Extreme ultraviolet lithography (EUVL) enables integrated circuit (IC) industry to manufacture chips with increased transistor density per volume unit, so the Moore’s law remains true to date. To support the endless requirement of reducing critical dimension (CD), chemically amplified resist (CAR) has been designed to address the resolution, line width roughness, and sensitivity (RLS) in nanoscale level. However, a good Litho performance from an EUV photoresist may not always be transferred into a good etch performance, limiting the stochastic defects after patten transfer is the key to achieve a good after etch inspection (AEI) defectivity. In this paper, we report the EUV photoresist design strategies to acquire good AEI defectivity with the understanding of CAR’s property in a defined pattern transfer scheme with special focus on small molecule in photoresist. The CAR’s Litho performance and the corelated etch performance will be discussed, the component etch rate and its correlation to photoresist etch performance will be covered.
We report on the relationship between resist make-up, filtration process & CH AEI defectivity for an advanced CAR resist with fast dose. In particular, the effect of a pattern transfer scheme on a resist platform with formulation & filtration variation is examined. Resist design & manufacturing strategies for continuous improvement of EUV CAR lithographic performance will be discussed.
Chemically amplified resists (CAR) enable the transition of extreme ultraviolet (EUV) lithography to high-volume manufacture (HVM). Novel photoresists continue to be designed to meet the simultaneous improvement of resolution, line width roughness, and sensitivity (RLS) trade-off. The absorption of EUV photons in the photoresist film leads to emission of primary electrons to form secondary electrons by inelastic scattering events which in turn leads to the activation of the photoacid generator compound. A unique challenge for the use of CAR in EUV lithography is their poor absorption at 13.5nm wavelength. Understanding the photoresist EUV absorption impact on lithographic performance parameters is critical for photoresist design. In this study, we designed photoresist polymers with tuned EUV absorption coefficients by incorporating EUV absorption group(s) onto different CAR polymers. The effect of the EUV absorption increase on polymer properties as well as on resist lithographic performance will be presented.
The drive toward tighter pitch and higher density integrated circuits requires continual advancement in lithography. Advanced photolithography tools use extreme ultraviolet (EUV) light with a wavelength of 13.5nm. The high energy nature of EUV light generates secondary electrons in the photoresist that are responsible for the photochemistry that induces the solubility switch. This distinct mechanism has provided the driving force for the development of new photoresists that are sensitive to EUV and highly reactive toward secondary electrons. Despite the considerable change in acid generation mechanism going from DUV to EUV, chemically amplified photoresists continue to be leading photoresist candidates for new process nodes at low NA EUV (0.33 NA) and their use is expected to extend into early high NA (0.55 NA). Herein the after-developer defects (ADI) and EUV P36 LS trench printing performance of a series of chemically amplified photoresists (CAR) with distinct chemistry developed specifically for EUV lithography are compared. In particular, the relationship of different leaving group chemistries and polymer manufacturing processes on stochastic defectivity is explored as well as the connection to photoresist polymer hydrophobicity and homogeneity. The insights gained from this study guide design strategies for improvement of advanced chemically amplified photoresists for EUV lithography.
Extreme ultraviolet (EUV) lithography technology empowers integrated circuit industry to mass produce chips with smaller pitches and higher density. Along with EUV tool advancement, significant progress has also been made in the development and advancement of EUV chemically amplified resist (CAR) materials, which allows for the improvement of resolution, line edge roughness, and sensitivity (RLS) trade-off. The scarce number of EUV photons has triggered the development of resist material with high absorption at 13.5 nm. However, a review of open literature reveals very limited reports on the effect of high EUV absorption elements on etch properties of advanced EUV resist. To ensure Moore’s Law continues to move forward, further resist performance improvement is required. In this regard, stochastic defects originating from photon shot noise, materials, and processing variabilities present a unique challenge for the extension of CAR platform for the patterning of smaller nodes. Notably, less attention has been paid to defects formed during the etching process used for pattern transfer. In this paper, we report on the relationship between resist make-up and etch properties. In particular, the effect of incorporation of EUV high absorbing elements are examined. New resist material design strategies for continuous improvement of EUV CAR lithographic performance will be discussed.
Chemically amplified resist (CAR) materials are widely used in advanced node patterning by extreme ultraviolet lithography (EUVL). To support the continuous requirement of reducing critical dimension (CD), CAR has been designed to process at tens of nanometer coating thickness while taking into consideration film roughness, aspect ratio, and etch transfer challenge. In this study, we investigated the impact of the photoresist’s different spin speed for same film thickness on resolution, line width roughness, and sensitivity (RLS) trade-off for Line and Space (L/S) patterns. We selected photoresists with identical chemical composition that differed only in total wt solid% in the solution. Photoresist films at constant thickness were investigated for the spin speed impacts on photoresist film density, hydrophobicity on the film surface, and film surface roughness. The corresponding EUV lithographic performance will be presented.
Conventional chemically amplified resists for extreme ultraviolet (EUV) lithography are comprised of three fundamental components: a photoreactive, acid-generating species (PAG), an acid reactive polymer for solubility switching, and a basic component for acid diffusion control. The PAG component is typically derived from an organic onium salt, wherein the cation’s capacity to capture secondary electrons generated upon EUV irradiation of the resist underscores their reactivity in lithographic applications. Thus, effective rational design of these materials is critical for controlling both sensitivity of the resist and feature regularity. Herein, we describe a robust method for in silico prediction of fundamental properties of onium cations including electron affinity, LUMO energy, and relative charge distribution. We correlate these theoretical values to experimental measurements and further to the influence of PAG cation properties on resist performance under EUV exposure. In addition to the reactive properties of these cations, we analyze these lithographic data in the context of the physicochemical properties of the cations, particularly polarity. In all, the results of this study suggest that while electron affinity of the PAG cation may drive reactivity in response to EUV exposure, multiple factors must be considered in the design of cations for optimal overall resist performance.
Linewidth Roughness (LWR) remains a difficult challenge in resist materials. In previous work we focused on showing how roughness Power Spectral Density (PSD) parameters were affected by aerial image and basic resist parameters such as diffusion. This highlighted the relationship between PSD(0) and correlation length in optimizing LWR. By measuring the unbiased PSDs with MetroLER we showed LWR measurements could be expressed as a ratio between the roughness PSD parameters. In this paper we show how LWR improvement can be achieved by several strategies that focus on both PSD(0) and correlation length and not a single LWR number.
Linewidth Roughness (LWR) remains a difficult challenge for improvement in all resist materials. In previous work we focused on the impact of key components of LWR by analyzing the Power Spectral Density (PSD) curves which can be obtained using Fractilia’s MetroLER computational software. [1] By measuring the unbiased PSD (with SEM image noise removed), accurate assessment of PSD(0) (the low-frequency limit of the PSD) and correlation length (the length scale of the transition from white to correlated noise) is possible. We showed there was an important relationship between ArF resist frequency components and LWR through lithographic process (before and after a resist trim step) as a function of resist formulation. In this paper we will study how key frequency components such as PSD(0) and correlation length change as we vary basic resist properties such as diffusion. The impact of aerial image on LWR and its frequency components will also be studied with particular attention to how correlation length affects LWR as feature size decreases. We will also look at the impact of diffusion or resist blur on PSD(0) as a function of aerial image Normalized Image Log-Slope (NILS). Understanding the relationship between PSD(0) and correlation length and how to manipulate these variables to minimize LWR for different features is crucial for more rapid LWR improvement at different nodes.
[1] Charlotte Cutler, et al., “Roughness power spectral density as a function of resist parameters and its impact through process,” Proc. SPIE 10587, Optical Microlithography XXXI, 1058707 (23 March 2018).
Linewidth roughness (LWR) remains a difficult challenge for improvement in all resist materials. In this paper, we intend to focus on the impact of key components of LWR by analyzing the Power Spectral Density (PSD) curves which can be obtained using Fractilia’s MetroLER computational software. We will study systematic changes to ArF resist formulations and correlate these changes to the overall PSD curves. In this manner, we can extract LER/LWR 3σ values as well as resist correlation length and the low/high-frequency roughness components. We will also investigate the relationship between PSD and LWR through lithographic/etch processing and demonstrate which components correspond with the largest impact. In order to achieve quality data over low and high frequency ranges we changed our standard metrology setup to capture longer lines. By making systematic changes to the ArF resists, we can determine the key impacts of various controllable resist factors on the PSD. Through systematic analysis, we can deconvolute LWR improvements both after develop and after an etch process.
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