Damage recovery of FIB modified Si for directed-assembly of semiconductor nanostructures

Abstract

Focused ion beam (FIB) techniques have previously been shown to have applications in templating semiconductor nanostructure growth on Si. To assess crystalline quality in this method, or in other FIB-based nano-fabrication methods in Si, we assess in this work FIBimplantation damage in Si and subsequent recovery by annealing. Specifically, we study Si substrates implanted to 1 9 10 12 -5 9 10 15 ions cm -2 fluences of 30 kV Si 2? , Ge 2? and Ga ? incident normally at room temperature, covering a structural damage regime from almost no damage to amorphization. Raman spectroscopy with incident photons of wavelength 405 and 514 nm were used for probing structural damage in different depths in as-implanted and thermally annealed substrates. Annealing was performed for varying times at 730-900°C in ultra-high purity nitrogen ambient. Structural damage quantification was performed through measurements of peak height and position of the crystalline Si peak at 520 cm -1 . Our analysis shows that a structural damage parameter, D, (defined by subtracting from unity, the ratio of the height of the Si Raman peak in implanted/annealed samples to that for the Si peak in an unimplanted standard, such that D = 0.00 and D = 1.00 correspond to pristine single crystal and amorphous Si respectively) is 0.05 or less in all the Si and Ge implants after annealing to 900°C, 1800 s. However, D for the Ga implants is close to zero for Ga fluences up to 3 9 10 13 cm -2 but increases steadily to 0.19 for 5 9 10 15 Ga cm -2 under these annealing conditions. The underlying damage recovery mechanisms are discussed.

Directed Self-Assembly of Ge Quantum Dots Using Focused Si2+ Ion Beam Patterning

“…3(b) . The central recovered regions are relatively defect free, in agreement with the damage recovery measured with Raman spectroscopy on annealing Si substrates rendered amorphous by a focused Si 2+ ion beam 36 , 37 . These data confirm that Si 2+ implantation at doses relevant to quantum dot patterning, followed by heating to the temperature required for nanostructure growth, can result in defect-free regions beneath the grown nanostructure but with defects around the perimeter of the implanted area.…”

“…As mentioned above, compared to Ga + , the higher dose required for Si 2+ patterning and the longer implantation range of Si 2+ means that greater amorphization of the substrate 36 is expected during implantation. The heat treatment that is part of the Ge quantum dot growth needs to recover this damage if we are to optimize the electronic properties of the resulting nanostructures.…”

Laser-assisted atom probe tomography of semiconductors: The impact of the focused-ion beam specimen preparation

“…For a dose > 10 14 cm −2 , the PMOR signal starts to saturate. This saturation has been observed for Si damaged with Au, Kr, Ar, Si, Ge and Ga [24,25] using a similar dose, and is referred to as the dose required for partial amorphization. As observed in Fig.…”

“…This process has been studied extensively in the field of ion implantation [23] and shown that a minimum dose is required to form a fully amorphized layer. Full amorphization is both energy-and mass-dependent, but typically requires a dose in the range 10 14 −10 15 cm −2 [24,25] .…”

Mechanisms of Focused Ion Beam Implantation Damage and Recovery in Si

“…Additional measurement details are provided elsewhere. 16 Errors for D in this work are derived from the sum of the standard deviations in the measurements of H and H 0 normalized to the average value of H 0 . Error in the c-Si peak shift measurements at a given fluence is the standard deviation in the peak shift measurements.…”