Low pressure chemical vapor deposition of silicon nitride and silicon oxynitride layers and their application in optical waveguide based chemical sensors / Ahmed Tamim [original]

FAKULTÄT FÜR

ELEKTROTECHNIK,

INFORMATIK UND

MATHEMATIK

Low Pressure Chemical Vapor Deposition of Silicon

Nitride and Silicon Oxynitride Layers and their

Application in Optical Waveguide based

Chemical Sensors

Zur Erlangung des akademischen Grades

DOKTORINGENIEUR (Dr.-Ing.)

der Fakultät für Elektrotechnik, Informatik und Mathematik

der Universität Paderborn

genehmigte Dissertation

von

M.-Eng. Ahmed Tamim

Paderborn

Referent: Prof. Dr.-Ing. U. Hilleringmann

Korreferent: apl. Prof. Dr. rer. nat. Reinhart Job

Tag der mündlichen Prüfung: 24.08.2007

Paderborn, den 05.09.2007

Diss. EIM-E/SEN

FAKULTÄT FÜR

ELEKTROTECHNIK,

INFORMATIK UND

MATHEMATIK

Low Pressure Chemical Vapor Deposition of Silicon

Nitride and Silicon Oxynitride Layers and their

Application in Optical Waveguide based

Chemical Sensors

A Thesis Submitted to the Faculty of Electrical Engineering,

Computer Science and Mathematics – University of Paderborn in

Partially Fulfillment of the Requirements for the Degree of

Doctor-Engineer (Dr.-Eng)

Electrical Engineering

M.-Eng. Ahmed Tamim

Reviewers:

Prof. Dr.-Eng. Ulrich Hilleringmann

apl. Prof. Dr. rer. nat. Reinhart Job

Date of Thesis Submission: 30.05.2007

Date of Defence Examination: 24.08.2007

Paderborn, Germany

Acknowledgement

I would like to express my deepest gratitude towards my supervisor Prof. Dr.-Eng.

Ulrich Hilleringmann, for his guidance, moral support, assistance and encouragement

during my study here in Paderborn.

I would also like to thank apl. Prof. Dr. rer. nat. Reinhart Job for acting as second

reviewer, and Prof. Dr. techn. F. Gausch, Prof. Dr.-Eng. R. Noe, Prof. Dr.-Eng. U.

Rückert and Prof. Dr.-Eng. A. Thiede for being in my examination committee.

I would also like to thank also Dr.-Eng. Christoph Pannemann and all my

colleagues in sensor technology department for their help and friendship.

Finally I would like to thank my parents, my wife, my children and my brothers.

Acknowledgement

Abstract

This work involves optimization and characterization of low pressure chemical

vapour deposition (LPCVD) of silicon nitride and silicon oxynitride layers. The

optimized parameters of this deposition were used in fabricating the guiding layer of an

optical Mach-Zehnder interferometer which was used as a transducer for a waveguide

based sensor used to detect chemical gases such as ammonia. In this sensor a titanium

heater with aluminium contacts was integrated near to the reference arm in order to

increase the sensitivity of the sensor by using the thermo-optical effect. A chemo-

optical sensitive material to ammonia (its refractive index changes with changing the

amount of ammonia that diffuses into it from the ambient air) was spin coated on a

sensing window in the sensing arm.

The work in this thesis is split into three main areas of study. The first is designing

a monomode silicon oxynitride waveguide using the imaginary distance beam

propagation method (ID-BPM), also a design of waveguide parameters which increase

the sensitivity, designing the Mach-Zehnder interferometer and the heater. The masks

for the whole structure were designed using the Cadence program.

In the second area, LPCVD of silicon nitride and silicon oxynitride films were

optimized by the adjustment of the deposition temperature and the gases flow rate. The

homogeneity of the deposited layers, the deposition rate and the thickness variations

along the wafers and the boats were discussed.

In the third area, the detailed fabrication procedures of the sensor are discussed

including several important standard processes such as the thermal oxidation of the

silicon substrate, the low pressure chemical vapour deposition (LPCVD), the

photolithography for mask transfer, the reactive ion etching for a ridge waveguide

formation, the metal evaporation and wet etching. Also the characterizations of the

sensor were carried out. The waveguide was analyzed to make sure that the sensor is

working as expected. The heater also was tested to see how much dissipated power the

resistor can withstand during its heating, the heating effect on its resistance and the

heating effect on the transmission intensity were checked too. Finally, the refractive

index change in the sensitive layer during exposure to ammonia was measured. Also the

sensor response, the response time and sensitivity of the sensor were discussed.

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