a low temperature technology on the base of hydrogen enhanced thermal donor formation for future...

A Low Temperature Technology on the Base of Hydrogen Enhanced Thermal Donor Formation

for Future High-Voltage Applications

R. Job 1, A.G. Ulyashin 1, W.R. Fahrner 1, 1 University of Hagen, Dept. of Electrical Engineering and Information

Technology (LGBE), Germany

F.J. Niedernostheide 2, H.J. Schulze 2, 2 Infineon AG, Munich, Germany

E. Simoen 3, C.L. Claeys 3, 4, 3 IMEC, Leuven, Belgium

4 University of Leuven (KU), Dept. of Electrical Engineering, Belgium

G. Tonelli 5 5 INFN, Pisa, Italy

Dr. Reinhart Job, University of Hagen, Germany

Outline of the Talk

• Introduction

• Experimental (substrates, H-plasma treatments & annealing)

• Experimental Results (analysis by SRP measurements, I-V and C-V curves, DLTS, Raman spectroscopy, SEM, TEM )

• Discussion (low temperature doping by thermal donors

low thermal budget technology for special devices,i.e. high-voltage devices, radiation detectors, etc.)

• Summary


Thermal Donors (TDs)

• 'Old thermal donors' (TDs), oxygen related double donors (TDDs)

– formation at T 300 - 500 °C

– T > 550 °C TDs are dissolved

– family of 'bistable' double donors TDD1, TDD2, ... , TDD16, ... (?)

– classification by IR-absorption spectroscopy

– 2 energy levels of the donor: 70 meV, 150 meV

– formation rate R correlated with [Oi] and [Cs]: [Oi] high R high, [Cs] high R low

• Our investigations: 'Old thermal donors' (i.e. TDDs)

• Other types of TDs: NDs, NTDs, STDs


Thermal Donors

• 'New donors' (NDs) – formation at T 550 - 800 °C

– R correlated with [Oi] and [Cs]: [Oi] high R high, [Cs] high R high

– energy level of the donor: 17 meV

• 'New thermal donors' (NTDs)– formation at T 300 - 500 °C

– NTDs appear only after very long annealing times (> 105 min)

– NTDs double donors

– large agglomerates of oxygen (?)

• 'Shallow thermal donors' (STDs)– formation at T 300 - 500 °C (low concentrations)

– family of 7 single donors


Low Thermal Budget Doping by Thermal Donors

• Hydrogen enhances thermal donor (TD) formation in Cz silicon

• Thermal donors: 'old' TDs, i.e. TDDs (oxygen related double donors)

• Counter doping of initial p-type Cz Si by hydrogen enhanced TD formation formation of deep p-n junctions

• Developed process routes:- "1-step-process"- "2-step-process"


Experimental

• Substrates:

– p-type Cz Silicon wafers

( = 3 inches, d 370 - 380 µm, (100)-oriented)

Impurities:

[Oi] 7 - 81017 cm-3 (specified, IR-Absorption)

[Cs] < 51016 cm-3 (specified)

Doping:

= 12 - 20 cm, = 5 - 10 cm, = 1 - 2 cm

[B] 61014 cm-3 - 1.31016 cm-3


Experimental

Applied measurements:

“Spreading-Resistance-Probe”- (SRP-) measurements- resistance profiles in dependence on the depth- estimation of the location of p-n junctions

Thermoelectrical Microprobe Method (‘Seebeck-Effect’)- determination of the type of doping (n-type / p-type)

C(V) measurements- characterization of p-n junctions due to TD formation

Infrared- (IR-) absorption measurements- characterization of TD types (”TDDi- family")

I(V) measurements- characterization of diodes (”TD-Diodes”)


"1-Step-Process" for TD Formation

• Hydrogen enhanced TD formation in Cz Si only by H-plasma treatment

• "1-step-process":TDD formation during H-plasma treatment(Tplasma = 400 - 450 °C, tplasma 30 min)

• Cz Si wafers: [B] = 11015 cm-3, [Oi] = 7 - 81017 cm-3

• Example: DC plasma treatment (RIE setup, 500 V plate voltage, 440 µA/cm2) formation of TDDs, [TDD] 11016 cm-3 formation of deep p-n junctions (counter doping)


Formation of p-n Junctions ("1-Step-Process")

SRP measurements:

p-n junction location

Substrate:12 cm Cz Si, [B] = 11015 cm-3

(p-type)

H-Plasma:30 min at 400 °C (1-step-process)

0 100 200 300 400 50010

3

104

105

106

30 min DC H-Plasma

Tpl = 400 °C

p-typen-type

p-n junctionSR

(

)

Depth (µm)



Free carrier concen-tration Nc in depen-dence on the depth


(p-type)


0 100 200 300 400 500 60010

14

1015

1016

30 min DC H-Plasma

Tpl = 400 °C

n-type p-type

p-n junction

NA

[Nc]

(cm

-3)

Depth (µm)



Electron concentra-tion Ne(TD) due to TDDs in dependence on the depth


(p-type)


0 100 200 300 400 50010

14

1015

1016

p-type

n-type

p-n junction

NAN

e(T

D) (

cm-3

)

Tiefe (µm)



C(V) measurements:

C-3 Vbias linear graded junction


(p-type)


0 -5 -10 -15 -20 -25 -300

1x10-6

2x10-6

3x10-6

4x10-6

5x10-6

C-3

(p

F-3

)

VBIAS

(V)



SRP measurements:

p-n junction location


(p-type)


0 100 200 300 400 50010

3

104

105

106

45 min DC H-Plasma / Tpl = 400 °C

p-typen-type

p-n junctionSR

(

)

Depth (µm)



Free carrier concen-tration Nc in depen-dence on the depth


(p-type)


0 100 200 300 400 50010

14

1015

1016


p-typen-type

pn-junction[N

c] (

cm-3

)

Depth (µm)



SRP measurements:

p-n junction depth in dependence on the initial p-type doping

Substrate:1, 12 cm Cz Si, [B] 1015, 1016 cm-3

(p-type)


0 100 200 300 400 50010

3

104

105

106

107

12 cm1 cm


SR

(

)

Depth (µm)



SRP measurements:

p-n junction depth in dependence on the amount of incorpo-rated hydrogen


(p-type)


0 100 200 300 400 50010

3

104

105

106

107

108


440 µA cm-260 µA cm

-2

SR

(

)

Depth (µm)



C(V) measurements:

Ne(TD) in dependen-ce on the hydrogen dose


(p-type)

H-Plasma:at 400 °C (1-step-process)

0 5x1018

1x1019

2x1019

2x1019

0

5x1015

1x1016

2x1016

2x1016

Ne

(TD

) (cm

-3)

H-dose (cm-2

)



SRP measurements:

p-n junction depth in dependence on the plasma treatment time


(p-type)

H-Plasma:30 - 120 min at 400 °C

(1-step-process)

0 100 200 300 400 50010

3

104

105

106

107

DC H-Plasma / Tpl = 400 °C

120 min

45 min

30 min

SR

(

)

Depth (µm)


Kinetic Analysis of the "1-Step-Process"

]H[K]H[Kt

]H[

]H[K]H[K2x

]H[D

t

]H[

222

12

222

12

2

H

DH: diffusion constant of atomic hydrogen

K1 : rate of H2 formation

K2 : dissociation constant of H2 molecules

Time dependences of H and H2 concentrations:



kT

48.0exp1067.9D

kT

EexpK,DR8K

3H

b2H01

K1 : rate of H2 formation

K2 : dissociation constant of H2 molecules

DH: "Van Wieringen-Warmholtz" relation diffusion constant

R0 : capture radius (R0 = 5 Å *))

: vibration frequency of the dissociation of H2

Eb: binding energy (Eb = 1.6 eV)

*) J.T. Borenstein et al., J. Appl. Phys. 73, 2751 (1993)



]H[Kt

]N[3

TD

NTD: concentration of thermal double donors ("TDD")

compensation (p-n junction): 2 [NTD] = [B]

K3 : free parameter (deduced by fitting of experimental data)

K3 = 3.810-2 s-2

Boundary condition:

x = 0, t 0: [H0], with [H0] = 1014 cm-3

(constant hydrogen concentration at the wafer surface)

Time dependence of [TD] :



Simulated curves:

[TDD], [H], [H2] in dependence on the depth

Assumption:T = 400 °Ct = 30 min(1-step-process)

[TDD]-profile:

K3 = 3.810-2 s-2 (Fit to exp. Data)

0 100 200 300 400 50010

10

1011

1012

1013

1014

1015

1016

[H2]

[H]

[TDD]

[H],

[H

2],

[T

D]

(cm

-3)

Depth (µm)



Comparison of simulated [TD] profiles & experimental data

Assumption:T = 400 °Ct = 30, 45, 120 min(1-step-process)

Fit to exp. Data:

K3 = 3.810-2 s-2

0 100 200 300 400 50010

13

1014

1015

1016

1017

p-n junctions (exp.)

tplasma = 120 min

tplasma = 45 min

tplasma

= 30 min

[TD

] (c

m-3

)

Depth (µm)



Summary / Conclusions:

• "1-Step-Process": various processes occur

– T > 200 °C no acceptor passivation

– incorporation of hydrogen from the plasma ambient

– formation and decay of H2 complexes

– diffusion of H via interstitial lattice sites

– H lowers the barrier for the diffusion of Oi

– probability is enhanced that Oi forms a TD complex

hydrogen supports the TD formation

– loss of Oi due to the incorporation of Oi into TD-complexes

Question: Charge state of hydrogen (H0, H+, H-) ?


"2-Step-Process" for TD Formation

• Hydrogen enhanced TD formation in Cz Si by H-plasma treatment and subsequent annealing

• "2-step-process":TDD formation during post-hydrogenation annealing- H-plasma exposure: Tplasma 250 °C, tplasma = 60 min - annealing: Tanneal 450 °C, tanneal 15 min

• Cz Si wafers: [B] = 11015 cm-3, [Oi] = 7 - 81017 cm-3

• Example: PECVD plasma treatment (110 Mhz, 50 W, 440 µA/cm2) formation TDDs / p-n junctions, [TDD] 11016 cm-3



SRP measurements:

p-n junction depth in dependence on the post-hydrogenation annealing time

Substrate:1.8 - 2.6 cm Cz Si, [B] 71015 cm-3

(p-type)

H-Plasma:60 min at 250 °C Annealing:at 450 °C/air

0 100 200 300 40010

3

104

105

106

15'10'

= 1.8 - 2.6 cm

480'240'120'60'45'30'20'

wafer thickness: 367 + 5 µm

SR

(

)

Depth (µm)



SRP measurements:

p-n junction depth in dependence on the post-hydrogenation annealing time

Substrate:5 - 10 cm Cz Si, [B] 21015 cm-3

(p-type)

H-Plasma:60 min at 250 °C Annealing:at 450 °C/air

0 100 200 300 40010

3

104

105

106

240'480'

30' 120'60'45'10' 15' 20'

= 5 - 10 cm

wafer thickness: 378 + 5 µm

SR

(

)

Depth (µm)



• "2-step-process": 60 min RF H-plasma at 250 °C+ annealing at 450 °C/air

• Hydrogen supports the formation of TDs, i.e. TDDs

• Supposition: TD formation / depth of p-n junctions penetration of n-type regions into

the wafer bulk are driven by H diffusion

• "Fick's Diffusion Law":

[H]: hydrogen concentration, D: diffusion constant, t: time,

]H)[D(t

]H[



• "Fick's Law":

• if D = const.

(D: diffusion constant, d: depth, t: time, [H0]: surface concentration)

• mean diffusion length:

• assume: p-n junction depth dpn proportional to diffusion length L:

dpn L, i.e. dpn t1/2

tD4

derfc]H[]H[ 0

tD4L

]H)[D(t

]H[



p-n junction depth:

description by the "Fick's diffusion law"

(D: diffusion constant)

linear slope

D = 2.9 10-7 cm2s-1 (5 - 10 cm Cz Si)

D = 7.9 10-7 cm2s-1

(1.8 - 2.6 cm Cz Si)

0 50 100 150 2000

100

200

300

400

= 5 - 10 cm

= 1.8 - 2.6 cm

De

pth

(µ

m)

t1/2

(s1/2

)

tD4L



• Relation of Van Wieringen and Warmholtz (VWW):

(Ea = 0.48 eV)

• VWW equation holds for atomic hydrogen !

• extrapolation to 450 °C: DVWW = 4.36 10-6 cm2/s

• experiment: D 7.9 10-7 cm2s-1 (1 cm Cz Si) D 2.9 10-6 cm2s-1 (5 cm Cz

Si)

Tk

Eexp67.9D a

H



RF H-plasma exposure at room temperature:

p-n junction formation only after long time annealing at 450 °C (t > 8 hours)

Substrate:12 - 20 cm Cz Si, [B] 1.11015 cm-3

(p-type)

H-Plasma:60 min at RTAnnealing:at 450 °C/air

0 50 100 150 200 250 300Depth (microns)

104

105

106

107

SR

(O

hm

)

8h 30'

8h

8h 15'

p-n junction

p-n junction



Summary / Conclusions (1):

• Hydrogen is amphoteric (standard model: H+ in p-type Si, H0 and H- in n-type Si)

• Estimated diffusion constants neutral atomic hydrogen H0 plays the major role for the TD formation

• H0 is responsible for the enhancement of the TD formation in p-type and n-type Cz Si

• D(H0) is several orders of magnitude larger than the diffusion constant D(H+) of positively charged H+ ions

D(H0)/D(H+) 105 *)

*) D. Matthiot, Phys. Rev. B 40, 5867 (1989)




• "2-Step-Process": various processes occur

– T > 200 °C no acceptor passivation occurs

– T 250 °C immobile hydrogen complexes are created

– T 400 - 450 °C immobile hydrogen complexes are dissolved high concentration of mobile H0

– diffusion of H0 via interstitial lattice sites

– H0 lowers the barrier for the migration of Oi

– probability is enhanced that Oi forms a TD complex

hydrogen supports the TD formation




• Dominant reaction at T 250 °C (H-plasma treatment):

H+ + H0 H2 + h+ *)

(H+, H0: hydrogen in positive, neutral state, h+: hole, compensated by crystal field)

*) S.M. Myers et al., Rev. Mod. Phys. 64, 559 (1992)

immobile H2 species: "zero spin clusters (ZSC)"

• Dominant reaction at T 450 °C (annealing):

decay of ZSCs large concentration of H0

• "2-step-process" indirect way for H0 incorporation

"1-step-process" direct way for H0 incorporation


Formation of Extremely Deep p-n Junctions

SRP measurements:

ultra-deep p-n junc-tion in highly oxidi-zed Cz Si

[Oi] = 1.151018 cm-3

Substrate:12 cm Cz Si, [B] 11015 cm-3

(p-type)

H-Plasma:60 min at 450 °C µ-wave H-plasma (1-step-process)

0 500 1000 1500 200010

3

104

105

106

107

p-typen-type

p-n junction

> 1.2 mm (!)

SR

(

cm)

Depth (µm)


Formation of Extremely Deep Graded Doping

SRP measurements:

ultra-deep graded doping in highly oxidized Cz Si

[Oi] = 1.21018 cm-3

Substrate:5 cm Cz Si, [P] 11015 cm-3

(n-type)


0 500 1000 1500 200010

3

104

105

H from the

backside

H from the

frontside

n-type Cz Si (5 cm)

SR

(

cm)

Depth (µm)


Hydrogen Enhanced Thermal Donor Formation

IR-absorption measurements:

verification of TDDs (neutral species up to the 5th generation)


(p-type)

[Oi] = 1.151018 cm-3


400 425 450 475 500 525 5501,5

2,0

2,5

3,0

3,5

4,0

4,5

: TDDi (i = 1 - 5)

Oi

p-type

Cz Si

Ab

so

rpti

on

Co

eff

icie

nt

(cm

-1)

Wavenumber (cm-1

)




verification of TDD+s (singly ionized spe-cies up to the 5th generation)


(p-type)

[Oi] = 1.151018 cm-3


600 700 800 900 1000 1100 1200 13000,0

0,5

1,0

1,5

2,0

2,5

3,0

3,5

: TDDi

+ (i = 1 - 5) p-Typ

Cz Si?

Oi

Ab

so

rpti

on

Co

eff

icie

nt

(cm

-1)

Wavenumber (cm-1

)






(n-type)

[Oi] = 1.21018 cm-3

H-Plasma:8 h at 270 °C1 h at 450 °C µ-wave H-plasma (1-step-process)

400 420 440 460 480 500 520 540 5600

2

4

6

8

10

12

14

16

Oi

b)

a)

a) H-plasma: Tpl = 270 °C, t

pl = 8 h

b) H-plasma: Tpl = 450 °C, t

pl = 1 h

n-Typ

Cz SiA

bs

orp

tio

n C

oe

ffic

ien

t (c

m-1

)

Wavenumber (cm-1

)





(n-type)

[Oi] = 1.21018 cm-3

H-Plasma:8 h at 270 °CAnnealing:1 h / 4 h at 450 °C/air(2-step-process)


400 420 440 460 480 500 520 540 5600

2

4

6

8

10

12

14

16Annealing:

T temp = 450 °C

b) ttemp = 1 h

c) ttemp = 4 h

Oi

c)

b)

a)

n-Typ

Cz Si

H-Plasma:

Tpl = 270 °C,

tpl = 8 h

a) as plasma

treatedA

bs

orp

tio

n C

oe

ffic

ien

t (c

m-1

)

Wavenumber (cm-1

)


Formation of Diodes by Thermal Donor Doping

• Substrates:

– p-type Cz Si (1.8 - 2.6 cm , 5 - 10 cm, 12 - 20 cm)[B] 6 1014 cm-3 - 1.3 1016 cm-3 [Oi] = 7 8 1017 cm-3, [Cs] < 5 1016 cm-3

• TD formation (plasma treatment / annealing):

– H-plasma: µ-wave 2.45 GHz, tpl = 30 min, Tpl = 450 °Cannealing: no annealing

(1-step-process: TD-diode No. 1)

– H-plasma: 110 MHz, 50 W, tpl = 60 min, Tpl = 250 °Cannealing: tann = 20 or 30 min, Tann = 450 °C/air

(2-step-process: TD-diodes No. 2, 3)

also alternative plasma hydrogenation possible:

– H-plasma: DC, 500 V, Tpl = 400 - 450 °C, tpl 30 min (1-step-process)


TD-diode (No. 1):

contact area: 1 mm2

- SRP profile p-n junction depth: d = 40 µm

- I(V) curves at T = RT

Substrate:12 - 20 cm Cz Si



-100 -80 -60 -40 -20 0

0,00

0,02

0,04

0,06

0,08

0,10

I (A

)

VBIAS (V)

0 25 50 75 100 125 15010

4

105

106

107

n-type

region

p-type region

p-n junction

SR

(

)

Depth (m)


TD-diode (No. 2):

contact area: 1 cm2

- SRP profile p-n junction depth: d 170 µm

- I(V) curves at T = RT


H-Plasma:60 min at 250 °C Annealing:30 min 450 °C/air (2-step-process)


-100 -80 -60 -40 -20 0-0,01

0,00

0,01

0,02

0,03

0,04

I (A

)

Vbias

(V)

0 50 100 150 200 250 30010

4

105

106

n-type region p-type region

p-n junction

SR

(

)Depth (µm)


TD-diode (No. 1):

contact area: 1 mm2

(1-step-process)

TD-diode (No. 2):

contact area: 1 cm2

(2-step-process)

Comparison

I(V) curves at T = RT:

Data normalized to contact size !


-100 -80 -60 -40 -20 0 1 210

-5

10-4

10-3

10-2

10-1

100

101

2)2)

1)

1)

2) TD-diode (2-step-process)

1) TD-diode (1-step-process)

I (A

cm-2

)

Vbias

(V)


TD-diode (No. 1):

contact area: 1 mm2

- I(V) curves at T = RT 150 °C



Analysis of TD-Diodes

-100 -80 -60 -40 -20 0-0,02

0,00

0,02

0,04

0,06

0,08

0,10

TD-Diode No. 1

T = 22°C, 100°C, 150°C

I (A

)

VBIAS

(V)


TD-diode (No. 1):

contact area: 1 mm2

- C(V) measurements

linear slope

C V-3 linearly graded p-n junction (if C V-2 abrupt junction)



Analysis of TD-Diodes

-30 -25 -20 -15 -10 -5 01x10

-11

2x10-11

3x10-11

4x10-11

5x10-11

6x10-11

f = 1 MHz "reverse bias"

VBIAS (V)

C (

F)

0,0

5,0x1031

1,0x1032

1,5x1032

2,0x1032

1/C

³ (1

/F³)


TD-diode (No. 3):

contact area: 1 mm2

- p-n junction depth: d 100 µm

- I(V) curves, mapping at T = RT


H-Plasma:60 min at 250 °C Annealing:20 min 450 °C/air (2-step-process)

Analysis of TD-Diodes / Wafer Mapping

-25 -20 -15 -10 -5 0 5-0,01

0,00

0,01

0,02

0,03

0,04

"2-step-process":

- 60 min H plasma at 260°C

- 20 min annealing at 450°C/air

wa

fer

rad

ius

I (A

)

Vbias

(V)


• appropriate plasma hydrogenation enhanced TD formation

• counter doping of p-type Cz Si can occurs due to TDs formation of deep p-n junctions (low thermal budget < 500 °C, process time 1 hour)

• graded doping in n-type Cz Si

• p-n junction formation due to TDs rapid and low thermal budget technology for high voltage or power device applications

Summary

a low temperature technology on the base of hydrogen enhanced thermal donor formation for future...

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