Search query: mechanism of chemically amplified resist

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abstract: The photo mask in lithographic process of semiconductor device has an important role to transfer the downsized target image to the wafer. Due to the development of information society, demand for semiconductor devices has been growing. In order to increase photo mask manufacturing throughput, the current density of electron beam (EB) has been getting higher. EB exposure increases the resist temperature on mask substrate inhomogeneous depending on its current density, shot size, writing order and etc. It is known that the resist sensitivity increases with irradiated resist temperature (heating effect) So, inhomogeneous temperature increase of resist on mask substrate disturbs precise pattern formation. However, the physical or chemical mechanism of heating effect has been still unknown. Here, we examined temperature dependence of acid generation process in chemically amplified resists (CARs) Poly(4 hydroxystyrene) (PHS) and poly(4 (tert butoxycarbonyl)oxy]styrene co 4 hydroxystyrene) (PTBSHS) were used as CAR resin. Monte Carlo simulation moving thermalized electron under the electric field between polymer radical cations were performed with changing the temperature. From the simulation, it was revealed that the energy increase of thermalized electron contributes to the acid yield by 0.038 /K. Quantification of the acid yields in resist films upon exposed to EB were performed with changing the temperature by titration method using Coumarin 6 (C6) as an acid sensitive dye. The acid yield increased by 0.14 /K in PHS film and 0.21 /K in PTBSHS film, respectively. Both values were higher than the simulation value (0.038 /K) Pulse radiolysis experiment was also performed to observe deprotonation of polymer radical cations at 298 and 343 K. The decay of dimer radical cation of PTBSHS became 1.6 times faster at 343 K than that at 298 K. From the results, it is suggested that the heating effect mainly caused by the temperature dependence of deprotonation rate from the radical cations of PTBSHS.
author_names: Yoshihiro Ikari

N Maeda

Akihiro Konda

Takahiro Kozawa

Toshihiko Tamura
title: Mechanism of resist heating effect in chemically amplified resist
venue: Advanced Lithography
year: 2020

abstract: EUV lithography utilizes photons with 91.6 eV energy to ionize resists, generate secondary electrons, and enable electron driven reactions that produce acid in chemically amplified photoresist. Efficiently using the available photons is of key importance. Unlike DUV lithography, where photons are selectively utilized by photoactive compounds, photons at 13.5nm wavelength ionize almost all materials. Nevertheless, specific elements have a significantly higher atomic photon absorption cross section at 91.6 eV. To increase photon absorption, sensitizer molecules, containing highly absorbing elements, can be added to photoresist formulations. These sensitizers have gained growing attention in recent years, showing significant sensitivity improvement. But there are few experimental evidences that the sensitivity improvement is due to the higher absorption only, as adding metals salts into the resist formulation can induce other mechanisms, like modification of the dissolution rate, potentially affecting patterning performance. In this work, we used different sensitizers in chemically amplified resist. We measured experimentally the absorption of EUV light, the acid yield, the dissolution rate and the patterning performance of the resists. Surprisingly, the absorption of EUV resist was decreased with addition of metal salt sensitizers. Nevertheless, the resist with sensitizer showed a higher acid yield. Sensitizer helps achieving higher PAG conversion to acid, notably due to an increase of the secondary electron generation. Patterning data confirm a significant sensitivity improvement, but at the cost of roughness degradation at high sensitizer loading. This can be explained by the chemical distribution of the sensitizer in the resist combined with a modification of the dissolution contrast, as observed by Dissolution Rate Monitor.
author_names: Yannick Vesters

Jing Jiang

Hiroki Yamamoto

Danilo de Simone

Takahiro Kozawa

Stefan De Gendt

Geert Vandenberghe
title: Sensitizers in EUV chemically amplified resist: mechanism of sensitivity improvement
venue: Advanced Lithography
year: 2018

abstract: Extreme ultraviolet (EUV) lithography is one of the most promising techniques in the semiconductor industry to enhance resolution, line edge roughness (LER) and sensitivity of chemically amplified resist (CAR) pattern. Post exposure bake (PEB) process, a major process in EUV lithography, has been studied by experimental approach, but they are confronted by time consuming tasks for massive combinatorial research. Also, theoretical models have been reported to explain fundamental mechanism of the process, but the single scale simulation studies show obvious limitations for accurate prediction of photo chemical reactions in photoresist (PR) matrix and the resulting morphology of line pattern. In order to settle the problem, a multiscale model (density functional theory (DFT) molecular dynamics (MD) finite difference method (FDM) integration) was developed to simulate chemical reactions including PAG dissociation, acid diffusion, and deprotection of photoresist in our previous study, which is based on two components system (PAG and PR) Herein, we propose the multiscale model for three molecular components consisting of PAG, PR, and photo decomposable quencher (PDQ) which is widely used for fine PR pattern fabrication by neutralizing acid in unexposed region of the resist. The newly constructed model reflects more realistic acid diffusion and chemical reactions on PEB process. This achievement will be helpful to identify critical design parameters and suggest optimized design materials in EUV lithography process.
author_names: Hyungwoo Lee

Muyoung Kim

Jung-Nim Moon

Sungwook Park

Byunghoon Lee

Changyoung Jeong

Maenghyo Cho
title: Multiscale approach for modeling EUV patterning of chemically amplified resist
venue: Advanced Lithography
year: 2019

abstract: The reaction mechanism of chemically amplified resist (CAR) after irradiation with ionizing radiation is important for developing extreme ultraviolet and electron beam lithography. The acid generation after the ionization is an essential reaction in CAR. In this study, the intermediate of the proton source of acid (a radical cation of the base polymer) in the presence of a photoacid generator (PAG) was investigated by the pulse radiolysis method. The deprotonation kinetics of the radical cation of poly(4 hydroxystyrene) (PHS) in solutions with and without PAG shows only a small difference. However, the yield of radical cations of poly(4 methoxystyrene) (PMOS) as a model of the resist with a protecting (releasing) group increases upon adding PAG. The formation of the ion pair between the PMOS radical cation and the dissociated anion with a lifetime of approximately 30 to 40 us is suggested. The lower acid yield in PMOS than in PHS film is also discussed in terms of the stability of the radical cation.
author_names: Kazumasa Okamoto

Hiroki Yamamoto

Takahiro Kozawa

Ryoko Fujiyoshi

Kikuo Umegaki
title: Pulse radiolysis study of polystyrene based polymers with added photoacid generators: Reaction mechanism of extreme ultraviolet and electron beam chemically amplified resist
year: 2015

abstract: The elevation of resist temperature during exposure to electron beam (EB) deforms the patterns of chemically amplified resists. The resist heating effect is a significant problem in mask production using a high current EB mask writer. However, its mechanism is still unknown. In this study, the effects of electron thermal energy on the sensitization process of chemically amplified EB resists were investigated using simulation on the basis of their sensitization mechanism. The decomposition yield of sensitizers increased with resist temperature. The effect of the increase of decomposition yield on the critical dimension (CD) was calculated on the basis of the reaction mechanism. When the exposure pattern width was set to the same as the half pitch (16 nm) the values of dCD/d T were 0.019, 0.013 and 0.010 nm K 1 for the sensitizer concentrations of 0.2, 0.3 and 0.4 (molecules) nm 3, respectively. dCD/d T was decreased by decreasing the exposure pattern width.
author_names: Takahiro Kozawa

Takao Tamura
title: Theoretical study on effects of electron thermal energy on sensitization process of chemically amplified electron beam resists contribution to resist heating effect in electron beam mask writing
venue: Japanese Journal of Applied Physics
year: 2019

abstract: The acid diffusion in chemically amplified resists (CARs) which are a current standard resist for semiconductor device manufacturing is a significant concern in the development of highly resolving resists. Thus, high resolution CARs are reduced the number of the acid catalytic reaction per acid by high amount of acid quencher to suppressed acid diffusion blur for remaining low line width roughness (LWR) number. Non chemically amplified resists (non CARs) are generally lower LWR than CARs. However, non CARs are generally less sensitive to radiation than CARs due to lack of amplification mechanism. Recently, we proposed a negative type resist utilizing non CAR and CAR reactions on the same platform. This resist use radiation induced non catalitic reactions which are polarity change of onium decomposition and radical crosslinking of radiation decomposed monomers. And also, the resist uses an acid catalytic etherification utilizing diphenyl methanol derivative and aliphatic alcohol. These combination reaction by non CARs and CAR are expected to contribute the sensitivity improvement for high resolution resist. The synthesized resists were composed of triarylsulfonium cations as a polarity changer and radical generator, 2,2,2 trisubstituted acetophenone as a radical generator, triphenyl(4 vinylphenyl)stannane (TPSnSt) as an EUV absorption enhancer and a quencher, and 4 (2,4 Dimethoxyphenyl)hydroxymethyl]phenylmethacrylate (ARMA) as a polymer bound acid reactive unit. As the result, a 25 nm HP pattern could be obtained with 2.1 nm LWR and at 160 mC/cm2.
author_names: Satoshi Enomoto

Kohei Machida

Michiya Naito

Takahiro Kozawa
title: Study of RLS trade off mitigation utilizing a novel negative chemically amplified resist for high resolution patterning
venue: Photomask Technology
year: 2019

abstract: The stochasticity in the sensitization processes of resist materials is a significant concern in the fine patterning. Such stochasticity results in the protected unit fluctuation in the case of a chemically amplified resist, which is a standard resist for photomask production. After development, the protected unit fluctuation comes to surface as line edge roughness, stochastic pinching, and stochastic bridging. In this study, the protected unit fluctuation after postexposure baking was investigated, assuming the fabrication of line and space patterns. The standard deviation of the number of protected units connected to a polymer molecule was calculated using a Monte Carlo method on the basis of the sensitization mechanism of chemically amplified electron beam (EB) resists. The dependences of the standard deviation on half pitch, sensitivity, sensitizer concentration, and exposure pattern width were clarified.
author_names: Takahiro Kozawa

Takao Tamura
title: Theoretical study on protected unit fluctuation of chemically amplified resists used for photomask production by electron beam lithography
year: 2020

abstract: Abstract. Extreme ultraviolet (EUV) lithography utilizes photons with 92 eV energy to ionize resists, generate secondary electrons, and enable electron driven reactions that produce acid in chemically amplified photoresists. Efficiently using the available photons is of key importance. To increase photon absorption, sensitizer molecules, containing highly absorbing elements, can be added to photoresist formulations. These sensitizers have gained growing attention in recent years, showing significant sensitivity improvement. Aside from an increasing absorption, adding metal salts into the resist formulation can induce other mechanisms, like higher secondary electron generation or acid yield, or modification of the dissolution rate that also can affect patterning performance. In this work, we used different sensitizers in chemically amplified resists. We measured experimentally the absorption of EUV light, the acid yield, the photoelectron emission, the dissolution rate, and the patterning performance of the resists. Addition of a sensitizer raised the acid yield even though a decrease in film absorbance occurred, suggesting an apparent increase in chemically resonant secondary electrons. While patterning results confirm a significant sensitivity improvement, it was at the cost of roughness degradation at higher sensitizer loading. This is hypothesized by the chemical distribution of the sensitizer in the resist combined with a modification of the dissolution contrast, as observed by dissolution rate monitor measurements.
author_names: Yannick Vesters

Jing Jiang

Hiroki Yamamoto

Danilo de Simone

Takahiro Kozawa

Stefan De Gendt

Geert Vandenberghe
title: Sensitizers in extreme ultraviolet chemically amplified resists: mechanism of sensitivity improvement
year: 2018

abstract: The influence of degree of copolymerization of poly(styrene ran methyl methacrylate) [P(S MMA) on the deprotonation mechanism for EUV chemically amplified resists were investigated by pulse radiolysis, quantity of the acid yield, and density functional theory methods. The degradation of MMA unit occurs immediately before the hole transfer to the styrene unit in P(S MMA) in the low PS mole fraction 50 The hole transfer from MMA unit to styrene units occurred in the high PS mole fraction 70 It is assumed that the formation of styrene multimer (n 3) causes the hole transfer.
author_names: Yasuharu Tajima

Kazumasa Okamoto

Takahiro Kozawa

Seiichi Tagawa

Ryoko Fujiyoshi

Takashi Sumiyoshi
title: Deprotonation mechanism of poly(styrene acrylate) based chemically amplified resist
venue: Advanced Lithography
year: 2011

abstract: As EUV approaches its insertion point into high volume manufacturing the semiconductor industry is increasingly focusing on photoresist performance. Recently metal containing resists have been proposed as alternatives to standard Chemically Amplified (CA) systems. Both approaches suffer from an incomplete knowledge of the EUV imaging mechanism. In particular the origin, number and fate of the secondary electrons believed to be active in the resist reactions is poorly understood. In this contribution we describe a study designed to try and characterize these processes and quantify the reactions that determine resist performances. We will describe experiments on a series of model CA systems doped with inorganic salts. Photoacid yields and relative rates of deprotection will be reported for metal salts that can be incorporated into polymer films at concentrations as high as 10 molal. In addition to comparing the relative performance at EUV we will also be characterizing the response at 248 nm and 100 KeV e beam. The results of these studies will be discussed in terms of the metal ion crossection, ionization potential and redox potential. In addition we will describe some unanticipated EUV reactivity of standard acid indicators that may impact the accepted electron yield/photospeed measurements that have been reported for EUV CA resists.
author_names: Gregory M Wallraff

Hoa Dao Truong

Martha I Sanchez

Noel Arellano

Alexander M Friz

Wyatt A Thornley

Oleg Kostko

Daniel S Slaughter

D Frank Ogletree
title: Model studies on the metal salt sensitization of chemically amplified photoresists (Conference Presentation)
venue: Advances in Patterning Materials and Processes XXXVI
year: 2019