In 1981 A. N. Broers suggested that the spatial limit of direct writing electron beam lithography (DWEBL) would be limited to ~10 nm by the laterally scattered fast secondary electrons (FSE) even in atomically thin resist. One possible solution to this restriction would be to use low- or ultralow-energy electrons. Experiments and simulations have been carried out to quantify the contribution of FSE to the energy deposition that results in exposure of the resist over high-beam energies. To examine the effects of FSE on low-voltage operations, studies of electron-beam lithography (EBL) in the low- to ultralow-energy range, employing commonly used resists such as PMMA, were performed, and the results were compared to those from conventional high-voltage processing. DWEBL was performed in a Schottky field emission gun scanning electron microscope (SEM), used in cathode-lens mode for ultralow-voltage operation. The exposure characteristics and sensitivity of the system at these energies have been investigated using Monte Carlo simulation methods. Saturation doses were calculated at low energies, which would give a useful condition to target for routine exposure because it ensures the critical dimensions will not be affected by any random changes in beam intensity.
Proc. SPIE. 6151, Emerging Lithographic Technologies X
KEYWORDS: Lithography, Electron beam lithography, Electron beams, Optical lithography, Polymethylmethacrylate, Scattering, Laser scattering, Electron microscopes, Scanning electron microscopy, Monte Carlo methods
To examine the practical limits and effects of low voltage operation, studies of electron beam lithography (EBL) in the low (few keV) to ultra-low (E < 500eV) energy range, employing commonly used resists such as PMMA was done, and the results were compared to those from conventional high voltage processing. The direct writing was performed at low energies by our homemade scan generator and a Schottky field emission gun scanning electron microscope (SEM), used in cathode-lens mode for ultra-low voltage operation. The exposure characteristics and sensitivity of the system at these energies have been investigated using an advanced Monte Carlo simulation method. Our modeling of the lithographic process showed a significant increase in resolution and process latitude for thinner resists.
In this work, a new grid was added to a grid corona discharge TEA CO<SUB>2</SUB> laser. The new grid was mounted under the cathode and inside the laser tube. The effect of this new mesh on the uniformity of the glow discharge was investigated. Experiments showed that the new mesh extends the arcing limit of oxygen concentration up to 9.5%. In this study, the effect of the tube size and the electrode spacing was tested on the output and loading energy density in the medium aperture of 2.5 cm on the laser tube.
As the life time of the vibrational modes (001) and (100) of CO<SUB>2</SUB> are different, the population inversion in gasdynamic laser (GDL) is sensitive to the cooling rate of gas. If the cooling rate of gas is too fast, both levels will stay hot and so the gain decreases. However, if the cooling rate is too slow, two lasing levels cool down accordingly and again it lowers the gain. In turn, the slope of the supersonic nozzle affects the cooling rate of the levels and also the population inversion. Thus, the shape of a supersonic nozzle is an important factor in small signal gain of CO<SUB>2</SUB> gasdynamic laser. On the basis of mean value theorem, one would expect that for every family of supersonic nozzle shapes (shock free, wedged, logarithmic, and exponential), there will be a specific one having an optimum cooling and gain. Small signal gain of a GDL was calculated for the different nozzle shape of the different families. It was found that the exponential nozzle shapes would give an optimum population inversion.
Plasma injection method has been used to stabilize the main electric discharge in the atmospheric high power cw CO<SUB>2</SUB> lasers. In this work, an analytical perturbative method is introduced for solving Boltzmann equation for a general plasma. This method is applied to a specific plasma injection CO<SUB>2</SUB>-N<SUB>2</SUB>-He laser. Small signal gain and output power of the laser are calculated in the steady state as a function of gas mixture and pressure. Dependence of small signal gain and output power on the main discharge current also were considered.
A variable quasi specific heat ratio along the supersonic nozzle of a gasdynamic laser (GDL) is introduced as a sequence. This simplifies the energy equation of the expanding gas and reduces it to a linear first order differential equation. By introducing an L2 metric on the induced gain sequence g(n) , it was observed that the sequences converge on the first step quickly. Furthermore, this precise method requires less computation time compared with the other methods.