Pulsed Plasma with Synchronous Boundary Voltage for Rapid Atomic Layer Etching

University Of Houston, Houston TX

Investigators

Abstract

Proposal Title: Pulsed Plasma with Synchronous Boundary Voltage for Rapid Atomic Layer Etching Principal Investigator: Economou, Demetre J. Institution: University of Houston Proposal No: CBET-0903426 This proposal will conduct research to develop the principles and techniques for a practical method of etching surfaces away, one atomic monolayer at a time, by pulsing the electronics of an etching device. Creating such a method is a critical need for advancing nanoscience and nanotechnology. The novel, promising central idea is to pulse the plasma and ion bombardment rather than the reactive gases. Current plasma etching techniques do not have the level of control or damage-free nature that is needed for patterning delicate structures smaller than 20 nm. It should be far easier to control electrical plasma applicators as compared to fast acting mechanical valves used to pulse gas injection. Furthermore, conventional Atomic Layer Etching (ALET) is very slow because it pulses the introduction of etching gases with long reactant adsorption and purging steps, but the new type of ALET should have a much faster etching rate (x30) because electrical pulsing can be performed much faster than mechanical pulsing. Basic knowledge will emerge on pulsed plasmas, plasma-surface interactions, and new methods for plasma-aided formation of nanostructures. The latter will have broad impact on diverse areas of nanotechnology, permitting the fabrication of emerging technologies including abrupt heterostructure interfaces and extremely thin layers for optoelectronics, quantum devices, and nanostructures In the research carried out under this award, novel pulsed plasma methods with synchronous boundary voltage will be developed for rapid ALET. An electrostatically shielded, inductively coupled plasma (ICP) will be employed, containing mostly rare gas with a trace (e.g., <1% Cl2) of reactive gas. Because the plasma potential will lie below the ?chemical sputtering? threshold, it should be possible to form a saturated product (e.g., SiClx for Si etching) layer in about 1 s, without etching. This layer will then be removed by nearly monoenergetic ion bombardment, created in a short period (~0.5 s) of rapidly pulsed ICP power (e.g., 50ì ON / 100ì OFF), combined with synchronous pulses of a positive DC bias voltage applied to a boundary electrode (boundary voltage) during most of the afterglow (ICP power OFF). During this period, the ion energy will be precisely controlled to lie above the threshold for chemical sputtering but below the threshold for physical sputtering of the substrate, resulting in self-limiting etching. Synchronous pulsing of the boundary voltage will also sharpen the ion angular distribution (IAD) to about ±3°. Narrow IADs are essential for highly anisotropic etching with vertical sidewalls, especially for etching nanoholes. Plasma experiments and simulations will be performed to understand the complex interactions between the pulsed ICP and the synchronous boundary voltage, including measurements of time-resolved ion bombardment energy and angular distributions. These will be coupled with etching experiments including the effect of noble gas ion mass, and reactant (Cl, Br, I) mass and electronegativity on sub-surface lattice damage and ALET monolayer accuracy. In-situ and ex-situ diagnostics will be employed to measure product removal rate as a function of chemisorbed layer surface coverage and substrate damage. Silicon and GaN ALET will be investigated, but the method will be applicable to a variety of substrates. Educationally, the research will involve two PhD students, two undergraduates, and several outreach activities, including a collaboration with the Coalition for Plasma Science to increase public awareness for societal benefits of plasmas. Undergraduate students (more than 50% of the University of Houston students are minorities) as well as a teacher will be recruited with the help of the Research Experience for Undergraduates (REU) and Research Experience for Teachers (RET) programs of the university.