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Novel Self-shrinking Mask for Sub-3 nm Pattern Fabrication.

Yang PS, Cheng PH, Kao CR, Chen MJ - Sci Rep (2016)

Bottom Line: It is very difficult to realize sub-3 nm patterns using conventional lithography for next-generation high-performance nanosensing, photonic, and computing devices.Here we propose a completely original and novel concept, termed self-shrinking dielectric mask (SDM), to fabricate sub-3 nm patterns.In addition, numerous patterns with assorted shapes can be fabricated simultaneously using the SDM technique, exhibiting a much higher throughput than conventional ion beam lithography.

View Article: PubMed Central - PubMed

Affiliation: Department of Materials Science and Engineering, National Taiwan University, 1, Roosevelt Road, Sec. 4, Taipei, 106, ROC Taiwan.

ABSTRACT
It is very difficult to realize sub-3 nm patterns using conventional lithography for next-generation high-performance nanosensing, photonic, and computing devices. Here we propose a completely original and novel concept, termed self-shrinking dielectric mask (SDM), to fabricate sub-3 nm patterns. Instead of focusing the electron and ion beams or light to an extreme scale, the SDM method relies on a hard dielectric mask which shrinks the critical dimension of nanopatterns during the ion irradiation. Based on the SDM method, a linewidth as low as 2.1 nm was achieved along with a high aspect ratio in the sub-10 nm scale. In addition, numerous patterns with assorted shapes can be fabricated simultaneously using the SDM technique, exhibiting a much higher throughput than conventional ion beam lithography. Therefore, the SDM method can be widely applied in the fields which need extreme nanoscale fabrication.

No MeSH data available.


Related in: MedlinePlus

SEM images of the nanopatterns fabricated by the SDM method.(a) An initial pattern (an Al2O3 line array) fabricated by the focused Ga ion beam. (b) Cross section of the initial pattern with a V-shaped structure before the ion irradiation. (c) Cross section of the shrunk line array with a high aspect ratio of ~30. The nanogap on the left side of the figure was filled by the debris of Al2O3 during the fabrication of the cross section using the focused Ga ion beam. A protection layer was not deposited upon the dielectric mask for the fabrication of the cross section because it would fill the gap so that we could not observe the gap width clearly. In fact, the absence of the protection layer does not result in the change of the lateral width of the nanogaps. It may only influence the surface morphology due to the sputtering away of the surface. (d) The line array shrunk after the ion irradiation, and a linewidth as low as 2.9 nm was shown in the inset. (e) A top view of the nanogap in the line array after the further ion exposure, exhibiting a minimum linewidth as low as 2.1 nm. (f) Line patterns were transferred to the substrate by subsequent ion irradiation, revealing a critical dimension less than 10 nm (minimum linewidth is ~5.4 nm). It should be noticed that the patterns were transferred from the hard mask shown in Fig. 3f. It is seen that the linewidth of patterns transferred to the substrate (f) is comparable to that of the hard mask (Fig. 3f).
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f2: SEM images of the nanopatterns fabricated by the SDM method.(a) An initial pattern (an Al2O3 line array) fabricated by the focused Ga ion beam. (b) Cross section of the initial pattern with a V-shaped structure before the ion irradiation. (c) Cross section of the shrunk line array with a high aspect ratio of ~30. The nanogap on the left side of the figure was filled by the debris of Al2O3 during the fabrication of the cross section using the focused Ga ion beam. A protection layer was not deposited upon the dielectric mask for the fabrication of the cross section because it would fill the gap so that we could not observe the gap width clearly. In fact, the absence of the protection layer does not result in the change of the lateral width of the nanogaps. It may only influence the surface morphology due to the sputtering away of the surface. (d) The line array shrunk after the ion irradiation, and a linewidth as low as 2.9 nm was shown in the inset. (e) A top view of the nanogap in the line array after the further ion exposure, exhibiting a minimum linewidth as low as 2.1 nm. (f) Line patterns were transferred to the substrate by subsequent ion irradiation, revealing a critical dimension less than 10 nm (minimum linewidth is ~5.4 nm). It should be noticed that the patterns were transferred from the hard mask shown in Fig. 3f. It is seen that the linewidth of patterns transferred to the substrate (f) is comparable to that of the hard mask (Fig. 3f).

Mentions: The scanning electron microscope (SEM) pictures of nanopatterns fabricated by SDM method are shown in Fig. 2. In Fig. 2a, an Al2O3 line array with ~145 nm gap width was fabricated by focused Ga ion beam to act as the initial pattern for SDM. Figure 2b shows the cross section of the line array with a V-shaped geometry (a top width of ~145 nm and a bottom width of ~83 nm) which is mostly due to the redeposition effect33. This is hard to avoid when using focused Ga ion beam to fabricate deep nanopatterns. Afterwards, the Al2O3 line array was exposed to the Ga ions, and the gap size started to shrink during the ion irradiation. After a couple of minutes, the gap shrunk to the sub-10 nm scale. Figure 2c shows an example of the cross section of the nanogap after the ion irradiation. The gap was estimated to be ~280 nm in depth with an opening of only 9.2 nm in width. This aspect ratio is ~30 which is quite extraordinary for sub-10 nm patterns34. Figure 2d illustrates a tiny gap size on the Al2O3 mask of a critical dimension as low as 2.9 nm after the subsequent ion exposure. Further ion irradiation leads to a minimum gap width down to 2.1 nm as shown in Fig. 2e. This narrow linewidth is much smaller than the spot size of the focused Ga ion beam even with the lowest beam current (The smallest spot size is ~7 nm at the lowest beam current of ~1.1 pA for FEI Helios Nanolab 600i focused ion beam system). In fact, there is no need to focus the ion beam to get nanopatterrns using the SDM technique. The beam current we used in the experiment is as large as 2.5 nA, and the focused spot size at this beam current is about 133 nm35. Accordingly, with a 2.5 nA beam current, the optimal resolution for Ga ion beam lithography is not smaller than 133 nm. Nevertheless, a pattern down to 2.1 nm has been achieved by the SDM method, which clearly indicates that focusing the beam is not necessary to get a sub-3 nm pattern using SDM. Additionally, it is known that the ion milling rate is proportional to the beam current36. As a result, by using a more than two thousand times larger beam current (2.5 nA beam current rather than 1.1 pA), we have saved over 99.9% of time to fabricate sub-10 nm patterns. Finally, after the patterns were transferred to the substrate underneath the Al2O3 layer, the Al2O3 mask was removed by wet etching. An example of the sub-10 nm linewidth on the substrate is shown in Fig. 2f, demonstrating a linewidth as low as ~5.4 nm.


Novel Self-shrinking Mask for Sub-3 nm Pattern Fabrication.

Yang PS, Cheng PH, Kao CR, Chen MJ - Sci Rep (2016)

SEM images of the nanopatterns fabricated by the SDM method.(a) An initial pattern (an Al2O3 line array) fabricated by the focused Ga ion beam. (b) Cross section of the initial pattern with a V-shaped structure before the ion irradiation. (c) Cross section of the shrunk line array with a high aspect ratio of ~30. The nanogap on the left side of the figure was filled by the debris of Al2O3 during the fabrication of the cross section using the focused Ga ion beam. A protection layer was not deposited upon the dielectric mask for the fabrication of the cross section because it would fill the gap so that we could not observe the gap width clearly. In fact, the absence of the protection layer does not result in the change of the lateral width of the nanogaps. It may only influence the surface morphology due to the sputtering away of the surface. (d) The line array shrunk after the ion irradiation, and a linewidth as low as 2.9 nm was shown in the inset. (e) A top view of the nanogap in the line array after the further ion exposure, exhibiting a minimum linewidth as low as 2.1 nm. (f) Line patterns were transferred to the substrate by subsequent ion irradiation, revealing a critical dimension less than 10 nm (minimum linewidth is ~5.4 nm). It should be noticed that the patterns were transferred from the hard mask shown in Fig. 3f. It is seen that the linewidth of patterns transferred to the substrate (f) is comparable to that of the hard mask (Fig. 3f).
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f2: SEM images of the nanopatterns fabricated by the SDM method.(a) An initial pattern (an Al2O3 line array) fabricated by the focused Ga ion beam. (b) Cross section of the initial pattern with a V-shaped structure before the ion irradiation. (c) Cross section of the shrunk line array with a high aspect ratio of ~30. The nanogap on the left side of the figure was filled by the debris of Al2O3 during the fabrication of the cross section using the focused Ga ion beam. A protection layer was not deposited upon the dielectric mask for the fabrication of the cross section because it would fill the gap so that we could not observe the gap width clearly. In fact, the absence of the protection layer does not result in the change of the lateral width of the nanogaps. It may only influence the surface morphology due to the sputtering away of the surface. (d) The line array shrunk after the ion irradiation, and a linewidth as low as 2.9 nm was shown in the inset. (e) A top view of the nanogap in the line array after the further ion exposure, exhibiting a minimum linewidth as low as 2.1 nm. (f) Line patterns were transferred to the substrate by subsequent ion irradiation, revealing a critical dimension less than 10 nm (minimum linewidth is ~5.4 nm). It should be noticed that the patterns were transferred from the hard mask shown in Fig. 3f. It is seen that the linewidth of patterns transferred to the substrate (f) is comparable to that of the hard mask (Fig. 3f).
Mentions: The scanning electron microscope (SEM) pictures of nanopatterns fabricated by SDM method are shown in Fig. 2. In Fig. 2a, an Al2O3 line array with ~145 nm gap width was fabricated by focused Ga ion beam to act as the initial pattern for SDM. Figure 2b shows the cross section of the line array with a V-shaped geometry (a top width of ~145 nm and a bottom width of ~83 nm) which is mostly due to the redeposition effect33. This is hard to avoid when using focused Ga ion beam to fabricate deep nanopatterns. Afterwards, the Al2O3 line array was exposed to the Ga ions, and the gap size started to shrink during the ion irradiation. After a couple of minutes, the gap shrunk to the sub-10 nm scale. Figure 2c shows an example of the cross section of the nanogap after the ion irradiation. The gap was estimated to be ~280 nm in depth with an opening of only 9.2 nm in width. This aspect ratio is ~30 which is quite extraordinary for sub-10 nm patterns34. Figure 2d illustrates a tiny gap size on the Al2O3 mask of a critical dimension as low as 2.9 nm after the subsequent ion exposure. Further ion irradiation leads to a minimum gap width down to 2.1 nm as shown in Fig. 2e. This narrow linewidth is much smaller than the spot size of the focused Ga ion beam even with the lowest beam current (The smallest spot size is ~7 nm at the lowest beam current of ~1.1 pA for FEI Helios Nanolab 600i focused ion beam system). In fact, there is no need to focus the ion beam to get nanopatterrns using the SDM technique. The beam current we used in the experiment is as large as 2.5 nA, and the focused spot size at this beam current is about 133 nm35. Accordingly, with a 2.5 nA beam current, the optimal resolution for Ga ion beam lithography is not smaller than 133 nm. Nevertheless, a pattern down to 2.1 nm has been achieved by the SDM method, which clearly indicates that focusing the beam is not necessary to get a sub-3 nm pattern using SDM. Additionally, it is known that the ion milling rate is proportional to the beam current36. As a result, by using a more than two thousand times larger beam current (2.5 nA beam current rather than 1.1 pA), we have saved over 99.9% of time to fabricate sub-10 nm patterns. Finally, after the patterns were transferred to the substrate underneath the Al2O3 layer, the Al2O3 mask was removed by wet etching. An example of the sub-10 nm linewidth on the substrate is shown in Fig. 2f, demonstrating a linewidth as low as ~5.4 nm.

Bottom Line: It is very difficult to realize sub-3 nm patterns using conventional lithography for next-generation high-performance nanosensing, photonic, and computing devices.Here we propose a completely original and novel concept, termed self-shrinking dielectric mask (SDM), to fabricate sub-3 nm patterns.In addition, numerous patterns with assorted shapes can be fabricated simultaneously using the SDM technique, exhibiting a much higher throughput than conventional ion beam lithography.

View Article: PubMed Central - PubMed

Affiliation: Department of Materials Science and Engineering, National Taiwan University, 1, Roosevelt Road, Sec. 4, Taipei, 106, ROC Taiwan.

ABSTRACT
It is very difficult to realize sub-3 nm patterns using conventional lithography for next-generation high-performance nanosensing, photonic, and computing devices. Here we propose a completely original and novel concept, termed self-shrinking dielectric mask (SDM), to fabricate sub-3 nm patterns. Instead of focusing the electron and ion beams or light to an extreme scale, the SDM method relies on a hard dielectric mask which shrinks the critical dimension of nanopatterns during the ion irradiation. Based on the SDM method, a linewidth as low as 2.1 nm was achieved along with a high aspect ratio in the sub-10 nm scale. In addition, numerous patterns with assorted shapes can be fabricated simultaneously using the SDM technique, exhibiting a much higher throughput than conventional ion beam lithography. Therefore, the SDM method can be widely applied in the fields which need extreme nanoscale fabrication.

No MeSH data available.


Related in: MedlinePlus