Akinori Shibayama

Application of two-wavelength optical heterodyne alignment system in XS-1

This article presents the alignment performance of the two- wavelength optical heterodyne alignment system in the x-ray stepper XS-1. The alignment accuracy obtained by the double- exposure method with a single mask and a Si trench wafer was better than 20 nm. The dependence of the alignment accuracy on Si trench depth indicated that the two wavelengths compliment each other and ensure a 3(sigma) of less than 20 nm. The alignment capabilities for other processed test wafers were also investigated by mix-and-match exposure. For etched SiO2 and poly-Si film on a Si trench, an accuracy below 20 nm was obtained. For AlSiCu film sputtered on etched SiO2, there appeared systematic alignment offsets depended on die position, which are thought to be due to a wafer-induced shift. The systematic offset errors were eliminated by the use of send-ahead wafer and corrections for individual offsets on each die, and thus the alignment accuracy was improved to 20-40 nm for each alignment axis. The two-wavelength heterodyne alignment system of the XS-1 has sufficient potential for 130-nm lithography and below.

EB60: An advanced direct wafer exposure electron‐beam lithography system for high‐throughput, high‐precision, submicron pattern writing

A high‐throughput, high‐precision e‐beam direct writing system, the EB60, has been developed for both submicron VLSI memories and application specific integrated circuits (ASICs). The throughput is twenty and eighty 4‐in. wafers per hour for 0.5 μm VLSI memories and 0.8 μm ASICs, respectively, with ±0.1 μm overlay accuracy. To achieve this performance, a novel drawing method and the following key subsystems were developed: (1) Vector beam scanning during continuous stage movement with an advanced three dimensional registration method, which has reduced overhead time and results in a well balanced system design. (2) Variable shaped beam electron optical column with 0.2 μm beam edge resolution at 2.0×1.5 (1.5×2.0) μm maximum beam size and a current density of up to 70 A/cm2. (3) High‐speed beam deflection and dynamic focus system, including high‐speed analog circuits, all‐electrostatic deflectors, and an electrostatic dynamic focus lens. (4) Fast pattern controller, which executes 16 Mshot/s pattern data ge...

X-Ray Mask Inspection Using Replicated Resist Patterns

A new X-ray mask inspection method using replicated resist patterns is proposed. It is able to detect fatal opaque defects on the back surface of the mask and at the bottom of the hole pattern, in addition to those on the front surface. It can also ignore transparent defects on the mask. This method is useful even for defect detection on a single-die mask through die-to-die comparison. For the false process defects occurring during the replication process, a discrimination procedure using a 2-step die-to-die comparison is proposed. In inspection tests with SEMSpec, we investigate the relation between the detection sensitivity to small resist defects and the conductive-coating thickness on them.

X-Ray Projection Lithography Using a Fresnel Zone Plate.

In this article, we experimentally confirm the possibility of X-ray projection using a Fresnel zone plate (FZP) and monochromatic synchrotron radiation (SR) light at a wavelength of 10 A by pattern replication. To evaluate the characteristics and patterning ability of the FZP, we designed one with a 4000-A Ta absorber on a 0.2-µ m SiN membrane with a 0.159-µ m outermost zone width for 0.2-µ m resolution. Using the designed linear and circular FZPs, the focusing image of the X-ray source we obtained was almost equal to that predicted theoretically. We used FZP projection optics to obtain single-layer resist patterns as projection images. Moreover, using a penetrating mask, which is the conventional transmission type, We successfully replicated 0.2-µ m line and space and a mesh with a reduction ratio of 1/2.

Overlay accuracy of a synchrotron radiation stepper evaluated by two‐mask double exposure

The overlay accuracy of a synchrotron radiation stepper has been evaluated when different masks are used as in actual exposure. Using several masks requires both high repeatability and accurate offset controllability to perform the proper alignment of the stepper. To this end, a two‐mask double‐exposure method that considers mask error has been devised. It yields a 3σ deviation of 25 nm for the overlay repeatability of our SS‐1 stepper. This is almost the same as in the one‐mask double‐exposure method, which means that the stepper effectively has an alignment repeatability of less than 25 nm. In addition, a mask stage is developed to improve the offset controllability and enlarge the stroke. The resolution and stroke of the stage are 20 nm and ±1000 μm, respectively, for x and y directions, and 0.5 and ±800 μrad, respectively, for theta. This stepper facilitates the reduction of alignment offset deviations to less than ±10 nm in the x and y directions and less than ±1.0 μrad for rotation.

Overlay Repeatability in Mix-and-Match Exposure Using the SR Stepper: SS-1

Proximity X-ray lithography using synchrotron orbital radiation (SR) is potentially able to replicate patterns with a width of less than 0.2 µ m. We developed a die-by-die alignment basis SR stepper, which is equipped with air-lubricated lead screws for the XY stage and an optical heterodyne alignment system. An overlay repeatability of 23 nm (3σ) is obtained with only X and Y alignment when evaluated by the double exposure method. In practice, the mix-and-match scheme between the SR and optical exposures is important for reducing the cost of lithography. In the mix-and-match exposure between the SR and optical steppers, an overlay repeatability of 45 nm (3σ) is achieved with the X, Y, and θ alignment mode of the SR stepper. Analysis of the error factors in this overlay exposure experiment showed that the optically printed patterns have chip shape distortions causing overlay error of about 35 nm (3σ).

A high‐speed patterning controller for the EB60 electron beam lithography system

A high‐speed patterning controller consisting of a pattern generator, beam deflection circuits, and a mark signal processor has been developed for the EB60 electron beam lithography system. To achieve a throughput of 16M shots per second and high accuracy for pattern writing during continuous movement of the stage, three key developments are incorporated into the pattern generator: (1) a buffer memory of 128M bytes for storing an entire VLSI chip pattern and eliminating the need for the repetitious storing of the same pattern data; (2) six‐stage pipelining with a 400 MHz basic clock for performing dynamic corrections in under 60 ns (about five times faster than former systems); (3) feed‐forward control architecture for eliminating the beam position error caused by the data transmission system delay time. The major and minor deflection systems are equipped with the beam deflection circuits consisting of high‐accuracy digital to analogue converters (DACs) and high‐speed amplifiers. For the minor field defle...

A Solid State Electron Detector for the EB60 Electron Beam Lithography System

This paper discusses the development of a new solid state electron detector (SSD), which is a key component for a high-precision, high-throughput EB direct exposure system, the EB60. The SSD is a low-noise, fast-response detector for a weak input electron beam signal having a nanoampere current and energy of approximately ten kilo electron volts. The SSD has a new metallization structure on the active area for eliminating the effect of incident photons coming from an optical wafer height sensor. For the smallest input signal (15 keV electrons) operation, an SSD with a wide active area of 25 mm2 has a current gain of 2300, a rise time of less than 350 ns and a leakage current of 80 pA; this is negligible to the output signal of a microampere. A long-term stability of a 3% current gain decrease after electron beam bombardment for 1000 hours, and a leakage current of 100 pA after bombardment for 5000 hours have been obtained. A highly accurate, high-speed registration mark detection of 0.02 µm and 50 ms per mark has been achieved through the SSD.