With state-of-the-art EUV lithography moving to the 3 and 2 nm nodes, yield control and connected to that particle contamination control are crucial aspect of High-Volume Manufacturing (HVM). While much progress has been made in recent years, the continuously tightening node requirements translate into ever more stringent requirements on particle contamination control. Besides for lithographic scanners, operating in a low background pressure hydrogen gas environment, particle contamination control is also important for space exploration (which also operates in low pressure environments), where particles may lead to malfunctioning moving parts, loss of solar power generation, and human health hazards. A key factor in release of particles in these low-pressure environments is the ionization of the low-pressure background gas by energetic photons (for instance EUV in lithographic scanners, and broadband energetic radiation in space), and resulting plasma with fast electrons of 25 eV and above. Experiments show that these electrons can mobilize and remove particles on most materials, and that the governing effects strongly depend on the substrate material, coating and surface finishing. This paper will discuss work on understanding and modeling these effects and describe possible solution paths to improve particle contamination control, both for lithographic scanners and for space exploration.
Driven by the continuous decrease of the length scales of fabricated semiconductor structures, ultraclean semiconductor processing equipment suffers more and more from contamination with nano- and micrometer sized particles, which may be introduced in such systems from the outside via gas flows either externally injected or through translational and/or rotational (robotic) feedthroughs. One promising approach to filter contaminating particulates from these gas flows is the application of a plasma particle seal in which airborne particles carried by a gas flow pick up free charges from a plasma and then are deflected by an externally applied electric field in the plasma’s afterglow region. Consecutively, these contaminating particles may be guided to less harmful locations in the system or even be fully removed. In this contribution, we present measurements that reveal the importance of additional drag forces imposed on the particles and the influence of these drag forces on the particles’ trajectories when the plasma is operated in pulsed mode.
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.
With the introduction of EUV lithography, the control of contamination in advanced semiconductor processes has become increasingly critical. Our work is a joint effort (TU/e and VDL-ETG) and is aimed at the development of plasma-assisted contamination control strategies mainly focusing on airborne particles in a low pressure gas. We present experiments comparing the charge-to-mass ratio of single spherical micron-sized particles with that of non-spherical agglomerates thereof in the spatial plasma afterglow. It is shown that the charge-to-mass ratio of two-particle clusters deviates only 6% from that of singlets. This means that for the proposed mitigation strategy, of which the efficiency is based on the charge-to-mass ratio, it is acceptable to study the charging of spherical particles and to extrapolate the results towards non-spherical particles within a reasonable range.
With the introduction of Extreme Ultraviolet (EUV) lithography, the control of contamination has become crucial. Sources for contamination in EUV lithography scanners are not limited to only particle generation and release inside the scanner environment but may be introduced from outside as well, e.g. through translational and/or rotational (robotic) feedthroughs.
In this contribution we highlight our joint (TU/e and VDL ETG) research efforts aimed at the development of plasma-enabled contamination control strategies. The focus in this research is on airborne particles immersed in a low pressure gas flow that interact with both the afterglow of a plasma and an externally applied electric field.
A flexible experimental setup has been developed and will be introduced which is able to study the interaction between contaminants, plasmas and externally applied electric fields. Our results show that the designed configuration allows to carefully control the residual charges of the particles as well as their positions and trajectories with respect to the gas flow in which they are immersed. These results, together with the understanding of the underlying principle processes, open-up various possibilities to achieve improved cleanliness of the mentioned systems.
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