Structure of high-reflectance La/B-based multilayer mirrors with partial La nitridation

Abstract

We investigate a hybrid thin film deposition procedure that significantly enhances reflectivity of La/B based nanoscale multilayer structures to be used as Extreme UV mirrors at 6.7 nm wavelength and beyond. We have analyzed the La-nitridation process in detail, and proposed a growth mechanism and deposition procedure for full, stoichiometric passivation of La, avoiding the formation of optically unfavorable BN formation at the LaN-on-B interface. A partial nitridation was applied and studied as a function of the nitridation delay.

In situ and real-time monitoring of structure formation during non-reactive sputter deposition of lanthanum and reactive sputter deposition of lanthanum nitride

“…This satellite structure is a fingerprint of the chemical environment of La: La(OH) 3 formation leads to a smaller satellite peak, while La 2 O 3 is characterized by two peaks of similar height (Sunding et al, 2011). The satellite peak with higher intensity observed here is characteristic of LaN (Coss et al, 2009;Kuznetsov et al, 2016a). The La-N research papers Experimental setup and schematic of the measurement geometry.…”

“…Experimentally, a reflectance of 64.1% for near-normal incidence was obtained by a hybrid process combining non-reactive and reactive sputter deposition of La. Delayed nitridation of the La layer avoids the formation of undesired BN at the La-on-B interface, while a fully passivated LaN layer on top significantly reduces the B-on-La interface width (Makhotkin et al, 2013;Kuznetsov et al, 2015Kuznetsov et al, , 2016a.…”

“…Only limited information is available on the local atomic ordering and microstructures of La and LaN thin films and nanostructures (Nyabero et al, 2014;Kuznetsov et al, 2016a;Zhang et al, 2017). For bulk lanthanum, the low-temperature double hexagonal close-packed phase (Inorganic Crystal Structure Database entry ICSD-641382; a = 3.772, c = 12.144 Å ; Beaudry & Palmer, 1974) with a phase transition to a hightemperature face-centred cubic (f.c.c.)…”

Grazing-Incidence La/B-Based Multilayer Mirrors for 6.x nm Wavelength

“…The conditions for the synthesis of the fully-passivated LaN are taken from our past work. 8 La target was used both for La and LaN deposition, with LaN being deposited by reactive sputtering in Ar + N 2 mixture. All the multilayers had 15 periods and were covered by a B cap of the same thickness as in the stack (about 9 nm for 15 nm period).…”

“…There is also a small amount of BN present in XPS spectra originating from the interaction with air, which is also observed for the reference B layer samples. 8 The measured percentages of contaminants after half a year of storage in air are totally related to the aging, since as-deposited samples do not show measurable by XPS amount of top layer contamination.…”