tailieunhanh - Giáo trình môn học công nghệ vi điện tử 7

Mọi quá trình công nghệ chế tạo mạch tổ hợp được tiến hành trong phòng sạch. Đó là nơi con người cần phải xử lý các thông số môi trường như nhiệt độ, độ ẩm và lưu thông khí sao cho số hạt bụi có trong một đơn vị thể tích là nhỏ hơn rất nhiều so với môi trường bình thường. | DIFFUSION. Diffusion in the sense of an IC processing step refers to the controlled forced migration of impurities into the substrate or adjacent material. The resultant impurity profile which plays a major role in the performance of the integrated circuit is affected by temperature and time as well as the temperature-time relationship during processing. Subsequent diffusions generally cause some additional migration of earlier diffusions. Actually the diffusion process continues indefinitely but at normal operating temperatures of the integrated circuit it takes tens of years or longer for the additional movement to become significant. The method by which the impurities arc introduced varies. A solid deposition layer or a gaseous layer above the surface can be used as the source of impurities. Impurities can also be accelerated to selectively bombard the substrate so that they actually become lodged inside the substrate very near the surface. This technique termed ion implantation offers very accurate control of impurity concentrations but causes significant crystal damage near the surface. The purpose of a diffusion following deposition is to cause a migration of carriers into the substrate from either solid or gaseous surface layers. A diffusion step following ion implantation is used to mend or anneal bombardment-induced fractures in the single crystalline structure at the surface of the subsưate as well as to cause additional impurity migration. As in the etching process the direction of impurity diffusion is difficult to control with accuracy. Impurities typically diffuse both vertically and laterally from the surface at comparable rates in a manner similar to that observed for the isotropic etch of Fig. -2a. f CONDUCTORS AND RESISTORS. Aluminum or other metals arc often used as conductors for interconnection of components on an integrated circuit These metals are typically deposited patterned and etched to leave interconnects where desired. The thickness