超大型積體電路之金屬連線破壞分析之研究

Abstract

護層應力造成鋁接線破洞是積體電路製造中常面臨之問題。除鋁接線本身 之性質外, 護層之特性會嚴重影響鋁接線之破洞形成。在本文中, 使用大 氣壓化學氣相沉積磷玻璃(APCVD PSG) 薄膜為第一層護層, 再以電漿輔助 化學氣相沉積氮化矽薄膜(PECVD SiN) 作為第二層護層以研究其對金屬接 線之影響。含不同磷含量的磷玻璃在曝露於不同環境中之吸水性及應力變 化皆被測量, 並研究烘烤及回火的效應。磷玻璃在不同磷含量下會有不同 之吸水性並導致不同之應力變化。其應力變化與回火造成局部外凸變形會 嚴重影響鋁金屬接線在回火後形成破洞。磷玻璃之應力可由剛濺度時所承 受之拉伸應力逐漸變為壓縮應力。量測結果顯示, 應力變化與水氣吸收量 相關連。含4%磷之磷玻璃之應力變化最大並承受最大之壓縮應力, 進而造 成鋁含1%矽之金屬接線遭受拉伸形成破洞。同時, 含低磷之磷玻璃於回火 後在金屬接線周圍形成外凸變形, 進而增加冷卻時金屬層之應力。X-ray 繞射光譜顯示, 鋁含1%矽金屬線藉破洞之形成來釋放應變。磷玻璃之應力 變化及局部外凸變形可以解釋為何護層會造成鋁含 1%矽金屬線在回火後 形成破洞。如果將鋁含1%矽中再添加0.5%銅則可以阻止此破洞形成。另一 方面, 控制磷玻璃曝露空氣中之時間或放入氮氣環境中, 可以減少金屬接 線孔洞之發生。 The phosphours wt% of APCVD PSG, which is used as the passivation-1, and the exposure time in air after deposition could make a great influence on stress-induced metal voiding of Al-1%Si lines after alloy. The water absorption in APCVD PSG film gives rise to a compressive stress . The APCVD PSG with 4wt% phosphours content has the most stress change from tension to compression during storage in air . This stress change will induce the metal viods on Al-1%Si lines. Further- more, the passivation local convex bending surrounding the metal line is observed for the APCVD PSG containing lower phosphours after alloy. The X-ray diffraction shows the Al- 1% Si film release its strain by metal voiding. The stress change and local convex bending of the APCVD PSG film could explain why the passivation induces the metal voids on Al-1% Si line after alloy. If Al-1%Si is replaced by Al-1%Si-0.5% Cu, the metal voids are inhibited . It is because the Al-1% Si-0.5%Cu film has more resistance to stress-induced metal voiding.On the other hand,to shorten the exposure time to air or to store in dry N2 ambient after APCVD PSG deposition can reduced the stress-induced metal voiding.