Semiconductor reliability testing is an essential part of the research and development of these devices. The idea behind reliability tests is to cause a semiconductor device to fail on purpose, thereby allowing researchers to discover any potential weaknesses. This can lead to improvements in the manufacturing process, allowing those in the semiconductor industry to craft better and more robust products that last.
So let’s find out why testing for semiconductor device reliability is important, the many methods it can be done including the technology required, and why its an important part of the manufacturing process.
Why It’s Important To Test For The Reliability Of Semiconductor Devices
Semiconductor devices or integrated circuits are susceptible to contamination and manufacturing defects throughout the production process. From the formation of Silicon ingots, through the various stages of wafer processing, and up to the finished microchip at the very end, there could be various factors that compromise the quality of the final product. If anything goes wrong, it is highly impractical to repair or fix the compromised product to work as intended.
This is further complicated by the new materials and processes that are introduced all the time as a result of the rapid advances in the semiconductor field. Furthermore, factories need to achieve economies of scale to be profitable, and manufacturing is done in extremely large volumes. Due to the high demand for microchips for use in everything from your smartphone to vital medical equipment, it is very costly to make big changes or slow down production.
As a result, to maintain supply at a pace that can match the global demand, and ensure a high level of quality in the product, it is very important to reduce any variation in the production process. Reliability testing is what allows semiconductor manufacturers to find what the most optimal conditions are for production, and to reduce stress factors that can introduce reliability issues in the finished product.
Factors That Cause Reliability Issues
The reliability of a semiconductor device can be affected by environmental conditions like the temperature or humidity of the factory, contaminants like dust, impurities present in Silicon crystals, and due to issues inherent in the production process itself. Manufacturers conduct their most sensitive processes within semiconductor cleanrooms which can help maintain the most optimal environmental conditions and reduce the chance of contamination. Find out more about cleanrooms at What Is a Semiconductor Clean Room and What Is It For?
Manufacturing defects like cracks and impurities can be identified through the use of specially designed semiconductor microscopes at various stages of production. To learn more about the different types of cameras and microscopes used in the inspection of wafers, read What Does A Semiconductor Microscope Do?
While methods like the use of cleanrooms and microscopic camera technology can definitely help improve the reliability of a semiconductor device, other factors come into play when the device is being put to use. These are voltage, temperature, humidity, and electrostatic discharge to name a few. Reliability testing of semiconductors involves subjecting the device under study to various extremes of voltages, temperatures, and humidities to find the points of failure.
The Types Of Reliability Testing For Semiconductor Devices
Since even consumer devices are made to last at least a few years with normal use, researchers cannot wait that long for a failure to get results. Therefore reliability is evaluated through accelerated testing, where applied stresses on the device are enhanced or accelerated to obtain faster results. Accelerants are usually voltage, current, temperature, and humidity. Accelerated testing does not alter the physics of the failure, but simply shifts the time taken to obtain results.
This allows manufacturers to understand what the failure mechanisms for their devices are, helping them make improvements to their production line when necessary. This is an iterative process, with continuous reliability testing followed by changes to the manufacturing methods.
High-Temperature Operating Life (HTOL)
In HTOL tests, integrated circuits are subject to voltages and high temperatures over an extended period while under operating conditions. The device is monitored under stress and also tested at various intervals. Each substructure of the circuit is put to the test, and manufacturers can get a clear idea of what the lifespan of the device is as well as potential points of failure.
HTOL is conducted over a long period, although the same test machines can be utilized to perform a burn-in test which gives clues into the early life of an integrated circuit. These burn-in tests are conducted on short durations and devices are placed under normal operating conditions within a tightly controlled environment. Burn-in tests prevent defective products from being sold to the end user.
In these tests, the temperature and the rate of change of temperature are the accelerants. A machine called a Temperature Cycle Chamber is used to subject the sample to extremely low temperatures and then to extremely high temperatures according to a specified set of cycles. This can help study failure mechanisms like package cracking, die cracking and bond lifting issues as well as neck, heel, or wire breaks.
Biased Highly Accelerated Stress Test (BHAST)
An integrated circuit is put under high temperature and high humidity conditions while a voltage bias is applied. The goal here is to accelerate the metal corrosion of the die surface of the device. It used to take weeks to perform these tests, but with modern machines capable of handling more extreme stress conditions, the BHAST time has been reduced to about 96 hours.
High-Temperature Storage (HTS)
This test is also called ‘Bake’ and attempts to find out the effects of long-term storage under high temperatures without any electrical stresses applied. The semiconductor parts are stored inside a bake chamber at a particular ambient temperature for a set duration of time. Afterward, they are removed and undergo electrical testing as well as visual inspection.
Other Types Of Reliability Testing For Semiconductor Devices
There are many other ways to study the reliability of semiconductor devices, such as the Intermittent Operating Life Test (IOL) where a bias is given and removed when the junction temperature reaches a certain value. This switching on and off is repeated up to 5,000 times, replicating the stresses experienced under normal operating conditions.
There is also High-Voltage Switching which can test for reliability for newer semiconductor materials that do not have the proven track record of Silicon-based products. Finally, there is also reliability modeling which is purely theoretical and done using computers before the actual devices are produced. All of these methods can help researchers understand failure mechanisms, and discover the most optimal methods to manufacture integrated circuits in the most efficient manner.
Semiconductor devices like integrated circuits are put through reliability testing which involves subjecting the device to various extremes of voltages, temperatures, and humidities to find the points of failure
Yes. Manufacturing defects can negatively affect the performance of a semiconductor device or integrated circuit. Reliability testing allows manufacturers to improve their methods to produce better devices that can perform reliably for longer.