Performance enhancements with the high opacity multi-trigger resist

Single exposure EUV patterning for lower pitches (below 32 nm L/S) proves to be challenging and dependent on a series of factors including exposure tool related parameters such as illumination conditions but also material related parameters such as sensitivity to EUV photons and resist chemistry. While the industry is focused on developing a set of universal exposure conditions that can be applied to all resist systems, material suppliers must constantly enhance the exposure mechanism of the resists in order to support further advance in technology. The multi-trigger concept involves a reaction that will only occur when multiple elements of the resist are initiated concurrently and in close spatial proximity in order to enable the catalytic reactions. In high dose areas the resist behaves like a traditional CAR, whilst in low dose areas, such as line edges, the reaction is second-order increasing the chemical gradient. Effectively there is a dose dependent quenching-like behaviour built into the resist, enhancing chemical contrast and thus resolution, whilst eliminating the materials stochastics impact of a separate quencher reducing roughness. The multi-trigger resist (MTR) presented consists of a novel multi-trigger control molecule and a crosslinker, which represent the resist matrix, together with a photoacid generator (PAG). Here we present results from work focused on the enhancement of the high-opacity MTR resist. The absorptivity of the resist can be increased by replacing the standard crosslinker with a high-opacity crosslinker. The absorptivity of the crosslinking molecule can itself be changed by varying both the number of attached photo-absorption groups and by varying the specific choice of the high opacity group. Other modifications to the crosslinking molecule, which are presented, include reducing the steric hindrance of the molecule by changing the structure. The high-opacity crosslinker molecules have been synthesized and then formulated into the MTR resist. We report results obtained using the new MTR system containing this high-opacity cross-linker with a variation of process conditions, and with formulation variations. The lithographic performance of a formulation containing this crosslinker, at pitch 32nm patterned on an NXE3400 is presented. The sensitivity of the resist can be increased by 25% by varying the length of the crosslinker arm whilst keeping other factors such as the number of high opacity groups constant. Furthermore, we have also investigated increasing the activation energy of the self-quenching aspect of the MTR system. In the case presented, MTR8 has a higher activation energy than MTR2 and MTR4. Having a higher activation energy is predicted to allow the introduction of a post exposed bake (PEB) to increase crosslinking and reduce pattern collapse, whilst simultaneously preserving the self-quenching behaviour. We will present results which show using a higher activation energy molecule (MTR8) results in a minimisation of Z-factor and LWR, when increasing the PEB temperature by 10 degrees compared to MTR4. Pitch 32nm dense line spaces can be patterned at a dose of 49.5mJ/cm², a line width of 15.5nm and an biased LWR of 3.69nm. Pitch 28nm dense patterns can be patterned at a dose of 59mJ/cm², a line width of 12.5nm, and a biased LWR of 3.91nm. These resist formulations have also been used to pattern 25nm diameter pillars on a 40nm pitch with a dose of 50mJ/cm², and a CDU of 2.98nm. High photospeed approaches, which have patterned p24 and p28 lines and p34 hex pillars at sub-30 mJ/cm² doses are also introduced

Extreme ultra-violet lithography (EUVL) has been prepared for next generation lithography for several years. We could get sub-22 nm line and space (L/S) pattern using EUVL, but there are still some problems such as roughness, sensitivity, and resolution. According to 2007 ITRS roadmap, line edge roughness (LER) has to be below 1.9 nm to get a 22 nm node, but it is too difficult to control line width roughness (LWR) because line width is determined by not only the post exposure bake (PEB) time, temperature and acid diffusion length, but also the component and size of the resist. A new method is suggested to reduce the roughness. The surface roughness can be smoothed by applying the resist reflow process (RRP) for the developed resist. We made resist profile which has surface roughness by applying exposure, PEB and development process for line and space pattern. The surface roughness is calculated by changing parameters such as the protected ratio of resin. The PEB time is also varied. We compared difference between 1:1 L/S and 1:3 L/S pattern for 22 nm. Developed resist baked above the glass transition temperature will flow and the surface will be smoothed. As a result, LER and LWR will be much smaller after RRP. The result shows that the decreasing ratio of LER due to RRP is larger when initial LER is large. We believe that current ~ 5 nm LWR can be smoothed to ~ 1 nm by using RRP after develop.

Extreme Ultraviolet Lithography (EUVL) embedded phase shift mask (EPSM) can further extend lithography resolution limit and provide better pattern fidelity as compared to that of EUVL binary mask for 16nm node technology and beyond generations. In our previous study, we have demonstrated in wafer printing that EUVL EPSM can provide improved process window for both the dense lines and contacts and the low shadowing effect when compared to that of the EUVL binary mask. Due to limitation of current EUVL resist performances, certain advantages of EUVL EPSM, such as line width roughness (LWR) improvement, cannot be readily seen at wafer resist level. This is because that the aerial image quality improvement in LWR is over shadowed by the current large resist intrinsic and process induced LER. We believe that when EUV resist and wafer process improves in future, mask induced pattern fidelity difference will start to play an observable role in wafer printing. In this study, we focused on comparing EUV actinic aerial image performance of a EUVL EPSM and a binary mask for both lines and contacts. Without convoluting with resist effect, the mask aerial image performance comparison of two different masks can better reflect all the effects that are due to mask differences. Our analysis of the EUV actinic aerial images of a EUVL EPSM and a binary mask showed not only the process window advantages of the EPSM as demonstrated previously, but also the improved LWR performance of EUVL EPSM when compared to that of the EUVL binary mask. The matrix used to analyze the aerial images includes aerial image contrast, LWR, process windows (focus-exposure plot), etc. Our detailed analysis is performed for various line and contact features.

Line width roughness (LWR) in EUV lithography is known to be caused by “Stochastic effects”, such as the chemical composition distribution within the resist thin film and the non-uniformity of chemical reactions. The compositions of chemically amplified resists before coating film on silicon wafer typically include a base polymer, a photoacid generator, a quencher, and a solvent. In this paper, we investigated about solvent effect, which is the main volume of the resist solution. We investigated solvent effect of resist solution by dynamic light scattering (DLS) measurement. The particle size of polymer in several solvents revealed diameters from 4 to 6 nm. The solvent effect in thin film was measured by resonant soft X-ray scattering (RSoXS) method. It was found the distribution of resist compositions differs depending on the type of solvents and the pre-bake temperatures. These results suggested the selection of resist solvent may also contribute to reducing LWR.

Since its installment in 2004, Intel's extreme ultraviolet (EUV) micro-exposure tool (MET) has demonstrated significant improvements in ultimate resolution capability. Initially capable of printing 45nm half-pitch (HP) lines with a 160nm depth of focus (DOF), it is now capable of printing 22nm HP lines with up to a 275nm DOF and demonstrating modulation down to 18nm HP. Initial improvements in resolution have been chiefly attributable to the maturation of EUV masks and photoresists. Recent improvements that have enabled the 22nm HP imaging with a sizeable process window are largely due to new illumination options that have become available as a result of recent tool upgrades. In particular, the installation of a new nested Wolter collector with an additional outer shell that extended the maximum partial coherence (σ) from 0.55 to 0.68, in conjunction with an updated pupil wheel and apertures, has enabled new rotated quadrapole and on-axis dipole illumination settings with 0.36 inner σ and 0.68 outer σ. Here we present simulated contrast curves alongside the experimental imaging results for the Intel MET using the newly available quadrapole and on-axis dipole illumination settings and discuss our future plans for continued improvements to the Intel MET aerial image.

Achieving the specifications of resolution, sensitivity and line width roughness (LWR) of wafer resist is one of the top challenges of bringing extreme ultraviolet lithography (EUVL) into high volume manufacturing. Contributions to the resist LWR on wafer can be divided into two categories; chemical properties of the resist and aerial image. Chemical properties of the resist are complicated and many factors contribute to LWR, such as polymer size, sensitivity, surface reaction etc. Aerial image LWR is much simply determined by the optical properties of a mask and a scanner. Since very small LWR value of the resist is needed, EUV mask LWR is also set very severely from ITRS ^[1]. In our previous work ^[2], we demonstrated current mask LWR as comparing them with mask resist LWR and absorber LWR. As a result, we found that the absorber's LWR almost depends on resist patterning. In this paper, we will present the influence of resist patterning on absorber LWR comparing resist materials and EB tools. From the results, LWR has been reduced by 10-20% by improving EB tool. However, the LWR value at line and space pattern for 22nm-hp case have not met target of ITRS' roadmap while, by using Non-CAR, the LWR value has met the target. In particularly, the value at isolated line is dramatically improved using Non-CAR.

Three major technological lithography options have been reviewed for high volume manufacturing at the 32 nm half pitch node: 193 nm immersion lithography with high index materials, enabling NA > 1.6; 193 nm double patterning and EUV lithography. In this paper the evolution of these three options over 2008 is discussed. The extendibility of these options beyond 32 nm half pitch is important for the final choices to be made. During 2008, the work on high index 193 nm immersion lithography has been stopped due to lack of progress in high index optical material and high index liquid development. Double patterning has made a lot of progress but cost concerns still exist. Preferred are those resists which support pattern or image freezing techniques in order to step away from the complex litho-etch-litho-etch approach and make double patterning more cost effective. For EUV, besides the high power light source, the resist materials need to meet very aggressive sensitivity specifications and need to maintain simultaneously performance in terms of resolution and line width roughness. Furthermore, EUV reticles encounter serious challenges, primarily related to mask defectivity.

Extreme ultraviolet (EUV) lithography is considered to be the most effective strategy for realize 7 nm generation manufacturing and beyond. A key factor for the realization of EUV lithography is the choice of EUV resist material that is capable of resolving below 15-nm half pitch with high sensitivity. Chemical Amplified Resist (CAR) using positive-tone development (PTD) is still one of the strongest candidates for EUV lithography. Recently, some researchers have reported concerns on the limitations in the performance of CAR materials. Consequently, there is a critical need for new chemistry and development of new resist materials. However, new resist materials still have lots of concerns for manufacturing, such like a non-CAR materials including metal resist. Therefore, CAR materials are still most important items for EUV lithography manufacturing. We’ve been developing negative-tone imaging (organic solvent development) with EUV exposure (EUV-NTI) for a long time. EUV-NTI has advantages for line-width roughness (LWR) due to their low swelling and dissolving smoothly. New EUV-NTI performances will be shown and also process condition progress will be updated. Also, the basic study will be reported, which is high absorption unit including materials for improving stochastic effect. We report herein recent progress of CAR materials, both positive-tone and negative-tone for EUV lithography.

With the decrease of semiconductor device dimensions, line width roughness (LWR) becomes a challenging parameter that needs to be controlled below 2nm in order to ensure good electrical performances of CMOS devices of the future technological nodes. One issue is the significant LWR of the photoresist patterns printed by 193nm lithography that is known to be partially transferred into the gate stack during the subsequent plasma etching steps. This issue could be partially resolved by applying plasma pre treatment on photoresist before plasma transfer. Another issue is linked to the noise level of the metrology tool, that causes a non negligible bias from true LWR values. Recently we proposed an experimental protocol combining CD-SEM measurements and Power Spectral Density (PSD) fitting method for an accurate estimation of the CDSEM noise level and extraction of unbiased LWR. In this article, we use the developed CDSEM protocol to extract roughness parameters (true LWR, correlation length, fractal exponent) of dense and isolated photoresist patterns exposed to various plasma treatments (HBr, H2, He, Ar), and also to follow the evolution of the LWR during the subsequent plasma etching steps involved in gate patterning. We show that the resist LWR is less improved in isolated than in dense lines with HBr plasma treatment because of carbon species redeposition more important on isolated resist pattern sidewalls. Plasmas such as H₂ that limit carbon redeposition are more efficient to decrease significantly resist LWR in both dense and isolated lines. In addition we show that all frequency roughness components are not equally transferred during gate patterning, and more particularly that the high frequency roughness components are lost.

Extreme ultraviolet lithography (EUVL) mask multi-layer (ML) blank surface roughness specification historically comes from blank defect inspection tool requirement. Later, new concerns on ML surface roughness induced wafer pattern line width roughness (LWR) arise. In this paper, we have studied wafer level pattern LWR as a function of EUVL mask surface roughness via High-NA Actinic Reticle Review Tool. We found that the blank surface roughness induced LWR at current blank roughness level is in the order of 0.5nm 3σ for NA=0.42 at the best focus. At defocus of ±40nm, the corresponding LWR will be 0.2nm higher. Further reducing EUVL mask blank surface roughness will increase the blank cost with limited benefit in improving the pattern LWR, provided that the intrinsic resist LWR is in the order of 1nm and above.

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.

The semiconductor community is well aware of the challenges that exist in developing lithographic methods that can pattern features at sub-20 nm periodic feature spacing (pitch, L0). Optical lithography already utilizes complex multiple patterning schemes to overcome diffraction limitations at 193-nm exposure wavelengths, and the delayed insertion of EUV lithography will likely require the use of multiple patterning or other assistive processes to further reduce the achievable feature sizes. An alternative to these techniques employs the directed self-assembly (DSA) of block copolymers. Block copolymers (BCPs) can naturally micro-phase separate into morphologies such as lamellae, cylinders, spheres, and gyroids at length scales down to sub-10 nm dimensions. Using the ability of BCPs to micro-phase separate in conjunction with alignment methods such as graphoepitaxy and chemoepitaxy to produce well-ordered structures, a process referred to as DSA, offers a possible method for producing sub-20 nm features in conjunction with optical patterning processes at greatly reduced cost and complexity. One of the many challenges in implementing line-space type DSA processes is the lack of methods for effective modulation and tuning of the pattern pitch (L0) produced by a given BCP. Previous studies have shown that blending homopolymer into the BCP thin films can allow for tuning of both: (1) L0 to be larger than that provided naturally by the BCP's molecular weight (MW) and (2) the relative size line-space size ratio. However, this tuning ability comes at the expense of increased line edge roughness (LER) and line width roughness (LWR). It has also been shown that either higher or lower MW BCP can be blended into a primary BCP in order to modulate and tune the pattern pitch produced from the BCP mixture, but the effects of this BCP blending on pattern LER and LWR have not been explored or reported in detail. In this study, coarse-grained molecular dynamics simulations of BCP DSA on a chemoepitaxial underlayer were implemented to characterize the impacts that blending controlled amounts of two different MW BCPs together have on DSA pattern LER and LWR. The blends shown here had LER and LWR values as much as 20% higher than those of pure, monodisperse BCPs; however, reducing the MW difference between the 2 BCPs could reduce this effect.

In extreme ultraviolet (EUV) lithography, 92 eV photons are used to expose photoresists. Typical EUV resists are organic-based and chemically amplified using photoacid generators (PAGs). Upon exposure, PAGs produce acids which catalyze reactions that result in changes in solubility. In EUV lithography, photo- and secondary electrons (energies of 10- 80 eV) play a large role in PAG acid-production. Several mechanisms for electron-PAG interactions (e.g. electron trapping, and hole-initiated chemistry) have been proposed. The aim of this study is to explore another mechanism – internal excitation – in which a bound PAG electron can be excited by receiving energy from another energetic electron, causing a reaction that produces acid. This paper explores the mechanism of internal excitation through the analogous process of electron-induced fluorescence, in which an electron loses energy by transferring that energy to a molecule and that molecule emits a photon rather than decomposing. We will show and quantify electron-induced fluorescence of several fluorophores in polymer films to mimic resist materials, and use this information to refine our proposed mechanism. Relationships between the molecular structure of fluorophores and fluorescent quantum yield may aid in the development of novel PAGs for EUV lithography.

Implementation of extreme ultra violet lithography (EUVL) for printing features of dimensions around 32nm and below has faced multiple challenges that have been overcome mostly through tool and process engineering. Currently, the main concern for implementation of EUVL in high volume manufacturing is related to stochastic defects, such as line bridges or breaks, which may occur randomly and have an impact on device performance.1 Photon shot noise, in addition to the inherent process variability and material non-homogeneities can lead to defects on the final patterned structures. As the pitch and critical dimension (CD) approach 32nm pitch and below, the dependency of stochastics defects increases exponentially. This paper fits within imec’s EUV stochastics and defectivity program, which investigates the key parameters for the generation and mitigation of defects from both a theoretical and practical approach. Initially, a reference process has been established and a methodology has been developed to capture and characterize bridge-type defects after pattern transfer into relevant layers for metrology and applications. Optical inspection and scanning electron microscopy (SEM) review are used to collect information on the number and types of defects present over large patterned areas (in the order of cm2). With a well-defined inspection technique, experiments related to fundamentals as well as materials and processes are continuously run. In the past years, imec has been leading the fundamental work on stochastic defects.2,3 De Bisschop et al. identified the “defect cliff”, or the exponential dependency of defect density as a function of space CD for multiple parameters, such as resist formulation and exposure/imaging conditions. More recently, the focus has changed to the investigation of the “defect floor”, which as the name suggests, is a flat response of defects to CD. The defect floor suggests that defectivity cannot be further improved, making one of the most relevant problems to solve for implementation of EUV in high volume manufacturing (HVM). Our results show a decomposition of the potential contributors to explore the effect of processing conditions related to scanner, track and pattern transfer on final defect density for a chemically amplified resist and attempt a comparison to a metal-oxide resist. Goal is to understand the contributors to the defect floor and identify an effective route to avoid/minimize defect formation.

The shot noise, line edge (LER) and quantum efficiency of EUV interaction with seven resists related to EUV-2D (SP98248B) are studied. These resists were identical to EUV-2D except were prepared with seven levels of added base while keeping all other resist variables constant. These seven resists were patterned with EUV lithography, and LER was measured on 100-200 nm dense lines. Similarly, the resists were also imaged using DUV lithography and LER was determined for 300-500 nm dense lines. LER results for both wavelengths were plotted against Esize. Both curves show very similar LER behavior-the resists requiring low doses have poor LER, whereas the resists requiring high doses have good LER. One possible explanation for the observed LER response is that the added base improves LER by reacting with the photogenerated acid to control the lateral spread of acid, leading to better chemical contrast at the line edge. An alternative explanation to the observed relationship between LER and Esize is that shot-noise generated LER decreases as the number of photons absorbed at the line edge increases. We present an analytical model for the influence of shot noise based on Poisson statistics that preidicts that the LER is proportional to (Esize)-1/2. Indeed, both sets of data give straight lines when plotted this way (DUV r2 = 0.94; EUV r2 = 0.97). We decided to further evaluate this interpretation by constructing a simulation model for shot noise resulting from exposure and acid diffusion at the mask edge. In order to acquire the data for this model, we used the base titration method developed by Szmanda et al. to determine C-parameters and hence the quantum efficiency for producing photogenerated acid. This information, together with film absorptivity, allows the calculation of number and location of acid molecules generated at the mask edgte by assuming a stochastic distribution of individual photons corresponding to the aerial image function. The edge roughness of the acid molecule distribution in the film at the mask edge is then simulated as a function of acid diffusion length and compared to the experimental data. In addition, comparisoins between of the number of acid molecules generated and photons consumed leads to values of quantum efficiencies for these EUV resists.