Investigating the Formation of Time-Dependent Haze on Stored.pdfVIP

Originally appeared in the March 2001 issue of Micro Magazine. © Canon Communications 2001 Investigating the Formation of Time-Dependent Haze on Stored Wafers Larry W. Shive, Richard Blank and Karen Lamb MEMC Electronic Materials, Inc. Abstract: 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. Introduction Silicon wafer users expect that the surface of the wafers they receive from wafer makers will meet all requirements for light point defects (LPDs), metals, grown-on film quality and cleanability regardless of the storage history of the wafers. Yet, many users have observed wafers with a very large number of 0.12um LPDs that were not present when the wafers left the manufacturer’s facility. This phenomenon has come to be called “time- dependent haze” (TDH). Its appearance may or may not cause a LPD rejection at incoming Quality Assurance or a performance problem in the device line but it will always suggest to the user