Low Pressure Chemical Vapor Deposition Films Research Articles

Boron Carbonitride Films with Tunable Composition: LPCVD and PECVD Synthesis Using Trimethylamine Borane and Nitrogen Mixture and Characterization

This study reports the chemical vapor deposition of amorphous boron carbonitride films on Si(100) and SiO2 substrates using a trimethylamine borane and nitrogen mixture. BCxNy films with different compositions were produced via variations in substrate temperature and type of gas-phase activation. The low-pressure chemical vapor deposition (LPCVD) and plasma-enhanced chemical vapor deposition (PECVD) methods were used. The “elemental composition—chemical bonding state—properties” relationship of synthesized BCxNy was systematically studied. The hydrophilicity, mechanical, and optical properties of the films are discussed in detail. The composition of films deposited by the LPCVD method at temperatures ranging from 673 to 973 K was close to that of boron carbide with a low nitrogen content (BCxNy). The refractive index of these films changed in the range from 2.43 to 2.56 and increased with temperature. The transparency of these films achieved 85%. LPCVD films were hydrophilic and the water contact angles varied between 53 and 63°; the surface free energy was 42–48 mN/m. The microhardness, Young’s modulus and elastic recovery of LPCVD films ranged within 24–28 GPa, 220–247 GPa, and 70–74%, respectively. The structure of the PECVD films was close to that of hexagonal boron nitride, and their composition can be described by the BCxNyOz:H formula. In case of the PECVD process, the smooth films were only produced at low deposition temperatures (373–523 K). The refractive index of these films ranged from 1.51 to 1.67. The transparency of these films achieved 95%; the optical band gap was evaluated as 4.92–5.28 eV. Unlike LPCVD films, they were very soft, and their microhardness, Young’s modulus and elastic recovery were 0.8–1.4 GPa, 25–26 GPa, and 19–28%, respectively. A set of optimized process parameters to fabricate LPCVD BCxNy films with improved mechanical and PECVD films with high transparency is suggested.

Effects of hydrogen content in films on the etching of LPCVD and PECVD SiN films using CF4/H2 plasma at different substrate temperatures

AbstractThe dependences of etching characteristics on substrate temperature (Ts, from –20 to 50°C) of the plasma‐enhanced chemical vapor deposition (PECVD) SiN films (PE‐SiN) and low‐pressure chemical vapor deposition (LPCVD) SiN films (LP‐SiN) with CF4/H2 plasma were investigated. The Fourier‐transform infrared spectroscopy shows that both film types were N–H bond‐rich films, but in different hydrogen contents (PE‐SiN 22.7 at% and LP‐SiN 3.8 at%) from the Rutherford backscattering spectroscopy analyses. A higher hydrogen content led to a thinner fluorocarbon thickness because of the reaction between hydrogen outflux and C and N to form an HCN byproduct. The etch rates (ER) for the PE‐SiN were higher than that of the LP‐SiN at all Ts, due to the different FC thickness and etching mechanisms proposed. The formation of the N−Hx layer on PE‐SiN at low temperature caused the decrease in ER. For the LP‐SiN, the weak dependences of Ts on surface structure and ER were observed.

Material loss of silicon nitride thin films in a simulated ocular environment

The dissolution behavior of silicon nitride in a simulated eye environment is studied as a function of temperature and ion concentration. Thin films of silicon nitride were manufactured using plasma-enhanced chemical vapor deposition (PECVD) and low-pressure chemical vapor deposition (LPCVD), respectively. The thickness of the films was measured as a function of time under various conditions. The experimental results showed that the films dissolve in saline solution over time. For the case of a thin membrane of 500 µm diameter and 200 nm thickness, typical dissolution rates are 1 nm/day for PECVD and 0.3 nm/day for LPCVD films. Dissolution of silicon nitride was found to be reduced using sputtered titanium oxide as protective overcoat.

Effect of thermal and pulse laser annealing on photoluminescence of CVD silicon nitride films

The light-emitting properties of Si-rich silicon nitride films deposited on the Si (100) substrate by plasma-enhanced (PECVD) and low-pressure chemical vapor deposition (LPCVD) have been investigated. In spite of the similar stoichiometry (SiN1.1), nitride films fabricated by different techniques emit in different spectral ranges. Photoluminescence (PL) maxima lay in red (640 nm) and blue (470 nm) spectral range for the PECVD and LPCVD SiN1.1 films, respectively. It has been shown that equilibrium furnace annealing and laser annealing by ruby laser (694 nm, 70 ns) affect PL spectra of PECVD and LPCVD SiN1.1 in a different way. Furnace annealing at 600 °C results in a significant increase of the PL intensity of the PECVD film, while annealing of LPCVD films result only in PL quenching. It has been concluded that laser annealing is not appropriate for the PECVD film. The dominated red band in the PL spectrum of the PECVD film monotonically decreases with increasing an energy density of laser pulses from 0.45 to 1.4 J/cm2. Besides, the ablation of PECVD nitride films is observed after irradiation by laser pulses with an energy density of > 1 J/cm2. This effect is accompanied by an increase in blue emission attributed to the formation of a polysilicon layer under the nitride film. In contrast, the LPCVD film demonstrates the high stability to pulsed laser exposure. Besides, an increase in the PL intensity for LPCVD films is observed after irradiation by a double laser pulse (1.4 + 2 J/cm2) which has not been achieved by furnace annealing.

Characteristic Study of Silicon Nitride Films Deposited by LPCVD and PECVD

This paper analyzes and compares the characteristics of silicon nitride films deposited by low pressure chemical vapor deposition (LPCVD) and plasma enhanced chemical vapor deposition (PECVD), with special attention to the hydrogenation and chemical composition of silicon nitride films. Three different LPCVD processes at various DCS and NH3 gas flow rates and deposition temperatures, together with PECVD using SiH4 and NH3 and ICP CVD using SiH4 and N2, were compared. The silicon nitride film deposition rate decreases with an increasing NH3/DCS ratio in LPCVD, which also leads to an increase in the refractive index and a decrease in the residual stress in the film. There is nearly no hydrogen incorporated in the LPCVD films, which differs from PECVD and ICP CVD that show significant Si-H and N-H bonds. The chemical composition of silicon nitride films is mostly Si-rich, except for the LPCVD process at high NH3/DCS ratio with near stoichiometric chemistry.

A comparison of the mechanical stability of silicon nitride films deposited with various techniques

A comparison of mechanical properties of amorphous silicon nitride thin films deposited with various techniques used for microelectronic applications was conducted. Nitride films with thicknesses less than 80nm were deposited on (001) oriented silicon wafers by using various methods: low pressure chemical vapor deposition (LPCVD), rapid thermal CVD (RTCVD), atomic layer deposition (ALD) and plasma enhanced CVD (PECVD). The wafer curvature method was used to show that the as-deposited LPCVD, RTCVD and ALD films exhibited tensile residual stresses that decreased with silicon richness. In contrast, the stress of the PECVD as-deposited layers ranged from tensile to ultra-compressive, depending on the exposure to high plasma power and ion bombardment during growth. After high temperature annealing, the LPCVD, RTCVD and ALD nitride stresses were almost unchanged, indicating that these films/substrate systems have significant thermal mechanical stability. In contrast, it was observed that, regardless of the initial stress, the annealed PECVD films developed tensile stress after high temperature treatment, with the same dependence of stress on refractive index as was found with the other deposition techniques. The Young's moduli, measured by performing nano-indentation on 200nm thick nitride layers, were found for most samples to be correlated with film density.

Epitaxial film growth of chromium dioxide by low pressure chemical vapor deposition using chromium carbonyl

Epitaxial chromium dioxide (CrO 2) thin films have been deposited by low pressure chemical vapor deposition (LPCVD) on (100) TiO 2 substrates using the precursor chromium hexacarbonyl (Cr(CO) 6) within a narrow temperature window of 380–400 °C. Normal θ–2 θ Bragg x-ray diffraction results show that the predominant phase is CrO 2 with only a small amount of Cr 2O 3 present, mostly at the film surface. The LPCVD films have a reasonably smooth surface morphology with a root mean square roughness of 4 nm on a scale of 5 μm. Raman spectroscopy confirms the existence of rutile CrO 2 in the deposited films, while transmission electron microscopy confirms the single-crystalline nature of the films. The LPCVD films showing a dominant CrO 2 phase exhibit clear uniaxial magnetic anisotropy with the easy axis oriented along the c direction.

Comparing magnetotransport and surface magnetic properties of half-metallic CrO2 films grown by low pressure and atmospheric pressure chemical vapor deposition

CrO2 films prepared by low pressure chemical vapor deposition (LPCVD) using Cr(CO)6 precursor have been investigated and compared with epitaxial half metallic CrO2 films prepared at atmospheric pressure (APCVD) using CrO3 precursor for their magnetotransport and surface magnetic properties. LPCVD films showed higher resistivity than APCVD epitaxial (100) CrO2 films prepared on (100) TiO2 substrates. Magnetoresistance of LPCVD films is comparable to that of APCVD films. X-ray magnetic circular dichroism suggests a reduced surface magnetic moment for LPCVD films. This reduced magnetic moment is attributed to antiferromagnetic alignment of the uncompensated Cr spins in the Cr2O3 surface layer.

Atomic Layer Deposition of Silicon Oxide Thin Films by Alternating Exposures to Si[sub 2]Cl[sub 6] and O[sub 3

We report the process for the atomic layer deposition (ALD) of silicon dioxide thin films on a silicon wafer by alternating exposures to Si 2 Cl 6 and O 3 . The deposition was governed by a self-limiting ALD reaction at 403-453°C, and the growth rate at 453°C was saturated at 0.32 nm/cycle for Si 2 Cl 6 exposures over 1 X 10 8 L. However, at 471°C or higher temperatures, the thermal decomposition of Si 2 Cl 6 and the oxidation of Si by O 3 dominated the deposition, resulting in high growth rates and Si-rich films. The ALD films exhibited excellent electrical properties that were equivalent to those of low-pressure chemical vapor deposition films.

Correlation between infrared transmission spectra and the interface trap density of SiO 2 films

This work is an attempt to estimate the electrical properties of SiO 2 thin films by recording and analyzing their infrared transmission spectra. In order to study a big variety of films having different infrared and electrical properties, we studied SiO 2 films prepared by low pressure chemical vapor deposition (LPCVD) from SiH 4 + O 2 mixtures at 425 °C and annealed at 750 °C and 950 °C for 30 min. In addition thermally grown gate quality SiO 2 films of similar thickness were studied in order to compare their infrared and electrical properties with the LPCVD oxides. It was found that all studied SiO 2 films have two groups of Si–O–Si bridges. The first group corresponds to bridges located in the bulk of the film and far away from the interfaces, the grain boundaries and defects and the second group corresponds to all other bridges located near the interfaces, the grain boundaries and defects. The relative population of the bulk over the boundary bridges was found equal to 0.60 for the LPCVD film after deposition and increased to 4.0 for the LPCVD films after annealing at 950 °C. Thermally grown SiO 2 films at 950 °C were found to have a relative population of Si–O–Si bridges equal to 3.9. The interface trap density of the LPCVD film after deposition was found equal to 5.47 × 10 12 eV −1 cm −2 and decreases to 6.50 × 10 10 eV −1 cm −2 after annealing at 950 °C for 30 min. The interface trap density of the thermally grown film was found equal to 1.27 × 10 11 eV −1 cm −2 showing that films with similar Si–O–Si bridge populations calculated from the FTIR analysis have similar interface trap densities.

Comparative study between silicon-rich oxide films obtained by LPCVD and PECVD

A comparative study of compositional and optical properties of silicon-rich oxide (SRO) films deposited by low-pressure chemical vapor deposition (LPCVD) and plasma-enhanced chemical vapor deposition (PECVD) is presented. Infrared spectra revealed the presence of hydrogen bonded to silicon atoms in the SRO–PECVD films, whereas in SRO–LPCVD films the IR spectra looked like the stoichiometric thermal silicon oxide. Moreover, X-ray photoelectron spectroscopy (XPS) studies showed that the SRO–PECVD films contain a higher content of nitrogen than SRO–LPCVD films. In spite of differences, the SRO films obtained by both methods show a strong room-temperature photoluminescence (PL). However, the highest PL intensity was emitted by SRO films obtained by LPCVD.

Elastic Properties of Several Silicon Nitride Films

AbstractWe have measured the internal friction (Q-1) of amorphous silicon nitride (a-Si3Nx) films prepared by a variety of methods, including low-pressure chemical-vapor deposition (LPCVD), plasma-enhanced chemical-vapor deposition (PECVD), and hot-wire chemical-vapor deposition (HWCVD) from 0.5 K to room temperature. The measurements are made by depositing the films onto extremely high-Q silicon double paddle oscillator substrates with a resonant frequency of ~5500 Hz. We find the elastic properties of these a-Si3N4 films resemble those of amorphous silicon (a-Si), demonstrating considerable variation, depending on the film growth methods and post deposition annealing. The internal friction for most of the films shows a broad temperature-independent plateau below 30 K, characteristic of amorphous solids. The values of Q-1, however, vary from film to film in this plateau region by more than one order of magnitude. This is typical for tetrehedrally bonded amorphous thin films, like a-Si, a-Ge, and a-C. The PECVD films have the highest Q-1 just like an ordinary amorphous solid, while LPCVD films have an internal friction more than one order of magnitude lower. All the films show a reduction of Q-1 after annealing at 800°C, even for the LPCVD films which were prepared at 850°C. This can be viewed as a reduction of structural disorder.

A monolithic CMOS microhotplate-based gas sensor system

A monolithic CMOS microhotplate-based conductance-type gas sensor system is described. A bulk micromachining technique is used to create suspended microhotplate structures that serve as sensing film platforms. The thermal properties of the microhotplates include a 1-ms thermal time constant and a 10/spl deg/C/mW thermal efficiency. The polysilicon used for the microhotplate heater exhibits a temperature coefficient of resistance of 1.067/spl times/10/sup -3///spl deg/C. Tin(IV) oxide and titanium(IV) oxide (SnO/sub 2/,TiO/sub 2/) sensing films are grown over postpatterned gold sensing electrodes on the microhotplate using low-pressure chemical vapor deposition (LPCVD). An array of microhotplate gas sensors with different sensing film properties is fabricated by using a different temperature for each microhotplate during the LPCVD film growth process. Interface circuits are designed and implemented monolithically with the array of microhotplate gas sensors. Bipolar transistors are found to be a good choice for the heater drivers, and MOSFET switches are suitable for addressing the sensing films. An on-chip operational amplifier improves the signal-to-noise ratio and produces a robust output signal. Isothermal responses demonstrate the ability of the sensors to detect different gas molecules over a wide range of concentrations including detection below 100 nanomoles/mole.

LP-CVD Silicon-Based Film Formation in Submicrometer Trenches in Industrial Equipment: Experiments and Simulation

Step coverage mechanisms involved in four low pressure chemical vapor deposition (LP-CVD) processes, silicon from silane, in-situ boron-doped silicon from silane and boron trichloride, in-situ phosphorus-doped silicon from silane and phosphine, and partly oxidized silicon from silane and nitrous oxide, are studied in detail for various microscale feature shapes and dimensions. Experimental thickness profiles within trenches are compared with simulation results obtained from two diffusion-reaction trench models developed in connection with pre-existing reactor models. Analysis of the contribution of each reactive species to step coverage offers opportunities for progress, particularly in the design of the shape and dimensions of trenches in respect of the kinetic characteristics of each deposit.

Comparison of the characteristics of TiO2 films prepared by low-pressure and plasma-enhanced chemical vapor deposition

Thin films of titanium dioxide (TiO2) were deposited on silicon wafers at 450 °C by low-pressure chemical vapor deposition (LPCVD) and plasma-enhanced chemical vapor deposition (PECVD), in the same reactor, using Ti(O-i-C3H7)4 and oxygen as the reactants. The crystal structure, surface morphology, composition, chemical binding state and refractive index of the TiO2 films, deposited with various r.f. powers, were characterized. Without plasma, LPCVD TiO2 films show polycrystalline anatase structure, with a rough, granular surface and a typical refractive index of 2.43. On the contrary, the PECVD TiO2 films are amorphous, with a smooth surface. By varying the r.f. power from 50 to 150 W, the refractive index of PECVD TiO2 film increases with increasing power and becomes higher than 2.8 at 125 and 150 W. Despite the very different crystal structure, surface morphology and optical properties, the composition and chemical binding states of LPCVD and PECVD TiO2 films are similar. The effect of plasma on the characteristics of CVD TiO2 films is discussed.

Comparative study of atomic layer deposition and low-pressure MOCVD of copper sulfide thin films

Thin films of copper sulfide (Cu x S) have been prepared on fluor-doped tin dioxide (SnO 2 :F) coated glass and on uncoated glass by atomic layer deposition (ALD) and low-pressure chemical vapor deposition (LPCVD). In both cases, copper(II) bis-tetramethylheptanedionate (Cu(thd) 2 ) and H 2 S are used. Cu x S films form between 125 and 300 °C with ALD and between 127 and 505 °C with LPCVD. Deposition rates are obtained between 1 and 109 A/min by LPCVD and between 0.15 and 0.40 A/cycle by ALD. Self-limited grow by ALD is achieved up to 250 °C at 2 mbar. It is found that in both processes the temperature determines the crystalline phase of the films. CuS is obtained at low deposition temperatures when using either ALD or LPCVD. A phase transition occurs at 175 °C from pure CuS into pure Cu 9 S 5 with ALD. In the LPCVD process the phase composition of the films starts to change at 230 °C from pure CuS into a mixture of CuS and Cu 9 S 5 . Pure Cu 9 S 5 is obtained between 285 and 315 °C. The morphology of LPCVD films are fine-structured with an average grain size of 100 nm for films of 500 nm, while 40 nm thinn ALD films consist of grains with an average grain size of ∼100 nm grown in columns perpendicular to the surface.

A comparative study on inductively-coupled plasma high-density plasma, plasma-enhanced, and low pressure chemical vapor deposition silicon nitride films

Silicon nitride films have been deposited using inductively-coupled plasma high-density plasma chemical vapor deposition (HDP CVD), plasma-enhanced chemical vapor deposition (PECVD), and low pressure chemical vapor deposition (LPCVD) methods. Characterization and comparison of the three films were performed using Fourier-transform infrared spectroscopy, secondary-ion mass spectroscopy, Rutherford backscattering spectrometry, and hydrogen forward-scattering spectrometry, in addition to wet-etch rate and stress measurement studies. It was found that silicon nitride films deposited using HDP CVD method have several advantages over the silicon nitride films that were deposited using the LPCVD and PECVD methods. The HDP CVD silicon nitride film can be deposited at much lower temperatures (⩽400 °C) than LPCVD silicon nitride, and has substantially less hydrogen (5.5 at. %) than the PECVD film. In addition, the PECVD film contains some oxygen in the film. The wet-etch rate of HDP CVD silicon nitride film is comparable to that of LPCVD film and is significantly less than that of PECVD film in both hot phosphoric acid and buffered HF solutions. The stress of the HDP CVD film is similarly compressive to the PECVD silicon nitride, and not as highly tensile as that of LPCVD silicon nitride.

Luminescence Quenching in Erbium-Doped Hydrogenated Amorphous Silicon

AbstractHydrogenated amorphous silicon thin films, co-doped with oxygen, are made using lowpressure chemical vapor deposition (LPCVD) or plasma-enhanced chemical vapor deposition (PECVD). The films are implanted with Er to a peak concentration of 0.2 at.%. Roomtemperature photoluminescence at 1.54 μm is observed in both amorphous materials, after thermal annealing at 300–400 °C. The PECVD films with low 0 content (0.3, 1.3 at.%) show a luminescence intensity quenching by a factor 7–15 as the temperature is raised from 10 K to room temperature. The quenching is well correlated with a decrease in luminescence lifetime, indicating that non-radiative decay of excited Er3+ is the dominant quenching mechanism as the temperature is increased. In the LPCVD films, with 31 at.% 0, the quenching is only a factor 3, and no lifetime quenching is observed. The results are interpreted in the context of an impurity Auger excitation model, taking into account the fact that oxygen modifies the Si bandgap and the Er-related defect levels in the gap.

LPCVD WSi2 Films Using Tungsten Chlorides and Silane

This paper makes a systematic study of blanket and selective low pressure chemical vapor deposition (LPCVD) films from tungsten chlorides, silane, hydrogen, and argon on silicon as well as on patterned oxidized silicon substrates. Experiments were performed by varying the initial gaseous to ratio or the deposition temperature . Initially, yield and CVD‐phase diagrams of the W‐Si‐Cl‐H‐Ar chemical system were drawn, based on thermodynamic simulations. The deposition of pure phase and mixed solid phases involving W, , , and Si was predicted to occur in relation to process parameters. The corresponding films were grown in a cold‐wall reactor and characterized by x‐ray diffraction, scanning electron microscopy, four‐point probe, and Auger electron spectroscopy studies. Good agreement was found between experimentally observed solid phases and thermodynamically simulated results, under the same conditions. The growth rate of films for an value varying between 0.3 and 1.0 at 873 K reaches a maximum at . The Arrhenius plot of films grown between 773 and 1073 K shows a linear increase in growth rate up to 923 K, followed by saturation at high temperatures. Films processed above 823 K have a smooth surface and interface, indicating that the chloride‐based chemistry does not affect the silicon substrate even at high temperatures. Based on the above mentioned studies, a set of process parameters was defined, and selective LPCVD films were deposited on fine‐patterned oxidized silicon.

Analysis of rapid thermal annealings of boron and arsenic in polysilicon emitter structures

The codiffusion of implanted boron and arsenic during rapid thermal annealing in a polysilicon/monocrystalline silicon system used for high speed bipolar integrated circuit technology has been investigated. Such a process allows a uniformly high concentration in the emitter regions. It induces a very shallow emitter-base junction depth for an n-p-n transistor. On the contrary, in p-n-p configuration, when the arsenic dose is lower than the boron dose, boron deeply penetrates the single-crystal silicon, causing problems for fabricating shallow junctions. The rapid thermal annealing-induced redistribution of arsenic and boron implanted at various implant doses in a 380 nm low-pressure chemical vapor deposition (LPCVD) polysilicon layer has been studied by secondary ion mass spectroscopy measurements. A strong lowering of the minority dopant diffusion in the polysilicon film is observed due to the high concentration of the other dopant. This effect is mainly related to grain boundary trap saturation while the electric field issued from dopant activation in the fastly recrystallized amorphous layer due to arsenic implantation in the upper region of the LPCVD film has a lesser effect. Transmission electron microscopy measurements show that recrystallization extends deeper than the amorphous layer, which is responsible for the increase of grain size. Sheet resistance measurements have been performed as an approach to the electrical behavior for these structures.