Micromechanical component

Abstract

A micromechanical component, having a carrier wafer having at least one micromechanical structure that is situated in a cavern; a thin-layer cap situated on the carrier wafer, by which the cavern is hermetically sealed; and a cap wafer situated on the thin-layer cap in the region of the cavern having the micromechanical structure, the cap wafer hermetically sealing a region of the thin-layer cap above the cavern.

Claims

1. A micromechanical component, comprising: a carrier wafer having at least two micromechanical structures that are situated in a cavern; a thin-layer cap situated on the carrier wafer by which the cavern is hermetically sealed; and a cap wafer situated on the thin-layer cap in a region of the cavern having the micromechanical structures, the cap wafer hermetically sealing a region of the thin-layer cap above the cavern.

2. The micromechanical component as recited in claim 1, wherein the cap wafer is a glass cap wafer.

3. The micromechanical component as recited in claim 1, wherein the cap wafer is an ASIC wafer.

4. The micromechanical component as recited in claim 1, wherein the carrier wafer has a buried wiring level in the carrier wafer underneath the micromechanical structure.

5. The micromechanical component as recited in claim 1, wherein filled insulating trenches are in the thin-layer cap.

6. The micromechanical component as recited in claim 5, wherein a metallic layer is on the thin-layer cap in a region of the filled insulating trenches.

7. The micromechanical component as recited in claim 1, wherein the micromechanical component is an inertial sensor having at least one sensor element.

8. The micromechanical component as recited in claim 7, wherein the inertial sensor has an acceleration sensor and a rotational rate sensor.

9. A micromechanical component comprising: a carrier wafer having at least one micromechanical structure that is situated in a cavern; a thin-layer cap situated on the carrier wafer by which the cavern is hermetically sealed; and a cap wafer situated on the thin-layer cap in a region of the cavern having the micromechanical structure, the cap wafer hermetically sealing a region of the thin-layer cap above the cavern, wherein two micromechanical structures are in the carrier wafer, a respective micromechanical structure being situated in a respective cavern, regions above the caverns being hermetically sealed by the cap wafer, a fluid duct being formed between a cavern of the cap wafer and the cavern of the carrier wafer.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows a specific embodiment of a micromechanical component.

(2) FIG. 2 shows a further specific embodiment of a micromechanical component.

(3) FIG. 3 shows a further specific embodiment of a micromechanical component.

(4) FIG. 4 shows a further specific embodiment of a micromechanical component.

(5) FIG. 5 shows a further specific embodiment of a micromechanical component.

(6) FIG. 6 shows a schematic sequence of a specific embodiment of the method according to the present invention for producing a micromechanical component.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

(7) Micromechanically-based inertial sensors are subject to a large number of demands that all have to be met as well as possible. Highly precise and energy-saving micromechanical rotational rate sensors can most advantageously be realized as so-called high-quality oscillators that represent systems having high resonance magnifications. To achieve the highest possible degree of quality, the micromechanical oscillator has to be enclosed in as good a vacuum as possible in order to minimize attenuation due to enclosed gas. In addition, the encapsulation has to be moisture-tight over the operating life of the equipment. Moreover, thermomechanical influences due to component packaging must be minimized, in order to exclude to the greatest possible extent any temperature drift of the sensor signal.

(8) Also importantly, for combined inertial sensors (acceleration and rotational rate sensors), two different internal pressures have to be provided in the same component in adjacent caverns.

(9) In order to achieve the greatest possible vacuum, the micromechanical structure is first sealed with a thin-film or thin-layer cap, for example in an epitaxial reactor at temperatures greater than 1000 C. At these high process temperatures in a hydrogen atmosphere, generally all of the surface-deposited molecules decompose and go into the gas phase. During cooling after the cavern sealing, there results a very low internal pressure, in accordance with Gay-Lussac's second law. The resulting thin-layer cap is in addition advantageously moisture-tight.

(10) Due to its low thickness, typically less than approximately 50 m, the thin-layer cap can however disadvantageously bend strongly as soon as the component is exposed to normal atmospheric pressure. Encapsulating the component with molding compound can cause further pressure loading. Conventionally, excessive deformation of the thin-film cap is avoided by building in supporting columns, which however requires additional surface area.

(11) Therefore, in accordance with an example embodiment, to avoid supporting measures by placing an additional wafer cap on the thin-film cap, and producing a vacuum hollow space therein. In this way, the wafer cap shields the thin-layer cap against external pressure and mechanical stress influences. The bonding areas of the wafer cap are here formed in the same areas as the hollow space walls of the caverns situated thereunder.

(12) The wafer cap can be realized either as a pure cap wafer or as an ASIC substrate, or ASIC wafer. The second capping provides the possibility of opening one of the thin-film-capped hollow spaces, and setting a higher internal pressure therein during the cap bonding process.

(13) FIG. 1 shows a cross-sectional view through a first specific embodiment of a micromechanical component 100 in accordance with the present invention, in the form of an inertial sensor. Visible is a carrier wafer 10 on which there is formed a micromechanical functional layer 20 having a micromechanical structure 23 (MEMS structure). Micromechanical structure 23 is formed within a cavern 21 having a vacuum (vacuum hollow space), which is subject to various quality requirements depending on the type of sensor. Carrier wafer 10 with micromechanical structure 23 is capped with a thin-layer cap 30, for example made of polysilicon. Cavern 21 is hermetically sealed by thin-layer cap 30. Thin-layer cap 30 is preferably attached using the named high-temperature sealing process, thus providing a low internal pressure in cavern 21. Insulating trenches 31, filled with an insulating material, can be provided in thin-layer cap 30 in order to electrically separate areas regions of thin-layer cap 30 from one another in order in this way to make it possible to supply different electrical potentials to the various regions of thin-layer cap 30.

(14) Above filled insulation trenches 31, there is partly situated a metallic layer 32 for the electrical contacting of the named areas of thin-layer cap 30. In the area above cavern 21 having micromechanical structure 23, a cap wafer 50 is attached by a bonded connection 40, so that in this way a hermetic seal of thin-layer cap 30 against the surrounding environment is realized. In this way, thin-layer cap 30 is protected from the effects of air pressure and/or mechanical stress in the area above cavern 21, so that thin-layer cap 30 cannot be pressed in above cavern 21. As a result, in this way micromechanical structure 23 formed in cavern 21 is better protected, and is therefore capable of functioning longer.

(15) An insulating layer 33 is provided between bonding frame 40 and metallic layer 32 in order to prevent electrical short circuits between electrically conductive bonding frame 40 and metallic layer 32.

(16) Metallic layer 32 acts as a wiring level for realizing electrical conductor paths for controlling or carrying away sensor signals of movable micromechanical structure 23 in functional layer 20 of carrier wafer 10. In addition, metallic layer 32 also acts as a gas-tight seal for insulating trenches 31, filled with insulating material, so that in this way the vacuum in cavern 20 can be maintained over a long period of time and with good quality.

(17) FIG. 2 shows a cross-sectional view through another specific embodiment of micromechanical component 100. In this case, cap wafer 50 is formed as a glass cap wafer. Advantageously, through-glass-vias 51 are provided inside glass cap wafer 50, which in combination with solder balls 60 enable an electrical contacting of switching structures of micromechanical component 100. Advantageously, in this way no additional external wiring outlay is required compared to the topology of FIG. 1.

(18) FIG. 3 shows a cross-sectional view through a further specific embodiment of a proposed micromechanical component 100. In this variant, micromechanical component 100 contains a buried wiring level 24 underneath micromechanical functional layer 20. Via buried wiring level 24, an electrical supply to micromechanical structure 23 can be realized.

(19) FIG. 4 shows a cross-sectional view through a further specific embodiment of micromechanical component 100. In this case, cap wafer 50 is formed as an ASIC wafer, preferably a CMOS-ASIC wafer having electronic evaluation circuits, digital circuits, memories, interfaces, etc., in the transistor level (not shown). Carrier wafer 10 is connected to cap wafer 50, formed as an ASIC wafer, via a bonded connection 40. In this way, an evaluation or computing capacity can advantageously be integrated into micromechanical component 100, enabling a compact constructive design.

(20) Advantageously, an external electrical contacting of the micromechanical component 100 takes place via through-silicon-vias (TSV) 51 in the ASIC wafer and solder balls 60 on the ASIC wafer.

(21) FIG. 5 shows a cross-sectional view through a further preferred specific embodiment of micromechanical component 100. In this case, it is provided that two caverns 21, 21a are formed in functional layer 20, in each of which a micromechanical structure 23 is preferably formed. In this way, different sensor topologies can be realized with micromechanical structures 23. Here it is advantageously possible to enclose different pressures in the two caverns 21, 21a. This is realized by a cap wafer 50 that enables two caverns 52, 52a, separate from one another, above caverns 21, 21a.

(22) In this way it is possible first to enclose a first pressure inside the two caverns 21, 21a of carrier wafer 10. Subsequently, through etching a fluid duct 53 is opened through thin-layer cap 30. Given a suitable second pressure, cap wafer 50 is then bonded onto thin-layer cap 30, thereby forming the second pressure via fluid duct 53 in second cavern 52a of cap wafer 50.

(23) As a result, in this way it is advantageously possible to enclose different internal pressures in the two caverns 21, 21a, whereby an inertial sensor can be realized having two sensor topologies, for example in the form of an acceleration sensor and a rotational rate sensor. For the rotational rate sensor, in the described manner a very low first pressure can be provided in first cavern 21, and for the acceleration sensor, which requires a defined attenuation, a second pressure, larger by a defined amount, can be provided in second cavern 21a.

(24) FIG. 6 shows a schematic diagram of a specific embodiment of an example method in accordance with an example embodiment of the present invention for producing a micromechanical component.

(25) In a step 200, a carrier wafer 10 is provided.

(26) In a step 210, a micromechanical structure 23 is formed in a cavern 21 of carrier wafer 20.

(27) In a step 220, a thin-layer cap 30 is situated on carrier wafer 10, hermetically sealing cavern 21.

(28) In a step 230, a cap wafer 50 is situated on thin-layer cap 30 above cavern 21 having micromechanical structure 23, a region of thin-layer cap 30 above cavern 21 being hermetically sealed by cap wafer 50.

(29) In sum, the present invention provides a micromechanical component, and a method for producing such a component, having a thin-layer cap without additional supporting elements, and thus being compact in size. Compared to conventional micromechanical components having thin-layer caps or wafer caps, in this way small constructive volumes can be realized.

(30) Although the present invention has been described above on the basis of concrete examples of use, a person skilled in the art may also realize specific embodiments not described above, or only partly described above, without departing from the present invention.