Alignment systems on photolithography tools are generally designed to work with specific types of alignment marks on the wafer. The alignment system acquires an alignment signal by optically scanning an alignment mark. The alignment signal received from the alignment mark is then analyzed to determine the location of the alignment mark on the wafer. This is repeated for several alignment marks in different exposure fields on the wafer. The data from this group of alignment marks is then processed with a computer in the photolithography tool to determine the location of the wafer.

Alignment systems are used to fabricate a wide array of semiconductor devices, including Resistive Random Access Memory (RRAM) devices. RRAM devices are an emerging non-volatile memory technology with various advantages in terms of cell area, device density, power consumption, programming/erasing speed, three-dimensional integration, multi-value implementation, and the like over FLASH memories. The RRAMs include a vertical arrangement of Metal/Insulator/Metal (MIM). As a result, the RRAMs can achieve high-density storage by means of a crossbar array configuration. In the crossbar array configuration, memory cells are disposed at respective intersections between sets of parallel lines, which are vertically spaced apart and extend in directions perpendicular to each other. Each of the memory cells can be independently selected and subsequently read or written.