Recently, a patent application from TSMC [1] revealed target EUV doses used in the range of 30-45 mJ/cm2. However, it was also acknowledged in the same application that such doses were too low to prevent defects and roughness. Recent studies [2,3] have shown that by considering photon density along with blur, the associated shot… Read More
Author: Fred Chen
The Challenge of Working with EUV Doses
Blur, not Wavelength, Determines Resolution at Advanced Nodes
Lithography has been the driving force for shrinking feature sizes for decades, and the most easily identified factor behind this trend is the reduction of wavelength. G-line (436 nm wavelength) was used for 0.5 um in the late 1980s [1], and I-line (365 nm wavelength) was used down to 0.3 um in the 1990s [2]. Then began the era of deep-ultraviolet… Read More
Cautions In Using High-NA EUV
High-NA EUV has received a lot of attention ever since Intel put the spotlight on its receiving the first 0.55 NA EUV tool from ASML [1], expected in 2025. EUV itself has numerous issues which have been enumerated by myself and others, most notoriously the stochastic defects issue. There are also a host of issues related to the propagation… Read More
Stochastic Effects from Photon Distribution Entropy in High-k1 EUV Lithography
Recent advances in EUV lithography have largely focused on “low-k1” imaging, i.e., features with pitches less than the wavelength divided by the numerical aperture (k1<0.5). With a nominal wavelength of 13.5 nm and a numerical aperture of 0.33, this means sub-40 nm pitches. It is naturally expected that larger… Read More
Stochastic Origins of EUV Feature Edge Roughness
Due to the higher energy of EUV (13.3-13.7 nm wavelength) compared to ArF (193 nm wavelength) light, images produced by EUV are more susceptible to photon shot noise.
Figure 1. (Left) 40 nm dense (half-pitch) line image projected onto wafer at 35 mJ/cm2; (Right) 20 nm dense (half-pitch) line image projected onto wafer at 70 mJ/cm2.… Read More
Contrast Reduction vs. Photon Noise in EUV Lithography
The stochastic behavior of images formed in EUV lithography has already been highlighted by a number of authors [1-3]. How serious it appears depends on the pixel size with which the photons are bunched. Generally, though, for features of around 20 nm or less, even 1 nm can have at least a +/- 15% gradient across it, which is still a
SALELE Double Patterning for 7nm and 5nm Nodes
In this article, we will explore the use of self-aligned litho-etch-litho-etch (SALELE) double patterning for BEOL metal layers in the 7nm node (40 nm minimum metal pitch [1]) with DUV, and 5nm node (28 nm minimum metal pitch [2]) with EUV. First, we mention the evidence that this technique is being used; Xilinx [3] disclosed the… Read More
Calculating the Maximum Density and Equivalent 2D Design Rule of 3D NAND Flash
I recently posted an insightful article [1] published in 2013 on the cost of 3D NAND Flash by Dr. Andrew Walker, which has since received over 10,000 views on LinkedIn. The highlight was the plot of cost vs. the number of layers showing a minimum cost for some layer number, dependent on the etch sidewall angle. In this article, the same… Read More
The Complexities of the Resolution Limits of Advanced Lithography
For advanced lithography used to shrink semiconductor device features according to Moore’s Law, resolution limits are an obvious consideration. It is often perceived that the resolution limit is simply derived from a well-defined equation, but nothing can be further from the truth.
Optical Lithography: the fine print
… Read MoreHow Line Cuts Became Necessarily Separate Steps in Lithography
Pretty much all the semiconductor nodes in the last two decades have had at least one layer where the minimum pitch pushes the limitation of the state-of-the-art lithography tool, with a k1 factor < 0.5, i.e., the half-pitch is less than 0.5*wavelength/numerical aperture. A number of published reports [1-4] have touched upon… Read More
Rapidus, IBM, and the Billion-Dollar Silicon Sovereignty Bet