Method for producing a micromechanical component, and corresponding micromechanical component

Abstract

A method for producing a micromechanical component includes providing a substrate with a monocrystalline starting layer which is exposed in structured regions. The structured regions have an upper face and lateral flanks, wherein a catalyst layer, which is suitable for promoting a silicon epitaxial growth of the exposed upper face of the structured monocrystalline starting layer, is provided on the upper face, and no catalyst layers are provided on the flanks. The method also includes carrying out a selective epitaxial growth process on the upper face of the monocrystalline starting layer using the catalyst layer in a reactive gas atmosphere in order to form a micromechanical functional layer.

Claims

1. A production method for a micromechanical component, comprising: forming a catalyst layer on an upper side of a silicon on insulator substrate, the catalyst layer suitable for promoting silicon growth of the upper side, the substrate including a first silicon layer, an oxide layer, and a starting layer that has exposed structure regions, the structure regions defined by the upper side and lateral flanks, with no catalyst layer formed on the lateral flanks; performing a selective growth process on the upper side of the exposed structure regions of the starting layer via the catalyst layer in a reactive gas atmosphere to form a micromechanical functional layer; and removing at least a portion of the oxide layer of the substrate via sacrificial layer etching such that at least a portion of the micromechanical functional layer is movable relative to the substrate.

2. The production method as claimed in claim 1, wherein the starting layer is monocrystalline.

3. The production method as claimed in claim 2, wherein the starting layer consists of monocrystalline silicon.

4. The production method as claimed in claim 1, wherein the upper side has a tilt of less than 0.5 in relation to a low-index crystal plane.

5. The production method as claimed in claim 4, wherein the upper side has a tilt of less than 0.5 in relation to the (111) plane.

6. The production method as claimed in claim 1, wherein the upper side extends substantially flatly and the lateral flanks extend substantially vertically in relation to the upper side.

7. The production method as claimed in claim 1, further comprising: providing a planar unstructured starting layer that defines the upper side of the substrate; forming a planar unstructured catalyst layer on the upper side of the substrate so that the planar unstructured catalyst layer is on top of the planar unstructured starting layer; and jointly structuring the planar unstructured catalyst layer and the planar unstructured starting layer via an etching process to form the structure regions of the starting layer and to form the catalyst layer, with portions of the catalyst layer on the upper side of the structure regions.

8. The production method as claimed in claim 1, wherein the catalyst layer is formed over the structure regions of the starting layer, the method further comprising structuring the formed catalyst layer such that portions of the catalyst layer are on the upper side of the structure regions and such that no portions of the catalyst layer remain on the lateral flanks.

9. The production method as claimed in claim 8, further comprising: forming spacers on the lateral flanks before forming the catalyst layer; subsequently depositing the catalyst layer such that the catalyst layer reacts with the upper side and does not react with the spacers; and selectively removing the unreacted part of the catalyst layer from the spacers.

10. The production method as claimed in claim 1, further comprising forming spacers on the lateral flanks before performing the selective growth process.

11. The production method as claimed in claim 1, wherein the catalyst layer is formed from an element of one of periodic table groups four through fifteen.

12. The production method as claimed in claim 1, wherein a silane-containing gas atmosphere is used for performing the selective growth process.

13. The production method as claimed claim 12, wherein a silane-containing gas atmosphere is used for performing the selective growth process at a temperature of greater than 600 C.

14. The production method as claimed in claim 1, further comprising removing the catalyst layer after performing the selective growth process.

15. A micromechanical component, comprising: a substrate that includes: a first silicon layer; and an oxide layer; and a micromechanical functional layer that has exposed structure regions defined by an upper side and lateral flanks, the micromechanical functional layer formed by selectively growing structure regions which were disposed on the oxide layer, the selective growing including vertical growth and substantially no width growth of the structure regions; wherein at least a portion of the oxide layer is under-cut relative to the micromechanical functional layer such that at least a portion of the micromechanical functional layer is movable relative to the substrate.

16. The micromechanical component as claimed in claim 15, wherein the functional layer is a component of an inertial sensor.

17. The micromechanical component as claimed in claim 16, wherein the functional layer is a component of a rotation rate sensor.

18. A method of producing a micromechanical component, comprising: forming a planar unstructured catalyst layer on an upper side of a planar unstructured starting layer of a substrate; jointly etching the planar unstructured catalyst layer and the planar unstructured starting layer via an etching process to form: a plurality of structure regions that define a structured starting layer, each structure region defined by the upper side and respective lateral flanks; and a plurality of catalyst portions that define a structured catalyst layer, each catalyst portion disposed on the upper side of a respective structure region, wherein no portions of the catalyst layer are disposed on the lateral flanks of the structure regions; and selectively growing the upper side of the structure regions of the starting layer via the respective catalyst portions in a reactive gas atmosphere to form a micromechanical functional layer.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The present disclosure will be explained in greater detail hereafter on the basis of exemplary embodiments indicated in the schematic figures of the drawings. In the figures:

(2) FIGS. 1a)-f) show schematic cross-sectional illustrations to explain a micromechanical component and a corresponding production method according to a first embodiment of the present disclosure; and

(3) FIGS. 2a)-f) show schematic cross-sectional illustrations to explain a micromechanical component and a corresponding production method according to a second embodiment of the present disclosure.

DETAILED DESCRIPTION

(4) In the figures, identical reference signs identify identical or functionally identical elements.

(5) FIGS. 1a)-f) show schematic cross-sectional illustrations to explain a micromechanical component and a corresponding production method according to a first embodiment of the present disclosure.

(6) In FIGS. 1a) to e), reference sign 1 identifies an SOI substrate having a first silicon layer 1a, an oxide layer 1b located on the first silicon layer 1a, and a second monocrystalline silicon layer 1c located on the oxide layer 1b.

(7) The monocrystalline silicon layer 1c is formed in the present example as a (111) crystal plane. According to FIG. 1a), a catalyst layer 2, which comprises, for example, Zn, Ag, Al, Cu, Au, Ni, or Pt, is formed on the monocrystalline silicon layer 1c.

(8) In principle, numerous metallic elements of the periodic system are known to come into consideration as catalysts for VLS (vapor-liquid-solid) or VSS (vapor-solid-solid) growth of silicon.

(9) Some of these catalysts form a solid or liquid silicide in this case, and others form a silicon eutectic material. The catalysts ideally have the following properties. Firstly, they promote a high growth rate by way of the high solubility thereof for silicon or by way of the low activation energy thereof for the growth. Secondly, they are ideally compatible with CMOS processes, so that the processing can be performed in known semiconductor technology. Thirdly, they have a low vapor pressure, so that the catalyst is not vaporized during the growth. In particular the use of solid silicides promises a high structural accuracy, since therefore structures can be designed and produced independently of surface tensions of the liquid silicides.

(10) On the basis of these specified requirements, in particular, but not exclusively, the above-mentioned metals Zn, Ag, Al, Cu, Au, Ni, and Pt are of interest for forming the catalyst layer 2, but the disclosure is not restricted thereto, but rather in principle all elements of the 4th to 15th main groups of the periodic system can be used for this purpose.

(11) During the deposition of the catalyst layer 2 on the monocrystalline silicon layer 1c, the catalyst metal reacts with the silicon located underneath, i.e., for example, to form a corresponding silicide.

(12) In a following process step, which is illustrated in FIG. 1b), a step of jointly structuring the catalyst layer 2 and the monocrystalline silicon layer located underneath is performed in structure regions 3a to 3e, wherein the latter therefore forms a starting layer having a precursor structure 3 of a micromechanical functional layer 3 to be formed later therefrom by selective additive growth (cf. FIG. 1e)). The structuring is preferably performed by means of an etching process, which stops at the oxide layer 1b.

(13) As is apparent from FIG. 1b), after the etching step, an upper side O of the structured monocrystalline silicon layer 1c is covered with the catalyst layer 2, while in contrast the flanks F of the structure regions 3a to 3e of the structured monocrystalline polysilicon layer 1c are not covered thereby.

(14) Furthermore, with reference to FIG. 1c), a further oxide layer 5 is deposited over the structured monocrystalline polysilicon layer 1c having the catalyst layer 2 located on the upper side O.

(15) In a subsequent process step, which is illustrated in FIG. 1d), dry back-etching of the oxide layer 5 is performed by way of a dry etching process, whereby spacers 5 arise from oxide on the flanks of the structure regions 3a to 3e.

(16) The oxide spacers 5 ensure structurally accurate imaging during the later growth process, because they prevent, for example, contraction of a liquid phase due to capillary effects in convex corners. However, they can also be omitted under certain circumstances in dependence on the deposition process and material used.

(17) Then, with reference to FIG. 1e), a selective growth process is performed on the upper side O of the structure regions 3a to 3e of the structured monocrystalline silicon layer 1c by means of the catalyst layer 2 in a reactive gas atmosphere, whereby vertical growth and substantially no width growth of the structure regions 3a to 3e occurs. A micromechanical functional layer 3 having structure regions 3a to 3e made of monocrystalline silicon is thus formed on the oxide layer 1b and under the catalyst layer 2.

(18) During the performance of the selective growth process, preferably a silane-containing gas atmosphere (for example, having dichlorosilane) at a temperature of greater than 600 C. is used. The fact that no silicon growth results on the flanks F is because a thermodynamic equilibrium forms between a deposition process and an etching process on the flanks F.

(19) The VLS or VSS growth of structure flanks takes place completely symmetrically in relation to the crystal planes. This is because the surface and therefore the flanks of the structures grown using the VLS or VSS methods are oriented to thermodynamically favorable crystal surfaces. The incorrect orientation between the two flank angles of structures grown using the VLS or VSS method is therefore directly provided in a good approximation by the incorrect orientation of the starting layer in the form of the monocrystalline silicon layer 1c.

(20) Finally, with reference to FIG. 1f), sacrificial layer etching is performed, for example, by means of HF gas-phase etching, to remove the oxide layer 1b, which is used as the sacrificial layer, in regions, so that the structure regions 3a, 3b, 3c, and 3d above the first silicon layer 1a are made movable, while in contrast the structure region 3e above a remaining part of the oxide layer 1b remains connected to the first silicon layer 1a as an anchor. A micromechanical functional layer 3 formed in this manner is, for example, an anchored spring structure as a component of an inertial sensor, in particular a rotation rate sensor.

(21) With respect to the catalyst layer 2, it is to be mentioned that it, as shown in the present exemplary embodiment, can optionally be removed by means of ion beam etching or plasma etching. However, there can also be applications in which the catalyst layer 2 can be left on the micromechanical functional layer 3.

(22) FIGS. 2a)-f) show schematic cross-sectional illustrations to explain a micromechanical component and a corresponding production method according to a second embodiment of the present disclosure.

(23) In the second embodiment, in contrast to the first embodiment, firstly the monocrystalline silicon layer 1c is structured in an etching process in the structure regions 3a to 3e of the precursor structure 3 without catalyst layer 2 located thereon, as shown in FIG. 2a).

(24) Subsequently, with reference to FIG. 2b), a further oxide layer 5 is deposited above the monocrystalline silicon layer 1c, which is structured in the structure regions 3a to 3e.

(25) Spacers 5 made of oxide may be generated on the flanks F of the structure regions 3a to 3e by way of oriented back-etching of the oxide layer 5, while in contrast the upper side O remains uncovered by the oxide, as shown in FIG. 2c).

(26) As furthermore shown with reference to FIG. 2d), subsequently the catalyst layer 2 is formed above the structured monocrystalline silicon layer 1c having the spacers 5 by depositing the catalyst metal at a corresponding temperature, wherein the catalyst layer 2 reacts with the exposed upper side O, but not with the spacers 5 made of oxide or the oxide layer 1b. Thus, in a further process step (not shown), the unreacted part of the catalyst layer may be selectively removed from the spacers 5 and the oxide layer 1b, which results in a process state similar to FIG. 1b).

(27) As shown in FIG. 2e), similarly to the first embodiment, the selective growth process is performed to form the micromechanical functional layer 3 from the monocrystalline silicon layer 1c having the structure regions 3a to 3e.

(28) In the present exemplary embodiment, sacrificial layer etching is also performed similarly to the above first exemplary embodiment, but the catalyst layer 2 remains on the micromechanical functional layer 3. The catalyst layer 2 can therefore either be used to reduce the electrical resistance and/or as a eutectic bonding metal layer for a sensor cap on the micromechanical functional layer 3.

(29) Although the present disclosure was described above entirely on the basis of preferred exemplary embodiments, it is not restricted thereto, but rather is modifiable in a variety of ways.

(30) In particular, the specified materials and structures are only specified as examples and not as restrictive.

(31) The method according to the disclosure is suitable, as noted, in particular for preparing structures which are symmetrical in cross section, in particular spring structures, in MEMS components having an asymmetry of less than 0.5. Such structures are used in particular in methods for producing inertial sensors, in particular rotation rate sensors. However, it is generally applicable to any arbitrary micromechanical functional structures.