The continued miniaturization of integrated circuit features has been made possible through multilayer patterning processes where different etch steps transfer the patterned photoresist image through various hardmasks to the underlying substrate. Wet etchants, such as the aqueous mixture of ammonium hydroxide and hydrogen peroxide known as SC-1 (Standard Clean -1), are often used for the selective removal of metal surfaces (i.e. TiN) from the substrate. To ensure that this metal removal is indeed selective, organic underlayers are used to protect the metal surface in regions where metal removal is unwanted. Unfortunately, these harsh basic and oxidative conditions are often incompatible with many underlayers which result in their delamination from the substrate, exposing and damaging the metal surface.
Here we report our work on improving the SC-1 wet etch resistance of an underlayer coated over TiN. By increasing the film’s binding to the metal surface and decreasing its brittleness through polymer design or additive choice, we improve the time for film delamination in an SC-1 bath from 1 minute to over 20 minutes. Furthermore, we have developed a new method to evaluate SC-1 resistance by quantifying TiN removal by measuring the amount of titanium leached into the solution during wet etching by using inductively coupled plasma mass spectrometry (ICP-MS). We demonstrate with this method and XSEM images that TiN can be removed if the film does not act as a sufficient barrier to prevent SC-1 penetration, even if no film delamination is observed, which will be used to optimize future underlayer formulations.
KEYWORDS: Etching, Absorbance, Carbon, Resistance, System on a chip, Reactive ion etching, Polymers, Image processing, Photoresist materials, Optical lithography
The continued miniaturization of integrated circuit features has been made possible through multilayer patterning processes where different etch steps transfer the patterned photoresist image through various hardmasks and ultimately to the underlying substrate. Spin-on carbons (SOCs) are a type of a solution-dispensable carbon hardmask that can offer excellent resistance to various etch gases for good pattern transfer fidelity, while simultaneously conferring desirable gap fill and planarization properties onto the underlying substrate. We recently reported on the development of a new SOC platform with excellent etch resistance, having a relative reactive ion etch (RIE) rate of 1.08 compared to amorphous carbon. However, one drawback we observed for this polymer was its relatively high absorbance between 400-700 nm which can complicate lithographic alignment. Here we report our work on reducing the absorbance of our SOC platform while maintaining its excellent etch resistance. We identify that the origin of high absorbance is from side reactions that occur during curing and discuss the various polymer modifications or additives that prevent these unwanted processes. We additionally look at any trade-offs that are observed between decreasing absorbance and etch resistance and optimize the SOC’s composition to minimize absorbance while having a minimal effect on its etch resistance.
As the critical dimension (CD) in semiconductor devices continues to shrink, the multilayer patterning process to transfer fine line patterns into an underlying substrate is becoming increasingly important. The trilayer processes consist of a photoresist film, a silicon-containing layer and a carbon rich underlayer. The distinctive difference in etch selectivity toward fluorine and oxygen based reactive ion etching (RIE) chemistry is critical to provide highly selective pattern transfer to the substrate. In response to the need for high etch resistant underlayers, we have developed carbon rich spin-on carbon (SOC) materials with good solubility in preferred casting solvents, high thermal stability and high dry etch resistance. To better understand structure-property relationships of high etch resistant SOC films, cured SOC films were analyzed by Fourier-transform infrared spectroscopy (FT-IR), ultraviolet-visible spectroscopy (UV-Vis), X-ray reflectivity (XRR), X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS). The design considerations for high etch resistance SOC underlayers, such as Ohnishi parameter, crosslinking and film density, will be discussed in this paper.
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