Application Note | Thin Film Thickness
Wafer Coating Thickness Measurement Using 3D Profilometry
Coating Thickness as a Step Height, Plus Areal Roughness, from One Non-Contact Scan
Research & Experimental Testing
Jocelyn Esparza
Visual Design & Editorial
Andrew Shore
Introduction
Silicon wafers are widely used in the making of integrated circuits and other micro devices used in a vast number of industries. A constant demand for thinner and smoother wafers and wafer coatings makes the NANOVEA 3D non-contact Profilometer a great tool to quantify coating thickness and roughness of just about any surface. The measurements in this article were taken from a coated wafer sample in order to demonstrate the capabilities of our 3D Non-Contact Profilometer.
Importance of 3D Non-Contact Profilometry for Step Height and Roughness Measurement
Unlike other techniques such as touch probes or interferometry, the 3D Non-Contact Profilometer, using axial chromatism, can measure nearly any surface, sample sizes can vary widely due to open staging and there is no sample preparation needed. Nano through macro range is obtained during surface profile measurement with zero influence from sample reflectivity or absorption, has advanced ability to measure high surface angles and there is no software manipulation of results. Easily measure any material: transparent, opaque, specular, diffusive, polished, rough etc.
The technique of the Non-Contact Profilometer provides an ideal, broad and user friendly capability to maximize surface studies when step height will be needed; along with the benefits of combined 2D & 3D capability.
ℹ️ Learn more about surface profiling lab services.
Measurement Objective
In this application the NANOVEA PS50 is used to measure the step-height of a silicon wafer coating and its roughness. Assuming that the coating thickness is relatively uniform, the coating was removed to expose the substrate in order to measure it as the reference plane. The height of the coating will be measured to characterize the thickness and roughness of the coating.
NANOVEA PS50 Compact
Optical Profilometer
Results: 3D Surface
The 3D View and False Color View of the selected area on the sample surface after the form has been removed. It provides users a straightforward tool to directly observe the distribution and morphology of the surface features from different angles.
Results: 2D Surface Analysis
The surface features can be quantified in numerous ways using built-in software tools as shown in the following figures as examples. It can be observed that the average coating thickness is 3.532 µm and has an average surface roughness of 0.111 µm.
| Parameter (µm) | Step 1 | Step 2 |
|---|---|---|
| Maximum height | 3.942 | 4.122 |
| Mean height | 3.543 | 3.340 |
Table 1: Profile step heights (from Fig. 4).
| ISO 25178 height parameter | Value |
|---|---|
| Sa | 0.1113 µm |
| Sq | 0.1417 µm |
| Sp | 1.175 µm |
| Sv | 1.515 µm |
| Sz | 2.690 µm |
| Ssk | 0.1406 |
| Sku | 4.189 |
Table 2: Areal roughness of the coating surface (from Fig. 5).
Conclusion
In this application, we have shown how the NANOVEA 3D Non-Contact Profilometer is capable of precisely characterizing the height and surface roughness of a metal coating. The data shows the coating to have a mean step-height of 3.532 µm and average surface roughness of 0.111 µm. The data shown here represents only a portion of the calculations available in the analysis software.
Frequently Asked Questions About Wafer Coating Thickness Measurement
How can a profilometer measure coating thickness?
By measuring a step height. Assuming the coating is relatively uniform, part of it is removed to expose the substrate as a reference plane, and the height of the coating above it gives the thickness.
What thickness and roughness did the wafer coating show?
The area step height analysis gave 3.485 µm, and two profile steps had mean heights of 3.543 and 3.340 µm. The coating surface had an Sa of 0.1113 µm.
Why non-contact axial chromatism instead of a stylus or interferometer?
It measures nearly any surface with no sample preparation, from nano to macro range, with no influence from reflectivity or absorption, steep angles measurable, and no software manipulation of results.
Can both 2D and 3D analysis be done?
Yes. The same scan gives 3D and false-color views, an area step height between two planes, profile step heights along an extracted line and ISO 25178 areal roughness.
Which roughness parameters were measured?
ISO 25178 height parameters: Sa 0.1113 µm, Sq 0.1417 µm, Sp 1.175 µm, Sv 1.515 µm, Sz 2.690 µm, Ssk 0.1406 and Sku 4.189.
Which instrument was used?
The NANOVEA PS50 3D non-contact profilometer.
