GeTe films for PCRam elaborate by pulsed injection MOCVD and PEMOCVD for phase change memory

Transcription

1 GeTe films for PCRam elaborate by pulsed injection MOCVD and PEMOCVD for phase change memory P. Michallon 1, E. Gourvest 2, C. Vallée 3, J. Vitiello 4, R. Blanc 3, D. Jourde 1, L. Dussault 3, P.Noé 1, J. Ferrand 1, S. Lhostis 2, and S. Maitrejean 1 1 CEA-LETI LETI-Minatec Minatec, Grenoble France 2 STMicroelectronics, Crolles France 3 CNRS-LTM LTM, Grenoble - France 4 Alatetch, Montbonnot - France

2 Outline General aspects of memories Material screening for PCRAM by PVD Set up GeTe by MOCVD GeTe by PECVD Conformity aspects Conclusions and perspectives Philippe Michallon - Workshop on Innovative Memory Technologies June; 29th 2

3 What is the phase change memory effect? Selected materials germanium antimony tellurium composition diagram PVD Layer the most popular phase change material =>Ge 2 Te 2 Sb 5 Resistivity [ Ω*m] Information is stored thanks to variation of a resistive element (Due to Joule effect on the heater element) Specifications and needed for memory are: highly resistive amorphous state lower resistive crystalline state Resistivity Ω.m 10 3 Morphology Phase change Amorphous phase high resistivity (low reflectivity) crystalline diagram for Ge 2 Sb 2 Te 5 crystallization temperature Tc Tc Temperature [ C] Crystalline phase low resistivity (low reflectivity) => highly electrical contrast between amorphous and crystalline phase (> 2 decades) Philippe Michallon philippe.michallon@cea.fr - Workshop on Innovative Memory Technologies June; 29th 3

4 material issue The main issues 1- low data retention at high temperature Due to the thermal instability of the amorphous phase Embedded application (automobile for example). requirement: no spontaneous crystallization for C => 150 is precisely near of the crystallization temperature for Ge 2 Sb 2 Te 5!!! Solution : new materials with phase change at higher temperature. technological issue 2- high I RESET ( > 200 µa) high current to reach the melting temperature (go back to amorphous state) requirement: reducing I reset level consumption I reset divide by 2 to 4. Solution : use of confined structures to reduce the contact area with low electrode and phase memory material to increase heating efficiency (Joule effect) => fill holes by CVD Philippe Michallon philippe.michallon@cea.fr - Workshop on Innovative Memory Technologies June; 29th 4

5 Outline General aspects of memories Material screening for PCRAM by PVD Set up GeTe by MOCVD GeTe by PECVD Conformity aspects Conclusions and perspectives Philippe Michallon - Workshop on Innovative Memory Technologies June; 29th 5

6 Materials Screening by PVD (to find a solution for issue 1) Several materials elaborate by PVD were tested (planar configuration) Investigated materials: (germanium antimony tellurium) Perniola et al, Electron. Dev. Lett ternary : Ge 2 Sb 2 Te 5 binary : GeTe & GeTe + doping Carbon or Nitrogen GST (225) Thermal stability criteria: crystallization temperature crystallization activation energy consequently retention time (Arrhénius law) GeTe Retention time (GST and GeTe comparison) Philippe Michallon philippe.michallon@cea.fr - Workshop on Innovative Memory Technologies June; 29th 6

7 Materials Screening by PVD (to find a solution for issue 1) Retention time comparison: 85 C 110 C 127 C 154 C data retention of 10 years at : Ge 2 Sb 2 Te 5 GeTe C(10%)-GeTe N(2%)-GeTe - electrical contrast > endurance > 10 6 cycles - electrical contrast > endurance > 10 6 cycles - SET speed < 30 ns - 25% I RESET reduction / GST - electrical contrast > SET speed < 50 ns - data ret. automotive spec. evidence of new stable materials: base GeTe and N or C-doped GeTe Development of a PECVD tool (issue 2) for the deposition of GeTe material Ge and Te precursors are containing N and C atoms that can improve the material properties Philippe Michallon philippe.michallon@cea.fr - Workshop on Innovative Memory Technologies June; 29th 7

8 Outline General aspects of memories Material screening for PCRAM by PVD Set up GeTe by MOCVD GeTe by PECVD Conformity aspects Conclusions and perspectives Philippe Michallon - Workshop on Innovative Memory Technologies June; 29th 8

9 Set up : CVD Tool with in situ characterization New pulsed injection PEMOCVD tool in Leti= answer for second issue Development of a new PECVD industrial tool: Tool developed in frame work of the French Ministry project in close collaboration with Altatech. New evaporator 4 independent precursor lines high vaporization capability: High control of the stœchiometry Shower dual channels High thickness homogeneity on 200 mm wafer (<2%) Plasma assistance (Radio Frequency, Low Frequency) Heater until 600 C Set up on Brooks platform 6 slots in situ diagnostics In situ plasma characterization by OES (optical emission spectrometer) Quasi in situ XPS (ADIXEN system) Quasi in situ Ellipsometer with heater up to 600 C Philippe Michallon philippe.michallon@cea.fr - Workshop on Innovative Memory Technologies June; 29th 9

10 Outline General aspects of memories Material screening for PCRAM by PVD Set up GeTe by MOCVD GeTe by PECVD Conformity aspects Conclusions and perspectives Philippe Michallon - Workshop on Innovative Memory Technologies June; 29th 10

11 GeTedeposition by MOCVD Deposition at 350 C strong non homogeneity Gerich layers -3D growth! Process optimization XRD intensity [a. u.] rhombohedral GeTe *theta [ ] Philippe Michallon philippe.michallon@cea.fr - Workshop on Innovative Memory Technologies June; 29th 11

12 GeTedeposition by MOCVD XPS composition Intensité XPS [u. a.] Te 4d oxyde de Ge expérimental simulé Ge 3d C Te Ge Quantification relative [% at] Energie de liaison [ev] granular depositions (crystalline phase) 3D growth stoichiometry easily tunable (GeTe ratio ~ 1,2) carbon content can be very low (< 5%) Te adding thanks to surface preparation (pattern on going) Philippe Michallon philippe.michallon@cea.fr - Workshop on Innovative Memory Technologies June; 29th 12

13 Outline General aspects of memories Material screening for PCRAM by PVD Set up GeTe by MOCVD GeTe by PECVD Conformity aspects Conclusions and perspectives Philippe Michallon - Workshop on Innovative Memory Technologies June; 29th 13

14 PECVD of GeTe: first step Plasma assistance (50 W RF) is added to the standard CVD deposition process at T dep = 350 C Deposition of crystalline GeTe (gain faceting) homogeneity improved stickiness improved Philippe Michallon philippe.michallon@cea.fr - Workshop on Innovative Memory Technologies June; 29th 14

15 PECVD of GeTe Temperature effect Substrate Temperature reduction down to 200 C Deposition of thin amorphous layer Good homogeneity Carbon contamination ~ 11 % at. Thickness 150 nm in 300 s deposition 150 nm Amorphous Ge Te Layer Intensité XPS [u. a.] Te 53 % PE-MOCVD 200 C expérimental simulé Ge 47 % Intensité XPS [u. a.] Experimental 100 expérimental W, 5 Torr, 300 s simulation simulé Surface pollution carbon surfacique pollution Organics contaminants contamination organiques C 1s Before surface etching avant gravure C-GeTe after surface après gravure etching Energie de liaison [ev] Ge Te Layer composition Energie de liaison [ev] Carbon evaluation on layer GeTe Philippe Michallon philippe.michallon@cea.fr - Workshop on Innovative Memory Technologies June; 29th 15

16 Process optimization: GeTe by PECVD Amorphous GeTe deposition : T substrat decreasing Level carbon reduction : plasma adaptation (=> 3%at) 60 nm Amorphous GeTe : Ge 0.56 Te 0.44 Control stoichiometry Optical reflectivity [%] carbon rate increase then temperature of crystallization increase Tc Low level carbon lower ~ 3 at.% speed deposition 12 nm by mn C(0%)-GeTe Phase variation conform to the results obtain by PVD GeTe PECVD GeTe PVD Tc C(4%)-GeTe Annealed temperature [ C] Phase cycle variation : Variation reflectivity with temperature variation crystalline GeTe after thermal cycle Philippe Michallon philippe.michallon@cea.fr - Workshop on Innovative Memory Technologies June; 29th 16

17 Control process : thickness uniformity, stoichiometry Stoichiometry : control by variation of injector frequency f inj (Ge) (Hz) 1 0,8 0,6 0,5 f inj (Te) (Hz) 0,5 0,5 0,5 0,5 composition XPS Ge 0,47 Te 0,53 Ge 0,43 Te 0,57 Ge 0,36 Te 0,66 Ge 0,35 Te 0,65 thickness uniformity (9 pts on wafer 200 mm): 57 nm standard deviation ~ 2% Good improvement of reproducibility Good control of Ge/Te ratio Carbon content Thickness and uniformity Thickness Epaisseur moyenne (nm) [nm] nettoyage plasma Plasma clean Variation Ecart type (%) [%] Philippe Michallon philippe.michallon@cea.fr - Workshop on Innovative Memory Technologies June; 29th 17 Number of deposit Dépôts [#] process

18 Control process PECVD of amorphous GeTelayer at 160 C (a) PECVD of crystalline GeTelayer at 250 C (b) Optical Réflectivité reflectivity optique [%] 70 Ge 0,56 Te 0,44 Ge 0,42 Te 0, (b) (a) Crystalline deposited layer (b) Amorphous deposited layer (a) Température [ C] Layer morphology is controlled by: => substrate temperature => level power of plasma => gas flow rate Optical reflectivity Intensité [%] GeTe par PVD GeTe par PE-MOCVD GeTe(C 4%) par PVD T c phase change temperature (Tc) Tc is controlled by "doping": T c Température [ C] => carbon content Philippe Michallon philippe.michallon@cea.fr - Workshop on Innovative Memory Technologies June; 29th 18

19 Role of the plasma The plasma ratio gasses and RF power influence the GeTe carbon content Particular plasma also can help to decompose the Ge and Te precursors But plasma can also etch Ge or Te atoms : competitive effect between deposition and etching Control of the process thanks to OES Te H Optical Emission Spectroscopy 2 Ge* and Te* emission lines between 230 and 320 nm Intensity (a.u.) Intensité [%] Ge CN H α Longueur wavenumber d'onde [nm] (nm) Philippe Michallon philippe.michallon@cea.fr - Workshop on Innovative Memory Technologies June; 29th 19

20 Outline General aspects of memories Material screening for PCRAM by PVD Set up GeTe by MOCVD GeTe by PECVD Conformity aspects Conclusions and perspectives Philippe Michallon - Workshop on Innovative Memory Technologies June; 29th 20

21 Conformity on dense lines : Amorphous layer lignes 250 nm lines 100 nm 160 C, 200 W Amorphous layer (3 min deposited) Low roughness Good conformity 250, 100 and 75 nm width aspect ratio of 2.5 and 1 => Next step : on dense lines 35 nm HP with aspect ratio 1,2 and3. Philippe Michallon philippe.michallon@cea.fr - Workshop on Innovative Memory Technologies June; 29th 21

22 Conclusions and perspectives Conclusions PECVD (AltaCVD-200) α-tool available in Leti In complete metrology line developed to target memory phase material is available Good control stoichiometry, and carbon rate Control conformity up to 75 nm aspect ratio 1,2 Deposit time compatible for industrial applications Process for Phase memory GeTeon going on Leti Perspectives: New precursors evaluation Others GeTe + doping evaluation layer Philippe Michallon philippe.michallon@cea.fr - Workshop on Innovative Memory Technologies June; 29th 22

23 acknowledgments Special thanks to partners on the French Ministry Project Special thanks to E. Gourvest, C. Vallée, J. Vitiello, R. Blanc, D. Jourde, S. Maitrejean, D. Bensahel, B. Pelissier, C. Bourasseau, N. Blasco, A. Pinchard, JM Baradat, L. Dussault, P. Noé, J Ferrand Philippe Michallon philippe.michallon@cea.fr - Workshop on Innovative Memory Technologies June; 29th 23

24 Merci de votre attention