Papers

AVS1996 Session VT+FP-WeA: Issues in Vacuum Processing and Flat Panel Displays

Wednesday, October 16, 1996 2:00 PM in Room 104A/B

Wednesday Afternoon

Start	Invited?	Item
2:00 PM		VT+FP-WeA-1 Vacuum Requirements for Next Wafer Size Physical Vapor Deposition System I. Hashim, I. Raaijmakers (Applied Materials) The next generation of physical vapor deposition (PVD) equipment for semiconductor industry will be able to provide metallization for < 0.25 mm feature sizes on a larger wafer size (300 mm). The motivation for this work is to determine vacuum requirements for this next generation PVD equipment. In particular, it will be important to find cost effective solutions for achieving ultrahigh vacuum, as pumping system costs do not scale linearly with size. Furthermore, it is important to know to what extent interconnect device properties i.e., electromigration and metal-metal contact resistance, are impacted by impurities, and where these impurities originate from. The major sources of impurities in sputtered Al alloy films for interconnects, include those originating from the target material, residual gases present in the vacuum system, and those introduced through the gas delivery system. In this study, the contribution of impurities from residual gas phase contamination in a state-of-the-art sputtering vacuum environment (base pressure ~ 1 x 10-8 Torr) is compared to that from a sputtering target with state-of-the-art purity (99.999%). Introduction of controlled amounts of isotope gases H2O18, N215, O218, and C13H4, in 10-6 - 10-8 Torr range during the sputtering process makes it possible to distinguish the impurities originating from residual gases from those originating from other sources. The sputtering target is found to be the major source of H and O impurities in the film, whereas N atoms originate mainly from impurities in the gas phase. The effect of these impurities on film microstructure has been analyzed by X-ray diffraction and transmission electron microscopy. Furthermore, these films have been patterned into 0.6 mm wide lines and test structures to study their electromigration behaviour. Nitrogen contamination is found to be particularly harmful to electromigration resistance.
2:20 PM		VT+FP-WeA-2 Vacuum Environment Considerations in Field Emission Displays P. Schwoebel (SRI International) The lifetime and rate of degradation of FEDs are profoundly affected by a number of factors, particularly materials selection and tube processing. In this talk, certain aspects of vacuum envelope processing, phosphor treatments, gettering, emitter tip materials selection and surface chemistry will be discussed. The use of microfabricated field emitter arrays in FP cathodluminescent displays is a challenging task if defect free lifetimes comparable to conventional CRT (20,000 hrs) are to be realized. A significant portion of this challenge lies in the realm of vacuum technology since field emission stability is sensitive to the vacuum environment. The absolute pressure is important because it controls the electron mean free path, and this characteristic length is directly related to phenomena such as gaseous breakdown and cathode sputtering rate. The relative partial pressures in the envelope are the most important because they influence the long and short term emission current stability by governing the effect of adsorption and desoprtion. With Mo Spindt-tpye field emission cathodes, stable lifetimes on the order of 10\super 5\ hrs have been obtained employing thoroughly cleaned metallic anodes in an actively pumped, hydrogen dominated, hydrocarbon-free, UHV environment. The production and maintenance of such an environment in a FED is difficult due to the large surface area-to-volume ratio, outgassing from the phosphor-coated anode, and the use of passive getter pumping over long timeframes. Such considerations lead quickly to the conclusion that the appropriate combination of vacuum envelope and anode processing techniques, emitter tip material, and getter selection and management is essential if FEDs are to be commercially viable.
3:00 PM		VT+FP-WeA-4 Field Emission Cathode Arrays: Effect of Various Gases on Device Performance B. Chalamala (University of North Texas); R. Wallace, B. Gnade (Texas Instruments Inc.) Field emission devices (FEDs) have been studied extensively for possible applications in high resolution displays. Several serious issues need to be addressed before FEDs can be incorporated in commercial display systems including long term vacuum reliability and device integrity under extreme operating conditions. FEDs are extremely sensitive to contamination of the tips to various residual gases. These gases, apart from changing the surface properties of the tips, are ionized by the field emitted electrons. The impact of these ions on the tips causes surface modifications leading to emission current instabilities and subsequent device failures. In this paper, we present the results of ongoing studies on the effect of various gases on Spindt arrays with Mo tips. The arrays were subjected to oxygen, hydrogen, water and methane under well controlled experimental conditions. Gases were introduced into a clean UHV system and measurements were made of the emission characteristics for gas doses up to 10000 Langmuirs. Using a quadrupole mass analyzer, we have measured the relative ion yields of various ion fragments produced by array exposure for pressures in the range 1x10\super -10\ to 1x10\super -6\ Torr. These results permit an estimate of device lifetime and ambient vacuum requirements.
3:20 PM		VT+FP-WeA-5 Vacuum Considerations in Sealing Flat Panel Displays L. Kovacic, P. Stromberg, J. Jordan (Sandia National Laboratories) Under a DARPA grant, we have designed and fabricated an alignment and sealing device for flat panel displays. The device includes a modular vacuum chamber for pre-sealing vacuum bake-out of the display panels and post-sealing final evacuation of the sealed display. This presentation will discuss vacuum considerations in flat panel displays with respect to the alignment and sealing operations performed on our device. Some of those considerations include the modular construction of the device which allows it to be functional with or without the vacuum system, design requirements for holding panels in a vacuum or in the open air, the characteristics required in sealing glasses to enable them to seal properly in a vacuum environment, the current state of process development in vacuum alignment and sealing of displays on our device, and ideas for future design modifications to make the device adaptable to a production setting.
4:00 PM		VT+FP-WeA-7 Improvements in Signal-to-Noise and Minimization of Analyzer Related Background Contributions in Ultra High Vacuum Residual Gas Analysis J. Wei, R. Pedder (ABB Extrel, Quadrupole Mass Spectrometry) Typically, when a quadrupole mass filter is used to characterize an ultra high vacuum environment, the indicated chamber pressure is seen to rise upon enabling of the ionizer filament. This escalation in residual gas pressure is commonly attributed to thermal desorption of gases from the ionizer and chamber surfaces as they are radiatively heated from the hot ionizer filaments. Desorbed gas originating from the ionizer surface may possibly be differentiated from residual chamber gas through the use of an energy analyzer between the ionizer and the quadrupole mass analyzer. Desorption from chamber walls can be minimized through judicious selection of analyzer voltages. This presentation will include an examination into the mechanism for this desorption and consequent residual gas pressure increase, along with new experimental techniques to minimize these sources of gas desorption, while improving overall quadrupole partial pressure detectability.
4:20 PM		VT+FP-WeA-8 Evaluation of Low Cost RGA's for UHV Applications M. Rao, C. Dong (CEBAF) In recent years several low cost RGA's have been introduced into the market place. It would be very useful to know these RGA's performance characteristics in order to make an informed selection for UHV applications. The UHV applications include the extreme sensitivity helium leak detection and monitoring of the residual gas spectra in the UHV systems. In this paper we present the performance characteristics of several RGA's with respect to the quantitative analysis of the residual gases in the UHV systems. Further, the resolution, sensitivity and linearity data of the RGA's will be presented for hydrogen, helium and nitrogen. A direct comparison method is used in obtaining this data. Spinning rotor and extractor gauges are the transfer standard gauges used in CEBAF's vacuum gauge calibration facility, with which all the above measurements were carried out. *Work supported by the Department of Energy, Contract DE-AC05-84ER40150.
4:40 PM		VT+FP-WeA-9 Fast Pump-down System Combined the Chemical Treatment and Ultra-Dry Gas Introduction using Oxygen-Ion Conductor as a Moisture Remover K. Tatenuma, K. Uchida, T. Itoh (Kaken Co., Mito Institute, Japan); H. Ishimaru (National Laboratory for High Energy Physics, Japan) A fast pump-down system combined the chemical treatment and ultra-dry gas introducing treatment has been developed. The former is to acquire the ultra-high vacuum quickly by removing adsorbed water and the latter is to preserve ultra-high vacuum clean by suppressing water adsorption. The vacuum test has been studied on an aluminum alloy chamber of 8.5 m long with elliptical aperture for Recycler Ring in Fermilab by exposing air of 95% relative humidity. After evacuation to 10e -5 Torr, dichloropropane gas of 1 Torr was injected into the chamber at 80\super o\ C. After the chemical treatment, the ultimate pressure was 2-4 x10e-10 Torr. After the ultimate pressure was obtained, ultra-dry nitrogen generated by an ultra-dry gas generator was introduced into the chamber to atmospheric pressure. The chamber was evacuated again. After 5-7 minutes of the pump-down by a turbo-molecular pump, the pressure reached 10e-10 Torr range. In the case of a reference test without the chemical treatment and with introduction ordinary room air to atmospheric pressure, the ultimate pressure after baking at 150\super o\ C for 24 hours was 4-10 times higher than that of the chemical treatment and was not obtained after 1 week evacuation. The moisture in the gas treated by the ultra-dry gas generator based on a new principle using heated ceramics (yttria stabilized zirconia) to remove moisture in gases by electrolytical decomposition can not be detected using a high sensitive hygrometer with detection limit of 1 ppbv. Therefore, the fast pump-down system is useful in the many fields of vacuum technology; accelerator and semiconductor facilities, surface analyses with high resolution and nuclear fusion technology.