M. Vulpio

Nanocrystal metal-oxide-semiconductor memories obtained by chemical vapor deposition of Si nanocrystals

We have realized nanocrystal memories by using silicon quantum dots embedded in silicon dioxide. The Si dots with the size of few nanometers have been obtained by chemical vapor deposition on very thin tunnel oxides and subsequently coated with a deposited SiO2 control dielectric. A range of temperatures in which we can adequately control a nucleation process, that gives rise to nanocrystal densities of ∼3×1011 cm−2 with good uniformity on the wafer, has been defined. The memory effects are observed in metal-oxide-semiconductor capacitors or field effect transistors by significant and reversible flat band or threshold voltage shifts between written and erased states that can be achieved by applying gate voltages as low as 5 V. The program-erase window does not exhibit any change after 105 cycles on large area cells showing that the endurance of such a memory device which uses a thinner tunnel oxide is potentially much higher than that of standard nonvolatile memories. Moreover, good retention results are ...

Nucleation kinetics of Si quantum dots on SiO2

The formation of Si quantum dots on SiO2 by chemical vapor deposition of SiH4 has been investigated in the range from the submonolayer to the complete coverage with Si. In order to investigate the very early stages of the nucleation process of Si on SiO2, the energy filtered transmission electron microscopy has been chosen as the main characterization technique, because of the high spatial resolution typical of the transmission electron microscopy analysis, coupled to the compositional information obtained by the electron energy loss spectroscopy. The plan view configuration has been used to measure the dot size distributions down to dimensions of about 1 nm, and in cross section to evaluate the dot wetting angle. For all the several experimental conditions, a wetting angle distribution has been obtained and has shown to be centered at about 90°. Data on the dot size distributions are shown and discussed in the framework of a continuous nucleation model, which has been implemented to take into account the...

Residual Crystalline Silicon Phase in Silicon-Rich-Oxide Films Subjected to High Temperature Annealing

Structural properties of silicon rich oxide films (SRO) have been investigated by means of micro-Raman spectroscopy and transmission electron microscopy (TEM). The layers were deposited by plasma enhanced chemical vapor deposition using different SiH 4 /O 2 gas mixtures. The Raman spectra of the as-deposited SRO films are dominated by a broad band in the region 400-500 cm -1 typical of a highly disordered silicon network. After annealing at temperatures above 1000°C in N 2 , the formation of silicon nanocrystals is observed both in the Raman spectra and in the TEM images. However, most of the precipitated silicon does not crystallize and assumes an amorphous microstructure.

Electrical and structural characterization of metal–oxide–semiconductor capacitors with silicon rich oxide

Metal–oxide–semiconductor capacitors in which the gate oxide has been replaced with a silicon rich oxide (SRO) film sandwiched between two thin SiO2 layers are presented and investigated by transmission electron microscopy and electrical measurements. The grain size distribution and the amount of crystallized silicon remaining in SRO after annealing have been studied by transmission electron microscopy, whereas the charge trapping and the charge transport through the dots in the SRO layer have been extensively investigated by electrical measurements. Furthermore, a model, which explains the electrical behavior of such SRO capacitors, is presented and discussed.

Memory effects in MOS capacitors with silicon quantum dots

Abstract To form crystalline Si dots embedded in SiO 2 , we have deposited thin films of silicon-rich oxide (SRO) by plasma-enhanced chemical vapor deposition of SiH 4 and O 2 . Then the materials have been annealed in N 2 ambient at temperatures between 950°C and 1100°C. Under such processing, the supersaturation of Si in the amorphous SRO film produces the formation of crystalline Si dots embedded in SiO 2 . The narrow dot size distributions, analyzed by transmission electron microscopy, are characterized by average grain radii and standard deviations down to about 1 nm. The memory function of such structures has been investigated in MOS capacitors with a SRO film sandwiched between two thin SiO 2 layers as insulator and with an n + polycrystalline silicon gate. The operations of write and storage are clearly detected by measurements of hysteresis in capacitance–voltage characteristics. A model which explains both the occurrence of steady-state conduction through the SiO 2 /SRO/SiO 2 stack at a relatively low voltage and the shift of flat-band voltage is presented and discussed.