Resist Film Thickness Research Articles

Grazing-Incidence Soft-X-ray Scattering for the Chemical Structure Size Distribution Analysis in EUV Resist

In extreme ultraviolet lithography (EUVL), it is required to develop EUV resist which has low line width roughness (LWR) for the further miniaturization of circuit pattern. In order to reduce LWR, it is necessary to analyze and control the chemical-components spatial distribution in the resist thin film. We have reported that the measurement of chemical-components spatial distribution in the resist thin film coated on the Si3N4 membrane using the method of the transmission-mode resonant soft X-ray scattering (RSoXS). In this study, in order to analyze the chemical-structure-size distribution in the resist thin film on a Si wafer under similar condition adapted to the resist-coating actual process, we examined the grazing-incidence RSoXS (GI-RSoXS). A chemically amplified resist (CAR) and a non-CAR were spin-coated on silicon wafers, which had varied film thickness of 20, 50, and 100 nm. The scattering profile of each sample was measured at the incident photon energy of 280 and 296 eV. As a result, it is suggested that the chemical-structure-size distribution in the resist thin films depends on the resist film thickness. It is confirmed that the GI-RSoXS method is very effective to evaluate the chemical-structure-size distribution of resist thin films.

Resist reflow methodology development to investigate interfacial interactions

BackgroundTo enable printing of smaller feature sizes, lithography has progressed into the extreme ultraviolet lithography (EUVL) regime. Alongside the wavelength scaling, a reduction in resist film thickness (FT) is observed to avoid large aspect ratios that would lead to pattern collapse. The further progression to high numerical aperture (NA) EUVL will require a further reduction in resist FT moving toward an ultra-thin film regime (<30-nm resist FT). This reduction in resist FT will make the interfacial interactions between resist and underlayer more dominant, potentially influencing material behavior and making resist design challenging.AimWe assess a reflow process as a means to investigate interfacial effects and in this way deconvolute the correlation between resist line volume, interfacial effects, and the reflow temperature (TR), defined as the temperature at which the resist line starts broadening, which is indicative of the glass transition temperature (Tg).ApproachWe pattern a model EUV chemically amplified resist at different nominal resist FTs and different critical dimensions (CDs) and half-pitch (HP) combinations to quantify changes in the TR.ResultsThe TR increases with the inverse of the CD, as well as the inverse of the resist FT. Moreover, the TR also scales with the area ratio (the ratio of the area in contact with the ambient to the area in contact with the underlayer).ConclusionsA linear relationship between TR and its volume factor (CD × FT) normalized for the area ratio (area in contact with the ambient to the area in contact with the underlayer) is found, revealing a combined dependency on line volume and interfacial interactions. This opens the potential for the use of the reflow methodology in investigating interfacial interactions.

Chemically amplified resist CDSEM metrology exploration for high NA EUV lithography

Background: The chemically amplified resist (CAR) has been the workhorse of lithography for the past few decades. During the evolution of projection lithography to extreme ultraviolet lithography (EUVL), a continuous reduction in feature size is observed. Also, a reduction in resist film thickness (FT) is required to prevent large aspect ratios that lead to pattern collapse. A further reduction in resist FT, into an ultrathin film regime (<30 nm resist FT), is expected when advancing to high NA EUVL. This brings along associated challenges with (1) resist critical dimension scanning electron microscope (CDSEM) metrology and (2) resist patterning performance. Aim: Assessment of metrology challenges and patterning limits of a CAR working in this ultrathin film regime. Deconvoluting the metrology and patterning effect on the determination of the unbiased line width roughness (uLWR). Approach: Patterning a CAR at different nominal resist FTs on two different underlayers to quantify the changes in CDSEM image quality and resist patterning performance with the resulting uLWR changes. Results: The CDSEM image signal-to-noise ratio (SNR) depends on resist FT and the underlayer. The uLWR increases with a reduction in resist FT but scales differently on the two underlayers. Conclusions: A relationship between CDSEM image SNR and uLWR is found. The SNR and uLWR scaling difference on the two underlayers, as well as the uLWR dependency on SNR was determined to be a metrology effect. The general uLWR increase for a reduced resist FT was determined to be a patterning effect.

Enabling nanoimprint simulator for quality verification: process-design co-optimization toward high-volume manufacturing

Computational technologies are still in the course of development for nanoimprint lithography (NIL). Only a few simulators are applicable to the nanoimprint process, and these simulators are desired by device manufacturers as part of their daily toolbox. The most challenging issue in NIL process simulation is the scale difference of each component of the system. The template pattern depth and the residual resist film thickness are generally of the order of a few tens of nanometers, whereas the process needs to work over the entire shot size, which is typically of the order of several hundred square millimeters. This amounts to a scale difference of the order of 106. Therefore, in order to calculate the nanoimprint process with conventional fluid structure interaction simulators, an enormous number of meshes is required, which results in computation times that are unacceptable. We introduce a process simulator which directly inputs the process parameters, simulates the whole imprinting process, and evaluates the quality of the resulting resist film for jet and flash imprint lithography process. To overcome the scale differences, our simulator utilizes analytically integrated expressions which reduce the dimensions of the calculation region. In addition, the simulator can independently consider the resist droplet configurations and calculate the droplet coalescence, thereby predicting the distribution of the non-fill areas which originate from the trapped gas between the droplets. The simulator has been applied to the actual NIL system and some examples of its applications are presented here.

Theoretical study of interfacial effects on low-energy electron dynamics in chemically amplified resist processes of photomask fabrication

The resist thickness has decreased with the miniaturization of transistors. In chemically amplified electron beam resists used for photomask fabrication, thermalized electrons play an important role in acid generation. The interfacial effects of low-energy electrons strongly affect the latent image formation in thin resist films. In this study, we investigated the relationships between the boundary conditions of low-energy electrons at interfaces and the protected unit distribution in terms of resist thickness, concentrations of photoacid generators and photodecomposable quenchers (PDQs), and sensitivity. The dependences of chemical gradient and optimum PDQ concentration on the boundary conditions at the interfaces for low-energy electrons were clarified. It was found that the PDQ concentration should be optimized, depending on not only the boundary conditions but also the resist film thickness. That is, the resist depth profile can be controlled by the boundary conditions at the interfaces for low-energy electrons.

Power spectral density as template for modeling a metal-oxide nanocluster resist to obtain accurate resist roughness profiles

Background: The metal-oxide resist (MOR) is a promising type of nonchemically amplified resist (CAR) for EUV lithography. This family of resists shows some advantages over the conventional CARs. Even though a prior MOR model exists, no documented references for the application described could be found in open literature to develop a physically rational lithographic model that can accurately simulate and predict lithographic results for these resists. Aim: Increase the fundamental understanding of this class of resists by creating a model that also considers these aspects of the resist. Approach: Model the metal-oxo clusters of the MOR as nanoparticles with an effective radius that operate under excluded volume. Results: We show the possibility to include both the packing noise effect, as well as accurate roughness (characteristics) predictions by utilizing power spectral density (PSD) plots. Conclusions: Varying the calibrated model parameters has a clear effect on the overall roughness of the resist lines and is reflected in the PSD behavior. In contrast to experimental data, changing the resist film thickness did not result in a change in PSD behavior.

Resist thickness dependence of line width roughness of chemically amplified resists used for electron beam lithography

Transistors have been miniaturized to increase their integration. With miniaturization, the thickness of the patterning material, called a resist, has been decreased to prevent them from collapsing. In this study, the resist thickness dependence of the pattern formation of chemically amplified electron beam resists was investigated. The line width roughness (LWR) of resist patterns increased with the decrease of initial resist film thickness. It was found that the dissolution kinetics depended on the initial resist film thickness. The escape of low-energy electrons to the substrates is considered to have resulted in the difference in the dissolution kinetics and LWR.

Investigation of external electrode shape for resist film thickness control by application of external electric field in electrostatic spray coating processes

Investigation of external electrode shape for resist film thickness control by application of external electric field in electrostatic spray coating processes

High efficient deposition using resist film thickness distribution for TSV

High efficient deposition using resist film thickness distribution for TSV

Nanomechanical Analysis of Polydimethylglutarimide Based Lift Off Resist Used for Temporary Bonding and Film Transfers

Temporary bonding has attracted renewed interest for the integration of dissimilar materials in device structures, which cannot be achieved by epitaxial growth techniques alone when the lattice mismatch between the dissimilar materials is too large. In this quest polydimethylglutarimide (PMGI) based lift-off (LOR) resist has been found suitable to serve as a temporary sacrificial adhesive for clean film exfoliation, layer transfer and temporary bonding applications [1]. Furthermore polydimethylglutarimide (PMGI) lends itself easily for temporary bonding purposes, because subsequent complete de-bonding can be readily achieved using an n-methyl-2-pyrrolidone (NMP)-based solvent. In this study we focus on the nanomechanical analysis of PMGI using the Nanoindenter XP by Agilent with continuous stiffness measurement (CSM) attachment. This investigation is aiming to elucidate the relationship between bonding parameters, bond strength and the nanomechanical properties of Young’s modulus and hardness of polydimethylglutarimide (PMGI) as a function of prebake temperature and PMGI resist film thickness. The influence of the spin-on process and the pre-bake treatment on the structure and properties of the PMGI adhesive layers is discussed and correlated to the resulting hardness, modulus and final bond strength and the corresponding Thermal Gravimetric Analysis (TGA) tracking the mass loss of the resist as a function of temperature. . For this experiment Si wafers were first cleaned with standard clean 1 (H2O:NH4OH:H2O2=5:1:1). Afterwards the wafers were spin coated at 2000 rpm with LOR 5A (from MicroChem), which is based on PMGI, and subsequently pre-baked in order to partially evaporate the solvent in the resist. The spin speeds were optimized to achieve 1.00 μm and 500 nm resist thickness for this investigation. Thicker lift-off resist thickness is not practical for a load-depth analysis with a Berkovich tip, because the nanoindenter is depth limited. The solvent, which is used with PMGI lift-off resist is cyclopentanone with a boiling point of 131ºC. With a glass transition point (Tg) of 180-190 ºC, we have chosen to conduct a series of prebakes at 50 °C, 70 °C, 90 °C, 110 °C and 130 °C, 150 °C & 160 °C each for 5 min and to benchmark the results against the hardness and bond strength achieved after thermal compression bonding of Silicon wafer pairs via adhesive PMGI layers at 250 C. This series of different thermal treatments influenced the resist mechanical properties, hardness and modulus. Our nanoindentation experimental results are indicated in Figure 1. As expected, the 500 nm films exhibited high hardness values as compared to the 1 µm thick films. Both PMGI lift-off resist films hardness approach the Si substrate hardness.

A novel simple sub-15 nm line-and-space patterning process flow using directed self-assembly technology

In order to evaluate process performances of directed self-assembly (DSA) lithography for semiconductor device manufacturing, we developed a novel simple sub-15nm line-and-space (L/S) patterning process using polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA) lamellar block copolymer (BCP). The new process with grapho- and chemo-hybrid coordinated line epitaxy, using trimming resist and shallow etching spin-on-glass (SOG) as pinning guide, requires neither special pinning guide materials to control surface free energy on guideline patterns nor any resist strip process after guideline pattern fabrication. In this process, insolubility and thermal resistance of pinning guide are provided by shallow SOG etching deposition residue consisting of SOG-occurring Si and CF4 gas-occurring CF compound. By optimization of guide resist critical dimension (CD) and resist film thickness, the half-pitch (HP) 15nm L/S patterns after dry development were fabricated with the maximum dose margin of approximately 15%. The HP 15nm L/S DSA patterning after SOG full etching was demonstrated on 300mm wafer with 85 chips. The presence of characteristic 3-dimensional (3D) BCP internal defects related to PS short defects was suggested by observation at SOG half-depth etching condition, and defects could be minimized by optimization of neutral layer (NL) material and sufficient phase-separation annealing. The 15nm PS line patterns were transferred to SOG and spin-on-carbon (SOC) stacked substrate.

Material Development for ArF Immersion Resist Extension

ArF immersion process is being widely applied for advanced device manufacturing. ArF immersion lithography can cover 4x nm hp lithography. In addition, double patterning process allows extendibility towards 2x nm hp lithography. From the point of view of photoresist, it is utterly important for materials to bring out the maximum performance of ArF immersion process. In this study, we focused on photoresist development and substrate optimization, demonstrating good lithographic performance of sub-40nm hp resolution with well controlled line width roughness (LWR).First of all, we studied photo acid generator (PAG) behavior focusing on shortening acid diffusion length during Post Exposure Bake (PEB). Secondly, high dissolution contrast polymers in which dissolution properties are changed by acid catalyzed reaction through exposure and PEB are being studied. Thirdly, reflectivity control from substrate through optimization of light intensity over resist film thickness has been carried out. In this report, we have achieved 36.5nm line and space (LS) resolution with LWR of less than 10% of patterned critical dimension (CD). This achievement is very useful especially when utilized in combination with process tricks such as multiple patterning for extending existing ArF immersion lithography towards sub-20nm hp lithography.

Comparison of positive tone versus negative tone resist pattern collapse behavior

In this work, e-beam lithography patterns have been specifically designed and fabricated which provide the opportunity to probe the collapse behavior of both positive and negative tone systems. The pattern layout includes adjacent parallel line structures that both vary in the line size and also in the distance by which they are separated by the space between them. This type of structure allows for the control and modulation of the capillary forces, and ultimately the stresses, experienced by the photoresist line pairs during the final rinse and drying steps of the development process. Using such structures, it is possible to determine the critical stress, i.e., the maximum stress experienced by the photoresist lines before collapse, as a function of a variety of parameters including: material type, substrate preparation conditions, resist film thickness, and resist feature width. In this article, such a modular approach has been used to compare the pattern collapse behavior of a prototypical positive tone resist formulated using a protected hydroxystyrene-based copolymer and a prototypical negative tone epoxide-based molecular photoresist (4-EP). It was found that the critical stress at the point of pattern collapse decreased both as the thickness and the feature width of the resist lines decreased, though this trend was observed to a much lesser extent in the negative tone 4-EP material. It is observed that the negative tone resist, whose imaging mechanism involves cross-linking, shows far superior pattern collapse performance as compared to the positive tone deprotection based resist and is in general able to achieve significantly higher aspect ratio patterning at equivalent feature linewidths.

Simulation and Experimental Study on Photoresist Flow and Deforming Behavior in Imprint Lithography Process

Abstract ：It is necessary to understand and predict the photoresist flow and filling behavior in imprint lithography process to obtain high fidelity replication of the template patterns. The finite element model based on viscosity fluid for resist flow and filling is established considering the properties of the resist adopted in this study and the influences of geometric characteristics of template patterns, initial resist film thickness and micro/nano effect on resist rheologic properties are investigated to distinguish different flow driving mechanisms by tracing the resist moving boundary by using volume of fluid (VOF) method. The calculation results show that the resist filling is accomplished in single or dual peak deformation mode. The mode transition point can be predicted from the ratio of characteristic groove width to initial resist film thickness and the transition point is influenced by the surface/interface effects. The required from pressure is minimized when the aspect ratio of the template patterns is approximately 0.8. The optimal initial resist thickness is about twice of the depth of the patterns on the template considering both the pattern transfer quality and residual resist thickness. The numerical simulations are compared with the related experimental results in imprint lithography and it shows that the calculation results are in good agreement with the experimental results, which indicates that the conclusions from simulation analysis are valid and can be used as the process layout rules for the template pattern geometry, initial resist thickness and template surface treatment.

Fundamental Decomposition Analysis of Chemically Amplified Molecular Resist for below 22nm Resolution

Molecular resists of Prot-2 and Prot-1 were synthesized for decomposition analysis and lithographic evaluation. After checking their structure, purity and thermal property, decomposition behavior was analyzed by high performance liquid chromatography (HPLC). From the analysis, it was found that the main reaction in an exposed area was the deprotection reaction of the protecting group in electron beam (EB) and extreme ultraviolet (EUV) lithography. The exposure dose at which the conspicuous deprotection reaction occurs coincides with the exposure dose at which the resist film thickness reduces. Furthermore, the resists which include completely deprotected group, partially deprotected group and completely protected group, which dissolution rates were different coexist at the boundary between an exposed and an unexposed region. The fundamental decomposition-analysis results indicate that the line edge roughness (LER) is caused by the existence of the different dissolution rates of resist component materials at the boundary between an exposed and an unexposed region. After confirming the fundamental analysis, these molecular resists were evaluated on a lithographic performance by EB lithography. Resist-A consisting of Prot-1 showed 20 nm hp resolution at the exposure dose of 36 μC/cm2. In this paper, we will discuss about the resolution and the LER property of molecular resists at the point of their decomposition behavior.

Processing effects on the dissolution properties of thin chemically amplified photoresist films

Resist film thickness is anticipated to be 60nm in the 22nm technology node setting significant processing challenges due to resist non-bulk behavior. The changes in the dissolution rate of a positive DUV polymer based chemically amplified resist due to various processing conditions such as film thickness, exposure dose, and thermal processing conditions, are experimentally investigated. It is quantified among others, the way an increase of PAB temperature deteriorates dissolution rate at low exposure dose, while in higher exposure doses increasing PAB temperature enhances dissolution rate. Also, an analytic model for the dissolution rate is imported on a stochastic lithography simulator and first quantitative results for thin films are reported.

438 MEMS用微小レジスト構造部材 : 基板間の接合強度に及ぼす膜厚の影響(T09-3 微小機械システムにおけるマイクロ・ナノ力学(3) マイクロ・ナノ実験力学,大会テーマセッション,21世紀地球環境革命の機械工学:人・マイクロナノ・エネルギー・環境)

438 MEMS用微小レジスト構造部材 : 基板間の接合強度に及ぼす膜厚の影響(T09-3 微小機械システムにおけるマイクロ・ナノ力学(3) マイクロ・ナノ実験力学,大会テーマセッション,21世紀地球環境革命の機械工学:人・マイクロナノ・エネルギー・環境)

RIMS (real-time imprint monitoring by scattering of light) study of pressure, temperatureand resist effects on nanoimprint lithography

To optimize nanoimprint lithography (NIL), it is essential to be able to characterize andcontrol the NIL process in situ and in real time. Recently we have developed a real-timeimprint monitoring by the scattering-of-light (RIMS) approach, which allows us to detectthe degree of resist deformation and the duration of resist penetration by a mould duringthe imprint process in real time. In this paper we report the performances of RIMS under abroad range of working conditions. RIMS data shows that the resist penetration isfacilitated by increasing processing temperature, pressure and the resist film thickness; aprolonged pre-NIL resist baking step, on the other hand, has the effect of slowing it down.Our results provide further demonstration of the effectiveness of this method underdifferent working conditions. RIMS measurements show not only how long animprint takes to complete, but also how an imprint progresses with time andhow it is affected by differences in processing parameters. These measurementsprovide information crucial for a better understanding and process optimization inNIL.

Analysis of Outgassing from EUV Resists

Outgassing evaluations of polyhydroxystyrene (PHS) based chemically amplified EUV positive photoresist was performed. As a result, the strong dependencies of outgassing increase to various process conditions such as pre-bake temperature and time, resist film thickness and pre-exposure retarding time in vacuum were understood. Of these process conditions, the most significant process factor was known to be the variation of pre-bake temperature. It was concluded that the main cause of such variations were the effect of residual solvent in the photoresist film. From a re-analysis of the mass spectrum, outgassing components released during EUV exposure have been observed and classified into two general types of release trends; fast and slow reaction rate components. Fast reaction rate components were assumed to have originated from photoresist photo-acid generator (PAG) (48amu and 64amu). On the other hand, slow reaction rate components assumed to be mostly CxHy, have been speculated to originate from the decomposition of the photoresist protecting group after reaction with the released photoacids of PAG. Based on these results, the further analysis of photoresist outgassing release mechanisms upon EUV exposure was made possible.

Electron beam lithography with negative Calixarene resists on dense materials: Taking advantage of proximity effects to increase pattern density

A high-resolution negative Calixarene resist has been used to pattern 2-nm-thick TiO2 films on 50-nm-thick Pt layers by electron beam lithography, in order to carry out site controlled growth of Pb(Zr,Ti)O3 structures. Single dot structures have been written in a 60-nm-thick Calixarene layer at e-beam acceleration voltages of 10 kV (100 pA) and 20 kV (200 pA). The necessary dose for complete dot development ranged from 5 to 25mC∕cm2. Due to the high density Pt layer, the dot-size depended very much on the volume of backscattered electrons. The minimum dot size (70 nm) was found to lie in the range of the resist film thickness. Proximity effects have been studied. At smaller beam energies, a reversed proximity effect has been observed, in the sense that the dot size decreased due to proximity. An irradiation model is proposed based on exposure from bottom to top, and taking into account a competition between cross-linking and bond-scission.