DE102018222724A1 - Method for producing a three-dimensionally stress-decoupled substrate arrangement - Google Patents

Abstract

Disclosed is a method for producing at least one stress-decoupled substrate arrangement for a micromechanical sensor, wherein a wafer-shaped substrate with a buried cavity is provided, at least one sensor structure for forming a sensor is applied to a front side of the substrate, the sensor structure at least in regions by material removal of the substrate from the front is released laterally at least in some areas and the sensor structure in connection with the lateral clearance and the buried cavity is exposed on all sides. Furthermore, a substrate arrangement and a micromechanical sensor are disclosed.

Description

The invention relates to a method for producing at least one stress-decoupled substrate arrangement for a micromechanical sensor, a substrate arrangement and a sensor with such a substrate arrangement.

State of the art

Pressure sensors are known which have a pressure-sensitive sensor section. The pressure-sensitive sensor sections are increasingly mechanically decoupled from the remaining section of the sensor by means of a resilient arrangement. Such a structure can be referred to as a stress decoupled pressure sensor. External influences that put the pressure sensor under mechanical stress are, for example, mechanical tension during manufacture, different materials in the construction with different thermal expansion coefficients, and soldered connection of the assembled sensor on an external printed circuit board. Such a pressure sensor is from the DE 10 2017 203 384 B3 known.

The previous pressure sensors or stress-decoupled sensors have to be processed both from the front and from the rear during manufacture. In particular, so-called rear-side processes can complicate the manufacture of the sensors.

Disclosure of the invention

The object on which the invention is based can be seen in proposing a production method and an improved substrate arrangement which avoid the use of rear-side processes.

According to the invention, this object is achieved by means of the respective subject matter of the independent claims. Advantageous refinements and developments of the invention are the subject of dependent subclaims and are evident from the description.

According to one aspect of the invention, a method for producing at least one stress-decoupled substrate arrangement for a micromechanical sensor is provided. In one step, a wafer-shaped substrate with a buried cavity is provided. The buried cavity can be designed in the form of a cavity. Subsequently, at least one sensor structure for forming a sensor is applied to a front of the substrate. For example, the sensor structure is exposed laterally, at least in regions, by material removal from the front of the substrate up to the buried cavity. Due to the lateral release of the sensor structure, a release from the rear can be achieved due to the cavity.

According to a further aspect of the invention, a substrate arrangement for forming at least one micromechanical sensor is provided. The arrangement has a substrate section with a front side and a rear side, the substrate section having a cavity arranged between the front side and the rear side. Furthermore, the arrangement has a sensor structure, which is arranged on the front side and is exposed laterally by at least one trench trench introduced into the front side. The at least one trench trench establishes a fluid-conducting connection between the front side of the substrate section and / or the sensor structure and the cavity, the at least one trench trench being shaped as a mechanical spring.

According to a further aspect of the invention, a micromechanical sensor is provided which has a substrate arrangement according to the invention.

Rear processes lead to additional effort in the development and production. This is characterized, for example, by additional steps for protecting the sensor structure located on the front of the substrate or to avoid leakage paths from the back of the substrate to the front in critical processes. Such protective measures must be taken in particular in trench processes. In addition to the increased effort, so-called handling steps on the sensitive sensor structure on the front of the substrate can also result in an increased loss of yield.

The process can be used to implement a process flow for realizing a substrate arrangement, which can serve as the basis for a stress-decoupled sensor, such as a pressure sensor. The all-round exemption or the so-called three-dimensional stress decoupling of the sensor section relevant for the sensor can take place here without the use of rear processes.

In one possible implementation form of the method, a buried cavity is first formed in a wafer-shaped substrate, such as, for example, a silicon wafer, for later removal from the rear. The buried cavity can be created, for example, in a so-called APSM (Advanced Porous Silicon Membrane) process. The buried cavity is preferred between a front and a back of the substrate.
After the buried cavity has been formed in the wafer-shaped substrate, a sensor structure can be applied or produced on the front and / or rear silicon surface, which is now completely closed again. The sensor structure can be produced by deposition processes and material removal processes on the front side of the wafer-shaped substrate, or can be integrally connected to the front side of the substrate, for example by an adhesive connection or a solder connection. The sensor structure can be used, for example, to form a capacitive pressure sensor.

In order to decouple the sensitive section of the sensor structure from the remaining section of the sensor structure or a sensor frame, all-round release is carried out after the sensor structure has been completed. In a first step, a lateral exemption can be implemented. The lateral release takes place in the form of a material removal, which is carried out from the front of the sensor structure and / or the substrate. In particular, this allows at least one trench or groove to be introduced into the arrangement, which extends vertically from the front of the arrangement in the direction of the rear of the substrate. For example, a trench process can be used for this.

Due to the lateral clearance using the cavity, a three-dimensional clearance of the sensor structure on the front of the substrate can be realized, the process being able to be carried out without rear-side processes and also reducing the handling steps required for this. In particular, a section of the sensor structure can be decoupled from a remaining sensor structure or a sensor frame.

A plurality of substrate arrangements, which can be separated from one another in one step, can preferably be formed on the wafer-shaped substrate. The respective substrate arrangements preferably each have a circumferential distance in the form of a channel, which can be used for separation.

The method enables a sensor with a three-dimensional stress decoupling without rear processes or the use of a second wafer-shaped substrate.

The closed rear side of the wafer-shaped substrate achieved by avoiding rear-side processes is advantageous in the production of an all-round exemption, since perforation of the substrate is avoided here. In particular in the case of process steps which require cooling of the wafer-shaped substrate or wafer by means of gas from the rear, perforation of the substrate can make processing more difficult.

The closed back is also advantageous in the construction and connection technology, since full-surface adhesives such as a DAF (Die Attached Film) can be used. This means that processes that are already in large series can be used.

Furthermore, the method enables the substrate to be ground back to almost any wafer thickness and thus later chip thicknesses. The restriction in rear-side processes, in which the target wafer thickness and thus the chip thickness is set before the rear-side processes and is limited to a manageable minimum wafer thickness in the production of, for example, 300300 μm, also does not apply to a substrate arrangement produced according to the method.

The micromechanical sensor can be a capacitive pressure sensor, for example, but is not limited to this. The concept can also be transferred to other MEMS sensors in surface micromechanics. Corresponding MEMS sensors can also be acceleration or rotation rate sensors.

According to one embodiment, the wafer-shaped substrate is provided by a so-called “Advanced Porous Silicon Membrane” (APSM) process. As a result, in one step, for example by etching processes or anodic oxidation, a porous section can be introduced into a wafer-shaped substrate, which is subsequently covered, for example by vapor deposition or deposition, on the front or rear. A thermal cavity of the porous section creates a cavity, i.e. a buried cavity. In particular, typical cavity depths of 2-8 µm and the thickness of the silicon layer above it can be realized in the range of 3-30 µm. A buried cavity is thus created below the original silicon surface, which is available for other functions, such as, for example, the release of the sensor core on the back. The use of this cavity for releasing a stress-decoupled sensor core from the back can be made possible by a capacitive sensor core, for example by applying a reference pressure cavity above the original wafer surface or the front of the substrate.

The sensor core preferably forms a section of the sensor arrangement which is suitable for functional tasks, such as a capacitive pressure measurement, is designed.

According to a further embodiment, the sensor structure is laterally exposed by at least one trench trench introduced into the substrate and the sensor structure on the front side, the at least one trench trench extending as far as the buried cavity. The at least one trench can be introduced into the substrate arrangement by plasma-assisted etching, such as reactive ion depth etching. Alternatively, a wet chemical etching process using a mask to make the trench can be used.

According to a further embodiment, the introduction of the at least one trench trench forms at least one mechanical spring which connects an exposed sensor core to a sensor frame. By forming a resilient section of the front side of the substrate and / or the sensor structure, a mechanical decoupling of the, for example pressure-sensitive area from the surrounding substrate or the surrounding sensor frame can be made possible. The at least one trench trench forms at least one spring which has damping and vibration properties that are defined based on the shape and thickness. The at least one spring formed on the front preferably has two end sections, one end section being connected to the sensor core and one end section being connected to the sensor frame or the section surrounding the sensor core. The introduction of the trench trench and the simultaneous formation of a resilient connection between the sensor core and the sensor frame correspond to the lateral release of the sensor structure.

According to a further embodiment, after the sensor structure has been released from the side and from the back, the exposed sensor structure is covered with a protective cap. This enables the sensor to be integrated, for example in a mold package. In particular, after the separation, the entire substrate arrangement can be positioned by casting or gluing in a housing or on a printed circuit board.

In the case of a pressure sensor, the pressure access in the protective cap and the cap thickness can be configured almost as desired. For example, only a few trench holes with a very small diameter can be created along the edge of the protective cap. This is advantageous for achieving a high media and particle resistance of the sensor and for maintaining the mechanical stability of the protective cap.

According to a further embodiment, the sensor structure has at least one membrane and at least one reference pressure cavity, which are decoupled from stress by the lateral and rear exemption. In particular, after the buried cavity has been formed, a complex sensor structure, for example in the form of a capacitive pressure sensor, can be produced on the front side of the substrate that is now completely closed again.

The substrate arrangement or a plurality of substrate arrangements that can be produced by the method can preferably be used as the basis for sensors in surface micromechanics in the consumer and automotive sectors.

• 1 einen schematischen Schnitt durch ein waferförmiges Substrat gemäß einer Ausführungsform der Erfindung,
• 2 einen schematischen Schnitt durch das waferförmige Substrat mit einer aufgebrachten Sensorstruktur gemäß einer Ausführungsform der Erfindung und
• 3 einen schematischen Schnitt durch eine Substratanordnung gemäß einem Ausführungsbeispiel der Erfindung.

Preferred exemplary embodiments of the objects according to the invention are explained in more detail below on the basis of highly simplified schematic representations. Show here

• 1 2 shows a schematic section through a wafer-shaped substrate according to an embodiment of the invention,
• 2nd a schematic section through the wafer-shaped substrate with an applied sensor structure according to an embodiment of the invention and
• 3rd a schematic section through a substrate arrangement according to an embodiment of the invention.

In the figures, the same structural elements have the same reference numbers. The 1 to 3rd are used in particular to illustrate a method for producing at least one stress-decoupled substrate arrangement.

The 1 shows a schematic section through a wafer-shaped substrate 1 according to an embodiment of the invention. In particular, is a portion of the substrate 1 or a substrate section 1 shown. A wafer consists of a plurality of sections of the substrate 1 which can be separated from one another in at least one method step.

The substrate 1 has a front 2nd and a back 4th on which is a buried cavity 6 Cover on both sides in the vertical direction V. According to the exemplary embodiment, the horizontal extent of the buried cavity 6 limited.

The buried cavity 6 is designed according to the embodiment as a cavity.
In the 2nd is a schematic section through the wafer-shaped substrate 1 with an applied sensor structure 8th according to an embodiment of the Invention shown. The sensor structure 8th is going to the front 2nd of the substrate 1 applied in the context of the inventive method. This can be done in layers or by making the sensor structure separately 8th and then integrally connecting the sensor structure 8th with the substrate 1 respectively.

The on the wafer-shaped substrate 1 applied sensor structure 8th is designed as a capacitive pressure sensor according to the exemplary embodiment.

The sensor structure indicates this 8th at least one membrane 10 on which is a pressure chamber 12th covered. The membrane 10 is here as a reference chamber membrane 10 formed which is a reference pressure chamber 12th at least partially closed.

The 3rd shows a schematic section through a substrate arrangement 14 according to an embodiment of the invention. In particular, is a cross section through one for a capacitive pressure sensor 16 usable sensor arrangement 14 after all-round exemption.

The substrate arrangement has a substrate section 1 with a front 2nd and a back 4th on. On the substrate section shown 1 is the front in 2nd described sensor structure 8th upset. In one step, the sensor structure 8th and the front 2nd of the substrate section 1 sideways through at least one trench 18th exempt. The at least one trench 18th runs horizontally on the circumference and forms a sensor core 20 from which of a sensor frame 22 should be decoupled from stress. The trench is for this 18th designed in the form of a spring.

After forming the substrate assembly 14 can the sensor core 20 with a protective cap 24th be covered. The protective cap 24th can be on the front of the sensor frame 22 can be arranged cohesively or positively and the sensor structure 8th protect. The protective cap 24th lies according to the embodiment on a sensor frame 22 the sensor structure 8th on.

QUOTES INCLUDE IN THE DESCRIPTION

This list of documents listed by the applicant has been generated automatically and is only included 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 102017203384 B3 [0002]

Claims (8)

Method for producing at least one stress-decoupled substrate arrangement (14) for a micromechanical sensor (16), wherein a wafer-shaped substrate (1) with a buried cavity (6) is provided, at least one sensor structure (8) for forming a sensor (16) is applied to a front side (2) of the substrate (1), - The sensor structure (8) is at least partially released laterally at least partially by removing material from the front of the substrate (1) - The sensor structure (8) is exposed by means of the regionally front material removal of the substrate (1) through the cavity (7). Procedure according to Claim 1 The wafer-shaped substrate (1) with the buried cavity (6) is provided by an APSM process. Procedure according to Claim 1 or 2nd The sensor structure (8) is laterally exposed by at least one trench trench (18) introduced into the substrate (1) and the sensor structure (8) on the front side, the at least one trench trench (18) extending as far as the buried cavity (6). Procedure according to Claim 3 wherein at least one mechanical spring is formed by introducing the at least one trench trench (18), which connects an exposed sensor core (20) to a sensor frame (22). Procedure according to one of the Claims 1 to 4th The exposed sensor structure (8, 20) is covered with a protective cap (24) after the sensor structure (8) has been released from the side and from the rear. Procedure according to one of the Claims 1 to 5 The sensor structure (8) has at least one membrane (10) and at least one reference pressure cavity (12), which are decoupled from stress by the lateral and rear exemption. Substrate arrangement (14) with a micromechanical sensor (16), comprising a substrate section (1) with a front side (2) and a back side (4), the substrate section (1) being between the front side (2) and the back side (4) Has arranged cavity (6), comprising a sensor structure (8), which is arranged on the front (2) and is laterally released by at least one trench trench (18) introduced into the front (2), characterized in that the at least one trench (18) provides a fluid-conducting connection between the front (2) of the substrate section (1) and / or the sensor structure (8) and the cavity (6) for all-round exposure, the at least one trench (18) being shaped as a mechanical spring . Micromechanical sensor (16), the micromechanical sensor (16) following a substrate arrangement (14) Claim 7 having.

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