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1、Band Diagram and Carrier ConductionMechanismin Zr02/Zr-silicate/SiMIS Structure Fabricatedby Pulsed-laser-ablationDepositionTakeshi Yamaguchi,Hideki Satake, Noburu Fukushimaand Akira Toriumi* AdvancedLSI TechnologyLaboratory,ToshibaCorporation, 8, Shinsugita-cho,Isogo-ku,Yokohama235-8522,Japan Phone
2、: +81 -45-770-3687Fax: +81 -45-770-3578E-mail: ta-yamawchi(iilamc.toshiba.co.ipAbstract On the basis of the experimentalresults of XPS analysis and the carrierseparation,the band diagramand carriertransport mechanismin Zr02dielectricswere clarifiedfor the first time. Zr02-MISstructureconsistsof Zr02
3、layer and the interracial Zr-silicatelayer.Thecarrierconductionin Zr02layeris dominantin theZr02/Zr-silicate/SiMISstructure.It was foundthat the holeconductionmechanismis differentfrom electron conductionmechanismin Zr02gate dielectrics.Introduction Highdielectricconstant(high-k)materialssuchas Zr02
4、, Hf02,have drawn much attentionfor futuregate dielectrics. Althoughthe characteristicsof Zr02-MISFETshavealready reported,the carrier conductionmechanismin Zr02dielectrics has not been understoodyet 1. Recently,we demonstrated the ultra-thinZr02dielectricswith a large dielectricconstant anda smooth
5、interfacebyusingthepulsed-laser-ablation deposition(PLD)method2. In this paper,on the basisof XPS analysis and carrier separationmeasurements,for the first time, we will reportthe energy band diagramand the carrier conductionmechanismsofelectronandholein Zr02/Zr-silicate/SiMIS structure.Experimental
6、 The Zr02films were depositedon the diluted HF-treatedSi substratesby the PLDmethod.Theoxygengas pressureat depositionwasabout0.1Torr.TheZr02-NMISFETs (W=l Om, L=2Lm)were fabricatedby using the sourceand drainpre-fabricationmethodwiththeAl gateelectrodeof 200-nmthick.The Zr02-MIScapacitorswith using
7、Au gate electrodewere also fabricated.No annealingprocesswas used afterdepositionofZr02dielectrics.Asthereference, Sputter-Zr02gate NMISFETSwere also fabricated.Results and discussion Fig.1 shows a cross-sectionalTEM image of the interface ofZr02-MISstructure.Theamorphousinterraciallayer betweenZr02
8、andSisubstrateisZr-silicate,whichwas confirmedbyEDXanalysis2.FromC-VandJ-V characteristicsof Zr02MISstructureshownin Fig.2, we confirmedthat the equivalentoxide thickness(EOT) was about 1.3nm,whichwasestimatedfromtheaccumulation capacitancemeasuredby the two-frequencyC-V method3. Furthermore,it was
9、found that the leakage current density was about10-2 Alcm2 at the gate voltageof 2 V, whichis much smallerthan thatofSi02filmofthesameEOT.(Jsioz 1 O*A/cm* 4).ThePLD-Zr02-NMISFETcharacteristics were shown in Fig. 3. The subthresholdslope of 80 mVldecade is obtained with the good cut-off characteristi
10、cs.Fig. 1 Cross-sectionalTEM image of PLD-Zr02-MIScapacitor with the interracial Zr-silicatelayer which is fabricated at 500“C,in 02 ambient.2.5_100kHz /TzIoz=4.2nmI 0-7-$b10-8=0.79 eV I0-9 f ()-10 10-11Gate(-) 10-12 10-13b=o.T8ev10-14o10002000300040005000E“2 V/cm”2t10-5(b)Sputter- Zr024n-6EOT=2.7 n
11、m ,“10-TzIoz=7.Znm?lo:/Gate (+)zI(J9q()-10 .($blJJ10-11=0.98eVGate (-) :10-12I 0-1310-14=l.01 eV I(-)-15 o1000200030004000 E1/2,Cl/2Fig. 6Gate leakage characteristicsof Zr02-MISFET.(a) Poole-Frenkelplots of the leakage currents for gate(+) and gate(-), in PLD-Zr02dielectrics. Tbe trap energy barrier
12、 ($b) is around 0.8 eV.(b) Poole-Frenkelplots for the leakage currents of Sputter- Zr02 dielectrics.The $b is around 1.0 eV that is larger than that of PLD-Zr02dielectrics.0-7803-6441-4/00/$10.00 (C) 2000 IEEE10-5 IIFig.10indicatesthegatevoltagedependenceoftheg 10-6.PLD-Zr02“o, *,.b -0.8evd meESecon
13、dly,in order to obtain the informationconcerningtheIo-s hole transportmechanism,we performedthe carrier separationIo-9Igmeasurement6by using PLD-Zr02gate NMOSFETS.Figure10-10 9 shows the typical experimentalresults.Ig is the gate currentn10-i fkom the inversionlayerinto dielectrics,whichgeneratethe1
14、0-2 holes at the gate electrode/dielectricsinterface7. Holes flow back through the Zr02,to be measuredas the substratecurrent, Isub. The hole-generationratio, IIsub/Ig Iis also shown in Fig.o10002000300002468I 0.3I ()-4FqPLD-Zr02 ITzrOz=4.8 nm 10-610-7I9 I LbI Ig I10-8I 0-910-1010-11gI 0-12,IgQb-FN-
15、1.4eVFig. 12Schematic energy-band diagram and possible carrier transport mechanism in PLD-Zr02dielectrics.Electron can transport in the trap-assistedmechanism with b-O.8 eV. Hole can transport in the F-N like tunneling mechanism with b-FN(m*/m=4)-l.4eV.Figure13 showsthe J-V characteristicsof this in
16、terracial Zr-silicatelayer of EOT -0.9nm. The leakage propertyof the interracialZr-silicatelayerwithoutan annealingwas poor, however,theleakagecurrentof interracialZr-silicatelayer could be dramaticallyreducedafter 02annealingat 600 (Fig.13).In order to”clarify the causes of the improvementin leakageproperties,the O 1s energyloss spectraof interracial Zr-silicatelayersbeforeandafterannealingprocesswere examinedby XPSanalysis,focusing
