Low-pressure Chemical Vapor Deposition Reactor Research Articles

Multi-component diffusion phenomena in multiple-wafer chemical vapour deposition reactors

A comparative study has been made as to different methods for modelling diffusion phenomena in multi-component reacting gas mixtures in multiple-wafer low-pressure chemical vapour deposition reactors. Two typical processes for the deposition of thin films on silicon wafers in microelectronics manufacturing were studied: the deposition of tungsten from WF 6 and the deposition of polycrystalline silicon from SiH 4. The two-dimensional axisymmetric equations for the hydrodynamics and the concentration distributions in the reactor were solved numerically. Multi-component diffusion was accounted for through either Fick's law for binary diffusion in the carrier gas, or Wilke's effective diffusivity approach, or the Stefan-Maxwell equations. It has been shown that, compared to the exact Stefan-Maxwell equations, the use of Fick's law or Wilke's approach can lead to inconsistent results when the reactant gases and the reaction product gases are not sufficiently diluted in a bulk carrier gas. This is especially true when there are large variations in the molar masses and in the diffusivities of the various gases in the mixture.

Thermal modeling of tubular horizontal hot-wall low pressure chemical vapor deposition reactors

Low pressure chemical vapor deposition (LPCVD) reactors are intensively used in the microelectronics industry for depositing thin films of polysilicon. In this paper, a thermal model is presented, involving computations of the water temperature and taking into account radiative exchanges occurring inside an LPCVD reactor, with non-isothermal tube walls. This thermal model was incorporated in a global multiwafer model (CVD1), developed in our laboratory for prediction of the evolution of the longitudinal growth rate of polysilicon. Comparison between simulation results and experimental data led to the conclusion that the large drop-off in growth rate, at both ends of the reactor load, can be attributed to thermal variations within the reactor. This model can also be applied to the treatment of deposition processes involving temperature ramping, which are commonly used.

A Simple and Efficient Pretreatment Technology for Selective Tungsten Deposition in Low-Pressure Chemical Vapor Deposition Reactor

In this paper we develop a two-step pretreatment method which is a simple but effective cleaning process that can be used to achieve a high deposition rate and excellent interface characteristics, as well as improve the selectivity. In the first step, we use CF4/O2 mixing gases as a plasma etching system without substrate bias. The removal of damage and contaminants by reactive ion etching (RIE) during contact hole opening can thus be obtained. We consider that the role of oxygen is first to oxidize the polymer residues (i.e., fluorocarbons like Cx Fy ) and the RIE-damaged regions on the silicon surface, and it is then followed with CF4 to remove these oxides. In experiments, the plasma modification rate can be controlled at 120 Å/min. Results of the high deposition rate, smooth interface, low selectivity loss and the other improvements are observed. These are superior to those of cases without pretreatment. The second step is that anhydrous HF cleaning was used to remove surface oxide which was formed during the first step. Obviously, this new cleaning technology is very efficient not only for contact hole pretreatment but also for polysilicon materials. This also implies that this technology may have potential for polycide gate applications.

A new CVD reactor for semiconductor film deposition

The concept and design of a new chemical vapor deposition (CVD) reactor is presented for both epitaxial and nonepitaxial film deposition in semiconductor processing. The reactor is designed in such a way that a stagnant semiconductor source fluid of uniform concentration is provided for the film deposition without causing free or forced convection. The supply of the source gas for the deposition is by diffusion through a porous material such as quartz or graphite. Compared to the low pressure CVD (LPCVD) reactor with mounted wafer configuration, the new reactor should give a better film thickness uniformity and about an order of magnitude reduction in the amount of the source gas required. Further, at least for polycrystalline silicon deposition, the deposition rate can be much higher than is currently practiced with the LPCVD reactor. Design equations for the reactor are given. Details on the design for the polycrystalline silicon deposition are also given.

A Monte Carlo Simulation Study of Radiation Heat Transfer in the Multiwafer LPCVD Reactor

A direct simulation Monte Carlo technique is used to simulate the radiation heat transfer in a multiwafer low pressure chemical vapor deposition (LPCVD) reactor. The model accounts for the heat transfer between the stack of closely spaced Si wafers, the quartz reactor tube, the stainless steel ends of the reactor, and the surrounding furnace. Spectral and thermal variations in the materials properties are included directly in the model. In addition, conductive heat transfer through the quartz tube is computed using a finite difference approach. The cooled ends of the reactor result in a suppression of the temperature of several wafers at each end of the wafer stack. Simulations show that the extent of this cooling effect is influenced by direct radiative heat losses from the end wafers as well as dissipation of the furnace heat flux by conductive heat losses through the quartz tube. The calculated temperature profiles are then used as thermal boundary conditions in simulations of rarefied gas flows in the LPCVD reactor. The thermal variations along the quartz and wafer surfaces give rise to significant temperature and density variations in the gas flow. The simulation results show excellent agreement with experimental data.

Co-pyrolysis of hydrocarbons and SiEt4for the synthesis of graduated SixC1–xceramic thin films by chemical vapour deposition

The thermal decomposition of hydrocarbons has been investigated under particular conditions in a low-pressure chemical vapour deposition reactor in order to select suitable carbon sources for the preparation of carbon-rich or graduated SixC1–x layers. Growth of pyrolitic carbon thin films (pyro-C) starts at ca. 1050 K and only above 1273 K using C6H5Pri and CH4, respectively. The microstructure of the pyro-C layers is more dependent on the deposition temperature than on the nature of hydrocarbons. Their co-pyrolysis with SiEt4 used as SiC precursor has been achieved in the temperature range 1050–1250 K. As expected, the film composition does not change significantly at 1173 K using CH4 as an additional C source. By contrast, the C content of the films deposited by co-pyrolysis of SiEt4 and C6H5Pri increases continuously from 0.48 to 1 by increasing the mole fraction ratio x(C6H5Pri)/[x(C6H5Pri)+x(SiEt4)] from 0 to 1. Multilayers and compositional gradient layers can be prepared by discrete or continuous changes of the gas-phase composition, respectively. These films were successfully used as interphase in ceramic–ceramic composite materials to weaken the fibre/matrix bond and to improve their ductility.

A class of single-source precursors to titanium disulfide films. Synthesis, structure, and chemical vapor deposition studies of [TiCl4(HSR)2

Titanium disulfide is one of the desirable cathode materials for lithium batteries. Recent emphasis on the development of thin-film batteries has underscored the need for high-purity, crystallographically oriented, stoichiometric coatings. The majority of chemical vapor deposition (CVD) routes of TiS[sub 2] films are based on the reaction between titanium tetrachloride and hydrogen sulfide, organic sulfides, or disulfides. Recently we reported a new atmospheric pressure CVD process for TiS[sub 2] films, which relies upon the reaction of titanium tetrachloride with organothiols at temperature [ge]200 [degrees]C and affords highly pure, crystallographically oriented, stoichiometric, adhesive coatings[sup 5]. It was envisaged the use of a single-source precursor in the deposition of TiS[sub 2] films could provide precise control of titanium and sulfur stoichiometry, could reduce toxic/odiferous waste, and would eliminate the problem of mixing two or more gaseous reactants in a low-pressure CVD reactor. However, no such precursor had been described in the literature. Herein the authors report the synthesis of the first class of single-source precursors to high quality TiS[sub 2] films. These complexes are of the formula [TiCl[sub 4](HSR)[sub 2]] and are obtained upon treatment of titanium tetrachloride with alkanethiols. Significantly, the crystallographic orientation of the films produced from these precursors ismore » ideal for use as cathodes in lithium batteries.« less

Optimized silicon-rich oxide (SRO) deposition process for 5 V only flash EEPROM applications

A process for depositing in-situ very-thin (<10 nm) SiO/sub 2/ films on top of a silicon-rich oxide (SRO) layer in a standard low-pressure chemical vapor deposition (LPCVD) reactor has been optimized. Polysilicon-gate MOS capacitors using this stacked dielectric have shown high tunneling current at low voltages and an extraordinary endurance to electrical stress. Capacitors with 7 nm LPCVD SiO/sub 2/ on top of 10 nm SRO did not show any relevant shift on either the low or high portion of the I-V characteristic, after a fluence of more than 500 C/cm/sup 2/ at J=0.1 A/cm/sup 2/. The results add further support to the usefulness of implementing these stacked dielectric structures in a variety of nonvolatile memory devices.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Comments on the influence of the entrance zone in LPCVD reactors for in situ phosphoros-doped polysilicon deposition

The objective of the article is to present several original results, obtained through the combined approach of experiments and two-dimensional modeling, which could suggest solutions in order to improve the choice of the operating conditions in an LPCVD (low-pressure chemical vapor deposition) reactor for this kind of deposition

Surface-sensitive multiple internal reflection spectroscopy as a tool to study surface mechanisms in CVD: the example of UV photodeposition of silicon dioxide and silicon nitride

Multiple internal reflection-absorption spectroscopy is used here in situ in a low pressure CVD reactor, in order to demonstrate its potential as a surface analysis tool with a sensitivity well below monolayer coverages in many growth and deposition configurations. Two examples of its capacity to provide evidence for new surface processes are given in the particular case of photodeposition of silicon dioxide and silicon nitride: (i) identification of the molecular configuration associated to the photochemisorbed silane site on the Si 3N 4 photodeposition front in the SiH 4/NH 3 system, in a case where its infrared signature is buried in a large contribution from bulk species; (ii) evidence for the oxidization of silicon hydride and dihydride species by photoexcited N 2O in the UVCVD of SiO 2 in the SiH 4/N 2O precursor system. Such a reaction could be expected to occur from standard chemical knowledge, but deposited films analyzed ex situ did not offer any evidence for it in the form of water and silanol groups incorporated into the films.

Influence of Flow Dynamics on The Morphology of CVD Aluminum Thin Films

AbstractAluminum thin films were deposited by chemical vapor deposition on SiO2 substrates using trimethylamine alane (TMAA) in a low pressure CVD reactor system. A high TMAA flow rate during deposition, combined with an initial burst of added argon during the nucleation of the substrate surface resulted in the growth of aluminum thin films with excellent purity and surface morphologies. Film resistivities averaged 3.4 μΩ-cm, and the average surface peak-to-valley height for each film was found to be &lt;4% of the film thickness. The surfaces of films with thicknesses of ≤ 1 μm were extremely smooth and reflective. In contrast, the use of a high alane flow rate in the absence of any added argon resulted in the growth of films with extremely textured surface morphologies. Furthermore, films grown using an argon carrier gas, but with a slow alane flow rate, exhibited both textured surface morphologies and whisker growth.

Thermal dissociation of disilane: Quadrupole mass spectrometry investigation

The thermal dissociation of disilane Si 2H 6 as a function of temperature has been studied in an impinging jet-type low-pressure chemical vapour deposition reactor in both cold and hot wall configurations, in order to investigate the influence of homogeneous gas-phase reactions. A quadrupole mass spectrometer (QMS) coupled to the reactor with a system of prélèvement near the substrate surface has been used to follow the gas-phase composition. Si 2H 6 begins to decompose at 400°C, giving SiH 4. The formation of polysilanes Si n H 2( n+1) ( n = 3–5) is demonstrated and is highest at 600°C. The gas-phase evolution is correlated with the type of heating and with the growth rates observed on the substrates.

Rapid thermal low-pressure chemical vapour deposition of tungsten films onto InP using WF6 and H2

Tungsten (W) films were deposited onto InP in a cold wall, rapid thermal low-pressure chemical vapour deposition (RT-LPCVD) reactor, from a tungsten hexafluoride (WF6) gas reduced by hydrogen (H2). W films of thickness 50-450 nm were deposited in the temperature range 350-550 degrees C, pressure range 0.5-4.5 Torr at deposition rates up to 4 nm s-1 with an apparent activation energy of about 1.12 eV. The film stress varied depending upon the deposition pressure, from low compressive for deposition at 0.5 Torr to moderate tensile for deposition at about 4.5 Torr. The films were aged at temperatures as high as 300 degrees C for about 800 h and exhibited an excellent mechanical stability. Post-deposition sintering of the W films at temperatures up to 600 degrees C led to reduction of the resistivity with a minimum value of about 55 mu Omega cm as a result of heating at 500 degrees C. Conditions for both selective and blanket deposition were defined, and a dry etching process for further geometrical definitions of the films was developed, providing etch rates of 40-50 nm min-1. This report reflects the first attempt to deposit W films onto III-V semiconductor at a very high rate by means of RT-LPCVD.

InP substrate temperature measurements in a horizontal, low-pressure metalorganic chemical vapor deposition reactor by infrared laser interferometric thermometry

Infrared laser interferometric thermometry was used to measure InP substrate temperatures in a horizontal, low pressure metalorganic chemical vapor deposition (MOCVD) reactor. These measurements were made by using a 1.53 μm distributed feedback laser, demonstrating the use of semiconductor lasers to diagnose an epitaxial crystal growth process. The laser beam was reflected off of 2 inch diameter (100) n-type InP substrates in a commercial low-pressure MOCVD reactor. Substrate temperature profiles were taken as a function of reactor pressure from 20–1000 mbar and as a function of substrate position on the susceptor. For a constant susceptor set-point temperature of 640°C, temperatures increase monotonically from 600 to 615°C at 20 mbar along the substrate in the gas flow direction, increasing to 621 to 655°C at 1000 mbar for a substrate positioned in the downstream location of a two-well susceptor used for normal epitaxial growth runs. The variation in temperature decreases when the substrate is placed in a center well susceptor. The data shows that improvements in temperature uniformity, and hence compositional uniformity can be achieved by judicious choice of substrate position and reactor pressure. In particular, uniform temperature profiles resulted in improved compositional uniformity obtained for 1.15 μm InGaAsP layers grown on a 2 inch diameter substrate placed in the center well susceptor.

Thermal and kinetic modelling of low-pressure chemical vapour deposition hot-wall tubular reactors

A mathematical model, describing the complete behaviour of low-pressure chemical vapour deposition (LPCVD) reactors has been developed. The improvement of this model over existing ones reported in the literature consists in that it gives a more detailed account of the temperature profile on the solid surfaces in an LPCVD reactor. On the other hand, the proposed model is considerably simpler than most others already proposed, since it utilizes a continuously stirred tank reactor approach for mass balances. This approximation makes the model only relevant but, nevertheless, particularly useful to the case of depositions naturally leading to uniform layers across each wafer and, therefore, to the case of pure polycrystalline deposition from silane. A systematic use of this model, combined with a comparison of its predictions with experimental data, has served as an incentive for further investigations of other chemical vapour depositions systems ( in situ boron-doped polysilicon and semi-insulating polyoxide silicon depositions) and is of interest for the choice of new industrial processes.

Preparation of silicon dioxide films by low-pressure chemical vapor deposition on dense and porous alumina substrates

Thin silicon dioxide films were grown on dense α-alumina wafers as well as porous α-alumina and γ-alumina substrates by low pressure chemical vapor deposition (LPCVD), via oxidation of triisopropylsilane (C 3H 7) 3SiH within a cold-wall LPCVD reactor. In the temperature range of 650–850°C deposition rates of 8 to 78 nm/min were attained. The SiO 2 films were transparent, amorphous, uniform and they adhered very well to the alumina support. Most importantly, the films were dense, free of porosity and exhibited excellent stability for chemical applications. SEM images showed that SiO 2 films grown on alumina wafers exhibit a featureless surface morphology, while the microstructure of films grown on porous alumina substrates consists of clusters of grains that are tightly packed together. Tailoring of ultrathin films on porous substrates by chemical vapor deposition offers attractive opportunities for the synthesis of high-temperature, selective ceramic membranes and the design of novel composite catalyst structures.

Molecular simulation of a gas-phase reaction in a low-pressure CVD reactor

Abstract Flows of SiEH4 in a model CVD reactor are examined by use of the Monte Carlo Direct Simulation method. Decomposition of SiH4 into SiH2 and H2 in gas-phase is taken into consideration by introducing a reactive-collision model. On the substrate surface, only the SiH2 molecule is assumed to decompose into Si and H2 with a given probability, depositing a Si film. Effects of the Knudsen number and the SiH2 deposition probability on the distribution of the growth rate of Si film are examined in detail. As the Knudsen number decreases, the uniformity of the growth rate increases.

Analysis of Transition Regime Flows in Low Pressure Chemical Vapor Deposition Reactors Using the Direct Simulation Monte Carlo Method

The direct simulation Monte Carlo method has been used to simulate transition regime flows in a horizontal multiple‐wafer low pressure chemical vapor deposition (LPCVD) reactor. Both the region between two wafers and a long section of the entire LPCVD reactor tube were investigated. In the interwafer simulations, a binary mixture consisting of a representative reactant molecule and was used as a model system and the reactive sticking coefficient, configuration of wafers and gas composition were varied to determine their effects on growth rate uniformity. Additionally, a comparison was made with a continuum‐based analytical model where the effective diffusion coefficient in the transition regime was determined and the importance of gas‐surface interactions was established. In the multi‐wafer simulations, the pressure drop and residence time distribution were determined for various wafer configurations and entering gas conditions with the bulk of the pressure drop occurring across the wafers as the molecules resided primarily in the upstream region. The distribution of species for gas mixtures was largely governed by diffusive effects with evidence of species separation occurring by means of pressure diffusion. For reactive gas flows, nonuniformity effects persisted in the simulations for reaction probabilities greater than 0.01.

Silicon nitride films deposited from SiH 2Cl 2NH 3 by low pressure chemical vapor deposition: kinetics, thermodynamics, composition and structure

The growth of stoichiometric and non-stoichiometric silicon nitride films was studied experimentally on 100 mm silicon wafers by batch depositions from the dichlorosilane (SiH 2Cl 2)-ammonia (NH 3) system in a hot-wall horizontal low pressure chemical vapor deposition (LPCVD) reactor. The growth kinetics were discussed in terms of the Langmuir adsorption isotherm. The kinetic parameters were determined by comparing the experimental data with a one-dimensional simulation model. The decomposition of NH 3 at high temperatures was included in the simulation procedure. When the SiH 2Cl 2:NH 3 ratios were greater than 1.5, a quantity higher than the thermodynamic critical values above which Si-rich nitride films begin to deposit, various SiN x films with x < 4 3 were obtained. The composition of the SiN x films was found to vary along the LPCVD reactor. The film stoichiometry was examined by Rutherford backscattering and ellipsometry measurements. According to kinetic and thermodynamic studies, the pyrolysis of dichlorosilane at elevated temperatures (> 700 °C) is the cause for the deposition of Si-rich nitride films. Furthermore, two types of deposited SiN x films were observed; one type showed a typical film density around 3.70 g cm −3 while the other type exhibited a remarkably lower film density below 3.50 g cm −3.

Modeling and scale‐up of multiwafer LPCVD reactors

AbstractThe deposition of thin films in a hot‐wall multiwafer low‐pressure chemical vapor deposition (LPCVD) reactor is an important unit operation in the manufacture of modern integrated circuits. In this article, our previously published model for the multiwafer LPCVD reactor has been combined with in‐situ temperature measurements to accurately predict the axial and radial film thickness distributions for a polysilicon deposition process. The model describes in detail multicomponent mass transport, the reactor's thermal environment based on in‐situ temperature measurements, and the reactor geometry including inlet and outlet sections as well as downstream injectors. Model predictions were compared with experimental data from two industrial‐scale polysilicon reactors at SEMATECH and from a smaller research reactor. Approximate scale‐up rules for the important special case of larger wafers were derived from the model equations and tested by simulation. The rules compare well with the results from a nonlinear program in which the axial variation of film growth rate was minimized.