Optimization of the depth resolution for profiling SiO₂/SiC interfaces by dual‐beam TOF‐SIMS combined with etching

Abstract

To examine precise depth profiles at the interface of SiO2/SiC, a high resolution that can detect slight discrepancies in the distribution is needed. In this study, an experimental method to achieve a high resolution of less than 1 nm was developed by using dual‐beam time‐of‐flight secondary ion mass spectrometry (TOF‐SIMS). The analysis was preceded by the following three steps: (1) determination of the optimal analytical conditions of the analysis beam (Bi+) and sputtering beam (Cs+), (2) verification of the etching methods to thin the SiO2 layer, and (3) confirmation of the benefits of the low‐energy sputtering beam directed toward SiO2/SiC samples. By using the secondary ion intensity peak‐to‐valley ratio of BN− and BO− of a sample with delta‐doped boron multilayers, the appropriate Bi+/Cs+ condition for a high depth resolution was determined for each energy level of the sputtering beam. Upon verification of the etching methods to thin the SiO2 layer, slight discrepancies were found between samples that were obtained with different etching methods. The difference in the roughness values of the etched surfaces was proactively utilized for the performance confirmation of the low‐energy sputtering beam by means of precise observation of the profiles at the SiO2/SiC interface. The use of a Cs beam with a low energy between 0.25 and 0.5 keV enabled the detection of slight discrepancies in the roughness of less than 1 nm between samples. The aforementioned method has the potential to accurately detect discrepancies in the intrinsic distribution at the SiO2/SiC interface among samples.

Profiling with Depth Resolution of Sub-nm for SiO₂/ SiC Interface by Dual-Beam TOF-SIMS Combined with Simulation

“…In this study, an application of simulation was conducted for these experimental depth profiles obtained with high depth resolution mode. It aims to confirm if the simulation can duplicate slight differences of depth profiles appeared experimentally among samples in the previous report [8]. Additionally a possibility of acquiring a more authentic distribution at the SiO2/SiC interface was examined.…”

“…Hence, depth profiling for steep distribution such as that at the SiO2/SiC interface needs a high depth resolution suppressing mixing and knock-on effect and detecting slight discrepancies in the distribution at the interface in SIMS measurement. In a previous study, an experimental method to achieve the high resolution depth profiling of sub-nm by using dual-beam time-of-flight SIMS (TOF-SIMS) was developed, in which the determination of the optimal dual-beam analytical conditions, verification of the etching methods to thin the SiO2 layer, and confirmation of the benefits of the low-energy sputtering beam had been established [8], and the roughness of the etched surface and mixing effect due to sputtering ion beam have been minimized. Nevertheless, an uncertainty in the experimental profiles remains unsolved due to the slight roughness of both at the surface and at the SiO2/SiC interface, and due to ion mixing caused by sputtering ion beam.…”

Behavior and process of background signal formation of hydrogen, carbon, nitrogen, and oxygen in silicon wafers during depth profiling using dual‐beam TOF‐SIMS

“…The raster scanned area of the Bi + beam, which is equivalent to the detection field area, was set as 20 μm × 20 μm or 100 μm × 100 μm, whereas the ion current was adjusted between 4.0 and 4.3 pA. After setting the Cs + and Bi + parameters, the potential damage due to excessive irradiation of high‐energy Bi + primary ions was taken into consideration. Based on previous studies, 21,22 a primary ion to sputtering ion ratio that would not exceed the damage threshold was determined. In addition, the raster scanning areas of both ion beams were appropriately chosen to exclude the crater edge effect.…”

Calculations of Stopping Power, Straggling and Range Projected of FeKr<sup>+</sup>

“…Utilizing the approximation of binary collisions and the Monte Carlo method as its foundation, the simulations were performed using the SRIM 2013 software (Stopping and Range of Ions in Matter). This software is a collection of Windows-based tools that allow one to model both the trajectory of recoiling atoms in a solid and the trajectory of an ion at incidence energies between 10 eV and 2 GeV [41,42]. The three primary programs are the stopping power of ions computation (Stopping/Range Tables) and the detailed calculation (TRIM computation), both of which have an easy-to-use interface.…”