Electron-beam Direct-write Lithography System Research Articles

Efficient layout data compression algorithm and its low-complexity, high-performance hardware decoder implementation for multiple electron-beam direct-write systems

A lossless electron-beam layout (EBL) data compression algorithm, LineDiff Entropy v2.0, and its low-complexity, high-performance hardware decoder for multiple electron-beam direct-write lithography systems are proposed. The algorithm compares consecutive data scanlines and encodes the data based on the change/no-change of pixel values and the lengths of pixel sequences. Then, the compaction steps of data omission, merging, and encoding of consecutive long identical scanlines are applied. Unique short codes are assigned to data with high occurrence frequency. The hardware decoder is designed as three circuit blocks that perform entropy decoding, decompaction, and EBL data generation through parallel outputs. The results demonstrate that our algorithm can achieve excellent compression performance and that the hardware decoder can decompress data at very high data rates.

Lossless layout image compression algorithms for electron-beam direct-write lithography

Electron-beam direct-write lithography systems must in the future transmit terabits of information per second to be viable for commercial semiconductor manufacturing. Lossless layout image compression algorithms with high decoding throughputs and modest decoding resources are tools to address the data transfer portion of the throughput problem. The earlier lossless layout image compression algorithm Corner2 is designed for binary layout images on raster-scanning systems. The authors propose variations of Corner2 collectively called Corner2-EPC and Paeth-EPC which apply to electron-beam proximity corrected layout images and offer interesting trade-offs between compression ratios and decoding speeds. Most of our algorithms achieve better overall compression performance than portable network graphics, Block C4, and LineDiffEntropy while having low decoding times and resources.

LineDiff Entropy: Lossless Layout Data Compression Scheme for Maskless Lithography Systems

This letter presents a new lossless electron-beam layout data compression and decompression algorithm named LineDiff Entropy. The algorithm is designed to facilitate high volume data transfer and massively-parallel decompression in electron-beam direct-write lithography systems. LineDiff Entropy first compares consecutive electron-beam data scanlines and encodes the data based on change/no-change of pixel values and length of corresponding sequences. Then LineDiff Entropy utilizes the entropy encoding technique to assign unique short codes to data of frequent occurrence. Because the code format is simple and effective, LineDiff Entropy decompression can be achieved with limited computing resources. The benchmark results show that LineDiff Entropy is capable of achieving excellent compression factors and very fast decompression speed.

Solution-Refined Method for Electrostatic Potential Distribution of Large-Scale Electron Optics

The solution-refined method is developed to solve electrostatic fields of the electron-beam direct-write lithography system. The prediction of accurate electron trajectories and the geometry of the developed photoresist patterns rely on high-resolution electrostatic fields in the whole system. Considering fabrication errors, such electrostatic fields cannot be solved using a cylindrical symmetry. Thus, this problem is a multiscale problem that requires a huge computer memory to solve. In our cases, the minimum number of grids of 1 nm length are applied and the total memory required approaches 75 Gbyte. Since the proposed solution-refined technique has a tradeoff with computational time, fewer central processing units (CPUs) are needed to solve this system because each CPU that solves the problem exceeds its available storage memory. The proposed technique can be used to solve the electron-beam direct-write lithography system at higher resolution and the problems exceed the available storage memory.

Image based in situ electron-beam drift detection by silicon photodiodes in scanning-electron microscopy and an electron-beam lithography system

► Silicon-photodiode detector for in-situ beam position sensing in an scanning electron microscope (SEM). ► Applying image processing technique to the backscattered-electron image to reach nanometer resolution. ► The performance in detecting the drift of the electron beam over time was analyzed. ► This detection mechanism is useful for beam position feedback in the electron-beam direct-write lithography system. A silicon-photodiode detector can be used to sense the position of the electron beam in a scanning-electron microscope. In order to validate the implementation of a electron beam drift detector, a silicon photodiode was constructed with a low profile and small working distance. The performance in detecting the drift of the electron beam over time was analyzed. It was also shown that a back scattered-electron image can be created with electron scanning, which allows the development of highly sensitive in situ beam position feedback in the electron-beam direct-write lithography system.

Silicon photodiodes for electron beam position and drift detection in scanning electron microscopy and electron beam lithography system

A silicon photodiode detector can be used for position sensing of the electron beam in the Scanning Electron Microscope (SEM). In order to validate the implementation of the multi-beam detector array, the silicon photodiode was made thin and fitted within a small working distance. The performance of drift detection of the electron beam as time varies is investigated. Besides, a backscattered electron image can be created by scanning the electron beam. It may allow the development of a massively parallel electron beam direct-write lithography system with electron imaging capability.

Electron optical column for a multicolumn, multibeam direct-write electron beam lithography system

Electron beam direct-write lithography systems are capable of meeting the resolution requirements of all future ITRS nodes and have a significant cost of ownership advantage over masked technologies, but these systems typically have very poor throughput due to space charge limitations. Ion Diagnostics has developed a multicolumn, multibeam (M×M™) direct-write system that circumvents the space charge limitations by spreading the electron current over the wafer. The resulting lithography system can achieve critical dimensions of less than 100 nm with production throughputs greater than 60 wafers per hour, independent of wafer size. In this article we describe the electron optical column used in this system. We have developed a novel, microfabricated electron gun that produces 32 parallel electron beams that are individually controlled and blanked and contain deflectors that allow the gun optics to act as a perfect lens. Each column is 2 cm×2 cm and can align and scan the 32 beams in parallel on the wafer. The wafer voltage is typically held at 50–100 kV, and backscattered electrons are collected for imaging and alignment information. Theoretical results and some performance results for a prototype column are presented.

Design aspects of the optics of the VLS-1000 electron-beam direct-write lithography system

Some of the basic considerations in the design of the electron optics of a variable line scanning (VLS) system, a particular form of variable‐shape electron‐beam lithography system, are discussed. In the VLS system, the electron beam is projected on the resist‐coated wafer in the form of a narrow line whose length and position can be varied simultaneously as it is scanned. The writing is done as the stage is moved in a serpentine fashion under laser control with the pattern features placed using both raster and vectorial placement techniques. The line can be produced in either of two orthogonal directions in order to maximize the exposure rate. In general, the required source brightness is greater than that of a more conventional‐shaped‐beam system, however, this can be achieved readily with LaB6 at a desirable operating temperature. Exposed and developed patterns demonstrate the resolution capabilities of the optics.