Preparation and electrical properties of (Ba 1-x ,Sr x )(Ti 1-y ,Zr y )O 3

1. Preparation and electrical properties of (Ba1-x,Srx)(Ti1-y,Zry)O3 thin films for application at high density DRAM Sang-Shik, Park Dept. of Materials Engineering, Sangju National University, Sangju, kyungbuk, 742-711, Korea

2. OUTLINE ▶ Requirements of capacitor for high density DRAM - High dielectric Constant - Low leakage current density - Fast dielectric response Most promising dielectric material : (Ba1-x Srx )TiO3 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 0.1μm2 ≫ - Lower leakage current at thinner film - Higher dielectric constant and lower loss compared to BST - Long life time under dc voltage stress

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

4. Introduction ▶ Ti4+ ; major paths of leakage current in BaTiO3, BST Zr4+ ; More stable than the Ti4+ with respect to Degradation Study of Ba(Ti1-xZrx) O3 (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 (Ba1-xSrx)(Ti1-yZr y)O3 with variation of chamber pressure - Effect of composition on structure and electrical properties of BSTZ film

5. Deposition Conditions Control of Chamber Pressure ; MFC and main valve

6. RBS Analysis RBS spectrum(a) and depth profile(b) of BSTZ film deposited at 50mTorr. Table ; composition of films deposited at various pressure.

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

8. XRD Analysis Target X-ray diffraction patterns of the BSTZfilms as a function of chamber pressure.

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

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

11. er and tan d vs. Frequency Variation of dielectric constant and dissipation factor of BSTZ films as a function of chamber pressure.

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

13. Leakage current density Current-voltage(a) and current-E1/2 plot(b) of BSTZ films as a function of chamber pressure.

14. Summary • (Ba1-x,Srx)(Ti1-yZry)O3 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~ 10-8A/cm2 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.