Document Type
Thesis
Date of Award
9-30-1990
Degree Name
Master of Science in Electrical Engineering - (M.S.)
Department
Electrical and Computer Engineering
First Advisor
Marek Sosnowski
Second Advisor
Kenneth Sohn
Third Advisor
Armen K. Jermakian
Abstract
The goal of this research was to study the mass distribution of ions generated in the Ionized Cluster Beam (ICB) deposition system. The ICB deposition method has been used to form high quality films of metals and other materials. It was postulated that the clusters consisting of hundreds and thousands of atoms produced by vapor expansion in the ICB source are responsible for the superior film properties. However, consistent experimental evidence concerning the cluster mass distribution, or even the existence of such clusters in the ICB apparatus, was lacking.
Two methods of cluster ion mass spectroscopy were used in this study: the retarding potential method and the time of flight method. In the retarding potential method, two types of ionizers were used: (1) a wire-cage type ionizer in which a neutral beam passed through the anode wire cage and was showered by electrons from a loop cathode; (2) an electron-gun type ionizer in which an electron beam, rectangular in cross section, intersected the neutral beam. The electron-gun type ionizer was also used in a pulsed mode in the time of flight measurements. In the latter measurement, a data acquisition and control system based on the ATT PC 6300 computer and CAMAC interface was used. The time of flight spectra in the 0 - 200 usec range were obtained with the distance between the ionizer and the ion detector 22 cm.
The retarding potential measurements with the wire-cage ionizer showed no evidence for large clusters (hundreds of atoms) above the sensitivity level equal to 0.18% of single ion intensity. The measurements with the electron-gun type ionizer showed that if there were clusters, the cluster ion current was below 0.25% of the single ion current. The above limits on the sensitivity of the measurements are due to a background current in the ion collector recorded at large retarding voltages. A considerable effort was made to minimize this current by careful source design and the control of the electrical fields in the apparatus. The results of the time of flight measurements show that the maximum possible fraction of clusters in the ion beam was no more than 0.3%. This limit depends on the electrical noise in the ion collector resistor and the amplifier.
The research failed to produce any evidence that large clusters of gallium are produced in qualities which would influence the film deposition process, by the ICB source. Rather, the results indicate that the presence of energetic atomic ions accelerated toward the substrate is responsible for the properties of films deposited by the ICB method.
Recommended Citation
Wang, Yung-Kuan, "Measurement of cluster size by retarding potential and time-of- flight methods in an ionized cluster beam deposition system" (1990). Theses. 2990.
https://digitalcommons.njit.edu/theses/2990
