Non-contact mapping of heavy metal contamination for silicon IC fabrication

Abstract

We present the principles and application examples of a recently refined, computerised, surface photovoltage (SPV) method. This new method is capable of wafer-scale, non-contact mapping of metal contaminants in the bulk and on the surface with sensitivities as high at 10'aatomscm-3. W e demonstrate the unique abilityofsw to measure product wafers with finished integratedcircuits.

Surface photovoltage phenomena: theory, experiment, and applications

“…A recent example may be found in [218], where the ®xed and vibrating plates are located adjacent to each other. Another important advantage of the MIS approach is that the Ohmic back contact, crucial for Kelvin probe measurements, may be replaced by contactless capacitive coupling (e.g., by means of a spacer) [12]. An appropriate equivalent circuit is shown in Fig.…”

“…Hence, the ac voltage on the back capacitor will be negligible and the measurement will not lose in accuracy. This condition may be met either by decreasing the thickness of the back insulator (which may be dif®cult), or simply by making the back capacitor area much larger than that of front capacitor [12].…”

“…More recently, Lagowski et al have suggested the arrangement shown in Fig. 2.29 [12]. In their device, the illumination point is ®xed in space and applied to the sample via a ®ber optic cable inserted in the small metal electrode.…”

“…29) [12]. By speci®cally targeting the Si industry, both in terms of developing tools suitable for an industrial environment and in terms of aggressively exposing the new tools to the relevant community, these scientists have contributed to the promotion of SPV methods considerably.…”

“…Lagowski et al have scanned the SPV across an entire Si wafer, relating areas of different voltage to areas of heavy metal contamination or to surface defects [12]. Several groups have applied scanning tunneling microscopy (STM) [13,14] and atomic force microscopy (AFM) [15] tips for obtaining SPV measurements with a greatly improved lateral resolution.…”