Proximity effect (electron beam lithography)

About: Proximity effect (electron beam lithography) is a research topic. Over the lifetime, 940 publications have been published within this topic receiving 8508 citations.

Hochauflösende Röntgenlithografie zur Herstellung polymerer Submikrometerstrukturen mit großem Akspektverhältnis

Abstract: In this work the process for X-ray lithography in PMMA was further developed to generate structures in PMMA layers with lateral dimensions in the submicron range and heights of several micrometers resulting in aspect ratios of 10 and higher. PMMA films of 2 ÷ 10 μm could be structured with aspect ratios up to more than 12 using Synchrotron radiation with λ c = 0.4 nm after the systematic analysis and optimization of the development- and exposure process. An X-ray mask technique using a free suspended membrane of 1 μm thick silicon nitride with 2 pm high gold absorbers was introduced. After optimizing the entire process for mask production, the limits of electron beam lithography could be determined. Due to the proximity effect, CAD data of lateral dimensions need to be shrunken by -100 ÷ 150 nm per edge in order to receive nominal values in the PMMA structures produced via lithography. Locally minimized walls of resist may be used as templates for electroplating to reproducible create minimal slit sizes down to 75 nm in 2 μm high gold absorbers with tolerances of ± 25 nm on the same substrate. To spincoat the requested PMMA films, resist systems offered for electron beam lithography were used. Both examined resists, MicroChem 950k PMMA A11 and All Resist AR SX-P 6540, have a higher contrast in the dose regime above 1 kJ/cm 3 compared to the dose regime below this value. Surface tension during drying as part of the development process limits the achievable aspect ratio as function of the actual structure height for walls and columns. Rising the pre-bake temperature of MicroChem 950k PMMA A11 from 111°C to 180°C results in more stable structures. Adding 10 ppm fluoride tenside to the rinse bath during the wet development process reduces the structure collapse. Using an adhesion layer out of polyimide avoids cracks in the resist even for lateral dimensions of several 10 pm. The proximity gap during X-ray exposure influences the structure quality via diffraction effects significantly. Reducing this gap from 100 μm to 15 μm minimizes the influence of this effect. The process optimized in this study could be used to generate submicron structures for fluidic applications with aspect ratios more than 10. It enables the creation of polymer moulds and masks for the production of submicron structures in metals. By electroforming, e.g. gold structures with aspect ratios more than 12 and lateral dimensions around 500 nm were fabricated. This allows for batch-fabrication of SAW-filters for frequencies above the presently used ones. In addition the optimized process can be used to build metallic filters with high aspect ratios for the use as band-pass filters with sharp cut-off-frequencies in the infrared.

Resist Heating in Cell Projection Electron Beam Direct Writing

Abstract: Electron beam (EB) direct writing systems have often been used for fabricating sub-half-micron advanced devices because EB direct writing is the most practical method for making the required patterns. Recently, the cell projection (CP) method has become indispensable for increasing the writing throughput in the EB direct writing system. However, it is considered that resist heating may be seriously aggravated below the quarter-micron level when the CP method is used, because the total deposited energy, which is irradiated by one CP EB shot, is almost the same as that irradiated by one variably shaped (VS) EB maximum size shot. Resist heating in the case of the CP method is calculated by a finite element method using the ANSYS (Ver. 5.0A: ANSYS, Inc.) program. In particular, thermal diffusion calculation is mainly carried out under the conditions of 50 kV acceleration voltage and 10 A/cm2 current density for practical application to advanced device fabrication. The calculated results suggest that resist heating in the CP method is mainly caused by the horizontal thermal flux between plural EB shots within the area of one CP shot, by the same mechanism as proximity resist heating under the VS method. Therefore, CP EB writing causes horizontal-mode resist heating. In particular, when a low current density is used, this resist heating mode arises significantly. However, CP writing with high acceleration voltage causes a reduction in the rise of the resist temperature, which causes resist heating. When the EB irradiation time is longer than 1.0 µ s under practical EB writing conditions, the resist temperature increases proportionally to the decrease of writing pattern size in the case of the CP writing with a maximum shot size of 5.0×5.0 µ m. It is also shown that the larger the beam blur of an incident beam, the more serious is the resist heating. When a highly sensitive resist (10 µ C/cm2) is used under these practical conditions, however, resist heating in the CP method is prevented without writing throughput degradation regardless of the CP maximum shot size, because the resist temperature does not rise above the thermal denaturation temperature of standard EB resists. Accordingly, the maximum CP shot size, which affects the writing throughput, is determined by the proximity effect and the Coulomb interaction for fine pattern fabrication.

Thermal superconducting quantum interference proximity transistor

Abstract: Superconductors are excellent thermal insulators at low temperatures owing to the presence of an energy gap in their density of states1. Through the so-called proximity effect2, superconductors can influence the density of states of nearby metallic or superconducting wires. In this way, the local density of states of a wire can be tuned by controlling the phase bias (φ) imposed across it3. Here we demonstrate a thermal superconducting quantum interference proximity transistor (T-SQUIPT) that enables the phase control of heat currents by exploiting the superconducting proximity effect. Our T-SQUIPT device comprises a quasi-one-dimensional aluminium nanowire forming the weak link embedded in a superconducting ring4,5. Controlling the phase bias by changing the magnetic flux through the ring shows temperature modulations of up to 16 mK, yielding a temperature-to-flux transfer function that reaches approximately 60 mK Φ0–1. We also demonstrate a hysteretic dependence of the local density of states of T-SQUIPTs on the applied magnetic field due to phase-slip transitions. This allows the T-SQUIPT device to operate as a phase-tunable thermal memory6,7, where the information is encoded in the temperature of the metallic mesoscopic island. Heat transport in electronic systems is influenced by nearby superconductors due to the so-called proximity effect. Combining this with the manipulation of superconductivity using magnetic fields enables the control of nanoscale thermal transport.

Proximity effect correction in variably shaped electron‐beam lithography

Abstract: Proximity effect in electron‐beam lithography is studied with an emphasis on physical understanding. Computer simulation is used to explore correction schemes which specifically include the resist behavior and yet are theoretically manageable in formulating the pattern correction for mathematical analysis. Both energy density part way through the resist and relative importance of background on critical edge are investigated. It is shown that one‐third of the resist thickness from the substrate appears to be where the process parameters should be characterized, and that the total effective deposited energy at the nominal edge must be reduced as the background contribution increases. A mathematical model and design graphs are developed so that the impact of the background on the edge control is directly related to fundamental physics through the Monte Carlo calculation. The nominal edge is used as the critical aspect to be controlled and the constraint of constant bias can be applied.

Manufacture of optical proximity effect correction mask

Abstract: PROBLEM TO BE SOLVED: To manufacture an optical proximity effect mask capable of highly precisely correcting optical proximity effect without lowering the throughput by adding the exposure correction data of at masked electron beam plotting that are decided based on the correction amount of the optical proximity effect in a photolithography process to mask pattern data SOLUTION: Relation between the correction value of mask dimension and the dimensional error of a resist pattern in the photolithography process is obtained with respect to the designed mask patterns having the various kinds of dimension by the simulation of an optical image or an exposure experiment result Then, the correction value of the mask dimension required for minimizing the dimensional error is decided Based on the correction value, the ideal corrected pattern 6 obtained by correcting the dimension of the designed pattern of a mask is formed Besides, the mask pattern data is constituted of mask shape data and the exposure correction data of a mask electronic beam plotting device decided based on the correction amount of the optical proximity effect Then, the mask is exposed by changing exposure according to the exposure correction data