Promising lithography techniques for next generation logic devices : a review

Continuous rapid shrinking of feature size made the authorities to seek alternative patterning methods as the conventional photolithography comes with its intrinsic resolution limit. In this regard, some promising techniques have been proposed as next generation lithography (NGL) that have the potentials to achieve both high volume production and very high resolution. This article reviews the promising next generation lithography techniques and introduces the challenges and a perspective on future directions of the NGL techniques. Extreme Ultraviolet Lithography (EUVL) is considered as the main candidate for sub-10 nm manufacturing and it could potentially meet the current requirements of the industry. Remarkable progress in EUVL has been made and the tools will be available for commercial operation soon. Maskless lithography techniques are used for patterning in R&D, mask/mold fabrication and low volume chip design. Directed Self Assembly (DSA) has already been realized in laboratory and further effort will be needed to make it as NGL solution. Nanoimprint Lithography has emerged attractively due to its simple process-steps, high-throughput, high-resolution and low-cost and become one of the commercial platforms for nanofabrication. However, a number of challenging issues are waiting ahead and further technological progresses are required to make the techniques significant and reliable to meet the current demand. Finally, a comparative study is presented among these techniques

Block Copolymer Nanolithography for Sub-50 nm Structure Applications

As high technology device patterns are continuing to move towards decreasing critical dimensions and increasing pattern density, there is a need for lithography to move in the same direction. Block copolymer (BCP) lithography is a promising technique, which has single digit nanometer resolution, has a pattern periodicity of about 7-200 nm, and easily scales up to large area at a low cost. The use of BCPs with high immiscibility of constituent blocks, so-called high-Chi material, enables smaller pattern dimensions and is therefore of special interest. However, for lithography techniques to be applicable, also integration into existing nanofabrication processes is necessary. Furthermore, development of techniques to perform sub 10 nm pattern transfer is an enabler for continued device development. This dissertation first provides an overview of the BCP lithography field, to thereafter study the selective infiltration synthesis of alumina into the maltoheptaose block in high-Chi poly(styrene)-block-maltoheptaose of 12 nm pattern periodicity. The infiltration was studied using neutron reflectometry, and a subsequent sub-10 nm pattern transfer was performed into silicon. Also, it studies the process of surface reconstruction of high-Chi poly(styrene)-block-poly(4-vinylpyridine) of 50 nm pattern periodicity, more specifically the effect of time and temperature on pore diameter. Furthermore, pattern transfer of the surface reconstructed BCP film into silicon nitride, and selective area metal-organic vapor phase epitaxy (SA-MOVPE) of indium arsenide vertical nanowires on a silicon platform, using directed self-assembly is demonstrated. By directing the self-assembly along different crystal directions of the substrate, two vertical nanowire configurations were grown. Demonstration of gate all-around stack deposition of oxide/metal to the densely packed nanowire configurations was thereafter made. The results have contributed to the knowledge on BCP lithography and pattern transfer in the sub 50 nm regime, enabling new approaches for applications such as vertical nanowire, or fin transistors

Advanced resist materials for next generation lithography

With the advancement in technology the minimum lithographic feature size decreases more and more for every generation. The development of lithographic techniques and resist materials capable of meeting the requirements for the up- graded technology (resolution, sensitivity, roughness) started to play a trivial role. However, the issue represents a fundamental principle in lithography (the RLS trade-off) and it proves difficult to overcome. Addition of quenchers in chemically amplified resists reduces the acid diffusion length and improves the line edge roughness and increases the resolution of the patterned features, but decreases the sensitivity. The current most commonly researched approach to boost the sensitivity in organic resists is the addition of metals embedded in the molecular structure by covalent bonds. This approach was investigated in this thesis, and an extension towards high-Z organic additive compounds and high-Z cross-linkers was conducted. Furthermore as feature sizes less than 20 nm are routinely required, pattern col- lapse driven by the capillary forces upon development has become a serious limiting factor, independent of the lithography technique involved. Alongside with constantly developing the resist platforms there is also the need to improve the adhesion of the resist material to the silicon substrate, reducing pattern collapse and allowing for ultra high resolution and high aspect ratio patterning. In this thesis I will present the research I have undertaken in order to implement a resist platform suitable for next generation lithography and I will introduce and describe the new multi-trigger mechanism concept developed for this resist system. I will also present a study on active underlayes investigated for improved adhesion between the resist and the substrate

Novel resists for next generation lithography

With progress in the semiconductor industry, transistor density on a single computer chip has increased dramatically. This has resulted in a continuous shrinkage of the minimum feature size printed through microlithography technology. Resist, as the pattern recording medium of such printing, has been extensively studied to achieve higher resolution, higher sensitivity and lower line edge roughness. For decades this has been realized through chemical amplification. With the feature size continuously shrinking and the energy of exposure source therefore exceeding the resist ionization threshold, the performance of conventional chemically amplified resists is approaching the limits. Novel high-performance chemically amplified resists or non-chemically amplified resists are urgently needed to meet the requirement of next generation lithography. In this work a negative tone chemically amplified resist system based on a novel method to control the catalytic chain reaction is presented. The method to control the catalytic chain reaction is demonstrated using two model polymer resists. This method is then applied to a fullerene-based molecular resist system and a combination of good industrial compatibility, high resolution and good sensitivity has been achieved in this resist. Through a chromatographic separation, another chemically amplified molecular resist was also developed with further improved performance. An alternative route to sensitivity improvement other than chemical amplification is then introduced and a family of fullerene-based metal containing materials is presented. Lithographic performance is compared between the fullerene-metal resists and their control materials without metal. Using an aberration corrected scanning transmission electron microscope, the distribution of metal in the resist film and its behavior during the lithography process is evaluated and discussed