Kenji Hoshiko

Novel EUV resist development for sub-14nm half pitch

Extreme ultraviolet (EUV) lithography has emerged as a promising candidate for the manufacturing of semiconductor devices at the sub-14nm half pitch lines and spaces (LS) pattern for 7 nm node and beyond. The success of EUV lithography for the high volume manufacturing of semiconductor devices depends on the availability of suitable resist with high resolution and sensitivity. It is well-known that the key challenge for EUV resist is the simultaneous requirement of ultrahigh resolution (R), low line edge roughness (L) and high sensitivity (S). In this paper, we investigated and developed new chemically amplified resist (CAR) materials to achieve sub-14 nm hp resolution. We found that both resolution and sensitivity were improved simultaneously by controlling acid diffusion length and efficiency of acid generation using novel PAG and sensitizer. EUV lithography evaluation results obtained for new CAR on Micro Exposure Tool (MET) and NXE3300 system are described and the fundamentals are discussed.

Novel EUV resist materials for 16nm half pitch and EUV resist defects

Extreme ultraviolet (EUV) lithography is a candidate for the manufacturing of semiconductor devices at the 22 nm half pitch node and below. EUV lithography requires high performance resist with limited outgassing property. The key challenge for EUV resist is the simultaneous requirement of ultrahigh resolution (R), low line edge roughness (L) and high sensitivity (S) for lines and spaces (LS) features. To achieve high resist sensitivity EUV resist absorbance should be increased. Resin containing fluorine atom is one of the most attractive methods to improve absorbance level of EUV resist because the fluorine atom absorbs EUV light strongly. However, resist hydrophobicity (or high contact angle) also increase due to presence of fluorine atoms in the resist polymer. It is difficult to rinse high CA resist during development process so the resist containing polymer with fluorine atom may produce additional defects. In this paper, we will report the relationship between line edge roughness and acid diffusion length. We will also show the method to diminish defects caused by high contact angle (CA) resist. We achieved good resolution and LER improvement by controlling acid diffusion length. Moreover, we found the relationship of the number of defects and the structure of the monomers containing fluorine units.

XAS photoresists electron/quantum yields study with synchrotron light

The main roadblock for EUV lithography to be successfully adopted for high-volume manufacturing is the current lack of source power. One way to help mitigate this problem is to optimize the photoresist by increasing both absorbance and quantum yield. The latter represents the ratio between the sums of generated acids and absorbed photons. Yield is also thought to be limited by the number of generated electrons per absorbed photon, or electron yield, that may be generated after a photo absorption event. While absorbance is relatively easy to measure, yields are extremely difficult to quantify, and the debate on upper limits is far from settled. In this paper, we present how, using synchrotron light with tunable energy, we directly measured dispersion curves and electron yield for ArF, KrF and EUV photoresists using X-ray Absorption Spectroscopy. Knowing the electron yield allowed us to better model organic EUV materials: stochastic simulations show how both electron yield and blur are very similar for organic materials, and how the electron blur is not a fixed property of the material, but may vary spatially, depending on a combination of photoresist formulation and local photon absorption density.

Roughness and variability in EUV lithography: Who is to blame? (Part 1)

Process variability in today’s EUV lithography might be a showstopper for features below 27nm dimensions. At these feature sizes, electrical devices are influenced by quantum effects and thus have to face the discrete behavior of light and matter. More in general, lithography uncertainties arise from each lithographic element: the source, the photomask, the optical system, and the photoresist. In order to individually assess all the different contributions to the final resist roughness, a EUV mask with known absorber pattern variability was used to expose different resists at different process conditions. CD-SEM analyses were performed on both mask absorber and resist pattern and then used to build a stochastic resist model. In this first paper, we present a complete characterization of the root causes which are responsible of the CD nonuniformity for 27nm half-pitch dense contact-holes exposed with the ASML NXE:3100 scanner installed at imec. Using the same stochastic model, a simulated evaluation to quantify the possible impact of the different elements composing the lithographic process is performed at higher numerical aperture.

Immersion topcoat and resist material improvement study by using immersion scanner

ArF (193nm) immersion lithography is considered as the most promising next generation technology and significant effort to establish the immersion process for semiconductor device HVM is currently focused on the tool, material and process development. Immersion lithography enables the design of hyper numerical aperture (NA>1) lens systems by filling the gap between lens and resist with an immersion medium. Water is the ideal medium for 193nm immersion lithography and the water immersion system could reach up to 1.3 NA, giving higher resolution capability. There are several immersion specific requirements such as scanning properties and leaching characteristics. High speed scanning is necessary for mass production, so the water has to follow the lens and move on the resist film at considerably high speed. Direct water contact with resist film can cause the leaching of some resist components e.g. PAG. This leaching phenomenon could cause lithographic performance degradation and lens damage. Leaching and scanning phenomena are quite complicated and difficult to estimate the amount exactly with chemical analysis tools, so it is important to check the lithographic performance and scanning capability with a real immersion scanner. We have done many immersion experiments on various resists and top-coat materials using a Nikon immersion scanner (EET: Engineering Evaluation Tool). From the results, it was found that the properties of topcoat materials were closely related with immersion characteristics, such as scanning speed and defect formation. Specifically, defectivity evaluation results revealed that PAG leaching suppression was important for not only preventing lens damage but also reducing defect formation in the immersion process.