INTEGRATED CIRCUITS Dr. Esam Yosry Lec. #5

Epitaxial Growth Introduction Epitaxy Deposition Chemical Vapor Deposition (CVD) Physical Vapor Deposition (PVD) Molecular Beam Epitaxy (MBE) Metal Deposition Manufacturing Methods CVD and PVD Epitaxial Growth

Introduction (Chip Fabrication Cycle)

Introduction (Processes) Oxidation Diffusion Ion Implantation Deposition Etching Lithography Deposition Removal Patterning Modification of electrical properties Introduction (Processes)

Epitaxy Epitaxy is the process of growing a crystalline layer of a material on top of a crystalline substrate . Epitaxial means arranged upon (epi). The epi silicon layer is usually of different doping. Single crystal of Si over crystalline Si substrate Epi layer can be doped independent of substrate

Epitaxy Necessary if buried layers are needed Needed to form isolation islands in bipolar Grown by CVD or MBE An epitaxial layer can be doped during deposition by adding impurities to the source gas. The concentration of impurity in the gas determines its concentration in the deposited film

Epitaxy

Selective Epitaxial Growth (SEG) Nucleation rate: Si > Si3N4 > SiO2 Used for device isolation

Deposition Depositing a material onto a substrate or onto previously deposited layers. Thin-film deposition: layer thickness within a few tens of nanometres. Molecular Beam Epitaxy (MBE): allows a single layer of atoms to be deposited at a time. (layers of insulators, semiconductors, conductors) Deposition techniques: Chemical or Physical

Chemical Deposition Chemical change at a solid surface, leaving a solid layer. Chemical Vapor Deposition (CVD): uses a gas-phase, often a halide or hydride of the element to be deposited.

Physical Deposition Uses mechanical, electromechanical or thermodynamic means to produce a thin film of solid. Molecular Beam Epitaxy (MBE) :slow streams of an element can be directed at the substrate, so that material deposits one atomic layer at a time.

Chemical Vapor Deposition (CVD) CVD is a chemical process used to produce high-purity, high-performance solid materials Needs a CVD reactor at around 1000o C Typical Si sources: *silicon tetrachloride SiCl4 (STC) *silane SiH4

Chemical Vapor Deposition (CVD)

Chemical Vapor Deposition (CVD) Process: 1. Wafers are on a heated substrate holder. 2. Process gases are flowed into the system. 3. Chemical reaction occurs at the wafer surface. Hot wafer surface accelerates the reaction. 4. Solid material which deposits on the wafer. CVD used to deposit materials in: monocrystalline, polycrystalline, amorphous, and epitaxial (single crystal)

Chemical Vapor Deposition (CVD) Commercially materials prepared by CVD Polysilicon: SiH4  Si + 2H2 (low T) (single crystal) Si Dioxide: SiH4+O2  SiO2+2H2 (amorphous) Si Nitride: SiH4+4NH3  Si3N4+12H2 Silicon nitride is often used as an insulator and chemical barrier in manufacturing ICs

Chemical Vapor Deposition (CVD) Types Classified by operating pressure: Atmospheric pressure CVD (APCVD). Low-pressure CVD (LPCVD) – CVD at sub-atmospheric pressure. Reduced pressures tend to reduce unwanted gas-phase reactions and improve film uniformity across the wafer. Ultrahigh vacuum CVD (UHVCVD) – CVD at very low pressure.

Physical Vapor Deposition (PVD) Describes a variety of vacuum deposition methods used to deposit thin films by a vaporized form of the desired film material onto wafers. These methods are purely physical processes such as high-temperature vacuum evaporation with subsequent condensation, or plasma sputter bombardment rather than a chemical reaction at the surface as in chemical vapor deposition.

PVD Process

Physical Vapor Deposition (PVD)

Physical Vapor Deposition (PVD) Bell Jar Physical Vapor Deposition (PVD) Mostly line-of-sight since low pressure. Deposition rate is determined by emitted flux and by geometry of target.

Molecular Beam Epitaxy (MBE) Thermal evaporation is used instead of CVD Evaporation in Ultra High Vacuum (10-10 Torr) “molecular beam” since the UHV pressure causes a pure beam of molecules incident on the substrate Multiple material sources are used to make doping Low temperature process Precise doping control

Molecular Beam Epitaxy (MBE) Suitable for heteroepitaxy (layers of compounds) Doping during deposition or after Expensive equipment (compared to reactors) Atomically smooth interface Can use low deposition rate

CVD and PVD Isotropic arrival angle High pressure Chemical reaction Vertical arrival angle Low pressure No chemical reaction

Metal Deposition

Metal Deposition evaporation Metal evaporation can’t ensure metal continuity for large contact window aspect ratio (shadowing effect and step coverage problems) CVD can fill a contact window more efficiently (this is called a plug process) CVD plug Incomplete fill

Aluminum Deposition To obtain a thin-uniform coating of aluminum, one must spray or evaporate it from a liquid form. Aluminum melts at 600°C but will not evaporate at atmospheric pressure (Low pressure is required). Evaporation must be in a non-oxidizing ambient to prevent formation of Al2O3 and keep s low. Deposition could be done by sputtering, chemical vapor deposition, or evaporation. We choose Evaporation because it is simple.

Manufacturing Methods

Thanks Many thanks to Prof. Hany Fikry and Prof Wael Fikry for their useful materials that help me to prepare this presentation.