Double Exposure Lithography Research Articles

The new method of fabrication of submicron structures by optical lithography with mask shifting and mask rotation

Abstract This paper presents the methods of fabricating narrow parallel submicrometric stripes in silicon dioxide and a resist layer. The experiments were conducted by two techniques: double patterning lithography and double exposure lithography. In addition to the above mentioned processes, mask translation was applied. For all conducted experiments, chrome masks and a 405 nm line of the high pressure mercury lamp of an MA-56 Mask Aligner System were used. The main aim of the performed tests was to establish the utility and the possible applications of the methods used.

Depth of focus enhancement for sub-<inline-formula><math display="inline" overflow="scroll"><mrow><mn>110</mn><mtext>-</mtext><mi>nm</mi></mrow></math></inline-formula> technology by using KrF double-exposure lithography

Traditional double-exposure lithography (DEL) or double-patterning lithography (DPL) methodologies stem most from the resolution enhancement standpoint. A single mask with high feature densities is split into two exposure steps, each with lower feature densities that can be easily resolved. The DEL is proposed as the process window enhancement technology for sub-110-nm technology. Features with sparse pitches are printed by a first step of dense pitch exposures and a second exposure with dummy features removed. The pattern decomposition strategy described is similar to that of subresolution assisting features (SRAF). So it is compatible with the traditional rule-based SRAF implementation methodology. By comparing the depth of focus (DOF) of the 110-nm lithography process between the single exposure and the double exposure, it is found that the DOF for marginal features is extended by using double-exposure methodology, and thus extends the capability of KrF exposure tools. Furthermore, the link between the overlay performance and the overlap of the second exposure's trim slots over the first exposure is studied. The results show that the overlay control is within the KrF scanner capability. As a further study, the proposed double-exposure methodology for the 90-nm lithography process is evaluated.

Materials modeling and development for use in double-exposure lithography applications

The current optical photolithography technology is approaching the physical barrier to the minimum achievable feature size. To produce smaller devices, new resolution enhancement technologies must be developed. Double-exposure lithography has shown promise as a potential pathway that is attractive because it is much cheaper than double-patterning lithography and can be deployed on existing imaging tools. However, this technology is not possible without the development of new materials with nonlinear response to exposure dose. The performance of existing materials such as reversible contrast enhancement layers (rCELs), and theoretical materials such as intermediate state two-photon (ISTP) and optical threshold layer (OTL) materials in double-exposure applications have been investigated through computer simulation. All three materials yielded process windows in double-exposure mode. OTL materials showed the largest process window (depth of focus (DOF) 0.14 µm, exposure latitude (EL) 5.1%). ISTP materials had the next-largest process window (DOF 0.12 µm, EL 3.2%), followed by the rCEL (0.11 µm, 0.58%). This study is an analysis of the feasibility of using the materials in double-exposure mode.

Toward the Design of a Sequential Two Photon Photoacid Generator for Double Exposure Photolithography

A 2-methoxynaphthalene dimer system is demonstrated as a sequential two photon photoacid generator for double exposure (DE) lithography. DE is based on the use of staggered exposures and is proposed as a replacement for conventional optical lithography. The linear behavior of conventional resist materials disqualifies their use in DE photolithography. The design of reversible nonlinear responsive materials is therefore required.

Double-exposure mask synthesis using inverse lithography

Inverse lithography mask design and double-exposure lithog- raphy are two technologies that have gained a lot of attention in the recent past. Inverse lithography consists of synthesizing the input mask that leads to the desired output wafer pattern by inverting the mathemati- cal forward model from mask to wafer. Double-exposure lithography uses two pairs of mask and exposure to print a single desired wafer pattern. It usually involves splitting the latter into two parts. In this work, we present some preliminary results in our unique effort to combine the previous two powerful techniques. The goal is to use the inverse imaging approach to automatically synthesize the masks required to print the desired wafer pattern employing double-exposure lithography. We em- ploy the pixel-based mask representation, analytically calculate the gra- dient, and use a cyclic coordinate descent optimization algorithm to syn- thesize the two masks. We present results for chromeless phase-shift masks for an idealized case of a coherent imaging system =0 using the Kirchhoff approximation. The results indicate that our algorithm au- tomatically splits the target pattern into two overlapping parts, which are used separately during the individual exposures. Furthermore, the proposed approach is also capable of resolving the phase conflicts. The comparison with a single-exposure case indicates a superior contrast and no hot-spots. © 2007 Society of Photo-Optical Instrumentation Engineers.