Clauws, Paul

Gaubas, Eugenijus

Lauwaert, Johan

Romandic, Igor

Simoen, Eddy

Spiewak, Piotr

Vanhellemont, Jan

Vrielinck, Henk

English

Ghent University Academic Bibliography

Department of Solid State Sciences Jan VanhellemontJ. Vanhellemont1, P. Spiewak2, E. Gaubas3, J. Lauwaert1, H. Vrielinck1, P. Clauws1, E. Simoen4 and I. Romandic51Ghent University, Krijgslaan 281 S1, B-9000 Ghent, Belgium2Warsaw University of Technology, Wołoska 141, 02-507 Warsaw, Poland3Vilnius University, Sauletekio al 10, LT-10223 Vilnius, Lithuania4Imec, Kapeldreef 75, B-3001 Leuven, Belgium5Umicore EOM, Watertorenstraat 33, B-2250 Olen, BelgiumRecent developments in understanding and modeling of defects in Czochralski germanium Department of Solid State Sciences 2Jan Vanhellemont   Introduction   COP's on polished Ge wafer surfaces   Intrinsic point defects properties: experimental   Calculation of intrinsic point defect properties   Simulation of void formation in Cz germanium   ConclusionsContent Department of Solid State Sciences 3Jan VanhellemontIntroduction• Today main application of Ge substrates for GaAs epitaxy: highly doped, 100 mm diameter. Also for optical compon-ents (mirrors, lenses) and HR Ge for detectors.• Renewed interest to use Ge in nano-electronics due to high carrier mobility.• Limited reserves, high cost  GeOI.• Development of electronics grade Cz Ge “donor” wafers:– grown-in lattice defects– metallic impurities– geometry. Department of Solid State Sciences 4Jan VanhellemontBonded GeOI wafer• XTEM of implanted Ge (a); after thermal treatment (b); after bonding and cleaving (c) and after CMP (d).C.J. Tracy et al. Journ. Electron. Mater. 33, 887 (2004) Department of Solid State Sciences 5Jan VanhellemontCz germanium for nano-electronics 200 mm Ge wafers commercially available.• Ge wafers fulfilling 300 mm wafer geometry specs demonstrated.• Dislocation free; metals below detection limit. Department of Solid State Sciences 6Jan VanhellemontSurface pits on Cz germanium wafers• Optical micrographs showing surface pits occasionally observed with the naked eye on Cz Ge wafer surfaces.7  COP'S on Cz silicon wafers AFM images of a typical double COP after 4h SC1 delineation. Left: top view. Right: 3D-view.1  µ m ( µ m )126 0 00( n m ) Department of Solid State Sciences Jan Vanhellemont8  COP'S on Cz germanium wafers?Department of Solid State Sciences Image obtained with a SURFSCAN surface in-spection tool, revealing the presence of  large COP’s on a polished germanium wafer. Jan Vanhellemont9  SEM after coordinate transfer of COP positions SEM images of surface pits on Ge wafer surfaces, corresponding with and octahedral (left) and truncated octahedral void (right).Department of Solid State Sciences Jan Vanhellemont Department of Solid State Sciences 10Jan VanhellemontVoid formation in Czochralski germanium• Schematic view of a growing Ge crystal as a solid-state reactor for point defects. • Tweet JAP 30, 2002 (1959): – pit size depending on thermal history; – pit density reduction when pulling slower or post-heating the crystal in the puller;– density reduction accompanied by size increase;– vacancy clustering mechanism.  Department of Solid State Sciences 11Jan Vanhellemont Self-diffusion coefficient (left) and vacancy transport capacity (right) in Si and Ge as a function of temperature normalized with respect to the melt temperature.Self-diffusion and vacancy transport capacity Department of Solid State Sciences 12Jan VanhellemontVacancies in germanium: quenching experiments• Thermal equilibrium concentration of different charge states of the vacancy. Department of Solid State Sciences 13Jan VanhellemontQuenching experiments: DLTS• DLTS spectra measured in quenched samples. No known Cu-related deep levels are observed. Department of Solid State Sciences 14Jan Vanhellemont Formation energy of the vacancy calculated ab initio with LDA+U as a function of the position of the Fermi level in the bandgap and of the charge state.Ge vacancy formation energy: impact of Fermi level Department of Solid State Sciences 15Jan VanhellemontCharged vacancies in GeCharge state 2− 1− 0 1+ 2+LDA+U PAW 3d 2.00 2.05 2.33 2.97 4.01Quenching 2.19 +/− 0.11 1.98 +/− 0.11 2.35 +/− 0.11 − −Reference 0/1- 1-/2- MethodThis work 0.02 0.26 DFT LDAThis work 0.02 0.26 DLTSKonorova (1969) 0.025 +/- 0.005 0.15 +/- 0.05 Hall effectHiraki (1965) 0.03-0.05 0.15 - 0.20 Hall effectZhidkov (1961) 0.04 0.25 Hall effect-• Calculated vacancy formation energies in eV (EF = 0.305 eV). Acceptor levels in eV for the Ge vacancy. Department of Solid State Sciences 16Jan VanhellemontMultiscale model for defect dynamics during Cz growth Department of Solid State Sciences 17Jan VanhellemontThermal simulations• Thermal simulations of 200 and 300 mm Ge crystal growth. Department of Solid State Sciences 18Jan Vanhellemont Simulations illustrating the one order of magnitude larger void size in Ge and the four orders of magnitude lower volume density compared to Si.Simulation of intrinsic point defect clustering Department of Solid State Sciences 19Jan VanhellemontSimulation of vacancy clustering in Cz Ge Comparison between measured COP and simulated void distribution. The COP distribution was measured using a confocal review station. Department of Solid State Sciences 20Jan Vanhellemont2D unsteady-state simulations: decreasing pull rate Temperature, vacancy concentration, vacancy cluster concentration and size distributions for increasing pull rate. Department of Solid State Sciences 21Jan Vanhellemont2D unsteady-state simulations: full crystal 2D distributions of T, V concentration, V cluster concentration and size distribution in a 8” Ge crystal grown with constant pull rate. Department of Solid State Sciences 22Jan VanhellemontEpilogue: grown-in dislocations in HR-Ge• Optical micrograph of preferentially etched HR-Ge crystal slice revealing dislocation lineage and mosaic structures as well as isolated dislocations. Van Sande et al, Appl.Phys. A 40, 257 (1986). Department of Solid State Sciences 23Jan VanhellemontGrown-in dislocations• HVEM of lineage dislocations (Class 1) in a HR germanium crystal. Top) Tilted about 35° away from the [001] crystal pulling axis.  Bottom) The same area viewed along the [001] axis. Dislocations are seen end-on. Department of Solid State Sciences 24Jan VanhellemontEpilogue: grown-in dislocations in HR-Ge• HR-Ge is grown with well defined dislocation density to suppress V2H and void formation:– 90° (class 1) dislocations form low angle grain boundaries showing up as lineage or mosaic structures of etch pits;– 60° (class 2) dislocations: few thousand per cm2;– 30° (class 3) and 90° (class 4) difficult to avoid and radial distribution. • Dislocation and impurity specs HR Ge crystals:25  Conclusions The (negatively charged) vacancy is the dominant intrinsic point defect in germanium. Quantitative simulation of vacancy introduction and clustering during Czochralski pulling is possible. Further work:– impact of extrinsic point defects on vacancy thermal equilibrium concentration;– experimental data on vacancy and self-interstitial formation energy, diffusivity and recombination;– (impact of dislocations).Department of Solid State Sciences Jan Vanhellemont

Recent developments in understanding and modeling of defects in Czochralski germanium

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Recent developments in understanding and modeling of defects in Czochralski germanium

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