Fraunhofer ENAS Current results and future approaches in Wafer-level-packaging FRANK ROSCHER

Transcription

1 Fraunhofer ENAS - Current results and future approaches in Wafer-level-packaging FRANK ROSCHER Fraunhofer ENAS Chemnitz System Packaging Page 1

2 System Packaging Outline: Wafer level packaging for MEMS Low Temperature Bonding Reactive Multilayers Silver Nanoparticles Photostructurable glass for MEMS Evaluation tools for bond quality Page 2

3 Fraunhofer ENAS Products / Technology and Services Multi Device Integration Reliability and Security Printed Functionalities Back-End of Line System Packaging Advanced System Engineering NIR / MIR micro spectrometer Wafer Level Packaging Nano tomography Printed battery Airgaps Ultrasonic transducer Surface current Microfluidic cartridge Analysis of nanodeformations Printed RFID antennas Through silicon vias (TSV) Nano needles Near field scanner Nanocomposite moisture sensor Stress concentration at a via (FEA) Holes in printed micro sieves Aligned single wall CNTs Interposer Thin Film Packaging Electro magnetic field Page 3

4 Department System Packaging Core - Competences: Wafer bonding Integration of new materials (III/V semiconductors, polymers, ceramics) Chip to wafer bonding Wire bonding Dicing Bonding and conducting with nano structures Nanoimprint Technologies 3D Integration und MEMS Packaging Equipment: Aerosol Jet PLD (Creavac) Cleaner Süss CL 200 Bondaligner Süss BA6 Substrate Bonder Süss SB6 & SB 8, EVG Die Bonder (Tresky) High Temperature Furnace (Centrotherm) Dicing Saw (Disco) CMP of Si, SiO 2, Al, Cu, Ge, Ceramics (IPEC) VIS, IR Microscope (Nikon) Wire Bonder Page 4

5 Conventional Wafer Bond Solutions Bonding for MEMS, MOEMS, µ-electronics and 3D Integration Anodic- Bonding Adhesive Bonding Glass Frit Bonding Eutectic Bonding Direct Bonding Thermo compression Si-Glass Si-LTCC SU 8 BCB Epoxy Polymer Screenprintable glass paste Spin-on glasses Au-Si Au-Sn Cu-Sn-Cu Laser- Assisted Bonding High- Temperature Low- Temperature Surface Activated Bonding Au-Au Cu-Cu Ti-Si Page 5

6 Reactive Bonding - Motivation Thermal flow in bonding technology - An overview External heat source: Heat up whole components (>300 C) Thermo-mechanical stress Problems: joining temperature sensitive components and components with high CTE mismatch Example: Eutectic bonding Internal heat source: Located heating Reduced thermomechanical stress Sequential writing Time consuming Laser bonding Searching for new technologies? Faster! Reactive Bonding Component A Component A Komponente Component B Component B Ultra-fast (~ ms) bonding of heterogeneous materials (Si-metal, Siceramics ) at room-temperature J. Braeuer et al, Transducers 2011, China/Peking, 2011 Page 6

7 Reactive Bonding Chip Room temperature Reactive Ni/Al foil Component A Component B Solder- Preform Ni/Al Foil Initiation (NanoFoil ) A Pressure Pressure Atomic diffusion y Propagation direction Product Bilayer period δ Reaction zone Thermal diffusion x Exothermic Reaction As-deposited A B Steel Quartz [Mikrotechni&Sensorik] Mechanical application CaF Covar [Silicon Sensors] Optical application Individual layers within the nano scale! > 1000 layers Page 7 B Fraunhofer IWM Si 3 N 4 Covar [Siegert TFT] Optical application Ni Si [MIT, USA] Space application Demonstrators ENAS (some examples!) J. Braeuer et al., Sensors & Actuators A, 2011

8 Reactive Bonding Results on Wafer Level Pressure Integrated reactive system Component A Component B Initiation Thickness: <5 µm Width: <0.1 mm <100 individual layers (costs!!!) Pressure Reaction velocities up to 50 m/s! Room-temperature bonding of 8 wafer within 4 µs (theory)! Highspeed imaging of reaction front in a 500 µm frame Prior to bonding Substrate Au Sn Multilayer After bonding 1 µm Substrate 1 µm Al Pd Sn Au Al Pd Sn Au J. Braeuer et al., SHS Symposium, Athens/Greece, 2011 SEM crosssection prior to and after bonding; Bottom: EDX analysis Page 8

9 Photostructurable glass for MEMS devices FOTURAN -glass Process Flow 1. Photostructuring 2. Metalization 2. Waferbonding 3. Waferbonding 3. Metalization Page 9

10 Photostructurable glass for MEMS devices Structuring Process FOTURAN -glass 1. Cleaning of FOTURAN glass 2. Exposure to UV-light Mask aligner exposure (UV radiation with nm) Ag-atom formation Ce 3+ + hν(310 nm) Ce 4+ + e - (sensitizer) Ag + + e - Ag (nucleating agent) 3. Heat treatment Crystallization of exposed areas 500 C: nuclei formation 600 C: glass crystallizes around the silver nuclei and forming lithium-metasilicate 4. Etching Etching of the crystallized areas Ratio 20 (exposed) :1 (unexposed) Etch solution: 10% HF Cleaning Exposure Heating Etching T.R. Dietrich et al. / Microelectronic Engineering 30 (1996) Page 10

11 Photostructurable glass for MEMS devices Results: Waferbonding of FOTURAN -glass and Silicon Bond-process: Low temperature (150 C) direct bonding using atmospheric pressure plasma activation surface conditioning and activation by: CMP CMP + Plasma (process gas variation) Fig.: Silicon - Foturan wafer stack Results: Characterization of the bond strength with Micro Chevron structure etched into silicon Tensile force of 10 N - no significant increase of the bond strength after plasma-process Bond strength of the bonded interface after CMPprocess is comparable to the bulk material Bond strength for activated Si/Foturan glass wafer stacks using CMP and AP-Plasma activation Page 11

12 Silver Nano Particles for Waferbonding Production of Bondframes at the end of the bond process Bonding of MEMS and Cap Wafer Sintering of Nanoparticles due to temperature and mechanical force + no additional wet chemical structuring + no expensive ECD or Lithography to produce pattern + Low Temperature due to Nano effects heterogeneos material compinations are possible Page 12

13 Silver Nano Particles for Waferbonding Deposition of Nanoparticles by Aerosol - Jet Page 13

14 Silver Nano Particles for Waferbonding Results: Sintered Ag Nanoparticles Sintered Ag paths 100 C, 120 min Particles start to sinter Low density, low conductivity Sintered Ag paths 250 C, 120 min Grain growth High density, high conductivity Page 14

15 Evaluation Tools Can you trust your bond? Micro-Chevron-Test Shear-Test Hermeticity evaluation by membrane deflection Maszara-Blade-Test SAM bonding yield IR-transmission test Bond interface Blade thickness Crack length Page 15

16 Contact us Fraunhofer ENAS Dept. System Packaging Technologie Campus 3 D Chemnitz Phone: Fax: Frank.Roscher@enas.fraunhofer.de Thank you for your attention Page 16