Confocal scanning photoluminescence for mapping electron and photon beam-induced microscopic changes in SiN _x during nanopore fabrication

Abstract

Focused electron and laser beams have shown the ability to form the nanoscale pores in SiNx membranes. During the fabrication process, areas beyond the final nanopore location will inevitably be exposed to the electron beams or the laser beams due to the need for localization, alignment, and focus. It remains unclear how these unintended exposures affect the integrity of the membrane. In this work, we demonstrated the use of confocal scanning photoluminescence (PL) for mapping the microscopic changes in SiNx nanopores under the influence of electron and laser beam exposure. We developed and validated a model for the quantitative interpretation of the scanned PL result. The model shows that the scanning PL result is insensitive to the nanopore size.Instead, it is dominated by the product of two microscopic material factors: quantum yield profile (i.e., electronic structure variations) and thickness profile (i.e., thinning down of membrane thickness). We experimentally demonstrated that the electron and laser beams could alter the material electronic structures (i.e., quantum yield) even when no thinning down of membrane thickness occurs. Our results suggest the minimizing the unintended e-beam or laser beam to the SiNx during the fabrication is crucial if one desires the microscopic integrity of the membrane.

Direct Observation of Redox-Induced Bubble Generation and Nanopore Formation Dynamics in Controlled Dielectric Breakdown

“…For both samples, the corresponding PL (middle panel) and laser-enhanced ionic current mapping results (right panel) both showed distinguishable features in the nanopore location. It is noteworthy that the PL reduction in SiN x is very sensitive to the electronic structure change and does not necessarily indicate the location of a physical nanopore. , In this work, we mostly used the laser-enhanced ionic current mapping for determining the nanopore numbers and locations, while the complementary PL result was only used for reference. It is also worth mentioning that while increasing the laser power can help to improve the signal-to-noise ratios in laser-induced ionic current enhancement (Supporting Figure S1), high laser power is detrimental to the material integrity of SiN x membrane. ,, In this work, we used 6 mW laser for the laser-enhanced ionic current mapping, unless otherwise noted.…”

“…It is also worth mentioning that while increasing the laser power can help to improve the signal-to-noise ratios in laser-induced ionic current enhancement (Supporting Figure S1), high laser power is detrimental to the material integrity of SiN x membrane. 5,39,40 In this work, we used 6 mW laser for the laser-enhanced ionic current mapping, unless otherwise noted.…”

Localized Nanopore Fabrication via Controlled Breakdown

“…Optical measurements also have no interference with the electrical signal and hence can be implanted in a system as an orthogonal source of information. Three different optical signals have been explored for monitoring nanopore formation during the breakdown in real time: (1) photoluminescence (PL) intensity [ 86 , 88 , 89 , 145 ], (2) measuring ionic current while laser scanning [ 87 , 95 ], and (3) Ca 2+ ions and Ca 2+ indicator [ 10 , 88 , 90 ]. We will discuss these optical feedback controls in Section 3.2 .…”

“…Therefore, laser-thinning CBD has a strong dependence on the Si:N composition and is accelerated in alkaline solutions [ 86 , 87 , 158 ]. This photo-active etching results in a locally thinned membrane, where the electric field strength is much higher than that in other regions, promoting the breakdown in this laser-thinned region [ 86 , 88 , 89 , 90 , 145 , 159 ]. Figure 3 c(i) illustrates the CBD process in combination with laser thinning.…”

“…Although the PL intensity provides additional feedback on the pore-formation process, it does not indicate any information on the pore size, since the laser spots are typically of the order of several hundred nanometers. By scanning the PL over the membrane, one can obtain the location as well as the number of nanopores formed by laser etching [ 86 , 88 , 89 , 145 , 159 ].…”