Mindaugas Silinskas

Hot Wire Chemical Vapor Deposition of Ge2Sb2Te5 Thin Films

Germanium-antimony-telluride or, particularly, Ge 2 Sb 2 Te 5 (GST) thin films were deposited by hot wire (HW) chemical vapor deposition (CVD). Tetraallylgermanium, triisopropylantimony, and diisopropyltelluride were used as precursors for germanium, antimony, and tellurium, respectively. The influence of deposition parameters, such as temperature, pressure, and hydrogen content, was investigated. It was found that higher temperature, higher pressure, and lower hydrogen flow yielded higher growth rates of the films. An admixture of hydrogen reduced the Te concentration in the GST thin films and enhanced the content of Ge and Sb. The chemical composition could also be altered by other deposition parameters but these dependencies were not as well pronounced as in the hydrogen case. Generally, a higher Ge concentration was related to a smaller amount of Te. The films deposited at a higher pressure showed a significantly higher roughness. In addition, the switching from a low to high resistivity state was tested.

Hot wire chemical vapor deposition of germanium selenide thin films for nonvolatile random access memory applications

Thin films of germanium selenide (GexSe100−x with 0<x<57) were deposited on different substrates by hot wire metalorganic chemical vapor deposition using tetraallylgermanium and di-tert-butylselenide. The growth kinetics of the deposition process as well as the properties of the films were investigated. The growth rate was found to decrease with increasing temperature and decreasing pressure. The conformal step coverage was demonstrated. Germanium selenide films covered and subsequently diffused by silver were used as programmable metallization cells for a verification of the electrical switching properties.

EVALUATION OF DIFFERENT METALORGANIC PRECURSORS FOR Ge-Sb-Te THIN FILM DEPOSITION

ABSTRACT In this work, various alkyl-precursors were tested, including: tetraethylgermanium (TEGe), tetraisopropylgermanium (TiPGe), triethyl-tert-butylgermanium (TEtBGe), trimethylantimony (TMSb), triisopropylantimony (TiPSb), dimethyltelluride (DMTe), diisopropyltelluride (DiPTe), and di-tert-butyltelluride (DtBTe), in order to deposit Ge-Sb-Te and Sb-Te thin films on Ni/SiO2/Si, Ni/Ti/SiO2/Si, Cu/SiO2/Si, and Ir/Ti/SiO2/Si substrates using pulsed metalorganic chemical vapor deposition. The deposition of Ge-Sb-Te films from methyl-group precursors is possible only at high temperatures (600–650°C). Using of TiPSb and DtBTe precursors significantly reduces the deposition temperature (≥300°C). By changing from DtBTe to DiPTe higher deposition temperatures were required (∼500°C) but the thermal stability of the Te-precursor was improved.

STRUCTURAL AND ELECTRICAL CHARACTERIZATION OF HIGH-k STRONTIUM TANTALATE DEPOSITED BY LIQUID DELIVERY MOCVD

ABSTRACT The strontium tantalate films were prepared by metalorganic chemical vapor deposition using Sr[Ta(OEt)5(OC2H4OMe)]2 precursor. Transmission electron microscopy, X-ray diffraction, and ellipsometry indicated that the as-deposited and the annealed at 800°C films were uniform and amorphous. Significant crystallization takes place only at temperatures of ∼ 1000°C and these films are unhomogeneous and the thickness of the interlayer SiO2 highly increases. Annealing at temperatures about 800°C was found to improve the electrical characteristics (effective dielectric constant up to 40, the leakage current up to 7 · 10− 8 A/cm− 2, and low interface state density value of 8 · 1010 eV− 1cm− 2).

STRONTIUM BISMUTH TANTALATE THIN FILM DEPOSITION BY LIQUID-DELIVERY MOCVD USING NOVEL LIQUID BISMUTH PRECURSORS

ABSTRACT Novel liquid bismuth precursors (triallylbismuth (Bi(CH2CH═CH2) and tributylbismuth (Bi(C4H9)3)) were tested for metalorganic chemical vapor deposition (MOCVD). Strontiumbis-pentaethoxy methoxyethoxy tantalate (Sr[Ta(OEt)5(OC2H4OMe)]2) was used as Sr-Ta source. The growth rates were ≤10 nm/h for triallylbismuth and for triphenylbismuth, ≤1000 nm/h for tributylbismuth, and ≤60 nm/h for Sr[Ta(OEt)5(OC2H4OMe)]2. The deposition rate of SBT was always lower than the rate of bismuth oxide. A decrease of the deposition pressure improved uniformity of the film thickness but reduced the deposition rate of the films. XPS depth profiling indicated more metallic bond characteristics of Ti, Sr, and Bi after ion bombardment.

CHARACTERISATION OF FERROELECTRIC PbZrXTi1-XO3 (PZT) THIN FILMS PREPARED BY LIQUID-DELIVERY METALORGANIC CHEMICAL VAPOR DEPOSITION

ABSTRACT A growth of leaf shape crystals was observed by SEM in the case of excess of Pb in the MOCVD grown films. Contrary, when the lead content was 20 at% or lower, the PZT-films were transparent and smooth. X-ray diffraction (XRD) measurements showed a presence of lead oxide phase additionally to the perovskite phase in the as-deposited PZT films. A pyrochlore phase began to form at an annealing temperature at 600°C. PZT films annealed at 520°C exhibit square hysteresis loop with peak Pr values of 60 μ C/cm2 and coercive voltage of 2 V.

ELECTRICAL CHARACTERIZATION OF ZIRCONIUM OXIDE LAYERS GROWN BY LIQUID DELIVERY MOCVD

ABSTRACT ZrO2 films were prepared on 150 mm (100) silicon substrates using liquid delivery MOCVD and Zirconium-tert-butoxide as precursor. The substrate temperature and the total process pressure were varied from 400°C to 500°C and from 1.5 mbar to 7.5 mbar, respectively. The surface roughness of the ZrO2 films was measured by atomic force microscopy (AFM). X-ray diffraction measurements (XRD) indicated the coexistence of monoclinic and cubic/tetragonal phases, whose ratio depended on the deposition temperature. The relative dielectric constant was calculated from the capacitance at strong accumulation. The values of the as grown layers were ranging from 14 for the thinnest layer up to 30 for the thickest layer. The density of interface states was determined from quasi-static CV-curves and admittance spectroscopy. Annealing decreased the interface trap density and the leakage current density but the measured dielectric constant was also lowered. After a temperature treatment at 800°C the best electrical properties were observed.

Plasma-assisted atomic layer deposition of germanium antimony tellurium compounds

Plasma atomic layer deposition of Ge-Sb-Te (GST) thin films using halogen-free precursors is reported. The Sb and Te precursors tris(aziridinyl)antimony (III) (Sb[cyclo-NC2H4]3) and di-n-butylditelluride [Te2(n-C4H9)2] were employed for the first time in the deposition of GST thin films. Conformal filling of trenches has been demonstrated. The film thickness ratio between the top and the wall/bottom of trenches was evaluated: for “wide” (7:1 aspect ratio) trenches—dbottom/dtop ≈ 0.65, and for “narrow” (23:1 aspect ratio) trenches dwall/dtop > 0.63. Due to the use of amino precursors the as-deposited GST films were doped with nitrogen.

Characterization of non-dispersive infrared gas detection system for multi gas applications

Abstract In this work, we present a low cost multi gas detection system for simultaneous measurement of up to three gases. The main conclusions are based on the investigation of the concentrations of CO2 gas as well as of CH4 gas and of H2O vapor. It was found that the continuous heating of the IR source and the absolute values of thermopile voltages are not suitable parameters for the gas detection because of their high sensitivity to the influence of temperature and/or gas flow parameters. A sine like signal is preferential for our measurement system. The amplitude of the sine is very stable and is proportional only to the concentration of particular gas (according to the optical filter) and is not dependent on the concentration of other gases or on temperature. In this way, the CO2 gas concentration can be measured from 50 ppm to 400000 ppm with the same measurement setup. The lowest detectable concentration of CH4 was about 500 ppm.

TRIBUTYLBISMUTH AS A LIQUID BISMUTH PRECURSOR IN AN AVD SYSTEM FOR STRONTIUM BISMUTH TANTALATE THIN FILM DEPOSITION

ABSTRACT In this study, tributylbismuth has been tested as a bismuth source for strontium bismuth tantalate (SBT) deposition using atomic vapor deposition (AVD) system. The effects of annealing temperature on the structural and electrical properties of deposited films were investigated. SBT films annealed at 750°C were crystallized in ferroelectric perovskite phase. Ferroelectric hysteresis loops of the SBT films have been measured, from which a remnant polarization of 3.5 μC/cm2 and a coercive voltage of 3 V of the crystallized SBT layer have been evaluated. SBT thin films annealed at 750°C also showed good fatigue properties. Fatigue was found to be about 4% after 109 cycles.