CROSS-REFERENCE TO PRIOR APPLICATIONS

This application is a U.S. National Phase Application under 35 U.S.C. § 371 of International Application No. PCT/DE2019/100701, filed on Jul. 31, 2019, and claims benefit to German Patent Application Nos. DE 10 2018 119 405.6, filed on Aug. 9, 2018, and DE 10 2019 107 114.3, filed on Mar. 20, 2019. The International Application was published in German on Feb. 13, 2020, as WO 2020/030222 A1 under PCT Article 21(2).

FIELD

The invention relates to a method for producing microstructures, in particular MEMS and MOEMS (microelectromechanical systems and microoptoelectromechanical systems) in a substrate having membrane-like, bridging or overhanging surfaces as a result of a material weakening caused by an etching process through material removal in order to produce a cut-out (cavity) in the substrate.

BACKGROUND

Such microstructures are already known, for example, as pressure sensing devices or microphones based on microelectromechanical systems (MEMS) of this type, wherein a bridging structure is created, which forms the basis for the micromechanical system as a membrane. A significant aspect is therefore a targeted material weakening, by means of which flexible surfaces are created.

The overhanging or bridging structures are therefore optimally suited for microphones or sensors. The method currently used in practice for the production of such structures is deep reactive ion etching (DRIE), which enables a controlled removal to reduce the layer thickness up to the desired residual thickness. This method is currently only usable in connection with silicon, which leads to high material costs.

For example, U.S. Pat. No. 4,236,137 A discloses a semiconductor pressure transducer. Further, U.S. Pat. Nos. 5,178,016 A and 6,093,579 A also disclose semiconductor pressure sensors.

DE 10 201 7216418 A1 relates to a pressure sensing device with an elongated flat polygonal cavity, in particular a pressure sensing device based on a micromechanical system (MEMS). This has a silicon carrier substrate, an elongated flat polygonal cavity formed in an upper surface of the silicon carrier substrate, an embedded silicon dioxide layer, a device layer formed on the silicon dioxide layer, and at least four bond pads formed and arranged on an upper surface of the device layer. The at least four bond pads are spaced from the elongated flat polygonal cavity. More specifically, the at least four bond pads are spaced from the elongated flat polygonal cavity so as not to be in connection with the elongated flat polygonal cavity. The pressure detection device may include a membrane arranged over the polygonal cavity, the shape of which is defined by the shape of the polygonal cavity and the size of which is essentially equal to the size of the polygonal cavity.

It is known that in MEMS pressure detection devices, pressure nonlinearity may occur due to deflection of a silicon membrane. However, the ability of a membrane to deflect also determines the ability of the MEMS pressure sensing device to detect pressure changes. As the membrane deflection increases, the output linearity also increases.

The pressure sensitivity of a MEMS pressure sensing device becomes more problematic as the membrane size decreases. Smaller membranes and smaller MEMS pressure sensing devices, however, enable a reduction in manufacturing costs for both the MEMS pressure sensing device itself and the housing in which the MEMS pressure sensing device is to be placed.

Microphones constructed from such microstructures are also known, which are constructed similarly to a pressure sensor and which convert the sound pressure into an electrical signal, while a leakage path ensures a static pressure equalization between volumes in front of and behind the microphones. They consist of at least one free-standing structure which is exposed to the environment and which moves in accordance with an acting sound pressure.

Movement of a diaphragm is detected by measuring a capacitance between the membrane and a perforated counter-electrode positioned in front of or behind the membrane.

An alternative known basic principle which allows detection of the movement of the free-standing structure is based on the direct piezoelectric effect. In such a microphone, a piezoelectric layer is influenced by the bending of a structure, whereupon an electrical charge is produced on its surface. This charge can be detected and evaluated as an electrical output voltage.

SUMMARY

In an embodiment, the present invention provides a method for producing a microstructure in a substrate with a membrane-like bridging or overhanging surface. The method includes modifying the substrate, which is made of glass, by laser radiation along a peripheral contour. A membrane layer is applied over a surface of the substrate for producing the bridging or overhanging surface, wherein, at least in partial surfaces enclosing the peripheral contour of the laser modifications, a sacrificial layer is disposed between the substrate and the membrane layer. A side of the substrate facing away from the membrane layer is exposed to an etching attack such that material is removed primarily along the peripheral contour until the sacrificial layer is reached and there is a disintegration or reduction of the sacrificial layer and a separation of a connection of a part of the substrate enclosed by the peripheral contour from the surrounding substrate and from the membrane layer.

