Hotwire-assisted Atomic Layer Deposition of Pure Metals and Metal Nitrides

Transcription

1 Hotwire-assisted Atomic Layer Deposition of Pure Metals and Metal Nitrides Alexey Kovalgin MESA+ Institute for Nanotechnology Semiconductor Components group 1

2 Motivation 1. Materials 2. Deposition method Multi-gate transistor (chipworks.com) CMOS backend: seed layers & barriers (chipworks.com) Group III Nitride TFTs (S. Bolat et al. Appl. Phys. Lett. 2014) High aspect ratio structures (e.g. memories) (chipworks.com) 2

3 Classic example of thermal ALD TiCl HCl 4 TiCl 4 OH + TiCl OTiCl HCl Courtesy of Hao Van Bui Metallic TiN films ALD: Self-limiting reactions Thickness control High aspect ratio structures NH 3 HCl NH TiCl + NH TiNH + HCl 3

4 Need for extra activation M(CH 3 ) 3 ALD of AlN and GaN compared M = Al, Ga CH 3 CH 3 M H H C H X X NH 3 CH 4 H N H H N H H H CH 3 CH 3 M H H C H X X Readily occurs for Al, difficult for Ga 4

5 Plasma-Enhanced ALD (PEALD) 1 st precursor: plasma off 2 nd precursor: plasma on 5

6 ALD classification Atomic Layer Deposition Thermal Radical-Enhanced PEALD Making radicals w/o plasma? Purpose: Hot-wire generated radicals (H, NH x, ) for ALD w/o plasma Cat. dissociation of H 2 on hot tungsten filament Joe N. Smith and Wade L. Fite, J. Chem. Phys. 32, 898, (1962) 6

7 Plasma versus Hot Wire Plasma 1. Breaking molecules by electrons or excited species 2. Number of chemical reactions can be significant 3. Ions are present => more reactions & charging 4. UV light emission 1. Catalytic dissociation by a hot ( o C) tungsten wire 2. Lower pressures possible 3. Number of reactions is limited 4. No ions Hot Wire 5. No UV 7 7

8 Outline Hotwire-assisted Atomic Layer Deposition of Pure Metals and Metal Nitrides Motivation Hotwire-Assisted Deposition: Confirmation of the Presence of Atomic Hydrogen HWALD of Tungsten (W) Films On the Growth of Titanium (Ti) Films Confirmation of the Presence of Nitrogen radicals On the Growth of Aluminum Nitride (AlN) Films Conclusions 8

9 Topic of the presentation HWALD: Which radicals can be formed? Confirmation of the Presence of Atomic Hydrogen 9

10 Reactor details A. Y. Kovalgin, and A. I. I. Aarnink, US Patent A1, Ellipsometer Hot-wire chimney Substrate Inner reactor Reactor 2 10

11 Is at-h delivered to the wafer surface? Atomic hydrogen reacts with Te surface producing TeH 2 : 2H + Te(s) TeH 2 (g) etching Te film There is no reaction between molecular hydrogen and Te. 11

12 Real-time monitoring of Te etching The etching of Te was real-time monitored by insitu SE (1) Introducing H 2, FILAMENT OFF (2) Stop introducing H 2, heat up the filament (3) Introducing H 2 with FILAMENT ON Te H. Van Bui et.al., ECS J. Solid State Sci. Technol. 2 (4) P149-P155 (2013). Substrate 100 nm Thickness verification by SEM 12

13 Etching of Te by H-pulses H. Van Bui et al.: ECS journal of solid state science and technology 2 (4) P149-P155 (2013). Bridge to Hot Wire ALD (HWALD) 13

14 Delivering atomic-h goes easily Adv. Mater. Interfaces 2017, Horizontal HW H 2, NH 3 Reactor 2 ~70 L Wafer few ml Reactor 1 H 2, NH 3 Vertical HW (line-of-sight) few ml Wafer Reactor 3 14

15 Topic of the presentation HWALD of Tungsten (W) Films 15

16 In-situ SE monitoring Sequential pulses of WF 6 and at-h Well-defined ALD window can be found One ALD cycle: Starting pulses here Stopping pulses here 1. at-h 2. Purge 3. WF 6 4. Purge 27

17 Properties of W High purity Excellent step coverage Yang et al., Thin Solid Films, 17

18 Crystallinity Yang et al., Thin Solid Films, 18

19 Resistivity Yang et al., Thin Solid Films, Film thickness: nm RMS: 1.4 nm 14.8 µω cm Resistivity: Resistivity mapping 100 µω cm, β-phase 15 µω cm, α-phase Ω cm 19

20 Topic of the presentation HWALD: On the Growth of Titanium (Ti) Films 20

21 Reference: ALD of TiN by TiCl 4 /NH 3 pulses 1 cycle 50% N 46% Ti 4% O H. Van Bui, A. Y. Kovalgin, and R. A. M. Wolters. ECS journal of solid state science and technology 1 (6) P285-P290 (2012). 21

22 TiCl 4 /H/NH 3 pulses H. Van Bui et al.: ECS journal of solid state science and technology 2 (4) P149-P155 (2013). Surface passivation by a-si pro Base pressure mbar N1s Si2p O1s Ti2p 43 at.% Ti 25 at.% N 35 at.% O (was 3-5 %) Atomic Atomic concentration Concentration (%) (%) Arrival of contaminants: 0,1 monolayer/s Sputter Depth (nm) Sputter depth (nm) 22

23 Cl TiCl 4 /H pulse sequence H reduces Cl groups, releasing HCl and leaving dangling bonds Cl Ti Cl Cl Cl Ti Cl Cl Cl Ti Cl Cl Cl Ti Cl Cl H H Ti Ti Cl H Cl H-O Ti O Ti Cl O-H Case #1: H atoms occupy dangling bonds Would be great but: 10-7 mbar of residual H 2 O Case #2: O atoms occupy dangling bonds TiO 2 will continue growing but very slowly as it is limited by the supply of H 2 O 23

24 Topic of the presentation It does work for W Why not for Ti, Al,? 24

25 Topic of the presentation HWALD: Which radicals can be formed? On the Presence of Nitrogen Radicals 25

26 Thickness (nm) 0,5 0,4 0,3 0,2 0,1 N-radicals delivered in line of sight Real-time SE acquisition Nitridizing Si wafer 0, Time (min) HW off HW horizontal HW vertical NH 3 Adv. Mater. Interfaces 2017, Horizontal HW Wafer Vertical HW (line-of-sight) NH 3 Wafer 26

27 Towards AlN: HW out of line-of-sight Adv. Mater. Interfaces 2017, HW on Horizontal HW NH 3 Atomic % O Al N Sputter time (min) HW off N Al Si O 350 o C Wafer 27

28 Towards AlN: HW in line-of-sight Adv. Mater. Interfaces 2017, NH 3 Vertical HW (line-of-sight) 350 o C Wafer 28

29 Conclusions ALD = self-limiting surface reactions => advantages Additional means to supply energy sometimes required HW can (to some extent) replace plasma: Generation of at-h confirmed by etching of Te films at-h: delivery in both in and out of line-of-sight possible Generation of Nitrogen radicals confirmed by nitridation of Si Nitrogen radicals: delivery in line-of-sight only Obviously (residual) oxidants can also be activated by HW Metal oxidation and reduction of the oxides should be taken into account HWALD enables (so far): Area-selective growth of high-qiality W using WF 6 /at-h Deposition of TiO x using TiCl 4 /at-h Deposition of AlN y O z using TMA and NH 3 via HW 29

30 Many thanks to: Mengdi Yang (PhD student HWALD W) Sourish Banerjee (PhD student AlN/GaN ALD) Hao Van Bui (graduated PhD student Te etching, TiN ALD) Ramazan Oguzhan Apaydin (PhD student BN) Tom Aarnink (technical support of deposition tools) Rob Wolters (discussions) Jurriaan Schmitz (discussions) Dirk Gravesteijn (discussions) Mark Smithers, Gerard Kip (MESA+) for SEM and XPS analyses. This work is financially supported by the Netherlands Organization for Scientific Research (NWO) and ASM International. 30

31 Thank you for your attention!