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

Dr. Reinhart Job, University of Hagen, Germany Thermal Donors (TDs) 'Old thermal donors' (TDs), oxygen related double donors (TDDs) – formation at T  °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 [O i ] and [C s ]: [O i ] high  R high, [C s ] 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  °C –R correlated with [O i ] and [C s ]: [O i ] high  R high, [C s ] high  R high –energy level of the donor: 17 meV 'New thermal donors' (NTDs) –formation at T  °C –NTDs appear only after very long annealing times (> 10 5 min) –NTDs  double donors –large agglomerates of oxygen (?) 'Shallow thermal donors' (STDs) –formation at T  °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  µm, (100)-oriented) Impurities: [O i ]   cm -3 (specified, IR-Absorption) [C s ] < 5  cm -3 (specified) Doping:  =  cm,  =  cm,  =  cm [B]  6  cm  cm -3

Dr. Reinhart Job, University of Hagen, Germany 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 (”TDD i - family") I(V) measurements - characterization of diodes (”TD-Diodes”)

Dr. Reinhart Job, University of Hagen, Germany "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 (T plasma = °C, t plasma  30 min) Cz Si wafers: [B] = 1  cm -3, [O i ] =  cm -3 Example: DC plasma treatment (RIE setup, 500 V plate voltage, 440 µA/cm 2 )  formation of TDDs, [TDD]  1  cm -3  formation of deep p-n junctions (counter doping)

Dr. Reinhart Job, University of Hagen, Germany Formation of p-n Junctions ("1-Step-Process") SRP measurements:  p-n junction location Substrate: 12  cm Cz Si, [B] = 1  cm -3 (p-type) H-Plasma: 30 min at 400 °C (1-step-process)

Dr. Reinhart Job, University of Hagen, Germany Formation of p-n Junctions ("1-Step-Process") Free carrier concen- tration N c in depen- dence on the depth Substrate: 12  cm Cz Si, [B] = 1  cm -3 (p-type) H-Plasma: 30 min at 400 °C (1-step-process)

Dr. Reinhart Job, University of Hagen, Germany Formation of p-n Junctions ("1-Step-Process") Electron concentra- tion N e(TD) due to TDDs in dependence on the depth Substrate: 12  cm Cz Si, [B] = 1  cm -3 (p-type) H-Plasma: 30 min at 400 °C (1-step-process)

Dr. Reinhart Job, University of Hagen, Germany Formation of p-n Junctions ("1-Step-Process") C(V) measurements: C -3  V bias  linear graded junction Substrate: 12  cm Cz Si, [B] = 1  cm -3 (p-type) H-Plasma: 30 min at 400 °C (1-step-process)

Dr. Reinhart Job, University of Hagen, Germany Formation of p-n Junctions ("1-Step-Process") SRP measurements:  p-n junction location Substrate: 12  cm Cz Si, [B] = 1  cm -3 (p-type) H-Plasma: 45 min at 400 °C (1-step-process)

Dr. Reinhart Job, University of Hagen, Germany Formation of p-n Junctions ("1-Step-Process") Free carrier concen- tration N c in depen- dence on the depth Substrate: 12  cm Cz Si, [B] = 1  cm -3 (p-type) H-Plasma: 45 min at 400 °C (1-step-process)

Dr. Reinhart Job, University of Hagen, Germany Formation of p-n Junctions ("1-Step-Process") SRP measurements: p-n junction depth in dependence on the initial p-type doping Substrate: 1, 12  cm Cz Si, [B]  10 15, cm -3 (p-type) H-Plasma: 120 min at 400 °C (1-step-process)

Dr. Reinhart Job, University of Hagen, Germany Formation of p-n Junctions ("1-Step-Process") SRP measurements: p-n junction depth in dependence on the amount of incorpo- rated hydrogen Substrate: 12  cm Cz Si, [B] = 1  cm -3 (p-type) H-Plasma: 120 min at 400 °C (1-step-process)

Dr. Reinhart Job, University of Hagen, Germany Formation of p-n Junctions ("1-Step-Process") C(V) measurements: N e(TD) in dependen- ce on the hydrogen dose Substrate: 12  cm Cz Si, [B] = 1  cm -3 (p-type) H-Plasma: at 400 °C (1-step-process)

Dr. Reinhart Job, University of Hagen, Germany Formation of p-n Junctions ("1-Step-Process") SRP measurements: p-n junction depth in dependence on the plasma treatment time Substrate: 12  cm Cz Si, [B] = 1  cm -3 (p-type) H-Plasma: min at 400 °C (1-step-process)

Dr. Reinhart Job, University of Hagen, Germany Kinetic Analysis of the "1-Step-Process" D H : diffusion constant of atomic hydrogen K 1 : rate of H 2 formation K 2 : dissociation constant of H 2 molecules Time dependences of H and H 2 concentrations:

Dr. Reinhart Job, University of Hagen, Germany Kinetic Analysis of the "1-Step-Process" K 1 : rate of H 2 formation K 2 : dissociation constant of H 2 molecules D H : "Van Wieringen-Warmholtz" relation  diffusion constant R 0 : capture radius (R 0 = 5 Å * ) ) : vibration frequency of the dissociation of H 2 E b : binding energy (E b = 1.6 eV) * ) J.T. Borenstein et al., J. Appl. Phys. 73, 2751 (1993)

Dr. Reinhart Job, University of Hagen, Germany Kinetic Analysis of the "1-Step-Process" N TD : concentration of thermal double donors ("TDD")  compensation (p-n junction): 2  [N TD ] = [B] K 3 : free parameter (deduced by fitting of experimental data) K 3 = 3.8  s -2 Boundary condition: x = 0, t  0: [H 0 ], with [H 0 ] = cm -3 (constant hydrogen concentration at the wafer surface) Time dependence of [TD] :

Dr. Reinhart Job, University of Hagen, Germany Formation of p-n Junctions ("1-Step-Process") Simulated curves: [TDD], [H], [H 2 ] in dependence on the depth Assumption: T = 400 °C t = 30 min (1-step-process) [TDD]-profile: K 3 = 3.8  s -2 (Fit to exp. Data)

Dr. Reinhart Job, University of Hagen, Germany Formation of p-n Junctions ("1-Step-Process") Comparison of simulated [TD] profiles & experimental data Assumption: T = 400 °C t = 30, 45, 120 min (1-step-process) Fit to exp. Data:  K 3 = 3.8  s -2

Dr. Reinhart Job, University of Hagen, Germany Kinetic Analysis of the "1-Step-Process" 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 H 2 complexes –diffusion of H via interstitial lattice sites –H lowers the barrier for the diffusion of O i –probability is enhanced that O i forms a TD complex  hydrogen supports the TD formation –loss of O i due to the incorporation of O i into TD-complexes Question:Charge state of hydrogen (H 0, 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: T plasma  250 °C, t plasma = 60 min - annealing: T anneal  450 °C, t anneal  15 min Cz Si wafers: [B] = 1  cm -3, [O i ] =  cm -3 Example: PECVD plasma treatment (110 Mhz, 50 W, 440 µA/cm 2 )  formation TDDs / p-n junctions, [TDD]  1  cm -3

Dr. Reinhart Job, University of Hagen, Germany Formation of p-n Junctions ("2-Step-Process") SRP measurements: p-n junction depth in dependence on the post-hydrogenation annealing time Substrate:  cm Cz Si, [B]  7  cm -3 (p-type) H-Plasma: 60 min at 250 °C Annealing: at 450 °C/air

Dr. Reinhart Job, University of Hagen, Germany Formation of p-n Junctions ("2-Step-Process") SRP measurements: p-n junction depth in dependence on the post-hydrogenation annealing time Substrate:  cm Cz Si, [B]  2  cm -3 (p-type) H-Plasma: 60 min at 250 °C Annealing: 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]: hydrogen concentration, D: diffusion constant, t: time,

Dr. Reinhart Job, University of Hagen, Germany Kinetic Analysis of the "2-Step-Process" "Fick's Law": if D = const.  (D: diffusion constant, d: depth, t: time, [H 0 ]: surface concentration) mean diffusion length: assume: p-n junction depth d pn proportional to diffusion length L:  d pn  L, i.e. d pn  t 1/2

Dr. Reinhart Job, University of Hagen, Germany Formation of p-n Junctions ("2-Step-Process") p-n junction depth:  description by the "Fick's diffusion law" (D: diffusion constant) linear slope  D = 2.9  cm 2 s -1 (  cm Cz Si) D = 7.9  cm 2 s -1 (  cm Cz Si)

Dr. Reinhart Job, University of Hagen, Germany Kinetic Analysis of the "2-Step-Process" Relation of Van Wieringen and Warmholtz (VWW): (E a = 0.48 eV) VWW equation holds for atomic hydrogen ! extrapolation to 450 °C: D VWW = 4.36  cm 2 /s experiment: D  7.9  cm 2 s -1 (1  cm Cz Si) D  2.9  cm 2 s -1 (5  cm Cz Si)

Dr. Reinhart Job, University of Hagen, Germany Formation of p-n Junctions ("2-Step-Process") RF H-plasma exposure at room temperature:  p-n junction formation only after long time annealing at 450 °C (t > 8 hours) Substrate:  cm Cz Si, [B]  1.1  cm -3 (p-type) H-Plasma: 60 min at RT 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, H 0 and H - in n-type Si) Estimated diffusion constants  neutral atomic hydrogen H 0 plays the major role for the TD formation H 0 is responsible for the enhancement of the TD formation in p-type and n-type Cz Si D(H 0 ) is several orders of magnitude larger than the diffusion constant D(H + ) of positively charged H + ions  D(H 0 )/D(H + )  10 5 * ) * ) 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  °C  immobile hydrogen complexes are dissolved  high concentration of mobile H 0 –diffusion of H 0 via interstitial lattice sites –H 0 lowers the barrier for the migration of O i –probability is enhanced that O i 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 + + H 0  H 2 + h + * ) (H +, H 0 : hydrogen in positive, neutral state, h + : hole, compensated by crystal field) * ) S.M. Myers et al., Rev. Mod. Phys. 64, 559 (1992)  immobile H 2 species: "zero spin clusters (ZSC)" Dominant reaction at T  450 °C (annealing):  decay of ZSCs  large concentration of H 0 "2-step-process"  indirect way for H 0 incorporation "1-step-process"  direct way for H 0 incorporation

Dr. Reinhart Job, University of Hagen, Germany Formation of Extremely Deep p-n Junctions SRP measurements: ultra-deep p-n junc- tion in highly oxidi- zed Cz Si [O i ] = 1.15  cm -3 Substrate: 12  cm Cz Si, [B]  1  cm -3 (p-type) H-Plasma: 60 min at 450 °C µ-wave H-plasma (1-step-process)

Dr. Reinhart Job, University of Hagen, Germany Formation of Extremely Deep Graded Doping SRP measurements: ultra-deep graded doping in highly oxidized Cz Si [O i ] = 1.2  cm -3 Substrate: 5  cm Cz Si, [P]  1  cm -3 (n-type) H-Plasma: 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: verification of TDDs (neutral species up to the 5 th generation) Substrate: 12  cm Cz Si, [B]  1  cm -3 (p-type) [O i ] = 1.15  cm -3 H-Plasma: 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: verification of TDD + s (singly ionized spe- cies up to the 5 th generation) Substrate: 12  cm Cz Si, [B]  1  cm -3 (p-type) [O i ] = 1.15  cm -3 H-Plasma: 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: verification of TDDs (neutral species up to the 5 th generation) Substrate: 5  cm Cz Si, [P]  1  cm -3 (n-type) [O i ] = 1.2  cm -3 H-Plasma: 8 h at 270 °C 1 h at 450 °C µ-wave H-plasma (1-step-process)

Dr. Reinhart Job, University of Hagen, Germany IR-absorption measurements: verification of TDDs (neutral species up to the 5 th generation) Substrate: 5  cm Cz Si, [P]  1  cm -3 (n-type) [O i ] = 1.2  cm -3 H-Plasma: 8 h at 270 °C Annealing: 1 h / 4 h at 450 °C/air (2-step-process) Hydrogen Enhanced Thermal Donor Formation

Dr. Reinhart Job, University of Hagen, Germany Formation of Diodes by Thermal Donor Doping Substrates: –p-type Cz Si (  cm,  cm,  cm) [B]  6  cm  cm -3 [O i ] = 7  8  cm -3, [C s ] < 5  cm -3 TD formation (plasma treatment / annealing): –H-plasma:µ-wave 2.45 GHz, t pl = 30 min, T pl = 450 °C annealing: no annealing (1-step-process: TD-diode No. 1) –H-plasma:110 MHz, 50 W, t pl = 60 min, T pl = 250 °C annealing: t ann = 20 or 30 min, T ann = 450 °C/air (2-step-process: TD-diodes No. 2, 3) also alternative plasma hydrogenation possible: –H-plasma:DC, 500 V, T pl = °C, t pl  30 min (1-step-process)

Dr. Reinhart Job, University of Hagen, Germany TD-diode (No. 1): contact area: 1 mm 2 - SRP profile p-n junction depth: d = 40 µm - I(V) curves at T = RT Substrate:  cm Cz Si H-Plasma: 30 min at 450 °C µ-wave H-plasma (1-step-process) Formation of Diodes by Thermal Donor Doping

Dr. Reinhart Job, University of Hagen, Germany TD-diode (No. 2): contact area: 1 cm 2 - SRP profile p-n junction depth: d  170 µm - I(V) curves at T = RT Substrate:  cm Cz Si H-Plasma: 60 min at 250 °C Annealing: 30 min 450 °C/air (2-step-process) Formation of Diodes by Thermal Donor Doping

Dr. Reinhart Job, University of Hagen, Germany TD-diode (No. 1): contact area: 1 mm 2 (1-step-process) TD-diode (No. 2): contact area: 1 cm 2 (2-step-process)  Comparison I(V) curves at T = RT:  Data normalized to contact size ! Formation of Diodes by Thermal Donor Doping

Dr. Reinhart Job, University of Hagen, Germany TD-diode (No. 1): contact area: 1 mm 2 - I(V) curves at T = RT  150 °C Substrate:  cm Cz Si H-Plasma: 30 min at 450 °C µ-wave H-plasma (1-step-process) Analysis of TD-Diodes

Dr. Reinhart Job, University of Hagen, Germany TD-diode (No. 1): contact area: 1 mm 2 - C(V) measurements linear slope   C  V -3  linearly graded p-n junction (if C  V -2  abrupt junction) Substrate:  cm Cz Si H-Plasma: 30 min at 450 °C µ-wave H-plasma (1-step-process) Analysis of TD-Diodes

Dr. Reinhart Job, University of Hagen, Germany TD-diode (No. 3): contact area: 1 mm 2 - p-n junction depth: d  100 µm - I(V) curves, mapping at T = RT Substrate:  cm Cz Si H-Plasma: 60 min at 250 °C Annealing: 20 min 450 °C/air (2-step-process) Analysis of TD-Diodes / Wafer Mapping

Dr. Reinhart Job, University of Hagen, Germany 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