The scalar photoinduced changes of the optical absorption edge and the optical constants in amorphous Se75Ge25 chalcogenide thin film have been studied using XeCl excimer laser light with a wavelength of 306 nm. The glass transition temperature (Tg) of this material is evaluated to be approximately 220 °C, at which the as-deposited film is initially annealed. The optical energy gaps Eop of as-deposited and initially annealed Se75Ge25 thin films are 1.90 and 1.84 eV, respectively. When initially annealed films are exposed to a 4.05 eV excimer laser (≫Eop) with energy densities of 100, 120 and 180 mJ/cm2, a photodarkening effect that exhibits a decrease in the optical transmittance (Top) and Eop and an increase of the refractive index n and the extinction coefficient k in the vicinity of the absorption edge (1.4–3.0 eV) is observed. In particular, in the case of a thin film exposed by 120 mJ/cm2, Eop and n+ik measured at 673.7 nm(1.84 eV), i.e., an absorption edge of initially annealed thin film, are 160 eV...

Photoinduced transformations in amorphous Se75Ge25 thin film by XeCl excimer-laser exposure

Proximity effect in e-beam lithography is mainly due to the “nonideal” distribution of exposure (energy deposited in the resist). The proximity effect correction schemes developed so far employ a two-dimensional (2D) model, i.e., exposure variation along the resist depth dimension is not considered. The exposure distribution estimated by the 2D model can be significantly different from the actual exposure distribution, especially for the nanoscale patterns. In this article, a three-dimensional (3D) correction method which uses a 3D point spread function in controlling e-beam dose distribution within each circuit feature in order to achieve a certain desired 3D remaining resist profile after development is described. The dose to be given to each region of a feature is determined based on the estimated remaining resist profile (with the emphasis on the sidewall shape) through iterations. Simulation results demonstrating the potential improvements by the 3D correction are provided.

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True three-dimensional proximity effect correction in electron-beam lithography

Particle beams, in their broadest context, have become the most common tools in the kit of the IC process engineer, In this paper the general characteristics of particle-beam technologies are systematically classified and critical applications issues are outlined. The uses of ion, electron, and photon beams for various processes (e.g., thin-film deposition, lithography, etching, doping) are reviewed and critical issues are highlighted. The feasibility of integrating several advanced beam processes to achieve a totally in situ process is discussed. Particulate contamination in "clean"- room environment and under vacuum conditions is addressed and related to chip defects and yield. The relative advantages, in terms of facility and operating cost, flexibility, device performance, of an in situ process are considered.

Particle-beam fabrication and in situ processing of integrated circuits

I review the work of proximity effect correction (PEC) in electron-beam (e-beam) lithography with emphasis on dose modification and shape modification PEC techniques.

A Review of Proximity Effect Correction in Electron-beam Lithography

The potential of excimer laser lithography was studied by using a newly developed KrF excimer laser exposure system which employed an achromatic lens of 0.37 NA. As a result, a resolution limit of 0.3 μm was achieved by the use of PMGI resist on a tri-level structure. However, for the case of resist exposure on a bare Si wafer, the resist film remailed locally in layers along the nodes of the standing waves, and fine pattern could not be obtained. This phenomenon is called spotted development in this paper. The spotted development, which is due to strong standing waves within the resist film, was successfully solved by the use of new resist process technologies such as a bias exposure method and excimer laser image reversal process.

Submicron Optical Lithography Using A KrF Excimer Laser Projection Exposure System

The proximity effect reduction was achieved by electron beam (EB) uniform exposure (bias exposure) on the target covered with PMMA resist of 1 μm in addition to conventional high voltage EB writing. At an acceleration voltage of 50 kV and a dosage of 50 μC/cm2, a pattern size error of 0.5 μm pattern due to the proximity effect amounted to 0.25 μm, which was improved to 0.12 μm by bias exposure. When dosage was large, the pattern size error was further improved by bias exposure. For 50 kV and 140 μC/cm2 writing, 0.25 μm pattern including isolated window, line and window, and isolated line was formed with an accuracy of ±0.025 μm. The pattern size error for conventional EB writing was almost independent of dosage. For 20 kV and 20 μC/cm2 writing, the pattern size error was hardly improved by bias exposure.

T. Takigawa

Papers

Proximity effect reduction in high voltage electron‐beam lithography by bias exposure method