Investigation of crystallization processes from Hafnium silicate powders prepared from an oxychloride sol-gel

Hafnium oxide and silicate materials are now incorporated into working CMOS devices; however, the crystallization mechanism is still poorly understood. In particular, addition of SiO₂ to HfO₂ has been shown to increase the crystallization temperature of HfO₂, hence, allowing it to remain amorphous under current processing conditions. Building on earlier study, we herein, investigate bulk Hf_xSi_1-xO₂ samples to determine the effect of SiO₂ on the crystallization pathway. Techniques, such as XRD, HTXRD, thermal analysis techniques and TEM are used. It is found that the addition of SiO₂ has very little affect on the crystallization path at temperatures below 900°C, but at higher temperatures, a second t-HfO₂ phase nucleates and is stabilized due to the strain of the surrounding amorphous SiO₂ material. With an increase in SiO₂ content, the temperature at which this nucleation and stabilization occurs is increased. The effect of strain has implications for inhibiting the crystallization of the high-k layer, reduction of grain boundaries and hence diffusion, reduction of formation of interface layers and the possibility of stabilizing t-HfO₂ rather than m-HfO₂, hence, increasing the dielectric of the layer.