
ALD原子层沉积技术的前驱体工艺及材料.ppt
22页NANO-MASTER, INC.,NANO-MASTER ALD 原子层沉积 前驱体、工艺和材料,吴运祥2017年7月25日,,NANO-MASTER, INC.,概述,New ALD processes and materials are being actively developed at several Universities. ALD was demonstrated for the TFEL application for the first time by ZnS deposition using elemental zinc and sulfur in the mid-1970s, followed by the use of ZnCl2 and H2S. After the initial period, several other inorganic precursor types have emerged. During the second half of the 1980s metal organic precursor chemicals were adapted for ALD material research. This opened up plenty of possibilities for new ALD chemistries and processes. A large number of ALD processes have been demonstrated and published to date, and the list keeps growing (Below Table).,,NANO-MASTER, INC.,概述 Table:ALD沉积材料举例,,NANO-MASTER, INC.,ALD前驱体概述,General ALD precursor requirements differ from other chemical gas-phase methods since all gas-phase reactions should be excluded and reactions take place only at the surface. Although chemical vapor deposition (CVD) precursors can sometimes be used for ALD, nowadays specific precursors have been synthesized for ALD because this deposition technique allows the use of significantly more reactive precursors than CVD. In the ALD method, in order to avoid uncontrolled reactions, sufficient thermal stability of the precursors is needed in the gas phase as well as on the substrate surface within the deposition temperature range, which is typically 150–500◦C,,NANO-MASTER, INC.,ALD前驱体概述,Since ALD relies on self-limiting reactions, a sufficient amount of the precursor is only required during one pulse to cover the adsorption sites on the surface and the excess will be purged by the inert gas between the reactive precursors. Because ALD is a gas-phase process, solid and liquid precursors must be volatile under the operating temperature and pressure, and if heating is required to obtain sufficient vapor pressure, thermal stability of the precursor over a prolonged period is necessary. Stability is key issue, especially when stable industrial processes are designed.,,NANO-MASTER, INC.,ALD前驱体概述,In summary, there are some general requirements for ALD precursors, which include: sufficient volatility at the deposition temperature no self-decomposition allowed at the deposition temperature precursors must adsorb or react with the surface sites sufficient reactivity towards the other precursor, e.g. H2O no etching of the substrate or the growing film availability at a reasonable price safe handling and preferably non-toxicity.,,NANO-MASTER, INC.,非金属前驱体,Because of the sequential nature of ALD, metal and non-metal precursors are typically separated from each other. The ability to select an oxidizing or reducing precursor in conventional ALD processes makes it possible to control reactivity and reactions of the metal precursor.In a non-oxidizing regime, reducing the precursor is also necessary for depositing elemental metal films. Hydrogen is perhaps the most widely used reducing agent, but metallic zinc vapor, silanes, and B2H6 have also been successfully applied. Molecular hydrogen is quite inert towards typical metal precursors and therefore quite high deposition temperatures are needed to maintain ALD reactions.,,NANO-MASTER, INC.,非金属前驱体,Deposition of nitride thin films by ALD requires both a nitrogen source and a reducing agent in order to obtain clean surface reactions. In many cases one compound, e.g. NH3, serves as both nitrogen source and reducing agent. Ammonia has been used for depositing, for example, TiN, Ta3N5,W2N, NbN, and WCN thin films by ALD, although its reactivity at low temperatures is limited. Other nitrogen-containing compounds, such as (CH3)NNH2,tBuNH2,and CH2CHCH2NH, have also been studied.,,NANO-MASTER, INC.,非金属前驱体,For chalcogenide thin films it is possible to use elemental S, Se, and Te as precursors provided that the other source is a volatile and reactive metal. The first ALD process to be developed was ZnS deposition using elemental zinc and sulfur. For other precursor types, including halides, β-diketonates, and organometallics, simple hydrides, such as H2S, H2Se, and H2Te, have typically been used as a second precursor, although their toxicity must be carefully addressed. Recently, novel Se and Te precursors have been utilized for ALD, enabling the deposition of selenides and tellurides.,,NANO-MASTER, INC.,非金属前驱体,Typically in the case of ALD-processed oxide films, precursors attached to the surface can be oxidized with H2O, H2O2,N2O4,N2O,O2,orO3, the choice dependent on the metal precursor selected. Water has frequently been used as an oxygen source and indeed it readily reacts with many metal halides, alkyls, and alkoxides. For metal β-diketonate-type compounds, only ozone or oxygen plasma can be used owing to the higher thermal stability of the precursor. The use of a strong oxidizer guarantees that only a small amount of carbon is left in the film, as well as ensuring better interface quality.,,NANO-MASTER, INC.,。












