1. Electro-Ceramics Lab. Preparation and electrical properties of (Ba 1-x,Sr x )(Ti 1-y,Zr y )O 3 thin films for application at high density DRAM thin films for application at high density DRAM Sang-Shik, Park Dept. of Materials Engineering, Sangju National University, Sangju, kyungbuk, 742-711, Korea

2. Electro-Ceramics Lab. OUTLINE - High dielectric Constant - Low leakage current density - Fast dielectric response ▶ Requirements of capacitor for high density DRAM Most promising dielectric material : (Ba 1-x Sr x )TiO 3 BST films by CVD,PLD,Sputtering, MOD showed good properties ▶ Requirements of dielectric films for Gbit-scale DRAM application ≪ 25fF/cell in a cell size smaller than 0.1μm 2 ≫ - Lower leakage current at thinner film - Higher dielectric constant and lower loss compared to BST - Long life time under dc voltage stress

3. Electro-Ceramics Lab. Introduction Ref. ; IBM J. Res. Develop., 43(3), 367 (1999) BST - Uniformity - Thickness - Composition - Grain size / Orientation DRAM cell structure and Key issues

4. Electro-Ceramics Lab. Introduction ▶ Ti 4+ ; major paths of leakage current in BaTiO 3, BST Zr 4+ ; More stable than the Ti 4+ with respect to Degradation Study of Ba(Ti 1-x Zr x ) O 3 (R. Waser etal, Integrated Ferroelectrics 17, 141 (1997), T. B. Wu etal, Thin Soild Films 334, 77 (1998)) ▶ In this study, Zr doping in BST thin films - Composition control of (Ba 1-x Sr x )(Ti 1-y Zr y )O 3 with variation of chamber pressure - Effect of composition on structure and electrical properties of BSTZ film

5. Electro-Ceramics Lab. Deposition Conditions Target Target diameter Substrates Target-substrate distance Base pressure of system Working Pressure R.F. Power density Sputtering gas(Ar:O 2 ) Substrate temperature (Ba 0.65,Sr 0.35 )(Ti 0.65,Zr 0.35 )O 3 with 30mole% excess BaCO 3 and SrCO 3 5.08 ㎝ (2inch) Pt/Ti/SiO 2 /Si 40mm 1x10 -6 Torr 5, 10, 30, 50mTorr 3.5W/ ㎠ 1:1 600 ℃ Control of Chamber Pressure ; MFC and main valve

6. Electro-Ceramics Lab. RBS Analysis RBS Analysis Target(Ba0.65Sr0.35)(Ti0.65Zr0.35)O3.00 5mTorr(Ba0.69Sr0.32)(Ti0.28Zr0.77)O2.96 10mTorr(Ba0.65Sr0.31)(Ti0.39Zr0.66)O2.98 30mTorr(Ba0.65Sr0.30)(Ti0.45Zr0.67)O2.92 50mTorr(Ba0.66Sr0.32)(Ti0.54Zr0.56)O2.92 RBS spectrum(a) and depth profile(b) of BSTZ film deposited at 50mTorr. Table ; composition of films deposited at various pressure.

7. Electro-Ceramics Lab. Variation of composition Variation of Composition(a) and deposition rate(b) of SBT films as a function of chamber pressure.

8. Electro-Ceramics Lab. XRD Analysis X-ray diffraction patterns of the BSTZ films as a function of chamber pressure. Target

9. Electro-Ceramics Lab. SEM images SEM surface images of BSTZ films; (a) 50mTorr, (b) 30mTorr, (c) 10mTorr and (d) 5mTorr. 200nm (a) (c)(d) (b) 200nm (d) 200nm

10. Electro-Ceramics Lab. AFM images AFM images of BSTZ films as a function of chamber pressure. 50mTorr(Ave. rough. ; 7.08Å) 5mTorr(Ave. rough. ; 2.63Å) 10mTorr(Ave. rough. ; 3.18Å) 30mTorr(Ave. rough. ; 5.21Å)

11. Electro-Ceramics Lab.   r and tan  vs. Frequency Variation of dielectric constant and dissipation factor of BSTZ films as a function of chamber pressure.

12. Electro-Ceramics Lab. C-V & P-E characteristics Capacitance-voltage(a) and polarization-voltage(b) behavior of BSTZ films as a function of chamber pressure.

13. Electro-Ceramics Lab. Leakage current density Current-voltage(a) and current-E 1/2 plot(b) of BSTZ films as a function of chamber pressure.

14. Electro-Ceramics Lab. Summary (Ba 1-x,Sr x )(Ti 1-y Zr y )O 3 thin films were deposited by r.f. magnetron sputtering Zr/Ti ratio of films decreased significantly with increasing chamber pressure. This variations affected microstructure and electrical properties.  ▶  when increasing chamber pressure  - Decrease of Zr content - Decrease of Crystallinity - Increase of grain size and roughness - Increase of dielectric constant due to decrease of Zr - Increase of leakage current density ▶ Electrical properties of BSTZ thin films - Dielectric constant and dissipation factor : 380~525 and 0.03~0.05 @ 100kHz - Leakage Current Density : 10 -7 ~ 10 -8 A/cm 2 order @ 200kV/cm - Paraelectric properties and schottky emission conduction ▶ BSTZ films appeared to be attractive for high density DRAM and should be further studied together BST.