Improving AlN & ScAlN Thin Film Technology for Next...
Transcript of Improving AlN & ScAlN Thin Film Technology for Next...
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 50Wafer Count
Str
ess
(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 St
ress
(MPa
)
Wafer Diameter(mm)
0
20
40
60
80
100
120
80W,288 MPa
100W,210 MPa
120W,-265 MPa
140W,-621 MPa
Def
ects
/100
um2
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