Over the years process development engineers found creative ways to extent the capabilities of existing imaging techniques to enable production of the next technology node. For the 45nm node the immersion technology is being prepared for production, along with other resolutions enhancement techniques such as illuminator polarization. In parallel with the development of these tools, modeling techniques are being developed, which are needed in order to establish the design flows and to set up the Optical Proximity Correction (OPC) and mask data preparation. There is a clear need to validate these models and verify them in an early stage. With the equipment not being available yet, other methods like Maxwell simulators and special test equipment are used for such validations. In this paper initial model verification and validation work is presented of a hyper NA models developed for the 45nm technology node. Models with different illuminator settings are used and compared with Maxwell simulators and experimental measurements obtained with an Exitech MS-193i immersion micro-exposure tool.
Using a polarized illumination source is a promising RET technique for improvement of wafer printability for features of 65 nm and below. Polarization effects could be considered in several different stages of lithography modeling and simulation. For example, light propagation in thin films, wave superstition and interference in the thin film stack, and mask-induced polarization all deserve special attention and delicate treatment because TE and TM waves have different behaviors through these stages. In this paper we consider effects of polarized illumination in photo resist, using the Kirchhoff approximation for masks. We discuss some theoretical aspects of our vector modeling methods and show an example of simulation for polarized illumination effects.
Immersion lithography has been accepted as the major breakthrough for enabling next generation deep subwavelength chip production. As it extends the resolution capability of optical lithography to the next technology node, it brings fresh challenges to resolution enhancement techniques (RET). Accurate lithography modeling becomes even more critical for RET at the sub-65nm nodes. On the other hand, immersion models need to be fully compatible within the context of existing optical proximity correction (OPC) flow.
With the hyper NA approach, modeling of immersion lithography requires full vector treatment of the electric fields in the propagating light wave. We developed a comprehensive vector model that considers not only the plane wave decomposition from the mask to the wafer plane, but also the light propagation through a thin film stack on the wafer. With the integration of this model into Synopsys OPC modeling tool ProGen, we have simulated and demonstrated several important enhancements introduced by immersion. In the mean time, the modeling and correction flow for immersion is completely compatible with the current OPC infrastructure.
The ever-increasing demand for shrinkage of IC device dimensions has been pushing the development of new technologies in micro lithography. Polarized illumination source is one of the emerging techniques in lithography to increase wafer printability, especially for 65 nm features and below. In the mean time, most RET techniques, which are showing more and more importance in lithography, are based on a highly accurate optical lithography model and simulator. Consequently, simulation and modeling tools for optical lithography may have to include the effects of source polarization in thin film stacks. In this paper we discuss some theoretical aspects of vector modeling methods that are utilized for polarization modeling and show results from Synopsys’ simulation tool Progen.
Immersion lithography has been regarded as the most viable contender to extend the resolution capability of optical lithography using 193nm wavelength. In parallel with the tremendous effort of overcoming the engineering challenges in immersion, support from modeling and simulations is strongly needed. Although immersion simulation has become available through a number of simulation tools, we need to investigate the model generation and its compatibility within the context of full-chip optical proximity correction (OPC).
In this paper, we will describe the physics of a full vector model that is necessary for the high NA optical modeling under immersion. In this full vector model, we consider not only the plane wave decomposition as light travels from the mask to wafer plane, but also the refraction, transmission and reflection of light through a thin film stack on the wafer. We integrated this comprehensive vector model into Synopsys OPC modeling tool ProGen. Through ProGen simulation results, we will discuss several important merits of immersion lithography, as well as the full portability of immersion models into OPC process flow.
As an important resolution enhancement technique (RET), alternating aperture phase shift masks (AAPSM) has been widely adopted in 90 nm technology node and beyond. Mask topographical effect due to the 3D nature of the shifter features is becoming an increasingly important factor in lithography modeling. Rigorous 3D modeling of PSM is very computationally demanding thus impractical for full chip optical proximity correction (OPC). Here we introduce an alternative approach employing boundary layers to effectively approximate the 3D mask effect. We will present the model calibration versus real wafer data using the boundary layers and the corresponding OPC correction flow.
Electron beam exposure of masks and wafers results in charging of the insulting resist film. This charging results in an electric field which deflects incoming electrons and can be a serious source of pattern placement error in electron-beam lithography. In earlier work (Ingino et al. 1992) the surface potential was found to be positive or even zero under certain conditions. In this study, a model is developed to explain this effect and the surface potential is measured by an independent method, a Kelvin probe non-contacting electrostatic voltmeter. This new study confirms qualitatively the findings of the first study. An area of PBS resist measuring a few square millimeters is exposed using a Gaussian focused probe and moved under the Kelvin probe immediately after exposure to measure the surface potential. Thicker resist tended to charge more negatively. The model and experiments confirm early studies that the surface potential is a function of resist thickness, and that there may exist a resist thickness where the surface charge is essentially zero.