Micromechanical sensor

Abstract

A micromechanical sensor includes a base substrate, a cap substrate, and a MEMS substrate that is connected to each of the base and cap substrates by respective metallic bond connections and that includes a mechanical functional layer including movable MEMS elements, an electrode device for acquiring an indication of a movement of the MEMS elements and fashioned by layer deposition, and a sacrificial layer that is lower than the mechanical function layer, is fashioned by layer deposition, and is omitted in a region underneath the movable MEMS elements.

Claims

1. A micromechanical sensor comprising a base substrate; a cap substrate; and a third substrate that is connected to each of the base and cap substrates by respective metallic bond connections, and that includes: a mechanical functional layer including movable elements; an electrode device for acquiring an indication of a movement of the moveable elements and fashioned by layer deposition; a layer of sacrificial material that is lower than the mechanical function layer, and includes portions beyond opposite ends of the movable elements, no part of the layer being in a region underneath the movable elements, and an etch stop layer between the sacrificial layer and the electrode device.

2. The micromechanical sensor of claim 1, wherein the mechanical functional layer includes monocrystalline silicon.

3. The micromechanical sensor of claim 2, wherein the metallic bond connections provide an electrical connection through the cap substrate, third substrate, and base substrate.

4. The micromechanical sensor of claim 1, wherein a first cavity is fashioned in the base substrate.

5. The micromechanical sensor of claim 4, wherein a second cavity is fashioned in a second substrate.

6. The micromechanical sensor of claim 5, wherein different pressures are in the first and second cavities.

7. The micromechanical sensor of claim 4, wherein a cap cavity is fashioned in the cap substrate.

8. The micromechanical sensor of claim 7, wherein a through-opening extends from the first cavity to the cap cavity.

9. The micromechanical sensor of claim 1, wherein a cap cavity is fashioned in a third substrate.

10. The micromechanical sensor of claim 1, wherein the micromechanical sensor is an acceleration sensor.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows a cross-sectional view of a micromechanical sensor according to a first example embodiment of the present invention.

(2) FIG. 2 shows a cross-sectional view of a micromechanical sensor according to a second example embodiment of the present invention.

(3) FIG. 3 shows a cross-sectional view of a micromechanical sensor according to a third example embodiment of the present invention.

(4) FIG. 4 is a flowchart that illustrates a schematic flow of a method for producing a micromechanical sensor, according to an example embodiment of the present invention.

DETAILED DESCRIPTION

(5) Example embodiment of the present invention provide a micromechanical sensor having a high degree of detection quality. The proposed micromechanical sensor and the associated production method can result in the realization of highly sensitive micromechanical inertial components.

(6) FIG. 1 schematically shows a simplified cross-sectional view through a first example embodiment of a micromechanical sensor 100. Visible is a first substrate 10 in which a mechanical functional layer 11 (e.g., monocrystalline or polycrystalline silicon) is fashioned, movable micromechanical elements 16 (MEMS elements) being fashioned in mechanical functional layer 11.

(7) In comparison with polycrystalline material, monocrystalline material has the advantage that its mechanical properties are very defined, which has the effect of low scatter of functional parameters of the finished components in production.

(8) On first substrate 10, through a layer deposition process there is further fashioned a sacrificial layer 18 (e.g., SiO.sub.2), at least one electrically conductive wiring layer 13 (e.g., tungsten, aluminum), and insulating layers 12 (e.g., SiO.sub.2), vertical electrodes for the movable MEMS elements 16 and supply lines for the horizontal electrodes being realized by wiring layers 13. In addition, in first substrate 10 an etch stop layer 14 is visible, e.g., in the form of SiCN or Si-rich nitride. Etch stop layer 14 prevents an attack on the insulating layers, and thus underetching of wiring layers 13, during a sacrificial layer etching process (e.g., using hydrofluoric acid vapor).

(9) As a result, in this way in first substrate 10 a low-ohmic wiring is fashioned having electrode structures on first mechanical functional layer 11.

(10) During operation of micromechanical sensor 100, movable MEMS elements 16 interact with the horizontal electrodes of first functional layer 10 and the vertical electrodes in wiring layers 13, and, when there is a defined movement of movable MEMS elements 16, they capacitively generate an electrical measurement signal of micromechanical sensor 100.

(11) With sacrificial layer 18 fashioned by layer deposition on first substrate 10 and with a well-defined positioning of electrodes in wiring layers 13 on first substrate 10, the positioning including a very precisely dimensioned spacing of the electrodes from the movable MEMS elements 16, as a result, a precise realization of a capacitive measurement design is thus possible in particular for the vertical electrodes and the associated movable MEMS elements 16 when there is a vertical deflection of movable MEMS elements 16.

(12) In first substrate 10, stop elements 15 can be seen on etch stop layer 14, which are intended to prevent adhesion of movable MEMS elements 16.

(13) First substrate 10 is eutectically connected to second substrate 20 by metallic bond connections 40. In addition, first substrate 10 is connected to a cap wafer 30 by further metallic bond connections 50. In both cases, the bond connections include a hermetically sealed bond frame that runs peripherally around MEMS elements 16, in order to enable targeted setting of a pressure in the interior of the micromechanical sensor. Before the application of cap wafer 30, first substrate 10 is thinned back to the provided thickness of functional layer 11, e.g., by a grinding process, the bonding material is applied, MEMS elements 16 are structured out from the functional layer, and sacrificial layer 18 is at least partly removed.

(14) At least one stop element 31, intended to prevent adhesion of movable MEMS element 16, is fashioned in cap wafer 30. Metallic bond connections 40, 50 have the advantage that only low demands are made on the bonding partners with regard to surface characteristics, so that surface roughness, and even particles that may be present on the bonding surfaces, are less critical, because they sink in in a liquid phase of the eutectic bond connection.

(15) Examples of suitable metallic bonding methods are AlGe, AuSi, CuSn, AlAl, CuCu, AuAu. Here, different material systems, having different re-melting points, are preferably used for bond connections 40, 50, in order to prevent the first bond connection from melting again during the second bonding process. Advantageously, in this way the yield is increased and production costs are lowered.

(16) The metallic bond connections 40 to second substrate 20 can either be made over the whole surface or can be structured as shown in FIG. 1. A bonding boundary surface between first substrate 10 and second substrate 20 is here dimensioned such that adequate strength of the overall system is provided, advantageously resulting in adequate rigidity of the overall system, and thus resulting in a low degree of bending (wafer bow) of the system in an automatic production process (e.g., using robotic systems) (bow engineering).

(17) FIG. 2 shows a cross-section through a second example embodiment of micromechanical sensor 100.

(18) It can be seen that in this example embodiment a first cavity 21 is fashioned in second substrate 20 (buried cavern). It can be seen that cap cavity 32 of third substrate 30 and first cavity 21 of second substrate 20 are connected by a through-opening 23. This enables a pressure or fluid compensation between cap cavity 32 and first cavity 21 in second substrate 20.

(19) First cavity 21 in second substrate 20 can optionally also contain support columns and/or support walls (not shown) having a bond connection to first substrate 10 situated there-above. These support elements provide an adequate anchoring of the various elements on second substrate 20 situated below them.

(20) An additional cavern volume provides a lower pressure increase per outgassed molecule in first cavity 21, and thus for more stable pressure conditions overall. In addition, buried first cavity 21 results in a stress decoupling relative to stress coupled into micromechanical sensor 100 from outside. In addition, with the additional cavern volumes of first cavity 21, parasitic capacitances of wiring layers 13 with second substrate 20 are significantly reduced.

(21) FIG. 3 shows a cross-sectional view through a third example embodiment of micromechanical sensor 100. It can be seen that in this variant, a further cavity 22 is fashioned in second substrate 20. In addition, it can be seen that a further cap cavity 33 is also fashioned in third substrate 30. The named cap cavities 32, 33 of third substrate 30 are connected fluidically with cavities 21, 22 of second substrate 20 by through-openings 23, 24.

(22) A sealing region 17 is visible for the hermetic sealing of a pressure access opening fashioned under it.

(23) As a result, when there is a plurality of caverns hermetically sealed from each other, communicating pressure access holes through first substrate 10 are realized. The pressure access hole of a cavity can be sealed by a later method step at a different gas pressure (for example by local melting using a laser) than a different cavity already sealed previously during the bonding. In combined acceleration-rotational rate components, it is particularly advantageous if different internal pressures are enclosed in cavities 21, 22 or 32, 33.

(24) FIG. 4 shows a schematic example flow of a method for producing a micromechanical sensor.

(25) In a step 200, a first substrate 10 is provided.

(26) In a step 210, an application is carried out of a sacrificial layer 18 onto first substrate 10, and a formation is carried out of an electrode device 13, as well as, if warranted, of a metallic bonding material, by layer deposition, and a layer structuring is carried out in first substrate 10.

(27) In a step 220, first substrate 10 is connected to a second substrate 20 by metallic bonding.

(28) In a step 230, first substrate 10 is thinned back to a provided thickness of a functional layer 11, and metallic bonding material is applied and structured.

(29) In a step 240, a formation is carried out of movable MEMS elements 16 in functional layer 11.

(30) In a step 250, sacrificial layer 18 is removed in a region underneath movable MEMS elements 16.

(31) In a step 260, first substrate 10 is connected to a third substrate 30, fashioned as cap wafer, by a metallic bond connection.

(32) In summary, the present invention proposes a micromechanical sensor and a method for its production with which a precise, well-defined distance between electrodes, in particular vertical electrodes, and the associated movable MEMS elements is provided in that the named elements are realized by a sacrificial layer deposition process on a single substrate.

(33) In this way, for example Coriolis forces, which can manifest as out-of-plane deflections of the movable MEMS elements in a micromechanical sensor fashioned as a rotational rate sensor, can advantageously be capacitively acquired very precisely.

(34) Although the present invention has been described above on the basis of concrete practical examples, the person skilled in the art can also realize specific embodiments not disclosed above, or disclosed above only partially, without departing from the core of the present invention.