tcad simulations of isolation structures for n + -on-p silicon microstrip detectors

CERN, 14-16 November 2005RD50 workshopClaudio Piemonte

TCAD simulations of isolation structures TCAD simulations of isolation structures for nfor n++-on-p silicon microstrip detectors-on-p silicon microstrip detectors

Claudio PiemonteClaudio [email protected]@itc.it


OutlineOutline

• Why is this work needed?

• Device Simulations

- p-spray

- p-spray experience @ ITC-irst

- p-stop

- combined p-spray/p-stop

• Conclusion


Why are simulations needed?Why are simulations needed?

3 techniques available (from n+-on-n technology):

n+ n+oxide

strip 1 strip 2

p+

p- substrate

backplane

+ + + + + + + +

electron layer

isolation structureneeded to interrupt theinversion layer betweenthe strip

S1 S2S1 S2 S1 S2

p-spray p-stop p-spray/p-stop

Each technique affects differently VBR and Cint

simulations are needed to evaluate impact

high-field regions high-field regions


Simulated structureSimulated structure

n+ n+

strip 1 strip 2

p+

p- substrate

backplane

oxide

½ strip½ strip

2D simulations of a cross section orthogonal to the strips

Reference structure: pitch = 80m n+ width = 30m Na = 7e11cm-3

W = 300m Qox=4e11cm-2

0E+00

1E-13

2E-13

3E-13

4E-13

5E-13

6E-13

0 20 40 60 80 100Bias voltage (V)

Inte

rstri

p C

apac

itanc

e (F

/cm

)

w = 40m

30m

20m

w=40mm -> w/p=0.5w=30mm -> w/p=0.375w=20mm -> w/p=0.25

w=40m -> w/p=0.5w=30m -> w/p=0.375w=20m -> w/p=0.25

Pure geometrical Cint

(i.e. Qox=0, no isol. struct)


p-sprayp-spray


Transition voltage depends on the substrate concentration

Slope depends on w/p

Np1=Np2=Np3

Breakdown (1)Breakdown (1)strip 1 strip 2

oxiden+ n+

strip 1 strip 2oxide

n+ n+

VJBR = potential difference between p-spray and strip which causes breakdownVBR = bias voltage for which we reach VJBR

High Np => High VJBR

=> high VBR

Three p-spray peak concentrations:- Np1=4e16cm-3

- Np2=8e16cm-3

- Np3=12e16cm-3

0

20

40

60

80

100

120

0 200 400 600 800Bias Voltage (V)

p-s

pra

y p

ote

ntia

l (V

)VJBR

VBR

Np = 12e16cm-3

Np = 8e16cm-3

Np = 4e16cm-3

no impact ionizationmodel enabled

0

20

40

60

80

100

120

0 200 400 600 800Bias Voltage (V)

p-s

pra

y p

ote

ntia

l (V

)VJBR

VBR

Np = 12e16cm-3

Np = 8e16cm-3

Np = 4e16cm-3

VJBR

VBR

Impact ionizationenabled

0

20

40

60

80

100

120

0 200 400 600 800Bias Voltage (V)

p-s

pra

y p

ote

ntia

l (V

)VJBR

VBR

Np = 12e16cm-3

Np = 8e16cm-3

Np = 4e16cm-3


Breakdown (2)Breakdown (2)

VBR depends on:1) slope of Vp-spray vs VBIAS which depends on w/p and Na 2) VJBR level which depends on NP, QOX and field-plate

0

20

40

60

80

100

120

0 200 400 600 800

Bias voltage (V)

p-s

pra

y p

ote

ntia

l (V

)

1. 0e11cm-2

2. 4e11cm-2

3. 8e11cm-2

4. 12e11cm-2

5. 20e11cm-2

1

2

3

4

5

0

20

40

60

80

100

120

0 200 400 600 800

Bias voltage (V)

p-s

pra

y p

ote

ntia

l (V

)

1

2

3

4

5

1. 0e11cm-2

2. 4e11cm-2

3. 8e11cm-2

4. 12e11cm-2

5. 20e11cm-2

Np2=8e16cm-3 Np3=12e16cm-3

VBR increasesfor increasing Qox

because VJBR level increases

no isol.


Interstrip capacitance (1) Interstrip capacitance (1)

0.0E+00

2.0E-13

4.0E-13

6.0E-13

8.0E-13

1.0E-12

1.2E-12

1.4E-12

1.6E-12

1.8E-12

2.0E-12

0 50 100 150 200

Bias voltage (V)

Inte

rstr

ip C

ap

aci

tan

ce (

F/c

m)

1. Qox= 0e11cm-2

2. 4e11cm-2

3. 8e11cm-2

1

3

Np = 4e16cm-3

geometrical value

0.0E+00

2.0E-13

4.0E-13

6.0E-13

8.0E-13

1.0E-12

1.2E-12

1.4E-12

1.6E-12

1.8E-12

2.0E-12

0 50 100 150 200

Bias (V)

Inte

rstr

ip C

ap

aci

tan

ce (

F/c

m)

1. Qox = 0e11cm-2

2. 4e11cm-2

3. 12e11cm-2

4. 20e11cm-2

5. 25e11cm-2

6. 30e11cm-2

1

6

Np = 12e16cm-3

geometrical value

Np1=4e16cm-3

Np3=12e16cm-3

Cint increases with Np

Cint decreases with Qox

p-spray completely compensated => no isolation


0.0E+00

5.0E-13

1.0E-12

1.5E-12

2.0E-12

2.5E-12

3.0E-12

0 100 200 300 400 500Bias voltage (V)

Inte

rstr

ip c

ap

aci

tan

ce (

F/c

m)

High-dose p-spray case

no field-plate

5m field plate - Tox=500nm

5m field plate - Tox=900nm

Interstrip capacitance (2) Interstrip capacitance (2)

n+ n+

increases Cint by:

C=0.5 *ox *(FPW*L) *Tox-1

Effect of field-plate

Additional component decreases because p-spray is progressively depleted by field-plate

Tox

FPW


p-spray @ irstp-spray @ irst

First n+-on-p detectors with p-spray fabricated in 2004

n+

p-spray

p-spray profile along cut-lineNet-doping conc.

dose=3e12cm-2

dose=5e12cm-2

2 p-spray doses were used(labeled as low-doseand medium-dose)

Both doses isolate before irradiation


p-spray @ irst - breakdownp-spray @ irst - breakdown

SMART2 - FZ - Bias Line current @ 100V

1E+1

1E+2

1E+3

1E+4

1E+5

S1 S2 S3 S4 S5 S6 S7 S8 S9 S10Sensor #

I_B

L [n

A/c

m2]

low-dose

p-spray

med-dose p-spray

3 51 2 4 8 106 7 9

Vbias=100V

- Low dose p-spray no BD- Medium dose p-spray: 50m pitch no BD 100m pitch BD

- Exception: med. dose 100m pitch no BD because of larger p+

det# pitch w/pmetal

overhang[um]

1 50 0.3 42 50 0.4 43 50 0.5 44 50 0.3 25 50 0.3 6

6 100 0.15 47 100 0.25 48 100 0.35 49 100 0.25 6

10 100 0.25 8


Low-dose p-spray

High-dose p-spray

- At “low” voltages cap. dominated by field-plate: - larger field plate => higher capacitance - higher dose p-spray

=> longer decay

p-spray @ irst – interstrip capacitancep-spray @ irst – interstrip capacitance

det# pitch w/pmetal

overhang[um]

1 50 0.3 42 50 0.4 43 50 0.5 44 50 0.3 25 50 0.3 6

6 100 0.15 47 100 0.25 48 100 0.35 49 100 0.25 6

10 100 0.25 8


p-stopp-stop


BreakdownBreakdown

0

10

20

30

40

50

60

70

0 100 200 300 400 500 600 700 800bias voltage (V)

p-s

top

po

ten

tial (

V)

5um 10um15um 20um30um 40um

Qox = 1e12cm-2

Qox = 2e12cm-2

Similar approach to p-spray:1. determine Vp-spray = f(VBIAS)2. determine VJBR level

S1 S2

high-field regions

increasing p-stop width

p-stop potential is higher for wide implants better narrow p-stop from the breakdown viewpoint

VJBR

VJBR


0.0E+00

2.0E-13

4.0E-13

6.0E-13

8.0E-13

1.0E-12

1.2E-12

1.4E-12

1.6E-12

1.8E-12

2.0E-12

0 100 200 300 400 500Bias voltage (V)

Inte

rstr

ip C

ap

aci

tan

ce (

F/c

m)

Qox=4e11cm-2

growing p-stop width

40m30m

20m15m

10m

5m

Interstrip capacitanceInterstrip capacitance

S1 S2

inversion layer acts as an extensionof the n+ strip

narrow p-stop implies higher capacitance(opposite trend with respect to breakdown)

As Qox increases, interstrip capacitance increases


combinedcombinedp-spray/p-stopp-spray/p-stop


ConceptConcept

p-spray: VBR - low before irradiation - improves for increasing QOX

Cint - improves with irradiationp-stop: VBR - high before irradiation - decreases for increasing QOX

Cint - high and deteriorates for inc. QOX

improves with QOX

deteriorates with QOX

interesting solution is to combine the previous two using:- medium dose p-spray (to have sufficiently high initial VBR)

- 20/30m wide p-stop (to have low capacitance for high QOX)

Technology: - moderated p-spray (isolation structure realized with single implantation step)

- combined p-spray/p-stop (two implantation steps)


BreakdownBreakdown

0

30

60

90

120

150

0 200 400 600 800 1000Bias voltage (V)

p-s

top

po

ten

tial (

V)

1

2

3

4

5

VBR1 VBR2 VBR3

VBR4VBR5

1. Qox=0

2. Qox=4e11cm-2

3. Qox=10e11cm-2

4. Qox=20e11cm-2

5. Qox=30e11cm-2

For increasing QOX:S1 S2p-stopS1 S2p-stopS1 S2p-stop

1 3 4high-field regions high-field regions high-field regions2 5

VBR first increases(typical of p-spray)than decreases (typical of p-stop)as QOX grows


0.0E+00

2.0E-13

4.0E-13

6.0E-13

8.0E-13

1.0E-12

1.2E-12

1.4E-12

1.6E-12

1.8E-12

2.0E-12

0 100 200 300 400 500Bias voltage (V)

Inte

rstr

ip c

ap

aci

tan

ce (

F/c

m)

1. Qox=4e11cm-2

2. Qox=8e11cm-2

3. Qox=12e11cm-2

4. Qox=20e11cm-2

1

2

3

4

Interstip capacitanceInterstip capacitance

S1 S2p-stopS1 S2p-stopS1 S2p-stop

1 3 42

Cint first decreases(typical of p-spray)than increases (typical of p-stop)as QOX grows


ConclusionConclusion

• simulations well reproduce both breakdown and interstrip capacitance behavior in the p-spray case

• Among the simulated isolation structures, the combined p-spray/p-stop technology seems to be the most effective (as for n+-on-n detectors)

tcad simulations of isolation structures for n + -on-p silicon microstrip detectors

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