This work reports on the measurements of ion flux composition and ion energy distribution functions (IEDFs) at surfaces in contact with hydrogen plasmas induced by extreme ultraviolet (EUV) radiation. This special type of plasma is gaining interest from industries because of its appearance in extreme ultraviolet lithography tools, where it affects exposed surfaces. The studied plasma is induced in 5 Pa hydrogen gas by irradiating the gas with short (30 ns) pulses of EUV radiation ( λ= 10–20 nm). Due to the low duty cycle (10–4), the plasma is highly transient. The composition and IEDF are measured using an energy resolved ion mass spectrometer. The total ion flux consists of H+, H2+, and H3+. H3+ is the dominant ion as a result of the efficient conversion of H2+ to H3+ upon collision with background hydrogen molecules. The IEDFs of H2+ and H3+ appear similar, showing a broad distribution with a cut-off energy at approximately 8 eV. In contrast, the IEDF of H+ shows an energetic tail up to 18 eV. Most probably, the ions in this tail gain their energy during their creation process by photoionization and dissociative electron impact ionization.

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Ion energy distributions in highly transient EUV induced plasma in hydrogen

After a long period of relatively low interest, science related to effects in the Extreme Ultraviolet (EUV) spectrum range experienced an explosive boom of publications in the last decades A new application of EUV in lithography was the reason for such a growth Naturally, an intensive development in such area produces a snowball effect of relatively uncharted phenomena EUV-induced plasma is one of those While being produced in the volume of a rarefied gas, it has a direct impact onto optical surfaces and construction materials of lithography machines, and thus has not only scientific peculiarity, but it is also of major interest for the technological application The current article provides an overview of the existing knowledge regarding EUV-induced plasma characteristics It describes common, as well as distinguishing, features of it in comparison with other plasmas and discusses its interaction with solid materials This article will also identify the gaps in the existing knowledge and it will propose ways to bridge them

EUV-induced plasma: a peculiar phenomenon of a modern lithographic technology

Advances in test and measurement of the interface adhesion and bond strengths in coating-substrate systems, emphasising blister and bulk techniques

A new diagnostic approach using multi-mode microwave cavity resonance spectroscopy (MCRS) is introduced. This can be used to determine electron dynamics non-invasively in an absolute sense, as a function of time and spatially resolved. Using this approach, we have for the first time fully mapped electron dynamics specifically during the creation and decay of a highly transient pulsed plasma induced by irradiating a background gas with extreme ultraviolet (EUV) photons. In cylindrical geometry, electron densities as low as 1012 m−3 could be detected with a spatial resolution of (sub)100 µm and a temporal resolution of (sub)100 ns. Our experiments clearly show production of electrons even after the in-band EUV irradiation fades out. This phenomenon can be explained by both photoionization by out-of-band EUV radiation emitted by the EUV source later in time and delayed electron impact ionization by electrons initially created by in-band EUV photoionization. From the analysis, the absolute width of the electron cloud in the probing volume could also be retrieved temporally resolved. This data clearly indicates cooling of electrons. From an application perspective, it is demonstrated that the method can be used as a non-invasive and in-line monitor for ionizing radiation in terms of beam power, profile and pointing stability.

/pdf/mapping-electron-dynamics-in-highly-transient-euv-photon-2lxfj9m8d3.pdf

Mapping electron dynamics in highly transient EUV photon-induced plasmas: a novel diagnostic approach using multi-mode microwave cavity resonance spectroscopy

We report on blister formation in nanometer thick Mo/Si multilayer structures due to exposure to hydrogen ion fluxes The influence of hydrogen flux and ion energy for blister formation have been measured and compared to a blister model The blister number density increases significantly around 100 eV when increasing the ion energy from 50 to 200 eV This stepwise behavior could be explained by the fact that for energies >100 eV hydrogen ions could directly penetrate to the depth where delamination takes place From the blister model also the blisters internal pressure and surface energy was calculated to be around 100–800 MPa and respectively

https://iopscience.iop.org/article/10.1088/1361-6463/aa7323/pdf

Blister formation in Mo/Si multilayered structures induced by hydrogen ions

We introduce a model for hydrogen induced blister formation in nanometer thick thin films. The model assumes that molecular hydrogen gets trapped under a circular blister cap causing it to deflect elastically outward until a stable blister is formed. In the first part, the energy balance required for a stable blister is calculated. From this model, the adhesion energy of the blister cap, the internal pressure and the critical H-dose for blister formation can be calculated. In the second part, the flux balance required for a blister to grow to a stable size is calculated. The model is applied to blisters formed in a Mo/Si multilayer after being exposed to hydrogen ions. From the model the adhesion energy of the Mo/Si blister cap was calculated to be around 1.05 J/m2 with internal pressures in the range of 175-280 MPa. Based on the model a minimum ion dose for the onset of blister formation was calculated to be d = 4.2*10^18 ions/cm2. From the flux balance equations the diffusion constant for the Mo/Si blister cap was estimated to be D_H2 = (10+-1) *10^18 cm2/s.

/pdf/a-model-for-pressurized-hydrogen-induced-thin-film-blisters-kqxfvd0vhs.pdf

A model for pressurized hydrogen induced thin film blisters

We introduce a model for hydrogen induced blister formation in nanometer thick thin films. The model assumes that molecular hydrogen gets trapped under a circular blister cap causing it to deflect elastically outward until a stable blister is formed. In the first part, the energy balance required for a stable blister is calculated. From this model, the adhesion energy of the blister cap, the internal pressure, and the critical H-dose for blister formation can be calculated. In the second part, the flux balance required for a blister to grow to a stable size is calculated. The model is applied to blisters formed in a Mo/Si multilayer after being exposed to hydrogen ions. From the model, the adhesion energy of the Mo/Si blister cap was calculated to be around 1.05 J/m2 with internal pressures in the range of 175–280 MPa. Based on the model, a minimum ion dose for the onset of blister formation was calculated to be d = 4.2 × 1018 ions/cm2. From the flux balance equations, the diffusion constant for the Mo/Si blister cap was estimated to be D H 2 =(10±1)×10 −18  cm 2 /s 
DH2=(10±1)×10−18 cm2/s
.

/pdf/a-model-for-pressurized-hydrogen-induced-thin-film-blisters-3hkzzpy8w6.pdf

A Mo/Si multilayer film may blister under hydrogen exposure. In this paper, we investigate the impact of intrinsic stress on blister formation in multilayers by varying the Si thickness between 3.4-11 nm and changing the hydrogen ion exposure conditions. Increasing the thickness of a-Si is found to introduce a higher average compressive stress in the multilayer film. Measurements of the average film stress before and after hydrogen exposure did not reveal a correlation between stress relaxation and the observation of surface blisters. Comparing the experimentally observed blister size distribution to that predicted by elastic models of blistering due to pressure, and thin film buckling showed that increasing hydrogen pressure under the blister cap is the main cause of the observed blisters. It is also shown that hydrogen diffusion plays an essential role in the blister formation process as sufficient hydrogen is required to pressurize the blister.

/pdf/influence-of-internal-stress-and-layer-thickness-on-the-34fpzztphw.pdf

R.A.J.M. van den Bos

Papers

Blister formation in Mo/Si multilayered structures induced by hydrogen ions

A model for pressurized hydrogen induced thin film blisters

A model for pressurized hydrogen induced thin film blisters

Influence of internal stress and layer thickness on the formation of hydrogen induced thin film blisters in Mo/Si multilayers