Process Monitoring

In order for semiconductor processes to repeatably produce reliable, high-quality devices and circuits, each unit process must be strictly controlled. Many diagnostic tools are used to maintain systematic control. Such control requires that the key output variables for each process step (i.e., those that are correlated with product functionality and performance) be carefully monitored. Process monitoring enables operators and engineers to detect problems early on to minimize their impact. The economic benefit of effective monitoring systems increases with the complexity of the manufacturing process. Manufacturing line monitors consist of extremely sophisticated metrology equipment which can be divided into tools which characterize the state of features on the semiconductor wafers themselves and those which describe the status of the fabrication equipment operating on those wafers. The issues involved in understanding and implementing both wafer state and equipment state measurements will be discussed in detail in this chapter.