HOD thin films for Silicon on Insulator Technology

S.D. Wolter, F. Okuzumi, K. M. Lee, N. Govindaraju, and Z. Sitar

Department of Materials Science and Engineering, North Carolina State University, Raleigh, NC 27695, USA

J.T. Prater

Army Research Office, Research Triangle park, NC 27709-2211, USA

Abstract

As a material with the highest thermal conductivity and high breakdown voltage, diamond can play a crucial role as a heat spreading interlayer for high power silicon devices. In order to produce high quality HOD films, and thus maximize their thermal and insulating properties, we have undertaken a systematic study of HOD formation on Si as a function of bias frequency and duty cycle. In contrast to the DC substrate biasing, a pre-carburization was not necessary in AC biasing, thus simplifying the processing of the aligned crystallites formation. Pulse biasing at frequencies from 1 Hz to 2 kHz revealed somewhat thinner plasma sheaths and higher bias currents at high frequencies. Correspondingly, we observed a decline in the time to film formation from ~60 min. to ~40 min., as well as a reduction in the highly oriented diamond percentage from ~50% for frequencies below 100 Hz to less than 20% above 1kHz.

The variation of the duty cycle for a 60Hz square waveform from 10% to 75% revealed a hyperbolic trend in the total bias time required to form a film of diamond. Likewise, a hyperbolic trend in the highly oriented diamond percentage was observed with a maximum of ~50% for the shorter pulse ON fractions. Stress created at the silicon diamond interface may be responsible for this plateau in the percentage of oriented nuclei on (100) Si.

Films grown at the optimum conditions were used for the thermal conductivity studies performed via the 3w method. As expected, thermal conductivity depended strongly on diamond quality and film thickness and was the highest for the thick films with the highest percentage of oriented nuclei.

The paper will also discuss challenges in creating SOI structures by wafer bonding of HOD films to silicon. The bonding experiments were performed in a dedicated HPHT ultra high vacuum apparatus.

Corresponding Author:

Zlatko Sitar

Department of Materials Science and Engineering

North Carolina State University

1001 Capability Dr. Box 7919

Raleigh, NC 27695

Phone: 919-515-8637

Fax: 919-515-3419

Email: sitar@ncsu.edu

Keywords: highly oriented diamond, AC bias, thermal conductivity, wafer bonding