JP2007044847A - Electrodeposition method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrodeposition method for use in forming an organic film, by which the organic film can be selectively formed in an area where voltage application is desired such as an electrode while preventing abnormal deposition in an area where voltage is not applied. <P>SOLUTION: According to the method, oxygen plasma is applied to carbon-based contaminants (organic matter) remaining on surfaces of a control electrode 118 and a mobile portion electrode 109, in order to eliminate the contaminants. Next a substrate 101 subjected to oxygen plasma treatment, is treated with an hydrochloric acid, and the substrate is soaked in a hydrofluoric acid solution of a 0.5% concentration for 30 seconds, for instance. Thereafter the substrate 101 is washed with water, and immediately electrodeposited, whereby the organic film 110 is formed by electrodeposition only on a surface where the control electrode 118 is exposed. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an electrodeposition method in which an organic film is selectively formed on an electrode portion or the like used in MEMS post-surgery.

  In the MEMS (Micro-Electro-Mechanical Systems) technology, a fine movable portion made of a silicon or metal structure is driven by an electrostatic force generated by an electrode disposed opposite thereto. In the driving of such a movable part, sticking becomes a problem as will be described later. For example, in the MEMS shown in FIG. 3A, a movable portion 304 made of silicon supported by a support portion 303 is disposed on a substrate 301 made of silicon on which an insulating film 302 is formed. It is driven by an electric signal applied between an electrode 305 provided on 301 and an electrode 307 connected to the support portion 303.

  In such a configuration, it is not easy to draw the movable portion 304 toward the electrode 305 due to static electricity generated from the electrode 305 and keep it at an arbitrary distance from the underlying electrode 305. This is because the balance between the attractive force attracted by the electrode 305 and the elastic force that the movable portion 304 tries to return to is original and unstable. If these balances are lost and, for example, the attractive force is better, the tip of the movable portion 304 comes into contact with the surface of the electrode 305.

  When a conductive material is used for the movable part 304 and the electrode 305 and the movable part 304 are electrically connected when they come into contact with each other, as shown in FIG. The rebound (restoring force) due to the elastic force of the movable part 304 may not return to the original state. This phenomenon is called sticking or sticking, and is a problem when driving a movable part in the MEMS. The cause of this phenomenon is presumed that a kind of resistance welding is occurring because the contact between the movable part and the electrode is exactly the same as a so-called spot welder in a state where a high voltage is applied.

  Since the restoring force decreases as the size of the micromachine (movable part) decreases, it is not easy to increase the restoring force of the movable part in a MEMS configured with a fine micromachine. For this reason, in the micromachine, when the electrode and the movable part come into contact, in most cases, the above-described sticking state is obtained. Thus, as the micromachine has a smaller size of the movable part, sticking is more likely to occur, which is a particular problem. In order to prevent the above-mentioned sticking state, a technique for forming a film of an organic material (anti-sticking film) on the surface of an electrode has been proposed (see Non-Patent Document 1). In this technique, an organic film is selectively formed on the surface of the electrode by electrodeposition to prevent the sticking described above.

T.Sakata, H.Ishii, Y.Okabe, M.Nagase, M.Yano, K.Kudou, T.Kamei, K.Machida: "Selective Organic Dielectric Deposition for Encapsulation of MEMS Structure", Tech.Dig.JSAP Microprocesses and Nanotechnology 2004, pp.308-309, 0saka, Japan (2004).

  However, as shown in FIG. 4A, when the electrodeposition film 410 is formed by coating the exposed surface of the electrode 418 with an organic material by electrodeposition, not only the exposed portion of the electrode 418 but also In some cases, a portion 410 a extending to the side of the supporting insulating layer 402 and the portion of the substrate 401 is formed. Note that the MEMS whose partial cross section is shown in FIG. 4A is formed by a support portion 403 disposed on an insulating layer 402 on a substrate 401 made of silicon, as shown in the perspective view of FIG. A movable part 404 made of supported silicon and an electrode 409 formed on the support part 402 are provided. In addition, in another region on the substrate 401 different from these, an electrode 418 made of gold is provided on the substrate 401 with an insulating layer 402 interposed therebetween. In this MEMS, the movable portion 404 is driven and controlled by an electric signal applied between the electrode 409 and the electrode 418.

  As described above, even when an organic film (electrodeposition film) is selectively formed by electrodeposition, conventionally, an organic film may be formed even in a region of an insulating material to which no voltage is applied. It has occurred. Further, the organic film may be deposited even when it is immersed in the electrodeposition solution and no voltage is applied.

  The present invention has been made to solve the above problems, and in the formation of an organic film by electrodeposition, abnormal deposition in a region where no voltage is applied is suppressed, An object is to enable an organic film to be selectively formed in a desired region to which a voltage is applied, such as a portion.

  A gold electrodeposition method according to the present invention includes a first step in which an insulating layer is formed on a substrate, and a second step in which a metal structure is formed on the insulating layer. The organic film is formed on the surface of the structure by electrodeposition on the surface of the third step by immersing the substrate in the electrodeposition solution and applying a positive voltage to the structure. And at least a fourth step that is formed. After the treatment with the hydrofluoric acid solution, no precipitation occurs on any surface including the structure and the insulating layer when no voltage is applied.

  The electrodeposition method may include a fifth step of heating the organic film formed on the surface of the structure. In the fifth step, the heating may be performed at a temperature in the range of 20 ° C. higher than the glass transition temperature of the organic film. In addition, the structure is what causes the micromachine.

  As described above, according to the present invention, since electrodeposition is performed after the treatment with the hydrofluoric acid solution, the abnormal deposition in a region where no voltage is applied is suppressed, and the electrode portion For example, it is possible to obtain an excellent effect that an organic film can be selectively formed by electrodeposition in a desired region to which a voltage is applied.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a process diagram illustrating an example of an electrodeposition method according to an embodiment of the present invention. In FIG. 1, (a) and (a ′), (b) and (b ′), (c) and (c ′), (d) and (d ′), (e) and (e ′) , (F) and (f ′), (g) and (g ′) respectively indicate different regions in the same process.

  First, as shown in FIGS. 1A and 1A ′, an insulating layer 102 is formed on a substrate 101 made of single crystal silicon, and a predetermined region is formed as shown in FIG. 1A ′. A support portion 103 made of n-type silicon doped with impurities at a high concentration and a movable portion (not shown) are formed. The movable part is formed continuously (connected) to the support part 103. These may be formed, for example, by using an SOI (Silicon on Insulator) substrate and processing the SOI layer on the buried insulating layer of the SOI substrate by a known photolithography technique and etching technique. The buried insulating layer of the SOI substrate corresponds to the insulating layer 102, and the movable portion and the support portion 103 are obtained by processing the SOI layer.

  Next, as shown in FIGS. 1B and 1B ′, a lower seed layer 105 made of, for example, titanium and having a thickness of about 0.1 μm is formed so as to cover the insulating layer 102 and the support portion 103. Subsequently, the upper seed layer 106 made of, for example, gold and having a thickness of about 0.3 μm is formed on the lower seed layer 105. Subsequently, a photoresist is applied on these, and the formed photoresist film is patterned by a known photolithography technique, so that a resist pattern 107 having an opening 107a in a predetermined region is formed. .

  Next, as shown in FIG. 1C, gold is deposited on the upper seed layer 106 exposed in the opening 107a of the resist pattern 107 by electrolytic plating to form a metal pattern 108. Next, as shown in FIG. . The formed metal pattern 108 has a height from the surface of the insulating layer 102 that is substantially the same as that of the support portion 103. At this time, as shown in FIG. 1C ′, a gold film is not formed in a region covered with the resist pattern 107 such as the support portion 103.

  Next, after removing the resist pattern 107, as shown in FIGS. 1D and 1D ′, the upper seed is formed by wet etching using an iodine / ammonium iodide solution using the metal pattern 108 as a mask. The layer 106 is selectively removed by etching, and then the lower seed layer 105 is selectively removed by wet etching using a hydrofluoric acid solution. As a result, the control electrode 118 including the metal pattern 108 and the remaining lower seed layer 105 and upper seed layer 106 is formed on the insulating layer 102.

  Next, as shown in FIG. 1E and FIG. 1E ′, the movable portion electrode 109 is formed on the support portion 103. For example, a resist pattern in which a part of the front surface of the support portion 103 is opened is formed, and a gold plating film is formed on the open portion of the resist pattern by an electrolytic plating method, and then the resist pattern is removed. Thus, the movable portion electrode 109 can be formed.

  Next, in order to remove carbon-based contaminants (organic matter) remaining on the surfaces of the control electrode 118 and the movable part electrode 109, these oxygen plasmas are irradiated. For example, the entire region of the substrate 101 may be exposed to oxygen plasma generated at an RF power of 100 W for about 6 minutes. Next, the substrate 101 that has been treated with oxygen plasma is immersed in a hydrochloric acid solution having a pH of about 4.8, for example, and hydrochloric acid acts on the surfaces of the control electrode 118 and the movable portion electrode 109. And By this acid treatment, gold oxide formed by irradiating the surfaces of the control electrode 118 and the movable portion electrode 109 made of gold with oxygen-containing plasma is removed.

  Next, the substrate 101 on which the control electrode 118 and the movable portion electrode 109 are formed is immersed in a hydrofluoric acid solution. For example, the substrate 101 is immersed in a 0.5% concentration hydrofluoric acid solution for about 30 seconds. Thereafter, the substrate 101 is washed with water and immediately subjected to the following electrodeposition treatment. As shown in FIGS. 1 (f) and 1 (f ′), only the exposed surface of the control electrode 118 is subjected to electrodeposition. The organic thin film 110 is formed by deposition. Hereinafter, the formation of the organic thin film 110 will be described in more detail. First, an electrodeposition liquid in which a sulfonium cation having an epoxy group is dispersed (for example, Nippon Paint Co., Ltd., INSULEDED 3020) is adjusted to 30 ° C. In the electrodeposition liquid, the substrate 101 on which the control electrode 118 described above is formed and the counter electrode made of platinum are immersed. In this state, a negative voltage is applied to the control electrode 118 and a positive voltage is applied to the counter electrode. That is, the control electrode 118 is used as a negative electrode, the counter electrode is used as a positive electrode and immersed in an electrodeposition solution, and a voltage is applied using a constant voltage source to perform cationic electrodeposition. The organic thin film may be selectively formed using other electrodeposition.

  By this electrodeposition, the organic thin film forming material dispersed in the electrodeposition liquid is deposited on the surface of the control electrode 118 to which a negative voltage is applied, and the organic thin film 110 having a film thickness of about several tens of nm to 5 μm is formed. . The material dispersed in the electrodeposition liquid does not adhere to the surface of the insulating layer 102 to which no negative voltage is applied, the movable portion electrode 109, the support portion 103, and the movable portion (not shown). It selectively deposits on the portion of the control electrode 118 being applied. As a result, the organic thin film 110 is selectively formed on the exposed surface of the control electrode 118. As described above, since the treatment with hydrofluoric acid is performed before the electrodeposition treatment, the organic film 110 is formed in a state in which abnormal precipitation in a region where no voltage is applied is eliminated and high selectivity is maintained. A formed state is obtained.

  As described above, after the organic thin film 110 is formed by electrodeposition, the substrate 101 is washed with water (for 10 minutes), dried, and then subjected to heat treatment at 190 ° C. for 25 minutes in a nitrogen atmosphere. The organic thin film 110 is in a thermally cured state. The organic thin film 110 formed by electrodeposition under the conditions described above has a glass transition temperature of 178 ° C. and a heating temperature in the range up to 20 ° C. Thus, by heating at a temperature that exceeds the glass transition temperature of the organic thin film 110 to some extent, the organic thin film 110 can be made fluid and the thickness of the organic thin film 110 can be made uniform. In addition, it is confirmed that the organic thin film 110 can be formed with high uniformity in a state where excessive flow of the organic thin film 110 in the above-described thermosetting is suppressed within the above-described temperature condition range. Yes.

  In addition, when the film thickness uniformity is not required for the electrodeposited (deposited) organic film 110 or when uniformity is obtained only by electrodeposition, it is not necessary to heat the glass transition temperature or higher. What is necessary is just to heat to about 150 degreeC by which thermosetting is carried out. Further, depending on the organic material used for electrodeposition, only heating at a low temperature that can remove the solvent (water) may be performed, and curing by heating is not necessarily required. For example, it may be in a state in which it is heated to about 100 to 110 ° C. and moisture contained in the organic film 110 is simply removed.

  Finally, the insulating layer 102 is selectively removed by wet etching using a hydrofluoric acid solution, so that the substrate as shown in the perspective views of FIGS. 1 (g), 1 (g ′), and FIG. On the substrate 101, a MEMS is obtained in which the control electrode 118 is supported by the insulating support 113 and the support 103 is supported by the insulating support 112 having a thickness of about 2 μm. As shown in FIG. 2, the movable portion 104 is continuously connected to the support portion 103. Further, the movable portion 104 is arranged in a state of being close to the side portion of the control electrode 118.

  In addition, since the movable portion 104 is formed thinner than the support portion 103, the insulating layer 102 under the movable portion 104 is removed on the substrate 101 in the selective removal of the insulating layer 102 by the hydrofluoric acid solution described above. It will be in the state arrange | positioned about 2 micrometers apart. The movable part is formed to have a cross-sectional shape of about 2 × 2 μm and a length of about 10 μm to 1 mm, and is arranged on the side of the control electrode 118 so as to be separated by about 2 μm. One end of the movable portion 104 is supported by the support portion 103 and is separated from the substrate 101 by a predetermined distance (2 μm) so that it can be displaced (deformed). Further, the support portion 103 is disposed on the substrate 101 at the same height as the control electrode 118. As described above, a micromachine including the fine movable portion 104 is formed by the above-described manufacturing method. In the MEMS using the micromachine, an electric signal is applied to the control electrode 118, and the movable portion 104 is applied by the action of an electric field. Can be actuated in a predetermined direction.

  In the above description, the organic thin film 110 is formed only on the control electrode 118. However, the present invention is not limited to this. For example, an organic thin film may be formed only on the support portion 103 and the movable portion 104 by applying a negative voltage only to the support portion 103 and the movable portion 104 before forming the movable portion electrode 109. . Further, before forming the movable portion electrode 109, a negative voltage is applied to the movable portion 104 (including the support portion 103), and after the movable portion electrode 109 is formed, a negative voltage is applied to the control electrode 118. In this state, an organic thin film may be formed on both the movable portion 104 (including the support portion 103) and the control electrode 118.

  By the way, in the method described with reference to FIG. 1, the processing control electrode 118 uses the lower seed layer 105 made of titanium in order to improve the adhesion with the lower layer. In this case, in order to prevent titanium from diffusing into gold, the heating temperature is preferably set to 300 ° C. or lower. However, if a layer made of a material having a function as a diffusion barrier that suppresses diffusion of titanium is used, heat treatment can be performed under higher temperature conditions. For example, a layer such as titanium oxide may be used.

  In the above description, the movable part is made of n-type silicon doped with a high concentration of n-type impurities, and the control electrode is made of gold / titanium. These are made of a conductor capable of forming an organic thin film by electrodeposition. It only has to be done. As the above-mentioned conductor, for example, gold / chrome, copper / chromium or copper / titanium, metal such as SUS, iron, or p-type silicon or polysilicon doped with a high concentration of p-type impurities, or Hydrocarbon conductive polymers such as polyacetylene, polyazulene, polyphenylene, polyphenylene vinylene, polyacene, polyphenylacetylene, polydiacetylene, or heteroatom-containing conductive polymers such as polypyrrole, polyaniline, polythiophene, polythienylene vinylene, Alternatively, it may be a charge transfer complex.

  In FIGS. 1 and 2, the MEMS made up of a micromachine having a three-dimensional structure has been described as an example. However, the present invention is not limited to this, and two-dimensional (such as an isolated wiring pattern found in an LSI or the like) The same applies to a micromachine having a planar structure. As described above, by performing electrodeposition after the treatment with hydrofluoric acid, abnormal deposition in a region where no voltage is applied is suppressed, and high selectivity is maintained. A deposited film (organic film) can be formed. The hydrofluoric acid treatment may be performed before the hydrochloric acid treatment described above.

It is process drawing explaining the example of the electrodeposition method in embodiment of this invention. It is a perspective view which shows the structural example of MEMS manufactured by applying the electrodeposition method in embodiment of this invention. It is explanatory drawing for demonstrating the problem of the sticking in the drive of MEMS. It is explanatory drawing for demonstrating the state of the abnormal precipitation in electrodeposition.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 ... Board | substrate, 102 ... Insulating layer, 103 ... Support part, 104 ... Movable part, 105 ... Lower seed layer, 106 ... Upper seed layer, 107 ... Resist pattern, 107a ... Opening part, 108 ... Gold pattern, 109 ... Movable part Electrode, 110: organic thin film, 112, 113: insulation support, 118: control electrode.

Claims (4)

A first step in which an insulating layer is formed on the substrate;
A second step in which a structure made of metal is formed on the insulating layer;
A third step in which the substrate is immersed in a hydrofluoric acid solution;
At least a fourth step of immersing the substrate in an electrodeposition solution and applying a positive voltage to the structure to form an organic film on the surface of the structure by electrodeposition. A characteristic electrodeposition method. The electrodeposition method according to claim 1,
A fifth step of heating the organic film formed on the surface of the structure. The electrodeposition method according to claim 2, wherein
In the fifth step, the electrodeposition method is characterized by heating at a temperature in the range of 20 ° C. higher than the glass transition temperature of the organic film. In the electrodeposition method of any one of Claims 1-3,
The electrodeposition method, wherein a micromachine is constituted by the structure.

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