FIB Induced Deposition

FIB is a charged particle beam with a much greater mass than the charged particles (electron) used in FEB (Focused Electron Beam). As shown in several other applications and tutorials here, this greater mass allows the FIB to sputter away matter as the beam hits the surface of the targeted material. It is possible to reverse this process if a gas is introduced in the vicinity of the impact point: this is called FIB induced deposition (FID).

Gas Nozzle Injection Nozzle on a Zeiss NVision
     Gas Injection Nozzle on a Carl Zeiss NVision

The gas is introduced by a nozzle which is positioned a few hundreds of microns above the area of interest. The gas is then adsorbed on the surface of the material. When the FIB beam hits the surface, secondary electrons with energy ranging from a few eV to a few hundreds of eV are generated. These secondary electrons will break chemical bounds of the adsorbed gas molecules which will separate into different components: some of which remains volatile, others will form a deposition on the surface.

If the FIB beam sits too long on the same location, the freshly deposited material will be sputtered away. The gas needs to be replenished in order to maintain a net positive yield. For this reason, once the beam has dissociated much of the adsorbed gas, it moves to another location before coming back to the same point. The time between two subsequent "visits" is called the refresh time. Once additional molecules have been adsorbed on the surface, the beam can revisit the same point and then increase the deposition thickness.

A tight beam control (refresh time, beam spacing, focus, dwell time) is critical to a successful FID since the precursor gas can  easily be depleted and then result in material sputtering instead of deposition.

Different precursor gases create different depositions. Common deposition materials include Tungsten, Platinum, Carbon and Insulator.