Yield Problems? Master 3D Surface Topography with 4 Methods

Designed to solve the limitations of traditional measurement tools, the Surface 3D Profiler offers non-contact, high-speed 3D scanning over large areas. It uses optical fringe projection to cast light patterns on a sample; surface height variations distort the pattern, which is then converted into height data based on known incident angles.

Easy to use, this tool automatically scans the area, height, and curvature of a sample without the need for complex pre-processing. With built-in auto-alignment and high-resolution algorithms, it improves data stability and repeatability, minimizing human interference.

The Surface 3D Profiler that iST has implemented is equipped with Fringe Projection and HDR (High Dynamic Range) scanning technology. This allows us to accurately acquire data from challenging samples, including highly reflective materials (like CoWoS and wafers), low-reflectivity materials (like black molding compounds), and even transparent samples, thanks to its built-in compensation features.

With a maximum measurement range of 300×150×70 mm and up to 25 million data points, this profiler can cover everything from small dies to large modules. It boasts impressive repeatability, achieving 0.4 μm in height and ±5 μm in width.
This Profiler is widely applied across a variety of samples, including wafers, bare dies, packages, BGA, capacitors, IC chips, passive components, CSP, PCB, PCBA, QFN, connectors, and sockets. This makes it an ideal solution for comprehensive quality control and process monitoring, from pilot runs to full-scale production lines.

WLI employs the theory of optical interference (Figure 4), i.e., spacing of constructive interference fringes equal to the fixed wave path difference, to calculate the height into a 3D topography based on surface profiling (Figure 5) which, in turn, is used to calculate surface roughness and provides nanometer-level height resolution through non-contact measurement. WLI is ideal for samples of a larger size, up to 100um or even a couple of millimeters, as it relies on optical microscope for the measuring.

WLI is most likely adopted for profiling the surface of opaque materials including metals, circuits, plastics rather than translucent ones (e.g., glass). Other analysis technology is required when the surface of the material under test cannot be applying metal plating for WLI measurement.

For example, post-acid-washed metal surfaces (300 μm² area) measured with WLI show average roughness (Ra) greater than 1 μm.

See Figure 6 for a metal surface after acid cleaning and its roughness (average greater than 1um) measured over a surface square of 300um.

AFM employs nanometer-radius silicon probe to profile samples of very flat surfaces or soft polymers (e.g., photoresist) for surface roughness measurement. It is widely adopted in micro analysis over an area of tens of microns on the surface of the wafer or glass pre- and post-cleaning, coating and etching.

In recent years, AFM has been increasingly used for surface measurement and monitoring in research related to Integrated Circuit (IC) processes such as Chemical Mechanical Polishing (CMP), Redistribution Layer (RDL), and Under Bump Metallization (UBM), both before and after their etching stages. This is crucial because abnormal roughness can lead to subsequent thin film delamination or even reliability issues.

As shown in Figure 7, the profile of a 2um square surface on PI polymers with an average roughness at around 8nm. To accurately compare its pre- and post-roughness, a non-destructive measurement method is essential. While AFM (Atomic Force Microscopy) provides the necessary measurement capabilities for such nanoscale features, the device must also be able to accommodate samples larger than 300mm, specifically for measuring 12-inch wafers.