Did you know that silicon wafer surfaces are usually contaminated with trace impurities that include ionic materials, molecular compounds, elemental particles, and airborne dust? To ensure high-quality performance, wafers have to go through various processes that aim to eliminate these contaminants. Although the gettering process represents up to about 10% of the silicon wafer manufacturing costs, it helps ensure that only clean wafers reach the end-users.
Gettering refers to the process of eliminating metal impurities from the surface of the silicon wafer. It converts these trace impurities into stable compounds that are insoluble in the liquid metal by localizing them in the wafer’s predetermined and passive regions. To collect these contaminants, certain elements called getters are immersed in the liquid metal.
Intrinsic gettering involves the creation of impurity trapping sites by precipitating supersaturated oxygen from the silicon wafer. As the process of precipitation takes place, stress is introduced to the wafer while clusters are produced and continuously grown.When these stresses reach a certain point where they have to be relieved, stacking faults or dislocation loops are formed to serve as trapping sites for trace impurities. It’s important to note that the intrinsic gettering process requires the use of starting wafers that contain sufficient oxygen levels that can range from 15 to 19 ppma.Intrinsic gettering doesn’t require manufacturers to subject the wafers to other treatments except for heating. Additionally, it offers a significantly larger volume of impurity sink than what external gettering does on the backside of the wafer. Lastly, its gettering regions are known to be closer to the device regions.
Extrinsic gettering creates the stress in the silicon lattice to form chemically reactive trapping sites that are located at the backside of the silicon wafer. Some of the methods used to produce such stresses include the introduction of mechanical damage via grooving, abrasion, or sandblasting. However, extrinsic gettering may potentially initiate and propagate the micro-cracks on the wafer’s backside. This will compromise the wafer’s mechanical strength.
At Wafer World, you can expect to find high-quality wafers for your next project. Contact us today for inquiries.