Photolithography is commonly utilized during semiconductor processing. For instance, photolithography may be utilized during integrated circuit fabrication. Photolithography comprises patterning of photoresist by exposing the photoresist to patterned actinic energy and developer.
A continuing goal in semiconductor processing is to reduce the size of individual electronic components, and to thereby enable smaller and denser integrated circuitry. A concept commonly referred to as “pitch” can be used to quantify the density of an integrated circuit pattern. Pitch may be defined as the distance between an identical point in two neighboring features of a repeating pattern. However, due to factors such as optics and actinic radiation wavelength, a photolithographic technique will tend to have a minimum pitch below which the particular photolithographic technique cannot reliably form features. Thus, minimum pitches associated with photolithographic techniques present obstacles to continued feature size reduction in integrated circuit fabrication.
Pitch multiplication, such as pitch-doubling, is one proposed method for extending the capabilities of photolithographic techniques beyond their minimum pitch. Such may involve forming features narrower than minimum photolithographic resolution by depositing layers to have a lateral thickness which is less than that of the minimum capable photolithographic feature size, F. The layers may be anisotropically etched to form sub-photolithographic features. The sub-photolithographic features may then be used for integrated circuit fabrication to create higher density circuit patterns than can be achieved with conventional photolithographic processing.
Difficulties may be encountered in processing associated with sub-photolithographic structures. Specifically, it may be advantageous to utilize traditional photolithography for processing occurring before or after formation of the sub-photolithographic features; but traditional photolithography will form structures having minimum feature sizes of at least F. It can be difficult to align a photolithographic-scale structure to a sub-photolithographic-scale structure. It would therefore be desirable to develop new methods for aligning photolithographic-scale structures to sub-photolithographic-scale structures.