November_EDFA_Digital

ELECTRONIC DEVICE FAILURE ANALYSIS | VOLUME 20 NO. 4 30 EDFAAO (2018) 4:30-36

1537-0755/$19.00 ©ASM International ®

GEOLOCATION OF Cu WIRES DURING SENSITIVE IC ACID DECAPSULATION Michael Obein DC Engineering, Caen, France

Digit Concept, SEB, France m.obein@digit-concept.com

it was evident that when using the method of polarizing at a constant voltage, the current varied significantly in time. This finding enabled the possibility of localization during the chemical etch. This article describes tests that were carried out by Digit Concept in order to understand and exploit this phe- nomenon. First, newand differentmethods of decapsula- tion bymixing acids and adjuvants will be reviewed. Next, the article will present amethod of end-of-etch detection and how to improve the rinsing process in order to com- plete itmore quickly and consistently after decapsulation. LASER Twelve years ago, laser ablation was introduced as a means to facilitate the pre-decapsulation of packages aiming at completion by wet chemistry (acids) or dry chemistry (plasma). Advanced laser ablation (sublima- tion and plasma) is nowwidely used for creating pockets, allowing different levels of elements inside the package to be reached during etching, while avoiding damage to the Ag wires, for example. PLASMA DECAPSULATION Despite progressmade by the CNES DC patent and the last Cold Etching Microwaves Induced Plasma (iCE_MIP) European Project [1] from the past three years of Digit Concept R&D, the industry has been limited to use of the wet chemistry technique. The plasma method was not relevant in some cases or could not be used successfully in others. Standard gases such as pure O 2 or O 2 mixedwith Ar, H, or CF 4 may not be compatiblewith certainmaterials. In addition, in some industries like back-end packaging, spendingmany hours on plasma etching cannot be toler- ated. Further, the MIP equipment can be cost prohibitive.

INTRODUCTION Integrated circuit (IC) packages have been greatly improved over the past several years due to the adop- tion of newmaterials and processes. As a result, both the initial quality check of the assembly and any required failure analysis are critical to continued IC progress. Some examples of recent technical advancements include the use of Cu, Cu/Pd, and Ag wires, the new green epoxy molding compound (EMC), suppression of lead, use of Cu pillars and an increased number of dies with different materials like Si and GaAs, and use of polyimide instead of SiO 2 . It is imperative to preserve and protect those materials by stopping the acid decapsulation process at the right moment. One of the new package technologies uses copper as a metal layer and a chip coating polyamide and benzocy- clobutene (BCB) low-k dielectric as described in a paper by Amandine Aubert [2] from STMicroelectronics Tours, France. This technology (Fig. 1) is currently gaining wider adoption in the automotive industry. Inmany cases, decapsulationwith acid is the preferred method. In the packaging industry, for example, decap- sulation in less than 10 minutes is required for quality inspection reasons. During decapsulationwith acid tests,

Fig. 1 Schematic cross section of a component using BCB Cu technology. ST Microelectronics pending.

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