Turkish scientists seek co-operation on low-k cryptocrystal
Technical co-operation is sought with manufacturers, industrial companies and venture capitalists interested in and willing to benefit from the know-how to improve the prototype processes, to develop new tools and bring the technology to an industrial scale.
A prototype method has been developed to synthesise cryptocrystal layers of ammonium silicon fluoride ((NH4)2SiF6) on silicon wafers using gaseous chemicals at room temperature. As-grown layers consist of a white granular crystalline film with thicknesses of up to about 8microns, which were synthesised with growth rates of around 1micron/hour. X-ray diffraction analysis indicates an isometric hexoctahedral system with (NH4)2SiF6 cryptohalite crystals. These results have been confirmed by the presence of (NH4)2SiF6 vibrational absorption bands in Fourier transform infrared (FTIR) analysis.
Detailed optical, electrical, structural and thermal properties of the layers are under investigation. The current work involves further characterisation of this low dielectric constant material (k=1.87) and selective writing on Si wafers for nanofabrication applications. Low and high frequency dielectric properties will be determined on both the granular films and isolated crystals.
The crystal nucleation mechanism has been explained in terms of anodic and cathodic reactions. It was shown that the crystal grains have sizes up to 20microns, thus indicating the possibility of forming solid compound layers with fine grain sizes on silicon.
The method shows that selective writing on substrates is possible for the direct formation of lithographic structures on silicon. Tools are currently being designed to write selectively on wafers for nanotechnology and information storage applications. It is expected that selective writing with resolution down to the nanometre scale will be achievable with the development of new tools.
Cryptocrystal materials exhibit different physical properties depending on grain size. The possibility of using these crystals in Si microelectronics is very promising, say the researchers. As a low-k-dielectric, the crystals exhibit properties that could be used in microelectronics for semiconductor, photonics, interconnection and packaging applications. Ammonium silicon fluoride cryptocrystal layers could also be used to buffer large lattice mismatches between Si and other materials. Water solubility of fluorides means that such buffer layers can be readily lifted-off for applications, such as heat sinking and regrowth. The scientists also believe that such fluoride layers could be synthesised on other substrates such as SiO2, SiN and SiGe.
Contact Dr Seref Kalem, TUBITAK UEKAE s.kalem@uekae.tubitak.gov.tr
