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Fabrication of HfO2 patterns by laser interference nanolithography and selective dry etching for III-V CMOS application.

Benedicto M, Galiana B, Molina-Aldareguia JM, Monaghan S, Hurley PK, Cherkaoui K, Vazquez L, Tejedor P - Nanoscale Res Lett (2011)

Bottom Line: Pattern transfer to the HfO2 film was carried out by reactive ion beam etching using CF4 and O2 plasmas.A combination of atomic force microscopy, high-resolution scanning electron microscopy, high-resolution transmission electron microscopy, and energy-dispersive X-ray spectroscopy microanalysis was used to characterise the various etching steps of the process and the resulting HfO2/GaAs pattern morphology, structure, and chemical composition.We show that the patterning process can be applied to fabricate uniform arrays of HfO2 mesa stripes with tapered sidewalls and linewidths of 100 nm.

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Affiliation: Instituto de Ciencia de Materiales de Madrid, CSIC, C/Sor Juana Inés de la Cruz 3, 28049 Madrid, Spain. ptejedor@icmm.csic.es.

ABSTRACT
Nanostructuring of ultrathin HfO2 films deposited on GaAs (001) substrates by high-resolution Lloyd's mirror laser interference nanolithography is described. Pattern transfer to the HfO2 film was carried out by reactive ion beam etching using CF4 and O2 plasmas. A combination of atomic force microscopy, high-resolution scanning electron microscopy, high-resolution transmission electron microscopy, and energy-dispersive X-ray spectroscopy microanalysis was used to characterise the various etching steps of the process and the resulting HfO2/GaAs pattern morphology, structure, and chemical composition. We show that the patterning process can be applied to fabricate uniform arrays of HfO2 mesa stripes with tapered sidewalls and linewidths of 100 nm. The exposed GaAs trenches were found to be residue-free and atomically smooth with a root-mean-square line roughness of 0.18 nm after plasma etching.PACS: Dielectric oxides 77.84.Bw, Nanoscale pattern formation 81.16.Rf, Plasma etching 52.77.Bn, Fabrication of III-V semiconductors 81.05.Ea.

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Schematic of the HfO2 nanostructuring process. (a) Schematic drawing of the starting multilayer structure. (b) Patterning of the photoresist by laser interference lithography. (c) Pattern transfer to the SiO2 layer by CF4 ICP-RIE. (d) Pattern transfer to the ARC by O2 ICP-RIE. (e) Selective ICP-RIE of the HfO2 layer with CF4. (f) Elimination of the ARC with O2 ICP-RIE and final cleaning with HCl/H2O.
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Figure 4: Schematic of the HfO2 nanostructuring process. (a) Schematic drawing of the starting multilayer structure. (b) Patterning of the photoresist by laser interference lithography. (c) Pattern transfer to the SiO2 layer by CF4 ICP-RIE. (d) Pattern transfer to the ARC by O2 ICP-RIE. (e) Selective ICP-RIE of the HfO2 layer with CF4. (f) Elimination of the ARC with O2 ICP-RIE and final cleaning with HCl/H2O.

Mentions: Figure 3b illustrates the sample cross-section after HfO2 selective etching with CF4. This process has been estimated to occur at a rate of 0.06 nm/s. Such slow HfO2 etching rate is advantageous with respect to previous reports using SF6/Ar [8] from the process control viewpoint, as it allows to process a typical 2-nm-thick gate oxide in a practicable etching time, i.e. approximately 30 s. As shown in the image, a tapered etch profile with a 70° inclination angle is achieved by the formation of a sidewall passivation layer comprised of non-volatile reaction by-products of the CF4 etching process. It should be noted here that the patterned resist mask had been completely eliminated during the previous O2 plasma treatment and, consequently, the exposed SiO2 stripes and the ARC layer are gradually etched by the CF4 plasma during pattern transfer to the HfO2 film. This contributes to a further reduction of the pattern linewidth and to the formation of an HfO2 foot on both mesa edges, which is only observable by HR-TEM (see below). The width of the HfO2 mesa top measured from Figure 3b was 98 nm at this stage of the process. The width of the mesa bottom could not be determined from the same image due to the presence of re-deposited material. Notwithstanding, we have estimated that the bottom linewidth is approximately 105 nm, taking into account that the 70° ARC sidewall inclination is transferred to the HfO2 layer without any significant variation. Comparison of this value with the final dimension of the HfO2 stripes (Figure 3c), i.e. 100 nm, suggests that the last HCl/H2O wet etch further contributes to narrow the linewidth. The schematic diagram shown in Figure 4 illustrates the HfO2 nanofabrication process flow.


Fabrication of HfO2 patterns by laser interference nanolithography and selective dry etching for III-V CMOS application.

Benedicto M, Galiana B, Molina-Aldareguia JM, Monaghan S, Hurley PK, Cherkaoui K, Vazquez L, Tejedor P - Nanoscale Res Lett (2011)

Schematic of the HfO2 nanostructuring process. (a) Schematic drawing of the starting multilayer structure. (b) Patterning of the photoresist by laser interference lithography. (c) Pattern transfer to the SiO2 layer by CF4 ICP-RIE. (d) Pattern transfer to the ARC by O2 ICP-RIE. (e) Selective ICP-RIE of the HfO2 layer with CF4. (f) Elimination of the ARC with O2 ICP-RIE and final cleaning with HCl/H2O.
© Copyright Policy - open-access
Related In: Results  -  Collection

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Figure 4: Schematic of the HfO2 nanostructuring process. (a) Schematic drawing of the starting multilayer structure. (b) Patterning of the photoresist by laser interference lithography. (c) Pattern transfer to the SiO2 layer by CF4 ICP-RIE. (d) Pattern transfer to the ARC by O2 ICP-RIE. (e) Selective ICP-RIE of the HfO2 layer with CF4. (f) Elimination of the ARC with O2 ICP-RIE and final cleaning with HCl/H2O.
Mentions: Figure 3b illustrates the sample cross-section after HfO2 selective etching with CF4. This process has been estimated to occur at a rate of 0.06 nm/s. Such slow HfO2 etching rate is advantageous with respect to previous reports using SF6/Ar [8] from the process control viewpoint, as it allows to process a typical 2-nm-thick gate oxide in a practicable etching time, i.e. approximately 30 s. As shown in the image, a tapered etch profile with a 70° inclination angle is achieved by the formation of a sidewall passivation layer comprised of non-volatile reaction by-products of the CF4 etching process. It should be noted here that the patterned resist mask had been completely eliminated during the previous O2 plasma treatment and, consequently, the exposed SiO2 stripes and the ARC layer are gradually etched by the CF4 plasma during pattern transfer to the HfO2 film. This contributes to a further reduction of the pattern linewidth and to the formation of an HfO2 foot on both mesa edges, which is only observable by HR-TEM (see below). The width of the HfO2 mesa top measured from Figure 3b was 98 nm at this stage of the process. The width of the mesa bottom could not be determined from the same image due to the presence of re-deposited material. Notwithstanding, we have estimated that the bottom linewidth is approximately 105 nm, taking into account that the 70° ARC sidewall inclination is transferred to the HfO2 layer without any significant variation. Comparison of this value with the final dimension of the HfO2 stripes (Figure 3c), i.e. 100 nm, suggests that the last HCl/H2O wet etch further contributes to narrow the linewidth. The schematic diagram shown in Figure 4 illustrates the HfO2 nanofabrication process flow.

Bottom Line: Pattern transfer to the HfO2 film was carried out by reactive ion beam etching using CF4 and O2 plasmas.A combination of atomic force microscopy, high-resolution scanning electron microscopy, high-resolution transmission electron microscopy, and energy-dispersive X-ray spectroscopy microanalysis was used to characterise the various etching steps of the process and the resulting HfO2/GaAs pattern morphology, structure, and chemical composition.We show that the patterning process can be applied to fabricate uniform arrays of HfO2 mesa stripes with tapered sidewalls and linewidths of 100 nm.

View Article: PubMed Central - HTML - PubMed

Affiliation: Instituto de Ciencia de Materiales de Madrid, CSIC, C/Sor Juana Inés de la Cruz 3, 28049 Madrid, Spain. ptejedor@icmm.csic.es.

ABSTRACT
Nanostructuring of ultrathin HfO2 films deposited on GaAs (001) substrates by high-resolution Lloyd's mirror laser interference nanolithography is described. Pattern transfer to the HfO2 film was carried out by reactive ion beam etching using CF4 and O2 plasmas. A combination of atomic force microscopy, high-resolution scanning electron microscopy, high-resolution transmission electron microscopy, and energy-dispersive X-ray spectroscopy microanalysis was used to characterise the various etching steps of the process and the resulting HfO2/GaAs pattern morphology, structure, and chemical composition. We show that the patterning process can be applied to fabricate uniform arrays of HfO2 mesa stripes with tapered sidewalls and linewidths of 100 nm. The exposed GaAs trenches were found to be residue-free and atomically smooth with a root-mean-square line roughness of 0.18 nm after plasma etching.PACS: Dielectric oxides 77.84.Bw, Nanoscale pattern formation 81.16.Rf, Plasma etching 52.77.Bn, Fabrication of III-V semiconductors 81.05.Ea.

No MeSH data available.


Related in: MedlinePlus