The EG2001x is an automatic system designed to probe semiconductor wafers. As configured at the MTW, the probers are equipped to handle 150mm wafers of silicon, glass, or polyimide-coated glass. Other substrates such as stainless steel, PEN (polyethylene napthalate) on alumina, etc., are possible to utilize as well. The tool is typically employed to automatically load, align, and probe multiple locations on a wafer or series of wafers. It is also possible to utilize the tool manually. In this case wafers or pieces of wafers are individually placed on the chuck and guided by means of a microscope viewer to the probe needles. Electrical tests are then manually initiated by the user.
Wafer probers are commonly employed when it is necessary to acquire large amounts of test data. A typical situation of this type is when statistical analysis is to be performed on the data set or when numerous devices must be screened for product validation. Wafers which are intended to receive automatic testing on a wafer prober must have certain features designed into them. These typically include features (“alignment keys”) which the prober can identify with a vision system to accurately align the wafer and bring it into a precise locational relationship to the probe card. Devices on the wafer targeted for testing must have contact locations (“test pads”) which match needle positions on the probe card, and are sufficiently large to accommodate nominal targeting errors in the prober’s alignment system.
The prober is only one component of the test system, responsible for bringing the DUT (Device Under Test) into contact with a probe card which is in turn connected to a suitable test instrument. A computer running a test executor program coordinates the interactions between the prober, probe card, and test instrument. The test executor program (written in Labview™) aligns the wafer, brings the DUT into contact with the probe card, and operates the test instrument to obtain the test data. Common test instruments include semiconductor parameter analyzers for transistor characterization, multi-meters for resistance or current measurements, capacitance meters, and sometimes custom-built devices.
The probers are configured to accept a 4” diameter round probe card fabricated on standard pcb material 0.063” in thickness. The MTW experience is that probe pads are ideally a minimum of 150um square, with a spacing of 150um, giving a probe needle pitch of 300um. Users are encouraged to supply their own probe cards; the MTW can provide some guidance for design and suggested suppliers. Installation and calibration of a probe card requires assistance from MTW personnel and will typically require a minimum of one day (8hrs). Alternate probe card (e.g., rectangular) geometries are possible with a significant penalty in setup time. Users are strongly encouraged to have at least two probe cards to provide redundancy in the event of probe breakage. This is especially true for new setups.
Users will also require assistance in writing their first test executor programs and should be prepared to provide geometric information (i.e., layout gdsii) for their wafers. Depending on the test instrument(s) to be employed, new Labview™ control routines may need to be developed and integrated into the test executor program. The MTW personnel can advise on the need for this activity.
Once configured and integrated with a test instrument, the probers are capable of running unattended for extended intervals. It is possible to conduct tests of many hours duration, or to test hundreds or even thousands of devices, accumulating large quantities of test data in support of research or production goals.
- Semiconductor wafer probing