Evolution of the semiconductor manufacturing industry is placing ever greater demands on yield management and, in particular, on metrology and inspection systems. Critical dimensions are shrinking while wafer size is increasing. Economics is driving the industry to decrease the time for achieving high-yield, high-value production. Thus, minimizing the total time from detecting a yield problem to fixing it determines the return-on-investment for the semiconductor manufacturer.
It is necessary to test integrated circuits as part of the manufacturing process. The testing is performed by creating a temporary electrical contact between a test probe or probes with selected points on the integrated circuit or witness sample being tested. A predetermined programmed test is then undertaken utilizing signals applied to the circuit and derived therefrom through the probes. Because of the complexity and the small size of the circuits, particularly extremely compact integrated circuits, the numbers of contacts that must be made with the circuit for appropriate testing demands strict control over the positioning of contact probes. Furthermore, the force with which the probes are placed against the predetermined circuit pads or points may be important. Controlling the precise positioning of the probes as well as the force on each probe requires accuracy in the manufacture of probe systems.
Such probe systems have typically used probes that are normally in the form of fine needles. The probes are individually attached to a printed circuit board by either soldering the probe directly to the printed circuit board or to a holding device which in turn is soldered to the printed circuit board. The probes typically extend from the mounting place, such as the blade, in a cantilever arm fashion reaching out as much as several hundred mils to the point on the integrated circuit to be tested. To change the force on the probe requires either changing the probe diameter to make the probe stiffer or more flexible, or changing the probe length or cantilever length. Furthermore, the use of such probes does not provide a convenient means for implementing a controlled impedance transmission line.
In an instance, a four-point probe can be used to test the electric properties of an integrated circuit by generation of resistivity or carrier concentration profiles of the surface of a processed semiconductor wafer. A conventional four-point probe technique typically has the points positioned in an in-line configuration. By applying a current to the two peripheral points, a voltage can be measured between the two inner points of the four-point probe. Thus the electric resistivity ρ of the test sample can be determined through the equation ρ=c(V/I), wherein V is voltage measured between inner points, wherein I is current applied to the peripheral points and, wherein c is a geometry factor depending on the surface contact separation d and the dimensions of the test sample.
Conventionally probe tips are made by planar microelectromechanical systems (MEMS) manufacturing processes. The probe cantilevers extend out parallel to the supporting body surface, which is referred to as planarity, for easy manufacturing as well as simultaneous landing on a flat wafer surface. When the cantilever makes contact with wafer surface, it bends and scrubs with wafer surface and form a sizeable contact. The contact size is relevant to the contact force and probe wear. This design eventually loses conductive materials, loses the capability for passing electric current thereby limiting precision of the measurement, and shortens the lifetime of the probe. Due to the co-planarity of probe tip to the supporting chip surface, and the angle about 30° between the cantilevered probes to wafer surface, the contact size is variable related to probe tip wear, and the conductive coating can be easily removed during landing and measurement. A change of contact size and removal of conductive coating will deteriorate the measurement accuracy, shortening probe lifetime significantly.
The metal coating deforms and quickly wears off on existing probes, which results in an approximate lifetime of 100-500 touches or measurements. The fragile SiO2 cantilevers also can easily break. Therefore, improved resistivity probe designs are needed.