CH711248B1 - Silicon-based part with at least one chamfer and its method of manufacture - Google Patents

Abstract

The invention relates to a silicon-based micromechanical part (101), such as a timepiece anchor, with at least one chamfer (106) formed from a manufacturing process combining at least one step of etching oblique flanks (46) with a step of deep reactive ion etching of vertical flanks (47). This method notably allows the aesthetic improvement and improvement of the mechanical strength of parts formed by micro-machining of a silicon-based wafer.

Description

Description

Field of the Invention [0001] The invention relates to a silicon-based micromechanical part with at least one chamfer and its method of manufacture. More particularly, the invention relates to such a part formed by micro-machining a silicon-based wafer.

BACKGROUND OF THE INVENTION [0002] The document CH 698 837 discloses the manufacture of a watch component by micromachining of a wafer of amorphous or crystalline material such as silicon in crystalline or polycrystalline form.

Such micromachining is generally obtained from a deep reactive ion etching (also known by the abbreviation "DRIE"). As illustrated in FIGS. 1 to 4, a known micromachining consists of a structuring of a mask 1 on a substrate 3 (see Fig. 1, step A) followed by a deep reactive ion etching of the "Bosch" type successively combining a phase of etching (see Fig. 1, steps B, D, E) followed by a passivation phase (see Fig. 1, step C, layer 4) to obtain, from the pattern of the mask 1, a anisotropic etching 5, that is to say substantially vertical, in the wafer (see Figs 2 and 4).

As illustrated in FIG. 3, an example of deep-reactive ion etching of the "Bosch" type is represented with, in full line, SF6 SCCM flux as a function of time in seconds allowing the etching of a silicon wafer and, in broken line, the C4F8 SCCM flux versus time in seconds allowing passivation, i.e., protection, of the silicon wafer. It can thus be clearly seen that the phases are strictly consecutive and have a flow and a time of their own.

In the example of FIG. 3, a first etching phase is shown with SF6 flux at 300 SCCM for 7 seconds, followed by a first passivation phase with a flow of C4F8 at 200 SCCM for 2 seconds, followed by a second etching phase with a SF6 stream at 300 SCCM again for 7 seconds and finally followed by a second passivation phase with a flow of C4F8 at 200 SCCM for 2 seconds. It is therefore noted that a certain number of parameters make it possible to vary the deep-reactive ionic etching of the "Bosch" type in order to have a more or less marked undulation of the wall of the vertical etching 5.

After several years of manufacture, it turned out that these vertical engravings 5 were not completely satisfactory especially because of the edges at right angles sensitive to the grits and the "raw" character of the pieces obtained. SUMMARY OF THE INVENTION [0007] The object of the present invention is to overcome all or part of the aforementioned drawbacks by proposing a new type of silicon-based micromechanical part and a new type of manufacturing process that makes it possible, in particular, to improve aesthetic and improving the mechanical strength of parts formed by micro-machining a silicon-based wafer.

For this purpose, the invention relates to a method for manufacturing a silicon-based micromechanical part comprising the following steps: a) providing itself with a silicon-based substrate; b) forming a mask with perforations on a horizontal part of the ubstrat; c) etching, in an etching chamber, along oblique walls, in a portion of the thickness of the substrate from the apertures of the mask to form chamfered upper surfaces of the micromechanical part; d) etching, in the etching chamber, in substantially vertical walls, in at least a portion of the thickness of the substrate from the bottom of the first etching to form the peripheral walls of the micromechanical part beneath the chamfered upper surfaces ; e) releasing the micromechanical part of the substrate and the mask.

It is understood that in the same etching chamber, two distinct types of etching are obtained without the substrate being removed from the chamber. It will be understood immediately that the oblique etching of step c) makes it possible to dispense with the substantially straight angles between respectively the peripheral or internal vertical walls etched to form several micromechanical parts on the same substrate and the upper and lower surfaces of the substrate. It can also be seen that the oblique etching of step c) allows a much more open angle and a substantially rectilinear etching direction which avoids being limited by the parameters of a deep reactive ion etching of the "Bosch" type. which is, however, used in step d) according to its optimized vertical etching parameters.

According to other advantageous variants of the invention: - step c) is carried out by mixing etching gas and passivation gas in the etching chamber to form oblique walls; during step c), the etching gas and passivation flows are continuously pulsed to promote passivation at the bottom of the cavity; step d) is carried out by alternating a flow of etching gas and a passivation gas flow in the etching chamber in order to form substantially vertical walls; the method further comprises, between step d) and step e), steps f): forming a protective layer on the oblique walls and the substantially vertical walls leaving the etching background of step d ) without protective layer and g): engrave, in the etching chamber, along oblique walls, in the remainder of the substrate thickness from the bottom without a protective layer to form chamfered lower surfaces of the micromechanical; step g) is carried out by mixing etching gas and passivation gas in the etching chamber in order to form oblique walls; during step g), the etching gas and passivation flows are continuously pulsed to promote etching in the cavity bottom; step f) comprises the phases f1): oxidizing the oblique walls and the substantially vertical walls to form the protective layer made of silicon oxide and f2): directionally etching the protective layer in order to selectively remove the part of protective layer only at the etch floor of step d); the method further comprises, before step e), step h): filling a cavity formed during etching of the micromechanical part, formed by a chamfered upper surface, a peripheral wall and a chamfered lower surface, a metal or metal alloy to provide a fastener to the micromechanical part.

In addition, the invention relates to a micromechanical part obtained from the method according to one of the preceding variants, characterized in that it comprises a silicon-based body whose substantially vertical peripheral wall borders a horizontal upper surface through a chamfered upper surface.

Advantageously according to the invention, the micromechanical part has a clear aesthetic improvement by forming parts that have a much more aesthetic rendering worked. In addition, the substantially rectilinear chamfered surface provides an improvement in the mechanical strength including reducing the possibility of gritty substantially straight angles between respectively the vertical peripheral or internal walls and the upper or lower surfaces of the micromechanical part.

It is also understood that the vertical peripheral or internal walls offer a reduction of their contact surface making it possible to improve the tribology against another part or the entry of an organ along a distance. internal wall of the micromechanical part. Finally, the recesses of the peripheral or internal vertical walls are more open thanks to the chamfered surface, which may in particular allow an increase in the volume capacity to receive glue or lubricant.

According to other advantageous variants of the invention: - the vertical peripheral wall of the body further borders a horizontal lower surface through a chamfered lower surface; - The micromechanical part further comprises at least one cavity having a substantially vertical inner wall also comprising upper and lower chamfered surfaces intermediate said horizontal upper and lower surfaces; said at least one cavity is at least partially filled with a metal or a metal alloy in order to provide a fastener to the micromechanical part; the micromechanical part forms all or part of a movement or dressing member of a timepiece.

BRIEF DESCRIPTION OF THE DRAWINGS [0015] Other features and advantages will become clear from the description which is given below, by way of indication and in no way limitative, with reference to the appended drawings, in which: FIGS. 1 to 4 are representations intended to explain the deep-reactive ion etching of the "Bosch" type, used in the context of the invention; figs. 5 to 10 are representations of manufacturing steps of a micromechanical part according to a first embodiment of the invention; figs. 11 to 16 are representations of manufacturing steps of a micromechanical part according to a second embodiment of the invention; fig. 17 is a representation of a step of manufacturing a micromechanical part according to a third embodiment of the invention; fig. 18 is a block diagram of the manufacturing methods according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS [0016] The invention relates to a method 11 for manufacturing a silicon-based micromechanical component. As shown in fig. 18, the method 11, according to a first embodiment illustrated in single line, comprises a first step 13 intended to provide a substrate based on silicon.

The silicon-based terms mean a material comprising monocrystalline silicon, doped monocrystalline 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 can be used.

Typically, as illustrated in FIG. 9, the substrate 41 based on silicon may be silicon on insulator (also known by the abbreviation "SOI") comprising an upper layer 40 of silicon and a lower layer 44 of silicon connected by an intermediate layer 42 of oxide silicon. However, alternatively, the substrate could comprise a silicon layer reported on another type of base such as, for example, metal.

The method, according to the first embodiment, continues with step 15 for forming a mask 43 provided with openwork 45 on a horizontal portion of the substrate 41. In the example of FIG. 9, the mask 43 is formed on the upper part of the upper layer 40 of silicon. The mask 43 is formed from a material capable of withstanding the subsequent etching steps of the method 11. As such, the mask 43 may be formed from silicon nitride or silicon oxide. In the example of FIG. 9, the mask 43 is formed from silicon oxide.

Advantageously according to the invention, the method 11, according to the first embodiment, continues with a step 17 for engraving, from the perforations 45 of the mask 43, according to oblique walls 46, in a part of the the thickness of the substrate 41 in an etching chamber to form chamfered upper surfaces of the micromechanical part.

Step 17 oblique etching is not a deep reactive ion etching of the type "Bosch" described above. Indeed, step 17 allows a much more open angle and a direction of substantially rectilinear etching that avoid being limited by the parameters of a deep reactive ion etching of the "Bosch" type. Indeed, it is generally considered that, even by modifying the parameters of a deep reactive ion etching of the "Bosch" type, the opening angle can not exceed 10 degrees by having a curved etching direction.

Indeed, as shown in FIGS. 5 and 6, step 17 is advantageously according to the invention, carried out by mixing etching gas SF6 and passivation gas C4F8 in the etching chamber in order to form the oblique walls 46. Specifically, the SF6 gas flow C4F8 etching and passivation are preferably continuously pulsed to promote passivation cavity bottom.

It is therefore clear that step 17 allows a much wider angle typically around 45 degrees in the example of FIG. 5 instead of the 10 degrees best obtained by a deep reactive ion etching of the "Bosch" type with an optimized modification of the parameters. In addition, the pulsation of the continuous flows allows a better etching directivity, or even obtain perfect truncated cone walls, and not spherical (sometimes called isotropic etchings) as with a wet etching or dry etching as, for example, with SF6 gas alone.

To obtain the shape of walls 46 of FIG. 5, it is possible, for example, to apply the sequence of FIG. 6. This sequence has a first phase represented with a flow of SF6 at 500 SCCM mixed with a flow of C4F8 at 150 SCCM for 1.2 seconds, followed by a second phase represented with a flow of SF6 at 400 SCCM mixed with a flow from C4F8 to 250 SCCM for 0.8 seconds, followed by a third phase with again a stream of SF6 at 500 SCCM mixed with a flow of C4F8 at 150 SCCM for 1, 2 seconds and followed by a fourth phase with a SF6 stream at 400 SCCM mixed with a flow of C4F8 at 250 SCCM for 0.8 seconds and so on.

It is therefore noted that this pulsation of the continuous flows promotes passivation in the cavity bottom which will restrict, as and when step 17, the possible opening of the etching 49 according to its depth and, incidentally, a larger etch aperture 49 at the upper portion of the upper layer 40 to begin to obtain an etch aperture 49 wider than the aperture 45 at the top of the top layer 40 as visible in fig. 5.

The method 11, according to the first embodiment, continues with step 19 for etching, in the same etching chamber and with the same mask 43, according to walls 47, this time substantially vertical, in the at least a portion of the thickness of the layer 40 of the substrate 41 from the bottom of the first etching 49 to form the substantially vertical peripheral walls of the micromechanical part beneath the chamfered upper surfaces.

The step 19 of substantially vertical etching is typically a deep reactive ion etching of the "Bosch" type described above, that is to say by alternating a flow of etching gas and a flow of passivation gas in the etching chamber to form substantially vertical walls.

Thus, step 19 allows a substantially vertical direction of etching relative to the mask 43 as shown in FIG. 7 which is a section obtained after step 19. This gives a shape of etching section 51 whose base substantially forms a straight quadrilateral followed by a substantially conical flare.

The first embodiment ends with step 21 for releasing the micromechanical part of the substrate 41 and the mask 43. More specifically, in the example shown in FIG. 7, to perform a deoxidation phase 21 for removing the silicon oxide mask 43 and, optionally, a portion of the intermediate layer 42 of silicon oxide and a phase 23 of release of the substrate 41 using, for example , a selective chemical attack.

The first embodiment of the method 11 illustrated in single line in FIG. 18 allows, in the same etching chamber, two distinct types of etching without the substrate is removed from the chamber. It is immediately understood that the oblique etching of step 17 makes it possible to overcome the substantially right angles between respectively the vertical peripheral or internal etched walls and the upper and lower surfaces of the layer 40 of the substrate 41 to form one or more pieces of micromechanical on the same substrate 41.

It can also be seen that the oblique etching of step 17 allows a much more open angle and a substantially straight direction of etching which avoid being limited by the parameters of a deep reactive ion etching of the type " Bosch "and use it in step 19 according to its optimized parameters of vertical engraving.

Advantageously according to the invention, the micromechanical part 101 forming an anchor in the example of FIG. 16 has a clear aesthetic improvement by offering a much more worked rendering. Indeed, in comparison with FIG. 4, one can immediately detect the worked character of the micromechanical part 101.

As best seen in FIG. 8 which is an enlarged view on a part of the part 101, the micromechanical part 101 thus comprises a body 103 based on silicon whose vertical peripheral wall 105 borders a horizontal upper surface 104 via a chamfered upper surface 106.

It is therefore understood that the substantially rectilinear chamfered upper surface 106 provides an improvement in the mechanical strength, in particular by reducing the possibility of grinding of substantially straight angles between respectively the vertical peripheral or internal walls 105 and the upper or lower surfaces 104 of FIG. the micromechanical part 101.

It is also understood that the vertical peripheral wall 105 offers a reduction of its contact surface to provide an improvement in the tribology against another room or the entry of a pallet between two walls 105 of the Finally, the recesses of the vertical peripheral or internal walls 105 are more open thanks to the chamfered upper surface 106, which can in particular allow an increase in the volume capacity to receive glue or lubricant as in the case of recesses 107 visible in FIG. 16 which are used to receive a material suitable for attaching a pallet to the anchor.

According to a second embodiment of the invention, the method 11 performs the same steps 13 to 19 as the first embodiment with the same characteristics and technical effects. The second embodiment of the method 11 further comprises the steps visible in double lines in FIG. 18.

Thus, after the step 19 forming the etching 51, the method 11, according to the second embodiment, continues with the step 25 intended to form a protective layer 52 on the oblique walls 46 and the vertical walls. 47 leaving the etching background 51 without a protective layer as shown in FIG. 12.

Preferably, the protective layer 52 is formed of silicon oxide. Indeed, as visible in figs. 11 and 12, step 25 may then comprise a first phase 24 for oxidizing the entire top of the substrate 41, that is to say the mask 43 and the walls of the etching 51 to form an extra thickness on the mask 43 and a thickness on the oblique walls 46, the vertical walls 47 and the bottom of the etching 51 to form the protective layer 52 made of silicon oxide as can be seen in FIG. 11.

The second phase 26 could then consist in etching, in a directional manner, the protective layer 52 in order to selectively remove the horizontal silicon oxide surfaces from a portion of the mask 43 and from the entire portion of the protective layer. protection 52 only at the bottom of the engraving 51 as shown in FIG. 12.

The method 11 according to the second embodiment can then continue with the step 27 for etching, in the etching chamber, oblique walls 48, in the rest of the thickness of the substrate 41 from the bottom without protective layer 52 to form chamfered lower surfaces of the micromechanical part.

The oblique etching step 27, as step 17, is not a deep reactive ion etching of the "Bosch" type as the step 19 described above. Thus, step 27 allows, in combination with the protective layer 52, a much more open angle and a substantially rectilinear etching direction which avoids being limited by the parameters of a deep reactive ion etching of the "Bosch" type. . Indeed, it is generally considered that, even by modifying the parameters of a deep reactive ion etching of the "Bosch" type, the opening angle can not exceed 10 degrees by having a curved etching direction.

Therefore, as visible in FIGS. 13 and 15, the step 27 is advantageously according to the invention, carried out by mixing etching gas SF6 and passivation gas C4F8 in the etching chamber in order to form the oblique walls 48. Specifically, the SF6 gas flow of C4F8 etching and passivation are preferably continuously pulsed in order to promote etching in the cavity bottom.

It is therefore clear that step 27 allows a much wider angle typically around 45 degrees in the example of FIG. 13 instead of the 10 degrees best obtained by a deep reactive ion etching of the "Bosch" type with an optimized modification of the parameters. In addition, the pulsation of the continuous flows allows a better etching directivity, or even obtain perfect truncated cone walls, and not spherical (sometimes called isotropic etchings) as with a wet etching or dry etching as, for example, with SF6 gas alone.

To obtain the shape of walls 48 of FIG. 13, it is possible, for example, to apply an inverse sequence in FIG. 6. This sequence could thus comprise a first phase with a flow of SF6 mixed with a flow of C4F8 for a first duration, followed by a second phase with an increased flow of SF6 mixed with a decreased flow of C4F8 for a second duration, then again the first and second phase and so on.

It is therefore noted that this pulsation of the continuous flows favors the engraving in the cavity bottom which will widen, as and when the step 27, the possible opening of the etching 53 as a function of its depth and, Incidentally, a wider etching aperture 53 at the lower portion of the upper layer 40 until starting to obtain an etching aperture 53 wider than the opening 45 of the mask and etching background 51 at the beginning of step 27 as shown in FIG. 13.

The second embodiment is finished, as the first embodiment, with the step 21 for releasing the micromechanical part of the layer 40 of the substrate 41 and the mask 43. More specifically, in the example presented in fig. 14 and 15, to perform a deoxidation phase 21 for removing the mask 43 of silicon oxide, the protective layer 52 and possibly all or part of the intermediate layer 42 of silicon oxide as shown in FIG. 15, then a phase 23 of release of the substrate 41 using, for example, a selective etching as illustrated in FIG. 14.

The second embodiment of the method 11 illustrated in single and double lines in FIG. 18 makes it possible to overcome the substantially straight angles between respectively the vertical peripheral or internal etched walls and the upper and lower horizontal surfaces of the layer 40 of the substrate 41 to form one or more micromechanical parts on the same substrate 41.

It can also be seen that the oblique etching of steps 17 and 27 allows a much more open angle and a substantially straight direction of etching which avoid being limited by the parameters of a deep reactive ion etching of the type " Bosch "and use it in step 19 according to its optimized parameters of vertical engraving.

Advantageously according to the invention, the micromechanical part 101 forming an anchor in the example of FIG. 16, has a clear aesthetic improvement by offering a much more aesthetic rendering. Indeed, in comparison with FIG. 4, one can immediately detect the worked character of the micromechanical part 101 on both the upper face 104 and the lower face 108.

As best seen in FIG. 8 which is an enlarged view on a part of the part 101, the micromechanical part 101 thus comprises a body 103 based on silicon whose vertical peripheral wall 105 borders a horizontal upper surface 104 via a chamfered upper surface 106 and, as shown in FIG. 14, a horizontal lower surface 108 through a chamfered lower surface 109.

It is therefore understood that the chamfered upper and lower surfaces 106, 109 substantially rectilinear provide an improvement of the mechanical strength including reducing the possibility of gritty substantially straight angles between respectively the vertical peripheral or inner walls 105 and the upper surfaces or lower horizontal 104, 108 of the micromechanical part 101.

It is also understood that the vertical peripheral wall 105 provides a reduction of its contact surface to provide an improvement in the tribology against another room or the entry of an organ along a wall internal part of the micromechanical part.

Finally, the recesses of the vertical peripheral or inner walls 105 are more open thanks to the chamfered upper and lower surfaces 106, 109 which may in particular allow an increase in the volume capacity to receive glue or lubricant as in the case recesses 107 visible in FIG. 16 which are used to receive a material suitable for attaching a pallet to the anchor.

According to a third embodiment of the invention, the method 11 performs the same steps 13 to 27 and the phase 22 as the second embodiment with the same characteristics and technical effects. The third embodiment of the method 11 further comprises the steps shown in triple line in FIG. 18.

Thus, after the deoxidation phase 22 of the substrate 41, the method 11, according to the third embodiment, continues with the step 29 intended to fill a cavity 53 formed during engraving 17, 19 and 27 of the micromechanical component, formed by a chamfered upper surface, a peripheral wall and a chamfered lower surface, a metal or a metal alloy to provide a fastener to the micromechanical part.

As a preferred example, the lower layer 44 of the substrate 41 is heavily doped and used as a direct or indirect basis for electroplating filling. Thus, step 29 could comprise a first phase 30 intended to form a mold, for example, a photoresist on the top of the mask 43 and in part of the etching 53. A second phase 32 could consist of electroforming a metal part from the lower layer 44 at least between the silicon micromechanical part and a part of the mold formed in the etching 53. Finally, a third phase could consist in removing the mold formed during the phase 30.

The third embodiment ends with the release phase 23 of the composite micromechanical component of the substrate 41 by a selective etching.

The third embodiment of the method 11 illustrated in single, double and triple lines in FIG. 18 makes it possible to overcome the substantially right angles between respectively the vertical peripheral or internal etched walls and the upper and lower horizontal surfaces of the substrate 41 to form one or more composite micromechanical parts 111 formed (s) based on silicon and metal on the same substrate 41.

It can also be seen that the oblique etching of steps 17 and 27 allows a much more open angle and a substantially straight direction of etching which avoid being limited by the parameters of a deep reactive ion etching of the type " Bosch "and use it in step 19 according to its optimized parameters of vertical engraving.

Advantageously according to the invention, the composite micromechanical part, which can form an anchor as in the example of FIG. 16, has a clear aesthetic improvement by offering a much more worked rendering. Indeed, in comparison with FIG. 4, it is immediately possible to detect the worked character of the composite micromechanical component 111 both on the upper face 104 and on the lower face 108.

As best seen in FIG. 17, the composite micromechanical component 111 thus comprises a silicon-based body 103 whose vertical peripheral wall 105 borders a horizontal upper surface 104 via a chamfered upper surface 106 and, in addition, a horizontal lower surface 108 via a chamfered lower surface 109.

It is therefore understood that the chamfered upper and lower surfaces 106, 109 that are substantially rectilinear provide an improvement in the mechanical strength, in particular by reducing the possibility of grinding of the substantially straight angles between respectively the vertical peripheral or internal walls 105 and the upper surfaces. or lower horizontal 104, 108 of the composite micromechanical component 111.

It is also understood that the vertical peripheral wall 105 provides a reduction of its contact surface to provide an improvement in the tribology against another room. In addition, the recesses of the vertical peripheral or internal walls 105 are more open thanks to the chamfered upper and lower surfaces 106, 108, which may in particular allow an increase in the volume capacity to receive the metal or metal alloy portion, for example , the recesses 107 visible in FIG. 16 which could be filled during galvanic deposition. It is then understood that the galvanic deposition would be, by the shapes of chamfered surfaces 104, 106 and recesses 107, impossible to remove and would even benefit from a high shear strength.

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 a fastener to the composite micromechanical component 111. Thus, in the example of fig. 17, the cavity 110 could leave a cylindrical recess 113 capable of enabling the composite micromechanical component 111 to be driven onto an element such as, for example, a shaft, with a very high mechanical strength when the metal part is being stripped or metal alloy 112 thanks to the shapes of chamfered surfaces 104, 106 and, optionally, recesses 107.

Of course, the present invention is not limited to the illustrated example but is susceptible of various variations and modifications that will occur to those skilled in the art. In particular, an oxidation step 20, 28 for smoothing the silicon walls can be performed respectively between steps 19 and 21 or between steps 27 and 21.

In addition, the portion of metal or metal alloy 112 could overflow the etching 53 in step 29 so as to form an additional functional level of the composite micromechanical part 111 which would then be formed only metal or metal alloy.

Finally, the micromechanical part 101 or the composite micromechanical part 111 can not be limited to the application of an anchor as shown in FIG. 16. Thus, the micromechanical part 101 or the composite micromechanical part 111 may form all or part of a movement or dressing member of a timepiece.

By way of non-limiting examples, the micromechanical part 101 or the composite micromechanical part 111 may thus form all or part of a spiral, an ankle, a balance, an axis, a a tray, an anchor such as a rod, a rod, a fork, a pallet and a dart, a mobile like a wheel, a tree and a pinion, a bridge, a plate, a an oscillating weight, a winding stem, a pad, a case like the middle and horns, a dial, a flange, a bezel, a pusher, a crown, a caseback, a needle, a bracelet like a link, a decoration, a wall lamp, an ice cream, a clasp, a dial, a crown rod or a push rod.

Claims (14)

claims A method (11) for manufacturing a silicon-based micromechanical part (101, 111) comprising the steps of: a) providing a silicon-based substrate (40); b) forming a mask (43) with cut-outs (45) on a horizontal portion of the substrate (40); c) etching, in an etching chamber, along oblique walls (46), in a portion of the thickness of the substrate (40) from the apertures (45) of the mask (43) to form surfaces (106). chamfered upper parts of the micromechanical part (101, 111); d) etching in the etching chamber in substantially vertical walls (47) in at least a portion of the thickness of the substrate (40) from the bottom of the first etching (49) to form the peripheral walls (105) of the micromechanical part (101, 111) under the chamfered upper surfaces (106); e) releasing the micromechanical part of the substrate and the mask. 2. Method (11) according to the preceding claim, characterized in that step c) is carried out by mixing etching gas and passivation gas in the etching chamber to form oblique walls (46). 3. Method (11) according to the preceding claim, characterized in that, in step c), etching gas flows and passivation are continuously pulsed to promote passivation cavity bottom. 4. Method (11) according to one of the preceding claims, characterized in that step d) is performed by alternating a flow of etching gas and a flow of passivation gas in the etching chamber to form walls (47) substantially vertical. 5. Method (11) according to one of the preceding claims, characterized in that the method (11) further comprises, between step d) and step e), the following steps: f) forming a layer ( 52) on the oblique walls (46) and the substantially vertical walls (47) leaving the etching background (51) of step d) without a protective layer; g) etching, in the etching chamber, along oblique walls (48), in the remainder of the thickness of the substrate (40) from the bottom without a protective layer to form chamfered lower surfaces (109) of the micromechanical part (101, 111). 6. Method (11) according to the preceding claim, characterized in that step g) is performed by mixing etching gas and passivation gas in the etching chamber to form walls (48) oblique. 7. Process (11) according to the preceding claim, characterized in that, during step g), the etching gas flow and passivation are continuously pulsed to promote etching cavity bottom. 8. Method (11) according to one of claims 5 to 7, characterized in that step f) comprises the following phases: f1) oxidize the walls (46, 48) oblique and walls (47) substantially vertical to forming the protective layer (52) of silicon oxide; f2) directionally etching the protective layer (52) to selectively remove the protective layer portion only at the etch floor (51) of step d). 9. Method (11) according to one of claims 5 to 8, characterized in that the method (11) further comprises, before step e), the following step: h) fill a cavity (53) formed during engraving of the micromechanical part (101,111), formed by a chamfered upper surface (46), a peripheral wall (47) and a chamfered lower surface (48), of a metal or a metal alloy in order to providing a fastener to the micromechanical part (101, 111). 10. micromechanical part (101, 111) obtained from the method according to one of the preceding claims, characterized in that it comprises a body (103) based on silicon whose peripheral wall (105) substantially vertical borders a horizontal upper surface (104) through a chamfered upper surface (106). 11. Micromechanical part (101, 111) according to the preceding claim, characterized in that the vertical peripheral wall (105) of the body further borders a horizontal lower surface (108) via a lower surface (109). chamfered. 12. micromechanical part (101, 111) according to claim 10 or 11, characterized in that it further comprises at least one cavity (110) having a substantially vertical inner wall (105) also comprising surfaces (106, 109). ) upper and lower chamfered intermediate to said surfaces (104, 108) upper and lower horizontal. 13. micromechanical part (101, 111) according to the preceding claim, characterized in that said at least one cavity (110) is at least partially filled with a metal or a metal alloy (112) to provide a attaches to the micromechanical part (101, 111). 14. micromechanical part (101,111) according to one of claims 10 to 13 characterized in that it is an organ or part of a body movement or dressing of a room d watchmaking.