In the presented work solvent-free film preparation from molecular glass resists, the evaluation of the patterning performance using thermal scanning probe lithography (tSPL) and an efficient etch transfer process are demonstrated. As the presented materials have a high tendency to crystallize and thus form crystalline films of bad quality when processed by solution casting, two component mixtures prepared by coevaporation were investigated. Stable amorphous films were obtained by selecting compatible material pairs for the coevaporation. One optimized material pair is based on trissubstituted, twisted resist materials with a distinct difference in molecular design. Here a high resolution tSPL prepared pattern of 18 nm half pitch in a 10 nm thick film is demonstrated. <p> </p>A further optimization is reported for “small” cubic silsequioxane molecules. Again single component films show independent to applied film preparation techniques bad film forming properties due to the high crystallinity of the symmetric cubic silsequioxane molecules. But coevaporation of the phenyl substituted octaphenylsilsequioxane combined with the fully aromatic 2,2',7,7'-tetraphenyl-9,9'-spirobi[fluorene] results in stable amorphous thin films. tSPL investigations demonstrate the patternability by writing high resolution line features of 20 nm half pitch. An important advantage of such a silicon rich resist material is that it can be directly converted to SiO<sub>2</sub>, yielding to a patterned hardmask of SiO<sub>2</sub>. This proof of principle is demonstrated and an efficient pattern transfer of 60 nm half pitch line into the underlying HM8006 is reported.
In the presented work solvent-free film preparation from tailored molecular glass resists, their thermal analysis, the characterization of etch resistance for plasma etching transfer processes, and the evaluation of the patterning performance using scanning probe lithography (SPL) tools, in particular electric field and thermal based SPL, are demonstrated. Therefore a series of fully aromatic spiro-based and tris-substituted twisted resist materials were systematically investigated. The materials feature very high glass transition temperatures of up to 173 °C, which allows solvent-free thin film preparation by physical vapor deposition (PVD) due to their high thermal stability. The PVD prepared films offer distinct advantages compared to spin coated films such as no pinholes, defects, or residual solvent domains, which can locally affect the film properties. In addition, PVD prepared films do not need a post apply bake (PAB) and can be precisely prepared in the nanometer range layer thickness. An observed sufficient plasma etching resistance is promising for an efficient pattern transfer even by utilizing only 10 nm thin resist films. Their lithographic resolution potential is demonstrated by a positive and a negative tone patterning using electric field, current controlled scanning probe lithography (EF-CC-SPL) at the Technical University of Ilmenau or thermal scanning probe lithography (tSPL) investigations at the IBM Research - Zurich. High resolution tSPL prepared patterns of 11 nm half pitch and at 4 nm patterning depth are demonstrated.
The performance of novel molecular glass resists is demonstrated in this work for the purposes of performing nano-pattern transfer. In order to improve the etch durability, post apply bake (PAB) and mixing two resists platforms were investigated. These resists showed a promising etch durability for efficient pattern transfer with films as thin as 5 nm. Etch rate, surface roughness, evolution of the refractive index of these materials are presented to establish a good baseline and select appropriate candidate materials for patterning beyond-CMOS.
Within last two years, we have shown the positive-tone, development-less patterning of calixarene molecular glass resists using highly confined electric field, current-controlled scanning probe lithography scheme. Herein, we give a more detailed view insight describing the applied Scanning Probe Lithography (SPL) technology platform applying selfactuating, self-sensing cantilever. The experimental results are supported by first preliminary simulation results estimating the local electric field strength, the electron trajectories, and the current density distribution at the sample surface. In addition, the diameter of Fowler-Nordheim electron beam, emitted from SPL-tip, was calculated as function of the bias voltage for different current set-points and tip radii. In experimental part we show the reproducible writing of meander line patterns as well as the patterning of individual features using specially developed pattern generator software tool.
The presented work deals with molecular glass resist materials based on (i) calixresorcinarene resist systems, (ii) twisted fully aromatic biscarbazole-biphenyl materials, and (iii) fully aromatic spiro resist materials as new promising materials for Scanning Probe Lithography (SPL). Because of the non-chemically amplified resist nature and the absence of corresponding material diffusion, the novel SPL resists have the potential to increase the patterning resolution capabilities at a simultaneous reduction of the edge roughness (LER). In addition, these low molecular weight molecular glasses offer the advantage of solvent-free film preparation by physical vapor deposition (PVD). The PVD prepared films offer a number of advantages compared to spin coated ones such as no more pinholes, defects, or residual solvent domains, which can locally affect the film properties. These high-quality PVD films are ideal candidates for the direct patterning by SPL tools. Presented highlights are the thermal scanning probe lithography (tSPL) investigations at IBM Research - Zurich and the patterning by using electric field, current controlled scanning probe lithography (EF-CC-SPL) at the Technical University of Ilmenau. Further investigations on film forming behavior, etch resistance, and etch transfer are presented. Owing to the high-resolution probe based patterning capability in combination with their improved etch selectivity compared to reference polymeric resists the presented molecular glass resists are highly promising candidates for lithography at the single nanometer digit level.
Star block copolymer synthesis was performed in a controlled fashion by an in-situ core first ATRP route. The obtained
resist materials on the basis of industrial used monomers with tailored star block copolymer architecture were
systematically characterized and patterned. In dissolution investigations an excellent dissolution contrast between
exposed and unexposed state was identified for this new resist material type. Additionally, the materials show an
excellent sensitivity, which surpass the reference linear copolymer by a factor of eight. By a combinatorial resist
optimization realized high resolution features are presented. Finally, preliminary results utilizing a further improved
resist material design are shown.
As the semiconductor industry moves forward, resolution limits are being pushed to the sub-30 nm regime. In order to
meet these demands, radical new resist design and processes must be explored. We have developed a molecular glass
system for all-dry processing conditions. Physical vapor deposition (PVD) has been used for film formation onto silicon
wafers. PVD deposits a uniform film of controlled thickness free from impurities that are often introduced by casting
solvents used in traditional spin coating methods. Thermal development is used as an alternative to processing in
solvents in order to prevent resist swelling and pattern collapse by capillary forces. The deposited molecule is designed
to crosslink upon E-beam irradiation without additives, and therefore form a homogeneous, single component film.
PAG-attached molecular glasses have been synthesized in order to promote film homogeneity as well. By tethering PAG
directly to the molecular glass core, issues such as PAG aggregation can be remedied. Acid migration, which increases
blur and LER, can also be hindered.
The aim of the paper is the development of an all-dry photolithographic process in which the film preparation step as
well as the development step is performed without the use of solvent. To implement an all-dry photoresist system we
focused on coumarin derivatives, as this class can be photodimerized in the solid state and features sufficient high
thermal stability. The dimerized product exhibits sufficiently different physical properties. The monomer can be
evaporated at elevated temperatures whereas the dimerized product remains non-volatile under these conditions. With a
tailored glass forming coumarin derivative we demonstrated the capability to develop clear patterns. A combinatorial
approach, i.e. producing a compositional library in combination with the variation of exposure dose was utilized to
efficiently optimize the all-dry photoresist system.