Low temperature plasma deposition of silicon nitride to produce ultra-reliable, high performance, low cost sealed chip-on-board (SCOB) assemblies

Plasma enhanced chemical vapor deposition (PECVD) has existed for many years in the integrated-circuit industry and has established itself as a superior method of applying various inorganic coatings to integrated circuitry on silicon wafers. The initial emphasis for developing such a coating was an attempt to find a durable film which could be deposited at a temperature which is less than the transition point of aluminum (approximately 420°C). Plasma-deposited silicon nitride deposited at less than 400°C could thus be applied to a finished integrated circuit. The silicon nitride provided mechanical protection to the soft aluminum traces during the thinning, scribing, and dicing operations used to separate the circuits into individual chips prior to assembly and packaging. Plasma-deposited silicon nitride has established itself over the years as the premier coating to act as a barrier to both moisture and mobile ions. This paper will report the details of and the results obtained with a unique plasma deposition process which deposits high quality silicon nitride films at essentially room temperature (<30°C). The films thus formed are able to be deposited on a variety of substrates including assembled chips making an ultra-reliable sealed multichip assembly without costly and thermally inefficient packages