Study Of Ultrasonic Wedge Bond Process Of Phase Change Memory

Phase change random access memory(PCRAM),as the next generation of the most promising memory,has significant advantages in terms of R&W speed,storage density,power consumption,etc.Microelectronic packaging and testing is one of the key issues in PCRAM development.Wire bonding technology is the mainstream technology of microelectronic package.At present,the research of wire bonding process mainly focuses on the thick pad of traditional materials such as Cu,Al and Au.The electrode pad materials of PCRAM are variety,and the pads are thin.The researches of wedge bonding process are very important practical significance and scientific significance on PCRAM.This thesis focuses on the wedge bonding process parameters of six kinds of electrode materials commonly used in PCRAM,such as Pt,Ti,Cu,TiW,Ag,Ta.The main contents are as follows:(1)The international standards of wire bonding quality evaluation were introduced,and the necessity of exploring bonded surface materials was discussed.(2)A 230 nm Pt electrode samples were prepared.The forming characteristics of wedge bonding were observed by using SigmaSEM.It was found that the formation of Bond 1 and Bond 2 are consistent.(3)The Al wires at the bonding point were removed by chemical etching.The SEM results showed that the bonding marks were composed of inner and outer ellipses.The influence of bonding power and bonding time on the major axis and minor axis of the outer ellipse was further studied.It was found that bonding power and bonding time has no effect on the major axis of the outer ellipse,but has a significant effect on the minor axis of the outer ellipse.It revealed that the vibration direction of the wedge is in the direction of the horizontal axis.(4)EDS analysis of the center and the edge of the wedge bonding showed that there was no IMC in the center and IMC was only generated in the edge.According to the feature analysis of bond marks,it was deduced that bonding occurred only in bond marks between the inner and outer the ellipse.(5)Design the method of destructive bond pull test of double bonds.Destructive bond pull force of six common electrode materials(Pt,Ti,Cu,TiW,Ag,Ta)were tested respectively under different bonding power and bonding time,and fitted the destructive bond pull force as a function of bonding power.(6)Finally,the influencing factors of the destructive bond pull force were analyzed from the bonding area and wire deformation rate.It was pointed out that the dual influence of the bonding area and the wire deformation rate leads to the destructive bond pull force increasing and then decreasing with the increase of bonding power.