ESSDERC 2015

Substrate Noise Isolation Improvement by

Helium-3 Ion Irradiation Technique in a

Triple-well CMOS Process

Ning Li1, Takeshi Inoue2, Takuichi Hirano1, Jian

Pang1, Rui Wu1, Kenichi Okada1, Hitoshi

Sakane2, and Akira Matsuzawa1

1Tokyo Institute of Technology2S.H.I. Examination & Inspection, Ltd

Outline

• Background

• Methods to improve isolation

• Helium-3 ion irradiation

• Simulation results

• Experimental results

• Conclusion

Slide 1

Background

• Analog and digital circuits are integrated on the

same chip.

• Increase of digital circuit speed causes more

substrate noise coupling problems.

• Analog circuit supply voltage decreases.

Slide 2

Methods to Improve Isolation

• Decreasing noise

injection and noise

reception

– Guard rings

• Cutting the

propagation path

– Silicon on insulator

(SOI)

• High cost

– Proton bombardment

• High cost

– Helium-3 ion irradiation

Slide 3

Top view

Cross view

Noise

injectionNoise

reception

Noise propagation

High resistive region

Digital

circuitAnalog

circuit

Low Resistive

Si Substrate

Digital

circuit

Analog

circuit

Rsub,high»Rsub,low

Csub

Noise

injectionNoise

receptionHigh resistive region

Helium-3 Ion Irradiation

Slide 4

• Cutting the propagation path by increasing the substrate

resistivity

• Can be integrated into the standard process

• The design margin is about 15-mm for active device [1].

Helium-3

• high irradiation

efficiency

• small dose

• low process cost

Ref: [1] Ning Li, et al., TED, vol. 62, no. 4, April 2015.

High

resistive

region Low Resistive

Si Substrate

Al mask

Helium-3 Ion Beam from a cyclotron

Helium-3 bombardment from front

side to create a high resistive region

Aggressor

circuitVictim

circuit

Helium-3 Ion Irradiation Machine

Slide 5

Ion irradiation machine

Ref: https://www.shiei.co.jp/english/cyclotron_iis.html

(a)(b)

(c) (d)

(e)

(f) (g) (h)(i)

(j)

(a), (b): Vertical/horizontal scanning magnets

(c), (d), (e): Turbomolecular pumps

(f): Beam shutter

(g), (h): wafer gate valves

(i): Wafer

(j): Automatic wafer handling device

Configuration of Irradiation System

0

5

10

15

20

25

0 5 10 15 20 25 30 35 40

Qu

alit

y F

acto

r

Frequency [GHz]

Non-irradiation

w/ irradiation

Helium-3 Ion Irradiation Applications

Slide 6Ref.: Ning Li, et al., TED, vol. 62, no. 4, April 2015.

Irradiated area

270mm

Voltage controlled

oscillator

1-nH Inductor

• For inductor

– Improving inductor quality factor

• For voltage controlled oscillator

– 8.5dB improvement in phase noise

0 20 40 60 80 100 120 140

Re

sis

tivity (

Ω∙c

m)

Depth (μm)

Non-irradiation

w/ irradiation

100

101

103

104

105

102

Substrate Resistivity

Slide 7

Si surface

Dose : 2x1013cm-2

40mm 140mm

• Resistivity after helium-3 ion irradiation

0 20 40 60 80 100 120 140

Re

sis

tivity (

Ω∙c

m)

Depth (μm)

Non-Annealing

200℃×1h

400℃×1h Non-irradiation

100

101

103

104

105

102

Substrate Resistivity Cont’d

Slide 8

• Resistivity after annealing at 200ºC and 400ºC for 1h.

Dose : 2x1013cm-2

40mm 140mm

Si surface

Isolation Test

(c) diffusion tap with deep n-well (DNW) guard ring (GR) at one side

Slide 9

Low Resistive Si Substrate

Port1 Port2

High

resistive

region

N+/P+ N+/P+

Low Resistive Si Substrate

Port1Port2GND

P+/N+

GR

N+/P+ N+/P+High

resistive

region

Port1Port2GND

Deep N-well

N+/P+N+/P+

Low Resistive Si Substrate

High

resistive

region

(a) diffusion taps

(b) diffusion tap with

guard ring at one side

EM Simulation

• EM simulator

– HFSS

• Two-port

• P-diff. taps

– Area: 35x70μm2

– Distance: 100μm

• High resistive region

– Width: 50μm

– Thickness

• 65μm

• 130μm

Slide 10

50mm65mm, 130mm

130mm

100mm

High resistive region

P-diffusion35x70mm2

100mm

Top view

Cross view

Simulation Results

• A 10-dB improvement at 2GHz

• As frequency increases, the improvement

decreases due to the capacitive coupling

Slide 11

-50

-45

-40

-35

-30

-25

-20

0 1 2 3 4 5 6 7 8 9 10

S2

1(d

B)

Frequency (GHz)

Before helium-3 ion irradiation

65-mm thickness

130-mm thickness

10 dB improvement

Test Patterns

• W: diffusion width

• L: diffusion length

• D: diffusion taps

distance

Slide 12

Size (W*L)

(mm2)

Diff. Guard Ring

(GR)

Dist.

(mm)

① 35*140 N+ None 100

② 35*140 N+ None 150

③ 35*140 N+ None 200

④ 35*70 N+ None 100

⑤ 35*35 N+ None 100

⑥ 35*140 N+ P+ GR 100

⑦ 35*140 N+ P+ GR

and DNW

100

⑧ 35*140 P+ None 100

⑨ 35*140 P+ N+ GR 100

⑩ 35*140 P+ N+ GR

and DNW

100

DNW: deep n-well

Top view of test

structures

G

G

G

G

S

Top Metal

M1

WLS

3He2+

irrad.

region

D

Chip Photo

• A 180-nm standard CMOS process

• Substrate resistivity about 3~4 Ω∙cm

Slide 13

Chip photo1

2

3

45

6 7

8 109

Chip photo

Mask

Measurement Results (1)

• Measured noise isolation with respect to tap distance

• Increasing D from 100μm to 150μm improves noise

isolation 5dB, from 150μm to 200μm of 3dB at 10GHz

• Increasing D will increase chip area.

Slide 14

G

G

G

G

S

Top Metal

M1

WLS

3He2+

irrad.

region

D

-40

-35

-30

-25

-20

0 5 10 15 20 25 30 35 40

S2

1(d

B)

Frequency (GHz)

D=100

D=150

D=200

①

②

③

Measurement Results (2)

• Measured noise isolation with respect to tap size

• Large diffusion area causes more coupling.

Slide 15

G

G

G

G

S

Top Metal

M1

WLS

3He2+

irrad.

region

D

-40

-35

-30

-25

-20

0 5 10 15 20 25 30 35 40

S2

1(d

B)

Frequency (GHz)

W=35, L=140

W=35, L=70

W=35, L=35

①

④

⑤

-70

-65

-60

-55

-50

-45

-40

0 5 10 15 20 25 30 35 40

S2

1(d

B)

Frequency (GHz)

Non-irradiation

w/ irradiation

w/ annealing

⑦

Measurement Results (3)

• Isolation is maintained after annealing at 200ºC for 1 hour.

Slide 16

TEG Guard Ring

(GR)

⑦ P+ GR

and DNW

G

G

G

G

S

Top Metal

M1

WLS

3He2+

irrad.

region

D

Measurement Results (4)

• Isolation is improved for all test patterns after helium-3 ion irradiation.

• A 10-dB improvement (90% noise reduction) is achieved for patters with GR.

Slide 17

Guard Ring

(GR)

① None

⑥ P+ GR

⑦ P+ GR and

DNW

⑧ None

⑨ N+ GR

⑩ N+ GR and

DNW

G

G

G

G

S

Top Metal

M1

WLS

3He2+

irrad.

region

D

Dist. (mm)

① 100

② 150

③ 200

Size (W*L)

(mm2)

① 35*140

④ 35*70

⑤ 35*35

-60

-55

-50

-45

-40

-35

-30

-25

-20

S2

1(d

B)@

2G

Hz

Test structrue number

Non-irradiation

w/ irradiation

① ② ③ ④ ⑤ ⑥ ⑦ ⑧ ⑨ ⑩

Conclusions

• Helium-3 bombardment is proposed to create a local semi-insulated substrate of high resistibility.

• Noise isolation is improved about 10dB at 2GHz after helium-3 ion irradiation.

• A 90% noise reduction has been achieved for test structures with guard rings.

• The noise isolation can be kept even after annealing at 200ºC for 1 hour.

Slide 18

Acknowledgements

• This work was partially supported by MIC,

SCOPE, and VDEC in collaboration with Cadence

Design Systems, Inc., and Mentor Graphics, Inc.

Slide 19

Thank you for your attention

Slide 20