Short course on Atomic Layer Deposition

Transcription

1 Short course on Atomic Layer Deposition Erwin Kessels & Jan-Pieter van Delft

2 Vapor phase deposition technologies Physical Vapor Deposition (PVD) sputtering Chemical Vapor Deposition (CVD) Energetic ions! Heat!

3 More applications have stricter requirements on 1. Precise growth and thickness control 2. High conformality/step t coverage 3. Good uniformity on large substrates 4. Low substrate temperatures

4 Very demanding applications Nanoelectronics Photovoltaics Protective thin films Flexible electronics

5 CMOS scaling in nanoelectronics graphene??? nanowires Active Area??? Spacers Gate Field Ge/IIIV??? FinFET metal gate L=35nm HfO 2 high - strain SiGe USJ silicide time Time Courtesy of Marc Heyns, IMEC

6 Intel roadmap Scaling enabled by Lithography h Materials 3 rd Dimensioni

7 Field-effect transistor: replacing SiO 2 by HfO 2 32 nm Thermally grown SiO 2 Precise deposition of nanometer-thick Hf-based oxides

8 Field-effect transistor: going from 2D to 3D gates 22 nm Precise deposition of nanometer-thick Hf-based oxides with excellent conformality

9 Going 3D: memories and interconnects DRAM deep trench capacitors (aspect ratio up to 70) Through-silicon vias (4 µm wide & 40 µm deep) Precise deposition of ultrathin films with excellent conformality in very high aspect ratio (>10) trenches and vias Courtesy of Ivo Raaijmakers, ASM

10 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

11 Atomic Layer Deposition (ALD) Chemisorption of reactant A Sub-monolayer A Saturation Purge Cycle Purge Sub-monolayer B Saturation Chemisorption of reactant B Reactants (precursors) are pulsed into reactor alternately and cycle-wise (ABAB..) Precursors react through saturative (self-limiting) limiting) surface reactions Asub-monolayer of material deposited per cycle

12 Atomic layer deposition (ALD) - movie

13 Thickness vs. number of cycles Film thickness is ruled by the number of cycles chosen 50 1 Al O Al 2 O 3 Thick kness (n nm) SiO 2 3. Ta 2 O 5 4. TiO 2 5. TiO 2 6. TiO ALD Cycles Potts et al., J. Electrochem. Soc., 157, P66 ( 2010). Dingemans et al., J. Electrochem. Soc. 159, H277 (2012)

14 Key features of ALD 1. Control of film growth and thickness Digital thickness control 2. High conformality/step coverage Self-limiting surface reactions 3. Good uniformity it on large substrates t 300 mm and even bigger 4. Low substrate temperatures Between C 5. Multilayer structures and nanolaminates Easy to alternate between processes 6. Large set of materials and processes Many different materials demonstrated

15 Line-of-sight vs. conformal growth

16 Key features of ALD 1. Control of film growth and thickness Digital thickness control 2. High conformality/step coverage Self-limiting surface reactions 3. Good uniformity it on large substrates t 300 mm and even bigger 4. Low substrate temperatures Between C 5. Multilayer structures and nanolaminates Easy to alternate between processes 6. Large set of materials and processes Many different materials demonstrated

17 Materials deposited ALD After: Puurunen J. Appl. Phys. 97, (2005)

18 Recent literature on ALD N. Pinna and M. Knez (Eds.) Wiley VHC (2011) MRS Bull. 36, 907 (2011)

19 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

20 Single wafer ALD reactor Flow-type reactor (hot wall reactor) Shower head reactor (warm or hot wall reactor) Temporal ALD Reactor pressure Torr Pulse-train of precursors Applications: semiconductor (CMOS)

21 Batch ALD reactor Batch reactor Temporal ALD Typically substrates in a single deposition run Single-side deposition can be challenging g Applications: TFEL displays, DRAM, Flash memories, solar cells, etc.

22 Plasma ALD reactors Plasma-assisted ALD can yield additional benefits for specific applications: Improved material properties Deposition at lower temperatures (also room temperature) Higher growth rates/cycle and shorter cycle times More versatility/freedom in process and materials etc. Direct plasma Substrate part of plasma creation zone Remote plasma Substrate downstream of plasma creation zone Heil et al., J. Vac. Sci. Technol. A 25, 1357 (2007).

23 Oxford Instruments OpAL reactor - Movie

24 Plasma ALD: pros and cons 1. Improved material properties Lower impurity levels Higher film density Benefits 2. Deposition at reduced substrate temperatures Gas phase species deliver high reactivity to deposition surface 3. Increased choice of precursors and materials Precursors with high thermal and chemical stability Deposition of difficult metals 4. Good control of film stoichiometry and film composition Additional process parameters Use of plasma gas mixtures 5. Increased growth rate Higher growth per cycle Shorter purges Shorter purges Shorter nucleation time 6. More process versatility in general In situ plasma pretreatment Reactor conditioning & cleaning (etching) Challenges 1. Reduced conformality or step coverage Surface recombination of plasma species 2. Plasma-induced damage Substrate oxidation/nitridation Damage induced by ion bombardment Damage induced by plasma radiation 3. Industrial scale-up of the PE-ALD processes More complex equipment

25 Recent literature on plasma ALD Recent review article: Profijt et al., J. Vac. Sci. Technol. A (2011)

26 ALD equipment suppliers (incomplete list) R&D / Pilot Semiconductor Solar / R2R

27 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

28 AlOH*+ Al(CH3)3 AlOH * are surface species H 2O Al(CH 3)3 H 2O Al(CH 3)3 CH AlOAl(CH 3)2* + CH Time (s) AlCH3* + H2O Purge H 2O H2O Cycle Al(CH 3) H 2O Purge Al(CH 3)3 Al(CH3)3 exposure Mass spectrometrry signal (A) Metalorganic and H2O: ligand exchange (Al2O3) H2O exposure AlOH* + CH4 Surface chemistry rules ALD process: ligand exchange between Al(CH3)3 and OH surface groups and H2O and CH3 surface groups leads to CH4 reaction products

29 Metalorganic and H 2 O: ligand exchange (Al 2 O 3 ) Al(CH 3 ) 3 exposure Purge spectrometr ry signal (A) 10-8 Al(CH 3 ) 3 H 2 O H O CH 4 Al(CH 3 ) 3 H 2 O Al(CH 3 ) 3 H 2 O Al(CH 3 ) 3 H 2 O Cycle Mass Time (s) Surface chemistry rules ALD process: 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

30 Metalorganic and H 2 O: ligand exchange (Al 2 O 3 ) Al(CH 3 ) 3 exposure Purge rbance frared abso In 4x10-5 Al(CH 3 ) 3 chemisorption 2940 cm cm -1 OH CH x CH x stretching stretching deformation H 2 O exposure Cycle Wavenumber (cm -1 ) Surface chemistry rules ALD process: Surface alternately covered by OH surface groups and CH 3 surface groups Purge H 2 O exposure

31 Metalorganic and H 2 O: ligand exchange (Al 2 O 3 ) Al(CH 3 ) 3 exposure Purge Gro owth per Cycle (Å) Cycle Al(CH 3 ) 3 dose (ms) 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

32 Metalorganic and H 2 O: ligand exchange (Al 2 O 3 ) Al(CH 3 ) 3 exposure Cycle Purge Grow wth per Cy ycle (Å) H 2 O dose (ms) Conditions such that precursors react through saturative surface reactions: H 2 O does not react with OH surface groups Purge H 2 O exposure

33 Metalorganic and H 2 O: ligand exchange (Al 2 O 3 ) Al(CH 3 ) 3 exposure Purge 1.6 Cycle Grow wth per Cyc cle (Å) CVD+ALD ALD Purge after Al(CH 3 ) 3 dose (s) Precursors and reactants should be very well evacuated/separated from reactor before pulsing the next precursor/reaction: Otherwise parasitic CVD Purge H 2 O exposure

34 ALD process: saturation curves (Al 2 O 3 ) Grow wth per Cycle (nm/cycle) le) Growth per Cycle (nm/cycl (a) Thermal ALD -Al(CH 3 ) 3 & H 2 O Dose time (ms) CVD Purge time (s) (b) Plasma ALD -Al(CH 3 ) 3 & O 2 plasma CVD Subsaturation H 2 O dose (ms) Subsaturation CVD Purge time (s) Dose time (ms) Purge time (s) Plasma time (s) Purge time (s)

35 ALD process: substrate temperature (Al 2 O 3 ) Growth rate (nm/cycle e) (a) 6 (b) Plasma ALD Thermal ALD # Al atoms per cycle (10 15 cm -2 ) Substrate temperature ( o C) AlOH* + Al(CH 3 3) 3 AlOAl(CH 3 3) 2 * + CH 4 AlCH 3 * + H 2 O AlOH* + CH 4 Van Hemmen et al., J. Electrochem. Soc. 154, G165 (2007) Potts et al., J. Electrochem. Soc., 157, P66 ( 2010).

36 ALD process: substrate temperature (ideal case) Grow wth per Cycle B A ALD Temperature Window C D A. Condensation B. Insufficient thermal energy C. CVD D. Evaporation H 2 O OH OH T O Substrate Temperature Substrate/film surface

37 Materials deposited ALD After: Puurunen J. Appl. Phys. 97, (2005)

38 Metal halide: ligand exchange (HfO 2 and TiN) Metal oxides: ligand exchange HfOH* + HfCl 4 HfCl* + H 2 O HfOHfCl 3 * + HCl HfOH* + HCl Metals nitrides: ligand exchange TiNH* + TiCl 4 TiCl* + NH 3 TiNTiCl 3 * + HCl TiNH 2 * + HCl * are surface species

39 Metals: combustion (Pt) and reduction (W) Noble metals: combustion by chemisorbed O 2 3 O* + 2 (MeCp)PtMe 3 2 (MeCp)PtMe 2 * + CH 4 + CO 2 + H 2 O 2 (MeCp)PtMe 2 * + 24 O 2 Pt 2 Pt* + 3 O* + 16 CO H 2 O Metals: fluorosilane elimination reactions F F F W F F F WSiF 2 H* + WF 6 WWF 5 * + SiF 3 H WWF 5 * + Si 2 H 6 WSiF 2 H* + SiF 3 H + 2H 2 * are surface species

40 Plasma-based chemistry (Al 2 O 3 and TiN) Metal oxides: combustion AlOH*+ Al(CH 3 ) 3 AlOAl(CH 3 ) 2 * + CH 4 AlCH 3 * + 4O AlOH* + CO 2 + H 2 O Metal nitrides: ligand exchange and reduction TiNH* + TiCl 4 TiCl* + 3H + N TiNTiCl 3 * + HCl TiNH 2 * + HCl * are surface species

41 Plasma-based chemistry (metal oxides) 1. Al(CH 3 ) 3 H 3 C Al CH 3 CH 3 2. SiH 2 {N(C 2 H 5 )} 2 Si 3. Ta{N(CH 3 3) 2 } 5 (H 3 C) 2 N Ta 4. Ti(O i Pr) 4 5. Ti(Cp Me )(O i Pr) 3 6. Ti(Cp*)(OCH 3 ) 3 H 3 C H i PrO i PrO N(C 2 H 5 ) 2 H N(CH 3 ) 2 N(CH 3 ) 2 N(CH 3 ) 2 N(CH 3 ) 2 O i Pr Ti i O i Pr O i Pr CH 3 N(C2H5)2 TiO2 2 0Al2O3 - Ti(OiPr)4 per Cycle (Å/cycle e) Growth ( ) 4 SiO 2 TiO 2 - Ti(Cp Me )(O i Pr) 3 Ta 2 O 5 TiO 2 - Ti(Cp*)(OMe) CH 3 Ti O i Pr O i Pr CH 3 Substrate Temperature ( C) H 3 C CH 3 Ti OCH H 3 CO 3 OCH 3 Potts et al., J. Electrochem. Soc., 157, P66 ( 2010). Dingemans et al., J. Electrochem. Soc. 159, H277 (2012)

42 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

43 Thin-film electroluminescent (TFEL) displays New large-area display in 1983 Atomic layer deposited ZnS:Mn 1974 First patent on ALD filed by Tuomo Suntala 1983 Introduction of first ALD (non)-transparent inorganic TFEL display Since 1989 Commercial production of ALD-TFEL displays by Planar T. Suntola, Mater. Sci. Rep. 4, 261 (1989)

44 Encapsulation of OLED Devices Thin-film-encapsulated OLEDs after testing No encapsulation 40 nm ALD Al 2 O 3 film Thin film encapsulation requires: low deposition temperatures low water vapor transmission rates low pinhole (black spot) density Langereis et al., Appl. Phys. Lett. 89, (2006). Keuning et al., J. Vac. Sci. Technol. A 30, 01A131 (2012).

45 Defect (dust particle) encapsulation Courtesy of Jian Jim Wang (NanoNuvo Corporation, USA)

46 Surface passivation for c-si solar cells Surface passivation on n-, p-, and p + -type crystalline silicon Reduction of electric losses at the Si surface Chemical passivation and field-effect passivation Hoex et al., Appl. Phys. Lett. 89, (2006); Hoex et al., J. Appl. Phys. 104, (2008).

47 Buffer layers for CIGS solar cells Replacement for CdS buffer layers Control of film composition, band gap and conduction band offset (CBO) (Zn,Mg)O, Zn(O,S) and In 2 S 3 are the most promising materials 2 3 Törndahl et al., Prog. Photovolt. Res. Appl. 15, 225 (2007)

48 Encapsulation of CIGS and Organic PV cells Protection against moisture and oxygen from the ambient Level of protection by ALD layers approaches the one of glass Carcia et al., Sol. Energy Mater. Sol. Cells 94, 2375 (2010)

49 Recent literature on ALD for PV (ALD4PV) c-si solar cells CIGS solar cells Van Delft et al., Semicond. Sci. Technol. 27 (July 2012) Organic Oga csolar cells Dye-sensitized solar cells Bakke et al., Nanoscale 3, 3482 (2011)

50 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

51 Large substrate ALD reactors Temporal ALD Can be (inline) single wafer or batch reactor Substrate size up to 120 x 120 cm 2 Applications: Thin-film transistors, encapsulation, CIGS solar cells, transparent conductive oxides

52 Batch ALD reactor Temporal ALD Typically substrates in a single deposition run Single-side deposition can be challenging Applications: DRAM, Flash memories, TFEL displays, solar cells, etc.

53 Spatial ALD concept ALD cycles are carried out in the spatial domain precursor and reactant pulsing occur at different positions The substrate or the ALD deposition head must move Purge areas created by inert gas barriers prevent CVD reactions requires operation at high pressure No gas switching nor vacuum pumps are needed No deposition on the reactor walls

54 Spatial and in-line ALD reactor (Levitech) Developed for surface passivation of c-si solar cells by Al 2 O 3 Wafer moves continuously in one direction Throughput of 3600 wafers/hour

55 Spatial and in-line ALD reactor (Levitech) - Movie

56 Spatial and in-line ALD reactor (SoLayTec) Developed for surface passivation of c-si solar cells by Al 2 O 3 Wafer moves back and forth Throughput of 3600 wafers/hour (high-volume tool)

57 Roll-to-roll ALD reactors (Beneq) Spatial ALD concept Ideally suited for coating of flexible substrates OLEDs, flexible PV cells, etc. Low temperature deposition on polymers Throughput h of 2 m/min

58 Roll-to-roll ALD reactors (Lotus AT) Spatial ALD concept Coating of flexible substrates OLEDs, flexible PV cells, etc. Low temperature deposition on polymers Also in plasma-enhanced dald configuration Throughput of 20 m/min

59 Further reading and downloads Recent literature on ALD Pinna and Knez (Eds.) Wiley VHC (2011) MRS Bull. 36, 907 (2011) Recent literature on plasma ALD Profijt et al., J. Vac. Sci. Technol. A (2011) Recent literature on ALD for PV Van Delft et al., Semicond. Sci. Technol. 27 (July 2012) Bakke et al., Nanoscale 3, 3482 (2011) Downloads

60 Title /Department of Applied Physics