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Parametric Wafer Acceptance Test

Parametric testing, or wafer acceptance test (WAT), is a unique application for IC manufacturers to ensure that the wafer production process is consistent and maximizes yields. FormFactor's parametric test solutions help to ensure quality.

To reduce the amount of batch processing errors, it is important to confirm that the wafers are being properly fabricated. On larger wafers, process variable control becomes even more critical. With parametric tests, suppliers can develop new wafer process technologies, monitor existing in-line and end-of-line processes, and check wafer-level reliability.

When a new process is being developed, it undergoes a series of tests in a reliability lab. These tests are designed to stress the process with extreme conditions, such as high temperatures and long test periods.

Pyramid Parametric and Takumi for In-line and End-of-line Testing

During in-line and end-of-line tests, the manufacturer makes electrical contact with special structures on the wafer between layers of metal and dielectric. These test structures, including resistors and capacitors, are stand ins for actual devices. Depending on the maturity of the product, the structures are sometimes located in the area of the die itself, and sometimes in the scribe line – or the area between the die. In the latter especially, the requirement is for very small pads to fit in the scribe line. We see these pads as small as 40um today and they are on track to shrink further. Chip manufacturers can quickly collect device performance data from these tests and make process adjustments depending on the feedback.

Pyramid Parametric probe cards are used for in-line testing and are a high performance, low-cost alternative to the existing solutions. These cards are compatible with all major parametric tester platforms and designed to enable the accurate monitoring of 65 nm and 45 nm parametric test structures. FormFactor’s innovative PyramidPlus™ manufacturing process ensures a substantially lower cost of ownership, while delivering superior signal integrity and faster settling time, compared to traditional probe technologies. The Pyramid Parametric series is ideal for applications such as final process development, DC-only parametric volume production (in-line and end-of-line), and Wafer-Acceptance Testing (WAT).

Takumi™ probe cards for in-line and end-of-line parametric testing give IC manufacturers earlier insight into opportunities to validate their designs, verify process performance, and achieve higher yields. The proprietary interchangeable architecture allows manufacturers to rapidly switch FormFactor probe heads with minimal production downtime. Utilizing our 3D MEMS MicroSpring® technology, Takumi probe cards provide superior thermal stability, probe positioning accuracy, precise electrical measurements, and long test device lifetimes in the parametric test environment.

The Takumi wafer probe solution enables excellent thermal stability that supports probing from -40 C to 150 C without loss of production time. The extremely accurate and stable electrical measurements allow better and faster insight into semiconductor performance. Takumi’s precise probe pad placement ensures greater test accuracy on parametric pads as small as 30×30 um. Since the test pads that are required for wafer probing are built into the scribe lines that separate each device on a wafer, wafer probe card technology must be sufficiently scalable to make robust and repeatable contact with smaller pads without damaging adjacent die. The scalability of FormFactor’s MicroSpring technology allows IC manufacturers to narrow their scribe lines and increase the number of die that can be produced per wafer.