The mask house will hold the mask-build request until corrected. It is important to prevent these errors before they create wasted engineering and failure-analysis effort. Pattern-density requirements are one subset of the design rules requiring specialized checking. These are specified at design levels associated with wafer-etch processes where the ratio of area etched to area not etched can greatly affect the etching results. Pattern-density rules are often violated because they cannot be verified until late in the design cycle, when the physical design is nearly complete.
Typical violations have density values below the minimum requirement.
To correct this error, fill shapes must be added to the physical design to bring the density into compliance. Gross violations of pattern-density rules would result in incomplete etching in manufacturing. Many IBM technologies require that metal wiring and CMOS gates be connected back to the wafer substrate through a diode or substrate contact. These rules are intended to help prevent the buildup of charge during wafer processing, which could result in damaged gates or metal wiring. Allowing floating-gate errors can lead to yield loss or to CMOS device parameter degradation over time.