An object is to provide a semiconductor device of which a manufacturing process is not complicated and by which cost can be suppressed, by forming a thin film transistor using an oxide semiconductor film typified by zinc oxide, and a manufacturing method thereof. For the semiconductor device, a gate electrode is formed over a substrate; a gate insulating film is formed covering the gate electrode; an oxide semiconductor film is formed over the gate insulating film; and a first conductive film and a second conductive film are formed over the oxide semiconductor film. The oxide semiconductor film has at least a crystallized region in a channel region.

Semiconductor device, and manufacturing method thereof

In all imaging systems, the forward process introduces undesirable effects that cause the output signal to be a distorted version of the input. A typical example is of course the blur introduced by the aperture. When the input to such systems can be controlled, prewarping techniques can be employed which consist of systematically modifying the input such that it (at least approximately) cancels out (or compensates for) the process losses. In this paper, we focus on the optical proximity correction mask design problem for "optical microlithography," a process similar to photographic printing used for transferring binary circuit patterns onto silicon wafers. We consider the idealized case of an incoherent imaging system and solve an inverse problem which is an approximation of the real-world optical lithography problem. Our algorithm is based on pixel-based mask representation and uses a continuous function formulation. We also employ the regularization framework to control the tone and complexity of the synthesized masks. Finally, we discuss the extension of our framework to coherent and (the more practical) partially coherent imaging systems

Mask Design for Optical Microlithography—An Inverse Imaging Problem

Inverse Lithography Technology (ILT) is a rigorous approach to determine the mask shapes that produce the desired on-wafer 
results. In this paper, we briefly describe an image (or pixel))-based implementation of ILT in comparison to OPC 
technologies, which are usually edge-based. Such implementation is more computationally scalable and avoids laborious 
segmentation script-writing, which becomes more complex for newer generations because of complicated proximity 
effects. In this paper, we will give an overview of ILT, present some simulation and wafer examples to demonstrate the 
benefit of ILT, clarify common myths about ILT, discuss and show examples to illustrate the impact in every step of the 
mask making process. Specifically, studies done with several leading mask shops around the world on mask 
manufacturability (including data fracturing, writing strategy and writing time, mask inspection), will be shown.

Inverse lithography technology (ILT): What is the impact to the photomask industry?

Inverse lithography technology (ILT) synthesizes photomasks by solving an inverse imaging problem through optimization of an appropriate functional. Much effort on ILT is dedicated to deriving superior masks at a nominal process condition. However, the lower k1 factor causes the mask to be more sensitive to process variations. Robustness to major process variations, such as focus and dose variations, is desired. In this paper, we consider the focus variation as a stochastic variable, and treat the mask design as a machine learning problem. The stochastic gradient descent approach, which is a useful tool in machine learning, is adopted to train the mask design. Compared with previous work, simulation shows that the proposed algorithm is effective in producing robust masks.

https://iopscience.iop.org/article/10.1088/2040-8978/12/4/045601/pdf

Machine learning for inverse lithography: using stochastic gradient descent for robust photomask synthesis

Optical lithography has enabled the printing of progressively smaller circuit patterns over the years. However, as the feature size shrinks, the lithographic process variation becomes more pronounced. Source-mask optimization (SMO) is a current technology allowing a co-design of the source and the mask for higher resolution imaging. In this paper, we develop a pixelated SMO using inverse imaging, and incorporate the statistical variations explicitly in an optimization framework. Simulation results demonstrate its efficacy in process robustness enhancement.

/pdf/pixelated-source-mask-optimization-for-process-robustness-in-498fazra2f.pdf

Pixelated source mask optimization for process robustness in optical lithography

In this paper, we present the Luminescent's ILT approach that can rapidly solve for the optimal photomask design. We
will discuss the latest development of ILT at Luminescent in the areas of sub-resolution assist feature (SRAF)
generation, process-window-based ILT and mask rule compliance (MRC). Results collected internally and from
customers demonstrate that ILT is not only an R&D tool, but also a tool quickly maturing for production qualification at
advanced technology nodes. By enforcing the proper constraints while optimizing the masks, ILT can improve process
windows while maintaining mask costs at a reasonable level.

Inverse lithography technology (ILT): a natural solution for model-based SRAF at 45-nm and 32-nm

In this paper we present unintuitive patterns generated by inverse lithography technology. We show examples of contact hole masks designed with ILT that enjoy larger process windows than OPC. We also show variations in ILT-generated masks as the pitch of the contact hole array changes. In another example, we show poly masks designed for better process window to be substantially different from poly masks designed for better fidelity at nominal exposure-defocus (ED) condition. The mask with better fidelity has broken lines in comparison to the original layout. In a third example, we show deep trench mask patterns designed with ILT that, at first glance, bear no resemblance to the original layout, yet provide high fidelity in optical images. These patterns, although complex at first sight, can be generated in substantially simpler form with proper constraints without losing the spirit of ILT masks.

Inverse lithography technology principles in practice: unintuitive patterns

In this paper, we present the Luminescent's ILT approach that can rapidly solve for the optimal photomask design. We
will discuss the latest development of ILT at Luminescent in the areas of sub-resolution assist feature (SRAF) generation
and optimization to improve process window, and mask rule compliance (MRC). Results collected internally and from
customers demonstrate that ILT is not only an R&D tool, but also a tool quickly maturing for production qualification at
advanced technology nodes. By enforcing the proper constraints while optimizing the masks, ILT can improve process
windows while maintaining mask costs at a reasonable level.

Inverse lithography technology (ILT): keep the balance between SRAF and MRC at 45 and 32 nm

This paper presents the results of applying ILT to SMIC's first 65nm tape out. ILT mathematically determines the mask features that produce the desired on-wafer results for best pattern fidelity, largest process window or an desired combination of both. SMIC applied this technology to its first 65nm tape-out to study its performance and benefits for deep sub-wavelength lithography. SMIC selected 3 SRAM designs as the first set of test cases, because SRAM bit-cells contain features which are lithographically challenging. Firstly, three experiments were performed to optimize the illumination and mask design of a pair of layers by optimizing exposure energy, enabling SRAF, and enforcing mask constraints. Secondly, mask manufacturability (including fracturing and writing time) and wafer print performance of ILT was studied. Thirdly, mask patterns generated by both conventional Optical Proximity Correction (OPC) and ILT, both using only their optical models, were placed on the mask side-by-side. The results demonstrated that ILT achieved better CD accuracy and produced significantly larger process window than conventional OPC.

Yong Liu

Papers

Inverse lithography technology (ILT): What is the impact to the photomask industry?

Inverse lithography technology (ILT): a natural solution for model-based SRAF at 45-nm and 32-nm

Inverse lithography technology principles in practice: unintuitive patterns

Inverse lithography technology (ILT): keep the balance between SRAF and MRC at 45 and 32 nm

Pushing the lithography limit: applying inverse lithography technology (ILT) at the 65nm generation