On a DRAM chip, the patterning of features outside the cell array can be just as challenging as those within the array itself. While the array contains features which are the most densely packed, at least they are regularly arranged. On the other hand, outside the array, the regularity is lost, but the in the most difficult cases, … Read More
Author: Fred Chen
Application-Specific Lithography: Sense Amplifier and Sub-Wordline Driver Metal Patterning in DRAM
BEOL Mask Reduction Using Spacer-Defined Vias and Cuts
In recent advanced nodes, via and cut patterning have constituted a larger and larger portion of the overall BEOL mask count. The advent of SALELE [1,2] caused mask count to increase for EUV as well, resulting in costs no longer being competitive with DUV down to 3nm [3]. Further development by TEL [4] has shown the possibility for… Read More
Predicting Stochastic Defectivity from Intel’s EUV Resist Electron Scattering Model
The release and scattering of photoelectrons and secondary electrons in EUV resists has often been glossed over in most studies in EUV lithography, despite being a fundamental factor in the image formation. Fortunately, Intel has provided us with a laboriously simulated electron release and scattering model, using the GEANT4… Read More
The Significance of Point Spread Functions with Stochastic Behavior in Electron-Beam Lithography
Electron beam lithography is commercially used to directly write submicron patterns onto advanced node masks. With the advent of EUV masks and nanometer-scale NIL (nanoimprint lithography), multi-beam writers are now being used, compensating the ultralow throughput of a single high-resolution electron beam with the use… Read More
Extension of DUV Multipatterning Toward 3nm
China’s recent achievement of a 7nm-class foundry node using only DUV lithography [1] raises the question of how far DUV lithography can be extended by multipatterning. A recent publication at CSTIC 2023 indicates that Chinese groups are currently looking at extension of DUV-based multipatterning to 5nm, going so far… Read More
Stochastic Model for Acid Diffusion in DUV Chemically Amplified Resists
Recent articles have focused much effort on studying the stochastic behavior of secondary electron exposure of EUV resists [1-4]. Here, we consider the implications of extending similar treatments to DUV lithography.
Basic Model Setup
As before, the model uses pixel-by-pixel calculations of absorbed photon dose, followed… Read More
Modeling EUV Stochastic Defects with Secondary Electron Blur
Extreme ultraviolet (EUV) lithography is often represented as benefiting from the 13.5 nm wavelength (actually it is a range of wavelengths, mostly ~13.2-13.8 nm), when actually it works through the action of secondary electrons, electrons released by photoelectrons which are themselves released from ionization by absorbed… Read More
Enhanced Stochastic Imaging in High-NA EUV Lithography
High-NA EUV lithography is the anticipated new lithography technology to be introduced for the 2nm node. Essentially, it replaces the 0.33 numerical aperture of current EUV systems with a higher 0.55 numerical aperture (NA). This allows the projection of smaller spot sizes and smaller pitches, roughly 60% smaller compared … Read More
Application-Specific Lithography: Via Separation for 5nm and Beyond
With metal interconnect pitches shrinking in advanced technology nodes, the center-to-center (C2C) separations between vias are also expected to shrink. For a 5/4nm node minimum metal pitch of 28 nm, we should expect vias separated by 40 nm (Figure 1a). Projecting to 3nm, a metal pitch of 24 nm should lead us to expect vias separated… Read More
NILS Enhancement with Higher Transmission Phase-Shift Masks
In the assessment of wafer lithography processes, normalized image log-slope (NILS) gives the % change in width for a given % change in dose [1,2]. A nominal NILS value of 2 indicates 10% change in linewidth for 10% change in dose; the % change in linewidth is inversely proportional to the NILS. In a previous article [2], it was shown… Read More
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