Overview

The semiconductor industry had a phenomenal growth in the past 25 years. It is a $150 billion dollar industry, and because of its tremendous growth, it is also facing several environmental issues. Semiconductor manufacturing can be grouped broadly into three categories: (1) Silicon crystal wafer growth and preparation, (2) semiconductor or wafer fabrication, and (3) final assembly and packaging. The semiconductor fabrication processes are always performed in a clean room and include the following steps: oxidation, lithography, etching, doping (through processes such as vapor phase deposition and ion implantation), and layering (through processes such as metallization). Figures 14-1 to 14-3 provide a flowsheet of the entire process.

Silicon in the form of ingots is grown from seed crystals. Ingots are shaped into wafers through a series of cutting and grinding steps. The ends of the silicon ingots are removed, and individual wafers are cut from the ingot. The wafer is then polished using an aluminum oxide-glycerine solution. Further polishing is done using a slurry of silicon dioxide particles suspended in sodium hydroxide. Contaminants from the wafer are cleaned by either using a spray or immersing the wafers in acids, bases, or organic solvents.

To create the desired electronic components like transistors and resistors, impurities or dopants are introduced into the wafer to change the conductivity of the silicon. Deposition of thin films onto the silicon wafer substrate involves chemical vapor deposition, sputtering (electric deposition of a metal onto the substrate under conditions of high vacuum), and oxidation. The raw...