JP2004276201A - Micro structure and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a micro structure which is high in reliability, and enables efficient mounting thereof, and to provide a method of manufacturing the same. <P>SOLUTION: The micro structure is arranged on a silicone substrate 50, and has arranged therein at least one pair of comb-shaped fixed electrodes 22 and at least one pair of comb-shaped movable electrodes 24, such that their teeth engage with each other, to thereby generate planar oscillation. According to the micro structure, the substrate 50 has pad electrode sections 26, 52 and rear pad electrode sections 54, 56 conductively arranged on both sides thereof. The pad electrode sections 26, 52 and the rear pad electrode sections 54, 56 functions to impress driving voltage so as to generate electrostatic attraction between the fixed electrodes 22 and the movable electrodes 24. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a microstructure formed on a substrate such as a silicon wafer and vibrating in a direction parallel to the substrate surface and a method of manufacturing the same, and more particularly, to a method of forming a pad electrode portion for applying a driving voltage.
[0002]
[Prior art]
Such a microstructure that vibrates in a planar manner is used as a microresonator (resonator), a microfilter, or the like in a watch, a mobile phone, or the like. As disclosed in Patent Documents 1 and 2, the structure is such that a comb electrode of a fixed electrode and a movable electrode formed on a silicon substrate are engaged with each other in parallel with the substrate surface, and a movable electrode having a comb tooth portion is provided. Is connected to a beam portion having a spring property supported on a silicon substrate, and such a comb-shaped fixed electrode and a comb-shaped movable electrode that mesh with each other are arranged on both sides of an intermediate beam portion, one set at a time. It has a configuration. The comb-shaped fixed electrode, movable electrode, beam portion, and pad electrode portion are formed using a polysilicon film formed on a silicon substrate. Attempts have also been made to form these structural parts (also referred to as chips) by using an active layer part of an SOI (Silicon On Insulator) substrate.
[0003]
[Patent Document 1]
U.S. Pat. No. 5,025,346 (column 3, line 37-column 6, line 2; column 6, line 55-column 7, line 52; FIGS. 1-4)
[Patent Document 2]
US Pat. No. 5,537,083 (column 4, line 43 to column 10, line 33, FIGS. 4 to 8)
[0004]
Such a microstructure is formed by applying an AC voltage between an input terminal electrode (pad electrode section) of one of the comb-shaped fixed electrodes and a ground electrode (pad electrode section). An electrostatic attractive force is generated between the fixed electrode and the movable electrode, and the comb-like movable electrode is planarly pushed in the direction in which the comb teeth mesh (the length direction of the comb teeth) by the electrostatic attractive force. Vibrate. This vibration is transmitted to a beam portion having a spring property integrated with the movable electrode, that is, a resonance portion, and vibrates the other comb-shaped movable electrode, which is also in a meshing state, two-dimensionally.
The vibration generated between one of the comb-shaped fixed electrodes on the input side and the movable electrode is transmitted to the resonance section (beam section) including the movable electrodes on both sides, and the resonance section causes a resonance phenomenon. Is taken out from the pad electrode portion of the other comb-shaped fixed electrode on the output side.
[0005]
[Problems to be solved by the invention]
However, in the conventional microstructure, even when a silicon substrate or an SOI substrate is used, it is necessary to form an electrode extraction portion (pad electrode portion) of a certain size on the surface side of the substrate. In this method, a polysilicon film on a silicon substrate or a part of an active layer on an SOI substrate is formed as an electrode extraction portion (pad electrode portion), and a metal having lower electric resistance than silicon is formed on the pad electrode portion. Electrical connection is made externally by mounting technology such as wire bonding. When a microstructure is formed using, for example, an SOI substrate, a pad electrode portion may be formed at the center of the structure portion (chip) in order to reduce the occupied area of the structure portion. In some cases, the pad electrode portion also serves as a support portion for the structure portion. In this case, the pad electrode portion is formed to have a minimum required size.
[0006]
In such a case, there is a problem that it is difficult to connect to the pad electrode portion by a method such as wire bonding for the following reasons.
(1) Since the microstructure is very fragile and fragile as compared with a conventional semiconductor element, the yield is reduced in a conventional mounting method such as a method in which ultrasonic vibration is applied and a wire is effectively crimped and connected. .
(2) Even if the wire can be hooked, the electrical connection is made across the structure part, and the wire and the structure part interfere with each other due to external disturbance after mounting, and the Operation is hindered and reliability cannot be maintained.
(3) Wire hanging increases the space above the chip (space covering the height of the wire loop) required on the package, and in particular, the size of the resonator package, which requires vacuum sealing, is limited. come.
(4) As the dimensions of the element are reduced, the area occupied by the pad electrode portion (several tens of μm to about 100 μm square) becomes relatively large, which hinders chip shrinkage.
[0007]
The present invention has been made in view of the above problems, and has as its object to provide a microstructure having high reliability and capable of being efficiently mounted, and a method for manufacturing the same.
[0008]
[Means for Solving the Problems]
The microstructure provided according to the present invention is provided on a substrate, and at least one set of comb-shaped fixed electrodes and comb-shaped movable electrodes mesh with each other and vibrate in a planar manner. A pad electrode portion for applying a drive voltage to generate an electrostatic attraction between the fixed electrode and the movable electrode is provided on both sides of the substrate in a conductive state.
[0009]
With this configuration, the voltage for driving the movable electrode can be obtained from the back pad electrode portion provided on the back surface side of the substrate. Therefore, mounting on an external substrate is facilitated, and reliability is improved. In addition, since no space is required on the front side of the board for hooking wires, the microstructure can be made smaller and thinner, and the degree of freedom in the arrangement of pad electrodes and chip shrink is greatly improved. To improve.
Note that the microstructure (MicroElectroMechanical Systems: MEMS) of the present invention may have a configuration in which planar vibration is generated, and therefore, may have a configuration including at least one set of comb-like fixed electrodes and comb-like movable electrodes. Just fine.
Further, in the present invention, for example, a silicon substrate and an SOI (Silicon On Insulator) substrate are used as the substrate.
[0010]
In the microstructure of the present invention, the electrical connection between the front pad electrode portion and the back pad electrode portion is formed by a hole provided in the substrate and a conductor provided on the inner surface of the hole via an insulating film. It becomes.
The hole is provided in the substrate portion below the front pad electrode portion. The front pad electrode portion and the back pad electrode portion are electrically connected by a conductor on the inner surface of the hole. With this configuration, the back surface of the substrate can be effectively used, and the above effects can be realized.
[0011]
Further, the conductor is formed of a metal film, and a hole portion formed of the metal film is filled with a metal or nonmetal filler.
In brief, the front pad electrode portion and the back pad electrode portion are electrically connected by a metal film. In the case of a metal film, a hole is formed. By filling this hole with a metal or a non-metal, conduction and strength can be improved in the case of a metal-filled material. In the case of, for example, resin, the strength can be improved.
[0012]
Further, in the microstructure of the present invention, the movable electrodes are provided on both sides of a frame-shaped beam portion, and the fixed electrodes are engaged with each of the movable electrodes in a planar manner.
When the present invention is applied to a micro-resonator (resonator), a micro-filter (for example, SAW (Surface Acoustic Wave) filter) or the like, it is configured to have two sets of fixed electrodes and movable electrodes. In this case, the movable electrodes are arranged on both sides of the frame-shaped beam portion, and the beam portion including the two movable electrodes is configured as a resonance portion. Therefore, the beam portion only needs to constitute the resonance portion, and the shape thereof is not limited to a square, but may be a suitable shape such as a circle, an oval, and a spindle shape. Further, since the pad electrode portions are provided on both sides of the substrate in a conductive state as described above, mounting is easy and reliability is high.
[0013]
When the present invention is applied to a microactuator, the microstructure of the present invention has a configuration in which the movable electrode is provided on a beam supported at both ends, and a rod protrudes from the movable electrode on the side opposite to the comb teeth. Things.
With this configuration, the rod can be operated using planar vibration as a driving source. Therefore, also in this case, since the pad electrode portions are provided in a conductive state on both surfaces of the substrate, various micromachines that are easy to mount and have high reliability can be configured.
[0014]
The method for manufacturing a microstructure according to the present invention includes a microstructure provided on a substrate, wherein at least one pair of comb-shaped fixed electrodes and comb-shaped movable electrodes are engaged with each other to vibrate in a plane. In the manufacturing method of
Forming a pad electrode portion with a polysilicon film via an insulating film on the front and back surfaces of the substrate;
Forming a hole reaching the front pad electrode portion from the back surface of the substrate;
Forming a metal film conducting to the front pad electrode portion and the back pad electrode portion via an insulating film on the inner surface of the hole;
It is characterized by having.
According to this method, it is possible to manufacture a microstructure in which pad electrode portions that become conductive are provided on both surfaces of the substrate.
The method may further include a step of filling a hole formed by the metal film with a metal or a nonmetal.
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
Embodiment 1 FIG.
FIG. 1 is a plan view of a microstructure according to a first embodiment of the present invention, FIG. 2 is a cross-sectional view taken along line AA of FIG. 1, and FIG. 3 is a rear view of the substrate of the microstructure.
The microstructure 10 is configured as a filter having the same function as a transversal type SAW (Surface Acoustic Wave) filter.
On an insulating film 51 made of an oxide film formed on the surface of a silicon substrate 50, a transmitting-side IDT (Interdigital Transducer) 20 and a receiving-side IDT 30 are arranged on both sides, and a resonance section 40 is arranged in an intermediate portion between the two. . The transmission-side IDT 20, the reception-side IDT 30, and the resonance unit 40 are formed using a polysilicon (p-SiO) film formed on a silicon substrate 50.
[0016]
Each of the transmission-side IDT 20 and the reception-side IDT 30 includes fixed electrodes 22 and 32 having comb teeth and movable electrodes 24 and 34, respectively. The fixed electrode 22 of the transmitting IDT 20 and the fixed electrode 32 of the receiving IDT 30 have comb teeth portions 21 and 31 each having a plurality of comb teeth, and input terminal electrodes (pad electrode portions) via leads 25 and 35. 26, an output terminal electrode (pad electrode section) 36; Reference numeral 52 denotes a ground electrode (pad electrode portion) common to the pad electrode portions 26 and 36.
The resonating part 40 is formed integrally with a beam part 42 formed of a rectangular frame so that the comb teeth are outward on both sides of the beam part 42, and the comb teeth parts 21 and 31 of the fixed electrodes 22 and 32 are formed. And movable electrodes 24 and 34 having comb teeth 23 and 33 provided so as to mesh with each other.
[0017]
The comb teeth 21 and 31 of the fixed electrode and the comb teeth 23 and 33 of the movable electrode mesh with each other in parallel with the surface of the silicon substrate 50 with a gap (comb gap) on a predetermined plane. ing.
The frame-shaped beam portion 42 in which the movable electrodes 24 and 34 are integrally formed has a structure in which a support portion 46 is fixed on a silicon substrate 50 via a cantilever 44 coupled to the frame. I have. As described above, the outer shape of the beam portion 42 is not particularly limited to a square shape. The movable electrodes 24 and 34 are connected by a connection beam 43.
[0018]
As shown in FIG. 2, the beam portion 42 is supported in a state of floating above the insulating film (oxide film) 51 of the silicon substrate 50 in parallel with the substrate surface. Similarly, the movable electrode 32 and the movable electrodes 24 and 34 are meshed with each other in a state of floating in parallel with the substrate surface. The flying height of the comb-shaped electrode, that is, the electrode gap with the insulating film 31 of the silicon substrate is about 2 to 3 μm.
[0019]
In this embodiment, as shown in FIGS. 2 and 3, back pad electrode portions 54, 55 and 56 electrically connected to the pad electrode portions 26, 36 and 52 are provided on the back surface of the silicon substrate 50. It is a thing. A method of electrically connecting the pad electrode portions 26, 36, 52 and the back pad electrode portions 54, 55, 56 will be described in detail later. Holes 53 that reach the parts 26, 36, 52 are provided, respectively, and a conductor 58 that makes electrical connection is formed on the inner surface of each hole 53 via an insulating film 57.
The microstructure 10 is electrically connected to an external substrate (not shown) by directly bonding, wire bonding, or a flat cable to the back pad electrode portions 54, 55, and 56. It is also possible to connect using a connector.
[0020]
The operation of the microstructure 10 is performed in such a manner that the pad electrode 26 serving as the input terminal electrode of the comb-shaped fixed electrode 22 and the pad electrode 52 serving as the ground electrode are connected via the back pad electrodes 54 and 56 connected to the external substrate. By applying an AC voltage between the electrodes, an electrostatic attraction is generated between the comb teeth of the comb-shaped fixed electrode 22 and the comb electrodes of the movable electrode 24, whereby the movable electrode 24 is moved in the direction in which the comb teeth engage (the length of the comb teeth). 1 (ie, the left-right direction in FIG. 1) by virtue of being pulled and pushed through the beam portion 42 having spring properties. This vibration is transmitted to the beam portion 34 having the spring property integrated with the movable electrode 24, that is, the resonance portion 40, and the other comb-like movable electrode 34, which is also in mesh with the comb-like fixed electrode 32, is planarized. Vibrate.
When the vibration generated between the one comb-shaped fixed electrode 22 and the movable electrode 24 on the input side reaches the natural frequency of the resonating portion (beam portion) 40, the resonating portion 40 generates a resonance phenomenon. The frequency is extracted from the back pad electrode section 55 via the pad electrode section 36 of the other comb-shaped fixed electrode 32 on the output side.
The resonance frequency or the oscillation frequency is determined by the restoring force (elastic force of the beam portion 42) for the displacement determined by the mass of the resonance portion 40 including the movable electrodes 24 and 34 and the spring constant of the beam portion 42. The oscillation frequency is, for example, 16 kHz, 32 kHz, 72 kHz or the like as a design target value.
[0021]
As described above, in the microstructure 10 of the present embodiment, the pad electrode section 26 on the front surface side of the silicon substrate 50 is the same as the back pad electrode section 54 provided on the back side, and the pad electrode section 36 is also the back pad electrode section 55 And the pad electrode portion 52 is electrically connected to the back pad electrode portion 55 by a conductor 58 provided through an insulating film 57 on the inner surface of the hole 53, respectively. It is very easy because it can be performed via the parts 54, 55, 56. Moreover, since no mounting method such as wire bonding is used for connection between the pad electrode portions 26, 36, 52 and the back pad electrode portions 54, 55, 56, the structure portion (chip) may be damaged. In addition, the reliability is improved, and the production yield is improved. Furthermore, since the upper space required for packaging the microstructure 10 can be reduced as much as possible, further miniaturization and thinning can be achieved.
In addition, the degree of freedom in the arrangement of the pad electrode portions 26, 36, 52 and the back pad electrode portions 54, 55, 56 and the degree of freedom in designing shrinkage of the element are improved.
[0022]
Embodiment 2 FIG.
FIG. 4 is a plan view of a microstructure according to a second embodiment of the present invention, and FIG. 5 is a rear view of a substrate showing a back pad electrode portion of the microstructure.
The microstructure 12 of the present embodiment has a configuration in which some pad electrode portions 61 and 62 are arranged near the center of the structure portion. That is, the pad electrode portions 61 and 62 are arranged near the support portion 46 of the beam portion 42. Back pad electrode portions 63 and 64 are electrically connected to the pad electrode portions 61 and 62, respectively, in a configuration similar to that of FIG. Similarly, the back pad electrode portions 54 and 55 are electrically connected to the other pad electrode portions 26 and 36. Other configurations are the same as those of the above-described embodiment. The pad electrode portions 61 and 62 may be formed integrally with the support portion 46.
[0023]
As in this embodiment, when a part of the pad electrode portion is arranged at the center of the structure portion or the like in order to reduce the area occupied by the microstructure 12, the pad electrode portion 61 has the same configuration as that of FIG. , 62 provided on the back surface of the silicon substrate 50 are electrically connected to an external substrate (not shown) very easily. Therefore, the reliability, the production yield, and the design freedom of the microstructure 12 are improved, and the size and thickness can be further reduced.
[0024]
Embodiment 3 FIG.
FIG. 6 is a plan view of a microstructure according to Embodiment 3 of the present invention, and shows an example in which the microstructure is configured as a microactuator.
The microstructure 14 has a configuration including a pair of comb-shaped electrodes 22 and 24. That is, as described above, the comb-tooth portions 21 and 23 of the comb-tooth-shaped fixed electrode 22 and the movable electrode 24 are meshed with each other in a planar manner while floating above the silicon substrate 50. Here, the comb-tooth-shaped movable electrode 24 is integrally formed at the center of the beam 47 of the support at both ends (support portions 49), and a rod 48 is protruded from the side opposite to the comb-tooth portion 23. .
Each of the pad electrode portions 26 and 28 is provided with back pad electrode portions 71 and 72 that are electrically connected to each other on the back surface of the silicon substrate 50 in the same configuration as in FIG.
[0025]
The operation of the microstructure 14 is basically as described above. By applying a drive voltage to the comb-shaped fixed electrode 22, an electrostatic attraction is generated between the fixed electrode 22 and the movable electrode 24, and this static The movable electrode 24 attached to the double-supported beam 47 is vibrated by the attraction. Since the rod 48 is attached to the movable electrode 24, the rod 48 can reciprocate.
Therefore, if a functional element or a passive element is connected to the rod 48 directly or through an appropriate link or the like, a micromachine that moves, for example, a reflecting mirror or a lever can be manufactured.
Further, since the position of the comb teeth of the movable electrode 24, that is, the displacement of the rod 48 is proportional to the square of the driving voltage, it is possible to provide functions such as a sensor and a switch.
[0026]
Embodiment 4 FIG.
Next, a method of manufacturing the above-described microstructures 10, 12, and 14, mainly a method of forming an electrical connection between the pad electrode portion 26 and the back pad electrode portion 54 shown in FIG. This will be described with reference to FIG. The method of manufacturing the structure parts such as the comb-shaped electrodes 22 and 24 is as described in the above-mentioned Patent Documents 1 and 2.
[0027]
First, an oxide film (SiO ₂ ) 81 having a thickness of 0.5 μm is formed on the front and back surfaces of a silicon substrate 80 having a thickness of about 500 μm which has been polished on both sides by a reduced pressure chemical vapor deposition (CVD) method. A 0.2 μm-thick nitride film (SiN ₄ ) 82 is formed in this order, and a 0.2 μm-thick polysilicon (p-SiO) for the pad electrode portion 26 and the back pad electrode portion 54 is formed on the nitride film 82. A film 83 is formed (FIG. 7A). Note that an SOI substrate may be used instead of the silicon substrate 80.
[0028]
Next, a photoresist 84 for forming a hole communicating with the pad electrode portion 26 is patterned on the nitride film 82 and the polysilicon film 83 on the back surface side (FIG. 7B), and a freon gas (CF ₄ ) is formed. A hole 53 is formed by dry etching until the hole 53 reaches the back surface of the pad electrode portion 26 (FIG. 7C).
[0029]
Then, after removing the resist 84, an oxide film (SiO ₂ ), that is, an insulating film 85 having a thickness of 0.2 μm is formed on the back surface of the silicon substrate including the holes 53 by a plasma CVD method (FIG. 8D).
Further, a window is opened in the insulating film 85 (FIG. 8E). That is, windows 86 and 87 are formed in the portion corresponding to the bottom surface (the upper surface in FIG. 8) and the back pad electrode portion 54 of the insulating film 85 by resist patterning and dry etching.
[0030]
Then, a gold or copper metal film 88 having a thickness of about 0.03 to 0.1 μm is applied to the hole 53 and its peripheral portion by vapor deposition or sputtering so as to cover these windows 86 and 87 (FIG. 8F). . Finally, resist patterning and dry etching are performed so as to leave only the hole 53 and the metal film 88 in the peripheral portion thereof (FIG. 9G).
[0031]
According to the above-described method, as shown in FIG. 2, the conductive metal film 88 is applied to the pad electrode portion 26 on the front surface side of the silicon substrate 50 via the insulating film (SiO ₂ ) 85 on the inner surface of the hole 53. A back pad electrode portion 54 for making a connection can be formed on the back surface of the silicon substrate 50.
[0032]
Further, as shown in FIG. 9I, a portion of the hole 53 formed by the metal film 88 can be filled with a filler 90 of a conductive metal such as copper. In this case, a metal film 88 is formed of gold, copper, chromium, or silicon as shown in FIG. 9G, and a resist 89 is patterned thereon as shown in FIG. The hole 53 is filled with a conductive metal filler 90 by inkjet.
According to this method, since the hole 53 is filled with the conductive metal filler 90, there is an advantage that both strength and conduction are satisfied.
In place of the conductive metal, an insulator (non-metal) such as a resin can be filled by using an ink jet or the like. In this case, the strength of the hole can be improved.
[0033]
The microstructure of the present invention is not limited to its use as long as it generates planar vibration of the comb-shaped fixed electrode and movable electrode. For example, it can be used in various fields such as watches, mobile phones, personal computers, information terminal devices (PDAs), home appliances, audio devices, and other electronic devices.
Further, the microstructure of the present invention can also be used as an electronic microdevice (RF circuit, local oscillation circuit, filter circuit, and the like) monolithically integrated by being integrated with a semiconductor element such as an IC.
[Brief description of the drawings]
FIG. 1 is a plan view of a microstructure according to a first embodiment of the present invention.
FIG. 2 is a sectional view taken along line AA of FIG.
FIG. 3 is a rear view of FIG. 1;
FIG. 4 is a plan view of a microstructure according to a second embodiment of the present invention.
FIG. 5 is a rear view of FIG. 4;
FIG. 6 is a plan view of a microstructure according to a third embodiment of the present invention.
FIG. 7 is a process chart showing a method for manufacturing a microstructure of the present invention.
FIG. 8 is a process drawing following FIG. 7;
FIG. 9 is a process drawing following FIG. 8;
[Explanation of symbols]
10, 12, 14 microstructure, 20 transmitting side IDT, 21 comb-shaped portion, 22 comb-shaped fixed electrode, 23 comb-shaped portion, 24 comb-shaped movable electrode, 25 lead portion, 26 pad electrode portion, 28 pad electrode Unit, 30 receiving-side IDT, 31 comb-shaped portion, 32 comb-shaped fixed electrode, 33 comb-shaped portion, 34 comb-shaped movable electrode, 35 lead portion, 36 pad electrode portion, 40 resonance portion, 42 beam portion, 43 connection Beam, 44 cantilever, 46 support, 47 beam, 48 rod, 49 support, 50 silicon substrate, 51 insulating film, 52 pad electrode, 53 hole, 54, 55, 56 back pad electrode, 57 conductor , 60 lid substrate, 61, 62 pad electrode portion, 63, 64 back pad electrode, 71, 72 back pad electrode portion, 80 silicon substrate, 81 oxide film, 82 nitride film, 83 polysilicon film, 84 photoresist, 85 insulating film, 86, 87 window, 88 metal film, 89 resist, 90 filling

Claims (8)

A microstructure provided on a substrate and vibrating two-dimensionally by engaging at least one set of comb-shaped fixed electrodes and comb-shaped movable electrodes with each other.
A microstructure, wherein pad electrode portions for applying a drive voltage so as to generate an electrostatic attraction between the fixed electrode and the movable electrode are provided on both sides of the substrate in a conductive state. The electrical connection between the front pad electrode portion and the back pad electrode portion includes a hole provided in the substrate and a conductor provided on the inner surface of the hole via an insulating film. 2. The microstructure according to 1. The microstructure according to claim 2, wherein the conductor is formed of a metal film. 4. The microstructure according to claim 3, wherein the hole formed by the metal film is filled with a metal or a nonmetal filler. The microstructure according to any one of claims 1 to 4, wherein the movable electrodes are provided on both sides of a frame-shaped beam portion, and the fixed electrodes are engaged with each of the movable electrodes in a planar manner. . The microstructure according to any one of claims 1 to 4, wherein the movable electrode is provided on a beam supported at both ends, and a rod protrudes from the movable electrode on a side opposite to a comb portion. A method for manufacturing a microstructure provided on a substrate, in which at least one set of comb-shaped fixed electrodes and comb-shaped movable electrodes are meshed with each other to vibrate in a plane,
Forming a pad electrode portion with a polysilicon film via an insulating film on the front and back surfaces of the substrate;
Forming a hole reaching the front pad electrode portion from the back surface of the substrate;
Forming a metal film conducting to the front pad electrode portion and the back pad electrode portion via an insulating film on the inner surface of the hole;
A method for producing a microstructure, comprising: 8. The method according to claim 7, further comprising a step of filling a hole portion formed by the metal film with a metal or a nonmetal.

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