Study On Preparation Of A Novel Metal Nanocrystal Thin Film For Next Generation Non-Volatile-Memory Application

Compared with conventional floating-gate memories, metal nanocrystal memories, which are based on the storage mechanism of discrete charge trapping, have showed much excellent performance as lower operation voltage and longer retention time, etc, and are able to resolve the difficulties in continued scaling of device structure beyond 65-nm nod in integration application. It is considered as one of the most promising non-volatile memories in next generation. Nowadays, the most widely used metal nanocrystal fabrication process is called post-annealing nano-crystallization method, which is operated after metal thin film being deposited. However, this process needs high temperature, 600~900℃usually, suffers high thermal budget which has negative influence on process integration and will worsen the performance and reliability of devices.In this paper, a novel metal nanocrystal fabrication process, which has low thermal budget and is simple, completely compatible with CMOS processes, is proposed, named metal thin film synchronously in-situ nano-crystallization process. It is able to resolve these problems mentioned above. Also, the mechanism of metal thin film synchronously in-situ nano-crystallization process is investigated, and a tungsten (W) nanocrystal layer is fabricated in the experiment using this process, then follow the observation, analyses and discussion of the experiment result.The experiment result demonstrates that: (1) 3nm tungsten metal layer which underlies control oxide can effectively achieve nano-crystallization when the wafer substrate is synchronously heated, only 300 needed, during the control oxide deposition process, And the nanocrystals' sizes are about 25nm; (2) In the process of control oxide deposition through sputtering, the metal thin film can be successfully urged to nano-crystallize as long as the activating energy for nano-crystallization can be offered by the combining energy brought by incident sputtering atoms and wafer heating.Furthermore, since there is a growing tendency in using high dielectric constant (high K) materials as the oxide layers in metal nanocrystal memories. A stacked structure of Al nanocrystals embedded in Al2O3 layers is prepared in experiment. The failed experiment result indicates a series of problems in experiment process; reasons have been concluded and discussed. Improvement should be handled in next period.In the end, the whole paper is summarized and research contents are arranged. And the expectations of future metal nanocrystal memory investigation are also made.