Development of Novel Metal Ion Beam Systems with Liquid-Metal Ion Sources

Yasuhito Gotoh
The present dissertation dealt with the issues related to the development of novel ion beam systems based on liquid-metal ion sources (LMIS). Unlike the conventional application of LMIS, which is represented by the focused ion beam (FIB) technology, argument made here was how to use a large portion of the ions extracted from the source. An LMIS has unique features. Among these features, ultra high vacuum (UHV) compatibility with no use of a harmful source material is one of the most attractive
more » ... dvantages. Use of pure metal causes no pollution of environments, which will be important for the manufacturing in the new century. In Chapter 1, Introduction, the author emphasized the current status and problems in the application and technology of LMIS's, pointing out three major problems. The author dealt with these issues in the following three parts: part I: undetermined ionization mechanism at a high current regime, part II: diMculties in converging a strongly divergent beam, and part III: insufficient,ion current with the conventional type LMIS's. Part I dealt with the fundamentals of the ion beam characteristics. In Chapter 2, fundamental characteristics of the ion beam extracted from some element metal ion sources, which were experimentally obtained, were given. The author showed that the electric field at the ionization point decreases with an increase in the source current. Paying an attention to this phenomenon, the author pointed out that at the high current regime, the conventional theoretical model does not work. Introducing an qssumption to one of the fundamental equations which dominate the liquid cone formation, the author successfully explained the behavior of the decrease in the electric field at the high current regime. In Chapter 3, the author proposed a high temperature field evaporation (HTFE) model of which formulation is similar to that of the conventional theory but allows extremely high temperature at the apex, extending the theory to molecular ions. So far, high temperature was suggested but nobody could show an evidence for this HTFE. The author explained the atom flux ratio of doubly charged ions to singly charged ions (R2i), and that of molecular ions (Rd.). In Chapter 4, the author investigated the characteristics of alloy ion sources and extended the HTFE model to the alloy ion source. As a result, the author could show that HTFE model also holds for alloy ion sources, especially for the behavior of jR2i• Part II dealt With the development of novel ion beam systems to demonstrate successful transport of the ion beams extracted from an LMIS. Chapter 5 dealt with the issue related to focusing of the divergent beam extracted from the LMIS. The author designed a novel electrostatic lens system suitable for use in focusing the divergent beam. The property of this lens was evaluated both by computer simulation and by experiments. Next, the author designed and constructed an ion implantation system. A unique implantation, molecular i ii ion implantation, was demonstrated with the gold-antimony ion source. Doubly charged heterogeneous molecular ions were implanted to a silicon substrate. In Chapter 6, the author applied the lens system to the novel thin film formation process of metal ion beam self-sputter deposition. Copper thin films were deposited by this unique deposition. It was found that the films show a low electrical resistivity. Since the feasibility of the metal ion beams was shown, the author finally developed high current metal ion sources in Part III, Chapter 7. Arranging the ion emission points up to approximately 40 in a linear array, a metal lon beatn of 9.1 mA' was obtained. The details of the solutlons to the problems in heating the system and in holding system were given. Analyzing the ion beam profiIes, the author showed a distortion of beam profile from axial symmetry. This means presence of self-convergent effect due to the shielding effect by the neighboring cusps. Based on the above experimental results and the system developed in Chapter 5, the a•uthor designed the lens for the linear array source, and demonstrated the
doi:10.14989/doctor.r10927 fatcat:z2z4yy6wbrh3zfdxdl6he7raeq