effects of dual bias frequency on sio2 contact hole etching ......dual bias frequency (1.8mhz +...

C O N F I D E N T I A L

Etch Product Business Group

Effects of Dual Bias Frequency on SiO2 Contact Hole Etching in Very High Frequency Fluorocarbon Plasmas

Wonseok Lee, Shawming Ma, Jang Gyoo Yang, Daniel Hoffman and Yan Ye

Dielectric EtchApplied Materials

PEUG Meeting, Mar 10, 2005

Applied Materials Confidential

2


WS Lee

Outline

Requirement of High Aspect Ratio (HAR) contact etch– Polymer deposition and ion energy distribution

Dual bias effect on ion energy distribution– Bias frequency selection– Simulation of ion energy distribution

Process results of high frequency source/dual bias chamber– Profile control– Process window

Conclusion


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Why High Ion Energy Necessary for HARC?

Typical requirements for advanced HAR etching process- Highly selective process (to mask and sub-layer) : thick polymer generation- vertical profile is necessary : need easy penetration of reactive ion through polymer layer

: Polymer layer: Reactive layer

2000 AVS, ASET

Oxide etching surface

High selectivity Thick polymer deposition over the reactive layer Decreases net ionenergy penetrating through polymer layer low etch rate & tapered profileHigh aspect ratio Ion energy decreases at the bottom of hole due to ion scattering and shading effect from hole entrance low etch rate & tapered profileHigh incident Ei is necessary for high etch rate and vertical prHigh incident Ei is necessary for high etch rate and vertical profile in HARofile in HAR


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Vrf Behavior with VHF and 13.56MHz Bias

- Measuring tool : z-scan(z-Ware)- Wafer type : Si dummy wafer - Measuring plasma condition : HARC etching condition with PET process

- Measuring Vrf at 10sec processing time

Measuring plasma condition : HARC etching condition with PET process

Source power

0 1000 2000 3000 4000 50000

200

400

600

800

1000

1200

1400

1600

1800

1850Watts

Waf

er V

olta

ge (-

V)

Bias Power(W)

0Ws 100Ws 200Ws 300Ws 400Ws 500Ws 600Ws 700Ws 800Ws 900Ws 1000Ws 1500Ws 2000Ws

The efficiency of The efficiency of VVrfrf rise withrise withbias power starts to get gentlebias power starts to get gentle

over reasonable source and bias powersover reasonable source and bias powers

Low

High


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Candidates for Increasing Ion Energy

- Increase the ratio of Area_ground/Area_powered cathode: Asymmetric sheath-> area ratio improvements already obtained.

- Increase RF bias generator capacity and try higher bias power: Vrf can only increase 1.4X with 2 X power increaseSome customers restrict available maximum power.Match box and ESC durability at very high power

- Low frequency (2MHz): Limited plasma striking capability at low pressure

More limited RIE mode plasma at low pressure

- Dual frequency (13.56MHz/2MHz): Best candidate for HAR process regime


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WS Lee

Enabler DFB Chamber Overview

Very high frequency source (>100MHz) giving very low DC bias on the top electrode

Controllable plasma density and neutral dissociation for different applications

Two additional knobs –CSTU and NSTU to tune etch rate and CD uniformities

Very wide, easily tunable and usable operating windows

Ion Energy Distribution tunability by DFB

~

~

Polymer/plasma confinement

2.0 MHz RF Bias Power

Charged species tuning unit (CSTU)

Neutral species tuning unit (NSTU)

Wafer Temperature Control

>100 MHz VHF Source

~

13.56 MHz RF Bias Power


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Ion density/power input

100% 1.8 MHz

50% 1.8 MHz

100% 13.56 MHz

Ion Energy

Ion Energy Distribution

By Total Bias Power

By B

ias

Pow

er R

atio

13

25

60

>100

100

Plasma Technology for Critical EtchDual Bias Frequency (1.8MHz + 13.56MHz) for Ion Energy Distribution (IEDF) Tunability

Frequency (MHz)

Application of 2 & 13 MHz bias enables ion energy tuning and maintainsplasma density decoupling

The width of distribution is tunable by changing the bias power ratio of 2 frequenciesThe center of distribution is tunable by changing the total bias power

Dual bias frequency (2.0MHz + 13.56MHz) can provide the right ion energy distribution needed for future critical etch applications


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WS Lee

Tunable Ion Energy Distribution by Dual Frequency Bias (2.0/13.56MHz)


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200 400 600 800 1000 1200 1400

0.02

0.04

0.06

0.08

Energy (Volts)

Den

sity

(arb

uni

ts)

.

.

.

.

.

.

.

.

.

.

.Freq

uenc

y Mix

(13MHz /

2MHz)

100% / 0%

80% / 20%

60% / 40%

40% / 60%

20% / 80%

0% / 100%

By properly mixing2MHz and 13MHz,the IEDF width canbe controlled whilemaintaining constant average energy

IEDF Overlay–13MHz / 2MHz Mixing FractionConstant Vpp Waveform Across Sheath


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Other Frequency Considerations

2 or 13MHz/VHF (and 2MHz/>100MHz)– Even though we top-launch, our >100MHz high voltage point is on

the wafer (by design, typically Vwafer/Vroof~3)– The >100MHz rf voltages on the wafer are very low, so the major

effect is source modifies 2 or 13MHz distribution by only relative density impact

2/27MHz or 2/60MHz– Complex: the 27MHz/60MHz contributes to both density creation and

to ion energy adjustment– This leads to less orthogonality.

2/13MHz bias with >100MHz source– 2/13 achieves the “dialable” energy distribution– >100MHz independently adjusts the density effect


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WS Lee

Window of Deep Etch Comparison

green is (n,Emin, Emax) space; red is achievable by Enabler

Single Frequency Bias withVHF source

Dual Frequency Bias withVHF source

10 mT 30 mT

vlow vhigh, n,( ) eminopt emaxopt, nopt,( ),vlow vhigh, n,( ) eminopt emaxopt, nopt,( ),vlow vhigh, n,( ) eminopt emaxopt, nopt,( ), vlow vhigh, n,( ) eminopt emaxopt, nopt,( ),

10 mT 30 mT

Large fractions of the(n, Emin, Emax)

volume are achieved

We can just achieve the lowerend of this space,

and only at lower pressures


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Blanket Thermal Oxide Etching with DFB

Baseline Process(single frequency bias)

Bias Ratio(13.56MHz/2MHz)

Power Ratio (2MHz/13.56MHz)

Cotour Map

Etch Rate(A/min) 3820 3729 3624 3530Uniformity(1sigma,% 1.5 1.52 2.3 1.59

Uniformity(M-m,%) 3.02 3.03 4.91 3.08Bias Power(W)

(13.56MHz-2MHz)Power Ratio

(2MHz/13.56MHz)

Contour Map


Uniformity(M-m,%) 6.66 6.24 7.1 7.65

13.56 only 7 3 1.7

0 0.14 0.33 0.6

1 0.6 0.33 0.14

1 1.67 3 7

-1 0 1 2 3 4 5 6 7 83000

3100

3200

3300

3400

3500

3600

3700

3800

3900

2

3

4

5

6

7

8

9

Etc

h R

ate

(A/m

in)

Ratio of [P2MHz/P13.56MHz]

Mm

Uni

form

ity(%

)

As 2MHz fraction increases, uniformity is getting worse buttends to be saturated at 7% Mm over 1:1 ratio and also

etch rate drops due to lower density.


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WS Lee

Uniformity Tuning by CSTU

Baseline ProcessDual Frequency Bias (75% 2 MHz) vs CSTU

Outer CSTU(A) 4.5 5 5.5 6

Cotour Map


Uniformity(M-m,%) 7.22 5.22 6.82 5.95

Inner CSTU(A) 4.5 5 5.5 6

Contour Map


Uniformity(M-m,%) 14.78 12.35 11.52 11.83

4.0 4.5 5.0 5.5 6.0 6.53000

3100

3200

3300

3400

3500

3600

3700

3800

3900

2.0

2.5

3.0

3.5

4.0

4.5

5.0

5.5

6.0

6.5

7.0

7.5

8.0

Etc

h R

ate

(A/m

in)

Outer CSTU (A)

Mm

Uni

form

ity(%

)

4.0 4.5 5.0 5.5 6.0 6.52800

2900

3000

3100

3200

3300

3400

3500

6

8

10

12

14

16

Etc

h R

ate

(A/m

in)

Inner CSTU (A)

Mm

Uni

form

ity(%

)

Outer CSTU

Inner CSTU

Outer CSTU looks more effective totune the etch rate uniformity


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Polymer Deposition Shape With DFB

P13.56MHz/(P13.56MHz+ P2MHz)

Pre 100% 71% 19%

Internal Data

Higher ratio of [2MHz/13.56MHz]– Less sidewall polymer deposition, – Reduce necking and bowing. – Etch front improved with the mixed bias powers


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WS Lee

Pattern Wafer Etching with DFB0.18µm hole/248nm resist/TEOS

0 1 2 3 4 5 660

80

100

120

140

160

180

0.40

0.45

0.50

0.55

0.60

0.65

CD

(nm

)

Ratio of [2MHz/13.56MHz]

BT

Rat

io (%

)

Btm CD

Top CD

BT Ratio

Top/Btm CD & BT Ratiovs. DFB Ratio

0 1 2 3 4 5 63000

3500

4000

4500

5000

5500

6000

4.0

4.5

5.0

5.5

6.0

6.5

7.0

7.5

8.0

Etc

h R

ate

(A/m

in)

Ratio of [2MHz/13.56MHz]

Sel

ectiv

ity to

PR

Etch rate & Selectivity to PRvs. DFB Ratio

As 2MHz fraction increase (up to 1:3)- Profile is getting more vertical(Btm CD/BT ratio increase)

- No significant effect on etch rate- Selectivity to resist increases


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WS Lee

Striation Comparison with DFB0.18µm hole/248nm resist/TEOS


100% 78% 47% 26% 16%57% 37%

Data Shown with Customer Permission

More 2MHz Fraction

No impact on striation (resist integrity)


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WS Lee

0.15µm hole/248nm resist/TEOS

Pattern Wafer Etching with DFB

TEOS Etch Rate Facet Sel. PR Bottom CD

-0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8

4550

4600

4650

4700

4750

4800

4850

4900

4950

Center Edge Avg

TEO

S E

tch R

ate

@0.1

5um

(A/m

in)

2.0/13.56MHz Bias Ratio(Ptotal

=3800W)

-0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8

5.5

6.0

6.5

7.0

7.5

8.0 Center Edge Avg

Face

t Sel

ectivi

ty t

o P

R @

0.1

5um


=3800W)

-0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8767880828486889092949698

100102

Center Edge Avg

Bott

om

CD

@0.1

5um

(nm

)


=3800W)

Almost same trend as 0.18um etching characteristics


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WS Lee

Etch Stop Window and Etching Profilevs DFB Mix (x% 13 MHz power)

E

100% 73% 50%

50% increase

37%23%,

More power

incr

easi

ng

O2

Vdc

Wider etch stop window

Getting more vertical

Internal Data



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WS Lee

0.15um 0.20um 0.25um 0.30um

13.56MHzonly

Mixed DFB50%

Hole size

PositiveRIE lag(DFB)

ReverseRIE lag(Single)

Etch stop

RIE Lag (ARDE) vs DFB Ratio

0.14 0.16 0.18 0.20 0.22 0.24 0.26 0.28 0.30 0.321.501.551.601.651.701.751.801.851.901.952.002.052.10

Etch

ing

Dep

th (u

m)

Hole Size (um)

13.56 only bias13.56/2.0 mixed bias (50/50%)

Internal Data


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WS Lee

Optimized Process Comparison Between 13.56MHz Single and 13.56/2MHz Dual frequency Bias

13.56MHz only 13.56MHz/2.0MHz Mixed

Top CD 152nmBtm CD 93nmBow CD 172nm

Top CD 152nmBtm CD 112nmBow CD 165nm


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WS Lee

Conclusion

Dual bias 2/13.56 MHz frequency with VHF source is capable of modulating ion energy distribution while maintaining similar iondensity

Combination of VHF source(>100MHz) and 2/13.56 MHz dual frequency bias has wider process window – Larger bottom/top CD ratio – Wider etch stop window– Better control of microloading/RIE lag– Some selectivity improvement– No striation dependence on the bias power ratio

effects of dual bias frequency on sio2 contact hole etching ......dual bias frequency (1.8mhz +...

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