A Brief Introduction To Parametric Testing

Automated test systems and research & development labs use Parametric measurement unit PPMU and other parametric measurement instruments to characterize and test electrochemical cells, semiconductors, and electronic devices. You can also use these instruments to test the electronic properties of a material. When you apply current or voltage, these instruments take accurate current and voltage measurements. Depending on the device under test, you need digital isolators, switch power controllers, high-performance amplifiers, constant current and constant voltage linear controllers, D/A and A/D converters and Parametric measurement unit (PMU). 

Designers require a range of products to optimize for speed, density and precision at different performance levels. In addition to electrical testing, general parametric testing involves characterization of semiconductor devices including capacitors, transistors, diodes and resistors. However, parametric measurement unit (PMU) and other systems are also used to test other types of devices.

Some people also use the term “DC” for parametric testing. However, this term does not accurately describe parametric testing. Some source/monitor units may take milliseconds to seconds to measure. Most standard functional testers measure in nanosecond or even picosecond range. 

When it comes to testing devices, we need speed and accuracy. You should be able to take fast parametric measurements. The importance of extremely fast measurement will continue to increase in the future as well. It’s because transistor lithographies are shrinking. The industry is incorporating exotic materials into semiconductor processes. 

Reliability testing is one of the subcategories of parametric testing. This testing relies on Arrhenius equation. This well known equation expresses a chemical reaction’s rate constant. In reliable testing, large voltages and/or currents are applied to devices to lower activation energy value and increase failure mechanism rate. Testers also increase temperature. When the failure mechanism occurs, under operating conditions, this can extrapolate expected failure rate using a variety of statistical and mathematical techniques. 

Why Perform Parametric Testing  

Parametric testing determines semiconductor manufacturing process’s characteristics. This testing covers the following main areas: 

  • Process control  
  • Device modelling
  • Process development

Device modelling and process development are covered in the following environments: 

  • Laboratory 
  • Research & development 
  • Pre-production environment    

Manufacturing environment is required for process control. Different environments have different parametric equipment requirements. The final product does not always go through parametric test. The purpose of this testing is to produce information about the process. It requires specially designed structures. Parametric testers test semiconductor wafers. In order to minimize the semiconductor wafer area the device takes, parametric test structures in production test is located in “streets” of the wafer or the scribe lanes. 

Wafers are subjected to parametric tests in production after the completion of the wafer fabrication process. Each wafer in the lot is tested to collect and store data in database. Testing creates a massive amount of data. An array of software tools manipulate data into different formats. Wafer map is one of the popular formats. Due to innate complexity, more testing is required for advanced processes. 

To ensure that you get accurate testing results, you need to use the right parametric measurement unit (PPMU) and other instruments.