==Figures of Merit==
Deposition rate, usually expressed in Å/sec, is measured at the substrate using various methods. It is set using deposition time on the sputter tools
*In sputtering the deposition rate is measured for a set power and pressure. Rates can be changed by varying the power and pressure but it then needs to be characterized for the new settings.
**Stress can be moved by varying power and pressure of the deposition.
**Heating and substrate bias can affect materials deposited on the substrate.
**Deposition rates vary greatly by material (sputtering yield) and deposition method (power supply.) In general, softer metals deposit quickly using DC while harder insulating materials will have slower deposition rates using pulsed DC or RF.
**In the ALN tool, the wafer is centered over two targets which are larger than the substrate. Uniformity can be only be adjusted using the DC supply which raises and lowers the power to the center target.
Stress is a a measure of the force that the film exhibits on itself and the substrate. It is usually measure in mega-Pascals (MPa) with positive stress being called "tensile" and negaitve stress referred to as "compressive." Stress in thin films can affect devices and substrates as well as poorly affect adhesion and other properties. In terms of deposition parameters, stress is affected by the energy and angle of the material as it strikes the substrate.
*In sputtering, stress is determined by the vertical energy of the material as it strikes the substrate.
**Lower pressure and higher power drive stress more compressive (atoms colliding with energy and "packing into" the film, driving it compressive.) High pressure and lower power do the opposite. Very high pressure can lower the absolute stress in the film but usually this is associated with high gas inclusion which means the film quality of poor.
**Substrate bias can also add energy to the incoming atoms and drive stress compressive.
Resistivity is an electrical measurement of the characteristic of the film It can be measured on electrical structures (lengths of wiring lines) or on blanket films using the four-point probe. It is expressed in many units, typically μ-ohm-cm.
is typically used to measure the quality of the film in terms of source purity or vacuum purity but it can be changed by altering the density of the film (pressure, power and bias during sputtering ) *In sputtering, step coverage is increased by creating more non- normal incident atoms **Higher pressure and lower power can help step coverage at the expense of dep rate. **Substrate Bias and Ar Etching (bias with no sputtering plasma) can sometimes be used to knock material off of via bottoms and redeposit them on sidewalls