The combination of conductivity, optical transparency, and wide anodic potential window has driven significant interest in indium tin oxide (ITO) as an electrode material for electrochemical measurements. More recently, ITO has been applied to the detection of trace metals using cathodic stripping voltammetry (CSV), specifically manganese (Mn). However, the optimization of ITO fabrication for a voltammetric method such as CSV is yet to be reported, nor have the microstructural properties of ITO been investigated for CSV. Furthermore, CSV does not require optical transparency, thereby allowing nontransparent substrates to be used for deposition. This enables microfabrication procedures to be expanded and simplified compared to glass or quartz. Combining this with the profound importance of sensitive, selective detection of toxic metal ions in environmentally and biologically relevant samples makes ITO especially attractive. In this work, we report a thorough investigation of ITO deposition and processing on silicon (Si) substrates for CSV analysis using Mn as the model analyte. Several ITO process parameters were examined such as heated deposition and post-process annealing. Each ITO film was characterized using a variety of surface, bulk (X-ray diffraction), and electrochemical measurements. Although each ITO film type showed electrochemical activity, the heated and annealed (HA) ITO fabrication process yielded superior results for Mn CSV; a limit of detection (LOD) of 0.1 ppb (1.8 nM) was obtained. This work exemplifies new applications of ITO as an electrode material while providing a baseline for trace detection of toxic metals and other contaminants amenable to detection by CSV.
We used electrical characterization as well as surface analytical methods to understand leakage behavior and breakdown mechanisms of three different interlayer dielectrics (ILD) in detail. Leakage current measurements were conducted on Back End of Line (BEoL) metal comb structures with variations of line spaces. Schottky barriers as well as trap potential heights were estimated. Furthermore the Schottky barrier height was determined on blanked wafers by X-Ray Photoelectron Spectroscopy (XPS) and Reflection Electron Energy Loss Spectroscopy (REELS). A correlation between the two methods was established. In addition REELS studies were performed on samples with etch induced damage that was emulated by argon sputtering of pristine ILDs. Two defect states have been found within the band gap of all ILDs, which could influence the electron transport at the dielectrics interface.
We demonstrate the utilization of parallel angle-resolved X-ray photoelectron spectroscopy (pAR-XPS) as a useful tool to analyze ultrathin sputtered tantalum nitride (TaN) thin films in complementary metal-oxide-semiconductor (CMOS) trenches. The chemical composition of TaN was estimated by pAR-XPS using a Theta 300i from Thermo Fischer. An improved lateral resolution was achieved by analyzing periodic structures. The XPS data was correlated with transmission electron microscopy (TEM) in combination with energy-dispersive X-ray spectroscopy (EDX) and time-offlight secondary ion mass spectrometry (ToF-SIMS) data. The results show that the nitrogen content in the TaN thin films was about 6% higher at the sidewall compared with the top and bottom of the trench.
Toxic heavy metals such as lead (Pb), cadmium (Cd), and mercury (Hg) cause serious health complications and ingestion of these toxins through contaminated drinking water, even at trace levels, has become a prominent issue. Chronic exposure to toxic metals such as Pb, Cd, and Hg is carcinogenic while causing other problems like kidney failure, severe neurotoxicity, and IQ loss. These problems are only magnified in children as several stages of bodily development can be severely hindered. Electroanalytical methods are an attractive technique for trace detection of heavy metals due to low cost of experimental tools, low limits of detection, multi-element analysis capability, and the possibility to package them into sensing devices. Specifically, boron-doped diamond (BDD) is a rugged, yet sensitive electrode material with significant potential in electrochemical sensing. Using square-wave stripping voltammetry (SWSV), we have developed BDD micro-electrode arrays (MEAs) as well as macro-electrode disks, achieving detection limits as low as 200 parts-per-trillion (ppt) for Pb with a deposition time of just 2 minutes. This is nearly 100x below the 15 ppb maximum contaminant level (MCL) in drinking water set by the Environmental Protection Agency (EPA). MEAs of various diameter and spacing were investigated to find the optimum geometry for both single and multi-element detection of Pb, Cd, Hg, Cu and Mn where results were compared with those obtained at various macro-electrode sizes. Additionally, pen-like sensors incorporating the optimized BDD working electrode, a BDD reference electrode, and BDD counter electrode were constructed and used for the detection of the aforementioned metal ions. Long-term stability of the BDD quasi-reference electrode was investigated in detail. The applicability of all electrode constructions for the detection of metal ions in drinking and environmental water samples were studied for rapid detection at home or in the field. Figure 1
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