Atomic Layer Deposition Atomic Layer Deposition (ALD) Erwin Kessels w.m.m.kessels@tue.nl www.phys.tue.nl/pmp
Vapor phase deposition technologies Physical Vapor Deposition (PVD) Chemical Vapor Deposition (CVD) – sputtering – Heat! Energetic ions! g /Applied Physics - Erwin Kessels
More applications have stricter requirements on 1. Precise growth and thickness control 2 2. Hi h High conformality/step coverage f lit / t 3. Good uniformity on large substrates 4. Low substrate temperatures /Applied Physics - Erwin Kessels
Very demanding applications Nanoelectronics Photovoltaics Protective thin films f Flexible electronics /Applied Physics - Erwin Kessels
CMOS scaling in nanoelectronics g graphene graphene g ??? ??? p p nanowires nanowires ??? ??? Active Area Active Area Active Area Active Area Active Area Active Area Gate Gate Gate Gate Gate Gate Field Field Field Field Field Field Spacers Spacers Spacers Spacers Spacers Spacers Ge/IIIV Ge/IIIV ??? ??? FinFET FinFET metal gate metal gate HfO HfO 2 L=35nm L=35nm L=35nm - high high - SiGe SiGe strain strain USJ USJ time silicide silicide Time Courtesy of Marc Heyns, IMEC /Applied Physics - Erwin Kessels
Field-effect transistor: replacing SiO 2 by HfO 2 32 nm Thermally grown SiO 2 Thermally grown SiO 2 Precise deposition of nanometer-thick Hf-based oxides www.chipworks .com /Applied Physics - Erwin Kessels
Field-effect transistor: going from 2D to 3D gates 22 nm Precise deposition of nanometer-thick Hf-based oxides with excellent conformality with excellent conformality www.chipworks .com /Applied Physics - Erwin Kessels
Outline 1. Atomic layer deposition (ALD): basics and key features 2. ALD equipment 3. Materials & ALD surface chemistries 4. Some applications of ALD 5. Recent developments in high-throughput ALD /Applied Physics - Erwin Kessels
Atomic Layer Deposition (ALD) • Reactants (precursors) are pulsed into reactor alternately and cycle-wise (ABAB..) • Precursors react through saturative ( self-limiting ) surface reactions • A sub-monolayer of material deposited per cycle /Applied Physics - Erwin Kessels
ALD of Al 2 O 3 films: Al(CH 3 ) 3 - H 2 O process /Applied Physics - Erwin Kessels
Thickness vs. number of cycles CH 3 Film thickness is ruled 1. Al(CH 3 ) 3 Al H 3 C CH 3 by the number of cycles chosen N(C 2 H 5 ) 2 30 30 2 S 2. S iH {N(C H )} iH 2 {N(C 2 H 5 )} 2 Si 1. Al 2 O 3 N(C 2 H 5 ) 2 H H 2. SiO 2 m) 3. Ta 2 O 5 N(CH 3 ) 2 ( 3 ) 2 ness (nm 3 T {N(CH ) } 3. Ta{N(CH 3 ) 2 } 5 2 5 20 N(CH 3 ) 2 4. ZnO 2 Ta (H 3 C) 2 N N(CH 3 ) 2 5. TiO 2 N(CH 3 ) 2 Thickn H 2 H 2 4. Zn(CH 2 CH 3 ) 2 10 C C H 3 C Zn CH 3 CH 3 5. Ti(Cp*)(OCH 3 ) 3 H 3 C CH 3 0 0 50 100 150 200 250 H 3 C CH 3 Ti OCH 3 + + H 3 CO H 3 CO ALD Cycles ALD C l OC OCH 3 H 2 O, O 3 , or O 2 plasma Potts et al. , J. Electrochem. Soc., 157 , P66 ( 2010). /Applied Physics - Erwin Kessels Dingemans et al ., J. Electrochem. Soc. 159 , H277 (2012)
Key features of ALD 1. Control of film growth and thickness ‘Digital’ thickness control 2. High conformality/step coverage Self-limiting surface reactions 3. 3 G Good uniformity on large substrates d if it l b t t 300 mm and even bigger 4. Low substrate temperatures p Between 25 - 400 °C 5. Multilayer structures and nanolaminates Easy to alternate between processes 6. Large set of materials and processes Many different materials demonstrated Many different materials demonstrated /Applied Physics - Erwin Kessels
Line-of-sight vs. conformal grow th /Applied Physics - Erwin Kessels
Materials deposited ALD Puurunen, J. Appl. Phys. 97 , 121301 (2005) /Applied Physics - Erwin Kessels Miikkulainen et al ., J. Appl. Phys. 113, 021301 (2013).
Outline 1. Atomic layer deposition (ALD): basics and key features 2. ALD equipment 3. Materials & ALD surface chemistries 4. Some applications of ALD 5. Recent developments in high-throughput ALD /Applied Physics - Erwin Kessels
Single w afer ALD reactor Flow-type reactor Shower head reactor (hot wall reactor) (warm or hot wall reactor) • Temporal ALD • Pulse-train of precursors P l t i f • Reactor pressure 1-10 Torr • Applications: semiconductor (logic) pp ( g ) /Applied Physics - Erwin Kessels
Batch ALD reactor Batch reactor • Temporal ALD Temporal ALD • Typically 50-500 substrates in a single deposition run • Single-side deposition can be challenging g p g g • Applications: semiconductor (memory) , displays , solar cells , etc. /Applied Physics - Erwin Kessels
Plasma ALD reactors Plasma-assisted ALD can yield additional benefits for specific applications: 1. Improved material properties 2. Deposition at lower temperatures (also room temperature) p ( p ) p 3. Higher growth rates/cycle and shorter cycle times 4. More versatility/freedom in process and materials etc . Direct plasma Direct plasma Remote plasma Remote plasma Substrate part of plasma creation zone Substrate “downstream” of plasma creation zone Heil et al ., J. Vac. Sci. Technol. A 25 , 1357 (2007). /Applied Physics - Erwin Kessels Profijt et al ., J. Vac. Sci. Technol. A 29 050801 (2011)
Plasma-based chemistry (metal oxides) 1. CH 3 H 3 C Al CH 3 Al(CH 3 ) 3 N(C 2 H 5 ) 2 2. e) Al 2 O 3 TiO 2 - Ti(O ( i Pr) 4 ) 4 2 0 2.0 e (Å/cycle Si Si 2 3 2 N(C 2 H 5 ) 2 SiH 2 {N(C 2 H 5 )} 2 Me )(O H SiO 2 TiO 2 - Ti(Cp i Pr) 3 H Ta 2 O 5 TiO 2 - Ti(Cp*)(OMe) 3 1.6 N(CH 3 ) 2 3. N(CH 3 ) 2 Ta Ta{N(CH 3 ) 2 } 5 ( 3 ) 2 5 (H 3 C) 2 N per Cycle N(CH 3 ) 2 (C ) 1.2 N(CH 3 ) 2 4. O i Pr 0.8 Ti(O i Pr) 4 Ti Ti 4 O i Pr i Growth i PrO O i Pr 0.4 CH 3 5. Ti(Cp Me )(O i Pr) 3 0.0 0 0 3 Ti Ti O i Pr 0 50 100 150 200 250 300 i PrO O i Pr Substrate Temperature (°C) CH 3 6. H 3 C CH 3 Ti(Cp*)(OCH ) Ti(Cp*)(OCH 3 ) 3 H 3 C CH 3 Ti OCH 3 H 3 CO OCH 3 Potts et al. , J. Electrochem. Soc., 157 , P66 ( 2010). /Applied Physics - Erwin Kessels Dingemans et al ., J. Electrochem. Soc. 159, H277 (2012)
Oxford Instruments OpAL reactor – Plasma ALD /Applied Physics - Erwin Kessels
ALD equipment suppliers (incomplete list) R& D / Pilot Semiconductor Solar / R2R /Applied Physics - Erwin Kessels
Outline 1. Atomic layer deposition (ALD): basics and key features 2. ALD equipment 3. Materials & ALD surface chemistries 4. Some applications of ALD 5. Recent developments in high-throughput ALD /Applied Physics - Erwin Kessels
Metalorganic and H 2 O: ligand exchange (Al 2 O 3 ) ry signal (A) ry signal (A) ry signal (A) Al(CH 3 ) 3 exposure Purge Al(CH 3 ) 3 Al(CH 3 ) 3 Al(CH 3 ) 3 Al(CH 3 ) 3 Al(CH 3 ) 3 Al(CH 3 ) 3 Al(CH 3 ) 3 Al(CH 3 ) 3 H 2 O H 2 O H 2 O H 2 O H 2 O H 2 O H 2 O H 2 O -8 -8 -8 10 10 10 H 2 O H 2 O H 2 O H O H O H O spectrometr spectrometr spectrometr -9 -9 -9 10 10 10 AlOH*+ Al(CH 3 ) 3 AlOH Al(CH 3 ) 3 AlOAl(CH 3 ) 2 * + CH 4 AlOAl(CH 3 ) 2 CH 4 -10 -10 -10 10 10 10 CH 4 CH 4 CH 4 4 4 4 Mass Mass Mass -11 -11 -11 10 10 10 0 0 0 25 25 25 50 50 50 75 75 75 100 100 100 Cycle Time (s) Time (s) Time (s) AlCH 3 * + H 2 O AlOH* + CH 4 Surface chemistry rules ALD process: ligand exchange between Al(CH ) and ligand exchange between Al(CH 3 ) 3 and –OH surface groups and H 2 O and –CH 3 surface groups leads to CH 4 reaction * are surface species products Purge H 2 O exposure /Applied Physics - Erwin Kessels
Metalorganic and H 2 O: ligand exchange (Al 2 O 3 ) ry signal (A) ry signal (A) ry signal (A) Al(CH 3 ) 3 exposure Purge Al(CH 3 ) 3 Al(CH 3 ) 3 Al(CH 3 ) 3 Al(CH 3 ) 3 Al(CH 3 ) 3 Al(CH 3 ) 3 Al(CH 3 ) 3 Al(CH 3 ) 3 H 2 O H 2 O H 2 O H 2 O H 2 O H 2 O H 2 O H 2 O -8 -8 -8 10 10 10 H O H 2 O H O H O H 2 O H 2 O spectrometr spectrometr spectrometr -9 -9 -9 10 10 10 -10 -10 -10 10 10 10 CH 4 CH 4 CH 4 4 4 4 Mass Mass Mass -11 -11 -11 10 10 10 0 0 0 25 25 25 50 50 50 75 75 75 100 100 100 Cycle Time (s) Time (s) Time (s) Surface chemistry rules ALD process: ligand exchange between Al(CH ) and ligand exchange between Al(CH 3 ) 3 and –OH surface groups and H 2 O and –CH 3 surface groups leads to CH 4 reaction products Purge H 2 O exposure /Applied Physics - Erwin Kessels
Metalorganic and H 2 O: ligand exchange (Al 2 O 3 ) Al(CH 3 ) 3 Al(CH 3 ) 3 exposure Purge -5 4x10 chemisorption rbance 2940 cm 1 2940 cm -1 1207 cm -1 1207 cm 1 frared abso OH CH x CH x stretching stretching deformation H 2 O H O In exposure 4000 3500 3000 2500 2000 1500 1000 -1 ) Cycle Wavenumber (cm Surface chemistry rules ALD process: Surface alternately covered by –OH Surface alternately covered by –OH surface groups and –CH 3 surface groups Purge H 2 O exposure /Applied Physics - Erwin Kessels
Metalorganic and H 2 O: ligand exchange (Al 2 O 3 ) 1.2 Al(CH 3 ) 3 exposure Purge Cycle ( Å ) 0.8 owth per C 0.4 Gro 0.0 0 20 40 60 Al(CH 3 ) 3 dose (ms) Cycle Conditions such that precursors react through saturative surface reactions: Al(CH 3 ) 3 does not react with –CH 3 surface groups Purge H 2 O exposure /Applied Physics - Erwin Kessels
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