| With the scaling down of the semiconductor technology, the size of the nonvolatile Flash memory becomes smaller and smaller but the integration density denser and denser. Hence, the Flash memory based on poly-silicon floating gate has encountered serious challenges, mainly on the data retention degradation versus the thinned tunneling layer. The nanocrystal (NC) memory based on discrete charge storage could prevent the charge leakage. Thus, fast Program/Erase operations at low voltage can be fulfilled, which made the NC memory one of the promising candidates for the next generation nonvolatile memory. The metal NC memory has attracted a lot of research attentions because of its superiority. In this thesis, diverse fabrication methods of metal NCs are the chief study subjects. Embedded in the atomic-layer-deposited (ALD) high-k dielectrics, the memory effect of the metal NC metal-oxide-semiconductor (MOS) capacitor is then investigated. Besides, the cobalt (Co) NC memory and the organic MOS capacitor are preliminarily analyzed. Consequently, several useful results are achieved and listed as below:(1) Gold (Au) NCs are grown on the surface of ALD Al2O3 and HfO2 films by chemically self-assembly growth and their thermal stability is studied. The results show that the size of the Au NCs is in the range of 5～8 nm with a density of 4×1011 cm-2. After rapid thermal annealing (RTA) at 300℃in N2 atmosphere, the size of Au NCs are increased, while their constituents maintained. The (3-aminopropyl)-trimethoxysilane (APTMS) is also stably absorbed after RTA at 300℃. In addition, the substrate might influence the growth of Au NCs. Therefore, the single-and the double-layer Au NCs are embedded in HfO2 films. The influence of the control layer thickness and the number of NC layer on the memory effect of Au NC MOS capacitors are thus compared via the capacitance-voltage (C-V) hysteresis window、the program characteristics and the retention characteristics. The electrical characteristics imply that the hysteresis window of the double-layer NC capacitor of 20 nm control layer is 11.9 V under±11 V sweep voltage, which is 4.2 V larger than that of the single-layer NC capacitor. The flat band voltage is increased until saturation with the program voltage for both the single-and the double-layer NC capacitors. During the fastest leakage period of first 200 s, the double-layer Au NC capacitor of 20 nm control layer remains 75% of the initial charge. The above results can be reasonably explained from the energy band diagram by means of leakage path.(2) Through the magnetron sputtering and RTA, ruthenium (Ru) NCs are formed on the surface of ALD Al2O3 film. The influences of the initial ruthenium film thickness and the RTA temperature and the RTA time on the NC formation are discussed. The NC density formed by 2 nm initial thickness and RTA at 900℃is 2～5×1012 cm-2 with the average size around 5 nm and uniform distribution. The X-ray photoelectron spectrum (XPS) reveals the existence of metallic Ru after RTA, but oxidized RuO3 near the interface of Ru NCs/Al2O3 film. As for the memory effect of Ru NCs embedded in the Al2O3 dielectric with palladium electrode, the net hysteresis window of the capacitor is 11.2 V under±11 V sweep voltage, indicating a remarkable charge trapping capability. Moreover, excellent performance is represented by this capacitor at low program/erase (P/E) voltage. The influence of thickness ratio of the tunneling layer and the control layer (T/B) on the memory effect is further investigated. By changing the T/B thickness ratio, the total Al2O3 dielectric thickness is fixed at 28 nm. The C-V hysteresis window and the effective charge density decrease with the increment of the T/B ratio at low operation voltage, but almost do not change at high operation voltage. The hysteresis window of the capacitor with T/B thickness ratio of 6/22 nm is 6.3 V after±8 V P/E voltage and 1 ms pulse time and still 5.2 V when extrapolated to 10 years.(3) The process parameters of magnetron sputtering Co NCs are systemically explored. And the optimal parameters for the Co NCs are as follows:power is 70 W, initial film thickness is 3 nm, substrate temperature is 100℃, and substrate rotation is 7.68 rpm. The density of Co NCs deposited on the silicon oxide after RTA at 600℃for 30 s is about 1.3×1011 cm-2. Furthermore, the Co NC memory is fabricated using SiO2 and HfO2 as the tunneling layer and the control layer, respectively. The output characteristics and the transfer (hysteresis) characteristics of Co NC memory state that the charging and discharging of the channel/oxide interface have nothing to do with the memory effect, but the Co NCs play a major part. However, the Id-Vg curves of the memory cells with the same dimension but different locations display performance fluctuations. The memory window might be affected by the channel length and the width. The memory windows after±6 V operation voltage and 1 ms pulse time are bigger than 1 V and the retention characteristic of this memory under erase operation is better than that of the program operation.(3) In the end some primary researches about the key materials are carried on. (a) The thermal stability of the ALD Nb2O5 film and its nanolaminate film Nb2O5/Al2O3 on silicon substrate is compared. The～3 nm as-deposited Nb2O5 film would be evolved into islands after RTA, and the size of the islands increases gradually with the RTA temperature. In contrast, the Nb2O5/Al2O3 nanolaminate film is more stable during the RTA treatment. The Nb2O5 film experiences a transformation from the as-deposited amorphous texture to a partial crystal after RTA at 700℃. The X-ray diffraction (XRD) data show the crystallization of the as-depostied Nb2O5 film after RTA at 500℃and the transformation to the TT phase after RTA at 800℃. For the XPS measurement, there is the interfacial Nb-O-Si bond in the as-deposited Nb2O5 film, and its intensity increases after RTA at 800℃. Meanwhile, the interfacial Si-O-Si bond is detected after RTA at 800℃. Incorporating Al2O3 between the Nb2O5 film and the silicon substrate can successfully suppress the formation of interface layer. The refractive index interpolated from the spectroscopic ellipsometry (SE) of the Nb2O5 and the Nb2O5/Al2O3 filsms first increases then decreases with the RTA temperature. This can be explained by the densification at 500℃, and the interaction between the Nb2O5 and the silicon substrate in the case of Nb2O5 film/inter-diffusion between the Nb2O5 and the Al2O3 film in the case of Nb2O5/Al2O3 nanolaminate. The deduced optical band gap of Nb2O5/Al2O3 increases from 2.90 eV to 3.53 eV with the RTA temperature, (b) Platinum (Pt) NCs are obtained by RTA following e-beam evaporation. The NC formation is impacted by the RTA temperature and the RTA time. Specifically speaking, the density of Pt NCs first increases then decreases with the elevation of the RTA temperature and the extension of the RTA time. Pt NCs are uniformly distributed with a density of 3×1011 cm-2 after RTA at 800℃for 20 s. The hysteresis window of the Al2O3/Pt NCs/HfO2 capacitor amounts to 2.01 V under sweep voltage of -3～+8 V. The flat band voltage prominently shifts when the program voltage increases to 9 V at the same pulse time, which may be associated with the tunneling mechanism changing from DT to F-N. The Pt NC capacitor displays electron trapping capability with pulse time, too. (c) The antimony (Sb) film deposited by thermal evaporation will form discrete NCs on the surface of organic semiconductor copper phthalocyanine (CuPc) spontaneously with the size approximately 10～15 nm. The C-V hysteresis characteristic of the organic MOS capacitor manifests a notable memory effect. And the hysteresis window is 2.78 V for the Sb NC capacitor under±10 V sweep voltage. |
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