Metrology targets are an essential tool for evaluating the performance of imaging systems and maintaining their accuracy over time. Ideally, the pattern on the target is simple enough that the expected image is intuitive or, at least, easily simulated. Although many such targets exist for frontside imaging, until recently, few if any could be found for backside applications. In this article, the first of a two-part series, the authors explain how they addressed this gap by converting a readily available frontside target for backside use. The conversion process is described step by step in enough detail that it can be replicated in order to convert other frontside targets. Due to the success of the converted target, an unmounted, backside-specific version has subsequently been developed, the availability of which not only eliminates one of the more difficult steps in the original conversion process, but also provides additional benefits. Using one of these newer targets, the authors evaluated a backside imaging system consisting of a laser scanning microscope (LSM) and a solid immersion lens (SIL). The results are presented here along with the criteria used for the evaluation. Other applications of the new metrology target as well as its limitations are discussed in the May 2015 issue of EDFA.

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