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Optimising surface chemistry after plasma dicing
Keywords: surface chemistry, Plasma Dicing, alternating etch and deposition
Plasma dicing has shown many benefits over other dicing techniques such as increased die strength, smaller/thinner die and reduced cost of ownership1. The dicing process uses alternating etch and deposition steps to create anisotropic structures. The process is well established and is used in plasma dicing as means to etch through the wafer quickly with control of the profile and sidewall quality. The nature of the process means that there will be F residues remaining at completion due to the CFx polymer layer deposited on the wafer surface and feature sidewalls2. This can be removed by an O2 plasma however when solder bumps are present and subjected to the same dicing/Bosch process, the bumps can react with F radicals to form SnF2 which cannot be removed by an O2 plasma alone. An additional plasma process can be performed to reduce the F levels further, however, this still leaves F present. Studies are underway to determine whether this is an issue for subsequent steps or indeed whether the presence of F may help solderability3. However, in this work, the effectiveness of post-dicing wet cleans to remove the SnF2, and avoid any potential issues, is investigated. A series of tests were carried out comparing plasma DAG (dicing after grind) processes with different post residue treatments. A screening test was carried out using several different wet etch formulations, and two suitable formulations were identified. Further tests were carried out to optimise the conditions and to check the dicing tape compatibility. The F levels, measured by EDX, were reduced to <1% at a level comparable to the control sample, figure 1. The work has shown that a wet chemistry post plasma dicing treatment is capable of removing F residues and is compatible with the plasma dicing process flow.
Janet Hopkins,
SPTS technologies Newport
Newport, UK
United Kingdom

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