JP2008119756A - Method for manufacturing micro-machine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a micro-machine having excellent switching performance and high reliability in a high yielding ratio. <P>SOLUTION: The method for manufacturing the micro-machine having movable electrodes having a cantilever structure, includes steps of: preparing a substrate, a step of forming at least a suction electrode on the substrate; forming a first sacrificial layer so as to cover the suction electrode; selectively forming a second sacrificial layer on the first sacrificial layer covering the stepped portion of the suction electrode; forming a movable electrode on the first sacrificial layer and the second sacrificial layer; and removing the first sacrificial layer and the second sacrificial layer. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a micromachine, and more particularly to a method for manufacturing a micromachine switch having an electrode having a cantilever structure.

In a conventional method of manufacturing a micromachine switch, first, a metal film is formed on a substrate by sputtering or vapor deposition, and suction electrode, input signal line, output signal line, and ground electrode are formed by photolithography and dry etching. The pattern is formed.
Next, after forming a metal film or a photoresist film, patterning is performed to form a sacrificial layer that covers the suction electrode. In the sacrificial layer, dimples are formed at positions overlapping the output side signal lines.
Next, after forming a metal film on the sacrificial layer by plating or sputtering, this is patterned to form a movable electrode having a cantilever structure. The movable electrode is provided with a projecting portion serving as a contact at a portion overlapping the output side signal line.
Finally, the sacrificial layer is removed by etching. Thus, a micromachine switch having a cantilever structure movable electrode connected to the input side signal line and facing the suction electrode is completed.
Shinichi Deo et al. "Evaluation of power durability of high-frequency MEMS switches", Proceedings of the IEEJ National Convention Vol.3, pp.188, 2005. Ronald A Coutu Jr et al “Selecting metal alloy electric contact materials for MEMS switches”, J. Micromech. Microeng. 14 (2004) 1157-1164

In the conventional micromachine switch, first, there is a problem that a contact resistance increases at a contact point between the movable electrode and the output side signal line, and a sufficient current does not flow even when the switch is turned on.
Second, when the movable electrode and the output-side signal line are in contact with each other at the contact point, the suction electrode and the movable electrode are in contact with each other, and the suction electrode and the movable electrode are welded so that the movable electrode does not operate. .

On the other hand, as a result of intensive studies, the inventors have found that the first problem occurs when a photoresist film is used as the sacrificial layer. It was found that it was caused by contamination. In other words, when a photoresist film is used as the sacrificial layer, the photoresist is formed by spin coating, so that the film property at the stepped portion is good, while the metal film that becomes the movable electrode is formed on the photoresist. For this reason, the protrusions serving as the contacts are in contact with the photoresist film made of an organic material. Therefore, even if the photoresist film is removed by ashing in the sacrificial layer removing step, a small amount of organic matter remains on the surface of the protrusion, and the contact resistance between the movable electrode and the output side signal line is high.
The second problem occurs when a metal film is used as the sacrificial layer, and it has been found that the distance between the movable electrode and the suction electrode is narrower than the design value. That is, when a metal film is used for the sacrificial layer, the metal film is generally formed by sputtering or vapor deposition. However, the sputtering method and the vapor deposition method have poor step coverage, and the sacrificial layer is thinner than the flat portion at the stepped portion around the suction electrode. That is, in the vicinity of the suction electrode (near the stepped portion), the distance between the suction electrode and the movable electrode is narrowed, and the suction electrode and the movable electrode are in contact with each other and welded during switching.

  Accordingly, an object of the present invention is to provide a method for manufacturing a highly reliable micromachine having high switching performance and high yield.

  The present invention is a method of manufacturing a micromachine having a movable electrode having a cantilever structure, the step of preparing a substrate, the step of forming at least a suction electrode on the substrate, and the first sacrificial layer so as to cover the suction electrode A first sacrificial layer forming step for forming the second sacrificial layer, a second sacrificial layer forming step for selectively forming the second sacrificial layer on the first sacrificial layer covering the step portion of the suction electrode, and the first sacrificial layer and the second sacrificial layer. A method of manufacturing a micromachine, comprising: forming a movable electrode on a sacrificial layer; and removing the first sacrificial layer and the second sacrificial layer.

  As described above, in the method for manufacturing a micromachine according to the present invention, the contamination of the electrodes can be prevented, the micromachine having the size as designed can be manufactured, and a highly reliable micromachine can be provided with a high manufacturing yield.

Embodiment 1 FIG.
FIG. 1 is a perspective view of a micromachine switch according to a first exemplary embodiment of the present invention, which is denoted as 100 as a whole. 2 is a cross-sectional view of the micromachine switch 100 shown in FIG. 1 as viewed in the II-II direction.
As shown in FIGS. 1 and 2, the micromachine switch 100 includes a substrate 10 made of a semiconductor such as Si. On the substrate 10, a suction electrode 101, an input side signal line 201, an output side signal line 202, and an electrode pad 206 are provided. These electrodes are made of, for example, Au. On the input-side signal line 201, a movable electrode 104 having a cantilever structure facing the suction electrode 101 is provided. A protrusion 105 is formed on the movable electrode 104 above the output signal line 202. The movable electrode 104 is made of, for example, Au.

  In the micromachine switch 100, when a voltage is applied to the suction electrode 101, an electrostatic force is generated between the suction electrode 101 and the movable electrode 104. As a result, the movable electrode 104 having a cantilever structure moves in the direction of the suction electrode 104, and the protrusion 105 formed at the tip of the movable electrode 104 comes into contact with the output-side signal line 202. As a result, the input side signal line 201 and the output side signal line 202 are electrically connected, and the micromachine switch 100 is turned on.

  On the other hand, when the voltage application to the suction electrode 101 is stopped, the electrostatic force between the suction electrode 101 and the movable electrode 104 disappears. As a result, in the movable electrode 104 having the cantilever structure, the protrusion 105 formed at the tip of the movable electrode 104 is separated from the output-side signal line 202. As a result, the input side signal line 201 and the output side signal line 202 are electrically disconnected from each other, and the micromachine switch 100 is turned off.

  Next, a method for manufacturing the micromachine switch 100 according to the first embodiment of the present invention will be described with reference to FIGS. The manufacturing method of the micromachine switch 100 includes the following steps 1 to 7.

  Step 1: As shown in FIG. 3, a substrate 10 made of, for example, non-doped Si is prepared. Subsequently, a metal layer made of Au is formed on the substrate 10 by sputtering. The film thickness of the metal layer is, for example, 500 nm. In order to enhance the adhesion between the substrate 10 and the metal layer, the metal layer may be formed after the Cr layer is formed on the substrate 10 to a thickness of about 30 nm. Subsequently, the metal layer is processed by patterning using photolithography and dry etching to form the suction electrode 101, the input-side signal line 201, the output-side signal line 202, and the like.

  Here, as a material of the substrate 10, a substrate material having low conductivity such as glass, sapphire, or a low-temperature sintered substrate may be used in addition to Si. In addition to Au, a low-resistance metal material such as Cu, Al, Pt, Ru, Rh, or an alloy thereof may be used as the material for the metal layer that forms the suction electrode 101 and the like.

  Step 2: As shown in FIG. 4, a metal layer made of Cu is formed by, for example, sputtering so as to cover the surface of the substrate 10, and then patterned to form a first sacrificial layer 102. In the region where the movable electrode 104 is formed on the input side wiring layer 201, the first sacrificial layer 102 is not formed. The film thickness of the first sacrificial layer 102 is, for example, 2 μm, but the film thickness is thin above the step portion 106.

  The first sacrificial layer 102 may be made of another metal material that can be wet etched, such as Ni or Al, instead of Cu.

  Next, the first sacrificial layer 102 is patterned on the output-side wiring layer 202 to form dimples. The depth of the dimple is, for example, 1 μm.

  Step 3: As shown in FIG. 5, a photoresist layer 203 having a film thickness of, for example, about 500 nm is formed by spin coating or spray coating so as to cover the surface of the substrate 10.

  Step 4: As shown in FIG. 6, the photoresist layer 203 is patterned to leave the photoresist layer 203 so as to cover the inclined portion of the first sacrificial layer 102 above the stepped portion 106.

  Step 5: As shown in FIG. 7, the photoresist layer 203 is subjected to a heat treatment (baking treatment) at 120 ° C. for 10 minutes, for example, so that corners are formed on the inclined portion of the first sacrificial layer 102. The rounded photoresist layer 203 is left and this is used as the second sacrificial layer 103. That is, the photoresist layer 20 patterned in the step 4 has side surfaces substantially perpendicular to the surface of the substrate 10 as shown in FIG. 6, but is rounded as shown in FIG. It has a (smooth) shape.

  Step 6: As shown in FIG. 8, a metal layer made of, for example, Au is formed so as to cover the entire surface, and this is patterned to form a movable electrode 104 having a cantilever structure. The thickness of the metal film is, for example, about 5 μm. As the material for the metal layer, a material having good conductivity such as Cu, Rh, or AuPt may be used instead of Au. In addition to the sputtering method, a pattern plating method may be used for forming the metal layer. In the case of using the pattern plating method, a seed layer made of Au or the like is formed on the first sacrificial layer 102 and the second sacrificial layer 103 by using a sputtering method or an evaporation method, and then plated thereon. The movable electrode 104 is formed by the method.

Step 7: Finally, the first sacrificial layer 102 and the second sacrificial layer 103 are removed by wet etching, whereby the micromachine switch 100 having the cantilever-structure movable electrode 104 shown in FIG. 2 is completed.
In the drying process after the wet etching of the first sacrificial layer 102 and the second sacrificial layer 103, the movable electrode 104 is prevented from adhering to the substrate due to the surface tension of the liquid (this phenomenon is called sticking). For example, the substrate is dried using a supercritical point drying method or the like.

As described above, in the manufacturing method according to the first embodiment, the second sacrificial layer 103 is formed so as to cover the first sacrificial layer 102 above the step portion 106, and the film thickness of the first sacrificial layer 102, The sum of the thickness of the two sacrificial layers 103 is substantially equal on the stepped portion 106 and the flat portion 107.
As a result, the distance between the suction electrode 101 and the movable electrode 104 is substantially equal between the vicinity of the stepped portion 103 and the vicinity of the flat portion 107.

  In particular, since the second sacrificial layer 103 is made of a material having good coverage such as a photoresist layer, the second sacrificial layer 103 is also formed on the inclined first insulating layer 102 above the stepped portion 106. Can be formed. In addition, since the photoresist layer can be easily and accurately patterned using a lithography method without using a complicated dry etching process, the manufacturing cost can be reduced.

FIGS. 10 and 11 are cross-sectional views of a micromachine switch having a conventional structure, which is generally indicated by 200, and is a cross-sectional view seen in the same direction as the II-II direction of FIG.
In the manufacturing process of the conventional micromachine switch 200, the sacrificial layer has a single-layer structure formed from a metal film or a photoresist film. For this reason, the thickness of the sacrificial layer is reduced in the vicinity of the stepped portion 106. For this reason, as shown in FIG. 9, the distance between the suction electrode 107 and the movable electrode 104 is narrower around the suction electrode 107 (step 106) than in other portions.

  As a result, as shown in FIG. 11, in the conductive state in which the movable electrode 104 is attracted by the suction electrode 107, the suction electrode 107 and the movable electrode 104 are easily in contact with each other, and the suction electrode 107 and the movable electrode 104 are welded to each other. There arises a problem that 107 does not operate.

  On the other hand, in the micromachine switch 100 according to the first embodiment, as shown in FIG. 2, the distance between the suction electrode 107 and the movable electrode 104 is substantially the same as that of other portions even in the vicinity of the step portion 106. . As a result, even in the conductive state in which the movable electrode 104 is attracted, the suction electrode 107 and the movable electrode 104 are not in contact with each other, a failure due to welding can be prevented, and the highly reliable micromachine switch 100 can be provided.

  Further, in the micromachine switch 100 according to the first embodiment, since the first sacrificial layer 102 with which the protrusion 105 comes into contact is made of metal, the tip of the protrusion 105 is not contaminated with organic matter, and the protrusion 105 and the output side signal are not contaminated. In a conductive state where the line 202 is in contact, the contact resistance is reduced, and good switching characteristics can be obtained.

Embodiment 2. FIG.
In the method for manufacturing the micromachine switch 100 according to the second embodiment of the present invention, a coating-deposited silicon oxide film (SOG: Spin On Glass) is used as the material of the second sacrificial layer 103 instead of the photoresist. Other steps are the same as those in the first embodiment.

  As described above, by forming the second insulating layer 103 using SOG instead of the photoresist, the possibility of organic contamination of the protrusion 105 can be further reduced, and the micromachine having good switching characteristics. A switch can be provided.

  In addition, since SOG has higher heat resistance than a photoresist, the temperature of the substrate 10 can be raised during the formation of a seed layer using a sputtering method (step 6 shown in FIG. 8). In this case, the seed layer covering the protrusion 105 becomes a more stable and dense film, and further, the contact resistance between the protrusion 105 and the output-side signal line 202 can be reduced, and a micromachine switch having good switching characteristics can be provided. It becomes possible.

It is a perspective view of the micromachine switch concerning Embodiment 1 of the present invention. It is sectional drawing of the micromachine switch concerning Embodiment 1 of this invention. It is sectional drawing of the manufacturing process of the micromachine switch concerning Embodiment 1 of this invention. It is sectional drawing of the manufacturing process of the micromachine switch concerning Embodiment 1 of this invention. It is sectional drawing of the manufacturing process of the micromachine switch concerning Embodiment 1 of this invention. It is sectional drawing of the manufacturing process of the micromachine switch concerning Embodiment 1 of this invention. It is sectional drawing of the manufacturing process of the micromachine switch concerning Embodiment 1 of this invention. It is sectional drawing of the manufacturing process of the micromachine switch concerning Embodiment 1 of this invention. It is sectional drawing of the micromachine switch concerning Embodiment 1 of this invention. It is sectional drawing of the conventional micromachine switch. It is sectional drawing of the conventional micromachine switch.

Explanation of symbols

  10 Substrate, 100 Micromachine Switch, 101 Suction Electrode, 102 First Sacrificial Layer, 103 Second Sacrificial Layer, 104, Movable Electrode, 105 Dimple (Contact after Movable Electrode Formation), 106 Stepped Part of Suction Electrode, 201 Input Side signal line, 202 Output side signal line, 206 Electrode pad.

Claims (5)

A method of manufacturing a micromachine having a movable electrode with a cantilever structure,
Preparing a substrate;
Forming at least a suction electrode on the substrate;
A first sacrificial layer forming step of forming a first sacrificial layer so as to cover the suction electrode;
A second sacrificial layer forming step of selectively forming a second sacrificial layer on the first sacrificial layer covering the step portion of the suction electrode;
Forming the movable electrode on the first sacrificial layer and the second sacrificial layer;
And a step of removing the first sacrificial layer and the second sacrificial layer. The first sacrificial layer forming step is a step of forming the first sacrificial layer including a flat portion parallel to the surface of the substrate and an inclined portion inclined with respect to the surface of the substrate covering the stepped portion. ,
2. The method of manufacturing a micromachine according to claim 1, wherein the second sacrificial layer forming step is a step of selectively forming the second sacrificial layer on the inclined portion.   3. The method of manufacturing a micromachine according to claim 1, wherein the second sacrificial layer forming step includes a step of heat-treating the second sacrificial layer to smooth the surface of the second sacrificial layer.   The method for manufacturing a micromachine according to claim 1, wherein the first sacrificial layer is made of a metal material selected from the group consisting of Cu, Ni, and Al.   The method of manufacturing a micromachine according to claim 1, wherein the second sacrificial layer is made of a material selected from the group consisting of a photoresist and SOG.

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