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Epitaxial Deposition. 1. Abu Syed Md. Jannatul Islam Lecturer, Dept. of EEE, KUET, BD. Department of Electrical and Electronic Engineering Khulna University of Engineering & Technology Khulna-9203. Epitaxy. 2. The term E pitaxy comes from the G reek word meaning ‘ordered upon’.
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Epitaxial Deposition 1 • Abu Syed Md. JannatulIslam • Lecturer, Dept. of EEE, KUET, BD • Department of Electrical and Electronic Engineering • Khulna University of Engineering & Technology • Khulna-9203
Epitaxy 2 • The term Epitaxy comes from the Greek word meaning ‘ordered upon’. • Epitaxy means the growth of a single crystal film on top of a crystalline substrate. • For most thin film applications (hard and soft coatings, optical coatings, protective coatings) it is of little importance. • However, for semiconductor thin film technology it is crucial.
Types of Epitaxy 3 • Homoepitaxy: • The film and the substrate are the same material. • Often used in Si on Si growth (A on A) • Epitaxiallygrown layers are purer than the substrate and can be doped independently of it. • Heteroepitaxy: • Film and substrate are different materials.(Growth of AlAson Si or GaAs on Si). • Trying to grow a layer of a different material on top of a substrate leads to unmatched lattice parameters. • This will cause strained or relaxed growth and can lead to interfacial defects. • Such deviations from normal would lead to changes in the electronic, optic, thermal and mechanical properties of the films. • Allows for optoelectronic structures and band gap engineered devices.
Epitaxial Growth 4 • High Quality Film (1μm or less thickness) deposited on a high quality substrate. • To ensure high crystalline quality, the lattice parameters of the thin layer should match with that of the substrate (to minimize strain). NOT epitaxial Ordered, crystalline growth Epitaxial growth
Why Epitaxial Growth 5 • While Si is not the ideal material from an electronic and optical point of view, its abundance, ease of processing and availability of a good native oxide have made it the backbone of semiconductor industry. • Combining Si substrates with compound semiconductor films would enable higher optoelectronic functionality and higher speeds.However, there are severe lattice mismatch and chemical compatibility issues between Si and most III-V alloys that preclude direct growth. • Metal-Semiconductor Hetero-epitaxy: Metal-semiconductor structures are used for contact applications. While not essential, epitaxial growth allows increased electron mobility through a junction. • Epitaxial growth is useful for applications that place stringent demands on a deposited layer: • High purity, Low defect density, Abrupt interfaces, Controlled doping profiles • High repeatability and uniformity, Safe, efficient operation • Can create clean, fresh surface for device fabrication
Why Epitaxial Growth 6 Engineered wafers Clean, flat layer on top of less ideal Si substrate On top of SOI structures Ex.: Silicon on sapphire Higher purity layer on lower quality substrate (SiC) In CMOS structures Layers of different doping Ex. p- layer on top of p+ substrate to avoid latch-up To make layer which is not available in nature Very important in III-V semiconductor production Bipolar Transistor (Needed to produce buried layer) III-V Devices (Interface quality key, Hetero-junction Bipolar Transistor, LED, Laser).
Epitaxial Growth Steps & Parameters 7 Steps: Absorption of ad atoms Surface diffusion Crystal growth Evaporation of adatoms Parameters: Growth temperature Growth pressure Flow amount of reactants Substrate and treatment
Epitaxial Deposition Techniques 9 Epitaxial growth can be performed at temperatures considerably below the melting point of the substrate crystal. A variety of methods are used to provide the appropriate atoms to the surface of the growing layer. Vapor Phase Epitaxy/Chemical vapor deposition (grown from Vapor) Liquid phase epitaxy (grown from a Melt) Molecular beam epitaxy (an evaporation of the elements in a Vacuum) With this wide range of epitaxial growth techniques, it is possible to grow a variety of crystals for device applications, having properties specifically designed for the electronic and optoelectronic device being made.
Epitaxial Deposition Techniques 10 Liquid Phase Epitaxy Reactants are dissolved in a molten solvent at high temperature Substrate dipped into solution while the temperature is held constant Example: SiGe on Si Bismuth used as solvent Temperature held at 800°C High quality layer Molecular Beam Epitaxy Very promising technique Beams created by evaporating solid source in UHV Not ideal for large area layers or abrupt interfaces Thermodynamic driving force relatively very low
Epitaxial Deposition Techniques 11 MOMBE---means when Metel Organic Source used for MBE Sputtering---the layer quality is very poor. Thus it is used for making contact with the help of metal related source. HVPE---Hydride Vapor Phase Epitaxy Pulse laser Deposition (PLD) Reactive Evaporation Electron Beam Plasma Technique Solvo thermal Method *Advantages, Disadvantages, and Applications of all these techniques are very much important. Please collect all the information……………….
