIG. 4A, a substrate 1 made of GaAs (for example, having a thickness of several tens to
About several hundred μm). Next, as shown in FIG. 4B, desired active elements are formed on the substrate 1. Here, an example of manufacturing an FET will be described. Therefore, in order to form the active layer 2, Si ions are implanted shallowly into the substrate 1, and then Si ions are implanted deeper into the regions to be the source and the drain.

Next, as shown in FIG. 4C, an interlayer insulating film 5 made of silicon oxide is deposited on the surface of the substrate 1 on which the active layer 2 is formed by using a CVD method or the like. Next, as shown in FIG. 4D, after opening a contact hole in the interlayer insulating film 5 corresponding to the gate region and the control electrode region, metal deposition and etch back are performed.
In the contact hole, the gate electrode 3g and the control electrode 3
Prepare c. Specifically, a gate electrode 3g having a thickness of about 0.5 μm is formed by sputtering tungsten silicide and gold.

Next, as shown in FIG. 4E, a contact hole is opened in the interlayer insulating film 5 corresponding to the source and drain regions, metal is deposited and etched back, and a heat treatment is further performed to form an ohmic contact. Electrode 4s,
4d is produced. Next, as shown in FIG. 5F, silicon oxide is further deposited on the interlayer insulating film 5, and the thickness of the interlayer insulating film 5 is increased. Next, as shown in FIG. 5 (g), after opening a through hole in the interlayer insulating film 5 on the ohmic electrodes 4s, 4d, metal deposition and etch back are performed to produce the electrodes 6s, 6d, 6c. .

Next, as shown in FIG. 5H, a metal 70 is further deposited thereon. Next, as shown in FIG. 5I, the source electrode 7s, the drain electrode 7d, and the electrode pad 23 are formed by lithography and etching. Next, as shown in FIG. 5J, a sacrificial film 100 is formed on the interlayer insulating film 5 so as to cover the source electrode 7s, the drain electrode 7d, and the electrode pad 23.
Is deposited. Next, as shown in FIG. 5 (k), after opening a through hole in the sacrificial film 100 corresponding to the source electrode 7s, metal is deposited and etched back to form an electrode 8s.

Next, as shown in FIG.
The metal 90 is deposited on the s and the sacrificial film 100. Next, as shown in FIG. 5 (m), the metal 90 is lithographically etched and etched to form the air bridge wiring 9.
Prepare b. Finally, as shown in FIG. 5 (n), by removing the sacrificial film, an FET having the air bridge wiring 9b is completed.

By the way, the micromachine switch 25 shown in FIG. 1 is manufactured by the above-described steps shown in FIGS. 6 (k) to 6 (n), and only the manufacturing steps of the micromachine switch 25 are extracted as follows.

FIGS. 7 (k ') to 7 (n') show cross sections taken along the line CC ', and FIGS.
It corresponds to each process of (n). First, as shown in FIG. 7 (k ′), a gate electrode g, a control electrode 3c, an interlayer insulating film 5, and the like are already formed on the substrate 1. As in the case of FIG. 6 (k), an electrode 8sw is formed on the signal line 7sw. Next, as shown in FIG. 7 (l ′), a metal 90 is deposited so as to cover the electrode 8sw and the sacrificial film 100. Next, as shown in FIG. 7 (m ′), a cantilever arm 9sw is manufactured by lithography and etching. Finally, by removing the sacrificial film 100, a micromachine switch is completed. As described above, by using the present embodiment, the micromachine switch can be easily manufactured by using the manufacturing process of the air bridge wiring in the manufacturing process of the MMIC.

Next, another embodiment of the present invention will be described. FIG. 8 is a block diagram showing another embodiment of the present invention, in which a micromachine switch is used for a transmitting / receiving section of a wireless communication device. 9, the same reference numerals as those in FIG. 9 denote the same or equivalent parts. In the present embodiment, the micromachine switch 31 shown in FIG.
b and 32b are employed.

Here, the operation of the present embodiment will be described. As shown in FIG. 8A, at the time of reception, when the switch 31b is opened and the switch 32b is closed, the signal received by the antenna 33 is input to the MMIC 32 of the receiving system through the switch 32b. You. On the other hand, as shown in FIG.
The signal input from 6 to the MMIC 31 of the transmission system is input to the antenna 33 through the amplifier 31a and the switch 31b. The control of the micromachine switches 31b and 32b is performed according to the voltage applied to the control electrodes 34 and 35.

As an application circuit using the above-mentioned micromachine switch, in addition to the above-mentioned amplifier,
Phase shifter, duplexer, variable attenuator (frequency attenuator), frequency converter, frequency multiplier, frequency filter,
It goes without saying that there are an oscillator, a modulator, a demodulator and the like. That is, by using the present invention, various high-frequency integrated circuits and micromachine switches can be integrated on the same chip.

[0045]

As described above, according to the present invention, it is possible to form a signal on / off circuit by a micromachine switch without changing a conventional MMIC through process having an air bridge structure. The loss can be reduced in an integrated circuit including a phase shifter, an attenuator, and the like, and a conventional integrated circuit including a micromachine switch.

[Brief description of the drawings]

FIG. 1 is a block diagram showing one embodiment of the present invention.

FIG. 2 is a circuit diagram showing an equivalent circuit of FIG.

FIG. 3 is a cross-sectional view taken along a line AA ′ (a), a line BB ′ (b), and a line CC ′ (c) in FIG. 1;

FIG. 4 is a cross-sectional view (a cross-section taken along line CC in FIG. 1) illustrating a manufacturing step of the high-frequency semiconductor integrated circuit according to FIG. 1;

FIG. 5 is a sectional view showing a continuation of FIG. 4;

FIG. 6 is a sectional view showing a continuation of FIG. 5;

7 is a cross-sectional view (cross-sectional view taken along the line BB 'of FIG. 1) illustrating the manufacturing process of the high-frequency semiconductor integrated circuit of FIG. 1;

FIG. 8 is a block diagram showing another embodiment (transmitter / receiver of a wireless communication device) of the present invention.

FIG. 9 is a block diagram showing a conventional example (transmitter / receiver of a wireless communication device).

10A is a plan view showing a conventional micromachine switch, and FIG. 10B is a cross-sectional view taken along line DD ′.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Substrate, 2 ... Active layer, 3g ... Gate electrode, 3c ... Control electrode, 4s, 4d ... Ohmic electrode, 5 ... Interlayer insulating film,
6s, 6d, 6c, 6g ... electrode, 7s ... source electrode, 7
d ... drain electrode (signal line), 7sw ... signal line, 8s,
8sw: Electrode, 9b: Air bridge wiring, 9sw: Cantilever arm, 21, 22, 23: Electrode pad, 24: Micromachine switch, 25: FET, 26: Ground electrode, 31, 32: MMIC, 31a, 32a ... Amplifier,
31b, 32b: Micromachine switch, 33: Antenna, 36, 37: Terminal, 34, 35: Control terminal, 7
0, 90: metal, 100: sacrificial film.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01L 27/04 H01L 21/822

Claims (8)

(57) [Claims] A semiconductor substrate having an integrated circuit including an active element and a passive element; an interlayer insulating film covering a main surface of the semiconductor substrate; and a semiconductor substrate provided on the interlayer insulating film and connected to the integrated circuit. A first signal line, a second signal line provided on the interlayer insulating film and having an end provided at a predetermined distance from an end of the first signal line;
And a switch means for controlling conduction / non-conduction between the second signal lines, wherein the switch means is provided at one of ends of the first or second signal lines and is electrically conductive. A support member made of a conductive member, a cantilever arm provided on the support member and extending above the other signal line and made of a conductive member, and ends of the first and second signal lines And a control electrode provided immediately below the cantilever arm between the two. 2. The semiconductor high-frequency integrated circuit according to claim 1, wherein the semiconductor substrate is a silicon substrate or a compound semiconductor substrate. 3. The integrated circuit according to claim 1, wherein the integrated circuit includes at least one of a phase shifter, a transmission / reception switch, a variable attenuator, a frequency converter, a frequency multiplier, a frequency filter, an oscillator, a modulator, a demodulator, or an amplifier. A semiconductor high-frequency integrated circuit provided with a micromachine switch including any one of the above. 4. The semiconductor high-frequency integrated circuit according to claim 1, wherein the first and second signal lines are one of a microstrip line, a coplanar line, and a slot line. 5. A step of forming an integrated circuit including an active element and a passive element on a semiconductor substrate, a step of forming an interlayer insulating film on a main surface of the semiconductor substrate, and a step of forming the integrated circuit on the interlayer insulating film. Forming a first signal line connected to the first signal line and forming a second signal line having an end at a position separated by a predetermined distance from an end of the first signal line; and Forming a sacrificial film having a thickness covering the first and second signal lines thereon; and opening a through hole in the sacrificial film on one end of the first or second signal line. Forming a support member on the one end by filling the through hole with a conductive member; and extending the conductive member on the support member to the other signal line. Forming a cantilever arm comprising: The method of manufacturing a semiconductor high-frequency integrated circuit, characterized in that a step of removing the 牲膜. 6. The method according to claim 5, wherein the semiconductor substrate is a silicon substrate or a compound semiconductor substrate. 7. The integrated circuit according to claim 5, wherein the integrated circuit includes at least one of a phase shifter, a transmission / reception switch, a variable attenuator, a frequency converter, a frequency multiplier, a frequency filter, an oscillator, a modulator, a demodulator, or an amplifier. A method for manufacturing a semiconductor high-frequency integrated circuit, including any one of the above. 8. The method according to claim 5, wherein the first and second signal lines are one of a microstrip line, a coplanar line, and a slot line.