Advanced Detection of Ti Nanoparticles on Photovoltaic Silicon Wafers Using EXPEC 7350 ICP-MS/MS
EXPEC Technology
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The Importance of Clean Silicon Wafers in Photovoltaic and IC Production
Clean silicon wafers are critical in the production of photovoltaic cells and integrated circuits, as their cleanliness directly impacts the final performance, efficiency, and stability of the products. Silicon wafers, cut from silicon ingots, often have damaged surface lattice structures that are susceptible to contamination by impurities, such as nanoparticles and metal ions. These contaminants can reduce dielectric strength, increase reverse leakage current in photovoltaic P-N junctions, and lower the carrier lifetime, all of which negatively affect device performance.
With the growing use of new materials in the photovoltaic and semiconductor manufacturing process, there is an increasing need to characterize the size and number of nanoparticles on silicon wafer surfaces. This study presents the use of the EXPEC 7350 ICP-MS/MS from EXPEC Technology to analyze Ti nanoparticles on the surface of photovoltaic silicon wafers.
SP-ICP-MS for Nanoparticle Characterization
Principle of Single Particle ICP-MS
Since its introduction, Single Particle-Inductively Coupled Plasma Mass Spectrometry (SP-ICP-MS) has become a widely used method for nanoparticle characterization across various fields, including food, pharmaceuticals, and environmental science. In SP-ICP-MS, particles are introduced into the ICP as individual particles in suspension, where they undergo desolvation, atomization, and ionization before being analyzed for their mass-to-charge ratio. The number of ion clouds correlates with particle concentration, while the signal intensity correlates with particle size.
Due to its high sensitivity and specificity, SP-ICP-MS excels in measuring the size distribution and concentration of nanoparticles. As the demand for detecting nanoparticles on silicon wafers grows, this study showcases how the EXPEC 7350 ICP-MS/MS is used to characterize Ti nanoparticles.
EXPEC Technologys Single Particle Data Analysis Software
EXPEC Technology’s latest "Single Particle Data Analysis Software" provides robust functions for nanoparticle analysis and data processing. Key features include:
The software is compatible with all of EXPEC Technology’s ICP-MS products, including the SUPEC 7000 ICP-MS, EXPEC 7350 ICP-MS/MS, and EXPEC 7910 ICP-Q-TOF-MS. It can collect data for multiple elements during a single sample analysis.
Sample Preparation of Silicon Wafers
Step-by-Step Process
1. Sample Collection: Use clean PFA tweezers to collect 4g of broken silicon wafer samples.
2. Cleaning: Wash the samples twice with UPW (ultra-pure water).
3. Extraction: Add an extraction solution (HNO3, HF, H2O2, UPW) to the PFA bottle, ensuring the sample is fully submerged. Heat at 70°C for 1 hour.
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4. Transfer: Cool the solution and transfer it into a new bottle, ensuring that any residual particles are collected.
5. Final Preparation: Dry the solution, then dissolve the sample with 5% nitric acid and UPW to obtain the final test solution.
ICP-MS/MS Operating Conditions
Ti Isotope Interference Removal
The EXPEC 7350 ICP-MS/MS system was used for analysis, with optimized sample introduction conditions. Titanium has five stable isotopes, with 48Ti being the most abundant. However, 48Ti suffers from interference with isotopes like 48Ca. To address this, the ICP-MS/MS system was set to filter out these interferences using ammonia-helium mixed gas in the collision cell.
By setting Q1 to m/z = 48 and using a reaction product (48Ti-NH) with m/z = 63, potential interferences were eliminated, ensuring accurate detection of Ti nanoparticles.
Characterization of Ti Nanoparticles on Silicon Wafers
1. Transmission Efficiency and Particle Sizing
SP-ICP-MS/MS measurements rely on transmission efficiency for accurate nanoparticle characterization. EXPEC’s software allows for separate corrections of particle number concentration and particle size distribution, eliminating potential errors introduced by using a single transmission efficiency.
The test used a gold nanoparticle standard (60nm) to determine transmission efficiency. The resulting data was processed using EXPEC’s single particle software, providing detailed size distribution and concentration information.
2. Experimental Results
The extracted silicon wafer solution was analyzed using SP-ICP-MS/MS. The software identified clear pulse peaks of 48Ti-NH+, representing Ti nanoparticle signals. The size distribution data revealed three parallel samples with average particle sizes of 107.28 ± 6.65 nm and Ti ion concentrations of approximately 1.55 ng/mL.
3. Observations
One of the parallel samples exhibited a significantly larger average particle size (114.19 nm) compared to the others, while the Ti ion concentrations remained consistent across all samples. This suggests that Ti nanoparticle distribution on the wafer surface may vary across different regions, indicating the need for broader sampling for more comprehensive characterization.
Conclusion
This study demonstrates the ability of the EXPEC 7350 ICP-MS/MS system, operating in single particle mode, to accurately detect and measure Ti nanoparticles on photovoltaic silicon wafers. The advanced "Single Particle Data Analysis Software" offers automated, high-precision nanoparticle analysis, making it an essential tool for characterizing nanoparticle contamination in photovoltaic and semiconductor processes.