Electron Beam Mask Writing System for High-precision ...

1 Electron beam Mask Writing System for High-precision Reticles The HL-900M Series 206(a) m serif-pattern image(b) m serif-pattern imageElectron beam Mask Writing System for high -precisionReticles The HL-900M Series OVERVIEW: Along with the accelerated miniaturization of semiconductordevices, the specifications for reticles used in lithography processes arerapidly demanding higher levels of accuracy. Many semiconductormanufacturers are already developing 130-nm nodes, and the Electron beamwriting systems used in manufacturing reticles must also follow the trendtoward higher accuracy that is seen in devices.

2 In December 1999, Hitachi,Ltd. announced the HL-900M Series Electron beam photomask writingsystem, which was developed in response to user demand for high -precisionreticles1). This System is based on the HL-800M Series and introduces newelectron optics, a low-distortion stage, and parallel processing function forcoping with large volumes of data to achieve higher accuracy and higherthroughput. The Writing System is not the only factor in achieving advancedmasks; the fabrication processes are also important, and progress is beingmade in the use of chemically amplified resists in the mask MatsuokaKazui MizunoTetsuji NakaharaHidetoshi Sat INTRODUCTIONRAPID progress is being made in the furtherminiaturization of semiconductor devices.

3 Accordingto the ITRS (International Technology Roadmap forSemiconductors) published by the SIA (theSemiconductor Industry Association of the US) in1999, the mass production of 130-nm devices isexpected in 2002 (Fig. 2). Among semiconductormanufacturing processes, the lithography process isthe one that must cope with increasing miniaturizationFig. 1 Resist Images for a Fine OPC (Optical Proximity Correction) Pattern Obtained with a high -end OPC patterns for a 300-nm OPC dimension ZEP7000 resist dosed at 25 C/cm2 and observedwith an S-7840 scanning Electron microscope are shown. Using an Electron beam makes it possible todraw OPC patterns, etc.

4 At higher resolutions than can be achieved with laser Review Vol. 49 (2000), No. 4 207 FeatureEffectsHigh resolution , high accuracyHigh throughputHigh accuracy, high throughput, and ability to handle large data volumesEase of operationEase of operationHigh acceleration voltage (50 kV) Variable-shape beam and vector scanningParallel processing capabilityAutomatic mask transport functionGraphical operation screenthe earliest, and the demands placed on the reticlesused in that process are becoming severe. Currently,most advanced reticles are fabricated by using anelectron beam Writing System , so the accuracydemands of the specifications of that equipment arealso increasing in the other hand, the wavelength of lightemployed by the optical reduction exposure equipment(stepper) that is used in the lithography process isbecoming increasingly shorter, and new trends in thefield of reticle fabrication include the addition of OPC(optical proximity correction) patterns (see Fig.)

5 1), theuse of phase shifting masks, and so on to further extendthe resolution this report, we describe the HL-900M Serieselectron beam Writing System that was developed byHitachi, Ltd., the current situation regardingchemically amplified resists, and the future of theelectron beam Writing systems that are used in FEATURESThe HL-900M Series targets High-precision reticlefabrication at resolutions of 150 nm or better. Thissystem is based on the HL-800M2, 3), and, in order toincrease accuracy, introduces (1) high -precisionelectron optics, (2) a low-distortion stage, (3) a highlyaccurate temperature control System , and (4) a parallelprocessing function for dealing with large-volumepattern main features of the HL-900M Series and theireffects are listed in Table 1.

6 This System employs avariable beam shape, vector scanning, and acontinuous-stage-movement Writing method. Theacceleration voltage is 50 kV, the maximum beamcurrent density is 10 A/cm2, and the maximum beamsize is 2 2 m2. beam deflection is accomplished byusing three types of deflectors, with a main deflectionarea of 2 2 mm2, a secondary deflection area of 480 480 m2, and a sub-secondary deflection area of 60 60 m2. The approximate corresponding mask sizesare cm (5 inches), cm (6 inches), and (7 inches).The System configuration of the HL-900M Seriesis shown in Fig. 3. The control workstation performsdata preparation, equipment calibration, writingcontrol, and other System control functions.

7 Thewriting data that is transferred from the workstationto the buffer memory of the equipment is expandedfrom a compressed format into the basic pattern proximity effect correction unit calculates theamount of dose correction at Writing time based onthe Electron beam energy accumulation due todifferences in pattern density. The shot controllerprovides real time feedback of the position data forthe continuously moving stage to the deflector and alsoexecutes correction of the Electron beam shape,position, and , duplication of the control circuitmakes it possible to do the processing for the writingoperation and the proximity effect correction inparallel.

8 That shortens the Writing time and increasesthe accuracy of the proximity effect correction. At thesame time, easing some of the limitations on theTABLE 1. Main Features of the HL-900M Series and TheirEffectsA System that meets the requirements for High-precision reticlesof 150 nm or 2 Accuracy Requirements for changes in accuracy requirements for reticle over time areshown here. For 130-nm nodes, the required dimensionalaccuracy has become 10 nm or accuracy (nm)Required accuracy (nm)Minimum dimensionsPositional accuracyDimension uniformityHL900M SeriesDevice node (nm)Year60402005604804003202401301002000 20022005 Reference data.

9 International Technology Roadmap for Semiconductors 1999 Electron beam Mask Writing System for High-precision Reticles The HL-900M Series 208 Control softwareData preparationWriting controlSystem calibrationWrite dataControl circuitPattern fracturing circuitProximity effect correction circuitParallel processing circuitLens and deflector control circuitCalibration circuitStage loader control circuitVacuum exhaust control circuitStageMask loaderElectron opticsamount of pattern data makes it possible to write morethan 20 gigabytes of pattern mask transport mechanism employs anautoloader and an automatic batch System and iscapable of continuous processing of up to six waferswith the C to C (carrier to carrier) scheme.

10 Applicationto an automatic mask transport System is also , we revised the stage structure so as toprevent table deformation when the stage moves. Thestage position is measured with high accuracy by laserinterferometer, but the interference mirror must beattached to the stage. Mechanical deformation of thestage during movement causes displacement of themirror, and thus reduces the accuracy of the amount of stage deformation may be minute, buteven slight deformation cannot be permitted in orderto achieve nanometer-level Writing accuracy. Thestructure of the new stage used in this System has aseparate Y table, with the reflection mirror and platemounted on the top table.