In this paper we discuss the detection, investigation and remediation of a silicon pitting defect in gate oxide patterning processes. The pitting defect is detected by optical inspection after an oxide wet etch operation. The cause of the physical defect is discovered as the result of Non-Visual Defect (NVD) inspection at process steps prior to the wet etch. A particular type of NVD, electric charge on a photoresist film, is detected at a process step immediately prior to the wet etch. A positive charge exceeding a specific level is highly correlated with the pitting defect, which only occurred on silicon that is doped to create an excess of free holes (p-type silicon). The manufacturing process is modified to reduce the level of process-induced charge, which also reduces the occurrence of pitting defects. A similar pitting defect is subsequently detected on a second manufacturing line at a different technology node. In this case, our investigation reveals that high negative charge on photoresist resulted in pitting only on silicon that is doped to create an excess of electrons (n-type silicon). Finite element modeling is used to identify a possible explanation for the charge-induced pitting defect.

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The monitoring and optimization of wet clean and surface preparation processes is a major challenge in the microelectronics industry [1, 2]. Today, the main methods used in clean rooms are visual inspection by light scattering (principally applied to particle detection) and metallic contamination detection by Total-reflection X-Ray Fluorescence (TXRF). These methods, despite good sensitivity and recent progress [3, 4] are not sufficient, especially considering non-visual defects not measurable by light scattering, nor TXRF due to their chemical nature or to their size and location (TXRF is not applicable to light elements – with Z < 11 – and is typically a 1 cm resolution tool, with 1 to 2 cm edge exclusion). Non-vibrating Surface Potential Difference Imaging (SPDI), introduced in 2005 under the name of ChemetriQ® is an in-line, non-contact, non-destructive inspection technique based on the imaging of surface Work Function (WF) lateral non-uniformities [5]. Recent studies show very promising results for SPDI: high sensitivity to traces of metals on Si wafers with native oxide [6]; fast imaging capabilities of unpatterned or patterned wafers with sensitivity to chemical residues and charge [7, 8]. In this work, the ChemetriQ method is evaluated for in-line control of wet clean processes. The variation of SPDI data from various contaminants is compared to intra- and inter-wafer variations related to the cleaning and measurement conditions. Note that all wafer maps are presented with the notch oriented at 6:00.

In the later half of 2000, display manufacturers will begin mass producing displays with resolutions from 150 to 200 pixels/in. These displays will have a color sub-pixel pitch of from 42 to 56 mm. For array inspection and test equipment, reduced pixel feature sizes and increased pixel counts will present new challenges in the areas of resolution, test time, and test coverage. The implications of these challenges for functional electrical testing will be discussed, and tradeoffs between test coverage and test time will be presented.