Correlation Mechanics for Transferred Analog Block Yield Distributions across Secondary Wafer Foundries
Transferring analog blocks across secondary foundries requires mapping PCM covariance matrices to maintain targeted circuit yield distributions.
Poly-Silicon Sheet Resistance
Meaning
Electrical resistance of a thin film of polycrystalline silicon measured in ohms per square provides a metric for the conductivity of gates and local interconnects. This poly-silicon sheet resistance is sensitive to the concentration of dopant atoms and the grain size of the silicon crystals. It determines the signal delay of the paths within the transistor level of the chip.
The measurement is independent of the size of the square being measured.
Doping Influence
Implantation of phosphorus or boron atoms into the film lowers the resistivity of the material. After the poly-silicon sheet resistance is set by the implant dose, a high temperature anneal is required to activate the dopants. Insufficient activation leads to higher resistance.
Thermal Treatment
Rapid thermal processing cycles adjust the grain boundaries of the film to optimize carrier mobility. Changes in the duration of this heat step cause the poly-silicon sheet resistance to fluctuate across the wafer. Consistent heating is necessary for uniform electrical performance.
Patterning Precision
Etching the poly-silicon into narrow lines increases the effective resistance of the wire. If the poly-silicon sheet resistance is not tightly controlled, the timing of different logic paths will vary. This variation can lead to race conditions in synchronous circuits.