Directed self-assembly of block copolymers over chemically patterned substrates has proven to be an effective method for sublithographic patterning. Features on these chemical patterns can be multiplied by the natural domain-spacing of the block copolymer assembled on top of the substrate through pattern interpolation. The LiuNealey (LiNe) chemoepitaxy flow for directed self-assembly allows for modification of the geometry and chemistry of the nanopatterned substrate. The critical dimensions and period along with the chemical composition of the patterned features in the LiNe flow govern the equilibrium morphology of the assembled block copolymer. We demonstrate how the construction of the chemical pattern affects the selection for desired, well-registered assembly of block copolymer melts by using a theoretically informed coarse-grained many-body model of block copolymers. The molecular simulations are used to provide an explanation for how to best design the chemical pattern in the LiNe flow for the directed self-assembly (DSA) of block copolymers to achieve desired line-andspace structures.
Directed self-assembly (DSA) of block copolymers (BCP) is attracting a growing amount of interest as a technique to expand traditional lithography beyond its current limits. It has recently been demonstrated that chemoepitaxy can be used to successfully direct BCP assembly to form large arrays of high-density features using the ‘LiNe’ flow. This process uses lithography and trim-etch to produce a “prepattern” of stripes of alternating chemical composition, which in turn guide the formation of assembled BCP structures. The entire process is predicated on the preferential interaction of the respective BCP domains with particular regions of the underlying prepattern. The natural and relative strength of these interactions are at least partially responsible for many aspects of the resulting assembled BCP film, including equilibrium morphology, type and persistence of kinetically trapped defects, and domain roughness. This study develops the understanding of how various guiding chemistries ultimately govern BCP morphology and characteristics in the LiNe flow. In particular, the work focuses on how stronger affinity between chemical patterns and the guided BCP film leads to faster assembly, lower ultimate defectivity levels, and better incommensurability tolerance, as well as the relationship between pattern strength and domain roughness. One issue in generating finely controllable chemical patterns is that all materials are affected to some degree by processing, which can modify or weaken the guiding ability of the pattern. This investigation addresses the non-idealities introduced in production processing and explores how this knowledge can be employed in improving BCP DSA for lithography.
Directed self-assembly (DSA) of lamellae-forming block copolymers (BCP) via chemo-epitaxy is a potential lithographic solution to achieve patterns of dense features. Progress to date demonstrates encouraging results, but in order to better understand the role of all parameters, systematic analysis of each factor needs to be assessed. Small changes in the volume fraction of a lamellae-forming BCP have been shown to change the connectivity of unguided domains. When an asymmetric lamellae-forming BCP is assembled on chemical patterns generated with the LiNe flow, the patterning performance and defect modes change depending on whether the majority or minority volume fraction phase is guided by the chemical pattern. Asymmetric BCP formulations were generated by blending homopolymer with a symmetric BCP. The patterning performance of the BCP formulations was assessed for different pattern pitches, guide stripe widths, backfill materials and annealing times. Optical defect inspection and SEM review are used to track the majority defect mode for each formulation. Formulation-dependent trends in defect modes show the importance of optimizing the BCP formulation in order to minimize the defectivity.
Grazing-Incidence Small Angle X-ray Scattering (GISAXS) offers the ability to probe large sample areas, providing three-dimensional structural information at high detail in a thin film geometry. In this study we exploit the application of GISAXS to structures formed at one step of the LiNe (Liu-Nealey) flow using chemical patterns for directed self-assembly of block copolymer films. Experiments conducted at the Argonne National Laboratory provided scattering patterns probing film characteristics at both parallel and normal directions to the surface. We demonstrate the application of new computational methods to construct models based on scattering measured. Such analysis allows for extraction of structural characteristics at unprecedented detail.
Directed self-assembly (DSA) of block copolymers (BCP) via chemo-epitaxy is a potential lithographic solution to
patterns of dense features. The LiNe (Liu-Nealey) flow was used to fabricate the chemical pattern, which guides the BCP
due to the different wetting behavior of the materials. Fine control of both the chemical pattern chemistry and geometry
are important for DSA of BCP. Furthermore, wetting behavior considerations for DSA extend beyond pattern design and
include the surrounding region. BCP DSA would be easier to integrate into device design if the patterned region were
isolated with a featureless region (horizontal lamellar BCP assembly) rather than undirected BCP fingerprint structures.
This paper addresses two processing steps found to be modifying the guide material. For one, the backfill brush grafts to
the cross-linked polystyrene (XPS), albeit at a lower rate than the brush grafts to the exposed substrate. Undersaturating
the backfill brush only moderately improves the XPS wetting behavior, but also negatively impacts the background
region of the chemical pattern. Replacing the brush grafting functionality so that the brush grafts at lower annealing
conditions also did not avoid the side reaction between the brush and the XPS. The other step modifying the XPS is the
trim etch. Replacing the trim etch process was effective at generating a chemical pattern that can orient the BCP
horizontally on a stripe 11 L0 wide passing through a field of chemical pattern.
Resolution requirements for photolithography have reached beyond the wavelength of light.
Consequently, it is becoming increasingly complicated and expensive to further minimize feature
dimensions as required to push the limits of Moore’s law. EUV lithography has been the much
anticipated solution; however, its insertion timing for High Volume Manufacturing is still an uncertainty
due to source power and EUV mask infrastructure limitations.
Extending the limits of 193nm immersion lithography requires pitch division using either Double
Patterning Pitch Division (DPPD), and/or Spacer Based Pitch Division (SBPD) schemes (e.g. Hard mask
image transfer methods (Double, Triple, Quadruple)). While these approaches reduce pitch, there is an
associated risk/compromise of process complexity, and overlay accuracy budget issues.
Directed Self Assembly (DSA) processes offer the promise of providing alternative ways to extend optical
lithography cost-effectively for sub-10nm nodes and present itself as an alternative pitch division
approach. As a result, DSA has gained increased momentum in recent years, as a means for extending
optical lithography past its current limits. The availability of a DSA processing line can enable to further
push the limits of 193nm immersion lithography and overcome some of the critical concerns for EUV
Robust etch transfer of DSA patterns into commonly used device integration materials such as silicon,
silicon nitride, and silicon dioxide had been previously demonstrated [1,2]. However DSA integration to
CMOS process flows, including cut/keep structures to form fin arrays, is yet to be demonstrated on
relevant film stacks (front-end-of-line device integration such as hard mask stacks, and STI stacks). Such
a demonstration will confirm and reinforce its viability as a candidate for sub-10nm technology nodes.