MICROMECHANICAL SENSOR DEVICE AND CORRESPONDING MANUFACTURING METHOD

Abstract

A micromechanical sensor device and manufacturing method. The micromechanical sensor device is provided with a cap substrate, which has a first front side and a first back side, and which has a through-opening as a media entry region; and with a sensor substrate, which has a second front side and a second back side, and which has, on the second front side, a sensor region that is embedded in an island-like region suspended on the remaining sensor substrate. The island-like region is mechanically decoupled from the remaining sensor substrate by a lateral stress-relief trench and by a cavity situated in the sensor substrate, underneath the island-like region. The first back side is bonded to the second front side so that the through opening is situated above the sensor region. The sensor region is covered by a gel, which fills the through-opening and the stress-relief trench at least partially.

Claims

1-10. (canceled)

11. A micromechanical sensor device, comprising: a cap substrate which has a first front side and a first back side, and which has a through-opening as a media entry region; and a sensor substrate which has a second front side and a second back side, and which has, on the second front side, a sensor region that is embedded in an island-like region suspended on a remaining sensor substrate, the island-like region being mechanically decoupled from the remaining sensor substrate by a lateral stress-relief trench and a cavity situated in the sensor substrate, underneath the island-like region; wherein the first back side is bonded to the second front side in such a manner, that the through opening is situated above the sensor region; and wherein the sensor region is covered by a gel, which fills the through-opening and the stress-relief trench at least partially.

12. The micromechanical sensor device as recited in claim 11, wherein the cavity is connected to the second back side via trenches, and a cover film is provided on the second back side.

13. The micromechanical sensor device as recited in claim 11, wherein the second back side is bonded directly or indirectly to a carrier substrate, and a molded package is provided, which surrounds the micromechanical sensor device in such a manner, that the through-opening is at least partially uncovered.

14. The micromechanical sensor device as recited in claim 11, wherein the sensor region includes a pressure-sensor region.

15. The micromechanical sensor device as recited in claim 11, wherein the cap substrate is an SOI substrate including a first silicon layer situated on the first front side, a second silicon layer situated on the first back side, and an insulating layer situated between the first silicon layer and the second silicon layer, and the through-opening is formed to be wider in the first silicon layer than in the second silicon layer.

16. A method for manufacturing a micromechanical sensor device, comprising the following steps: providing a cap substrate in the form of an SOI substrate, which has a first front side and a first back side, the cap substrate including a first silicon layer situated on the first front side, a second silicon layer situated on the first back side, and an insulating layer situated between the first silicon layer and the second silicon layer; forming a trench grid which extends through the second silicon layer to the insulating layer; forming a first through-opening underneath the trench grid, the first through-opening extending through the first silicon layer to the insulating layer; providing a sensor substrate which has a second front side and a second back side, and which has, on the second front side, a sensor region, which is suspended on s remaining sensor substrate and is mechanically decoupled from the remaining sensor substrate by a lateral stress-relief trench; bonding the first back side to the second front side in such a manner, that the first through-opening is situated above the sensor region; starting from the second back side, forming a cavity in the sensor substrate in such a manner, that the sensor region is embedded in an island-like region, the island-like region being mechanically decoupled from the remaining sensor substrate by the lateral stress-relief trench and the cavity situated in the sensor substrate; forming a second through-opening, which extends through the second silicon layer to the insulating layer, by removing the trench grid; removing the insulating layer between the first and second through-openings, so that a through-opening is formed as a media entry region; and covering the sensor region with a gel, which, starting from the first front side, fills the through-opening and the stress-relief trench at least partially.

17. The manufacturing method as recited in claim 16, wherein the cavity situated in the sensor substrate is formed, starting from the second back side, in such a manner, that in a two-step etching process, trenches are initially formed on the second back side, and subsequently, the cavity is formed through the trenches.

18. The manufacturing method as recited in claim 17, wherein during the two-step etching process, the second back side is cooled a process gas.

19. The manufacturing method as recited in claim 18, wherein the process gas helium.

20. The manufacturing method as recited in claim 16, wherein the first and second through-openings are formed in such a manner, that the through-opening is wider in the first silicon layer than in the second silicon layer.

21. The manufacturing method as recited in claim 16, wherein the second back side is bonded directly or indirectly to a carrier substrate, and a molded package is provided, which surrounds the micromechanical sensor device in such a manner, that the through-opening is at least partially uncovered.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Additional features and advantages of the present invention are explained below in light of specific example embodiments, with reference to the figures.

[0024] FIGS. 1a)-1l) show schematic cross-sectional views for explaining a micromechanical sensor device and a corresponding manufacturing method according to a specific example embodiment of the present invention.

[0025] FIGS. 2a)-2d) show different embodiments of the trench grid of the cap substrate of the micromechanical sensor device according to the specific example embodiment of the present invention.

[0026] FIG. 3a), 3b) show different embodiments of the second through-opening of the cap substrate of the micromechanical sensor device according to the specific example embodiment of the present invention.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

[0027] In the figures, the same reference symbols denote identical or functionally equivalent elements.

[0028] FIGS. 1a)-1l) are schematic cross-sectional views for explaining a micromechanical sensor device and a corresponding manufacturing method according to a specific example embodiment of the present invention.

[0029] In FIG. 1a), reference character K denotes a cap substrate in the form of an SOI substrate, which has a first front side VK and a first back side RK. A first silicon layer S1 is situated on first front side VK, and a second silicon layer S2 is situated on first back side RK; an intermediate insulating layer O, for example, a silicon oxide layer, being situated between first and second silicon layers S1, S2.

[0030] In addition, with reference to FIG. 1b), a trench grid G, which extends through second silicon layer S2 to insulating layer O, is formed by a trench etching process starting from first front side VK. Trench grid G is optimized with regard to rigidity, promotes the rigidity of the remaining insulating layer O during the subsequent method steps, and should have as low a rib width as possible, since it is removed in a later method step.

[0031] Subsequently, with reference to FIG. 1c), a first through-opening KV, which extends to insulating layer O, is formed in first silicon layer S1, underneath trench grid G, starting from first back side RK.

[0032] In the two trench etching steps, insulating layer O is used as an etch stop layer and accordingly remains intact and, thus, impervious to media.

[0033] As shown in FIG. 1d), a sensor substrate SE is provided, which has a second front side VS and a second back side RS. On second front side VS, sensor substrate SE includes a sensor region SB, which is suspended on the remaining sensor substrate SE by a spring device (not shown) and is mechanically decoupled from the rest of sensor substrate SE by a lateral stress-relief trench TR.

[0034] Sensor region SB is, for example, a pressure sensor region, which includes a diaphragm (not shown) and piezoresistive resistors that are placed on it and have electrical leads (not shown, as well).

[0035] First back side VR of cap substrate K is bonded to second front side VS of sensor substrate SE in such a manner, that first through-opening KV in first silicon substrate S1 is situated above sensor region SB at a distance from it. For example, an annular seal-glass layer SG is used for the bonding.

[0036] Other methods are also possible for the bonding, such as a eutectic bonding method or an oxide-to-oxide bonding method, provided that the necessary layers have been suitably introduced into the substrates K, SE involved.

[0037] In addition, with reference to FIG. 1e), a cover film TA, e.g., in the form of a tape or a viscous lacquer, is optionally applied to first front side VK as upper-side protection, and makes possible a particularly smooth surface for a later package molding operation, e.g., for more effective sealing.

[0038] Furthermore, the rigid composite of cap substrate K and sensor substrate SE may be ground back to the desired target thickness (not shown). This is used, in particular, to satisfy restrictions in the later cloud-trenching operation with regard to the attainable trench depth and, consequently, the maximum residual thickness of sensor substrate SE.

[0039] As shown in FIG. 1f), the cloud-trenching operation then takes place, starting from second back side RS. This operation may be carried out, using a two-step etching process; starting from back side RS, trenches TC initially being formed, using suitable masking. In the second step of the etching process, with reference to FIG. 1g), a cavity CK situated in the interior of sensor substrate SE is formed underneath sensor region SB. Cavity CK, which undercuts and, therefore, mechanically decouples sensor region SB, may be formed, for example, by eliminating a passivation and sputtering portion in a DRIE process, which means that undercutting for the production of cavity CK is accomplished by continuing to etch nondirectionally at the base of trenches TC.

[0040] In the second substep of the two-step etching process, sensor substrate SE is cooled from second back side RS with the aid of a process gas, for example, helium. The remaining insulating layer O above first through-opening KV provides an etch stop and, at the same time, provides sealing of the substrate composite during the helium cooling.

[0041] As a result of the cloud-trenching process, sensor region SB is embedded in an island-like region IB suspended on the remaining sensor substrate SE; island-like region IB being mechanically decoupled from remaining sensor substrate SE by lateral stress relief trenches TR and the cavity CK situated in sensor substrate SE, underneath sensor region SB.

[0042] As an alternative to the cloud-trenching process, a large-area trenching process starting from second back side RS is also possible, if a large back-side through-opening of second back side RS can be tolerated for the later process.

[0043] In a subsequent method step, which is shown in FIG. 1h), if present, optional front-side cover film TA is removed, whereupon the processing of first front side VK follows.

[0044] A cover film TB, e.g., in the form of a tape or a viscous lacquer, is optionally applied to second back side RS as upper-side protection, in order to prevent damage from particles, for example, in the event of support by a chuck. During the front-side processing, trench grid G is removed in a brief silicon etching step, which is also possible without a mask; insulating layer O being used again as an etch stop. A second through-opening KV′, which extends through second silicon layer S2 to insulating layer O, is formed by removing trench grid G. This results in the process state shown in FIG. 1i).

[0045] In a further etching step, with regard to FIG. 1j), the remaining diaphragm-like insulating layer O is removed, for example, using HF gas-phase etching. In order to prevent the formation of poisonous ammonium hexafluorosilicate, this may also be accomplished by dry oxide etching (dry RIE), using C.sub.4F.sub.8 or the like. The attack on pressure-sensor region SB is tolerable, since only a thin insulating layer O must be removed and, consequently, a small amount of overetching time may be operated with.

[0046] In addition, with reference to FIG. 1k), sensor region SB is then covered with a gel GE, which, starting from first front side VK, fills through-opening DR and stress-relief trench TR at least partially. In the present example, gel GE fills stress-relief trench TR and through-opening DR nearly completely.

[0047] Since first through-opening KV in first silicon layer S1 has a larger diameter than the second through-opening in second silicon layer S2, it is easily possible to reach trench TR without forming bubbles and, therefore, to provide damping in trench TR while maintaining the stress-decoupling.

[0048] Finally, with reference to FIG. 1l), back-side tape TB may be positioned on a carrier substrate TR, and in a molding method, e.g., using a stamp, the sensor device may be molded around with a molding material MO, so that through-opening DR remains uncovered and forms a media entry to sensor region SB.

[0049] Alternatively, cover film TB on second back side RS may be removed, and subsequently, trenches TC may be filled in with a gel, as well.

[0050] FIGS. 2a)-2d) show different embodiments of the trench grid of the cap substrate of the micromechanical sensor device according to the specific example embodiment of the present invention.

[0051] As shown in FIG. 2a) through d), different geometries are possible for trench grid G, G′, G″, G′″, as long as the rigidity requirements are satisfied.

[0052] FIGS. 3a), 3b) show different embodiments of the second through-opening of the cap substrate of the micromechanical sensor device according to the specific embodiment of the present invention.

[0053] The representations of the second through-opening KV′, KV″ in second silicon layer S2 for the configurations according to FIG. 2a) and b) are shown in FIG. 3a) and b).

[0054] Although the present invention has been described with the aid of preferred exemplary embodiments, it is not limited to these. In particular, the above-mentioned materials and topologies are only illustrative and not limited to the examples explained.