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