4PP provides a simple and direct measurement of resistance, where a probe consisting of four conductive pins contacts a conductive surface with a controlled force, with a non-conductive blocking layer between the measured conductive layer and the substrate. The standard pin configuration applies a current across the two outside pins and measures the voltage across the two inside pins. For measuring sheet resistance, the conductive layer thickness should be less than ½ the pin spacing of the probe. KLA pioneered the R50 dual configuration technique that measures the voltage on alternate pins, applying dynamic correction for edge effects and adjusting for pin spacing error. KLA offers a wide range of probe pin configurations for any conductive film or ion implant layer to optimize for surface material properties.

      EC provides a non-contact technique for measuring conductive films. A time-varying current is applied through a coil to produce a time-varying magnetic field that, when brought close to a conductive surface, induces time-varying (eddy) currents in that surface. These eddy currents in turn create their own time-varying magnetic field that couples with the probe coil to create a signal change that is proportional to the sheet resistance of the sample. KLA's unique EC solution uses a single top side probe that dynamically adjusts for the probe sample height at each measured point, which is critical to measurement accuracy and repeatability. The EC method is unaffected by probe size or surface oxidation and is ideal for softer samples that are not well suited to the 4PP contact method.

●〈 KLA 4PP and EC Solutions Demonstrate Over 99% Correlation of Each Method. 〉●

■ Metal Film Uniformity:
   Sheet resistance uniformity of metal films is critical to ensure device performance, and most metal films can be measured by both APP and EC. EC is recommended for thicker, highly conductive metal films and 4PP for thinner metal films (> 100/sq), but very high 4PP/EC correlation ensures accurate results using either method. The R50 resistivity maps highlight film uniformity, deposition quality, and other process variations. This EC map of a 2um AlC film identifies and quantifies an off-center deposition.

■ Ion Implantation Characterization:
      The 4PP probe is the standard technique for measuring ion implant processes. Mapping an ion implant after thermal annealing can identify hot and cold spots due to lamp failure, poor wafer/platen contact, or implant dose variations. For an ion implanted silicon layer, thermal annealing is required to activate the dopant ions. In the example at left, the three red (high resistance) spots indicate locations of greatest heat loss during ion (example right) implant anneal due to the three wafer supports. Temperature uniformity is critical for the annealing process, and heat loss at the wafer edge and contact points can be a serious challenge to activation uniformity.

■ Film Thickness/Resistivity/Sheet Resistance:
     Measured wafer data can be mapped as sheet resistance, film thickness, or resistivity. By entering a resistivity value for a material, the thickness can be calculated and displayed; the resistivity can be calculated if the thickness value is entered.

■ Data Acquisition and Visualization:
      RSMapper is the R50 intuitive user interface that combines data acquisition and analysis features into a single platform that can be used on the tool itself or for offline analysis. Data acquisition for measurement sites can be easily specified using a variety of coordinate layouts. The RSMapper platform can display the measurement results in either 2D or 3D for quick visualization of critical film uniformity data, as shown for the ion beam scanning issue shown above. The software easily switches between maps of individual measurement parameters and rotatable 3D profiles to deliver customized views of the process parameters. Whether measuring sheet resistance, resistivity or metal film thickness, RSMapper delivers compelling visual data