Recently, memory-cells employing discrete traps as the charge storage media have been attracting a lot of attention as a promising candidate to replace conventional DRAM or Flash memories. Conventional floating gate (FG) non-volatile memories (NVMs) present critical issues on device scalability beyond the sub-50nm node. In achieving non-volatility in conventional FG memories, thicker control and tunnel oxide (~8nm) are required to guarantee longer retention time. Relatively, nano-dots memories causes more resistant leakage charges by localized storage sites, thus improving the device retention characteristics. Hence, nano-dots memories allow more aggressive scaling of the tunnel oxide and exhibit superior characteristics compared to Flash memories in term of operation voltage, write / erase speed, retention time and endurance.
The advantages of metal nano-dots compared with other material counterparts include higher density of states , stronger coupling with the channel, better size scalability, and the design freedom of engineering the work function to optimize device characteristics. However, tungsten nano-dots are the most interested in all of metal dots is that tungsten metal has more extra attractive advantages, such as ultra high melting point make high process temperature caused superior thermal stability of device and wide application in VLSI technology nowadays caused real possibility of tungsten nano-dots NVMs fabricated in industry in practice.
This dissertation is divided into four sections: (1) discussion of basic properties for tungsten nano-dots memory devices; (2) Tunneling Oxide Engineering,; (3) Improvement by novel processes; and (4) The influence with supercritical CO2 (SCCO2) and vapor treatment. Initially, formative mechanism of tungsten nano-dots and electrical characteristics of devices was investigated in the first section. Tungsten nano-dots were formed by oxidizing tungsten silicide / amorphous silicon double stack film at high temperature condition. From electrical measurement, the better characteristics have been achieved for oxidation condition at 1050¢XC / 120 sec. Secondly, the rapid thermal anneal (RTA) oxidation is used to grow tunnel oxide by two different forming gas (O2/N2O). Comparison of electrical characteristics, program characteristics of the device using tunnel oxide with N2O process is inferior than the common device. However, endurance is a important electrical characteristics in the semiconductor device especially apply on the non-volatile memory. Thirdly, novel processes were employed into fabrication of tungsten nano-dots memory devices, include the N2O oxidation and NH3 plasma treatment. The purpose of novel processes is production additional trapping states in nonvolatile memories, which is considerably as combination nano-dots with SONOS structure. In the final section, the application of supercritical CO2 with vapor on tungsten nano-dots memoery devices have been studying. It is found that the device treated by SCCO2 which electrical characteristics is improved obviously. Furthermore, this technology also can fabricate the nano-dots memory which is like the device used high temperature oxidation process. It suggests that the SCCO2 with vapor treatment could oxidize silicide film under a low temperature environment. This novel oxidation process has some advantages and could be noticed in the semiconductor industry.
| Identifer | oai:union.ndltd.org:NSYSU/oai:NSYSU:etd-0723107-184604 |
| Date | 23 July 2007 |
| Creators | Xi, Peng-bo |
| Contributors | Tzyy-Ming Cheng, Ting-Chang Chang, Ying-Lang Wang, Po-Tsun Liu |
| Publisher | NSYSU |
| Source Sets | NSYSU Electronic Thesis and Dissertation Archive |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.lib.nsysu.edu.tw/ETD-db/ETD-search/view_etd?URN=etd-0723107-184604 |
| Rights | not_available, Copyright information available at source archive |
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