Cleanroom Facilities: Experience from an user

Mark Ming-Cheng Cheng Electrical and Computer Engineering Wayne State University Detroit MI USA [email protected]

WAYNE STATE UNIVERSITY Cheng Cleanroom 8/2 Thin Micro/NanoFilm Deposition Fabrication

Microfabrication is the term that describes processes of fabrication of miniature structures, of mironmeter sizes and smaller. Historically the earliest processes were used for fabrication, also known as “ semiconductor manufacturing ”, ” microelectronic fabrication ”, ” VLSI technology ”.

65nm

2 cores; Introduced 2006 291 millions transistors 1.8 ~3GHz Die size 111mm 2; 65W

WAYNE STATE UNIVERSITY Cheng Cleanroom Thin Micro/NanoFilm Deposition Fabrication

In the last two decades, microfabrication has been used in many research fields, including * Micro Electromechanical System (MEMS) * RF MEMS (resonators, filters, switches, phase shifters) * Microfluidics/ Lab-on-Chip * Bio MEMS * Solar cells * Flat panel display * NEMS

WAYNE STATE UNIVERSITY Cheng Cleanroom EnablingThin Film Deposition Technology in iPhone

Microphone

Accelerometer

GPU (graphic processor) 45nm

WAYNE STATE UNIVERSITY Cheng Cleanroom ThinHow Film Deposition to Make Sandwiches?

Add bread Cut bread Cut vegetables Place vegetables … METHOD AND APPARATUS FOR MAKING A SANDWICH International Publication Number WO 2006/068865 AW Section (54) WAYNE STATE UNIVERSITY Cheng Cleanroom How to Make Devices?

/etching

pMOS

Deposition Module Photolightography Module (Pattern Transfer) Etching Module

WAYNE STATE UNIVERSITY Cheng Cleanroom Materials

Semiconductor Insulator Metal

(Si, C, SiC, GaAs ) (SiO 2, Si 3N4,glass, (Au, Pt, Al, Cr, Ti, Ni..) , ceramics)

WAYNE STATE UNIVERSITY Cheng Cleanroom Thin Film Deposition (overview)

0 I. Furnace (Few hundred~1100 C, atmosphere): SiO 2, P++

II. Low Pressure Chemical Vapor Deposition System (LPCVD): polycrystalline Si, amorphous SiO 2

III. Plasma Enhanced Chemical Vapor Deposition System (PECVD): amorphous Si, nitride, SiO 2

IV. E-beam Evaporator : metals (Al, Cr, Cu, Au, Ni, Pt, Ti, Mo),Si, Ge

V. Sputtering: Target Ti, Al, Al with 1%Si, 1%Cu), Mo, Au, Pt, Ta, Ni, Co, Cr,

Si, Pyrex, ITO Gas Ar, N 2, O 2

WAYNE STATE UNIVERSITY Cheng Cleanroom Furnace Few hundred~1100 0C, atmosphere Thermal oxide (dry): excellent electrical property, 10nm~300nm

S i + O 2 → S i O 2 Thermal oxide (wet): 100nm~1-2µm

Boron diffusion (BN source):boron doping, P++ etching stop

Metal annealing (N 2 gas)

WAYNE STATE UNIVERSITY Cheng Cleanroom Low Pressure Chemical Vapor Deposition

I . Polysilicon 600 o C SiH 4   → Si + 2H2 Pressure 50-150Pa Deposition rate 100~200 0A/min, 600~650 0C Polycrystalline Si ~2µm

Polysilicon is widely used as metal gate in CMOS as well as structural layers in MEMS .

II. Low temperature oxide (LTO) 400 o C SiH 4 + O2  →SiO 2 + 2H2

WAYNE STATE UNIVERSITY Cheng Cleanroom Plasma Enhanced Chemical Vapor Deposition

Reaction Gas SiH 4, NH 3, N 2O Power max 400W Temperature 25~300 0C Deposited Materials

α-Si : gas SiH 4 Si xNy: gas SiH 4, NH 3 Si xOy: gas SiH 4, N 2O SiO xNy: gas SiH 4, NH 3, N 2O

Typically used for depositing passivation layers Deposition rate 400 0A/min (deepening on power and temp)

WAYNE STATE UNIVERSITY Cheng Cleanroom E-beam evaporator x2

wafers

Two evaporators: BJD, FC Available sources: metals (Al, Cr, Cu, Au, Dual Guns with 4 pockets Ni, Pt, Ti, Mo),Si, Ge Substrate heating ~250 0C * There will be additional material fee for Au and Pt

WAYNE STATE UNIVERSITY Cheng Cleanroom Photographic Process

WAYNE STATE UNIVERSITY Cheng Cleanroom

“ Print with the light”

Cr mask in contact with wafers Light sensitive film

Contact Aligner Provide alignment in x,y,z directions Exposure resolution ~0.8µm

WAYNE STATE UNIVERSITY Cheng Cleanroom Photolithography (steps)

I. Spin-coating PR II. Soft Bake III. Alignment/ Exposure IV. Developer (Selectively remove PR)

WAYNE STATE UNIVERSITY Cheng Cleanroom SU-8

SU-8 ( from Microchem) A viscos polymer that can be spin- coated and produce microstructures

Negative Photoresist Thickness 1~300µm Microstructures with high aspect ratio 20

WAYNE STATE UNIVERSITY Cheng Cleanroom Thin Film Etching (Overview) I. Wet etching, isotropic etching: Au etch, Al etch, Cr etch, Ni etch

II. Wet etching, anisotropic etching (bulk micromachining): TMAH etch

III. Metal Lift-off

VI. RCA clean: wafer cleaning

V. Dry etching, anisotropic etching

LAM etcher ( polysilicon, nitride, SiO 2) DRIE (silicon); high aspect ratio silicon microstructures.

VI . Dry etching, isotropic etching Drytech (PR, PDMS)

XeF 2 (silicon) WAYNE STATE UNIVERSITY Cheng Cleanroom Wet etching

I. Isotropic Si HNO 3:HF:CH 3COOH

Substrate orientation II. Anisotropic (110) Si TMAH, KOH

Crystal Plane Orientation (111) Si

WAYNE STATE UNIVERSITY Cheng Cleanroom DRIE (Deep Reactive Ion Etching)

Bosch Process Silicon etch rate 0.6-0.7µm/loop; 3-4 µm/min

Mask: PR, SiO 2, Al

WAYNE STATE UNIVERSITY Cheng Cleanroom Drytech

Dry Isotropic etching of (Oxygen plasma, Asher)

Reaction gas: O 2, Ar, CF 4 Power Max 300W

Oxygen plasma is widely used for (1)Substrate cleaning (2)Removal of PR (3)Removal of polymer/organic materials (4)PDMS bonding

WAYNE STATE UNIVERSITY Cheng Cleanroom XeF 2

Xenon Difluoride (XeF2) Etching • Home-made equipment (Cheng, Xu) • Dry, Isotropic etching of Si

2XeF 2 + Si →2Xe + SiF 4

• High selectivity for Al, SiO 2, Si 3N4,PR,PSG • Typical etch rates of 1 to 3 µm/min

• XeF 2 reacts with water (or vapor) to form HF

WAYNE STATE UNIVERSITY Cheng Cleanroom Other Capabilities

Packaging Wafer Bonder Dicing Saw Wire Bonder

Characterization Surface Profiler Interferometer

WAYNE STATE UNIVERSITY Cheng Cleanroom On-Going Projects

Dr Yong Xu (Joined Wayne State 2002) NSF ECCS A novel 3-dimensional neural probe technology combining electrical and chemical interfaces (PI) NSF CMMI Collaborative Research: Fish-Inspired Ultra-Sensitive Infrasound Sensor for Critical Infrastructure Monitoring and Geo-Hazards Early Warning (PI) NSF ECCS CAREER : Wearable accelerometers for continuous respiratory sound monitoring (PI) NIH R21 Development of a neurotransmitter based epiretinal prosthesis (co-PI) NSF CBET Neurophysiologically-based computational platform for the characterization and optimization of retinal prosthetic stimulation (Co-PI)

Dr Amar Basu (Joined Wayne State 2008) NSF CBET Microfrationation in Droplets (FD) - Linking Proteomic Separations to High Throughput Functional Screening (PI)

Dr Mark Ming-Cheng Cheng (Joined Wayne State 2008) NSF CBET CAREER : A Robust, Chronic Neural Prosthesis Using High-Capacity Graphene Electrodes and Biodegradable Silicon Support (PI)

WAYNE STATE UNIVERSITY Cheng Cleanroom Resources

Related Courses ECE 5575 Introduction to Micro and Nano Mechanical Systems ECE 6570 Smart Sensor Technology I: Design ECE 7570 Smart Sensor Technology II: Characterization and Fabrication

Schedule https://my.ilabsolutions.com/service_center/show_external/2964/nan o-fabrication-core-facility

WAYNE STATE UNIVERSITY Cheng Cleanroom Nanotechnology

Nanotechnology deals with structures sized between 1 to 100 nanometers in at least one dimension, and involves developing materials or devices possessing at least one dimension within that size.

WAYNE STATE UNIVERSITY Cheng Cleanroom