Crystal Growth Techniques

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1、CrystalGrowthTechniquesRonGrahamOctober31,2006Agenda•Summarizecurrenttechniques•Discussadvantages/disadvantages•ProposehybridmethodBasicMethods•Czochralski(CZ)•Bridgman(andvariations)•Variousfloatingzonemethods•EBdripmelting•Strainannealing•Othermetho

2、dsCzochralski•Czochralski(CZ)typicallyusedforSi•Cangrowboulesto300mmwith400mmbeingintroduced•Usesseedcrystal•“Pulls”bouleoutofthemeltCzochralskiPuller•ResistanceorRFheatingSeedView-Crystalport•MeltcontainedinquartzorSiNcrucible34•ChamberunderArgonHeat

3、ersMelt•Simelts1421°CCzochralski•Growthspeedis1–2mm/min•Crucibleintroducesoxygencontamination•Feedmaterialformisunconstrained•Axialresistivityuniformityispoor•Heatup/cooldowntimesarelong•MaterialsofconstructionareissueNbT=m2477°C•Ingotweightcanreach40

4、0kgCzochralski•Modificationisa“Tri-arc”furnace•Meltingaccomplishedby3arcs•Rotating,water-cooledCucrucible•Meltconductedundervacuum•Reportedlycanmeltto3000°CBridgmanTechnique•Verticalorhorizontal•Usesacrucible•Requiresseedcrystal•Directionalsolidificat

5、ion•PrecisetemperaturegradientrequiredBridgmanTechniqueMoltenzoneFurnacetubeHeaterPolycrystalPullMoltenPullCrystalSeedCrystalSeedBridgmanTechniquesolid-liquidinterfaceCarefullycontrolledtemperaturegradientrequired.TemperatureTMBridgmanTechnique•Growth

6、ratesofabout1mm/hr•Cruciblesusuallyusedonetime•UsedforsmallNbcrystals10x40–60mm•Requiresonlytipofseedtobemolten•Canreach200mmforSiandGaAscrystalsFloatingZoneTechniques•Electronbeamfloatingzone(EBFZ)•RFfloatingzoneEBFloatingZone•Actualexperiencewithref

7、ractoryalloysincludingNb,Ta,Mo,Re,andW•Vacuummeltingchamber,annularEBgun•Crystalrotatorandtranslator•Nocrucible•0.5–50mm/mingrowthratesEBFloatingZoneMeltstock(anode)WfilamentcathodeLiquidmetalFocusingelectrodesEBFloatingZone•Zonerefiningisaddedbenefit

8、•Diametersupto110mmreportedforNb•Diameterslimitedbysurfacetension/runout•EBheatingpenetrationlimited•Doesnotseempracticalfor300mmEBFloatingZoneO<0.03C<0.3N<50ImpurityconcentrationH<0.1ofNbasreportedbySi<0.03GiebovskyandSemenovAl<0.03K<0.03Ca<0