Nanolithography in the Large

The papers presented at SPIE’s 2012 Advanced Lithography Conference are beginning to appear on line. Follow these links:
EUV
Alternative Litho
Metrology & Inspection, …
Resist
Optical Litho
DFM
Etch

Happy reading.

Chris Mack gave an insightful talk on line edge roughness (LER). One of the points he made is that talking about σ_LER is not enough. Consider the power spectral density (PSD) plots in the figure. Which curve shows “better” LER? If both curves integrate to the same area, they cannot be distinguished by the variance (σ^2). We must also consider the correlation length and roughness exponent. The correlation length influences where the “break” of the curve appears, while the roughness exponent influences how rapidly the curve declines from there. (The PSD plot of white noise would be a horizontal line.)

A recent article in JMM attempts to quantify just this effect, that the impact of LER is not constant with constant variance. One must instead specify the PSD at least to the level of the three parameters: variance, correlation length, and roughness exponent.

REBL has undergone big changes since the last report. The rotary stage is now gone. We recall that an early KLA-Tencor proposal was to have multi-column clusters arrayed on opposing sides of a circle as in Figure 1.

Fig. 1 Previous REBL stage concept.

Entire wafer areas can be covered by moving the stage along one axis in addition to rotating. However, throughput was found to be inadequate, necessitating the addition of more column clusters. Unfortunately, with more clusters arrayed around the circle, one cannot cover the wafer areas by a simple one-dimensional stage motion. Instead, one must move each column cluster in and out radially. This is clearly not possible mechanically.

Fig. 2 New REBL stage concept.

K-T’s latest proposal shows two X/Y maglev stages moving side by side in opposing directions. Each stage carries multiple wafers. (See Figure 2.) Obviously, this configuration suffers stage turn-around overhead. Because K-T targets the 16 nm node, and expects a higher dose requirement, they claim that the overhead is negligible.

K-T claims to have “some” functional modulator chips, but clearly continues to have difficulties here. The next column design (Column 4) due this year will operate at 100 kV and will have 100X demagnification. K-T expects 5 nm to 12 nm beam blur. Throughput will be limited to a few wafers per hour. Importantly, K-T may be targeting the cut pattern market rather than fully general patterning.