The analysis of surface structures is of great importance in many industries, such as chip/sensor manufacturing, inkjet printing or membrane production. In these industries surface analyses are used for instance as quality control, checking surface roughness or finding the root cause of defects.
As an example, one of our customers had approached us to help solve an issue with a curable resin product. The application of this product requires a very flat surface. At first, the resin was cast on a Teflon film, in order to ‘copy’ the flat surface of these films onto the resin product. By the naked eye, such a film indeed appears very flat, but surface profiling revealed that the film has depth differences of 1-1,5 micrometers (see Figure 1). A silicon wafer, a known flat substrate material, shows depth differences of just 30 nanometers (see Figure 2). Using this silicon wafer as substrate for the curable resin did result in the desired smoothness of the final product. Therefore, surface profiling enabled our customer to choose the right substrate for their product.
Figure 1: Surface profile of Teflon foil.
Figure 2: Surface profile of the silicon (Si) wafer with a line profile analysis, indicated by the pink raster. The line profile is represented in the graph.
Another example below shows a microchip, which can be found in everyday devices like laptops or smartphones. A detailed image of its complex surface profile can be used to inspect the chip for any damages or incorrect assembly. The surface images in Figure 3 were obtained by an optical surface profiling technique.
Figure 3: Surface profile in 2D and 3D of a microchip in common electronics.
Using this technique, surfaces can be analysed quickly and accurately. Surface profiling can be done optically (optical profilometry), in which case light is used to illuminate a surface. The reflected light is detected and translated into a 2D/3D profile image. However, profiling can also be performed physically (stylus profilometry), where a stylus is used to probe a surface. Both techniques are extremely sensitive, capable of measuring depth differences of less than 1 nanometer. The choice of which technique is preferred mostly depends on the sample surface. For a very soft surface, you want to choose optical profilometry, so the surface is not changed as a result of the measurement. If a surface is absorbing (almost) all light, stylus profilometry is preferred.
At PTG/e, we offer both optical and stylus profilometry, as each technique has its pros and cons (which can often be compensated by the other technique). As such, we will always decide together with our customers which technique is best suited for their samples.
Interested in optical and physical surface profiling? Please contact us, it’s our pleasure to discuss the possibilities.