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A high-performance membrane mask for electron projection lithography (EPL) systems is proposed. The design and material selection of the mask described here were carefully executed by considering not only the lithographic performance but also various properties. The mask described in this article consists of a 600-nm-thick diamond-like carbon (DLC) scatter on a DLC membrane 30–60 nm thick. The optimum thicknesses are obtained by calculating angular distributions of the transmitted electrons by our in-house Monte Carlo simulator. It is expected to have an electron transmission of up to 80% and a beam contrast of 100% with an appropriate limiting aperture. A 1-mm-sq membrane of thickness of down to 30 nm could be successfully prepared. The high-performance membrane mask can obtain high resolution and high throughput of the EPL systems simultaneously.

Proximity effect correction (PEC) by the SCALPEL GHOST method, using a scattering stencil mask in which mask-scattered electrons are used as a correction beam, is discussed and a new correction dose adjustment method is proposed. We simulate electron scattering in order to trace electron trajectories in the Si membrane and obtain exiting angular distribution by using a Monte Carlo method. We found that the GHOST can be used for a PEC using a Si scattering stencil mask of about 0.3–2 μm thickness under a 100 kV accelerating voltage. In the SCALPEL technique, the correction dose is adjusted by changing the radius of the annular aperture size for different mask conditions and for various under-layer conditions. In the method proposed, the vertical position of an additional correction dose adjustment aperture is shifted. The angular range becomes narrow as the aperture shifts so that the electron transmission determining the correction dose can be corrected in the doublet optics. This method can also be appli...

In the measurement of patterned resists, deviation of the critical dimension (CD) is frequently observed. We have found that contamination on the resist on a Si wafer can degrade the static repeatability more than the charging phenomenon at low accelerating voltage (Vacc), that is, near 1 kV. We investigate the dependence of contamination rate (Rc) and the normalized yield of secondary electrons (δ’) on Vacc and emission current (Ie) in order to clarify the influence of the contamination and charging effects. Experimental results indicate that we can minimize the Rc by optimizing Vacc and Ie. The Rc change cannot be attributed only to the contamination and charging effects, however. It seems, instead, that two competitive reactions (deposition and etching) occur simultaneously during the measurement at low voltage. The etching effect can be interpreted as a dissociation reaction at the resist surface. To reduce the CD deviation and improve the accuracy of the CD measurement, the accelerating voltage and c...

The effect of incident electron‐beam conditions, which are acceleration voltage and beam blur of variable‐shaped electron‐beam direct writing, is investigated using the deposited energy distribution to realize a fine pattern of ≤0.25 μm in trilayer resist process. The deposited energy distribution is calculated using a three‐dimensional Monte Carlo method. In a trilayer resist system, a thin bottom resist layer can be used, because the contrast value derived from the Monte Carlo calculation is independent of the bottom layer thickness. The beam blur of 0.05 μm does not degrade 0.25 μm line‐and‐space (L/S) patterns, but seriously degrades 0.1 μm L/S patterns. Higher acceleration voltage is effective for improving the contrast. At lower acceleration voltage, the slope of the deposited energy profile defined at the resist bottom is mainly influenced by electron scattering. On the other hand, at higher acceleration voltage, the slope of deposited energy profile mainly depends on the beam blur. The 0.1 μm L/S patterns are expected to be resolved at 30 kV when there is less than 0.02 μm beam blur with trilayer resist system. The possibility of using a single layer resist process for 0.1 μm L/S pattern will be barely realized at the conditions of 50 kV and 0.02 μm beam blur.

In variably shaped electron beam (EB) lithography, the horizontal thermal diffusion in a resist cannot be neglected when, high‐current density, a high‐speed deflector amplifier, and a multiple‐layer resist system are used. These cause a horizontal‐mode resist heating (labeled ‘‘proximity resist heating’’). Calculation of proximity resist heating is accomplished by a finite element method, using ansys (Ver.4.4A) program. The calculation results suggest that the proximity resist heating is caused by the horizontal thermal flux from previous EB shot through a top layer resist. Especially, in case a high‐current acceleration voltage is used, the thermal effect is not caused by the vertical‐mode resist heating, but by the horizontal‐mode resist heating. It is also shown that the shorter settling time, which is the interval between shots, results in a higher resist temperature and a closer position of maximum resist temperature to the previous EB shot position, and that a high‐acceleration voltage in case of using a fixed current density brings out the reduction in resist heating.

A horizontal‐mode resist heating is proposed and a suitable method for avoiding it in variably shaped electron beam lithography is described. The horizontal thermal diffusion through a top layer resist between electron beam shots cannot be neglected when using a high current density electron beam, a high speed deflector amplifier, and a multiple layer resist because these cause a horizontal‐mode resist heating (labeled ‘‘proximity resist heating’’) which depends on the pattern size and on the time interval between shots. A method, suitable to avoid this resist heating, is proposed where the pattern size dependent optimum repetition number of exposures for each pattern is used. There is a slight throughput degradation of typically 10%–20% increase.

The dynamic responses of the electron beam direct writing system (EB direct writing system) are analyzed using the finite element method (FEM). The equipment is found to have a column swing vibration mode around 160 Hz. The column swing is caused by a bending vibration in the upper plate of the chamber. This vibration is initiated by the movement of the stage drive within the chamber. When column swing occurs, the resulting change in angle of the beam line creates a positioning error. FEM is also used to calculate the relative rotation angle of the column top to the stage surface. The maximum amplitude occurring after stage movement has stopped is 0.208 μrad. Since the distance between the upper plate of the chamber and the stage surface is 79 mm, the beam positioning error is 0.208 μrad×79 mm=16.4 nm. This error can be lessened by stiffening the upper plate. Utilizing cross ribs on this plate, the relative rotation angle can be lessened to 0.073 μrad. Thus, beam positioning error can be reduced to 0.073 μrad×79 mm=5.8 nm. Further, the increase in equipment weight is only 2%.