Improving Semiconductor Wafer Inspection using Master-Slave Synchronization and Multi-Channel Flash


In semiconductor manufacturing, yield is a critical parameter that drives operating cost. Improving yield in semiconductor fabs depends on in-line inspection systems. These systems are often deployed at every process step in semiconductor device manufacturing — from raw wafers and complete packaged ICs. The goal is to capture defects at a very early stage to reduce costly waste.

 

Shrinking geometries of semiconductor devices have made resolving defects on a micron and sub-micron scale a challenge for inspection systems, especially with the industry demanding shorter and shorter inspection times. This has furthered the trend towards more points of inspection systems being installed along the production line.

 

Before we delve into the actual system, you should understand the two classifications of major defects in wafers:

1)        Micro defects < 1µm

2)        Macro defects > 1µm

 

Few micro defects and nano scale defects can be measured only through time-consuming microscopy techniques, but they can be identified indirectly by macro defects. Therefore, a system that identifies Macro defects will be useful in also detecting Micro defects.

By using high-resolution line-scan machine vision cameras, today’s inspection systems are capable of detecting macro defects and therefore can be relied upon for 100% inspection of wafer production. High throughput can be realized by covering the full width of the wafer by a single acquisition. Deploying such macro defect inspection systems has a range of important advantages:

  • 100% in-line quality control / high throughput
  • Direct feedback to process engineers enabling increased yield
  • Traceability of every single wafer in different stages of the production
  • Cost effective process control
  • Fast return of investment.

 

Types of defects captured with this system include cracks, scratches, stains, chipping, saw lines, foreign particles, wafer peeling, incomplete dicing streets, and defects after dicing (chip missing).

 

Line scan technology plays a crucial role in building such macro defect scanners for wafer inspection. Basically, a line scan camera has a single row of pixels that captures visual data very quickly. As an object under inspection moves past a line scan camera, a complete image can be reconstructed in software line by line, making these cameras more effective in high-speed processing or fast-moving conveyor line applications than traditional area scan cameras.

 

For those interested in building such a line scan system for wafer inspection systems there are two features of the cameras that are essential for success:

1)        Master slave synchronization

2)        Multi-channel flash control

 

MASTER SLAVE SYNC

Covering the complete FOV (field of view) of a wafer of 300mm at a resolution of 5-15 µm/pixel requires multiple cameras to be perfectly synchronized and optically aligned. Master Slave camera synchronization ensures that multiple cameras are synchronized in such a way that each line is captured at the same moment by all cameras. This is critical for applications such as 3D measurements or when enlarging the FOV through stitching two camera images. In this mode one of the cameras is the “master” that receives the encoder signal and determines the line acquisition timing for both cameras.


Additional products to consider...