Pulsed-Laser Deposition of Titanium Nitride
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XPERIMENTAL Titanium nitride films were formed by focusing a Lambda Physik EMG203 excimer laser operating on KrF (k = 248 nm) onto a hot-pressed TiN target supplied by Target Materials Inc. The laser fluence was 4 J/cm 2 , the pulse duration was 20 ns, and the pulse repetition rate was in the range 4 to 8 Hz. The films were deposited in vacuum (base pressure 10-6 torr). Two types of substrate material were used in the present study: (100)-oriented single crystal silicon and rocksalt. (No attempt was made to remove the native oxide layer on the silicon substrates.) The substrates were mechanically clamped onto the stainless steel plate of a small resistive heater and were positioned parallel to the target. The distance between the target surface and the substrate was ~ 5 cm. The temperature of the substrate heater was monitored by a thermocouple embedded into the heater block at a position just behind the substrate. All the temperatures reported here are those of the substrate heater as measured by the thermocouple. The rocksalt substrates were used to facilitate sample preparation for transmission electron microscopy (TEM) and for parallel electron energy loss spectrometry (PEELS). Thin (~10 to 30 nm thick) TiN films were deposited onto freshly cleaved (100)-oriented NaCl substrates. Following deposition, the NaCl was dissolved in deionized water and the film collected on a slotted 400 mesh copper grid and dried in air. This specimen preparation method produces excellent samples for PEELS analysis- they are thin and of a uniform thickness. All the films were analyzed either immediately after deposition or after being stored in a desiccator for a few days. A Hitachi H600 TEM operated at 100 kV was used to examine the films. PEELS was performed with a Philips EM400T/FEG analytical electron microscope operated at 100 kV. The surface morphology of the films was characterized with a Digital Instruments Nanoscope III Multimode atomic force microscope (AFM) operated in either contact mode or tapping mode. The images shown here are top view images with linear gray scale encoding of the height of features. The films were also examined using a JEOL JSM 6400 scanning electron microscope (SEM) operated at 20 kV. No conductive coating was applied to the samples prior to SEM analysis. RESULTS AND DISCUSSION The first obvious feature of all the films grown in this study was their golden-yellow color, which is characteristic of TiN [5]. The surfaces of the films were fairly free of the ubiquitous particulates associated with films formed by PLD. The occurrence of particulates on the film surface is highly dependent on the nature of the target [1]. TiN films formed from the ablation of titanium may have large spherical particles on the surface as a result of the ejection of molten metal from the target [2]. Films made from pre-formed TiN targets often show a lower number of particulates [1]. Examination of the surface morphology of the films by AFM showed that they were extremely smooth for all the substrate temperatures used in this
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