Aluminum Etching usingReactive Ion Etch (RIE)

Felynncia Rainey

Advisor: Dr. James Zhou

Summer Undergraduate ResearchSomething(SURE)

08/1/03

Overview

• Introduction

• Plasma Etching

• Aluminum Etching

• Sample Composition/Creation

• Experiment

• Conclusion

• Acknowledgements

Introduction

• The purpose of this research was toinvestigate the effect that the variation ofdifferent factors, such as plasma chemicalcomposition and pressure, had on featuresidewalls.

Plasma Formation

qExcitation of incidentelectron

qChain reaction ofmolecules

Plasma Etching

qSurface chemistryqAdsorption

qChemical Bond Formation

qBy-product Molecule

qDesorbtion of by-product molecule

qRemoval by-product from chamber

RIE Etching

• Wafers sit on apowered electrode.This sets up anegative bias on thewafer whichacceleratespositively chargeions toward thewafer surface

Aluminum Etching

qChlorine Plasma CompositionqBCl3qCHCl3qCl2

qChemical purposeqBCl3 – removes aluminum oxideqCHCl3 – passivates the sidewallsqCl2 – etches aluminum

Overview of ExperimentqFour VariablesqCl2 flowqBCl3 flowqCHCl3 flowqPressure

qStandard RecipeqCl2 (10 sccm)qBCl3 (40 sccm)qCHCl3 (3 sccm)qPressure (40 mT)

qExamine: Effect on Sidewalls

Terminology

qIsotropic

qAnisotropic

qRe-entrant sidewalls

qPositive sidewalls

Sample Composition/Preparation

qSilicon Wafer

qDeposit SiO2

qDeposit Al

qPhotolithography

qEtch

Silicon Wafer

SiO2

Al

SEM Picture: Etch feature

Experiment: Variation of BCl3

PressureCHCl3 flowBCl3 flowCl2 flowSample

4032210Sample 7

4032810Sample 6

4033410Sample 5

4035810Sample 4

4035210Sample 3

4034610Sample 2

4034010 Sample 1

Experiment: Variation BCl3

• Sidewalls close to vertical (90±3% )

• Difference between extremes significantProfile of Side Walls

92.55

87.0186.7

89.94

88.7388.7888.99

83

84

85

86

87

88

89

90

91

92

93

22 28 34 40 46 52 58

BCl3 (sccm)

Sid

ewal

l An

gle

(d

egre

es)

SEM Picture: Sample 4

• BCL3 (58 sccm)

• Angle: 89.54°

SEM Picture: Sample 7

• BCl3 (22 sccm)

• Angle: 88.99°

SEM Picture: Control Sample

• BCl3 (40 sccm)

• Angle: 88.55°

Experiment:Variation of CHCl3

6

5

4

3

2

1

0

CHCl3

404010Sample 23

404010Sample 24

404010Sample25

404010Sample 22

404010Sample 1

404010Sample 21

404010Sample 20

PressureBCl3 flowCl2 flowSample

Experiment: Variation of CHCl3

• Lowest flow rate: Sidewalls re-entrant (< 90°)

• Vertical sidewalls (90°±3%)

• Highest flow rate: Sidewalls positive slope (> 90°)Side Wall Profiles

91.67 93.1788.99

92.54 93.4

124.65

86.07

0

20

40

60

80

100

120

140

0 1 2 3 4 5 6CHCl3 (sccm)

Side

wal

l Pro

file

(deg

rees

)

SEM Picture: Sample 20

• CHCl3 (0 sccm)

• Angle: 86.07°

SEM Picture: Control Sample

q CHCl3 (2 sccm)

q Angle: 88.99 °

SEM Picture: Sample 25

• CHCl3 (22 sccm)

• Angle: 124.65°

Experiment:Variation of Cl2

3

3

3

3

3

3

3

CHCl3

404014Sample29

404018Sample30

404022Sample31

404010Sample 1

40406Sample28

40403Sample27

40400Sample26

PressureBCl3 flowCl2 flowSample

Experiment:Variation of Cl2

• Positive Initial Sidewalls (> 90°)

• Vertical Sidewalls (90°±3%)

• Re-entrant sidewalls (< 90°)Sidewall Profile

104.35

91.15

106.7

87.99

66.97

75.96 74.11

0

20

40

60

80

100

120

0 3 6 10 14 18 22

Cl2 (sccm)

Sid

ewal

l Ang

le(d

egre

es)

SEM Picture: Sample 26

• Cl2 (0 sccm)

• Angle: 104.35°

SEM Picture: Sample 27

• Cl2 (3 sccm)

• Angle: 91.15°

SEM Picture: Sample 31

• Cl2 (22 sccm)

• Angle: 74.11°

Experiment:Variation ofPressure

PressureCHCl3flow

BCl3 flowCl2 flowSample

6034010Sample 13

5234010Sample 12

4434010Sample 11

4034010Sample 10

3634010Sample 1

2834010Sample 9

2034010 Sample 8

Experiment: Variation ofPressure

• Lower pressure samples: Re-entrant sidewalls• Control: Nearly Vertical (90±3% )

• Higher pressure samples: Positive sidewallsSidewall Profile

79.82

62.62 65.48

106.96

97.46

88.99 98.34

0

20

40

60

80

100

120

20 28 36 40 44 52 60

Pressure (mT)

Sid

ew

all

An

gle

(De

gre

es

)

SEM Picture: Sample 9

q Pressure (28 mT)

q Angle: 62.42°

SEM Picture: Sample 11

• Pressure (44 mT)

• Angle: 106.96°

SEM Picture: Sample 12

• Pressure (52 mT)

• Angle: 98.34°

Best Sidewall Profile

q Sample 27

q Cl2 (3 sccm)

q Angle: 91.15 °

Conclusion

qBCl3

qBCl3 did not significantly affect the profile ofthe side walls.

qCHCl3

qCHCl3 does affect the profile of the side walls.qNo CHCl3 – isotropic etchqIncrease CHCl3 - more anisotropicqHighest levels of CHCl3 - Positive sidewalls

Conclusion (cont)

qCl2qPositive Sidewalls-Low Cl2 etch rate is less. Did

not etch target area completelyqVertical Side wall-Enough Cl2 to etch target areaqRe-entrant- Over etching of sidewalls. Isotropic.

qPressureqRe-entrant- Molecules not hitting vertically.qPressure where sidewalls are more verticalqPositive Slopes-Molecules hitting the sample hard.

Low selectivity of etch target.

Acknowledgements

Dr. Gray May

Dr. James ZhouEric Woods

Somaskanda Thyagaraja

Leslie George

Matthew Leidy