Quantitative SIMS depth profiling of diffusion barrier gate-oxynitride structures in TFT-LCDs

Area of Science:

• Materials Science
• Semiconductor Device Physics
• Analytical Chemistry

Background:

• Investigating gate oxynitride structures in Thin-Film-Transistor Liquid-Crystal Displays (TFT-LCDs) is crucial for understanding device performance and longevity.
• Challenges in Secondary Ion Mass Spectrometry (SIMS) analysis of multilayered TFT-LCD structures include charging effects, matrix effects, and small pattern sizes.

Purpose of the Study:

• To overcome SIMS analysis challenges for TFT-LCD gate oxynitride structures.
• To investigate material composition differences across TFT-LCD substrates.
• To understand the aging behavior and control voltage shifts in TFT-LCDs.

Main Methods:

• Secondary Ion Mass Spectrometry (SIMS) with exponential relative sensitivity functions for quantitative analysis.
• Transmission Electron Microscopy (TEM) for microstructural analysis.
• Semi-quantitative depth profiling for diffusion analysis.

Main Results:

• Minor differences in gate oxynitride composition were found between the center and edge of TFT-LCD substrates with molybdenum-capped aluminum-neodymium metallization.
• No composition differences were observed with molybdenum-tungsten metallization.
• Inhomogeneous molybdenum capping thickness influenced device electrical behavior.
• Neodymium enrichment at the molybdenum interface confirmed diffusion protection during aging.
• Sodium diffusion from the glass substrate was identified as the cause of control voltage shifts.
• Molybdenum-tungsten proved a superior buffer for charge carriers compared to aluminum-neodymium.

Conclusions:

• Optimized SIMS analysis enabled detailed investigation of TFT-LCD gate oxynitride structures.
• Molybdenum-tungsten metallization offers improved stability and charge carrier buffering over aluminum-neodymium.
• PVD silicon oxynitride as a diffusion barrier and gate insulator on aluminum-neodymium layers yielded optimal results.