Abstract:
The invention relates to a silicon-based component with at least one chamfer formed from a method combining at least one oblique side wall etching step with a “Bosch” etching of vertical side walls, thereby enabling aesthetic improvement and improvement in the mechanical strength of components formed by micromachining a silicon-based wafer.

Description:
[0001]    This application claims priority from European Patent Application No. 15173823.4 filed on Jun. 25, 2015, the entire disclosure of which is hereby incorporated by reference. 
       FIELD OF THE INVENTION 
       [0002]    The invention relates to silicon-based micromechanical component with at least one chamfer and a method for fabrication of the same. More specifically, the invention relates to such a component formed by micromachining a silicon-based wafer. 
       BACKGROUND OF THE INVENTION 
       [0003]    CH Patent 698837 discloses the fabrication of a timepiece component by micromachining a wafer of amorphous or crystalline material, such as crystalline or polycrystalline silicon. 
         [0004]    Such micromachining is generally obtained by deep reactive ion etching (also known by the abbreviation “DRIE”). As illustrated in  FIGS. 1 to 4 , a known micromachining method consists in structuring a mask  1  on a substrate  3  (cf.  FIG. 1 , step A) followed by a “Bosch” deep reactive ion etching combining in succession an etching phase (cf.  FIG. 1 , steps B, D, E) followed by a passivation phase (cf.  FIG. 1 , step C, layer  4 ) in order to obtain from the pattern of mask  1 , an anisotropic, i.e. substantially vertical, etch  5 , in the wafer (cf.  FIGS. 2 and 4 ). 
         [0005]    As illustrated in  FIG. 3 , an example of a “Bosch” deep reactive ion etching is shown with, in solid lines, the flow of SF 6  in sccm as a function of time in seconds, for etching a silicon wafer and, in dotted lines, the flow of C 4 F 8  in sccm as a function of time in seconds, for the passivation, i.e. the protection, of the silicon wafer. It is thus clearly seen that the phases are strictly consecutive and each have a specific flow and time. 
         [0006]    In the example of  FIG. 3 , there is shown a first etching phase G 1 , with a flow of SF 6  at 300 sccm for 7 seconds, followed by a first passivation phase P 1  with a flow of C 4 F 8  at 200 sccm for 2 seconds, followed by a second etching phase G 2  with a flow of SF 6  at 300 sccm for 7 seconds again, and finally, followed by a second passivation phase P 2  with a flow of C 4 F 8  at 200 sccm for 2 seconds again, and so on. It is thus noted that a certain number of parameters enable the “Bosch” deep reactive ion etch process to be varied to obtain more or less marked scalloping in the wall of vertical etch  5 . 
         [0007]    After several years of fabrication, it was found that these vertical etches  5  were not entirely satisfactory, particularly due to the right-angled edges which are prone to chipping and to the “crude” nature of the components obtained. 
       SUMMARY OF THE INVENTION 
       [0008]    It is an object of the present invention to overcome all or part of the aforecited drawbacks by proposing a new type of silicon-based micromechanical component and a new type of fabrication method, in particular, to improve the aesthetics and to improve the mechanical strength of components formed by micromachining a silicon-based wafer. 
         [0009]    The invention therefore relates to a method for fabricating a micromechanical component made of a silicon-based material including the following steps:
       a) taking a silicon-based substrate;   b) forming a mask pierced with holes on a horizontal portion of the substrate;   c) etching, in an etching chamber, predetermined oblique walls, in part of the thickness of the substrate from holes in the mask, in order to form upper chamfered surfaces of the micromechanical component;   d) etching, in the etching chamber, substantially vertical walls, in at least part of the thickness of the substrate from the bottom of the first etch made in step c), in order to form peripheral walls of the micromechanical component beneath the upper chamfered surfaces;   e) releasing the micromechanical component from the substrate and the mask.       
 
         [0015]    It is understood that two distinct types of etch are obtained in the same etching chamber without removing the substrate from the chamber. It is immediately clear that the oblique etching in step c) removes the substantially right-angled edges respectively between the vertical peripheral or inner walls etched to form several micromechanical components in the same substrate and the upper and lower surfaces of the substrate. It can also be observed that the oblique etching in step c) allows for a considerably more open angle and a substantially rectilinear direction of etching, which avoids being limited by the parameters of a “Bosch” deep reactive ion etching, which is, conversely used in step d) with optimised vertical etching parameters.
       In accordance with other advantageous variants of the invention:   step c) is achieved by mixing the etching gas and the passivation gas in the etching chamber in order to form the predetermined oblique walls;   in step c), the continuous etching and passivation gas flows are pulsed to enhance the passivation at the bottom level;   step d) is achieved by alternating an etching gas flow and a passivation gas flow in the etching chamber in order to form the substantially vertical walls;   between step d) and step e), the method further includes the following steps: f): forming a protective layer on the predetermined oblique walls and the substantially vertical walls leaving the bottom of the etch of step d) without any protective layer and g): etching, in the etching chamber, second predetermined oblique walls, in the remaining thickness of the substrate from the bottom of the etch made in step d) without any protective layer, in order to form lower chamfered surfaces of the micromechanical component;   step g) is achieved by mixing the etching gas and the passivation gas in the etching chamber in order to form second predetermined oblique walls;   in step g), the continuous etching and passivation gas flows are pulsed to enhance the etching at the bottom level;   step f) includes the following phases: f1): oxidising the predetermined oblique walls and substantially vertical walls to form the protective silicon oxide layer; and f2): directionally etching the silicon oxide protective layer in order to selectively remove only the part of the protective layer from the bottom of the etch made in step d);   before step e), the method further includes step h): filling a cavity created during the etchings of the micromechanical component, formed by an upper chamfered surface, a peripheral wall and a lower chamfered surface, with a metal or metal alloy in order to provide an attachment to the micromechanical component.       
 
         [0025]    Moreover, the invention relates to a micromechanical component obtained from the method according to any of the preceding variants, wherein the component includes a silicon-based body whose substantially vertical peripheral wall borders a horizontal upper surface via an upper chamfered surface. 
         [0026]    Advantageously according to the invention, the micromechanical component enjoys a considerable aesthetic improvement by forming components which have a much more elaborate aesthetic finish. Further, the substantially rectilinear chamfered surface provides improved mechanical strength, particularly by reducing the possibility of chips to the substantially right-angled edges respectively between the vertical peripheral and/or inner walls and the upper and/or lower surfaces of the micromechanical component. 
         [0027]    It is also clear that the vertical peripheral and/or inner walls provide a reduced contact surface offering an improvement as regards tribological contact with other components or as regards the insertion of a member along an inner wall of the micromechanical component. Finally, the recessed areas of the vertical peripheral and/or inner walls are more open as a result of the chamfered surface which may enable an increase in volume capacity for receiving adhesive or lubricant. 
         [0028]    In accordance with other advantageous variants of the invention:
       the substantially vertical peripheral wall of the body also borders a horizontal lower surface via a lower chamfered surface;   the micromechanical component also includes at least one cavity including a substantially vertical inner wall also including intermediate upper and lower chamfered surfaces between said upper and lower horizontal surfaces;   said at least one cavity is at least partially filled with a metal or a metal alloy to provide an attachment to the micromechanical component;   the micromechanical component forms all or part of an element in the movement or external parts of a timepiece.       
 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0033]    Other features and advantages will appear clearly from the following description, given by way of non-limiting illustration, with reference to the annexed drawings, in which: 
           [0034]      FIGS. 1 to 4  are diagrams intended to explain the “Bosch” deep reactive ion etching process used within the scope of the invention; 
           [0035]      FIGS. 5 to 10  are diagrams of the fabrication steps of a micromechanical component according to a first embodiment of the invention; 
           [0036]      FIGS. 11 to 16  are diagrams of the fabrication steps of a micromechanical component according to a second embodiment of the invention; 
           [0037]      FIG. 17  is a diagram of a fabrication step of a micromechanical component according to a third embodiment of the invention; 
           [0038]      FIG. 18  is a flow diagram of the fabrication methods according to the invention. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0039]    The invention relates to a method  11  for fabricating a silicon-based micromechanical part. As illustrated in  FIG. 18 , method  11  according to a first embodiment illustrated in a single line, includes a first step  13  consisting of taking a silicon-based substrate. 
         [0040]    The term “silicon-based” means a material including single crystal silicon, doped single crystal silicon, polycrystalline silicon, doped polycrystalline silicon, porous silicon, silicon oxide, quartz, silica, silicon nitride or silicon carbide. Of course, when the silicon-based material is in crystalline phase, any crystalline orientation may be used. 
         [0041]    Typically, as illustrated in  FIG. 9 , the silicon-based substrate  41  may be a silicon-on-insulator substrate (also known by the abbreviation “SOI”) comprising an upper silicon layer  40  and a lower silicon layer  44  joined by an intermediate silicon oxide layer  42 . However, alternatively, the substrate could comprise a silicon layer added to another type of base such as, for example, a metal base. 
         [0042]    The method according to the first embodiment continues with step  15  of forming a mask  43  pierced with holes  45  on a horizontal portion of substrate  41 . In the example of  FIG. 9 , mask  43  is formed on the upper portion of upper silicon layer  40 . Mask  43  is formed from a material capable of withstanding the future etching steps of method  11 . Thus, mask  43  may be formed from silicon nitride or from silicon oxide. In the example of  FIG. 9 , mask  43  is formed from silicon oxide. 
         [0043]    Advantageously according to the invention, method  11  according to the first embodiment continues with a step  17  of etching, from holes  45  in mask  43 , predetermined oblique walls  46 , in a part of the thickness of substrate  41 , in an etching chamber, in order to form upper chamfered surfaces of the micromechanical component. 
         [0044]    Oblique etching step  17  is not a “Bosch” deep reactive ion etching described above. Indeed, step  17  allows for a much more open angle and a substantially rectilinear etching direction, which avoids being limited by the parameters of a “Bosch” deep reactive ion etching. Indeed, it is generally considered that, even by modifying the parameters of a “Bosch” deep reactive ion etch, the opening angle cannot exceed  10  degrees with a curved etching direction. 
         [0045]    Indeed, as seen in  FIGS. 5 and 6 , advantageously according to the invention, step  17  is achieved by mixing the SF 6  etching gas and the C 4 F 8  passivation gas in the etching chamber in order to form oblique walls  46 . More specifically, the continuous SF 6  etching and C 4 F 8  passivation gas flows are pulsed to enhance the passivation at the bottom level of the progressively formed cavity. 
         [0046]    It is thus understood that step  17  allows for a much more open angle, typically around 45 degrees in the  FIG. 5  example, instead of the maximum of 10 degrees obtained using a “Bosch” deep reactive ion etching with most optimised parameter modification. Advantageously according to the invention, step  17  can thus give a precise opening angle. The angle between the future vertical walls  47  and oblique walls  46  is highly reproducible and can advantageously be comprised between substantially 0° and substantially 45°. As explained above, it is particularly the possibility of etching at an angle of more than 10° which is remarkable compared to a “Bosch” deep reactive ion etch. Preferably, the angle according to the invention between the future vertical walls  47  and oblique walls  46  is greater than 10° and less than 45°, and even more preferably, greater than 20° and less than 40°. 
         [0047]    Further, the continuous flow pulsation allows for improved etching directivity, and can even provide substantially truncated cone-shaped walls and not spherical walls (sometimes called isotropic etches) as with a wet etch or a dry etch, for example, using only SF 6  gas. 
         [0048]    To obtain the shape of walls  46  in  FIG. 5 , the sequence of  FIG. 6  may, for example, be applied. This sequence includes a first phase P 1  with a flow of SF 6  at 500 sccm mixed with a flow of C 4 F 8  at 150 sccm for 1.2 seconds, followed by a second phase P 2  shown with a flow of SF 6  at 400 sccm mixed with a flow of C 4 F 8  at 250 sccm for 0.8 seconds, followed by a third phase P 1  again with a flow of SF 6  at 500 sccm mixed with a flow of C 4 F 8  at 150 sccm for 1.2 seconds and followed by a fourth phase P 2  with a flow of SF6 at 400 sccm mixed with a flow of C 4 F 8  at 250 sccm for 0.8 seconds and so on. 
         [0049]    It is thus noted that the continuous flow pulsation enhances the passivation at the bottom level of the progressively formed cavity which will gradually restrict, in step  17 , the possible opening of etch  49  as a function of its depth and, incidentally, a wider etch opening  49  in the upper portion of upper layer  40  until there is obtained an etch opening  49  wider than hole  45  in the upper portion of upper layer  40 , as seen in  FIG. 5 . 
         [0050]    Method  11  according to the first embodiment continues with step  19  of etching, in the same etching chamber and with the same mask  43 , substantially vertical walls  47 , in at least part of the thickness of layer  40  of substrate  41  from the bottom of the first etch  49 , in order to form the substantially vertical peripheral walls of the micromechanical component beneath the upper chamfered surfaces. 
         [0051]    The substantially vertical etching step  19  is typically a “Bosch” deep reactive ion etching described above, i.e. alternating an etching gas flow and a passivation gas flow in the etching chamber so as to form substantially vertical walls. 
         [0052]    Thus, step  19  allows for a substantially vertical etching direction relative to mask  43 , as seen in  FIG. 7 , which is a section obtained after step  19 . There is thus obtained an etching section  51  whose base substantially forms a right-angled quadrilateral followed by substantially conical tapering. 
         [0053]    The first embodiment ends with step  21  of releasing the micromechanical component from substrate  41  and from mask  43 . More specifically, in the example shown in  FIG. 7 , step  21  may include a deoxidation phase  22  to remove the silicon oxide mask  43  and, possibly, part of the intermediate silicon oxide layer  42 , and then a release phase  23  from substrate  41  with the aid, for example, of a selective chemical etch. 
         [0054]    The first embodiment of method  11  illustrated in single lines in  FIG. 18  allows for two different types of etching in the same etching chamber without removing the substrate from the chamber. It is immediately clear that the oblique etching of step  17  removes the substantially right-angled edges between the etched vertical peripheral and/or internal walls and the upper and lower surfaces of layer  40  of substrate  41  to form one or more micromechanical components on the same substrate  41 . 
         [0055]    It can also be observed that the oblique etching of step  17  allows for a much more open angle and a substantially rectilinear direction of etching, which avoids being limited by the parameters of a “Bosch” deep reactive ion etching and using the latter in step  19  with optimised vertical etching parameters. 
         [0056]    Advantageously according to the invention, the micromechanical component  101  that forms a pallets in the example of  FIG. 16  enjoys a considerable aesthetic improvement by offering a much more elaborate finish. Indeed, in comparison to  FIG. 4 , the elaborate nature of micromechanical component  101  is immediately apparent. 
         [0057]    As seen more clearly in  FIG. 8 , which is an enlarged view of a portion of component  101 , micromechanical component  101  thus includes a silicon-based body  103  whose vertical peripheral wall  105  borders a horizontal upper surface  104  via an upper chamfered surface  106 . 
         [0058]    It is thus clear that the substantially rectilinear upper chamfered surface  106  provides improved mechanical strength, particularly by reducing the possibility of chips to the substantially right-angled edges respectively between the vertical peripheral and/or inner walls  105  and the upper or lower surfaces  104  of micromechanical component  101 . 
         [0059]    It is also clear that substantially vertical peripheral wall  105  provides a reduced contact surface offering an improvement as regards tribological contact with other components or as regards the insertion of a pallet-stone between two substantially vertical walls  105  of micromechanical component  101 . Finally, the recessed portions of the substantially vertical peripheral and/or inner walls  105  are more open as a result of upper chamfered surface  106 , which may enable an increase in volume capacity for receiving adhesive or lubricant, as in the case of recessed portions  107  seen in  FIG. 16 , which are used to receive a material capable of attaching a pallet-stone to the pallets. 
         [0060]    According to a second embodiment of the invention, method  11  comprises the same steps  13  to  19  as the first embodiment with the same features and technical effects. The second embodiment of method  11  further includes the steps shown in double lines in  FIG. 18 . 
         [0061]    Thus, after step  19  of forming etch  51 , method  11  of the second embodiment continues with step  25  of forming a protective layer  52  on oblique walls  46  and substantially vertical walls  47 , leaving the bottom of etch  51  without any protective layer, as seen in  FIG. 12 . 
         [0062]    Preferably, protective layer  52  is formed of silicon oxide. Indeed, as seen in  FIGS. 11 and 12 , step  25  may then comprise a first phase  24  intended to oxidise the entire top of substrate  41 , i.e. mask  43  (when made of silicon oxide), and the walls of etch  51 , to form an added thickness on mask  43  and a thickness on oblique walls  46 , vertical walls  47  and the bottom of etch  51 , to form the protective silicon oxide layer  52 , as seen in  FIG. 11 . 
         [0063]    The second phase  26  could then consist in directionally etching protective layer  52  in order to selectively remove the horizontal silicon oxide surfaces from a part of mask  43  and from the entire part of protective layer  52  only on the bottom of etch  51  as seen in  FIG. 12 . 
         [0064]    Method  11  according to the second embodiment may then continue with step  27  of etching, in the same etching chamber, second predetermined oblique walls  48 , in the remaining thickness of substrate  41  from the bottom of the etch  51  made in step  19  without any protective layer  52 , in order to form lower chamfered surfaces of the micromechanical component. 
         [0065]    Oblique etching step  27 , like step  17 , is not a “Bosch” deep reactive ion etching like step  19  described above. Thus, in combination with protective layer  52 , step  27  allows for a much more open angle and a substantially rectilinear etching direction, which avoids being limited by the parameters of a “Bosch” deep reactive ion etching. Indeed, it is generally considered that, even by modifying the parameters of a “Bosch” deep reactive ion etch, the opening angle cannot exceed 10 degrees with a curved etching direction. 
         [0066]    Consequently, as seen in  FIGS. 13 and 15 , advantageously according to the invention, step  27  is achieved by mixing the SF 6  etching gas and the C 4 F 8  passivation gas in the etching chamber in order to form second oblique walls  48 . More specifically, the continuous SF 6  etching and C 4 F 8  passivation gas flows are preferably pulsed to enhance the etching at the bottom level of the progressively formed cavity. 
         [0067]    It is thus understood that step  27  allows for a much more open angle, typically around 45 degrees in the  FIG. 13  example, instead of the maximum of 10 degrees obtained using a “Bosch” deep reactive ion etching with most optimised parameter modification. Advantageously according to the invention, step  27  can thus give a precise opening angle without modifying the surfaces of oblique walls  46  and vertical walls  47 . The angle between vertical walls  47  and oblique walls  48  is highly reproducible and can advantageously be comprised between substantially 0° and substantially 45°. As explained above, it is particularly the possibility of etching at an angle of more than 10° which is remarkable compared to a “Bosch” deep reactive ion etching. Preferably, the angle according to the invention between vertical walls  47  and oblique walls  48  is greater than 10° and less than 45°, and even more preferably, greater than 20° and less than 40°. 
         [0068]    Further, the continuous flow pulsation allows for improved etching directivity, and can even provide substantially truncated cone-shaped walls and not spherical walls (sometimes called isotropic etches) as with a wet etch or a dry etch, for example, using only SF 6  gas. 
         [0069]    To obtain the shape of walls  48  in  FIG. 13 , a reverse sequence to  FIG. 6  may, for example, be applied. This sequence could thus include a first phase with a flow of SF 6  mixed with a flow of C 4 F 8  for a first duration, followed by a second phase with an increased flow of SF 6  mixed with a reduced flow of C 4 F 8  for a second duration, and then the first and second phases again and so on. 
         [0070]    It is thus noted that the continuous flow pulsation enhances the etching at the bottom level of the progressively formed cavity which will gradually widen, in step  27 , the possible opening of etch  53  as a function of its depth and, incidentally, a wider etch opening  53  in the lower portion of upper layer  40  until there is obtained an etch opening  53  wider than hole  45  in the mask  43  and than the section of the bottom of etch  51  at the start of step  27 , as seen in  FIG. 13 , without modifying the previously performed etch  51 . 
         [0071]    The second embodiment ends, like the first embodiment, with step  21  of releasing the micromechanical component from layer  40  of substrate  41  and from mask  43 . More specifically, in the example shown in  FIGS. 14 and 15 , step  21  may include a deoxidation phase  21  to remove the silicon oxide mask  43 , protective layer  52  and, possibly, all or part of the intermediate silicon oxide layer  42  as illustrated in  FIG. 13 , and then a release phase  23  from substrate  41  with the aid, for example, of a selective chemical etch as illustrated in  FIG. 14 . 
         [0072]    The second embodiment of method  11  illustrated in single and double lines in  FIG. 18  removes the substantially right-angled edges between the etched vertical peripheral and/or internal walls and the upper and lower horizontal surfaces of layer  40  of substrate  41  to form one or more micromechanical components on the same substrate  41 . 
         [0073]    It can also be observed that the oblique etching of steps  17  and  27  allows for a considerably more open angle and a substantially rectilinear direction of etching, which avoids being limited by the parameters of a “Bosch” deep reactive ion etching and using the latter in step  19  with optimised vertical etching parameters. 
         [0074]    Advantageously according to the invention, the micromechanical component  101  that forms a pallets in the example of  FIG. 16  enjoys a considerably aesthetic improvement by offering a much more elaborate aesthetic finish. Indeed, in comparison to  FIG. 4 , the elaborate nature of micromechanical component  101  is immediately apparent, both on upper face  104  and on lower face  108 . 
         [0075]    As seen more clearly in  FIGS. 8 &amp; 14 , micromechanical component  101  thus includes a silicon-based body  103  whose vertical peripheral wall  105  borders a horizontal upper surface  104  via an upper chamfered surface  106  and a horizontal lower surface  108  via a lower chamfered surface  109 . 
         [0076]    It is thus understood that the substantially rectilinear upper and lower chamfered surfaces  106 ,  109  provide improved mechanical strength, particularly by reducing the possibility of chips to the substantially right-angled edges respectively between the vertical peripheral and/or inner walls  105  and the upper and/or lower horizontal surfaces  104 ,  108  of micromechanical component  101 . 
         [0077]    It is also clear that vertical peripheral wall  105  provides a reduced contact surface offering an improvement as regards tribological contact with other components or as regards the insertion of a member along an inner wall of the micromechanical component. 
         [0078]    Finally, the recessed portions of the vertical peripheral and/or inner walls  105  are more open as a result of upper and lower chamfered surfaces  106 ,  109 , which can enable an increase in volume capacity for receiving adhesive or lubricant, as in the case of recessed portions  107  seen in  FIG. 16 , which are used to receive a material capable of attaching a pallet-stone to the pallets. 
         [0079]    According to a third embodiment of the invention, method  11  comprises the same steps  13  to  27  and phase  22  as the second embodiment, with the same features and technical effects. The third embodiment of method  11  further includes the steps seen in triple lines in  FIG. 18 . 
         [0080]    Thus, after phase  22  of deoxidizing substrate  41 , method  11  according to the third embodiment continues with step  29  of filling a cavity created during etchings  17 ,  19  and  27  of the micromechanical component, formed by an upper chamfered surface, a peripheral wall and a lower chamfered surface, with a metal or metal alloy in order to provide an attachment to the micromechanical component. 
         [0081]    In a preferred example, lower layer  44  of substrate  41  is highly doped and used as the direct or indirect base for filling by electroplating. Thus, step  29  could include a first phase  30  of forming a mould, for example made of photosensitive resin, on top of mask  43  and in a part of etch  53 . A second phase  32  could consist in electroplating a metal part  112 , from lower layer  44 , at least between the micromechanical silicon-based component and a part of the mould formed in etch  53 . Finally, a third phase  34  could consist in removing the mould formed in the phase  30 . 
         [0082]    The third embodiment ends with phase  23  of releasing the composite micromechanical component from substrate  41  by a selective chemical etch. 
         [0083]    The third embodiment of method  11 , illustrated in single, double and triple lines in  FIG. 18 , removes the substantially right-angled edges respectively between the vertical peripheral and/or internal walls and the upper and lower horizontal surfaces of substrate  41  to form one or more composite silicon-based and metal micromechanical components  111  formed on the same substrate  41 . 
         [0084]    It can also be observed that the oblique etching of steps  17  and  27  allows for a considerably more open angle and a substantially rectilinear direction of etching, which avoids being limited by the parameters of a “Bosch” deep reactive ion etch and using the latter in step  19  with optimised vertical etching parameters. 
         [0085]    Advantageously according to the invention, the composite micromechanical component, able to form a pallets as in the  FIG. 16  example, enjoys a considerable aesthetic improvement by offering a much more elaborate finish. Indeed, in comparison to  FIG. 4 , the elaborate nature of composite micromechanical component  111  is immediately apparent, both on upper face  104  and on lower face  108 . 
         [0086]    As shown more clearly in  FIG. 17 , composite micromechanical component  111  thus includes a silicon-based body  103  whose vertical peripheral wall  105  borders a horizontal upper surface  104  via an upper chamfered surface  106 , and, further, a horizontal lower surface  108  via a lower chamfered surface  109 . 
         [0087]    It is thus understood that the substantially rectilinear upper and lower chamfered surfaces  106 ,  109  provide improved mechanical strength, particularly by reducing the possibility of chips to the substantially right-angled edges respectively between the vertical peripheral and/or inner walls  105  and the upper and/or lower horizontal surfaces  104 ,  108  of composite micromechanical component  111 . 
         [0088]    It is also clear that vertical peripheral wall  105  provides a reduced contact surface offering an improvement as regards tribological contact with other components. Further, the recessed portions of the vertical peripheral and/or inner walls  105  are more open as a result of upper and lower chamfered surfaces  106 ,  109 , which can enable an increase in volume capacity for receiving the metal or metal alloy part such as, for example, recessed portions  107  seen in  FIG. 16 , which could be filled during electrodeposition step  29 . It is thus understood that the electrodeposit would be impossible to remove, due to the shapes of chamfered surfaces  106 ,  109  and recessed portions  107 , and would even enjoy high shearing resistance. 
         [0089]    Finally, at least one cavity  110 , forming an inner wall, is at least partially filled with a metal or a metal alloy  112  to provide an attachment to composite micromechanical component  111 . Thus, in the example of  FIG. 17 , cavity  110  could leave a cylindrical recess  113  allowing composite micromechanical component  111  to be driven onto a member, such as, for example, an arbor, with very good mechanical strength when the metal or metal alloy part  112  expands with help of the shapes of chamfered surfaces  106 ,  109  and possibly recessed portions  107 . 
         [0090]    Of course, the present invention is not limited to the illustrated example but is capable of various variants and modifications which will appear to those skilled in the art. In particular, an oxidizing step  20 ,  28 , intended to smooth the silicon walls, may be performed respectively between steps  19  and  21  or between steps  27  and  21 . 
         [0091]    Further, the metal or metal alloy part  112  could even overlap over etch  53  in step  29  to form an additional functional level of composite micromechanical component  111  which would be formed only of metal or metal alloy. 
         [0092]    Finally, micromechanical component  101  or composite micromechanical component  111  is not limited to the application to a pallets seen in  FIG. 16 . Thus, micromechanical component  101  or composite micromechanical component  111  can form all or part of an element in the movement or external parts of a timepiece. 
         [0093]    By way of non-limiting example, micromechanical component  101  or composite micromechanical component  111  may thus form all or part of a balance spring, an impulse pin, a balance wheel, an arbor, a roller, a pallets such as a pallet-staff, pallet-lever, pallet-fork, pallet-stone or guard pin, a wheel set such as a wheel, arbor or pinion, a bar, a plate, an oscillating weight, a winding stem, a bearing, a case such as the case middle or horns, a dial, a flange, a bezel, a push-piece, a crown, a case back, a hand, a bracelet such as a link, a decoration, an applique, a crystal, a clasp, a dial foot, a setting stem or a push-piece shaft.