Fabrication Technology, Part II - MEMS...Fabrication Technology, Part II Agenda: ÊProcess Examples – TI Micromirror fabrication process – SCREAM – CMOS-MEMS processes ÊWafer
Post on 27-May-2020
9 Views
Preview:
Transcript
EEL5225: Principles of MEMS Transducers (Fall 2003)1
EEL5225: Principles of MEMS Transducers (Fall 2003)
Fabrication Technology, Part II
Agenda:Process Examples
– TI Micromirror fabrication process– SCREAM– CMOS-MEMS processes
Wafer BondingLIGA
Reading: Senturia, pp. 79-98.
Lecture 9 by H.K. Xie 9/15/2003
EEL5225: Principles of MEMS Transducers (Fall 2003)2
Process ExamplesSurface micromachining: TI Digital Micromirror Devices (DMDs)
Invented by L.J. Hornbeck
Ref. Maluf, Introduction to MEMS Engineering, p.145.
EEL5225: Principles of MEMS Transducers (Fall 2003)3
Process Examples
Bulk-MicromachinedPressure Sensor
Thermal oxideBoron implantationBoron drive-inLPCVD Si3N4
Backside KOH etch– Electrochemical etch stop
Metallization
Detailed process steps refer to Senturia p.93
Ref. Senturia, Microsystem Design, p.97
EEL5225: Principles of MEMS Transducers (Fall 2003)4
Process Examples
Single Crystal Reactive Etching and Metallization (SCREAM) Process
First demonstrated by MacDonald’s group at Cornell UniversitySingle crystal silicon (SCS) microstructuresLarge forceLarge displacementPost-CMOS process for electronics integration
Ref. Maluf, Introduction to MEMS Engineering, p.82.
EEL5225: Principles of MEMS Transducers (Fall 2003)5
CMOS-MEMS
Why CMOS-MEMS?“Smart” on-chip CMOS circuitryMulti-vendor accessibilityScalabilityCompact sizeMore functions Low cost
MEMS structures can be madeBefore CMOS processes (“pre-CMOS”)In-between CMOS processes (“intermediate-CMOS”)After CMOS processes (“post-CMOS”)
EEL5225: Principles of MEMS Transducers (Fall 2003)6
Pre-CMOS MEMS Process
www.sandia.gov
Pre-etched trench to house MEMS structuresCMP to planarize the wafer for regular CMOS processingWet etch to release MEMS structuresNeed a dedicated production line
EEL5225: Principles of MEMS Transducers (Fall 2003)7
Intermediate-CMOS MEMS
Form transistors on bare wafers firstThen deposit and anneal MEMS structural materialsNo CMP neededOnly one interconnect metal layerWet etch to release MEMS structuresNeed a dedicated production line
Thox
Nwell
BPSG
Sensor Poly
MetPassivations
NPN NMOS Sensor Area
EmitterBase NSD Courtesy of Mr. John Geen
of Analog Devices, Inc.
EEL5225: Principles of MEMS Transducers (Fall 2003)8
Thin-Film Post CMOS-MEMS
(a) After standard CMOS processes
CMOS
metallization layers
movable anchored
silicon substratedielectric layers
metal-3
metal-2
metal-1
gate polysilicon
statormicrostructure
regionmicrostructural
region
Proof mass
Spring beams
Sensing comb fingers
(b) Pattern microstructure• Metal as etching mask• Anisotropic etch • CHF3 + O2
(c) Release microstructure• Metal as etching mask• Undercut Si substrate• Isotropic etch• SF6 or XeF2 G. Fedder et al., Sensors & Actuators A,
v.57, no.2, 1996H. Xie et al., Thin-film z-axis accelerometer
EEL5225: Principles of MEMS Transducers (Fall 2003)9
DRIE CMOS-MEMS Process
CMOS-region(a) Backside etch
Single-crystal Si (SCS) membrane
metal-2metal-3
STS: 12-sec etching, 130-sccm SF6, 13-sccm O2, 23 mT, 600 W coil power, 12 W platen power; 8-sec passivation 85-sccm C4F8, 12 mT, 600 W coil power, 0 platen power.
metal-1
oxide
poly-Si
(b) Oxide etchPlasmaTherm-790: 22.5-sccm CHF3, 16-sccm O2, 100 W, 125 mT for 125 minutes and then 100 mT for 10 minutes.
CMOS layer(c) Deep Si etch
STS: same as Step (a).
H. Xie et al, Journal of Microelectromechanical Systems, April 2002
EEL5225: Principles of MEMS Transducers (Fall 2003)10
Flat structure
(d) Si undercutSCS layer (20~100µm)
Thin-film structure
STS: 130-sccm SF6, 13-sccm O2, 23 mT, 600 W coil power, and 0 platen power.
Proof mass
Spring beams
Sensing comb fingers
bimorph actuator
mirror
Xie et al, 1-D Scanning MicromirrorXie et al, DRIE z-axis accelerometer
EEL5225: Principles of MEMS Transducers (Fall 2003)11
Wafer Bonding
Wafer bondingAddresses need to obtain greater vertical dimensions and vacuum packaging, and to seal channels
MethodsEpoxy bonding (low temperature 100°C)Metal eutectic bonding (low-moderate temperature 100-400°C)Glass frit bonding (low-moderate temperature 450°C)Anodic bonding (moderate temperature 450-500°C)Silicon fusion bonding (high temperature 1000-1100°C)
Ref. Kovacs, Micromachined Transducers Sourcebook, p. 139.
EEL5225: Principles of MEMS Transducers (Fall 2003)12
Wafer Bonding
Anodic bondingModerate temperature 450-500°CSodium-rich glass plate (7740 Pyrex)500-1000V at 500°C to diffuse ions and to form electrostatic bond
Bond chamber
EVG501 Wafer Bonding System Ref. Kovacs, Micromachined Transducers Sourcebook, p. 120.
EEL5225: Principles of MEMS Transducers (Fall 2003)13
LIGALIGA
IssuesHigh energy radiation source
– AlternativesThick UV sensitive resist (‘poor man’s LIGA’)
AssemblyEnables fabrication of microsizemetal partsRef. Maluf, Introduction to MEMS Engineering, p.76.
LIGA: German acronym for X-ray Lithographie, electrodeposition(Galvanoformung), and molding (Abformung)
EEL5225: Principles of MEMS Transducers (Fall 2003)14
Project Issues
TeamsSchedule
top related