Sulfur corrodes silver metal in a continuous reaction. This corrosion is also found in semiconductor industry processes for the application of silver into Backside Grinding & Backside Metal (BGBM). In this paper two experiments were conducted for the sulfide corrosion behavior in a Circuit Probing (CP) clean room environment. They were Mixed Flowing Gas (MFG) and clean room environment exposure test. The MFG test of this research was conducted in a testing chamber with temperature, relative humidity, and concentration of H2S were carefully controlled and monitored. The MFG test conditions included the test temperature of 25°C, relative humidity of 75 %, and H 2 S gas concentration of 10 ppb. And the MFG tests lasted for over 72 hours. The X-ray photoelectron spectroscopy (XPS) was used to analyze the elements composition and Ag 2 S film thickness of the MFG test samples. The second test of this research was the direct exposure experiment. The silicon samples deposited with appropriate silver layer thickness were exposed in CP fab clean room environment with H 2 S concentration well monitored. The XPS analysis results of the corresponding exposure test samples indicated that the Ag 2 S contamination would continue to develop and wouldn't saturate. This would be indicative for the management of Ag 2 S contamination control. The results of MFG and Exposure test were help for Ardentec to setup Ag 2 S corrosion methodology. All the managements were applied into daily operation of the BGBM semiconductor products.

Circuit edit (CE) workflows are well established for FIB energies of 30kV and above. The small spot size associated with such energies provides good milling acuity and imaging resolution needed for advanced CE applications. However, with the introduction of FinFET transistors and decreasing technology nodes, the dramatic reduction in STI to gate distance reduction poses some challenges to circuit editing at these high energies. These include transistor performance degradation due to Ga+ implantation as well as significant lateral scattering beyond the Node Access Hole (NAH) as defined by the pattern. In addition, the relatively fast milling speeds may not give enough control to the user to endpoint at the appropriate layer. In this paper, a group of FinFET transistors on a special test chip was edited with the Ga beam at different energies. Transistor performances were then characterized to evaluate any degradation. The resulting characterization revealed how the transistor performance was affected by the injected ion beams and provided a guideline for the low-kV circuit edit workflow. A novel low-kV FIB workflow was proposed to minimize the transistor damage and maintain the IC functionality after the CE process. The workflow was applied to a challenging CE problem on a 5nm FinFET device. This task included step by step backside delayering at 5kV, preparing the sample for the final circuit edit operation at Metal-1. Working at low landing energies (e.g. 5kV) lowers subsurface damage and reduces etching speed, but with trade offs including lower image resolution, milling acuity, sputtering yield and signal to noise ratio (SNR). However, the consequences of these effects can be mitigated by use of appropriate chemistries with closed loop delivery control and extremely low beam currents (≤1pA), in concert with double aperture beam shaping to minimize beam tails. On the 5nm FinFET device, we demonstrate good delayering control by optimization of beam currents, and gas delivery on the Centrios HX circuit edit system from Thermo Scientific.

By using fluorocarbon gases for aluminum (Al) pad open plasma etch, the pad inevitably has a thin surface remnant layer of Al-oxyfluoride (AlOF) by-product. This layer is chemically stable and does not directly cause issues in chip testing or wire bonding. This is true until open Al pads were exposed to a humid environment causing pad corrosion over time. The F-assisted corrosion created so-called black mushroom (BM) defects on the Al pads according to the defects appearance, resulting in the non-stick pads for wire bonding. Experimental tests were carried out to induce the Al pad corrosion via placing random fab-out wafers in a cassette pod hosting about 90% RH over a period up to a week. Optical imaging revealed BMs nucleated, primarily at Al grain boundaries. BMs were found all to be composed of O, F, and Al. In the cross section, BMs were shown to have separations of F-rich region next to Al and O-rich region towards the surface. In addition, BMs were composed of small crystallites and were porous. The former indicates an ionic bonding involving in O, F, and Al. The latter indicates the corrosion generated gaseous byproduct. A moisture (H 2 O) involved cyclic chemical reaction incorporating these analyses has been formulated. Factors to prevent BM formation were discussed.

Copper ball bonding is the most widely used interconnection method in microelectronic packages. It has enabled many modern technologies, but the bond can fail due to corrosion. This paper concerns quantitative analyses of corrosion products of passing and failing copper ball bonds, and correlation with the corrosion thermodynamics. The role each element in the aluminum-copper intermetallic compound plays during crevice corrosion is described, and relative abundances of the oxidized elements are estimated. New insights regarding mechanisms of the highest vulnerability to corrosion attack in the thin film-stack across the bond are presented. Limited data indicate the same corrosion mechanisms for Au ball bonds.

Despite modern battery management systems, rechargeable lithium-ion batteries can be subjected to varying levels of overdischarge during transport, storage and use in the field. While the general degradation risks associated with overdischarge are well documented, there are not widely accepted cell voltages at which the onset of such degradation processes occur. In this work, reference electrode testing is performed to study a variety of commercial lithium-ion cells during varying levels of overdischarge. Common trends between different types of lithium-ion cells are first identified, and the resulting implications are discussed.

Fan Out - Panel Level Packaging (FO-PLP) has redistribution layers (RDLs) which connect IC to a substrate. And each layer in the RDLs is connected through copper micro-vias. Viarelated defects including via separation are very critical because they can escape from electrical test and be found in the field. So many cleaning methods have been developed to keep the target pad surface free of oxides or organic contamination before forming vias. In this paper, we present a via separation case caused by alkaline cleaning introduced before seed metal deposition for electroplating of copper. We investigated the cause by analyzing the microstructure and chemical composition using a focused ion beam (FIB) and a transmission electron microscope (TEM) equipped with an energy dispersive spectrometer (EDS). Via separation, interestingly occurred at the interface between the seed Ti and the seed Cu not the interface between the seed Ti and the target pad..Cu surface which is known to be weak. We suggest a mechanism that structural imperfections at the outer rim of via bottom and galvanic couple of titanium and copper are involved in the separation of vias. Since two dissimilar metals of Ti and Cu are in direct contact, galvanic corrosion can occur in the presence of alkaline solution and discontinuities in the seed Ti layer. We found that galvanic corrosion in the studied system can be further complicated by the existence of copper oxide and titanium oxide as well as Cu and Ti.

This paper describes the investigation of donut-shaped probe marker discolorations found on Al bondpads. Based on SEM/EDS, TEM/EELS, and Auger analysis, the corrosion product is a combination of aluminum, fluorine, and oxygen, implying that the discolorations are due to the presence of fluorine. Highly accelerated stress tests simulating one year of storage in air resulted in no new or worsening discolorations in the affected chips. In order to identify the exact cause of the fluorine-induced corrosion, the authors developed an automated inspection system that scans an entire wafer, recording and quantifying image contrast and brightness variations associated with discolorations. Dark field TEM images reveal thickness variations of up to 5 nm in the corrosion film, and EELS line scan data show the corresponding compositional distributions. The findings indicate that fluorine-containing gases used in upstream processes leave residues behind that are driven in to the Al bondpads by probe-tip forces and activated by the electric field generated during CP testing. The knowledge acquired has proven helpful in managing the problem.

In wafer fabrication (Fab), Fluorine (F) based gases are used for Al bondpad opening process. Thus, even on a regular Al bondpad, there exists a low level of F contamination. However, the F level has to be controlled at a lower level. If the F level is higher than the control/spec limits, it could cause F-induced corrosion and Al-F defects, resulting in pad discoloration and NSOP problems. In our previous studies [1-5], the theories, characteristics, chemical and physical failure mechanisms and the root causes of the F-induced corrosion and Al-F defects on Al bondpads have been studied. In this paper, we further study F-induced corrosion and propose to establish an Auger monitoring system so as to monitor the F contamination level on Al bondpads in wafer fabrication. Auger monitoring frequency, sample preparation, wafer life, Auger analysis points, control/spec limits and OOC/OOS quality control procedures are also discussed.

Contamination by particles is one of the major causes of failures in integrated circuits. In some cases, particles may absorb moisture leading to electrochemical migration, dendrite growth, and electrical leakage and short failures. This work presents two case studies of particle induced corrosion of copper wire bond that resulted in an electrical failure. In the first case, adjacent pin resistive short failures were found to fail due to corrosion and electrochemical migration at wires that were in contact with calcium chloride particles. Analysis showed that the highly hygroscopic calcium chloride particles absorbed moisture and resulted in corrosion and electrochemical migration of the copper wires. For the second case, an electrical open failure after temperature cycle reliability test was found to be due to an organophosphorus particle being in contact with the wire.

Recently a phenomenon has been found that shows different corrosion rates over Al bond pad regardless of different densities of Cl, F components on Al bond pads in different products. According to the results of analysis, the products showed different corrosion rates for different etch conditions of the bond pad opening. For the cause analysis, we conducted a cross-sectional profile comparison between two products with Al bond pads. Based on the result of comparison, we discovered that the side wall profile of the Al bond pad is affected by the etch conditions of the bond pad opening. In some severe cases, it was observed that a small void was formed between the side wall and Al bond pad. Under moist conditions, this void provided moisture between Al bond pad and TiN barrier metal that the electricity contacted. Through this study, we could conclude that the moisture in the void between Al bond pad and TiN barrier metal may create a galvanic corrosive condition.

In the authors' previous papers, the failure mechanism and elimination solutions of galvanic corrosion (Al-Cu cell) on microchip Al bondpads in the Al process (0.18un and above) have been studied [1-2]. In this paper, the authors will further study the failure mechanism and root cause of galvanic corrosion (Al-Cu cell) on microchip Al bondpads in the Cu process (0.13um and below) with Ta barrier metal. Based on our results, the root cause of galvanic corrosion (Al-Cu cell) in the Al process is only one way and Al-Cu cell is from Al alloy (Al + 0.5%Cu) on Al bondpads. However, in the Cu process it may be from two ways and Al-Cu cell can be from both Al alloy (Al + 0.5%Cu) on Al bondpads and the Cu metal layer below the barrier metal Ta when Ta has weak points or pinhole. As such, the pinhole defects on Al bondpad caused by galvanic corrosion (Al-Cu cell) in the Cu process might be more serious than that in the Al process. In this paper, TEM is used for root cause identification. Based on the TEM results, galvanic corrosion was due to the weak point/pinhole at the Ta barrier metal layer and Al-Cu diffusion.

Cu wires were bonded to AlSi (1%) pads, subsequently encapsulated and subjected to uHAST (un-biased Highly Accelerated Stress Test, 130 °C and 85% relative humidity). After the test, a pair of bonding interfaces associated with a failing contact resistance and a passing contact resistance were analyzed and compared, with transmission electron microscopy (TEM), electron diffraction, and energy-dispersive spectroscopy (EDS). The data suggested the corrosion rates were higher for the more Cu-rich Cu-Al intermetallics (IMC) in the failing sample. The corrosion was investigated with factors including electromotive force (EMF), self-passivation of Al, thickness and homogeneity of the Al-oxide on the IMC, ratio of the Cu-to-Al surface areas exposed to the electrolyte for an IMC taken into account. The preferential corrosion observed for the Cu-rich IMC is attributed to the high ratios of the surface areas of the cathode and anode that were exposed to the electrolyte, and the passivation oxide of Al with the lower homogeneity. The corrosion of the Cu-Al IMC is just a manifestation of the well-known phenomenon of dealloying. With the understanding of the corrosion mechanisms, prohibiting the formation of Cu-rich IMCs is expected be an approach to improve the corrosion resistance of the wire bonding.

In this study, a comprehensive investigation of the Ag-Al bond degradation mechanism in an electrically failed module using the argon ion milling, scanning electron microscopy (SEM), dual beam focused ion beam-SEM, scanning transmission electron microscopy energy dispersive x-ray spectroscopy, and time-of-flight secondary ion mass spectrometry is reported. It is found that the bond degradation is due to the galvanic corrosion in the Ag-Al bonding area. Specific attention is given to the information of microstructures, elements, and corrosive ions in the degraded bond. In this study, it is believed that the Ag-Al bond degradation is highly related to the packaging designs.

In wafer fabrication, Fluorine (F) contamination may cause fluorine-induced corrosion and defects on microchip Aluminum (Al) bondpads, resulting in bondpad discoloration or non-stick on pads (NSOP). Auger Electron Spectroscopy (AES) is employed for measurements of the fluorine level on the Al bondpads. From a Process control limit and a specification limit perspective, it is necessary to establish a control limit to enable process monitor reasons. Control limits are typically lower than the specification limits which are related to bondpad quality. The bondpad quality affects the die bondability. This paper proposes a simulation method to determine the specification limit of Fluorine and a Shelf Lifetime Accelerated Test (SLAT) for process monitoring. Wafers with different F levels were selected to perform SLAT with high temperature and high relative humidity tests for a fixed duration to simulate a one year wafer storage condition. The results of these simulation results agree with published values. If the F level on bondpad surfaces was less than 6.0 atomic percent (at%), then no F induced corrosion on the bond pads was observed by AES. Similarly, if the F level on bond pad surfaces was higher than 6.0 atomic per cent (at%) then AES measured F induced corrosion was observed.

This paper presents a quick, reliable, and fully quantitative method of measuring the intermetallic coverage of copper to aluminium bonding at time zero and post reliability stressing. This method is currently used in select manufacturing quality control processes, as well as during product release procedures. By applying this measurement method after various life-tests, it has been possible to collect information on degradation in the copper aluminium system which is currently being used to make a model of the corrosion mechanism in the copper aluminium system.

Lead-free manufacturing regulations, reduction in circuit board feature sizes and the miniaturization of components to improve hardware performance have combined to make data center IT equipment more prone to attack by corrosive contaminants. Manufacturers are under pressure to control contamination in the data center environment and maintaining acceptable limits is now critical to the continued reliable operation of datacom and IT equipment. This paper will discuss ongoing reliability issues with electronic equipment in data centers and will present updates on ongoing contamination concerns, standards activities, and case studies from several different locations illustrating the successful application of contamination assessment, control, and monitoring programs to eliminate electronic equipment failures.

A case study of Fluorine (F)-outgassing is presented in this paper that caused the corrosion of Aluminum bond pad. It will be shown that the source of F-contamination is not the typical residue left behind after the passivation etch with Fluorine-based gas chemistry and the subsequent removal of the etch polymer generated with solvent (chemical) clean. Rather, it is introduced as a result of F-outgas over a period of time from the intermetallic dielectric (IMD) film, fluorosilicate glass (FSG), during the post-fab wafer storage. The methodology used in our failure analysis (FA) lab to identify and characterize this type of failure mode is presented in the paper.

Cu needs a higher level of ultrasound combined with bonding force to be bonded to the Al pad properly, not just because Cu is harder than Au, but it is also harder to initiate intermetallic compounds (IMC) formation during bonding. This increases the chances of damaging the metal/low k stack under the bondpad. This paper presents a fundamental study of IMC as well as one example of a failure mode of Cu/Al bonded devices, all based on detailed analysis using scanning electron microscopy, scanning transmission electron microscopy, energy dispersive spectrometers, and transmission electron microscopy. It presents a case study showing a corrosion mechanism of Cu/Al ballbond after 168hr UHAST stress. It is observed that all Cu9Al4 was consumed, while very little copper aluminide remained after 168 hours of UHAST stressing.

Fluorine-induced corrosion is one of the well-known failure modes of Al bondpad leading to non-stick on pad (NSOP) issues. Exposure to moisture (H2O) and atmosphere (O2) play an important role in determining the shape and size of the Al-F corrosion defects on the Al bondpad surface. In this paper, we will propose a laboratory simulation methodology that can reproduce F-induced defects observed either at the wafer fab or the assembly house. The methodology, known as SLAT ( S helf L ifetime A cceleration T est), is used to study the relationship between the F-corrosion defects and the relative temperature (T) and humidity (RH %). It is observed that Al-F corrosion defects simulated are similar to the real defects found in wafer fab and assembly house in our previous studies. A relatively higher T and lower RH % results in the formation of the “crystal-like” defects, but if a relatively lower T and higher RH % condition is used, the “oxide-like” defects were formed. In this paper, we will compare the simulation results to the real defects found in the previous cases and discuss the failure mechanism. From the present study, the importance of controlling T and RH % during wafer storage to eliminate F-induced defects will be highlighted.

Degradation of contact mating surfaces can produce a wide range of problems including intermittent failures and also full functional failures in all computer systems. This paper discusses the complexity involved with investigating the failure mechanism and root cause for intermittent memory failures on a product from end customers. Also discussed in detail is the approach of fault isolation followed by hypothesis development & physical analysis to arrive at root cause of failure. Fault isolation was achieved through register probing. Three major hypotheses were put forth namely plastic debris, misalignment and contact area issues. The physical analysis data collected through optical inspection, 2D x-ray, cross section and SEM analysis coupled with EDX to prove or disprove the hypotheses, revealed contact area corrosion in the form of nickel oxide. Contributors like gold plating thickness and plating porosity of the mating surfaces was verified to be not an issue in this case. Further analysis on the connector pins, memory modules and the contact area indicated damage to the connector pins leading to nickel exposure. The root cause for damage to the pins was analyzed to be a result of memory modules being inserted at an angle. Further studies are planned to look into design issues of connectors and memory modules to minimize damage to the contact area.