Journal of Vacuum Science & Technology B Microelectronics and Nanometer Structures Processing Measurement and Phenomena · 1993 · 111 citations · 0 references
EngineeringElectron-beam LithographyMicroscopyOptic DesignOptical TestingInterferometryOptical MetrologyLaser ApplicationsOptoelectronic DevicesSpatial ScaleLaser FabricationLaser OpticsBeam LithographyOptical PropertiesPhotonic MetrologyInstrumentationOptical SystemsMultiple ExposuresPhotonicsOphthalmologyMedicineOptical TolerancingOptical ComponentsConventional LithographyApplied PhysicsOptical EngineeringMultiple-exposure Interferometric LithographyDiffractive Optic
Interference between coherent laser beams has long been used to generate simple grating patterns in photoresist, and the resulting moiré‑like structures relate to classic interference phenomena. The technique produces sub‑micron lines (~0.1 µm) by exposing photoresist with multiple laser patterns at quarter‑wavelength spacing, and conventional lithography, aperture, and phase masks further refine the pattern over large areas. Multiple exposures with varied period, phase, and orientation yield highly complex one‑ and two‑dimensional patterns with unlimited depth‑of‑focus, large‑area uniformity, sub‑micron interdigitated structures, and diffractive readout provides an effective monitoring technique.
Interference effects between two coherent laser beams have long been used to create simple grating patterns in photoresist. With the addition of multiple exposures with variations in period, phase, and orientation, in the same level of photoresist, highly complex one- and two-dimensional patterns of potential interest for device application are demonstrated. The spatial scale of the lines forming these patterns is ∼1/4 of the writing wavelength λ (period to λ/2 and line to space ratio of 1:1) and is in the extreme submicron range, ∼0.1 μm, for readily available laser sources, such as an Ar+-ion laser operating at 364 nm. Importantly, the depth-of-focus for these pairwise exposures is unlimited on the scale of typical semiconductor device topographies and large area, uniform exposures to scales much larger than projected integrated circuit die sizes (e.g., to 30×30 cm2) are easily achieved. These patterns are closely related to moiré interference patterns; relationships are illustrated. Diffractive readout is shown to be a powerful and intuitive technique for monitoring these structures. Additional flexibility in pattern fabrication is provided with conventional lithography to define areas on a larger scale and by the use of aperture and phase masks to isolate areas. An example is the fabrication of an interdigitated structure with submicron spaces over a large area.