Hideki Ina

Alignment mark optimization to reduce tool and wafer induced shift for XRA-1000

Summary form only given. As the most critical semiconductor device geometry shrinks down to 100 nm order, requirements for overlay accuracy also become increasingly critical in the actual semiconductor manufacturing process. Factors in overlay error (especially, alignment error) originate in the interaction of processes and tools. It is therefore necessary to improve alignment accuracy from both the process and the tool sides. The alignment errors can be separated into Tool Induced Shift (TIS), Wafer Induced Shift (WIS), and TIS-WIS interaction. The authors consider the optimization of the alignment mark in order to reduce not only TIS, but also WIS for the XRA-1000, which is the volume production stepper of proximity X-ray lithography.

Position measurement method for alignment in UV imprint using a high index mold and “electronic” moiré technique

In UV imprint, positioning errors can occur between a mold and a wafer due to pressure when there is a contact with the UV resin. The moire technique, which is produced by superimposition of two gratings, is a well-known and simple method for high-resolution position measurement. However, the authors believe that a direct observation of two separate gratings is more appropriate for higher positioning accuracy. Here they propose a new method for the position measurement, which obtains “electronic” moire fringes by combining the images of two separate gratings from different areas of the mold and the wafer. The fundamental detection error was σ=0.15nm. The repeatabilities of the total system was σ=0.68nm in air and σ=0.73nm in resin. The linearity of the measurement value to control signal was R2=0.97.

Alignment sensor corrections for tool-induced shift (TIS)

As the most critical semiconductor device geometries shrink down to the quarter micron order, requirements for overlay accuracy also become increasingly critical in the actual semiconductor manufacturing process. Factors in overlay error (especially, alignment error) originate in the interaction of process and tool. It is therefore necessary to improve alignment accuracy from both the process and the tool sides. In an effort to solve this as a tool supplier, we at Canon must minimize tool factors to reduce alignment errors caused by the interaction of process and tool factors. We though that we needed some evaluation criteria with such interaction take into account, and redefined the concepts of tool induced shift and wafer induced shift as a criterion. This paper introduces these new concepts and discusses validity of the criteria showing experimental results of alignment accuracy implementing the idea in the real process.

Critical issues study of nano-imprint tool for semiconductor volume production

Nano-imprint lithography (NIL) has the capability to transfer very fine patterns. As NIL was described in ITRS Roadmap in 2003, there are plans to apply NIL to semiconductor volume production at 32nm half pitch devices. This study is describes the critical issues of nano-imprint tool for semiconductor volume production. For an exposure tool supplier such as CANON, overlay control is not a critical issue for nano-imprint lithography because CANON has experience from proximity X-ray lithography (PXL). CANON can build an overlay system for nano-imprint tool using the CANON PXLs alignment and chip magnification correction technologies easily. Using our background, we focus on the Cost of Ownership (CoO) considering mold durability and compare NIL to Extreme Ultra Violet (EUV) and double patterning (DP) by immersion ArF lithography, to clarify the required specification of NIL from the viewpoint of productivity.

Focus and dose measurement method in volume production

We propose a new inspection method of in-line focus and dose control at semiconductor volume production. We have been referred to this method as Focus & Dose Line Navigator (FDLN). Using FDLN, the deviations from the optimum focus and exposure dose can be obtained by measuring the topography of resist pattern on a process wafer that was made with single exposure condition. Generally speaking, FDLN belongs to the technology of solving the inverse problem as scatterometry. The FDLN sequence involves following two steps. Step 1: creating a focus exposure matrix (FEM) using test wafer for building the library as supervised data. The library means relational equation between the topography of resist patterns (critical dimension (CD), height, side wall angle) and FEMs exposure conditions. Step 2: measuring the topography of resist patterns on production wafers and feeding the topography data into the library to extrapolates focus and dose. To estimate the accuracy of FDLN, we had some experiment. We made a FEM with ArF lithography tool and measured the topography of the FEM with optical CD measurement tool. By using the topography data, we obtained following result as accuracy of FDLN. Focus: 27.0nm (5.2nm) and Dose: 1.8% (1.4nm). The numerical value in a parenthesis shows the value of estimated accuracy into change of CD value. We also show other experimental results and some simulation result in this paper.

Log data extraction and correlation miner for lithography management system : LMS-LEC

To attain quick turn-around time (TAT) and high yield, it is very important to remove all the problems affecting the semiconductor volume production line. For this purpose, we have used a lithography management system (LMS) as an advanced process control system. The LMS stores the critical dimension and overlay inspection results as well as the log data of the exposure tool in a relational database. This enables a quick and efficient grasp of the productivity under the present conditions and helps to identify the causes of errors. Furthermore, we developed a mining tool, called a log data extraction and correlation miner (LMS-LEC), for factor analysis on the LMS. Despite low correlation between all data, a high correlation may exist between parameters in a certain data domain. The LMS-LEC can mine such correlations easily. With this tool, we can discover previously unknown error sources that have been buried in the vast quantity of data handled by the LMS and thereby increase of the effectiveness of the exposure and inspection tool. The LMS-LEC is an extremely useful software mining tool for “equipment health” monitoring, advanced fault detection, and sophisticated data analysis.

Focus and dose controls, and their application in lithography

We have proposed a new inspection method of in-line focus and dose controls for semiconductor volume production. We referred to this method as the focus and dose line navigator (FDLN). Using FDLN, the deviations from the optimum focus and exposure dose can be obtained by measuring the topography of the resist pattern on a process wafer that was made under a single-exposure condition. Generally speaking, FDLN belongs to the technology of solving the inverse problem as scatterometry. The FDLN sequence involves following the two steps. Step 1:creating a focus exposure matrix (FEM) using a test wafer for building the model as supervised data. The model means the relational equation between the multi measurement results of resist patterns ( e.g. Critical dimension (CD), height, sidewall angle) and FEMs exposure conditions. Step 2: measuring the resist patterns on a production wafers and feeding the measurement data into the library to extrapolate focus and dose. To estimate the accuracy of FDLN, we performed some experiments. We developed a FEM with an ArF lithography tool and measured the resist patterns of the FEM wafer with the advanced CD-SEM (Critical Dimension-Scanning Electron Microscope). Using the MPPC (Multiple Parameters Profile Characterization) data from the advanced CD-SEM, we obtained the following results. Focus: 21.5 nm (4.1 nm) and Dose: 1.5% (2.0 nm). The numerical value in a parenthesis shows the value of the estimated accuracy with changing CD. We also show other experimental results in this paper and the application of the focus and dose controls for semiconductor exposure tool.

TIS-WIS interaction characterization on overlay measurement tool

Modern overlay metrology tools achieve the required metrology accuracy by controlling critical asymmetries in the imaging optics, and by compensating for the remaining asymmetries through TIS-calibration. We extend our study on the TIS-WIS interaction in stepper alignment optics to the overlay metrology tool, and propose a new method for characterizing residual TIS. This method is based on the examination of the through-focus behavior of the metrology tool on a wafer with a simple, TIS-sensitive structure.

X-ray stepper development for volume production at Canon

We describe some results of exposure experiments using the present prototype SR stepper which Canon has developed and the novel technology development which is necessary to establish the next generation SR stepper for volume production. Concerning the technology development, we have established (1) two mirror condensing system for full field exposure, (2) ADGL alignment method, (3) magnification correction method, (4) high speed stage stepping method. By adopting these technologies, we have been developing a beta- site machine for volume production and its features and preliminary specifications are described.

Scatterometry sensitivity for NIL process

In this paper scatterometry sensitivity up to 28nm HP resin pattern and beyond by using RCWA (Rigorous Coupled Wave-analysis) simulation is described. A criterion, defined as the sum of the absolute difference of the reflectivity values between the nominal and slightly different conditions from nominal through the spectrum, is introduced. The criterion of this analysis is a kind of quantification of the sensitivity comparing with 65 nm HP resist pattern of ArF immersion lithography process.