The effect of post-deposition thermal processing on MOS gate oxides formed by remote PECVD

The effects of post-deposition thermal exposure, at temperatures typical of MOS fabrication processes, on gate oxides formed by remote plasma enhanced chemical vapor deposition (RPECVD) is discussed. SiO₂ films were prepared by (1) thermal oxidation of silicon at temperatures from 700 to 1150° C, and (2) by RPECVD at a substrate temperature of 350° C. Post deposition thermal processing was achieved by rapid thermal annealing for 100 sec from 850–1200° C. Film properties were studied by infrared spectroscopy (IR), ellipsometry, and by measurements of stress, capacitance voltage characteristics, and dielectric breakdown. Post-formation, thermal processing in the range of 850–1200° C was shown to modify both thermally grown and deposited oxides, but it has been shown that RPECVD films could be stabilized against post-deposition changes by rapid thermal annealing at temperatures of about 900° C for periods of at least 100 sec.     

Low temperature aluminum oxide deposition using trimethylaluminum

Aluminum oxide films (amorphous and γ-Al₂O₃) have been deposited by the oxidation of trimethy1aluminum. Process parameters have been evaluated and optimized to obtain reasonable growth rates and film properties for deposition temperatures between 300 and 400° C. Values of the dielectric constant (7.5 – 7.8), the dielectric strength (7.5 – 7.9 × 10⁶ V/cm), the index of refraction (1.54 – 1.67), and the resistivity (> 10 ohm-cm) compare favorably with Al₂O₃, films grown with other processes at higher deposition temperatures. Film analysis by secondary ion mass spectrometry identified a distribution of carbon and sodium impurities.     

Low Leakage Current Transport and High Breakdown Strength of Pulsed Laser Deposited HfO<Subscript>2</Subscript>/SiC Metal-Insulator-Semiconductor Device Structures

Hafnium oxide (HfO₂) thin films were deposited by the pulsed laser deposition (PLD) method on SiC substrates. The bandgap of HfO₂ thin films was observed to be 5.8 eV. The chemical nature and stoichiometry of the films were analyzed by x-ray photoelectron spectroscopy (XPS). Metal-insulator-semiconductor (MIS) structures with Ni as a top electrode and TiN as a bottom electrode were fabricated to study the leakage current properties. The devices exhibited leakage current density of 50 nA/cm². The dielectric constant of these films is estimated to be in the range 17–24 from capacitance-voltage (C-V) measurements. The frequency dependence of the interface trapped charges is studied.     

Deposition of High Purity Parylene- F Using Low Pressure Low Temperature Chemical Vapor Deposition

Parylene-F, poly(tetrafluoro-para-xylylene) (PA-F), has potential applications in microelectronics because of its high thermal stability and low dielectric constant. We found that a new precursor, 1,4-bis(trifluoromethyl) benzene (TFB) with a trace presence of α,α′-dibromo-α,α,α′,α′-tetrafluoro-p-xylene (DBX), can be used to produce PA-F films. PA-F films from this precursor are produced using a reaction line and a conventional deposition system. This process is simpler than previously reported processes and produces PA-F films with less impurities. The dielectric constant of the PA-F films produced by this process is 2.25 ± 0.05 at 1 MHz. The deposition process and the material properties of the PA-F films produced are presented.     

High density plasma chemical vapor deposition of diamond-like carbon films

This work was based on the studies of the influence of the plasma process on the characteristics of diamond-like carbon (DLC) films deposited by high density plasma chemical vapor deposition (HDP-CVD). DLC is a material that shows several good characteristics like high electrical resistivity, lower dielectric constant, high breakdown field, lower stress, high density, and hardness and chemical inertness. This material is important actually in mechanic, optic, and chemistry and mainly in microelectronic areas. For microelectronic process the best results were obtained by plasma of pure methane: low dielectric constant (1.7) and high resistivity 5×10¹³ Ω cm.     

A novel low-temperature method of SiO2 film deposition forMOSFET applications

Silicon dioxide dielectric films were deposited at low temperatures (250–300°) using a novel plasma enhanced MO-CVD process. In this process, the substrate was kept remote from the plasma region and the deposition of the film was achieved at low pressure (0.8-1.0 Torr) and low dc plasma power (0.3 W· cm⁻²). Films deposited using tetraethyloxysilane (TEOS) and nitrous oxide (N₂O) as reactant material had, under optimum deposition conditions, resistivities of ≥ 10¹⁵ ohm-cm, a refractive index of 1.46, a dielectric constant of 3.98 and a breakdown field strength ≥ 5x 10₆ V·cm⁻¹. AES and SIMS analysis indicated that the films were of high purity and were stoichiometric with no metallic silicon present. MOS-capacitors fabricated on Si-substrates showed no hysteresis and no frequency dispersion of capacitance in the accumulation region. An interface state density in the range of 10¹¹ cm⁻²eV⁻¹ was achieved for these MOS devices using our deposited SiO₂dielectric films.     

Formation of aluminum oxide films from aluminum hexafluoroacetylacetonate at 350–450° c

A study of the thermally activated decomposition of Al(hfa)₃ (aluminum hexafluoroacetylacetonate) from the gas phase to form Al₂O₃ on silicon substrates is reported. The decomposition process was carried out in an open tube atmospheric pressure reactor in either argon or oxygen/argon mixtures in the temperature range, 350–450° C. The chemical vapor deposition process resulted in the formation of aluminum oxide films in all instances. The dielectric strength of Al/Al₂O₃/Si capacitors which received a post-metal anneal, but did not receive a high temperature annealing treatment, with aluminum oxide films prepared from Al(hfa)₃ in argon, was found to be in the range 2–6 MV/cm. The difference between the flatband voltage of the MOS structures and the metal-silicon work function difference was positive, indicative of a net negative oxide charge with a density of approximately 3 × 10¹¹ – 3 × 10¹² cm^-2, assuming the charge is located at the oxide-silicon interface. Decomposition of Al(hfa)₃ was also carried out in oxygen/argon mixtures with the oxygen concentration in the range 10–60 vol %. This process led to the deposition of aluminum oxide films with breakdown fields in the range 8–9 MV/cm. However, the flatband voltages of the Al/Al₂O₃/Si capacitors were even more positive than those obtained with Al₂O₃ formed in pure argon. High temperature (800–1000° C) oxygen or nitrogen annealing treatments of alumina films deposited in either argon or oxygen/argon mixtures were evaluated from the point of view of their influence on the oxide film properties. In particular, an annealing process in oxygen at 1000° C for 15 min was found to result in a reduction of the net negative oxide charge, and an improvement of the dielectric strength of films deposited in argon. Films formed in oxygen/argon mixtures did not change appreciably following oxygen annealing, as far as breakdown fields are concerned, but the oxide net negative charge was reduced. As in an earlier study by the authors, of copper film deposition from Cu(hfa)₂, it was found that essentially carbon free films could be obtained under appropriate conditions.     

Polycrystalline silicon thin film transistors fabricated in various solid phase crystallized films deposited on glass substrates

In this work, we have characterized various types of polysilicon films, crystallized upon thermal annealing from films deposited by low pressure chemical vapor deposition in the amorphous phase and a mixed phase using silane or in the amorphous phase using disilane. Polysilicon thin film transistors (TFTs) were fabricated, at low processing temperatures, in these three types of films on high strain point Corning Code 1734 and 1735 glass substrates. Double layer films, with the bottom layer deposited in a mixed phase and the top in the amorphous phase, allowed TFT fabrication at a drastically reduced thermal budget; optimum values of thicknesses and deposition rates of the layers are reported for reducing the crystallization time and improving film quality. Optimum deposition conditions for TFT fabrication were also obtained for films deposited using disilane. The grain size distribution for all types of films was shown to be wider for a larger grain size. Fabricated TFTs exhibited field effect electron mobility values in the range of 20 to 50 cm²/V·s, subthreshold swings of about 0.5–1.5 V/dec and threshold voltage values of 2–4 V.     

Diamond-like carbon protective films for organic photoconductors

The deposition of a protective film to increase the hardness of an organic photoconductor (OPC) surface is an effective method of lengthening the lifetime of the OPC. In this work, diamond-like carbon (DLC) protective films were deposited onto OPC samples by the electron cyclotron resonance (ECR)-microwave plasma chemical vapor deposition (MPCVD) method with low substrate temperature. The DLC films were deposited with optimized deposition conditions and exhibited high transmissivity and high electrical resistivity. The films caused a remarkable increase in the hardness of the OPC surface, by a factor of 2.5∼5.4. The acceptance voltage, dark decay rate, photodischarge rate, and contrast potential of the OPC protected by DLC film were improved. These results show DLC is a suitable protective film for OPC.     

Deposition of tantalum oxide films by dual spectral source assisted metalorganic chemical vapor deposition (MOCVD)

Dual spectral source assisted metalorganic chemical vapor deposition (MOCVD) is an ideal technique for the deposition of high dielectric constant materials. Tungsten halogen lamps and a deuterium lamp are used as the sources of optical and thermal energy. In this paper, we have reported the deposition and characterization of tantalum penta oxide films. Ta₂O₅ films were deposited at 660°C for 15 min and annealed at 400°C for 1 h. The leakage current densities of 10.6 nm thick films are as low as 10₋₁₀ A/cm² for gate voltage under 4V. To the best of our knowledge, these are the best results reported to date by any researcher. The high energy photons used in the in-situ cleaning and deposition process play an important role in obtaining high quality films of Ta₂O₅.     

Plasma deposition of aluminum oxide films

A plasma deposition technique for amorphous aluminum oxide films is discussed. A 450 kHz or 13.56 MHz power supply was used to generate the plasma and the deposition of the film was achieved at low plasma power using trimethyl-aluminum and carbon dioxide reactant sources. It has been found that for the low frequency plasma the growth is strongly dependent upon TMA concentration, indicating that the growth process is mass transport limited. On the other hand using the 13.56 MHz discharge results in a surface controlled growth rate. An increase in the deposition temperature up to 300° C makes the films more dense and lowers their etching rate. FTIR and ESCA measurements showed that oxidation is only completed with high CO₂ concentrations and a deposition temperature above 250° C. The dielectric films were found to have a dielectric constant in the range 7.3=2-9 and a refractive index between 1.5–1.8 depending upon deposition conditions.     

High dielectric constant polymer-ceramic (Epoxy varnish-barium titanate) nanocomposites at moderate filler loadings for embedded capacitors

Polymer-ceramic nanocomposites are the major candidate dielectrics for embedded capacitors. Due to the poor adhesion and poor thermal stress reliability at high filler loadings, commercially available polymer-ceramic composites can only achieve a maximum dielectric constant of ∼30. However, a high dielectric constant of ∼50–200 is required to make the layout area small enough for embedding applications. In this work, we systematically studied the material formulations in order to obtain a high dielectric constant (κ>50) at the lowest ceramic filler loading. It was found that material design and processing were critical. By modifying the epoxy matrix with a chelating agent and using bimodal fillers and a proper amount of dispersing agent, dielectric constants ∼50 were obtained at moderate filler loadings.     

Pulsed laser deposition and processing of wide band gap semiconductors and related materials

The present work describes the novel, relatively simple, and efficient technique of pulsed laser deposition for rapid prototyping of thin films and multi-layer heterostructures of wide band gap semiconductors and related materials. In this method, a KrF pulsed excimer laser is used for ablation of polycrystalline, stoichiometric targets of wide band gap materials. Upon laser absorption by the target surface, a strong plasm a plume is produced which then condenses onto the substrate, kept at a suitable distance from the target surface. We have optimized the processing parameters such as laser fluence, substrate temperature, background gas pressure, target to substrate distance, and pulse repetition rate for the growth of high quality crstalline thin films and heterostructures. The films have been characterized by x-ray diffraction, Rutherford backscattering and ion channeling spectrometry, high resolution transmission electron microscopy, atomic force microscopy, ultraviolet (UV)-visible spectroscopy, cathodoluminescence, and electrical transport measurements. We show that high quality AlN and GaN thin films can be grown by pulsed laser deposition at relatively lower substrate temperatures (750–800°C) than those employed in metal organic chemical vapor deposition (MOCVD), (1000–1100°C), an alternative growth method. The pulsed laser deposited GaN films (∼0.5 μm thick), grown on AlN buffered sapphire (0001), shows an x-ray diffraction rocking curve full width at half maximum (FWHM) of 5–7 arc-min. The ion channeling minimum yield in the surface region for AlN and GaN is ∼3%, indicating a high degree of crystallinity. The optical band gap for AlN and GaN is found to be 6.2 and 3.4 eV, respectively. These epitaxial films are shiny, and the surface root mean square roughness is ∼5–15 nm. The electrical resistivity of the GaN films is in the range of 10⁻²–10² Θ-cm with a mobility in excess of 80 cm²V⁻¹s⁻¹ and a carrier concentration of 10¹⁷–10¹⁹ cm⁻³, depending upon the buffer layers and growth conditions. We have also demonstrated the application of the pulsed laser deposition technique for integration of technologically important materials with the III–V nitrides. The examples include pulsed laser deposition of ZnO/GaN heterostructures for UV-blue lasers and epitaxial growth of TiN on GaN and SiC for low resistance ohmic contact metallization. Employing the pulsed laser, we also demonstrate a dry etching process for GaN and AlN films.     

Properties of low-k SiCOH films prepared by plasma-enhanced chemical vapor deposition using trimethylsilane

The properties of low-k SiCOH film deposited by plasma-enhanced chemical vapor deposition using trimethylsilane are reported here. The deposition process was performed at different temperatures from 200 to 400 °C. The influence of deposition temperature on the films were characterized using Fourier transform infrared spectroscopy (FTIR) to understand its impact on the studied properties. The films were annealed at ∼450 °C in an inert ambient after deposition in all the cases. The deposition rate decreases with increase in deposition temperature. The refractive index of the films increases as a function of deposition temperature. From FTIR spectra, OH-related bonds were not detected in films even when deposited at 200 °C. The Si-CH₃ bonds were detected in all the films and decreased monotonically from 200 to 400 °C. All deposition conditions studied resulted in films with dielectric constant less than 3, the lowest being ∼2.7 when deposited at 200 °C. All films exhibited good thermal stability.     

Synthesis and characterization of porous polymeric low dielectric constant films

This paper reports the synthesis and dielectric properties of a porous poly(arylether) material with an ultra-low dielectric constant for interlayer dielectric applications in microelectronics. The porous polymer films were successfully fabricated by a method of organic phase separation and evaporation. A dielectric constant k of 1.8 was achieved for a porous film with an estimated porosity of 40% and average pore size of 3 nm. Electrical and mechanical properties as well as coefficient of thermal expansion for both dense and porous polymer films were measured.     

Effects of annealing in O2 and N2 on the electrical properties of tantalum oxide thin films prepared by electron cyclotron resonance plasma enhanced chemical vapor deposition

The tantalum oxide thin films with a thickness of 14 nm were deposited at 95°C by electron cyclotron resonance plasma enhanced chemical vapor deposition (ECRPECVD), and annealed at various temperatures (700∼850°C) in O₂ and N₂ ambients. The microstructure and composition of the tantalum oxide thin films and the growth of interfacial silicon oxide layer were investigated and were related to the electrical characteristics of the film. Annealing in an O₂ ambient led to a high dielectric constant (ε_r(Ta₂O₅) = 24) as well as a small leakage current (E_bd = 2.3 MV/cm), which were due to the improved stoichiometry and the decreased impurity carbon content. Annealing in an N₂ ambient resulted in poor and nonuniform leakage current characteristics. The as-deposited tantalum oxide films were crystallized into δ-Ta₂O₅ after annealing at above 750°C regardless of the ambient. The leakage current of the film abruptly increased after annealing at 850°C probably because of the stress caused by thermal expansion or contraction.     

用ECRC-VD方法制备非晶氟化碳薄膜

以C4F8为源气体,Ar为稀释气体,用电子回旋共振化学汽相淀积的方法制作了非晶氟化碳薄膜;使用XPS和FTIR分析薄膜的化学组分和成键类型;研究了微波功率对于沉积速率和薄膜光学性质的影响。沉积速率随Ar在混合气体中比例的增大先增大后降低,随微波功率的增加而增加,并最终趋于饱和值。沉积的薄膜介电常数约为2.0,在可见光区薄膜具有良好的透光性。在较高的微波功率条件下,沉积薄膜的光学带隙减小。     

Copper chemical vapor deposition from Cu(hexafluoroacetylacetonate)trimethylvinylsilane

Copper chemical vapor deposition using Cu-hexafluoroacetylacetonate (hfac) trimethylvinylsilane (TMVS) as precursor was performed in a cold-wall low pressure chemical vapor deposition (CVD) reactor. The design and operation of the reactor are described. Copper deposition on thermal SiO₂, W, and CoSi₂ substrate surfaces was investigated over the temperature range of 160–300°C and pressure range of 10–1000 mTorr. The activation energies of Cu CVD were determined to be 13.33 and 11.54 kcal/mole for the W and CoSi₂ substrates, respectively. The dependence of film resistivity, grain size, and growth rate on deposition pressure and temperature were also investigated. The film uniformity was found to be better than ten percent over a 4-inch diameter substrate. Experimental results also show that selective deposition can be achieved at a pressure of 10 mTorr within the temperature range of 160–200°C. In addition, hydrofluoric acid dipping was found to modify the SiO₂ surface and influence the copper deposition on it.     

Preparation of (Pb0.88La0.12)TiO3 thin films for dynamic random access memory by low pressure-metalorganic chemical vapor deposition

La-modified lead titanate (PLT) thin films were prepared by hot-wall type low pressure-metalorganic chemical vapor deposition method. Pb(dpm)₂, La(dpm)₃, and titanium tetraisopropoxide were used as source materials. The films were deposited at 500°C under the low pressure of 1000 mTorr and then annealed at 650°C for 10 min in oxygen ambient. Sputter-deposited platinum electrodes and 180 nm thick PLT thin films were employed to form MIM capacitors with the best combination of high charge storage density (26.7 μC/cm² at 3V) and low leakage current density (1.5 × 10^-7 A/cm² at 3V). The measured dielectric constant and dielectric loss were 1000∼1200 and 0.06∼0.07 at zero bias and 100 kHz, respectively.     

A high-quality stacked thermal/LPCVD gate oxide technology for ULSI

By stacking thermal and high-quality LPCVD (low-pressure chemical vapor deposition) SiO₂ films, gate oxides with very low defect densities are demonstrated. Whereas previous reports suggested that a thick layer of LPCVD oxide can improve the stacked gate oxide defect density, it is demonstrated that even 25 Å of LPCVD oxide is sufficient to dramatically reduce the defect density compared to thermal oxide films. The projected scaling limit for this technology is estimated to be as low as 70 Å for the total stack thickness. An optimized thermal/LPCVD oxide technology is very promising as the gate dielectric for sub-half-micrometer CMOS technology