Image formation in X-ray lithography
The development of ultra-large scale integrated circuits (ULSI) requires the ability to pattern features as small as 0.25 {approximately} 0.17 {mu}m with consistent quality. X-rays with wavelengths around 0.8 nm have inherently the required resolution. The application of this radiation in manufacturing needs several new techniques-sources, manipulation, and imaging. The authors address the imaging aspect of the technology - how X-rays can be used to define large area, high density patterns in a manufacturing environment. A physical model is first developed based on the propagation of partially coherent light, the absorption of photons and the scattering of electrons in the resist. The model is implemented with efficient algorithms which include (1) a modal expansion method to treat partially coherent light, (2) a beam propagation method to simulate light propagation in thick masks, (3) a double linear shift-invariant system method to simulate the diffraction of partially coherent light in the near field. A set of experiments is designed to verify the model`s predictions. A mask patterned with 0.9 {mu}m Au is used to print 0.25 {mu}m features at a gap of 38 {mu}m, yielding an exposure latitude of 33% for lines/spaces under non-optimized conditions. Excellent agreement between simulation and experiments is obtained. The model, after verification, is used to design an optimized XRL imaging system, leading to a simpler mask suitable for imaging to 0.1 {mu}m. The optimized system consists of partially coherent illumination, low contrast masks, and sloped sidewall absorber. The absorber sidewall roughness and photoelectron scattering in the resist are also found to have positive effects in X-ray lithography.
- Research Organization:
- Univ. of Wisconsin, Madison, WI (United States)
- OSTI ID:
- 39364
- Resource Relation:
- Other Information: TH: Thesis (Ph.D.); PBD: 1993
- Country of Publication:
- United States
- Language:
- English
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