Menachem Genut

Laser removal of foreign materials from semiconductor wafers

Removal of foreign materials formed during VLSI/ULSI processing, is one of the challenges of advanced semiconductor technology. As device geometries continue to shrink, microcontaminants such as particles, metallic contaminants, photoresists and other organic residues have an increasing impact on yield. As wafer processing becomes more aggressive and contaminants which are yield limiting become much smaller, traditional cleaning techniques based on wet-chemistry cleaning become less adequate. Only a completely dry cleaning process can overcome all the drawbacks associated with the problematic wet chemistry cleaning. A novel DUV-Excimer laser Dry removal method allows the elimination of these contaminants, in a single step process.

Excimer laser photoresist stripping

A new method for stripping the most challenging photoresists on deep sub-micron technology semiconductor wafers has been developed. The method uses a combination of UV excimer laser ablation and reactive chemistry to strip the photoresist in a single dry process, eliminating the wet acids or solvents often used following ashing of high dose implantation (HDI) and reactive ion etching (RIE). The stripping process combines new removal mechanisms: chemical assisted UV excimer laser ablation/etching, laser induced chemical etching of side walls and residues, and enhanced combustion. During the laser pulses photolysis of the process gas occurs, UV laser radiation breaks the photoresist polymer chain bonds, and the photoresist (including foreign materials imbedded in it) is ablated. The combustion is ignited by the ablative impact of laser radiation and enhanced by the radicals formed during photo-thermal decomposition of the process gases. Following this process, the volatilized products and gases are evacuated. The optimum laser stripping conditions were developed to provide a wide process window for the most challenging stripping conditions, such as after HDI and RIE (metal, polysilicon), without causing damage to the wafer devices. A photoresist stripping system based on the described technology was designed and built. The system has been designated as the L-StripperTM and provides stripping time of 0.15 s/(micrometer cm2).

Laser removal of deep submicron-patterned photoresist after RIE of polysilicon, contacts, and vias

Removal of tough compounds, which are formed during reactive ion etch (RIE) of polysilicon, contacts and vias, is one of the challenges in deep submicron patterned photoresist stripping. A novel UV-excimer laser photoresist stripping method proposed here allows the removal of these hard and mainly inorganic species, usually situated on sidewalls, in one dry step.