Introduction
In future generations of devices, photoresist (PR) removal of residues will become critical. After the front-end process (FEOL) ion implantation ( source / drain, extension, haIos, deep well ), the use of PR to seal part of the circuit results in PR being essentially hardened and difficult to remove. In back-end-of-line (BEOL) etch, the selectivity to remove resist and residue without removing low-level material is very challenging. The current situation, problems and some new methods are outlined.
Introduction
Photoresists are used to protect certain areas of the wafer from dry etching chemicals, ion implantation, etc. After the process is complete, the photoresist needs to be selectively removed and the surface cleaned to ensure the surface is free of residue and particles. In principle, it is possible to remove resist using wet chemicals such as thermal SPM, organic solvents or by "ashing" using dry plasma. However, during dry etching or implant processing, the resist is chemically modified, and this modification can significantly reduce the stripping rate. If a more aggressive - example were to use highly oxidizing chemicals, this could lead to undesirable erosion of other materials on the wafer . While these considerations have been important for cell process development for decades, certain roadmap requirements for 45 nanotechnology nodes and higher technology nodes are becoming increasingly stringent to the point where industrial labs are considering requirements for cMOS integrated flows. Several modules for a fundamental paradigm shift. At the same time, new alternative integration schemes, including the use of strained silicon, metal hard masks, and metal gate electrodes, result in different requirements. This makes research on this topic more complex.
In the following, we at Valincona summarize the current situation, problems and new methods, focusing on the source-drain injection module in FEOL and the low k dry etching module in BEOL.
FEOL: Resist stripping after implantation
Source - Drain Implantation Module The source / drain (S/D) junction is formed by implanting dopant ions into the silicon liner formed by the bottom. This implantation typically involves ions as, P, B or BF2 with an areal density of approximately. 1012 to several 1015cm. Ion energies range from a few 100eV for very shallow S/D extensions to tens of keV for deep implantation. To ensure that various devices fabricated on the same / wafer, specifically nFETs and pFETs, each device only receives the appropriate implant, selective implantation is required. This is achieved by masking with patterned photoresist, as schematically shown in Figure 1. Therefore, the complex dopant geometry in the S/D region is created through cycles of photoresist application and patterning, ion implantation, resist stripping, and surface cleaning.
Ions implanted into the resist result in chemical modification of near-surface areas. The chemical bonds of the resist polymer are broken by the energy from the striking ions, which causes the polymer backbone to break.
Conclusion
Developing the next generation of photoresist strippers and residue removers is not easy. It comes from a lot of hard work and dedication to creating a chemistry that meets the needs of technology at the 90 nanonode or below.
Our latest chemical technology effectively removes bulk photoresist, ash and anti-reflective coatings from low- dielectrics. It is also 100% water soluble, making it a more environmentally friendly solution.
