Thermal Oxidation of Silicon Processes

Thermal Oxidation of Silicon

• Silicon dioxide (SiO2) and the silicon/silicon dioxide interface are crucial to integrated circuit (IC) technology.
• SiO2 is easily etched using lithography.
• It effectively masks common impurities (e.g., boron, phosphorus, arsenic, antimony).
• SiO2 is a superior insulator (high breakdown field, high resistivity).
• It effectively passivates junctions and maintains stable electrical properties.
• It forms a stable and reproducible interface with silicon.

Oxidation Mechanisms

• Oxidation involves volume expansion (approximately 2.2 times).
• Stress effects are significant, especially in 3D structures.
• Field oxides are commonly grown using LOCOS (Local Oxidation of Silicon) process.
• Typical oxidation times at 1000°C in wet oxygen produce approximately 0.5 cm of oxide growth.

Oxidation Methods

• Oxidation systems are typically simple in concept (e.g., using furnaces with quartz tubes).
• Various approaches are used in practice, including vertical furnaces, rapid thermal oxidation (RTO) systems, and fast ramp furnaces.

Oxidation Rate

• Oxidation rates (dry and wet oxygen, and steam) are calculated using the Deal-Grove model.
• Different factors (e.g., temperature, time, and type of oxidizing atmosphere) affect oxidation rate.

Models of Oxidation

• Many oxidation models exist beyond the Deal-Grove model, including those accounting for volume expansion.
• The Deal-Grove model was initially met with some experimental challenges as it did not fully accurately model the oxidation kinetics of 20nm SiO2 films.
• Other models, such as those by Reisman et al., Han & Helms, and Massoud et al., have been advanced.
• Models are frequently implemented in simulation software to better predict oxidation behavior.

C-V Measurements

• C-V (capacitance-voltage) measurements are a crucial technique to characterize SiO2 layers and the silicon/silicon dioxide interface.
• Four key charges (fixed oxide, interface trapped, mobile oxide, and oxide trapped) influence the C-V curves.

Point Defect Based Oxidation Models

• Models focused on the atomistic picture of oxidation.
• Consider volume expansion during oxidation and the need for "free volume".
• Models include detailed information about diffusion and interstitials and vacancies to improve model accuracy.

Complete Process Simulation of Oxidation

• Advanced simulations, such as those using SSUPREM IV, can simulate full oxidation processes.
• These models often handle complex materials such as stressed SiO2 and Si3N4 layers and structures, as well as the interactions between these materials as they form.
• Simulation of Si structures (including recessed LOCOS structures) are handled in these programs, which need to combine multiple oxidation model components for accurate result.

Summary Facts

• Thermal oxidation is a fundamental aspect of silicon technology.
• SiO2 is excellent insulator.
• Oxidation kinetics are well understood but are still being refined and improved upon.
• Current models successfully account for stress effects, and can be extended for more diverse semiconductor fabrication.

Explore the critical role of silicon dioxide in integrated circuit technology through this quiz on thermal oxidation of silicon. Learn about the oxidation mechanisms and methods commonly used in industry, including the benefits of SiO2 and the impact of oxidation on 3D structures.