Before you learn what parametric testing is, let’s see what is involved in parametric testing. First of all, you need certain instruments such as a parametric measurement unit for parametric testing. This testing involves characterization and electrical testing of capacitors, diodes, resistors, and transistors. This does not mean that this testing is for these semiconductors only. You can use it for testing other devices as well. However, in the majority of cases, it involves semiconductors.
Why Parametric Testing?
Parametric testing is performed to determine the characteristics of the process of semiconductor manufacturing. The following are the main areas covered under parametric testing:
- Process development
- Device modeling
- Process control
Process development and device modeling take place in the following environments:
- Research and development environment
- Laboratory environment
- Pre-production environment
Process control takes place in the manufacturing environment. These are disparate environments and therefore, require a parametric measurement unit and other instruments with different requirements. You may think that this testing is performed in all stages of product development. However, this testing is not performed on the final product. You need to perform this testing on special structures. These are structures that provide you with information about the process. You will perform these tests on semiconductor wafers.
For the production test, you can locate the parametric test structures in the “streets” or the scribe of the wafer. This minimizes the wafer area these devices take up.
Where is Parametric Testing Performed?
In production, you will perform parametric tests on wafers after the completion of the wafer fabrication process. This is done before electrical short on the functional product dices. There are multiple wafers in each lot. You need to test each wafer from every lot. The goal is to collect data and store the data in a database. When you are testing every single wafer, you have a massive amount of data. This requires various software tools to store, modify and retrieve data in different formats. The most popular one is the wafer map. In this format, a scalar quantity using different colors is plotted across the wafer. These colors are used for different data value ranges. In the case of advanced processes, placing conventional test structures in the scribe lines may not be enough to characterize the process adequately.
Advanced processes are naturally complex and therefore require more testing. You may find it difficult to fit the test structures into the given area. The probe card’s tips have physical limitations. When made small, the reasonable lifetime of the probe card has also to be maintained. This limits the size of the probe pad. Arrays can solve this issue. The device shares pads and as a result, the test device to pad ratio is improved. This is much better than the conventional test device arrangements. This substantially reduces test time. However, you need to re-engineer parametric test processes.
When it comes to fast and accurate results, you need to choose the right parametric measurement unit and all other instruments required in the process.
