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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

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  1. 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

  2. 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

  3. Thermal Donors (TDs) • 'Old thermal donors' (TDs), oxygen related double donors (TDDs) • formation atT  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

  4. 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

  5. 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

  6. 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] < 51016 cm-3 (specified) Doping: = 12 - 20 cm,  = 5 - 10 cm,  = 1 - 2 cm[B]  61014 cm-3 - 1.31016 cm-3 Dr. Reinhart Job, University of Hagen, Germany

  7. 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”) Dr. Reinhart Job, University of Hagen, Germany

  8. "1-Step-Process" for TD Formation • Hydrogen enhanced TD formation in Cz Si onlyby H-plasma treatment • "1-step-process":TDD formation during H-plasma treatment(Tplasma = 400 - 450 °C, tplasma 30 min) • Cz Si wafers: [B] = 11015 cm-3, [Oi] = 7 - 81017 cm-3 • Example: DC plasma treatment (RIE setup, 500 V plate voltage, 440 µA/cm2) formation of TDDs, [TDD]  11016 cm-3 formation of deep p-n junctions (counter doping) Dr. Reinhart Job, University of Hagen, Germany

  9. Formation of p-n Junctions ("1-Step-Process") SRP measurements:  p-n junction location Substrate:12 cm Cz Si, [B] = 11015 cm-3(p-type) H-Plasma:30 min at 400 °C (1-step-process) Dr. Reinhart Job, University of Hagen, Germany

  10. Formation of p-n Junctions ("1-Step-Process") Free carrier concen-tration Nc in depen-dence on the depth Substrate:12 cm Cz Si, [B] = 11015 cm-3(p-type) H-Plasma:30 min at 400 °C (1-step-process) Dr. Reinhart Job, University of Hagen, Germany

  11. Formation of p-n Junctions ("1-Step-Process") Electron concentra-tion Ne(TD) due to TDDs in dependence on the depth Substrate:12 cm Cz Si, [B] = 11015 cm-3(p-type) H-Plasma:30 min at 400 °C (1-step-process) Dr. Reinhart Job, University of Hagen, Germany

  12. Formation of p-n Junctions ("1-Step-Process") C(V) measurements: C-3  Vbias  linear graded junction Substrate:12 cm Cz Si, [B] = 11015 cm-3(p-type) H-Plasma:30 min at 400 °C (1-step-process) Dr. Reinhart Job, University of Hagen, Germany

  13. Formation of p-n Junctions ("1-Step-Process") SRP measurements:  p-n junction location Substrate:12 cm Cz Si, [B] = 11015 cm-3(p-type) H-Plasma:45 min at 400 °C (1-step-process) Dr. Reinhart Job, University of Hagen, Germany

  14. Formation of p-n Junctions ("1-Step-Process") Free carrier concen-tration Nc in depen-dence on the depth Substrate:12 cm Cz Si, [B] = 11015 cm-3(p-type) H-Plasma:45 min at 400 °C (1-step-process) Dr. Reinhart Job, University of Hagen, Germany

  15. 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]  1015, 1016 cm-3(p-type) H-Plasma:120 min at 400 °C (1-step-process) Dr. Reinhart Job, University of Hagen, Germany

  16. 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1015 cm-3(p-type) H-Plasma:120 min at 400 °C (1-step-process) Dr. Reinhart Job, University of Hagen, Germany

  17. Formation of p-n Junctions ("1-Step-Process") C(V) measurements: Ne(TD) in dependen-ce on the hydrogen dose Substrate:12 cm Cz Si, [B] = 11015 cm-3(p-type) H-Plasma:at 400 °C (1-step-process) Dr. Reinhart Job, University of Hagen, Germany

  18. 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1015 cm-3(p-type) H-Plasma:30 - 120 min at 400 °C (1-step-process) Dr. Reinhart Job, University of Hagen, Germany

  19. Kinetic Analysis of the "1-Step-Process" Time dependences of H and H2 concentrations: DH: diffusion constant of atomic hydrogen K1 : rate of H2 formation K2 : dissociation constant of H2 molecules Dr. Reinhart Job, University of Hagen, Germany

  20. Kinetic Analysis of the "1-Step-Process" 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) Dr. Reinhart Job, University of Hagen, Germany

  21. Kinetic Analysis of the "1-Step-Process" Time dependence of [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 = 3.810-2 s-2 Boundary condition: x = 0, t  0: [H0], with [H0] = 1014 cm-3 (constant hydrogen concentration at the wafer surface) Dr. Reinhart Job, University of Hagen, Germany

  22. Formation of p-n Junctions ("1-Step-Process") Simulated curves: [TDD], [H], [H2] in dependence on the depth Assumption:T = 400 °Ct = 30 min(1-step-process)[TDD]-profile: K3 = 3.810-2 s-2(Fit to exp. Data) Dr. Reinhart Job, University of Hagen, Germany

  23. Formation of p-n Junctions ("1-Step-Process") Comparison of simulated [TD] profiles & experimental data Assumption:T = 400 °Ct = 30, 45, 120 min(1-step-process)Fit to exp. Data:  K3 = 3.810-2 s-2 Dr. Reinhart Job, University of Hagen, Germany

  24. 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 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

  25. "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

  26. Formation of p-n Junctions ("2-Step-Process") SRP measurements: p-n junction depth in dependence on the post-hydrogenation annealing time Substrate:1.8 - 2.6 cm Cz Si, [B]  71015 cm-3(p-type) H-Plasma:60 min at 250 °C Annealing:at 450 °C/air Dr. Reinhart Job, University of Hagen, Germany

  27. Formation of p-n Junctions ("2-Step-Process") SRP measurements: p-n junction depth in dependence on the post-hydrogenation annealing time Substrate:5 - 10 cm Cz Si, [B]  21015 cm-3(p-type) H-Plasma:60 min at 250 °C Annealing:at 450 °C/air Dr. Reinhart Job, University of Hagen, Germany

  28. 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

  29. Kinetic Analysis of the "2-Step-Process" • "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 Dr. Reinhart Job, University of Hagen, Germany

  30. 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 10-7 cm2s-1(5 - 10 cm Cz Si) D = 7.9 10-7 cm2s-1(1.8 - 2.6 cm Cz Si) Dr. Reinhart Job, University of Hagen, Germany

  31. Kinetic Analysis of the "2-Step-Process" • 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) Dr. Reinhart Job, University of Hagen, Germany

  32. 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:12 - 20 cm Cz Si, [B]  1.11015 cm-3(p-type) H-Plasma:60 min at RTAnnealing:at 450 °C/air Dr. Reinhart Job, University of Hagen, Germany

  33. 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

  34. 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

  35. 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

  36. Formation of Extremely Deep p-n Junctions SRP measurements: ultra-deep p-n junc-tion in highly oxidi-zed Cz Si [Oi] = 1.151018 cm-3 Substrate:12 cm Cz Si, [B]  11015 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

  37. Formation of Extremely Deep Graded Doping SRP measurements: ultra-deep graded doping in highly oxidized Cz Si [Oi] = 1.21018 cm-3 Substrate:5 cm Cz Si, [P]  11015 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

  38. Hydrogen Enhanced Thermal Donor Formation IR-absorption measurements: verification of TDDs (neutral species up to the 5th generation) Substrate:12 cm Cz Si, [B]  11015 cm-3(p-type) [Oi] = 1.151018 cm-3 H-Plasma:60 min at 450 °C µ-wave H-plasma (1-step-process) Dr. Reinhart Job, University of Hagen, Germany

  39. Hydrogen Enhanced Thermal Donor Formation IR-absorption measurements: verification of TDD+s (singly ionized spe-cies up to the 5th generation)Substrate:12 cm Cz Si, [B]  11015 cm-3(p-type) [Oi] = 1.151018 cm-3 H-Plasma:60 min at 450 °C µ-wave H-plasma (1-step-process) Dr. Reinhart Job, University of Hagen, Germany

  40. Hydrogen Enhanced Thermal Donor Formation IR-absorption measurements: verification of TDDs (neutral species up to the 5th generation)Substrate:5 cm Cz Si, [P]  11015 cm-3(n-type) [Oi] = 1.21018 cm-3 H-Plasma:8 h at 270 °C1 h at 450 °C µ-wave H-plasma (1-step-process) Dr. Reinhart Job, University of Hagen, Germany

  41. Hydrogen Enhanced Thermal Donor Formation IR-absorption measurements: verification of TDDs (neutral species up to the 5th generation)Substrate:5 cm Cz Si, [P]  11015 cm-3(n-type) [Oi] = 1.21018 cm-3 H-Plasma:8 h at 270 °CAnnealing:1 h / 4 h at 450 °C/air(2-step-process) Dr. Reinhart Job, University of Hagen, Germany

  42. 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) Dr. Reinhart Job, University of Hagen, Germany

  43. Formation of Diodes by Thermal Donor Doping 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 H-Plasma:30 min at 450 °C µ-wave H-plasma (1-step-process) Dr. Reinhart Job, University of Hagen, Germany

  44. Formation of Diodes by Thermal Donor Doping TD-diode (No. 2): contact area: 1 cm2 - SRP profile p-n junction depth: d  170 µm - I(V) curves at T = RT Substrate:12 - 20 cm Cz Si H-Plasma:60 min at 250 °C Annealing:30 min 450 °C/air (2-step-process) Dr. Reinhart Job, University of Hagen, Germany

  45. Formation of Diodes by Thermal Donor Doping 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 ! Dr. Reinhart Job, University of Hagen, Germany

  46. Analysis of TD-Diodes TD-diode (No. 1): contact area: 1 mm2 - I(V) curves at T = RT  150 °C Substrate:12 - 20 cm Cz Si H-Plasma:30 min at 450 °C µ-wave H-plasma (1-step-process) Dr. Reinhart Job, University of Hagen, Germany

  47. Analysis of TD-Diodes 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) Substrate:12 - 20 cm Cz Si H-Plasma:30 min at 450 °C µ-wave H-plasma (1-step-process) Dr. Reinhart Job, University of Hagen, Germany

  48. Analysis of TD-Diodes / Wafer Mapping TD-diode (No. 3): contact area: 1 mm2 - p-n junction depth: d  100 µm - I(V) curves, mapping at T = RT Substrate:12 - 20 cm Cz Si H-Plasma:60 min at 250 °C Annealing:20 min 450 °C/air (2-step-process) Dr. Reinhart Job, University of Hagen, Germany

  49. 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

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