TW202037555A - Method for producing a three-dimensionally stress-decoupled substrate arrangement - Google Patents

Abstract

A method is disclosed for producing at least one stress-decoupled substrate arrangement for a micromechanical sensor, wherein a substrate in wafer form having a buried cavity is provided, at least one sensor structure for forming a sensor is applied on a front side of the substrate, the sensor structure is laterally freed at least in regions by front-side material removal of the substrate, and the sensor structure is freed on all sides in conjunction with the lateral freeing and the buried cavity. A substrate arrangement and a micromechanical sensor are furthermore disclosed.

Description

Method for generating three-dimensional stress decoupling substrate configuration

The present invention relates to a method for generating at least one stress decoupling substrate configuration for micromechanical sensors, relates to a substrate configuration and relates to a sensor having such a substrate configuration.

The pressure sensor including the pressure sensitive sensor section is already known to us. Gradually, the pressure-sensitive sensor section is mechanically decoupled from the remaining sections of the sensor by elastic configuration. This type of structure can be referred to as a stress decoupling pressure sensor. For example, the external effects of placing a pressure sensor under mechanical stress are mechanical stress during manufacturing, different materials with different thermal expansion coefficients in the structure, and solder connections of sensors built on external circuit boards. This type of pressure sensor has been known to us since DE 10 2017 203 384 B3.

During manufacturing, the previous pressure sensor or stress decoupling sensor needs to be processed from the front side and the back side. In detail, the so-called backside procedure may make sensor manufacturing more difficult.

The objective of the present invention can be seen as providing a manufacturing method and an improved substrate configuration, and avoiding the use of backside procedures.

According to the present invention, this goal is achieved by means of the respective subject matter of the independent items of the patent application. The advantageous configurations and improvements of the present invention are the subject matter of the appended items of the respective patent applications and can be found in this specification.

According to one aspect of the present invention, there is provided a method for generating at least one stress decoupling substrate configuration for a micromechanical sensor. In one step, a substrate in the form of a wafer is provided, the substrate having a buried cavity. The buried cavity can be configured as a hollow space. Subsequently, at least one sensor structure is applied on the front side of the substrate for forming a sensor. For example, the sensor structure is free to move laterally at least in the area where the front side material is removed in the substrate, until it reaches the buried cavity. When the sensor structure is free to move laterally, due to the existence of the cavity, the back side can move freely at the same time.

According to another aspect of the present invention, a substrate configuration for forming at least one micromechanical sensor is provided. The configuration includes a substrate section having a front side and a back side, and the substrate section includes a cavity disposed between the front side and the back side. In addition, the configuration includes a sensor structure that is disposed on the front side and is free to move laterally by at least one groove introduced into the front side. At least one groove provides a fluid transport connection between the front side of the substrate section and/or the sensor structure and the cavity, the at least one groove being formed as a mechanical spring.

According to another aspect of the present invention, according to the present invention, a micromechanical sensor including a substrate configuration is provided.

The backside procedure will result in additional expenditure during R&D and manufacturing. For example, the backside process is characterized by some additional steps, which are to protect the sensor structure located on the front side of the substrate, or to avoid leakage paths from the back side of the substrate to the front side of the substrate in the critical process . In detail, this protective measure is required in the trench procedure. In addition, the so-called processing steps on the structure of the sensitive sensor on the front side of the substrate, in addition to increasing expenditure, can also lead to an increase in yield loss.

In this method, it is possible to implement a process flow for generating a substrate configuration that can be used as a basis for stress decoupling sensors such as pressure sensors. In this case, free movement or so-called three-dimensional stress decoupling on all sides of the relevant sensor section of the sensor can be performed, and no backside procedure is used.

In this method, in a possible implementation, the buried cavity for subsequent free movement of the back side is initially formed in a substrate in the form of a wafer (such as a silicon wafer). For example, the buried cavity can be created in the so-called APSM (Advanced Porous Silicon Membrane) procedure. The buried cavity is preferably placed between the front side and the back side of the substrate. After the buried cavity is formed in the substrate in the form of a wafer, a sensor structure can be applied or generated on the front and/or back silicon surface, which is now completely closed. The sensor structure can be produced by a deposition method and a material removal method on the front side of the substrate in the form of a wafer, or can be connected with a material suitable for the front side of the substrate, for example, by bonding or soldering. For example, the sensor structure can be used 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 from the sensor frame, free movement is performed on all sides after the sensor structure is manufactured. For this purpose, in the first step, lateral free movement can be implemented. The lateral free movement is performed in the form of material removal, and the material removal is performed from the front side of the sensor structure and/or the substrate. In detail, in this way, at least one groove or groove can be introduced into a configuration that extends perpendicularly from the side before the configuration in the direction of the back side of the substrate. For this, for example, a groove program can be used.

By using the cavity for lateral free movement, the three-dimensional free movement of the sensor structure can be performed on the front side of the substrate. In this case, the procedure can be performed without the backside procedure, and the required processing steps are also reduced. . In detail, the section of the sensor structure can be decoupled from the remaining sensor structure or the sensor frame.

A variety of substrate configurations can preferably be formed on a substrate in the form of a wafer, and can be separated from each other in a step. Preferably, the respective substrate configurations respectively include annular spacers in the form of channels, which can be used for spacing.

In this method, it is possible to provide a sensor with three-dimensional stress decoupling without back-side procedures or using a second substrate in the form of a wafer.

The closed back side of the substrate in the form of a wafer (the closed back side is obtained by avoiding the back side procedure) facilitates free movement on all sides, because in this case the perforation of the substrate is avoided. In particular, in a process step that requires the use of gas from the backside to cool a substrate or wafer in the form of a wafer, the perforation of the substrate may make the processing more difficult.

In addition, the closed back side facilitates construction and connection technology, as full surface adhesives such as DAF (die attached film) can be used. In this way, programs that already exist in mass production can be used. In addition, the method makes it possible to grind the substrate to almost any desired wafer thickness, and therefore subsequent wafer thickness. The restrictions in the backside process are also eliminated in the case of substrate configurations manufactured according to this method. In the backside process, the target wafer thickness and therefore the wafer thickness is set before the backside process and is limited to the manageable minimum Wafer manufacturing thickness, for example >300 μm.

For example, the micromechanical sensor can be a capacitive pressure sensor, but it is not limited thereto. In addition, the concept can also be applied to other MEMS sensors in surface micromechanical devices. The corresponding MEMS sensor can also be an acceleration or rotation rate sensor.

According to a specific example, the substrate in the form of a wafer is provided by the so-called "Advanced Porous Silicon Membrane" (APSM) process. In this way, in a step carried out, for example, by an etching method or anodization, a porous section can be introduced into the substrate in the form of a wafer, which section is then covered on the front or back side, for example by evaporation or deposition . By the thermal rearrangement of the porous section, a hollow space, that is, an embedded cavity, is formed. In detail, a typical cavity depth of 2-8 μm and a thickness of the upper silicon layer in the range of 3-30 μm can be produced. Therefore, a buried cavity based on the original silicon surface is formed, which can be used for other functions, such as the free movement of the back side of the sensor core. The capacitive sensor core, for example, by applying a reference pressure cavity above the surface of the original wafer or on the front side of the substrate makes it possible to use this cavity for free movement of the backside of the stress decoupling sensor core.

The sensor core preferably constitutes a section of the sensor configuration configured for functional tasks such as capacitive pressure measurement.

According to another specific example, the sensor structure is free to move laterally by introducing at least one groove on the front side into the substrate and the sensor structure, and the at least one groove extends to the buried cavity. The at least one trench can be etched with plasma assisted etching, for example by deep reactive ion etching, introduced into the substrate configuration. As an alternative, a mask can be used to adopt a wet chemical etching method to create trenches.

According to another specific example, at least one mechanical spring connecting the freely moving sensor core to the sensor frame is formed by introducing at least one groove. By forming the front side of the substrate and/or the elastic section of the sensor structure, for example, the mechanical decoupling of the pressure-sensitive area from the surrounding substrate or surrounding the sensor frame is possible. At least one groove forms at least one spring, which defines damping and oscillation properties based on shape and thickness. The at least one spring formed on the front side preferably includes two end sections, one end section is connected to the sensor core, and one end section is connected to the sensor frame or to the area surrounding the sensor core segment. The introduction of the groove and the elastic connection between the sensor core and the sensor frame simultaneously form a lateral free movement corresponding to the sensor structure.

According to another specific example, after the sensor structure is free to move laterally and on the back side, the freely moving sensor structure is covered with a protective cover. In this way, it is possible to integrate the sensor, for example, into a mold package. In detail, the entire substrate configuration can be positioned in the package or printed circuit board by casting or bonding after separation.

In the case of pressure sensors, the pressure access in the protective cover and the thickness of the cover can be configured in almost any desired way. For example, only a few groove holes with a very small diameter can be applied along the sides of the protective cover. This helps to obtain the high dielectric and particle resistance of the sensor and maintain the mechanical stability of the protective cover.

According to another specific example, the sensor structure includes at least one diaphragm and at least one reference pressure chamber for stress decoupling by lateral and back free movement. In detail, after the buried cavity is formed, a complex sensor structure, for example in the form of a capacitive pressure sensor, can be generated on the front side of the substrate, which is now completely closed.

In the fields of consumer goods and automobiles, the substrate configuration or multiple substrate configurations that can be produced by this method can be preferably used as the basis of sensors in surface micromechanical devices.

Preferred illustrative specific examples of the subject matter according to the present invention will be explained in more detail below with the aid of highly simplified schematic representations.

In the drawings, the same design elements have the same reference. In detail, FIGS. 1 to 3 are used to illustrate a method for generating at least one stress decoupling substrate configuration.

Fig. 1 shows a schematic cross-sectional view of a substrate 1 in the form of a wafer according to a specific example of the present invention. In detail, it means the section of the substrate 1 or the substrate section 1. The wafer is composed of various sections of the substrate 1 which can be separated from each other in at least one method step.

The substrate 1 includes a front side 2 and a back side 4, and both sides cover the buried cavity 6 in the vertical direction V. According to an illustrative example, the horizontal range of the buried cavity 6 is limited.

According to an illustrative specific example, the buried cavity 6 is configured as a hollow space.

2 shows a schematic cross-sectional view of a substrate 1 in the form of a wafer to which a sensor structure 8 is applied according to a specific example of the present invention. Within the scope of the method of the invention, the sensor structure 8 is applied to the front side 2 of the substrate 1. This situation can be performed layer by layer or by the separate operation of the sensor structure 8 and the subsequent material matching connection of the sensor structure 8 to the substrate 1.

According to an illustrative specific example, the sensor structure 8 applied on the substrate 1 in the form of a wafer is implemented as a capacitive pressure sensor.

For this purpose, the sensor structure 8 contains at least one diaphragm 10 which covers the pressure chamber 12. In this case, the diaphragm 10 is configured as a reference chamber diaphragm 10 which closes the reference pressure chamber 12 at least in several areas.

FIG. 3 shows a schematic cross-sectional view of a substrate configuration 14 according to an exemplary embodiment of the present invention. In detail, it shows the cross section of the sensor configuration 40 that can be used for the capacitive pressure sensor 16 after free movement on all sides.

The substrate configuration includes a substrate section 1 with a front side 2 and a back side 4. The section 1 is represented on the substrate, and the sensor structure 8 described in FIG. 2 is applied on the front side. In one method step, the sensor structure 8 and the front side 2 of the substrate section 1 are free to move laterally via at least one introduced groove 18. At least one groove 18 extends horizontally along the circumference and forms a sensor core 20 which is intended to be stress decoupled from the sensor frame 22. For this purpose, the groove 18 is configured in the form of a spring.

After the substrate configuration 14 is formed, the sensor core 20 may be covered with a protective cover 24. The protective cover 24 can be configured with a material or form suitable for the front side of the sensor frame 22 and can protect the sensor structure 8. According to the illustrative example, the protective cover 24 is carried on the sensor frame 22 of the sensor structure 8.

1: substrate 2: front side 4: back side 6: Buried cavity 7: cavity 8: Sensor structure 10: Diaphragm 12: Reference pressure chamber/reference pressure chamber 14: substrate configuration 16: Capacitive pressure sensor 18: groove 20: Sensor core 22: sensor frame 24: Protective cover V: vertical direction

[Fig. 1] A schematic cross-sectional view showing a substrate in the form of a wafer according to a specific example of the present invention. [FIG. 2] A cross-sectional schematic diagram showing a substrate in the form of a wafer to which a sensor structure is applied according to a specific example of the present invention, and [FIG. 3] A schematic cross-sectional view showing a substrate configuration according to an exemplary embodiment of the present invention.

1: substrate

2: front side

4: back side

6: Buried cavity

8: Sensor structure

10: Diaphragm

12: Reference pressure chamber/reference pressure chamber

V: vertical direction

Claims (7)

A method for generating at least one stress decoupling substrate configuration (14) for a micromechanical sensor (16), wherein Provide a substrate in the form of a wafer (1), the substrate has an embedded cavity (6), At least one sensor structure (8) is applied on the front side (2) of the substrate (1) to form a sensor (16), The sensor structure (8) is free to move laterally at least in the area where the front side material is removed in the substrate (1), and The sensor structure (8) is free to move in the cavity (7) by means of the regional front side material removal of the substrate (1), wherein after the sensor structure (8) is free to move laterally and back , The freely movable sensor structure (8, 20) is covered with a protective cover (24). The method of claim 1, wherein the substrate in the form of a wafer (1) is provided by an APSM program, and the substrate has the buried cavity (6). The method of claim 1 or 2, wherein the sensor structure (8) is laterally free by introducing at least one groove (18) in the substrate (1) and the sensor structure (8) on the front side Moving, the at least one groove (18) extends to the buried cavity (6). The method of claim 3, wherein the at least one mechanical spring connecting the freely moving sensor core (20) to the sensor frame (22) is formed by the introduction of the at least one groove (18). The method according to any one of claims 1 to 4, wherein the sensor structure (8) includes at least one diaphragm (10) and at least one reference pressure chamber ( 12). A substrate configuration (14) with a micromechanical sensor (16), the substrate configuration includes: a substrate section (1) with a front side (2) and a back side (4), the substrate section (1) includes the configuration The cavity (6) between the front side (2) and the back side (4); the sensor structure (8), which is arranged on the front side (2) and is introduced into the front side (2) The at least one groove (18) is free to move laterally, wherein the at least one groove (18) provides the front side (2) of the substrate section (1) and/or the sensor structure (8) and the The fluid conveying connection between the cavities (6) so as to move freely on all sides, the at least one groove (18) is formed as a mechanical spring, the sensor core (20) is covered by a protective cover (24), the protective The cover rests against the sensor frame (22). A micromechanical sensor (16), wherein the micromechanical sensor (16) includes the substrate configuration (14) as in claim 6.

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