Non-destructive laboratory-based X-ray diffraction mapping of warpage in Si die embedded in IC packages

Reliability issues as a consequence of thermal/mechanical stresses created during packaging processes have been the main obstacle towards the realisation of high volume 3D Integrated Circuit (IC) integration technology for future microelectronics. However, there is no compelling laboratory-based metrology that can non-destructively measure or image stress/strain or warpage inside packaged chips, System-on-Chip (SoC) or System-in-Package (SiP), which is identified as a requirement by the International Technology Roadmap for Semiconductors (ITRS). In the work presented here, a triple-axis Jordan Valley Bede D1 X-ray diffractometer is used to develop a novel lab-based technique called X-ray diffraction 3-dimensional surface modeling (XRD/3DSM) for non-destructive analysis of manufacturing process-induced stress/warpage inside completely encapsulated packaged chips. The technique is demonstrated at room temperature and at elevated temperatures up to 115C by in situ XRD annealing experiments. The feasibility of this technique is confirmed through the charactersation of die stress inside encapsulated commercially available ultra-thin Quad Flat Non-lead (QFN) packages, as well as die stress in embedded QFN packages at various stages of the chip manufacturing proces

On the use of total reflection x-ray topography for the observation of misfit dislocation strain at the surface of a Si/Ge–Si heterostructure

Synchrotron x-ray topography was used in total reflection topography (TRT) mode to observe strain-induced surface bumps due to the presence of underlying misfit dislocations in strained-layer SiGe on Si epitaxial heterostructures. In these experiments, the x rays approached the sample surfaces at grazing incident angles below the critical angles for total external reflection for a number of reflections, and hence, surface strain features nominally less than a few tens of angstrøms from the sample surface have been observed. These are similar to the surface bumpiness observed by atomic force microscopy, albeit on a much larger lateral length scale. The fact that TRT mode images were taken was confirmed by the observation of conventional backreflection topographic images of misfit dislocations in all samples when the grazing incidence angle became greater than the critical angle

X-ray imaging of silicon die within fully packaged semiconductor devices

X-ray diffraction imaging (XRDI) (topography) measurements of silicon die warpage within fully packaged commercial quad-flat no-lead devices are described. Using synchrotron radiation, it has been shown that the tilt of the lattice planes in the Analog Devices AD9253 die initially falls, but after 100 °C, it rises again. The twist across the die wafer falls linearly with an increase in temperature. At 200 °C, the tilt varies approximately linearly with position, that is, displacement varies quadratically along the die. The warpage is approximately reversible on cooling, suggesting that it has a simple paraboloidal form prior to encapsulation; the complex tilt and twisting result from the polymer setting process. Feasibility studies are reported, which demonstrate that a divergent beam and quasi-monochromatic radiation from a sealed X-ray tube can be used to perform warpage measurements by XRDI in the laboratory. Existing tools have limitations because of the geometry of the X-ray optics, resulting in applicability only to simple warpage structures. The necessary modifications required for use in situations of complex warpage, for example, in multiple die interconnected packages are specified

Experimental verification of the model by Klapper for 4H-SiC homoepitaxy on vicinal substrates

4H-SiC homoepitaxial layers free of basal plane dislocations (BPDs) are urgently needed to overcome the so-called bipolar degradation of high-voltage devices. BPDs being present in substrates are able to either propagate to the epilayer or convert to harmless threading edge dislocations (TEDs) in the epilayer. The model by Klapper predicts the conversion of BPDs to TEDs to be more efficient for growth on vicinal substrates with low off-cut angle. This paper aims to verify the model by Klapper by an extensive variation of epitaxial growth parameters and the substrates' off-cut. It is shown that the off-cut angle is the key parameter for growth of BPD-free epilayers. Furthermore, it is shown that the model also describes adequately the behavior of different types of TEDs, i.e., TED II and TED III dislocations, during epitaxial growth. Therefore, the model by Klapper is verified successfully for 4H-SiC homoepitaxial growth on vicinal substrates

Applicability of a Flat-Bed Birefringence Setup for the Determination of Threading Dislocations of Silicon Carbide Wafers

Abstract:Screw-type dislocations like micropipes (MP) and threading screw dislocations (TSD) are prohibiting the function or at least diminishing the efficiency of electronic devices based on silicon carbide (SiC). Therefore, it is essential to characterize wafers in an efficient and fast manner. Molten potassium hydroxide (KOH) etching or white-beam X-ray topography (SWXRT) are either destructive or not economically viable for an in-depth characterization of every wafer of one SiC crystal. Birefringence microscopy is being utilized as a fast and non-destructive characterization method. Instead of microscopic setups, commercially available flat-bed scanners equipped with crossed polarizer foils can be used for fast large-area scans. This work investigates the feasibility of such a setup regarding the detection rate of MPs and TSDs. The results of a full-wafer mapping are compared with birefringence microscopy and KOH etching. In the investigated sample clusters of MPs caused by a polytype switch in the beginning of the growth could be identified by both birefringence microscopy and the flat-bed scanner setup, as well as small angle grain boundaries and TED arrays. However, the resolution of the scanner was not sufficient to identify TSDs. Nevertheless the setup proves to be an easy-to-setup and cheap characterization method, able to quickly identify defect clusters in 4H-SiC wafers

Dynamical X-ray diffraction imaging of voids in dislocation-free high-purity germanium single crystals

White-beam X-ray topography has been performed to provide direct evidence of micro-voids in dislocation-free high-purity germanium single crystals. The voids are visible because of a dynamical diffraction contrast. It is shown that voids occur only in dislocation-free parts of the crystal and do not show up in regions with homogeneous and moderate dislocation density. It is further suggested that the voids originate from clustering of vacancies during the growth process. A general method is proposed to verify the presence of voids for any crystalline material of high structural perfection

Nondestructive monitoring of die warpage in encapsulated chip packages

We describe an X-ray diffraction imaging technique for nondestructive, in situ measurement of die warpage in encapsulated chip packages at acquisition speeds approaching real time. The results were validated on a series of samples with known inbuilt convex die warpage, and the measurement of wafer bow was compared with the results obtained by optical profilometry. We use the technique to demonstrate the impact of elevated temperature on a commercially sourced micro quad flat nonlead chip package and show that the strain becomes locked in at a temperature between 94 °C and 120 °C. Using synchrotron radiation at the Diamond Light Source, warpage maps for the entire 2.2 mm × 2.4 mm × 150-µm Si die were acquired in 50 s, and individual line scans in times as short as 500 ms.status: publishe

Nondestructive Monitoring of Die Warpage in Encapsulated Chip Packages

We describe an X-ray diffraction imaging technique for nondestructive, in situ measurement of die warpage in encapsulated chip packages at acquisition speeds approaching real time. The results were validated on a series of samples with known inbuilt convex die warpage, and the measurement of wafer bow was compared with the results obtained by optical profilometry. We use the technique to demonstrate the impact of elevated temperature on a commercially sourced micro quad flat nonlead chip package and show that the strain becomes locked in at a temperature between 94 °C and 120 °C. Using synchrotron radiation at the Diamond Light Source, warpage maps for the entire 2.2 mm × 2.4 mm × 150-μm Si die were acquired in 50 s, and individual line scans in times as short as 500 ms

Large-Scale Defect Clusters with Hexagonal Honeycomb-like Arrangement in Ammonothermal GaN Crystals

In this paper, we investigate, using X-ray Bragg diffraction imaging and defect selective etching, a new type of extended defect that occurs in ammonothermally grown gallium nitride (GaN) single crystals. This hexagonal “honeycomb” shaped defect is composed of bundles of parallel threading edge dislocations located in the corners of the hexagon. The observed size of the honeycomb ranges from 0.05 mm to 2 mm and is clearly correlated with the number of dislocations located in each of the hexagon’s corners: typically ~5 to 200, respectively. These dislocations are either grouped in areas that exhibit “diameters” of 100–250 µm, or they show up as straight long chain alignments of the same size that behave like limited subgrain boundaries. The lattice distortions associated with these hexagonally arranged dislocation bundles are extensively measured on one of these honeycombs using rocking curve imaging, and the ensemble of the results is discussed with the aim of providing clues about the origin of these “honeycombs”