Thermal Oxidation of Silicon Process

Thermal Oxidation of Silicon

• Thermal oxidation is a crucial process in integrated circuit (IC) fabrication
• Silicon dioxide (SiO2) and the Si/SiO2 interface are essential for silicon's dominance in ICs
• SiO2 is easily etched with lithography, masking common impurities (B, P, As, Sb)
• It's an excellent insulator (high breakdown field, stable electrical properties) and passivates junctions
• Thermal oxidation involves volume expansion (~ 2.2X), affecting 2D and 3D structures
• LOCOS (Local Oxidation of Silicon) process is used to grow field oxides (typically 90 minutes at 1000°C in water vapor results in ~ 0.5 cm growth)
• Thin oxides (~ 3-5 nm) are grown over active regions as gate oxides

Oxidation Mechanisms and Models

• Oxidation of silicon typically involves silicon reacting with either oxygen (O2) or water vapor (H2O). The reactions produce SiO2
• Deal-Grove Model: A basic model for oxidation that considers the rate of volume expansion and volume diffusion/chemical reactions, typically used for modeling field oxide oxidation (parabolic model)
• Point Defect Models: More advanced, atomistic approach to modelling oxidation that looks at how chemical reactions, and diffusion occur at an atomic level (involves interstitials and vacancies)

Oxidation Rate and Other Factors

• Oxidation rate depends on temperature, ambient (O2 or H2O), and other process parameters
• Calculated oxidation rates are often presented with graphs of oxide thickness against time
• This process is sensitive to structure; different shapes and thicknesses lead to different rates

Measurement Techniques

• CV (Capacitance-Voltage) measurements are a critical tool to characterize SiO2 and the Si/SiO2 interface
• This method monitors how charges are distributed in the oxide and in the Si/SiO2 interface, which leads to determining several important quantities like oxide thickness and doping concentration

Other Important Considerations

• Stress effects during oxidation are significant, especially in 2D and 3D structures, and must be considered
• Different oxidation environments and conditions will have different rates and outcomes of the process
• Advanced process models and simulations are essential for accurate results and understanding these complex processes

Explore the critical thermal oxidation process in integrated circuit fabrication. Understand the significance of silicon dioxide and its impact on silicon-based technologies. Learn about oxidation mechanisms, models, and the LOCOS process for growing field oxides.