Myrtle I. Blakey

The SCattering with Angular Limitation in Projection Electron-Beam Lithography (SCALPEL) System

A SCALPEL\circledR (SCattering with Angular Limitation in Projection Electron-beam Lithography) proof-of-concept lithography system, comprising a tool, a reticle and a resist, has been designed to address the critical issues that must be investigated to determine if this approach is viable as a practical lithographic technology.

Terahertz electroluminescence from superlattice quantum cascade structures

Intersubband electroluminescence is reported in a quantum-cascade structure based on asymmetric superlattice active regions and designed for emission in the THz range (λ≈80 μm). Comparison with a structure based on a “vertical transition” in a single quantum well shows an increased full width at half maximum (2.8 vs 0.9 meV) of the emission line. In both cases the dependence of the optical power on the injected current is linear or sublinear and remains in the pW range.

Preliminary results from a prototype projection electron‐beam stepper‐scattering with angular limitation projection electron beam lithography proof‐of‐concept system

We have designed and constructed a proof‐of‐concept projection electron beam lithography system based on the scattering with angular limitation projection electron beam lithography principle. In this system, a thin membrane mask is used in a 4:1 reduction projection system at 100 keV. Image contrast is formed by scattering in the mask and subsequent aperturing of the scattered electrons in the back focal plane of the projection system. We have employed a step‐and‐scan architecture which uses continuously moving mask and wafer stages to trace out the full pattern. The electron beam can thus be kept small (1×1 mm in our case) which greatly simplifies the design of the electron optical system. In addition, the membrane areas can be kept small in linear dimension in one direction, minimizing in‐plane pattern distortions. Our system will be constructed in two stages. In the first stage, the mask stage is static and the wafer stage operates in step‐and‐repeat mode. This initial version of the system allows for ...

Space-charge effects in projection electron-beam lithography: Results from the SCALPEL proof-of-lithography system

In projection electron-beam systems resolution and throughput are linked through electron–electron interactions collectively referred to as space-charge effects. Hence, a detailed understanding of these effects is essential to optimizing the lithographic performance of a projection electron-beam lithography system. Although many models have been developed to describe one or more of the various aspects of the Coulomb interactions that occur in the beam, there is minimal experimental data available. We have performed a series of experimental measurements in the scattering with angular limitation projection electron-beam lithography (SCALPEL) proof-of-lithography system to characterize the space-charge effects for such an optical configuration. The results of those measurements have been compared to a combination of computer simulations and analytical models. The agreement between the models and experiments was good, within the limits of experimental error. We determined the exponent in the dependence of blu...

The SCALPEL proof of concept system

Abstract We have designed and constructed a projection electron beam lithography system based on the SCALPEL (SCattering with Angular Limitation in Projection Electron beam Lithography) principle. The experimental tool was built to analyze the efficacy of this approach as an alternative to photolithography for future integrated circuit manufacturing. In this paper we will describe the design of the system and show preliminary results of test pattern exposures. We will show printed features down to 0.08 μm as well as lithographic properties, such as depth of focus, which has been measured at 75 μm for 0.25 μm lines and spaces.

Monte Carlo study of high performance resists for SCALPEL nanolithography

Abstract The semiconductor community continues to push the limits of device dimensions by exploring new high-resolution lithography technology. As part of the SCALPEL lithography resist program, our goal is to be able to print sub-100 nm structures at doses that will permit high throughput, reduce wafer heating and still maintain good process latitude. Using 100 KV exposures on a SCALPEL tool, 100 nm structures were printed at exposure dose of 5.8 μC/cm 2 (and 80 nm isolated trenches at 5.4 μC/cm 2 ) in positive resists. In negative resists, isolated 100 nm were printed at a dose of 6.8 μC/cm 2 , and 80 nm structures at 7.2 μC/cm 2 were resolved as well. These results are well below the 10 μC/cm 2 minimum dose requirement for high throughput. Monte Carlo simulations were used as means to understand energy absorption mechanisms of these e-beam optimized resists, DUV and 193 nm resists. Atomic composition was found to factor in improved resist ionization. The resin (or low-Z elements) is found to account for more than 99% of ionization events during exposure.

Commercialization of SCALPEL masks

To investigate the viability of large scale manufacture of SCALPEL masks, key components of the SCALPEL mask process have been performed by commercial suppliers. SCALPEL mask blanks have been fabricated by MCNC to specifications supplied by Lucent and have been delivered, patterned, and utilized. Patterning, inspection, and metrology have been performed by DuPont Photomask and Photronics using the standard set of tools used for photomasks. A wet chemical pattern transfer process has been developed that is compatible with the processing tools in the mask shops and is extensible to the 0.1 μm generation of integrated circuits. SCALPEL masks that have been fabricated using these processes and tools exhibit excellent pattern fidelity and feature edge quality.

Metrology of scattering with angular limitation projection electron lithography masks

Mask metrology is a vital part of any lithographic technology, both for control of the mask patterning process and also for ensuring that the contribution of the mask to the system error budget is within acceptable limits. For design rules of 0.13 μm and below, errors arising from metrology must be kept to less than 1 nm. We have examined the potential for achieving this, in the case of scattering with angular limitation projection electron lithography (SCALPEL) masks, by using high-energy (100 keV) electron transmission measurements. We have also performed extensive metrology using conventional scanning electron microscope techniques. These results show that the SCALPEL mask has the potential to meet the specifications necessary for lithography at the 0.13 μm generation and beyond.

SCALPEL proof-of-concept system: preliminary lithography results

We have designed, constructed, and are now performing experiments with a proof-of-concept projection electron-beam lithography system based upon the SCALPELR (scattering with angular limitation projection electron-beam lithography) principle. This initial design has enabled us to demonstrate the feasibility of not only the electron optics, but also the scattering mask and resist platform. In this paper we report on some preliminary results which indicate the lithographic potential and benefits of this technology for the production of sub-0.18 micrometer features.

CMOS compatible alignment marks for the SCALPEL proof of lithography tool

SCALPEL alignment marks have been fabricated in a SiO 2 /WSi 2 structure using SCALPEL lithography and plasma processing. The positions of the marks were detected through e-beam resist in the SCALPEL proof of lithography (SPOL) tool by scanning the image of the corresponding mask mark over the wafer mark and detecting the backscattered electron signal. Single scans of line space patterns yielded mark positions that were repeatable within 30 nm 3σ with a dose of 0.4 μC/cm 2 and signal-to-noise of 16 dB. An analysis shows that the measured repeatability is consistent with a random noise limited response. The mark detection repeatability limit, that can be attributed to SPOL machine factors, was measured to be 20 nm 3σ. By using a digitally sequenced mark pattern, the capture range of the mark detection was increased to 13 μm while maintaining 36 nm 3σ precision. The SPOL machine mark detection results are very promising considering that they were measured under electron optical conditions that were not optimized.