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A scalable submicron contact technology has been developed using a fully conformal LPCVD titanium nitride barrier metal that provides low contact resistance to salicide, low leakage, excellent adhesion and high thermal stability. Owing to the uniform step coverage, especially in deep, straight wall contacts, the CVD TiN overcomes the metal reliability and junction leakage issues associated with the physical sputtering of metals in high aspect ratio, submicron contacts. LPCVD TiN withstands 550°C thermal stress, maintaining low contact resistance and leakage, while physically deposited TiN fails at 500°C. The applicability of CVD TIN barrier technology to VLSI devices has been successfully demonstrated on production circuits. INTRODUCI'IONCVD titanium nitride has received attention from several sources (1,2) as a hard coating for steel and other metals. Recently CVD TiN has been evaluated as a barrier metal (3,4,5) for semiconductor devices due to its conformal step coverage and high thermal stability. As a result of these properties CVD TiN films can find applications a t the submicron level a s a barrier for laserplanarized, high-temperature or bias-sputtered aluminum as well as a glue layer for tungsten. In this work, we describe a scalable contact technology for submicron integrated circuits using CVD TiN as a barrier metal. Contact resistance, diode leakage, chemical and physical properties of the film are discussed. The excellent conformality of LPCVD TiN has been demonstrated in contacts as small as 0 . 4~ and in trenches with an aspect ratio greater than six. The use of LPCVD TiN as a reliable adhesion layer for tungsten in sub-half micron contacts is demonstrated for the first time. Trace concentrations of C1, a reactant byproduct, are a concern which is addressed with corrosion reliability data. EXPERIMENTALTwo submicron contact process sequences utilizing LPCVD TIN as a barrier and/or a n adhesion layer have been studied (Fig. 1). Both techniques were used to produce silicided contacts, yielding a low interfacial resistance for the resulting SiR'iSiR'iN structure. TiN films were deposited from Tic14 and N H 3 at 650°C in a single wafer LPCVD system to obtain uniform, reproducible films. Barrier integrity under thermal stress is a more critical issue for aluminum than for tungsten metallization. For this reason, the electrical results described in this paper were obtained with conventional Al/Cu/Si metal. In order to illustrate the use of LPCVD TiN as a n adhesion layer, its application with blanket tungsten as metal 1 or in conjunction with tungsten etchback for plug purposes is also demonstrated (Fig. 2).Diode leakage measurements were performed a t 10 V reverse bias. To distinguish the leakage contribution of the contacts from other sources, two structures were measured: a 15000 pm2 diode with three (1p.m dia) contacts, and a similar diode with 2904 contacts. Measurements are reported after wafer processing, as well as after a series of half hour thermal stresses starting at 450°C and including 550°C....

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The availability of 2k×2k or larger format CCD chips has made direct digital imaging more practical in electron microscopy. But the suboptimal performance of scintillating screens, particularly their inferior resolution as compared to film, is still an obstacle to a broader adaptation of digital imaging technology to electron microscopy. Thin-foil substrate screens have improved brightness and resolution over the more commonly used glass substrate screens, particularly at higher operating voltages, but further improvements are required for the optimum performance of the CCD imaging systems. Self-supporting single crystal YAG screens, approximately 30 μm in thickness, provide better resolution and detection-quantum-efficiency as compared to the phosphor screens, but their lower brightness, about 4 - 8 times lower, makes them less than ideal at least for low dose applications. Until brighter single crystal scintillators become available, powder phosphor screens may offer performance advantages for applications where radiation damage to the specimen is a concern.