In order to investigate the compatibility and reliability of copper (Cu) interconnects with glass substrates with different chemical properties, we prepared copper test structures on different glass substrates and conducted biased high acceleration stress testing (HAST).
A test structure composed of crossed copper wires was fabricated on 100mm glass chips and silicon control chips with different compositions. These structures are used for conducting biased HAST experiments. According to the JESD22-A110-B standard, the conditions for the HAST test chamber are set at 130 ℃, 85% relative humidity (RH), and the test duration is 96 hours. During the testing process, a DC bias of 5V was applied to the electrode at the testing point. At least one cross finger test structure (IDT) point on each wafer is not biased to distinguish the effects of high temperature and high humidity environments from the combined effects of voltage bias stress and high temperature and high humidity environments. These unbiased test points were not included in the average leakage current before and after the HAST test.
After completing the HAST test, the wafer was subjected to another electrical test using the same testing conditions to detect leakage current through the cross finger structure. For silicon control chips, fused silica, SGW3 glass, and SGW8 glass coated with Si3N4 barrier layer, there was almost no change in the results before and after testing. However, on the SGW8 wafer without a barrier layer coating, the resistance of all IDTs significantly decreased. Under a 5V bias voltage, white substance was observed to be generated at the test site of the non passivated SGW8 glass wafer through an optical microscope. This phenomenon did not occur in test points of the same substrate type that were not biased. Other substrates did not exhibit this appearance change after undergoing HAST.
In order to determine the chemical composition of the white substance observed on the uncoated SGW8 glass, samples of each wafer type were cut perpendicular to the Cu wire, imaged using a scanning electron microscope (SEM), and chemically analyzed using energy dispersive X-ray spectroscopy (EDS). Due to the sample being prepared by cutting, the Cu wire appears to be separated from the surrounding BCB dielectric due to its ductility. The SEM image of SGW3 is shown in Figure 8. On this substrate type, no differences in glass composition were detected between the bulk substrate material and the areas near the Cu line or between fingers at the BCB/glass interface. Specifically, no Cu was observed between adjacent Cu lines.
Biased HAST and thermal cycling tests are used to evaluate the reliability of engineering glass in intermediate layer applications in two key aspects. Firstly, the reliability of copper filled TGVs on SGW3 and SGW8 substrates was verified through 1000 thermal cycles ranging from -40 ° C to 125 ° C. In the second part of reliability testing, the compatibility of copper wiring metal with different types of glass substrates was studied using the biased HAST method. In SGW3 SGW8、 Cu IDTs with a line spacing of 10 μ m were prepared on SGW8 with a 1 μ m Si3N4 barrier layer, fused silica, and silicon chips with 3k Å thermal oxide. Leakage current measurements of IDTs before and after 96 hours of bias HAST testing showed a significant decrease in resistance only on the uncoated SGW8 substrate. On other substrates, including SGW3 glass, no significant changes in leakage current were observed after HAST. Through optical detection combined with SEM/EDS analysis, it was determined that the migration of copper along the top surface of the SGW8 glass substrate is the cause of the leakage path. The silicon nitride layer provides an effective barrier to prevent mechanisms that cause Cu migration. Therefore, a barrier layer should be used between copper metallization (whether it is surface wiring metal or TGV) and glass substrates used for high CTE.

The zonglen HAST-400 high acceleration life test chamber is mainly used to evaluate the reliability of products or materials in humid environments. It is achieved by setting and creating various conditions of temperature, humidity, and pressure in a highly controlled pressure vessel, which accelerates the penetration of moisture through external protective plastic packaging and applies these stress conditions to the material body or product interior. Compared to traditional high-temperature and high humidity testing, HAST increases the pressure inside the container, enabling temperature and humidity control under conditions exceeding 100 ℃. This can accelerate the aging effects of temperature and humidity (such as migration, corrosion, insulation degradation, material aging, etc.), greatly shorten the reliability evaluation testing cycle, and save time and cost. HAST high accelerated aging testing has become a standard in certain industries, especially in products such as PCBs, semiconductors, solar energy, display panels, etc., as a fast and effective alternative to standard high-temperature and high humidity testing.
Technical specifications for the HAST-400 high acceleration life test chamber with intermediate cooling and low temperature:
Dimensions: 970mm * 710mm * 1700mm (W * D * H)
Nominal chamber volume: Ф420mm*657mm(84.4L)
Weight: 260KG
Test temperature: 105.0 ℃~133.3 ℃/100% RH
110.0℃~140.0℃/85%RH
118.0℃~150.0℃/65%RH

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