Modeling the topography of uneven substrates post spin-coating

Abstract

The semiconductor industry has followed Moore's law for many decades and is currently preparing for high-volume manufacturing of the 7 nm technology node. To further scale down to the 5 nm technology node and below, research centers are constantly testing novel patterning and integration approaches. To enable a number of these new integration approaches, there is a growing need for a well-understood and well-controlled tone reversal technology. Tone reversal consists in inverting the tonality of all structures present on a wafer, e.g., turning a hole pattern into a pillar pattern. Examples of applications that advantageously integrate such tone reversal technology are multiple litho-etch block patterning, the fully self-aligned block concept, and the direct metal etch approach. A critical step in the tone reversal process is to achieve a good wafer planarization, i.e., limited wafer topography. This can be done by chemical mechanical polishing after filling the patterned features that need to be tone inverted. However, a more promising approach is to reduce the topography by using a planarizing spin-coating process to fill the patterns. Material vendors and research groups have done tremendous efforts to understand and improve the quality (uniformity, planarity, etch resistance, etc.) of spin-coating processes. When a spin-coating process is used to fill a given patterned structure, it is known that the degree of planarization is impacted by a set of parameters such as pattern width and density. However, it is not clear yet what the exact functional dependence is. In this work, the authors first present an experimental study of the planarization behavior of spin-coated materials as a function of pattern width, depth, and density. The authors observed a strong dependency of the width and the density of the patterns on the wafer topography post spin-coating, while the depth, within the boundaries of this study, showed no significant impact. The most striking result was the observation of the linear relationship between the pattern density difference between two areas and the relative height difference of those areas after spin-coating. Second, based on these experimental observations, the authors present a model that predicts the remaining wafer topography post spin-coating. The model calculates the topography for a given set of structures, using only one parameter as input. This parameter is a fixed number for a specific spin-coating process and is called the planarization length λ. The authors demonstrate that this model is capable of reproducing and predicting the experimentally measured height profiles on complex patterned structures for different spin-coating processes. These calculations can be done with commercially available electronic design automation software. Therefore, this model can become a powerful tool in mask design, both for applications based on tone reversal, and, in general, for patterning processes that make use of spin-coated materials.

Dual Block Copolymer Morphologies in Ultrathin Films on Topographic Substrates: The Effect of Film Curvature

“…Interestingly, we find that the deposited film is thinner both on the plateau and in the trench when the film is cast on a substrate featuring wide trenches than for similar plateau widths with narrower trenches (see Supplementary Table S1). This indicates that less material remains on the patterned area during spin coating when the plateaus are widely spaced, which is attributed to the influence of feature density, as has been previously reported [41,42]. Images of the deepest trench depths studied, 38 nm, show another interesting trend (Figure 5).…”

“…This dependence becomes more accentuated for deeper trenches, which means that a deeper topography offers more versatility because their film profile changes over a larger range with the topographic feature density (as was observed for the 31 and 38 nm feature depths). Additionally, Figure 8d Decoster et al found a similar dependence (∆h = pd, where p quantifies the remaining topography after the 'planarization' of topographic features by the spin-coated material) [41]. Our analysis shows that with our PS-b-PMMA copolymer, the extent of planarization is at least 18.6% (for wide plateaus and/or trenches), and it further increases in a linear fashion with increasing density of topographical features (i.e., decreasing plateau and/or trench widths), where complete planarization is expected at wpl + wtr ≈ 115 nm (which is Decoster et al found a similar dependence (∆h = pd, where p quantifies the remaining topography after the 'planarization' of topographic features by the spin-coated material) [41].…”

“…Additionally, Figure 8d Decoster et al found a similar dependence (∆h = pd, where p quantifies the remaining topography after the 'planarization' of topographic features by the spin-coated material) [41]. Our analysis shows that with our PS-b-PMMA copolymer, the extent of planarization is at least 18.6% (for wide plateaus and/or trenches), and it further increases in a linear fashion with increasing density of topographical features (i.e., decreasing plateau and/or trench widths), where complete planarization is expected at wpl + wtr ≈ 115 nm (which is Decoster et al found a similar dependence (∆h = pd, where p quantifies the remaining topography after the 'planarization' of topographic features by the spin-coated material) [41]. Our analysis shows that with our PS-b-PMMA copolymer, the extent of planarization is at least 18.6% (for wide plateaus and/or trenches), and it further increases in a linear fashion with increasing density of topographic features (i.e., decreasing plateau and/or trench widths), where complete planarization is expected at w pl + w tr ≈ 115 nm (which is outside the feature density range in this study).…”

“…As the casting solvent evaporates, the film undergoes further shrinkage and vitrifies [44][45][46][47]. The resulting films are characterized by non-planar contours over the topography, where the height contrast between plateau and trench areas is smaller for narrow features than for wider features [41,42,47,48]. In relatively thick films, it has been previously shown that the film profile is insensitive to small changes in trench depth [41].…”

“…The resulting films are characterized by non-planar contours over the topography, where the height contrast between plateau and trench areas is smaller for narrow features than for wider features [41,42,47,48]. In relatively thick films, it has been previously shown that the film profile is insensitive to small changes in trench depth [41]. The works cited herein, however, were all performed on homopolymer films, which lack an internal, microphase-separated structure.…”