DE102017200714A1 - Method for producing a micromechanical inertial sensor - Google Patents

Abstract

Method for producing a micromechanical inertial sensor (100), comprising: - providing a sensor wafer (10) with a movable MEMS structure (12) - providing a cap substrate (20) - forming a cavity (24) and an access opening (23) for supplying an anti-adhesion layer material in the cap substrate (20); and - connecting the sensor wafer (10) to the cap substrate (20) by means of a bonding process.

Description

The invention relates to a method for producing a micromechanical inertial sensor. The invention further relates to a micromechanical inertial sensor.

State of the art

In micromechanical sensors with movable vibrators, contact between parts of the sensor, e.g. of the vibrator with an immovable part of the sensor, can not be excluded.

So that this contact does not lead to an immobilization of the sensor ("gluing"), the surface of the relevant areas is provided with a layer of low surface energy. This lowers the forces necessary to release the "sticky" sensor after contact and thus reduces the risk of failure of the component.

As possible low surface energy layers ("non-stick coatings") on MEMS devices, fluorinated polymers or fluorine-containing carbon chain self-assembled monolayers (SAMs) are widely used.

The application of said non-stick coatings is carried out in gas phase or plasma processes. The entire relevant surface of the sensor is coated with the non-stick layer.

MEMS sensors are usually manufactured using semiconductor technology. The sensor is manufactured on a substrate and closed at the end by a cap.

When sealing the substrate with the cap, the non-stick coating on or between the sealing surfaces can lead to undesirable effects and imperfections of the seal and / or prevent the connection.

A possible remedy is to apply the non-stick layer to the movable sensor only after the bonding has taken place. This can be done by accessing the cap (or sensor), which is then closed again.

In making the access to the sealed sensor, already moving MEMS structures of the sensor are not protected against sticking. If necessary intermediate steps (for example lacquer slurries or machines with mechanical vibrations or vibrations that are unfavorable to the component), sticking events may occur before the component interior has been provided with an anti-adhesion layer.

Disclosure of the invention

It is therefore an object of the present invention to avoid the above-mentioned disadvantages when manufacturing a micromechanical inertial sensor.

• - Bereitstellen eines Sensorwafers mit einer beweglichen MEMS-Struktur;
• - Bereitstellen eines Kappensubstrats;
• - Ausbilden einer Kaverne und einer Zugangsöffnung zum Zuführen eines Antihaftschichtmaterials im Kappensubstrat; und
• - Verbinden des Sensorwafers mit dem Kappensubstrat mittels eines Bondprozesses.

The object is achieved according to a first aspect with a method for producing a micromechanical inertial sensor, comprising the steps:

• Providing a sensor wafer with a moveable MEMS structure;
• - Providing a cap substrate;
• Forming a cavity and an access opening for supplying an anti-adhesion layer material in the cap substrate; and
• - Connecting the sensor wafer with the cap substrate by means of a bonding process.

In this way, during the production of the micromechanical inertial sensor concerning the movable MEMS structures, force-intensive process steps are avoided in which the mentioned MEMS structures are bonded and / or damaged. This is advantageously achieved in that an access hole for feeding an anti-adhesion layer material into the cap wafer is already produced at a point in time before the bonding of the sensor substrate to the cap substrate. Advantageously, in addition to the protection of the sensitive MEMS structures, a quality of the bonding frame can also be improved because the bonding can be carried out without adhesive layer material on the bonding partners.

• - ein Sensorsubstrat mit einer beweglichen MEMS-Struktur; und
• - einen mit dem Sensorsubstrat mittels eines Bondrahmens verbundenen Kappenwafer;
• - wobei im Kappensubstrat eine Zugangsöffnung zum Zuführen eines Antihaftschichtmaterials ausgebildet ist, wobei die Zugangsöffnung vor dem Bonden des Kappensubstrats mit dem Sensorsubstrat ausgebildet wurde.

According to a second aspect, the object is achieved with a micromechanical inertial sensor, comprising:

• a sensor substrate having a movable MEMS structure; and
• a cap wafer connected to the sensor substrate by means of a bonding frame;
• wherein an access opening for supplying an anti-adhesion layer material is formed in the cap substrate, wherein the access opening has been formed with the sensor substrate before the bonding of the cap substrate.

Preferred developments of the method are the subject of dependent claims.

An advantageous development of the method provides that on the cap substrate with the Access opening a membrane is formed. In this way, particle protection or moisture protection is advantageously provided during the production of the micromechanical inertial sensor.

A further advantageous development of the method provides that the closing of the access opening is carried out with a laser. In this way, a proven reseal process can be performed with localized reflow of substrate material that readily provides a good and hermetic seal quality of the access port.

A further advantageous embodiment of the method provides that when closing the access opening, an anti-adhesive layer material is filled into the cavern. Thereby, due to the fact that the insertion of the anti-adhesion layer material into the cavern is performed only after the bonding, an improved quality of the bonding frame can be provided.

A further advantageous development of the method is characterized in that the closing of the access opening is carried out at a defined internal pressure within the cavern. By choosing the appropriate internal pressure, requirements for a specific type of sensor (e.g., rotation rate sensor, acceleration sensor, etc.) can be met.

A further advantageous development of the method provides that a loopback of the cap substrate to a defined target thickness is performed. In this way, requirements for geometric dimensions of the component can be met in a simple manner.

The invention will be described below with further features and advantages with reference to several figures in detail. Same or functionally identical elements have the same reference numerals. The figures are particularly intended to illustrate the principles essential to the invention and are not necessarily to scale. For better clarity, it can be provided that not all the figures in all figures are marked.

Disclosed method features are analogous to corresponding disclosed device features and vice versa. This means, in particular, that features, technical advantages and embodiments relating to the method for producing a micromechanical inertial sensor arise analogously from corresponding embodiments, features and advantages relating to the micromechanical inertial sensor and vice versa.

• 1 eine Querschnittsansicht einer Vorstufe einer Ausführungsform des vorgeschlagenen mikromechanischen Inertialsensors;
• 2 den vorgeschlagenen mikromechanischen Inertialsensor nach dem Einfüllen von Antihaftmaterialmaterial;
• 3 den vorgeschlagenen mikromechanischen Inertialsensor nach einem Verschließen der Zugangsöffnung;
• 4 den vorgeschlagenen mikromechanischen Inertialsensor nach einem Rückschleifprozess;
• 5 den vorgeschlagenen mikromechanischen Inertialsensor nach einem Einfügen einer weiteren Zugangsöffnung zum Freilegen eines elektrischen Kontaktes; und
• 6 einen prinzipiellen Ablauf eines Verfahrens zum Herstellen eines vorgeschlagenen mikromechanischen Inertialsensors.

In the figures shows:

• 1 a cross-sectional view of a precursor of an embodiment of the proposed micromechanical inertial sensor;
• 2 the proposed micromechanical inertial sensor after filling non-stick material;
• 3 the proposed micromechanical inertial sensor after closing the access opening;
• 4 the proposed micromechanical inertial sensor after a regrinding process;
• 5 the proposed micromechanical inertial sensor after insertion of a further access opening for exposing an electrical contact; and
• 6 a basic sequence of a method for producing a proposed micromechanical inertial sensor.

Description of embodiments

In particular, it is an essential idea of the present invention to provide an improved manufacturing process for a micromechanical inertial sensor in which movable MEMS structures are prevented from sticking and in which a quality of a bonding frame is improved. This is achieved by forming an access opening for supplying an anti-adhesion coating material (ASC material) prior to a bonding process in a cap substrate, wherein the bonding of the cap substrate to a sensor substrate is only then carried out.

In this way, no spin coating is required for the processing of the sensor substrate, whereby the sensitive, movable MEMS structures of the sensor substrate are not bonded or damaged. In addition, filling of an anti-adhesion layer material into a cavern takes place only after the bonding of sensor substrate and cap substrate, which considerably improves a quality of the bond connection. In this way, the sensitive micromechanical structures can be effectively protected, as a result of which a high production quality of the micromechanical inertial sensor is supported.

Advantages which result from this specific sequence of the production process of the micromechanical inertial sensor are, for example, the following:

The capping process and deposition of the organic anticorrosive layer can be completely decoupled from one another, allowing for the production of higher quality inertial sensors. The bonding process can be optimized for temperature and cleaning regardless of the release layer material. Furthermore, non-stick layers with better non-stick properties can be used, even if they are less temperature-resistant than previously used layers. The proposed manufacturing method also generates advantageous only small additional costs.

The proposed method allows high yields without the risk of sticking MEMS structures during the manufacturing process.

1 shows a highly simplified cross-sectional view of a precursor of a micromechanical inertial sensor 100 , eg in the form of an acceleration sensor. Visible is a sensor substrate 10 on which a sacrificial oxide layer 11 is deposited. In the sensor substrate 10 is a moving MEMS structure 12 formed, which is intended for detection of acceleration in the plane.

On the sensor substrate 10 is a cap substrate 20 with a recessed opening 22 arranged, wherein the cap substrate 20 by means of a bonding frame 30 with the sensor substrate 10 connected is. The bond frame 30 is preferably provided by a eutectic bonding method.

On the surface of the cap substrate 20 is an oxide membrane 21 formed, which also in the sunk opening 22 of the cap substrate 20 is formed and an access opening 23 of the cap substrate 20 closes. The access opening 23 is for introducing a Antiklebeschicht- or non-stick layer material in particular in a cavern 24 of the cap substrate 20 with the underlying movable MEMS structure 12 intended. The oxide membrane 21 forms effective protection against particulates or moisture during a manufacturing process (for example, during storage and / or transport between seal and coating) of the micromechanical inertial sensor 100 ,

Alternatively, it can also be provided that the cap substrate 20 without the oxide membrane 21 will be produced. In very clean and dry manufacturing environments, this alternative may be useful.

It is envisaged that the access opening 23 for feeding the non-stick layer material in advance in the cap substrate 20 is trained. This is for the cap substrate 20 an acceleration or force-intensive process step in the form of spin coating required. The thereby acting high mechanical forces are advantageous, however, uncritical, since the cap substrate 20 no movement and force sensitive parts are present.

1 shows the precursor of the micromechanical inertial sensor 100 after the bonding of the sensor substrate 10 with the cap substrate 20 , In the bonding process for creating the bonding frame 30 it is preferably a metallic bonding method, since not only a tightness of the cavern via such a bonding method 24 around the moveable MEMS structure area 12 is ensured, but also the electrical chip-to-chip contacts (not shown) between the sensor substrate 10 and the cap substrate 20 , Examples of suitable metallic bonding methods are Al-Ge, Au-Si, Cu-Sn, Al-Al, Cu-Cu, Au-Au. On the surface of the sensor substrate 10 is an electrical contact 31 for supplying / reading out electrical signals of the micromechanical inertial sensor 100 recognizable.

In the cross-sectional view of 2 it can be seen that the oxide membrane 21 from the cap substrate 20 removed or a cap substrate 20 is provided without oxide membrane 21, whereby the sunk by the opening 22 extending gas access / access opening 23 is exposed. Thereafter, the filling of the non-stick layer material takes place in the cavern 24 of the micromechanical inertial sensor 100 , Among other things, the non-stick layer material attaches itself to the movable MEMS structure 12 and prevents sticking of the movable elements of the MEMS structure 12 in normal operation of the micromechanical inertial sensor 100 ,

In the cross-sectional view of 3 is apparent that now the access opening 23 in the cap substrate 20 by means of a closure element 25 , which was preferably generated by means of a laser reseal process step, at a defined internal pressure within the cavern 24 hermetically sealed.

Preferably, the closing of the access opening takes place 23 for a micromechanical acceleration sensor at a high internal pressure and for a micromechanical rotation rate sensor at a low internal pressure.

Closing the access opening 23 by means of the laser reseal process is carried out by a local heating with a laser and thereby caused local melting of substrate material on the cap top, as it for example DE 10 2014 202 801 A1 is known. This assists that the already filled non-stick layer material in the sensor core is not affected.

The cross-sectional view of 4 shows a cross-sectional view of the micromechanical inertial sensor 100 , where now the cap substrate 20 was ground back to a suitable target thickness and thereby the entire assembly has suitable geometric dimensions for further processing.

5 shows a further cross-sectional view of the micromechanical inertial sensor 100 after a further process step, wherein an exposure of the electrical contact 31 by forming another access opening 26 in the cap substrate 20 was carried out.

6 shows a basic sequence of the proposed method for producing a micromechanical inertial sensor 100 ,

In one step 200 becomes a provision of a sensor wafer 10 with a moveable MEMS structure 12 carried out.

In one step 210 becomes a cap substrate 20 provided.

In one step 220 become a cavern 24 and an access opening 23 for supplying an anti-adhesion layer material in the cap substrate 20 educated.

In one step 230 becomes the sensor wafer 10 with the cap substrate 20 connected by means of a bonding process.

It goes without saying that the steps 200 and 210 respectively. 220 can also be executed in a different order.

Although the invention has been described above by means of concrete examples of application, the person skilled in the art can realize previously or only partially disclosed embodiments, without departing from the gist of the invention.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been 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.

Cited patent literature

• DE 102014202801 A1 [0037]

Claims (7)

A method of manufacturing a micromechanical inertial sensor (100), comprising: - providing a sensor wafer (10) with a movable MEMS structure (12); - Providing a cap substrate (20); - forming a cavity (24) and an access opening (23) for supplying an anti-adhesion layer material in the cap substrate (20); and - Connecting the sensor wafer (10) with the cap substrate (20) by means of a bonding process. Method according to Claim 1 , wherein on the cap substrate (20) with the access opening (23) a membrane (21) is formed. Method according to Claim 1 or 2 , wherein a closure of the access opening (23) is carried out with a laser. Method according to Claim 3 in that closing the access opening (23), an anti-adhesive layer material is filled into the cavern (24). Method according to Claim 3 or 4 wherein the closing of the access opening (23) is carried out at a defined internal pressure within the cavern (24). Method according to one of Claims 3 to 5 in which a loopback of the cap substrate (20) to a defined target thickness is performed. Micromechanical inertial sensor (100), comprising: a sensor substrate (10) having a movable MEMS structure (12); and - a cap wafer (60) connected to the sensor substrate (10) by means of a bonding frame (30); - wherein in the cap substrate (20) an access opening (23) for supplying an anti-adhesion layer material is formed, wherein the access opening (23) was formed prior to bonding of the cap substrate (20) with the sensor substrate (10).

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