Diane K. Stewart

Chemically enhanced FIB repair of opaque defects on molybdenum silicide photomasks

The characteristics of an ideally repaired opaque defect on a molybdenum silicide (MoSiaObNc) photomask are: (1) the total removal of the MoSiaObNc defect, leaving no residual MoSiaObNc; (2) a smooth, level quartz surface (no over-etch) after the MoSiaObNc is removed; (3) minimal riverbedding of the quartz at the perimeter of the MoSiaObNc defect; and (4) maximum light transmission (%T) at the i-line (365 nm) and DUV (248 nm) lithographic wavelengths. Achieving these ideal repair characteristics is becoming increasingly difficult as the patterned features become smaller, as the lithographic wavelength becomes shorter and as phase shifting mechanisms are implemented. A chemical process has been developed to enhance the FIB (focused ion beam) etching of MoSiaObNc defects. Using this chemical process, a FIB protocol has been developed which enhances the removal of a MoSiaObNc defect while inhibiting the removal of quartz. AFM (atomic force microscopy) indicates that (1) MoSiaObNc is totally removed, (2) the quartz remains smooth and level (no over-etch), and (3) the riverbends are, at this time, 10 - 45 nm; our target is 1 - 15 nm. The MoSiaObNc etch process reduces optical staining due to implanted gallium

Focused ion-beam-induced tungsten deposition for repair of clear defects on x-ray masks

A 25 key focused Ga ion beam was used to induce deposition of tungsten on a gold absorber on boron nitride X-ray mask with submicron features to simulate the repair of clear defects. Tungsten was deposited to fill holes, extend lines and add missing features, such as isolated contacts and lines. Deposits were placed between features and made to cross over both gold and tungsten features to evaluate proximity effects. Series of tungsten depositions that varied in thickness were exposed to an X-ray source and transferred into resist. Contrast equivalent to or better than the gold absorber was achieved for tungsten that was thinner than the gold.

Focused ion beam deposition of new materials: dielectric films for device modification and mask repair and tantalum films for x-ray mask repair

Two processes have been developed to enable both focused ion beam (FIB) repair of advanced masks and FIB device modification. Silicon dioxide- based films can be deposited by rastering a focused ion beam across a surface onto which a combination of siloxane and oxygen gases have been adsorbed. The deposited material exhibits sufficient dielectric strength to be used for FIB modification of devices. Applications of FIB dielectric deposition include: (1) Local passivation. (2) Backfilling vias to allow for probing buried metal layers without contacting exposed metal layers. (3) Electrical isolation between crossed metal lines. (4) Optically transparent films for phase shift mask repair. In the first half of this paper we discuss the gas delivery system, and the material and electrical characteristics of the films, as well as describing typical device modifications using FIB dielectric films. In the second half of the paper we describe a process for deposition of tantalum- containing films using a tantalum-based organometallic precursor for repair of clear defect on X-ray masks. Although FIB gold films are adequate for repair of gold-absorber, silicon-membrane X-ray masks, gold films are not acceptable in the fab line, and tantalum is preferred for repair of either tungsten or tantalum absorber X-ray masks.

State of the art in focused ion-beam mask repair systems

Focused ion beam (FIB) systems are commonly used to repair lithographic masks with features below one micron. We will summarize the development of focused ion beam mask repair systems starting from the original tools developed for photomasks approximately 10 years ago. The present state of the art in FIB mask repair systems is incorporated in two types of tools-one for repair of proximity print X-ray masks, and the other for repair of photomasks and some phase shift masks. Similarities of the two styles of systems include the gallium ion optics, the lithographic stage for accurate positioning, a thermal enclosure to minimize system drift, deflection and scanning electronics, and an interface to inspection data. The differences include the process chemistries, repair strategies, and imaging techniques. Examples of a variety of repaired defects on both X-ray and phase shift masks will be shown. Advanced masks such as those for EUV (Extreme Ultraviolet), DUV (Deep Ultraviolet), and SCALPEL (Scattering with Angular Limitation in Projection Electron Lithography) will have to be repaired should those technologies mature, and presumably with FIB tools. Preliminary research and development of advanced mask repair problems will be described and possible approaches will be suggested.

Chemically enhanced focused-ion-beam (FIB) repair of opaque defects on chrome photomasks

The characteristics of an ideally repaired opaque defect on a chrome (Cr) photomask are: (1) the total removal of the Cr defect, leaving no residual Cr; (2) a smooth, level quartz surface (no over-etch) after the Cr is removed; (3) minimal riverbedding of the quartz at the perimeter of the Cr defect and (4) maximum light transmission (%T) at the lithographic wavelength. Achieving these ideal repair characteristics is becoming increasingly difficult as the patterned features become smaller, as the lithographic wavelength becomes shorter and as phase shifting mechanisms are implemented. A chemical process has been developed to enhance the FIB (focused ion beam) etching of Cr defects. This chemical process enhances the FIB removal of a Cr defect 2.0 - 2.2 fold while inhibiting the removal of quartz by 60 - 80%. AFM (atomic force microscopy) indicates that (1) Cr is totally removed, (2) the quartz remains smooth and level (no over-etch) and (3) the riverbeds are 5 - 25 nm. If necessary, a second FIB-induced chemical process is used following the chrome etch process to reduce optical staining due to implanted gallium (a gallium ion beam is used in commerical FIB systems) such that the %T of the repaired areas at i-line(365nm) and DUV(248nm) wavelengths is 95%. In general, this second process is required at 248 nm but not at 365 nm. AIMS evaluations indicate a critical dimension variation between repaired and reference patterns of 10% at 35% light intensity at UV and DUV wavelengths. In summary: a. an FIB etch process has been developed which repairs opaque Cr defects, b. a second FIB etch process removes implanted gallium so that the %T is above 95% at i-line (if neccessary) and DUV wavelengths; c. these two etch processes are done sequentially, while the defect is positioned under the FIB column (post treatment processes are not required); d. clear defects can also be repaired at the same time by FIB-induced deposition of opaque carbon. Keywords: Mask repair, opaque defects, chrome defects, FIB

Advanced metrology and inspection solutions for a 3D world

Semiconductor devices and packages have firmly moved in to an era where scaling is driven by 3D architectures. However, most of the metrology and inspection technologies in use today were developed for 2D devices and are inadequate to deal with 3D structures. An additional complication is the need for specific structural and defect information that may be buried deep within a 3D structure. We present concepts and technologies that allow for 3D imaging as well as tomography, enabling engineers to view structural information with unprecedented clarity, detail and speed.

Repair and printability study of binary chrome masks with OPC features for 0.18-μm technology node

Binary chrome masks with optical proximity corrections (OPC) will be used to produce devices for the 0.18 micron generation. The complex shapes of OPC features make automated inspection and repair difficult. Specifically it is difficult to recognize what features are defective and what they are supposed to look like. One feature that can repair such defects is Pattern Copy. Pattern Copy is a powerful image- processing program that is used to repair defects on complex patterns. This is done by taking an image of the defective area and comparing it to an image of a known good area. These two images are subtracted and the result is a bit map of the repair that must be performed. In this study, a series of repairs on OPC features was made with Pattern Copy and other techniques. These repairs were performed on 0.18 micron OPC features that had CD errors, defects in assist bars and clear and opaque extensions. Some repairs were deliberately biased to evaluate the effect on printability. The repaired mask was printed at 248 nm at TSMC and the CDs of the printed features were evaluated as a function of repair size, feature size and bias of the repair on the mask. It was demonstrated that two techniques can be used to make repairs that print with good CDs on the wafer. One method involves postprocessing the mask to remove any implanted gallium and the other involves biasing the repair.

0.35-μm i-line attenuated phase-shift mask (PSM) repair by focused-ion-beam technology

This paper addresses the capabilities of the Micrion 8000 FIB (focused ion beam) phase shift mask repair tool to repair clear defects and opaque defects found on chrome-based binary and attenuated phase shift masks, and MoSi-based attenuated phase shift masks for 0.35 micrometer lithography. For a repair to be successful, the repair must: match size, shape, and position of the defect, reproduce the desired transmission, minimize damage to the underlying substrate, minimize damage to surrounding non-defect areas, and finally, the repair must be durable. For the production environment, a repair tool must be very reliable and easy to use as well. The Micrion 8000 FIB phase shift mask repair tool incorporates the above requirements.

Edge-placement accuracy of opaque and clear defect repairs using focused ion beam technology

On the standard Micrion 8000 PM Repair System platform, the repair accuracy for clear defect repair and opaque defect repair is plus or minus 75 nm. Incorporation of a new ion beam column has pushed the repair accuracy for clear and opaque defect repairs to smaller values. This new system can image isolated defects less than 200 nm in size. To characterize the repair accuracy of the system, experiments on edge placement accuracy were performed. This paper presents data on the accuracy of defect repairs using the Micrion 8000 PSM Repair System on Chrome masks. The study specifically looks at the edge placement of opaque defect and clear defect repairs on masks coated with a conductive layer versus masks not coated with a conductive layer. We also explore the edge placement accuracy of the repair due to the directionality of the repair scan. Finally we examine the shape of the distribution function of the repair measurements and also investigate differences in the measured edge placement accuracy of repairs using different measuring techniques.