Search

State-of-the-art extreme ultraviolet lithography requires the use of ultrathin photoresists (or resists) due to pattern stability concerns and reduced depth of focus of the extreme ultraviolet lithography scanners. Current resists for extreme ultraviolet lithography are less than 50 nm thick. These ultrathin resists further complicate pattern transfer as unintended plasma-induced damage during dry etching is more pronounced. A better understanding of the interaction of plasma species with ultrathin resists is critical for enabling pattern transfer of sub-10 nm features. Here, we study the impact of vacuum ultraviolet photons, argon ions, and argon plasma on a 40 nm thick polymethylmethacrylate film. Using a deuterium lamp, an industrial ion beam etch tool, and an industrial inductively coupled plasma etch tool, we exposed the polymer to photons, ions, and plasma, respectively. The exposed samples were then analyzed for chemical and physical changes using different characterization techniques. It was observed that the vacuum ultraviolet photons interact with the entire bulk of polymer film, while the ions only affect the surface and subsurface region. The photon exposed samples formed smaller polymer fragments at low exposure doses and further started to cross-link at high doses. In contrast, the ion modification leads to carbonization of only the top few nanometers of the polymer film, leaving the bottom bulk intact. The plasma exposed sample showed changes characteristic to both vacuum ultraviolet photons and ions and their synergism. It was stratified with a 1.34 ± 0.03 nm thick ion-caused carbonized layer on top of a 13.25 ± 0.12 nm photon-induced cross-linked layer. By studying the impact of plasma photons on ultrathin polymethylmethacrylate, we were able to establish a baseline for a testing methodology that can be extended to novel ultrathin resist platforms. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

To meet the demands for sub-20 nm feature devices in the semiconductor industry, minimizing the line width roughness (LWR) is a critical concern for ultra-large scale integrated circuit manufacturing. Post-lithography treatments should reduce the LWR by at least 50% to meet the technology requirements, but the available post-lithography strategies come short. To support the delayed progress, an in depth understanding of the interaction of such post-lithography treatments with EUV-specific resist functionalities is required. In this article, we analyze the change in line widths and LWR's for 30-35 nm lines using EUV photoresists. In addition we study the effect of the chemical composition on the reduction of LWR after hydrogen plasma treatment using 'artificially' prepared reference resists. We highlight the effect of the fluorine unit, ester functionalities and photo acid generator/quencher loading on the LWR improvement and H2 plasma induced reflow. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Background: Polyphthalaldehyde (PPA)-based systems can be interesting candidates for extreme ultraviolet (EUV) lithography as dry development resists with simple chemistry. Aim: We present EUV-induced mechanistic and contrast curve studies for the end-capped PPA. Approach: Fourier transform infrared (FTIR) spectroscopy and desorption studies were conducted to understand the EUV-induced mechanistic pathway. Although, contrast curve analysis was used to check its feasibility for EUV-patterning. Results: First, FTIR and desorption studies confirmed that the EUV-radiation is capable to remove the end-capping group and induce unzipping (direct depolymerization) reaction in the PPA polymer chain. Second, contrast curve analysis showed a gradual decrease in the film thickness with respect to the EUV dose, which is due to the low EUV sensitivity of the PPA polymer. A post exposure bake step is important to improve the contrast curve, as it helps to depolymerize any residual polymer remaining after exposure. Further, even though the polymer sublimates when exposed to the EUV radiation, eliminating the need to apply a wet development step, crosslinking at high doses causes deposition of residual film onto the wafer surface. Therefore, a thin film (below 20 nm) and a wet development process might be important to get clean patterns. Conclusion: This study confirms that the end-capped PPA, with a simple patterning mechanism, can be a useful system for the development of new dry development resists for EUV lithography. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Extreme ultra-violet lithography (EUVL) is the leading-edge technology to produce advanced nanoelectronics. The further development of EUVL is heavily based on implementing the so-called high numerical aperture (NA) EUVL, which will enable even smaller pitches up to 8 nm half pitch (HP). In anticipation of this high NA technology, it is crucial to assess the readiness of the current resist materials for the high NA regime to comply with the demanding requirements of resolution, line-edge roughness, and sensitivity (RLS). The achievable tighter pitches require lower film thicknesses for both resist and underlying transfer layers. A concern that is tied to the thinning down is the potential change in resist properties and behavior due to the interaction with the underlayer. To increase the fundamental understanding of ultra-thin films for high NA EUVL, a method to investigate the interplay of reduced film thickness and different patterning-relevant underlayers is developed by looking at the glass transition temperature (Tg) of polymer-based resists. To minimize the ambiguity of the results due to resist additives (i.e., photoacid generator (PAG) and quencher), it was opted to move forward with polymer-only samples, the main component of the resist, at this stage of the investigation. By using dielectric response spectroscopy, the results obtained show that changing the protection group of the polymer, as well as altering the polymer film thickness impacts the dynamics of the polymer mobility, which can be assessed through the Tg of the system. Unexpectedly, changing the underlayer did not result in a clear change in the polymer mobility at the tested film thicknesses. [ABSTRACT FROM AUTHOR]

[Display omitted] • Crystalline TiO 2 shows higher photocatalytic activity compared to amorphous. • Effective decomposition of SAM upon EUV exposure is a combined effect of EUV dose and photoactivity of the TiO 2 surface. • Promising selectivity of 0.85 achieved for ASD Ru hard mask target thickness of 1.6 nm. Patterning below 10 nm with conventional techniques such as Litho-etch (LE*), a subtractive self-aligned multiple patterning process, suffers from limitations due to edge placement errors, decreasing throughput, complexity, pattern collapse, photoresist non-uniformity. Bottom-up processes for fabrication of nano devices by means of Area selective deposition (ASD) are peaking up over top-down approaches to mitigate most of the above-mentioned problems. One of the ways to achieve ASD of an hardmask is by using extreme ultra-violet (EUV, λ-13.5 nm) lithography to single-step pattern self-assembled monolayers (SAM) on a photosensitive substrate (or layer) followed by atomic layer deposition (ALD). In this work, photo-catalytically active titanium oxide is considered as substrate for the deposition of organosilane SAMs of different chain length. Upon exposure to EUV, fragmentation of SAM's molecules is observed though a mechanism involving electron/hole pair exchange from TiO 2. This induces changes in the chemistry of the exposed area, allowing an ALD deposition in the SAM-cleared areas. [ABSTRACT FROM AUTHOR]