Metallurgical micro-structure of liquid metal-emitter interface of field emission liquid metal ion source

摘要

The stability of the liquid metal field-emission ion source for submicrometre lithography and ion im-plantation with a focused ion beam (FIB) system is of prime importance. Liquid metal ion sources (LMIS) in FIB systems have emerged as a new tool for a variety of microelectronic fabrication proces-ses. Some micro-fabrications, such as etch rate enhancement, resist exposure, and direct micro-beam ion implantation is possible because of the small virtual emitting source size, of the order of 5-60 nm [1,2]. The basic configuration of LMIS in the FIB system consists of a wetted polycrystalline needle emitter with tip diameter in the order of 1-10 jUm, and an alloy source reservoir (Fig. 1). Because of the nature of a polycrystalline emitter with grain boundaries, it is well established that the mean jump frequency of an atom in these regions is much higher than that of an atom in the lattice [3]. Several possibilities can occur in these regions, such as liquid metal diffusion into the grain boundary (Fig. 2a) and formation of solid precipitates along the shank of the emitter tip (Fig. 2b), thus leading to source emission instability by impeding the flow of liquid metal from the reservoir to the emitter tip, causing variation in dopant concentration.