Characterization of merged epitaxial lateral overgrowth (MELO) silicon and its use in fabricating single crystal silicon membranes for micromechanical sensor applications
Abstract
Selective Epitaxial Growth (SEG) and Epitaxial Lateral Overgrowth (ELO) of silicon has shown great potential for advanced device applications. Using ELO locally restricted Silicon-on-Insulator (SOI) device islands can be fabricated. However, one disadvantage of the present day ELO technology is that it has 1:1 aspect ratio, the ratio of lateral growth over vertical growth. To cover a large lateral distance, the vertical height of the ELO front has to be equally high and thereby requires a long growth. Merged Epitaxial Lateral Overgrowth (MELO) from the adjacently placed seed holes produces twice the horizontal extent of SOI in comparison to single ELO. In this thesis both the physical and electrical characterization of MELO is presented. A new processing scheme for obtaining excellent device-quality Merged Epitaxial Lateral Overgrowth (MELO) silicon has been successfully demonstrated. The average ideality factor of diodes fabricated on MELO silicon was 1.013 and the room temperature leakage through the junction was $<$1 $\times$ 10$\sp{-8}$ A/cm$\sp2$. These test results indicated a high quality of MELO silicon. As a defect reduction scheme, a novel double MELO growth process has been successfully implemented for the first time. The DMELO process was shown to reduce the defects in the merging seam by more than two orders of magnitude in comparison to a single MELO process. This process was also successfully implemented on the silicon grown from $\langle$110$\rangle$ oriented seed holes. The performance of diodes on $\langle$110$\rangle$ DMELO silicon was much better than the diodes on $\langle$110$\rangle$ MELO silicon, which again indicated an enhancement of material quality due to this new growth process. The use of ELO/MELO silicon as a micromechanical sensor base material is also explored in this thesis. Large area single crystal silicon membrane (250$\mu$m x 1000$\mu$m) was fabricated by using a novel etch stop technique. Fabrication of a bridge type accelerometer using this novel etch stop was successfully implemented. The sensitivity and the resonant frequency of the accelerometer were 389.42$\mu$v/v-g and 2.2kHz respectively. Also, an-all-top side ELO/MELO accelerometer concept is presented. A novel surface micromachining technique using ELO/MELO silicon to fabricate stress-free beams (cantilever or doubly supported) of single crystal silicon has been successfully demonstrated. This new technique will allow many of the previously fabricated polysilicon microstructures to be fabricated using single crystal silicon having a better thickness control and more predictable properties. Using this technique 1000$\mu$m long, 5$\mu$m wide, and 10$\mu$m thick stress-free beams (both cantilever and doubly supported) were fabricated. Finally, application of MELO silicon techniques to the fabrication of large-area SOI islands by a novel surface micromachining technique was successfully implemented.
Degree
Ph.D.
Advisors
Neudeck, Purdue University.
Subject Area
Electrical engineering
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