Navy Electricity and Electronics Training Series - Historic Naval ...

Q21. Describe the preparation of a silicon substrate.FABRICATION OF IC DEVICESFabrication of monolithic ICs is the most complex aspect of microelectronic devices we will discuss.Therefore, in this introductory module, we will try to simplify this process as much as possible. Eventhough the discussion is very basic, the intent is still to increase your appreciation of the progress inmicroelectronics. You should, as a result of this discussion, come to realize that advances inmanufacturing techniques are so rapid that staying abreast of them is extremely difficult.Monolithic Fabrication.Two types of monolithic fabrication will be discussed. These are the DIFFUSION METHOD and theEPITAXIAL METHOD.DIFFUSION METHOD.—The DIFFUSION process begins with the highly polished silicon waferbeing placed in an oven (figure 1-11). The oven contains a concentration impurity made up of impurityatoms which yield the desired electrical characteristics. The concentration of impurity atoms is diffusedinto the wafer and is controlled by controlling the temperature of the oven and the time that the siliconwafer is allowed to remain in the oven. This is called DOPING. When the wafer has been uniformlydoped, the fabrication of semiconductor devices may begin. Several hundred circuits are producedsimultaneously on the wafer.Figure 1-11.—Wafers in a diffusion oven.The steps in the fabrication process described here, and illustrated in figure 1-12, would produce annpn, planar-diffused transistor. But, with slight variations, the technique may also be applied to theproduction of a complete circuit, including diodes, resistors, and capacitors. The steps are performed inthe following order:1-12