CH711247B1 - Micromechanical part with a reduced contact surface and its manufacturing method. - Google Patents

Abstract

The invention relates to a micromechanical component (51) based on silicon, such as a wheel of a timepiece, with at least one reduced contact surface (54) formed from a process of manufacture combining at least one oblique flank etch step (37) with a deep vertical flank reactive ion etch step. This method makes it possible in particular tribological improvement of parts formed by microusinage of a wafer based on silicon.

Description

Description

Field of the invention The invention relates to a micromechanical part with a reduced contact surface and its manufacturing process. More particularly, the invention relates to such a part formed by micro-machining of a material plate.

Background of the invention [0002] The document CH 698 837 discloses the manufacture of a timepiece component by micromachining of a wafer made of amorphous or crystalline material such as silicon in crystalline or polycrystalline form.

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

As illustrated in FIG. 3, an example of deep reactive ionic etching of the "Bosch" type is shown with, in solid lines, the flow in SCCM of SF6 as a function of time in seconds allowing the etching of a silicon wafer and, in broken lines, the flux in SCCM of C ₄ F ₈ as a function of time in seconds allowing the passivation, that is to say the protection, of the silicon wafer. It is thus very easy to see that the phases are strictly consecutive and have their own flow and time.

In the example of FIG. 3, a first etching phase is represented with a flow of SF ₆ at 300 SCCM for 7 seconds, followed by a first passivation phase with a flow of C ₄ F ₈ at 200 SCCM for 2 seconds, followed by a second phase of etching with a flow of SF ₆ at 300 SCCM again for 7 seconds and, finally, followed by a second passivation phase with a flow of C ₄ F ₈ at 200 SCCM for 2 seconds. It is therefore noted that a certain number of parameters makes it possible to vary the deep reactive ion 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, particularly at the tribological level.

Summary of the invention The aim of the present invention is to overcome all or part of the drawbacks mentioned above by proposing a new type of micromechanical part and a new type of manufacturing process allowing in particular the tribological improvement of formed parts. by micro-machining a material plate.

To this end, the invention relates to a process for manufacturing a micromechanical part based on silicon, comprising the following steps:

a) be provided with a silicon-based substrate;

b) form a mask provided with openings on a horizontal part of the substrate;

c) etching, in an etching chamber, along substantially vertical walls, in at least part of the thickness of the substrate from openings in the mask in order to form peripheral walls of the micromechanical part;

d) form a protective layer on the vertical walls, leaving the etching base of step c) without a protective layer;

e) etching, in the etching chamber, along oblique walls, in the rest of the thickness of the substrate from the bottom without a protective layer in order to form oblique lower surfaces under the peripheral walls of the micromechanical part.

f) releasing the micromechanical part from the mask and the substrate.

It is understood that, in the same etching chamber, two different types of etching are obtained. It is immediately understood that the oblique etching of step e) makes it possible to form a second substantially oblique surface to form several pieces of micromechanics on the same substrate having a peripheral wall with reduced contact surface. We can also see that, thanks to the protective layer only on the vertical walls, the oblique etching of step e) allows a much more open angle and a substantially rectilinear etching direction.

CH 711 247 B1 which avoids being limited by the parameters of a deep reactive ion etching of the "Bosch" type which, on the other hand, is used during step c) according to its optimized vertical etching parameters.

[0010] In accordance with other advantageous variants of the invention:

- step c) is carried out by alternating a flow of etching gas and a flow of passivation gas in the etching chamber in order to form substantially vertical walls;

step d) comprises phases d1): oxidizing the etching obtained during step c) to form the protective layer of silicon oxide and d2): etching the protective layer in a directional manner in order to selectively remove the protective layer part only at the bottom of the etching of step c);

- step e) is carried out by mixing etching gas and passivation gas in the etching chamber in order to form oblique walls;

- during step e), the etching and passivation gas flows are continuously pulsed in order to promote etching at the bottom of the cavity.

In addition, the invention relates to a micromechanical part obtained from the method according to one of the preceding claims, characterized in that it comprises a silicon-based body whose peripheral wall has a first surface substantially vertical and a second oblique surface making it possible to reduce the contact surface of the peripheral wall.

Advantageously according to the invention, it is understood that the vertical peripheral or internal wall of the micromechanical part offers a reduction in its contact surface or as for the entry of an organ along an internal wall of the micromechanical part allowing to bring an improvement as for the tribology against another part.

[0013] In accordance with other advantageous variants of the invention:

- The micromechanical part further comprises at least one cavity comprising an internal wall also comprising a first substantially vertical surface and a second substantially oblique surface;

- the micromechanical part forms all or part of a movement or covering member of a timepiece.

Summary description of the drawings [0014] Other particularities and advantages will clearly match the description given below, by way of indication and in no way limitative, with reference to the attached drawings, in which:

fig. 1 to 3 are representations intended to explain the deep reactive ion etching of the "Bosch" type used in the context of the invention; fig. 4 to 10 are representations of steps in the manufacture of a micromechanical part according to an embodiment of the invention; fig. 11 is a representation of a micromechanical part according to an embodiment of the invention; fig. 12 is a block diagram of the manufacturing process according to an embodiment of the invention.

Detailed description of the preferred embodiments The invention relates to a method 11 for manufacturing a micromechanical part based on silicon. As illustrated in fig. 12, the method 11 comprises a first step 13 intended to be provided with a silicon-based substrate.

The terms based on silicon 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 the crystalline phase, any crystalline orientation can be used.

Typically, as illustrated in FIG. 4, the silicon-based substrate 31 can be silicon on insulator (also known by the abbreviation “SOI”) comprising an upper layer 30 of silicon and a lower layer 34 of silicon connected by an intermediate layer 32 of oxide of silicon. However, alternatively, the substrate could comprise a layer of silicon added onto another type of base such as, for example, metal.

The process continues with step 15 intended to form a mask 33 provided with openings 35 on a horizontal part of the substrate 31. In the example of FIG. 4, the mask 33 is formed on the upper part of the upper layer 30 of silicon. The mask 33 is formed from a material capable of withstanding the future etching steps of the method 11. As such, the mask 33 can be formed from silicon nitride or silicon oxide. In the example of fig. 4, the mask 33 is formed from silicon oxide.

Advantageously according to the invention, the method 11 continues with a step 17 intended to engrave, in an etching chamber, according to substantially vertical walls 36, in at least part of the thickness of the substrate 31 from the openings 35 of the mask 33 in order to form peripheral or internal walls of the micromechanical part.

CH 711 247 B1 [0020] The substantially vertical etching step 17 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 passivation gas in the etching chamber to form substantially vertical walls.

In fact, step 17 authorizes a direction of etching that is substantially vertical with respect to the mask 33 as shown in FIG. 5. An etching 39 is thus obtained, the section of which, visible in FIG. 5, is substantially in the form of a right quadrilateral. Of course, depending on the shape of the openings 35, the shape of the volume removed during engraving varies. Thus, a circular perforation will give a cylindrical engraving and a square perforation, a cube or a rectangular parallelepiped.

The method 11 continues with step 19 intended to form a protective layer 42 on the vertical walls 36, leaving the etching base 38 without protective layer as visible in FIG. 7.

Preferably, the protective layer 42 is formed of silicon oxide. Indeed, as visible in fig. 6 and 7, step 19 may then include a first phase 18 intended to oxidize the entire top of the substrate 31, that is to say the mask 33 and the walls 36, 38 formed by etching 39 to form an additional thickness on the mask 33 and a thickness on the vertical walls 36 and the bottom 38 of the etching 39 to form the protective layer 42 of silicon oxide.

The second phase 20 could then consist of etching, in a directional manner, the protective layer 42 in order to selectively remove the horizontal silicon oxide surfaces from part of the mask 33 and all of the layer part. protection 42 only at the bottom 38 of the engraving 39 as visible in FIG. 7.

The method 11 can then continue with step 21 intended to engrave, in the same etching chamber, but along oblique walls 37, in the rest of the thickness of the substrate 31 from the bottom 38 without layer of protection 42 in order to form oblique lower surfaces under the peripheral walls of the micromechanical part.

The oblique etching step 21 is not a deep reactive ion etching of the "Bosch" type described above. Indeed, step 21 allows, thanks to the protective layer 42, a much more open angle and a substantially rectilinear etching direction which avoid being limited by the parameters of a deep reactive ion etching of the “Bosch” type. . Indeed, it is generally estimated that, even by modifying the parameters of a deep reactive ion etching of the "Bosch" type, the opening angle cannot exceed 10 degrees by having a curved etching direction.

Advantageously according to the invention, step 21 is preferably carried out by mixing gas SF ₆ for etching and gas C ₄ F ₈ for passivation in the etching chamber in order to form the oblique walls 37. More precisely, the flows of gas SF ₆ for etching and passivation C ₄ F ₈ are continuously pulsed in order to promote etching at the bottom of the cavity. We therefore understand step 21 allows a largely open angle typically around 45 degrees in the example of FIG. 8 instead of the 10 degrees best obtained by deep reactive ion etching of the “Bosch” type with an optimized modification of the parameters. In addition, the pulsation of continuous flows allows better directivity of etching, even obtaining walls in trunk of perfect cones, and not spherical (sometimes called isotropic etchings) as with a wet etching or a dry etching as, for example, with SF ₆ gas only.

To obtain the shape of walls 37 of FIG. 8, it is for example possible to apply a sequence which may comprise 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 a flow increased by SF ₆ mixed with a flow decreased by C ₄ F ₈ for a second duration, then again the first and second phases and so on.

For example, this sequence could include a first phase with a flow of SF _{6 to} 500SCCM mixed with a flow of C ₄ F ₈ to 150 SCCM for 1.2 seconds, followed by a second phase represented with a flow of SF ₆ at 600 SCCM mixed with a flow of C ₄ F ₈ at 100 SCCM for 0.8 seconds, followed by a third phase with, again, 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 with a flow of SF ₆ at 600 SCCM mixed with a flow of C ₄ F ₈ at 100 SCCM for 0.8 seconds and so on.

We therefore note that this pulsation of continuous flows promotes etching at the bottom of the cavity which will widen, as step 21, the possible opening of etching 41 as a function of its depth and, incidentally, a wider etching opening 41 at the lower part of the upper layer 30 until starting to obtain an etching opening 41 wider than the opening 35 of the mask or the etching base 38 at the start of 'step 21 as visible when passing from fig. 7 in fig. 8.

The method 11 ends with step 23 intended to release the micromechanical part from the substrate 31 and from the mask 33. More specifically, in the example presented in FIGS. 9 and 12, step 23 may include a deoxidation phase 24 making it possible to remove the mask 33 of silicon oxide and, optionally, all or part of the intermediate layer 32 of silicon oxide and then a phase 25 of release of the substrate 31 using, for example, a selective chemical attack.

The method 11 illustrated in single lines in FIG. 12 allows, in the same etching chamber, two different types of etching. It can also be seen that the oblique etching of step 21 allows a much more open angle and a substantially rectilinear etching direction which avoid being limited by the parameters of a deep reactive ion etching of the “Bosch” type and to use the latter, during step 17, according to its optimized vertical etching parameters.

CH 711 247 B1 Advantageously according to the invention, the micromechanical part 51 forming a wheel in the example of FIG. 11 has a peripheral wall 54 forming a toothing which has a reduced contact surface.

As best seen in FIG. 10 which is an enlarged view on a part of the part 51, the micromechanical part 51 thus comprises a body 61 based on silicon, the peripheral wall 54 of which borders a horizontal upper surface and a horizontal lower 55 and comprises a first surface 56 substantially vertical and a second oblique surface 57.

It is therefore understood that the second oblique surface 57 substantially rectilinear brings to the peripheral wall forming toothing, a decrease in the contact surface allowing an improvement as to its tribology against another part. It is also understood that the internal wall 60 can also more easily receive a member.

Of course, the present invention is not limited to the illustrated example but is susceptible to various variants and modifications which will appear to those skilled in the art. In particular, an oxidation step 22 intended to smooth the silicon walls can be carried out between steps 21 and 23.

In addition, a metal or metal alloy part could be deposited in the etching 41, during an optional step between phases 24 and 25, so as to form a jacket 59 in a hole 60 of the workpiece. micromechanics 51 as illustrated in fig. 11.

This metal or metal alloy part could even overflow above the etching 41 in order to form an additional functional level of the composite micromechanical part 51 formed only of metal.

Thus, after phase 24 deoxidizing the substrate 31, the process 11 could continue with a step intended to selectively fill a cavity formed during etchings 17 and 21, with a metal or a metal alloy in order to offer a fastening to the micromechanical part.

As an example, preferably, the lower layer 34 of the substrate 31 could then be heavily doped and used as a direct or indirect base for filling by electroplating. Thus, a first phase could be intended to form a mold, for example in photosensitive resin, on the top of the mask 33 and in part of the etching 41. A second phase could consist in electroforming a metal part, starting from the layer bottom 34, at least between the silicon micromechanical part and a part of the mold formed in the etching 41. Finally, a third phase could consist in removing the mold formed during the first phase. The process would end with the phase 25 of release of the composite micromechanical part from the substrate 31 by a selective chemical attack.

Advantageously according to the invention, it is then understood that the galvanic deposition 59 is, by the shapes of the first substantially vertical surface 56 and a second oblique surface 57, more difficult to remove than with an essentially vertical surface and benefits from '' better shear strength.

In addition, said at least one cavity 60 which is at least partially filled with a metal or a metal alloy 59 makes it possible to offer an attachment to the composite micromechanical part 51. Thus, in the example of fig. 11, the cavity 60 could leave a cylindrical recess 62 capable of allowing the chase of the composite micromechanical part 51 on a shaft with good mechanical resistance during the expansion of the metal or metal alloy part 59 thanks to the shapes of the wall device 54.

Finally, the micromechanical part 51 cannot be limited to the application of a wheel as shown in FIG. 11. Thus, the micromechanical part 51 can form all or part of a movement or covering member of a timepiece.

By way of non-limiting examples, the micromechanical part 51 can thus form all or part of a hairspring, an ankle, a pendulum, an axis, a plate, a anchor like a rod, a rod, a fork, a pallet and a stinger, a mobile like a wheel, a tree and a pinion, a bridge, a plate, an oscillating mass, a winding stem, a cushion, a case like the middle and the horns, a dial, a flange, a bezel, a push-piece, a crown, a case back case, needle, bracelet like a link, decoration, applique, crystal, clasp, dial base, crown stem or d 'a push rod.

claims

Claims (8)

1. Method (11) for manufacturing a micromechanical part (51) based on silicon comprising the following steps: a) providing a substrate (30) based on silicon; b) forming a mask (33) provided with openings (35) on a horizontal part of the substrate (30); c) etching, in an etching chamber, along substantially vertical walls (36), in part of the thickness of the substrate (30), from openings (35) of the mask (33), in order to form peripheral walls (54) of the micromechanical part (51); d) forming a protective layer (42) on the vertical walls (36) leaving the etching base (38) (39) of step c) without a protective layer; CH 711 247 B1 e) etching, in the etching chamber, according to oblique walls (37), in the rest of the thickness of the substrate (30) from the bottom (38) without protective layer in order to form lower surfaces (57) oblique under the peripheral walls (54) of the micromechanical part, in order to reduce the contact surface; f) releasing the micromechanical part (51) from the mask (33) and from the substrate (30). 2. Method according to the preceding claim, characterized in that step c) is carried out by alternating a flow of etching gas and a flow of passivation gas in the etching chamber in order to form substantially vertical walls (36). 3. Method according to claim 1 or 2, characterized in that step d) comprises the following phases: d1) oxidize the etching (39) obtained during step c) to form the protective layer (42) of silicon oxide; d2) etching the protective layer (42) in a directional manner in order to selectively remove the protective layer part (42) only at the bottom (38) of the etching (39) of step c). 4. Method according to one of the preceding claims, characterized in that step e) is carried out by mixing etching gas and passivation gas in the etching chamber in order to form oblique walls (37). 5. Method according to the preceding claim, characterized in that, during step e), the etching and passivation gas flows are continuously pulsed in order to promote etching at the bottom of the cavity. 6. micromechanical part (51) obtained from the method according to one of the preceding claims, characterized in that it comprises a body (61) based on silicon, the peripheral wall (54) of which has a first surface (56 ) substantially vertical and a second oblique surface (57) making it possible to reduce the contact surface of the peripheral wall (54). 7. micromechanical part (51) according to the preceding claim, characterized in that it further comprises at least one cavity (62) comprising an internal wall also comprising a substantially vertical first surface (56) and a second surface ( 57) substantially oblique. 8. micromechanical part (51) according to claim 6 or 7, characterized in that it is a member or part of a movement member or covering a timepiece .