Lithography with low-energy electrons

T. H. Newman ◽  
R. F. W. Pease ◽  
K. J. Polasko ◽  
Y. W. Yau

Two prominent problems of electron beam lithography are slow throughput and proximity effects. The former arises from the serial nature of the exposure process; the current available in a beam of given resolution is limited by electron optical considerations and the resist sensitivity is limited by material considerations such that a dose of 1 μC/cm2 at 20 kV is required for the most sensitive resist and ten times that dose if high resolution is required.Proximity effects are caused by electrons scattered through lateral distances greater than the resolution of the pattern; a 20 keV electron in silicon has a range of about 3 μm whereas feature sizes are often less than 1 μm. Lowering the energy of the exposing electrons to, say, 2 keV would lower the electron range to less than 0.1 μm in silicon and thus effectively eliminate proximity effects as far as semiconductor circuit fabrication is concerned.

2000 ◽  
Vol 636 ◽  
Kenneth E. Gonsalves ◽  
Hengpeng Wu ◽  
Yongqi Hu ◽  
Lhadi Merhari

AbstractThe SIA roadmap predicts mass production of sub-100 nm resolution circuits by 2006. This not only imposes major constraints on next generation lithographic tools but also requires that new resists capable of accommodating such a high resolution be synthesized and developed concurrently. Except for ion beam lithography, DUV, X-ray, and in particular electron beam lithography suffer significantly from proximity effects, leading to severe degradation of resolution in classical resists. We report a new class of resists based on organic/inorganic nanocomposites having a structure that reduces the proximity effects. Synthetic routes are described for a ZEP520®nano-SiO2 resist where 47nm wide lines have been written with a 40 nm diameter, 20 keV electron beam at no sensitivity cost. Other resist systems based on polyhedral oligosilsesquioxane copolymerized with MMA, TBMA, MMA and a proprietary PAG are also presented. These nanocomposite resists suitable for DUV and electron beam lithography show enhancement in both contrast and RIE resistance in oxygen. Tentative mechanisms responsible for proximity effect reduction are also discussed.

TJ. Stark ◽  
Z. J. Radzimski ◽  
P.A. Peterson ◽  
D.P. Griffis ◽  
P. E. Russell

Recent advances in electron optical systems which allow reduction of electron beam voltage while maintaining sufficiently small spot size and high current density have opened new possibilities for electron beam lithography. The main advantage of low beam energy lithography is a reduction of backscattered electrons and, consequently, the reduction of problems associated with proximity effects. The other advantages of this technique are reduction in the dose required to modify a resist and minimization of substrate damage caused by energetic electrons. Proper electron energy must be chosen at which the beam deposits its energy mainly within the resist film with minimal penetration into the substrate. Monte Carlo simulation programs have been used widely to predict the scattering interactions and thus the area of proximity effects. Rutherford cross section for angle scattering and Bethe energy loss have been commonly used in Monte Carlo modeling. However, low energy lithography (<5keV) requires a more accurate approach based on Mott cross sections for scattering and a more precise formula for energy loss replacing the Bethe law which is invalid below 1 keV energy.

L. D. Jackel

Most production electron beam lithography systems can pattern minimum features a few tenths of a micron across. Linewidth in these systems is usually limited by the quality of the exposing beam and by electron scattering in the resist and substrate. By using a smaller spot along with exposure techniques that minimize scattering and its effects, laboratory e-beam lithography systems can now make features hundredths of a micron wide on standard substrate material. This talk will outline sane of these high- resolution e-beam lithography techniques.We first consider parameters of the exposure process that limit resolution in organic resists. For concreteness suppose that we have a “positive” resist in which exposing electrons break bonds in the resist molecules thus increasing the exposed resist's solubility in a developer. Ihe attainable resolution is obviously limited by the overall width of the exposing beam, but the spatial distribution of the beam intensity, the beam “profile” , also contributes to the resolution. Depending on the local electron dose, more or less resist bonds are broken resulting in slower or faster dissolution in the developer.

2015 ◽  
Vol 1 (1) ◽  
pp. 13-19 ◽  
G. Grenci ◽  
E. Zanchetta ◽  
A. Pozzato ◽  
G. Della Giustina ◽  
G. Brusatin ◽  

1994 ◽  
Vol 367 ◽  
P.O. Pettersson ◽  
R.J. Miles ◽  
T.C. Mcgill

AbstractWe present the results of electron beam assisted molecular beam epitaxy (EB-MBE) on the growth mode of silicon on CaF2/Si(111). By irradiating the CaF2 surface with low energy electrons, the fluorine is desorbed, leaving an ordered array of F-centers behind. Using atomic force microscopy (AFM), we do not detect any surface damage on the CaF2 layer due to the low energy electron irradiation. The surface free energy of the CaF2 is raised due to the F-center array and the subsequent silicon layer is smoother. Using AFM and X-ray photoelectron spectroscopy (XPS), we find an optimal range of exposures for high temperature (650°C) growth of the silicon overlayer that minimizes surface roughness of the silicon overlayer and we present a simple model based on geometrical thermodynamics to explain this.We observed a similar optimal range of exposures that minimizes the surface roughness for medium (575°C) and low (500°C) growth temperatures of the silicon layer. We present an explanation for this growth mode based on kinetics.

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