Lecture 9 Through Mask Plating

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1 Lecture 9 Through Mask Plating
柳 克 強 x 4324 References: Madou, M., “ Fundamentals of Microfabrication”, CRC Press, 1998.

2 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

3 Electroplating Reactions: e- Amount of deposited material :
Ni 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 #

4 Diffusion Limited Reactions
Diffusion limited cathode current: current density Nonlinear diffusion effect on microelectrodes

5 Effect of current density on stress
Nonlinear diffusion effect on microelectrodes Effect of current density on stress

6 電 鍍 鎳 (NTHU ESS Micro-fabrication lab)
配 方 電 鍍 結 果 氨基磺酸鎳 公克/公升 氯化鎳 公克/公升 硼酸 公克/公升 LN-MU (應力降低劑) LN-MA (平滑劑, 光澤劑) 針孔抑制劑

7 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

8 High Aspect Ratio Structure Plating
Challenges: Ni2+ current diffusion limited => deposition rate  H+ at bottom depleted => PH increase locally => form nickel hydroxide => deposition stopped