Estimation of sidewall skew angles of a structure
View Patent ↗An apparatus ( 36 ) includes a motion amplification structure ( 52 ), an actuator ( 54 ), and a sense electrode ( 50 ) in proximity to the structure ( 52 ). The actuator ( 54 ) induces an axial force ( 88 ) upon the structure ( 52 ), which causes a relatively large amount of in-plane motion ( 108 ) in one or more beams ( 58, 60 ) of the structure ( 52 ). When sidewalls ( 98 ) of the beams ( 58, 60 ) exhibit a skew angle ( 28 ), the in-plane motion ( 108 ) of the beams ( 58, 60 ) produces out-of-plane motion ( 110 ) of a paddle element ( 62 ) connected to the end of the beams ( 58, 60 ). The skew angle ( 28 ), which results from an etch process, defines a degree to which the sidewalls ( 98 ) of beams ( 58, 60 ) are offset or tilted from their design orientation. The out-of-plane motion ( 110 ) of element ( 62 ) is sensed at the electrode ( 50 ), and is utilized to determine an estimated skew angle ( 126 ).
1. An apparatus comprising:
a motion amplification structure suspended above a substrate, said motion amplification structure including a first beam, a second beam, and a paddle element, said first beam having a movable first end, a middle region configured to flex, and a second end, said second beam having a third end fixed to said substrate and a fourth end, wherein said second end of said first beam and said fourth end of said second beam are connected to said paddle element;
an actuator operative upon said first beam such that activation of said actuator induces an axial force upon said first end of said first beam to cause flexion of said middle region, wherein said actuator comprises:
a movable element suspended above said substrate and coupled to said first beam; anchor elements fixed to said substrate;
compliant members interconnected between said movable element and said anchor elements; and
at least one actuation electrode coupled to said substrate and positioned proximate said movable element, wherein an actuation signal applied to said at least one actuation electrode enables motion of said movable element relative to said anchor elements to induce said axial force upon said first end of said first beam; and
a sense electrode in proximity to said paddle element, wherein when a sidewall of said first beam exhibits a skew angle relative to an axis perpendicular to a planar surface of said substrate, said flexion of said first beam produces displacement of said paddle element, said displacement of said paddle element being sensed at said sense electrode.
2. An apparatus as claimed in claim 1 wherein said skew angle defines a degree to which said sidewall of said first beam is nonparallel to said axis.
3. An apparatus as claimed in claim 2 wherein said displacement of said paddle element corresponds to said degree of said skew angle.
4. An apparatus as claimed in claim 1 wherein:
said flexion of said first beam in response to said axial force is an in-plane motion of said first beam, said in-plane motion being approximately parallel to said planar surface; and
said displacement of said paddle element is an out-of-plane motion of said paddle element, said out-of-plane motion being approximately perpendicular to said planar surface.
5. An apparatus as claimed in claim 4 wherein said sense electrode is positioned on said planar surface of said substrate underlying said paddle element for detecting said out-of-plane motion of said paddle element.
6. An apparatus as claimed in claim 1 wherein said first and second beams are adjacent to one another such that said second end of said first beam and said fourth end of said second beam are coupled to a common edge of said paddle element.
7. An apparatus as claimed in claim 1 wherein said compliant members are stiff in a direction perpendicular to a planar surface of said substrate.
8. An apparatus as claimed in claim 1 further comprising:
multiple motion amplification structures suspended above said substrate, each of said motion amplification structures including said first beam, said second beam, and said paddle element; and
a plurality of sense electrodes, one each of said sense electrodes being in proximity to one each of said paddle element.
9. An apparatus as claimed in claim 8 wherein said multiple motion amplification structures include:
a first motion amplification structure;
a second motion amplification structure aligned with said first amplification structure;
a third motion amplification structure; and
a fourth motion amplification structure aligned with said third amplification structure, wherein said first, second, third, and fourth motion amplification structures are arranged such that said first beam of each of said first, second, third, and fourth motion amplification structures is connected at a central location of said apparatus.
10. An apparatus as claimed in claim 9 wherein:
each of said first, second, third, and fourth motion amplification structures has a longitudinal axis aligned with said first beam;
said longitudinal axis of each of said first and second motion amplification structures is aligned with a first axis that is approximately parallel to a planar surface of said substrate;
said longitudinal axis of each of said third and fourth motion amplification structures is aligned with a second axis that is approximately parallel to said planar surface and perpendicular to said first axis; and
said actuator includes a movable element coupled to each said first beam of said first, second, third, and fourth motion amplification structures, wherein an actuation signal applied by said actuator enables motion of said movable element in a direction that is approximately parallel to said planar surface and diagonal to each of said first and second axes, to induce said axial force upon said first end of said first beam of each of said first, second, third, and fourth motion amplification structures.
11. An apparatus as claimed in claim 9 wherein:
said actuator is operative upon each said first beam such that activation of said actuator induces said axial force upon each said first end of said each first beam to cause flexion of each said middle region; and
when any of said each first beam has a sidewall that exhibits said skew angle, said flexion of said each first beam produces displacement of a connected said paddle element, said displacement of said paddle element being sensed at an associated one of said sense electrodes.
12. A method comprising:
providing a device wafer containing a test apparatus, said test apparatus including a motion amplification structure suspended above a substrate of said device wafer, said motion amplification structure including a first beam, a second beam, and a paddle element, said first beam having a movable first end, a middle region configured to flex, and a second end, said second beam having a third end fixed to said substrate and a fourth end, wherein said second end of said first beam and said fourth end of said second beam are connected to said paddle element;
inducing an axial force upon said first end of said first beam to cause flexion of said middle region; and
determining a displacement of said paddle element in response to said axial force, wherein said flexion of said first beam in response to said axial force is an in-plane motion of said first beam, said in-plane motion being approximately parallel to a planar surface of said substrate, and when a sidewall of said first beam exhibits a skew angle relative to an axis perpendicular to said planar surface, said flexion of said first beam produces said displacement of said paddle element, said displacement of said paddle element being an out-of-plane motion of said paddle element, said out-of-plane motion being approximately perpendicular to said planar surface.
13. A method comprising:
providing a device wafer containing a test apparatus, said test apparatus including a motion amplification structure suspended above a substrate of said device wafer, said motion amplification structure including a first beam, a second beam, and a paddle element, said first beam having a movable first end, a middle region configured to flex, and a second end, said second beam having a third end fixed to said substrate and a fourth end, wherein said second end of said first beam and said fourth end of said second beam are connected to said paddle element, wherein an etch process is used to produce said first beam;
inducing an axial force upon said first end of said first beam to cause flexion of said middle region;
determining a displacement of said paddle element in response to said axial force; and
estimating a skew angle of a sidewall of said first beam in response to said displacement, said skew angle resulting from said etch process, and said skew angle defining a degree to which said sidewall of said first beam is nonparallel to an axis perpendicular to a planar surface of said substrate.
14. A method as claimed in claim 13 wherein:
said displacement is characterized by a capacitance change between a sense element and said paddle element relative to a baseline capacitance value, said baseline capacitance value being indicative of a zero degree skew angle; and
said estimating operation comprises comparing said capacitance change to a model of capacitance changes versus skew angles for said test apparatus to estimate said skew angle for said first beam.
15. A method as claimed in claim 13 further comprising rejecting said etch process for use in fabricating a microelectromechanical systems (MEMS) device when said estimated skew angle is outside of an allowable skew angle range.
16. A method as claimed in claim 13 further comprising accepting said etch process for use in fabricating a microelectromechanical systems (MEMS) device when said estimated skew angle is within an allowable skew angle range.