JPH0884484A - Formation of microstructure - Google Patents

Abstract

PURPOSE: To realize electrical connection with a substrate by bonding a sacrifice layer of resin film and an adhesive layer formed on a first substrate to a structure body layer formed on a second substrate, removing the second substrate, connecting the first substrate and the structure body layer mechanically through a supporting layer, and then removing the sacrifice layer and the adhesive layer. CONSTITUTION: A photoresist (PL) 101 is patterned on a second Si substrate 4 and then it is etched to form a beam pattern 5. An adhesive layer 7 is then formed on the first glass substrate 1. The second substrate is then pressure bonded to the first substrate on which a sacrifice layer 6 and the adhesive layer 7 are formed. The second substrate is further etched to form an Si beam 2 on which a supporting layer, i.e., a thin Al film 8, is formed followed by formation of a PL 102. Subsequently, the thin Al film 8 is patterned to form a pattern of supporting part 3. Finally, the resin film is removed from the PL 102 and the lower part of the beam 2 by plasma etching thus forming an air gap 9.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a microstructure manufactured by using micromechanics technology, and more particularly to a method for forming a microstructure formed by using a sacrificial layer.

[0002]

2. Description of the Related Art In recent years, micromachines having a small movable mechanism have been studied by micromechanics technology. In particular, a microstructure formed by using a semiconductor integrated circuit formation technique (semiconductor photolithography process) can form a plurality of small mechanical parts with high production reproducibility on a substrate. For this reason, it is relatively easy to form an array and reduce the cost, and due to the miniaturization, excellent high-speed response can be expected as compared with the conventional mechanical structure.

[0003]

There are the following four examples as typical methods for producing a microstructure on a substrate. The first method is to use a wobbled micromotor (M. Mehregany et al., "Operation
of microfabiricated harmonic and ordinary side-d
rive motors ", Proceedings IEEE Micro Electro Mecha
nical Systems Workshop 1990, pp.1-8), and linear microactuator (P. Cheung et al., "Modeling
and position-detection of a polysilicon linear mi
croactuator ", Micromechanical Sensors, Actuators, a
nd Systems ASME 1991, DSC-Vol. 32, pp.269-278), etc., which is a fabrication method for forming a sacrificial layer on a Si substrate and a polysilicon thin film forming a microstructure. , SOI (Si on Insulator) or SIM
OX (Separatin by ion implantation of oxygen, BD
iem et al., "SOI (SIMOX) as a Substrate for Surface
Micromachining of Single Crystalline Silicon and A
ctuators ", The 7th International Conferenceon Soli
d-State Sensors and Actuators, Transducers '93, Ju
ne 7-10, 1993, pp.233-236), a silicon oxide film is removed as a sacrificial layer by patterning the silicon film into a desired shape and then removing the silicon oxide film with an aqueous hydrofluoric acid solution.

However, in the first method, since the silicon oxide film is removed by etching with an aqueous solution of hydrofluoric acid, it is necessary to use a hydrofluoric acid corrosion resistant material as a structural body without being etched by hydrofluoric acid. It is not possible to wire electrodes such as aluminum electrodes. Furthermore, when polysilicon is used as a microstructure, it is necessary to control the film stress of polysilicon so that warpage due to film stress does not occur. When an SOI substrate is used, the silicon oxide film under the bulk Si thin film is removed, so that the silicon oxide film supporting the structure is etched back, and the structure becomes a beam shape and electrical connection between the substrate and the structure. Will be difficult.

The second method is a spatial light modulator (LJ Hornbec) comprising a micromirror of an aluminum (Al) thin film.
k: JP-A-2-8812),
After coating a photoresist to be a sacrificial layer on the substrate, forming an Al thin film and patterning it into a desired shape, the photoresist is removed by dry etching using oxygen plasma to form a microstructure composed of the Al thin film. Is the way to do it.

In the second method, by using the photoresist as the sacrificial layer, it is possible to form microstructures on various kinds of substrates without depending on the surface roughness of the substrate. This allows the sacrificial layer to be removed by dry etching with oxygen plasma,
Sticking between the microstructure and the substrate that occurs when removing the sacrificial layer by wet etching can be avoided.

However, it is necessary to form the structure thin film at a low temperature at which the photoresist is not thermally damaged during the manufacturing process, and the effect of the restriction of the structure material is great. Further, in order to form the microstructure by a thin film forming process such as vacuum deposition or sputtering, it is necessary to control the stress of the film so that the manufactured microstructure does not warp due to the film stress.

The third method is to form a pattern of a microstructure on a bulk Si substrate, then bond a part of the pattern to a glass substrate by anodic bonding, and etch the bonded Si substrate from the back surface. Then, the microstructure is formed by leaving only the microstructure on the glass substrate. Using this third method, a linear actuator (Y. Giancha
ndani et al., "Micron-Size, High Aspect Ratio Bulk
Silicon micromechanical Devices ", Proceedings IEE
E Micro Electro Mechanical Systems Workshop, 1992,
pp.208-213) and silicon nitride film AFM (Atom
ic force microscope) cantilever (TA Albrech
t et al., USP 5,221,415) and the like.

In the third method, it is not necessary to use a sacrificial layer, and it is possible to form a microstructure with a material having no hydrofluoric acid resistance. However, since it is necessary to perform anodic bonding with glass, as a material, conductive metals forming oxides such as Si and Al, Ti, Ni, etc., or a silicon nitride film capable of anodic bonding only in a thin film formed on a Si substrate are used. , And silicon oxide film. Further, the bonding temperature of the anodic bonding is 300 ° C. or higher, and in order to avoid the damage of the substrate at the time of bonding due to the distortion of thermal stress, the glass is S
It is necessary to have a coefficient of thermal expansion approximately equal to that of the i substrate.

The glass usable for this purpose is limited to glass such as Pyrex glass (trade name, # 7740, Corning). Furthermore, since the voids are formed in advance on the bonding surface, the electrodes and the like cannot be formed on the microstructure after bonding. Further, since it is necessary to use glass containing mobile ions as the substrate, it is not possible to integrate circuits on the substrate. Further, when the glass and the conductive material are bonded by anodic bonding, the surface roughness of the glass and the conductive material needs to be suppressed to 50 nm or less, and the bonding cannot be performed on the wiring having a large step.

In view of the above, the present invention aims to provide the following excellent method for forming a microstructure. That is,
The method has advantages that (1) the materials of the microstructure and the substrate are not limited, and (2) that an electrode pattern is formed on the microstructure and can be electrically connected to the substrate. Is.

[0012]

The above object can be achieved by the present invention described below. That is, in the method for forming a microstructure, the method comprises the steps of (1) forming a sacrificial layer and an adhesive layer made of a resin film on the first substrate;
(2) a step of forming a structure layer on the second substrate, (3) a step of adhering the first substrate and the structure layer via the adhesive layer,
(4) removing the second substrate, (5) forming a support layer for connecting the structure layer and the first substrate, (6) removing the sacrificial layer and the adhesive layer, Disclosed is a method for forming a microstructure, which comprises the steps of

The present invention will be described in more detail below. As a method for forming the sacrificial layer and the adhesive layer, a usual forming method can be used, for example, a method in which a liquid obtained by diluting a resin molecule with an organic solvent is applied by a spinner method, a dipping method, a spray method, or the like. It is performed using a resin film forming method. With the coating method, the resin film can be coated with good flatness even if there are surface irregularities on the substrate, which allows a good surface contact without depending on the substrate surface roughness in the step of adhering to the second substrate. Wearing is possible. As a resin material,
When forming a resin film on a Si substrate with integrated circuits,
A photoresist containing few impurities such as sodium ions is preferred. Further, a rubber-based photoresist having a rubber excellent in adhesion and mechanical strength is more preferable.

Examples of the rubber-based photoresist usable in the present invention include “Microfabrication and Resist” (Saburo Nonogaki, edited by The Society of Polymer Science, published by Kyoritsu Shuppan, 1990).
The rubber described on page 3, line 3 is preferred, and OMR is used as a high-resolution negative photoresist made by Tokyo Ohka Kogyo Co., Ltd.
A photoresist containing a rubber such as -83 can be preferably used.

After forming the sacrificial layer so that the sacrificial layer is not dissolved when the adhesive layer is formed, a hardening treatment is performed. As a method for curing treatment, a usual method for curing a resin film can be used, and for example, a curing treatment method such as heating or light irradiation is used. When using photoresist as the sacrificial layer,
The temperature of the heat curing treatment is a temperature at which the polymer in the photoresist is crosslinked and insolubilized. A negative photoresist is strongly insolubilized by being crosslinked by light irradiation.

As the second substrate on which the structure layer is formed,
Use of a substrate on which a structure pattern is formed by a semiconductor photolithography process and etching, a substrate on which a structure layer is formed as a thin film on a second substrate, a second substrate on which a structure layer is formed via a transfer sacrificial layer, and the like. Is possible.

For a substrate on which a structure pattern is formed by a semiconductor photolithography process and etching, and a substrate on which a structure layer is formed as a thin film on a second substrate, an etching suitable for the substrate material is performed in the step of removing the second substrate. The back surface is ground to leave only the structure layer by a wet etching method using a liquid, a dry etching method using a reactive gas, or a lapping method using abrasive grains. For example, when Si is used as the second substrate,
As an etching solution, potassium hydroxide solution (KOH),
4-methyl ammonium aqueous solution
Alkaline aqueous solution such as yd oxide) or a mixed aqueous solution of hydrofluoric acid and nitric acid, and the reactive gas is CF ₄ , S
This is performed using a plasma gas such as F ₆ and NF ₃ . If a bulk of Si or the like on which a pattern of a structure is formed by etching is used as the second substrate, the microstructure does not warp, which causes a problem when forming a thin film on the sacrificial layer to manufacture the microstructure. The problem of warpage due to the film stress can be avoided.

As the substrate on which the structure layer is formed via the transfer sacrificial layer, for example, a second substrate is a glass substrate, and a thin metal film to be a transfer sacrificial layer is formed on the structure layer.
A voltage is applied to the metal film and the glass substrate to form a substrate made of a bonded body formed by an anodic bonding method, an SOI substrate having a silicon oxide film as a transfer sacrifice layer and a silicon film as a structure layer, a SIMOX substrate, or the like. A substrate having an intermediate layer, second
A substrate in which a sacrificial layer for transfer and a structure layer are formed into a thin film on the substrate can be used. The material for the transfer sacrificial layer is selected from materials in which at least the adhesive layer and the structure layer are not corroded by an etchant for removing the transfer sacrificial layer. As a thin film forming method, a vacuum deposition method, a CVD (Chemic
thin film deposition method such as al Vapor Deposition) method is used. In the case of anodic bonding, the second substrate is a glass substrate containing alkali metal mobile ions (for example, sodium), and the metal film is a metal film capable of anodic bonding such as Si, Al, Ti, or Ni, or these elements. A metal film made of an alloy containing is used. By forming a thin film of these metal films on the structure layer, various materials such as insulators, semiconductors, and metals can be anodically bonded to the glass substrate as the material of the structure layer.

When the structure layer is bonded to the second substrate, the handling is difficult when the thickness of the structure layer is several tens of μm or less. For this reason, it is also possible to use a substrate such that a structure layer is formed by thinning the film after bonding to form a structure layer, or by removing the substrate on which the structure layer is previously formed. For thinning or removing the substrate, wet etching using an etching solution suitable for the substrate material, dry etching using a reactive gas, or lapping using polishing abrasive grains, polishing from the back surface using a polishing method is performed. For example, a structure layer having a desired thickness can be bonded onto the second substrate, and if a bulk substrate of Si, GaAs or the like is used as the structure material, the microstructure composed of the thinned bulk is warped. Therefore, it is possible to avoid the problem of warpage due to film stress, which is a problem when a thin film is formed on the sacrificial layer to manufacture a microstructure. In addition, it is possible to arbitrarily adjust the thickness of the bonded body layer by reducing the thickness.

In the step of adhering the first substrate and the structure layer, the first substrate and the second substrate are pressed against each other from the back side by pressure and then heat-treated to be included in the resin film which is the adhesive layer. This is performed by evaporating the organic solvent generated, curing the resin, and strengthening the adhesive force with each substrate. If the first substrate and the second substrate are conductors, it is also possible to apply a voltage to each to apply a pressure using the generated electrostatic force to bond them.

When the first substrate and the second substrate are warped or when the pressure is not uniformly applied to the surfaces of the substrates to be adhered, the adhesive layer is uncured when the sacrifice layer in the forming process of the present invention is omitted, The structure layer is embedded in the adhesive layer, making it difficult to keep the thickness of the adhesive layer uniform, and the distance between the structure layer and the first substrate is different in the plane. As a result, the gaps between the plurality of microstructures on the substrate surface and the substrate are different from each other. By forming a sacrificial layer made of a resin film in advance and curing it sufficiently, even if the structure layer is buried in the adhesive layer, it is not buried in the sacrificial layer.
This makes it possible to control the distance between the structure layer and the first substrate with good reproducibility in the plane of the substrate even if the substrate warps or the pressure at the time of adhesion is applied nonuniformly. Since the sacrificial layer is used as a layer for controlling the gap between the structure layer and the first substrate, the adhesive layer is preferably formed thinner than the sacrificial layer.

By forming a groove in the first substrate and / or the structure layer, the vapor of the organic solvent generated when the adhesive layer is heat-treated can be released through the groove. As the groove, it is possible to use the stepped portion of the pattern of the structure layer patterned by the semiconductor photolithography process as the groove.

The resin film as the adhesive layer can be cured at a relatively low temperature, and the first substrate and the second substrate can be cured.
It is possible to avoid substrate damage at the time of bonding due to the difference in the thermal expansion coefficient of the substrates, and there is no limitation on the material of the first substrate due to the difference in the thermal expansion coefficient.

In the step of removing the second substrate, the second substrate having the transfer sacrificial layer is subjected to the step of removing the transfer sacrificial layer, so that the second adhesive layer and the structure layer on the first substrate are adhered to each other. The substrate and the structure layer will be separated. That is, the structure on the second substrate is transferred onto the adhesive layer of the first substrate by this step.

The support layer mechanically connects the first substrate and the structure layer, and is formed before the sacrifice layer and the adhesive layer are removed to transfer the upper surface of the structure layer and the first substrate surface. It is formed on the top and has a structure in which the structure layer is caught from above. By using the metal thin film (Al or the like) as the support layer, the structure layer and the first substrate can be electrically connected.

The step of removing the sacrificial layer and the adhesive layer made of the resin film is performed by a method of removing the resin film by wet etching by immersing it in a solution that dissolves the resin film, or a method of dry etching by ashing using oxygen plasma. Since the sacrificial layer and the adhesive layer are made of resin, dry etching can be performed, and sticking, which is a problem when removing the sacrificial layer by wet etching, can be avoided.

The microstructure manufactured by the above-mentioned forming method comprises a first substrate, a support portion composed of a support layer, and a structure layer which is supported and patterned by the support portion with the first substrate through a gap. When the structure layer is supported through the gap, the supporting portion has a feature of connecting and supporting the first substrate and the upper surface of the structure layer. The fixed electrode and the drive electrode are formed on the first substrate, the structure layer is patterned into a beam shape, and the movable electrode is provided on the beam, so that the support portion electrically connects the movable electrode and the fixed electrode and mechanically. It is possible to manufacture an electrostatic actuator characterized in that the beam is displaced from the upper surface of the beam by applying a voltage to the driving electrode and the movable electrode. Microstructures that can be produced by the method of the present invention include, for example, electrostatic actuators, AFMs, STs.
It is possible to accurately manufacture a cantilever used in a microscope system for detecting tunnel current such as M (Scanning Tunneling Microscope), van der Waals force, magnetic force, electrostatic force, and wiring of an air bridge structure.

In the method for forming a microstructure of the present invention configured as described above, the sacrifice layer and the adhesive layer made of the resin film formed on the first substrate and the structure layer formed on the second substrate. After the bonding, the second substrate is removed, the supporting layer mechanically connects the first substrate and the structure layer, and the sacrificial layer and the adhesive layer are removed. By adhering with the resin film, the material of the structure layer formed on the first substrate, the second substrate, and the second substrate is not limited, and the structure layer is formed on the structure layer by the previous step of removing the resin film. Electrodes can be formed. Since the sacrificial layer and the adhesive layer are made of a resin film, they can be removed by a solvent, ashing, etc., and the electrodes are not etched. Then, by removing the sacrifice layer and the adhesive layer made of the resin film by dry etching, it is possible to avoid sticking, which is a problem when the conventional sacrifice layer is removed. Further, by forming a sacrificial layer made of a resin film in advance and sufficiently curing it, it becomes possible to control the distance between the structural body layer and the first substrate with good reproducibility in the plane of the substrate.

[0029]

EXAMPLES Examples of the method for forming a microstructure according to the present invention will be described below in detail with reference to the drawings of FIGS. 1 to 7, but the present invention is not limited thereto.

Example 1 FIGS. 1 and 2 are explanatory views of a manufacturing process showing a first example of a method for forming a microstructure according to the present invention, and FIG. 3 is a schematic diagram of a microstructure manufactured using the same. FIG. The microstructure of the present invention has the following structure from FIG. 1
Is a glass substrate serving as a first substrate, 2 is a beam composed of a structure layer formed by thinning a second substrate composed of Si, and 3 is a supporting portion of an Al thin film which is a supporting layer.
The beam 2 has a structure in which it is suspended from the upper surface of the beam by a supporting portion 3 through a gap 9, and the supporting portion 3 is
The substrate 1 and the substrate 1 are mechanically connected by an air bridge structure.

A method for forming the microstructure shown in FIG. 3 according to the present invention in the AA cross section will be described with reference to FIGS. Si substrate 4 made of bulk Si as the second substrate
Photoresist patterning is performed by using a photolithography process in which a photoresist 101 is applied onto the substrate, exposed and developed by using (FIG. 1A).
reference). The Si substrate 4 using the photoresist as a mask,
The Si substrate 4 was etched by reactive ion etching (RIE) using a mixed gas of SF ₆ and CCl ₂ F _2.
A beam pattern 5 is formed on top. Photoresist 10
1 is peeled off using a resist peeling liquid to manufacture a second substrate (see FIG. 1B). The step of the beam pattern 5 is 5μ
m.

Next, a glass substrate 1 (trade name, # 7059, Corning Co., Ltd.), which is the first substrate, is coated with a solution in which a polyimide precursor is dissolved by a spinner method which is one of the resin film forming methods. It is heat-cured at a temperature of ° C to form a 2 µm thick sacrificial layer 6 made of a polyimide resin film. Then, a solution of polymethyl methacrylate (PMMA) dissolved in methyl ethyl ketone (MEK) is applied by a spinner method to form a 0.5 μm thick adhesive layer 7 made of PMMA that has not been cured (see FIG. See C)).

The glass substrate has a thermal expansion coefficient about 1.4 times larger than that of Si. The second substrate of FIG. 1B and FIG.
The first substrate on which the sacrificial layer 6 and the adhesive layer 7 of (C) are formed,
Pressure is applied from the back surface of each substrate to bond them (see FIG. 1D).

As shown in the figure, the beam pattern 5 is not embedded in the sacrificial layer 6 even if it is embedded in the adhesive layer 7 '.
The sacrificial layer serves as a layer for controlling the gap between the structure layer and the first substrate, and the structure layer and the first substrate are not affected even if the substrate is warped or the pressure during bonding is unevenly applied. It has become possible to control the interval of with good reproducibility within the plane of the substrate. After adhering the first substrate and the second substrate via the adhesive layer, 150 ° C.
The adhesive layer was cured by heating to.

Thereafter, the Si substrate 4 is wet-etched with a 30 wt% KOH aqueous solution heated to 100 ° C.,
The second substrate was thinned (see FIG. 1E). Next, SF
The second substrate was further etched by RIE using ₆ gas to form a Si beam 2 having a film thickness of 1 μm (FIG. 1 (F)).
reference). Then, PMMA is performed by RIE using oxygen gas.
And polyimide were etched in the same pattern as the beam (see FIG. 1G).

On the Si beam formed as described above, an Al thin film 8 serving as a support layer is formed to a thickness of 1 μm by a sputtering method using an Al target, which is one of the vacuum deposition methods.
A film was formed. A photoresist 102 was applied, exposed, and developed on the Al film by a photolithography process (see FIG. 2 (I)). Next, the Al film 8 was patterned using an Al etchant composed of phosphoric acid, nitric acid and acetic acid to form the pattern of the supporting portion 3 (see FIG. 2 (J)).

Finally, the photoresist 102 and the resin film under the beam 2 were removed by etching with oxygen plasma to form the void 9. The microstructure shown in FIG. 3 in which the Si beam 2 having a film thickness of 1 μm and having the void 9 was supported by the Al film was formed by using the above forming method (see FIG. 2K). It was possible to avoid sticking, which is a problem when removing the sacrificial layer by conventional wet etching, without etching each electrode by etching with oxygen plasma.

In the forming method of the present invention, as shown in FIG. 1B, a beam-shaped structure layer pattern was first formed on the bulk Si substrate 4. Since the bulk Si was formed into a thin film, it was possible to form a warp-free beam having essentially no internal stress. In addition, a groove is formed on the Si substrate 4 by the pattern of the beam, and the solvent vapor generated when the adhesive layer made of PMMA is heat-cured by the process of FIG. 1D is allowed to escape through the groove. You can In the case where the structure layer has a large area, unless the content of the solvent contained in the resin-dissolved solution at the time of application is adjusted, the solvent vapor during the heat treatment may cause a gap between the adhesive layer and the second substrate. Bubbles may remain in the. In such a case, it is possible to prevent bubbles from remaining at the interface by performing pretreatment heating at a low temperature at which the resin does not harden and adjusting the content of the solvent contained in the resin film. In PMMA, it was possible to suppress the generation of bubbles by pretreatment at 50 ° C. for 10 minutes.

Further, by using the resin film as the adhesive layer, it is possible to bond at a low temperature of 150 ° C., and it becomes possible to use a substrate having a different thermal expansion from the second substrate as the first substrate. As shown in this embodiment, the resin film serves as an adhesive layer for adhering the first substrate and the second substrate together with a role of a sacrificial layer for forming a microstructure.

Although a metal thin film made of an Al thin film is used for the supporting portion, if an insulating film such as a silicon oxide film formed by vacuum vapor deposition at a temperature at which the sacrificial layer made of a resin film and the adhesive layer are not damaged by heat is used. Needless to say, it is possible to form an electrically insulating microstructure on the substrate by the same process. A glass substrate was used as the first substrate, but quartz and Al ₂ O were formed by the same forming process.
Other insulators such as ₃ , MgO, ZrO ₂ , Si, GaA
It goes without saying that various substrates such as semiconductors such as s and InP and metals can be used. Further, polyimide was used as the sacrificial layer, PMMA was used as the adhesive layer, and different resin films were used, but the sacrificial layer was sufficiently cross-linked so that the sacrificial layer did not dissolve when the adhesive layer was applied.
It is also possible to use the same organic resin film member.

As an evaluation of the reproducibility of the control of the distance between the structure layer and the first substrate, 200 nm of Cr was applied to the adhesive surface side of the first substrate.
A glass substrate having a diameter of 2 inches φ, which is formed so as to have a warp of the substrate due to film stress, and a second substrate made of a 2 inch φ Si wafer are used.
Four beam patterns each having a length of 10 mm are formed at intervals of 10 mm in the same manner as in FIG. 1B, and subsequently, FIGS.
By the step (F), four Si beams were formed on the sacrificial layer and the adhesive layer on the glass substrate.

After the beam was formed on the resin film by the process of FIG. 1G, the beam was removed by etching and the film thickness of the resin film was measured. The film thickness of the resin film was 2.0 to 2.2 μm.
It was within the range of m. On the other hand, except for the step of forming the sacrificial layer by the step of FIG.
The coating was applied to a thickness of μm, a beam was formed in the same manner as above, and then the beam was removed, and the film thickness of the resin film was measured. The sacrificial layer serves as a layer for controlling the distance between the structure layer and the first substrate, and the structure layer is a sacrificial layer made of a resin film even if the substrate is warped or the pressure during bonding is unevenly applied. It was possible to control the distance from the first substrate within the plane of the substrate with good reproducibility without being embedded in the layer.

Example 2 FIGS. 4 and 5 are explanatory views of a production process showing a second example of the method for forming a microstructure of the present invention, and FIG. 6 is a schematic diagram of a microstructure produced by using the same. FIG. The microstructure of the present invention has the following structure from FIG. 1
Reference numeral 0 is a Si substrate as a first substrate, 14 is an insulating layer made of a silicon oxide film, 15 and 16 are drive electrodes and fixed electrodes formed in a thin film on the insulating layer 14, and beam 12 is a patterned Si structure layer, It has a torsion bar 11 and is supported from the upper surface of the beam by supporting portions 13 and 13 ′ through a gap, and a movable electrode 17 is formed on the beam 12. The supporting portions 13 and 13 ′ are made of an electric conductor and electrically connect the movable electrode 17 and the fixed electrode 16. The microstructure of this embodiment can be displaced as an electrostatic actuator by applying a voltage to the fixed electrode 16 electrically connected to the drive electrode 15 and the movable electrode 17 on the beam 12.

As a result, the electrostatic actuator has a structure in which the beam 12 is suspended from the upper surface of the beam by the supporting portions 13 and 13 'through the gap, and the supporting portions 13 and 13' are provided.
Has a structure in which the beam 12, the insulating layer 14, and the fixed electrode 16 are mechanically and electrically connected to each other by an air bridge structure. By applying a voltage to the drive electrode 15 and the movable electrode 17, the torsion bar 11 is twisted and rotated, and the beam is displaced.

The forming method of the present invention in the BB cross section of the microstructure shown in FIG. 6 will be described with reference to FIGS. When forming a microstructure with a beam thickness of 2 μm,
The structure layer to be the beam is bonded to the second substrate. However, it is difficult in terms of handling to bond the structure layer having a thickness of 2 μm to the second substrate via the transfer sacrificial layer. For this reason, the Si substrate 20 which is thinned after the bonding and becomes the structure layer is used. Transfer sacrificial layer 21 made of Al film on Si substrate 20
By the electron beam evaporation method which is one of the thin film volume methods.
A film having a thickness of 0 nm is formed (see FIG. 4A). A second substrate 22 made of a glass substrate (trade name, # 7740, Corning Co.) and the sacrificial layer 21 for transfer are joined by an anodic joining method (see FIG. 4B).

The anodic bonding process will be described with reference to FIG. In the figure, 33 is a power supply for applying a voltage between the sacrificial layer (Al film) 21 for transfer formed on the Si substrate 20 and the glass substrate which is the second substrate 22, and the lead wires 32, 34. Are electrically connected to the needle electrodes 31 and 35. A platen 30 is electrically conductive and has a heater. The second substrate 22 is overlapped with the transfer sacrificial layer (Al film) 21 as a bonding surface. Platen temperature 300
While maintaining the temperature at 0 ° C., a voltage of 500 V was applied between the second substrate and the sacrifice layer for transfer for 20 minutes by the power supply 33,
The substrate and the sacrificial layer for transfer were bonded by the anodic bonding method. Next, the Si substrate 20 was lapped and polished by using abrasive grains until the thickness of the structure layer became 2 μm (FIG. 4).
(See C)).

Next, although not shown in the drawing, a photoresist is applied to the structure layer 23 to perform patterning by a photolithography process, and the structure layer is subjected to reactive ion etching (RIE) with CF ₄ gas using the photoresist as a mask. Etching was performed, and then the etching gas was changed to a mixed etching gas of BCl ₃ and Cl ₂ to etch the transfer sacrificial layer 21, the photoresist was peeled off, and a beam pattern 24 was formed (see FIG. 4D).

As the first substrate to be adhered, the Si substrate 10 having the insulating layer 14, the driving electrode 15 and the fixed electrode 16 was used. The insulating layer 14 is a silicon oxide film having a thickness of 1 μm obtained by thermally oxidizing the Si substrate 10 using an oxidizing gas. The drive electrode 15 and the fixed electrode 16 are formed by continuously depositing Cr with a thickness of 5 nm and Au with a thickness of 200 nm on the insulating layer by an electron beam evaporation method, applying a photoresist by a photolithography process, exposing the photoresist, and patterning the photoresist. On the first substrate, the electrode pattern shown in FIG. 6 is obtained by patterning Au and Cr as a mask with an Au etchant composed of an aqueous solution of iodine and potassium iodide and a Cr etchant composed of an aqueous solution of cerium ammonium nitrate and perchloric acid. Then, a resin film to be the sacrificial layer 25 is applied by a spinner method. A rubber resist OMR-83 (trade name) manufactured by Tokyo Ohka Co., Ltd. was used as the resin film. After applying the rubber-based resist, heat treatment is performed at 80 ° C. for 20 minutes to evaporate the solvent contained in the rubber-based resist,
After that, a photo-curing treatment is applied to crosslink by irradiating ultraviolet rays,
Finally, heat curing treatment was performed at 150 ° C. for 1 hour. The coating conditions were set so that the thickness of the sacrificial layer was 2 μm. Next, similarly to the sacrifice layer, a rubber resist OMR-83 (trade name) manufactured by Tokyo Ohka Co., Ltd. was applied by a spinner method to form an adhesive layer 26 of 0.4 μm thickness which was not cured (FIG. 4 (E)).

The same rubber-based resist as that used for the sacrificial layer was used for the resin film serving as the adhesive layer. However, even if the adhesive layer is applied, the sacrificial layer is not dissolved because the sacrificial layer is cured. There wasn't. As shown, the beam pattern 24 is not embedded in the sacrificial layer 25 even if it is embedded in the adhesive layer 26 ′. The sacrificial layer serves as a layer for controlling the distance between the structure layer and the first substrate, and the structure layer and the first substrate are separated from each other even if the substrate is warped or the pressure during bonding is unevenly applied. It has become possible to control the spacing within the plane of the substrate with good reproducibility.

After applying the adhesive layer 26, the second substrate of FIG. 4 (D) and the first substrate of FIG. 4 (E) are pressed against each other from the back surface, and then heat-treated at 150 ° C. The organic solvent contained in the resin film, which is the adhesive layer, was evaporated and cured to adhere (see FIG. 4 (F)). In the forming method of the present embodiment, by using the glass substrate as the second substrate, it is possible to perform the bonding while visually observing the bonding, and the alignment of the drive electrode and the beam at the bonding becomes easy.

Then, the patterned transfer sacrificial layer 21.
Al consisting of phosphoric acid, nitric acid and acetic acid heated to 80 ° C
By removing with an etchant and releasing the second substrate, the structure layer on the second substrate was transferred onto the adhesive layer of the first substrate (see FIG. 4G). The Al etchant does not corrode the photoresist and Si structure layer that are the resin film.

Subsequently, a metal film 100 of Cr and Au is formed in the same manner as the drive electrode 15 and the fixed electrode 16 are formed,
Photoresist 103 was applied and patterned by a photolithography process (see FIG. 5H). The metal film 100 was etched with the Au etchant and the Cr etchant using the photoresist 103 as a mask to form the movable electrode 17.

Next, the sacrificial layer and the adhesive layer made of a resin film were patterned into the same shape as the beam pattern by RIE with oxygen gas using the beam pattern 24 as a mask (see FIG. 5 (I)). Si formed as described above
An Al film 27 serving as a support layer was formed to a thickness of 2 μm on the beam and the movable electrode 17. A photoresist 104 was applied, exposed, and developed on the Al film by a photolithography process (see FIG. 5K). Then, the Al film 27 is subjected to RIE with a mixed etching gas of BCl ₃ and Cl _2.
Patterning was performed to form support portions 13 and 13 '(see FIG. 5L, the support portion 13 is not shown).

Finally, the sacrificial layer and the adhesive layer made of the resin film under the beam pattern 24 were removed by etching with oxygen plasma to form the void 29 (see FIG. 5M).

2 having a void 29 by using the above forming method
FIG. 6 in which the Si beam 12 having a thickness of μm is supported by the Al film.
The microstructure shown in was formed. Without etching each electrode by etching with oxygen plasma,
Moreover, sticking, which is a problem when removing the conventional sacrificial layer by wet etching, can be avoided.

By the forming method of this embodiment, the bulk Si substrate 20 can be thinned to form a beam. In addition, drive electrodes can be formed on the beam,
And, through the fixed electrode and the supporting portion formed on the first substrate,
It could be electrically connected. Further, by applying a voltage between the movable electrode and the driving electrode, the free end of the beam was displaced in the direction of the first substrate in accordance with the torsional rotation of the torsion bar.

By applying the resin film on the first substrate, it is possible to apply it evenly to the irregularities on the substrate caused by the drive electrodes, the fixed electrodes, etc., while maintaining the flatness of the adhesive surface. It became possible to bond the substrates to each other satisfactorily. Further, by using the photoresist as the resin layer, it goes without saying that the microstructure can be similarly formed even if the substrate in which the integrated circuit is formed on the Si substrate 10 which is the first substrate is used. Since the photoresist has a very low content of mobile ions, it does not cause a malfunction due to the mobile ions penetrating into electronic devices such as MOS transistors. Although Si is used as the substrate, it goes without saying that other substrates such as glass, GaAs, metal, and a glass substrate on which a metal film is formed can be used.

In FIG. 4D, the transfer sacrificial layer 21 is left without being removed in a beam pattern, and pressure is applied from the back surface of each substrate in the step of adhering the structure layer and the first substrate via the adhesive layer. Instead of pressing by pressing, a voltage of 100 V was applied to Al that is the sacrificial layer for transfer and the Si substrate that was the first substrate, and pressing was performed by the generated electrostatic force, so that it was possible to perform similar bonding.

In the forming method of this embodiment, bulk Si is used.
Was thinned with abrasive grains to produce a Si beam.
As another thinning method, a similar microstructure was manufactured by using an SOI substrate made of a silicon film having a thickness of 2 μm, which was directly bonded via a silicon oxide film on the silicon substrate instead of the Si substrate 20. As the process, after the Al film is formed on the silicon film, the second film is formed in the same manner as above.
The substrate is anodically bonded to the substrate, and the rear surface of the SOI substrate is subjected to Eut etching with a 30 wt% KOH aqueous solution heated to 100 ° C. to remove the SOI Si substrate. The silicon oxide film serves as an etch stop layer that blocks etching, and etching by KOH is stopped. After that, by etching the silicon oxide film with a hydrofluoric acid aqueous solution, as shown in FIG.
2μ through the sacrificial layer for transfer on the second substrate as shown in
It was possible to form a Si structure layer having a thickness of m. SO
By using the I substrate, the thickness of the structure layer can be ensured with high accuracy, and a structure layer having an arbitrary thickness can be obtained. As a method other than the above method for forming the Si structure layer, an SOI substrate can be used as the second substrate including the structure layer and the transfer sacrifice layer illustrated in FIG. 4C. In this case, an SOI Si substrate is used as the second substrate, and a silicon oxide film is used as the sacrifice layer for transfer.
A beam pattern is formed on the Si film in the same manner as in the step shown in (D), and is bonded to the first substrate shown in FIG. 4 (E). By etching away the silicon oxide film, which is the sacrificial layer for transfer, with an aqueous solution of hydrofluoric acid, the structure layer can be transferred onto the adhesive layer as in FIG. 4G.

Although the Al film was used as the material of the transfer sacrificial layer, another metal material capable of anodic bonding such as Ti or Ni was used, and an etchant that does not corrode the resin film and the structure layer was selected. It is possible to form similar structures.

Further, a groove was formed in the structure layer 23 by the beam pattern shown in FIG.
In the step (E), the solvent vapor generated when the resin film is heat-treated and cured can escape through the groove. If there is no groove, if the content of the solvent contained in the solution in which the resin is dissolved during application is not adjusted, bubbles will remain between the adhesive layer and the structure layer due to the solvent vapor during the heat treatment. There are cases. By forming the groove, the effect of preventing the generation of bubbles can be obtained.

Further, as shown in this embodiment, the resin film is an adhesive layer for adhering the first substrate and the structure, and also serves as a sacrificial layer for forming the microstructure.

In this example, the sacrificial layer and the adhesive layer made of the resin film were removed by dry etching using oxygen plasma. However, the sacrificial layer and the adhesive layer made of OMR-83 were removed by OMR of Tokyo Applied Chemical Industry Co., Ltd. It can be removed by immersing it in the stripping solution-502 (trade name). The stripper is an organic solution and does not etch the Al electrode. It goes without saying that the sacrifice layer and the adhesive layer can be removed by wet etching according to the method of this embodiment.

Although the same organic resin film material is used for the sacrificial layer and the adhesive layer, it goes without saying that different resin film materials can be used for each.

[0065]

As described above, according to the method of forming a microstructure of the present invention, a sacrificial layer made of a resin film formed on a first substrate, an adhesive layer, and a structure layer formed on a second substrate are formed. After adhering via the adhesive layer, the second substrate is removed,
By mechanically connecting the first substrate and the structure layer with the support layer and removing the sacrifice layer and the adhesive layer, a microstructure made of various materials such as an insulator, a metal, and a semiconductor can be formed. It is possible to form an electrode pattern on the microstructure and form a microstructure that can be electrically connected to the substrate.

Further, since the structure layer is manufactured by a process different from that of the first substrate, the materials for the first substrate and the structure layer are not limited. Further, a bulk material can be used as the beam, and a beam without warpage can be formed.

Further, since the resin film is an adhesive layer for adhering the first substrate and the second substrate and plays a role of a sacrifice layer for forming the microstructure, oxygen is used as a method for removing the resin film. Gas dry etching can be used, which is a problem when removing conventional sacrificial layers
Sticking can be avoided.

Further, the resin film can form a flat surface without being affected by the unevenness due to the electrode pattern or the like formed on the substrate, and good adhesion can be achieved without depending on the surface roughness of the substrate. Further, according to the method of the present invention, it is possible to form a microstructure by a relatively low temperature process, and it is possible to form a microstructure even using a substrate having a different coefficient of thermal expansion.

Further, by forming the sacrificial layer in advance and sufficiently curing it, it is possible to control the distance between the structural body layer and the first substrate with good reproducibility within the plane of the substrate.

[Brief description of drawings]

FIG. 1 is an explanatory view showing a manufacturing process of a first embodiment of a method for forming a microstructure of the present invention.

FIG. 2 is an explanatory view showing a manufacturing process of the first embodiment of the method for forming a microstructure of the present invention.

3 is a schematic perspective view showing a microstructure manufactured by using the method for forming a microstructure of Example 1. FIG.

FIG. 4 is an explanatory view showing a manufacturing process of a second embodiment of the method for forming a microstructure of the present invention.

FIG. 5 is an explanatory view showing a manufacturing process of a second embodiment of the method for forming a microstructure of the present invention.

FIG. 6 is a schematic perspective view showing an electrostatic actuator that is a microstructure manufactured by using the method for forming a microstructure of Example 2.

FIG. 7 is a second embodiment of the method for forming a microstructure of the present invention.
Explanatory diagram showing a step of forming a Si substrate to be a structure layer on the second substrate via the transfer sacrificial layer by the anodic bonding method of.

[Explanation of symbols]

 1 glass substrate 2,12 beam 3,13,13 'support part 4,10,20 Si substrate 5,24 beam pattern 6,25 sacrificial layer 7,7', 26,26 'adhesive layer 8,27 Al thin film 9, 29 Air gap 11 Torsion bar 14 Insulating layer 15 Driving electrode 16 Fixed electrode 17 Movable electrode 21 Transfer sacrifice layer 22 Second substrate 23 Structure layer 30 Platen 31, 35 Needle electrode 32, 34 Lead wire 33 Power supply 100 Metal film 101, 102, 103, 104 photoresist

Claims (11)

[Claims] 1. A method of forming a microstructure, the method comprising: (1) forming a sacrificial layer and an adhesive layer made of a resin film on a first substrate; and (2) a structure on a second substrate. A step of forming a layer, (3) a step of adhering the first substrate and the structure layer via the adhesive layer, (4) a step of removing the second substrate, (5) the structure layer and the first substrate 7. A method for forming a microstructure, comprising: a step of forming a support layer for connecting with a substrate; and (6) a step of removing the sacrificial layer and the adhesive layer. 2. The microstructure according to claim 1, wherein the step of forming the sacrificial layer and the adhesive layer is a step of forming the adhesive layer after curing the resin film to be the sacrificial layer. Forming method. 3. The formation of the microstructure according to claim 2, wherein the step of forming the sacrificial layer and the adhesive layer is performed by applying a thin film of a solution in which resin molecules are diluted with a solvent. Law. 4. The method of forming a microstructure according to claim 1, wherein the resin film is made of photoresist. 5. The method of forming a microstructure according to claim 4, wherein the photoresist contains a cyclized rubber. 6. The first substrate and / or the second substrate,
The method for forming a microstructure according to claim 1, wherein the microstructure is formed by forming a groove. 7. The method for forming a microstructure according to claim 1, wherein the adhering step includes a step of applying pressure to the first and second substrates. 8. The method for forming a microstructure according to claim 7, wherein the step of applying the pressure is performed by applying a voltage to the first substrate and the second substrate. 9. The method for forming a microstructure according to claim 1, wherein the support layer is made of a metal thin film. 10. The method for forming a microstructure according to claim 1, wherein the step of removing the sacrificial layer and the adhesive layer is performed by dry etching using oxygen. 11. The method for forming a microstructure according to claim 10, wherein the dry etching is performed by plasma etching.