Phosphosilicate Glass Films Research Articles

Characterization of PSG Films Reflowed in Steam Using Rapid Thermal Processing

ABSTRACTThis study describes the use of a steam environment to reflow phosphosilicate glass (PSG) samples using a HEATPULSE® rapid thermal annealer. The samples comprised PSG over poly steps and of open contacts in PSG. It was observed that reflow occurs 50°C lower in steam than in dry O2. An acceptable flow cycle for 8 w/o P in PSG glass is 1050°C for 10 seconds in steam, while for 6 w/o P PSG it is 1100°C for 10 seconds. Steam is found to be an effective amibient for densification of the PSG film. The thermal oxide grown in the contact during opening reflow was determined to be near 140 A. The operating regime for a junction depth <0.4 um and a reflow angle < 75° is presented for 8 w/o P.

Deposition and Reflow of Phosphosilicate Glass

The chemical vapor deposition (CVD) and reflow of phosphosilicate glass (PSG) have been reviewed. The CVD reaction from silane and phosphine has been simulated by SOLGAS thermochemical calculations. This equilibrium calculation method predicts stoichiometric conversion of silane and phosphine. In comparison to experimental determinations, the calculations underestimate the glass phosphorus content by about 1–3 weight percent. In addition, recent observations that the reflow of PSG is greatly enhanced by the presence of a steam ambient during heating have been examined. A possible mechanism of this reflow enhancement has been discussed. Experimental evidence, which support this mechanism, by electron microprobe, FTIR, and SIMS studies of PSG films, are presented.

Plasma‐Activated Deposition and Properties of Phosphosilicate Glass Film

Phosphosilicate glass film deposited by a plasma‐activated reaction system (P‐PSG) was studied. Fundamental characteristics of the P‐PSG were investigated by systematically varying deposition parameters. In this plasma deposition method, the P‐PSG having a high deposition rate (130 nm/min) and a high doped phosphorus concentration [about 10 weight percent (w/o) P] was deposited using the reaction gases , , and . The P‐PSG deposited by this method showed properties such as a strong film crack resistance during heat‐treatments, a conformai step coverage, and a controllable compressive stress, compared with those of conventional PSG film deposited under atmospheric pressure (AP‐PSG).

Void Formation in Phosphosilicate Glass Film with Heat‐Treatment in H 2 Atmosphere

The void formation process and phosphorus behavior in phosphosilicate glass film deposited by chemical vapor deposition techniques were investigated. The films were heat‐treated three times, first in atmosphere for densification, then in or atmosphere, and after that in atmosphere. It was found that (i) void formation takes place with the third heat‐treatment in atmosphere, (ii) with the second heat‐treatment in atmosphere, absorbance of P=O band at 1330 cm−1decreases and absorbance of band at 1250 cm−1 increases, but further absorbance change does not take place with the third heat‐treatment. The gain in absorbance of the band at 1250 cm−1 is proportional to the loss in absorbance of the P=O band at 1330 cm−1. The quantity of phosphorus products formed with heat‐treatment in atmosphere was estimated from the absorbance change of the P=O band at 1330 cm−1. Comparing the quantity of the phosphorus products with the void size and number, it was proposed that the phosphorus products are gaseous species at high temperature, and the quantity of the gaseous species determines the product of the void number in the PSG film and square of the void size.

Depletion trench capacitor technology for megabit level MOS dRAM

A new technology has been developed for future megabit level MOS dRAM's, in which a depletion-type capacitor is formed at a trench in the cell capacitor region. Trenches have been successfully formed by reactive ion etching utilizing CBrF <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> gas at a pressure of about 14 mTorr. Phosphorous could be doped onto the trench surface with sufficient controllability using a phospho-silicate glass film as a diffusion source. The capacitance of the depletion trench capacitor (DTC) was influenced by the surface orientation of the trench sidewalls. DTC breakdown voltage where gate oxide thickness was 20 nm was more than 7 V. This is large enough for practical use under 3-V operating conditions.

The Influence of Back End Processing on the Fixed Charges Density in the Si ‐ SiO2 Interface

Variations in the density of fixed surface charges at the interface during back end processing steps are reported. After the deposition of phosphosilicate glass (P‐glass) films (LPCVD at 630°C, from TEOS, phosphine, and oxygen), measured on aluminum gate capacitors is in the range of . Densification of the P‐glass by means of heat‐treatment affects in a similar fashion to previously reported post thermal oxidation treatments. The effectiveness of the densification ambient in reducing can be ranked in the order: steam > oxygen > argon > steam + argon. After polycrystalline silicon/aluminum metallization, which involves polysilicon deposition followed by heat‐treatment (doping) and aluminum deposition, depends very strongly on the premetallization treatment. When this metallization is applied over undensified glass, can be higher than . It increases with increasing the doping time, the doping temperature, the glass thickness, or the phosphine to oxygen flow rate ratio during the P‐glass deposition. Polysilicon/aluminum metallization applied over densified glass yields much lower , with the final value depending strongly on the densification conditions. For example, densification in steam or oxygen at 950°C for 10 min yields of less than after the silicon/aluminum metallization. The results can be explained on a basis of oxygen deficiency in as deposited P‐glass films and rearrangement of the interface in the presence of a polysilicon cap film over the glass.

Planarizing of phosphosilicate glass films on patterned silicon wafers

Patterned silicon wafers covered with both flowed and nonflowed phosphosilicate glass films have been planarized by argon ion‐beam etching. At the optimum planarizing angle of 50°, the nonflowed PSG surface, with 1 μm high topography, is transformed to a flat surface with maximum deviations from planarity of <500 A. The technique should alleviate resolution, linewidth control, and metallization coverage problems in very large scale integrated circuit fabrication.

Water Absorption and Densification of Phosphosilicate Glass Films

The interaction between phosphosilicate glass films and water vapor has been studied at the temperature range 70–100°C, using infrared spectroscopy. The films were deposited at 640°C using low pressure chemical vapor deposition. The infrared spectra change significantly during the exposure of the films to water vapor. In spite of the observed decrease in the intensity of the P=O band it has been found that phosphorus ions do not outflow from glasses that contain less than 8 m/o phosphorus oxide. The diffusion of water in the films can be described by a single activation energy, which increases with increasing phosphorus oxide concentration. Densification of the glass by means of heat‐treatment substantially increases the film resistance to water absorption. The densification of the phosphosilicate glass has been studied by infrared spectroscopy and etch rate measurements. The efficiency of the densification increases with increasing the temperature and time of the heat‐treatment. The effectiveness of the ambients used in this study can be ranked in the order: .

Low Pressure Deposition of Phosphosilicate Glass Films

Phosphosilicate glass films have been deposited on silicon substrates by the reaction of tetraethyl orthosilicate (TEOS), phosphine, and oxygen. The depositions are carried out at 630°–700°C in a low pressure CVD reactor. The dependence of the deposition rate, the phosphorus oxide concentration, the thickness uniformity across a wafer, and the depletion in the deposition rate across the deposition zone upon the deposition conditions have been investigated. The step coverage obtained in the reaction is conformal. The refractive index, the etch rate, and the film stress are reported.

Lateral growth of single-crystal InP over dielectric films by orientation-dependent VPE

Vertical and lateral vapor-phase epitaxial growth of InP by the PC1 3-InP-H 2 method has been investigated as a function of crystallographic orientation. To study lateral growth, a single-crystal low-index substrate is coated with a phosphosilicate glass (PSG) film, patterned openings are etched in the film along selected directions in the plane of the substrate, and growth conditions are fixed so that nucleation occurs only on the exposed areas of the substrate. When the thickness of the InP epilayers grown in the openings exceeds that of the PSG, these layers seed lateral growth over the PSG. This growth is negligible in low-index directions because of the formation of low-index facets. For higher index directions, significant lateral growth occurs because intersecting low-index facets form corners that act as nucleation sites. Such growth has been utilized to form continuous single-crystal InP layers over patterned PSG films. Lateral growth in polar directions is asymmetric.

Temperature dependence of the stress in PSG/AlSi structures

The temperature dependence of the stress in each layer of a film system comprising chemically vapour-deposited phosphosilicate glass (PSG) on an AlSi alloy film on a silicon substrate was investigated in the range 20–500°C. During a heating process in which the temperature exceeded 150°C, the deformation of the AlSi film was found to be caused by diffusional creep, and the stresses in both the AlSi film and the PSG film increased with increasing silicon concentration in the AlSi film. Deformation of AlSi film during a cooling process in which temperatures were higher than 150°C was found to be caused by the generation of dislocation loops or by grain boundary sliding. These phenomena are interpreted as representing relaxation of the total elastic energy of the system which results from the deformation of the AlSi film.

Suppression of Mobile Ion Related Instability in Mo‐Gate MOS Structures

Electrical instability in Mo‐gate devices, caused by the presence of mobile ions, has been successfully prevented by depositing phosphosilicate glass (PSG) film on Mo‐gate metal and carrying out high temperature annealing after PSG film deposition. It is concluded that mobile ions were gettered into PSG film along the perimeter of Mo‐gate metal after lateral diffusion of mobile ions at the metal‐oxide interface. The rate‐limiting step was PSG film gettering reaction, which was expressed by a first‐order reaction. Reaction velocity constant activation energy was . Mo‐gate MOSFET's, having good stability in short term BT stressing, were fabricated with satisfactory reproducibility.

The Use of Energy Dispersive Diffractometry to Measure the Thickness of Metal and Glass Thin Films

This paper presents a new method to measure the thickness of very thin films on a substrate material using energy dispersive x-ray diffractometry. The method can be used for many film-substrate combinations. The specific application to be presented is the measurement of phosphosilicate glass films on single crystal silicon wafers.

Temperature dependence of stresses in chemical vapor deposited vitreous films

Thermal stresses in chemical vapor deposited (CVD) vitreous silicate and phosphosilicate glass (PSG) films on Si substrates are measured in situ from room temperature (RT) to 900 °C. As-deposited films grown at one atmospheric (APCVD) and lower pressures (LPCVD) are found to be inherently under a tensile and compressive stress at RT, respectively. On heating to 500 °C, the tensile component of the stress develops in both CVD films. Tensile stress increases with time at a given temperature. In the range 500–900 °C, the tensile component is reduced with temperature and time. During the cooling process from a temperature between 700 and 900 °C, the stress component of APCVD and LPCVD films changes from tension to compression. With APCVD film, the temperature dependence of the stress in the range RT–500 °C can be represented as a function of phosphorous concentration in mol % P2O5. Temperature and time dependence, and thermal hysteresis are attributable to water content, sintering, and viscoelastic properties of CVD film. These are explained from the viewpoint of glass annealing and softening temperature points.

Changes in Thickness and Infrared Spectrum of Phosphosilicate Glass Film with Heat‐Treatment in H 2 Gas

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Indirect determination of phosphorus by non-dispersive atomic fluorescence spectrometry of antimony

Phosphate is converted to molybdoantimonylphosphoric acid, which is reduced and extracted into isobutyl acetate. The extracted material is atomized in a graphite furnace and antimony determined by non-dispersive atomic fluorescence spectrometry. The detection limit is 2 ng of phosphorus, limited by the reagent blank, and the linear analytical range covers three decades of concentration up to 2 μg. The technique is applied to the determination of phosphorus in a phosphosilicate glass film deposited on a silicon wafer.

Quantitative Analysis of Semiconductor Materials with Secondary Ion Mass Spectrometer

A simplified quantitative procedure for SIMS, based on the LTE (Local Thermal Equilibrium) model, was proposed and applied to Na concentration determination in Si and SiO2. The procedure validity was checked using In0.1Ga0.9As and PSG (phospho-silicate glass) films as standard samples. Na concentration determination was carried out using a Si wafer, whose CNa was measured by activation analysis. In the case of SiO2, borosilicate glasses were analyzed taking into account Na ionization yield. Then, Na distribution in SiO2 films was measured by SIMS and was compared with the total amount of Na in SiO2 films obtained by electrical measurement and Atomic Absorption Spectrophotometry (AAS).

Planar Diffusion in Gallium Arsenide from Tin‐Doped Oxides

A new technique for the fabrication of planar junctions in gallium arsenide, by diffusion from tin‐doped silicon dioxide layers, has been investigated. It has been found that the doped oxide should contain less than 10% by weight of tin to prevent the occurrence of molten phases at the diffusion temperature (∼1010°C). Under these conditions, the junction depth increases as the square root of diffusion time for thick oxides and short diffusion times. However, the junction depth can also decrease with increasing diffusion time due to dopant depletion in the oxide if the oxide is thin and the diffusion time is large. Planar diffusions from tin‐doped oxides have been performed in evacuated quartz ampuls, with no arsenic overpressure, using phosphosilicate glass films as diffusion masks. Lateral diffusions of less than twice the junction depth have been achieved by using masks with 15% by weight of . These diffusions have been performed under conditions that appear to be more severe than those expected during open‐tube diffusion. Thus, the results indicate that the doped oxide diffusion technique should be suitable for the development of an open‐tube planar diffusion process for the fabrication of gallium arsenide devices and integrated circuits.

Gettering of epitaxial gallium phosphide using phosphosilicate glass

Chemically vapour deposited phosphosilicate glass films were used to getter epitaxial gallium-phosphide layers. Significant improvements in the electroluminescent efficiency of yellow light-emitting diodes fabricated from the gettered material were observed. Results suggest that the gettering removes compensating impurities as well defects which influence minority carrier lifetime.

Cracks in Silicon Dioxide-Phosphosilicate Glass-Silicon Nitride Composite Layer on Silicon Substrates

Cracks occur more easily in the silicon dioxide (SiO2)-phosphosilicate glass (PSG)-silicon nitride (Si3N4) composite layer on silicon substrates than in the SiO2–Si3N4 composite layer. The Si3N4 limit thickness with respect to crack occurrence in the SiO2–PSG–Si3N4 composite layer decreases with increasing PSG film thickness within the range of 0–1500 Å, with increasing P2O5 concentration in PSG film within the range of 0–10 mol% and with increasing Si3N4 deposition temperature. The local reaction of Si3N4 with P2O5 is probably the reason for crack occurrence in the SiO2–PSG–Si3N4 composite layer.