Time-resolved ion energy distribution functions in the afterglow of an EUV-induced plasma

Since the introduction of extreme ultraviolet (EUV) lithography (EUVL), the inevitable presence of EUV-induced plasmas inside the lithography tools impacts the operation of EUV optical components. EUV-induced plasmas are created everywhere in the optical path due to the ionizing interaction between the high energy (92 eV) EUV photons and the tools' background gas, which typically is hydrogen gas at a pressure of 1–10 Pa. From a physical point of view, the main impact of the plasma is due to the presence of ions that imping the plasma-facing surfaces. Experimental research into the fluence and energy distribution functions (IEDFs) of ions from EUV-induced plasmas has been limited to time-averaged measurements. In this Letter, we present time-resolved measurements of IEDFs for H+, H2+, and H3+ ions from an EUV-induced plasma in pure hydrogen gas. To this end, an electrostatic quadrupole plasma (EQP) analyzer has been used. The measurements pinpointed momentary fluxes up to three orders of magnitude higher than earlier reported average ion fluxes. In addition, the mean ion energy was unexpectedly found to remain elevated up to 50 μs after the gas had been irradiated with EUV photons. Also, it was shown that the EQP detects H2+ ions on time scales much larger than expected. The presented results are valuable not only for the understanding of elementary processes regarding EUV-induced plasmas interacting with surfaces but also for simulating and predicting the impact of EUV-induced plasma on the lifetime and stability of optical components in EUVL

Morphology change and release of tin and lead micro-particles from substrates in hydrogen plasma

Extreme ultraviolet (EUV) lithography is a technology for high volume manufacturing (HVM) of integrated circuits. HVM defines critical specification for cleanliness of reticles (masks) used to impose a pattern on wafers. EUV-induced hydrogen plasma produced by photoionization of the H2 gas by the 13.5 nm photons plays an important role in the release and transport of particles from contaminated surfaces to the reticle. It was observed that the rate of particle deposition on the reticle in an EUV scanner scales with EUV power which in turn defines the properties of the EUV-induced plasma to increase the knowledge regarding this phenomenon. We demonstrate images, acquired by a scanning electron microscopy (SEM) to illustrate morphological changes, accumulating in particles of tin, lead and lead oxide that were subject to applied hydrogen plasma (non-EUV). These changes led to the potential loss of adhesion of these materials to the relevant surfaces or potential defectivity outbreaks via explosive fragmentation. This work proposes that the mechanical stress in particles' material lattice caused by accumulation of hydrogen bubbles under the surface plays the major role in the morphological changes observed.</p

Dynamics of the spatial electron density distribution of EUV-induced plasmas

We studied the temporal evolution of the electron density distribution in a low pressure pulsed plasma induced by high energy extreme ultraviolet (EUV) photons using microwave cavity resonance spectroscopy (MCRS). In principle, MCRS only provides space averaged information about the electron density. However, we demonstrate here the possibility to obtain spatial information by combining multiple resonant modes. It is shown that EUV-induced plasmas, albeit being a rather exotic plasma, can be explained by known plasma physical laws and processes. Two stages of plasma behaviour are observed: first the electron density distribution contracts, after which it expands. It is shown that the contraction is due to cooling of the electrons. The moment when the density distribution starts to expand is related to the inertia of the ions. After tens of microseconds, the electrons reached the wall of the cavity. The speed of this expansion is dependent on the gas pressure and can be divided into two regimes. It is shown that the acoustic dominated regime the expansion speed is independent of the gas pressure and that in the diffusion dominated regime the expansion depends reciprocal on the gas pressure

Extreme ultraviolet spectra of discharge sources in xenon and tin: comparison of computer simulations and experimental results

no abstrac

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

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

Low energy sputtering

No Abstract

Morphology change and release of tin and lead micro-particles from substrates in hydrogen plasma

Extreme ultraviolet (EUV) lithography is a technology for high volume manufacturing (HVM) of integrated circuits. HVM defines critical specification for cleanliness of reticles (masks) used to impose a pattern on wafers. EUV-induced hydrogen plasma produced by photoionization of the H2 gas by the 13.5 nm photons plays an important role in the release and transport of particles from contaminated surfaces to the reticle. It was observed that the rate of particle deposition on the reticle in an EUV scanner scales with EUV power which in turn defines the properties of the EUV-induced plasma to increase the knowledge regarding this phenomenon. We demonstrate images, acquired by a scanning electron microscopy (SEM) to illustrate morphological changes, accumulating in particles of tin, lead and lead oxide that were subject to applied hydrogen plasma (non-EUV). These changes led to the potential loss of adhesion of these materials to the relevant surfaces or potential defectivity outbreaks via explosive fragmentation. This work proposes that the mechanical stress in particles' material lattice caused by accumulation of hydrogen bubbles under the surface plays the major role in the morphological changes observed

Investigation of ion energy distribution functions in EUV-induced plasmas by ion mass spectrometry

The creation of plasma by direct photo ionization by extreme ultraviolet radiation (EUV, 13.5 nm) is a common phenomenon in extraterrestrial planetary nebulae. However, this process has been difficult to reproduce in a laboratory\u3cbr/\u3ebecause of the scarceness of EUV radiation sources. With the development of next-generation lithography tools, using EUV radiation to create smaller features on computer chips, EUV induced plasmas are now created in the low pressure background gas in lithography tools. Industries have realized that these plasmas are of significant importance with respect to machine lifetime.\u3cbr/\u3eEUV induced plasmas affect exposed surfaces due to impacting ions. In this research an ion mass spectrometer, capable of measuring mass resolved energy spectra, is used to investigate the ion fluxes and ion energy distribution functions (IEDF) of EUV-induced plasmas. A xenon pinch discharge produces EUV radiation, which is focused into a measuring vessel with a low pressure hydrogen environment. In this vessel photo ionization creates free electrons with energies up to 76 eV, which further ionize the background gas by electron impact ionization.\u3cbr/\u3eIons are sampled through a 50 μm orifice in the spectrometer’s front plate. The influence of pressure and EUV power on the IEDF of the EUV-induces plasma are\u3cbr/\u3einvestigated. The results show the fast transformation of H2+ to H3+ by collisions with the background gas as a decrease in H2+ / H3+-ratio with pressure and distance to the EUV beam. The creation of plasma by direct photo ionization by extreme ultraviolet radiation (EUV, 13.5 nm) is a common phenomenon in extraterrestrial planetary nebulae. However, this process has been difficult to reproduce in a laboratory because of the scarceness of EUV radiation sources. With the development of next-generation lithography tools, using EUV radiation to create smaller features on computer chips, EUV induced plasmas are now created in the low pressure background gas in lithography tools. Industries have realized that these plasmas are of significant importance with respect to machine lifetime. EUV induced plasmas affect exposed surfaces due to impacting ions. In this research an ion mass spectrometer, capable of measuring mass resolved energy spectra, is used to investigate the ion fluxes and ion energy distribution functions (IEDF) of EUV-induced plasmas. A xenon pinch discharge produces EUV radiation, which is focused into a measuring vessel with a low pressure hydrogen environment. In this vessel photo ionization creates free electrons with energies up to 76 eV, which further ionize the background gas by electron impact ionization. Ions are sampled through a 50 μm orifice in the spectrometer's front plate. The influence of pressure and EUV power on the IEDF of the EUV-induces plasma are investigated. The results show the fast transformation of H2+ to H3+ by collisions with the background gas as a decrease in H2+ / H3+-ratio with pressure and distance to the EUV beam