The present invention relates generally to semiconductor device manufacturing and, more particularly, to an apparatus and method for improved pressure sensing control during wafer probing of integrated circuits.
Integrated circuits are often manufactured on a semiconductor substrate, such as a silicon wafer. Typically, a single wafer will have numerous integrated circuit (IC) devices formed thereon a lattice pattern. Each IC device has of numerous layers of circuitry and a collection of external bonding pads, which are small sites made from a conductive material such as aluminum. The bonding pads eventually serve as the device's connections to the pin leads.
Since the packaging of a device is a costly procedure, it is desirable to test a device beforehand to avoid packaging faulty devices. The testing process involves initially establishing electrical contact between a probe card and the wafer, and thereafter running a series of tests on the devices on the wafer's surface. The probe card has a collection of individual electrical contact pins or probes that stand in for the normal pins and wire leads of a packaged device. The wafer is positioned relative to the probe card so that the contact pins on the probe card make contact with a wafer's bonding pads and probe pads while a special tester runs a series of electrical tests on the wafer's devices. A wafer prober is used to position the wafer with respect to the probe card.
In order to provide appropriately reliable electrical contact with a device under test (DUT), numerous and diverse types of probes have been developed in the technology, wherein it is normally recognized that each probe type necessitates the employment of a specific probing force. An insufficient contact force between the probe and the wafer will result in an unreliable electrical contact, while an excessive contact force will result in damage to the probes or contact pads on the DUT. Currently, most systems which are employed for wafer testing do not incorporate sufficiently reliable structure or testing steps which will readily or accurately determine the probe force that is being applied to each pad on the DUT during implementation of the testing procedure.
Each probe technology has a characteristic probe compliance or spring rate, and thus the correct probe force occurs at a specific probe displacement. Consequently, a current wafer testing practice is to overdrive or displace the wafer the specified distance into the probe system. Unfortunately, the resulting forces may result in significant deflection of the probe support structure. This is especially a problem with probe arrays that incorporate a large number of probes. In this case, the amount of overdrive must be increased to overcome deflection of the support structure. The actual amount of the resultant force is not readily determinable and may be open to conjecture. Thus, a typical overdrive is ordinarily determined experimentally for one particular product, and through extrapolation or assumptions employed for all similar systems and products.