Deep Silicon Etching - Increasingly Relevant >20 … Silicon Etching - Increasingly Relevant >20...

©2016 SPTS Technologies - Confidential & Proprietary

Deep Silicon Etching

- Increasingly Relevant >20 Years On!

229th Electrochemical Society Meeting Dr Dave Thomas

Senior Director, Etch Product Management

31 May 2016

2

This presentation and the information contained within it is the property of SPTS Technologies and is confidential. Any duplication, disclosure, distribution, dissemination or copying

of this presentation or its contents or use for any purpose other than that for which it is supplied is strictly prohibited, without the prior written consent of SPTS Technologies. © 2016 SPTS Technologies

■ Origins & basis of the Bosch process

■ End markets & technologies

■ Evolution of plasma sources

■ Overview of DRIE diversity

■ Examples of Si etch capability

■ High rate etching

■ Importance of polymer etch step

■ Controlling profile, bow, tilt, scallops

& notching

■ Extendibility

■ Emerging biomedical applications

■ TSV etching & plasma dicing

■ End-point detection for DRIE

■ Blanket Si etching

■ Competing technologies to Bosch etching

■ Summary

Contents

3



■ Awarded IEEE Jun-Ichi Nishizawa Medal in Amsterdam in 2014

■ Patented in 1994

■ Licensed to other manufacturers

■ SPTS was the first licensee & shipped the first

etch tool based on the Bosch process in 1995

■ SPTS has shipped ~1,200 modules since

Bosch Process – The ‘Foundation’ of MEMS

Franz Laermer (VP Corp Sector Research & Advanced Engineering, Bosch Stuttgart)

Andrea Urban (Senior Expert, Eng Sensor Process Technol Dept, Bosch Reutlingen)

The development of the deep reactive ion etching

process by Franz Laermer and Andrea Urban

revolutionized the micro-electro-mechanical

systems (MEMS) industry by enabling cost-

effective production and proliferation of devices

such as the tiny sensors found in automobile air

bag and anti-skidding systems, as well as in

today’s smartphones and laptop computers.

http://www.ieee.org/index.html?WT.mc_id=hpf_logo

http://www.google.co.uk/url?url=http://robert-bosh-odbytova.czechtrade.us/&rct=j&frm=1&q=&esrc=s&sa=U&ei=hR0YVJyOFM7y7Abb8IFo&ved=0CBwQ9QEwAg&usg=AFQjCNGhqSq3wPX-U-hzT1sIfPzoSLVJrw

4



■ High mask selectivity

■ Deep etching

■ High net etch rate

■ Productive

■ Vertical ‘macro’ profile

■ Dimensional control

■ Scalloped ‘micro’ profile

■ Roughness

Bosch Process

Polymer Deposition

D = C4F8

Polymer Etch

E1 = SF6 or O2

Silicon etch

E2 = SF6

Loop

5



Si Etch Technology/Market Overlap

Adv Pack MEMS

RF & Power

Si thinning Range of

DRIE

processes

TSV

Dicing

Si etch-off

Carriers

Active &

isolation

trenches

• CIS

• Interposers

• 3D stacking

• FO-WLP

• MOSFETs

• IGBTs

• Super-junction

• GaN on Si

• Automotive

• Consumer

• Micro-fluidics

• Biomedical

http://www.google.co.uk/url?sa=i&rct=j&q=&esrc=s&frm=1&source=images&cd=&cad=rja&uact=8&ved=0ahUKEwjVo_7ajOHMAhVHChoKHT4_A08QjRwIBw&url=http://www.ridgetopgroup.com/products/advanced-diagnostics-and-prognostics/sentinel-interconnect/tsv-bist/&psig=AFQjCNFsJ2B3ZCyzK73kkjBBP5dU8Lvg_w&ust=1463574144963662

http://www.extremetech.com/wp-content/uploads/2015/01/HBM-Memory.jpg

http://www.google.co.uk/url?sa=i&rct=j&q=&esrc=s&frm=1&source=images&cd=&cad=rja&uact=8&ved=0ahUKEwjLq8H2jeHMAhXGbBoKHT8eCEYQjRwIBw&url=http://www.infineon.com/cms/en/about-infineon/press/press-releases/2009/INFIMM200906-065.html&bvm=bv.122129774,d.d2s&psig=AFQjCNFlFd863JSMvijQvclL7whtBrGjFA&ust=1463574465999941

6



Decoupled, Single

Sources

Process Module Evolution for DRIE

Si E

tch

ra

te

Si E

tch

qu

alit

y

(CD

, pro

file

, tilt ..)

ICP DSi Pegasus Rapier

DSi-v

Module selection

determined by

rate/quality

balance

HDPs Dual Source

1995 ~2005 Today

7



DRIE Diversity

High Aspect Ratio

1.6 x 98 µm trenches

~60:1 AR

Smooth walls

<20nm scallops

Through Wafer

Sensors

Microphones

NEMS

50nm features

High Rate

Cavities, Caps,

ink-jets High Aspect Ratio

~0.4 µm trenches

~90:1 AR

SOI

2.5 x 25µm

Low Tilt

<0.1º

Mixed isotropic/

anisotropic

processing

High Aspect Ratio

4 x 160 µm trench/TSV

40:1 AR

Complex shapes

High Aspect Ratio

8 x 180 µm trench/TSV

22:1 AR

High Aspect Ratio

1 x 40µm trench

8



High Rate ‘Non-Critical’ Etching

90

95

100

105

110

115

120

125

20

22

24

26

28

30

32

34

36

38

-1 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27

Pro

file

(˚)

Etc

h r

ate

(µ

m/m

in)

Run No

etch rate

ProfileRapier Mode (R7 to R14)Dual Source Results

37µm/min

±2% uniformity

~1,200 atomic layers/s

9



Microphone Acoustic Cavities

400µm deep

45% open area

11µm/min

±3% uniformity

100:1 selectivity

91.5º profile

400µm deep

26% open area

12µm/min

±3% uniformity

200:1 selectivity

93º profile

400µm deep

40% open area

17µm/min

±5% uniformity

150:1 selectivity

93º profile

10



Importance of Polymer Etch Step (E1)

Non-uniform polymer etch

affects Si etch direction

problems with tilt

Non-uniform polymer etch

affects Si etch width

problems with profile, CD & bow

Wafer position

Non-uniform ion density?

Non-uniform ion direction?

11



■ O2 plasma blanket removal of etch polymer

■ Measure of ion density variation at the wafer level

Polymer Removal Uniformity

Single Source Dual Source ICP

12



■ Example of 3.5 x 70µm (20:1 AR) trench

Impact on Profile Control

Dual Source

Profile range = 0.11°

Single source

Profile range = 0.18°

Parameter Single Source Dual source

Etch Rate (µm/min) 3.46 3.52

Profile (°) 89.54-89.72 89.93-90.04

Sidewall Roughness (nm) <130 <140

Solid symbols: W→E

Open symbols: S→N

S = notch

13



■ Example of 8 x 180µm (22:1 AR) trench TSV

Impact on Profile & Bow Control

Profile ranges

Rapier = ~0.14°

Rapier-cd (avg) = ~0.07°

14



Impact on Tilt

Fine tilt ~±0.15º

Single source Dual source

Fine tilt ~±0.6º

Gyro electrical data

15



Scallop Control = Smoother Walls

Faster gas switching Polymer in E2 step

2.7 x 55µm trench

<20nm Sc

10 x 70µm TSV

<30nm Sc

Base

Top

5 x 50µm TSV

~5nm ‘waves’

<10nm Sc

80 x 500nm trenches

~5nm ‘waves’

16



Control of Notching at SOI Layers

750 x 500µm

cavity

12µm/min

No notch

3 x 50µm trenches

~3µm/min

<120 nm notch

No Notch in 30µm trench

>50% overetch 1.4µm trench open Notches in the range 0-120nm

Continuous bias

15% over-etch Pulsed bias

25% over-etch

SPTS IP on

bias pulsing for

notch control

17



■ Ability to cope with future device dimensions

Extendibility to Sub-Micron Features

1µm

spacing

150nm

50nm

10µm spacing

■ … and all with a single hardware set

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■ Driving the demand for flexible Si etch technologies

Emerging Biomedical Applications

Micro-needles

(drug delivery)

Pillar arrays

(mixing & reactions)

Neural probe

Cell sorter

http://www.google.co.uk/url?sa=i&rct=j&q=&esrc=s&frm=1&source=images&cd=&cad=rja&uact=8&ved=0ahUKEwi56L3W0LjLAhXJJZoKHXjICrsQjRwIBw&url=http://www.meddeviceonline.com/doc/imec-ku-leuven-nerf-electronics-photonics-neural-probes-0001&psig=AFQjCNFLIM1CFOL1RYad7g8kLDGGJvR5Yw&ust=1457785548268499

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■ Required Via shape depends on subsequent deposition technology

TSV Etching Evolution

Top ~85µm

Base ~47µm

Profile ~77°

Top ~89µm

Base ~49µm

Profile ~63°

10 x 100µm

Sc ~100nm

Profile 90°

5 x 50µm

Sc ~70nm

Profile 90°

8 x 180µm

Sc <200nm

4 x 160µm

Sc <50nm

Continuous process

SF6 + passivant

Switched (Bosch) process

SF6/C4F8 cycling

CIS MEMS

50 x 130µm

Sc ~500nm

Profile ≤92°

75 x 150µm

Sc ~200nm

Profile ≤91°

MEMS Semi

20



■ Higher throughput

■ Parallel process

■ Higher die density

■ Die shape/location can be varied

■ Narrower dicing lanes (<10µm)

■ Lower damage

■ Bosch etch creates clean scallops

■ No vibrations, debris, water

■ Increased die strength

Plasma Dicing

20 x 100µm

10 x 100µm

7 x 120µm

Die back face

(>15µm notch)

21



■ Large operating envelope

■ Applicable to all DRIE etches to a stop layer

■ Detection limit <0.05%

Claritas™ End-point Detection

Etch Chamber

Rapid fluorination

of SiF to SiF4

Unable to ‘see’

SiF*

Claritas Unit

High concentration

of SiF4 cracked to

re-form SiF*

Easily detected

22



■ Via Reveal

■ For stacking TSV wafers

■ 5-10µm to reveal TSV tips

■ Si etch-off

■ For FO-WLP

■ 50-65µm to dielectrics/metals

■ Extreme thinning for Via-Last

■ For low cost TSVs

■ ~50µm to leave 5µm

Blanket Si Etching

Etch rate ~9µm/min

Uniformity ~±2%

3mm EE on 300mm wafer

Etc

h d

ep

th (

µm

)

Wafer position (mm)

End-point detection:

• ReVia for Via Reveal

• OES for Si etch-off

• NIR interferometry

for Si thinning

23



■ Wet etching

■ Preferential etching along crystal planes

■ OK only for large non-critical devices

■ Non-Bosch etching

■ Depth limit 20-50µm

■ Limited mask selectivity of ~20:1

■ Grass in larger features

■ Cryogenic etching

■ Interesting to academics

■ Smooth sidewalls

■ Max etch rate 2-3µm/min

■ Not manufacturable (-110°C, PR cracking etc)

■ LASER drilling

■ Crude features

■ No selectivity to under-layers

■ New materials

■ Glasses, polymers ….

Competing Technologies for Si Etching

24



■ Bosch etching has greater relevance today than it did >20yrs ago when it was invented

■ Applicable to growing range of markets/technologies

■ MEMS, Advanced Packaging, Power, RF & Biomed

■ Plasma reactors have evolved to address key needs

■ Higher etch rates higher productivity

■ Higher quality CD, profile, bow & tilt control

■ High rate processes in production at 37µm/min

■ Polymer etch step (E1) controls etch quality

■ By improving polymer etch uniformity from ~±20% to 1% ....

■ Profile variation 0.35º 0.07º in a 22:1 AR TSV

■ Bow 250nm 0nm

■ Tilt ±0.6º ±0.15º

■ Scallops controlled through gas switching & chemistry

■ Notching control using bias pulsing & end-point detection

■ Scalable to 50nm feature size

■ Used for Plasma Dicing for increased die per wafer & die strength

■ Optimized Si etch step for Via Reveal, Si etch-off & extreme thinning

■ 9µm/min, ±2% on 300mm wafers

■ Still competitive vs wet, non-Bosch, Cryo & LASER drilling

Summary

25



■ Matt Muggeridge, Janet Hopkins, Nicolas Launay,

Huma Ashraf & Tony Barrass

Acknowledgements

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