阅读说明：本技术 微机械构件和用于制造微机械构件的方法 (Micromechanical component and method for producing a micromechanical component ) 是由 J·赖因穆特 R·毛尔 于 2019-06-27 设计创作，主要内容包括：本发明涉及一种微机械构件(1),尤其是转速传感器,具有具有主延伸平面的衬底(10)和至少一个质量振子(12),质量振子(12)通过一个或多个弹簧元件(13)相对于衬底(10)能振动地支承,其中,至少一个弹簧元件(13)具有第一弹簧部分元件(14)和第二弹簧部分元件(15),第一弹簧部分元件(14)和第二弹簧部分元件(15)在垂直于主延伸平面的垂直方向(18)上叠置地布置并且在该垂直方向(18)上彼此间隔开。本发明涉及一种制造微机械构件(1)的方法。(The invention relates to a micromechanical component (1), in particular a tachometer, having a substrate (10) having a main plane of extension and having at least one mass pendulum (12), the mass pendulum (12) being mounted so as to be able to oscillate relative to the substrate (10) by means of one or more spring elements (13), wherein the at least one spring element (13) has a first spring element part (14) and a second spring element part (15), the first spring element part (14) and the second spring element part (15) being arranged one above the other in a vertical direction (18) perpendicular to the main plane of extension and being spaced apart from one another in the vertical direction (18). The invention relates to a method for producing a micromechanical component (1).)

1. Micromechanical component (1), in particular a tachometer, having a substrate (10) with a main plane of extension and at least one mass pendulum (12), wherein the mass pendulum (12) is supported in a manner that can be vibrated relative to the substrate (10) by means of one or more spring elements (13), characterized in that the at least one spring element (13) has a first spring part element (14) and a second spring part element (15), wherein the first spring part element (14) and the second spring part element (15) are arranged one above the other in a vertical direction (18) perpendicular to the main plane of extension and are spaced apart from one another in the vertical direction (18).

2. Micromechanical component (1) according to claim 1, wherein a vertical distance between the first spring part element (14) and the second spring part element (15) is greater than a vertical extension of the first spring part element (14) and a vertical extension of the second spring part element (15).

3. Micromechanical component (1) according to claim 1 or 2, wherein a stiffening structure (27) is arranged between the first spring part element (14) and the second spring part element (15) at least in a partial region (28).

4. Micromechanical component (1) according to claim 3, wherein the stiffening structure (27) has a high stiffness and/or the spring part elements (14,15) have a large width in the region (28) of the stiffening structure (27).

5. Micromechanical component (1) according to any of the preceding claims, wherein the first spring part element (14) and the second spring part element (15) have substantially the same cross section and/or extend parallel to each other.

6. Method for producing a micromechanical component (1), in which,

-depositing a first functional layer having a main extension plane in a first step,

-producing a first spring part element (14) in a second step by etching the first functional layer,

-depositing a second functional layer in a third step, wherein the second functional layer is arranged above the first functional layer in a vertical direction (18) perpendicular to the main plane of extension,

-producing a second spring part element (15) in a fourth step by etching the second functional layer such that the second spring part element (15) overlaps the first spring part element (14) in the vertical direction (18).

7. The method of claim 6, wherein the depositing of the first and second functional layers is performed such that the first and second functional layers have substantially the same thickness.

8. Method according to claim 6 or 7, wherein the etching of the first and second functional layers is carried out such that the first spring part element (14) and the second spring part element (15) have substantially the same etching angle (20).

9. Method according to one of claims 6 to 8, wherein a third functional layer is deposited in a fifth step after the first step and before the third step, wherein the third functional layer is arranged between the first functional layer and the second functional layer.

10. Method according to one of claims 6 to 9, wherein a reinforcement structure (27) is produced in a step following the fifth step by etching the third functional layer such that the reinforcement structure (27) overlaps the first spring element (14) and the second spring element (15) in a vertical direction (18).

Technical Field

The present invention relates to a micromechanical component and to a method for producing a micromechanical component.

Background

Micromechanical components and methods for their production are known from the prior art in various embodiments. A method for producing micromechanical sensors acceleration sensors and rotational speed sensors is described in the publication DE 19537814 a1, for example. With this and similar methods, a silicon structure is created that also moves, the movement of which is measured by determining the change in capacitance. A feature and a further discussion of such methods is that the movable silicon structure is produced in a first step by an etching process, wherein trenches are produced in the silicon layer with a large aspect ratio (DE 4241045C 1). In a second step, the sacrificial layer (mostly an oxide layer, see for example DE 4317274 a1) is removed below the silicon layer. Thus, a silicon structure is obtained which is freely movable with respect to the base.

Furthermore, a method is known from DE 102011080978 a1, with which a plurality of movable MEMS structures can be arranged one above the other. With this and other OMM techniques (surface micromachining techniques), tacho sensors can be constructed. It is essential in all these methods that the structuring of the functional layer does not take place exactly vertically and that there is always a certain manufacturing deviation of the trench angle (i.e. the angle of the side walls of the structure produced by etching). Furthermore, there is always a certain manufacturing variation of the width of the trench structure. The trend is that the thicker the layer, the greater the width fluctuation of the trench structure. These effects lead to a reduction in the measurement accuracy of the known OMM tachometer sensors.

The known OMM rotational speed sensors are mostly based on the following basic concept:

the two masses (movable OMM structures) oscillate in anti-parallel. By means of coriolis forces, the masses are deflected perpendicularly to the respective direction of motion, wherein the perpendicular deflection of the two masses also takes place antiparallel. The deflection is measured and corresponds to the rotational speed to be measured. Due to the antiparallel deflections, the rotational speeds exerted on the component and the accelerations which lead to parallel deflections can be clearly distinguished in the measurement.

The above-mentioned non-precise vertical slot angles cause the masses to also respectively perform a movement perpendicular to the desired direction of movement. These masses thus perform an oscillating movement. The wobble movements always cause an error signal (so-called Quadratur, quadrature) due to their direction of movement. Such false signals are undesirable and reduce the sensitivity of the sensor.

For a sensor intended to detect rotation perpendicular to the plane of the substrate, the two moving masses are also excited to vibrate in this plane, here perpendicular to the detection direction. In this case, however, the deflection of the proof mass in a plane perpendicular to the direction of motion of the proof mass is detected. Due to the deviation of the width of the groove structure, in particular the spring structure, the movable mass is suspended on a spring of slightly different stiffness. This asymmetry in the spring suspension results in a swinging motion in the plane. This wobbling motion leads to undesired false signals similar to the first example.

Disclosure of Invention

Against this background, it is an object of the present invention to provide a device and a method for producing a rotation speed sensor, which have a reduced quadrature difference. Furthermore, it is an object of the invention to provide a device and a production method with which a reduced-size rotation speed sensor can be realized.

According to the invention, a micromechanical component, in particular a tachometer, is proposed, having a substrate with a main plane of extension and at least one mass resonator, wherein the mass resonator is supported in a manner that can be vibrated relative to the substrate by means of one or more spring elements, wherein the at least one spring element has a first spring part element and a second spring part element, wherein the first spring part element and the second spring part element are arranged one above the other in a vertical direction perpendicular to the main plane of extension and are spaced apart from one another in the vertical direction.

The micromechanical component according to the invention has the advantage over the prior art that the manufacturing tolerances in terms of width and groove angle are less important if the spring element is composed of two spring part elements spaced apart from one another than if it were a one-piece spring element with comparable vertical dimensions. The concept "vertical" refers to a direction perpendicular to the plane of the substrate, implying a relationship with the direction of gravity. The vertical dimension of the spring element or of the one-piece spring element corresponds to the thickness of the layer from which the corresponding structures are etched. The directions parallel to the substrate plane are also referred to below as "lateral", and the movements or deformations in these directions are referred to as vertical and lateral degrees of freedom, respectively. The shape and dimensions of the spring element, in particular the dimensions of the cross section, determine the behavior, in particular the bending stiffness, at various deformations (in addition to the material anisotropy caused, for example, by the crystal structure). The following discussion will be limited to a simple beam spring of constant cross-section with the upper and lower sides parallel to each other and the side walls defined by the groove angle. The inventive concept is not so limited and may be applied to more complex spring geometries. In the case of a perfect perpendicular groove angle, the cross section of the spring element is substantially rectangular. The transverse and vertical dimensions (i.e. width and height) of the cross-section determine here the flexural rigidity in the transverse and vertical directions, respectively. In the case of a perfectly rectangular cross section, these two degrees of freedom are decoupled from one another, i.e. bending in the vertical direction or in the transverse direction only produces a stress in the vertical direction or in the transverse direction, respectively, so that the transversely excited bending vibration of the spring element remains in the transverse plane over a further period of time. In contrast, deviations of the groove angle from the perpendicular angle (i.e. the cross section in the case of sides not perpendicular to each other) result in a mechanical coupling of these two degrees of freedom. In this case, in particular, bending in the transverse direction leads to stresses in the vertical direction, so that the transversely excited bending vibrations always contain a component in the vertical direction, as a result of which quadrature errors occur. The strength of the lateral-vertical coupling is determined on the one hand by the trench angle and on the other hand by the aspect ratio (i.e. the ratio of the lateral dimension to the vertical dimension or height to width), wherein the greater the aspect ratio the greater the degree of coupling.

The core idea of the invention is now to replace the one-piece spring element with a high aspect ratio with two spring part elements, the aspect ratios of which are respectively smaller and which together spring the suspended mass resonator by bending in the transverse direction. The prerequisite for a transverse vibration behavior that is as undistorted as possible is that the two spring element sections are arranged one above the other in the vertical direction as precisely as possible, so that the two spring element sections overlap one another when viewed in the vertical direction. "covering" is to be understood here to mean that, in the case of a perpendicular projection of the spring element part onto the main plane of extension, the two projections overlap or preferably overlap to the greatest extent or particularly preferably even overlap. Such a covering of the two spring part elements can be achieved in an advantageously simple manner if the two spring part elements are etched separately from the two superposed layers, since in modern production methods a high precision of the relative arrangement and orientation of the etched structures can be achieved.

In addition to an increased robustness against manufacturing tolerances, smaller sensors can be realized with the device according to the invention. Preferably, the spring element has a clearance between the first and second spring part elements. A spring element consisting of two spring part elements has a lower stiffness than a one-piece spring element with the same width and the same overall height, since the gap between the two spring part elements reduces the overall stiffness. Thus, a desired spring constant can be achieved with a shorter spring element, thereby advantageously reducing the size of the component.

According to a preferred embodiment of the invention, the vertical distance between the first and second spring part elements is greater than the vertical extension of the first spring part element and the vertical extension of the second spring part element. If the spring consists of two thin spring part elements, the distance in the vertical direction of the spring part elements being greater than the vertical extension of the spring part elements, the influence of the groove angle on the orthogonality is of minor importance. What is decisive for the Out-of-Plane (Out-of-Plane) pivoting movement is how well the two spring elements are aligned with each other. Overlay accuracy is well achieved in modern semiconductor manufacturing processes. This accuracy is significantly higher than the trench angle-dependent misalignment that can best be achieved from top to bottom on a 20 micron thick layer. Thus, a more sensitive sensor detecting rotation in the plane of the substrate can be manufactured.

According to a further preferred embodiment of the invention, a reinforcing structure is arranged between the first and second spring part elements at least in a partial region. The reinforcement structure can be realized, for example, by depositing three superimposed layers in the manufacturing process, wherein two spring part elements are etched out of the first and third layer and the reinforcement structure is etched out of the second layer. The reinforcing structure preferably does not extend over the entire length of the spring element, but rather connects the two spring sub-elements only in partial regions. By means of this local connection, the stiffness of the spring element in the transverse direction is only partially significantly changed, while the stiffness in the vertical direction is significantly increased. Since the rigidity in the vertical direction (out-of-plane rigidity) is improved, vibration in the vertical direction is suppressed and the orthogonal contribution is favorably reduced.

According to a further preferred embodiment of the invention, the stiffening structure has a higher stiffness and/or the spring part elements have a larger width in the region of the stiffening structure. In this way, the out-of-plane stiffness in the stiffening region is purposefully increased, so that the orthogonal contribution of the stiffening structure is advantageously minimized.

According to a further preferred embodiment of the invention, the first and second spring part elements have substantially the same cross section and/or extend parallel to one another.

The object of the invention mentioned at the outset is also achieved by the process according to the invention. According to the invention, a method for producing a micromechanical component is proposed, in which a first functional layer having a main plane of extension is deposited in a first step, a first spring element is produced in a second step by etching the first functional layer, a second functional layer is deposited in a third step, the second functional layer being arranged above the first functional layer in a vertical direction perpendicular to the main plane of extension, and a second spring element is produced in a fourth step by etching the second functional layer, such that the second spring element overlaps the first spring element in the vertical direction.

Each of the two spring part elements is produced in a separate deposition process and etching process, wherein the etching is carried out in such a way that the two spring part elements are arranged as precisely as possible one above the other. If the spring is formed from two thin spring part elements, then, due to the smaller layer thickness, smaller fluctuations in the width of the individual partial springs are achieved during the production process. Due to the expected smaller deviations in the width of the spring, the pendulum movement in the plane can also be reduced. A more sensitive sensor detecting rotation perpendicular to the plane of the substrate can thus be manufactured. Since the spring part element is made of a relatively thin layer, the desired mechanical properties, such as low fluctuation of the spring modulus or consistency of the crystal structure, can be achieved more easily. As a result, the spring element produced in this way is of better quality, for example with regard to pre-deflection or stiffness deviation.

According to a preferred embodiment of the method according to the invention, the deposition of the first and second functional layers is carried out such that the first and second functional layers have substantially the same thickness. In this way, a spring element with similar or identical vertical dimensions is advantageously produced by subsequent etching.

According to a further preferred embodiment of the method according to the invention, the etching of the first and second functional layers is carried out such that the first and second spring part elements have substantially the same etching angle. This can be achieved, for example, by: the first and second functional layers are etched with a technically identical or at least similar etching method, so that the two spring portions have the same or very similar etching angle. In this way, it is advantageously possible to produce spring element sections with substantially identical or very similar cross sections.

According to a further preferred embodiment of the method according to the invention, a third functional layer is deposited in a fifth step after the first step and before the third step, wherein the third functional layer is arranged between the first and the second functional layer. The third functional layer is advantageously such that the first and second layers deposited in the preceding and following steps are separated by the thickness of the third functional layer.

According to a further preferred embodiment of the method according to the invention, in a step following the fifth step, the reinforcement structure is produced by etching the third functional layer such that the reinforcement structure, viewed in the vertical direction, overlaps the first and second spring elements. In this manner, spring elements having the same or higher out-of-plane stiffness as prior art unitary spring elements can be manufactured (as described above with respect to the stiffening structures). The spring element thus produced has a greater overall height than a spring element etched out only from the thick functional layer, since it is constructed from partial elements which are each located below and above the thick functional layer and are combined with reinforcing elements. Thus, the new spring is significantly stiffer in the vertical direction. Parasitic vibration modes can be advantageously reduced.

Drawings

Fig. 1 shows a schematic representation of a rotational speed sensor according to the prior art.

Fig. 2 shows a schematic representation of another rotational speed sensor according to the prior art.

Fig. 3a-d show a schematic representation of the detection principle of the measurement signal of a tachometer and the distortions caused by manufacturing tolerances according to the prior art.

Fig. 4 shows a schematic representation of a rotation speed sensor according to the prior art and a cross section of the associated spring element in a schematic representation.

Fig. 5 shows a schematic representation of a cross section of a rotational speed sensor and a dependent spring element according to an embodiment of the invention.

Fig. 6 shows a schematic representation of a further cross section of a rotational speed sensor and a dependent spring element according to an embodiment of the invention.

Detailed Description

Fig. 1 shows a rotation speed sensor 1 according to the prior art. In the manufacture of such a sensor 1, the silicon structure 2 is typically manufactured by depositing a thick silicon layer and then etching the layer. Upon etching, a trench 3 (channel trench) having a high aspect ratio is generated in the silicon layer. The sacrificial layer arranged below the thick silicon layer is removed in a second step, so that a movement of the silicon structure 2 relative to the substrate 10 is made possible due to the resulting vertical gap 4. A thin polysilicon layer can also be arranged below the movable structure 2, from which further elements 5,6 are produced by etching, which elements can serve, for example, as suspension means 5 or electrodes 6.

Fig. 2 shows a further rotation speed sensor 1 according to the prior art. In the embodiment shown, the conductor rails 7 are produced by etching from a thin polysilicon layer. The movable structure 2 of the sensor 1 is protected hermetically by a cover 8. The cap wafer 8 can be applied to the sensor wafer with different bonding methods, for example by means of a connecting material 11 that secures the cap 8 to the sensor wafer. A set cavity 9 is reached in the cover 8.

The detection principle of a tachometer sensor 1 according to the prior art is shown in fig. 3 a-c. For this purpose, two mass oscillators 12, each suspended on a spring element 13, are excited to perform an anti-parallel oscillation. In fig. 3a, such an anti-parallel vibration is shown without external forces, i.e. in case the sensor 1 is stationary. If, on the other hand, a rotational speed 17 is applied to the sensor, the rotational axis of which has a component perpendicular to the oscillation direction of the mass oscillator 12 (fig. 3c), a coriolis force acts on the mass oscillator, which leads to an additional deflection perpendicular to the oscillation direction and perpendicular to the rotational axis. The antiparallel directions of movement are correspondingly subjected to antiparallel deflections here, while during the presence of an external (linear) acceleration 16 in the case shown in fig. 3b, the two masses 12 are caused to deflect in the same direction (downward in the case shown, in the direction of the substrate). Thus, by comparing the deflections of the two masses 12, the effect of the applied rotational speed 17 can be clearly separated from the effect of the applied acceleration 16. Fig. 3d shows the distortion of the measurement signal caused by manufacturing tolerances. In order to be able to fully utilize the detection principle of fig. 3c without distortion, the degrees of freedom of movement in the transverse direction 19 and in the vertical direction 18 must be decoupled from one another. The transverse direction 19 is understood here to be a direction parallel to the plane of the substrate. In the two-dimensional figure shown, the transverse direction 18 corresponds to the horizontal direction of the paper, but this schematically represents a motion which may also have a component perpendicular to the paper. Due to fluctuations in the production process, in particular due to the non-exactly vertical groove angle of the spring element 13, a mechanical coupling of the lateral and vertical degrees of freedom occurs, so that the movement of the mass pendulum 12, in addition to the desired oscillation direction 19, also contains a component in the vertical direction 18 without external forces and the mass pendulum 12 thus executes the pendulum movement shown in fig. 3 d. This oscillatory motion due to unwanted coupling cannot in principle be distinguished from the vertical deflection caused by the coriolis force in fig. 3 c. The corresponding error signal is also referred to as quadrature difference and disadvantageously reduces the sensitivity of the rotation speed sensor 1.

Fig. 4 shows a tachometer sensor with typical manufacturing tolerances. In the top view on the right in the figure, a mass oscillator 12 is shown, which is connected to the suspension 5 via four spring elements 13 and can be excited to vibrate relative to the substrate 10 (not shown in the top view) by means of an electrostatic drive 23. Also marked in this top view is a sectional plane a, which extends through the spring element 13. The corresponding cross-section is shown on the left side of the top view. To understand the way in which the device of the invention functions and its differences from the prior art, it is intuitive to see that the spring 13 can be broken into two parts. Roughly speaking, in the case of the prior art spring 13, no swinging motion is caused if the center of gravity 21 of the upper part is above the center of gravity 22 of the lower part (upper and lower are understood here with respect to the substrate 10). If the spring is slotted obliquely (i.e. at a non-zero angle 20 with respect to the vertical), the two centers of gravity 21,22 are no longer stacked one above the other and a swinging movement occurs.

Fig. 5 shows a rotation speed sensor 1 according to an embodiment of the invention. The section of the sectional plane B depending on and marked in top view is shown on the left. In contrast to the spring cross section shown in fig. 4, the spring element 13 is formed here from two spring part elements 14 and 15, which have a width 26 comparable to the spring element 13 in fig. 4. Each etched from two separate thin layers, where a non-precisely perpendicular channel angle is formed, similar to fig. 4. However, each spring part element 14 and 15 has a significantly smaller aspect ratio (height to width) itself, so that the oblique channel angle results in significantly less coupling between the lateral and vertical degrees of freedom. The coupling is also small for the entire spring 13, provided that the center of gravity 25 of the second spring element 15 is located as precisely as possible above the center of gravity 24 of the first spring element 14. Unlike fig. 4, the offset between lower center of gravity 24 and upper center of gravity 25 is not determined by the channel angle, but by the relative lateral position of spring elements 14 and 15 with respect to one another, which can be produced very precisely in modern manufacturing methods.

Fig. 6 shows the spring element 13 from fig. 5 together with a sectional plane C, which intersects the stiffening region 28 of the spring element 13. In the reinforcement region 28, on the one hand, the width 26 of the spring part elements 24 and 25 is selected to be greater than in the remaining regions (see the width 26 in the sectional plane B in fig. 5), and on the other hand, a reinforcement structure 27 is arranged between the spring part elements 24 and 25. In manufacturing, the reinforcing structure 27 is manufactured by depositing thick layers arranged between thin layers from which the spring part elements 24 and 25 are etched. By means of the reinforcing structure 27, the spring element 13 obtains a significantly higher bending stiffness in the vertical direction, so that vibrations in this direction are effectively suppressed.