利用化學金所開發之銅柱接合技術

Abstract

隨著發展更高效能且更小尺寸晶片的趨勢下，銅柱凸塊已經成為半導體業界普遍採用的技術，與傳統的銲錫凸塊相比，銅柱凸塊能夠克服焊錫凸塊之最小間距限制並提供更好的熱與電性質。然而，銅柱凸塊仍須用銲錫接合，當接點間距逐漸縮小，微量的銲錫會在迴焊過程或使用一段時間後轉變為全介金屬的結構，當接點裡只有銅與介金屬時，會產生性能與可靠度的疑慮。此外，熱壓接合技術用於銅柱凸塊接合時需要較高的操作溫度與壓力，也造成了許多可靠性問題，像是中介層的翹曲與熱敏材料之剝離或損壞。 為了克服目前所面臨的挑戰並持續縮小尺寸，低溫且無須加壓之微流體無電鍍接合技術已被成功開發，此技術藉由微流道系統控制無電鍍液在晶片中的流場來達到無銲錫之銅對銅接合。到目前為止，此技術已與無電鍍鎳、無電鍍銅與無電鍍金成功結合，但尚未充分研究流動條件與上鍍結果的關係。 本研究主要目的是探討不同流動條件對整體上鍍情形與上鍍均勻性之影響，同時也探討了流速與無電鍍副產物生成的關聯性，藉由持續流動、間歇流動與間歇震盪流動分別對微流道無電鍍鎳、銅與金系統進行實驗，接著銅柱之接合結果將使用掃描式電子顯微鏡進行觀察。本研究成功藉由優化控制流場實現全部無電鍍系統之高均勻接合，接著探討在此參數下的銅柱幾何形狀對接合區域之孔洞與孔隙的影響。

Under the trend of developing great performance chips with smaller packaging size, Cu pillar bumps have become the prevailing interconnection technology in the semiconductor industry. Compared with conventional solder bumps, Cu pillar bumps can overcome pitch limitation and provide better thermal and electrical property. However, as the pitch further deceases, smaller solder cap volume will transform to full intermetallic compound (IMC) after annealing for several hours. Cu/IMC/Cu joint causes performance and reliability concern. Besides, thermocompression bonding used for Cu pillars bumping requires high operating temperature and pressure and introduces many reliability problems including the warpage of interposer and the delamination of heat sensitive materials. To overcome these issues and further continue the trend of downsizing, an innovative low-temperature (< 100°C) and pressure-free bonding technology has been developed, which is called microfluidic electroless interconnections (MELI) process. By controlling the flow of electroless plating bath inside the stacking chips, the Cu-to-Cu interconnection was fabricated without any solder. So far, MELI process has been successfully combined with electroless Ni-P plating, electroless Cu plating, and electroless Au plating (abbreviated as MELI-Ni(P), MELI-Cu, and MELI-Au, respectively). However, the relationship between the flow patterns and the outcome has not been fully studied. In this study, the main objective is to investigate the effect of flow patterns on the overall plating condition and uniformity. Besides, the correlation between flow rate and the by-product formed during electroless plating were investigated. To reach this goal, MELI-Ni(P), MELI-Cu, and MELI-Au were carried out with continuous flow, intermittent flow, and intermittent oscillatory flow, respectively. Then, the bonding results for each Cu pillar were examined by scanning electron microscope (SEM). By optimizing the controlled flow, a high degree of bonding uniformity was achieved in all MELI process. The effect of the geometry of Cu pillar on the void and seam formation are included as well.