Oxford ICP-CVD SixNy Recipe Development

PRISM Cleanroom 2019

Oxford ICP-CVD open chamber

Gas Disc

Clamp

Stage

Oxford ICP-CVD SiN @ 250 ˚C

4% SiH4/Ar N2 Pressure ICP Temperature Dep RateThickness Non-

uniformityStress

AverageBOE etch

rate Avg. R.I.

sccm sccm mTorr W ºC Å/min ±% MPa Å/min

290 5.7 12 1500 250 97 < 3.0 -300 15 2.02

1.85

1.95

2.05

2.15

2.25

2.35

4.3 4.8 5.3 5.8 6.3

Refr

activ

e In

dex

N2 flow (sccm)

N2 flow vs Refractive Index

12/12/2018

12/21/2018

Linear (12/12/2018)

Linear (12/21/2018)

Optimized for R.I. and thickness uniformity SiN recipe parameters

y = 96.763xR² = 0.999

0

500

1000

1500

2000

2500

3000

3500

0 5 10 15 20 25 30 35

Thic

knes

s (A)

Deposition Time (min)

SiN at 250 deg C – thickness vs. deposition time

y = 15.639xR² = 0.9958

0

200

400

600

800

1000

1200

1400

0 20 40 60 80 100Si

N E

tch

dept

h (A

)

Etch Time (min)

SiN etch rate in BOE 10:1 analyzed by KLA profilometer

Oxford ICP-CVD SiN @ 250 ˚C – pinhole density analysis

Run 4% SiH4/Ar N2 Pressure ICP Temperature Time Average Thxsccm sccm mTorr W ºC mm:ss (Reflectometer) Å

Run13 290 5.7 12 1500 250 02:00 195Run14 290 5.7 12 1500 250 05:00 447

The KOH etching of Si (100) at 80 °C is fast: 75 µm/hour (https://cleanroom.byu.edu/KOH), highly anisotropic and forms pyramidal structures with (111) crystalplanes. If pinholes are present in SiN film deposited on Si wafer, the undercut beneath the film should be observed due to the highly anisotropic etching.

Nomarski microscopy analysis of Si/SiN (195 Å) after 10 min etch in 30 % KOH @ 80 °C

Nomarski microscopy analysis of Si/SiN (447 Å) after 10 min etch in 30 % KOH @ 80 °C

200 µm

200 µm

There were no pinholes observed for Si/SiN (195 Å) and Si/SiN(447 Å) when wafer surface was analyzed 10 mm form the edge.Single pinholes (< 5 pinholes/mm2) were observed only close tothe wafer edge.

200 µm

200 µm

Wafer center Wafer edge

Wafer center Wafer edge

Correlation between process parameters and SiN @ 250 ˚C film propertiesRun 4% SiH4/Ar N2 Chamber

Pressure ICP Thx. Non-uniformity

DepositionRate

(10 min deposition)

RefractiveIndex

Stress(Average on 4’’

wafer)MPa

BOE 10:1 etch rate(5 min etch)

A/minsccm sccm mTorr W % A/min

PressureRun43 290 5.7 14 1500 1.8 92 2.0464 -692 10Run44 290 5.7 13 1500 1.5 94 2.0308 -443 13Run42 290 5.7 12 1500 1.2 95 2.0239 -233 15Run45 290 5.7 11 1500 0.7 97 2.0096 -106 15Run46 290 5.7 10 1500 0.8 97 2.0067 -71 15PowerRun47 290 5.7 12 2000 1.2 140 1.9503 122 28Run48 290 5.7 12 1800 0.9 122 1.9815 106 22Run42 290 5.7 12 1500 1.2 95 2.0239 -233 15Run49 290 5.7 12 1300 1.7 81 2.0299 -818 11Run50 290 5.7 12 1000 2.6 61 2.0250 -1045 11

N2 flowRun53 290 4.5 12 1500 5.9 70 2.3206 -797 31Run54 290 5 12 1500 0.8 81 2.0978 -528 15Run55 290 5.5 12 1500 0.8 91 2.0372 -241 12Run42 290 5.7 12 1500 1.2 95 2.0239 -233 15Run57 290 6 12 1500 2.2 103 1.9765 41 17Run58 290 6.5 12 1500 3 110 1.9487 126 18

5“RED” - Selected ICP-CVD SiN @ 250 ˚C recipe

Effect of chamber conditioning

1.98

1.982

1.984

1.986

1.988

1.99

1.992

1.994

1.996

1.998

2

0 100 200 300 400 500 600 700 800

SiN

Ref

ract

ive

Inte

x

SiN Thickness [nm]

Thickness of SiN film on Chamber Walls vs. R.I.

88

89

90

91

92

93

94

95

96

97

98

0 100 200 300 400 500 600 700 800De

porit

ion

Rate

(A/m

in)

SiN Thickness [nm]

Thickness of SiN film on Chamber Walls vs. Deposition Rate.

More reproducible data can be obtained when chamber is conditioned with 350 nm of SiN.

Oxford ICP-CVD SiN @ 250 ˚C – process stability

4% SiH4/Ar N2 Pressure ICP Temperature Time Thx. Non-uniformity Avg R.I.sccm sccm mTorr W ºC mm:ss ±%290 5.7 12 1500 250 10:00 < 3.0 2.02

Oxford ICP-CVD SiN @ 250 ˚C – Recipe: OPT SiN @ 250 – 9 nm/min

9492

9496

88 87

92

86

8991 92

90 90 90 91

86 86

9193

91

99 100

95 95

101

91

80

82

84

86

88

90

92

94

96

98

100

102

Depo

sitio

n Ra

te (A

/min

)

Oxford ICP-CVD SiN @ 250 deg process check

SiN R.I.=2.02 ± 0.01Avarage stress: -340 ± 20 MPaThickness nonuniformity < 3% (on 4'' Si wafer, excluding 10mm from the edge)

Minimum deposition time to obtain uniform SIN thickness

Uniform SiN film was obtained after 1min deposition, but 30s deposition produced islands of SiN.

Cross-sectional SEM of the SiN deposited @ 250 ˚C on GaAs for 30 sec Cross-sectional SEM of the SiN deposited @ 250 ˚C on GaAs for 1 min

Data obtained by Ding Huang

Breakdown voltage for ICP-CVD SiN grown at 250 deg C

PECVD SiN @ 250 ˚C t = 952 ± 11 Å, n = 1.993

525±25µm Si: P/B (1-0-0) 0.001-0.005 ohm-cm

Ti/Au = 20/200 nm

Ti/Au = 20/200 nm

Effect of process temperature on SiN film properties

10

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

50 70 90 110 130 150 170 190 210 230 250 270

SiN

thic

knes

s non

-uni

form

ity (%

)

Process temperature (deg C)

SiN thickness non-uniformity vs. process temperature

1.96321.9784

2.00382.01834 2.01896

1.8

1.85

1.9

1.95

2

2.05

2.1

2.15

2.2

50 70 90 110 130 150 170 190 210 230 250 270

R.I.

Process temperature (deg C)

SiN refractive index vs. process temperature

0

10

20

30

40

50

60

70

80

50 70 90 110 130 150 170 190 210 230 250 270

Etch

rate

(A/m

in)

Process temperature (deg C)

SiN etch rate in BOE 10:1 vs. process temperature

SiN film properties such as: thickness uniformity, refractive index and BOE etch rate are getting wore with decreasing deposition temperature

Effect of SiH4 flow and RF power on low temperature SiN thickness and R.I non-uniformity

Run 4% SiH4/Ar N2Pressure

Process Value ICP RF Temperature Dep RateThickness Non-

uniformity Avg R.I.R.I. Non-

uniformity±%sccm sccm mTorr W W ºC Å/min ±%

Run11 290 5.7 12 1500 0 250 94.2 1.2 2.020 1.7Run111 290 5.7 12 1500 0 70 116 4.7 1.963 3.3Run119 320 5.7 12 1500 0 70 117 3.7 1.993 4.3Run117 350 5.7 12 1500 0 70 108 7.6 2.108 6.8Run113 290 5.7 12 1500 20 70 124 11.2 1.942 0.4Run120 320 5.7 12 1500 20 70 118 7.3 1.986* 0.4Run121 350 5.7 12.9 1500 20 70 126 16.7 2.142 2.3

* - Average from 4 points (TOP, BOTTOM, LEFT and RIGHT), R.I. can not be measured in the center

1.85

1.9

1.95

2

2.05

2.1

2.15

2.2

2.25

250 270 290 310 330 350 370 390 410 430 450

R.I.

4%SiH4 in Ar (sccm)

SiN R.I vs SiH4 flow

RF = 0 W

RF = 20 W

(Run 120) 4% SiH4/Ar = 320 sccm, RF = 20 W

(Run 121)4% SiH4/Ar = 350 sccm, RF = 20 W

Low temperature ICP-CVD SiN film characterize significant thickness and refractive index non-uniformity across the 4’’ wafer; Increased SiH4 flow and RF power does not improve low temperature SiN thickness uniformity

8 µm deep and 5 µm wide Si trench etched by Bosch RIE

8k mag level

Si

SiNx

Silicon nitride (SiN) on 8 µm deep and 5.2 µm wide Si trench

a

c

ba = 0.85 µmb = 0.38 µmc = 0.50 µm

ICP-CVD SiN coverage of 8 µm Si trench etched by Bosch RIE4% SiH4/Ar N2 Pressure ICP Temperature

sccm sccm mTorr W ºC290 5.7 12 1500 250