Limits...
Polystyrene negative resist for high-resolution electron beam lithography.

Ma S, Con C, Yavuz M, Cui B - Nanoscale Res Lett (2011)

Bottom Line: It demonstrated fairly well-defined patterning of a 20-nm period line array and a 15-nm period dot array, which are the densest patterns ever achieved using organic EBL resists.It is also considerably more resistant to dry etching than PMMA.With a low sensitivity, it would find applications where negative resist is desired and throughput is not a major concern.

View Article: PubMed Central - HTML - PubMed

Affiliation: Waterloo Institute for Nanotechnology (WIN), University of Waterloo, 200 University Ave, West, Waterloo, ON N2L 3G1, Canada. bcui@uwaterloo.ca.

ABSTRACT
We studied the exposure behavior of low molecular weight polystyrene as a negative tone electron beam lithography (EBL) resist, with the goal of finding the ultimate achievable resolution. It demonstrated fairly well-defined patterning of a 20-nm period line array and a 15-nm period dot array, which are the densest patterns ever achieved using organic EBL resists. Such dense patterns can be achieved both at 20 and 5 keV beam energies using different developers. In addition to its ultra-high resolution capability, polystyrene is a simple and low-cost resist with easy process control and practically unlimited shelf life. It is also considerably more resistant to dry etching than PMMA. With a low sensitivity, it would find applications where negative resist is desired and throughput is not a major concern.

No MeSH data available.


Related in: MedlinePlus

Dense line array with a period of (a) 100 nm; (b) 30 nm; (c) 25 nm; and (d) 20 nm. The polystyrene resist was exposed at 5 keV and developed using xylene for 1.5 min at room temperature. The pattern heights measured by AFM are in the range of 25-28 nm that is close to the original film thickness.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC3211865&req=5

Figure 2: Dense line array with a period of (a) 100 nm; (b) 30 nm; (c) 25 nm; and (d) 20 nm. The polystyrene resist was exposed at 5 keV and developed using xylene for 1.5 min at room temperature. The pattern heights measured by AFM are in the range of 25-28 nm that is close to the original film thickness.

Mentions: To study the ultimate resolution (half-pitch) of this resist, we exposed dense line arrays and dot arrays using 30-nm-thick polystyrene at 20 and 5 keV. Thin resist is generally used for high resolution patterning in to reduce the effect of capillary force during resist drying, which leads to pattern collapse (unless using critical point drying [12]), and the forward scattering of electrons that is more serious for thicker resist [13]. Note that even thinner resist was used for most previous high resolution studies on HSQ and calixarene resists. For 30-nm polystyrene, the forward scattering range is estimated to be 5 and 8 nm at 20 and 5 keV, respectively [13], which are both very low (yet slightly larger than or comparable to the beam spot size). Therefore, it is expected that EBL at 5 keV can achieve the same resolution as 20 keV, but with the additional benefit of considerably increased resist sensitivity. Figure 2 shows line array patterns of 100, 30, 25, and 20-nm periods developed by xylene for 90 s at room temperature. Line doses ranging from 4 to 10 nC/cm all resulted in well-defined patterns. The dose window is expected to be much narrower when exposing large area (> 1 μm × 1 μm) line array due to significant exposure from backscattered electrons. The next period in the experiment, 15 nm, was not well defined. The effort toward dense line array patterning by EBL has been driven by the fabrication of X-ray zone plates where the X-ray imaging resolution is close to the half-pitch of the outmost zones. Previously, the densest line array pattern demonstrated using organic resist was 24-nm period using ZEP resist developed at low temperatures [20] (as mentioned above, the record for inorganic HSQ resist is 9-nm period). As expected and shown in Figure 3, for exposure at 20 keV, a similar high resolution of 20-nm period could be achieved when using all the three developers (xylene, chlorobenzene, and cyclohexane) that are studied.


Polystyrene negative resist for high-resolution electron beam lithography.

Ma S, Con C, Yavuz M, Cui B - Nanoscale Res Lett (2011)

Dense line array with a period of (a) 100 nm; (b) 30 nm; (c) 25 nm; and (d) 20 nm. The polystyrene resist was exposed at 5 keV and developed using xylene for 1.5 min at room temperature. The pattern heights measured by AFM are in the range of 25-28 nm that is close to the original film thickness.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3211865&req=5

Figure 2: Dense line array with a period of (a) 100 nm; (b) 30 nm; (c) 25 nm; and (d) 20 nm. The polystyrene resist was exposed at 5 keV and developed using xylene for 1.5 min at room temperature. The pattern heights measured by AFM are in the range of 25-28 nm that is close to the original film thickness.
Mentions: To study the ultimate resolution (half-pitch) of this resist, we exposed dense line arrays and dot arrays using 30-nm-thick polystyrene at 20 and 5 keV. Thin resist is generally used for high resolution patterning in to reduce the effect of capillary force during resist drying, which leads to pattern collapse (unless using critical point drying [12]), and the forward scattering of electrons that is more serious for thicker resist [13]. Note that even thinner resist was used for most previous high resolution studies on HSQ and calixarene resists. For 30-nm polystyrene, the forward scattering range is estimated to be 5 and 8 nm at 20 and 5 keV, respectively [13], which are both very low (yet slightly larger than or comparable to the beam spot size). Therefore, it is expected that EBL at 5 keV can achieve the same resolution as 20 keV, but with the additional benefit of considerably increased resist sensitivity. Figure 2 shows line array patterns of 100, 30, 25, and 20-nm periods developed by xylene for 90 s at room temperature. Line doses ranging from 4 to 10 nC/cm all resulted in well-defined patterns. The dose window is expected to be much narrower when exposing large area (> 1 μm × 1 μm) line array due to significant exposure from backscattered electrons. The next period in the experiment, 15 nm, was not well defined. The effort toward dense line array patterning by EBL has been driven by the fabrication of X-ray zone plates where the X-ray imaging resolution is close to the half-pitch of the outmost zones. Previously, the densest line array pattern demonstrated using organic resist was 24-nm period using ZEP resist developed at low temperatures [20] (as mentioned above, the record for inorganic HSQ resist is 9-nm period). As expected and shown in Figure 3, for exposure at 20 keV, a similar high resolution of 20-nm period could be achieved when using all the three developers (xylene, chlorobenzene, and cyclohexane) that are studied.

Bottom Line: It demonstrated fairly well-defined patterning of a 20-nm period line array and a 15-nm period dot array, which are the densest patterns ever achieved using organic EBL resists.It is also considerably more resistant to dry etching than PMMA.With a low sensitivity, it would find applications where negative resist is desired and throughput is not a major concern.

View Article: PubMed Central - HTML - PubMed

Affiliation: Waterloo Institute for Nanotechnology (WIN), University of Waterloo, 200 University Ave, West, Waterloo, ON N2L 3G1, Canada. bcui@uwaterloo.ca.

ABSTRACT
We studied the exposure behavior of low molecular weight polystyrene as a negative tone electron beam lithography (EBL) resist, with the goal of finding the ultimate achievable resolution. It demonstrated fairly well-defined patterning of a 20-nm period line array and a 15-nm period dot array, which are the densest patterns ever achieved using organic EBL resists. Such dense patterns can be achieved both at 20 and 5 keV beam energies using different developers. In addition to its ultra-high resolution capability, polystyrene is a simple and low-cost resist with easy process control and practically unlimited shelf life. It is also considerably more resistant to dry etching than PMMA. With a low sensitivity, it would find applications where negative resist is desired and throughput is not a major concern.

No MeSH data available.


Related in: MedlinePlus