3D capacitors on silicon with high density pore network and ZrO2 dielectric films deposited by MOCVD

Transcription

1 3D capacitors on silicon with high density pore network and ZrO2 dielectric films deposited by MOCVD Magali Brunet 1, Gérald Leclerc 1, Emmanuel Scheid 1, Jean- Louis Sanchez 1 1 LAAS-CNRS, University of Toulouse, France. Karolina Galicka-Fau 2, Michel Andrieux 2, Isabelle Gallet 2, Mickaele Herbst 2, Corinne Legros 2. 2 LEMHE, University Paris-Sud 11, Orsay, France. P. Kleimann 3 3 Institut des Nanotechnologies de Lyon (Lyon) 1

2 Introduction: Context Portable electronics Numerous functionalities Miniaturization of DC-DC converters Passive components (L,C,R): from discrete to integrated solutions Low profile, miniaturization Reliability Cost reduction. How? Increase of systems operating frequencies New materials, adapted methods of microfabrication Converter PWM DC-DC On Semicond. Magali Brunet PwrSoC workshop, Cork, 23/09/2008 step-down [NCP1508] 3mm x 3mm 2

3 High density capacitors Objectives: High capacitance density : 1 µf/mm² Operating frequencies (500 khz 10 MHz) Power: few watts (V in = 5V, I in = 1 A) Breakdown voltage: 20V Efficiency: > 90% Low losses in materials and structures C = ε 0 ε r S e Solutions: Increase electrode surface Deep cavities in Si (bottom electrode) Use of high-k dielectrics Cross-section of silicon cavities Magali Brunet PwrSoC workshop, Cork, 23/09/2008 etched by DRIE 3

4 Outline I. Preliminary results and state of the art II. Towards higher capacitance density for 3D capacitors: II.a. Electrochemical etching of dense pore network in silicon. II.b. Integration of high-k material. ZrO 2 material characterization (2D and 3D) -Optimization of MOCVD conditions Electrical characterization (2D) of ZrO 2 films III. Conclusions and future work. Magali Brunet PwrSoC workshop, Cork, 23/09/2008 4

5 I. Preliminary results: 3D capacitors Fabrication SiO 2 (5 nm) / Si 3 N 4 (20 nm) In-situ boron doped polysi 1.5 mω.cm 5 masks process Au 120 µm Si- n + Pores aspect ratio (h/w) = 25 h w Performances: 60 nf/mm² f max = 1MHz ESR = 0.6Ω Capacitance density (nf/mm²) HP 4294A C33_TMAH+IP Pore width = 3 µm A C44_TMAH+IP Pore width = 4 µm A plan_tmah+ip Planar A Antimony doped silicon substrate mω.cm V in = 5.7 V V out = 10 V 10 0 A.Benazzi, EPE 2007, Aalborg, (Denmark) 1,0E+04 1,0E+05 1,0E+06 1,0E+07 1,0E+08 M. Magali Brunet, Brunet MME 2007, Guimaraes (Portugal). PwrSoC workshop, Frequency Cork, 23/09/2008 5

6 I. 3D capacitors: state of the art h w AR = Aspect Ratio = h/w NXP 2008 DRIE, AR = 20, TiN/Al 2 O 3, 3 layers NXP Siemens LAAS Univ. Helsinki Dielectric O = SiO 2 N = Si 3 N 4 C (nf/mm²) Siemens, 1996 Electrochemical etching AR = 85; ONO Univ. Helsinki, 2007 Porous Si, AR = 25, Al 2 O 3 or ZnO :Al NXP 2007 DRIE, AR = 20, ONO, 2 layers LAAS 2006 DRIE, AR = 25, w = 2 µm - ON NXP 2001 DRIE, AR = 20, w = 2 µm - ONO Breakdown voltage (V) Magali Brunet PwrSoC workshop, Cork, 23/09/2008 6

7 Outline I. Preliminary results and state of the art II. Towards higher capacitance density for 3D capacitors: II.a. Electrochemical etching of dense pore network in silicon. II.b. Integration of high-k material. ZrO 2 material characterization (2D and 3D) -Optimization of MOCVD conditions Electrical characterization (2D) of ZrO 2 films III. Conclusions and future work. Magali Brunet PwrSoC workshop, Cork, 23/09/2008 7

8 II.a. Electrochemical etching of Si HO 2 Ethanol HF 50% Counter electrode Reference electrode Pt Pt V ref V N-type substrate: Diffusion of minority carrier (holes) towards surface => Reaction with HF I Higher density pore network 3 regimes: electropolishing, etching (transition), porous silicon Space charge region Region width (nm) Largeur de la ZCE (nm) E-3 0,01 0, Resistivité (Ωcm) Si resistivity (Ω.cm) P. Magali Kleimann, BrunetX Badel, J. Linnros, APL 86, , PwrSoC workshop, Cork, 23/09/2008 8

9 II.a. Electrical results 3D Capacitors SiO 2 /Si 3 N 4 Pores : w = 1 µm Aspect ratio = 43 PolySi Comparison Porous Si / Pore network PolySi C (nf/mm²) regular pores network - pitch 2 µm 20 porous silicon ,0E+02 1,0E+03 1,0E+04 1,0E+05 1,0E+06 1,0E+07 1,0E+08 Magali Brunet Frequency (Hz) PwrSoC workshop, Cork, 23/09/2008 9

10 II.a. On-going developments 2 µm pitch pore network Adapted resistivity = 1 Ω.cm Maximum aspect ratio = nf/mm² expected (with SiO 2 / Si 3 N 4 ) 500 nm pitch pore network Ebeam lithography Adapted resistivity = 50 mω.cm Keeps component at the surface Magali Brunet PwrSoC workshop, Cork, 23/09/

11 Outline I. Preliminary results and state of the art II. Towards higher capacitance density for 3D capacitors: II.a. Electrochemical etching of dense pore network in silicon. II.b. Integration of high-k material. ZrO 2 material characterization (2D and 3D) -Optimization of MOCVD conditions Electrical characterization (2D) of ZrO 2 films III. Conclusions and future work. Magali Brunet PwrSoC workshop, Cork, 23/09/

12 II.b. 3D deposition of high-k material High-k material: ZrO 2 - Polycrystalline material Static dielectric responses : ε tetragonal = 40 ε cubic = 31.8 ε monoclinic = 15 X. Zhao, D. Vanderbilt, Phys. Rev. B, 65, , 2002 => Necessity to favour tetragonal phase for higher permittivities. Breakdown voltage: 3 MV/cm Minimum thickness = 70 nm 3D deposition: Direct liquid injection MOCVD Magali Brunet PwrSoC workshop, Cork, 23/09/

13 II.b. MOCVD system Direct liquid injection MOCVD Precursors evaporation: 250 C Gas carrier: O 2 and N 2 Fractionnal injection Substrate Temperature : 400 C 700 C Precursors tried: Zr(thd) 4 * Zr(thd) 2 (O i Pr) 6 *(thd =2,2,6,6-tetramethylheptane-3,5-dionate) Magali Brunet PwrSoC workshop, Cork, 23/09/

14 II.b. Structural analysis ZrO 2 X-Ray Diffractogramms - ZrO 2 on Si(100) 2,0 1,8 O2 annealed As deposited Intensity 1,6 1,4 1,2 1,0 0,8 0,6 0,4 (-111) m (111)t,c (111) t (111)m (020) m (200) m (002)t (200) t (200)t,c 0,2 0, Theta Tetragonal phase favoured thanks to: Low O 2 partial pressure Low deposition rate (0.6 nm/min) : low injection frequency - low temperature Characterised by smaller crystallites * After annealing at 900 C under O 2 : Monoclinic + tetragonal phase *L. Rapenne, M. Andrieux, Int Symp. EUROCVD 14, ECS, 2003, p. 325 Magali Brunet PwrSoC workshop, Cork, 23/09/

15 II.b. 3D deposition - Coverage Influence of temperature on coverage. 700 C (90nm) 500 C (20nm) Poly-Si ZrO 2 ZrO 2 Poly-Si Decrease of surface reactivity with lower temperatures Work at temperatures around C Magali Brunet PwrSoC workshop, Cork, 23/09/

16 II.b. 3D deposition - Coverage Pores with depth h > 10 µm Deposition of ZrO 2 : T = 550 C, P < 100 Pa w = 10µm h=40µm e 0 = 110nm e = 30nm Magali Brunet PwrSoC workshop, Cork, 23/09/

17 II.b. 3D deposition - Coverage e/e 0 = 1 e/e 0 = ,9 0,8 0,7 0,6 Surface reaction-limited e = thickness at the bottom e 0 = thickness at the top e/e0 0,5 0,4 0,3 0,2 0,1 Diffusion-limited Aspect ratio (h/w) Constant thickness for aspect ratio > 2 Magali Brunet PwrSoC workshop, Cork, 23/09/

18 Leakage current ZrO 2 II.b. Electrical measurements ZrO 2 Si n ++ 2e18 at/cm3 AuSb Si n ++ Ti/Au Ti/Au ZrO 2 =100 nm Leakage current due to : Extrinsic defects Current density (A/cm²) 1,E+03 1,E+01 1,E 01 1,E 03 1,E 05 1,E 07 1,E 09 Polycrystalline structure of ZrO 2 Grains boundaries Si/ZrO 2 interface not controlled Keithley 4200 SCS Bias (V) Estimation at 200 mv of R leakage = Rp = MΩ Magali Brunet PwrSoC workshop, Cork, 23/09/

19 II.b. Electrical measurements ZrO 2 Breakdown voltage Structure tested: ZrO 2 (195 nm) / Pt 1,E+03 Current density (A/cm²) 1,E+01 1,E 01 1,E 03 1,E 05 1,E MV/cm 1,E Bias (V) Magali Brunet PwrSoC workshop, Cork, 23/09/

20 II.b. Electrical measurements ZrO 2 C(V) on silicon substrates at 1MHz 43I (110 nm) µm *100 µm capacitors 2,4 C min = C C ZrO ZrO C inv + C inv C inv = 4.17 nf/mm² 2 2 C (nf/mm²) 2,2 2 1,8 1,6 1,4 1, Bias (V) Measurement C1 Measurement C2 Measurement C3 Measurement C4 Theory C ZrO2 = 2.2 nf/mm² Shifts due to oxide charges and interface states For MIM like structure => increase substrate doping Magali Brunet PwrSoC workshop, Cork, 23/09/

21 II.b. Electrical measurements ZrO 2 Frequency behaviour: Z(f) a) 1,E+05 Measurement Model Impedance analyser HP 4294A Z (Ohm) 1,E+04 Equivalent model b) 1,E ,0E+05 1,0E+06 1,0E+07 Frequency (Hz) -82 Measurement Model Phase ( ) ε ZrO2 = ,0E+05 1,0E+06 1,0E+07 Magali Brunet PwrSoC workshop, Cork, 23/09/2008 Frequency (Hz) 21-88

22 II.b. Electrical measurements ZrO 2 Summary Thickness (nm) 110 Leakage current density (A/cm²) at 200 mv Breakdown voltage (MV/cm) 2.3 C (nf/mm²) 2.2 Permittivity 27 Theory ε tetra = 40 ε cubic = 31.8 ε mono = 15 Sensitivity to monoclinic phase? 1000 (111) t 37I 39I 42I 43I (200) t 1,0 0,8 37I annealed 39I annealed 42I annealed 43I annealed 0,6 Counts 500 Count 0,4 0,2 0 0, Position [ 2Theta] -0, Magali Brunet PwrSoC workshop, Cork, 23/09/ Theta 22

23 III. Conclusions / futur work High aspect ratio pores in a dense network Electrochemical etching / DRIE Validation of capacitors with aspect ratio 133 Denser pore network : pitch 500 nm MOCVD of ZrO 2 : Tetragonal phase favoured Necessity to improve 3D deposition Electrical characterisation: Leakage and shifts in CV curves show necessity to improve interface chemistry and microcrystalline structure Electrical characterisation of ZrO 2 on 3D structures. Change of phase => change of permittivity? 3D breakdown voltage? Magali Brunet PwrSoC workshop, Cork, 23/09/

24 III. Performances NXP 2008 DRIE, AR = 20, TiN/Al 2 O 3, 3 layers Very high-k dielectrics (perovskite) LAAS - to be demonstrated Electrochemical etching, AR = 133, w = 1 µm ZrO 2 (90 nm) NXP Siemens LAAS Univ. Helsinki C (nf/mm²) Siemens, 1996 Electrochemical etching AR = 85; ONO Univ. Helsinki, 2007 Porous Si, AR = 25, Al 2 O 3 or ZnO :Al NXP 2007 DRIE, AR = 20, ONO, 2 layers LAAS - to be demonstrated Electrochemical etching, AR = 133, w = 1 µm ON LAAS 2006 DRIE, AR = 25, w = 2 µm - ON NXP 2001 DRIE, AR = 20, w = 2 µm - ONO Breakdown voltage (V) Magali Brunet PwrSoC workshop, Cork, 23/09/

25 Acknowledgements ANR : French Research National Agency for funding Program JC-JC Sylvie Schamm, Joël Jaud, CEMES, University of Toulouse Karine Isoird, LAAS-CNRS, University of Toulouse LAAS Services : clean room, electrical characterization. Magali Brunet PwrSoC workshop, Cork, 23/09/