Ana Paula Mousinho

Protective carbon layer for chemical corrosion of stainless steel

c ˜ EESC-USP-SC, Sao Carlos, SP, Brazil d ˜ Abstract Hydrogenated carbon (a-C:H) films were studied as an alternative material to be used as protective layer on steel, because of their chemical inertness, wear resistance, thermal stability, thermal conductivity. The films were deposited on stainless steel, plain steel and silicon wafers by a RF magnetron sputtering system at 0.6 Pa and RF power of 150 W, at room temperature. A methane plasma was used in these processes. Wet etching tests were carried out using acids (H SO , HNO , HCl, HF), alkaline solutions 24 3 (NH OH, KOH), organicsolvents (2-propanol, xylene and acetone). The samples were analysed by Fourier transformed infrared, 4 Raman spectroscopy, atomic force microscopy and cyclic voltammetry. The low degradation and corrosion levels of the samples show the high chemical resistance of the a-C:H films indicating that they are a promising material to be used as protective layer in many applications of the chemical industry. 2003 Elsevier Science B.V. All rights reserved.

Micro-machine fabrication using diamond-like carbon films

Abstract In this work we use diamond-like carbon (DLC) films deposited by a RF magnetron sputtering system in micro-electro mechanical systems (MEMS) development. The principal applications of DLC films in MEMS application are micro-channels for microfluidric devices, mechanical micro-machines, micro-optical devices, and mechanical actuators. These films were produced by a reactive RF magnetron sputtering system from a target of carbon in a stable graphite allotropic form with purity of 99.9999% and methane plasma. The DLC films were deposited on silicon substrates. The deposition rate was 2.5 nm/min and the films showed low mechanical stress. The films were patterned by a lithography step and the structures were obtained by a reactive ion etching using oxygen plasma. The etching rate in this process was 1 μm/min. The film thickness was measured with a height step meter and a ellipsometer. Fourier transform infrared (FTIR) and Raman spectroscopy were used to identify the sp2 and sp3 hybridization of C, CH bonds and other possible bonds that can appear; atomic force microscopy (AFM), was used to measure film roughness.

Low-temperature deposition of silicon oxide and silicon nitride by reactive magnetron sputtering

In this study, oxide and nitride films were deposited at room temperature through the reaction of silicon sputtered by argon and oxygen ions or argon and nitrogen ions at 250 and 350W with 0.67Pa pressure. It was observed that for both thin films the deposition rates increase with the applied RF power and decrease with the increase of the gas concentration. The Si/O and Si/N ratio were obtained through RBS analyses and for silicon oxide the values changed from 0.42 to 0.57 and for silicon nitride the values changed from 0.4 to 1.03. The dielectric constants were calculated through capacitance-voltage curves with the silicon oxide values varying from 2.4 to 5.5, and silicon nitride values varying from 6.2 to 6.7, which are good options for microelectronic dielectrics.

Low temperature deposition of low stress silicon nitride by reactive magnetron sputtering

Silicon nitride thin film is a well-know kind of material in semiconductor industries. These films are used in important applications such as protective layers; insulators for optical devices, as dielectric material for thin film transistors (TFTs), etc. In this work, silicon nitride thin films were deposited at room temperature through of the reaction of sputtered silicon by argon ions and nitrogen gas with relatively high deposition rates in sputtering reactive processes. We have obtained silicon nitride thin films with low stress for MEMS (Micro Electro Mechanical Systems) fabrication and in post-processing of sensors and actuators devices. Silicon nitride thin films obtained in this work showed stoichiometric (Si3N4) and/or rich in silicon with low mechanical stress and good dielectric properties. The films were analyzed by scanning electron microscope, micro-Raman spectroscopy, profilometry, current-voltage (I-V) and capacitance-voltage (C-V) measurements, laser-based measurement for determination the internal stress and Rutherford Backscattering.

Fabrication of Microlenses With a Novolak-type Polymer

In this work, the fabrication of arrays of parabolic convergent and divergent microlenses is presented. The used material is the Novolak-based polymer All-Resist AR P322, which can be used both for optical UV lithography and for electron beam direct write lithography. Gratings of parabolic divergent microlenses with f-number of 0.5 were fabricated using traditional optical lithography, employing the diffraction characteristics of de-focussed light during the photolithography exposure. Direct write electron beam lithography was used to obtain convergent parabolic microlenses, with different diameters and different heights, allowing the control of the focal length of these lenses. The same technique was employed to manufacture gratings of parabolic convergent microlenses with different diameter and focal length, what enables one to control the intensity of the different orders of the diffracted light. These structures have several applications in the fields of pattern recognition, robotic vision and optical sensors.

Development of Sub-half Micrometric Structures with High Aspect Ratio Using a Multi-layer Lithography e-beam Process and Plasma Dry Etching

In this work we are using the AR-P 322 ( All Resist GmbH ) DQN-novolac photoresist, with 3 µm resolution specified by the manufacturer in the development of sub micrometric structures with high aspect ratios (10:1). In order to obtain these structures (sub-half micrometric and nanometric) we are studying the possible application of electron beam lithography and plasma etching. The resolution limit of the photoresist AR-P 322 is increased to 0.25 µm (nanometric resolution), using an electron beam spot size of 50 nm and dry development.

The Influence of Thermal Annealing in Polymers Employed in Microelectronics

In this work we presented the influence of the thermal treatments in polymer employed in microelectronics and Micro Electro Mechanical System (MEMS) process. The thermal steps can cause adhesion failure, pin holes problems, hillocks and increase of stress in the devices structures. We studied three polymers type based in Novolac and PMMA matrix. These materials was analyzed by technique analyze thermal DSC (Differential Scanning Calorimetry) and the stress mechanical was measurement by substrate curvature. With those analyses we can possible obtained a relationship by a polymer glass transition and mechanical stress observed in structures of microelectronics devices.

Patterned growth of carbon nanotubes obtained by high density plasma chemical vapor deposition

Patterned growth of carbon nanotubes by chemical vapor deposition represents an assembly approach to place and orient nanotubes at a stage as early as when they are synthesized. In this work, the carbon nanotubes were obtained at room temperature by High Density Plasmas Chemical Vapor Deposition (HDPCVD) system. This CVD system uses a new concept of plasma generation, where a planar coil coupled to an RF system for plasma generation was used with an electrostatic shield for plasma densification. In this mode, high density plasmas are obtained. We also report the patterned growth of carbon nanotubes on full 4-in Si wafers, using pure methane plasmas and iron as precursor material (seed). Photolithography processes were used to pattern the regions on the silicon wafers. The carbon nanotubes were characterized by micro-Raman spectroscopy, the spectra showed very single-walled carbon nanotubes axial vibration modes around 1590 cm-1 and radial breathing modes (RBM) around 120-400 cm-1, confirming that high quality of the carbon nanotubes obtained in this work. The carbon nanotubes were analyzed by atomic force microscopy and scanning electron microscopy too. The results showed that is possible obtain high-aligned carbon nanotubes with patterned growth on a silicon wafer with high reproducibility and control.

Generation and characterization of polymeric tridimensional microstructures for micromachine application

In this work, we use the thick layer of polymethylmethacrylate polymer, for micromachining development. In the development of the structures, a three layer process is used. In a silicon wafer is deposited the thick layer spin coating. Over this layer is deposited a thin layer of silicon. The third layer is 1.5 μm of e-beam resist deposited by spin coating. After the deposition of the layers, we perform the e-beam lithography in the top layer resist. This pattern is transferred by plasma etching for the silicon layer. The resolution limits of this process is the resolution of the electron resist and is increased to 0.25 μm (nanometric resolution), using an electron beam spot size of 50 nm and dry development.

Fabrication of microlens arrays and gratings with a Novolak-type polymer

Novolak type polymers are the basic material for most commercial photoresists used in microelectronic processes, but are not often used for micro-optic applications. In this work, three types of optical devices were implemented in AR P322 novolak-based resist, which can be used as a positive photoresist and a positive electron resist. Gratings of parabolic divergent microlenses with f-number of 0.5 were fabricated using traditional optical lithography, employing the diffraction characteristics of de-focused light during the photolithographic exposure. The contrast curve of the AR P322 used an electron sensitive resist, was determined and yielded a gamma factor of 3.02. This relatively low contrast allows to obtain structures with well controlled curved walls. Direct write electron beam lithography was employed to manufacture gratings of parabolic convergent microlenses with different diameter and focal length, what enables one to control the intensity of the different orders of the diffracted light. This technique was also used to obtain convergent parabolic microlenses, with different diameters and different heights, allowing the control of the focal length of these lenses. These structures have several applications in the fields of pattern recognition, robotic vision and optical sensors.