Charge trapping characteristics of atomic-layer-deposited HfO₂ films with Al₂O₃ as a blocking oxide for high-density non-volatile memory device applications

Abstract

Charge trapping characteristics of high-relative permittivity (high-κ) HfO 2 films with Al 2 O 3 as a blocking oxide in p-Si/SiO 2 /HfO 2 /Al 2 O 3 /metal memory structures have been investigated. All high-κ films have been grown by atomic layer deposition. A transmission electron microscope image shows that the HfO 2 film is polycrystalline, while the Al 2 O 3 film is partially crystalline after a high temperature annealing treatment at 1000 • C for 10 s in N 2 ambient. A well-behaved counter-clockwise capacitance-voltage hysteresis has been observed for all memory capacitors. A large memory window of ∼7.4 V and a high charge trapping density of ∼1.1 × 10 13 cm −2 have been observed for high-κ HfO 2 charge trapping memory capacitors. The memory window and charge trapping density can be increased with increasing thickness of the HfO 2 film. The charge loss can be decreased using a thick trapping layer or thick tunnelling oxide. A high work function metal gate electrode shows low charge loss and large memory window after 10 years of retention. High-κ HfO 2 memory devices with high-κ Al 2 O 3 as a blocking oxide and a high work function metal gate can be used in future high-density non-volatile memory device applications.

Characterization of dielectric layers grown at low temperature by atomic layer deposition

“…Nowadays, these oxide materials are commonly used as gate dielectrics in silicon-based microelectronics devices [1,3,4]. Due to a wide range of desirable properties, various dielectric oxides can also be applied as gate insulators in transparent devices with low power consumption, resistance switching materials for semiconductor memories, optical coatings in lasers and in microscopes or charge-coupled devices, and barriers and/or active layers in photovoltaic structures [5][6][7][8][9][10]. Dielectric thin films can be deposited using either RF-magnetron sputtering technology, chemical vapour deposition or atomic layer deposition (ALD) method [11][12][13][14], the method originally developed for the fabrication of amorphous Al 2 O 3 insulator films for electroluminescent flat panel displays [15].…”

Improved performance of GeON as charge storage layer in flash memory by optimal annealing

“…In other words, at this high temperature, the effect of charge-trap elimination by the PDA should dominate its effect on charge-trap generation. It has been reported that Al 2 O 3 film grown by ALD using Al(CH 3 ) 3 and H 2 O as as precursors was oxygen-rich [19]. Also, it was observed that Al 2 O 3 film grown by low-pressure chemical-vapor deposition using Al(CH 3 ) 3 and O 2 as precursors was non-stoichiometric with excess oxygen and its non-stoichiometry decreased after PDA, even at a low temperature of 500°C, due to out-diffusion of the excess oxygen [20].…”

“…It has been reported that Al 2 O 3 film grown by ALD using Al(CH 3 ) 3 and H 2 O as as precursors was oxygen-rich [19]. Also, it was observed that Al 2 O 3 film grown by low-pressure chemical-vapor deposition using Al(CH 3 ) 3 and O 2 as precursors was non-stoichiometric with excess oxygen and its non-stoichiometry decreased after PDA, even at a low temperature of 500°C, due to out-diffusion of the excess oxygen [20]. Therefore, in this work, during the PDA at 700°C, the excess oxygen in the Al 2 O 3 film should significantly diffuse into the GeON film to remove its defects (charge traps) by forming Ge-O bonds, and even convert remnant Ge-N bonds to Ge-O-N bonds, thus resulting in smaller program window and lower program speed.…”

“…In order to simultaneously enlarge the memory window, lower the programming/erasing (P/E) voltages, increase the P/E speeds, and improve the charge retention, many dielectrics, e.g. HfO 2 [3], HfLaO x N y [4], HfON [5], TiO 2 [6], HfAlO [7], La 2 O 3 [8] and ZrON [9], have been investigated as CSL to replace Si 3 N 4 in MONOS-type flash memory devices. However, there is no work on Germanium Oxynitride (GeON) as CSL, which has been widely studied as the gate dielectric for Ge MOSFETs due to its higher permittivity, better thermal and chemical stability compared to the native oxide (GeO or GeO 2 ) [10,11].…”

Experimental evidence and modeling of two types of electron traps in Al2O3 for nonvolatile memory applications

“…12 To improve the Program/Erase (P/E) performance (erase speed and memory window closure) and data retention, Al 2 O 3 has been proposed as blocking layer, [13][14][15][16] giving rise to TaN/Al 2 O 3 /Si 3 N 4 /SiO 2 /Si (TANOS) charge-trap memories. [10][11][12][13][17][18][19][20][21][22][23][24] It has been reported that the density of as-grown electron traps in Al 2 O 3 , as other high-j dielectrics, is orders of magnitude higher than conventional SiO 2 . These traps contribute to the leakage current through the dielectric under low electric fields, due to trap-assisted-tunneling (TAT), which affects the reliability and data retention of the devices.…”