DE102020209936A1 - Micromechanical system, method for setting a partial pressure, wafer arrangement - Google Patents

Abstract

A micromechanical system with a cavern is claimed, characterized in that a gas diffusion path connects an interior of the cavern to an exterior of the cavern, the gas diffusion path being designed in such a way that at least partial diffusion of a first gas using the gas diffusion path from the interior of the cavern into the outdoor area is allowed.

Description

State of the art

The invention is based on a micromechanical system according to the preamble of claim 1.

Micromechanical systems are well known. With the help of micromechanical systems or microelectromechanical systems (MEMS), rotation rates or accelerations, for example, can be measured. The ambient pressure is crucial for the function of such micromechanical sensors. For this reason the sensors are usually arranged in a capped cavity. One of the purposes of this is to protect the sensors from environmental influences and to guarantee a defined atmosphere for operation. CMOS (complementary metal-oxide-semiconductor) ASICs (application-specific integrated circuits) and MEMS assemblies are known from the prior art, which contain one or more caverns, in particular with different internal pressures.

In the DE 102009000048 A1 a method is described with which different cavern pressures can be represented.

Also known from the prior art are getters which can cause reactive residual gases to react to form solids. However, the disadvantage of such methods can be that noble gases cannot be bound, additional space is required for the getter and the getter can become saturated.

Another disadvantage of known methods is that they cannot fix gas leaks that occur after the manufacturing process.

Disclosure of Invention

It is an object of the present invention to provide a micromechanical system with a cavern in which an effective and/or cost-efficient pressure adjustment, in particular a partial pressure adjustment, is possible in an interior space of the cavern. Furthermore, it is an object to provide a corresponding effective and/or cost-efficient method for adjusting a partial pressure.

The micromechanical system according to the invention according to the main claim has the advantage over the prior art that diffusion through the cavern or cavern wall along a pressure gradient (to an outside area) is made possible. A partial pressure of a first gas in the cavern can thus be adjusted. According to the invention, it is advantageously possible for the partial pressure of the first gas in the cavern to be lowered or kept low. In particular, it is possible that even if a leak occurs later (in particular after the system has been manufactured) or if the first gas later outgasses into the interior of the cavern (in particular after the system has been manufactured), pressure can be equalized with the outside area using the gas diffusion path takes place, whereby the partial pressure of the first gas in the interior of the cavern can be kept low. With the help of the diffusion path, a permanently stable vacuum or a permanently stable pressure in the interior of the cavern can be achieved in a cost-efficient and space-saving manner.

According to the invention, it is possible in an advantageous manner for the gas diffusion path to enable a selective exchange of a first gas along a partial pressure gradient and to hold back a second gas. This is to be distinguished from processes that work with open caverns and active pumping (because in this case there is open gas exchange and no diffusion along a gas diffusion path), and from processes that allow gases to react with a getter in the cavern.

According to the invention, it is conceivable that a sensor and/or actuator and/or a plurality of sensors and/or actuators are at least partially arranged in the cavern. For example, a yaw rate sensor and/or an acceleration sensor can be arranged in the cavern.

Advantageous configurations and developments of the invention can be found in the subclaims and the description with reference to the drawings.

The fact that, according to one embodiment of the present invention, the gas diffusion path comprises a semi-permeable membrane, the semi-permeable membrane being permeable to the first gas, the semi-permeable membrane being impermeable in particular to a second gas, it is particularly advantageously possible to reduce the partial pressure for the first adjust the gas in the cavern. The semi-permeable membrane allows additional first gas present in the cavern to pass to the outside, so that a partial pressure equalization for the first gas takes place between the inside and the outside. On the other hand, the membrane is impermeable to the second gas, so that the second gas cannot penetrate into the cavity from the outside and/or cannot get from the interior of the cavity to the exterior. Thus, a partial pressure of the second gas in the interior kon be kept constant and/or penetration of the second gas from the outside into the inside of the cavern can be prevented. The cavern is thus hermetically sealed off from the second gas. The second gas is a different gas than the first gas.

According to one embodiment of the present invention, it is conceivable that the gas diffusion path or the semipermeable membrane is permeable for a further first gas, so that a partial pressure of the further first gas in the interior of the cavern can also be adjusted or kept low.

Because, according to one embodiment of the present invention, the cavern is formed using a substrate and a cap, it is possible to provide a defined space for the micromechanical system. For example, the cap can be part of a MEMS wafer and the substrate an ASIC substrate.

Due to the fact that, according to an embodiment of the present invention, the cap comprises the semi-permeable membrane, in particular in such a way that the gas diffusion path is formed through the cap, it is possible to form a diffusion path in a cost-efficient manner.
The semipermeable membrane can in particular be formed using a bonded cap wafer and/or deposited using thin-film technology. It is conceivable, for example, for a plurality of cavities in a wafer arrangement to have corresponding diffusion paths in the cap wafer for the plurality of cavities. According to one embodiment, it is conceivable that the (entire) cap of the cavity is designed as a semi-permeable membrane.

The fact that, according to one embodiment of the present invention, at least part of a wall of the cavern is heated, with the gas diffusion path being formed using the heated part of the wall, it is possible for (local) heating to stimulate diffusion that occurs in partial areas the cavern or wall of the cavern increases the partial pressure equalization for the first gas. The wall can affect any part of the cavern, ie lateral areas, areas of the cap and/or areas of the bottom of the cavern. It is thus possible for (local) heating to stimulate diffusion, as a result of which the partial pressure equalization of a first gas that is rare or non-existent in the outside area is increased in some areas. For example, it is conceivable that the cap of the cavern is heated. It is also conceivable, for example, for the entire cavern, the entire cap and/or the entire bottom of the cavern to be heated.

The fact that, according to one embodiment of the present invention, the gas diffusion path comprises a semipermeable lateral gas diffusion path, the interior and the exterior being connected by means of the semipermeable lateral gas diffusion path, the semipermeable lateral gas diffusion path being permeable to the first gas, the semipermeable lateral gas diffusion path being particularly suitable for a second gas is impermeable, it is possible to create gas diffusion parallel to the wafer plane. It is conceivable that the semipermeable lateral gas diffusion sheet is a membrane.

Due to the fact that, according to one embodiment of the present invention, a metal and/or a dielectric is arranged in the cavern, it is conceivable that the first gas from the metal and/or the dielectric evaporates and/or diffuses out into the interior of the cavern. With the aid of the gas diffusion path, a permanently stable setting of the partial pressure in the interior of the cavern can nevertheless be achieved according to the invention.

Because according to one embodiment of the present invention the first gas comprises hydrogen, the first gas being in particular hydrogen gas, or the first gas being a process gas which is used in the production of the micromechanical system, the process gas preferably being argon it is possible to keep the partial pressures of hydrogen and/or process gases in the cavern low. According to the invention, it is possible to deal advantageously with internal leaks that release hydrogen, for example. Such leaks can in particular be a core problem in wafer assemblies or wafer arrangements with CMOS wafers.

It is conceivable, for example, that amounts of hydrogen escape from the SiOx and/or SiNx layers, which can make a yaw rate sensor unusable and are also problematic for acceleration sensors. These internal gas leaks in caverns can also be a major cause of field failure, especially in cases where a MEMS wafer is sealed by an ASIC wafer. According to the invention, however, advantageous countermeasures can be taken with the aid of the gas diffusion path. In particular, hydrogen diffusing out of the CMOS dielectrics and/or from the metals represents a decisive hurdle with regard to the creation of a permanently stable vacuum. Other process gases, such as argon, can also be a possible cause of excessive pressures in the cavern. According to the invention it is possible to keep a partial pressure of hydrogen and/or one or more process gases permanently at a stable level in the cavern using the diffusion path.

According to one embodiment of the present invention, it is preferably conceivable that the first gas and/or the further first gas are gases that do not or only rarely occur in the earth's atmosphere, for example as trace gases. This is also conceivable in an advantageous manner, in particular when the cavern borders on the air and the outer area of the cavern or a part of the outer area thus represents the environment or atmosphere. It is conceivable that the gas composition in the outside area can be adjusted. It is conceivable that the first gas and/or further first gas are gases that frequently occur in the atmosphere, but for which a (low) further partial pressure is set in the outside area around the cavern. It is conceivable that the first gas or the further first gas is an inert gas.

According to one embodiment of the present invention, it is conceivable that the outer area of the cavern forms the interior of a further cavern, the further cavern being formed, for example, as part of a cap wafer (or a MEMS wafer) or with the aid of a cap wafer (or a MEMS wafer ) is trained. Accordingly, it is conceivable that the further cavern (with a low partial pressure of the first gas) is formed in the cap. The other cavern can accordingly have a semi-permeable connection to the interior of the cavern with the aid of the gas diffusion path. It is conceivable, for example, to implement such an arrangement using a triple wafer stack or by further applying a thin-layer cap (preferably to the cap or the cap wafer). It is conceivable that the gas composition in the outer area (or in the inner area of the additional cavern) can be adjusted. It is conceivable that the first gas and/or the further first gas are gases which frequently occur in the atmosphere but for which a (very low) further partial pressure is set in the further cavern. It is conceivable that the first gas or the further first gas is an inert gas.

According to one embodiment of the present invention, it is conceivable that the diffusion path is realized with the aid of a pressure inlet, which enables a defined pressure inclusion. For example, it is possible that heated silver, in particular silver tubes, can serve as an inlet for oxygen in vacuum chambers. Similarly, according to one embodiment of the present invention, a defined pressure can also be set in the interior of the cavern by selective diffusion of a first gas with a suitable partial pressure in the exterior.

According to a preferred embodiment, it is conceivable that the gas diffusion path is formed using SiOx or includes SiOx or consists of SiOx. As a result, a diffusion of hydrogen is possible, for example.

Another subject matter of the present invention is a method for adjusting a partial pressure of a first gas in an interior of a cavern of a micromechanical system according to an embodiment of the present invention,
wherein the first gas at least partially diffuses from the interior of the cavern to the exterior with the aid of the gas diffusion path.

The advantages and refinements that have already been described in connection with the micromechanical system according to the invention or in connection with an embodiment of the micromechanical system according to the invention can be used for the method for setting a partial pressure of a first gas in an interior of a cavern of a micromechanical system.

Because, according to one embodiment of the method according to the invention, the gas diffusion path for the first gas is used to equalize the partial pressure of the first gas in the interior of the cavern and another partial pressure of the first gas in the exterior, it is possible that the at least partial diffusion of the first Gas is adjusted using the gas diffusion path of the partial pressure of the first gas in the interior of the cavern to a further partial pressure outside. Thus, even after the production of the micromechanical system - in the case of later leaks - a permanently stable pressure can be achieved in the cavern.

A further subject matter of the present invention is a wafer arrangement comprising a micromechanical system according to an embodiment of the present invention. It is conceivable that the wafer arrangement comprises a multiplicity of micromechanical systems according to embodiments of the present invention with corresponding caverns.

An embodiment of the present invention is shown in the drawing and explained in more detail in the following description.

character list

• 1 shows a schematic representation of a micromechanical system according to an embodiment of the present invention.

Embodiments of the invention

This in 1 Schematically illustrated micromechanical system 1 comprises a cavity 10. The cavity 10 is formed using a substrate 5 and a cap 6. The cavern 10 is sealed with seals 9, 9', which are arranged between the substrate 5 and the cap 6. FIG.

A further seal 9″ of a further cavity is also shown. A metal 7 and a dielectric 8 are arranged in the cavity 10. It is possible for the first gas 2 to outgas or diffuse out of the metal 7 and/or the dielectric 8. A gas diffusion path 20 through a wall of the cavern 10 allows the first gas 2 (represented by dots) to diffuse from the interior 11 of the cavern 10 to the exterior 30. The gas diffusion path 20 is permeable to the first gas 2, but impermeable to one second gas 3 (represented by circles).For this purpose, the gas diffusion path 20 comprises a semipermeable membrane 21. The cap 6 comprises the semipermeable membrane 21 and/or is designed as a semipermeable membrane 21, so that diffusion of the first gas 2 through the cap 6 is possible The cavern 10 or at least a part of the cavern 10 can be heated in order to increase or accelerate the diffusion he has a semipermeable lateral gas diffusion path 23, which laterally connects the interior 11 of the cavern 10 to the exterior 30 (parallel to a main plane of extension of the substrate 5). The semipermeable lateral gas diffusion path 23 is also permeable to the first gas 2 and impermeable to the second gas 3 .

The embodiment shown thus includes lateral and vertical diffusion paths in a chip assembly with dielectric and/or metallic layers, which enable a selective exchange of a first gas 2 along a partial pressure gradient and hold back a second gas 3 . This is to be distinguished from processes that work with open caverns and their active pumping out and from processes that allow gases to react with a getter in the cavern.

According to alternative embodiments, it is conceivable that the gas diffusion path only comprises a vertical path through the cap 6 or only a lateral gas diffusion path 23.

The semipermeable membrane 21 and/or the lateral gas diffusion path 23 are preferably made of a material that is permeable, for example, to hydrogen and/or a process gas such as argon (or another first gas 2 or other first gases). However, the semipermeable membrane 21 and/or the lateral gas diffusion path 23 do not allow any other gas (or other gases) frequently occurring in the environment or in an adjacent cavern to penetrate into the cavern 10 . Due to a partial pressure difference between the interior 11 and the exterior 30 the first gas 2 diffuses out of the cavern 10 . For example, the partial pressure in the air for hydrogen is in the range of <1 μbar, so that hydrogen diffuses outwards at a higher partial pressure in the interior 11 of the cavern 10 .

The cap 6 is in particular part of a MEMS wafer 6' and the substrate 5 is part of an ASIC wafer 5'. Further caverns can be formed with the aid of the MEMS wafer 6' and the ASIC wafer 5'. Correspondingly, a wafer arrangement 1' with a multiplicity of micromechanical systems 1 and cavities can be formed with the aid of the MEMS wafer 6' and the ASIC wafer 5'.

The semipermeable membrane 21 can be prepared from a bonded wafer, in particular an MEMS wafer 5', or deposited on the wafer using thin-film technology. Alternatively or additionally, the semi-permeable lateral gas diffusion path 23 can be provided, which adjusts the partial pressures of the first gas 2 and/or other first gases to the environment/adjacent cavern, but holds back a second gas 3 or other other gases.

Alternatively or additionally, it is conceivable to form a further cavern as part of a cap wafer (or a MEMS wafer 6') or with the aid of a cap wafer (or a MEMS wafer 6'). Accordingly, it is conceivable that the further cavern (with a low partial pressure of the first gas 2 ) is formed in the cap 6 . The further cavern can correspondingly have a semi-permeable connection to the interior 11 of the cavern 10 with the aid of the gas diffusion path 20 . It is conceivable, for example, to implement such an arrangement using a triple wafer stack or by further applying a thin-layer cap.

According to the invention, an arrangement is conceivable which enables diffusion through a MEMS cavity along a pressure gradient. For example, the partial pressure of hydrogen in air is in the µbar range. This makes it possible, for example, with a semi-permeable MEMS cavern (particularly MEMS cap) that is only for water substance is permeable to lower the partial pressure of hydrogen in the interior 11 of the cavern 10 automatically from a few mbar to a few μbar. Studies have shown that the highest partial pressure in ASIC/MEMS caverns is often due to hydrogen. In most media, hydrogen is significantly more diffusive than other gases, so that with a suitable cavern closure, the outdiffusion of the hydrogen can be guaranteed without other gases, for example those present in larger quantities in the air, diffusing. Hydrogen diffuses in particular between neighboring chip caverns along the partial pressure gradient. In particular, SiOx layers are conceivable as a main path. In order to shorten the diffusion time, the wafer assembly or the wafer arrangement 1′ can advantageously be heated, so that diffusion can also be used in volume production.

QUOTES INCLUDED IN DESCRIPTION

This list of documents cited by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent Literature Cited

• DE 102009000048 A1 [0003]

Claims (11)

Micromechanical system (1) with a cavity (10), characterized in that a gas diffusion path (20) connects an interior (11) of the cavity (10) to an exterior (30) of the cavity (10), the gas diffusion path (20) is designed in such a way that at least partial diffusion of a first gas (2) from the interior (11) of the cavern (10) to the exterior (30) is made possible with the aid of the gas diffusion path (20). Micromechanical system (1) according to claim 1 , characterized in that the gas diffusion path (20) comprises a semi-permeable membrane (21), wherein the semi-permeable membrane (21) for the first gas (2) is permeable, wherein the semi-permeable membrane (21) in particular for a second gas (3) is impermeable. Micromechanical system (1) according to one of the preceding claims, characterized in that the cavity (10) is formed using a substrate (5) and a cap (6). Micromechanical system (1) according to one of the preceding claims, characterized in that the cap (6) encompasses the semipermeable membrane (21), in particular such that the gas diffusion path (20) is formed through the cap (6). Micromechanical system (1) according to one of the preceding claims, characterized in that at least part of a wall of the cavity (10) is heated, the gas diffusion path (20) being formed with the aid of the heated part of the wall. Micromechanical system (1) according to one of the preceding claims, characterized in that the gas diffusion path (20) comprises a semipermeable lateral gas diffusion path (23), the interior (11) and the exterior (30) being connected by means of the semipermeable lateral gas diffusion path (23). are, the semipermeable lateral gas diffusion path (23) being permeable to the first gas (2), the semipermeable lateral gas diffusion path (23) being impermeable in particular to a second gas (3). Micromechanical system (1) according to one of the preceding claims, characterized in that a metal (7) and/or a dielectric (8) is arranged in the cavity (10). Method for setting a partial pressure of a first gas in an interior (11) of a cavern (10) of a micromechanical system (1) according to one of Claims 1 until 7 , The first gas (2) at least partially diffusing with the aid of the gas diffusion path (20) from the interior of the cavern (10) to the exterior (30). procedure after claim 8 , characterized in that with the help of the gas diffusion path (20) for the first gas (2) a partial pressure equalization of the partial pressure of the first gas (2) in the interior (11) of the cavern (10) and a further partial pressure of the first gas (2) in the exterior (30) takes place. Procedure according to one of Claims 8 or 9 , characterized in that the first gas (2) comprises hydrogen, wherein the first gas (2) is in particular hydrogen gas, or wherein the first gas (2) is a process gas which is used in the production of the micromechanical system, the process gas is preferably argon. Wafer arrangement (1 '), comprising a micromechanical system (1) according to one of Claims 1 until 7 .

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