Bodo Kalkofen

Ag films grown by remote plasma enhanced atomic layer deposition on different substrates

Silver (Ag) layers were deposited by remote plasma enhanced atomic layer deposition (PALD) using Ag(fod)(PEt3) (fod = 2,2-dimethyl-6,6,7,7,8,8,8-heptafluorooctane-3,5-dionato) as precursor and hydrogen plasma on silicon substrate covered with thin films of SiO2, TiN, Ti/TiN, Co, Ni, and W at different deposition temperatures from 70  to 200 °C. The deposited silver films were analyzed by x-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), scanning electron microscopy (SEM), transmission electron microscopy (TEM) with energy dispersive x-ray spectroscopy, four point probe measurement, ellipsometric measurement, x-ray fluorescence (XRF), and x-ray diffraction (XRD). XPS revealed pure Ag with carbon and oxygen contamination close to the detection limit after 30 s argon sputtering for depositions made at 120 and 200 °C substrate temperatures. However, an oxygen contamination was detected in the Ag film deposited at 70 °C after 12 s argon sputtering. A resistivity of 5.7 × 10−6 Ω cm was obta...

Fabrication and investigation of three-dimensional ferroelectric capacitors for the application of FeRAM

Ferroelectric capacitors made by lead zirconate titanate (PZT) thin films and iridium electrodes are fabricated on three-dimensional structures and their properties are investigated. The iridium films are grown by Plasma Enhanced MOCVD at 300°C, while the PZT films are deposited by thermal MOCVD at different process temperatures between 450°C and 550°C. The step coverage and composition uniformity of the PZT films on trench holes and lines are investigated. Phase separation of PZT films has been observed on both 3D and planar structures. No clear dependences of the crystallization and composition of PZT on 3D structure topography have been found. STEM EDX line scans show a uniform Zr/(Zr+Ti) concentration ratio along the 3D profile but the variation of the Pb/(Zr+Ti) concentration ratio is large because of the phase separation. 3D ferroelectric capacitors show good ferroelectric properties but have much higher leakage currents than 2D ferroelectric capacitors. Nevertheless, during cycling tests the degrad...

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.

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.

Use of B2O3 films grown by plasma-assisted atomic layer deposition for shallow boron doping in silicon

Plasma-assisted atomic layer deposition (PALD) was carried for growing thin boron oxide films onto silicon aiming at the formation of dopant sources for shallow boron doping of silicon by rapid thermal annealing (RTA). A remote capacitively coupled plasma source powered by GaN microwave oscillators was used for generating oxygen plasma in the PALD process with tris(dimethylamido)borane as boron containing precursor. ALD type growth was obtained; growth per cycle was highest with 0.13 nm at room temperature and decreased with higher temperature. The as-deposited films were highly unstable in ambient air and could be protected by capping with in-situ PALD grown antimony oxide films. After 16 weeks of storage in air, degradation of the film stack was observed in an electron microscope. The instability of the boron oxide, caused by moisture uptake, suggests the application of this film for testing moisture barrier properties of capping materials particularly for those grown by ALD. Boron doping of silicon was...

Investigation of Antimony Oxide Films Deposited by Atomic Layer Deposition

Atomic layer deposition of thin films of antimony oxide on silicon substrates was investigated and the deposited films were analysed by various methods. Such oxide films could be used as dopants for tin oxide but have also a variety of applications for optoelectronic and photoelectric devices due to their unique optical and physical properties. Moreover, they serve as synergists for flame retardants and polymerisation catalysts. The deposition experiments were carried out in a custom-built single wafer ALD reactor. It is equipped with two lines for liquid precursors and an ozone line. The liquids can be heated to adjust their vapor pressures. Dosing is achieved by “vapor-draw” into a nitrogen carrier flow by fast acting valves. Silicon wafers of 150 mm diameter were used as substrates. They were cleaned in hydrofluoric (HF) or buffered HF solution followed by short rinse in de-ionized water before being loaded into the vacuum chamber. For this study, triethylantimony (SbEt3) and ozone were used as ALD precursors. A variation of several process parameters was carried out in order to investigate and optimize the deposition process. Typical process parameters for the antimony oxide deposition were: SbEt3: 80°C source temperature, 15ms pulse time, 5s exposure time, 8s purge time; O3: 3s pulse time, 1s exposure time, 13s purge time. The film thickness was measured by spectroscopic ellipsometry, optical constants of the antimony oxide were identified from thicker layers. The films were further analysed by atomic force microscopy (AFM), Xray photoelectron spectroscopy (XPS), secondary ion mass spectrometry (SIMS), scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HR-TEM). Furthermore, the stability of the films against acid and high temperature treatments was investigated. The analysis of the deposition process showed that atomic layer deposition behaviour could be obtained. The growth per cycle (gpc) was constant even for small number of process cycles, as shown in Fig. 1 for a substrate temperature of 250 °C, which resulted in a gpc of 0.65 A. A result of substrate temperature variations is shown in Fig. 2. Here it can be seen, that appreciable growth was obtained for temperatures above 100 °C. The dependence of the gpc on temperature was linear for the investigated temperature range. Very homogeneous growth could be achieved on planar silicon wafers. For example, a 69 point thickness map on a 150 mm wafer measured by ellipsometry that gave a mean thickness of 7.5 nm showed a range in the high/low variation of only 1.6 A (about 1%). AFM measurements proved that these films were very smooth. Also conformal deposition of antimony oxide in trench structures could be obtained as shown in Fig. 3. The ellipsometric measurements suggested the existence of an interface of SiO2 of about 1.5 nm below the films on silicon. HR-TEM analyses clearly showed this SiO2 layer. This measurement also revealed a polycrystalline structure of the films deposited at 250 °C. This could explain the remarkable resistance of the asdeposited thin film against a number of tested acid solutions. However, high temperature treatments with rapid thermal annealing processes showed that the films were volatile at temperatures above 900 °C.

Epitaxial growth of Si nanowires by a modified VLS method using molten Ga as growth assistant

In this paper the deposition and morphological characterization of gallium island structures on silicon and first results of silicon wire growth assisted by the created gallium droplets is presented. The islands and wires were grown on (111)-oriented single crystalline p-doped silicon substrates by microwave plasma enhanced chemical vapor deposition (MW PECVD) using trimethylgallium (TMGa) and silane (SiH 4 ) as precursors for island and wire growth, respectively. The samples were investigated by SEM, EDS, XPS, and AFM.

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.

Enhanced ferroelectric properties of multilayer SBT-BTN thin films for NVRAM applications

ABSTRACT Ferroelectric SrBi2Ta2O9 – (Bi4Ti3)1-xNbxO12 (SBT-BTN) multilayer thin films with various stacking periodicity have been synthesized on Ir/Ti/SiO2/Si substrates by metal organic chemical vapor deposition technique (MOCVD). Tributylbismuth [Bi(C4H9)3], strontium-bis[tantal(pentane-ethoxy)(2-methoxyethoxide)] [Sr[Ta(OEt)5(OC2H4OMe)]2], titanium bis(isopropoxy)bis(1-methoxy-2-methyl-2-propoxide) [Ti(OiPr)2(mmp)2] and niobium-ethoxide [Nb(OC2H5)5] were selected as precursors. X-ray diffraction patterns show that the multilayer films annealed at 800°C consisted of a fully formed perovskite phase with polycrystalline structure. The remanent polarization (2·Pr) and coercive field strength (Ec) were 16.2 μC/cm2 and 230 kV/cm, respectively, values which are much higher compared to pure SBT film (2·Pr = 6.4 μC/cm2, Ec = 154 kV/cm).

High temperature reactive ion etching of iridium thin films with aluminum mask in CF4/O2/Ar plasma

Reactive ion etching (RIE) technology for iridium with CF4/O2/Ar gas mixtures and aluminum mask at high temperatures up to 350 °C was developed. The influence of various process parameters such as gas mixing ratio and substrate temperature on the etch rate was studied in order to find optimal process conditions. The surface of the samples after etching was found to be clean under SEM inspection. It was also shown that the etch rate of iridium could be enhanced at higher process temperature and, at the same time, very high etching selectivity between aluminum etching mask and iridium could be achieved.