高密度電漿天線效應之研究

Abstract

超大型積體電路製程中，薄閘極氧化層遭受之電漿損傷因直接對元件 可靠度造成嚴重影響已逐漸成為重要課題。源於閘極電荷累積效應之電漿 損傷也在螺旋式電漿系統中發現。在氧電漿環境下所造成的薄氧化層損傷 反映在過高之閘極漏電流與崩潰電荷敬的退化。以上電性退化可由氧化層 與矽基板之界面能態增加和氧化層內正電荷累積現象獲得圓滿解釋。在金 屬蝕刻過程中，此電荷累積現象僅發生在過蝕刻階段，且由於較差的電荷 收集能力，導致較輕微的氧化層傷害。在此論文裡，蝕刻條件將予以變化 來探討各個參數對薄閘極氧化層教穩定性及金屬蝕刻特性之影響。所變動 的參數包含射頻偏壓功率、氣體壓力、場源功率和CHF3氣體流量。研究結 果顯示場源功率和射頻偏壓功率對電荷累積現象具有較大的影響力，因此 我們建議在過蝕刻階段適度地降低場源功率和提高射頻功率將可減低氧化 層損傷。同時，不同的基板型式對此現象的表現也被詳細探討。最後並基 於實驗結果提出一個可能機制來解釋薄閘極氧化層在螺旋式電漿環境中所 受到的傷害。 Plasma charge-induced damages to gate oxides are increasingly becoming serious concerns because they directly impact device reliability in ultra-large-scale-integrated circuits. This charging effect was also observed afterexposing the antenna capacitor structures to the helicon wave plasma. The observed damages induced by O2 plasma exposure included the excessive gate leakage current, and a degradation in charge-to- breakdown. The increase of interface statedensity at the SiO2/Si interface and positive trapped charge density in bulk oxide were correlated well with the measured electrical degradation of the oxide films. For the metal etch step, charge build-up occurred only during the overetch stage and slight gate oxide degradation wasdetected due to the poor charge collection efficiency. A set of experiments were carried out to screen theeffects of plasma parameters on the thin oxidereliability and metal etch characteristics. These included the gas pressure, rf-bias power, helicon source power, and CHF3 gas flow rate. The major factorswhich affected the charging damages were helicon source powerand rf-bias power.It is therefore suggested thatthe oxide degradation would be suppressed bymoderately increasing rf-bias powerand by lowering helicon source power during the overetch period. Furthermore,the dependence of thin oxide degradation onthe substrate type was also examined. Finally, a possible mechanism is proposed to explain the damages.