Stochastic Effects from Photon Distribution Entropy in High-k1 EUV Lithography

Stochastic Effects from Photon Distribution Entropy in High-k1 EUV Lithography
by Fred Chen on 08-04-2021 at 10:00 am

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

Stochastic Origins of EUV Feature Edge Roughness
by Fred Chen on 07-11-2021 at 10:00 am

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

Contrast Reduction vs. Photon Noise in EUV Lithography
by Fred Chen on 05-30-2021 at 6:00 am

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

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SALELE Double Patterning for 7nm and 5nm Nodes

SALELE Double Patterning for 7nm and 5nm Nodes
by Fred Chen on 03-28-2021 at 6:00 am

SALELE Double Patterning for 7nm and 5nm Nodes 4

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

Calculating the Maximum Density and Equivalent 2D Design Rule of 3D NAND Flash
by Fred Chen on 02-21-2021 at 10:00 am

3D NAND Flash unit cell

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

The Complexities of the Resolution Limits of Advanced Lithography
by Fred Chen on 01-10-2021 at 6:00 am

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

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How Line Cuts Became Necessarily Separate Steps in Lithography

How Line Cuts Became Necessarily Separate Steps in Lithography
by Fred Chen on 12-08-2020 at 10:00 am

How 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


CD-Pitch Combinations Disfavored by EUV Stochastics

CD-Pitch Combinations Disfavored by EUV Stochastics
by Fred Chen on 11-29-2020 at 6:00 am

CD Pitch Combinations Disfavored by EUV Stochastics

Ongoing investigations of EUV stochastics [1-3] have allowed us to map combinations of critical dimension (CD) and pitch which are expected to pose a severe risk of stochastic defects impacting the use of EUV lithography. Figure 1 shows a typical set of contours of fixed PNOK (i.e., the probability of a feature being Not OK due… Read More


Impact of Defocus and Illumination on Imaging of Pitch

Impact of Defocus and Illumination on Imaging of Pitch
by Fred Chen on 10-26-2020 at 10:00 am

Impact of Defocus

In an earlier article [1], the resolution limit for the space between paired features was described by the Rayleigh criterion of ~0.6 wavelength/numerical aperture, where the numerical aperture (NA) represented the sine of the largest angle for a ray focused from the lens to a point. It is also given by the radius of the lens divided… Read More


Toshiba Cost Model for 3D NAND

Toshiba Cost Model for 3D NAND
by Fred Chen on 10-11-2020 at 8:00 am

Toshiba Cost Model for 3D NAND

Toshiba (now known as Kioxia) was the first company to propose a 3D stacked version of NAND Flash memory called BICS [1]. BICS (BICost Scalable) Flash used explicit process cost reduction based on depositing and etching multiple layers at once, avoiding multiple lithography steps. This strategy replaced the usual approach… Read More