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We have exposed 190 nm lines in photoresist by focusing a laser beam (λ=442 nm) in a solid immersion lens (SIL) that is mounted on a flexible cantilever and scanned by a modified commercial atomic force microscope. The scan rate was 1 cm/s, which is several orders of magnitude faster than typical reports of near-field lithography using tapered optical fibers. The enhanced speed is a result of the high optical efficiency (about 10−1) of the SIL. Once exposed with the SIL, the photoresist was developed and the pattern was transferred to the silicon substrate by plasma etching.

We have demonstrated that the atomic force microscope (AFM) operating in air may be used to pattern narrow features in resist in a noncontact lithography mode. A micromachined AFM cantilever with an integrated silicon probe tip acts as a source of electrons. The field emission current from the tip is sensitive to the tip-to-sample spacing and is used as the feedback signal to control this spacing. Feature sizes below 30 nm have been patterned in 65-nm-thick resist and transferred through reactive ion etching into the silicon substrate. We show that the same AFM probe used for noncontact patterning can be used to image the sample. In addition to eliminating the problem of tip wear, this noncontact system is easily adapted to multiple-tip arrays where each cantilever has an integrated actuator to adjust the probe height.

Imprint lithography for curved cross-sectional structure using replicated Ni mold Electron beam lithography ͑EBL͒ and scanning probe lithography ͑SPL͒ are electron exposure techniques capable of high resolution patterning of organic resists. This article compares the exposure properties of these two systems. We consider the resist sensitivity to EBL and SPL electrons, exposure tolerances, patterning linearity, and proximity effects. It is possible to print sub-50 nm features using both systems, but SPL has a wider exposure latitude at these small feature sizes. SPL requires a significantly higher incident electron dose for exposure than does EBL. In EBL, lithography control is most limited by proximity effects which arise from backscattered electrons whose range is considerably larger than the forward scattering range in the resist film. As a result, the exposed feature dimension depends strongly on the local feature density and size, leading to unacceptable linewidth variations across a wafer. These limitations are alleviated in the case of SPL exposures. We demonstrate improved linearity and reduced proximity effects with SPL. We have patterned 200 nm pitch grids with SPL where all individual features are resolved. The linewidth of features in these grids is the same as the width of an isolated line at the same dose. Finally, we suggest that the SPL exposure mechanism may be different than that for EBL.

Scanning probe lithography ͑SPL͒ is capable of sub-30-nm-patterning resolution and nanometer-scale alignment registration, suggesting it might provide a solution to the semiconductor industry's lithography challenges. However, SPL throughput is significantly lower than conventional lithography techniques. Low throughput most limits the widespread use of SPL for high resolution patterning applications. This article addresses the speed constraints for reliable patterning of organic resists. Electrons field emitted from a sharp probe tip are used to expose the resist. Finite tip-sample capacitance limits the bandwidth of current-controlled lithography in which the tip-sample voltage bias is varied to maintain a fixed emission current during exposure. We have introduced a capacitance compensation scheme to ensure continuous resist exposure of SAL601 polymer resist at scan speeds up to 1 mm/s. We also demonstrate parallel resist exposure with two tips, where the emission current from each tip is individually controlled. Simultaneous patterning with multiple tips may make SPL a viable technology for high resolution lithography.