In this paper, impact of carbon on threshold voltage in MOSFET-based device is studied by 3D-atom probe tomography (APT). Carbon is one of most difficult contaminants incorporated from fab-environment to be detected by typical analytical techniques such as TEM-EDS or SIMS. Here, we successfully demonstrated the detection of carbon segregated at gate oxide/Si substrate interface using 3D-APT with single-atom sensitivity and sub-nanometer spatial resolution. It was found that the carbon contaminants have significant effect on the threshold voltage shift (ΔVth), in which ΔVth increases slightly with increasing carbon concentration. The deterioration of device performance is explained by means of which the positively ionized carbons at the interface acting as additional positive charges affecting the inversion to n-channel.

An in situ air gaps fill-in approach was investigated by conducting a convenient way in dual-beam FIB. We employed a well-controlled deposition to precisely fill carbon into air gaps. It greatly reduced formation of the artifacts and avoided the profiles of air gaps by reducing striations and damages during FIB milling. Generally, the effect of air gaps between wordlines or between metal lines, as well as some unexpected defect voids can be eliminated in most cases if this ideal method is applied.

The device features have shrunk to sub-micron/nano-meter range, and the process technology has been getting more complicated, so TEM has become a necessary tool for PFA imaging and element analysis. Conventional FIB ex-situ liftout is the most common technique for precise sample preparation. But this method has some limitations: samples cannot be reprocessed for further analysis; the carbon film supported grid affects the EDS analysis for carbon elements. A new installation will be introduced in this article, which is set up in FIB chamber for in-situ lift-out application. It not only overcomes the above problems, but also covers a wide application of TEM sample preparation.