Patent Publication Number: US-2023152572-A1

Title: Micromechanical device

Description:
FIELD 
     The present invention relates to a micromechanical device, in particular a micromirror device, and to a method for producing the micromechanical device. 
     BACKGROUND INFORMATION 
     A micromirror device is described in U.S. Pat. Application Publication No. US 2018/0307038 A1 in the form of a micromechanical device in which mirror plate and spring element are arranged in different, mutually parallel planes and are joined together by a further element in an intermediate plane. This is intended to reduce the dynamic deformation of the mirror element. 
     One problem which arises in this connection is that, on displacement of the mirror, a peak strain arises locally at the right-angled transition from mirror plate to connection element which may lead to breakage of the component at this edge. 
     Starting from this related art, it is an object of the present invention to develop a micromechanical device which is more robust under dynamic load. 
     SUMMARY 
     To achieve the object, a micromechanical device, and a method for producing the micromechanical device are provided according to example embodiments of the present invention. 
     The micromechanical device in particular represents a micromirror device. Alternatively, the micromechanical device is configured in particular as a micromechanical pressure sensor or micromechanical inertial sensor or micromechanical pump. According to an example embodiment of the present invention, the micromechanical device has at least one first micromechanical component and one second micromechanical component. The first component and the second component are directly or indirectly joined to one another. The first and/or second micromechanical component preferably takes the form of a semiconductor material, in particular silicon. The first micromechanical component has a first sub-body and at least one second sub-body. The first micromechanical component is in this respect in particular of one-piece construction. The first sub-body extends in a first plane and the second sub-body in a second plane different from the first plane. The first and second planes extend parallel to one another, the first plane extending above the second plane. In particular, the first and second planes are horizontally extending planes. In particular, the first and second sub-bodies are separated from one another along a parting plane, in particular a horizontal parting plane. The second sub-body is arranged in a transitional region to the second micromechanical component. The transitional region here represents in particular an indirect or direct connection region of the first micromechanical component to the second micromechanical component. A second extent of the second sub-body in the longitudinal direction, in particular in the second plane, is here greater than a first extent of the first sub-body in the longitudinal direction, in particular in the first plane. The extents in the longitudinal direction of the respective sub-bodies are here in particular taken to mean the distances from outer edge to outer edge of the first and second sub-bodies in horizontal direction. The first and second sub-regions preferably overlap at least in part and the resultant, outwardly protruding step between first and second sub-bodies leads to the dynamic loading arising being subdivided between two edges. The micromechanical device can thus withstand higher dynamic loading. The first sub-body is preferably arranged centrally above the second sub-body. 
     According to an example embodiment of the present invention, the second micromechanical component is preferably arranged in a plane of the micromechanical device different from the first and second planes. The third plane here extends parallel to the first and second planes. Thus, the second micromechanical component fulfills a supporting function for the first micromechanical component. 
     According to an example embodiment of the present invention, the first and second micromechanical components are preferably made in one piece from silicon, in particular crystalline silicon. In this connection, the second sub-body of the first micromechanical component at least in part directly adjoins the second micromechanical component. In the transitional region between the first and second micromechanical components, the two micromechanical components are accordingly not materially separate from one another. Such a micromechanical device has the fabrication-related advantage that just one single, in particular plate-shaped, silicon substrate is required for fabrication. 
     Alternatively, the first and second micromechanical components are preferably made from silicon. The micromechanical device in this respect additionally has at least one silicon oxide layer. The first and second micromechanical components are joined, in particular bonded, by way of the silicon oxide layer. The second sub-body of the first micromechanical component preferably at least in part directly adjoins the silicon oxide layer. In the transitional region between the first and second micromechanical components, the two micromechanical components are accordingly materially separate from one another. 
     According to an example embodiment of the present invention, the micromechanical device is preferably configured as a micromirror device. In this connection, the first micromechanical component is configured as a micromirror and the second micromechanical component as an, in particular resilient, spring element. One challenge when designing micromirrors is how to achieve large displacement angles. The greater the displacement angle, the higher the stress loading on the spring. Such stress loading may however lead to breaks in the transitional edges between spring element and micromirror. The additional step between first and second sub-bodies now enables the dynamic loading arising to be subdivided between two edges. The consequence is that the micromirror device can be operated with greater displacement angles. 
     According to an example embodiment of the present invention, a shape and/or the second extent of the second sub-body in the longitudinal direction and/or a height of the second sub-body is/are preferably selected as a function of a predetermined mechanical strain distribution of the micromechanical device. Preferably, the height of the second sub-body in relation to the first sub-body is selected such that the stress is uniformly distributed and/or such that, in the case of the silicon oxide layer, as much strain as possible is removed from the silicon oxide layer. To this end, the height of the second sub-body is preferably selected to be distinctly less than the height of the first sub-body. The ratio of the height of the second sub-body to the height of the first sub-body preferably amounts to at least 1:10. A length of the outwardly protruding step between first and second sub-bodies, in particular a lengthwise extent of the second sub-face of the second sub-body, is preferably greater than the height of the second sub-body. In other words, the resultant step is preferably longer than it is high. The second sub-body preferably has a height of at least 10 µm and at most 20 µm. The outwardly protruding step between the first and second sub-bodies, in particular the lengthwise extent of the second sub-face of the second sub-body, has a length of at least 30 µm and at most 50 µm. 
     According to an example embodiment of the present invention, the first and second sub-bodies of the first micromechanical component preferably have a rectangular cross-section. The step between the first and second sub-bodies thus has an edge, in particular of 90°, and the outer side of the second sub-body extends in a sixth plane, which extends substantially perpendicular to the first and/or second planes. Alternatively, the second sub-body of the first micromechanical device has a first sub-face, which extends at least in part in a fourth plane. This fourth plane extends obliquely to the first and/or second and/or third planes. The step between the first and second sub-bodies may thus have an obliquely extending outer side, extending in particular concavely or convexly or with a uniform gradient. 
     The second sub-body of the first micromechanical device preferably has a second sub-face, which extends in a fifth plane, in particular a parting plane of the first from the second sub-body, the fifth plane extending parallel to the first and/or second and/or third planes. The step between the first and second sub-bodies thus has a planar sub-face. 
     The present invention also provides a method for producing a micromechanical device as described above, in particular a micromirror device. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1 A  shows a first example embodiment of a micromechanical device, according to the present invention. 
         FIG.  1 B  shows a method for producing the first example embodiment of the micromechanical device, according to the present invention. 
         FIG.  2 A  shows a second example embodiment of a micromechanical device, according to the present invention. 
         FIG.  2 B  shows a method for producing the second example embodiment of the micromechanical device, according to the present invention. 
         FIG.  3 A  shows a third example embodiment of a micromechanical device, according to the present invention. 
         FIG.  3 B  shows a method for producing the third example embodiment of the micromechanical device, according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS 
       FIG.  1 A  is a schematic representation of a first embodiment of a micromechanical device  1   a . The micromechanical device  1   a  is here preferably configured as a micromirror device. The micromechanical device  1   a  has a first micromechanical component  2   a  and a second micromechanical component  3   a . The first component  2   a  and the second component  3   a  are here indirectly joined to one another via a silicon oxide layer  7   a . The first micromechanical component  2   a  has a first sub-body  4   a  and at least one second sub-body  5   a . The first sub-body  4   a  extends in a first plane  20   a  and the second sub-body  5   a  in a second plane  21   a  different from the first plane  20   a . The first plane  20   a  and the second plane  21   a  extend parallel to one another, the first plane  20   a  extending above the second plane  21   a . The second sub-body  5   a  is arranged in a transitional region to the second micromechanical component  3   a . In this first exemplary embodiment, in the transitional region, the bottom  31   a  of the second sub-body  5   a  of the first micromechanical component 1a directly adjoins the silicon oxide layer  7   a . A second extent  26   a  of the second sub-body  5   a  in the longitudinal direction, in particular in the second plane  21   a , is here greater than a first extent  25   a  of the first sub-body  4   a  in the longitudinal direction, in particular in the first plane  20   a . A step thus arises between the first sub-body  4   a  and the second sub-body  5   a , which step has, in this first embodiment, a second sub-face  9   a  of the second sub-body  5   a , which extends in a fifth plane  23   a . This fifth plane  23   a  is here configured as a parting plane of the first  4   a  from the second  5   a  sub-body and extends parallel to the first  20   a  and/or second  21   a  planes. The lengthwise extent  34   a  of the second sub-face  9   a  of the second sub-body  5   a  is here greater than a height  33   a  of the second sub-body  5   a . In other words, the resultant step is preferably longer than it is high. 
     The second micromechanical component  3   a  is arranged in a third plane  22   a  of the micromechanical device  1   a  different from the first  20   a  and second  21   a  planes. The third plane  22   a  extends parallel to the first  20   a  and second  21   a  planes. 
     The micromirror device shown, as micromechanical device  1   a , has as first micromechanical component  2   a  a micromirror and as second micromechanical component  3   a  an, in particular resilient, spring element. 
     In the first embodiment, the first sub-body  4   a  and second sub-body  5   a  of the first micromechanical component  1   a  have a rectangular cross-section, such that the step between first sub-body  4   a  and second sub-body  5   a  has an edge  32   a , in particular of 90°, and an outer side  30   a  of the second sub-body 5a extends in a sixth plane (not shown here), which extends substantially perpendicular to the first  20   a  and/or second  21   a  planes. 
     The height of the second sub-body  33   b  in relation to the height  33   a  of the first sub-body  4   a  is here selected such that as much strain as possible is removed from the silicon oxide layer  7   a . To this end, the height  33   a  of the second sub-body  5   a  is selected to be distinctly less than the height  33   b  of the first sub-body  4   a . The ratio of the height  33   a  of the second sub-body  5   a  to the height  33   b  of the first sub-body  4   a  amounts here to substantially 1:10. 
     In this exemplary embodiment, the micromechanical device additionally has a second silicon oxide layer  6   a , which is arranged on the first sub-body  4   a  of the first micromechanical component  2   a . 
       FIG.  1 B  shows a method for producing the micromechanical device  1   a . In this method, in a first method step a silicon substrate  10   a , in particular a plate-shaped silicon substrate, is arranged above the second micromechanical component  3   a  and the silicon oxide layer  7   a . The structure of silicon substrate  10   a , silicon oxide layer  7   a  and micromechanical component  3   a  is in particular a silicon oxide wafer. Moreover, a first etching mask  6   a , in particular a further silicon oxide layer, is arranged on the top  29   a  of the silicon substrate. In a subsequent method step  15   a , a second etching mask  11   a  is applied to the first etching mask  6   a . The second etching mask is in particular a photoresist layer. In a method step  15   b , material of the silicon substrate  10   a  is then removed in a trenching process such that recesses  12   a  with a defined shape are produced in the top of the silicon substrate  10   a . In a subsequent method step  15   c , part of the first etching mask  6   a  is removed in an etch step in such a way that a sub-face  13   a  of the silicon substrate  10   a  is exposed to the outside. In a subsequent method step  15   d , material of the silicon substrate  10   a  is further etched away in a downward direction in a further, second trenching process in such a way that a first micromechanical component  2   a  is produced which has a first sub-body  4   a  and a second sub-body  5   a  according to  FIG.  1 A . In a final method step  15   e , the second etching mask  11   a  is removed. 
       FIG.  2 A  shows a second embodiment of a micromechanical device  1   b . Unlike in the first embodiment, the micromechanical device  1   b  here has a second sub-body  5   b , the outer side  30   b  of which is of curved, in particular concave, configuration. This outer side  30   b  thus extends, as a first sub-face of the second sub-body  5   b , at least in part in a fourth plane (not shown here), which extends obliquely to the first  20   a  and second  21   a  planes. 
     Here too, the micromechanical device  1   b  is configured as a micromirror device with a first micromechanical component  2   b  and a second micromechanical component  3   b . The first component  2   b  and the second component  3   b  are here indirectly joined to one another via a silicon oxide layer  7   b . Here too, the first micromechanical component  2   b  has a first sub-body  4   b  and at least one second sub-body  5   b . The first sub-body  4   b  extends in the first plane  20   a  and the second sub-body  5   b  extends in the second plane  21 . Here too, the second sub-body  5   b  is arranged in a transitional region to the second micromechanical component  3   b . A second extent  26   a  of the second sub-body  5   a  in the longitudinal direction in the second plane  21   a  is greater here too than a first extent  25   a  of the first sub-body  4   a  in the longitudinal direction in the first plane  20   a . 
       FIG.  2 B  shows a method for producing the micromechanical device  1   b . Here too, first of all a silicon oxide wafer is provided, which has a silicon substrate  10   b , in particular a plate-shaped silicon substrate, a second micromechanical component  3   b  and the silicon oxide layer  7   b . Moreover, a first etching mask  6   b  is arranged on the top  29   b  of the silicon substrate. In a subsequent method step  16   a , a second etching mask  11   b  is applied to the first etching mask  6   b  and the top  29   b  of the silicon substrate  10   b . The second etching mask  11   b  is in particular a photoresist layer. In a method step  16   b , an isotropic silicon etch step follows, in which material of the silicon substrate  10   a  is removed in such a way that recesses  12   b  with a defined shape are produced in the top  29   b  of the silicon substrate  10   b . In a subsequent method step  16   c , the second etching mask  11   b  is removed in an etch step. In a subsequent method step  16   d , material of the silicon substrate  10   b  is further etched away in a downward direction in a trenching process in such a way that a first micromechanical component  2   a  is produced which has a first sub-body 4b and a second sub-body  5   b  according to  FIG.  2 A .  FIG.  3 A  shows a third embodiment of a micromechanical device  1   c . In contrast to the first embodiment and second embodiment, the micromechanical device  1   c  here has a second sub-body  5   c , whose oblique outer side  30   c  has a uniform gradient. This outer side  30   b  thus extends, as a first sub-face of the second sub-body  5   b , completely in the fourth plane (not shown here), which extends obliquely to the first  20   a  and second  21   a  planes. 
     Here too, the micromechanical device  1   c  is configured as a micromirror device with a first micromechanical component  2   c  and a second micromechanical component  3   c . The first component  2   c  and the second component  3   c  are here indirectly joined to one another via a silicon oxide layer  7   c . Here too, the first micromechanical component  2   c  has a first sub-body  4   c  and at least one second sub-body  5   c . The first sub-body  4   c  extends in the first plane  20   a  and the second sub-body  5   c  extends in the second plane  21 . Here too, the second sub-body  5   c  is arranged in a transitional region to the second micromechanical component  3   c . A second extent  26   c  of the second sub-body  5   c  in the longitudinal direction in the second plane  21   a  is greater here too than a first extent  25   c  of the first sub-body  4   c  in the longitudinal direction in the first plane  20   a . 
       FIG.  3 B  shows a method for producing the micromechanical device  1   c . Here too, first of all a silicon oxide wafer is provided, which has a silicon substrate  10   c , in particular a plate-shaped silicon substrate, a second micromechanical component  3   c  and the silicon oxide layer  7   c . Moreover, a further silicon oxide layer is arranged as first etching mask  6   c  on the top  29   c  of the silicon substrate  10   c . In a subsequent method step  17   a , a second etching mask  11   c  is applied to the first etching mask  6   c  and the top  29   c  of the silicon substrate  10   c . 
     The second etching mask  11   c  is in particular a photoresist layer. The photoresist is applied or fully baked in such a way that it has a defined resist sidewall  38   a  in the marginal region of the second etching mask  11   c . In the subsequent etch step in method step  17   b , this resist sidewall is then imparted to the silicon body. In a subsequent method step  17   c , the remaining part of the second etching mask  11   c  is removed in a further etch step. In a subsequent method step  17   d , material of the silicon substrate  10   c  is further etched away in a downward direction in a further, second trenching process in such a way that a first micromechanical component  2   c  is produced which has a first sub-body  4   c  and a second sub-body  5   c  according to  FIG.  3 A .