The present invention relates to bonding pads for semiconductor chips.
Semiconductor chips have bonding pads which are relatively large areas of metalization providing a contact area for an assembler to solder a wire connection to one of the pins of an integrated circuit package. This wide metal area of the bonding pad is then coupled to the tiny metal connections of the integrated circuit. The semicustom method of designing and fabricating integrated circuits uses prefabricated semiconductor wafers which have completed circuits except for the final process step of device or component interconnection. A cost savings is realized by adapting a standard wafer, which has already been designed and manufactured, to a particular customer's needs by simply designing appropriate metal interconnections. Thus, for each customer, a metal mask is designed which connects the necessary active and passive semiconductor components to form the circuit configuration required by the customer. This method of design and fabrication allows development of a semicustom circuit in less time and at lower cost than if the entire wafer had to be independently designed for each customer.
One limitation in semicustom design is that the number of bonding pads required to form connections to a particular customer's circuit will vary from customer to customer. Accordingly, a standard chip design will have enough bonding pads to accommodate the largest number anticipated to be required by any customer. This results in a number of bonding pads being wasted space for a large number of customers. A bonding pad will typically be a cell area which is simply an N-doped epitaxial layer on top of a P-doped substrate. Inherent in this structure is a clamping diode or a capacitance. For the clamping diode, the N portion of the diode is the epitaxial region and the P portion of the diode is the substrate. The junction capacitor is formed at the junction of the substrate and the epitaxial region. Thus, in some circuit designs, it may be possible to take advantage of this inherent capacitance or clamping diode.