Being a II-VI semiconductor material with a wide direct band gap corresponding to the U-V region, ZnO finds important
applications in U-V light sensors. In this work, we have developed and characterized Au-ZnO-ITO based UV
photosensitive devices whose I-V characteristics show p+-i-n type behaviour and show an increased current under UV
illumination. ZnO is employed as the active region. Both ZnO and gold were deposited via rf magnetron sputtering. The
I-V characteristics of the fabricated UV sensor indicated a knee voltage of 0.69V. The resistance was observed to
decrease by a factor of 3.5 under illumination. Further, we have optically characterized ZnO thin films deposited at
different power levels to determine the dependency of various optical constants on deposition process parameters. These
thin films were characterized using VASE (Variable Angle Spectroscopic Ellipsometer) and their optical properties
including refractive index dispersion, band gap along with film thicknesses were extracted and modeled using WVASE
Plasma immersion Ion Implantation technique has been used to modify the diffusion barrier properties of titanium (Ti) metal layer against copper diffusion. Ti coated silicon wafer were implanted with doses viz. 1015ions/cm2 and 1017ions/cm2 corresponding to low and high dose regime. High dose of implantation of nitrogen ions in the film render it to become Ti(N). Cu/Ti(N)/Si structures were formed by depositing copper over the implanted samples. Diffusion barrier properties of Ti(N) was evaluated after annealing the samples up to 700 degrees C for 30 minutes. Sheet resistance, X-Ray Diffraction (XRD) and Scanning Electron Microscope (SEM) measurements were carried out to investigate the effect of annealing. Low dose implanted Ti layer does not show any change in its diffusion barrier properties and fails at about 400 degrees C. The failure of diffusion barrier properties of low dose implanted samples is attributed to the chemical reaction between titanium and copper films. The high dose implanted layer stops the diffusion of Cu metal through it even at high annealing temperature. The enhancement in its diffusion barrier properties is supposed to be due to nitridation of titanium film which increases the activation energy involved for its chemical reaction with copper metal film.
Experiments performed in a reactive ion etching (RIE) system are discussed with the purpose of studying the influence of the addition of O2 in different ratios in the main CF4 gas flow for silicon etching. Conventional planer reactive ion etching system has been utilized for etching of SiO2 and silicon in fluorine chemistry. The patterns were delineated in SiO2 using photo-resist as the mask material using CHF3 gas in combination with argon. Sidewall passivation technique has been employed to achieve microstructure profile control in silicon. The quantity of O2 gas was varied from 2 to 10% in the total CF4 gas flow (10 sccm) at self dc-bias of -250 volts and process pressure 30 mTorr to achieve a balance between fluorine and oxygen radicals. Anisotropic etched profiles with smooth bottom surfaces were obtained at 2% O2 flow in CF4. The usefulness of this technique has been demonstrated for the delineation of MEMS microstructures in silicon.
Plasma etching has been used for the fabrication of micromechanical structures in silicon with fine feature size. In this paper, reactive ion etching (RIE) is used for micromachining applications in two steps, first for etching of SiO2 layer and then machining of silicon. The first RIE step is for the patterning of the SiO2 layer using photo-resist as mask. This process involves the use of gas mixture of CHF3 and Ar. The photo-resist is then removed in the oxygen plasma. The second step is to delineate the patterned SiO2 layer onto the silicon wafer using SF6/O2 plasma. The oxygen flow is varied from 2-10 sccm in SF6. Silicon etch rates of 195 nm/min and Si/SiO2 selectivity of 10:1 has been obtained. The process parameters such as gas flow, rf-power and etch pressure are optimized as per our reactor's configuration to have compromise for best selectivity, anisotropy, and high etch rates. A pattern transfer with nearly vertical walls is obtained for RIE based on SF6/O2/CHF3 while maintaining the substrate at low temperature.