Rongwei Fan

The study and investigation of inline E-beam inspection for 28nm process development

The research aims at the VC (voltage contrast) of contact-loop defects in 28nm processes. A new type defect, contact W (tungsten) missing, was found during process developments, and the designed inline E-beam inspection was used to detect those defects by their VC features. The mechanism of defects and the method of the enhancement of the detection were described. An extreme high signal E-beam scan recipe is required in corresponding to the unique defect wanted and, in doing so, the partial-opened W missing defects can be found. Since the defect can be detected instantly by E-beam inspection, and therefore an inline monitoring index can be set up. Compared to the end-of-line electrical test, this inline monitor is very much closer to the trouble process and shrinks the response time. The following process experiments and evaluation can be instantly verified and examined. Finally, the W missing defect was fixed by an optimization of CT Etch process and controlling of CT loop minienvironment. Instead to the debug method of failure analysis, E-beam inspection can speed up 8nm development.

The detection and investigation of Tungsten-plug voids by electron-beam inspection

The study aims at the inline detection of invisible defects of tungsten (W) plug voids. Those voids inside contact holes would directly lead to chip yield fail or, even worse, reliability issues. A dedicated electron-beam (E-beam) inspection (EBI) method with “penetration mode” was performed to detect W plug voids. Then experiments showed the failure model involved poor CT hole profiles, the accumulating polymers in the CT hole, incompatible ILB/W DEP processes; furthermore, the quantified impacted factors of void defects were also discussed, including the aspect ratio (AR) and shape of CT holes, CT etch polymer status, the thermal effect of ILB/W DEP processes, and even the FOUP materials. The corresponding improvement actions including changing new material FOUP, reducing CT hole AR by optimization of the ILD loop and CT loop process and optimizing the ILB/W DEP process were executed. The W plug void defects obviously trended low accordingly.

The total inspection solutions of extreme tiny defect in BEOL advanced semiconductor process

In this paper, extreme tiny defects are detected and monitored by using brightfiled inspection system in 28nm back-end-of-the-line (BEOL) processes. Two main defects, including tiny bridge and tiny bump defects, were studied by a novel combination of dedicated scan settings such as spectrum mode, directional electrical field (DEF), focus offset and so on. The purpose of these studies is to capture defects more efficiently. After defect detecting, failure models of these defects were established and the effective defect reduction actions were carried out. Combining effective defect monitor and defect reduction actions can make BEOL yield improve rapidly.

The detection and investigation of SRAM data retention soft failures by voltage contrast inspection

The research was aimed at the inline detection of the electron leakage leading to end-of-the-line soft failures. The electron beam inspection was applied to detect the voltage contrast signal by the PMOS leakage, and the leakage would lead to SRAM data retention failures in CP test during 40nm technology development. A series of experiments, including retargeting the CD of NP lithography process and re-tape-out the mask with new optical proximity correct (OPC), were set up according to the inline detectable VC inspection method, and an optimal process integration condition without failures was achieved.