JP2005229057A - High-frequency integrated circuit and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high-frequency device, having simple structure and simple manufacturing processes, as compared with conventional technology and being capable of further reducing the transmission loss, and to provide a method for manufacturing the high-frequency device. <P>SOLUTION: A high frequency integrated circuit is constituted of forming two different elements out of a capacitor, an inductor, a line, and a switch on a silicon substrate by forming a plurality of depression parts which are mutually independent on one surface of the silicon substrate; forming a metal film, consisting of ground and a conductor pattern on the surface of the depression part side; forming a dielectric film on the surface of the metal film; and forming two different metallic patterns among the capacitor, the inductor, the line, or the switch on the dielectric film so as to correspond to the depression parts in the same process. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a high-frequency integrated circuit such as a high-frequency transmission line, a high-frequency device, or a high-frequency circuit that transmits or processes high-frequency signals such as microwaves, quasi-millimeter waves, and millimeter waves.

  In recent years, with increasing demand for improvement of high-frequency transmission technology, high-frequency passive circuits for processing high-frequency signals such as microwaves, quasi-millimeter waves, and millimeter waves have been developed to reduce insertion loss, such as gallium arsenide substrates. A low dielectric constant dielectric substrate such as a semiconductor substrate or a sapphire substrate is used, and the thickness of the substrate is reduced. However, a dielectric substrate having a low dielectric constant is generally expensive, and the thickness of the dielectric substrate can be reduced to about 100 μm at most, and there is a limit to improving the electrical performance in a high frequency band. On the other hand, an inexpensive semiconductor substrate such as a silicon substrate has a large dielectric loss, so that sufficient electrical characteristics cannot be obtained.

  In recent years, so-called RF MEMS (Radio Frequency Micro-Electro-Mechanical-Systems) devices, which are high-frequency devices using micromachining technology, have attracted attention. In this technique, since a high aspect structure and a membrane structure can be manufactured, even if a high-frequency circuit is manufactured on an inexpensive silicon substrate, it is hardly affected by the substrate, and therefore a high-performance high-frequency device can be expected at a low cost. In recent years, in a high-frequency silicon CMOS circuit, the upper limit frequency that can be used has been extended to the GHz band. By making the silicon CMOS active circuit and the RF-MEMS passive circuit monolithic, the high-frequency module has high functionality. And miniaturization is expected.

  Up to now, as a typical structure for reducing the dielectric loss of a substrate using RF MEMS technology, a structure in which a wiring conductor is formed on a dielectric membrane support film (hereinafter referred to as a membrane structure) is, for example, non-patent. It is disclosed in Document 1. In the shielded membrane microstrip line disclosed in Non-Patent Document 1, a dielectric membrane support film having a strip conductor on the upper surface is formed on a first semiconductor substrate having a ground conductor film on the upper surface. A microstrip line is configured by superimposing a second semiconductor substrate having a void formed on the lower surface and further overlapping a semiconductor substrate having a recess on the lower surface on the second semiconductor substrate.

  In the membrane microstrip line according to the related art configured as described above, when a high frequency signal is transmitted, the electromagnetic field of the high frequency signal is generated by the dielectric membrane support film between the strip conductor and the ground conductor film. However, since almost no electromagnetic field is generated in these semiconductor substrates, the transmission loss can be reduced.

Stephen V. Robertson et al., “A 10-60-GHz Micromachined Directional Coupler”, IEEE Transactions on Microwave Theory & Techniques, Vol.46, No.11, p.1845-1849, November 1998.

  However, since the membrane microstrip line according to the prior art uses two or more semiconductor substrates, the structure is complicated, the manufacturing process is complicated, and the manufacturing cost increases. It was. Further, this conventional technique still has a problem that the transmission loss is relatively high.

  The object of the present invention is to provide a high-frequency integrated circuit and a method for manufacturing the same, which solves the above-described problems and has a simple structure, a simple manufacturing process, and a further reduction in transmission loss compared to the prior art. There is to do.

  A high-frequency integrated circuit according to the present invention has a plurality of independent recesses formed on one surface of a silicon substrate, a metal film having a conductor pattern is formed on the surface of the recess, and an air layer is formed on the metal film. A dielectric film is further formed on both sides of the capacitor, and two different metal patterns of capacitors, inductors, lines, and switches are formed in the same process on the dielectric film and at positions corresponding to the recesses. Thus, two different elements such as capacitors, inductors, lines, and switches are formed on the silicon substrate.

  The method for manufacturing a high-frequency integrated circuit according to the present invention includes a step of etching a surface of a silicon substrate to form a recess having a predetermined depth, and a metal film is formed on the entire surface of the recess of the silicon substrate. A step of forming, a step of removing an unnecessary portion of the metal film to form a conductor pattern, a resist sacrificial layer is applied on the surface of the silicon substrate, its depression and the metal film, and the inside of the depression is resisted. A step of filling the sacrificial layer with a resist, a step of etching the resist sacrificial layer so as to leave a pattern portion larger than the recessed portion, and removing the other pattern portion; and a silicon substrate on which the resist sacrificial layer is formed. The step of polishing and planarizing the surface of the resist sacrificial layer using a chemical mechanical polishing method until the surface of the resist sacrificial layer is flush with the surface of the silicon substrate, and a dielectric film on the polished surface After forming, a metal wiring conductor film is formed on the dielectric film, and then the wiring conductor film is formed of any two or more of an inductor, a capacitor, a switch, and a line by using a photoengraving method and an ion beam etching method. A step of forming a wiring conductor film for any two or more of an inductor, a capacitor, a switch, and a line by etching in a predetermined pattern so as to be a conductor of a predetermined shape, and immediately above the resist sacrificial layer, In the portion of the dielectric support film where the wiring conductor film is not formed, a rectangular opening that penetrates the dielectric support film in the thickness direction is formed using a photoengraving method and a reactive ion etching method, And etching the resist sacrificial layer through the opening using a wet etching method to remove the resist sacrificial layer.

  According to the high frequency integrated circuit of the present invention, the substrate having a depression on the substrate surface, the first conductor pattern formed on the substrate including at least the depression, and the gap directly above the depression of the substrate. A dielectric film formed on the substrate across the substrate, and a second conductor pattern formed on a part of the surface of the dielectric film, wherein the first conductor pattern and the second conductor pattern are Two functional elements having different inductors, capacitors, switches, and lines are formed in the same process. Therefore, it is possible to provide a high-frequency device and a method for manufacturing the same that have a simple structure, a simple manufacturing process, and can further reduce transmission loss as compared with the prior art.

An embodiment of the present invention will be described below.
Embodiment 1 FIG.
FIG. 1 shows a phase shift circuit according to an embodiment of the present invention. 101, 102 are branch lines using hollow lines, 103, 104, 105, 106 are minute switches that operate by electrostatic force, 107, 108 are coils of a low-pass filter having a shape in which a plurality of U-shapes are alternately combined. , 109 are low-pass filter capacitors, 110 and 111 are high-pass filter capacitors, 112 is a spiral high-pass filter coil, 201 is an input terminal, 202 is an output terminal, and 203 is a control terminal for the switch 103. 204 are control terminals of the switch 104, 205 is a control terminal of the switch 105, and 206 is a control terminal of the switch.

Next, a creation method will be described.
FIG. 2 is a diagram showing processing of the silicon substrate. 300 is a silicon substrate, 301 is a recess for the branched hollow line of the input section, 302 is a recess for the branch hollow line of the output section, 303 is a recess for the switch 103, and 304 is for the switch 104. Indentation, 305 is indentation for switch 105, 306 is indentation for switch 106, 307 is indentation for coil 107, 308 is indentation for coil 108, and 309 is for capacitor 109 A depression 310 is a depression for the capacitors 110 and 111 and the coil 112 of the high-pass filter, and 311 is a protrusion left in the depression 310 to connect the coil 112 to the ground. The depressions on the silicon substrate are created by wet etching or dry etching.

FIG. 3 is a diagram showing a first conductor pattern layer on the silicon substrate of FIG. 400 is a common ground, 401a is an electrode for attracting the upper dielectric film of the switch 103, 402a is a contact point with a notch line on the dielectric film of the switch 103, 403a is a control line for applying the electrode voltage, 404a is an electrode pad for connecting the control line to the outside, 401b is an electrode for attracting the upper dielectric film of the switch 104, 402b is a contact with a notch line on the dielectric film of the switch 104, and 403b is the above-mentioned A control line for applying an electrode voltage, 404b is an electrode pad for connecting the control line to the outside, 401c is an electrode for attracting the upper dielectric film of the switch 105, and 402c is a cut on the dielectric film of the switch 105. 403c is a control line for applying the electrode voltage, 404c is for connecting the control line to the outside. 401d is an electrode for attracting the upper dielectric film of the switch 106, 402d is a contact point with a notch line on the dielectric film of the switch 106, 403d is a control line for applying the electrode voltage, 404d Is an electrode pad for connecting the control line to the outside, 405 is a ground removal unit for the input terminal, and 406 is a ground removal unit for the output terminal.
The conductor pattern is formed by forming a common ground 400 on the entire surface of the silicon substrate 300 using a sputtering method or the like, and then forming each pattern from the ground 400 by a photoengraving method or the like.

  FIG. 4 shows the second conductor formed after applying the resist pattern on the surface after forming the conductor pattern of FIG. 3, and then removing the resist agent other than the resist agent filled in the recesses by the planarization process. It is a figure which shows a pattern layer. Reference numeral 501 denotes a lower electrode of the low-pass filter capacitor 109, 502 a pattern for connecting the lower electrode and the common ground 400, 503 a lower electrode of the high-pass filter capacitor 110, and 504 a dielectric film to be formed later. A pattern for connecting the upper line and the lower electrode, 505 is a lower electrode of the capacitor 111 of the high-pass filter, and 506 is a pattern for connecting the line on the dielectric film to be formed later and the lower electrode. . These are formed on the resist agent filled in the depressions. Thereafter, a dielectric film such as silicon nitride is laminated with a thickness of about 1 μm to form a dielectric film, and a third conductor pattern is formed thereon as shown in FIG. The internal resist agent is removed using acetone or the like from the hole formed in the dielectric film formed on the top.

Next, the operation will be described.
FIG. 5 is a diagram showing an equivalent circuit of the phase shift circuit of FIG. Reference numeral 601 denotes an input terminal 101, 602 an output terminal 102, 603 a switch 103, 604 a switch 104, 605 a switch 105, 606 a switch 106, 607 a coil 107, 608 a coil 108, 609 a capacitor 109, and 610 a capacitor Reference numerals 110 and 611 denote capacitors 111 and 612 equivalently represent the coil 112. When the switches 603 and 604 are in the connected state and the switches 605 and 606 are in the open state, the high-frequency signal input from the input terminal 601 passes through the low-pass filter composed of the coils 607 and 608 and the capacitor 609 and passes through the output terminal 602. Is output. The coils 607 and 608 are low in loss without being affected by the silicon substrate because the lower part of the conductor is hollow.

  When the switches 603 and 604 are in the open state and the switches 605 and 606 are in the connected state, the high-frequency signal input from the input terminal 601 passes through the high-pass filter formed by the capacitors 610 and 611 and the coil 612, and the output terminal 602. Is output. The coil 612 is low in loss without being affected by the silicon substrate because the lower portion of the conductor is hollow. In either case, since the line from the input terminal 601 to the switch 603 or 605 is hollow, it is not affected by the silicon substrate and has a low loss. In either case, since the line from the switch 604 or 606 to the output terminal 602 is hollow, it is not affected by the silicon substrate and has a low loss. Furthermore, there is a large difference in the phase in the pass band between the low-pass filter and the high-pass filter, and the phase can be changed by switching these filters as described above.

  In this way, it is possible to simultaneously create a low loss line and a low loss changeover switch on a single substrate in a common process simultaneously with a low loss coil and capacitor in a high-performance high-frequency circuit. A high-frequency circuit can be manufactured at a low price.

  Although the above is an example of a phase shift circuit, a small mechanical switch for switching a circuit on a silicon substrate including a semiconductor circuit and a low-loss coil effective for improving the performance of a transmitter and an amplifier are prepared. Therefore, it is possible to obtain a high-performance portable terminal device at a low price.

Here, the principle of the minute switch (high frequency switch) will be described. FIG. 6 is a diagram for explaining the principle of the minute switch (high frequency switch). In the figure, when a voltage is applied to the control terminals 4a and 4b, for example, when a positive voltage is applied, positive charges are generated on the surfaces of the first electrodes 6a and 6b, and the second electrode is caused by electrostatic induction. Negative charges appear on the lower surfaces of 8a and 8b, and the second electrodes 8a and 8b are attracted toward the first electrodes 6a and 6b by the attractive force between them. At this time, the signal line 9 formed on the dielectric film 7 is simultaneously drawn toward the first electrodes 6a and 6b, and the signal line 9a and the ground conductor 3 are in contact with each other through the dielectric film 7a. Become.
The dielectric film 7a when the signal line 9a and the ground conductor 3 are in contact with each other can be regarded as a capacitor. In the high-frequency switch according to the second embodiment, the switch is turned off or on depending on the strength of electrical coupling. be able to.

  The present invention can produce a small mechanical switch for switching a circuit on a silicon substrate including a semiconductor circuit, a low-loss coil effective for improving the performance of a transmitter and an amplifier, and is a low-cost and high-performance portable terminal device. Applicable to.

It is a perspective view of the phase shift circuit by Embodiment 1 of this invention. It is a figure which shows the process of the silicon substrate of FIG. FIG. 3 is a diagram showing a first conductor pattern layer on the silicon substrate of FIG. It is a figure which shows the 2nd conductor pattern layer produced after the planarization process of a resist agent. FIG. 2 is a diagram showing an equivalent circuit of the phase shift circuit of FIG. It is a figure for demonstrating the principle of the micro switch of this invention.

Explanation of symbols

  4a, 4b; control terminal, 6a, 6b; first electrode, 8a, 8b; second electrode, 7; dielectric film, 9; signal line, 3; ground conductor, 7a; Branch line, 103, 104, 105, 106; minute switch, 107, 108; coil of low-pass filter, 109; capacitor of low-pass filter, 110, 111; capacitor of high-pass filter, 112; high Pass-pass filter coil, 201; input terminal, 202; output terminal, 203 to 206; control terminal, 300; silicon substrate, 301 to 310; recess, 311; projection, 400; common ground, 401a, 401b, 401c 401d; electrodes, 402a, 402b, 402c, 402d; contacts, 403a, 403b, 403c, 403d; control lines, 404a, 404b, 40 Electrode pad, 405; notch, 406; notch, 501; lower electrode, 502; pattern, 503; lower electrode, 504; pattern, 505; lower electrode, 506; pattern, 601; input terminal, 602 Output terminal 603; switch 604; switch 605; switch 606; switch 607; coil 608; coil 609; capacitor 610; capacitor 611; capacitor 612;

Claims (3)

  A plurality of independent recesses are drilled on one surface of the silicon substrate, a metal film conductor pattern is formed on the surface of the recess, and a dielectric film is formed on the metal film with an air layer in between. Then, two different metal patterns of capacitors, inductors, lines, and switches are formed in the same process on the dielectric film or on both surfaces of the film and corresponding to the depressions, and the capacitor is formed on the silicon substrate. , A high-frequency integrated circuit formed by forming two different elements of an inductor, a line, and a switch.   Etching the surface of the silicon substrate to form a recess having a predetermined depth; forming a metal film on the entire surface of the recess of the silicon substrate; and forming a metal film to form a conductor pattern A step of removing unnecessary portions, a step of applying a resist sacrificial layer on the surface of the silicon substrate, its depression and the metal film, and filling the inside of the depression with the resist of the resist sacrificial layer; and Of these, etching is performed so as to leave a pattern portion larger than the recess, and the other pattern portion is removed, and the silicon substrate on which the resist sacrificial layer is formed is formed on the resist sacrificial layer using a chemical mechanical polishing method. A step of polishing and planarizing the surface until it is flush with the surface of the silicon substrate, and forming a dielectric film on the polished surface, and then forming a metallic wiring conductor film on the dielectric film Then, using a photoengraving method and an ion beam etching method, the wiring conductor film is etched in a predetermined pattern so that it becomes a conductor having a predetermined shape of any two or more of an inductor, a capacitor, a switch, and a line. A step of forming a wiring conductor film for any two or more of an inductor, a capacitor, a switch, and a line; and a portion of the dielectric support film that is directly above the resist sacrificial layer and has no wiring conductor film formed thereon. A rectangular opening that penetrates the dielectric support film in the thickness direction is formed using photolithography and reactive ion etching, and the resist sacrificial layer is etched through the opening using wet etching. And a step of removing the resist sacrificial layer.   The high-frequency integrated circuit includes a high-pass filter circuit in which a grounded coil is connected between the capacitor and the capacitor in a series circuit of a switch and two capacitors, and the coil in a series circuit of the switch and two coils. 2. The high-frequency integrated circuit according to claim 1, wherein the phase shift circuit is switchable between a low-pass filter circuit connected between a coil and a capacitor grounded but connected.

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