Overview
This lecture introduces key concepts and definitions related to semiconductors, material types, relevant physical processes, and fabrication techniques, focusing on the fundamentals required for understanding semiconductor devices and production.
Types and Structure of Materials
- Crystalline materials have highly ordered atomic structures with few defects (e.g., diamond, quartz).
- Poly-crystalline materials consist of many small crystals or grains (e.g., silicon for solar cells, most metals).
- Amorphous materials have no specific atomic order and many defects (e.g., most glass).
- Silicon wafers are thin slices used as the foundation for manufacturing integrated circuits.
Electrical Properties and Material Classes
- Metals conduct electricity well and are used in wires (e.g., gold, copper).
- Semiconductors conduct electricity only when voltage is applied and are used in transistors and diodes (e.g., silicon, gallium arsenide).
- Insulators do not conduct electricity and are used for dielectrics and substrates (e.g., rubber, glass, ceramics).
- Bandgap energy determines how easily electrons can move to the conduction band; metals have no gap, insulators have a wide gap.
Key Semiconductor Materials and Alloys
- Silicon is the most common semiconductor (Eg = 1.1 eV).
- Germanium has higher conductivity than silicon (Eg = 0.7 eV).
- Silicon-Germanium alloys are used for high-speed, low-power devices.
- Silicon-carbide is used in high-power, high-temperature devices (Eg = 2.2 eV).
- Gallium-arsenide and gallium-nitride are used in LEDs and high-speed devices.
- Indium-phosphide is used in broadband lasers and optoelectronics.
Fabrication and Processing Techniques
- Photolithography uses light, and e-beam lithography uses electrons to pattern wafer surfaces.
- E-beam deposition and chemical vapor deposition deposit or grow thin films on wafers.
- Wet etching uses liquid chemicals for material removal; dry etching uses plasma for precision.
- Microscopy: Optical for quick overview, electron for high resolution, atomic force for surface mapping.
Physical Concepts
- Electrical conductivity measures the ability for electrons to move through a material.
- Thermal conductivity measures how easily heat spreads from hot to cold areas.
- Heat capacity is the amount of energy required to change a material's temperature.
- Black body radiation is emitted by objects due to temperature, mostly in the infrared.
- Gibbs free energy describes how systems evolve to minimize total energy (G = H - TS).
Device and Component Structure
- Front-end processing creates transistors; back-end connects them with wires.
- Wafer sizes vary and are standardized (e.g., 3, 4, 5, 6, 8-inch diameters).
- SiO2 substrates provide insulation; mask patterning defines circuit layout.
Key Terms & Definitions
- Bandgap energy — Energy needed to move an electron to the conduction band.
- Dielectric — Material that insulates and stores electric charge.
- Gibbs free energy — Measure of usable energy; G = H - TS.
- Photon — Quantum of light energy.
- Phonon — Quantum of vibrational energy.
- Fluxon — Quantized magnetic flux in superconductors.
- Octet Rule — Atoms are stable with eight valence electrons.
- Valence electron — Electron in the outer shell, important for bonding.
- Hole — Absence of an electron, behaves as a positive charge carrier.
Action Items / Next Steps
- Review definitions and material properties for common semiconductors and related materials.
- Practice differentiating between crystalline, poly-crystalline, and amorphous structures.
- Study the main fabrication processes and their purposes in microchip production.