Fundamental Research On Silicon Wafer Thinning By Back Grinding Of Wafer With Outer Rim

With the development of microelectronic products for high performance,high integration,high speed and miniaturization,it has not only greatly promoted the development of integrated circuit(IC)manufacturing technology,but also raised the processing efficiency and quality of wafers higher requirements.At present,the mainstream wafer diameter in IC manufacturing at home and abroad is 12 inches(300 mm),and the fourth-generation Through Silicon Via packaging technology requires that the wafer thickness be less than 50 ?m.Aiming at the problem of ultra-thinning of large-diameter wafers,Back Grinding of Wafer with Outer Rim(BGWOR)based on the principle of self-rotating grinding came into being,which greatly enhanced the rigidity of the wafer after thinning and effectively reduced the debris rate of the wafer.To deeply study the effects of grinding parameters on the grinding marks of wafers and the grain depth-of-cut during BGWOR,this paper established the kinematic model of BGWOR.And the model was verified by the experiments of BGWOR.The main research works and conclusions of the paper are as follows:(1)According to the principle and characteristics of BGWOR,and based on the kinematics theory,a mathematical model of the trajectory of grain and grain depth-of-cut of BGWOR was established.The MATLAB software was used to simulate the trajectory of grain.The influence of grinding parameters on the trajectory of grain was analyzed.The research results showed that the ratio of the wheel rotational speed to the wafer rotational speed affects the curvature of the trajectory of grain.The trajectory of grain tends to be less curved as the rotational speed ratio increases when contrarotation grinding,or the trajectory of grain tends to be more curved as the rotational speed ratio increases when homodromy grinding.(2)According to the model of the trajectory of grain,the evolution process of grinding marks and the effects of grinding marks on the surface quality of the ground wafer were further analyzed through comprehensively consider the grinding wheel infeed rate,the wheel rotational speed,the wafer rotational speed,the spark-out time and the maximum protrusion height of the grain.The MATLAB software was used to simulate the grinding marks patterns of the surface of wafers after BGWOR under different grinding parameters,and a series of experiments were performed to verified actual grinding marks patterns and the roughness of wafer after BGWOR.Finally,a surface quality of wafer promotion measure was proposed.The results showed that the pattern of the grinding marks of the wafers in BGWOR is depended on the grinding wheel infeed rate,the wheel rotational speed,the wafer rotational speed,the spark out time and the protruding height of the abrasive grains on the grinding wheel.Among them,the angle between two adjacent grinding lines changes as the change of the wheel rotational speed and the wafer rotational speed.Besides,compared with Back Grinding,the surface roughness of the wafer after BGWOR increases first in the wafer radial direction and then decreases.(3)According to the model of grain depth-of-cut,the relationship between the grinding marks and the grain depth-of-cut and the influence of the grinding parameters on the grain depth-of-cut were analyzed.The relationship between the grain depth-of-cut and the grinding force was also discussed.The model of grain depth-of-cut and the relationship between the grinding parameters and the grain depth-of-cut were verified by the experiments of BGWOR.The results showed that the grain depth-of-cut is affected by the rotational direction of the grinding wheel and the wafer.Regardless of contrarotation grinding or homodromy grinding,the grain depth-of-cut increases with the increase of the grinding wheel feed rate and decreases with the increase of the wheel rotational speed.However,the wafer rotational speed has an inconsistent influence on the grain depth-of-cut.The grain depth-of-cut decreases with the increase of the wafer rotational speed when contrarotation grinding and the grain depth-of-cut increases with the increase of the wafer rotational speed when homodromy grinding.