超微細氧化鋁粉體之製備及研磨粉體對高分子介電層之化學機械研磨特性研究

Abstract

隨著積體電路（IC）技術邁入下一世代（0.25微米或更小），半導體IC元件尺寸縮小致積集度增加的製程中，平坦化程序的要求程度將增加。綜合極大型積體電路金屬化新近發展的平坦化技術中，化學機械研磨（Chemical Mechanical Polishing, CMP）是目前可達到全域性平坦化（Global Planarization）的技術。為了減少多層金屬導線所造成的RC延遲，以銅金屬化與低介電常數的絕緣層材料，來建構導線連線為克服方法之一。由於高分子材料具有低薄膜應力與低介電常數，故目前為金屬層間的絕緣層之最佳材料。然而由於其薄膜的化學不活潑性與柔軟性，所以在化學機械研磨的製程中較為困難。本論文將探討超微細氧化鋁粉體的製備及低介電常數薄膜的化學機械研磨。 隨著元件線幅減小，對化學機械研磨平坦化中所使用的研磨粉體之要求愈來愈嚴格。本論文中，粉體合成實驗乃利用異丙醇鋁鹽之水解法來製備奈米級氧化鋁粉末（<150 nm），並利用不同的煆燒條件製備不同晶相或混合相（a+q）之氧化鋁粉末。而此自製的氧化鋁粉末對二氧化矽薄膜之化學機械研磨的結果，顯示利用在1170℃持溫20分鐘的煆燒條件，製備出的混合相（a+q）氧化鋁粉末，對二氧化矽薄膜可獲得較高的磨除率，論文中將對混合相氧化鋁粉體提出研磨機制的討論。 對於低介電常數（e: 2.5~2.9）薄膜（HOSP、FLARETM 2.0、Polyimide）之化學機械研磨的研究中，分別對此三種薄膜之性質做分析與探討。利用傅立葉轉換紅外線光譜儀分析其化學結構的鍵結情形，結果顯示HOSP薄膜在高溫加熱程序中，其結構會由籠狀（cage-like）轉變成立體網狀（network）的結構。而在薄膜應力對溫度之量測，其結果顯示HOSP與FLARETM 2.0薄膜結構穩定，而Polyimide薄膜在230℃時，會發生薄膜的熱塑性形變。 分別選用不同種類、晶相、粒徑大小的商用粉末來進行此三種薄膜的化學機械研磨，結果顯示對於粒徑愈大的研磨粉體，其磨除率愈大而且薄膜表面愈粗糙。是故，對於柔軟性高分子薄膜材料的拋光，仍是以機械的磨耗為主。然而，我們可在研磨漿料中藉由添加一些化學添加劑來增加對薄膜化學水解的反應，以降低其機械磨耗所造成的表面粗糙度，例如：在HOSP與Polyimide薄膜的研磨漿料中，加入氫氧四甲基銨（TMAH），而在FLARETM 2.0薄膜的研磨漿料中，加入氫溴酸（HBr）。 本論文並依田口實驗設計法對此三種薄膜之化學機械研磨的研磨參數做設計實驗。結果顯示在第一個研磨步驟中，可藉由改變化學機械研磨中的背壓與研磨轉速來獲得較高的磨除率及較低的磨除率之標準差，且磨除率皆遵循Peston定律，即在高轉速或高壓力下皆會提高磨除率。而在第二個研磨步驟中，對於改變化學機械研磨中的正向壓力與轉速之參數，並未顯現與表面粗糙度之相對關係。故在第二個研磨步驟中，漿料中研磨粉體之性質，乃是影響薄膜在研磨後表面粗糙度的主要因素。

Shrinking the dimensions of devices beyond 0.25 mm or less to increase packing density impose greater demands on the planarization process. Among the newly developed planarization technologies for Ultra Large Scale Integration (ULSI) metallization, chemical-mechanical polishing (CMP) is the only way known to achieve the global planarization. In order to reduce RC delays of multilevel interconnect that connects individual devices of silicon ICs, the industry is currently making a transition to copper metallization and low dielectric constant insulators. Polymers have shown the great promise for using as inter-level dielectric (ILD) films because of their low stress and low dielectric constant. CMP of polymers for ILD applications is difficult owing to the chemical inertness and softness. In this thesis, the synthesis of ultrafine alumina powders and the CMP of oxide and low dielectric constant thin films are presented. As the device line wide is gradually shrinking, the quality requirement of abrasive for CMP process is stricter. In this thesis, the study of synthesizing powder with using the method of hydrolyzing aluminum-tri-isopropoxide is preparing the nano-sized (< 150 nm) alumina powders and producing the different crystal phases or mixed-phase (a+q) alumina powders with various calcination conditions. Using these preparing alumina powders as abrasives for polishing oxide film, the results show that the higher removal rates of oxide films with the mixed-phase (a+q) alumina powders, prepared by calining at 1170℃ for 20 min. The mechanism of this CMP behavior is proposed and discussed in thesis. The study of low dielectric constant (e: 2.5~2.9) thin films (HOSP、FLARETM 2.0 and Polyimide) for CMP polishing. First, the properties of these films are analyzing and presenting. Using FT-IR to analyze chemical bonding, the results show that the structure of HOSP film would be changing from cage-like to network with increasing temperature. From film stress to temperature analysis, the results show HOSP and FLARETM 2.0 films structure are stabilized after curing, however, the polyimide film start to deform plastically at ca. 230℃. For polishing these three low-k thin film with using various types, crystal phases and particle sizes of commercial powders as abrasives. The results show that the higher removal rates and severe surface roughness with the larger abrasives. Therefore, the removal of these soft polymer films is mainly by mechanical abrasion. However, we could be improved surface roughness, caused from mechanical abrasion, by adding some chemical agents in slurry to increase chemical dissolution. For example, adding tetra-methyl-ammonium hydroxide in slurries for polishing HOSP and polyimide films; and adding hydrobromic acid in slurry for polishing FLARETM 2.0 film. Taguchi Design of experiment of CMP polishing parameters for these low-k thin films is study in this thesis. The results show that the higher removal rate and lower standard deviation of removal rates with changing back-pressure and platen speed could be obtained at first polishing step and the removal rates followed the Preston's law that the higher removal rates with the higher speeds and pressures. At second polishing step, surface roughness was found to be independent upon down force and platen speed of CMP polishing parameters. Therefore, the properties of abrasives in slurry are mainly effect that causes the surface roughness of polished films.