藉應變閘極工程及氟電漿處理提升鐵電氧化鋯之單電晶體動態隨機存取記憶體的特性

Abstract

不同於傳統的鐵電材料(PZT、SBT、BTO…)有無法微縮的問題，新型態的鐵電材料可微縮且整合於CMOS、DRAM製程。ZrO2是常見的high-k材料，被業界廣泛使用，因此有較高的製程成熟度，且可相容於DRAM製程，但至今為此對於ZrO2的鐵電特性研究卻相對較少。ZrO2目前已被證實具有反鐵電特性，且在特定條件下可轉為鐵電特性。反鐵電特性的材料，通常會有較好的endurance，但retention較差。因此若將反鐵電轉為鐵電特性，則可同時兼具優秀的endurance與有良好的retention。根據Landau-Khalatniov equation，可利用金屬功函數差，產生內建電位，使ZrO2表現出鐵電特性。此外利用較強的閘極應力，可增強ZrO2在T/O-phase的結晶性，並藉此提升鐵電特性。最後藉著氟電漿處理，可有效的減少ZrO2接面處、薄膜內的缺陷，此方法可降低漏電流並提升鐵電特性，與閘極應力工程可達到相輔相成的作用。

The emerging ferroelectric materials can be scaled and integrated in CMOS and DRAM processes. That is different from traditional ferroelectric materials that have a problem to be scaled. The ZrO2 that is a common high-k material is employed by industry. Therefore, it is a mature procedure and it can be compatible with DRAM fabrication. But the research of ferroelectricity of ZrO2 is scanty so far. The anti-ferroelectricity of ZrO2 has been verified and it can be transformed to ferroelectricity under certain condition. In general, the anti-ferroelectric material has an excellent endurance but poor retention. Hence if anti-ferroelectricity is transformed to ferroelectricity, ZrO2 will have both excellent endurance and well retention. According to Landau-Khalatniov equation, the metal work function difference is used to induce a built-in bias that it make the ZrO2 to show the ferroelectric behavior. In addition, metal gate strain can be used to enhance the T/O-phase of crystallization of ZrO2 and improve the ferroelectricity. Finally, the fluorine plasma treatment can effectively be used to decline the defects at interface and in bulk of ZrO2. This method can reduce the leakage current, improve the ferroelectricity and complement with metal gate strain.