Double-layer resist films for submicrometer electron-beam lithography

This paper describes a double-layer resist-film technique for submicrometer electron-beam lithography. The results of computer simulation and lithography experiments carried out on PMMA/MPR (LO/HI) and MPR/PMMA (HI/LO) double-layer films are reported in full detail. It is shown that an undercut profile suitable for the lift-off processing can be reproducibly obtained by the use of the LO/HI structure over a wide range of electron-beam exposure dose, while the HI/LO structure is of great advantage in the fabrication of lift-off metal gates with a mushroom-like cross section.     

Sub-5 keV electron-beam lithography in hydrogen silsesquioxane resist

We fabricated 9-30 nm half-pitch nested Ls and 13-15 nm half-pitch dot arrays, using 2 keV electron-beam lithography with hydrogen silsesquioxane (HSQ) as the resist. All structures with 15 nm half-pitch and above were fully resolved. We observed that the 9 and 10-nm half-pitch nested Ls and the 13-nm-half-pitch dot array contained some resist residues. We obtained good agreement between experimental and Monte-Carlo-simulated point-spread functions at energies of 1.5, 2, and 3 keV. The long-range proximity effect was minimal, as indicated by simulated and patterned 30 nm holes in negative-tone resist.     

Two-layer resist structure for electron-beam fabrication of a submicrometer gate length GaAs device

A two-layer resist structure using EBR-9 and PMMA for fabricating a fine metal line with a mushroom-like cross-sectional profile is reported. The structure provides T-shaped resist cavities with undercut profiles using electron-beam exposure. With the optimum developing condition, the bottom opening is as small as 0.1 µm, and the top opening is wide enough not to require an additional exposure in order to obtain a mushroom-like metal lift-off pattern. A Monte Carlo calculation is carried out in order to analyze the profile of the two-layer resist structure, and it is shown that an undercut T-shaped resist profile with a 0.1-µm bottom opening can be obtained using a high-sensitivity resist on a low-sensitivity resist structure. A 0.15-µn mushroom-like lift-off metal profile has been fabricated on a 0.1-µm recessed GaAs substrate by the use of this resist structure.     

Estimation of resist profile for line/space patterns using layer-based exposure modeling in electron-beam lithography

One of the essential tasks in the dose control for fabrication of 2-D and 3-D patterns using electron-beam lithography is estimation of remaining resist profiles after development. A conventional approach is to compute the exposure distribution for a target pattern through convolution with the point spread function (PSF) and then obtain the resist profile via simulation of the development process based on the exposure distribution. A new approach which does not require calculation of the exposure distribution and simulation of the resist development is proposed. It utilizes a set of experimental results on which estimation of the resist profile is based, and has a good potential to provide an alternative to the conventional approaches. In this paper, the proposed approach is described in detail along with the results obtained from an extensive simulation and also experiments.     

Controlling resist thickness and etch depth for fabrication of 3D structures in electron-beam grayscale lithography

In many applications such as optoelectronic devices, three-dimensional (3D) structures are required. Examples include photonic band gap (PBG) crystals, diffractive optical elements, blazed gratings, MEMS, NEMS, etc. It is known that the performance characteristics of such structures are highly sensitive to their dimensional fidelity. Therefore, it is essential to have a fabrication process by which such 3D structures can be realized with high dimensional accuracy. In this paper, practical methods to control thickness of the remaining resist and etch depth, which may be employed for fabrication of such 3D structures using grayscale electron-beam lithography, are described. Through experiments, explicit control of the remaining resist thickness and etch depth at the resolution of 20 nm for the feature sizes of 0.5 μm and 1 μm has been successfully demonstrated. Also, the 1:1 ratio of silicon to resist etching rates was achieved for transferring the remaining resist profile onto the silicon substrate.     

A new method of formation of the masking image (relief) directly during the electron-beam exposure of the resist

A new method of dry electron-beam etching of some positive resists directly during exposure is proposed. It is shown that exposure of the PMMA resist (the layer 80–85 nm thick on the Si wafer) by electrons with energy of 15–20 keV in vacuum at temperatures of 115–170°C (above the glass-transition temperature of the PMMA) leads to the effective etching of the resist at relatively low exposure doses by a factor of 10–100 smaller than the exposure doses of this resist in the conventional “wet” lithography. It is assumed that the direct etching proceeds by the mechanism of the radical-chain depolymerization of the PMMA resist to a monomer. The high efficiency of the suggested method for the formation of spatial 3D structures in the PMMA resist is shown.     

Fabrication of curved structures by electron-beam lithography

The suitability of electron-beam lithography for the fabrication of curved structures, of interest for integrated optical devices, can be limited by the available pattern data formats. Extensions to the input format of a Cambridge Instruments electron-beam microfabricator are reported, which have allowed complex patterns to be easily specified for both mask making and direct writing.     

外场下等离子体中波的增强和带电粒子流的加速

在不考虑碰撞机制的情况下,研究了外加高频电磁场(泵波)下等离子体中Langmuir波和离子声波的增强以及带电粒子流的加速.基于流体力学方程,推导了描述等离子体参量不稳定性的振动方程,进一步得到描述带电粒子流加速的数学表达式和有质动力的数学表达式.结果表明,在等离子体参量不稳定性的激发过程中,Langmuir波和离子声波得以增强以及带电粒子流由于泵波与Langmuir波(离子声波)的耦合而加速;有质动力的产生是由于泵波与Langmuir波(离子声波)的耦合而且它是参量不稳定过程的策动力,另外有质动力不仅存在高频分量,还存在低频分量.     

Visible absorption by electron-beam pumped rare gases

The temporal and spectral behavior of absorption in the visible bye-beam excited argon, krypton, and xenon have been investigated with and without additives. The probe light used was from an argon-ion pumped, tunable dye laser, or from the visible lines of the argon-ion laser itself. Strong absorption was observed at all wavelengths investigated (450-620 nm). Structured absorptions out of atomic and molecular excited states have been identified by their temporal, spectral, and pressure behavior. The ubiquity of these absorptions, which is not fully understood, should have serious implications for the development of new visible lasers that operate during the electron-beam pumping pulse.     

Negative X-ray resist produced by proton bombardment

Polymethylmetacrylate (PMMA) films of 580 nm have been irradiated by X-rays through a copper mask. Subsequent proton bombardment of the PMMA films (masked and unmasked regions) changes them, at doses ?2×1013 ions/cm2, from a positive to a negative resist.     

Lower submicron pattern definition by high-voltage electron-beam lithography

High-voltage electron-beam writing on polymethyl methacrylate (PMMA) at 50 kV with a dose of 50 ?C/cm2 has been found to give an outstanding result of the simultaneous formation of isolated and arrayed quarter-micron window patterns of the same size as the electron-beam diameter of a quarter micron.     

Measurement of VLSI power supply current by electron-beam probing

The measurement of power supply noise and current by electron-beam probing is described. Noise measurements can be made on the chip under test, and current measurements can be made on the circuit board. It is noted that power supply voltages are obtained simultaneously. This measurement method is particularly useful when combined with a larger program of circuit characterization, or design verification, by electron-beam probing     

Modification of porous ultra-low K dielectric by electron-beam curing

The impact of electron irradiation on ultra-low K (ULK) porous dielectric material used in advanced interconnects is analyzed using spectroscopic and electrical characterizations. The e-beam irradiation modifies the chemical composition, the porosity and the optical indexes. The effects of e-beam curing on electrical properties and dielectric reliability are also evaluated.     

Metal-oxide-semiconductor instability produced by electron-beam evaporation of Aluminum gates

The production of defect states in the oxide of MOS capacitors during the electron-beam metallization process was identified as the cause of the threshold voltage instability experienced at elevated temperatures with negative bias on the gate. Both n- and p-type silicon substrates,     

Molecular roughness analysis of developed resist by LER method

In this paper, line edge roughness (LER) analysis on top–down images acquired by means of a scanning electron microscope is here proposed as a powerful and non-invasive technique to map the molecular aggregate distribution in a chemically amplified resist: in particular the periodicity of the aggregates themselves is determined via power spectral density method (PSD). The roughness of two resist developers with different chemical composition will be compared on the base of 1D power spectral density function: in case of SEM acquisition, the profile to be analyzed is extracted from a top–down acquisition, while atomic force microscope (AFM) inspection of surface topography allows to calculate PSD along a user-defined line. The two approaches confirm a reduced surface roughness in case of development with smaller molecule.     

平面反射镜对激光诱导等离子体光谱的增强作用

为了获得高质量的激光诱导等离子体发射谱,在激 光诱导等离子体附近放置平面反射镜,通过改变平 面反射镜与等离子体中心轴线之间的距离,观测反射镜对土壤等离子体辐射强度的影 响;利用 Boltzmann图法和光谱线Stark展宽法测量了等离子体的电子温度Te和电子密度Ne,并解释了辐 射增强的机理。实验结果表明,平面反射镜对等离子体辐射有一定程度的增强作用, 当平面反射镜与等离子体中心轴线 的间距为3mm时,样品元素Cr、Fe和Ca的光谱线强度比无反射镜时的分别提高了49.3、50.1和75.9%,光谱信噪比(SNR )分别提 高了56.8、47.5和65.5%,Te升高了 1250K,Ne增 加了0.62×10¹⁵ cm－3;随着 反射镜与等离子体中心轴线之间距离的增大,等离子体辐射强度逐渐减弱。