Silicon wafer manufacturers need to pay attention to the gettering process because it is through gettering that device-degrading impurities are removed from the operating circuit regions of the wafer. Gettering can be done during crystal growth or in the next wafer fabrication steps. It is considered to be an important process for improving the yield of VLSI (very-large-scale integration) manufacturing. Read on to help you understand more about this process!
The process of removing impurities through gettering is done through the following:
There are two types of gettering: extrinsic and intrinsic. Extrinsic gettering refers to gettering that utilize external means to develop the damage or stress in the silicon mesh in such a way that extended defects needed for trapping impurities are produced. These chemically sensitive trapping sites are commonly found at the wafer backside. Various methods have been utilized to achieve external gettering.
For example, the addition of mechanical damage by abrasion, sandblasting, or grooving can create stresses at the backside of a wafer, which when hardened produces dislocations that tend to alleviate these stresses. This makes the area suitable as gettering sites. The only disadvantage of this method is its tendency to start and proliferate wafer backside microcracks that may jeopardize the mechanical strength of the wafer.
Another technique used for external gettering is diffusing phosphorous into the backside of the wafer. This technique results in phosphorous opening or dislocations that act as trapping areas for impurity atoms. Whatever technique is used by silicon wafer manufacturers to getter wafers, all are a viable solution in removing impurities.
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