陽極氧化鋁薄膜之特性研究

Abstract

本研究針對蒸鍍在硼磷玻璃╱熱氧化層╱矽晶片基材上的鋁薄膜，在各種 不同的陽極氧化製程條件下所生長的氧化鋁膜，進行完整且有系統的研究 ；並探討材料組成及微結構對於氧化鋁膜介電特性的影響；同時建立在積 體電路應用上的最佳製程條件。矽晶球析出於摻雜矽元素的鋁膜中，在陽 極氧化過程中會被氧化成不同程度的氧化矽，這些氧化矽以多孔狀非晶相 的形態存在，孔洞可能是氧氣伴隨矽晶球氧化而生成。在氧化鋁表面上每 一個矽晶球均被一個黑圈圍繞著，這些黑圈被証實是較厚的非晶相氧化鋁 ，導因於在矽晶球旁邊的鋁具有較快的氧化速率，因此呈現尖突狀。未經 前置熱處理之試片上所生長的氧化鋁均為非晶相，但經過熱處理後所生長 的氧化膜則相當複雜，可大略分為5層(非晶相Ⅰ、孔洞Ⅰ、結晶相、孔洞 Ⅱ、非晶相Ⅱ)。不管是否經過前處理，陽極氧化時最初形成的氧化膜均 是非晶相，經過前置熱處理過之試片所長的結晶層係由非晶相Ⅱ層轉換而 成。而孔洞Ⅰ層在結晶相層尚未生成之前就形成，這些孔洞可能是由結晶 型氧化物附近氧氣集結而形成。較小的孔洞Ⅱ層則是由非晶相Ⅱ層的非晶 相物質轉換成結晶相時體積收縮而造成。未經前置熱處理所生長的氧化膜 均較經前置熱處理者好，而純鋁試片的結晶型氧化物及孔洞量較鋁─矽或 鋁─矽─銅的試片來的多。在8℃及25℃所生長的氧化鋁均是非晶相，並 且有很好的介電特性，電場強度加到7.5MV/cm時還不會崩潰，漏電流密度 約為 1.25×10-3A/ cm2。在58℃所生長的氧化鋁其上半部含有g'的結晶 型氧化物，這種氧化膜之介電特性較低溫所生長的氧化膜差。來自於電解 液的碳元素會滲入氧化膜中，而碳元素的滲入對於氧化物結晶相的生成並 無顯著影響。氧在陽極氧化過程中會滲入氧化膜下的鋁層中，滲入深度隨 著氧化溫度升高而增加。 A systematic research about the effect of various processing parameters on the anodic oxide formation on Al thin films depos- ted on Si wafer coated with thermal oxide and borophosphosilica- te glass (BPSG) has been conducted in the present study. The co -rrelation of the compositional and microstructural results with dielectric properties was made. The best process condition of anodic aluminum oxide formation for IC applications has been es- tablished. Silicon nodules present in the Si dopped Al film are oxidized to various degree during anodizing. The silica formed in the Si nodules is amorphous and somewhat porous, possibly due to oxygen evoution associated with Si anodization. A dark rim was found to surround each nodule in the anodic oxide film. This rim is shown to be thicker amorphous Al2O3 material, and its origin is attri- buted to the faster oxidation rate in the vicinity of Si nodules , thus forming Al2O3 spike which lower the dielectric properties . Al2Cu present in the Cu dopped Al film are oxidezed to form Al2O3 at about the same rate as the surrounding Al matrix. Copp- er is rejected by Al2O3 and accumulates at the Al2O3/Al interfa- ce. The anodic oxide formed on pure Al films exhibit the best d- ielectric properties compared with those formed on films doped with Si and/or Cu. Large voids were formed at the oxide layer in the Al- Si film, this film exhibits the worst dielectric propert- ies compared with the Al and Al-Si-Cu films. Oxide films formed at 8 ℃ and 25 ℃ are amorphous with excelle- nt dielectric properties, leakage current lower than 500 nA at 7.5 MV/cm and no breakdown up to 7.5 MV/cm. Partially crystalli- ne r'-Al2O3 is grown at the upper half of the 58 ℃ oxide film. This film exhibits much inferior dielectric properties than the lower temperature films. Carbon is incorporated into the top po- rtion of the oxide films from the electrolyte during anodizing and it has little effect on the crystalline oxide formation. Ox- ygen penetrates