Test wafers are used for a variety of applications where a low cost alternative to prime wafers is necessary. The most common applications are for particle monitors, oxide growth monitors, etch rate monitors, implant dosing and for characterizing new and existing equipment and processes‹especially where large quantities of wafers are required. Test and monitor wafers may be used in very high level work where the use of prime wafers is limited to final evaluation.

Wafers become test wafers as a result of some irregularity (often minor) that disqualifies them for use as prime wafers; they are often supplied without backside specifications. Additionally, they may have some degree of fine scratching, and in some cases, a wide resistivity range (0-100 Ohm/cm).

Thermal oxide, with a 2-4% uniformity variation, can be grown quite easily on test wafers. Other deposited/sputtered thin films may be applied to these wafers as well. Test wafers with low TTV can be suitable for photolithography; however, it is important to note that since test wafers are not always as flat as prime wafers, resolution may not be the same across the entire wafer.

As 300 mm process characterization is brought up to speed, the requirement for test wafers fab-wide will become a budgetary mandate. In the final analysis, test wafers that meet SEMI specifications, as well as those set forth by the customer, will serve their intended purpose quite adequately. At the same time, these monitor wafers represent a significant savings over prime wafers.