精选优质文档-----倾情为你奉上A number of forms of CVD are in wide use and are frequently referenced in the literature. These processes differ in the means by which chemical reactions are initiated (e.g., activation process) and process conditions.· Classified by operating pressure: o Atmospheric pressure CVD (APCVD) – CVD processes at atmospheric pressure.o Low-pressure CVD (LPCVD) – CVD processes at subatmospheric pressures. Reduced pressures tend to reduce unwanted gas-phase reactions and improve film uniformity across the wafer. Most modern CVD processes are either LPCVD or UHVCVD.o Ultrahigh vacuum CVD (UHVCVD) – CVD processes at a very low pressure, typically below 10−6 (~10−8 ). Note that in other fields, a lower division between high and is common, often 10−7 Pa.· Classified by physical characteristics of vapor: o Aerosol assisted CVD (AACVD) – A CVD process in which the precursors are transported to the substrate by means of a liquid/gas aerosol, which can be generated ultrasonically. This technique is suitable for use with non-volatile precursors.o Direct liquid injection CVD (DLICVD) – A CVD process in which the precursors are in liquid form (liquid or solid dissolved in a convenient solvent). Liquid solutions are injected in a vaporization chamber towards injectors (typically car injectors). Then the precursor vapors are transported to the substrate as in classical CVD process. This technique is suitable for use on liquid or solid precursors. High growth rates can be reached using this technique.· Plasma methods (see also ): o Microwave plasma-assisted CVD (MPCVD)o (PECVD) – CVD processes that utilize to enhance chemical reaction rates of the precursors. PECVD processing allows deposition at lower temperatures, which is often critical in the manufacture of semiconductors.o Remote plasma-enhanced CVD (RPECVD) – Similar to PECVD except that the wafer substrate is not directly in the plasma discharge region. Removing the wafer from the plasma region allows processing temperatures down to room temperature.· Atomic layer CVD () – Deposits successive layers of different substances to produce layered, films. See .· (CCVD) – nGimat's proprietary Combustion Chemical Vapor Deposition process is an open-atmosphere, flame-based technique for depositing high-quality thin films and nanomaterials.· Hot wire CVD (HWCVD) – also known as catalytic CVD (Cat-CVD) or hot filament CVD (HFCVD). Uses a hot filament to chemically decompose the source gases.· (MOCVD) – CVD processes based on precursors.· (HPCVD) – Vapor deposition processes that involve both chemical decomposition of precursor gas and of a solid source.· Rapid thermal CVD (RTCVD) – CVD processes that use heating lamps or other methods to rapidly heat the wafer substrate. Heating only the substrate rather than the gas or chamber walls helps reduce unwanted gas phase reactions that can lead to formation.· Vapor phase epitaxy (VPE)UsesIntegrated circuitsVarious CVD processes are used for (ICs). Particular materials are deposited best under particular conditions.PolysiliconPolycrystalline silicon is deposited from (SiH4), using the following reaction:SiH4 → Si + 2 H2This reaction is usually performed in LPCVD systems, with either pure silane feedstock, or a solution of silane with 70–80% . Temperatures between 600 and 650 °C and pressures between 25 and 150 Pa yield a growth rate between 10 and 20 per minute. An alternative process uses a -based solution. The hydrogen reduces the growth rate, but the temperature is raised to 850 or even 1050 °C to compensate.Polysilicon may be grown directly with doping, if gases such as , or are added to the CVD chamber. Diborane increases the growth rate, but arsine and phosphine decrease it.Silicon dioxideSilicon dioxide (usually called simply "oxide" in the semiconductor industry) may be deposited by several different processes. Common source gases include and , (SiCl2H2) and (N2O), or (TEOS; Si(OC2H5)4). The reactions are as follows[]:SiH4 + O2 → SiO2 + 2 H2SiCl2H2 + 2 N2O → SiO2 + 2 N2 + 2 HClSi(OC2H5)4 → SiO2 + byproductsThe choice of source gas depends on the thermal stability of the substrate; for instance, is sensitive to high temperature. Silane deposits between 300 and 500 °C, dichlorosilane at around 900 °C, and TEOS between 650 and 750 °C, resulting in a layer of low- temperature oxide (LTO). However, silane produces a lower-quality oxide than the other methods (lower , for instance), and it deposits non. Any of these reactions may be used in LPCVD, but the silane reaction is also done in APCVD. CVD oxide invariably has lower quality than , but thermal oxidation can only be used in the earliest stages of IC manufacturing.Oxide may also be grown with impurities ( or ""). This may have two purposes. During further process steps that occur at high temperature, the impurities may from the oxide into adjacent layers (most notably silicon) a。