Eliminating residual polymer in the cleaning process of post pad etching

#The present invention relates to a method for eliminating residual polymer on a wafer in the cleaning process of post pads etching. In particular, the present invention relates to the method for reducing the defect rate of the bonding process and enhancing the cleaning process yield rate.

#In the manufacture of the semiconductor, the bonding pad is at the interface between the die and the package or the outside world. One side of a wire is soldered to the pad, while the other side of the wire is connected to a lead frame. After all devices and connections are formed on the wafer, a passivation layer is put down onto the wafer surface. This layer seals the device structures in the wafer from contaminants and moisture and also serves as a scratch protection layer. For connecting the pad with the wire to transmit the signal, a plurality of windows is then etched on the passivation layer. Generally, a photolithography process which transfers the pattern from mask to the photoresist on the wafer and an etching process which creates the windows on the passivation layer are used to produce the windows on the wafer. In the etching process, polymer is generated on the sidewalls of the windows of bonding pads. If the polymer peels from sidewalls of the windows, it may cause higher defect rate of the next process thereof. To reduce the defect rate of the manufacturing process, the wafer must be cleaned before the next process.

#Normally, the polymer is removed from the wafer in two cleaning processes, wet stripping and dry stripping. Wet stripping uses organic and inorganic photoresist strippers to remove the polymer, e.g. acetone, phenol base, sulfuric acid and H2 O2. The strippers may decompose the sidewall polymer and remove it from the wafer. But the inorganic photoresist stripper also corrodes the metal bonding pads. Therefore, the polymer must be removed with organic photoresist stripper when cleaning the sidewall polymer of the bonding pads. The dry stripping process is an O2-ashing process. The O2-ashing process is performed under oxygen plasma, which reacts with the sidewall polymer and therefore removes the polymer. The oxygen plasma reacts with the polymer to generate CO, CO2 and H2O gases which are drawn out by the exhaust system of the reaction chamber. O2-ashing may especially reduce the fluorine intensity on the surface of bonding pads. Therefore, the O2-ashing may prevent Al—F formation and then increase the yield rate of the bonding process because Al—F formations may cause bonding process defects.

#The foregoing aspects and many of the attendant advantages of this invention will become more readily appreciated as the same becomes better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein:

#FIG. 1 is a schematic top view of a residual polymer on a semiconductor after the etching process and cleaning process;

#FIG. 2 is a flow chart for a cleaning process according to the prior art;

#In view of description in the background of the invention, the residual polymer may cause a higher defect rate for a cleaning process and a higher defect rate for a bonding process. The whys and wherefores of the residual polymer on the wafer are found after repeated changing of the process parameters and practical changing process. The residual polymers are generated in two manufacturing processes. The first process is the etching process of bonding pad windows and the second process is O2-ashing, dry stripping process. The surface characters of the Polyimide passivation layer are changed by the two processes, and therefore the following process, wet stripping, peeling Polyimide pieces from the surface of the passivation layer to form residual polymer on the wafer. Because the wet strippers, e.g. EKC and ACT photoresist strippers, are hydroxylamine (HDA)-based chemical solutions with etching capability, they not only remove the polymer on the wafer surface but also etch the Polyimide passivation layer to form residual polymer.

#FIG. 3 shows a flow chart for a cleaning process according to the present invention. The differences between FIG. 2 and FIG. 3 are two steps. Step 320, a wet stripping process, is the same as step 230 and step 330, a dry stripping process, is the same as step 220. That is to say, the process in FIG. 3 changes the sequence of step 220 and step 230 in the process of FIG. 2.

#To further disclose the process according to the present invention, FIG. 4 shows a chart comparing cleaning process results of the present invention and different cleaning processes. The residual polymers pollute the wafer surface and induce defects in different processes. Referring to process 410, the passivation layer passes through an etching process only and there is no peeled polymer. In process 420, the passivation layer passes through etching and wet stripping processes and residual polymers are found on the wafer surface. In process 430, an etching process and dry stripping process with Oxygen plasma are performed and no residual polymer is found on the wafer surface. In process 440, etching, dry stripping and wet stripping processes are performed and a serious amount of residual polymers is found on the wafer surface. Finally, in process 450, etching, wet stripping and dry stripping processes are performed and no residual polymer is found on the wafer surface. Therefore, the conclusions are that the wet stripping process induces the surface of passivation layer to peel, the O2-ashing process enhances the peeling phenomenon of passivation layer when it occurs before the wet stripping process and the O2-ashing process may eliminate the residual polymer on the wafer surface. That is to say, using the process in accordance with the present invention not only protects the metal bonding pads fluoride formation, e.g. Al—F formation, by reducing the fluorine intensity on the surface of the pads but also eliminates the residual polymer on the wafer.