The increase in the demand of sub-10 nm feature size in semiconductor industries necessitates a new kind of resist material development which can absorb a large fraction of irradiation and retains the small size cluster distribution (1-2 nm). In this context, we developed a novel nickel-based organo-metallic cluster comprising high optical density inorganic nickel as metal building units (MBU), and 3,3-Dimethylacrylic acid as an organic ligand to form Ni-DMA clusters. The synthesised clusters have ~1 nm size with narrow size distribution. The formulated resist shows the negative tone pattern when exposed with a focused helium ion (He+) beam and e-beam. The high-resolution line patterns of ~8 nm at the dose of ~40 μC cm-2 were obtained with the minimum line edge roughness (LER) and line width roughness (LWR) of 2.16 ± 0.04 nm and 3.03 ± 0.06 nm, respectively.
To meet the International Roadmap for Device and Systems (IRDS), the development of an advanced lithography process for next-generation (NG) technology node is a vital and challenging task, as we are reaching to its physical limits. In the progress of high volume manufacturing (HVM) at sub-12 nm node, it is very important that resist materials should possess low line edge roughness (LER) and high sensitivity (E0) using extreme ultraviolet (EUV) and its analogous exposure systems. Apart from standard chemically amplified resist (CAR), acid-free non-CAR has been studied immensely as a potential candidate for NG patterning. To achieve sub-12 nm patterns, a complete study for newly developed n-CAR is required to make sure that developed resist formulation is performing optimally. Aside from the n-CARs, we adopted a novel patterning approach using He+ ion beam lithography with less proximity effect. Here we present the metallic nanoparticle photo-multiplier (high optical density materials for λ ~13.5 nm) embedded with n-CAR for better photo-absorption and high-resolution pattern development. The silver (Ag- OD 12 w.r.t Carbon) nanoparticles (NPs) with ~2 nm regime were embedded into MAPDST homo-polymer ((4-(methacryloyloxy)phenyl) dimethylsulfonium trifluoromethanesulfonate). To investigate the high-resolution patterning synthesized photoresist was exposed to e-beam (Ee) and Helium ion (EHe) beam lithography. The patterned samples were developed in aqueous solution and revealed the negative tone with the sensitivity of 172 μC/cm2 and 50.4 μC/cm2 for Ee and EHe respectively. The MAPDST-Ag resist found stable for more than 1 year, which clearly suggests that there is no sign of Ag-NPs agglomeration in the formulation. Thence, evidently, prove the considerable shelf life of developed resist formulation and can be used in NG semiconductor device HVM and other electronic device applications.
MAPDST (4-(methacryloyloxy)phenyl)dimethylsulfoniumtrifluoromethanesulfonate)) based resist analogous are reported to pattern high-resolution nano features (20 nm) under wide range of lithography tools including electron beam lithography (EBL), extreme ultraviolet lithography (EUVL), 193 nm immersion lithography etc. However, these resists have not yet patterned lower node features, especially at sub-15 nm regime with ultra-low line edge roughness (LER) and line width roughness (LWR). One of the methods to improve the resolution of a resist is the structural modification. Towards this, we have developed two new hybrid copolymer resists i.e MAPDST-co-ADSM and MAPDST-co-TPMA by the copolymerization of radiation sensitive organic MAPDST with hybrid tin monomers ADSM and TPMA (ADSM = acetyldibutylstannyl methacrylate; TPMA = triphenyl tin methacrylate) for high-resolution EBL applications. The developed resists were studied for their sub-15 nm line patterns with low LER and LWR features. Various line features, starting from 30-12 nm with different line/space (L/S to L/10S) characteristics were studied at various e-beam doses 200- 1200 μC/cm2. Isolated 12 nm line features have been achieved with the resist MAPDST-co-ADSM at a dose 1200 μC/cm2. Meanwhile, the MAPDST-co-TPMA resist patterned 15 nm features at the dose 700 μC/cm2. The estimated sensitivity and contrast of resists MAPDST-co-ADSM and MAPDST-co-TPMA were 1.60; 450 μC/cm2 and 1.55; 380 μC/cm2 respectively. Similarly, the computed LER and LWR parameters exhibited by the resists MAPDST-co-ADSM and MAPDST-co-TPMA for sub-30 nm features were 0.99; 1.22 and 1.8; 3 nm respectively. The e-beam studies revealed a resolution enhancement of the hybrid resists at 12 nm regime as compared to the neat poly(MAPDST) resist (where the resist resolution was 20 nm) indicating improvements in the lithography properties of these resists.
KEYWORDS: Ions, Electron beam lithography, Monte Carlo methods, Helium, Thin films, Electrons, Line edge roughness, Lithography, Optical lithography, Line width roughness
Patterning of the resist features down to 10 nm node is crucial for futuristic integrated circuits (ICs) technology advancements. In this regard, we design and developed a novel hybrid non-chemically amplified resist (n-CAR) i.e. MAPDST-co-ADSM (where MAPDST = (4-(methacryloyloxy)phenyl) dimethylsulfonium trifluoromethanesulfonate and ADSM = (acetyldibutylstannyl methacrylate)) for high-resolution Helium Ion (He+) Beam Lithography (HIBL) studies. The developed resist exhibits the high sensitivity toward Helium ion radiation and patterned sub-15 nm features at the dose ∼50 μC/cm2 onto negative tone resist formulation. In order to recognize the critical dimension (CD), the resist thin films were analyzed for single pixel exposure dose analysis at He+ exposure dose ranging from ∼30 pC/cm to ∼100 pC/cm. These investigations apparently reveal that 10 nm single pixel line features of the MAPDST-co-ADSM resist is patterned with the dose ∼50.48 pC/cm. The improved patterning resolution of the resist down to 10 nm is due to the inclusion of hybrid tin sensitizer in the resist structures. The MAPDST-co-ADSM showed coherent line edge roughness (LER) and line width roughness (LWR) values for 15 nm lines features as ∼1.67±0.27 nm and ∼2.20 nm respectively.
Monte Carlo-based simulation technique is a standard method for statistical analysis and modelling of stochastic processes; such as noise in circuits, carrier transport and study of ion implantation/interaction/trajectory on materials for integrated circuits. Thus Monte Carlo ion trajectory simulation for MAPDST-co-ADSM resist formulation showed that the negligible (∼0.5%) target damage and recoil generation (atom displacement) of total energy delivered to the system (MAPDST-co-ADSM/Si) in novel HIBL exposure due to much larger stopping power of He+ ion and low proximity effect.
Although extreme ultraviolet (EUV) lithography is being considered as one of the most promising next-generation lithography techniques for patterning sub-20 nm features, the development of suitable EUV resists remains one of the main challenges confronting the semiconductor industry. The goal is to achieve sub-20 nm line patterns having low line edge roughness (LER) of <1.8 nm and a sensitivity of 5 to 20 mJ/cm2. The present work demonstrates the lithographic performance of two nonchemically amplified (n-CARs) negative photoresists, MAPDST homopolymer and MAPDST-MMA copolymer, prepared from suitable monomers containing the radiation sensitive sulfonium functionality. Investigations into the effect of several process parameters are reported. These include spinning conditions to obtain film thicknesses <50 nm, baking regimes, exposure conditions, and the resulting surface topographies. The effect of these protocols on sensitivity, contrast, and resolution has been assessed for the optimization of 20 nm features and the corresponding LER/line width roughness. These n-CARs have also been found to possess high etch resistance. The etch durability of MAPDST homopolymer and MAPDST-MMA copolymer (under SF6 plasma chemistry) with respect to the silicon substrate are 7.2∶1 and 8.3∶1, respectively. This methodical investigation will provide guidance in designing new resist materials with improved efficiency for EUVL through polymer microstructure engineering.
It is expected that EUV resists must simultaneously pattern 20-nm half-pitch and below, with an LWR of <1.8 nm, and a sensitivity of 5–20 mJ/cm2. In order to make a resist perform optimally, new resist chemistry is required. One such approach being investigated by us is the development of polymeric non-CAR negative photo resists for sub 16 nm technology which is directly sensitive to radiation without utilizing the concept of chemical amplification (CARs). These resist designs are accomplished by homopolymers which are prepared from monomers containing sulfonium groups. We have achieved 20 nm patterns by e-beam lithography using this system. Here we will discuss in detail process parameters such as: spinning conditions for film thicknesses <50 nm and resulting surface topographies, baking regimes, exposure conditions and protocols on sensitivity, contrast, resolution and LER/LWR. Etch resistance data on these thin films will also be provided. Our results are aimed to provide a clear understanding of how these critical steps in the lithographic imaging process will affect extendibility of the non-CAR resist concept to sub 20 nanoscale features. Photodynamics and EUV exposure data will be covered.
The design, synthesis and characterization of non-chemically amplified negative tone electron-beam and EUV resists
based on the inclusion of a radiation sensitive sulfonium functional group are outlined.. MAPDST (4-(methacryloyloxy phenyldimethylsulfoniumtriflate) and MANTMS (1-(4-(methacryloyloxy)naphthalen-1-yl)tetrahydro-1H thiopheniumtrifluoromethane sulfonate) monomers each containing the sulfonium group underwent homo- and copolymerizations using free radical polymerization with 2,2'-azobisisobutyronitrile (AIBN) initiator. These resist materials were evaluated by EB lithography using 20 keV electron beam and EUV lithography to obtain sub-20 nm line patterns. These features were optimized ranging from resist coating, pre-exposure bake, exposure to e-beam, postexposure bake, development and imaging. Our investigation showed that these newly synthesized resists are potential viable candidates for EUV lithography based on their ability to form flaw free thin films < 50nm, sensitivity, resolution and LER control.
Herein, we describe preliminary results on organic-inorganic hybrid photoresists, capable of showing line
patterns up to 16 nm under e-beam exposure studies, prepared by incorporating polyoxometalates (POMs)
clusters into organic photoresist materials. Various Mo and W based clusters such as (TBA)2[Mo6O19],
(TBA)5(H)[P2V3W15O62] and (TBA)4[P2Mo18O61] (where TBA = tetrabutyl ammonium counter ion) have been
incorporated into PMMA matrix by mixing POM solutions and standard PMMA polymer in anisole (MW ~
95000, MicroChem) in 1:33 w/v ratio. E-beam exposure followed by development with MIBK solutions showed
that these new organic-inorganic hybrid photoresists show good line patterns upto 16 nm, which were not
observed in the case of control experiments done on pure PMMA polymer resist. The observed enhancement of
resist properties in the case of hybrid resists could possibly be due to a combination of features imparted to the
resist by the POM clusters such as increased sensitivity, etch resistance and thermal stability.
We report the lithography performance of novel non chemical amplified (n-CARS) negative photoresist materials which are accomplished by homopolymers and copolymers that are prepared from monomers
containing sulfonium groups. The latter have long been found to be sensitive to UV radiation and undergo polarity change on exposure. For this reason, these groups were chosen as radiation sensitive groups in non-
CARs that are discussed herein. Novel n-CAR negative resists were synthesized and characterized for EUVL applications, as they are directly sensitive to radiation without utilizing the concept of chemical amplification. The n-CARs achieved 20 and 16 nm L/2S, L/S patterns to meet the ITRS requirements. We will also discuss the
sensitivity and LER of these negative n-CARS to e-beam irradiation which will provide a basis for EUVL down
to the 16 nm node and below. These new negative tone resist provide a viable path forward for designing non-
chemically amplified resists that can obtain higher resolutions than current chemically amplified resists at competitive sensitivities.
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