Iraj Emami

Development Of An Optimal Sampling Strategy For Wafer Inspection

This paper presents a methodology for the development of an optimal sampling strategy for defect inspection, which is crucial for yield management of state-of-the-art technologies. This requires understanding of the defect-yield relationship and yield reducing process drift models. Further, the sampling plan is based on the trade-offs between the costs of sampling and of defective dies. Our methodology is demonstrated using data from different fabs.

Value-Added Metrology

The conventional premise, long-touted among the semiconductor processing community, that metrology is a ldquonon-value-added necessary evil,rdquo is a misleading and dangerous assertion, which must be viewed as obsolete thinking. Many metrology applications are key enablers to traditionally labeled ldquovalue-addedrdquo processing steps in lithography and etch, such that they can be considered integral parts of the processes. Various key trends in modern, state-of-the-art processing such as optical proximity correction, design for manufacturability, and advanced process control are based, at their hearts, on the assumption of fine-tuned metrology, in terms of uncertainty and accuracy. These trends are vehicles where metrology thus has large opportunities to create value through the engineering of tight and targetable process distributions. Such distributions make possible predictability in speed-sorts and in other parameters, which results in a high-end product. Additionally, significant reliance has also been placed on defect metrology to predict, improve, and reduce yield variability. The necessary quality metrology is strongly influenced by not only the choice of equipment, but also the quality application of these tools in a production environment. The ultimate value added by metrology is a result of quality tools run by a quality metrology team using quality practices. This paper will explore the relationships among present and future trends and challenges in metrology, including equipment, key applications, and metrology deployment in the manufacturing flow. Of key importance are metrology personnel, with their expertise, practices, and metrics in achieving and maintaining the required level of metrology performance, including where precision, matching, and accuracy fit into these considerations. The value of metrology will be demonstrated to have shifted to being a ldquokey enabler of large revenues,rdquo debunking the out-of-date premise that metrology is ldquonon-value-added.rdquo

Combined use of x-ray reflectometry and spectroscopic ellipsometry for characterization of thin film optical properties

Accurate characterization of the optical properties of thin film materials used in semiconductor manufacturing is essential for many metrology applications in the fab, including film thickness measurement and scatterometry. The most common method for measuring these optical properties is spectroscopic ellipsometry. In this work X-ray reflectometry is used as a means of independently determining the thickness of a film to be characterized. This information is then used in the conventional analysis of spectroscopic ellipsometry data to extract the optical properties. In addition, the use of a Cauchy dispersion model fitted to the transparent region of the spectrum (if it exists) was used to determine the film thickness. Once the thickness was determined, a point-by-point regression was performed on the ellipsometry data to extract the optical properties. The results from these techniques were compared with each other and with conventional analysis of the ellipsometry data using common dispersion models.

Intentional defect array wafers: their practical use in semiconductor control and monitoring systems

In the competitive world of semiconductor manufacturing today, control of the process and manufacturing equipment is paramount to success of the business. Consistent with the need for rapid development of process technology, is a need for development wiht respect to equipment control including defect metrology tools. Historical control methods for defect metrology tools included a raw count of defects detected on a characterized production or test wafer with little or not regard to the attributes of the detected defects. Over time, these characterized wafers degrade with multiple passes on the tools and handling requiring the tool owner to create and characterize new samples periodically. With the complex engineering software analysis systems used today, there is a strong reliance on the accuracy of defect size, location, and classification in order to provide the best value when correlating the in line to sort type of data. Intentional Defect Array (IDA) wafers were designed and manufacturered at International Sematech (ISMT) in Austin, Texas and is a product of collaboration between ISMT member companies and suppliers of advanced defect inspection equipment. These wafers provide the use with known defect types and sizes in predetermined locations across the entire wafer. The wafers are designed to incorporate several desired flows and use critical dimensions consistent with current and future technology nodes. This paper briefly describes the design of the IDA wafer and details many practical applications in the control of advanced defect inspection equipment.

Effective multi-stage test equipment capacity allocation for semiconductor fabrication yield enhancement

We formulate a multi-stage inspection planning model based on configurations in actual semiconductor fab-lines, specifically taking into account both the capacity constraint and the congestion effects at the inspection station. We propose a new mixed First-Come-First-Serve (FCFS) and Last-Come-First-Serve (LCFS) discipline for serving the inspection samples to expedite the detection of potential yield problems. Employing this mixed FCFS and LCFS discipline, we derive approximate expressions for the queueing delays in yield problem detection time and develop near-optimal algorithms to obtain the inspection logistics planning policies.