Konstantinos Giapis received the Dipl. from the National Technology University of Athens, and his PhD from the University of Minnesota
The hyperthermal neutral beam technology will also be explored as a tool for damage-free etching of nanoscale structures. Our modeling studies of photonic band gaps (PBGs) have revealed new periodic dielectric structures with larger absolute gaps that can have promising applications (e.g., solid-state lasers). The fabrication of such structures has been stalled as a result of unsurpassable difficulties associated with the etching of very high aspect ratio features. By minimizing bombardment and charge damage, our technique is uniquely suited to the manufacture of the challenging PBGs. Finally, a recently developed hyperthermal beam of atomic nitrogen will be used in the growth of wide band gap nitride semiconductors. Tunability of the translational eneergy of the beam, to within 0.5 eV in the regime between 2-25 eV, is expected to allow control of the crystalline phase of the growing materials (e.g., cubic vs. hexagonal GaN) under non-equilibrium conditions
My research focuses on understanding the dynamics of gas-surface interactions occurring during plasma etching and deposition of semiconductors. While difficult to study in complex plasma environments, the fundamental interaction dynamics can be revealed in controlled experiments with an energetic beam of reactive atoms directed at realistic surfaces. Studies at complex surfaces present a formidable challenge, but they are relevant to applications and are required to improve existing processes and devise new ones. We have already demonstrated that fundamental insight into the inelastic and reactive scattering dynamics of etching can be obtained, and how it can have immediate impact on the predictive modeling of semiconductor etching. Experiments are performed in a relevant translational energy regime (2-25 eV) by means of hyperthermal neutral halogen beams, produced by a novel technique which was co-invented and developed since my arrival at Caltech. We target measurements of energy and angular distributions of inelastically scattered halogen atoms from semiconductor surfaces under steady-state etching conditions. In addition, monitoring of reactive products has revealed that nonthermal reactions occur and influence significantly etch rates and profile evolution on patterned semiconductor surfaces. When these scattering mechanisms, supported by experimentally measured parameters, were incorporated into a phenomenological model of profile evolution, we were able to not only capture and explain the simultaneous appearance of many profile peculiarities but also predict new phenomena occurring in energy regimes beyond those studied. Recently, we have combined these models with ion transport in plasmas to model microstructure charging, ion deflection, scattering and reactions. Our complex stochastic simulations captured the peculiar "notching" effect (i.e., lateral sidewall etching), which has puzzled the etching community for many years, hampered the application of high density plasma tools and impeded progress towards smaller semiconductor devices. The fundamental understanding of the mechanisms responsible for the effect enabled prediction of new ways to minimize or eliminate notching.
My research will continue to evolve as a balance between experiment and theory: Reveal the scattering dynamics, describe it, and use the knowledge obtained to improve/invent the next generation etching and deposition processes. Immediate plans include a combination of molecular dynamics with stochastic simulations of scattering from liquid metal surfaces, and from highly-corrugated fluorinated and chlorinated Si surfaces. Experiments are planned on etching of various semiconductors by hyperthermal neutral halogen beams. Emphasis will be placed on the study of nonthermal reactions by monitoring hyperthermal products as a function of the surface adsorbate and scatterer (reactive vs. inert). Preliminary evidence suggesting that collision-induced desorption is a dominant nonthermal etch mechanism will be investigated further and compared with other direct reactions (Eley-Rideal, dynamic displacement). Our models of etching in high density plasmas will be further refined to describe other pattern-dependent effects, including the competition between deposition and etching when an inhibitor is present.
Aspect Ratio Independent Etching of Dielectrics G. S. Hwang and K. P. Giapis, Appl. Phys. Lett. 71, 458 (1997)
Inelastic Scattering Dynamics of Hyperthermal Fluorine Atoms on a Fluorinated Silicon Surface T. K. Minton, K. P. Giapis and T. A. Moore, Journal of Physical Chemistry , in press (Aug 6, 1997)
The Influence of Mask Thickness on Charging Damage during Overetching G. S. Hwang and K. P. Giapis, J. Appl. Phys. 82, 572 (1997)
On the Link between Electron Shadowing and Charging Damage G. S. Hwang and K. P. Giapis, Journal of Vacuum Science & Technology B 15(5) (Sep/Oct, 1997)
Prediction of Multiple-Feature Effects in Plasma Etching G. S. Hwang and K. P. Giapis, Appl. Phys. Lett. 70, 2377 (1997).
Aspect-Ratio-Dependent Charging in High-Density Plasmas G. S. Hwang and K. P. Giapis, J. Appl. Phys. 82, 566 (1997)
Pattern-Dependent Charging in Plasmas: Electron Temperature Effects G. S. Hwang and K. P. Giapis, Physical Review Letters, in print (July 28, 1997)