Since the introduction of copper metalization into mainstream semiconductor processes, new backend debug and failure analysis techniques are needed to deal with the different reaction rate and milling behavior of copper. Focused Ion Beam (FIB) systems have long been a major tool in debug and analysis of semiconductor chips. With the introduction of copper, many of the current FIB chemistries and techniques will need to be modified in order to accommodate this process. The metal etch gases currently in most FIB systems either have no effect on copper or have detrimental effects. Chlorine, iodine and bromine all will etch copper spontaneously and will undercut exposed copper lines. [1,2] The ion channeling properties of copper are also significantly greater than aluminum, which makes large area metal removal very difficult due to differential milling rates. Depending on the crystallographic grain orientation, straight sputter of copper could have up to 3 times differential milling rates. Various other FIB function will also need to be examined with regard to copper. This paper will discuss the differences in dealing with copper instead of aluminum chips. It will also offer a few application techniques and new system enhancements in dealing with copper and discuss some limitation of the current system hardware. [1]

While integrated circuits are routinely modified using Focused Ion Beam systems (FIB), the reliability of these modifications has not yet been thoroughly studied. For several years, researchers at Sandia National Labs and CNES have been involved in the evaluation of the impact of FIB exposure on semiconductor structures. We have all come to the same conclusion: the intrinsic behavior of a circuit is altered after FIB intervention and the damage cannot be completely recovered but can be controlled. Despite these results, modified circuits are used in many applications such as satellites or even more critical environments. Although FIB modifications are invasive to the circuit they provide a working sample that can prove out, in silicon, a design change. However, is the functionality of FIB modified ICs reliable? In more practical terms: Can we use modified devices for our applications and what guarantee do we have that they will work after a few months? To answer these questions, we have conducted extended studies addressing both MOS and bipolar circuits. We used basic structures (such as transistors and diodes) and complex structures (operational amplifiers, oscillators, etc) and studied the effects of two different FIB systems, a Schlumberger P2X and an FEI Vectra 986. We have investigated the reliability of the devices by monitoring intrinsic parameters, before FIB, after FIB, during life testing and after life testing.

A new TEM sample preparation technique was developed to meet the increasing demand and fast turn around time requirements in today’s semiconductor industry. The technique uses a FIB to deposit a thin strip of platinum over the desired structure. The strip then serves as a mask during subsequent etching in a reactive ion etcher. During etching, material on both sides of the strip are removed in a single etch process, leaving a thin wall that is transparent to the electron beam in a TEM. The major advantage of this technique is a 30% to 50% reduction in preparation time of multiple TEM samples.

Results of experimental studies are presented which address a concern that gallium staining from FIB imaging during backside editing might degrade IR navigation as well as signal acquisition during probing of flip chips by such techniques as Picosecond Imaging Circuit Analysis (PICA) and Laser Voltage Probing (LVP). Although optical transparency does depend on gallium implantation dose, Ga staining is, however, not necessarily a limitation to the implementation of photon optical tools in the debug laboratory. Comparisons are made on the results from devices under the following conditions: with and without an anti-reflective (AR) coating, with and without XeF2 enhancement during FIB etching, and with confocal laser scanning microscope (CLSM) imaging and CCD-based IR microscope imaging.

Secondary Ion Mass Spectrometry (SIMS) with a quadrupole detector has been used on FIB systems but it needs yields enhancement to become an effective tool. By introducing water vapor to the area of analysis, the secondary ion yield can be significantly increased for certain metals.