MECHANICAL MILLING AND POLISHING OF CROSS SECTIONS USING A MICRO CNC MACHINE FOR FAILURE ANALYSIS

摘要

Time is of the essence when supporting qualification milestones in a manufacturing environment and failure analysis plays a critical role in understanding the root cause of fails. In semiconductor failure analysis, especially in the case of packaged flip chip devices, a number of various tools and techniques are available to the analyst to isolate, prepare, and image the root cause of fails, depending on the nature and location of the defect. Focused ion beam techniques are effective for cross-section sample preparation over micron squared sized areas, but fall short because large delamination, multiple defects over a large distance, and large metallic puddling cannot be exposed by a single cross section. Rather, mechanical cross-sectioning by manual parallel lapping is a more appropriate method, especially when large areas of the cross-section must be exposed and analyzed. The main drawback with manual parallel lapping is that, inevitably, artifacts are induced in the sample, whose populations, severity, frequency of occurrence are contingent for a large part on the skill of the analyst. Owing to this, the finished surface of a polished mechanical cross-section can greatly vary depending on the operator preparing the sample. Micro CNC polishing tools have long been implemented in failure analysis labs for milling and polishing of planar surfaces such as for package decapuslation, and silicon thinning and polishing. In this work, by using CNC milling to perform parallel lapping of mechanical cross-sections, we have achieved an artifact-free cross-section with a uniform profile across the length of the sample. This is the first reported demonstration of leveraging micro CNC milling for mechanically cross-sectioning semiconductor packaged samples.