pulsed cvd/ald of amorphous gese for application as ots
TRANSCRIPT
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Pulsed CVD/ALD of Amorphous GeSe for
Application as OTS SelectorAli Haiderő, Shaoren Deng*, Elie Schapmanső, Michael Givens˝, Jan Willem Maes*, Karl Opsomerő, , Christophe Detavernier, Jean-Marc
Girard¤, Sven van Elshochtő, Matty Caymaxő
ŐIMEC Belgium, *ASM Belgium, ˝ASM microchemistry, TU Ghent, ¤Air Liquide France
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Chalcogenide materials
growth
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SELECTOR DEVICE
Dense memory arrays – cross bar memory
2 – terminal memory devices current sneak path problem
Need for a selector device to select a specific memory cell
Threshold switch
Non conductive for V<Vth, conductive for V>Vth
Amorphous Ge Chalcogenides showing Ovonic Threshold
Switching (OTS)
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CROSSBAR MEMORY AND SELECTOR DEVICES
Current sneakpath problem
Materials containing S, Se, or Te
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MOTIVATION TO GROW ALD GeSe
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1. 3D conformality for selector
2. Amorphous phase, thermally stable throughout full processing cycle (up to 400 °C)
3. Uniform films (300 mm wafer), thickness (10-20 nm), and composition control
Planar vehicle: PVD grown selector
3D vehicle: need ALD grown
selector
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MClx + x(Et3Si)2Te MTex + xEt3SiCl
1GeCl2.stabilizer + ((C2H5)3Si)2Te GeTe + 2(C2H5)3Si Cl + C4H8O2
90 °C
ALD OF GeTe BY UNI OF HELSINKI
1ASMM and Univ. of Helsinki, V. Pore et al., JACS Comm 131, 3478, 2009
Formation of alkylsilylchloride drives the reaction
What we are trying at IMECTe Se
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Experimental
1. Film growth in ASM Pulsar 300 mm cross flow reactor (various reactor conditions)
2. Total reflection X-ray fluorescence (TXRF) to study precursor chemisorption
Trace element analysis
Quantitative
Whole wafer (300 mm) analysis
3. Material characterization: SEM, TEM, ERD, EDX, XRR, Temp programmed XRD...
Ge precursors Se precursors
Stabilized germanium dichloride.
(GeCl2.stabilizer)
Bis(trimethylsilyl)selenide ((CH3)3Si)2Se (TMS)2Se
Bis(triethylsilyl)selenide ((C2H5)3Si)2Se (TES)2SeASM POLYGON 2 Pulsar platform
ALD
chalcogenides
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OUTLINE
Ge and Se precursor chemisorption studies by TXRF
GPC trends with processing conditions
GeSe properties
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OUTLINE
Ge and Se precursor chemisorption studies by TXRF
GPC trends with processing conditions
GeSe properties
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TXRF measurements: Precursor Chemisorption Studies
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Stabilized GeCl2Chemisorption
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GeCl2 chemisorption on SiOX is slow, limited by precursor supply/slower
injection
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~50 sec needed for Ge saturation on 300 mm wafer
Pulse/purge/no of repetitions
Saturation coverage = 2.7E+14 A/cm2, i.e. ~20-25% of potential surface sites; probably limited by steric
hindrance
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Se precursor chemisorption
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Se doesn’t chemisorb on SiOX
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Se chemisorbs on GeClX: Cl sites needed for precursor ligands exchange
reaction
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~400 sec needed for saturation: much slower
• Saturation coverage is ~3.5E+13A/cm2 (only ~15% of Ge sites)
ggg
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Se CONCENTRATION AT DIFFERENT REACTOR TEMPERATURES
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Se CONC DECREASE AT HIGHER REACTOR TEMPERATURE
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Se chemisorption becomes faster with (TMS)2Se on GeClX/Si
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~100 sec needed for saturation vs 400 sec for previous precursor
• Saturation coverage with (TMS)2Se is ~1.1E+14/cm2 (~75 % of Ge sites are covered)
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OUTLINE
Ge and Se precursor chemisorption studies by TXRF
GPC trends with processing conditions
GeSe properties
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Limited by Ge precursor delivery
Slow kinetics
Processing conditions
Best precursor combination
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OUTLINE
Ge and Se precursor chemisorption studies by TXRF
GPC trends with processing conditions
GeSe properties
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GPC is higher in (1) pulsed CVD regime, (2) with higher GeCl2 delivery,
and (3) low reactor temp
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ALD regime
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OUTLINE
Ge and Se precursor chemisorption studies by TXRF
GPC trends with processing conditions
GeSe properties
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GeSe is conformal, amorphous, uniform, smooth and near stoichiometric.
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3nm
20nm
GeSe
Native oxide
~ 20 nm
EDX analysis
Element at.%
Chlorine 4.1
Germanium 49.20
Selenium 46.71
Ge51Se49 if normalized to 100 atom% GeSe
C, O ignored (stemming from specimen storage
at air)
ERD depth analysis
Element at.%
Hydrogen ~5
Carbon ~5
XRR
Gas flow direction
GPC independent of substrate
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Thermal Stability Data by In-situ Temperature Programmed XRDGeSe on TiN and SiO2 substrates: Crystallization peaks at ~365-370 ºC
Si
20 nm Ge51Se49
10 nm TiN
Pulsed CVD Ge51Se49
This workOrthorhombic
GeSe phase
2 (33°)=(040)
2 (47°)=(002)
50 nm TiN
Si
20 nm Ge51Se49
10 nm TiN
100 nm SiO2
Pulsed CVD Ge51Se49
This work
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SUMMARY AND CONCLUSION
1. TXRF studies: Ge chemisorption limited by Ge precursor delivery, overall slow kinetics
2. Key parameters to obtain higher GeSe GPC
• Pulsed CVD regime
• Higher delivery of GeCl2 precursor
• Lower reactor temperature
3. GeSe is conformal and amorphous.
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OUTLOOK
Benchmarking PVD GeSe vs ALD GeSe
Optimization of GeSe process
Controlling the impurities in GeSe
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