W. Liu

Bio: W. Liu is an academic researcher. The author has contributed to research in topics: Electron-beam lithography & Lithography. The author has an hindex of 1, co-authored 1 publications receiving 56 citations.

Resist charging in electron beam lithography

Abstract: Charging of the workpiece in electron beam lithography is well recognized as a source of pattern placement error. Despite considerable previous effort there is little quantitative understanding of the problem. A new technique was recently reported in which the surface potential of a resist film during and after exposure was measured directly. Here we describe results obtained using an improved version of the technique for charging of resists under a wide variety of conditions. Some results are as expected, e.g., thicker resists tended to charge more negatively than did thinner ones. Other results are surprising; for example, under certain conditions (7 keV, 0.4 μm polybutene sulfone) there was zero potential at the surface and at higher energies (10 keV) the surface charged positively (0.7 V). The detailed mechanism for positive charging under these conditions is still unclear.

Principles of Lithography

Abstract: Lithography is a field in which advances proceed at a swift pace. This book was written to address several needs, and the revisions for the second edition were made with those original objectives in mind. Many new topics have been included in this text commensurate with the progress that has taken place during the past few years, and several subjects are discussed in more detail. This book is intended to serve as an introduction to the science of microlithography for people who are unfamiliar with the subject. Topics directly related to the tools used to manufacture integrated circuits are addressed in depth, including such topics as overlay, the stages of exposure, tools, and light sources. This text also contains numerous references for students who want to investigate particular topics in more detail, and they provide the experienced lithographer with lists of references by topic as well. It is expected that the reader of this book will have a foundation in basic physics and chemistry. No topics will require knowledge of mathematics beyond elementary calculus.

Fundamentals of Electron Beam Exposure and Development

Abstract: Electron Beam Lithography (EBL) is a fundamental technique of nanofabrication, allowing not only the direct writing of structures down to sub-10 nm dimensions, but also enabling high volume nanoscale patterning technologies such as (DUV and EUV) optical lithography and nanoimprint lithography through the formation of masks and templates. This chapter summarizes the key principles of EBL and explores some of the complex interactions between relevant parameters and their effects on the quality of the resulting lithographic structures. The use of low energy exposure and cold development is discussed, along with their impacts on processing windows. Applications of EBL are explored for the fabrication of very small isolated bridge structures and for high density master masks for nanoimprint lithography. Strategies for using both positive and negative tone resists are explored.

Charging and discharging of electron beam resist films

Abstract: Pattern placement imprecision due to charging of the workpiece is believed to be a significant contribution to the total positional error in electron beam lithography. In an earlier work, Liu et al. [J. Vac. Sci. Technol. B 13, 1979 (1995)] reported that the surface potential of exposed resist could be negative or positive according to the resist thickness and the electron energy. In that work the authors were constrained to use a flood beam. In this study, we report a new independent approach using a Kelvin probe electrometer to measure the surface potential after exposure by a focused beam. There is a qualitative agreement with the earlier work in that the surface potential tends to be less positive at lower electron energies and for thicker resists. We observed positive surface potentials at 10 and 20 keV beam irradiation. This positive charging is much more evident in polybutene sulfone than in UV5.

Charge induced pattern distortion in low energy electron beam lithography

Abstract: Charge induced pattern distortions in low voltage electron beam lithography in the energy range of 1 to 5 kV were investigated. Pattern distortion on conducting substrates such as silicon was found to be small, while significant pattern placement errors and pattern distortions were observed in the case of electrically insulating substrates caused by charge trapping and deflection of the incident electron beam. The nature and magnitude of pattern distortions were found to be influenced by the incident electron energy, pattern size, electrical conductivity, and secondary electron emission coefficient of the substrate. Theoretical modeling predicts the electron beam deflection to be directly proportional to the trapped surface charge density and inversely proportional to the accelerating voltage.

Modeling of charging effect and its correction by EB mask writer EBM-6000

Abstract: The impending need of double patterning/double exposure techniques is accelerating the demand for higher pattern placement accuracy to be achieved in the upcoming lithography generations One of the biggest error sources of pattern placement accuracy on an EB mask writer is the resist charging effect In this paper, we provide a model to describe the resist charging behavior on a photomask written on our EBM-6000 system We found this model was very effective in correcting and reducing the beam position error induced by the charging effect