Fortschrittliche Detektions-und Entfernungsmethode von Polymerrückständen in Through Silicon Vias (TSV)

With conventional planar monolithic integrated circuit designs approaching their limits, emerging 3D integration technology is enabling higher levels of performance and functionality using through-silicon vias (TSVs) for vertical interconnections. The basic TSV manufacturing process consists of four major components: formation, isolation, metallization, and passivation. Polymer contaminations formed inside the TSVs during processing can cause delamination of deposited metal and isolation layers, resulting in an immediate or delayed electrical failure of the device. The post-etch polymer removal process usually consists of a wet and dry cleaning sequence, which prepares the wafer surface for subsequent material deposition. With increasing aspect ratios, removal and inspection of the sidewall polymer residue are becoming increasingly difficult. The first goal of this thesis is to develop a cleaning evaluation method for TSVs after a wet-chemical cleaning that follows a through-spacer-oxide etching step (TSE). Special attention should be paid to the adaption to shrinking dimensions, reduction of the inspection duration, and specimen preparation complexity. Secondly, this thesis intends to formulate an improved cleaning method for a dry or wet cleaning subsequent to a TSE. The new or extended cleaning method should also be adaptable to shrinking dimensions, as well as reduce the cleaning duration compared to previous cleaning times. As part of a co-operation between the ams AG and FhG IISB, both a novel TSV wafer cleaning process evaluation method, as well as a cleaning method have been developed. Both methods have been experimentally investigated on the base of TSVs that have been processed up to and including the TSE. For each of these methods, wafers with specific TSV sizes, or rather specific aspect ratios (AR 1:5 and 1:2.5), have been provided by ams AG. For an accurate wafer cleaning evaluation, a new method for sidewall polymer residue detection inside the TSVs has been developed. In general, this method is based on labelling of the sidewall polymers with fluorophores. Due to polymer material characteristics, the small interaction volume, and the location of polymer residue, many of the conventional labelling methods such as chemical or physical activation of the polymer surface cannot be used. For this reason, the newly-developed polymer detection method operates with supercritical CO2 and its diffusion into the polymer matrix. To this end, an innovative laboratory autoclave has been designed and constructed. The residual polymers are labelled by means of impregnation with fluorophores, which are transported into the polymer matrix with CO2 as a carrier. A non-destructive examination under a confocal laser scanning microscope (CLSM) detects the existence and location of residue. This novel optical detection method, based on fluorophore pressure impregnation, circumvents the drawbacks of destructive analysis methods and provides an efficient and reproducible procedure to detect polymer residue on wafer-level. The second part of this thesis involves the development of a novel TSV sidewall polymer stripping method. This method, tested within different TSV aspect ratios following a TSE, consists of a dry and a wet-chemical cleaning, and is based on knowledge gained from fluorophore pressure impregnation experiments and on extended state-of-the art wet cleaning procedures. In accordance with the experimental results, TSV surface wetting behaviour, polymer stripping mechanism, and the influence of CO2 on polymer residue are discussed. With the novel sidewall polymer stripping method, a total cleaning with reduced cleaning process time for TSVs after the TSE has been realized. One of the primary findings of this research is that supercritical CO2 can be applied to polymer detection as well as to TSV cleaning processes. Characteristics such as non-toxicity, non-apparent wafer material interactions, operational simplicity, and competitive price have made CO2 attractive to the semiconductor manufacturing industry for many years. While CO2 will presumably not replace the complete wet cleaning chemistry in wafer cleaning technology, due to its many advantages it will likely reduce the cleaning agents to a minimum