Characterization of the Damage on the Back Side of Silicon Wafers

Abstract

AbstractGettering represents a standard procedure to remove harmful impurities from device active regions of a silicon wafer. An affordable technique for the creation of a defect free (denuded) zone is the introduction of gettering sites on the wafer back side via mechanical damage (i.e. lapping). However, optimizing the extrinsic gettering process requires a technique to quantify the extent of damage introduced through a typical back-side damaging step. Here, we present results from a study using triple axis x-ray diffraction. We characterized the level of damage present in wafers subjected to different lapping conditions. By comparing reciprocal space maps from samples that had undergone different lapping steps, we concluded that all the as-lapped samples showed similar levels of damage in terms of both strain variations and lattice tilts. However, the integrated diffuse scattering intensities decreased from medium to soft t.-double-soft lapping, which confirmed that the double soft lapping introduced the least damage. Typically, the damage step introduced a symmetrical distribution of both lattice strain and lattice tilts (mosaicity) in the surface layer. KOH etching was employed to determine the depth of the damaged layer. In all cases the as-lapped samples had integrated intensities two orders of magnitude greater than those of the etched samples. Analysis of the residual damage present in the lapped samples after chemical etching confirmed that the more aggressive lapping conditions introduced damage of greater depth.