The present application relates to semiconductor processing; more particularly, to a method of forming a template for the directed self-assembly (DSA) of block copolymers (BCPs) especially in the context of graphoepitaxcy DSA.
Directed self-assembly refers to the integration of block copolymer materials that undergo phase or domain separation with traditional semiconductor manufacturing processes. With DSA, nanoscale dimensions are achievable with dramatically reduced cost using novel material designs without the need for additional equipment upgrades. In order to form vertically oriented line-space patterns with block copolymer domains, a neutral layer must be present at the bottom of the block copolymer layer.
Whereas in DSA the sidewalls of the vertically oriented line-space pattern must have a preference for one polymer block over the other, e.g. via surface chemistry, in order to provide the impetus to properly align the DSA lines, the neutral layer should not. That is, the neutral layer must not show a strong wetting affinity for one of the polymer blocks over the other. The matter of neutrality is further complicated in graphoepitaxy uses inasmuch as the neutral layer must remain neutral after any processing prior to directed self-assembly, e.g. resist development and etch. Moreover, the neutral layer must be stable and remain neutral for a range of thicknesses and deposition conditions. Conventional neutral layers include polymers that graft onto the hard mask portion of the assembly, and include layers of cross-linked polymers. Other materials such as a silicon-containing antireflection film (SiARC) and a chemical vapor deposition (CVD) carbon film are not sufficiently neutral or stable.
There is thus a need for alternative methods for providing a neutral layer in etched template DSA graphoepitaxy processes, which layer can remain neutral or have its neutrality recovered BY any processing prior to DSA. Such a neutral layer would effectively decouple template lithography, template stack and etch processes from DSA formation; and would further provide for the use of techniques such as Extreme Ultra Violet (EUV) and etch trim processes for the patterning of DSA templates.