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With the rapid advances of deep submicron semiconductor technology, identifying defects is converted into a challenge for different modules in the fabrication of chips. Yield engineers often do bitmap on a memory circuit array (SRAM) to identify the failure bits. This is followed by a wafer stripback to look for visual defects at each deprocessed layer for feedback to the Fab. However, to identify the root cause of a problem, Fab engineers must be able to detect similar defects either on the product wafers in process or some short loop test wafers. In the photolithography process, we recognize that the detection of defects is becoming as important as satisfying the critical dimension (CD) of the device. For a multi-level metallization chemically mechanical polish backend process, it is very difficult to detect missing contacts or via at the masking steps due to metal grain roughness, film color variation and/or previous layer defects. Often, photolithography engineer must depend on Photo Cell Monitor (PCM) and short loop experiments for controlling baseline defects and improvement. In this paper, we discuss the findings on the Poly mask PCM and the Contact mask PCM. We present the comparison between the Poly mask and the Contact mask of the I-line Phase Shifted Via mask and DUV mask process for a 0.18 micron process technology. The correlation and the different type of defects between the Contact PCM and the Poly Mask are discussed. The Contact PCM was found to be more sensitive and correlated to contact failure at sort yield better. We also dedicate to study the root cause of a single closed contact hole in the Contact mask short loop experiment for a 0.18 micron process technology. A single closed contact defect was often caused by the developer process, such as bubbles in the line, resist residue left behind, and the rinse mechanism. We also found surfactant solution helps to improve the surface tension of the wafer for the developer process and this prevents/eliminates a single closed contact hole defects. The applications and effects of using different substrates like SiON, different thicknesses of Oxides, and Poly in the Contact Photo Mask is shown. Finally, some defect troubleshooting techniques and the root cause analysis are also discussed.
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