Shared by: qfc86623
Thin-film deposition •Thin-film deposition is any technique for depositing a thin film (about 1 mm) of material onto a substrate or onto previously deposited layers. •"Thin" is a relative term, but most deposition techniques allow layer thickness to be controlled within a few tens of nanometers, and some (molecular beam epitaxy) allow one layer of atoms to be deposited at a time. Critical radius •Critical radius is the minimum size that must be formed by atoms clustering together in the liquid before the solid particle is stable and begins to grow •The total free energy is the sum of surface energy and bulk energy. •The critical energy can be obtained by taking the derivation to the total free energy. 4 3 Δ G 4πr γ πr Gv 2 3 d ΔG Let 0 dr 2γ We have r* - Gv PVD (Physical vapor deposition) • Physical vapor deposition (PVD) is a group of vacuum coating techniques used to deposit thin films of various materials onto various surfaces. • Two technologies are often used: (1) Evaporator: - Thermal evaporator: Material is heated to attain gaseous state. - Electron beam evaporator (2) Sputtering: - Carried out under high-vacuum conditions (~5x10-7 torr) - Plasma as the particle source to strike the target Physical Vapor Deposition (continued): • Advantages: • 1. films can be deposited at high rates (e.g., 0.5 mm/min) • 2. low energy atoms (~0.1 eV) leave little surface damage • 3. little residual gas and impurity incorporation due to high-vacuum conditions • 4. no substrate heating Limitations: • 1. accurately controlled alloy compounds are difficult to achieve • 2. no in situ substrate cleaning • 3. poor step coverage • 4. variation of deposit thickness for large/multiple substrates • 5. x-ray damage •Thermal evaporator uses an electric resistance heater to melt the material and raise its vapor pressure to a useful range. This is done in a high vacuum, both to allow the vapor to reach the substrate •An electron beam evaporator fires a high-energy beam from an electron gun to boil a small spot of material. Sputtering (濺 鍍) •Sputtering is a physical process whereby atoms in a solid target material are ejected into the gas phase due to bombardment of the material by energetic ions. •The ions for the sputtering process are supplied by a plasma that is induced in the sputtering equipment. •Sputtering relies on a plasma (usually a noble gas, such as Argon) to knock material from a "target" a few atoms at a time. Sputtering Yield sputtered atoms Mm Em S bombing ions M m 2 U M M : mass of target atom m : mass of bombing ion Em : kinetic energy of bombing ion U M : Bonding energy of target metal : striking angle A magnetron sputter gun CVD •Chemical vapor deposition (CVD) is a chemical process often used in the semiconductor industry for the deposition of thin films of various materials. Process of CVD • Vaporization and Transport of Precursor Molecules into Reactor • Diffusion of Precursor Molecules to Surface • Adsorption of Precursor Molecules to Surface • Decomposition of Precursor Molecules on Surface and Incorporation into Solid Films • Recombination of Molecular Byproducts and Desorption into Gas Phase Types of Chemical Vapor Deposition •Atmospheric pressure chemical vapor deposition (APCVD) •Low pressure chemical vapor deposition (LPCVD) •Plasma assisted (enhanced) chemical vapor deposition (PACVD, PECVD) APCVD •Atmospheric pressure chemical vapor deposition •Operate at 1 atm. •Fast deposition rate •Continuous •May subject to particle contamination. LPCVD •Low Pressure Chemical Vapor Deposition (LPCVD) is a technique in which one or more gaseous reactors are used to form a solid insulating or conducting layer on the surface of a wafer under low pressure and high temperature conditions. PECVD •Plasma Enhanced Chemical Vapor Deposition (PECVD) is a technique in which one or more gaseous reactors are used to form a solid insulating or conducting layer on the surface of a wafer enhanced by the use of a vapor containing electrically charged particles or plasma, at lower temperatures.