Effect of annealing treatments on photoluminescence and charge storage mechanism in silicon-rich SiNx:H films

Abstract

In this study, a wide range of a-SiNx:H films with an excess of silicon (20 to 50%) were prepared with an electron-cyclotron resonance plasma-enhanced chemical vapor deposition system under the flows of NH3 and SiH4. The silicon-rich a-SiNx:H films (SRSN) were sandwiched between a bottom thermal SiO2 and a top Si3N4 layer, and subsequently annealed within the temperature range of 500-1100°C in N2 to study the effect of annealing temperature on light-emitting and charge storage properties. A strong visible photoluminescence (PL) at room temperature has been observed for the as-deposited SRSN films as well as for films annealed up to 1100°C. The possible origins of the PL are briefly discussed. The authors have succeeded in the formation of amorphous Si quantum dots with an average size of about 3 to 3.6 nm by varying excess amount of Si and annealing temperature. Electrical properties have been investigated on Al/Si3N4/SRSN/SiO2/Si structures by capacitance-voltage and conductance-voltage analysis techniques. A significant memory window of 4.45 V was obtained at a low operating voltage of ± 8 V for the sample containing 25% excess silicon and annealed at 1000°C, indicating its utility in low-power memory devices.

Figure 1

Atomic fraction of Si, N, and H versus gas flow ratio in SRSN films deposited on Si substrates, as measured by RBS and ERDA techniques.

Figure 2

Cross-sectional EFTEM image of the sample S4 containing 33 at.% of Si excess after annealing at 1100°C for 30 min in N₂ ambient.

Figure 3

FTIR transmission spectra of (a) as-deposited Si₃N₄/SRSN/SiO₂ films, (b) sample S4 containing 33 at.% of silicon excess and annealed within the temperature range of 500-1100°C for 30 min in N₂ ambient, (c) evolution of Si-N stretching band position of samples S1, S2, S3, and S4 as a function of annealing temperature.

Figure 4

Roomtemperature PL spectra of as-deposited Si₃N₄/SRSN/SiO₂ films. (a) (Color online) Room temperature PL spectra of as-deposited Si₃N₄/SRSN/SiO₂ films having an excess of silicon from 22 to 33 at.% (samples S1, S2, S3, and S4) in the middle SRSN layer, (b) PL energies and intensities of the as-deposited films as a function of silicon excess in the SRSN layer

Figure 5

Room temperature PL spectra. (a) (Color online) Room temperature PL spectra of the sample S3 (29 at.% of silicon excess) subjected to thermal annealing within the temperature range of 500-1100°C, evolution of PL intensities (b), and energies (c) as a function of annealing temperature, (d) evolution of PL intensity of the sample S2, which has been subjected to annealing at 1100°C in N₂, and subsequently in forming gas (10% H₂ + 90% N₂

Figure 6

(Color online) High-frequency (100 kHz) C-V characteristics of Al/Si₃N₄/SRSN/SiO₂/Si (MNNOS) memory capacitors of (a) the sample S4 containing 33 at.% of excess silicon, (b) the sample S2 containing 25 at.% of excess silicon, (c) evolution of memory window (calculated from flat-band shifts) versus excess silicon at two different annealing temperatures (1000 and 1100°C).

Figure 7

(Color online) Frequency-dependent G-V characteristics of Al/Si₃N₄/SRSN/SiO₂/Si (MNNOS) structure containing 25 at.% of Si excess in the range 10-500 kHz.