Metrology requirements at advanced nodes are not only tightening on specifications but also broadening in terms of flexibility needed to cover variety of product stacks. Metrology targets need to be process compatible and at the same time these targets should also be readable by the metrology system. In some cases, process conditions require a target pitch that is large compared to the wavelength used by the metrology system. Examples of these situations include for instance topography transfer or stacks with thick resist (for e.g. 3D-NAND). Traditionally overlay is extracted from the asymmetry in the positive and negative first diffraction order generated from μDBO targets. However, when the pitch is large, the targets generate multiple higher diffraction orders. Current state-of-the-art diffraction based overlay systems do not take into account the effect of these higher diffraction orders and typically only select the first diffraction order. This is done by reducing the pitch of the target, tuning the wavelength or by changing the angle of incidence of the illumination light. To address wavelength over pitch flexibility an advanced algorithm was introduced on a new metrology system in the fab, providing full flexibility in the selection of measurement wavelength and pitch. To obey the specifications on accuracy and throughput, we will present a new metrology system that is, compared to its predecessor, about 2x faster and able to measure more accurately because of the ability to measure multiple wavelengths within the same time frame.
All chipmakers understand that variability is the adversary of any process and reduction is essential to improving yield which translates to profit. Aggressive process window and yield specifications necessitate tight inline variation requirements on the DUV light source which impact scanner imaging performance. Improvements in reducing bandwidth variation have been realized with DynaPulse™ bandwidth control technology as significant reduction in bandwidth variation translates to a reduction in CD variation for critical device structures.
Previous work on a NAND Via layer has demonstrated an improvement in process capability through improve source and mask optimization with greater ILS and reduced MEEF that improved CDU by 25%. Using this Via layer, we have developed a methodology to quantify the contribution in an overall CDU budget breakdown. Data from the light source is collected using SmartPulse™ allowing for the development of additional methodologies using predictive models to quantify CD variation from Cymer’s legacy, DynaPulse 1 and DynaPulse 2 bandwidth control technologies. CD non-uniformities due to laser bandwidth variation for lot to lot, wafer to wafer, field to field and within field is now available based on known sensitivities and modeled. This data can assist in understanding the contribution from laser bandwidth variation in global and local CDU budgets.
We report on recent progress achieved in X-ray laser research at the Institute of Applied Physics of the University of Bern. Using the existing 10-TW Nd:glass CPA (chirped-pulse amplification) laser system in the grazing-incidence pumping (GRIP) scheme, saturated or near-saturated soft-X-ray lasing has been obtained on the 4d→4p, J = 0-1 lines of barium (Ba, Z = 56), lanthanum (La, Z = 57), and samarium (Sm, Z = 62) at wavelengths down to 7.36 nm, with weak lasing observed at 6.85 nm in Sm. This was achieved with main pulse energies of ~10 J at a pulse duration of 1.5 ps. A small-signal gain coefficient of ~30 cm-1 and a gain-length product of ~16 at saturation have been measured in the case of the 9.2-nm Ba laser. Crucial to these results was the introduction of a second, relatively intense (~20%) prepulse less than 50 ps before the main pulse, in addition to the 2.8% prepulse that irradiated the target ~3 ns earlier. Travelling-wave excitation was used throughout.
To gain insight into the processes mediating the cumulative action of subsequent laser pulses which gives rise to the
formation of nanogratings, we performed double pulse experiments with femtosecond laser pulses with a delay time
ranging from 0.5 ps to 1 ns. We determined the polarisation contrast intensity of the inscribed lines as a measure for the
birefringent strength of the nanogratings. Our experiments show an enhanced nanograting formation for pulse
separations below 500 ps. We attribute this to the presence of self trapped excitons serving as transient material memory
enhancing the impact of the second pulse. In contrast, nanograting formation at pulse separation times up to several
seconds is being mediated by dangling bond type defects as evidenced by spectrally resolved absorption measurements.
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