THEORY:

The Laser Lever Technique:

A laser is directed at the surface with a known spatial angle, and the reflected beam strikes a position sensitive photodiode.

• Measure curvature before and after deposition
• Use difference to calculate stress

The FLX Systems Measure Curvature and then Calculate Stress:

1. The FLX tools are designed to measure the shape change caused by the film deposition and calculate the corresponding film stress.
2. The stress is calculated from the curvature change caused by the addition of the film.
3. The key point is that the FLX tool measures the curvature of the wafer caused by the film deposition.
4. The film stress is calculated using elasticity equations.
5. Since stress is force normalized by area, it is a field variable, and therefore it cannot be measured directly only the effect of stress is measurable.
6. From the measurement results, the field strength is calculated from an equation.
7. The application of stress to any object will always be accompanied by some deformation, called strain.
8. The deformation can be measured, and the stress that caused the deformation can be calculated if a theory exists to relate stress to strain for the system being measured.
9. The tiny chemical or physical forces that develop in the thin film during the deposition will cause a stress in the film resulting in a slight bending of the wafer.