Ion beam exposure profiles in PMMA–computer simulation

Abstract

A comprehensive Monte Carlo program (piber) has been developed for the simulation of ion beam exposure of resists. piber has been used to study ion ranges, backscattering coefficients, and energy-loss distribution data for various combinations of incident ions and multilayered targets. For lithographic applications, the spatial ion energy-loss distribution in polymethyl methacrylate (PMMA) generated with piber for a δ-function exposure is convoluted with realistic incident ion beam shape (Gaussian, square, etc.) to produce latent images. A string development model is then used to generate developed ion beam exposure profiles in PMMA. The developed profiles for isolated lines have been studied as a function of parameters such as ion energy, resist thickness, and exposure dosage. Closely spaced lines have also been simulated in order to study proximity effects. It is demonstrated that proximity problems are greatly reduced in comparison with electron beam exposed patterns.

Computer Simulation of Processes at Electron and Ion Beam Lithography, Part 2: Simulation of Resist Developed Images at Electron and Ion Beam Lithography

“…The differences in the observed multiciphered dependencies are small and they could be neglected in numerical simulation of the development process in PMMA resist. In the case of ion exposure process a similar linear or non-linear solution processes were observed pertaining to ion mass (Brault & Miller, 1980;Karapiperis et al, 1981;Vutova & Mladenov, 2001) due to the different radiation ion efficiency to the energy transfer and subsequently, to different latent images. In Fig.3 one can see the non-linear (multi-valued) solubility rate obtained in the case of He + (Fig.3a) and Ar + (Fig.3b) irradiations of PMMA.…”

“…and for a chosen developer. The given data (Brault & Miller, 1980;Karapiperis et al, 1981) presents the sensitivity D 0 and the contrast γ d in the case of some ion beam resists. Generally, the sensitivity of the polymer resists at the ion exposure is assumed to be higher than at the electron exposure (Brewer 1980;Ryssel et al,1991).…”

Ion projection: the successor to optical lithography

“…Hydrogen or Helium ion beams are scattered much less in resist layers than electron beams [8]. Thus, pattern transfer is possible in single layer resists on wafers with substantial topography.…”

Lithographie par faisceaux d'ions : simulations et résultats expérimentaux

“…La rétrodiffusion des ions sur le substrat est négligeable. La figure 1 montre la simulation par ordinateur des trajets de 50 ions H + d'énergie 60 keV traversant une couche de PMMA déposée sur divers substrats [10]. On remarque qu'à une profondeur de 400 nm, la déviation latérale de la plupart des ions incidents ne dépasse pas 30 nm.…”