job

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,

1University 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

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





Dr. Reinhart Job, University of

Hagen, Germany

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

Dr. Reinhart Job, University of

Hagen, Germany

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

Dr. Reinhart Job, University of

Hagen, Germany

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"





Dr. Reinhart Job, University of

Hagen, Germany

Experimental



• Substrates:

– p-type Cz Silicon wafers

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



Impurities:

[Oi]  7 - 81017 cm-3 (specified, IR-Absorption)

[Cs] 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-) ?



Dr. Reinhart Job, University of

Hagen, Germany

"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] = 11015 cm-3, [Oi] = 7 - 81017 cm-3

• Example: PECVD plasma treatment

(110 Mhz, 50 W, 440 µA/cm2)

 formation TDDs / p-n junctions, [TDD]  11016 cm-3







Dr. Reinhart Job, University of

Hagen, Germany

Formation of p-n Junctions ("2-Step-Process")

SRP measurements: 6

10 20' 30' 480'

45' 60' 120' 240'

p-n junction depth in

dependence on the

post-hydrogenation

5

annealing time 10

SR (  )





4

Substrate: 10

1.8 - 2.6 cm Cz Si, 10' 15' wafer thickness: 367 + 5 µm

[B]  71015 cm-3

(p-type)  = 1.8 - 2.6  cm

3

H-Plasma: 10

0 100 200 300 400

60 min at 250 °C

Depth (µm)

Annealing:

at 450 °C/air

Dr. Reinhart Job, University of

Hagen, Germany

Formation of p-n Junctions ("2-Step-Process")

SRP measurements: 6

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

p-n junction depth in

dependence on the

post-hydrogenation

5

annealing time 10

SR (  )





4

Substrate: 10

5 - 10 cm Cz Si, wafer thickness: 378 + 5 µm

240'

480'

[B]  21015 cm-3

(p-type)  = 5 - 10  cm

3

H-Plasma: 10

0 100 200 300 400

60 min at 250 °C

Annealing: Depth (µm)

at 450 °C/air

Dr. Reinhart Job, University of

Hagen, Germany

Kinetic Analysis of the "2-Step-Process"



• "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 ]

 ( D   )[ H ]

t

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



Dr. Reinhart Job, University of

Hagen, Germany

Kinetic Analysis of the "2-Step-Process"



• "Fick's Law": [ H ]

 ( D   )[ H ]

t



 d 

• if D = const.  [ H ]  [ H 0 ]  erfc  

 4D  t 

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



• mean diffusion length: L  4D t

• assume:

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

 dpn  L, i.e. dpn  t1/2

Dr. Reinhart Job, University of

Hagen, Germany

Formation of p-n Junctions ("2-Step-Process")

p-n junction depth:

400

 description by the

"Fick's diffusion law"

300



L  4D t

Depth (µm) 200

(D: diffusion constant)



100  = 5 - 10  cm

linear slope 

 = 1.8 - 2.6  cm

D = 2.9 10-7 cm2s-1

(5 - 10 cm Cz Si) 0

0 50 100 150 200

D = 7.9 10-7 cm2s-1 1/2 1/2

t (s )

(1.8 - 2.6 cm Cz Si)



Dr. Reinhart Job, University of

Hagen, Germany

Kinetic Analysis of the "2-Step-Process"



• Relation of Van Wieringen and Warmholtz (VWW):



 Ea 

 kT 

DH  9.67  exp  

 

(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)







Dr. Reinhart Job, University of

Hagen, Germany

Formation of p-n Junctions ("2-Step-Process")

RF H-plasma exposure

7

at room temperature: 10



 p-n junction 8h 15' 8h 30'

formation only after

long time annealing at 6

10

450 °C (t > 8 hours)

8h

SR(Ohm)

Substrate: 5

10

12 - 20 cm Cz Si, p-n junction

[B]  1.11015 cm-3 p-n junction

(p-type)

4

10

H-Plasma: 0 50 10015020025030

60 min at RT Depth (m icrons

Annealing:

at 450 °C/air

Dr. Reinhart Job, University of

Hagen, Germany

Kinetic Analysis of the "2-Step-Process"

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)



Dr. Reinhart Job, University of

Hagen, Germany

Kinetic Analysis of the "2-Step-Process"

Summary / Conclusions (2):

• "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







Dr. Reinhart Job, University of

Hagen, Germany

Kinetic Analysis of the "2-Step-Process"

Summary / Conclusions (3):

• 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



Dr. Reinhart Job, University of

Hagen, Germany

Formation of Extremely Deep p-n Junctions

SRP measurements:

7

ultra-deep p-n junc- 10

tion in highly oxidi- > 1.2 mm (!)

zed Cz Si 6

10



[Oi] = 1.151018 cm-3 n-type p-type

SR (  cm) 5

10



Substrate:

12 cm Cz Si, 10

4



[B]  11015 cm-3 p-n junction

(p-type)

3

10

H-Plasma: 0 500 1000 1500 2000

60 min at 450 °C Depth (µm)

µ-wave H-plasma

(1-step-process)

Dr. Reinhart Job, University of

Hagen, Germany

Formation of Extremely Deep Graded Doping

SRP measurements:

5

10

ultra-deep graded

doping in highly n-type Cz Si (5  cm)

oxidized Cz Si



[Oi] = 1.21018 cm-3

SR (  cm) 4

10



Substrate:

5 cm Cz Si, H from the H from the

[P]  11015 cm-3

(n-type) frontside backside

3

10

H-Plasma: 0 500 1000 1500 2000

60 min at 450 °C Depth (µm)

µ-wave H-plasma

(1-step-process)

Dr. Reinhart Job, University of

Hagen, Germany

Hydrogen Enhanced Thermal Donor Formation

IR-absorption

4,5









Absorption Coefficient (cm )

measurements:









-1

p-type

verification of TDDs : TDD i (i = 1 - 5)

4,0

Cz Si

(neutral species up to

Oi

the 5th generation) 3,5



3,0

Substrate:

2,5

12 cm Cz Si,

[B]  11015 cm-3

2,0

(p-type)

[Oi] = 1.151018 cm-3 1,5

400 425 450 475 500 525 550

H-Plasma: -1

W avenumber (cm )

60 min at 450 °C

µ-wave H-plasma

(1-step-process)

Dr. Reinhart Job, University of

Hagen, Germany

Hydrogen Enhanced Thermal Donor Formation

IR-absorption

measurements: 3,5









Absorption Coefficient (cm )

-1

+

verification of TDD+s 3,0 : TDD i (i = 1 - 5) p-Typ

(singly ionized spe- ?

cies up to the 5th 2,5 Cz Si

generation)

2,0

Oi

Substrate: 1,5

12 cm Cz Si,

[B]  11015 cm-3 1,0

(p-type)

0,5

[Oi] = 1.151018 cm-3

0,0

H-Plasma: 600 700 800 900 1000 1100 1200 1300

-1

60 min at 450 °C W avenumber (cm )

µ-wave H-plasma

(1-step-process)

Dr. Reinhart Job, University of

Hagen, Germany

Hydrogen Enhanced Thermal Donor Formation

IR-absorption

measurements: 16

a) H-plasma: T pl = 270 °C, t pl = 8 h









Absorption Coefficient (cm )

14







-1

verification of TDDs

(neutral species up to 12 b) H-plasma: T pl = 450 °C, t pl = 1 h

the 5th generation)

10 n-Typ

Substrate: 8 Cz Si Oi

5 cm Cz Si,

[P]  11015 cm-3 6

(n-type) 4 b)

[Oi] = 1.21018 cm-3

2

a)

H-Plasma:

0

8 h at 270 °C 400 420 440 460 480 500 520 540 560

1 h at 450 °C -1

W avenumber (cm )

µ-wave H-plasma

(1-step-process)

Dr. Reinhart Job, University of

Hagen, Germany

Hydrogen Enhanced Thermal Donor Formation

IR-absorption

measurements: 16

H-Plasm a: n-Typ Annealing:









Absorption Coefficient (cm )

14







-1

verification of TDDs T tem p = 450 °C

T pl = 270 °C, Cz Si

(neutral species up to 12

the 5th generation) t pl = 8 h b) t tem p = 1 h

10 a) as plasm a c) t tem p = 4 h

Substrate:

8 treated Oi

5 cm Cz Si,

[P]  11015 cm-3 6

(n-type) c)

4 b)

[Oi] = 1.21018 cm-3

2 a)

H-Plasma:

0

8 h at 270 °C 400 420 440 460 480 500 520 540 560

Annealing: -1

W avenumber (cm )

1 h / 4 h at 450 °C/air

(2-step-process)

Dr. Reinhart Job, University of

Hagen, Germany

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 °C

annealing: no annealing

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

– H-plasma: 110 MHz, 50 W, tpl = 60 min, Tpl = 250 °C

annealing: 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)

Dr. Reinhart Job, University of

Hagen, Germany

Formation of Diodes by Thermal Donor Doping



TD-diode (No. 1): 0,10

7

10

contact area: 1 mm2

0,08

- SRP profile

6

p-n junction depth: 10 n-type p-type region

d = 40 µm 0,06









SR (  )

region

- I(V) curves at

I (A)

5



T = RT 0,04 10

p-n junction

Substrate: 0,02

12 - 20 cm Cz Si 10

4



0 25 50 75 100 125 150

H-Plasma: Depth (  m)

0,00

30 min at 450 °C

µ-wave H-plasma -100 -80 -60 -40 -20 0

(1-step-process)

V BIAS (V)



Dr. Reinhart Job, University of

Hagen, Germany

Formation of Diodes by Thermal Donor Doping



TD-diode (No. 2): 0,04 6

10

contact area: 1 cm2

- SRP profile 0,03 n-type region p-type region



p-n junction depth:

d  170 µm









SR (  )

5

10

0,02

- I(V) curves at

I (A)



T = RT p-n junction

0,01

Substrate: 10

4



0 50 100 150 200 250 300

12 - 20 cm Cz Si 0,00

Depth (µm)



H-Plasma:

60 min at 250 °C -0,01

Annealing: -100 -80 -60 -40 -20 0

30 min 450 °C/air

V bias (V)

(2-step-process)



Dr. Reinhart Job, University of

Hagen, Germany

Formation of Diodes by Thermal Donor Doping



TD-diode (No. 1): 10

1







contact area: 1 mm2 0

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

10

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

-1

TD-diode (No. 2): 10

I (Acm )

-2

-2

contact area: 1 cm2 10 1)

(2-step-process) -3

10

 Comparison -4

2) 2)

10

I(V) curves at T = RT: -5

10

 Data normalized -100 -80 -60 -40 -20 0 1 2

to contact size ! V bias (V)





Dr. Reinhart Job, University of

Hagen, Germany

Analysis of TD-Diodes



TD-diode (No. 1): 0,10

contact area: 1 mm2 TD-Diode No. 1

0,08

- I(V) curves at

T = RT  150 °C 0,06



0,04

I (A)



Substrate: 0,02

12 - 20 cm Cz Si T = 22°C, 100°C, 150°C

H-Plasma: 0,00

30 min at 450 °C

µ-wave H-plasma -0,02

(1-step-process) -100 -80 -60 -40 -20 0

V BIAS (V)





Dr. Reinhart Job, University of

Hagen, Germany

Analysis of TD-Diodes

TD-diode (No. 1):

contact area: 1 mm2 -11 32

6x10 2,0x10

- C(V) measurements

-11

f = 1 MHz "reverse bias"

5x10

linear slope  1,5x10

32





 C  V-3 4x10

-11









1/C³ (1/F³)

C (F)

 linearly graded 1,0x10

32



-11

p-n junction 3x10

(if C  V-2  abrupt 31

-11 5,0x10

junction) 2x10



Substrate: 1x10

-11 0,0

12 - 20 cm Cz Si -30 -25 -20 -15 -10 -5 0

V BIAS (V)

H-Plasma:

30 min at 450 °C

µ-wave H-plasma

(1-step-process)

Dr. Reinhart Job, University of

Hagen, Germany

Analysis of TD-Diodes / Wafer Mapping



TD-diode (No. 3):

"2-step-process":

contact area: 1 mm2 - 60 min H plasma at 260°C

- p-n junction depth: - 20 min annealing at 450°C/air

d  100 µm 0,04

- I(V) curves,

0,03

mapping at T = RT

0,02

Substrate:









iu s

12 - 20 cm Cz Si









ra d

I (A)









0,01









fe r

wa

H-Plasma:

0,00

60 min at 250 °C

Annealing: -0,01

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

20 min 450 °C/air V bias (V)

(2-step-process)



Dr. Reinhart Job, University of

Hagen, Germany

Summary



• 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









Dr. Reinhart Job, University of

Hagen, Germany