Freestanding HfO2 grating fabricated by fast atom beam etching
© Wang et al; licensee Springer. 2011
Received: 17 December 2010
Accepted: 28 April 2011
Published: 28 April 2011
We report here the fabrication of freestanding HfO2 grating by combining fast atom beam etching (FAB) of HfO2 film with dry etching of silicon substrate. HfO2 film is deposited onto silicon substrate by electron beam evaporator. The grating patterns are then defined by electron beam lithography and transferred to HfO2 film by FAB etching. The silicon substrate beneath the HfO2 grating region is removed to make the HfO2 grating suspend in space. Period- and polarization-dependent optical responses of fabricated HfO2 gratings are experimentally characterized in the reflectance measurements. The simple process is feasible for fabricating freestanding HfO2 grating that is a potential candidate for single layer dielectric reflector.
PACS: 73.40.Ty; 42.70.Qs; 81.65.Cf.
KeywordsHfO2 film grating fast atom beam etching
As an excellent optical material, hafnium oxide (HfO2) film presents high laser damage threshold, thermal and chemical stability [1–3]. Since HfO2 film is transparent from visible to infrared range, it often servers as the high refractive index material for fabricating multilayer reflection mirror [4, 5], or acts as the waveguiding layer for the realization of guide mode resonant optical filter . These optical devices are originated from the film deposition techniques of HfO2 material. On the other hand, freestanding structures are greatly developed as the promising candidates for producing resonant filter [7, 8] or in place of a traditional top distributed Bragg reflector to reflect light within a cavity [9–12]. As a single layer dielectric mirror, freestanding structures are often sandwiched with air on top and bottom. Compared with multilayer reflection mirror, freestanding structure is more compact and reflects light more efficiently . The high refractive index contrast between HfO2/air also endows the freestanding HfO2 micro/nano structures with the capacity to function as single layer dielectric reflector or guide mode resonant filter. HfO2 film is a hard material, and usually serves as etch stop layer [14, 15]. Recently, focused ion beam (FIB) milling was developed to fabricate sub-micron HfO2 gratings . In FIB milling, micro/nano structures could be achieved on various material systems by physically removing the sample material with a metal ion beam. However, FIB milling is a single process and difficult to be compatible with other fabrication processes for mass production. Moreover, this etching technology is expensive and time-consuming.
We demonstrate here a simple way to fabricate freestanding HfO2 grating by a combination of fast atom beam (FAB) etching and dry etching of silicon. FAB etching, which is capable of high anisotropy etching because it uses neutral particles or atoms for dry etching, is used as a well-controlled, low-damage etching technique to manufacture HfO2 film [17, 18]. To make grating structures freely suspend, the silicon substrate beneath the HfO2 grating region is removed in association of anisotropic and isotropic dry etching of silicon. Period- and polarization-dependent optical responses are experimentally characterized in reflectance measurements.
III. Experimental results and discussion
In summary, freestanding HfO2 gratings are realized by a combination of FAB etching of HfO2 film and dry etching of silicon substrate. Period- and polarization-dependent optical responses of fabricated HfO2 gratings are experimentally characterized in the reflectance measurements. The simple process is feasible for fabricating freestanding HfO2 grating that is a potential candidate for single layer dielectric reflector.
This work was partially supported by the JSPS Research Project (19106007 and P09070) and NJUPT Research Project (NY211001).
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