利用邊緣移動方法研究純錫薄膜之電遷移

Abstract

本實驗利用邊緣移動方法測量純錫薄膜的電遷移行為，並求得其電流的門檻電流密度以及其他參數。我們在矽晶片上面先鍍上一層1200 Å 的鈦膜，隨後在鈦膜上面鍍5000 Å厚的錫膜，在室溫(27 ℃~32 ℃)、50 ℃、75 ℃和100 ℃下，對純錫薄膜加以2.5 × 104 A/cm2到 1.5 × 105 A/cm2的電流密度，並觀察電遷移效應。實驗結果發現在室溫以及50 ℃下在陽極皆有看到針狀與島狀的錫凸塊，但是在75 ℃和100 ℃下在陽極只有見到島狀錫凸塊的生成，且在四個通電的環境溫度下，錫原子的漂移速率皆隨著電流密度增加而上升。實驗求得門檻電流密度在室溫、50 ℃、75 ℃和100 ℃下分別為1.93 × 104、9.65 × 103、9.57 × 103 和 7.93 × 103 A/cm2，並且求得純錫的電遷移活化能為0.32 eV。此外，在室外下由不同的錫條長度所算出的臨界長度為18 μm且由實驗結果計算得知純錫薄膜的DZ*值在室溫、50 ℃、75 ℃和100 ℃下分別為1.95 □ 10-10、4.84 □ 10-10、1.27 □ 10-9和1.99 □ 10-9 cm2/s。由於在無鉛銲料中錫的成分佔的比率皆相當高，所以這些純錫電遷移的基本研究顯得非常的重要。

Threshold current density and other electromigration parameters of pure Tin (Sn) films were measured using edge displacement method. Sn film with a thickness of 5000 Å was evaporated on a 1200Å-thick Ti film on a Si substrate. Electromigration behavior was investigated under the current densities of 2.5 × 104 to 1.5 × 105 A/cm2 at room temperature (R.T. = 27 ℃~32 ℃), 50 ℃, 75 ℃ and 100 ℃. Both needle-type and hillock-type whiskers grew in the anode end when the films were stressed at R.T. and 50 ℃, but only hillock-type whiskers were observed when they were stressed at 75 ℃ and 100 ℃. The electromigration rate increased linearly with the applied current density for the four stressing temperatures. The threshold current density (Jc) was measured to be 1.93 × 104, 9.65 × 103, 9.57 × 103 and 7.93 × 103 A/cm2 for R.T., 50 ℃, 75 ℃ and 100 ℃, respectively. The measured activation energy was 0.32 eV. In addition, the measured critical length of the Sn film was 18 μm at R.T. and the products of DZ* were 1.95 □ 10-10, 4.84 □ 10-10, 1.27 □ 10-9 and 1.99 □ 10-9 cm2/s for R.T., 50 ℃, 75 ℃ and 100 ℃, respectively.