Wafer Lithography Research Articles

Development of a Novel Dual Servo Magnetic Levitation Stage

The main objective of this paper is to propose, design, and control a novel dual servo magnetic levitation stage which is precise and vacuum compatible. The dual servo mechanism, comprising a coarse stage and a fine stage, was applied to a magnetic levitation stage system for the first time. The dual servo stage achieves high precision and a long stroke at the same time. The fine stage, which comprises voice coil motors, achieves high-precision motion by overcoming the limit of the coarse stage, the form of which is a planar motor. The planar motor was mathematically modeled and analyzed with respect to the main design parameters, after which the fine stage was optimally designed to be driven by high force. Both stages including a common heat exchanger were manufactured, and the heat exchanger cools down the heat given off from the planar motor and voice coil motors. The position measuring system consisted of laser interferometers and capacitive sensors, and the integrated dual servo stage was controlled with a master–slave control scheme. The experimental results showed a precision of 10 nm, thus confirming the suitability of the developed magnetic levitation stage for a high-precision fabrication process such as wafer lithography.

A Signal Processing Method for Homodyne Laser Interferometer Based on Model Parameter Self-Calibration With Redundant Information

In lithography wafer stage systems, laser interferometers are one of the most important precision measuring instruments. The homodyne interferometer is based on the single-frequency laser interference effect and is able to provide displacement resolution smaller than sub-nanometer. However, its accuracy is affected by AC amplitude variation, DC offset, and quadrature-phase error of the interference signal. In this paper, a high-precision signal processing method is proposed, which can make full use of the redundant multiphase information, obtain higher accuracy than the quadrature interferometer, and is more practical than the existing signal processing method in multiphase interferometers because it can approach the theoretical upper limit of accuracy for any number of detection signals. In this method, multiple detectors are installed on the interference optical path, and the Gauss-Newton algorithm is used to solve nonlinear equations containing redundant information. All the parameters are calibrated simultaneously, so the calculation accuracy is improved by avoiding the error transfer in different calculation processes. The simulation shows that by using the above methods, when the noise level is 66 dB, the relative errors of calibrated parameters are less than 0.03%, the standard deviation (STD) of the phase error is 5.13×10^-4 rad, and the equivalent STD of the displacement error is 15.9 pm. In the experiment, the root-mean-square error (RMSE) of the displacement is 0.846 nm under the signal noise level of 37.4 dB.

A new 6-degree-of-freedom measurement method of X-Y stages based on additional information

Abstract In some occasions, high accuracy and real-time 6-degree-of-freedom (6-DOF) displacements should be measured so that the control system can regulate the X-Y stages’ attitude in real time. The accuracy and real-time property of measurement's result depend on not only the sensors itself, but also the accuracy and effort of the computational algorithm using the sensors’ measured data. As the relation between sensors’ measured data and displacements is immensely complex and usually described as strong nonlinear coupling equation when 6-DOF displacements are all considered, computational accuracy and effort are difficult to be ensured simultaneously. This paper designs a 6-DOF displacements’ measurement setup for X-Y stages based on nine interferometers’ additional information, and derives the corresponding computational algorithm. For rotation, its range is usually very small and high accuracy computational results can be obtained using two interferometers’ differential computation; for translation, the closed form solutions without rotational displacement's computational error's transmission are derived by making full use of all additional interferometers’ information, so that the computational accuracy can be ensured. In addition, the algorithm has simple form and doesn’t involve iteration and transcendental function's computation, so that it helps real-time computation. This algorithm can acquire the computational accuracy of 10−15 rad and 10−13 mm for rotational and translational displacement separately, which can be seen in the simulation result for a lithography's wafer stage.

Prevention of Progressive Mask Defects through Residual Ammonium and Sulfuric Ion Control

Progressive defect generation has been a serious issue in wafer lithography, as illumination wavelength becomes shorter with the introduction of the 248 and 193 nm wavelengths. Several research groups have reported that cleaning residues, mostly ammonium and sulfate ions, on a mask surface are critical sources of progressive defect generation. A new cleaning process has been developed and studied to minimize progressive defect generation sources. The new cleaning process consists of dehydration baking, dry etching, and H2O2 treatment. Dehydration baking was proposed to reduce the concentration of sulfate residues while H2O2 treatment and dry etching are proposed to control ammonium ions. Dehydration baking is employed at 230 °C for 600 s to reduce the sulfate ion concentrations from 32 to 1.6 ppb on chrome on glass (COG) or binary intensity mask (BIM). ArF embedded attenuate phase shift mask (EAPSM) is associated with a high concentration of ammonium ions (>5000 ppb), and is easily susceptible to progressive defect generation under ArF illumination. More than 90% ammonium extraction (removal) efficiency was achieved by H2O2 treatment for ArF EAPSM. Moreover, the optimized new cleaning process has reduced the concentration of ammonium ions up to 50 ppb compared with the 1500 ppb reported by conventional RCA cleaning in ArF EAPSM. In a strictly controlled sulfate environment (less than 6 ppb), threshold defect energy has improved from 25 to 100 kJ by reducing the concentration of ammonium ions down to 45 ppb and below. Therefore, the concentration of residual ammonium ions along with residual sulfate ions should be strictly controlled to improve wafer and photomask yields.

Mechanical system construction for the EX-11 electron beam mask writer: A solution for 100 nm wafer lithography

An advanced mechanical system has been developed for the EX-11 electron beam mask writer. In particular, a new XY stage was designed so as to improve CD uniformity and image placement by reduction of vibration and heat generation, and by stabilization of the stage temperature. A direct-drive friction-drive unit and crossed-roller guides enable the stage to obtain low position fluctuation less than ±1.2 nm over 1 kHz. The active thermal control system of the XY stage using the thermal control plate whose temperature is controlled within 0.001 °C can stabilize that of the top plate of the XY stage. The improved EX-11 is expected to satisfy the requirements for 100 nm generation lithography.

Development of a vertical wafer stage for high-vacuum applications

Several new manufacturing techniques in the semiconductor industries increase the demands on the process equipment. Severe environment conditions, such as vacuum, aggressive media and high temperatures, often meet aspired accuracy in the sub-micron range. Outstanding examples for high-tech manufacturing equipment are step- and scan systems for wafer lithography. In particular, next generation lithography (NGL) tools for non-optical lithography techniques face challenges like suitability for high vacuum, low disturbing field emission, and extremely high position accuracy. The following paper presents the design, development, and first evaluation results of a wafer stage for the ion-beam lithography system.

A new mask lithography tool for advanced mask manufacturing

In this paper, we will describe the design and performance of a new mask lithography tool, the ALTA-3000 system produced by Etec System, Inc. The introduction of both step-and-repeat reduction wafer lithography and raster-scanned electron beam mask lithography in the early 1980s effectively minimized mask error contributions in IC manufacturing such that masks are now generally viewed as having only one distinguishing characteristic - price. The continual demand for greater performance has naturally led to smaller integrated circuit linewidths and tighter dimensional tolerances as well as greater data volume and density, which present new challenges to the mask maker. While smaller linewidths on the wafer do not directly place limits on the mask maker (mask dimensions are 4 to 5 times the size of the corresponding wafer dimensions), lithography limitations at the wafer level require operating steppers at lower k 1 factors, causing wafer lithography to be more sensitive to mask CD errors. In addition, techniques to enhance resolution and depth of focus at the wafer, including optical proximity correction and phase-shifting masks, add complexity to the mask in the form of increased data volume and density, multiple aligned levels, smaller dimensional addressability and tightened CD control. Finally, tighter placement and level-to-level overlay on the mask are needed to achieve acceptable yield as device scale decreases and density increases. The Etec ALTA-3000 is a new scanned laser mask lithography system that has been designed to address these issues in the mask manufacturing environment. This system employs a greatly enhanced raster printing scheme using 32 beams scanned in parallel, an 8-pass print strategy, interstitial printing grids and 5 levels of beam intensity control per beam to achieve high accuracy and high throughput simultaneously. Thirty-two exposure grey-levels provide a grid addressability of 8.333 nanometers independent of throughput. Advanced multi-pass averaging schemes are used to reduce systematic errors. A new expandable parallel datapath architecture has a raw rasterization rate of 80 million geometries/second, and a peak transfer rate of over 2 billion pixels/second to accommodate large, dense data files. An alignment system based on CCD camera image capture can be used to register the printing of multiple levels on the same mask. A new stage transport system can handle plate sizes up to 9″ by 9″ by 0.25″. The ALTA-3000 uses an argon-ion laser source operating at a wavelength of 383.8 nm, making it compatible with exisiting laser mask manufacturing processes.

Processing techniques for Permalloy field access bubble devices with 5-μm cell periods and submicron gap widths

The top down planar process1 for the fabrication of Permalloy field access devices was extended from a 6.75×7.50-μm cell2 to a 4.75×5.0-μm cell with no major changes in the processing sequence. Direct step on wafer lithography, ion milling of the Permalloy, and plasma etching of AlCu were used in the device fabrication. Device topology was scaled, reducing the thicknesses of the Permalloy, oxide, and aluminum layers in order to decrease the permalloy-garnet spacing. The results of this work show that Permalloy field access bubble devices with 5.0-μm cells, 0.7-μm gaps, and 1.5-μm control lines can be processed over areas of 0.25–0.5 cm2, giving device capacities of 512 Kbits to 1 Mbit and device bit densities of 2×106/cm2.

The Problems of Selecting a Proper Microlithographic Imaging System

Considering the increased importance of custom integrated circuits in electronic equipments and other products there is a research activity in Hungary to develop a “state-of-the-art” semiconductor development laboratory for technology development and prototype circuit fabrication. The most significant parts of this laboratory are circuit design, mask making and wafer lithography. The problems associated with these three parts are discussed.

Ion beams promise practical systems for submicrometer wafer lithography: R. L. Seliger and P. A. Sullivan Electronics. 142 (March 1980)

Ion beams promise practical systems for submicrometer wafer lithography: R. L. Seliger and P. A. Sullivan Electronics. 142 (March 1980)

Ion beams promise practical systems for submicrometer wafer lithography : Robert L. Seliger and Paul A. Sullivan. Electronics. 142 (27 March 1980)

Ion beams promise practical systems for submicrometer wafer lithography : Robert L. Seliger and Paul A. Sullivan. Electronics. 142 (27 March 1980)

Minicomputer controls evaluation of epitaxial deposition for ICs : C. A. Germano, M. R. Ellett and M. J. Russ. Electronics July 5 (1973). p. 102

This chapter discusses the lithography considerations prior to wafer processing, including layout design such as the rules concerning minimum lines and spaces, required overlaps, recommended and/or forbidden shapes. The selection of the required photoresists for different applications is discussed. The process sequence of wafer lithography is described. The various applications of thick resists are covered briefly. As well as optical lithography with photomasks, other, more niche, patterning techniques are discussed.