| Improved lithographic resolution has been and will continue to be the key enabler for the continued growth of the semiconductor industry. Electron beam lithography, projecting more than 10 million pixels in one shot, is being developed to push the resolution beyond 100nm. However the combination of space charge effects and lens limitations set limits to the throughput at a resolution of 100nm or less. The aim of this work is to examine what these limits are.; First, Monte Carlo simulation was employed to investigate the deterministic blur induced by lens-like action of the global space charge, and the stochastic blur due to the residual fluctuation of the neighboring-electron interactions. The deterministic blur was surprisingly serious. Then a fundamental theory, based on the variational principle and Maxwell equations, was developed to quantify the physics of the global space charge optics. One effect of the space charge is to act as a lens and the aberrations of this lens are the major contributor to the overall blur. Expanding the beam radially reduces the space-charge induced blur but exacerbates that due to the off-axis aberrations of the magnetic lenses, so there is an optimum radial extent of the beam. It appears that current designs are far from optimum for feature sizes of 50nm or less; there are enormous (square law) advantages to scaling down the length of the electron optical column.; To allow experimental verification, a complete set of scaling laws has been rigorously derived to describe how the various space charge effects exactly scale with the system parameters. A series of scaled experiments was designed and executed that indeed verified (within 15%) the scaling laws and the results of the simulations. This work is the first reported experimental verification of the space charge lens aberrations. The results also predict that a blur as small as 10nm might be achieved with a 50microamp beam of 50KeV electrons using a 2cm-long column (mask to wafer); this is more than an order of magnitude shorter than in current designs. |
