Productnews5300spring00

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Process Parametrics

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Oxide Etch Process Control Using a High Resolution Profiler by Kelly Barry, KLA-Tencor Corporation

Plasma etching is among the most critical steps in the fabrication of microelectronics devices. It is used in a variety of processes, including the manufacture of contacts and vias, shallow trench isolation, DRAM and dual damascene. A successful etch process must manage complex tradeoffs to optimize a number of parameters, including critical dimension uniformity (lateral and vertical), selectivity, and a high etch rate. Failure to do so will result in poor process control and device performance.

Of these etch process parameters, the largest barrier to consistent device performance is maintaining critical dimension uniformity. Currently, there are three ways to monitor etch depth. The most reliable, and hence most commonly used technique, is to crosssection the wafer and use scanning electron microscopy (SEM). This technique is undesirable since it requires the destruction of product wafers. In addition, it is time-consuming; a longer time to results means that more wafers will have gone through process prior to depth monitoring feedback, increasing the risk to these wafers. A high resolution profiler (HRP) such as the KLA-Tencor HRP-240ETCH has the capability of monitoring etch depths

in a repeatable, non-destructive manner with quick time-to-results. In this article, we present the results of a comparative study of oxide etch depth monitoring via SEM and HRP, in which the HRP demonstrates strong correlation to the SEM. Etch depth challenges

Etch depth monitoring is important in order to avoid poor electrical performance (under-etch) or underlying structural damage (over-etch). However, since plasma etching depends on the size and pattern density of the features comprising the array, measurements must be performed on the structures themselves and not on test structures.

F i g u re 1. The etched wa fer is broken in order to revea l t he contacts via SEM im aging. The depth measur ement of these contacts b y SEM was 1112. 5 nm.

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Spring 2000

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