Value

Test wafer consumption is a direct function of the process control and quality monitoring requirements at critical fabrication process steps.  Overall test wafer usage may exceed the total output of production wafers, however, the usage ratio of test to production wafers may be reduced by up to one half through well established process controls and metrology.  Furthermore, the cost of monitor wafers can be reduced by up to 70% by matching the test wafer restoration process to the monitor requirements. 
 

Full Reclaim - For High Quality Test and Monitor Wafers

By convention, a fully restored test wafer may have up to 25 microns of thickness removed to eliminate implant impurity doping, films and surface damage.  It then receives a surface polish, a number of cleaning steps, and a laser scan to verify surface particle counts are less than some predetermined limit.  This procedure produces a high quality wafer suitable for use at almost all process monitoring steps and is the standard requirement for all restored process monitor wafers at many semiconductor companies.  
 

Recycle/Mechanical Test Wafers - For Equipment Checks, Baffle and Dummies.

A significant number of semiconductor fabrication control operations do not actually require a full reclaim particle grade wafer to satisfy the quality control requirements of the monitored process.  Film deposition rates, thickness control, and etch rate processes require very clean monitor wafers, but do not benefit from a particle grade product because surface micro-roughness is not a concern.  Since these operations do not require light point defect free wafers the silicon stock removal process may be greatly reduced or eliminated and the life of the monitor wafer becomes indefinite.  MicroSil offers film monitor grade wafers with the same in-line controls and cleanliness as the full reclaim product.  This process results in several benefits over full reclaim:

• Lower reclaim costs up to 75% less

• Fast turn cycle time typically 50% shorter cycle

• Indefinite re-use potential minimum or no silicon stock removal

• High yields usually over 95%

• Process monitor quality product

• Same cleanliness as full reclaim