Geometrically Induced Dose Correction Method for e-Beam Lithography Applications

The e-beam lithography is faced with increasing challenges to achieve a satisfying patterning of structures with critical dimensions of about 32 nm or below. The reason for this issue is the unavoidable blurring of the deposited e-beam energy due to beam blur, electron scattering (forward and backward), and resist effects. The distribution of the finally deposited dose differs from the dose weighted geometry of the printed layout. In general, the finally deposited dose is described as convolution of the layout with a process specific proximity function being a model for the unavoidable blurring. This process proximity function (PPF) is often approximated by a superposition of two or more Gaussian functions. Thus, the electron forward scattering and resist effects, being most critical to the pattern fidelity, are often described altogether by the so called alpha-parameter of the PPF. Due to these physical reasons, when the desired critical dimension of a structure is near or below the alpha-parameter of the PPF, it may be just impossible to print the structure because of the vanishing image contrast due to the blurring. It was shown by means of the simulation feature of the ePLACE data prep package that in this situation a modification of both the geometry and the dose assignment of the shapes will significantly increase the contrast of the deposited energy and thus, even preserve the printability of critical structures. This geometrically induced dose correction (GIDC) method is implemented in the ePLACE package. The simulation results for test structures are now validated by exposures of test patterns and its results clearly establish the practical advantage of the new method. In this paper we will publish the results of the related exposures - done on Vistec SB3050 series shaped e-beam writers - demonstrating the practical importance of the GIDC method for layouts with critical dimensions of 32 nm and below.