Laser trimming of NiCr thin film resistors II: Thin film resistors with an SiO2 protective layer

Abstract Precision resistors made of thin NiCr films on oxidized silicon substrates are coated with an SiO2 protective layer for handling protection during the production process. Laser machining of the coated resistor films by an Nd:YAG laser revealed the possibility of trimming without damaging the protective layer and with only a very small alteration in the electrical parameters of the resistors. The effect of the vaporized part of the NiCr on the protective layer, involving expansion or even bursting, is explained by a theoretical model based on plastic deformation of the protective layer. Electron probe microanalysis showed that a substantial part of the NiCr in the trimming cut is incorporated into the SiO2 of the substrate as well as the protective layer, thus rendering it electrically inoperative.

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