WO2005044720A1

WO2005044720A1 - Layout measures for limiting the propagation of surface cracks in mems

Info

Publication number: WO2005044720A1
Application number: PCT/DE2004/001954
Authority: WO
Inventors: Matthias Fuertsch; Heribert Weber; Detlef Gruen; Andreas Duell; Christoph Schelling; Klaus Eberle-Goubet; Joerg Baisch
Original assignee: Robert Bosch Gmbh
Priority date: 2003-10-07
Filing date: 2004-09-03
Publication date: 2005-05-19
Also published as: DE10346576A1

Abstract

The invention relates to a micromechanical component and a method for production of a micromechanical component, comprising at least one first, one second and one third region. The first and the second regions of the micromechanical component preferably have the same layer construction. The third region is arranged between the first and the second region. During use of the micromechanical component, for example, as mounting for a sensor element, cracks can arise in the component. Under unfavorable circumstances, said cracks can become enlarged or propagate on the surface of the micromechanical component. On assembly of the three regions, the third region has a higher susceptibility to crack propagation than the first and/or second regions. According to the invention, the third region and the both other regions are embodied such that crack propagation is preferably stopped in the third region in given positions on the component.

Description

LAYOUT MEASURES TO LIMIT THE SPREAD OF SURFACES IN MEMS

State of the art

The invention is based on a micromechanical component or on a method for producing a micromechanical component.

Common micromechanical sensors use membranes or thin layers as sensor elements or as carriers for sensor elements. The membranes or the thin layers are usually arranged in an enclosure on a micromechanical component. If the micromechanical component is now damaged, cracks may form and crack propagation may continue. If the crack propagates beyond the border onto the membrane or the thin layer, this can lead to a change in the sensor characteristic / characteristic curve. In extreme cases, such damage can even cause the sensor to fail completely. For example, in the case of a mass flow sensor as described in DE 199 52 055 AI, a further air mass measurement is possible even if there is a crack in the membrane. In contrast, in a pressure sensor such as that described in DE 197 23 333 AI, a crack in the membrane leads to a total failure of the sensor. To detect damage to a sensor membrane, a mass flow sensor is described in DE 197 35 666 A1, in which the breakage of a thin carrier is detected by a resistance element. The resistance element can be arranged both on the thin support and on the solid support on which the thin support is clamped. Advantages of the invention

The invention describes a micromechanical component or a method for producing a micromechanical component which has at least a first, a second and a third region. The first and the second region of the micromechanical component advantageously have the same layer structure. The third area is arranged between the first and the second area. During the use of the micromechanical component, for example as a holder for a sensor element, cracks can occur on the component. Under unfavorable circumstances, these cracks can enlarge or spread on the surface of the micromechanical component. In the construction of the three areas, the third area is more susceptible to crack propagation than the first and / or second area. According to the invention, the third area and the other two areas are designed such that the crack propagation is preferably stopped in the third area at predeterminable positions on the component.

One embodiment of the invention provides that the micromechanical component has a passivation and / or cover layer. Cracks can preferably occur in the passivation and / or cover layer, for example by mech. Notch effect after

Damage or tension during temperature exposure. Cracks continue to spread mainly on the top of the top layer. A CVD oxide layer can be used as the passivation and / or cover layer. All three areas are preferably evenly covered with the passivation and / or cover layer.

At least one of the three regions advantageously has an electrically conductive material, for example in the form of a conductor track or a resistance element. In addition, however, it can also be provided that a microelectronic component is accommodated in at least one of the regions. For example, a piezoelectric or capacitive resistance layer can be provided as the microelectronic component. In a development of the invention, the first and / or the second region of the micromechanical component has at least part of a conductor track. To protect the conductor tracks from oxidation and / or other environmental influences, the conductor track is covered by a cover layer. Furthermore, the third region can electrically isolate the first and the second region from one another. As already mentioned, it can be provided that the micromechanical component serves as an enclosure for a sensor element. In particular, it is provided that the first or the second region is designed as an enclosure of a membrane. According to the invention, the design of the layer structure of the three areas means that the crack propagation preferably takes place in the third area. The layer structure and the design of the third area are chosen such that a transition of the crack from the third to the first or second area is prevented. This can happen, for example, in that the first and the second area in the layer structure have a lower mechanical tensile stress than the layer structure in the third area.

Further advantages result from the following description of

Embodiments or from the dependent claims.

drawings

Figures la to lc show exemplary structures of how the third area between the first and the second area can be designed. FIG. 2 shows a cross section along line AB through the structure of the micromechanical component. FIG. 3 uses an example in the form of a membrane sensor to show how the structures of the three areas can be designed in order to stop crack propagation at predetermined locations on the component and to prevent cracks from reaching the membrane.

embodiment

The construction of micromechanical components, for example, for edging

Membrane sensors such as pressure sensors and mass flow sensors are generally based on a defined sequence of dielectric layers (e.g. silicon oxide and silicon nitride), silicon and / or materials for resistance measurement (e.g. platinum, Nickel, polysilicon) or temperature measurement. A precise representation of the various implementation options can be found, for example, in the fonts mentioned at the beginning or in common publications and should not be discussed further here.

It is worth mentioning, however, that the mechanical stress states of the individual deposited layers have to be coordinated with one another in order to produce an optimal stability of the structure. One of the goals of the coordination of the stress states is to increase the stability of the membrane against potential destruction by cracks which are induced in the membrane border. Cracks in the membrane frame can result from mechanical damage or from inhomogeneous mechanical stresses due to temperature loads. Furthermore, crack formation and propagation can be adversely affected by environmental conditions, such as moisture.

The tension states of the deposited layers should therefore be set so that the membrane itself is stable and does not break the layers adhering to one another due to intrinsic stress - the layers and membranes do not break even under different temperature loads exposure to moisture does not change the resistance material and the tendency to crack.

Due to the complex layer structures used in modern micromechanical sensors, however, not all requirements can always be met at the same time.

In addition, the local stress states of the successively deposited layers are determined by structuring the layers below, e.g. from conductor tracks to

Resistance measurement, change. This is due, for example, to the fact that the individual layers mutually change their voltage setting when temperature is applied can influence. A possible consequence of the different stress condition can be a different susceptibility to crack propagation or notch effect.

In order to prevent cracks from spreading, which preferably arise on the surface of the micromechanical component, the present invention relates to:

Layout measures, in particular for the conductor tracks, are proposed which stop the propagation of cracks at predetermined locations on the surface. Various third areas 110 are shown in FIGS. 1 a to 1 c, which separate a first area 100 from a second area 140. The structures which have the third regions 110 make it possible to stop crack propagation, as shown in FIG. 1b with the aid of the crack 120, at a predetermined point 130. A combination of the structures, as shown for example in Figure la-c, can prevent crack propagation in several directions, since a multiple change in the course of the cracks with small, alternating positive and negative radii of curvature is very unlikely and can rarely be observed ,

A cross section along the line AB through the structure in FIG. 1a shows the structure of the micromechanical component. One or more layers 210 were deposited on a substrate 200. Conductor tracks 220 and 230 are partially applied to the last layer 210, for example to control one with the micromechanical one

Component connected sensor element are provided. However, in order to create a stop structure for cracks, structures as shown in FIGS. 1 a to 1 c are left out of the conductor tracks. One or more passivation and / or cover layers 240 are applied to the conductor tracks 220 and 230 in order to protect the conductor tracks from oxidation or other damaging environmental influences. By the shown in Figure 2

Construction of conductor tracks 220 and 230 with a covering cover layer 240 leads to the formation of different areas with different physical properties. If the cover layer 240 is applied uniformly, the first and third areas can be recognized by a height offset, for example (see FIG. 2). For simplification, it should be assumed in FIG. 2 that both the first and the second region have a conductor track 230 or 220 made of the same material. In addition, however, it can be provided that one of the conductor tracks consists of a dielectric material or that a conductor track is provided only on one side of the third region 110. In this case For example, the marked area 220 in FIG. 2 could have a special form of doping or passivation.

Assuming that the marked areas 220 and 230 consist of the same conductor material and the cover layer 240 is applied uniformly to the micromechanical component, first and second areas 100 and 140, which have a low tensile stress in the cover layer, are formed when the materials are selected accordingly , At the same time, this design of the component leads to a locally increased tensile stress in the cover layer (s) in the third region 110. This increased tensile stress in the third region 110 leads more easily to crack formation or crack propagation than in the other two

Areas 100 and 140. However, if this crack development meets a structure that consists of a different material or a differently designed layer system and would require a deflection of the crack with a small radius of curvature, this can inhibit the spread of the crack. This inhibiting effect is greater, the more different the materials of the first or second region and the third region are and the smaller the radii of curvature and the narrower the region 110. For example, it can be demonstrated that when platinum is used as the conductor or resistance material and CVD oxide as the passivation and cover layer, cracks in the cover layer preferentially propagate in the platinum-free area.

If a structure as shown in FIGS. 1 a to 1 c is now applied between the areas 100 and 140, a crack will preferably spread along the third area 110. However, if the crack encounters a transition from the third area 110 to the first (100) or second (140) area during its spreading, the tensile stress in the cover layer decreases in such a way that the crack cannot spread any further. This crack stop, as shown, for example, in FIG. 1b in area 130, is further supported by the fact that, as already mentioned, a multiple change in the course of the cracks with small, alternating positive and negative radii of curvature is very unlikely and can only be observed rarely. As a result, a structure of the third region 110, which is very jagged and angled, can generate a crack stop or at least significantly slow down the crack propagation. The spread of cracks on micromechanical components can have very devastating effects on the sensor properties, especially when the components are used as bezels for thin layers or membranes that are used as sensor elements. A crack can result in the irreversible failure of the sensor if the crack spreads to the membrane or the sensor element.

A possible application example of the proposed invention in the form of a membrane sensor is shown in FIG. 3. Here, a sensor element 300 is shown on a membrane 310, which in turn is housed in an enclosure 330. The critical transition for crack propagation is shown in FIG. 3 as a membrane edge 320 between the border 330 and the membrane 310. Crack stop structures are also shown in the region 340, which prevent a possible crack from propagating, for example, from the border 330 onto the membrane 310.

In addition to the angular shape of the membrane 300 shown in FIG. 3, however, any other shape of a membrane can also be at least partially surrounded with a corresponding design of the structures in the third region. Round, oval or hexagonal membranes are often used, which can then also be partially surrounded, for example, with crack stop structures according to FIGS. 1 a to c.

In the manufacture of a sensor according to FIG. 3, the membrane 300 and at least part of the surround 360 are usually realized by a similar structure of the layer structures. This has the consequence that cracks, for example due to damage or due to intrinsic stress in the casing 360 in structured areas with locally increased mech. Tensile stress, e.g. between conductor tracks, and then follow the areas of highest tensile stress, continue to the membrane without encountering any significant resistance. On the one hand, due to the layout - in the case of the conductor tracks discussed - the crack experiences a certain amount of guidance. On the other hand, for energy reasons, cracks propagate in a straight line, preferably in one direction. Changes in direction with small radii of curvature are therefore not observed (see

Figure lb). The first (100), second (140) and third (1 10) areas can thus be designed by suitable layout measures in such a way that crack propagation on the surface is at least partially restricted or significantly reduced to a defined area.

Claims

Expectations

1. Micromechanical component, the component at least - a first region (100) and

- A second area (140) and

- A third area (110), wherein it is provided that

- The first and the second region at least partially have the same layer structure, and

- The third area is at least partially arranged between the first and the second area, wherein

Cracks occur on the component and can spread and the third area is more susceptible to crack propagation than the first or second area, characterized in that the third area and at least one of the other two areas are designed such that the crack propagation is stopped at predefinable positions (130) on the component.

2. Micromechanical component according to claim 1, characterized in that the component has a passivation and / or cover layer (240), it being provided in particular that

- The cracks preferably in the passivation and / or top layer - arise and / or spread, and / or

- The passivation and / or cover layer covers all three areas and / or - is realized by a CVD oxide layer.

3. Micromechanical component according to claim 1, characterized in that at least one of the three areas has a dielectric material, and / or has a microelectronic component, a piezoelectric resistor being provided in particular as the microelectronic component.

4. Micromechanical component according to claim 1, characterized in that

- The first (100) and / or second (140) region has at least part of a conductor track (220, 230), it being provided in particular that the conductor track is covered with a cover layer, and / or

- The third (140) area the first and the second area electrically isolated from each other, and / or

- The first or second area has a border of a membrane (300) and / or

- Crack propagation in the third area (110) ends when the transition to the first or second area is reached.

5. Micromechanical component according to claim 1, characterized in that the third

Area (110) is shaped at least in sections so that it has multiple changes in direction with small positive and negative radii of curvature with a small lateral extent.

6. The micromechanical component according to claim 1, characterized in that the third region (III) stands out as a depression from a basic level, it being provided that the basic level defines itself over the surface of the first and / or second region.

7. The method for producing a micromechanical component, in particular a micromechanical component according to one of claims 1 to 6, wherein the component at least

- A first area (100) and

- A second area (140) and

- A third area (110), wherein it is provided that

- The first and the second region at least partially have the same layer structure, and - The third area is at least partially arranged between the first and the second area, wherein

- cracks appear on the component and can spread and

- The third area has a higher susceptibility to crack propagation compared to the first or second area, characterized in that the third area and at least one of the other two areas is designed in such a way that the crack propagation stops at predeterminable positions (130) on the component becomes.

8. The method according to claim 7, characterized in that a passivation and / or cover layer is applied to the component, it being provided in particular that

- The cracks preferably arise in the passivation and / or cover layer (240) - and / or can spread, and / or

- The passivation and / or cover layer - covers all three areas and / or is realized by a CVD oxide layer.

9. The method according to claim 7, characterized in that at least one of the three regions - has a dielectric material and / or has a microelectronic component, a piezoelectric resistor being provided in particular as the microelectronic component.

10. The method according to claim 7, characterized in that the first and / or second region has at least part of a conductor track (220, 230), it being provided in particular that the conductor track is covered with a cover layer, and / or - The third area the first and the second area electrically isolated from each other, and / or

- The first or second area has a border of a membrane (300) and / or

- Crack propagation in the third area ends when the transition to the first or second area is reached.

11. The method according to claim 7, characterized in that the third area stands out as a depression from a basic level, it being provided that the basic level defines itself over the surface of the first and / or second area.