etching of silk - an organic low-k material€¦ · etching of silk - an organic low-k material...

Etching of SiLK - an OrganicLow-k Material

Cecilia Quinteros, Ph.D.Helen Zhu

PEUG meeting - April 11, 2002

2

Lam Research Confidential PEUG 4/11/02

Outline

• Principles of Etching SiLK– SiLK - Basic Material Properties– Chemistry for SiLK Etching– Process Characterization and Trends

• Etch Challenges and Solutions

• Etching Porous SiLK

• Summary

Principles of Etching SiLK

4


SiLK - Organic, Spin-on, Low-k Dielectric Film.Basic Material Properties• SiLK: Aromatic Hydrocarbon -- Pure Organic

– No Fluorine, no Silicon -- C, H, O, …

• K < 2.65• Coat and Cure

– Coating is spin-on. Curing is needed.– SiLK J has 3.25% adhesion promoter which contains Si– Porous SiLK is based on SiLK I.

Ref. Scott Cummings - Dow Chemical ; PEUG March 2001

Process Step SiLK I SiLK J PorousDispense Promoter Yes No YesBake Promoter @ 185C for 60 secs Yes No YesDispense SiLK Yes Yes YesBake SiLK @ 325C for 90 secs Yes Yes YesCure SiLK on hot plate or furnace Yes Yes YesAdhesion Promoter No Yes No

5


1 1.5 2 3 42.5 3.5

Low K OSG

SiLK

High K OSGPorous SiLK

0.0

0.1

0.2

0.4

0.7

0.3

0.6

0.8

0.9

0.5

Dielectric Constant

To

ug

hn

ess,

MP

a-m

^1/2

SiO2

SiLK Properties:Dielectric Constant and Resistance to Stress


6


• SiLK + H2 C2H2, C2H4, *C3H2+, H2O, OH+, ...

(CxHyOz) + O2 CO2, CO, H2O, OH+, …

+ N2 *C3H2N+, CO, NO, NCO, NH+.

Graphitized SiLK (Carbon Skeleton)

* Polymer Precursors: Large Molecules or Radicals or Ions formed & decomposed, … yielding less or non-volatile products.

SiLK Etch ---- Reaction of SiLK with H2, O2, N2

7


Chemistry for SiLK Etch - SiLK Etch Rate (Blanket)*

• Conclusions:1). N2: More physical etching (compared to H2)2). H2: More chemical Etching3). O2: Chemical and Physical Etching (ER: O2>N2>H2)

* Ref: D.Fuard, et al., J. Vac Sci. & Technology., B19 (2001)447

SiLK Etch Rate (Blanket) *

0

20

40

60

80

100

120

140

0 20 40 60 80 100 120

H2 or O2 %

SiL

K E

tch

Rat

e (A

/s)

O2 %

H2 %

Etch Chemistry: N2+O2 or N2+H2

8


Process Characterization -Plasma Optical Signal Detection during SiLK Etch

387 nm (CN)

9


N/H Trends - SiLK ViaER and Uniformity: Wide Process Window for SiLK Etch

Increasing N/H ratio and/or total flow does not strongly influence ER butimproves ER uniformity

uniformity

0

10

20

200/600 500/600 900/350

N2/H2

Un

iform

ity (

+/-%

)

ER

0

100

200

300

1:3 ~1:1 ~3:1

N/H

ER

(n

m/m

in)

1:3 ~1:1 ~3:1

N/H

10


N/H Trends - SiLK ViaER and Uniformity: Effect of Generator Power

ER

0

100

200

300

1500/0 1000/500 1500/500

27MHz/2MHz

ER

(n

m/m

in)

Uniformity

0

2

4

6

1500/0 1000/500 1500/500

27MHz/2MHz

Un

ifo

rmit

y (+

/-%

)

Higher 27/2 RF power ratio and higher total power increases ER and improvesuniformity

Etch Challenges and Solutions

• Single Damascene• Dual Damascene

• Integration Schemes

• Process Challenges

• Lam Solutions for Integrated SiLK Etch

12


Dual-HM SiLK Single Damascene Trench Etch

• CD Bias <10nm • No bowing

Pre-etch Structure

SiN

SiLK

SiNSiO2

ARC

PRPR

Si

1. ARC/Mask OpenPR

ARC

SiN

SiNSiO2

PR

SiLK

2. SiLK Trench Etch

SiN

SiLK

3. Barrier Open

SiLK

Si SiCu

• Low Facet and

Mask Erosion• No undercut

SiO2SiN

SiO2SiN

13


Dual-Hard Mask SiLK Etch - Trench pattern definitionfor DD scheme

• CD Bias <10nm

Pre-etchStructure

SiN

SiLK

SiNSiO2

ARC

PRPR

Si

1. ARC/OxideMask Open

PRARC

SiN

SiO2

PR

SiLK

Cu

SiLK

SiN

• CD Bias <10nm

2. PR Strip

SiN

SiO2

SiLKSiLK

SiN

• Ready for DD

3. Arc Deposition4. PR Deposition

5. Via Lithography

SiN

SiLKSiLK

SiN

SiO2

PR PR

ARC

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Dual Hard Mask DD SiLK Etch without Stop Layer

SiLK

SiN

SiO2

ARC

Pre-etch Structure

PR PR

SiN

SiO2

ARC

• CD Bias<10nm

ARCPR PR

50nm

1. ARC/Via Mask Open

• No bowing

SiNSiO2

2. SiLK Via Etch

SiLKSiLK

SiN

Si CuSiN

Si CuSiN

Si Cu

~100nm

15


Dual Hardmask DD SiLK Etch without Stop Layer -continued

SiLK

•Minimal mask facet•No mask undercut

3. Trench Mask Open

SiLK

•No microtrenching•No residues

4. SiLK Trench Etch

SiLK


5. Finish Etch

SiN

Si CuSiN

Si CuSiN

Si Cu

SiO2

SiN

SiO2

SiN

SiO2

SiN

16


Dual Hardmask DD SiLK Etch Steps with Stop Layer

SiLK

SiN

SiO2

ARC

Pre-etch Structure

PR PR

SiLK

SiN

SiO2

ARC

• CD Bias<10nm

ARCPR PR

50nm

1. ARC/Via Mask Open

• No bowing

SiLK

SiNSiO2

2. SiLK Via Etch

SiN SiN SiN

SiNSi Cu

SiNSi Cu Si Cu

SiN

17


Dual Hardmask DD SiLK Etch Steps with Stop Layer-continued

SiLK


3. Trench Mask Etch

SiLK

• No microtrenching•No residues

4. SiLK Trench Etch

SiLK


5. Finish Etch

SiN SiN SiN SiN SiN SiN

SiO2

SiN

Si CuSiN

Si CuSiN

SiO2

SiN

Si CuSiN SiN

SiO2

SiN

18


Other possible SiLK DD Integration Schemes:

• Self Aligned

• Trench First Via Last

• Via First Trench Last

19


Etching Challenges and Solutions

• CD/Profile control– Pressure -- change in process regime– Pressure -- Neutral/ion ratio– Temperature -- sticking coefficient– Additives -- Polymer precursors

• Microtrenching– Bias power– Pressure– Temperature– Polymer addition

HighPress.

High T

Optimized:Verticalprofilewith goodCD andfacetcontrol

LowPressure

Low T HighCHxFy &highPressure

Optimized:

Vertical profilewith no bowing,no residue , andnomicrotrenching.

20


Etching Challenges and Solutions:Via CD:Knobs:

2 MHz Power (W)

ESC Temperature

500 W (2 MHz)/40 °C

0 W (2 MHz)/0 °C

Facet:Knobs:

2 MHz Power (W)

ESC Temperature

500 W (2 MHz) / 40 °C

0 W (2 MHz) / 0 °C

21


Dual HM SiLK Etch

• Etch Performance– Vertical profile– Minimum HM facet– Residue-free– No under cut, no bow– Flat and smooth trench etch front– No residue/ grass/ pitting, no

microtrenching– Etch rate– Good profile (No bowing)– Maintain critical dimensions

(CD)...

Etching of Porous SiLK

23


Porous Low-k Etch Integration:Similar Integration Schemes as Non-Porous Materials

Typical Film Stack for DD Porous or Non-porous SiLK:

100-150 nmSiO2

300-700 nmPorous SiLK

Silicon

40-60 nm SiN

40-100 nm SiN

SD Trench Post-Etch

Cu


Uniform Pore Distribution formechanical integrity and

performance

Not very large pores forprotection against shorts

Closed Pores. Channels cantrap chemicals

24


Dense and Porous SiLK Etch - SD Via Comparison

SiLK Porous SiLK

• Similar results obtained using the same process

• 10 to 30% higher etch rate for porous SiLK

25


Single Damascene processing with porous materials

Etch front roughness iseliminated when encountering astop layer

Etch Front Progression

26


Etch rate Comparison

SiLK ER (A/min) OSG ER (A/min)Non-Porous 2250 2437

Porous 2970 3286ER Ratio 1.32 1.35

• Porous low-k etch rates are typically 20-30% higherthan the non-porous film

27


SiLK Porous SiLK

Dense and Porous DD SiLK Etch - Comparison

• Dense and Porous SiLK: similar etch behavior: Etch Process recipe can be easily transferred fromdense SiLK

• Higher Etch Rates for porous material• Similar Integration• For porous SiLK, rough etch front might require stop layer

28


Dense and Porous SiLK Etch - Summary

• Optimized SiLK etch process for Single and Dual Damascene applications have beendeveloped on Lam Research dielectric etch systems, down to 130 nm feature CD.

• Different chemistries (reducing or oxidizing) can be used to etch SiLK.

• SiLK profile and microtrenching can be improved by gas additives and/or optimizingpressure, ESC temperature, and RF power.

• Responses such as HM facet, bowing and CD can be finely controlled using gasflows, 27 MHz power, 2 MHz power and pressure as factors. Process factors with thegreatest effect on process performance vary with feature dimension.

• Dense and Porous SiLK etching display similar process trends, making processestransferable from dense to porous SiLK with ease. An porous SiLK DD integratedscheme has been demonstrated

29


Acknowledgements

• Contributions for this presentation by:– Howard Dang– Seokmin Yun– Tom Choi– Charlie Chu– Hyun Ho Doh

are gratefully acknowledged

etching of silk - an organic low-k material€¦ · etching of silk - an organic low-k material...

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