Jeffrey F. Roeder

Metalorganic Chemical Vapor Deposition of Complex Metal Oxide Thin Films by Liquid Source Chemical Vapor Deposition

The implementation of ferroelectric thin films in advanced semiconductor devices is near ; facile integration at ULSI geometries requires chemical vapor deposition (CVD) process technology. The low volatility and thermal stability of many of the existing source reagents has driven the development of liquid source CVD, in which composition is set by volumetric metering of liquids followed by flash vaporization. The methodology as well as early results for Ba 1-x Sr x TiO 3 , Pb 1-x (La x Zr 1-y Ti y ) 1-z/4 O 3 and SrBi 2 Ta 2 O 9 thin films, which are among the best reported for any deposition method, will be reviewed. These results establish liquid source CVD as a leading candidate to become the predominant deposition technology enabling the integration of ferroelectric thin films in ULSI devices.

Ferroelectric strontium bismuth tantalate thin films deposited by metalorganic chemical vapour deposition (MOCVD)

Thin films of Sr 1-x Bi 2+x Ta 2 O 9 (SBT) have been deposited by metalorganic chemical vapor deposition (MOCVD) on 150 mm Si wafers with Pt/Ti electrodes. The choice of Bi precursor significantly affects the process; film homogeneity is significantly improved when using a β-diketonate Bi precursor in combination with compatible Sr and Ta precursors. A highly repeatable process has been developed, with good run-to-run composition and thickness control. Effects of Bi volatility have been investigated in annealing experiments that show the onset of Bi loss at ∼570°C at reduced pressure (1-10 Torr). Film properties relevant to integrated ferroelectric random access (Fe RAMS) memories have also been characterized. Remenant polarizations (2P r ) up to 24 μC cm -2 have been obtained at 5 V, with 90% saturation of 2P r at 1.5 V and a coercive voltage of 0.52 V for a 140 mn film. Electrical leakage current density values were < 2×10 -8 A cm -2 at 1.5 V. Fatigue endurance has been measured to 10 11 cycles with < 10% degradation in switched charge.

Liquid-delivery MOCVD: chemical and process perspectives on ferro-electric thin film growth

MOCVD processes for (Ba,Sr)TiO3 (BST) and Pb(Zr,Ti)O3 (PZT) are described based on different metal – organic precursors. In the case of BST, processes using polyamine and tetraglyme adducts of group II metals were compared. Similar incorporation efficiencies were obtained at 640 °C for both adducts, and electrical properties were comparable. Delivery methodologies were compared using the tetraglyme adducts for BST. Composition control was equivalent using liquid mass flow controllers versus a positive displacement pump. For PZT, Zr(thd)4 and Zr(OiPr)2(thd)2 were compared as source materials in combination with Ti(OiPr)2(thd)2 and Pb(thd)2(pmdeta). The mixed ligand Zr source increased Zr incorporation efficiency by a factor of nearly eight for otherwise equivalent processes centred at 590 °C, and run to run repeatability was 0.1 at% for Pb and 0.6 at% for Zr (1 σ) over a series of more than 300 films. The electrical properties of thin film PZT deposited with Zr(OiPr)2(thd)2 compared favourably with those obtained previously with Zr(thd)4. Copyright

Common and unique aspects of perovskite thin film CVD processes

Abstract In the past 5 years there has been a large amount of work to develop CVD technology for the deposition of the predominant perovskite oxide thin films, (Ba, Sr)TiO3, SrBi2Ta2O9 and Pb(Zr, Ti)O3. For each of these families of materials, CVD processes have matured such that state-of-the-art film properties may be achieved with this technique. Much of the progress is attributed to the use of the liquid delivery technique to transfer relatively involatile metalorganic precursors to the reactor. This paper will discuss common attributes of these thermal CVD processes, particularly the precursors, delivery methodology and reactor hardware. The paper will also highlight unique aspects that differentiate the processes, including the CVD decomposition regime, strategies for film composition control and approaches for forming the crystalline perovskite phase. Representative film properties are presented, demonstrating that these processes are becoming increasingly mature.

Origin and implications of the observed rhombohedral phase in nominally tetragonal Pb(Zr0.35Ti0.65)O3 thin films

The structural and electrical properties of Pb(Zr0.35Ti0.65)O3 (PZT) thin films ranging in thickness from 700 to 4000 A have been investigated. These (001)/(100)-textured films were grown by metalorganic chemical vapor deposition on (111)-textured Ir bottom electrodes. It was observed that, in the as-deposited state, the thinnest PZT films are rhombohedral even though bulk PZT of this composition should be tetragonal. Thicker films have a layered structure with tetragonal PZT at the surface and rhombohedral PZT at the bottom electrode interface. In this article we investigate the origin of this structure and its effect of the ferroelectric and dielectric properties of PZT capacitors. It has been suggested that thin films stresses can affect the phase stability regions of single domain PZT. This possibility has been investigated by piezoresponse microscopy and thin film stress measurements. In the as-deposited state the majority of PZT grains contain a single ferroelastic domain, whereas after a high tempe...

Structural analysis of coexisting tetragonal and rhombohedral phases in polycrystalline Pb(Zr 0.35 Ti 0.65 )O 3 thin films

Structural properties of polycrystalline Pb(Zr 0 . 3 5 Ti 0 . 6 5 )O 3 (PZT) thin films grown by metalorganic chemical vapor deposition on Ir bottom electrodes were investigated. Symmetric x-ray diffraction measurements showed that as-deposited 1500 A-thick PZT films are partially tetragonal and partially rhombohedral. Cross-section scanning electron microscopy showed that these films have a polycrystalline columnar microstructure with grains extending through the thickness of the film. X-ray depth profiling using the grazing-incidence asymmetric Bragg scattering geometry suggests that each grain has a bilayer structure consisting of a near-surface region in the tetragonal phase and the region at the bottom electrode interface in the rhombohedral phase. The required compatibility between the tetragonal and rhombohedral phases in the proposed layered structure of the 1500 A PZT can explain the peak shifts observed in the symmetric x-ray diffraction results of thicker PZT films.

Germanium ALD/CVD Precursors for Deposition of Ge/GeTe Films

In order to deposit conformal films in the high aspect ratio trench and via structures in future high-density phase-change memory devices, suitable ALD/CVD precursors are needed. We report on the development of novel germanium(II) metal-organic ALD/CVD precursors containing amide, cyclopentadienyl, and amidinate ligands. The physical properties, volatility, and thermal behavior of the precursors were evaluated by simultaneous thermal analysis (STA) and vapor pressure measurements. Stability studies were conducted to investigate the suitability of the precursors for use as ALD/CVD precursors for device manufacturing.

Liquid delivery MOCVD of PLT for pyroelectric detectors

Pb/sub 1-x/La/sub x/Ti/sub 1-x/4/O/sub 3/ (PLT) films have shown promise for uncooled infrared detector applications. A metalorganic chemical vapor deposition (MOCVD) process has been developed to deposit PLT at 535/spl deg/C using the liquid delivery technique on two inch Pt/ZrO/sub 2//Si substrates. Metalorganic /spl beta/-diketonate and mixed /spl beta/-diketonate-alkoxide precursors were flash vaporized and delivered into a large area MOCVD chamber and high quality crystalline perovskite films were deposited with La contents of 0.02/spl les//spl times//spl les/0.28. Room temperature dielectric constant varied between 400 940 for films /spl sim/1200 /spl Aring/ thick and increased with increasing La content. Pyroelectric measurements were carried out using the Byer-Roundy technique. The pyroelectric coefficients were found to depend on film orientation which varied between [100] and [111] with the Pb/Ti ratio; values between 6-13 nC/cm/sup 2/K were observed.

Chemical vapor deposition of Pb1−xLaxTiO3

Abstract We report chemical vapor deposition (CVD) of PbLaTiO3 films for integrated pyroelectric devices. Pb(thd)2, La(thd)3 and Ti(O-Pr)2(thd)2 were introduced to the reactor via a single liquid precursor solution that is vaporized. Substrate temperatures were approximately 535°C and post deposition annealing was not used. Films were deposited on fused silica and Pt metallized Si substrates. The liquid delivery technique permitted excellent composition control and films on fused silica were predominantly [100] oriented with trace amounts of [110] and [111] present. Pyroelectricity for 0.7μm thick films deposited on Pt metallized Si was measured using a modified Byer-Roundi technique and pyroelectric coefficients as high as 90 nC/cm2·K were observed. The high crystalline quality and pyroelectric properties are attributed to the excellent composition control afforded by the liquid delivery CVD technique.

Liquid delivery CVD of PLZT thick films for electro-optic applications

PLZT films in the composition range 7/0/100-32/0/100 have been deposited by CVD from a single source reagent using a liquid delivery/flash vaporization approach. Single phase perovskite films ranging in thickness from 1-5 /spl mu/m were deposited on fused silica substrates at 535/spl deg/C. The films had very strong crystallographic texture with [100] normal to the plane of the film. Optical loss per unit thickness was lower for thicker films suggesting that interfacial effects dominated losses. Very large electro-optic effects were observed in a number of the films. Birefringent shifts were measured by phase retardation in transmission mode with an electric field applied in the plane of the film using interdigitated electrodes. Birefringent shift varied quadratically with applied field and showed little hysteresis with R coefficients as high as 5/spl times/10/sup -16/ (m/V)/sup 2/. The strength of the electro-optic effect is attributed to the high degree of crystallinity of the films and the a-axis orientation.