Date of Award

Summer 2001

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Materials Science and Engineering - (Ph.D.)

Department

Committee for the Interdisciplinary Program in Materials Science and Engineering

First Advisor

Roland A. Levy

Second Advisor

Gordon A. Thomas

Third Advisor

John Francis Federici

Fourth Advisor

Dentcho V. Ivanov

Fifth Advisor

Matthew Schurman

Abstract

In this study, an integrated photonic sensor has been designed and fabricated for the purpose of monitoring hazardous organics in the environment. The operation of the sensor is based on the principles of the Mach-Zehnder interferometry. The sensor consists of a patterned waveguide structure made of phosphosilicate core and silica cladding. LPCVD processes were developed to produce undoped cladding and doped core silicon dioxide films. Diethylsilane (DES), Trimethylphosphite (TMP) and oxygen were used as the precursors for the deposition process. The effects of the O2/DES ratio and deposition temperature on the properties Of SiO2 films were investigated. It was observed that the oxide films deposited in the temperature range 550- 700 ºC followed an Arrhenius behavior with an apparent activation energy of 10 KCal/mol. It was found that the optimum conditions to synthesize underlying silicon dioxide films were 775 ºC, 200 mTorr and oxygen to DES flow ratio was 10: 1. After 20 hours deposition time under such conditions, the oxide film was ~15 μm thick, stress was compressive with a value of ~20 Mpa, and the refractive index was 1.458. The effect of TMP flow rate on the properties of PSG films was also studied. The composition and refractive index of PSG films varied with temperature and TMP flow rate. Optimum conditions to deposit PSG core layer were found to be at 600 ºC, 250 mTorr, 2 sccm TMP flow rate and an oxygen to DES flow ratio of 10:1.

After 5 hours deposition time under such conditions, Phosphosilicate layer was about 7 μm thick, stress was compressive with a value of I Mpa, the refractive index was 1.466, and phosphorous oxide was ~7.5 wt%. The growth rate varied with TMP flow rate and exhibited a maximum value of 254 Å/min at 2.5 sccm and 600 ºC. PECVD processes were used to synthesize the upper cladding silicon dioxide films. The deposition conditions were 250 ° C, 900 mTorr, N2O flow rate 900 sccm, and 400 sccm SiH4 (3%) flow rate. After 30 minutes deposition time under such conditions, the oxide film had a thickness of 1.2 μm, stress was compressive with a value of ~110 Mpa, and the refractive index was 1.453. For all deposits, FTIR spectroscopy showed that no carbon was present in the deposits while UV/visible spectroscopy indicated better than 99% optical transmission. Optical analysis proved this integrated photonic sensor could be used as a prototype to monitor the hazardous organics in the environment.

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