研發特殊清洗溶液及高介電常數閘極介電層在超大型積體電路上之應用

Abstract

在本論文中，我們提出一種新的濕式化學之一個步驟清洗過程的清潔溶液。神奇的一個步驟清潔溶液已經被研發來取代傳統RCA之兩個步驟清潔秘方，用來清洗在成長閘極氧化層之前清潔，包括APM (或SC-1)及HPM (或SC-2)。 Tetraalkylammonium hydroxide含有不同長度的碳氫鏈之取代基，例如：Tetramethylammonium hydroxide (TMAH)、Tetraethylammonium hydroxide (TEAH)、Tetrapropylammonium hydroxide (TPAH)與Tetrabutylammonium hydroxide (TBAH)，及 Ethylenediaminetetraacetic acid (EDTA)一起被加入在RCA之SC-1清潔溶液中來加強清潔效率。從實驗結果可知，使用神奇的一個步驟清潔溶液可以移除微小粒子與金屬離子的殘留在矽晶片的表面。研究不同清潔秘方和清潔溶液與矽晶片的表面交互作用機構。表面吸附與雙層模型可以解釋含有Tetraalkylammonium溶液如何去除微小粒子與金屬離子，以及如何造成表面粗糙。在成長閘極氧化層之前清潔，使用神奇的一個步驟清潔溶液比傳統RCA清潔溶液清洗有較好的MOS之電容電性。然而，這個神奇的一個步驟清潔過程是非常適合未來大尺寸的矽晶片清潔由於它有節省時間、降低成本與高效能的優點。 另一方面，Tetraalkylammonium hydroxide含有不同長度的碳氫鏈之取代基，例如：TMAH、 TEAH、 TPAH and TBAH ，與含有不同碳基酸鏈群(carboxyl acid group)的螯合劑，例如：EDTA、檸檬酸(citric acid)及草酸(oxalic acid)被研發應用經過化學機械研磨之後清潔，這些表面清潔劑與螯合劑被加入在3% 的氨水清潔溶液中可以來加強清除微小粒子與金屬離子的殘留在複晶矽晶片的表面。研究不同清潔秘方及清潔溶液與複晶矽晶片的表面交互作用機構。我們可以使用含有Tetraalkylammonium溶液的表面吸附及雙層模型，與螯合劑的不同分子大小及電荷來解釋不同清潔溶液的表面作用。依據這些模型，可以知道這些溶液如何去除微小粒子與金屬離子，以及如何造成表面粗糙。經過化學機械研磨之後中清潔，TMAH 與檸檬酸或草酸在的鹼性氨水清潔溶液可以獲得良好電性。 此外，我們研發一種超薄氮化矽薄膜(等效厚度為18埃)之7.15的等效介電常數之製造方法，以氨氣(NH3)來氮化(nitridation)矽基材成長超薄之氮化矽(Si3N4)薄膜再經一氧二氮(N2O)氣體氧化這層超薄之氮化矽薄膜具有高度良好電性，例如：低漏電流、低的體積缺陷(bulk trap)密度及缺陷產生率(trap generation rate)與高耐久的應力(endurance in stressing)。除此，這層超薄之氮化矽薄膜顯示相當弱的依賴性溫度由於它是Fowler-Nordheim (F-N)穿隧機構。這層超薄氮化矽薄膜非常適合應用於下一代的超級大型積體電路。然而，我們使用相同方法成長高品質複晶矽中的氮化矽(interpoly-oxynitride)薄膜。以氨氣(NH3)來氮化(nitridation)複晶矽再經一氧二氮(N2O)氣體氧化，再疊CVD TEOS在複晶矽的氮化矽，以及經快速退火過程用(RTA)一氧二氮(N2O)氣體氧化，這層薄膜具有高度良好電性，例如：高崩潰電場、低漏電流、高崩潰電荷(charge to breakdown)及低電子缺陷率(electron trapping rate)。這層超薄氮化矽薄膜非常適合應用於未來高密度的可抹除且程式化唯讀記憶體及快閃記憶體的複晶矽中薄膜。 最後地，我們首先提出神奇高介電常數的鈷鈦氧化層(CoTiO3)與鎳鈦氧化層(NiTiO3)，直接氧化從濺度(sputtered)的鈷/鈦與鎳/鈦。製造與量測鋁/鈷鈦氧化層/氮化矽/矽(Al/CoTiO3/ Si3N4/Si)與鋁/鎳鈦氧化層/氮化矽/矽(Al/NiTiO3/ Si3N4/Si)的電容結構。鈷鈦氧化層含有緩衝層(buffer layer)之等效介電常數是45比鎳鈦氧化層高。除此，這層鈷鈦氧化層同時顯示優良電的特性。這層金屬氧化層非常適合應用在超級大型積體電路的高介電常數薄閘極絕緣層。

In this thesis, we proposed an advanced wet chemical one-step cleaning process. A novel one-step cleaning solution had been developed for pre-gate oxide cleaning to replace the conventional RCA two-step cleaning recipe, which used ammonia/hydrogen peroxide/water mixture (or SC-1) and hydrochloric acid/hydrogen peroxide/water mixture (or SC-2) step. The tetraalkylammonium hydroxide with various chain-lengths of hydrocarbon substituents, such as tetramethylammonium hydroxide (TMAH), tetraethylammonium hydroxide (TEAH), tetrapropylammonium hydroxide (TPAH) and tetrabutylammonium hydroxide (TBAH), and ethylenediaminetetraacetic acid (EDTA) are added into the RCA SC-1 cleaning solution to enhance cleaning efficiency. From the experimental results, the particles and metallic contamination on the bare-Si wafer surface could be removed significantly by applying this novel one-step cleaning solution. The effectiveness of various cleaning recipes and their interaction mechanism with silicon surfaces were studied. The surface adsorption and double layer models could explain the surface behavior of tetraalkylammonium-containing solutions. Based on the model, the particle, surface roughness and the metallic contaminants can be realized. It was observed that the electrical properties of MOS capacitors after cleaning with this novel solution were better than these after the conventional RCA cleaning. Hence, this novel one-step cleaning process is very promising for future large-sized silicon wafer cleaning due to the advantages of time-saving, low cost and high performance. On the other hand, the tetraalkylammonium hydroxide with various chain-length of hydrocarbon substituents, such as TMAH, TEAH, TPAH and TBAH, and chelating agents with various carboxyl acid group (-COOH), such as ethylenediaminetetraacetic acid (EDTA), citric acid and oxalic acid, were developed for post-poly-Si CMP cleaning. These surfactants and other chelating agents were simultaneously added into 3% ammonium hydroxide water-based solutions to enhance the removal of particles and metallic impurities on the poly-Si surface. The effectiveness of various cleaning recipes and their interaction mechanism with poly-Si surfaces were studied. We could explain the surface behavior of various cleaning solutions by the surface adsorption and double layer models of tetraalkylammonium-containing solutions and the different molecular size and charge of chelating agents. Based on the model, the particle, surface roughness and the metallic contaminants can be realized. The co-existance of TMAH with citric acid or oxalic acid in the alkaline cleaning solutions can significantly enhance the electrical property for the capacitor. Furthermore, we developed a new method to grow robust ultrathin oxynitride (EOT=18 Å) film with effective dielectric constant of 7.15. By NH3-nitridation of Si substrate, grown ultrathin Si3N4 with N2O annealing shows excellent electrical properties in terms of significant lower leakage current, very low bulk trap density and trap generation rate, and high endurance in stressing. In addition, this oxynitride film exhibits relatively weak temperature dependence due to a Fowler-Nordheim (F-N) tunneling mechanism. This dielectric film appears to be promising for future ultralarge scale integrated (ULSI) devices. However, the same method to grow high quality interpolysilicon-oxynitride (interpoly-oxynitride) film is proposed. Samples, nitridized by NH3 with additional N2O annealing and CVD TEOS deposited on poly-oxynitride (poly-I) with RTA N2O oxidation, show excellent electrical properties in terms of very high electric breakdown field, low leakage current, high charge to breakdown, and low electron trapping rate. This novel film is a good candidate for an interpoly dielectric of future high density EEPROM and Flash Memory devices. Finally, we report for the first time a novel high-k cobalt-titanium oxide (CoTiO3) and nickel-titanium oxide (NiTiO3) were formed by directly oxidizing sputtered Co/Ti and Ni/Ti film. Al/CoTiO3/ Si3N4/Si and Al/NiTiO3/Si3N4/Si capacitor structures were fabricated and measured. The effective dielectric constant (k-value@ 45) with buffer layer for CoTiO3 is a larger than that of NiTiO3. In addition, CoTiO3 depicts excellent electrical properties at the same time. This metal oxide thus appears to be a very promising high-k gate dielectric for future ultralarge scale integrated (ULSI) devices.