Embodiments are disclosed that reduce gouging during multi-patterning processes using thermal decomposition materials. For one embodiment, gouging is reduced or suppressed by using thermal decomposition materials as cores during multiple patterning processes. For one embodiment, gouging is reduced or suppressed by using thermal decomposition materials as a gap fill material during multiple patterning processes. By using thermal decomposition material, gouging of an underlying layer, such as a hard mask layer, can be reduced or suppressed for patterned structures being formed using the self-aligned multi-patterning processes because more destructive etch processes, such as plasma etch processes, are not required to remove the thermal decomposition materials.