DE102017207453A1 - Micromechanical inertial sensor - Google Patents

Abstract

Micromechanical inertial sensor (100), comprising:
a substrate (10);
a mechanical functional layer (20) arranged on the substrate (10) with an inertial mass (23) formed therein; in which
- The inertial mass (23) has regions of different mass density, wherein the inertial mass (23) at least in sections, a second material (21) having a defined higher mass density than a first material of the inertial mass (23); in which
- The inertial mass (23) of at least one expansion gap (24) for compensating for different coefficients of expansion of the two materials is limited.

Description

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

State of the art

Micromechanical inertial sensors for measuring acceleration and yaw rate are known and mass-produced for various applications in the automotive and consumer sectors.

One trend is towards smaller and therefore cheaper inertial sensors. Among other things, the signals scale with the inertial mass of the sensors and the restoring forces of the springs. For high sensitivity, the inertial mass must be high and the spring constant must be as small as possible, which, however, may have a negative impact on the robustness of the inertial sensors, because e.g. an adhesion tendency is increased. The tendency of the surfaces to adhere becomes more and more critical as the miniaturization of the sensors progresses, since the surface adhesion forces remain the same, while the restoring forces of the springs have to be reduced to ensure the same sensitivity of the sensors. However, since basically the same overloads act on the sensor from the outside, gluing the sensors without additional measures becomes more and more likely. The inertial mass results from the area used, the deposited layer thickness and the specific material density. As the area decreases, either the layer thickness or the material density must be increased or, alternatively, the springs must be made narrower and thus softer.

In the case of the spring widths, it is already borderline in many cases today, because with the spring widths, the process tolerances for the spring widths must at the same time be reliably restricted so that sticking can be avoided. Tungsten has a significantly higher density with respect to silicon (W: 19,250 kgm ^-3 compared with Si: 2.330 kgm ^-3), and is also compatible with semiconductor processes. Because of the comparatively likewise very high elastic constants of tungsten compared to silicon (modulus of elasticity W: E _{W, Young} = 411 Gpa versus modulus of elasticity Si: E _{Si, Young} = 47 GPa), suitable feathers would have to be designed to be particularly narrow when used simultaneously as a spring material slight variations in the structural widths of W springs would already lead to large parameter variations of the components.

1 shows a diagram with different materials and their Young's modulus E in GPa and their density in Mg / m ³ .

Out US 2015/0336790 A1 is known an entirely made of tungsten inertial element. The production of thick tungsten layers by means of sputtering processes is very cost-intensive and, because of the expected high resonance scattering of the sensors, the yield is likely to be low.

US 2016/0178656 A1 discloses a silicon-based MEMS device with trenches filled with high-density metal. The MEMS device includes a silicon-based movable MEMS sensor element, wherein a plurality of wells are formed in at least one surface of the movable MEMS sensor element. The wells are filled with at least one metal to increase an effective mass of the movable MEMS sensor element. The metal may be tungsten or tantalum or an alloy with tungsten and tantalum. Unfavorable in this arrangement is that changes by the introduction of high-density material with a different thermal expansion coefficient over temperature, the stress state in the sensor, which has a temperature-dependent drift of the sensor signal result and must be compensated consuming.

Disclosure of the invention

It is an object of the present invention to provide an improved micromechanical sensor with a lower temperature dependence of the sensor signal.

• - ein Substrat;
• - eine auf dem Substrat angeordnete mechanische Funktionsschicht mit einer darin ausgebildeten Inertialmasse; wobei
• - die Inertialmasse Bereiche unterschiedlicher Massendichte aufweist, wobei die Inertialmasse wenigstens abschnittsweise ein zweites Material aufweist, das eine definiert höhere Massendichte aufweist als ein erstes Material der Inertialmasse; wobei
• - die Inertialmasse von wenigstens einem Expansionsspalt zum Ausgleichen von unterschiedlichen Ausdehnungskoeffizienten der beiden Materialien begrenzt ist.

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

• a substrate;
• a mechanical functional layer arranged on the substrate with an inertial mass formed therein; in which
• the inertial mass has regions of different mass density, wherein the inertial mass has, at least in sections, a second material which has a defined higher mass density than a first material of the inertial mass; in which
• - The inertial mass is limited by at least one expansion gap to compensate for different expansion coefficients of the two materials.

This advantageously provides a micromechanical sensor, which due to the increased specific gravity of the high-density metal compared to silicon has a favorable mechanical property and provides compensation for the different expansion coefficients of the two materials used in the inertial element. As a result, favorable operating characteristics such as a lower temperature dependence of the sensor signal of the micromechanical sensor are supported as a result.

• - Bereitstellen eines Substrats;
• - Anordnen einer mechanischen Funktionsschicht mit einer darin ausgebildeten Inertialmasse auf dem Substrat, wobei in der Inertialmasse Bereiche unterschiedlicher Massendichte ausgebildet werden, wobei in der Inertialmasse wenigstens abschnittsweise ein zweites Material angeordnet wird, das eine definiert höhere Massendichte aufweist als ein erstes Material der Inertialmasse; wobei
• - Angrenzend an die Inertialmasse wenigstens ein Expansionsspalt zum Ausgleichen von unterschiedlichen Ausdehnungskoeffizienten der beiden Materialien ausgebildet wird.

According to a second aspect, the object is achieved with a method for producing a micromechanical sensor, comprising the steps:

• - Providing a substrate;
• Arranging a mechanical functional layer with an inertial mass formed therein on the substrate, wherein regions of different mass density are formed in the inertial mass, wherein in the inertial mass at least partially a second material is arranged, which has a defined higher mass density than a first material of the inertial mass; in which
• - Is formed adjacent to the inertial mass at least one expansion gap for equalizing different expansion coefficients of the two materials.

Preferred embodiments of the micromechanical sensor are the subject of dependent claims.

An advantageous development of the micromechanical sensor is characterized in that a mass density of the second material is between approximately four times and approximately nine times higher than a mass density of the first material of the inertial mass. Thereby, a favorable ratio of the mass densities of the first material and the second material is provided, whereby a significantly increased mechanical sensitivity of the micromechanical sensor is supported.

A further advantageous development of the micromechanical sensor is characterized in that the second material has a mass density of preferably> 6 Mg / m ³ , even more preferably> 8 Mg / m ³ . Thereby, a favorable bulk density for the second high-density material is provided in relation to the main material of the inertial mass.

A further advantageous development of the micromechanical sensor is characterized in that the second material of the inertial mass is one of the following: tungsten, tantalum, hafnium, rhenium, osmium, iridium, platinum, gold, molybdenum, nickel or an alloy containing at least one of contains mentioned elements. As a result, several realization possibilities for the second high-density material are advantageously provided.

A further advantageous development of the micromechanical sensor is characterized in that the second material is arranged in a layer in the inertial mass. As a result, mechanical properties of the inertial mass can be advantageously adapted to specific requirements.

A further advantageous development of the micromechanical sensor is characterized in that the layering of the second material is formed laterally and / or vertically relative to a surface of the inertial mass. This advantageously provides several options for arranging the second high-density material within the inertial mass.

Further advantageous developments of the micromechanical sensor are distinguished by the fact that the second material is arranged in a grid-like manner in the inertial mass, or that the second material is arranged like a cylinder around through-holes of the inertial mass. In this way, mechanical properties of the inertial mass can advantageously be designed very finely.

A further advantageous development of the micromechanical sensor is characterized in that the second material has a defined higher elastic constant than the first material. As a result, spring elements of the sensor can be equipped without the second high-density material.

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 micromechanical sensor result analogously from corresponding features, technical advantages and embodiments relating to the method for producing a micromechanical sensor, and vice versa.

• 1 ein Diagramm mit spezifischen Materialeigenschaften von unterschiedlichen Materialien;
• 2 eine Querschnittsansicht einer ersten Ausführungsform des vorgeschlagenen mikromechanischen Sensors;
• 3 eine Draufsicht auf eine Inertialmasse der ersten Ausführungsform des vorgeschlagenen mikromechanischen Sensors;
• 4 eine Querschnittsansicht einer zweiten Ausführung des vorgeschlagenen mikromechanischen Sensors;
• 5 eine Draufsicht auf die Inertialmasse der zweiten Ausführungsform des vorgeschlagenen mikromechanischen Sensors;
• 6 eine Querschnittsansicht einer dritten Ausführungsform des vorgeschlagenen mikromechanischen Sensors;
• 7-12 einen Prozessfluss zum Herstellen einer Ausführungsform des vorgeschlagenen mikromechanischen Sensors; und
• 13 einen prinzipiellen Ablauf eines Verfahrens zum Herstellen eines vorgeschlagenen mikromechanischen Sensors.

In the figures shows:

• 1 a diagram with specific material properties of different materials;
• 2 a cross-sectional view of a first embodiment of the proposed micromechanical sensor;
• 3 a plan view of an inertial mass of the first embodiment of the proposed micromechanical sensor;
• 4 a cross-sectional view of a second embodiment of the proposed micromechanical sensor;
• 5 a plan view of the inertial mass of the second embodiment of the proposed micromechanical sensor;
• 6 a cross-sectional view of a third embodiment of the proposed micromechanical sensor;
• 7-12 a process flow for producing an embodiment of the proposed micromechanical sensor; and
• 13 a basic sequence of a method for producing a proposed micromechanical sensor.

Description of embodiments

2 schematically shows a highly simplified cross-sectional view through a first embodiment of the proposed micromechanical sensor 100 , One recognizes a first substrate 10 in which in one area 11 wiring layers 12 and insulating layers (eg of polycrystalline silicon and SiO ₂ ) are formed. The substrate 10 may be an ASIC substrate with a complete electronic evaluation circuit (not shown) for sensor signals or a MEMS substrate.

A mechanical functional layer 20 that on the substrate 10 is arranged, has an inertial mass 23 with movable micromechanical elements (MEMS elements) formed therein 22 on. The mobile micromechanical elements 22 the inertial mass 23 sections have a high density second material 21 , eg in the form of tungsten.

The second high-density material 21 may also be in the form of tantalum, hafnium, rhenium, osmium, iridium, platinum, gold, molybdenum, nickel or as an alloy containing at least one of said elements. In general, a "high density" material will be understood below to mean a material having a mass density greater by a factor of about four to about ten than the first material of the inertial mass 23 which is usually silicon.

One recognizes in the area 11 Further, an optional existing Ätzstoppschicht 13 , for example in the form of SiCN or Si-rich nitride. By means of the etch stop layer 13 becomes an attack of the insulation layers and thus an underetching of the wiring layers 12 during a sacrificial layer etching process (eg by means of hydrofluoric acid vapor).

By means of a metallic bond, for example 30 is the first substrate 10 eutectic with a cap substrate 40 bonded.

3 shows a plan view of the inertial material 23 the first embodiment of the proposed micromechanical sensor 100 , Visible is that the second, high-density material 21 crosswise or lattice-like around through holes or Opferschichtätzlöcher 26 the inertial mass 23 is arranged. It can be seen in the plan view of 3 furthermore a total of four expansion gaps 24 located in lateral lateral areas of the inertial mass 23 adjacent to the inertial mass 23 are formed, which for accommodation or to compensate for the different expansion coefficients of the base material of the inertial mass 23 and the second material 21 the inertial mass 23 are provided (W: 4.5 × 10 ^-6 K ^-1 versus Si: 2.6 × 10 ^-6 K ^-1 ). The mentioned different coefficients of expansion can in the absence of the expansion column 24 cause the temperature of the mechanical behavior of the inertial mass 23 (eg spring constant, stress in the layers, etc.) adversely changes.

In the top view of 3 It can also be seen that the movable MEMS elements 22 during operation of the micromechanical sensor 100 as moving electrodes with stator electrodes 25 interact, resulting in a defined movement of the movable MEMS elements 22 an electrical measurement signal of the micromechanical sensor 100 is generated.

Further, in the plan view of 3 recognizable that in a spring element 27 only the first material, but not the second high-density material 21 is available. As a result, the functions "inertial mass" and "elastic spring" of the micromechanical inertial sensor can be separated by suitable materials, whereby size and cost are optimized with increased robustness of the sensors. This is possible mainly because of the fact that the modulus of elasticity of the second high-density material 21 is much larger than the modulus of elasticity of the main material of the mechanical functional layer 20 and thus the spring element 27 , making the second material 21 (eg W) is substantially less elastic than the material (eg Si) of the spring element 27 ,

4 shows a cross-sectional view through a second embodiment of the proposed micromechanical sensor 100 ,

5 shows a plan view of the inertial material 23 the embodiment of the micromechanical sensor 100 from 4 , One recognizes in this case that the high-density, second material 21 around the through holes 26 the inertial mass 23 is formed around, creating the high-density material 21 the sacrificial layer etching holes 26 the inertial mass 23 as it were "wrapped in a cylinder". It can be seen in this embodiment, the expansion gap 24 located in lateral lateral sections of the inertial mass 23 are formed to different expansion coefficients of the high-density second material 21 relative to the first material ("main material") of the inertial mass 23 compensate.

6 shows a cross-sectional view of another embodiment of the proposed micromechanical sensor 100 , In this case, the high density, second material 21 as two intermediate layers in the mechanical functional layer 20 and thereby into the inertial mass 23 introduced ("vertical stratification"). The number two is merely exemplary in this case and more or less layers of the second material may also be used 21 in the inertial mass 23 be educated. The second material 21 can be either over the entire area or to local areas of the inertial mass 23 be formed limited. In this way, advantageously, a good distribution of the high-density second material 21 within the inertial mass 23 to be provided.

Another, not shown in figures embodiment of the micromechanical sensor 100 Foresees that the stratification of the second, high-density material 21 in the inertial mass 23 is formed laterally ("lateral stratification").

Based on 7 to 12 Subsequently, a manufacturing process for producing the micromechanical sensor 100 explained.

In the cross-sectional view of 7 It is shown that a first substrate 10 optionally with integrated wiring lines, optionally with a buried etch stop layer 13 as well as a sacrificial layer 14 , for example from SiO ₂ .

The cross-sectional view of 8th shows an application of a mechanical functional layer 20 of a first material, for example in the form of a poly-silicon deposition or alternatively by layer transfer (application of a second substrate followed by bonding) to the substrate 10 ,

9 shows the arrangement of 8th after introducing etching holes into the mechanical functional layer 20 and refilling with a high density second material 21 (eg tungsten) by means of chemical vapor deposition (CVD), preferably down to the sacrificial layer 14 ( "Folding"). In the variant "layer transfer" (not shown) are parallel to vertical contacts to the buried wiring layer 12 produced. With this folding thin layer deposits can also be used to produce thick tungsten layers, whereby very high mass densities can be achieved simply and inexpensively.

The cross-sectional view of 10 shows a result after superficially removed excess, high density second material 21 , eg by means of chemical-mechanical polishing (W-CMP) or by anisotropic etching back. The deposition thickness of the high density second material 21 is chosen in such a way (or previously the width of the etching holes to be backfilled) that close the previously introduced etching holes superficially. In the case of the production of the second embodiment of the micromechanical sensor 100 (please refer 4 . 5 ), the etch holes are not completely filled and will later be used directly for sacrificial layer etching.

11 shows a result of optional deposition of a metallization layer 30a (eg in the form of aluminum) for bond pads and optionally as a bond metallization for the bond 30 , In addition, there is a structuring of the mechanical functional layer 20 , creating a contour of inertial mass 23 is provided and Opferschichtätzlöcher and optionally electrodes for the micromechanical sensor 100 to be provided. Furthermore, the mechanical functional areas of the inertial mass are exposed 23 by sacrificial layer etching.

12 shows an optional possible capping of the arrangement of 11 by means of a cap wafer 40 Wafer bonding and exposed bond pads 31 ,

13 shows a basic sequence of a method for producing a micromechanical sensor.

In one step 200 becomes a provision of a substrate 10 carried out.

In one step 210 becomes a placement of a mechanical functional layer 20 with an inertial mass formed therein 23 on the substrate 10 performed, being in the inertial mass 23 Formed areas of different mass densities being, being in the inertial mass 23 at least in sections, a second material 21 is arranged, which has a defined higher mass density than a first material of the inertial mass 23 ,

In one step 220 becomes adjacent to the inertial mass 23 at least one expansion gap 24 designed to compensate for different expansion coefficients of the two materials.

In summary, the present invention proposes a micromechanical sensor and a method for the production thereof, with which a micromechanical sensor with improved sensing properties due to increased inertial mass is provided, whereby by providing at least one expansion gap, different coefficients of expansion of the materials used are taken into account.

As a result, advantageously inertial sensors can be built much smaller or are much more sensitive or robust with the same size. Advantageously, already existing materials can be used in semiconductor manufacturing, which advantageously no introduction of other exotic materials is required.

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

• US 2015/0336790 A1 [0006]
• US 2016/0178656 A1 [0007]

Claims (10)

Micromechanical inertial sensor (100), comprising: a substrate (10); a mechanical functional layer (20) arranged on the substrate (10) with an inertial mass (23) formed therein; in which - The inertial mass (23) has regions of different mass density, wherein the inertial mass (23) at least in sections, a second material (21) having a defined higher mass density than a first material of the inertial mass (23); in which - The inertial mass (23) of at least one expansion gap (24) for compensating for different coefficients of expansion of the two materials is limited. Micromechanical inertial sensor (100) after Claim 1 , characterized in that a mass density of the second material (21) is between about four times and about nine times higher than a mass density of the first material of the inertial mass (23). Micromechanical inertial sensor (100) after Claim 1 or 2 , characterized in that the second material (21) has a bulk density of preferably> 6 Mg / m ³ , more preferably> 8 Mg / m ³ . A micromechanical inertial sensor (100) according to any one of the preceding claims, characterized in that the second material (21) of the inertial mass (23) is one of: tungsten, tantalum, hafnium, rhenium, osmium, iridium, platinum, gold, molybdenum, nickel or an alloy containing at least one of said elements. Micromechanical inertial sensor (100) according to one of the preceding claims, characterized in that the second material (21) in the inertial mass (23) is arranged in layers. Micromechanical inertial sensor (100) after Claim 5 , characterized in that the lamination of the second material (21) is formed laterally and / or vertically relative to a surface of the inertial mass (23). Micromechanical inertial sensor (100) according to one of the preceding claims, characterized in that the second material (21) is arranged like a lattice in the inertial mass (23). Micromechanical inertial sensor (100) according to one of the preceding claims, characterized in that the second material (21) is arranged in a cylinder-like manner around through holes (26) of the inertial mass (23). Micromechanical inertial sensor (100) according to one of the preceding claims, characterized in that the second material (21) has a defined higher elastic constant than the first material. A method of manufacturing a micromechanical inertial sensor (100), comprising the steps of: - Providing a substrate (10); - Arranging a mechanical functional layer (20) with an inertial mass (23) formed therein on the substrate (10), wherein in the inertial mass (23) regions of different mass density are formed, wherein in the inertial mass (23) at least partially a second material (21 ) having a defined higher mass density than a first material of the inertial mass (23); in which - Is formed adjacent to the inertial mass (23) at least one expansion gap (24) for equalizing different expansion coefficients of the two materials.

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