Just enough die-level test: optimizing ic test via machine learning and decision theory
approved: Thomas G. Dietterich This research explores the hypothesis that methods from decision theory and machine learning can be combined to provide practical solutions to current manufacturing control problems. This hypothesis is explored by developing an integrated approach to solving one manufacturing problem the optimization of die-level functional test. An integrated circuit (IC) is an electronic circuit in which a number of devices are fabricated and interconnected on a single chip of semiconductor material. According to current manufacturing practice, integrated circuits are produced en masse in the form of processed silicon wafers. While still in wafer form the ICs are referred to as dice, an individual IC is called a die. The process of cutting the dice from wafers and embedding them into mountable containers is called packaging. During the manufacturing process the dice undergo a number of tests. One type of test is die-level functional test (DLFT). The conventional approach is to perform DLFT on all dice. An alternative to exhaustive die-level testing is selective testing. With this approach only a sample of the dice on each wafer is tested. Determining which dice to test and which to package is referred to as the "optimal test problem", and this problem provides the application focus for this research. Redacted for Privacy In this study, the optimal test problem is formulated as a partially observable Markov decision model that is evaluated in real time to provide answers to test questions such as which dice to test, which dice to package, and when to stop testing. Principles from decision theory (expected utility, value of information) are employed to generate tractable decision models, and machine learning techniques (Expectation Maximization, Gibbs Sampling) are employed to acquire the real-valued parameters of these models. Several problem formulations are explored and empirical tests are performed on historical test data from Hewlett-Packard Company. There are two significant results: (1) the selective test approach produces an expected net profit in manufacturing costs as compared to the current testing policy, and (2) the selective test approach greatly reduces the amount of testing performed while maintaining an appropriate level of performance monitoring. Just Enough Die-Level Test: Optimizing IC Test via Machine Learning and Decision Theory by Tony R. Fountain A THESIS submitted to Oregon State University in partial fulfillment of the requirements for the degree of Doctor of Philosophy Presented August 21, 1998 Commencement June 1999 Doctor of Philosophy thesis of Tony R. Fountain presented on August 21, 1998