Daniel Claire Baker

NA/sigma optimisation strategies for an advanced DUV stepper applied to 0.25 mu m and sub-0.25 mu m critical levels

In this paper, the results of an NA-sigma optimization study are reported, carried out experimentally for an advanced ASML PAS5500/300 deep-UV stepper. The work has been primarily focused on a 0.25 and sub-0.25 micrometers gate layer in a logic CMOS process. A positive and negative tone resist process have been compared in terms of CD control and line- end shortening. Dry etch effects and across-field behavior has been taken into account. Furthermore the contact level of the 0.25 micrometers process have been optimized. Effects of layer dependent NA-sigma settings on overlay have been studied.

Analysis of film reflectivity and its impact on photolithographic processing

Submicron photolithographic processes present significant manufacturing challenges due to the relatively small process windows often found with these technologies. Small upstream variations in the pre-expose portion of the photomodule or subtle radial variations in the imaged layers reflectivity can result in final critical dimensions which are outside of the desired specification. One important parameter which has been found to significantly impact the final critical dimension is film reflectivity. This parameter is difficult to control and is a function of the optical characteristics of the layer being imaged, its thickness, and the resist thickness. In our process, improved poly silicon CD control was sought for a 0.8 jim process. Resist and poly thickness were investigated and optimal thicknesses determined. Poly CD control improved as a direct result of this optimization process.

Manufacturable DUV lithography processes for 0.25mm technology contact and via layers

Abstract One of the critical applications of DUV (248nm) lithography for 0.25 μm technology is the imaging of contact and via holes. The goal of this work was to demonstrate and verify manufacturing process capability for imaging 0.25 μm design rule (300 nm) contacts and vias for integration into an existing process flow, including exposure on a first generation (NA-0.50, σ=0.51) production capable DUV stepper. Furthermore, a simulation study was carried out to estimate the optimised optical parameters for a next generation stepper with variable NA and Sigma. Finally, process latitudes for sub-300 nm contacts were measured and an estimate of minimum manufacturable contact sizes using conventional DUV lithography was made.

Critical dimension control for i-line 0.35-μm device using a new antireflective coating

Because of the tighter linewidth control requirements for 0.35 micrometer gate, adequate critical dimension control could not be achieved with a single layer photoresist. A top-side anti-reflective coating (TARC) was found to have limited line width control benefit and did not effectively reduce reflective notching. Since TARC or a single layer resist system could not adequately control linewidth variation a joint project between a bottom-side anti-reflective coating (BARC) supplier and user was undertaken to develop a new generation i-line material to address the gate linewidth control and reflective notching issues seen at 0.35 micrometer design rules. The newly developed BARC has improved optical properties compared to previous i-line compatible material as well as improved manufacturability. The new BARC is spin cup compatible with photoresist, is compatible with standard edge bead removal chemicals, has low defect density as spun, and is room temperature stable. Also, the spun material is resistant to chemical intermixing with a variety of resists having various safe solvent systems. This leads to excellent resist profiles. The joint development approach allowed quick selection of the best BARC material, optimization of the materials formulation and also timely verification of the performance for an actual 0.35 micrometer application. Prolith/2TM reflectivity simulations were used to predict and then verify optimum BARC process setup. Swing curve simulations were compared to actual product intradie linewidth variations for single layer resist, TARC, and BARC processes. Profiles for several resists on different BARC thicknesses were studied for image quality, resolution, and linewidth control.