Microstructure investigation of Cu/SnAg solid-liquid interdiffusion interconnects by Electron Backscatter Diffraction

Panchenko, Iuliana; Grafe, Juergen; Mueller, Maik; Wolter, K.-J.

doi:10.1109/eptc.2013.6745735

Cited by 6 publications

(4 citation statements)

References 8 publications

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“…Note that for microelectronic packaging applications, Cu and Sn layers are deposited by electrochemical process. In these cases, in addition to the classical Kirkendall voids defects, numerous porosities and large cavities are observed at end of TLPB process inside the joints as it was reported by several studies [1,[22][23][24]. At this stage, it is important to note that these large cavities observed in cross-section analyses at the end of TLPB were not observed at the initial stage of the process.…”

Section: Introductionsupporting

confidence: 65%

Bubble formation and growth during Transient Liquid Phase Bonding in Cu/SnAg system for microelectronic packaging

Barik

Gillot

Hodaj

2021

J Mater Sci: Mater Electron

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In this work, we study the Transient Liquid Phase Bonding (TLPB) for flip chip interconnexion using copper pillar and SnAg solder alloy technologies. Cu and SnAg bumps with a size of 90 9 90 lm 2 were deposited using electroplating process with a thickness of 20 lm and 15-30 lm, respectively. Two types of Cu were deposited: with or without additives. Before the TLPB process, soldering experiments with or without pre-reflow were carried out at 250 °C in order to insure a good filling of the joint. Afterwards, isothermal holdings up to 4 h were performed in the temperature range between 250 and 350 °C under air atmosphere. Two main aspects of Cu/SnAg system are studied and analyzed: (i) the evolution of morphology, microstructure, and growth kinetics of intermetallics (IMCs) during the TLPB and especially (ii) the formation and growth of gas bubbles within the liquid solder during TLPB process. Destructive (scanning electron microscopy) and non-destructive (X-ray) characterizations are performed to analyze and understand the evolution of microstructure as well as the formation and evolution of cavities within the joint during the TLPB process. Non-destructive X-ray radiography with 5 lm resolution and 3D X-ray tomography analysis with 0.7 lm resolution were conducted for the same joint at different steps of its evolution between its initial state (just after the soldering process: about 3 min at 250 °C) and 4 h at 250 °C in order to follow ''in situ'' the evolution of volume defects inside the joint and especially the evolution of gas bubbles within the joints.

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Section: Introductionsupporting

confidence: 65%

Bubble formation and growth during Transient Liquid Phase Bonding in Cu/SnAg system for microelectronic packaging

Barik

Gillot

Hodaj

2021

J Mater Sci: Mater Electron

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“…The “no contact” area is detected in the upper right die corner for most of the bonded sample pairs (the orientation of the dies was marked). This suggests that there may be a slight non-planarity between the bonding stage and head, which is a known issue for bonding in the literature [ 41 , 42 , 43 ]. This could lead to variations in fracture surface types and bonding strength across the sample pairs.…”

Section: Resultsmentioning

confidence: 99%

Cu-Cu Thermocompression Bonding with a Self-Assembled Monolayer as Oxidation Protection for 3D/2.5D System Integration

et al. 2023

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Cu-Cu direct interconnects are highly desirable for the microelectronic industry as they allow for significant reductions in the size and spacing of microcontacts. The main challenge associated with using Cu is its tendency to rapidly oxidize in air. This research paper describes a method of Cu passivation using a self-assembled monolayer (SAM) to protect the surface against oxidation. However, this approach faces two main challenges: the degradation of the SAM at room temperature in the ambient atmosphere and the monolayer desorption technique prior to Cu-Cu bonding. In this paper, the systematic investigation of these challenges and their possible solutions are presented. The methods used in this study include thermocompression (TC) bonding, X-ray photoelectron spectroscopy (XPS), shear strength testing, scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDX). The results indicate nearly no Cu oxidation (4 at.%) for samples with SAM passivation in contrast to the bare Cu surface (27 at.%) after the storage at −18 °C in a conventional freezer for three weeks. Significant improvement was observed in the TC bonding with SAM after storage. The mean shear strength of the passivated samples reached 65.5 MPa without storage. The average shear strength values before and after the storage tests were 43% greater for samples with SAM than for the bare Cu surface. In conclusion, this study shows that Cu-Cu bonding technology can be improved by using SAM as an oxidation inhibitor, leading to a higher interconnect quality.

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“…Shrinkage voids have also been discussed for the formation of Cu 6 Sn 5 and Cu 3 Sn IMCs in the Cu=Sn SLID system associated with a volume shrinkage of 5.23 and 4.39% respectively. 6) Since the density of liquid In and Sn at bonding temperature is much lower (7.03 g•cm −3 for In at 164 °C29) and 6.98 g•cm −3 for Sn at 232 °C31) ) compared to RT, the resulting volume shrinkage increases to 10.68% for Cu 11 In 9 and 7.83% for Cu 6 Sn 5 IMCs.…”

Section: Cu/in Bonding and High Temperature Storagementioning

confidence: 99%

“…The resulting bonding technologies are either thermo-compression bonding (TCB, for Cu=Cu) 4,5) or solid-liquid interdiffusion bonding (SLID, for Cu=Sn=Cu). 6,7) SLID can be easily implemented since it is a robust process and it does not require very high bonding pressures or temperatures compared to Cu=Cu TCB. A thin layer of a low-melting metal is typically electroplated on the top of a high-melting metal.…”

Section: Introductionmentioning

confidence: 99%

Characterization of low temperature Cu/In bonding for fine-pitch interconnects in three-dimensional integration

Panchenko

Bickel

Meyer

et al. 2017

Jpn. J. Appl. Phys.

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This study presents the results for Cu/In bonding based on the solid–liquid interdiffusion (SLID) principle for fine-pitch interconnects in three-dimensional integration. The microbumps were fabricated on Si wafers (55 µm pitch, 25 µm top bump diameter, 35 µm bottom bump diameter). In was electroplated directly on Cu only on the top die microbumps. Two different In thicknesses were manufactured (3 and 5 µm). The interconnects were successfully fabricated at a bonding temperature of 170 °C. High temperature storage was carried out at 150 and 200 °C for different times between 2 and 72 h directly after the interconnect formation in order to investigate the temperature stability. The microstructure was analyzed by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). The intermetallic compound (IMC) found in the microbumps after electroplating was CuIn2. The intermetallic interlayer consists of Cu11In9 and a thin layer of Cu2In after bonding and isothermal storage.

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Microstructure investigation of Cu/SnAg solid-liquid interdiffusion interconnects by Electron Backscatter Diffraction

Cited by 6 publications

References 8 publications

Bubble formation and growth during Transient Liquid Phase Bonding in Cu/SnAg system for microelectronic packaging

Bubble formation and growth during Transient Liquid Phase Bonding in Cu/SnAg system for microelectronic packaging

Cu-Cu Thermocompression Bonding with a Self-Assembled Monolayer as Oxidation Protection for 3D/2.5D System Integration

Characterization of low temperature Cu/In bonding for fine-pitch interconnects in three-dimensional integration

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