Delayering of 14 nm Node Technology IC with Xe Plasma FIB

Abstract

The burgeoning generation of electronic data and the growing need for fast processing is driving the development of unique architectures in microelectronic devices. High device performance, along with low energy consumption, decreasing device area and optimal production costs are the four basic tenets of operation in the microelectronics industry [1]. These rules have led to increasing area density of the elements in electronic devices and consequently to shrinkage of the elements to the nanometer scale. State‐of‐the‐art commercial electronic devices are based on 22 nm and 14 nm node technology and the next generation of 10 nm and 7 nm nodes are under development [1]. Mechanical polishing as a standard tool in the failure analysis of the devices does not meet the very strict requirements of these nodes. The thickness of metal interconnects and dielectric separating layers just above the transistors has shrunk to less than 100 nm. Therefore it is a challenge to stop the polishing process in a particular layer with the expected quality, accuracy and repeatability. Moreover, mechanical polishing is usually accompanied by surface artefacts like material chipping‐off and site‐specific fault excavation is usually impossible. Focused Ion Beam (FIB) technology has proven to overcome these restrictions. It offers the possibility to target a failure with nanometer accuracy in depth and the lateral direction. Therefore cross‐sectioning, site‐specific layer‐by‐layer excavation (delayering) and direct extraction of a Transmission Electron Microscopy (TEM) lamella containing the particular fault of interest have become standard methods in failure analysis. We present delayering of an Intel Skylake processor (G4400) based on 14 nm node technology [2]. The delayering is performed with a Xe plasma FIB. Beam currents of Xe FIB up to 2 µA has extended the dimensions of the analyzed volume of interest to several hundred micrometers in general [3] while simultaneously enabling homogeneous delayering with nanometer accuracy. Xe FIB is advantageous also because interaction of inert Xe atoms with the material surface does not significantly alter its properties and surface contamination is negligible. Moreover Xe ions considerably reduce surface amorphisation when compared to Ga ions [4]. Processor architecture is based on alternating metal and dielectric layers (Fig. 1). These layers have different sputtering rates when FIB delayering is applied. Uneven sputtering can be substantially suppressed by chemical means. In our experiments, water vapor was delivered to the point of patterning via a Gas Injection System (GIS) in order to equalize sputtering of metal interconnects and insulators. The result of processor delayering down to the first metal layer, just above the transistors is shown in Fig. 2. The damage‐free surface of the transistor contact layer is ready for electrical probing. Nanometer‐sized elements in state‐of‐the‐art electronics have posed a challenge also for imaging technologies. Clear observation of the very thin individual layers means suppressing the acceleration voltage of primary electrons to the sub‐1 kV range, ideally to 500 V. At higher energies, the electron signals from different layers would intermix as they are generated in a volume comparable to the thickness of those layers. However, sub‐nm resolution at low electron energies is a necessary condition due to the size of the observed features. High resolution pictures captured at 500 V are shown in Fig. 2. Low‐kV imaging has verified highly homogeneous delayering of the processor as can be seen by the absence of large contrast changes in the delayered region.