Alternative Lithographic Methods for Variable Aspect Ratio Vias

The foundation of semiconductor industry has historically been driven by scaling. Device size reduction is enabled by increased pattern density, enhancing functionality and effectively reducing cost per chip. Aggressive reductions in memory cell size have resulted in systems with diminishing area between parallel bit/word lines. This affords an even greater challenge in the patterning of contact level features that are inherently difficult to resolve because of their relatively small area, a product of their two domain critical dimension image. To accommodate these trends there has been a shift toward the implementation of elliptical contact features. This empowers designers to maximize the use of free space between bit/word lines and gate stacks while preserving contact area; effectively reducing the minor via axis dimension while maintaining a patternable threshold in increasingly dense circuitry. It is therefore critical to provide methods that enhance the resolving capacity of varying aspect ratio vias for implementation in electronic design systems. This work separately investigates two unique, non-traditional lithographic techniques in the integration of an optical vortex mask as well as a polymer assembly system as means to augment ellipticity while facilitating contact feature scaling. This document affords a fundamental overview of imaging theory, details previous literature as to the technological trends enabling the resolving of contact features and demonstrates simulated & empirical evidence that the described methods have great potential to extend the resolution of variable aspect ratio vias using lithographic technologies

Development of an image converter of radical design

A long term investigation of thin film sensors, monolithic photo-field effect transistors, and epitaxially diffused phototransistors and photodiodes to meet requirements to produce acceptable all solid state, electronically scanned imaging system, led to the production of an advanced engineering model camera which employs a 200,000 element phototransistor array (organized in a matrix of 400 rows by 500 columns) to secure resolution comparable to commercial television. The full investigation is described for the period July 1962 through July 1972, and covers the following broad topics in detail: (1) sensor monoliths; (2) fabrication technology; (3) functional theory; (4) system methodology; and (5) deployment profile. A summary of the work and conclusions are given, along with extensive schematic diagrams of the final solid state imaging system product

Photoresist Development on Sic and Its Use as an Etch Mask for Sic Plasma Etch

Photoresist is a light sensitive material whose physical and chemical properties change when exposed to light. Photoresist makes it possible to transfer the image of a circuit pattern directly onto a substrate. The first part of this work deals with developing a photo process using AZ 1518 and AZ P4330 positive resists on SiC substrate. The aim was to determine the optimal spin parameters, softbake time, and exposure time for these resists matching their thickness. AZ 1518 process was developed for a 1.76 um thickness and AZ P4330 for 4.3 um thickness. With the parameters obtained the resist had about 5% of difference in thickness across a wafer surface. The absence of practical wet chemical etching of SiC is the reason for the study of dry, plasma etching of SiC in this thesis. There is an interest in photoresist as an etch mask because it is cheap, easy to deposit, pattern and remove. However its ability to mask etching of materials with high bond strength like SiC is limited. This work examines its selectivity under various etching parameters and determines the effect of increase in the RF power on selectivity, SiC etch rate and photoresist etch rate

II-VI Semiconductor Nano-Structures for On-Chip integrated Photonics

Nanowires (NWs) and nanobelts (NBs) have been widely studied and fabricated into on-chip photodetectors, biosensors, LEDs/lasers, solar cells and computational components. Their highly tunable physical, electronic and optical properties have generated interest in this field over the past two decades. While there is tremendous potential for nano-structured devices, the wide spread application of NWs/NBs has been hindered by the difficulty in integrating multiple NW or NB structures together into more complex devices. This problem requires a completely novel approach to what has been previously attempted in order to effectively couple on-chip light sources, waveguides and detectors. Multiple factors must be considered including optical power of nanoscale light sources, propagation losses in waveguides and responsivity of nano-scale detectors. Only in combination is it possible to have fully on-chip integrated devices. In this thesis we report the design, optimization and fabrication of coupled self-aligned NB LED emitters and photodetectors. An etched cut is made into a single Cadmium Sulfide NB providing the ability to fabricate each section of a single NB into a separate device. This opens possibilities for on-chip devices such biological sensors. This self-aligned structure can also be coupled to an external light source. Additionally, we present a method for waveguideing and modulating second harmonic generation (SHG) in Cadmium Sulfide NBs as a light source for on-chip measurements. SHG is a coherent and tunable frequency doubled light source so the input laser does not interfere with measurements on-chip. The ability to reliably fabricate more complex devices with nano-structures will continue the trend of portability and point-of-care technology by integrating bulk components such as lasers and photodetectors onto on-chip devices

Electrochemical fabrication of semiconductor nanostructure arrays for photonic applications

Theoretical and experimental investigations of the properties of semiconductor nanostructures have been an active area of research due to the enhanced performance that is observed when electrons and holes are spatially confined in one, two or three dimensions. However, the development of viable photonic devices using this phenomenon requires the development of appropriate fabrication techniques that can provide control over nanostructure size, material composition, and periodicity for structures with dimensions less than 20 nm. To address these challenges, a nanostructure synthesis technique has been developed that is based on the self-organization of nanometer scale pores during the anodization of aluminum thin films. This template can then be used for direct synthesis of semiconductor material, or as a pattern transfer mask for the etching of structures in a semiconductor substrate.;In this work, alumina template technology has been transferred from the exclusive use of an aluminum substrate to a thin film technology that can be applied to an arbitrary substrate material. This thin film process has been developed and characterized to permit control and uniformity over both nanostructure length and diameter. In addition, a Al/Pt/Si structure has been developed to permit direct DC synthesis of semiconductor nanostructures. Finally, the ability of this template to serve as a mask for direct etching of nanoscale features on a semiconductor substrate has been evaluated. This technology is currently being developed to provide device applications in the area of photovoltaic devices and silicon electro-optic modulators

Controlled Lasing in Gallium Nitride Nanowires

There is considerable interest in ultra-small coherent light sources. A strong candidate is a semiconductor-nanowire laser, where a single, monolithic nanowire functions simultaneously as an optical microcavity and active medium, leading to an extremely compact and robust laser. Recent advances in nanowire synthesis have enabled realization of optically pumped nanowire lasers in different material systems, including III-V, III-nitride, and II-VI semiconductors. However, due to the limited lasing control techniques, most of the nanowire lasers operate in naturally-occurring multi-mode and randomly polarized states. Lasing control in nanowire lasers is strongly desired for many practical applications. For instance, specifically polarized lasing is desired for atom trapping and biological detection, and single-mode lasing is crucial for applications needing high beam quality and spectral purity such as nanolithography and on-chip communications. Motivated by these practical requirements, this dissertation concentrates on the study of fundamental lasing characteristics and their control in gallium nitride (GaN) nanowire lasers. GaN nanowire lasers typically operate in a combined multi-longitudinal and multi-transverse mode state. Two schemes are introduced here for controlling the optical mode and achieving single-mode operation of the nanowire lasers. The first method involves placing two nanowires side-by-side in contact to form a coupled cavity. The coupled cavity can generate a Vernier effect, which is able to suppress both multi-longitudinal and multi-transverse mode operation, giving rise to the single-mode lasing in these nanowire lasers. For the second method, single-mode lasing is achieved by placing individual GaN nanowires onto gold substrates. The nanowire-gold contact generates a mode-dependent loss, which can strongly attenuate high-order guiding modes and ensure single-mode operation. Additionally, polarization properties of the gallium nitride nanowire lasers are studied experimentally by direct analysis of light emission from the nanowire end-facets. Linearly and elliptically polarized emissions are both obtained from a single nanowire at different pump strength, and a clear switching of the polarization states is observed with the change of optical excitation. This polarization change is attributed to a switching of transverse modes due to their difference in cavity losses. Finally, lasing polarization control is allowed by the coupling of the GaN nanowire lasers to an underlying gold substrate. The gold substrate breaks the symmetry of the nanowire geometry and generates an inherent polarization-sensitive loss. These effects allow us to demonstrate linearly polarized emission of GaN nanowire lasers, with a large extinction ratio and a fixed polarization orientation parallel to the substrate surface