Investigating the Formation of Time-Dependent Haze on Stored Wafers

The storage life of bare silicon wafers has been historically defined as the elapsed time after packaging before small particles begin to form on the surface. Many silicon wafer users have observed this time-dependent haze formation on wafers that have seen extended storage. We have investigated the surface changes of silicon wafers during 6 months and 18 months of storage and show that although most wafers have a very high potential for surface degradation, strict control of moisture inside the wafer package is the primary key to 18-month storage life. We show that surface organics, ions, oxide thickness, metals and particles remain very stable in a well-controlled package environment. However, we also show that the typical levels of organics and ions that are present on commercially available silicon wafers have the potential to form over one million particles >0.12um diameter if the wrong storage conditions exist. A general mechanism for tdh formation is proposed.