In the race to improve transistor performance as well as reduce the size of transistors, transistors have been developed that do not follow the traditional planar format, such that the source/drain regions are not located in the substrate, but rather are non-planar transistors where the source/drain regions are located in a fin above the substrate. One such non-planar device is a multiple-gate FinFET. In its simplest form, a multiple-gate FinFET has a gate electrode that straddles across a fin-like silicon body to form a channel region. There are two gates, one on each sidewall of the silicon fine. The source/drain regions are located in the fin, away from the substrate.
Electrical contacts to the source/drain regions have traditionally followed a layout rule such that the contact is formed to connect to a portion of the top of the fin-like silicon body. Accordingly, from this layout rule, the contact width has been either less than, or at most equal to, the width of the fine. For example, in a device where the contact width is 60 nm, the width of the device would necessarily be either greater than or equal to 60 nm. In cases where the contact has necessarily exceeded the width of the fin in the channel region (for example, when the FinFET width is less than 60 nm), the width of the fin in the source and drain regions has been enlarged so that the width of the fin in these regions is larger than the width of the contact.
However, by adhering to this layout rule, a number of problems have arisen. One such problem is that, with the reduction of the contact area, the contact resistance of the contact has risen, thereby limiting improvements to the driving current of the device. Also, mis-alignment of the contacts during the manufacturing process has led to variations in the contact resistance between the device and the contacts, thereby leading to differences in resistance between various devices and reducing the overall circuit yield. Additionally, silicide formation is usually performed with an ultra shallow junction on the source/drain areas, thereby preventing improvements in the Schottky barrier height.
Accordingly, what is needed is a new contact design that allows for a reduced contact resistance while also reducing mis-alignment of the contacts during formation.