Plasma-enhanced Chemical Vapor Deposition Reactor Research Articles

Growth, trapping and abatement of dielectric particles in PECVD systems

The growth of solid residues within PECVD (plasma enhanced chemical vapour deposition) reactors has been extensively studied because of its implications for wafer particle contamination and is often referred to as dusty plasmas. On dielectric CVD (DCVD) production systems the coating of chamber walls and vacuum exhaust line with residues addresses also the issue of system maintenance. A common solution consists of periodically cleaning the deposition chamber by ionizing a PFC (perfluoro-compound) gas such as , or . This generates free fluorine radicals that dry etch the residues deposited on chamber walls. However, because of limited fluorine radical lifetime, this clean process is not efficient in the vacuum exhaust line where residues accumulate. We propose an active solution to address the issue of solid waste treatment on a production DCVD system. We review the particular case of silicon nitride deposition, which is one of the worst known processes in terms of particle generation. These considerations are also valid for silicon oxide, silicon oxynitride, silicon carbide and amorphous silicon deposition processes. Here we report on our investigation on the particle formation, composition and morphology within a PECVD chamber and the deposition of these particles on chamber walls and vacuum exhaust line. We describe a method to design an efficient precipitator that traps the particles immediately downstream of the deposition chamber. The trapping uses gravitational and electrostatic means. This system does not necessitate any disposal procedure because of its capability to perform an in situ plasma assisted clean, reactivating the effluent PFC gas from the processing chamber. Here, the system is referred to as downstream plasma apparatus (DPA).

Carbon Contamination Levels in Plasma-Enhanced Chemical Vapor Deposited Fluorinated Silica Glasses

In this study, the carbon levels in fluorinated silica glass (FSG) films were investigated. FSG films were deposited using a dual-frequency sequential-deposition plasma-enhanced chemical vapor deposition (PECVD) reactor using TEOS, O2 and C2F6 as source reagents. It was found that FSG films have substantially lower carbon levels than undoped PECVD TEOS-based silicon dioxide films. Carbon content was also found to be dependent on the fluorine content in the films.

Production of nanometric particles in radio frequency glow discharges in mixtures of silane and methane

The formation of silicon particles in rf glow discharges has attracted attention due to their effect as a contaminant during film deposition or etching. However, silicon and silicon alloy powders produced by plasma-enhanced chemical vapor deposition (PECVD) are promising new materials for sintering ceramics, for making nanoscale filters, or for supporting catalytic surfaces. Common characteristics of these powders are their high purity and the easy control of their stoichiometry through the composition of the precursor gas mixture. Plasma parameters also influence their structure. Nanometric powders of silicon–carbon alloys exhibiting microstructural properties such as large hydrogen content and high surface/volume ratio have been produced in a PECVD reactor using mixtures of silane and methane at low pressure (<1 Torr) and low frequency square-wave modulated rf power (13.56 MHz). The a-Si1−xCx:H powders were obtained from different precursor gas mixtures, from R=0.05 to R=9, where R=[SiH4]/([SiH4]+[CH4]). The structure of the a-Si1−xCx:H powder was analyzed by several techniques. The particles appeared agglomerated, with a wide size distribution between 5 and 100 nm. The silane/methane gas mixture determined the vibrational features of these powders in the infrared. Silicon–hydrogen groups were present for every gas composition, whereas carbon–hydrogen and silicon–carbon bonds appeared in methane-rich mixtures (R<0.6). The thermal desorption of hydrogen revealed two main evolutions at about 375 and 660 °C that were ascribed to hydrogen bonded to silicon and carbon, respectively. The estimated hydrogen atom concentration in the sample was about 50%.

Investigation of low temperature SiO2 plasma enhanced chemical vapor deposition

Low temperature (<270 °C) plasma enhanced chemical vapor deposition (PECVD) of SiO2 thin films using tetraethylorthosilicate (TEOS) and O2 plasma was investigated. Depositions were carried out in a PECVD reactor with a helical resonator discharge source. Transmission infrared spectroscopy, spectroscopic ellipsometry, and wet etch rate measurements were used to characterize the deposited films as a function of rf power, gas composition, and substrate temperature. Most pronounced effects were observed when the substrate temperature and TEOS:O2 flow ratio ℜR were varied. Good quality SiO2 films can be obtained at high temperature and/or low ℜR. For R≳0.1, while the deposition rate was weakly dependent on temperature between 260 and 100 °C, it increased almost by a factor of 2 between 100 and 45 °C. This is also accompanied by drastic changes in film properties such as refractive index, increase in OH and –OC2H5 content, and decrease in film density. Studies using in situ attenuated total reflection Fourier transform infrared (ATR FTIR) spectroscopy indicated that stable good quality SiO2 films without any SiOH at higher temperature (250 °C) and with very little SiOH at room temperature could be deposited using very low R. Based on the understanding provided by ATR FTIR, films with properties approaching to those of thermal oxide have been deposited at room temperature.

A Plasma Reactor for Solid Waste Treatment on Pecvd Production Systems

AbstractThe growth of particulates within a PECVD (Plasma Enhanced Chemical Vapor Deposition) reactor has been extensively studied in recent years. As one of the early concerns was wafer particle contamination, the attention of industry also shifted to environmental issues. In the particular case of Si3N4 film deposition, the amount of dust particles created within the plasma is great and a significant amount of dust is dragged out of the RF interelectrode region along with the exhausted process gases. On a production system, this results in solid residues accumulation in the exhaust line (or foreline), frequent maintenance and poor vacuum pump lifetime. We developed a DPA (Downstream Plasma Apparatus) placed downstream of the deposition chamber to solve the issue of solid waste treatment for thin films applications such as SiO2, Si3N4, SiC, SiOxNy,…, α‐Si,…). The DPA is designed to capture all the residue during deposition, using both a passive and an active mode. It consists of two labyrinth‐shaped electrodes that can trap particles by gravitation (passive) and electrostatically (active) by application of a DC electric field. The second function of the device is to vaporize the previously trapped residues using a periodic plasma assisted clean. The vaporization process is performed by re‐ionizing the effluent PFCs gas (PerFluoro‐Coumpounds) from the processing chamber. All byproducts of the reaction are gaseous and water soluble. This results in the elimination of solid waste as well as improving vacuum pump lifetime. There is also better clean gas utilization and the emission of PFCs in the atmosphere is reduced. In this paper, we review the particulate formation, their size and composition. We describe the DPA reactor designed to trap charged particulates with closed to 100% efficiency. We examine the plasma‐assisted cleaning process and the implications of the device in terms of solid waste treatment and environmental impact.

Investigation of the nucleation mechanism in bias-enhanced diamond deposition on silicon and molybdenum

Polycrystalline diamond films were deposited on Si and Mo substrates in a microwave plasma-enhanced chemical vapour deposition reactor employing bias-enhanced nucleation. The deposition process was subdivided into two consecutive steps: the pretreatment (bias-enhanced nucleation) and the diamond growth step. To investigate the nucleation process we kept the deposition parameters during the diamond growth step constant and only changed the parameters during the pretreatment. The methods employed to analyze the deposited films after the pretreatment step were electron energy loss spectroscopy (EELS), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy. The nucleation density ( N D) on Si following the complete deposition cycle (pretreatment and diamond growth step) increases considerably from 5 × 10 8 cm −2 to 5 × 10 10 cm −2 with an increase in the substrate temperature during the pretreatment ( T p) in the temperature range from 680 to 750 °C. For T p ≥ 770 ° C continuous films are formed. The structure of the pretreatment deposit undergoes likewise considerable changes: if T p exceeds 770 °C the appearance of an intense diamond plasmon at 34 eV is observed, indicative of an increase in the concentration of diamond crystallites embedded in an otherwise amorphous carbon matrix. Our experiments suggest that diamond crystallites formed during the pretreatment serve as nucleation centres for the subsequent diamond growth. The same deposition parameters which result in the formation of a continuous diamond film on Si, yield only low nucleation densities on Mo. An increase in N D from 6 × 10 6 cm −2 to 2 × 10 8 cm −2 can be achieved by raising the methane concentration [CH 4] in the gas phase during the pretreatment from 5 to 50% ( T p = 820 ° C). The carbon concentration at the surface for the pretreatment deposit, determined by XPS analysis, increases likewise with [CH 4]. According to the EELS analysis the structure of the pretreatment deposit is comparable with disordered graphite or a-C and no diamond plasmon is observed. The high [CH 4] is required to form the Mo-carbide interface and balance the diffusion of carbon into the metal before the a-C layer can be formed. The formation of nucleation centres during the bias-enhanced nucleation seems under these deposition conditions to proceed via different pathways on Si and Mo. While the nucleation on Si appears to be linked to the formation of diamond nanocrystals during the pretreatment, this is not the case for Mo.

Properties of fluorinated amorphous silicon-nitrogen-oxygen alloy (a-SiN xO y:H) deposited by plasma-enhanced chemical vapor deposition

The properties of fluorinated amorphous silicon-nitrogen-oxygen (a-SiN x O y :H:F) alloys deposited in a plasma-enhanced chemical vapor deposition reactor using a mixture of monosilane (SiH 4) and nitrogen trifluoride (NF 3) were investigated. The deposition rate of the a-SiN x O y :H:F alloys was found to increase with increasing NF 3 flow rate. Auger electron spectroscopy revealed a uniform chemical composition in these alloys. An abrupt increase in the bulk conductivity of the a-SiN x O y :H:F alloys was observed when the NF 3 flow rate was increased from 4 sccm to 7 sccm, whereas the bulk conductivity decreased as the NF 3 flow rate was increased from 7 sccm to 24 sccm. This phenomenon is attributable to a structural transformation in the alloys deposited with 7 sccm of NF 3. Carrier conduction in bulk alloys exhibited three activation energies with transition temperatures at 373 and 240 K. Carrier conduction above 373 K is by thermionic emission of carriers from silicon grains. Between 240 and 373 K, conduction is by thermionic field emission of carriers. Below 240 K, carrier tunneling is the predominant conduction mechanism. Undoped a-SiN x O y :H:F alloys formed rectifying heterojunctions on crystalline p-type silicon. The electrical characteristics of these heterostructures are dominated by the silicon/alloy interface.

Study of the material properties and suitability of plasma-deposited fluorine-doped silicon dioxides for low dielectric constant interlevel dielectrics

A major challenge for back-end interconnection technology as device geometries shrink is the development of low dielectric constant materials with good gap-filling properties that are suitable for microelectronics manufacturing. Recently, there has been much interest in fluorine-doped silicon dioxides (SiOF) as such a material. The advantages of a silicon dioxide based film from an integration standpoint make these films very attractive for manufacturing. In this study, SiOF films have been prepared in a conventional parallel-plate dual-frequency plasma-enhanced chemical vapor deposition reactor. By varying the deposition parameters, SiOF films with indices of refraction from 1.38 to 1.46 and corresponding changes of as much as 20% in the dielectric constants have been produced. Fourier transform infrared data for these films have been correlated with fluorine concentration by secondary ion mass spectroscopy measurements. The presence of fluorine can also be observed in the capacitance-voltage (CV) characteristics for the films. Fluorine interface states trap electrons which delay the onset of accumulation in the CV measurements for p-type silicon. In a similar way, the fluorine-induced trap states affect the onset of inversion for n-type silicon. Some films with high fluorine concentrations have been observed to be unstable with respect to moisture absorption. The reliability and stability data for these films are presented.

Hydrogenated amorphous silicon films prepared at low substrate temperature on a cathode of an asymmetric r.f. plasma CVD system

Growth of amorphous hydrogenated silicon (a-Si:H) films away from so-called standard conditions have recently assumed great importance for extending the range of applications or perhaps even to improve the performance of presently available a-Si:H material. In the present investigation by depositing such films on the cathode of an asymmetric r.f. plasma-enhanced chemical vapour deposition reactor, without any deliberate substrate heating, we could ascertain those conditions where as-grown films show preferentially IR absorption peaks centred around 2000 cm −1. Further, under hydrogen dilution of the feedstock and inducing high self-bias values, by essentially inputting a high r.f. power to the cathode, we find that photoconductivity of the films produced show an order of magnitude change ( σ ph ≈ 10 −6 Ω −1 cm −1 ). A systematic photothermal deflection spectroscopy study has been undertaken to follow the change in a-Si:H film properties through manipulation of the plasma conditions. Implications of the present results are critically examined in the light of other related available information and existing models of growth.

Analysis and numerical modelling of silicon nitride deposition in a plasma-enhanced chemical vapour deposition reactor. II. Simplified modelling, systematic analysis and comparison with experimental measurements

For pt. I see ibid., vol. 4, p. 94-106 (1995). In this part of the work, an experimental and a theoretical analysis of the reactor behaviour were performed. The two-dimensional treatment of mass transfer equations was simplified to shorten the calculation time. The results so obtained were found to be in good agreement with those of the bidimensional modelling. The simplified model was used to perform a systematic analysis and the axial variations in deposition rate profile were analysed. Some theoretical estimations were compared with a set of experimental measurements of deposition rate profile and film and gas phase composition. Satisfactory agreement between calculations and experiments was found for various values of electrical power and silane percentage, indicating that the assumptions were, on the whole, realistic.

Plasma Carburization of an Axisymmetric Steel Sample

A mathematical model is formulated to simulate a high temperature plasma-enhanced chemical vapor deposition (CVD) reactor This high temperature situation is applicable to plasma-enhanced carburization of steel. Plasma -enhanced carbCrization is an alternative fO traditional atmosphere carburization and may reduce many problems associated with the latter process The model includes coupling between the plasma physics the hydrodynamics of the gas phase, hydrodynamic transport of neutral species, chemical kinetic surface reactions, ion-assisted deposition, and diffusion into the steel. The model is limited to a dilute single species system, neglecting gas phase dissociation mechanisms It also assumes a uniform distribution of electrons throughout the bulk The model is analyzed and solved using asymptotic methods to simplify the governing equations Through the development of quasi analytical solutions sortie of the complex interactions and couplings among the physical mechanisms acting in the plasma CVU process are' elucidated.

Characterization of phosphosilicate glass films obtained using plasma-enhanced chemical vapor deposition from tetraethylorthosilicate and trimethylphosphite

We examine the deposition rate, step coverage and film thickness uniformity of 2 μm (8.4 wt.% P) phosphosilicate glass (PSG) films obtained using plasma-enhanced chemical vapor deposition (PECVD) from tetraethylorthosilicate (TEOS), trimethylphosphite and O 2 as reactants in an Ar diluent. A 2 6-2 fractional factorial screening equipment was performed to evaluate the effects of r.f. power, pressure, temperature, O 2-to-TEOS feed ratio, plasma duty cycle and Ar flow in a batch PECVD reactor. Factor effects are considered to have a significant influence at an 85% confidence level. The deposition rate increases with increasing duty cycle, power and pressure and decreasing Ar flow. Step coverage is characterized for rectangular trenches with two initial aspect ratios, 0.64 and 2.5, by three ratios; (1) the film thickness S 1 in the plane of the original trench mouth to the thickness T on the wafer surface, (2) the film thickness S 2 where it is the thinnest at the base of the side wall to T and (3) the thickness B at the center of the base to T. S 1/ T increases with increasing duty cycle, pressure and temperature for an aspect ration of 0.64. For feature with an aspect ratio of 2.5; (1) S 1/ T increases with increasing temperature and decreasing Ar flow, (2) S 2/ T increases slightly with increasing temperature and (3) B/T increases with increasing temperature and Ar flow and decreasing O 2-to-TEOS ratio and power. Step coverages are superior to those of low pressure chemical vapor deposited PSG films from SiH 4, O 2 and PH 3. The inter-wafer film thickness uniformity is independent of the factor level settings in this experiment. The intra-wafer film thickness variability increases with increasing temperature and O 2-to-TEOS ratios.

Highly conductive silicon films via plasma-enhanced chemical vapor deposition at low temperatures

The primary advantage of using plasma-enhanced chemical vapor deposition (PECVD) over conventional chemical vapor deposition is lower substrate temperatures, i.e., 200–300 °C. Using heavy hydrogen dilution, highly conductive poly or single-crystal silicon films were deposited in a conventional parallel plate, ultrahigh vacuum, PECVD reactor at temperatures as low as 200 °C. The source gas used was silane mixed with 1% PH3. The hydrogen concentration was varied between 80% and 98% of the total gas flow. The films were characterized both electrically and optically. The optical properties of the films were evaluated using Fourier-transform infrared spectroscopy. The electrical characterization was done by measuring resistivity and activation energy. P–N diodes were fabricated using these hydrogen-diluted films and I–V characteristics were plotted to obtain the diode quality factor. The current conduction mechanism was determined using I–V curves. The results obtained in this work suggest that PECVD can be successfully employed to deposit highly conductive silicon films at temperatures as low as 200 °C, with preservation of the crystalline structure of the underlying substrate.

A New Method of Depositing Amorphous Hydrogenated Silicon Carbide with Low Ir-Detected Microstructure

ABSTRACTWe report a new method of depositing amorphous hydrogenated silicon carbide thin films with low IR-detected microstructure in a plasma-enhanced chemical vapor deposition reactor. Films prepared at various conditions are studied with Fourier-transform infrared absorption. Their optical band gaps and photoconductivities are also measured. The amount of microstructure can be controlled by adjusting the powered-electrode potential during deposition, and the microstructural changes are reflected in the film properties. By applying an external dc voltage to the rf-excited powered electrode, we can shift the optimal deposition temperature from 250 °C to as low as 100 °C. We find that films deposited at positive powered-electrode potential and low substrate temperature exhibit less microstructure, wider optical band gaps, and faster deposition rates than films deposited at conventional conditions.

Plasma enhanced chemical vapor deposition modeling

Abstract We are developing a model to simulate the plasma enhanced chemical vapor deposition (PECVD) of thin diamond films. The emphasis to date has been on the development of stand-alone modules to simulate the microwave-induced time-dependent electric and magnetic fields, the generation and energization of plasma electrons in the discharge, the non-equilibrium hydrocarbon chemistry, and the development of a two-dimensional unstructured mesh hydrodynamics solver capable of simulating flow through geometrically realistic reactors. The coupling of the various modules, and the incorporation of a surface chemistry module for the substrate deposition, into a self consistent reactor model is underway. We present some preliminary results from components of a model 2.45 GHz microwave reactor employing H 2 with 1% CH 4 and operating at a gas pressure of 5.3 × 10 3 Pa (40 Torr). We have completed an electromagnetic model of the microwave energy deposition in the plasma and calculated the field patterns in the reactor. We have also performed point calculations of the time-dependent electron distribution and of the build-up of atomic hydrogen, the gas temperature, and the resulting generation of CH 3 , C 2 H 2 , and other hydrocarbon radicals. We have also completed a fluid simulation of the flow through the reactor using unstructured mesh techniques. The results we discuss in this paper indicate that careful treatment of non-equilibrium processes in PECVD reactors as well as accurate representation of reactor geometry are essential to a useful simulation capability.

Adhesion improvements in silicon carbide deposited by plasma enhanced chemical vapour deposition

Abstract The ability to deposit a hard, adherent, wear resistant, inert thin coating on complex geometries at temperatures at and below 350 °C will find application both in the cutting industry and where coatings on cheaper substrates can replace expensive bulk material. This study describes the deposition of silicon carbide coatings from a conventional plasma-enhanced chemical vapour deposition reactor. The deposition was conducted at 350 °C from source gases of SiH 4 , NH 3 , C 2 H 4 , N 2 , and H 2 in a 300 kHz high frequency plasma. A variety of substrates including M2 high speed steel, tool steel and cemented carbides were coated. The coatings were characterized in terms of their mechanical properties, tribological properties and composition, especially at the interfaces. The ex situ and in situ pretreatment of the substrates using different etching processes was found to be of paramount importance in achieving good adhesion. The effects which interface layers have on the change in adhesion of silicon carbide to the substrate were also addressed.

Oxidation of InP in a plasma-enhanced chemical vapor deposition reactor

During the plasma-enhanced chemical vapor deposition (PECVD) of SiO 2 onto InP, an oxide may grow. This oxide could affect the electrical properties of the SiO 2-InP interface. In this paper we report on the temperature dependence of the growth rate, composition and topography of oxides grown in a PECVD reactor which has a separate plasma chamber. The oxide growth rate in the main chamber was found to be a function of the transfer tube length and was greater than the thermal oxidation rate for T<350°C. The oxide composition was found to be primarily InPO 4 with some In 2O 3 in the thicker layers. The topography varied with processing.