This invention relates to the field of semiconductor fabrication, and specifically to testing for surface defects and/or particles in semiconductor wafer production.
It is critically important in semiconductor manufacturing to reduce or minimize surface defects in integrated circuits formed on wafers. Surface detects, for example, may include particles that are added to the surface of a wafer. The number of particles on a wafer surface may be determined and monitored to assure that production yield is maintained at an acceptable level, and to prevent detect density from reaching an unacceptable level. For example, one source of particles is semiconductor tools or equipment. The number of particles added to a wafer per product pass through the tool may be determined or specified by running a test wafer through the tool before production semiconductor wafers are started. Thus, periodic defect monitoring may be used to test the cleanliness or condition of a tool and/or process before production semiconductor wafers are processed or handled by that tool or process.
In periodic defect monitoring, one or more test wafers may be used. A virgin test (xe2x80x9cVTxe2x80x9d) wafer is a bare silicon slice that has not been used or exposed to the conditions or steps of process characterization. VT wafers may be suitable for monitoring particles or defects that are added by a particular tool or process. The number and type of particles added to the VT wafer may depend on the status and condition of the tool, for example.
After a VT wafer has been used for periodic defect monitoring, a grinding, lapping or polishing tool may be used to remove silicon from the wafer surface, reducing the wafer thickness by between about 10 microns and about 20 microns or more. Typically, this reduction in wafer thickness means that the virgin test wafer cannot be reused again more than once or, at most, very few times.
In some instances, such as where defect quality is measured on process films, a VT wafer may not be reused again. For example, test wafers having thin epitaxial surfaces of about 2 microns to about 4 microns cannot be reclaimed or reused because grinding, lapping or polishing processes remove a greater thickness.
Use of VT wafers to monitor defects or particles added by semiconductor processing tools or equipment is very costly. For example, several VT wafers may be used for each new production wafer start, and the number of VT wafers used may vary depending on the maturity of the tool and the process.
A system and method are needed to extend the useful life of virgin test wafers and to allow them to be reclaimed and reused repeatedly in the testing for particles and surface defects produced in various tools and processes.