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Li Xiaomin
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Proceedings Papers
ISTFA2022, ISTFA 2022: Conference Proceedings from the 48th International Symposium for Testing and Failure Analysis, 365-368, October 30–November 3, 2022,
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In wafer fabrication, silicon defects on the substrate directly affect the yield of the wafer. In this paper, we will study and discuss a chemical delayering and delineate method for silicon defects in wafer fabrication using Secco etch. It is well-known that during delayering process of wafer, the removal of polysilicon (Poly-Si) layer is very difficult, especially for the wide-layer polysilicon (Poly-Si) which is difficult to completely remove with HF acid solution. We introduce a chemical recipe to fast delayer polysilicon layer completely before delineating silicon defects on silicon substrate using Secco etch. Those skilled in the art could be experiment within half an hour to get analysis results. It saves time and improves operational efficiency. Moreover, based on the experimental results we think that it is possible to identify the root cause according to the shapes of silicon defects using Secco etch.
Proceedings Papers
ISTFA2022, ISTFA 2022: Conference Proceedings from the 48th International Symposium for Testing and Failure Analysis, 374-377, October 30–November 3, 2022,
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Currently, wire bonding is still the dominant interconnection mode in microelectronic packaging, and epoxy molding compound (EMC) is the major encapsulant material. Normally EMC contains chlorine (Cl) and sulfur (S) ions. It is important to understand the control limit of Cl and S in the EMC to ensure good Au wire bond reliability. This paper discussed the influences of Cl and S on the Au wire bond. Different contents of Cl and S were purposely added into the EMC. Accelerated reliability tests were performed to understand the effects of Cl, S and their contents on the Au wire bond reliability. Failure analysis has been conducted to study the failure mechanism. It is found that Cl reacted with IMCs under humid environment. Cl also caused wire bond failure in HTS test without moisture. On the other hand, the results showed that S was not a corrosive ion. It was also not a catalyst to the Au bond corrosion. Whilst, high content of S remain on the bond pad hindered the IMCs formation and caused earlier failure of the wire bond.
Proceedings Papers
ISTFA2015, ISTFA 2015: Conference Proceedings from the 41st International Symposium for Testing and Failure Analysis, 278-281, November 1–5, 2015,
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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.
Proceedings Papers
ISTFA2015, ISTFA 2015: Conference Proceedings from the 41st International Symposium for Testing and Failure Analysis, 295-297, November 1–5, 2015,
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In authors’ previous paper, an OSAT [Optical, SEM (Scanning Electron Microscopy), Auger (Auger Electron Spectroscopy) and TEM (Transmission Electron Microscopy)] methodology was developed for qualification of microchip aluminum (Al) bondpads. Using the OSAT methodology, one can qualify microchip Al bondpads. In this paper, we will further study the NSOP (Non-Stick On Pad) problem on microchip Al bondpads. A new qualification methodology, OSSD [(Optical, SEM, and Surface and Depth profiling X-ray Photoelectron Spectroscopy (XPS)] will be proposed, in which XPS surface analysis is used to check the contamination level of fluorine and carbon on bondpad surfaces instead of Auger analysis. XPS depth profiling analysis will also be used to measure Al oxide thickness instead of TEM analysis. By using OSSD, Al bondpads can be qualified with both reduced costs and shortened turnaround times versus OSAT.
Proceedings Papers
ISTFA2014, ISTFA 2014: Conference Proceedings from the 40th International Symposium for Testing and Failure Analysis, 215-217, November 9–13, 2014,
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It is well-known that underetch material, contamination, particle, pinholes and corrosion-induced defects on microchip Al bondpads will cause non-stick on pads (NSOP) issues. In this paper, the authors will further study NSOP problem and introduce one more NSOP failure mechanism due to Cu diffusion caused by poor Ta barrier metal. Based on our failure analysis results, the NSOP issue was not due to the assembly process, but due to the wafer fabrication. The failure mechanism might be that the barrier metal Ta was with pinholes, which caused Cu diffused out to the top Al layer, and then formed the “Bump-like” Cu defects and resulted in NSOP on Al bondpads during assembly process.