Research On Semiconductor Wafer Bonding Technology Based On Ar Ion Beam Irradiation Surface Activation

Wafer bonding is one of the key technologies of integrating homogenous or heterogeneous materials.In recent years,it has been extensively used in a lot of fields,such as radio frequency and power electronic device fabrication,micro-electro-mechanical system(MEMS)packaging,system-in-package,and 3D integration.The conventional bonding method usually needs high-temperature treatment,which will lead to a residual thermal stress at the bonding interface due to the thermal expansion coefficient mismatch between heterogeneous materials.Therefore,realizing bonding at low temperature is of great significance.Semiconductor wafer bonding based on Ar ion beam irradiation surface activation(Surface Activated Bonding)is one of the low-temperature(even room-temperature)bonding methods,which has attracted extensive attention.In order to optimize process parameters and improve bonding quality,the process of Si-Si surface activated bonding,thermal stability,and interface resistance were investigated in depth in this work,which could promote its applications in the advanced fields of 5G communication,phased array radars,and high performance computing.Firstly,the room-temperature Si-Si surface activated bonding process based on Ar ion beam irradiation was studied in depth.The effects of Ar ion beam irradiation time,Ar ion beam current and Ar ion acceleration voltage on bonding quality were investigated,respectively,through characterization methods of surface roughness,interfacial voidage,bonding strength,thermal conductivity and interfacial thermal resistance.In the study of the effects of Ar ion beam irradiation time(60 s-540 s)on bonding quality,the results show that these bonded Si-Si specimens activated under the Ar ion beam irradiation time of 60 s-540 s have low interfacial voidages(≤0.5 %).300 s-420 s specimens have comparatively higher bonding strength,which is due to adequate surface activation and thinner amorphous Si layer produced by surface activation.In the study of the effects of Ar ion beam current(10 mA-50 mA)on bonding quality,the results show that the bonded Si-Si specimens activated under the Ar ion beam currents of 10 mA-30 mA have lower interfacial voidages(<0.2 %)and comparatively higher bonding strength,which is due to adequate surface activation and thinner amorphous Si layer produced by surface activation.A larger beam current leads to a thicker amorphous Si layer,and 10 mA-30 mA correspond to 8.2 nm-13 nm.In addition,the higher the Ar ion beam current is,the lower the thermal conductivity is and the higher the interfacial thermal resistance is,which is because the thicker amorphous Si layer is produced by the larger the Ar ion beam current leading to the poorer thermal conductivity.In the study of the effects of Ar ion acceleration voltage(100 V-300 V)on bonding quality,the results show that these specimens activated under the Ar ion acceleration voltage of 100 V-300 V have low interfacial voidages(≤1 %).150 V-200 V specimens have comparatively higher bonding strength,which is due to adequate surface activation and thinner amorphous Si layer produced by surface activation.Secondly,in order to evaluate thermal stability of Si-Si bonded specimens and improve bonding quality,the effect of annealing treatment on Si-Si bonding quality was investigated.The results show that for Ar ion beam irradiation time,180 s-540 s samples have good thermal stability.For Ar ion beam current,10 mA-30 mA samples have good thermal stability.For Ar ion acceleration voltage,samples except 150 V and 300 V have good thermal stability.In the study of the effects of annealing temperature on bonding quality,200 ℃-600 ℃ help to reduce interfacial voidage.Finally,based on the research on 10 mm×10 mm room-temperature Si-Si bonding,2-inch room-temperature Si-Si surface activated bonding process was explored.The results show that in the case of overlap area accounting for 70 % of the wafer,the bonded Si-Si samples activated under 200 s-350 s have lower interfacial voidages(≤0.5 %),and the sample under250 s has the highest bonding strength(18.9 MPa).After improving the fixture,the overlap area between the two wafers was increased to 90 %,all the bonded Si-Si specimens have higher interfacial voidages(up to 4.8 %).After comparing cases of 10 mm×10 mm,70 %and 90 % overlap area,we could find that the larger Si wafer is,the more difficult the bonding process is.In the study of the effects of annealing temperature on bonding quality,400 ℃-600 ℃ help to reduce interfacial voidage through interfacial atom rearrangement.