Last time, I introduced the “wiring process” that creates a path for passing current inside the semiconductor, which is the sixth of the eight semiconductor manufacturing processes. This time, we will deliver the “test process” that will be the subsequent process.
Testing process to choose the perfect semiconductor
The test process is the process of determining whether a semiconductor chip that has completed various processes is good or bad. The purpose is to improve the reliability of the chip by checking that the semiconductor chip has reached a certain quality level and there are no defective products. The process reduces costs and time by detecting defective products and avoiding packaging them. This time, we will mainly discuss electrical die sorting (EDS), which is tested in a wafer state.
What is Electrical Die Sorting (EDS)?
EDS is a process that aims to improve the yield of semiconductors by inspecting electrical characteristics and testing each chip in the wafer state. The EDS process is divided into the following five stages.
Step 1: Electrical Parameter Monitoring (EPM)
EPM is the first stage of semiconductor chip testing. Test the electrical characteristics of each device, such as transistors, capacitors, and diodes, required to operate a semiconductor integrated circuit to see if they work. The main purpose of EPM is not to find defective products, but to provide data on measured electrical characteristics to improve the efficiency of semiconductor manufacturing processes and product performance.
Step 2: Wafer burn-in
Semiconductor defect rates include high manufacturing defect rates in the early stages and defect rates due to product life in later stages. Wafer burn-in applies an AC / DC voltage to a wafer at a constant temperature during the early detection of possible defects to improve product reliability. This process detects potential defects and effectively improves product reliability.
Process 3: Test
After the wafer burn-in stage, a “probe card” is used to connect the semiconductor chip to the test equipment and perform temperature, speed, and operation-specific tests on the wafer to examine the behavior of the semiconductor. Please refer to the table for the procedure of each test.
Process 4: Repair
The repair process is the most important stage of testing. In some cases, defective chips are repaired using spare cells designed on the chip.
Process 5: Inking
Chips that fail the electrical test and are initially sorted out must be marked to distinguish them. In the past, special inks were used during the inking stage to identify defective chips with the naked eye, but now the system automatically sorts chips based on test data values.
Next time, we will introduce the final stage of the semiconductor manufacturing process, the “packaging process” that makes semiconductor chips ready for assembly into equipment.
Test process related terms
The ratio of successful chips actually manufactured to the maximum number of IC chips designed on the wafer. It means the amount of output with respect to the amount of input.
Controllable variables previously defined and used programmatically.
A device that connects a semiconductor wafer to a test device to inspect the operation of a semiconductor. The probe needle on the probe card sends electricity while in contact with the wafer and sorts out defective semiconductors based on the returned signal.
(Next time, it will be posted in April 2021)