Thermal Decomposition of Silicon-rich Oxides Deposited by the LPCVD Method

Silicon-rich oxide (SiOx, 0 < x < 2) thin films were deposited using the Low Pressure Chemical Vapor Deposition (LPCVD) method at temperature of 570 °C using silane (SiH4) and oxygen as the reactant gasses. The films were annealed at temperatures of 800, 900, 1000, and 1100 °C to induce the separation of excess silicon in the SiOx films into nanosized crystalline silicon particles inside an amorphous SiOx matrix. The size of the silicon particles was determined using Raman spectroscopy. (doi: 10.5562/cca1969

Low temperature synthesis and characterization of LPCVD silicon dioxide films using diethylsilane

Diethylsilane (DES) has been used as a precursor to produce silicon dioxide films by low pressure chemical vapor deposition. These films were synthesized in the temperature range of 350 to 475°C thus allowing the use of the material as an intermetal dielectric or as a top layer passivation coating in microelectronic devices. In that process, the growth rate was observed to follow an Arrhenius behavior yielding an activation energy of 10 kcal/mol. The growth rate was also observed to increase with higher pressure and to vary as a function of the square root of the DES flow rate and O2/DES ratio. In both the pressure and the O2/DES ratio studies, there were points of abrupt cessation in deposition. The density of the films was measured to be close to 2.2 g/cm3 regardless of deposition conditions. RBS measurements revealed the absence of incorporated carbon and a near stochiometric composition of SiO2.2. The dielectric breakdown strength of an SiO2 film deposited at 400 °C was found to be 2 MV/cm. Infrared spectra of the films showed the usual Si-0 bond stretching and bond bending absorption bands centered at 1060, 810, and 440 cm-1. Si-H bending band at 880 cm-1 was also observed in SiO2 films prepared under certain processing conditions. The refractive index of the films was found to be at 1.46 independent of deposition temperature

Low pressure chemical vapor deposition of silicon dioxide and phosphosilicate glass thin films

Silicon dioxide thin films were synthesized on silicon and quartz wafers using Ditertiarybutylsilane(DTBS) and oxygen as precursors. Trimethylphosphite (TMP) was injected to obtain phosphosilicate glass. The films were processed at different temperatures between 700°C and 850°C at a constant pressure, and at different flow ratios of the precursors. The films deposited were uniform, amorphous and the composition of the films varied with deposition temperature and precursor flow ratios. The deposition rate increased with increasing temperature and with increasing TMP flow rate. The stresses were very low tensile in the case of undoped silicon dioxide film and tended towards being less tensile with increasing deposition temperature. The refractive index increased with increasing deposition temperature. The higher refractive index was probably because the films were rich in carbon. A less transparent film at higher temperatures also suggested presence of carbon at higher temperatures. In the case of the binary silicate glass, the stresses tended to be progressively compressive with increasing phosphorus content. The density and refractive index increased with increasing phosphorus content. Both undoped and doped oxides showed almost 99% optical transmission at a deposition temperature of 700°C. The undoped and the binary oxides showed best properties, especially optical properties, at 700°C

Development of plasma enhanced chemical vapor deposition (PECVD) gate dielectrics for TFT applications

This study investigated a variety of electrically insulating materials for potential use as a gate dielectric in thin-film transistor applications. The materials that were investigated include silicon dioxide and oxynitride films deposited using PECVD and LPCVD techniques. Silicon source materials included tetraethylorthosilicate (TEOS) and silane (SiH4). Oxygen sources included diatomic oxygen (O2) and nitrous oxide (N2O). The optical, electrical, and material properties of the dielectrics were analyzed using Variable Angle Spectroscopic Ellipsometry (VASE), Fourier Transform Infrared Spectroscopy (FTIR), Capacitance-Voltage (C-V) analysis and current-voltage (I-V) analysis. Transistors were also fabricated at low temperatures with different gate dielectrics to investigate the impact on device performance. While a deposited gate dielectric is intrinsically inferior to a thermally grown SiO2 layer, an objective of this study was to create a high quality gate dielectric with low levels of bulk and interface charge (Qit & Qot~1x1010 cm2); this was achieved

Investigation of induced charge damage on self-aligned metal-gate MOS devices

MOS capacitors and NMOS transistors were fabricated with various gate oxides and inter- level dielectrics (ILDs) in order to study the effects of plasma induced charging during the post-metal plasma deposition of an insulating oxide layer. The gate oxides investigated include thermal SiO 2, a low temperature oxide (LTO) deposited by low pressure chemical vapor deposition (LPCVD) using silane and oxygen, and an oxide deposited by plasma enhanced chemical vapor deposition (PECVD) using tetra-ethylortho- silicate (TEOS) as a precursor. A standard-recipe TEOS-based ILD was studied, as well as an alternative recipe that utilized decreased power. Additional wafers were fabricated with an LTO ILD to serve as a control group in order to isolate the influence of the ILD deposition on the respective gate dielectric. By studying C-V and I-V characteristics, both interfacial degradation as well as bulk charging was demonstrated as a result of the PECVD ILD deposition. The investigation demonstrated clear differences in plasma- induced charge effects on the various gate dielectrics. A correlation between the ILD deposition power and the resulting charge influence was established. In addition, post-plasma annealing experiments were done to study the thermal stability of induced charge

Synthesis and characterization of silicon dioxide films using diethyl silane and oxygen

This study focuses on producing thin and thick silicon dioxide films towards the fabrication of integrated optical sensor capable of monitoring and determining in-situ, the concentration of numerous analyze species simultaneously. In this study, diethylsilane (DES) has been used as a precursor to produce silicon dioxide films by low pressure chemical vapor deposition. The films were synthesized with two different flow ratios of oxygen to DES in the temperature range of 550°C to 800°C at a constant pressure of 200mTorr. The films deposited with lower oxygen to DES flow ratio have very high growth rate but suffer from high tensile stress leading to cracks in the films. However the films deposited with higher oxygen to DES flow ratio were crack free. The stress was found to be very low and tensile in these films and tended towards compressive with increasing deposition temperature which is necessary in producing thick films. The films were form and amorphous. The growth rate followed an Arrhenius behavior with an apparent activation energy of 10.59Kcal/mol in case of lower oxygen to DES ratio. Also, depletion was observed with increase in the distance between the wafers. The refractive index of the films were found to be near 1.45 and the films were highly transparent. The thick silicon dioxide films showed excellent properties at a deposition temperature of 775°°C, a pressure of 200mTorr and an oxygen to DES flow ratio of 10:1

Single-Crystalline Graphene by Low-Pressure CVD Method: Nucleation Limited Growth, Transfer, and Characterization

Graphene has attracted enormous attention due to its unique characteristics. However, the LPCVD graphene grown on copper turns out to be polycrystalline because of the high nucleation density (ND) on the copper foil surface. In order to realize better quality LPCVD graphene, this ND needs to be significantly reduced. Based on the observations from our initial graphene growths on as-received copper, we figured that the uneven Cu surfaces with defects produce large NDs. At a large ND, the graphene flakes nucleated at different sites coalesced to produce polycrystalline graphene. Due to such issues, we have implemented an electropolishing technique to smoothen the native surface of the copper foil. We will discuss the successful implementation of the surface smoothening process to reduce nucleation site formation while limiting the surface defects (which leads to wrinkle formation). The annealing process was also helpful to flatten the surface during the growth process further. We have also observed that graphene grows across Cu grain boundaries and, in the process, produces an additional surface area for graphene growth. That later causes to form wrinkles, which affect graphene properties negatively. In the next project, the effect of multi-step copper surface oxidization, base pressure vacuum in the middle of the process, and integration of Cu enclosures on suppressing the ND will be discussed. The technique is based on the self-cleaning characteristics of copper oxides and the metal evaporation in a high vacuum at high temperatures. The ND has reduced to ~5 nucleation/cm2 on average (an improvement compared to the previously reported minimum value, ten nucleation/cm2 which was obtained using copper enclosures), and the graphene/copper surface has become smoother. The self-aligned graphene island geometry and shape of the flakes have reflected the symmetry and the single crystallinity of graphene. The final project will discuss the growth of cm-scale graphene flakes on Cu and 3D-multilayered graphene on 3D-Ni foams and used Ni\u27s gettering carbon diffusion effect to make the Cu foil carbon-free. The Ni-foam/Cu enclosure was oxidized in situ to assist with the self-cleaning process of metal oxides. The ND has been reduced to ~0.57 nucleation/cm2 and obtained cm-scale graphene flakes

Synthesis and characterization of silicon dioxide thin films by low pressure chemical vapor deposition using ditertiarybutylsilane and oxygen

This study is focused on the synthesis and characterization of silicon dioxide thin films deposited on silicon wafers by Low Pressure Chemical Vapor Deposition (LPCVD), using ditertiarybutylsilane (DTBS) as a precursor and oxygen as the oxidant. The dependence of film growth rate on various process parameters were studied. The growth rate was found to follow an Arrhenius curve with the variation in the temperature with an activation energy of 12.6 kcal/mol. The growth rate was found to be inversely proportional to the temperature in the range 550-750 °C. The refractive index and density were observed to be close to 1.47 and 2.71 g/cm3 respectively with flow rate ratio O2/DTBS = 2/1. Producing crack-free thick oxide films were performed at two different conditions. One was at 850 °C with flow rate ratio O2/DTBS = 5/1 which produced compressive stress with lower growth rate, and the other was at 700 °C with flow rate ratio O2/DTBS = 10/1 which produced tensile stress with higher growth rate. Both conditions were able to produce about 10 μm oxide films with no sign of cracking