With the introduction of its fifth-generation EUV scanner, the NXE:3400B, ASML has brought EUV to High-Volume Manufacturing for sub-10nm node lithography. This paper presents lithographic performance results obtained with the NXE:3400B, characterized by an NA of 0.33, a Pupil Fill Ratio (PFR) of 0.2 and throughput capability of 125 wafers per hour (or wph).
Advances in source power have enabled a further increase of tool productivity requiring an associated increase of stage scan speeds. To maximize the number of yielding die per day a stringent Overlay, Focus, and Critical Dimension (CD) control is required. Tight CD control at improved resolution is obtained through a number of innovations: the NXE:3400B features lower aberration levels and a revolutionary new illumination system, offering improved pupil-fill ratio and larger sigma range. Overlay and Focus are further improved by implementation of a new wafer clamp and improved scanner controls.
The NXE:3400B also offers full support for reticle pellicles.
Response surface modeling (RSM) is described as a tool to perform optimizations and sensitivity analysis in optical
modeling. With this method, the behavior of the system is first mapped out using a limited set of ray-tracing simulations,
carefully spanning the full parameter space. This can already be done before the full merit function is known. The
relation between design parameters and system performance is then approximated by fitting the simulation results to
functional forms. All subsequent optimizations are then performed very time-efficiently on the functional descriptions of
the dependencies. This contrasts with direct optimization, where the computationally intensive optical modeling is in the
loop of the optimization algorithm, and where changes in merit function, mapping out trade-offs, and determining
sensitivities, are very time consuming. The paper will discuss the advantages of RSM with respect to direct optimization
and give recommendations for the type of problems that are preferentially addressed by RSM. The method will be
illustrated by a case: how optical simulations were used in the design of LumiramicTM phosphor conversion components
for LEDs.
Optical coherence tomography (OCT) and confocal laser scanning microscopy (CLSM) were applied to characterize non-invasively and in vivo the upper layers of human skin on the back of the
hand. The techniques enable a detailed determination of the thickness and location of various skin layers in the epidermis and superficial dermis. Due to differences in spatial resolution and
penetration depth of these methods, OCT and CLSM give complementary information on the composition and structure of skin. OCT signals of the back of the hand show three reflecting layers at different depth in the skin. A direct comparison with CLSM enables the assignment of these layers: the first one is due to the reflection at the skin surface, the second one appears to be caused by the reflection at the basal epidermal layer and the third layer can be ascribed to reflection at fibrous structure in the upper dermis. A comparison of methods reveals a consistent interpretation of the images.
Two noninvasive optical techniques, optical coherence tomography (OCT) and confocal laser scanning microscopy (CLSM) were used to measure the thickness of the epidermis of volunteers. It was found that due to their different resolution and penetration behavior, these two techniques are sensitive to different markers of the epidermal-dermal boundary. In CLSM, the tops of the dermal papillae are clearly and individually visible, whereas in OCT the fibrous structures immediately below the basal cell layer show up most clearly. Image segmentation algorithms were devised for automatic epidermal thickness determination. Both techniques were applied in a study into the effects of ultraviolet irradiation on the thickness of the epidermis. After exposure to a cumulative does of 15.7 (+/- 1.0) personal minimal erythema doses over three weeks, the changes were so small that only CLSM was able to discern them, due to its superior resolution. On average, it was found that the epidermis increases in thickness by 3 micrometers (p=0.011), which could be attributed entirely to a thickening of the stratum corneum.
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