Roughness Pad - Measurements Report  


General

  1. The following report describes the results obtained in measuring a roughness pad (AKA polishing pad) sample.
  2. The objective was to measure the roughness of the polishing pad and demonstrate Optimet’s unique capability of measuring the translucent polymer material.
  3. Two types of measurements were performed:
    1. High resolution 3D measurement of Pad roughness
    2. Repeatability test by scanning 10 times the same line on the pad
  4. The surface properties of the pad indicates that the material is translucent implying that the laser beam penetrates inside the material spreading the beam internally causing wrong measurements in most technologies available in the market such as triangulation methods.
  5. The roughness of the surface can’t be measured using traditional touch methods due to the softness and flexibility of material.
  6. In order to overcome the beam spread we inserted special optical elements on the lens allowing high accuracies and repeatable measurements.
  7. The scans were performed using a CP-10 with 25mm lens on Optimet’s laboratory demonstrator scanner as depicted in figure 1.
  8. In order to confirm the accuracy of our scan results and the structure of the material we checked the samples with a microscope and saw that the formation was as measured.



Customer requirement

  1. Measure roughness of the polishing pad.
  2. Repeatability test over 1 line of the pad.

Test Set Up

  1. The sample was put on a flat platform on the laboratory conoscan 3000 system.
  2. The scans were performed using a CP-10 with 25mm lens.
  3. The analysis was done in using Optimet’s viewer program and TrueMap (from TrueGage) program.
  4. The results were confirmed using a microscope with a micrometer scale.


Sensor parameters:
  • Type: ConoPoint-10
  • Lens: 25mm
  • Other elements: QWP
Main sensor specifications:

Lens type25mm
Measurement range (mm)1.8
Standoff (mm)18
Accuracy (µm)3

Scanning parameters:
  • Lateral resolution [X*Y]: 5μm X 5μm
  • Scanning axis: X axis
  • Measurement frequency: 9000Hz
  • Laser power: 780
  • Auto exposure: on
Scanner system:
  • Laboratory Conoscan3000

Measurement analysis

  1. The surface’s general properties are shown below. It is observed that the surface is chracterized by a numerous amount of holes and relative high roughness.
  2. The roughness of the lage pad is a bit higher than the small pad, and the holes are more noticable and are cacrachterized with a larger diameter as seen in the pictures above.
  3. The Ra of the small pad is 7-8um, and Rq is ~10um as shown in picture below.
  4. The Ra of the large pad is 8-9um, and Rq is ~11-12um as shown in picture below.
  5. One can observe the amount of holes even in the small area of about 5X5mm. The particulear hole shown in following picture shows a depth of ~47um ( blue and red lines)
  6. Using a microscope with amplification of X100 and a micrometer scale clearly shows a difference in focaus between the bottom and top of the surface of ~44um which matches the measurements with the sensor.
  7. The polymer surface is highly non uniform as can be seen when putting a little black ink on it and the difference in depth can be observed.
  8. Repeatability Test
    We performed a repeatability test by scanning the same line 10 times. The results for Ra, Rq and Rz are shown in the table below:

    from the results it is clear that the sensor is highly repeatable with STD = 0.044μm
    The Max-Min value =0.134μm

Results

  1. Requirements:
    1. Measure roughness of both samples – Accomplished.
      1. Small pad: Ra ~ 7-8um; Rz ~ 40um.
      2. Large pad: Ra ~ 8-9um; Rz ~ 45um.
    2. Measure repeatability over one line – Accomplished.
      1. STD = 0.044μm
      2. Max-Min delta =0.134μm
  2. As seen from the pictures above, the CP-10 with 25mm lens and QWP is fully capable of measuring the requested roughness and can even notice large and deep holes in the surface.

Download Roughness Pad - Measurements Report (pdf)