> (1) what range of stress can cause reliability issues in microelectronics
> thin film ? Is 500 MPa in a 0.5 um thick metal thin film a lot of stress to
> cause undesired failure ?

Sorry, but the answer is not straight and easy.
Roughly, <100Mpa is considered "low" , >1000MPa "high" stress.

> (2) does compressive stress cause yielding like tensile stress does ?

Depends on the material. In Aluminum, e.g., it leads to hillock growth.

best regards,
klaus
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Klaus Beschorner
Metron Technology Europe, PVD (Eclipse) Process Manager
Drosselweg 6,71120 Grafenau,Germany. Tel +49-7033-45683