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This paper presents a detailed study on computer simulations of resist profiles obtained in x-ray lithography for exposures made either with synchrotron radiation or with an Al–Kα source. It is assumed, for purposes of the calculations, that the vacuum windows consist of kapton and that silicon is used as the mask material. The influence of edge shape and mask absorber thickness upon the resist structure is of special interest. The other parameters affecting resist profiles, such as Fresnel diffraction (especially in the case of semitransparent absorbers) and photoelectron range, are taken into consideration. In the case of the x-ray tube, the penumbral blur caused by the finite dimensions of the source spot leads to an additional deterioration of the edge sharpness. For the calculations, the intensity distribution over the spot area was assumed to be uniform (with Gaussian-shaped edges). The influence of the photoelectron range upon the resist profiles is calculated, using the simple depth-dose relationship of Gruen. The calculated resist profiles are compared with typical experimental results.

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This paper presents a detailed discussion of problems concerning mask heating, temperature distributions and resulting distortions of a boron-doped silicon mask which is exposed to intense x-ray radiation (from electron storage rings or plasma sources), having different spatial geometries and different distributions over time. For the calculations, all significant heat-loss mechanisms, e.g., radiation, thermal conduction in the mask, and heat transfer through an ambient gas, have been taken into consideration. The line-shaped synchrotron beam has a vertical Gaussian intensity distribution, with nearly time-constant radiation power. The influences of different scan modes on the temperature rise are taken into account. In the case where helium is used as the coolant gas, the temperature rise remains within acceptable limits, even at the highest possible radiation power. The plasma source emits extremely short, high power x-ray pulses having a homogeneous spatial distribution. The short pulse duration leads to a considerable temperature rise in the mask, which would introduce appreciable distortions. However, the homogeneity of the exposure combined with the stress in the mask membrane can suppress this effect.

Resolution in x-ray lithography is influenced mainly by the exposure geometry, the resist's behavior, and by the Fresnel diffraction as well. The range of photoelectrons created by the soft x rays, which can also effect the resolution, has been investigated theoretically and experimentally. The effective range remains below 20 nm depending on the resist material and on the exposure wavelength. As the photoelectrons do not limit the resolution in synchrotron lithography under practical conditions (proximity gap;>20 ,urn), this effect is not considered explicitly in the x~ray lithography simulator XMAS which enables the three-dimensional simulation of resist profiles. The application of XMAS to synchrotron lithography and the related one-layer resist systems reveals a Fresnel-limited resolution somewhere between 0.1 and 0.2 ,urn, depending on the actual resist parameters.