Controlling gold nanoparticle assembly on electron beam-reduced nitrophenyl self-assembled monolayers <i>via</i> electron dose

Electron beam lithography is a well-established tool suitable for the modification of substrate surface chemistry. It therefore follows that the deposition and self-assembly of nanoparticles on a surface can be directed using this method. This work explores the effect of electron dose on the electron beam lithographic patterning of self-assembled monolayers (SAMs) on gold surfaces. Electron beam irradiation of the sample induces conversion of the SAM terminal functional aromatic nitro (NO2) moieties to aromatic amino (NH2) moieties. The cationic NH2 functionalised regions direct the site-specific assembly of anionic citrate-passivated gold nanoparticles in aqueous solution at pH 4.5. Control of nanoparticle attachment to the SAM is demonstrated over the exposure range 5000–125,000 uC/cm2. Overexposure led to significant numbers of secondary electrons reaching the surface, causing conversion of functional aromatic moieties outside of the regions irradiated, which reduced feature quality and regional selectivity of adsorption

Alternative resist approaches

As the challenges of next generation lithography have increased it has become increasingly difficult to maintain progress with traditional photoresists. A substantial research effort in to nonconventional approaches for extreme ultraviolet (EUV) resist materials is now underway. In this chapter a variety of approaches including resists with low, or with high, EUV absorbance, and resists formulated from organic-metal oxides and organic-nanoparticle composites are examined.</p

Negative-tone organic molecular resists

Negative-tone molecular resists are organic small molecule resists that can be lithographically patterned in the negative tone. This chapter examines a wide variety of different resists of this type that have been developed and investigated including fullerene, triphenylene, calixarene, noria, and polyphenol-based resists along with other unique compounds. A review of the chemistry and physics of cationic polymerization and cross-linking of functional groups such as epoxides and oxetanes is also included, as this approach is used in many different resist designs. Resolution below 20 nm has been reported in a number of different designs in extreme ultraviolet and electron beam, and isolated lines of 10 nm and below are seen in some resists with electron beam patterning. Negative-tone molecular resists have shown good combinations of resolution, sensitivity, and line-edge roughness and continue to hold promise for use in the next generation lithography.</p

Negative-tone organic molecular resists

Negative-tone molecular resists are organic small molecule resists that can be lithographically patterned in the negative tone. This chapter examines a wide variety of different resists of this type that have been developed and investigated including fullerene, triphenylene, calixarene, noria, and polyphenol-based resists along with other unique compounds. A review of the chemistry and physics of cationic polymerization and cross-linking of functional groups such as epoxides and oxetanes is also included, as this approach is used in many different resist designs. Resolution below 20 nm has been reported in a number of different designs in extreme ultraviolet and electron beam, and isolated lines of 10 nm and below are seen in some resists with electron beam patterning. Negative-tone molecular resists have shown good combinations of resolution, sensitivity, and line-edge roughness and continue to hold promise for use in the next generation lithography.</p

High-carbon fullerene based spin-on organic hardmask

Irresistible Materials has previously introduced the HM340 series of fullerene based spin-on carbon, and reported on material characterization, including very high carbon content and high thermal stability. The materials have a low Ohnishi number providing high etch durability and the low hydrogen level allows for high-resolution etching without wiggling. Here we present further investigation of the spin-on-carbon, and demonstrate the flexibility of the platform. Film carbon content can be easily varied from as high as 95% (suitable for high durability etches) to as low as 80% (for instance to use as a sacrificial etch material). We present characterisation of the optical properties of the materials, and process and formulation developments. Work to vary the curing temperature between 200 and 300°C, and to reduce cure times to 90 seconds or less has been successfully undertaken. Alternative casting solvents have been investigated and work to achieve spin coatable film thickness ranges from less than 50 nm to significantly more than 500nm is described. and spin-coatable film thickness ranges from less than 50 nm to significantly more than 500nm are described. Results from initial planarisation trials are presented together with initial results from on-going work on spin-on carbon formulations that exceed 95% carbon content.</p

Dynamic absorption coefficients of CAR and non-CAR resists at EUV

The dynamic absorption coefficients of several CAR and non-CAR EUV photoresists are measured experimentally using a specifically developed setup in transmission mode at the XIL beamline of the Swiss Light Source. The absorption coefficient α and the Dill parameters ABC were measured with unprecedented accuracy. In general the α of resists match very closely with the theoretical value calculated from elemental densities and absorption coefficients, whereas exceptions are observed. In addition, through the direct measurements of the absorption coefficients and dose-to-clear values, we introduce a new figure of merit called Chemical Sensitivity to account for all the post-absorption chemical reaction ongoing in the resist, which is also predicts a quantitative clearing volume, and respectively clearing radius, due to the photon absorption in the resist. These parameters may help in deeper insight into the underlying mechanisms of EUV concept of clearing volume and clearing radius are then defined and quantitatively calculated.</p

Optimization and sensitivity enhancement of high-resolution molecular resist for EUV lithography

We have recently introduced a new molecular resist system that demonstrates high-resolution capability. A series of studies such as quencher choice and loading was conducted in order to optimize the performance of this material. The optimized conditions allowed patterning 14 nm half-pitch (hp) lines with a line width roughness (LWR) of 3.56 nm at the XIL beamline of the Swiss Light source. Furthermore it was possible to resolve 11 nm hp features with 5.9 nm LWR. First exposure results on an NXE3300 are also presented. We have also begun to investigate the addition of metals to EUV photoresist as a means to increase sensitivity and modify secondary electron blur. Initial results for one of the metal additives show that the sensitivity could be enhanced by up to 60 percent.</p

Sub-20 nm Si fins with high aspect ratio via pattern transfer using fullerene-based spin-on-carbon hard masks

We report on a novel and simple pattern transfer process into Si via fullerene-based spin-on-carbon (SOC) hard masks in this work. Electron beam lithography and extreme ultraviolet interference lithography techniques are used to pattern high-resolution and dense lines on a resist/SOC bilayer. The patterns are subsequently transferred by a low-pressure O 2 plasma etching (SOC) and reactive ion etching process with a gas mixture of SF 6 and C 4 F 8 (Si). Si sidewall trimming can be controlled by modifying the Si etching rate, achieving Si fins with dimension down to 15 nm half-pitch with aspect ratio as high as of 7:1.</p