Lecture 9 Through Mask Plating 柳 克 強 x 4324 kcleou@ess.nthu.edu.tw References: Madou, M., “ Fundamentals of Microfabrication”, CRC Press, 1998.
Electro-deposition for Micro-devices Through Mask Plating Damascene Plating Insulator deposition and patterning Seed-layer deposition Seed layer deposition and Patterning seed layer substrate Plating Plating Mask removal Seed-layer etching Planarization
Electroplating Reactions: e- Amount of deposited material : Ni2+ + 2 e- Ni (cathode reaction) 2Cl- 2 e- + Cl2 (anode reaction) cathode anode NiCl2 Ni + Cl2 2H+ + 2 e- H2 (competing reaction at cathode ) => PH value important !! KCl NiCl2 Na2+ Cl+ Amount of deposited material : KCl : Supporting electrolyte NiCl2 : Electro-active species F: Faraday constant (electricity required to deposit 1 g equivalent of substance) I : current t : deposition time M : molecular weigh of the depositing material z : ion’s charges #
Diffusion Limited Reactions Diffusion limited cathode current: current density Nonlinear diffusion effect on microelectrodes
Effect of current density on stress Nonlinear diffusion effect on microelectrodes Effect of current density on stress
電 鍍 鎳 (NTHU ESS Micro-fabrication lab) 配 方 電 鍍 結 果 氨基磺酸鎳 300 公克/公升 氯化鎳 20 公克/公升 硼酸 40 公克/公升 LN-MU (應力降低劑) LN-MA (平滑劑, 光澤劑) 針孔抑制劑
電 流 密 度 影 響 電流密度 15 mA/cm2 電流密度 40 mA/cm2 其他參數:PH 值、溫度、表面活化劑
High Aspect Ratio Structure Plating Challenges: Ni2+ current diffusion limited => deposition rate H+ at bottom depleted => PH increase locally => form nickel hydroxide => deposition stopped