A Guide to Optical Surface Inspection for Semiconductors

The inspection of structured and unstructured wafers during the entire manufacturing process is permitted by the optical inspection system MicroProf® DI. FRT's automated defect inspection allows for maximum quality. Productivity can be increased as a result, and costs can be saved by avoiding the further processing of defective wafers.

Intelligent Defect Analysis

Intelligent defect analysis is based on advanced software that enables semiconductor manufacturers to prevent yield losses by detecting defects at an early stage. It monitors inspection result data, detects and classifies defects such as spot defects, scratches, smears and inclusions in seconds based on user-defined criteria.

It meets the defect analysis needs of semiconductor fabs and supplies the user with multiple functions for checking and displaying inspection data produced by the MicroProf® DI, and the data can also be managed and analyzed. The software also enables the user to define regions of interest (ROIs) and classify defects located within these regions.

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Image Credit: FRT

Die-to-Die

A die-based evaluation technique is utilized for structured wafers. With the "die to die" evaluation technique, an ROI is first established, which is employed to create the "golden image".

The "Golden Image" is the averaged image of all dies. Next, the "Golden Image" is taken away from the respective input image to detect any deviations from the averaged Die.

A threshold method is used to detect possible defects, marked in the input image and exported into the KLARF format. Although, there is a disadvantage with this method, if errors repeatedly occur on the dies, they are not recognized as defects.

Golden Die

The "Golden Die" evaluation technique can be employed in order to avoid this, where the individual Dies are compared with an ideal Die. However, shape deviations can be a result of an incorrect alignment between the "Golden Image" and the respective input image. This can be due to a slight rotation or shift between the "Golden Image" and the input image, so a very precise alignment is vital.

Blob Analysis

A wafer-based evaluation technique is utilized for unstructured wafers, which is based on the contrast of the pixel gray values via blob analysis. First, the established wafer structures are excluded automatically, then the defect inspection is carried out.

Defect Inspection Software

The software permits the user to optimize the recipe for gathering data for each inspection step, ensuring enhanced process control. The recipe monitors the memory for the software and reads every file with the inspection results which are written to the folder.

Next, it analyzes the error distribution of the results file according to user-defined criteria and then outputs a KLARF file where the error signatures are classified. The analyzed KLARF file may then be loaded into the inspection results database.

FRT’s defect inspection software supplies versatile processing, effective visualization, and quick generation of wafer maps, in addition to precise quantification and comprehensible documentation of defects.

The software allows the user to display different views of a chosen data set, for example wafer map and defect list with position, size, number, and grey value of the respective defects.

The software supplies a wafer map revealing the location of each defect in the chosen data set. The defects are assigned according to user-defined criteria and synchronized with the defect list.

Flexible Combination of Metrology and Inspection in One Fully Automated Measurement Tool

In the semiconductor industry, packaging technologies are quickly evolving to achieve the speed, functionality, and form factor needed for the mobile market with its state-of-the-art electronics products.

Wafer Level Packaging (WLP) is paving the way for High Volume Manufacturing (HVM), with 3D IC stack devices following right behind it. The multiple process steps mean a high level of stress on the wafers, which often causes quality problems.

In order to ensure product quality and high yield, the complexity and cost of these new packaging technologies need cost-effective inspection and metrology solutions throughout the entire process.

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Image Credit: FRT

MicroProf® DI

The optical inspection tool MicroProf® DI means it is now possible to inspect structured and unstructured wafers throughout the entire manufacturing process. By preventing the further processing of defective wafers, this enhances the yield and saves costs.

High quality can be ensured during the entire wafer production process with the MicroProf® DI. Using this approach, MicroProf® DI locates, identifies and classifies defects at the earliest possible stage and so provides the basis for high-quality wafers and later chips.

Innovative Lighting Concept and Modular Construction Convince

The innovative illumination concept of the MicroProf® DI makes a number of defect types visible and detects local failures, inclusions and other defects regardless of their position. For efficient process control the MicroProf® DI has a number of modules which can be combined flexibly on the same tool platform, covering all wafer surfaces at high throughput.

The modules include:

  • Optical inspection and classification of defects via single-shot and step module
  • Review of defects via a high-precision microscope
  • Comprehensive multi-sensor metrology with different topography and layer thickness sensors

Interferometric layer thickness sensors with infrared light source and an IR microscope are also available for the non-contact, optical, and non-destructive 2D analysis of hidden structures and inclusions in the wafer.

As it is designed to merge the boundaries between bright field macro inspection and dark field micro inspection, the MicroProf® DI supplies automated inspection of defects for quality control in the front, mid and back end in various illumination techniques.

The 2D imaging technology permits quick and reliable inspection of defects down to the micrometer range. Optionally, the setup can be extended with a high-precision review microscope.

This provides a motorized turret with bright and dark field inspection, quick autofocus, five objective positions, differential interference contrast (DIC) and fluorescence microscopy (FL). So, an inspection of defects down to the sub-µm range is possible.

The MicroProf® DI provides measurement solutions for a variety of applications by combining metrology and 2D inspection, including defect inspection on structured and unstructured wafers and wafer-level metrology for micro-bumps, RDL, overlay and through silicon via (TSV) in one single measuring tool.

Perfect for Every HVM Wafer Fab

The MicroProf® DI provides high throughput and perfectly fit in any HVM wafer fab, with a wafer handling system that is within an Equipment Front End Module (EFEM) and almost maintenance-free hardware components.

The system may be configured for 6 '', 8 '', and 12 '' wafers, both exclusively or as a bridge tool which enables the handling of two wafer sizes in one system. It can also be configured to handle non-SEMI standard wafers, like highly warped wafers (e.g. eLWB), TAIKO, wafers on tape, bonded wafers, bare and thinned wafers, and panels.

The handling unit has a single-arm robot with end effector, two load ports including mapper and RFID reader, pre-aligner and OCR reader stations if needed. The MicroProf® DI has Filter Fan Units (FFU), which ensures ISO class 3 clean room conditions in the tool.

The tool is equipped with a SECS/GEM data interface for integration into the shop floor automation. Then, measurement tasks are triggered by the host and the measurement results are automatically transferred to the fab control system.

The Benefit Of MicroProf® DI

The MicroProf® DI provides a reliable platform technology, including highly flexible software with an unrivaled level of usability. The powerful software turns defect data into feasible process control quickly, improves classification and decreases process times.

It allows users to develop and analyze new processes reliably, whilst reducing the delivery time of new products until market launch at the same time. The modular configuration of the MicroProf® DI covers the complete range of different applications in chip and wafer manufacturing including wafer qualification, incoming process qualification, research and development and process monitoring.

The MicroProf® DI meets industry demands for throughput, reliability, and accuracy by combining 2D and 3D technologies to detect defects and measure the features which are vital to today's advanced packaging technology. With maximum quality, decreased space required in manufacturing, and reduced processing times, the MicroProf® DI reaches the highest customer satisfaction.

This information has been sourced, reviewed and adapted from materials provided by FRT.

For more information on this source, please visit FRT.

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