Younger Scientists
Hiroyuki Fujiwara
The JSAPI would like to introduce Dr. Hiroyuki
Fujiwara who is one of the 38 recent recipients ofthe Young Investigator Award of the 1998 Japan
Society of Applied Physics Spring Meeting, for his
outstanding research while at Pennsylvania State
University. Currently, he is a research associate at
the Electrotechnical Laboratory (ETL) in Japan,
where he specialises in the real time monitoringof thin film growth using spectroscopic
ellipsometry and infrared spectroscopy.

I was honoured to receive the Young Investigator Award from the Japanese Society forApplied Physics for my research into the application of real time spectroscopic ellipsometry(RTSE) to the depth-profiling of graded amorphous silicon alloy (a-SixC1-x:H). The research
was carried out in the laboratory of Drs. Collins
and Wronski at Pennsylvania State University,where I was a research fellow of the Japan Society for the Promotion of Science (JSPS) and,later, a postdoctoral researcher.
It was after finishing my Doctor of Engineering Degree at Tokyo Institute of Technology in 1996 that I decided to go to the laboratory of Dr. Collins., Dr. Collins has been perfecting real time spectroscopic ellipsometry instrumentation and data analysis procedures forthe last decade. RTSE is a unique film
characterisation method in which the structuresof thin films, including surface roughness, layer
thickness, bulk layer thickness and optical properties during deposition, are characterised byutilising white light as a probe.
My motivation for joining that particularlaboratory lay in my expectation that the monitoring of thin film growth in real time would
become an important technique for thecharacterisation of many different thin film fabrications, since the structure of devices had become increasingly complicated in recent years.
A good collaboration between Drs. Collins,
Wronski and Prof. I. Shimizu, who had been
my advisor throughout my post-graduate studies, also encouraged me in my decision to join
Dr. Collins’ laboratory.
During my two years as a research associate at Pennsylvania State University, I focused
mainly on the application of RTSE to alloy com-positions in compositionally-graded a-SixC1-x:H
thin films fabricated by plasma-enhanced
chemical vapour deposition. Such characterisation
is technologically important in, for example,theoptimisation of a-Si:H-based solar cells because
the introduction of a-SixC1-x graded layers at thep/i interface in a p-i-n solar cell structure is
known to improve solar cell performance.
Since RTSE alone cannot be used to determine C-content, the first task was toparameterise the optical response (dielectricfunction) of the a-SixC1-x:H layer as a functionof C-content. 1) I then determined alloy compositions in the graded film structure from thedata set obtained during a-SixC1-x:H graded layer
deposition by applying the parameterised optical constant as a database. This demonstrated that the application of RTSE to thecharacterisation of a a-SixC1-x graded layer wasdestined to be a powerful tool, since it made it
possible to provide details, simultaneously andduring deposition, of the time-evolution of alloy composition, the instantaneous deposition
rate and the surface roughness layer thickness.
Furthermore, the depth-profile on an atomic
scale could readily be obtained by integrating
the instantaneous deposition rate against theknown time of deposition. 2)
These results represent just one exampleof the real time monitoring techniques that are
now being developed in order to fill the needfor a better understanding of thin film growthphenomena in layered structures. At this stageof the work, however, a broader database of
optical functions for a wide variety of films isnecessary if RTSE is to reach its full potential asa tool for the analysis of more complicated film
structures and for the achievement of real timeprocess control.
I am now engaged in a study of hydrogenated amorphous and microcrystalline siliconthin films using real time spectroscopicellipsometry and infrared spectroscopy in thelaboratory of Dr. Matsuda at the ElectrotechnicalLaboratory. In this research, twin measurements
using spectroscopic ellipsometry and infrared
spectroscopy are performed simultaneously inreal time in order to find a correlation between
the evolution of film structure as investigatedby RTSE and the local bonding states of Si-Hn(n = 1~3) as characterised by infrared spectroscopy. I hope that this real time film- growthmonitoring will give us a deeper insight
into the fundamental mechanism of thin film
growth. The understanding gained should thenallow us to modify film and device structures
more effectively and in new ways.

References
1) H. Fujiwara, Joohyun Koh, C. R. Wronski,
R. W. Collins, and J. S. Burnham,
J. Non-Cryst. Solids 227, 460 (1998).
2) H. Fujiwara, Joohyun Koh, C. R. Wronski,
R. W. Collins, and J. S. Burnham,Appl. Phys. Lett. 74, 2993 (1998).
Hiroyuki Fujiwara received his BS degree in applied chemistry from Waseda University and hisDoctor of Engineering Degree in electronic
chemistry from Tokyo Institute of Technology.
He was awarded a fellowship from the Japan
Society for the Promotion of Science in 1996.
He was a visiting scientist and a post-doc at
the Pennsylvania State University prior to joining Electrotechnical Laboratory in 1998.

JSAP International No.1 (January 2000)

JSAPI

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