Surface Potential Difference Imaging Applied to Wet Clean Monitoring

Abstract

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.

SOI and Other Semiconductor-On-Insulator Substrates Characterization

“…The non-contact Surface Potential Difference Imaging technique introduced in 2005 (also named Chemetriq) is very useful for analysing traces of metals, particle residues left after wet-cleaning and organics (7)(8). Fast to use on Cz Silicon (n and p-type), it has also been tested on standard SOI wafers (9). It is based on the Work Function (WF) difference between a probe material and the silicon surface, what can also be expressed as a Surface Potential Difference.…”