CONTRACT MANUFACTURING
shortage, manufacturers are producing wafers in large quantities. However, the supply of chips cannot be turned on and off with a switch. Multibillion-dollar wafer fabrication plants are finely tuned and run 24/7, 365 days a year. Changing the production line for a new chip product can take weeks, if not months, and adding a significant new wafer fabrication capacity can take years and billions of dollars. To keep up with demand, wafer inspection must be fast, accurate, and repeatable. Microscopes equipped with motorised stages and wafer navigation software help this work go as quickly as possible. Inspectors should look for optical microscopes that offer fast image measurement technology by combining advanced hardware and analysis software.
Choosing a microscope
The hardware you choose depends on your applications. For example, trinocular, upright microscopes are available that support 4-inch, 8-inch, and 12-inch wafers as well as various high-resolution digital cameras and infrared (IR) cameras. Together with modern image analysis software, microscopes can capture high-resolution, sub-micrometer wafer images at various locations, perform measurements, provide OK/NOK judgements, and save all the data. Some systems even
offer guaranteed measurement accuracy and repeatability so that you can be confident in the results.
Simple multiposition wafer inspection
Metrology inspections are typically performed at multiple known positions on a wafer. Automating this process greatly improves inspection efficiency. One of the most time-consuming parts of setting up the automation is programming the software to carry out the repeated inspections. When choosing metrology software, look for one that offers predefined workflows. This feature enables you to quickly and easily set up an automated inspection. Likewise, make sure the hardware you choose can locate the inspection positions quickly and accurately. Automated wafer inspections can be set up in different ways depending on the information available to you. Here are two options:
1. With a known wafer layout Since wafers are predesigned, manufacturers normally have a corresponding map layout file describing the 2D structures on different chips. This file can be used to build the wafer navigation map if you are using metrology software that can read these files. To do this,
Figure 3: Schematic of a wafer sample. Layout definition is row- and column-based using three chips (blue dots). The defined points of interest (POIs) are the red dots (left). Sample images (right) are shown on POIs
open the wafer design file in CAD software and define the points of interest on the chip. Save this information and then transfer it to your metrology software.
Users must confirm the two or three points’ locations and their focus in the software every time they load a new wafer. After, the software will drive the motorised stage to move to all predefined measurement points (red dots in Figure 2a) to capture in-focus images or perform live analysis. Figure 2b shows the individual images that the hardware and software captured. They look almost the same since the points of interest are in the same locations on different chips. Users can easily modify the positions in the original definition file and transfer the updated file to the metrology software to modify the imaging process. Make sure to choose a software vendor that will work closely with you to help adjust and review all CAD files so that the software meets your specific inspection workflow.
MARCH 2022 | ELECTRONICS TODAY 33
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46
