Extreme Ultraviolet (EUV) mask has Critical Dimension (CD) errors from various kinds of sources. Those errors are controlled for and corrected by proper correction methods such as fogging effect correction (FEC), loading effect correction (LEC), proximity effect correction (PEC), mask process correction (MPC) and so on. The corrections are mostly done independently. For example, conventionally CD nonlinearity has been the scope of mask process correction (MPC) and proximity effect has been that of proximity effect correction (PEC) because the interaction range considered is different from each other. But in order to improve the CD quality, we may need to consider the residual errors of PEC in MPC as well. For this purpose, we evaluated a new MPC method, named PEC-aware MPC, which considers writer's internal PEC for both model optimization and correction.
For the era of multi-beam mask writer, in the 2019 BACUS conference, we proposed the formation of a data format working group to address the need for curvilinear data representation. The new working group was formed in October 2019 driven by major semiconductor companies with representations from Mentor, Synopsys, Nippon Control Systems, D2S, Aselta, and ASML-BRION with the initial goals to quantify the curvilinear data volume problem; develop, test and implement new or revised formats based on OASIS; and to formalize the working group as a SEMI task force (TF). In this paper, the necessity of a new curvilinear data format and the progress of our TF will be introduced. Furthermore, we demonstrate that given the nature of curvilinear data, representing it using native curve formats has significant value to reduce file size for future mask making flows.
Inverse lithography technology (ILT) optical proximity correction is going to play a critical role in addressing challenges of optical and EUV lithography as the industry pushes toward advanced nodes. One major barrier in adoption of ILT has been the mask writer’s inability to efficiently write curvilinear patterns. With the introduction of multibeam mask writers, this barrier has been removed and widespread adoption of ILT is imminent. Traditionally, mask writers have accepted only trapezoidal inputs to the tool, though recent trends show that mask writers are adopting newer formats that already reduce file size. However, as the ILT shape complexity and data volume increases further for 5 nm nodes and beyond, the explosion of mask pattern data file size becomes a major concern. Therefore, there is a need for the industry to look toward other compact formats of data representation that will be capable of serving well for multiple generations of mask making. We compare various curvilinear data representation schemes and their value in the curvilinear ILT-based mask manufacturing flow. We demonstrate that given the nature of curvilinear data, representing it using native curve formats has significant value to reduce file size for future mask making flows. The same format may not be applicable for all types of features in the input mask. These options will be discussed. We will compare the value of such exotic representations with regular simplification approaches that reduce data volume using standard methods and discuss the extents and limits of all these techniques. To evaluate practical use of curvilinear representation in place of conventional piecewise linear representation, we manufacture and measure a photomask to evaluate the accuracy of curvilinear representations. Finally, we use EUV AIMS to assess the impact of curvilinear representation on wafer process window.
Multi-beam mask writers (MBMW) offer the potential to enable the use of ideal curvilinear shapes for ILT masks, but current layout formats are not sufficient to represent complex ILT designs efficiently from OPC through mask making.
In the 2019 BACUS conference, we proposed the formation of a data format working group to address the need for curvilinear data representation for MBMW. The Curvilinear data format working group was first initiated in October 2019 with participation from EDA companies and advanced mask makers.
In this paper, the necessity of a new curvilinear data format and our working group will be introduced. We will discuss the progress and the plan of the working group.
Data technology for data handling, correction, and verification has become the essential technology of photomask. By the shrinkage of device pitch and the development of lithography technology, the data volume of photomask has been increased continuously and the correction and verification technology based on design data has an important role to meet the target of patterning quality. Especially, because EUV lithography makes single patterning possible, the decrease of device pitch rises to the challenge on the data technology for EUV photomask. Furthermore, the multi-beam mask writer which enables dose modulation for each pixel requires fundamental changes such as data format, data flow, and correction algorithm. Here, we will discuss about 7 kinds of data technologies and one proposal for the era of EUV lithography.
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