Deposition Of O-BN Films By Jet-RF-PEPLD And Investigation On Characteristics Of O-BN Films

In this thesis, we generalize the researches on BN films and itsdevelopments, properties, applications and phase transformations of thisinteresting Ⅲ-Ⅴcompound. It has been deserved great attention forinvestigation and application due to its super-hardness, high thermalconductivity, high chemical stability, high immunity to particlebombardment, low negative electron affinity (4.5eV), potential excellentemission properties, low cost, large area depositing uniform film, etc.unique properties.Most people think that boron nitride in the crystalline form has fourmodification, the hexagonal (h-BN), the zincblende or cubic (c-BN)structure, the wurtzite structure (w-BN) and the rhombohedricalmodification (r-BN). While, in 1965, Batzanov et al.10 discovered anew structure of boron nitride, orthorhombic structure, using the methodby explosion a mixture of graphite-like h-BN and amorphous BN. Andthe orthorhombic BN was also named explosion boron nitride (E-BN)after the method. The new phase was identical components to the knownBN phase but differed from them in its IR absorption region and X-raydiffraction pattern. It was another high pressure phase of boron nitride.Although this allotropic form of boron nitride was first obtained nearly40 years, until the late 1980s its physical and chemical properties werenot known (except the diffraction data given in the ASTM 18-251 chartand the IR absorption spectrum). This was primarily so because theamounts of o-BN obtained by the explosion synthesis were very smalland the thermodynamic conditions of the synthesis of this phase and itsstructure were not known. But as a new phase of boron nitride,orthorhombic boron nitride, must has many new particular properties forapplication, as cubic boron nitride and wurtzite boron nitride, and it isdifficult to estimate its merit and value. Because of the increasing needfor new materials felt by manufacturers and scientists all over the world,the investigation for o-BN has become more and more important. Inorder to find its particular properties for application for people, more andmore people begin to search new methods for preparing o-BN.In our present study, for the first time, we prepared the orthorhombicBN crystallization films on Si(100) substrate and characterized the filmsby Fourier transform infrared spectroscopy (FTIR), X-ray diffraction(XRD), Raman spectra, scanning electron microscopy (SEM), atomicforce microscopic (AFM) and X-ray diffraction photoelectronspectroscopy (XPS). We have obtained the appropriate deposition parameters of o-BNfilms by jet-RF-PEPLD by many experiments. They are the laser powerof 20～24J/cm2, the substrate pulsed bias of -80～-120V, the RF powerof 60～150W, the substrate temperature of 300～500℃,the depositionpressure of 5～20 Pa, the target-substrate distance of 5cm, and thedeposition time of 20 minutes. We have study the sample under the conditions: the laser power of24J/cm2, the substrate pulsed bias of -120V, the RF power of 120W, thesubstrate temperature of 500℃,the deposition pressure of 20 Pa, thetarget-substrate distance of 5cm, and the deposition time of 20 minutes.From the FTIR of o-BN films, we can see three peaks, one is strongeraround 1189cm-1 and the other two are weak around 1585cm-1 and1450cm-1, be used to distinguish o-BN phase. From the Raman spectra,we can get a strong sharp peak at ν=1576cm-1 which can be attributedto the o-BN phase. The diffraction peaks for o-BN (111), (020), (021),(310) and (243) all appeared by using of XRD, especially (243) and(310) crystal plane diffraction are very strong. From the XPS spectra, weobtain the B1s and N1s spectra of o-BN around 191eV and 398eVrespectively, and we cannot observed other element spectra, so thecompositions of the o-BN film are made of only two elements, B and N.The surface morphology and densely arrayed crystal particles of theo-BN films are clearly observed by AFM and SEM photographrespectively. The films showing good stability and no peeling areobserved even after deposition for over six months. As a conclusionfrom above results, high quality orthorhombic boron nitridecrystallization films have been prepared by jet-RF-PEPLD.The FTIR, UV-VIS spectra, Raman spectra of o-BN films havebeen studied. And we find that the several factors can attribute to IRpeak shifting, including crystal grain size, the crystalline imperfectionand compressive stress of the films. The influence of the compressivestess on the IR peak shift with heat treatment is investigated. The absorption bands 233nm of o-BN films are observed byultraviolet visible spectra. The band gap of 5.3eV～5.5eV is calculated.And the hardness about 3300HV of the o-BN film of thickness of 1μm isestimated by Vickers hardness tester. From the results we know o-BN isa semiconductor material with broad band gap and a superhard material,at same time it has good adhesion for the substrate, so it has manypotential wide-ranging applications. The deposition of o-BN films is influenced by many extraneousfactors, such as target materials, substrate pulsed bias, substratetemperature, deposition time, target-substrate distance and so on. Theseries experiments show, 1, that the target materials and how to make thetarget are very important for deposition o-BN films. 2, that anappropriate substrate pulsed bias is necessary to get high quality o-BNfilms, and the film with high content of 90% o-BN has been prepared onSi(100) substrate at pulsed bias of -120V. With the bias creasing, theFTIR spectra became broad, and more impurities are introduced in filmsdue to discharging with vacuum chamber. Excessive bias can causeplasma strong bombard the substrate, plasma etch the film, plasmarebound, the deposition rate become low and even the film cannot beenprepared. 3, the deposition of o-BN films influenced by the substratetemperature is obscure. The temperature doesn't influence the spectra.Even at room temperature, good quality films can be obtained atappropriate deposition conditions. 4, the experimental results indicatethe target-substrate distance of 5cm is better for getting high qualityo-BN films. 5, Deposition time can strong influence thickness andcompositions of o-BN films. A thin layer h-BN (101) is deposited beforedepositing o-BN phase. The o-BN content become creasing with thedeposition time expand. It has a strong influence for growth of o-BN films by radiofrequency and laser. The main factors are RF plasma, RF power, laserpower and the direction of the laser plasma plume. The seriesexperimental results show that: 1, RF plasma plays a key role duringdepositing o-BN films. It can bombard the substrate, activate substratesurface, supply reaction Nion, activate and ionize the laser plasma andreaction gas, generate residual stress of the o-BN films, and cause theFTIR spectra shifting to high wave-number. The results show that RFplasma is propitious to growth o-BN phase of the films. 2, with theincreasing of RF power, the ionization degree of the reaction gasincrease, the density and energy of plasma increase, the residual stress ofthe films increase, and the FTIR spectra of o-BN shift to highwave-number. The results indicate that high RF power help to deposito-BN and inhibit h-BN growth. 3, the deposition pressure has a stronginfluence upon the thickness of the films, but no influence upon theFTIR spectra of the o-BN films. 4, the reaction gases easily ionize withthe N2 content increasing. And more N2 content of gases more generateplasma. 5, the laser plasma energy increases with the laser powerincreasing, which is propitious to growth o-BN phase and causes theFTIR spectra shifting to high wave-number. 6, the direction of the laserplasma plume has a strong influence upon the growth of o-BN films.The film growth conditions are different at the different sites of substrate.The best deposition region is chosen at the site of RF plasma and laserplasma crossing through many more experiments. The experimental results indicate that the o-BN films prepared byRF-PEPLD have excellent field emission characteristics. 1, all thecurves of the FN plots of the o-NB films present that electron emissionis due to through the surface-potential barrier of the films to vacuum bythe applied electric field. 2, thickness is an important factor on fieldemission characteristics of o-BN films. It is found that the thinnersamples have lower turn-on electric field and easily emission electronthan the thicker ones, but theirs emission current density and withstandvoltage are lower. The thicker samples have higher turn-on electric field,but theirs emission current density and withstand voltage are higher. Alower turn-on electric field of 8V/μm is obtained for the o-BN films of150nm. A turn-on electric field of 18V/μm, an emission current densityof 375μA/cm2 and a withstand voltage over 5900V are obtained for theo-BN film of 220nm. 3, the deposition pressure has a strong influenceupon field emission characteristics of o-BN films. It is found that theturn-on electric field and the emission current density are decreased withincreasing of deposition pressure, while the withstand voltage isincreased. 4, the RF plasma and react gases during depositing o-BNfilms also strong effect on field emission characteristics of the films.They make the tip density of the surface of the films increased, whichcan decreased the turn-on electric field of the films and make theelectron easy emission. 5, RF power is another one important factor forinfluence on the field emission characteristics of o-BN films. With theRF power increasing, the effective work function, the turn-on electricfield, the effective emission surface and the emission current density ofthe films are increased. The turn-on electric field of 11 V/μm isobtained for the BN film deposited at RF power 30W. The samples ofRF power 60W and 80W have proximate effective work function, sothey have proximate turn-on electric field of 18 V/μm and 20 V/μmrespectively, and have proximate emission current density of 345μA/cm2 and 357μA/cm2 separately. And they have good withstandvoltage characteristics. The turn-on electric field of 36 V/μm isobtained for the BN film deposited at RF power 150W. The resultsindicate that RF power during depositing o-BN films is not over low andnot over high, if over low, the turn-on electric field will be lower, but theemission current density is faintness and easily breakdown, if over high,the effective work function will be very high, so the turn-on electric fieldwill be very high and the electron will be hard to emission. For the first time, we present the result of layer structure growth of...