[click images to enlarge]

SEMI AUTOMATED WAFER PROBING STATION

[back to labview solutions]

CHALLENGE

To create a custom LabVIEW application capable of instructing a Wentworth Pegasus wafer probing station (and peripherals) to automatically perform QA inspections on silicon wafers with devices targeted for biomedical applications.

Two major components to this inspection were to consist of:

(1) consume pre-loaded definition files and image thousands of electrodes while streaming said images to disk in a structured fashion based on specific, calculated coordinates and

(2) using the same pre-loaded map, step through a series of test structures, placing a probe card in contact and performing a series of V-I measurements via GPIB controlled Keithley instrumentation.

SOLUTION

As discussed above, the solution to this application was essentially two-part. The customer wished to develop a test station capable of performing a series of electrical tests on a number of test structures as a means of verifying quality and repeatability of their manufacturing process. Additionally, this station was also required to establish a preliminary means for identifying visual defects by streaming high-resolution images of wafer product to disk for subsequent stitching and analysis. Locations of devices on a wafer (for the purposes of performing electrical measurements and acquiring images) were dictated by a series of pre-loaded definition files, chosen based on User input.

Hardware involved included:

• Wentworth Laboratories Pegasus wafer probing station (communications handled via GPIB requiring a custom-developed instrument driver developed in LabVIEW)
• Qioptiq A-Zoom2 Microscope (communications handled via RS232 requiring a custom-developed instrument driver developed in LabVIEW)
• Imaging Source PCIe frame grabber (communications handled via manufacturer supplied LabVIEW driver but requiring further enhancements/modifications to fit the requirements)
• Keithley 2611A single channel SourceMeter (communications handled via GPIB and manufacturer supplied driver set)
• Keithley 3706A-NFP Six-Slot System Switch with (1) Keithley 3721 Dual 1x20 Multiplexer Card (communications handled via GPIB and manufacturer supplied driver set)

Although both tests are treated independently, there is some common ground; most notably, the Pegasus. The final solution involved a handful of UI?s capable of inter-communicating with one another. The main interface handles the bulk of all processing: it acts as the primary user interface; delegates processes such as image acquisition, chuck position and measurement results display; streams acquired images (or measurement results, depending on the test mode) to disk in an efficient and coordinated manner, etc.

Other interfaces include:

• wafer position feedback coupled with other useful runtime information
• an image acquisition UI that can either be used independently by the user for taking snapshots of the field-of-view or be invoked automatically by a commanding process
• Electrical measurements results display, including visual pass/fail indicators

The final result was a user-friendly, flexible application allowing the users to not only treat this as a fully functional production-based test station but also allow practically full manual control for diagnostics and R&D purposes.