Metal-oxide-nitride-oxide-silicon ͑MONOS͒ type memory devices with TaN/HfN gate and a high dielectric constant ͑high-k) charge trapping layer were experimentally realized by employing a SiO 2 /high-k/SiO 2 structure that used Al 2 O 3 , HfO 2 , or HfAlO films, instead of Si 3 N 4 film. The charge storage and retention characteristics of capacitors with Al 2 O 3 , HfO 2 , or HfAlO as the charge storage layer are compared to conventional MONOS (Si 3 N 4 film͒ capacitors. Mixing 10 atom % of Al 2 O 3 with 90 atom % of HfO 2 to form HfAlO improves the charge retention capability of HfO 2 without severely degrading its programming speed. Unlike conventional MONOS memory devices, HfAlO devices also exhibit better resistance to over-erase. The differences in the program/erase characteristics and the charge storage capability between the different structures are discussed.The applications of digital electronics have resulted in a strong demand for nonvolatile memories that are densely integrated, fast, and consume little power. The metal-oxide-nitride-oxidesemiconductor ͑MONOS͒ device is a promising candidate to replace existing forms of flash memory. 1 The MONOS structure generally has better charge retention than polysilicon floating-gate type memory as the charges are stored in spatially isolated deep-level traps. Hence, a single defect in the tunnel oxide generally does not cause the discharge of the memory cell. 2,3 In addition, floating gate memories typically employ tunnel oxide with thickness greater than 60 Å while single-bit MONOS devices use much thinner tunnel oxide, generally around 30 Å. In MONOS device operation, electrons are involved in the program operation while both electrons and holes are involved in the erase operation. 4 Hence threshold voltage control after erasing is difficult. If the electrical erase continues beyond a specified point, it results in more positive charges on the silicon nitride (Si 3 N 4 ) resulting in over-erase. 5 Our previous work on using hafnium dioxide (HfO 2 ) as the charge storage layer has demonstrated memory devices which were resistant to over-erase; however, such devices have poor charge retention. 6 Although memory structures with aluminum oxide (Al 2 O 3 ) as the charge storage layer have superior charge retention capability, 7 such devices have noticeably slower programming speeds. Hence, by adding aluminum to HfO 2 to form hafniumaluminum oxide ͑HfAlO͒, we hope to improve its charge retention capability while maintaining the good over-erase resistance of HfO 2 and a reasonably fast programming speed. In this work, the charge storage and retention characteristics of different MONOS-type capacitor structures, with the same physical thickness of the gate stack but with either Al 2 O 3 , HfO 2 , or HfAlO as the charge storage layer, are compared to conventional MONOS ͑with Si 3 N 4 as the charge storage layer͒ devices and their differences discussed. ExperimentalWe have fabricated four different memory capacitor structures. For each device, the processing conditions a...
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