Metrological Step Height Verification for Cluster Processed Amorphous Substrates
Step height verification on cluster-processed amorphous substrates requires guardbanded metrology and tip-force or dispersion compensation to prevent yield loss.
Tip Force
Loading Pressure
Mechanical loads applied by a measurement probe onto a sample surface during a scan determine the degree of contact and the potential for deformation. Adjusting the tip force is a required step in stylus profilometry to ensure the probe remains in constant contact with the topography without carving a permanent track into the material. This value is typically measured in milligrams or micronewtons.
The chosen setting must be high enough to overcome the surface tension of any adsorbed moisture but low enough to remain within the elastic limit of the substrate.
Measurement Integrity
Insufficient pressure causes the needle to bounce or lose contact at high speeds, leading to false readings of peaks and valleys. Conversely, excessive force can crush the delicate structures of a circuit, such as narrow gold traces or thin dielectric layers. Finding the balance between tracking accuracy and surface protection requires knowledge of the material hardness.
Damage Threshold
Automated systems often use a feedback loop to maintain a constant load throughout the entire scan. If the force deviates from the setpoint, the vertical actuator adjusts the height to compensate. This stabilization prevents the probe from damaging the sample when it encounters a steep uphill slope or a sudden drop.