Principle of the OBIRCH approach is as follows: By scanning with a laser beam on the IC surface, part of laser energy is absorbed by the IC and converted into heat, rendering temperature change in the scanned area. In case metal wires in the IC consist of defects or voids, the heat conduction in the place nearby will differ from that in normal areas, resulting in a different temperature change in the area, which in turn causes an ohmic change ΔR in the metal.
If a constant voltage is added to the bonding wire while scanning, its current change can be established as ΔI= (ΔR/R)I. By associating ohmic change (cause by heat) with current change based on this relationship, and converting the value of current change into brightness change of pixels in the image and recording the position, the pixel positions can then be overlapped with the positions scanned by the laser beam where the current changes.
This produces an OBIRCH image that locates the defect. OBIRCH is normally used for high and low resistance analyses inside the chip, and current leak analysis of a circuit. OBIRCH enables effective spotting of circuit defects such as cavities in metal wires, cavities under vias, high-resistance area at bottom of vias, etc., and detects short or current leak successfully as well.
OBIRCH is applicable to detect the following defects:
Metal short or metal bridge.
Gate oxide pin hole.
Active area short.
Poly short or contact spiking.
Well short or source / drain short.
Higher via / contact / metal / poly / AA resistance fail.
Any IC failure (short or bridge or leakage or high resistance) associated with a differential material or its thickness.
Products with unstable output current are not suitable for OBIRCH detection. Power to the tested circuit must be supplied by this machine.
|Front-side OBIRCH spot ||
|Back-side OBIRCH spot || |