Development And Investigation Of A Novel Dry Etch Silicon Smoothing Process

This thesis describes the development of a dry plasma etch smoothing technique to replace the conventional Chemical Mechanical Polishing process within a device manufacturing scheme in the semiconductor industry. An important semiconductor manufacturing process is 3D wafer packaging, which allows vertical stacking of wafer die. 3D wafer packing represents a significant component of the total wafer level processing cost. A critical step in the 3D packaging process flow is the Chemical Mechanical Polishing process. Replacement of the CMP process step with a corresponding dry etch can yield significant time and cost savings. This is achievable through reductions in metrology and wafer handling requirements and lower volumes of materials needed for plasma-etch based processes compared with CMP. Incorporating equipment already utilized in the 3D integrated wafer packaging process during the subsequent Through Silicon Via (TSV) reveal step, process efficiencies can be achieved, with overall die yields being maintained. Using dry etch technology to treat a 200 nm rough back-ground silicon surface, a smooth surface with a peak to valley roughness of less than 6 nm is demonstrated, which is comparable to a virgin silicon wafer. This patented process differs from other dry etch smoothing techniques in that it aims to eliminate any visual grind marks rather than just reducing the surface roughness. The elimination of visible grind marks is critical in later optical inspection where these surface scratches are falsely identified as defects. The quality of the plasma polished surface is equivalent to that of a CMP processed wafer and as such, this process has been implemented in manufacturing replacing the CMP step. The novel process described combines a surface modification process followed by a roughness reduction iteratively, to produce a smooth surface without visible grind marks. Further work describes the application of the smoothing process to microneedles, with the aim of improving the process flow. Smoothing of silicon carbide has been performed. Finally, an extension of the TSV reveal process is described, called extreme thinning, with the development of a predictive model to minimize final total thickness variation. Silicon smoothing can also be beneficial to this application.