SILICON NANOWIRE GROWTH AND TRANSISTOR FABRICATION BY SELF-ASSEMBLING “GROW-IN-PLACE” APPROACH

Open Access
- Author:
- Shan, Yinghui
- Graduate Program:
- Engineering Science and Mechanics
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- May 25, 2007
- Committee Members:
- Stephen Joseph Fonash, Committee Chair/Co-Chair
S Ashok, Committee Member
Jerzy Ruzyllo, Committee Member
Osama O Awadelkarim, Committee Member
Jian Xu, Committee Member - Keywords:
- Grow-in-Place
Self-assembling
Transistor
Silicon Nanowire
Nanochannel Template - Abstract:
- Nanowires have attracted much attention recently owing to their ability to serve as critical building blocks for emerging nanotechnologies. Silicon nanowires (SiNWs) are particularly promising because of the central role of silicon in semiconductor industry. SiNWs would allow device fabrication with high density and their high surface to volume ratio offers high sensitivity. In addition, the possible quantum confinement in SiNWs may further enhance device performances and open windows for exploiting fundamental properties. Intense researches have been carried out in SiNW growth and device fabrication. However, there are still challenges in SiNW growth controls, such as size, number, shape, position, orientation, and inter-wire spacings. To make devices from these SiNWs, post-growth processing steps are needed, such as SiNW collecting, picking, positioning, aligning, and assembling. Due to the extremely small size of SiNWs, there are also challenges in SiNW device fabrication. To solve these challenges in both SiNW growth control and device fabrication, we introduced a novel self-assembling “grow-in-place” approach. Our approach combined vapor-liquid-solid (VLS) nanowire growth mechanism and pre-fabricated nanochannel template. The VLS growth mechanism offers the ability of controlling nanowire size and shape by nanochannel templates. The pre-fabricated nanochannel template guides nanowire growth and offers good SiNW growth control. SiNWs and silicon nanoribbons (SiNRs) with different sizes have been successfully grown in our nanochannel templates. Characterizations on their size, shape, composition, and crystallinity of the SiNW/Rs have confirmed that our “grow-in-place” approach offers good controls on crystalline SiNW/Rs size, shape, number, orientation, position, and inter-wire spacing. So our approach solved the challenges in SiNW growth control. Our grow-in-place approach also solved the challenges in SiNW device fabrication. We introduced two versions of nanochannel templates. The first one is the encapsulated/long nanochannel template. The nanochannels in these templates are long and SiNW/Rs grow inside these nanochannels. The grown SiNW/Rs are totally confined by the nanochannels, which offer total and precise control on SiNW growth. The electrodes can be built-in to the templates before SiNW growth. The growing SiNWs are self-positioned, self-assembled, and self-contacted with the built-in electrodes. After SiNW growth, SiNW devices are ready, without any post-growth processing and fabrication steps. The second one is the extruded/short nanochannel template. The nanochannels in these templates are short, only “nurse” the initial growth of SiNWs, and guide SiNW growth out of nanochannels. SiNWs are fixed by the extruded/short nanochannels for easy device fabrications. So there are no post-growth device fabrication difficulties. SiNW transistors have been successfully fabricated from our grow-in-place SiNWs. The transistors showed high performances with on/off ratio of 6 order of magnitude and subthreshold slope of 130 mV/dec. In addition, a new accumulation type transistor model and configuration were proposed to build device model and extract carrier mobility. As a summary, our novel “grown-in-place” approach allows us to produce self-assembled and self-positioned crystalline SiNW/R devices directly from a silicon precursor gas (e.g., SiH4), without any intervening silicon material formation or collection, positioning, assembling steps. Our approach offers a way to make size controllable, position-controllable, contacted nanowires in an environmentally safe way and to assemble the nanowires into rational device geometries. These templates can be an integral component of the final devices and can provide contacts, interconnects, and passivation/encapsulation. The approach results in self-assembly of the SiNW/Rs into interconnected devices without any “pick-and-place” or printing steps, thereby avoiding the most serious problems encountered in process control, assembly, contacting, and integration of SiNW/Rs for IC applications. The approach we have developed is also environmentally safe since the fabricated nanowires are always confined and only the exact number needed is fabricated. In addition, the application of our approach is not limited in SiNW growth control and transistor fabrication. Nanowires from other materials, such as Ge and ZnO2, and other devices, such as sensors, could also be developed from our grow-in-place approach.