Koichi Sentoku

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.

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.

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.

Advanced synchrotron radiation stepper alignment system performance

Canon has been developing a synchrotron radiation stepper system for volume production known as the XR1. The system incorporates many-original technologies. In this article, the key features of the XR1 alignment system and its performance will be discussed. To align the mask and wafer, the alignment system uses Fresnel zone plates as alignment marks. Our alignment is based on an advanced dual grating lens method. In order to attain high alignment accuracy and large process latitude, we improved the design of alignment marks and optics of the alignment scope. The alignment marks are optimized to minimize alignment error resulting from changing the gap distance between the mask and wafer, which is called telecentricity. Using these newly designed alignment marks, we have evaluated alignment accuracy. We obtained alignment accuracy 3σ of 11.9(X) and 10.2 nm(Y) using etched SiN patterns on a Si substrate. Furthermore, the alignment scope is designed with multiwavelength light sources to illuminate the alignme...

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.

A first order analysis of scatterometry sensitivity for NIL process

In this paper the first order analysis of the scatterometry sensitivity up to 45nm 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 varied conditions thorough 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 process. Furthermore, the simulated result in this analysis can be used to discuss the extendibility of scatterometry.

Focus and Dose Control for High Volume Manufacturing

We have proposed a new inspection method of in-line focus and dose controls for semiconductor high volume manufacturing. 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 manufacturing wafers and feeding the measurement data into the library to extrapolate focus and dose. In this paper, we explain again about the theorem of the FDLN and show experimental results using the many kind CDmeasurement tool(the advanced CD-AFM, optical CD measurement tool, the advanced CD-SEM and the Overlay measurement tool).

Focus and dose control to actual process wafer

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. In this time, we have evaluated the estimated accuracy of Focus and dose for actual process wafer using the advanced CD-SEM and we also have developed new algorithm for considering against thermal dose error.

The first intrinsic process monitoring system for 90nm device with focus and dose line navigator (FDLN)

Focus and exposure dose control in lithography is a key challenge for CD (critical dimension) control at 90 nm technology node and beyond. Specially, more high accurate focus control will be necessary for low power MOS devices. Focus and dose line navigator (FDLN) is one of the candidates as in-line controller. The FDLN methodology involves two steps: first, create a focus-dose matrix (FEM) for building the library as supervised data using test wafer. The library means relational equation between the topography of photoresist patterns (line width: CD, height: HT, a side wall angle: SWA) and FEM exposure conditions, second, measure standard production wafer and feed the raw data into the library (which extrapolate focus and dose), which is then provided to the user. Using FDLN, current volume production’s focus and dose deviation from the best condition can be obtained. In this time, we have evaluated FDLN using an optical CD measurement tool and process wafer. STI, Cu-CMP ,metal wafers are used in this time as actual process. We acquired several FEM set of image feature from wafers, which were exposed by ArF scanner. According to our experiment, the estimation precision for focus and dose are below 24nm and below 1.7% respectively. And CD difference in a chip can reduce to one third as compared with the conventional QC method. These results suggest that FDLN can be the solution as in-line focus controller for volume production, enabling the progression toward Advanced Process Control (APC)

Novel strategy for wafer-induced shift (WIS)

Alignment error that originates in the actual wafer process is one of the factors that deteriorates total overlay accuracy. This error is known as wafer induced shift (WIS). WIS occurs through a change of alignment mark topography during the actual wafer processing. To reduce this error, we propose a tool that will simulate an alignment offset generated by WIS. We have called this tool the Alignment Offset Analyzer. The Alignment Offset Analyzer consists of a profiler for measuring the alignment mark topography and a simulator that simulates the alignment offset. By using the Alignment Offset Analyzer, we simulate the alignment signals from a Tungsten chemical mechanical polishing (CMP) wafer. The simulated alignment signals have an asymmetric shape due to the wafer processing. With these signals, the alignment offset caused by WIS can be estimated prior to the exposure sequence.