Jeroen Herman Lammers

Novel method for characterizing resist performance

The use of a single figure of merit to judge resist performance with respect to resolution, linewidth roughness LWR, and sensitivity is proposed and evaluated. Chemically amplified photoresists used in advanced lithography nodes need to fulfill stringent requirements for a considerable number of resist and process characteristics. Along with resolution, linewidth roughness and resist sensitivity are important examples where the specifications have become very tight. Previously, it has been shown that resolution, linewidth roughness, and resist sensitivity are fundamentally interdependent. Hence, when evaluating or optimizing resist performance, it is very important to take these three characteristics into consideration simultaneously. We propose to combine these characteristics into a single photoresist figure of merit KLUP. This figure of merit, which is determined from sizing dose, imaging wavelength, resist thickness, exposure latitude, acid diffusion length, linewidth roughness, and pitch, allows for a direct comparison of very different resist formulations independent of the exposure tool used. Thus, KLUP has great potential to assist in evaluating resist performance for the next lithography nodes, for both ArF and for EUV wavelengths.

Lithographic importance of acid diffusion in chemically amplified resists

Since their introduction in the semiconductor industry, chemically amplified resists have proven to offer very valuable benefits to lithography processes, of which improved resist contrast and higher throughput are just two examples. However, the inherent acid diffusion mechanism starts to create some issues. For instance, the reduced chemical contrast due to pronounced acid diffusion during the post-exposure bake will decrease the exposure latitudes and would impact the ultimate resolution. On the other hand, reducing the acid diffusion length will have a negative impact on line edge roughness if one wants to simultaneously keep exposure doses and shot noise effects under control. In this paper, acid diffusion lengths in present-day photoresists at different process conditions are characterized using a lithographic technique. The observed tendencies are correlated with trends in exposure latitude, resolution and the frequency spectrum of line edge roughness. The relationship between acid diffusion length and exposure latitude as well as the relationship between acid diffusion and line edge roughness are addressed in a more fundamental way. The results of this paper highlight the major impact of acid diffusion on important lithographic process characteristics, and the investigated scaling behavior gives guidelines for optimizing exposure latitude and line edge roughness for future technology nodes.

Resist effects at small pitches

The ITRS roadmap and Moore’s law are driving us to print ever smaller features and ever tighter pitches. For these ultrasmall features and pitches, resist effects are expected to play a dominant role in limiting the overall lithographic process capability. To study the impact of resist parameters such as acid diffusion and quencher level on the lithographic performance, we have designed and formulated a matrix of 14 extreme ultraviolet (EUV) resists. In this article, we discuss results that we have obtained from EUV exposures of those resists on the 0.3 numerical aperture EUV Micro Exposure Tool at the Advanced Light Source at Lawrence Berkeley National Laboratories. In addition to exposure latitude and line edge roughness, acid diffusion lengths were characterized using a modification of the extended Nijboer–Zernike theory for each photoresist. A simple theory for the drop in resist contrast as function of the diffusion length is tested and leads to a verified correlation between exposure latitude and di...

A novel method for characterizing resist performance

In this paper, the use of a single Figure-of-Merit to judge resist performance with respect to line width roughness, resolution and sizing dose is proposed and evaluated. Chemically amplified photoresists used in advanced lithography nodes need to fulfill stringent requirements for a considerable number of resist and process characteristics. Along with resolution, line width roughness and resist sensitivity are important examples where the specifications have become very tight. Previously, it has been shown that resolution, line width roughness and resist sensitivity are fundamentally interdependent. Hence, when evaluating or optimizing resist performance it is very important to take these three characteristics into consideration simultaneously. We propose to combine these characteristics in a single photoresist Figure of Merit KLUP. This Figure of Merit, which is determined from sizing dose, imaging wavelength, exposure latitude, acid diffusion length, line width roughness and pitch allows for a direct comparison of very different resist formulations independent of the exposure tool used. Thus, KLUP has great potential to assist in evaluating resist performance for the next lithography nodes, for both ArF and for EUV wavelengths.

The effect of the solvent on the cross-link density of SiO2 coatings

With increasing screen size of television and computer monitor tubes the spin-coating of tetraethylorthosilicate (TEOS) based sol-gel coatings becomes an increasingly difficult task. To retain sufficient uniformity and scratch resistance of the coatings, changes in the composition of the coating liquids and the coating procedures are needed. Changing solvents and adding catalysts can lead to increased cross-link density which has been measured by 29 Si-NMR. The cross-link density increases with increasing average number of hydroxy groups on the Si atoms in the drying phase, which can be tailored by adjusting the water concentration, by using water vapour or by using solvents which do not cause the re-esterification of alkoxy groups on the Si atoms during drying.

Performance of EUV photoresists on the ALS micro exposure tool

The new high NA (0.3) Micro Exposure Tool at the Advanced Light Source (MET@ALS) at Lawrence Berkeley National Laboratories provides the first opportunity to evaluate the ultimate resolution capabilities of chemically amplified resists using EUV lithography. We characterized the imaging capabilities of a well-known tool-test resist (EUV-2D, XP98248B) and a new high resolution resist (MET-1K, XP3454C). Emphasis was placed on evaluating resists for focus and exposure latitude at 50 nm dense and isolated lines. MET-1K is capable of resolving 30 nm lines and shows modulation in 25 nm dense lines. We describe some early process optimization experiments using MET-1K that show further advances in lithographic capability. Another new series of resists (MET-2A, 2B, 2C, 2D) also show great promise for good resolution, LER and sensitivity.

Do we need complex resist models for predictive simulation of lithographic process performance

This paper describes different simplified simulation models which characterize the behavior of the photoresist during lithography processes. The effectiveness of these models is compared with the results of more physics and chemistry containing simulators. The strengths and weaknesses of the simplified models are demonstrated for practical applications. Simplified resist model parameters are calibrated for 193nm chemically amplified resists (CAR). The results are compared with calibration of full simulation models. The validity of the simulation models under different process conditions is investigated.

Enhanced processing: sub-50 nm features with 0.8-μm DOF using a binary reticle

With the ever-increasing demand for reducing the size of devices on a chip, one frequently meets the lithographic challenge of printing very small lines on a wafer. The rapidly shrinking process latitudes, especially the depth-of-focus (DOF), really become a burden when trying to print sub-80nm resist lines on a wafer with 193nm lithography. In this paper, we report on a method that is capable of enlarging the process windows for printing small lines, while also reducing a line collapse issue, by using an enhanced resist processing procedure. In this procedure, the PEB time duration, in combination with the exposure dose, is used as a tuning process parameter. It is shown that, by using this procedure, a significant increase in DOF is obtained for printing small (down to 40nm) isolated and semi-dense lines, while the pitch is not scaled down. While using a binary mask and annular 193nm illumination with a NA of 0.63 and s of 0.87/0.57, we show that it is possible to print 50nm lines on a 240nm pitch with 0.8 micron DOF, whereas the standard process, using the vendor recommended PEB, can only print 80nm lines with a comparable DOF. The large process enhancement, among which the reduced curvature in the Bossung plots, is explained by the more efficient use of the acid and quencher present in the photoresist, as well as by the peculiarities of acid diffusion near regions where quencher is remaining. The results obtained are explained by a compact resist model in which acid-quencher reaction-diffusion is incorporated.

Process extensions in optical lithography enabling 45-nm technologies

This work describes approaches in the field of process extensions, complementary to the more traditional optical extension techniques, to enable the extension of optical lithography to 45-nm technologies.