| Summary: | 碩士 === 國立交通大學 === 電子工程系 === 87 === Recently, it is reported that more reliable dielectrics grown on the polysilicon can be obtained by using deposited instead of thermally grown dielectrics. Since defects located in the polysilicon are not incorporated into the deposition dielectric and the surface of the polysilicon layer is not roughened (due to no polysilicon consumption)[1]. Hence, the deposition dielectric potentionally has a defect density relatively independent of the bottom polysilicon. Among all the CVD process, the decomposition of tetraethylorthosilicate (TEOS) is reported to be the simplest and safest without any dangerous media in the process as compared with the Silane-based CVD.
In this thesis, we investigated the properties of TEOS interpoly dielectric layers with N2O/N2 rapid thermal anneal and characteristics of fluorinated TEOS interpoly dielectrics through ion implantatiom into bottom polysilicon electrode.
In order to obtain good data retention characteristics for nonvolatile menory, the interpoly dielectrics with low conductivity and high breakdown fileds have long been sought. Therefor, the characteristics of interpoly dielectrics deposited by pyrolysis of tera-ethyl-ortho-silicate (TEOS) instead of conventional thermal oxide layers with N2O or N2 RTA treatment have been investigated. The dielectrics were subjected to viscous rapid thermal N2O or N2 annealing temperature. Experimental results showed that the dielectrics with N2O or N2 RTA treatment exhibit desirable properties such as lower leakage current, higher breakdown field (Ebd), lower electron trapping rate, and higher charge to breakdown (Qbd). These improvements were due to the incorporation of nitrogen into polyoxide and at the polyoxide/polysilicon interface[2-11]. Moreover, the improvement is more dramatic on samples that received N2O-RTA treatment than those that received N2-RTA treatment. This is believedto be due to oxygen atoms available in N2O RTA tratment can also repair the dangling bonds and strained bonds.
The effects of fluorine-incorporation through ion implantation on TEOS dielectric characteristics were investigated, also. It was found that the fluorine-implanted polyoxides had a lower leakage current and a higher electrical breakdown field for both positive and negative bias [12-18]. The improvements were due to the incorporated fluorine could passivate the danging bonds and breakdown the strained Si-O-Si bonds to form stronger Si-F bonds in the polyoxide and at the polyoxide/polysilicon interface [18-20] . This relaxes the local stress in the dielectric and makes the polsilicon/polyoxide interface morphology more smoother. However, they exhibited higher trapping rate. This implied that fluore-implanted polyoxides had higher electron trapping rate during constant current injection. Athough fluorine-implanted polyoxides had higher trapping rate, but they still exhibited higher charge to breakdown. This may be due to stronger Si-F hardly breakdown.
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