Gettering of copper and nickel in p/p(+) epitaxial wafers

We studied whether the theory and practice of segregation gettering are app licable to copper and nickel in p/p+ epitaxial wafers of different substrat e resistivities. The gettering test consisted of a reproducible spin-on con tamination of the wafers, followed by a metal drive-in at 800 degrees C for 30 min under argon with a cooling rate of 50 degrees C/min at the end. For evaluating the metal profile in the wafer, we developed a new analytical m ethod: wafers were etched step by step using a mixture of hydrofluoric and nitric acid. Then these "stratigraphical" etching solutions were analyzed b y inductively coupled plasma mass spectrometry. This enabled the evaluation of stratigraphical metal concentration profiles in the wafers with detecti on limits of between 10(12) and 10(12) atoms/cm(3). Copper was found to be gettered in the substrate due to the high boron concentration. No precipita ted copper was detected at the stress field of the epi/substrate interface. We explained the behavior of copper in terms of its increased solubility i n heavily boron-doped silicon. Calculations of the gettering efficiency wer e in good agreement with our experimental results. Nickel, by contrast, was not gettered by the heavily boron-doped substrate wafers. it also did not precipitate at the stress field of the epitaxial layer/substrate wafer inte rface. Instead, it was found only in the near-surface layers. From the gett ering behavior of nickel we conclude that interstitial nickel in silicon is uncharged. (C) 2000 The Electrochemical Society.