US-12619065-B2 - Process for manufacturing a microelectromechanical mirror device and microelectromechanical mirror device

US12619065B2US 12619065 B2US12619065 B2US 12619065B2US-12619065-B2

Abstract

A process for manufacturing a microelectromechanical mirror device includes, in a semiconductor wafer, defining a support frame, a plate connected to the support frame so as to be orientable around at least one rotation axis, and cantilever structures extending from the support frame and coupled to the plate so that bending of the cantilever structures causes rotations of the plate around the at least one rotation axis. The process further includes forming piezoelectric actuators on the cantilever structures, forming pads on the support frame, and forming spacer structures protruding from the support frame more than both the pads and the stacks of layers forming the piezoelectric actuators.

Inventors

Roberto Carminati
Nicolo' BONI
Irene Martini
Massimiliano Merli
Laura Oggioni

Assignees

STMICROELECTRONICS S.R.L.

Dates

Publication Date: 20260505
Application Date: 20220426
Priority Date: 20210430

Claims (15)

1 . A microelectromechanical mirror device, comprising: a support frame formed of semiconductor material; a plate connected to the support frame so as to be orientable around at least one rotation axis; a micro-mirror on the plate; cantilever structures extending from the support frame and coupled to the plate so that bending of the cantilever structures causes rotation of the plate around the at least one rotation axis; piezoelectric actuators on the cantilever structures; pads on the support frame; and spacer structures protruding from the support frame more than both the pads and stacks of layers forming the piezoelectric actuator; wherein the spacer structures comprise a dummy actuator having a dummy bottom electrode, a dummy piezoelectric region and a dummy top electrode, portions of a first passivation layer overlaying the dummy actuator, dummy lines formed by respective portions of a routing metallization layer, and portions of a second passivation layer covering the dummy lines, and wherein the spacer structures further comprise, on the portions of the second passivation layer covering the dummy lines, adhesion regions and dummy contacts formed from a metallization layer.
2 . The device according to claim 1 , wherein the spacer structures protrude from the support frame farther than the pads and the stacks of layers forming the piezoelectric actuators.
3 . The device according to claim 1 , wherein: each piezoelectric actuator comprises an actuator bottom electrode, an actuator piezoelectric region and an actuator top electrode.
4 . The device according to claim 3 : wherein the first passivation layer is at least partially overlaying the piezoelectric actuators and the dummy actuators; and further comprising connection lines between the first passivation layer and the second passivation layer; and wherein the piezoelectric actuators comprise actuator contacts connected to respective connection lines through the first passivation layer.
5 . A picoprojector apparatus, comprising: a control unit; the microelectromechanical mirror device according to claim 1 , controlled by the control unit; and a light source, oriented towards the microelectromechanical mirror and controlled by the control unit to generate a light beam based on an image to be generated.
6 . A portable electronic apparatus comprising a system processor and the picoprojector apparatus according to claim 5 coupled to the system processor.
7 . The device according to claim 1 , wherein the plate includes a reinforcement structure comprising at least one rib extending into a cavity delimited by the support frame.
8 . The device according to claim 1 , further comprising a cap bonded to the support frame, wherein the cap and the support frame define a cavity enclosing at least a portion of the plate.
9 . The device according to claim 1 , wherein the cantilever structures are arranged symmetrically with respect to a center of the plate in respective quadrants.
10 . A microelectromechanical scanning device, comprising: a semiconductor support structure defining a cavity; a movable plate partially closing the cavity and connected to the semiconductor support structure through elastic elements; a reflective element disposed on the movable plate; a plurality of actuator assemblies extending from the semiconductor support structure toward the movable plate, each actuator assembly comprising: a cantilever arm having a fixed end coupled to the semiconductor support structure and a free end coupled to the movable plate; and a piezoelectric stack on the cantilever arm; electrical contact pads disposed on the semiconductor support structure and electrically coupled to the piezoelectric stacks; and protective spacer elements disposed on the semiconductor support structure and protruding farther from a surface of the semiconductor support structure than both the electrical contact pads and the piezoelectric stacks: wherein the protective spacer elements comprise a dummy actuator having a dummy bottom electrode, a dummy piezoelectric region and a dummy top electrode, portions of a first passivation layer overlaying the dummy actuator, dummy lines formed by respective portions of a routing metallization layer, and portions of a second passivation layer covering the dummy lines, and wherein the protective spacer elements further comprise, on the portions of the second passivation layer covering the dummy lines, adhesion regions and dummy contacts formed from a metallization layer.
11 . The device of claim 10 , wherein the protective spacer elements further comprise polymeric material.
12 . The device of claim 10 , wherein: the movable plate is orientable around at least one rotation axis; and the plurality of actuator assemblies are arranged symmetrically with respect to the at least one rotation axis.
13 . The device of claim 10 , further comprising a cap bonded to the semiconductor support structure and arranged to close the cavity on a side opposite to the movable plate.
14 . The device of claim 10 , wherein the movable plate includes a reinforcement structure extending into the cavity.
15 . The device of claim 10 , wherein the plurality of actuator assemblies are independently controllable to orient the movable plate in multiple directions.

Description

PRIORITY CLAIM This application claims the priority benefit of Italian Application for Patent No. 102021000011039, filed on Apr. 30, 2021, the content of which is hereby incorporated by reference in its entirety to the maximum extent allowable by law. TECHNICAL FIELD This disclosure relates to a process for manufacturing a microelectromechanical mirror device and the microelectromechanical mirror device so manufactured. BACKGROUND As is known, the so-called shadow mask technique is widely used in the manufacture of microelectromechanical micro-mirror devices and is particularly appreciated for its simplicity of execution and for the high reflectivity values that may be obtained. The technique is applied in the final manufacturing steps, after support structures and actuation structures, normally of a piezoelectric type, have been defined in a semiconductor wafer and metallization and passivation layers have been deposited and shaped. Basically, a mask, specifically called a “shadow” mask, is formed separately from the semiconductor wafer and has openings corresponding in shape and arrangement to the micro-mirrors to be formed. The shadow mask is aligned and applied to the wafer being processed, then micro-mirrors are formed through the openings in the shadow mask itself using a sputtering deposition process to deposit, for example, gold/aluminum. A frequent problem occurs when the shadow mask is applied to the semiconductor wafer for depositing the micro-mirrors or when the mask itself is subsequently removed. The wafer being processed has prominent structures having the shadow mask resting thereon. The most prominent parts are usually stacks of layers corresponding to the contacts of the piezoelectric actuation structures and therefore perform a critical function for the operation of the micro-mirror device. When the shadow mask is applied and removed, some of the structures in contact may be damaged relatively easily, compromising the functionality of the entire device. Consequently, the yield of the manufacturing process may not be satisfactory. As such, further development into manufacturing techniques in this area is desired. There is a need in the art to provide a process for manufacturing a microelectromechanical mirror device and the microelectromechanical mirror device so manufactured that allow the described limitations to be overcome or at least mitigated. SUMMARY In an embodiment, method for manufacturing a microelectromechanical mirror device comprises: in a semiconductor wafer, defining a support frame, a plate connected to the support frame so as to be orientable around at least one rotation axis, and cantilever structures extending from the support frame and coupled to the plate so that bending of the cantilever structures causes rotation of the plate around the at least one rotation axis; forming piezoelectric actuators on the cantilever structures; forming pads on the support frame; and forming spacer structures protruding from the support frame more than both the pads and stacks of layers forming the piezoelectric actuator. The method may also include: applying a shadow mask to the spacer structures; forming a micro-mirror on the plate using the shadow mask; and removing the shadow mask. The spacer structures may protrude from the support frame farther than the pads and the stacks of layers forming the piezoelectric actuator. Forming the piezoelectric actuators may comprise: depositing, in succession, a bottom electrode layer, a piezoelectric layer and a top electrode layer on the semiconductor wafer; and for each piezoelectric actuator, forming an actuator bottom electrode, an actuator piezoelectric region and an actuator top electrode respectively from the bottom electrode layer, from the piezoelectric layer, and from the top electrode layer. Forming the spacer structures may include, for each spacer structure, forming a dummy actuator. Forming the dummy actuator may include forming a dummy bottom electrode, a dummy piezoelectric region and a dummy top electrode respectively from the bottom electrode layer, from the piezoelectric layer and from the top electrode layer. The method may further include: depositing a first passivation layer on the top electrode layer; opening contact windows in the first passivation layer; depositing a routing metallization layer; forming actuator contacts in the contact windows from the routing metallization layer; and depositing a second passivation layer covering the first passivation layer and the actuator contacts. Forming the spacer structures may comprise, for each spacer structure: forming dummy lines from the routing metallization layer on portions of the first passivation layer overlying the respective dummy actuator; and covering the dummy lines with respective portions of the second passivation layer. The method may also include: depositing an adhesion layer on the second passivation layer and a pad metallization layer on the adhesion layer; and