Optical Analyses (SE and ATR) and Other Properties of LPCVD Si[sub 3]N[sub 4] Thin Films

Abstract

Thin silicon nitride films ͑less than 20 nm͒ deposited on ͑100͒ silicon substrates via low pressure chemical vapor deposition ͑LPCVD͒ at three temperatures ͑730, 760, and 825°C͒ were analyzed by spectroscopic ellipsometry ͑SE͒, attenuated total reflection ͑ATR͒, and other tools. Films appeared to have similar optical bandgaps ͑ϳ5 eV͒, and the values decreased slightly with the higher deposition temperature. Second ionic mass spectroscopy results showed that a similar amount of oxygen exists in the interface between silicon and silicon nitride. ATR spectra showed no sign of Si-H bonds and decreasing N-H bonds at higher deposition temperature in the thin films. The electrical properties of the films are also discussed.Silicon nitride films have been widely used in very large scale integration ͑VLSI͒ technologies, such as diffusion mask, passivation, antireflection coatings, and gate dielectrics. 1-4 Various processing methods of silicon nitride films were reported, such as thermal nitridation, 5 atmospheric pressure chemical vapor deposition ͑CVD͒, 6 plasma-enhanced CVD ͑PECVD͒, 7 hot wall CVD ͑HWCVD͒, 8 and low pressure CVD ͑LPCVD͒. 9 Among the fabrication techniques, LPCVD is commonly chosen. Even though LPCVD nitride films cannot be used for gate dielectrics due to their poor interface quality and high bulk trap density, they are widely chosen for applications such as diffusion mask, nitride spacers, etc. We studied the LPCVD silicon nitride thin films deposited by using a mixture of dichlorosilane ͑DCS͒ and ammonia (NH 3 ) with nitrogen as dilute at three temperatures in a conventional batch reactor.The purpose of this work was to analyze the optical properties of thin to ultrathin ͑below 10 nm͒ silicon nitride films via spectroscopic ellipsometry ͑SE͒ analysis and directly study the bond structure ͑es-pecially bonds with hydrogen such as Si-H and N-H͒ of the films by attenuated total reflection ͑ATR͒. SE is a nondestructive optical technique used to determine the optical properties of substrates and thin films based on measuring the polarization ellipse of a light beam reflected off a sample at a given angle. From this data, the complex index of refraction and film thickness can be determined using a computer model fit. ATR provides a way of directly analyzing very thin films with much higher sensitivity than normal Fourier transform infrared ͑FTIR͒ analysis. A schematic plot of ATR measurement is shown in Fig. 1. The infrared radiation signal penetrated into the monolayer film only once during the measurement. Typical thickness for normal FTIR analysis is equal or larger than 1000 Å to get desirable signal noise ratio. However, the actually used films in electronic devices may not necessarily meet this thickness requirement. In this work, all the films' thicknesses are less than 20 nm. By using ATR and Woollam SE analysis we can directly study the optical properties of these ultrathin nitride films. Other films properties like electrical data were also discussed. ExperimentalSingle crystal ͑100͒ p-type silico...

Review—Silicon Nitride and Silicon Nitride-Rich Thin Film Technologies: Trends in Deposition Techniques and Related Applications

“…Alternatively, the pre-adsorption reactions in the case of PA-CVD or PE-CVD could produce more active reactant species, leading to higher surface reaction rates at shorter surface diffusion lengths, potentially producing less contaminated SiN x films but with poorer step coverage and lower etch resistance. 107 Although a significant body of research in thermal CVD SiN x can be found in the literature prior to 2010, 73,105,106,[111][112][113][114][115] there are very few recent reports (within the last five years) on the topic, due most likely to the high thermal budget required for dissociation and reaction of the Si and N chemistries, except for 34 included the use of pulsed RF generated by modulating a continuous 200Hz low-frequency wave signal generator with 50% duty cycle in the PE-CVD reaction of SiH 4 and NH 3 at 150…”

“…Alternatively, the pre-adsorption reactions in the case of PA-CVD or PE-CVD could produce more active reactant species, leading to higher surface reaction rates at shorter surface diffusion lengths, potentially producing less contaminated SiN x films but with poorer step coverage and lower etch resistance. 107 Although a significant body of research in thermal CVD SiN x can be found in the literature prior to 2010, 73,105,106,[111][112][113][114][115] there are very few recent reports (within the last five years) on the topic, due most likely to the high thermal budget required for dissociation and reaction of the Si and N chemistries, except for 284 * The table is intended to provide baseline comparisons of bond dissociation energies of selected organic and inorganic Si and N source chemistries with the most commonly used precursors. 102,103 generator with 50% duty cycle in the PE-CVD reaction of SiH 4 and NH 3 at 150 • C. The process yielded film densification (over 20% increase in film density) and smoothing (a decrease in average surface grain size standard deviation from 0.2nm 2 to 0.04nm 2 ), with the SiN x films exhibiting smoother surface morphology and lower void density.…”