Inorganic resists

In recent progress, calixarene resists have been prominent [105]. Hexaacetate p-methylcalix[6]arene was demonstrated to work as a high-resolution negative resist. This resist also shows high etch resistance. Calixarene resist has an advantage in its molecular size (about 1 nm). Liquid crystal resists and inorganic resists show high resolution [106]. These resists are suitable for the fabrication of nanostructures. However, the resist sensitivities are lower than those of chemically amplified resists, even PMMA. 

Figure 14. Sensitivity and contrast plot for electron irradiation of Ge-Se inorganic resist. (Reproduced with premission from Ref. 109.)...

The inorganic resist system is unique with respect to optical sensitivity coupled with 02 plasma resistance. Most organic polymers do not possess sufficient plasma etching resistance to withstand oxygen plasma etching of... 

The inorganic resist is a bi-layer system composed of a thin Ag or Ag-compound film such as Ag-Se, on top of an amorphous Se-Ge film. The film thickness of the Ag and Se-Ge layers is typically 7 nm and 0.2 ni, respectively. A composition at about Sego Gc2o was found to be most suitable for resist applications. 

The e-beam sensitivity is not particularly high being about 300 fiC/crn for an accelerating voltage of 20 to 30 kV which is comparable to PMMA. However, the contrast is extremely high with a 7-value equal to 8 (8). The resist has been reported to be sensitive to ion beams (9) and to soft x-ray irradiation as well. Thus, the inorganic resists are applicable to all non-optical lithographies. 

YOSHIKAWA AND UTSUGI Inorganic Resist for Bilayer Applications... 

Figure 1. Spectral photosensitivity of the SegoGe2o inorganic resist. The optical absorption coefficient is also shown (2).

Figure 4. SEM micrographs showing inorganic resist pattern profiles developed by (a) RIE and (b) wet chemical method. ...

The linewidth differences between the mask and the corresponding resist pattern were precisely evaluated for isolated line and isolated space patterns. The deviation in linewidth versus linewidth shows a maximum or minimum with inorganic resists (13). This behavior is in contrast to that for organic polymeric resists, in which the linewidth deviations gradually increase as the mask feature size decreases. This difference may be explained in terms of selfcompensation of the optical proximity effect due to lateral Ag diffusion. 

Figure 6. Inorganic resist pattern replicated by synchrotron radiation exposure, width is 0.5...

Inorganic resists have many advantages over conventional polymeric resists, especially in regard to resolution, linewidth control latitude, focus depth tolerance, and dry processability. These features make them very suitable for application to submicron VLSI fabrication. Efforts to improve processing technologies will open the way for practical use in LSI fabrication. 

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