Polishing the Wafer Smooth

Before the real work begins, one side of each wafer must be polished absolutely smooth. These wafers will be so smooth after they're finished that you couldn't detect any imperfections on the surface even with a microscope. The process is called chemical-mechanical polishing (CMP). As the name implies, it involves bathing the wafers in special abrasive chemicals and gently grinding any imperfections away.

The wafers need to be smooth and flat because the features that will be projected onto them in the chip “darkroom” are extremely small and close together. In photography, it's important to keep the print lying flat as it develops because any warping or bending will throw the picture out of focus. Each part of the print must be the same distance from the projecting lens, and the principle is the same for chip making. Any variations in the surface of the silicon wafer will make the chip design out of focus, possibly causing shorts and other faults.