Abstract:
There is provided a method for fabricating a device, preferably for a micro electro electro mechanical system. The method includes forming a first electrode on a substrate, where the first electrode has a first sloped end at least at one end thereof; forming a sacrificial layer on the first electrode, where the sacrificial layer has a first sloped edge, the first sloped edge and the first sloped end are overlapped each other so that a thickness of the first sloped edge decreases as a thickness of the first sloped end increases; forming a first spacer on the first electrode, where the first spacer has contact with the first sloped edge; forming a beam electrode on the sacrificial layer and the first spacer; and removing the sacrificial layer after the forming the beam electrode.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is based upon and claims the benefit of priority of the prior Japanese Patent Application No. 2010-048008, filed on Mar. 4, 2010 the entire contents of which are incorporated herein by reference. 
       FIELD 
       [0002]    The present embodiments according to the invention relates to a method for fabricating a device such as a microstructure device and a device, such as the microstructure device, fabricated by the method. 
       BACKGROUND 
       [0003]    Micromachining technology has been developed to fabricate microstructure devices which are recently applied in various fields. The micromachining technology is referred to as micro electro mechanical systems technology (MEMS technology) and the microstructure devices also referred to as MEMS devices. 
         [0004]    A mobile communication device such as a mobile phone is an example of the fields as the application of the MEMS technology. MEMS technology makes MEMS devices such as variable capacitors and switches as radio frequency devices (RF devices) suitable to be used in radio-frequency circuits in the mobile phone, for example. 
         [0005]    The variable capacitors and the switches in MEMS devices, often need a beam structure which gives a function permitting vertical movement on a substrate on which the MEMS device is formed. 
         [0006]    The beam structures having the above-mentioned function are described in Japanese Laid-open Patent Publications No. 2005-313276 and No. 2006-289520. There is described in the former Patent Publication that the MEMES device has a piezoelectric film disposed over a cavity formed in a substrate, a movable beam having a first electrode disposed at the central part of the piezoelectric film, and a second electrode disposed in the cavity so as to face the first electrode. 
         [0007]    There is described in the latter patent application that MEMS device has a lower electrode disposed at the bottom of a cavity, an actuator disposed over or inside the cavity, and an upper electrode connected to the actuator. 
       SUMMARY 
       [0008]    According to an aspect of the invention, a method for fabricating a device includes forming a first electrode on a substrate, where the first electrode has a first sloped end at least at one end thereof; forming a sacrificial layer on the first electrode, where the sacrificial layer has a first sloped edge and the first sloped edge and the first sloped end are overlapped each other so that a thickness of the first sloped edge decreases as a thickness of the first sloped end increases; forming a first spacer on the first electrode, where the first spacer has contact with the first sloped edge; forming a beam electrode on the sacrificial layer and the first spacer; and removing the sacrificial layer after the forming the beam electrode. 
         [0009]    The object and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the claims. 
         [0010]    It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention, as claimed. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0011]      FIGS. 1A and 1B  are diagrams schematically illustrating a structure of a MEMS device in this embodiment; 
           [0012]      FIG. 2  is a diagram illustrating an exemplary structure of a movable electrode in a step in a MEMS device fabrication process; 
           [0013]      FIGS. 3A to 3C  are diagrams illustrating illustrate steps in the MEMS device fabrication process; 
           [0014]      FIGS. 4A to 4C  are diagrams illustrating steps in the MEMS device fabrication process; 
           [0015]      FIGS. 5A to 5C  are diagrams illustrating steps in the MEMS device fabrication process; 
           [0016]      FIGS. 6A to 6C  are diagrams illustrating steps in the MEMS device fabrication process; 
           [0017]      FIG. 7A  is a diagram illustrating a positional relationship between masks, and  FIG. 7B  is a diagram illustrating a positional relationship between the layers; 
           [0018]      FIG. 8A  is a diagrams illustrating another positional relationship between masks, and  FIG. 8B  is a diagrams illustrating a positional relationship between the layers; 
           [0019]      FIGS. 9A and 9B  are diagrams illustrating cross sectional views of experimentally fabricated MEMS devices around movable electrodes, which were drawn on the basis of their photos; 
           [0020]      FIG. 10  is a flowchart schematically illustrating fabrication processes in this embodiment; 
           [0021]      FIGS. 11A and 11B  are diagrams illustrating a MEMS switch having the movable electrode; and 
           [0022]      FIG. 12  is a diagram illustrating a MEMS filter in which a MEMS capacitor is included. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0023]    A MEMS device which has been known may usually have a structure in which a second electrode as a movable beam is provided above a first electrode. The first electrode serves for supporting the second electrode or for energizing the second electrode. As layers are sequentially formed during MEMS device fabrication, the second electrode is formed on a resultant uneven surface of a layer over the first electrode. 
         [0024]    In order to prevent occurrence of stress concentration or other undesirable effect in a movable beam, it is preferable to form the movable beam on a flat surface as much as possible. For forming the flat surface, it is usually adopted that a sacrificial layer is formed flat by spin coating a resin material such as a resist and a layer to be the movable beam is deposited on the sacrificial layer. By removing the sacrificial layer after patterning the sacrificial layer with a material to be formed to the movable beam, the movable beam is formed above a cavity which has been occupied by the sacrificial layer. 
         [0025]    If a resin is used as a sacrificial layer material, a thermal characteristic of the resin imposes various restrictions on processes before removing the sacrificial layer. Therefore, a heating and a lift-off processes are difficult to be applied to the processes. 
         [0026]    Instead of the resin material, an adoption of a silicon (Si) material as the sacrificial layer material makes it possible to apply the heating and the lift-off processes more freely in the MEMS device fabrication processes due to the high melting point of the silicon material. 
         [0027]    Forming the sacrificial layer with the silicon material may introduce a process such as spattering or another operation for growing silicon crystal to a desired thickness on a substrate. As silicon crystal grows easily, fine irregularities on the substrate, on which a silicon layer will be formed, are duplicated so as to emphasize during layer forming process by growing the Si crystal. Accordingly, the resultant Si sacrificial layer frequently has a surface including emphasized irregularities. A portion at which a wall intersects with the substrate at an angle may also function like the irregularity on the substrate surface because the Si crystal grows from on both the wall and the substrate to form a resultant recess at a boundary of both the grown Si crystals. 
         [0028]    Since the surface of the sacrificial layer made with Si material tends to be uneven as described above, it is difficult to appropriately form the second electrode serving as a movable beam on the uneven surface. 
         [0029]    Therefore, a fabrication method is desired to form with Si material the sacrificial layer of which the surface is flat as much as possible to appropriately form a second electrode as a movable beam thereon. 
         [0030]    According to the present invention, even if silicon is used as a sacrificial layer material, the surface of the resulting sacrificial layer may be flattened as much as possible and a second electrode as a movable beam may be appropriately formed on the sacrificial layer. 
         [0031]    As an embodiment, a variable capacitor will be described in detail below as a MEMS device. 
         [0032]    The MEMS capacitor  1  in  FIGS. 1A and 1B  includes a substrate  11 , a fixed electrode  12 , a dielectric layer  13 , supports  14 , and a movable electrode  15 .  FIG. 1A  is a section view taken along the line  1 A- 1 A in  FIG. 1B  which illustrates a plan view of the MEMS capacitor  1 . 
         [0033]    The MEMS capacitor  1  has the fixed electrode  12  and movable electrode  15  which are disposed on the substrate  11 . The movable electrode  15  warps when an electrostatic attractive force is generated by a voltage applied between the fixed electrode  12  and the movable electrode  15 , and the capacitance therebetween will be changed. The movable electrode  15  is just an example of a movable beam. 
         [0034]    The dielectric layer  13  increases the capacitance between the fixed electrode  12  and the movable electrode  15  to ∈r times more than that in vacuum (∈r is the dielectric constant of the dielectric layer  13 ), ands also prevents a short-circuit therebetween. 
         [0035]    The supports  14 , each of which has a base electrode  14   a  and a spacer  14   b , are disposed so as to support both ends of the movable electrode  15 . Specifically, each support  14  is disposed at the root of the movable electrode  15 . The base electrodes  14   a  are a base for both the movable electrode  15  and the supports  14 . 
         [0036]    A glass substrate, a Si substrate having a thermally oxidized film, or the like is used as the substrate  11 . The fixed electrode  12 , the base electrodes  14   a , and the movable electrode  15  are formed of gold, copper, aluminum, or another metal material. The spacers  14   b  are also made of aluminum, copper, gold, or another metal material. 
         [0037]    Various structures other than the structure illustrated in  FIGS. 1A and 1B  may also be used for the MEMS capacitor  1 . 
         [0038]      FIG. 2  is an enlarged view of a portion around the support  14  on the right side of the MEMS capacitor  1  in  FIG. 1A . The support  14  on the left side of the MEMS capacitor  1  is substantially symmetric to the support  14  on the right side in  FIG. 2 . The base electrodes  14   a  on the right and left sides are formed at the same time, and the spacers  14   b  on the right and left sides are also formed at the same time. 
         [0039]    As illustrated in  FIG. 2 , the movable electrode  15  is supported on the substrate  11  by supports  14 , each of which includes the base electrode  14   a  and spacer  14   b , at both ends. 
         [0040]    During fabrication of the MEMS capacitor  1 , the base electrodes  14   a , spacers  14   b , and sacrificial layer  21  are formed by, for example, patterning or lifting-off process. Then, the movable electrode  15  is formed on the spacers  14   b  and sacrificial layer  21  by, for example, sputtering or lifting-off process. When the sacrificial layer  21  is removed, a cavity is formed under the movable electrode  15 . 
         [0041]    Next, the method of fabricating the MEMS capacitor  1  will be described, centered around the supports  14  and sacrificial layer  21  adjacent to them for the clarity of description. 
         [0042]      FIGS. 3A to 3C  to  FIGS. 6A to 6C  illustrate fabrication processes for the part illustrated in  FIG. 2 . To clearly illustrate the shape of each part,  FIGS. 3A to 3C  to  FIGS. 6A to 6C  are laterally larger than those in  FIGS. 1A and 1B  and  FIG. 2 . 
         [0043]    As illustrated in  FIG. 3A , an electrode layer BM, from which the fixed electrode  12  and base electrodes  14   a  will be formed, is formed on the substrate  11  by spattering or plating by use of gold, copper, aluminum, or the like. The thickness of the electrode layer BM is 0.5 to several micrometers, for example. A resist BR 1  is then applied to the electrode layer BM. 
         [0044]    As illustrated in  FIG. 3B , the resist BR 1  is patterned to form a patterned resist BRP 1 . In this patterning, the end of a mask M 1 , which is not illustrated, for forming the base electrode  14   a  is aligned to a mask position PM 1 . The mask M 1  will be illustrated in  FIG. 7A . 
         [0045]    The mask position PM 1  is nearer to the center of the MEMS capacitor  1  than a mask position PM 2  described later. Accordingly, the resist BRP 1  to the right of the mask position PM 1  is left, and the base electrode  14   a  will be patterned by the resist BRP 1 . 
         [0046]    Specifically, as illustrated in  FIG. 3C , an appropriate etchant is used to etch the electrode layer BM, forming the base electrode  14   a . That is, the electrode BM includes a portion uncoated and a portion coated with the resist BRP 1 . After etching process using the appropriate etchant, the portion coated with the resist BRP 1  is left to form resultantly the base electrode  14   a  after several processes. 
         [0047]    Using a liquid including an appropriate surfactant as the etchant during the etching process, the etchant enters between the resist BRP 1  and electrode layer BM. Accordingly a portion of the electrode layer BM adjacent to the position PM 1  is removed to some extent by the etchant as illustrated in  FIG. 3B  to form a sloped side wall TS 1  having a relatively gentle inclination at its ends. 
         [0048]    The leftmost end of the sloped side wall TS 1  is substantially the same as the mask position PM 1 . The base electrode  14   a  and fixed electrode  12  at the other end are also formed at the same time. It suffices to form the dielectric layer  13  in an appropriate process after the fixed electrode  12  was formed. 
         [0049]    After the resist BRP 1  was removed, a new resist BR 2  is applied. The applied resist BR 2  is then patterned to form a patterned resist BRP 2  as illustrated in  FIG. 4A . 
         [0050]    The resist BRP 2  is patterned to lift off a sacrificial layer later. The end of a mask M 2  used for this patterning of the resist BRP 2  is aligned to a mask position PM 2 . Accordingly, the resist BRP 2  to the right of the mask position PM 2  is left. 
         [0051]    The mask position PM 2  is to the right of the mask position PM 1  as illustrated in  FIG. 4A , and is near the vertex of the sloped side wall TS 1  of the base electrode  14   a  or at a position in a flat part to the right of the vertex. 
         [0052]    Next, a first sacrificial layer BG 1  is formed by spattering or the like on the base electrode  14   a  formed on the substrate  11  and resist BRP 2  formed on the base electrode  14   a , as illustrated in  FIG. 4B . In this embodiment, silicon (Si) is used as the material of the first sacrificial layer BG 1 . In this case, the thickness around a portion of which the first sacrificial layer BG 1  contacts with the substrate  11  is preferably as same as the thickness of the flat portion of the base electrode  14   a.    
         [0053]    The resist BRP 2  is then lifted off together with the first sacrificial layer BG 1  formed thereon. A first patterned sacrificial layer BGP 1  is thereby formed by the lift-off, as illustrated in  FIG. 4C . 
         [0054]    A second sacrificial layer BG 2  is further formed by spattering or the like on the first patterned sacrificial layer BGP 1  and base electrode  14   a , as illustrated in  FIG. 5A . The thickness of a flat portion of the second sacrificial layer BG 2  is such that its upper surface is at the same height as the lower surface of the movable electrode  15 , which will be formed later. A resist BR 3  is then applied on the second sacrificial layer BG 2  as indicated by solid lines and a dash-dot-dot line in  FIG. 5B . 
         [0055]    The applied resist BR 3  is patterned to form a patterned resist BRP 3  as indicated by solid lines in  FIG. 5B . The end of a mask M 3  used for this patterning of the resist BRP 3  is aligned to the mask position PM 2  as in the case of the mask M 2 . Accordingly, the resist BRP 3  to the left of the mask position PM 2  is left. 
         [0056]    Next, the second sacrificial layer BG 2  is patterned by, for example, dry etching. A second patterned sacrificial layer BGP 2  is thereby formed as illustrated in  FIG. 5C . At least the second patterned sacrificial layer BGP 2  is undercut by etching, with respect to the resist BRP 3 . A sloped end surface TS 2  is formed at the end of the undercut part. The sloped end surface TS 2  inclines in a direction opposite to the direction in which the sloped side wall TS 1  of the base electrode  14   a  inclines. 
         [0057]    That is, the first patterned sacrificial layer BGP 1  and second patterned sacrificial layer BGP 2  are combined to form a sacrificial layer BGP 0  ( 21 ) as a whole. The sacrificial layer BGP 0  extends from an area in which the base electrode  14   a  is not formed and overlaps the sloped side wall TS 1  of the base electrode  14   a , with the sloped end surface TS 2  being formed at the end. 
         [0058]    The sloped end surface TS 2  of the sacrificial layer BGP 0  is formed above the sloped side wall TS 1  of the base electrode  14   a  as illustrated  FIG. 5C . Therefore, the angle of the sloped end surface TS 2  with respect to the surface of the substrate  11  is smaller than when the sloped end surface TS 2  is formed on a surface parallel to the surface of the substrate  11 , enabling the inclination of the sloped end surface TS 2  to be gentle. 
         [0059]    Next, a spacer layer BS used to form the spacer  14   b  is formed by, for example, sputtering as illustrated in  FIG. 6A . The thickness of the spacer  14   b  is such that its upper surface is at the same height as the lower surface of the movable electrode  15 , which will be formed later, that is, at the same height as the upper surface of the sacrificial layer BGP 0 . 
         [0060]    The resist BRP 3  is then lifted off together with the spacer layer BS formed thereon. The spacer  14   b  is thereby formed as illustrated in  FIG. 6B . The end surface of the spacer  14   b  touches or contacts the sloped end surface TS 2  of the sacrificial layer BGP 0 . 
         [0061]    Accordingly, the mask M 3  functions as a mask for sacrificial layer BGP 0  etching and as a mask for the lifting-off of the spacer  14   b.    
         [0062]    Next, the movable electrode  15  is formed on the spacer  14   b  and sacrificial layer BGP 0  by, for example, sputtering or lifting-off as illustrated in  FIG. 6C . When the sacrificial layer BGP 0  is removed, a cavity is formed under the movable electrode  15 . 
         [0063]      FIG. 7A  illustrates a positional relationship between the masks M 1  to M 4 , and  FIG. 7B  illustrates a positional relationship between layers patterned by the masks M 1  to M 4 , where the mask M 4  functions for patterning forming of the movable electrodes  15 . 
         [0064]    In  FIG. 7A , the mask M 1  used to pattern the base electrode  14   a  is disposed at the mask position PM 1 , while the mask M 2  used to pattern the first sacrificial layer BGP 1  and the mask M 3  used to pattern the sacrificial layer BGP 0   21  and spacer  14   b  are disposed at the mask position PM 2 . 
         [0065]    The mask M 1  and the masks M 2 , M 3  are disposed so that the edges patterned using them are disposed at different positions as illustrated in  FIG. 7A . Therefore, as illustrated in  FIG. 7B , the sacrificial layer BGP 0  is formed so that at least part of the sloped end surface TS 2  of the sacrificial layer BGP 0  matches a position within the range of a width as same as the thickness L 1  of the sacrificial layer BGP 0 , where the center of the range is the vertex TB 1  of the sloped side wall TS 1  of the base electrode  14   a.    
         [0066]    It is preferable to form the sacrificial layer BGP 0  so that the vertex TB 2  of the sloped end surface TS 2  of the sacrificial layer BGP 0  is disposed above the sloped side wall TS 1  of the base electrode  14   a  as illustrated in  FIG. 6A . However, this is not necessarily so. 
         [0067]    When the sacrificial layer BGP 0  is formed by disposing the masks M 1  to M 3  as described above, irregularities on the surface of the sacrificial layer BGP 0  are lessened and an adequately flat surface may be obtained. Accordingly, the movable electrode  15  formed on the sacrificial layer BGP 0  and spacer  14   b  is appropriately shaped, enabling the movable electrode  15  to have an enough strength and thereby may perform fully its function. 
         [0068]    Now, a case in which a MEMS device is fabricated with the masks  1  to  3  disposed at the same position will be described for comparison with the fabrication method in this embodiment. 
         [0069]    In the comparison example, the three masks M 1  to M 3  are all disposed at the same mask position PM 2 , as illustrated in  FIG. 8A , which is a diagram illustrating a plan view for explaining the positional relationship among the masks.  FIG. 8A  is a diagram illustrating a sectional view, taken along the line B-B in  FIG. 8A , of a laminated structure including the base electrode  14   aj , the sacrificial layer BGP 0   j , the spacer  14   bj , and the movable electrode  15   j . Operations other than disposing the masks M 1  to M 3  are the same as in this embodiment described above. 
         [0070]    The sloped side wall TS 1   j  is formed at the end of the base electrode  14   aj  as in the embodiment of the present invention. Accordingly, the end of the sloped side wall TS 1   j  is disposed at almost near to the position as the mask position PM 2  (see  FIG. 8B ). Since the sacrificial layer BGP 0   j  does not overlap the sloped side wall TS 1   j  of the base electrode  14   aj , a large V-shaped groove HB is resultantly formed between the sacrificial layer BGP 0   j  and sloped side wall TS 1   j . Therefore, as the spacer  14   bj  is formed along the groove HB, a similar groove is formed. 
         [0071]    As a result, the movable electrode  15   j  formed on the spacer  14   bj  has an inappropriate shape that is largely V-shaped by the groove generated near the mask position PM 2 . The strength of the movable electrode  15   j  may be then weakened and its function may not be fully executed with ease. 
         [0072]      FIGS. 9A and 9B  are cross sectional views of experimentally fabricated movable electrodes  15  and  15   j , which were drawn on the basis of their photos. 
         [0073]    As illustrated in  FIG. 9A , in the fabrication based on the method in the present embodiment according to the invention, the surface of the sacrificial layer BGP 0  was considerably flat, and thereby the movable electrode  15  formed on the sacrificial layer BGP 0  could be appropriately flattened. 
         [0074]    When the three masks M 1  to M 3  were all disposed at the same mask position PM 2 , however, the movable electrode  15   j  was V-shaped with a large groove as illustrated in  FIG. 9B , and may not have an appropriate flat shape. 
         [0075]    When the three masks M 1  to M 3  are all disposed at the same mask position PM 2  as described above, the sacrificial layer BGP 0   j  does not overlap the sloped side wall TS 1   j  of the base electrode  14   aj . Therefore, when the sacrificial layer BGP 0   j  is formed, it is deposited directly on the surface of the substrate  11 , and its sloped end surface TS 2   j  becomes significantly abrupt, that is, nearly vertical. 
         [0076]    As a result, a void KG (see  FIG. 9B ), which was not filled with a spacer material, was generated between the sacrificial layer BGP 0   j  and spacer  14   bj , preventing the movable electrode  15   j  from being appropriately shaped. 
         [0077]    By contrast, in the method in this embodiment, the mask position PM 1 , at which the mask M 1  used to form the base electrode  14   a  is disposed, is different from the mask positions PM 2 , at which the other masks M 2  and M 3  are disposed, so that the sloped side wall TS 1  of the base electrode  14   a  extends outside the spacer  14   b.    
         [0078]    Specifically, as described above, the sloped side wall TS 1  of the base electrode  14   a  is formed so as to externally extend and then the sacrificial layer BGP 0  is formed so as to overlap the sloped side wall TS 1 . At least part of the sloped end surface TS 2  of the sacrificial layer BGP 0  preferably matches a position within the range of the thickness L 1  of the sacrificial layer BGP 0 , the center of which is the vertex TB 1  of the sloped side wall TS 1 . The masks M 1  to M 3  are designed so that the mask position PM 2  has an adjustment margin as described above. 
         [0079]    When the sacrificial layer BGP 0  is formed on the sloped side wall TS 1  in this way, the sacrificial layer BGP 0  overlaps the sloped side wall TS 1 , and thereby the inclination of the sloped end surface TS 2  of the sacrificial layer BGP 0  becomes gentle. The void KG or a similar void was not generated between the sacrificial layer BGP 0  and spacer  14   b  as illustrated in  FIG. 9A . 
         [0080]    Specifically, the side wall at the end of the spacer  14   b  was formed so that it was placed in tight contact with the entire sloped end surface TS 2  of the sacrificial layer BGP 0 . Therefore, the sacrificial layer BGP 0  formed a continuous surface with the spacer  14   b , which was placed beneath the movable electrode  15 , enabling the movable electrode to be flatly shaped. The strength of the movable electrode  15  may be thereby maintained. 
         [0081]    If the sloped end surface TS 2  of the sacrificial layer BGP 0  extends upward at an intermediate point on the sloped side wall TS 1  of the base electrode  14   a , the inclination of the sloped end surface TS 2  may be made further gentle. This suppresses expansion of the sloped end surface TS 2  at its vertex, and thereby enables the movable electrode  15  to be further flattened. 
         [0082]    In the method in this embodiment described above, silicon may be used as the material of the sacrificial layer  21 , therefore, temperature restrictions on processes may be significantly reduced. Accordingly, for example, substrate temperature during formation of the movable electrode  15  may be changed, and freedom in design may be largely improved for internal stress and warp after it is released. 
         [0083]    By comparison, if a resin is used as the material of the sacrificial layer, various restrictions are imposed on fabrication processes; process temperature is limited to a maximum of about 100° C. until the sacrificial layer is removed. However, the use of a resin as the material of the sacrificial layer  21  is not inhibited. 
         [0084]    Although one of the two supports  14  disposed at both ends of the movable electrode  15  has been described so far, the two supports  14  are formed in the same process at the same time, as described above. 
         [0085]    For example, the two base electrodes  14   a  are formed so that each of their ends, which mutually oppose with a spacing therebetween, becomes the sloped side wall TS 1 . The sacrificial layer BGP 0  is formed so that it develops from an area between the sloped side walls TS 1  of the two base electrodes  14   a  and overlaps the sloped side walls TS 1  of the two base electrodes  14   a . At this time, the sloped end surface TS 2  is formed at each end of the sacrificial layer BGP 0 . 
         [0086]    The spacers  14   b  are formed on the two base electrodes  14   a  so that the spacers  14   b  abut against the relevant sloped end surfaces TS 2  of the sacrificial layer BGP 0 . 
         [0087]    Next, the fabrication method in this embodiment will be described with reference to the flowchart in  FIG. 10 . 
         [0088]    First, the base electrode  14   a  having the sloped side wall TS 1  at its end is formed on the substrate  11  (step # 11 ). The fixed electrode  12  is also formed at the same time. The sacrificial layer BGP 0  is then formed so that it extends from an area in which the base electrode  14   a  is not formed and overlaps the sloped side wall TS 1  of the base electrode  14   a , with the sloped end surface TS 2  being formed at the end, the sloped end surface TS 2  inclining in a direction opposite to the direction in which the sloped side wall TS 1  inclines (step # 12 ). 
         [0089]    The spacer layer BS (spacer  14   b ), which abuts against the sloped end surface TS 2  of the sacrificial layer BGP 0 , is formed on the base electrode  14   a  (step # 13 ). The movable electrode  15  is formed on the sacrificial layer BGP 0  and spacer  14   b  (step # 14 ). After the movable electrode  15  has been formed, the sacrificial layer BGP 0  is removed (step # 15 ). 
         [0090]    In the embodiment described above, the materials, shapes, dimensions, fabrication methods, and fabrication processes of the substrate  11 , fixed electrode  12 , dielectric layer  13 , spacer  14   b , and movable electrode  15  are not limited to those described above, but other various forms may be used. The method of fabricating the sacrificial layer BGP 0  is not also limited to that described above, but various other methods may be used. 
         [0091]    In the embodiment described above, the MEMS capacitor  1  has been taken as an example to describe a method of fabricating it. However, a MEMS capacitor having a different structure may also be used. For example, a structure in which the drive electrode for driving the movable electrode  15  is disposed separately from the fixed electrode  12  may be used. In addition to MEMS capacitors, the embodiment may also be applied to MEMS switches, radio-frequency filters, and other MEMS devices. 
         [0092]      FIG. 11A  is a plan view of an example of the MEMS switch which is fabricated by a method similar to the method used in the fabrication of the MEMS capacitor illustrated in  FIGS. 1A and 1B .  FIG. 11B  is a diagram illustrating a sectional view taken along the B-B line in  FIG. 11A . Each material of a substrate  111 , a fixed electrode  112 , a dielectric layer  13 , a base electrode  114   a , a spacer  114   b  and a movable electrode  115  is similar to each material of the substrate  11 , the fixed electrode  12 , the dielectric layer  13 , the base electrode  14   a , the spacer  14   b  and the movable electrode  15 , respectively. On the movable electrode  115 , dielectric layer  116  is disposed and at the both ends thereof, contacts  117  made of metal are provided. Opposing to each of the contacts  117 , two pair of contact electrodes are formed, one includes contact electrodes  118   a  and  118   b , the other contact electrodes  119   a  and  119   b . These contacts and the contact electrodes are made of metal. The movable electrode  15  is bent to the dielectric layer  113  by electrostatic force induced between the movable electrode  115  and the dielectric layer  113  when electric potential is applied between fixed electrode  112  and the movable electrode  115 . The thicknesses of the contact electrodes  118   a ,  118   b ,  119   a , and  119   b  are the same to or slightly larger than the height of the dielectric layer  113  from the surface of the substrate  111 . Accordingly, each pair of contact electrodes  118   a  and  118   b , and  119   a  and  119   b  are electrically switched on or off depending on whether the movable electrode  115  is bent to move toward the fixed electrode  112  or not. 
         [0093]      FIG. 12  is a diagram illustrating a MEMS filter  130  which composes a resonant circuit. In the MEMS filter  130 , an inductor  132  and a MEMS capacitor  133  are coupled in parallel and the MEMS capacitor  133  is controlled by a voltage Vcon which is applied from an external circuit. Capacitance of the MEMS capacitor  133  is controlled by Vcon and the resonant frequency of the MEMS filter  130  may be selected according to Vcon. The MEMS filter  130  illustrated in  FIG. 12  is composed with each of the electrical elements, however, it may be possible to fabricate the filter in a package using MEMS technology. 
         [0094]    All examples and conditional language recited herein are intended for pedagogical purposes to aid the reader in understanding the invention and the concepts contributed by the inventor to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions, nor does the organization of such examples in the specification relate to a showing of the superiority and inferiority of the invention. Although the embodiments of the present inventions have been described in detail, it should be understood that the various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention.