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One of the challenges of surface characterization at the nano-scale is that analytical tools which are capable of topological nano-scale analysis have limited capabilities for molecular characterization. Here we present a study on molecular characterization of positive tone photo-resist films with varying exposure dose. The technique is based on secondary ion mass spectrometry, SIMS, with gold nanoparticles (e.g. Au4+400). In the methodology a sequence of individual gold nanoparticles is used to stochastically bombard the photoresist films, where each impact results in the emission of ions from a region 10-20 nm in diameter. The technique has several unique features which enable molecular characterization at the nano-scale. Firstly, the use of individual massive clusters impacts which sample nano-volumes, and from these nano-volumes multiple molecular ions can be ejected simultaneously. Secondly, the acquisition of the mass spectra from each projectile impact allows co-ejected ions to be collected in the same mass spectrum. These two features allow for tests on the nano-scale homogeneity of molecules. This is of particular interest for photoresist films, where nano-scale inhomogeneity may result in poor quality films. In this study we examined bulk photoresist films with varying dose post development, in order to probe physical aggregation and chemical transformation on the partially exposed resist pattern side wall and surface. We found that the cation and anion of the photoacid generator were not removed equally during development, and we found that the quencher is not completely removed by the developer.

Here we describe a methodology for molecular analysis at the nano-scale and present its capabilities. The analysis method is based on secondary ion mass spectrometry, SIMS, with gold nanoparticles (e.g. Au4004+). The methodology presented here has unique features which enable molecular analysis at the nanoscale, namely the method of acquiring the mass spectrum and the nature of the impacting projectile. In the method a sequence of individual gold nanoparticles (Au4004+) are used to bombard the sample, each impact results in ion emission from an area 10-20 nm in diameter. For each of impact of Au4004+, the emitted ions are mass analyzed by time of flight mass spectrometry, detected and stored together in one mass spectrum prior to the arrival of the subsequent projectile. Each mass spectrum contains elementals, and molecules which were co-localized within 10-20 nm of one another. Examining the co-emitted ions allows to test the molecular homogeneity, and chemical composition at the nanoscale. We applied this method to a chemically amplified resist before and after exposure and development. After development the method was used to chemically characterize defect sites, which were not removed by the developing solution.

As the semiconductor industry continuously pursues smaller and more advanced device nodes, improving the lithographic performance of photoresists becomes more critical and challenging. The homogeneity of the photoresist formulation components within the thin film, such as the distribution of photoacid generator (PAG) molecules, are critical factors influencing resolving capability and the sidewall roughness after development. However, there is still lack of fundamental experimental approaches to probe the distribution of these components at the nanoscale throughout the photoresist film. Herein, we present the use of a new methodology, namely, massive cluster secondary ion mass spectrometry (MC-SIMS), to determine PAG homogeneity on a 10-15 nm scale within a photoresist film. In comparison to conventional SIMS, of which the detection spatial resolution is limited to large domains and the data is aggregated prior to analysis, MC-SIMS bombards the sample with a sequence of massive Au400 +4 nanoprojectiles, each separated in time and space, collecting and mass analyzing the co-emitted secondary ions from each projectile impact. Each sample is analyzed with a large quantity (106-107) of individual projectile impacts within an analysis area 125 μm in diameter. Analysis of co-emission of these independent 106-107 mass spectra allows for identification of co-localized molecules within nanodomains ~10-15 nm diameter and ~10 nm in depth (the emission area of a single impact) from the film surface. This unique method therefore reveals spatial distributions of molecules at the nanoscale. Using MC-SIMS methodology, we directly measured key factors influencing the PAG homogeneity at the nanoscale including (1) PAG concentration, (2) the nature of the polymer matrix, (3) the nature of the PAG, and (4) additives. We discovered that 85-95% of PAG salts aggregate at the nanoscale. The majority of the PAG aggregates are less than 10 nm in size and are highly homogeneously distributed within the polymer matrix in the film. Furthermore, the size of the PAG aggregates can be manipulated by additives through an ion-exchange mechanism.

We describe a novel deterministic bottom-up / top-down approach to sub-30 nm photolithography using a film composed of assembled block brush polymers of highly uniform composition and chain length. The polymer architecture consists of a rigid backbone of polymerized norbornene, each linked to flexible short side brush chains. The resultant ‘bottle brush’ topology has a cylindrical shape with short brush chains arranged concentrically around the backbone, in which the cylinder radius is determined by the number of monomers within the brush fragment, while the cylinder length is determined by the degree of backbone polymerization. The modularity of the synthetic system allows a wide diversity of lithographically useful monomers, sequencing, dimension and property variation. Sequential grafting of pre-synthesized blocks allows for facile formation of either concentric or lengthwise block copolymers. Placement of brush chains of different compositions along different regions of the cylinder, along with variation of the relative concentric and lengthwise dimensions, provides mechanisms to align and control placement of the cylinders. These polymers are compatible with photoacid generators (PAGs) and crosslinker functionality. Our results are consistent with a model that the bottle brush polymers assemble (bottom-up) in the film to yield a ‘forest’ of vertically arranged cylindrical block brush polymers, with the film thickness determined by the coherence lengths of the cylinders. Subsequent imaging via electron beam (EB or ebeam) or optical radiation yields a (top-down) mechanism for acid catalyzed crosslinking of adjacent cylinders. Uncrosslinked cylinders are removed in developer to yield negative photoresist patterns. Exposure doses are very low and throughputs are amenable to the requirements of Extreme Ultraviolet (EUV) lithography. The limiting resolution with ebeam exposure is potentially about two cylinder diameters width (< 8 nm), with the smallest observed patterns approaching 10 nm.