Atomic Layer Deposition Platinum Nanocrystals And Storage Effect Research

Advancement of semiconductor processes drives the miniaturization of semiconductor devices, thus posing great challenge to the dominance of conventional polysilicon-floating-gate Flash memory. Metal nanocrystal memory based on discrete-node storage, however, can grasp candidacy for the next generation Flash memory on the basis of its great data retention and fast write/erasure response under low voltage. Consequently, the thesis investigates how to prepare Pt nanocrystals by resorting to ALD technique, and explores the memory characteristics of ALD-deposited Pt nanocrystals memory. The thesis configuration is outlined as follows.1. ALD-deposited Pt nanocrystal processes are elaborately explored by using (MeCp)Pt(CH3)3and O2as precursors. The process parameters include substrate temperature, precursor pulse and reaction cycles. Experimental results demonstrate that300℃substrate temperature and Is (MeCp)Pt(CH3)3pulse are the optimum temperature and precursor pulse, respectively for ALD-deposited Pt nanocrystals. Under such conditions, ALD-deposited Pt NCs for70cycles are well separated and uniformly dispersed with great densities.(about2×1012cm-2). With increasing reaction cycles, adjacent Pt nanocrystals coalesce, eventually forming Pt metal film. Moreover, ALD-deposited Pt is greatly contiguous on substrates. It is difficult to achieve ALD-deposited Pt on silicon substrate, while ALD-deposited Pt can be achieved on Al2O3and SiO2substrates. And it is easier to deposit Pt on Al2O3than SiO2substrate because the former possesses a lot more hydroxyl groups than the latter.2. Investigated in detail are characteristics of ALD-deposited Pt nanocrystals under rapid thermal annealing. The experimental results show that increasing temperature from700to900℃leads to larger, more separate and spherical nanocrystals. But the density decreases from9.94×1011to8.31×1011cm-2. When annealing duration increases from15to60s at800℃, Pt nanocrystals grow in size. Their densities increase from9.29×1011to4.5×1011cm-2while disperse less uniformly. And XPS analysis indicates the occurrence of partly-oxidized Pt nanocrystals at900℃, which may be due to reaction between Pt nanocrystals and Al2O3substrate at high temperature.3. Memory characteristics are investigated of ALD-deposited Pt nanocrystals. Device is fabricated by resorting to in-situ ALD deposition. The memory capacitor is composed of Al2O3blocking oxide and tunneling oxide as well as Pt nanocrystals charge-trapping layer. Compared with control sample’s negligible0.28V C-V hysteresis window, the memory capacitor’s C-V hysteresis window can reach10.2V under+/-15V sweeping voltage. And it also exhibits a perfect memory window as large as5.1V for100μs P/E at the voltage of+/-12V. Moreover, when P/E duration is increased to1ms under+/-12V, memory window as large as8.2V is achieved. And superior charge retention of about5.3V flatband voltage shift is extrapolated after ten years.