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