The Role of Underlayers in EUVL

Abstract

There is a growing awareness that underlayers (UL) are important in EUV lithography (EUVL). In previous lithography generations ULs were required to overcome reflectivity, however that is not a concern in EUVL. Nevertheless, surface interactions are becoming prevalent because the different layers of the stack are becoming thinner. This work focuses on the influence of the spin on carbon (SOC) layer used to print line-space patterns with metal containing resists (MCR). A significant impact of underlayers on the MCR performance in EUVL is demonstrated. There are large effects on the dose to size, resist profile and stochastic nanofailures. The main contributor is the interaction between photoresist and underlayer driven by the density of the SOC UL and, to a lesser extent, other chemical interactions. The key message is that underlayer effects cannot be neglected and should be considered when evaluating the lithographic performance of photoresist materials.

Dielectric Response Spectroscopy as Means to Investigate Interfacial Effects for Ultra-Thin Film Polymer-Based High NA EUV Lithography

“…Moreover, this interfacial layer may also affect the homogeneity of resist additives, such as the photoacid generator (PAG) and quencher, which most certainly will affect the resist patterning performance. This sensitivity might also partially explain the differences in patterning behavior of EUV resists on different substrates [ 7 ].…”

“…Moreover, this interfacial layer may also affect the homogeneity of resist additives, such as the photoacid generator (PAG) and quencher, which most certainly will affect the resist patterning performance. This sensitivity might also partially explain the differences in patterning behavior of EUV resists on different substrates [7]. Since the previous section indicated that the polymer film was sensitive to the substrate, two relevant commercial patterning spin-on underlayers (organic and inorganic) were tested to assess the impact of different underlayers on the Tg.…”

“…This means that the interface interactions between the different layers (e.g., resist and underlayer) become increasingly dominant in ultra-thin films (≤30 nm), possibly changing material characteristics and thus making it challenging for the formulation of the resist to obtain good patterning performance on (different) underlayers. These changes include changes in dose to size (DtS), resist nanopattern profile, and amount of nanofailures, as well as inducing chemical inhomogeneity of the resist additives causing pattern degradation [ 7 , 8 ]. Therefore, an in-depth characterization of these properties versus film thickness is necessary to detect any future possible issues of the current patterning materials.…”

Metal Based Materials for EUV Lithography

“…It has been very well documented that under EUV exposures, the presence of ULs affects significantly the performance of the resists [7]. This is mainly happening due to the fact that very thin photoresists layers are now used; that means that interactions at the interface of resist and UL will have a much larger impact on the photoresist compared to exposures done at other wavelengths.…”

Metal Organic Cluster Photoresists for EUV Lithography

“…4. Recently, improvement of lithography performance by using underlayer was reported and certain underlayer improved not only sensitivity but also nano-scale defect resistance [12]. A zinc organic cluster resist was evaluated on different underlayer with NXE tool at imec and the results are summarized in Fig.…”