EXTREMELY LOW TEMPERATURE COOLING VESSEL

PURPOSE:To prevent the croock of an element bonding part, and enable the sufficient cooling of a semiconductor element, by bonding a semiconductor element to a sapphire buffer material wherein a parts fixing member composed of low expansion alloy with a specific thermal expansion coefficient and a buffer member composed of sapphire are bonded in order on koval. CONSTITUTION:A semiconductor element 21 is bonded to a sapphire plate 2 of 0.6mm thick with silver paste and the like, and the sapphire plate 2 is bonded to an INVAR plate 3 with silver paste and the like. The INVAR plate 3 is subjected to silver soldering to a kovar substrate 24. The INVAR plate 3 whose thermal expansion coefficient is less than or equal to 3X10 is sandwiched between the sapphire plate 2 and the koval substrate 24. Stress caused by the sapphire plate 2 and the INVAR plate 3 and stress caused by the Koval sub strate 24 are effectively cancelled, and the crook of an element bonding part combining the sapphire plate 2, the INVAR plate 3 and the kovar subetrate 24 can be prevented.