Precision embedded thin film resistors for multichip modules (MCM-D)

A precision integral resistor process has been successfully developed using a 10 Ω/sq. tantalum nitride thin film. Although the integral resistors are overcoated by 6 μm of PECVD silicon dioxide, a precision laser trimming process was developed which is capable of trimming the embedded resistors to 50 Ω with an accuracy of better than ±0.5 Ω (1%) and with no damage to the surrounding structure. The stability of the trimmed resistors has been demonstrated and the average post-trim TCR value can be improved by up to 33%, depending upon the characteristics of the laser system. Trimmed integral resistors have also been examined by transmission electron microscope (TEM). Secondary grain growth within the trimmed resistor and spherical inclusions in the oxide near to trimmed resistor regions were observed by this analysis. As part of a reliability evaluation, the trimmed resistors were subjected to a severe manual thermal shock test over a ΔT of ~500°C without catastrophic failure