gliederunggraduierten-kurse.physi.uni-heidelberg.de/sose2006/lectures/heidelberg_2006...boss...
TRANSCRIPT
1
Institute for Microtechnology - Technical University of Braunschweig - Germany
Gliederung
Einführung: Technik en miniatureBasis-Prozesse der Mikrotechnologie
þ Spezielle Technologien der MikromechanikDesign von MikrokomponentenMikrosensoren und MikroaktorenCase Studies
• Piezoresistive Sensoren• Formgedächtnis-Aktoren• Magnetische Mikrosysteme• Optisches Mikrofon• Mikrofluidische Systeme• Mikroplasmaquellen
Institute for Microtechnology - Technical University of Braunschweig - Germany
Silicon Bulk Micromachining
Check valve Silicon grid
Removal of large amounts of silicon substratesBasic structures: diaphrams, beams, bridges, channels, cavities
Anisotropic etchants: KOH, EDP, TMAH
Etch stops: p+ silicon, p-n junction
Etch masks: SiO2, Si3N4
Vibration sensor
2
Institute for Microtechnology - Technical University of Braunschweig - Germany
Anisotropic Wet Etching (1)
Etch rates depend on:Crystal directionEtch solution
Example: KOH, 30%, 70 ºCR(100) : R(110) : R(111) ≈ 40 : 80 : 1
Institute for Microtechnology - Technical University of Braunschweig - Germany
Anisotropic Wet Etching (2)(100)
(111)Frontside mask
p+-dopedSi membrane
(111)
Backside mask
54.7º
p+-dopedSi membrane
<100>(111) Self-limiting etches
<110>Slanted (111)Vertical (111)
Slanted (111)
(111)
70.5º
109.5º
Top view
3
Institute for Microtechnology - Technical University of Braunschweig - Germany
Underetching of Convex Corners
Mask
Compensatingelement
Example: underetchingof convex mask corners
Well-defined cornersemerge from compen-sating mask elements
Defining the manufacturing sequence of silicon micro components several con-straints due to incompatibilities of materials and processes have to be considered
Institute for Microtechnology - Technical University of Braunschweig - Germany
Boss Membrane
Boss
Mask
Compensating elementK = 2 · etch depthL = 1.6 K
Boss with spiral suspension
4
Institute for Microtechnology - Technical University of Braunschweig - Germany
Laser Machining and Anisotropic Etching (1)
The {111} octahedron and its extended form for visualization of possible micro channels in silicon
Schematic view of possible micro channels in silicon formed by intercepting the extended octahedron with the surfaces of (100), (110), and (111) wafers
Institute for Microtechnology - Technical University of Braunschweig - Germany
Laser Machining and Anisotropic Etching (2)
Experimental setup
Si
(110) Si
(100) Si
Laser beamMasking layer
w
Damaged zone
d
d
d/w = 0.35
d/w = 0.71
{111}{111}
5
Institute for Microtechnology - Technical University of Braunschweig - Germany
Laser Machining and Anisotropic Etching (3)
Micro channels and vertical-walled shafts fabricated in (110) silicon by photolithography, laser machining, and anisotropic etching
Institute for Microtechnology - Technical University of Braunschweig - Germany
Laser Machining and Anisotropic Etching (4)
Monolithic beams with triangular cross-section fabricated in (110) silicon
6
Institute for Microtechnology - Technical University of Braunschweig - Germany
Deep Silicon RIE
Bioreactor Microgripper
250 µm
Etch rate 4 µm / minselectivity Si : photoresistabout 80 : 1
Deep RIE based on an ASE process has revolutionized bulk silicon micro-machining
90° sidewall profiles possible through thewaferGeometric freedom
Institute for Microtechnology - Technical University of Braunschweig - Germany
ASE Process
Alternating passivation / etch cyclesPassivation
C4F8 plasma deposits fluorocarbonpolymer
Mask
Sidewall polymericpassivation (nCF2)
Silicon
CFx+
CFx+
nCFx*
nCFx*
EtchSF6 plasma etches siliconIon bombardment provides etch directionalityEtch directionality removes polymer from baseat much higher rate than from side-walls
Silicon
CFx
SFx+
SFx+
F*
SiFx
7
Institute for Microtechnology - Technical University of Braunschweig - Germany
ICP Etch System
13,56 MHz
RF Match.Unit
Weighted Clamp
Pumping Port
Helium CoolingGas Inlet
RF Match.Unit
Ceramic Process Chamber
Process Height
Wafer/Sample
MESC CompatibleIsolation Valve
Temperature ControlledBellows Sealed Electrode
Plasma Chamber
Gas Inlet
13,56 MHz
Institute for Microtechnology - Technical University of Braunschweig - Germany
ICP Operation Principle
Time varying B fieldLow loss dielectricchamber wall
RF13,56 MHz
MatchingUnitInduced electric field E
Coil
A time varying axial magnetic field induces an azimuthalelectric field which effectively confines the plasma current
The circulatory current path does not intersect the chamber walls which minimizes contaminants or particles resulting from direct chamber sputtering
The energy of ions impinging on the wafer surface can be independently controlled by using RF biasing
tBE∂∂
−=×∇
Typical process pressure: 1 - 100 mtorrplasma density: ca. 5·1011/cm3
Ion Energy (~ RF bias) dependent on the RF table power Ion Current (Plasma Density) dependent on ICP power
8
Institute for Microtechnology - Technical University of Braunschweig - Germany
Wafer Bonding
Joining of two or more substrates in order to createsealed cavities and complex 3D structures
Silicon fusion bonding: bonding of silicon wafers by thermal treatment
Anodic bonding:bonding of silicon to glass/silicon by applying an electric field
Institute for Microtechnology - Technical University of Braunschweig - Germany
Silicon Fusion Bonding
RCA clean to create hydro-philicsurfaces with hydroxyl groupsSi wafers brought together and adhere due to the bonding of hydroxyl groups and Van derWaals forcesWafers annealed in N2 or O2 at a temperature above 800 ºCH2 freed from the surface hy-droxyl groups and diffuses out leaving Si-Si and Si-O bonds
Buried cavity under a silicon membrane
Thinning of top wafer
Fusion bonding
Processingof twowafers
9
Institute for Microtechnology - Technical University of Braunschweig - Germany
Anodic Bonding
Si wafer placed on heated plate (450 ºC) and a glass wafer placed on top with a high negative voltage applied to the glass (200 V to 1000 V)As glass is heated, the positive Na ions become mobile and drift to-words the negative electrodeA depletion region is formed in the glass at the Si interface, resulting in a high field at the interface and forcing intimate contactThe oxygen atoms from the glass bond to the Si in the wafer, forming a hermetic seal
+ + + + + + + + +
- - - - -
Kathode
Anode
Glass
Silicon
Hot plate
Na2O - O2- + Na+
Institute for Microtechnology - Technical University of Braunschweig - Germany
Inspection of Bonding Quality
Inspection of bonding quality using an IR cameraAbove: imperfect bonding (interference fringes)Bottom: perfect bonding
Check valve
Silicon membrane Pump
chamber
Silicon
Edge seal
Glass cover
Membrane-typemicro pump
10
Institute for Microtechnology - Technical University of Braunschweig - Germany
Surface Micromachining (1)
Micromotor Case Western Reserve University
Microresonator UC Berkeley GyroscopRobert Bosch GmbH
Microstructures are fabricated on the surface of the waferStructural layers: material layers that form the final free-standing or movablemicrostructures (e.g. polysilicon)Sacrificial layers: material layers that separate the structural layers and are removed in the final step of fabrication (e.g. silicon dioxide)Release: the step of dissolving the sacrificial layers (predominantly RIE)
Institute for Microtechnology - Technical University of Braunschweig - Germany
Surface Micromachining (2)
RotorStator Bearing post Bearing
Flange underetch Flange
PolysiliconSiO2
Substrate
11
Institute for Microtechnology - Technical University of Braunschweig - Germany
SREAM Process
SREAM - Single Crystal Reactive Etching and MetallizationMicromachining is performed in the top few microns of the substrateCombines the advantages of both bulk and surface micromachining
Oxide mask
First deep trench etch
PECVD oxide layer
Removal of oxide
Second trench etch
Isotropic plasma etch
Final step: metal sputtering
Institute for Microtechnology - Technical University of Braunschweig - Germany
Miniaturisierte Quarz-Resonatoren
Array von Quarz-Resonatoren für biochemische Analysen in Flüssig-keiten (Dickenscherschwinger)
Wafer mit Quarz-Stimmgabeln
hergestellt mittels nasschemischer
Ätztechnik10 mm
Quarzstimmgabeln
2.5 mm
12
Institute for Microtechnology - Technical University of Braunschweig - Germany
Anisotropes nasschemisches Ätzen von Quarz
Dreidimensionale Darstellung der Ätzraten in NH4HF2
Temperaturabhängigkeit der ÄtzratenÄtzprofile von Quarzblanks mit -Schnitt
Institute for Microtechnology - Technical University of Braunschweig - Germany
Ätzapparatur zum nasschemischen Ätzen von Quarz
13
Institute for Microtechnology - Technical University of Braunschweig - Germany
Standardprozess für das nasschemische Ätzen von Quarz
Kantenprofil (48% HF / 40% NH4F-Lösung im Verhältnis 3:2, T = 82 °C)
Institute for Microtechnology - Technical University of Braunschweig - Germany
Fabrication of FOTURAN Microstructures (1)
1. UV Exposure
mask
glass
2. Heating 4. Diffusion bonding
3. Anisotropic etching
14
Institute for Microtechnology - Technical University of Braunschweig - Germany
Fabrication of FOTURAN Microstructures (2)
Two layered structurePlate thickness: 150 µm
Diameter top layer: 1.5 mmDiameter bottom layer: 30 µm
Hole diameter: 1 mmHole depth: 1.5 mm
connecting technique: thermal diffusion bonding
Channels: 500 x 500 µm
Layer 1: unstructuredFOTURAN substrate
Layer 3: unstructuredFOTURAN substrate
Layer 2: structured FOTURAN substrate
mgt mikroglas technik AG
Institute for Microtechnology - Technical University of Braunschweig - Germany
High Aspect Ratio Micro Structures
Based on depth lithography, electroplating, and molding
Extends the range of materials and forcesMetals, ceramics, polymersCollimated X-rays: LIGAUV light and thick resists: Poor man‘s LIGA
Micro turbine (nickel) FZ Karlsruhe Micro valve (SU8)
Pneumaticmicro gripper (SU8)
15
Institute for Microtechnology - Technical University of Braunschweig - Germany
LIGA-Technik
LIGA (Lithographie, Galvanoformung, Abformung)Strukturhöhen: 100 µm ... mmLaterale Auflösung im SubmikrometerbereichWerkstoffe: Metalle, Polymere, Keramiken
REM-Aufnahmen einer mit dem LIGA-Verfahren hergestellten Trenndüsenstrukturdurch Röntgentiefen-lithographie erzeugte primäre Resiststruktur
durch Galvanoformung erzeugte primäre
Struktur aus Nickel
durch Abformung erzeugte sekundäre Kunststoffstruktur
durch galvanische Metallabscheidung erzeugte sekundäre
Nickel-StrukturFZ Karlsruhe
Institute for Microtechnology - Technical University of Braunschweig - Germany
LIGA-Technik: Prozessschritte (1)
16
Institute for Microtechnology - Technical University of Braunschweig - Germany
LIGA-Technik: Prozessschritte (2)
Institute for Microtechnology - Technical University of Braunschweig - Germany
LIGA-Masken
Transparenz verschiedener Werkstoffe für Röntgenstrahlung mit λ = 1 nm
Arbeitsschritte:Herstellung der Trägerfolien (z.B. Be, Si, BN)Strukturierung der Resistschicht einer Zwischenmaske (z.B. Photolithographie)Goldgalvanik der Absorberstrukturen der Zwischenmaske (< 3 µm)Kopieren der Zwischenmaske zur Arbeitsmaske (weiche Röntgenstrahlung, 0.5 – 2 keV)Goldgalvanik der Absorberstrukturen der Arbeitsmaske (> 10 µm)Röntgentiefenlithographie (2 – 15 keV)
)(λ
chE ⋅=
17
Institute for Microtechnology - Technical University of Braunschweig - Germany
Synchrotron-Strahlungsquellen
Spektrale Brillianz als Funktion der Photonenenergie für verschiedene europäische Synchrotronstrahlungs-quellen
Institute for Microtechnology - Technical University of Braunschweig - Germany
UV-Tiefenlithographie
Optimierte Novolak-basierte Positivresists (AZ-Lacke), Lackdicke < 100 µmNegativresist SU8 (Epoxydharz), Lackdicke < 1 mm)
Belackunginfolge der mitrotierenden lösemittel-haltigen Atmosphäre werden turbulen-te Strömungen an der Lackoberfläche vermieden und eine gleichmäßigere Schichtdicke erreicht SU8-
Strukturen
3 µm Graben in 14 µm AZ-Lack
42 µm hohe AZ-Lack-Struktur
18
Institute for Microtechnology - Technical University of Braunschweig - Germany
Positivresist auf Novolak-Basis
Optimierter Prozess für das hochviskose Resist AZ 9260 (Clariant):
Schichtdicken von 90-100 µm strukturierbar10 µm breite Strukturen in 90 µm Schichtdicke auflösbar: Aspektverhältnis von 9 sehr steile und glatte Lackflanken in einem Winkel von 92° zum SubstratUV-Tiefenlithographie zur Herstellung von Galvanoformen
Institute for Microtechnology - Technical University of Braunschweig - Germany
Negativresist auf Epoxidharz-BasisOptimierter Prozess für das photosensitive Epoxidharz SU8:
Schichten von mehreren 100 µm strukturierbar10 µm breite Strukturen in 360 µm Schichtdicke auflösbar: Aspektverhältnis von 36 senkrechte und glatte Flanken hohe thermische und chemische BeständigkeitIsolations- und Planarisierungsschichten in magnetischen Mikrosystemenmikromechanische Komponenten
19
Institute for Microtechnology - Technical University of Braunschweig - Germany
Micro Coils for Magnetic MEMS
Spiral structure• planar coil• vertical flux generation• simple conductor fabrication• flux guiding structures complex in
multi-layers
Helical and 3-D meander structure• three dimensional coil• horizontal flux generation• simple fabrication of flux guiding structures • conductor fabrication complex in multi-layers
Institute for Microtechnology - Technical University of Braunschweig - Germany
Grundsätzlicher Aufbau und Anforderungen
Metalle und Legierungen • galvanisch abscheidbar• Cu und Au für Leiter• NiFe für magnetische
Flussführungsstrukturen
Photoresist• hochauflösend für
tiefenlithographische Galvanoformen
Isolationsmaterial• mehrfach strukturierbar
(Trockenätzen) • Galvanoform für
magnetische Kernstrukturen
Isolationsmaterial• photostrukturierbar
(vias)• planarisierend
20
Institute for Microtechnology - Technical University of Braunschweig - Germany
Spiralspulen mit SU8-Isolation und NiFe-Kern
Startschicht
NiFe-Kernboden
Spulenlagen
NiFe-KernIsolations-schichten
Substrat
Institute for Microtechnology - Technical University of Braunschweig - Germany
Helixspulen mit SU8-Isolation und NiFe-Kern
oberer Leiter
Durchkontaktierung (Via)
NiFe-KernIsolations-schichten
Substratunterer Leiter
Helixspule mit NiFe-Ringkern Vertikale Mäanderspule um Polstrukturen
21
Institute for Microtechnology - Technical University of Braunschweig - Germany
Spanende Mikrobearbeitung
Spanende Verfahren mit geometrisch bestimmter Schneide: Drehen, Fräsen, Bohren
Spanende Verfahren mit geometrisch unbestimmter Schneide: Schleifen
Mikroschleifen, einkristallines Silizium
Gefräste Strukturen, Messing
Institute for Microtechnology - Technical University of Braunschweig - Germany
Mikrofunkenerosion
Drahterodieren Senkerodieren
Elektroden für das funkenerosive Bohren, Durchmesser 40 µm und 12 µm
LIGA-Funkenerosion: Elektroden und funkenerodiertes Getrieberad
22
Institute for Microtechnology - Technical University of Braunschweig - Germany
Mikrourformen und Mikroumformen
Mikroumformen• Stanzen• Biegen• Warmmassivumformung• Kaltmassivumformung• Prägen
Mikrourformen• Kunststoffspritzguss
(Thermoplaste)• Pulverspritzguss
(metallische und keramische Werkstoffe)
Spritzgegossene Labormuster: Mikrogetrieberadsystem (Kunststoff), Mikro-Zahnräder(Al2O3, ZrO2)