Scanning tunneling microscope lithography: A solution to electron scattering

Abstract

The scanning tunneling microscope (STM) operated in the field emission mode is shown to have important lithographic applications. The technological potential of the technique is demonstrated by patterning films up to 80 nm thick of SAL-601-ER7, a negative resist from Shipley. With the STM, 22 nm lines of developed resist have been written on Si and 35 nm lines on GaAs. For comparison, exposures were made with a 50 kV, 17 nm lie diameter electron beam in identically prepared and processed resist films on a variety of substrates. The 50 kV probe produced minimum linewidths of: 60 nm on a 200 nm Si3N4 membrane; 70 nm on a 200 nm Si3N4 film on a bulk Si substrate; 95 nm on a bulk Si substrate; and 186 nm on a bulk GaAs substrate.The strong substrate dependence indicates that the resolution, at 50 kV, is determined by electron scattering rather than the post exposure processing of the resist. Low voltage lithography with an STM offers a technique which greatly reduces the effects of electron scattering with a consequent improvement in resolution. In addition, the results of the S(,N 4 film suggest a novel way to reduce the effects of back scattered electrons in 50 kV lithography.

Formation of Nanometer-Scale Grooves in Silicon with a Scanning Tunneling Microscope

“…3, inset). This rules out mechanisms such as electromigration (12), local melting (1 3), and electron beam-induced reactions (14). all of which , 7 , vary strongly with current or total electron than that of the sample, @, , the result is a positive tip bias (a, -@,)/e, where e is the electron charge and @, and @, are measured in electron volts.…”

STM writing of artificial nanostructures in ultrathin PMMA and SAM resists and subsequent pattern transfer in a Mo/Si multilayer by reactive ion etching

“…The resolution potential is limited by the proximity effect [11,12]. As the proximity effect is eliminated, the resolution of STM lithography is limited by the size of the resist molecules [10]. This is why feature sizes below 10 nm are expected when optimized structuring parameters are used.…”

“…STM lithography in the field-emission mode is known to establish a kind of low-energy electron lithography in an ultrathin PMMA e-beam resist, thus surpassing the problems of secondary electron scattering (proximity effect) in conventional high energy e-beam lithography [10][11][12].…”

Electron-beam nanolithography, acid diffusion, and chemical kinetics in SAL-601

“…CARs are technologically important because they have high sensitivity, high resolution, and are resistant to subsequent semiconductor etching processes. Of this class of resists, Microposit™ SAL-601 has had the highest reported resolution with 20-40 nm wide lines [1][2][3][4] and 100 nm period gratings. 3 However, reports of sub-50 nm resolution in SAL-601 have been rare and the resolution limitations of SAL-601 or CARs in general have only barely been addressed.…”

“…3 However, reports of sub-50 nm resolution in SAL-601 have been rare and the resolution limitations of SAL-601 or CARs in general have only barely been addressed. 1,[3][4][5][6] SAL-601 is a negative tone electron beam resist that is composed of three components: an alkaline soluble polymeric novolak resin, an acid generator, and a melamine crosslinking agent. Exposure to electrons generates a latent image of free acid.…”