Post on 26-Jul-2019
Improving AlN & ScAlN Thin Film Technology for
Next Generation PiezoMEMS
SEMICON Taiwan 2016 - MEMS FORUM
Nick Knight
PVD Product Manager, SPTS Technologies
SPTS Technologies
• Global presence
– Headquartered in the UK
– Manufacturing sites in UK and US
• Deep domain expertise
• Established and long standing partnerships with major industry players
A leading manufacturer of etch and deposition process solutions and
equipment for the semiconductor manufacturing industry
CVD Etch PVD *Thermal Release Etch *Sold under agreement with
SPP Technologies
Volume AlN Adoption in MEMS / RF
• AlN key resonator component in BAW filters
• Precise control of film properties required
• Front end equipment used for volume MEMS
Courtesy of Qorvo
AlN resonator layer
Deposited by PVD
BAW Filter Market Trends
• 41 separate RF bands supported by a smartphone
– Different countries, different carriers, GSM to 4G
• There are 20 BAW filters in an iPhone 6S
– Duplexers for 9 bands. Bandpass & rejection filters
• We estimate 8B BAW filters were shipped in 2015
• Although phone growth slowing, BAW content increasing
Source: Qorvo Website
Source: Qorvo Website
MEMS Microphone Content Increasing
• Up to 4 MEMS mics in a modern smartphone
• Large arrays give stronger signal, better pick-up
• To support large arrays need:
– High signal to noise ratio (SNR)
– Tight tolerance, mic to mic
• Capacitive mic read signal across two near surfaces
– Surfaces can stick together. Sensitive to dust & moisture
– Acoustic resistance (air in gap), has noise
• In a piezo mic, sound deflects AlN plates
– Creates strain, converts into electrical signal
– Insensitive to particles, moisture – hydrophone potential
– No acoustic resistance, high Signal to Noise Ratio (SNR), 68 dB(A) vs 65 for Cap
PiezoMEMS Microphones
PiezoMEMS Capacitive
pMUT Fingerprint Sensors
• Capacitive sensors rely on pushing surfaces together
– A ridge closes the gap, valley does not. Can be fooled by dirt, moisture,
oils
• A pMUT sensor uses ultrasonic reflections
– Finger valleys contain air – strong echo
– Ridges give weak echo
– Generate a 3D image, with some depth information
• Impervious to moisture, grime. More fool-proof
• AlN used for the ultrasonic resonator material
• Rapidly growing market – 17% CAGR to $14B by 2020
Sigma fxP is used for development/pilot production
AlN
Market Leader for Piezo AlN
• Working with AlN since 1998
• Example applications:
– BAW filters/duplexers
– Sensors, actuators
– Gyroscopes, Energy Harvesters
– Microphones/speakers
– Si oscillators
• Largest AlN install base
– ~50% market share More AlN shipments
and more production
accounts than any
other vendor
Sigma c2L Sigma fxP
R&D Production
Loadlocks 1 1 or 2
Degas/Pre-clean 1 1
PVD Modules Up to 2 Up to 5
≤ 200mm PVD System Options
Cavity
AlN
Electrodes
Substrate
Typical PiezoMEMS Process Flow
• SPTS has expertise in all deposition & etch steps
Sigma® PVD Omega® Synapse
plasma etch
HF or XeF2
vapor etch
Underlayer
Preparation
AlN etch
AlN
Deposition
Top
Electrode
Deposition
Release etch
Electrode
Deposition
Process Module Hardware
• Planar rotating magnetron
– Adjustable magnet position
– Adjustable motor speed
• AlN Sputter in Ar/N2 environment
– Reactive deposition by Pulsed DC
• Electrode uses same hardware
• >90% uptime in AlN production fab
13.56 MHz Platen RF
Platen
13.56 MHz Coil RF
Process Gas • Combined degas/pre-clean
• ICP Ar sputter etch
‒ High density plasma above wafer
‒ Wafer separately biased
‒ Low energy, high flux at wafer
• Patented smoothing etch
Smoothing Etch AlN Texture FWHM
“Rough” oxide underlayer No >2.5°
“Rough” oxide underlayer Yes 1.4°
RHSE
Module
Platen
Target
Magnetron
PVD
Module
Doped AlN
• AlN is the CMOS friendly choice
– Able to integrate into monolithic devices – CMOS MEMS
– Mature, understood, cost-effective
• Sc-doped AlN
– Higher coupling coefficient
– Kt2 6.5% → 8.5%
– Improved signal strength
– Improved battery life
• Other materials considered
– MgX-AlN (X = Hf, Zr) – Taiyo Yuden
– Y-AlN – TU Wien
– Ti-AlN – Univ Linkoping, Univ Madrid
– Cr-AlN – Univ Penn
Film stress, MPa
AlN
ScAlN
Source: Internet
Sc Adoption
• BAW
– Working in 5 - 15 Wt% Sc range
– Several BAW manufacturers now working with ScAlN
• MEMS
– Ideally looking for up to 43 Wt% Sc for sensors
– Improved sensitivity vs PZT
– BUT…costs need to be considered
Sigma fxP used for ScAlN programs at major
BAW and MEMS manufacturers
BKM recipes available
AlSc PVD Target Manufacturing
• Melt Casting Target
– Challenging alloy system prone to macro
segregation
– Currently limited to < 15 at% Sc
– Exhibits low oxygen content < 200ppm
– Higher Sc% extremely brittle & can fracture
during processing
– >15 At% Sc development continues
• Powder Processed Target
– Currently required for Sc >15 at% due to the
presence of brittle intermetallic
– Highest Sc content of interest ≤ 43 at%
– Powder based products exhibit high oxygen
content >>1000ppm
Casting Powder
Processing
Super Uniformity ScAlN
• WIW thickness uniformity critical to yield
– Thickness determines resonant frequency
• ‘Super Uniformity’ hardware developed
• Radial NU changed by adjusting magnet offset
– Fine tuning through magnet rotation speed
adjustment
• Non-radial NU adjusted by rotating the wafer
N N S S
Increasing offset gives more
deposition at centre of wafer
Wafer Rotating Platen
1.3 µm ScAlN
< 0.3% 1σ, 3 mm EE 200 mm wafer
• Steep reduction in AlN thickness at wafer edge on 200 mm wafers
– High density ions near major erosion zone re-sputtering AlN film below
– Films create surfaces too steep/thin for trim correction
• B-MAX solution steers ions away from wafer edge
• 200 mm WIW NU Spec based on 10 mm EE
– B-MAX extends mm EE for spec to 3 mm EE
• Qualified and in production
B-MAX - Improving AlN Yield
Previous B-MAX
ScAlN Stress Control
• RF Bias used to control stress of AlN film
– More ion bombardment -> more compressive film
• Control Options
– Forward Power
– DC Bias
• Film Thickness
– Increasing thickness requires higher bias
for set stress level
• Sc doped films require enhanced stress control
Ar+ e- Ar+ e-
e-
Matching
Unit 13.56 MHz
Generator
0
50
100
150
200
0 5 10 15 20 25 30 35 40 45 50
Wafer Count
Str
es
s (
MP
a)
Don’t Trust 2D Linescans!
• New hardware optimizes WIW stress range
• Resolves any non-radial stress component
– Often hidden with 2D Line Scans
Region of non-radial
compressive AlN.
Tests suggest plasma
related.
Stress Range < ± 50 MPa
ScAlN Grain Morphology
• ScAlN films have tendency to form high density single crystal defects
• Reduces Q, etch issues, affects top electrode growth
• Highest density in wafer centre
centre centre centre
edge edge
Controlling Crystal Defects
• Defect density strongly dependant on stress
– Density increases with high tensile stress
– Defect density highest in wafer centre matching max tensile stress
-200
-100
0
100
200
300
400
0 50 100 150
Str
ess
(MP
a)
Wafer Diameter(mm)
0
20
40
60
80
100
120
80W,288
MPa
100W,210
MPa
120W,-265
MPa
140W,-621
MPa
Def
ects
/100u
m2
Defects Density with Stress -1200nm ScAlN
center
mid
edge
Increasing
tensile stress
Centre
Tensile stress
Edge
compressive
Stress Control Techniques Applied
• 1300 nm (< 10At%) ScAlN on Si
• Mean stress ~360 MPa
• Patent application in progress
Centre Edge
<1 defects per 100um2 <1 defects per 100um2
AlScN WIW Thickness & Stress
• 1µm AlSc8.2%atN Film
– NU < 0.3%1σ
• Symmetrical stress profile
200mm wafer
3 mm EE
Summary
• RF BAW continues to grow
• New devices increases AlN adoption
• ScAlN needed for both BAW and MEMs devices
– Increased Kt2
– Improved SNR, low power efficiency
• Thickness and Stress are key requirements
• We provide high performance, highly productivity solutions
– 20+ years experience
– Excellent thickness uniformity and stress control features
– Reliable systems
If you would like to ….
• …. find out more about SPTS & ScAlN deposition or any of our other
served markets….
• Please come and visit us at Booth #324