BURN-IN RELIABILITY TESTING AND MANUFACTURING OF SEMICONDUCTORS Prepared

BURN-IN, RELIABILITY TESTING, AND MANUFACTURING OF SEMICONDUCTORS Prepared By Cagatay Bozturk C. Bozturk, School of Technology, KSU

Index n n What is BURN-IN? Reliability of Semiconductors What is Reliability&Life Testing Semiconductor Manufacturing C. Bozturk, School of Technology, KSU

What is BURN-IN? Burn-In is the application of thermal and electrical stress for the purposes of inducing the failure of "marginal (microelectronic) devices, those with inherent defects or defects resulting from manufacturing aberrations which cause time and stress dependant failures. C. Bozturk, School of Technology, KSU

Reliability of Semiconductors To evaluate the reliability of an electronic system, reliability information on the components used in that system is important. Failure rates are often used as an index for reliability. A failure rate indicates how often a failure occurs per unit time, and failure-rate values generally change overtime as shown below C. Bozturk, School of Technology, KSU

Early Failure Stage During this stage, failures occur at a high rate following the initial operation of semiconductor devices. They occur very soon and thus the failure rate declines rapidly over time. This Is because the potential' failures that could not be removed through a selective process are included and surface in a short time if a stress such as temperature or voltage is applied after use of the device is started. In the case of semiconductors, these failures are usually due to defects that could not be removed during production, such an micro dust collecting on the wafer, or to material defects. C. Bozturk, School of Technology, KSU

Random Failure Stage When early failures are eliminated, the failure rate drops to an extremely low value. However, there is always the possibility of a potential failure accidentally occurring after a long time. Consequently the failure rate never decreases to zero. It is almost constant because failures occur sporadically C. Bozturk, School of Technology, KSU

Wear-out Failure Stage During this stage, failures occur with increasing frequency over time and are caused by age-related wear and fatigue. In the case of a semiconductor device, electronic migration or oxide film destruction (TDDB) may occur. C. Bozturk, School of Technology, KSU

What is Reliability & Life Testing? The reliability of a semiconductor device is determined by its ability to perform its required functions under the stipulated conditions for a finite period of time. Quantifiable yardsticks such as the reliability rate, failure rate, and mean time to failure (MTTF) are used to measure reliability. C. Bozturk, School of Technology, KSU

Objective of Reliability Testing The objective of reliability testing is to confirm a semiconductor device's fault-free operation and estimated useful life by exposing the device to accelerated or marginal stress, based on the amount of stress (thermal stress, mechanical stress, electrical stress etc) that the device is estimated to undergo during manufacture, shipping and normal use. C. Bozturk, School of Technology, KSU

Semiconductor Manufacturing Semiconductor manufacturing consists of the following steps: 1) production of silicon wafers from very pure silicon ingots 2) fabrication of integrated circuits onto these wafers 3) assembly of every integrated circuit on the wafer into a finished product 4) testing and back-end processing of the finished products. C. Bozturk, School of Technology, KSU

Wafer Fabrication Wafer fabrication generally refers to the process of building integrated circuits on silicon wafers. Prior to wafer fabrication, the raw silicon wafers to be used for this purpose are first produced from very pure silicon ingots, through either the Czochralski (CZ) or the Float Zone (FZ) method. The ingots are shaped then sliced into thin wafers through a process called wafering. Wafer fab processes, allowing the device designer to optimize his design by selecting the best fab process for his device. C. Bozturk, School of Technology, KSU

Assembly 1. 2. 3. 4. The process of putting the integrated circuit inside a package to make it reliable and convenient to use is known as semiconductor package assembly, or simply 'assembly'. In general, an assembly process would consist of the following steps: die preparation die attach bonding encapsulation C. Bozturk, School of Technology, KSU

Steps of Assembly die preparation, which cuts the wafer into , individual integrated circuits or dice; die attach, which attaches the die to the support structure (e. g. , the leadframe) of the package; bonding, which connects the circuit to the electrical extremities of the package, thereby allowing the circuit to be connected to the outside world; and encapsulation (usually by plastic molding), which provides 'body' to the package of the circuit for physical and chemical protection. C. Bozturk, School of Technology, KSU

Test Once assembled, the integrated circuit is ready to use. However, owing to the imperfection of this world, assembled devices don't always work. Many things can go wrong to make a device fail, e. g. , the die has wafer fab-related defects, or the die cracked during assembly, or the bonds were poorly connected or not connected at all. Thus, prior to shipment to the customer, assembled devices must first be electrically tested. C. Bozturk, School of Technology, KSU

Electrical Testing Electrical testing of devices in big volumes must be done fast and inexpensively. Mass-production electrical testing therefore requires an automated system for doing the test. Equipment used to test devices are called, well, testers, and equipment used to handle the devices while undergoing testing are called, well, handlers. Tester/handler systems are also known as automatic test equipment (ATE). C. Bozturk, School of Technology, KSU

BURN-IN Burn-in is an electrical stress test that employs voltage and temperature to accelerate the electrical failure of a device. Burn-in essentially simulates the operating life of the device, since the electrical excitation applied during burn-in may mirror the worst-case bias that the device will be subjected to in the course of its useable life. Depending on the burn-in duration used, the reliability information obtained may pertain to the device's early life or its wear-out. C. Bozturk, School of Technology, KSU

BURN-IN Burn-in is usually done at 125 deg C, with electrical excitation applied to the samples. The burn-in process is facilitated by using burn-in boards (see Fig. 1) where the samples are loaded. These burn-in boards are then inserted into the burn-in oven (see Fig. 2), which supplies the necessary voltages to the samples while maintaining the oven temperature at 125 deg C. The electrical bias applied may either be static or dynamic, depending on the failure mechanism being accelerated. C. Bozturk, School of Technology, KSU Figure 1 Photo of Bare and Socketpopulated Burn-in Boards Figure 2 Two examples of burn-in ovens

Conclusion Burn-in helps us to detect problem trends / determine critical components in a system failure (s), and, analyze the system for Effective reliability. Thanks to burn-in, we can predict reliability performance and Lifecycle of the products. It provides valid field “failure data” and timely corrected actions. C. Bozturk, School of Technology, KSU

References n n http: //www. semiconfareast. com http: //www. reltech. co. uk C. Bozturk, School of Technology, KSU