A.R. Shakhmayeva1, E. Kazalieva2

1,2 Dagestan State Technical University (DSTU) (Makhachkala, Russia)
1 fpk12@mail.ru, 2 kazanova.em@mail.ru

The reliability of semiconductor high-power transistors largely depends on the technology of planting the transistor crystal structure on the base of the housing. Poor-quality crystal planting can lead to hidden defects forming areas with abnormally high thermal resistance under the crystal. During operation, such devices can become potentially unreliable. The purpose of this study is to improve the technology of planting a high-power transistor crystal, to increase the reliability of semiconductor high-power transistors by developing an effective technology for processing the reverse side of silicon wafers to obtain a high-quality relief of the wafer surface, metallization technology with a multilayer composition, as well as technology for planting a semiconductor high-power transistor on the base of the housing using a new solder.

All this will reduce the thermal resistance of the crystal case, increase the percentage of usable devices, increase the reliability of the device in extreme operating conditions. As a result of the research, an effective technology of sandblasting the reverse side of silicon wafers has been proposed and developed to obtain a high-quality relief of the surface of the wafers with the required surface roughness without chips, cracks and stresses.

In scientific works, metallization compositions from various metals, such as chromium-nickel (Cr-Ni), titanium-nickel (Ti-Ni), titanium-nickel-silver (Ti-Ni-Ag), have been used for good wettability of the reverse side of the transistor crystal with solder. But such compositions do not always provide reliable contact during planting due to the rapid oxidizability of the last layers of metals, especially nickel. The analysis of the comparison with the basic metallization technology with the chromium-nickel (Cr-Ni) composition showed that when the crystal is planted, voids are formed, which are the result of nickel oxidation during soldering of the crystal to the base of the housing, which leads to an increase in thermal resistance.

To eliminate these disadvantages, a four-layer metallization technology is proposed, consisting of barrier, adhesive, protective and solder layers of metals – chromium-nickel-tin-silver (Sg-Ni-Sn-Ag). As a result of studying the selected layers and modes of metal deposition on the reverse side of the transistor crystal, certain values of the thicknesses of each selected metal layer were obtained. The thickness of the metal film was measured using an Alpha-Step profilometer. The combination of these layers ensures reliable contact with the collector area when the crystal is placed on the base of the housing, which leads to a decrease in thermal resistance.

The technology of metallization with a multilayer composition of metals from chromium-nickel-tin-silver has been developed, which allows for good adhesion to the surface of the transistor crystal to eliminate the appearance of voids during landing by preventing nickel oxidation. A technology has been developed for planting a semiconductor high-power transistor on the base of the housing using import-substituting solder POS-5. There were no visible differences when soldering using imported solder and POS-5 solder at temperatures from 360° to 400 °C. There are no differences in the separation of the crystal, the destruction of the solder seam was not detected.

The proposed methods provide reliable contact with the collector region of the transistor and a high-quality fit of the crystal on the base of the housing, which leads to a decrease in thermal resistance and obtaining a high-quality device that works reliably in extreme operating conditions.

Shakhmayeva A.R., Kazalieva E. Crystal on the base of the case with improved characteristics. Science Intensive Technologies. 2023. V. 24. № 8. P. 5–11. DOI: https://doi.org/10.18127/j19998465-202308-01 (in Russian)

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