KEYWORDS: Computer programming, Electron beam direct write lithography, Raster graphics, Electron beam lithography, Image compression, Logic, Detection and tracking algorithms, Semiconducting wafers, Data compression, Data processing
Data throughput is a critical metric in a multiple electron-beam direct-write (MEBDW) system so that heavy-duty data processing equipment is required. The main challenge is about how to achieve high performance with cost-effective techniques. We propose a high compression rate algorithm for efficient data transfer and high speed decompression hardware to raise data throughput of the system. The hardware decoder uses pipeline architecture, a run-length encoding first-in-first-out queue, and parallel dispatch logic to increase the throughput. The decoder is evaluated on field-programmable gate array and simulated with layout images that are compressed using the proposed compression software. The results demonstrate 18.2% better compression rate and 254.8% better throughput than the previous work with similar hardware cost. Because no static random-access memory is used in the design, the channel numbers of the system can be easily scaled up, which makes it possible for the next-generation MEBDW system to achieve higher wafer per hour targets.
As one of the critical stages of a very large scale integration fabrication process, postexposure bake (PEB) plays a crucial role in determining the final three-dimensional (3-D) profiles and lessening the standing wave effects. However, the full 3-D chemically amplified resist simulation is not widely adopted during the postlayout optimization due to the long run-time and huge memory usage. An efficient simulation method is proposed to simulate the PEB while considering standing wave effects and resolution enhancement techniques, such as source mask optimization and subresolution assist features based on the Sylvester equation and Abbe-principal component analysis method. Simulation results show that our algorithm is 20× faster than the conventional Gaussian convolution method.
Post exposure bake (PEB) Diffusion effect is one of the most difficult issues in modeling chemically amplified resists. These model equations result in a system of nonlinear partial differential equations describing the time rate of change reaction and diffusion. Verifying such models are difficult, so numerical simulations are needed to solve the model equations. In this paper, we propose a high speed 3D resist image simulation algorithm based on a novel method to solve the PEB Diffusion equation. Our major discovery is that the matrix formulation of the diffusion equation under the Crank– Nicolson scheme can be derived into a special form, AX+XB=C, where the X matrix is a 3D resist image after diffusion effect, A and B matrices contain the diffusion coefficients and the space relationship between directions x, y and z. These matrices are sparse, symmetric and diagonal dominant. The C matrix is the last time-step resist image. The Sylvester equation can be reduced to another form as (I⊗A + BT⊗I) X =C, in which the operator ⊗ is the Kronecker product notation. Compared with a traditional convolution method, our method is more useful in a way that boundary conditions can be more flexible. From our experimental results, we see that the error of the convolution method can be as high as 30% at borders of the design pattern. Furthermore, since the PEB temperature may not be uniform at multi-zone PEB, the convolution method might not be directly applicable in this scenario. Our method is about 20 times faster than the convolution method for a single time step (2 seconds) as illustrated in the attached figure. To simulate 50 seconds of the flexible PEB diffusion process, our method only takes 210 seconds with a convolution set up for a 1240×1240 working area. We use the typical 45nm immersion lithography in our work. The exposure wavelength is set to 193nm; the NA is 1.3775; and the diffusion coefficient is 1.455×10-17m2/s at PEB temperature 150°C along with PEB time 50 seconds with image resolution setup to be 1240×1240.
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