Enhanced Block Copolymer Lithography Using Sequential Infiltration Synthesis

Abstract

INTRODUCTIONSelf-assembly of block copolymer (BCP) thin films has been explored extensively as a strategy to make periodic nanostructures. 1À4 Because these nanoscale features can be formed reproducibly and at low-cost, there is tremendous interest in transferring such patterns to functional materials. In particular, BCP films are promising for microelectronics and data storage applications where highly dense and periodic nanoscale patterns are needed over a large area. 5À8 BCP films can self-organize to form nanostructures of various morphologies with tunable length scales. Furthermore, by guiding BCP self-assembly using surface topography, highly regular patterns can be generated over macroscopic area with low defect density. 9,10 Since BCP films with a single layer of laterally ordered domains have a thickness on the order of the domain size, they are generally too thin for transferring patterns into the underlying substrate using plasma etching. Because carbon-based polymer blocks erode quickly in a plasma, the masking BCP film is completely removed before features with significant depth can be transferred. For example, polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA), one of the most widely studied BCPs (including in lithography experiments), has an overall poor etch resistance, and the etch contrast between the blocks is only about two. 11 As a result, the depth that can be etched is only on the order of the thickness of the film at best, which is tens of nanometers in most cases. Significant effort has been invested in developing BCPs containing etch-resistant blocks such as polystyrene-block-polydimethylsiloxane (PS-b-PDMS) 12,13 or polystyrene-block-poly(ferrocenylsilane) (PS-b-PFS), 14À17 but many of these BCPs have poor wetting properties or are difficult to remove after the etching process. The synthesis of these polymers can also be challenging. Furthermore, organometallic blocks (such as PFS) are undesirable for microelectronics manufacturing, a major potential application of BCPs, because the uncontrolled diffusion of metals in a semiconductor can degrade the performance of microelectronic devices.For the reasons stated above, a BCP that is easy to synthesize, applicable over large areas, and resistant to plasma etching remains elusive. To etch high aspect-ratio structures, a common scheme is to first transfer the BCP pattern to an intermediate hard mask layer that provides greater etch resistance. The insertion of a hard mask layer adds complexity and cost to the fabrication process due to complications from stress and adhesion as well as the risk of damaging the underlying substrate during deposition. The interfacial interaction between the hard mask and the BCP may also change dramatically how the BCP self-assembles. Furthermore, transferring the pattern with high fidelity into the hard mask layer still requires etch contrast between the polymer blocks. Consequently, strong etch contrast between the BCP blocks is highly desired, regardless of the overall pattern transfer scheme.In this ...

Strategies for Inorganic Incorporation using Neat Block Copolymer Thin Films for Etch Mask Function and Nanotechnological Application

“…Figure 9 b-d shows highfi delity silicon nanostructures perpendicular and parallel to the substrate plane following pattern transfer using an Al 2 O 3 hardmask via SIS. [ 113 ] Subsequently, Black and co-workers illustrated high-aspect ratio pattern transfer using the same SIS approach for PSb -PMMA (see Figure 9 e-g). [ 114 ] Systematic studies were carried out analysing the Al 2 O 3 infi ltration effect on domains which showed that image quality suffered with higher ALD cycles.…”

“…Impressive reports by Checco et al [ 117,118 ] and Rahman et al [ 119,120 ] [ 113 ] Copyright 2011, American Chemical Society. e-g) Reproduced with permission.…”

Hybrid Photovoltaics – from Fundamentals towards Application

“…[145][146][147][148][149][150][151] Driven by entropic and enthalpic interactions between both blocks micro-phase separation structures are formed which have characteristic repeat distances on the order of 10 nanometers. [152][153][154] The polymer-polymer interaction parameter between the blocks, the block ratio, the polydispersity, as well as the molecular weight of the block copolymer determine the morphology of the micro structures. [155,156] Thermodynamic equilibrium results in well-defined nanostructures, which can be spherical, cylindrical, gyroid and lamellar structures.…”

Polymer masks for structured surface and plasma etching

“…Interestingly, they can also serve as intermediate patterns for the preparation of inorganic nanostructures, with a myriad of potential applications such as active devices [26] or hard mask for lithographic process [27]. The transformation of such organic films into silica templates can be performed using sequential infiltration synthesis (SIS) if one polymer could be selectively infiltrated with inorganic gas-phase precursors by diffusion [27][28][29]. This has been done with poly(styrene) (PS) and poly(methyl methacrylate) (PMMA) blends, where gaseous trimethylaluminum (TMA) and water selectively diffuse into PMMA.…”