Using the OptiGlow ACE RIE/Plasma system to remove mold compound from packaged IC devices with copper interconnect or copper wire bonded devices.
Plasma and Reactive Ion Etching (RIE) have been used to etch various films in the semiconductor industry from over 40 years. Using a combination of reactor configurations (RIE, plasma), along with use of the proper combination of O2, Ar, CF4 and SF6 chemistry can be a good alternative to the use of fuming nitric or sulfuric acid to remove various mold compound from packaged devices. The key process goal is to balance the proper configuration with the proper mix of available
gas to minimize the etching of the die.
Plasma/RIE system used:
Samples were etched in the Glow Research OptiGlow ACE system to determine the best method for removing mold in a decapulation process without damaging the copper. It was found that using only oxygen under RIE conditions was too slow. Adding CF4 to O2 produced the best results and a satisfactory etch rate was achieved. The sample was moved to the lower shelf for treatment under plasmaconditions for the final clean-up step. The OptiGlow ACE system is a high conductance system, which allows the system to quickly pump down should the operator want to blow off the filler material to increase the etch rate.
The addition of a small amount of fluorine to the oxygen in the gas mixture improves the etch rate of the polymer filler. Lower amounts of fluorine can be used towards the end of the process to lower the removal rate. Care should be taken not to overetch into the dielectric below the bond pads. It is suggested that the FA engineer may want to switch to a more selective chemistry (with less fluorine) or switch the sample to the plasma electrode for a more “gentle” removal of the final epoxy mold that remains.
Copper wire bonds and copper connections have presented challenges to the FA engineer due to the etch properties of the metals, and the decap acids used are often not compatible, or are difficult to use. Often the FA engineer simply does not want to bother with fuming acid equipment or the safety regulations associated with buying and installing acid equipment. It is estimated that the cost for a dual acid decap/micro mill combination and all the associated materials will cost over $50K.
The cost of the ACE Plasma system and vacuum pump is well below this
cost (<$25K) and is very simple to plug in and use. The OptiGlow ACE plasma/RIE system and the vacuum pump plug in to a standard wall electrical outlet.
Laser ablation with RIE plasma:
Laser ablation can be used to remove the gross amount of mold compound from the top or back of the package. The FA engineer would want to use Laser ablation to remove mold material down to the point where the copper wires are starting to be exposed. The RIE plasma system is used to expose the copper wires and it is suggested that plasma conditions be used for the final steps of process
The Glow Research OptiGlow ACE system is an extremely versatile system that can provide the following:
- RIE anisotropic etching
- Plasma isotropic etching
- Designed for fluorine and oxygen chemistry
- Much lower price when compared to fuming acid
removal systems (under $25K)