Pattern noise in electron beam resists: PMMA, KRS-XE, TOK, HSQ

Abstract

The variation in the printing of nominally identical contacts with electron-beam exposure is used to quantitatively determine the statistical variation in chemically amplified resists (KRS-XE with and without top coat, TOK) and non-chemically-amplified resists (PMMA and HSQ). Uniform 17×23 arrays of 24 and 32nm contacts were exposed at fixed doses with a 100keV electron beam. By looking at data observed from top view scanning electron microscopy images, a normal distribution was fitted to the fraction of contacts that printed versus dose to determine the standard deviation of the distribution relative to the dose at which 50% of the contacts printed. The top coat on KRS-XE increased contact uniformity and reduced the required dose. Quantitative analysis shows that PMMA contained as much noise as the chemically amplified resist systems, KRS-XE and TOK. Except HSQ, this normalized standard deviation ranged from 0.16 to 0.21 which is indicative that the contact hole printing process may be dominated by less than 40 events. HSQ exhibited lower standard deviation values, corresponding to over 1000 effective events.

Theoretical study on effects of exposure pattern width on line edge roughness and stochastic defect generation in fabrication of 16-nm-half-pitch line-and-space patterns by electron beam lithography

“…In the development of highly resolving and highly sensitive resist materials, stochastic phenomena such as LER are a critical issue because the number of electrons used for pattern formation is small. [3][4][5][6] Besides LER, pattern defects such as pinching and bridging are stochastically generated. [7][8][9][10] Pinching is the local narrowing of resist lines.…”

Highly robust electron beam lithography lift-off process using chemically amplified positive tone resist and PEDOT:PSS as a protective coating

“…Another issue concerning CA resists is that due to their high sensitivity, shot noise effects get more prominent. This results in an exposure-related, increased line edge roughness (LER [30][31][32][33]) which ultimately limits the critical dimension (CD). In addition to shot noise, the LER is also greatly affected by resist properties such as resist graininess, acid generation efficiency, the acid diffusion, and concentration [33].…”