| Abstract: | 快閃記憶體因具有資料不會隨著電源的中斷而流失的非揮發特性，因此近來已廣泛地運用於可攜帶電子產品內成為記憶體的主流。為了確保一般快閃記憶體的非揮發特性，穿隧氧化層的厚度必須維持7 nm 以上避免所儲存的電荷藉由穿隧氧化層中的缺陷而流失，但是這也付出了寫入與抹除速度慢的代價。如果採用分散獨立的奈米晶體取代連續的懸浮閘極則可降低所需穿隧氧化層的厚度，進而提昇寫入與抹除的速度。儘管有許多新穎的快閃記憶體元件被發展出來，然而快閃記憶體的操作，仍然是藉由使用電子穿過絕緣氧化層而達到快閃記憶體的寫入與抹除；隨著寫入與抹除的次數增加，元件的可靠度劣化將漸趨嚴重，而如何提高快閃記憶體的可靠度仍然是快閃記憶體的重要課題，快閃記憶體有幾項指標性的可靠度分析，包括：寫入/抹除耐力、干擾、電荷保持等等。本兩年期研究計畫的主要目標是以傳統成熟的矽製程設備，研製溝槽式的鍺奈米晶體快閃記憶體單胞元及探討其物理機制，同時配合快閃記憶體的發展，研製多位元的鍺奈米晶體快閃記憶體單胞元。我們利用TMAH 溶液對Si 的非等向性蝕刻製作出溝槽形狀的結構，然後在溝槽上製作鍺奈米晶體，爾後利用微影製程技術製作在溝槽的側壁上才留有鍺奈米晶體，而達到將儲存位元自然的分立，進而達到多位元的快閃記憶體操作。在第一年中我們將據以製作雙位元溝槽式結構的鍺奈米晶體快閃記憶體單胞元，並探討與分析此記憶元件的直流特性、耐力、干擾與電荷保持等等。第二年我們將製作多位元溝槽式的鍺奈米晶體快閃記憶體單胞元，且量測及分析相關的電特性。希冀藉此計畫能將奈米晶體早日順利的應用於快閃記憶體工業。 ; Because of the nonvolatile characteristic of flash memory, floating-gate (FG) flash memory has been widely used in current portable information devices. However, the issues in FG flash memory are slow programming/erasing speed, and the endurance, which are mainly restrained by the required minimum thickness limitation of tunneling oxide thickness (> 7 nm) due to the weakness of charge loss from the conductive floating-gate through the defects in the tunneling oxide after considerable writing/erasing cycles. Therefore, the nanocrystal-based flash memory which store charges in discrete and isolated nanocrystals inside the gate dielectric has been proposed to scale down the thickness of tunneling oxide without increasing the amount of charge loss. Even though there are many flash memory cells with novel structures or operation modes have been developed and announced, the basic operation principles of flash memory cells still depend on the electrons which tunnel or pass through the tunneling oxide and charged or discharged in storage medium. As the number of programming and erasing times increase, the reliabilities of flash memory cells toward to worsen. So, how to improve the reliability is still one of the key issues of flash memory cells. There are some crucial criteria about the reliability of a flash memory cell, such as programming/erasing endurance, disturbance and charge retention. This 2-year project is proposed to investigate the fabrication and physics of flash memory cells based on the high-density Ge nanocrystals formed with the selective oxidation, which is compatible and could be integrated with the traditional Si process, of multiple stack of a-(poly)SiGe/a(poly)-Si layers, and then, based on this obtained technique, to fabricate and characterize the trench flash memory cells, and multi-bit trench flash memory cells with Ge nanocrystal charge medium. By using the anisotropic etching of TMAH solution with respect to Si substrate, the trench pattern could be formed and the Ge nanocrystals embedded in an oxide matrix were grown on this trench structure. Furthermore, with the lithography technique, the Ge nanocrystals embedded in an oxide matrix were remained only on the sidewalls of trench structure. As the storage medium separated naturally on the sidewalls, the flash memory cells with two-bit operation could be achieved. In the first year of this project, a two-bit trench flash memory cell will be fabricated and its dc characteristics, writing/erasing endurance, disturbance and retention time etc. will be measured and analyzed. In the second year, with the extension of flash memory cell with trench structure, a multi-bit flash memory cell will be fabricated and investigated. It is expected that the nanocrystal-based flash memory could be improved in performances and adopted by the current flash memory industries. ; 研究期間 9708 ~ 9807 |
