Low-pressure Chemical Vapor Deposition Furnace Research Articles

Implementation of SiN thin film in fiber-optic sensor working in telecommunication range of wavelengths

Mirrors are used in optical sensors and measurement setups. This creates a demand for mirrors made of new materials and having various properties tailored to specific applications. In this work, we propose silicon covered with a thin silicon nitride layer as a mirror for near-infrared measurements. SiN layer was deposited on a standard silicon wafer with a Low-Pressure Chemical Vapor Deposition furnace. Then, the created layer was investigated using ellipsometry and scanning electron microscope. Subsequently, the mirror was used as a reflecting surface in a Fabry–Perot fiber-optic interferometer. The mirror performance was investigated for wavelengths used in telecomunication (1310 nm and 1550 nm) and then compared with results obtained with the same measurement setup, with a silver mirror instead of silicon covered with SiN, as reference. Results showed that the proposed mirror can replace the silver one with satisfying results for investigated wavelengths.

Doped polycrystalline 3C-SiC films with low stress for MEMS: part II. Characterization using micromachined structures

Surface micromachined resonators, stress pointers and cantilevers were used to characterize nitrogen doped polycrystalline 3C-SiC (poly-SiC) films for their suitability as structural materials for MEMS applications. The films were deposited on 100 mm diameter silicon (Si) and silicon dioxide (SiO2) wafers using dichlorosilane (SiH2Cl2) and acetylene (C2H2) as precursors and ammonia (NH3) as the dopant source gas in a high throughput, low-pressure chemical vapor deposition furnace. The average Young's modulus was found to be 330 GPa for the films with the best combination of resistivity and residual stress. The device level tensile stress and stress gradient measured by stress pointers and cantilevers indicated that the residual tensile stresses were significantly affected by doping gas flow rate and deposition pressure. The best films deposited on SiO2 exhibited an average tensile stress of 74.2 MPa and an average stress gradient of 222 MPa µm−1.

Doped polycrystalline 3C–SiC films with low stress for MEMS: part I. Deposition conditions and film properties

This paper details the development of low-stress, heavily-doped polycrystalline 3C–SiC films suitable for microelectromechanical systems applications. The films were deposited on 100 mm-diameter silicon (Si) and silicon dioxide (SiO2)-coated Si wafers in a large-volume, low-pressure chemical vapor deposition furnace using dichlorosilane (DCS) (SiH2Cl2) and acetylene (C2H2) as precursors and ammonia (NH3) as the dopant source gas. The effects of NH3 and deposition pressure on the deposition rate, film residual stress and electrical resistivity were studied. Deposition parameters optimized for a combination of resistivity and residual stress yielded an average resistivity of 0.02 Ω cm and a residual tensile stress of 59 MPa as measured using wafer-scale methods. X-ray photoelectron spectroscopy indicated that the nitrogen concentration in the films was less than 0.5 at%. Variations in the flow rate of NH3 did not affect the surface roughness of the films, but changes in deposition pressure had an obvious effect on the surface roughness.

Nitrogen-Doping of Polycrystalline 3C-SiC Films Deposited by Low Pressure Chemical Vapor Deposition

This paper reports the effect of deposition temperature on the deposition rate, residual stress, and resistivity of in-situ nitrogen-doped (N-doped) polycrystalline 3C-SiC (poly-SiC) films deposited by low pressure chemical vapor deposition (LPCVD). N-doped poly-SiC films were deposited in a high-throughput, resistively-heated, horizontal LPCVD furnace capable of holding up to 150 mm-diameter substrates using SiH2Cl2 (100%) and C2H2 (5% in H2) precursors, with NH3 (5% in H2) as the doping gas. The deposition rate increased, while the residual stress decreased significantly as the deposition temperature increased from 825oC to 900°C. The resistivity of the films decreased significantly from 825°C to 850°C. Above 850°C, although the resistivity still decreased, the change was much smaller than at lower temperatures. XRD patterns indicated a polycrystalline (111) 3C-SiC texture for all films deposited in the temperature range studied. SIMS depth profiles indicated a constant nitrogen atom concentration of 2.6×1020/cm3 in the intentionally doped films deposited at 900°C. The nitrogen concentration of unintentionally doped films (i.e., when NH3 gas flow was zero) deposited at 900°C was on the order of 1017/cm3. The doped films deposited at 900°C exhibited a resistivity of 0.02 -cm and a tensile residual stress of 59 MPa, making them very suitable for use as a mechanical material supporting microelectromechanical systems (MEMS) device development.

Non-stoichiometric silicon oxide deposited at low gaseous N 2O/SiH 4 ratios

Semi-insulating polycrystalline silicon films were deposited using different N 2O/SiH 4 ratios, different pressures, at 650 and 700 °C, in a low-pressure chemical vapor deposition furnace. The deposition rate of the films increased with increasing pressure, increasing temperature and decreasing N 2O/SiH 4 ratio. At higher N 2O/SiH 4 ratios, more oxygen is incorporated in the film. Oxygen rich films had lower conductivities and lower dielectric constants than silicon rich films. The annealing of the films, at only 430 °C, decreased the conductivity indicating that more silicon-oxygen bonds are formed. The films also proved to be photoconductive.

Computationally efficient modeling of wafer temperatures in a low-pressure chemical vapor deposition furnace

A new thermal model is developed to predict wafer temperatures within a hot-wall low pressure chemical vapor deposition furnace based on the furnace wall temperatures as measured by thermocouples. Based on an energy balance of the furnace system, this model is a transformed linear model which captures the nonlinear relationship between the furnace wall temperature distribution and the wafer temperature distribution. The model can be solved with a direct algorithm instead of iterative algorithms which are used in all existing thermal models. Since the direct algorithm is noniterative, there is no convergence problem, nor local minima problem, related to nonlinear optimization. In addition, the direct algorithm greatly reduces the computation effort. Configuration factors are calculated by a finite area to finite area method. This avoids numerical integration methods which are much more difficult to implement and require more computation. The simplicity of the model form and the fast algorithm make the model useful for real-time updating and control. Model predictions show excellent agreement with experimental data.

Impact of ex-situ and in-situ cleans on the performance of bipolar transistors with low thermal budget in-situ phosphorus-doped polysilicon emitter contacts

This paper investigates the effects of an in-situ hydrogen bake and an ex-situ hydrofluoric acid (HF) etch prior to polysilicon deposition on the electrical characteristics of bipolar transistors fabricated with low thermal budget in-situ phosphorus-doped polysilicon emitter contacts. Emitter contact deposition in a UHV-compatible low pressure chemical vapor deposition (LPCVD) cluster tool is also compared with deposition in a LPCVD furnace. Transmission electron microscopy (TEM) and secondary ion mass spectroscopy (SIMS) are used to characterize the emitter contact material and the interface structure and a comparison is made with Gummel plots and emitter resistances on bipolar transistors. The SIMS results show that an in-situ hydrogen bake in a cluster tool gives an extremely low oxygen dose at the interface of 6.3/spl times/10/sup 13/ cm/sup -2/, compared with 7.7/spl times/ 10/sup 14/ and 2.9/spl times/10/sup 15/ cm/sup -2/ for an ex-situ HF etch and deposition in a cluster tool or a LPCVD furnace, respectively. TEM shows that the in-situ hydrogen bake results in single-crystal silicon with a high density of defects, including dislocations and twins. The ex-situ HF etch gives polycrystalline silicon for deposition in both a cluster tool and a LPCVD furnace. The single-crystal silicon emitter contact has an extremely low emitter resistance of 21 /spl Omega/./spl mu/m/sup 2/ in spite of the high defect density and the light emitter anneal of 30 s at 900/spl deg/C. This compares with emitter resistances of 151 and 260 /spl Omega/./spl mu/ m/sup 2/ for the polycrystalline silicon contacts produced using an ex-situ HF etch and deposition in a cluster tool or a LPCVD furnace, respectively. These values of emitter resistance correlate well with the interface oxygen doses and the structure of the interfacial oxide layer. The high defect density in the single-crystal silicon is considered to be due to the high concentration of phosphorus (>5/spl times/10/sup 19/ cm/sup -3/) in the as-deposited layers.

Low pressure chemical vapor deposition of silicon dioxide below 500 °C by the pyrolysis of diethylsilane in oxygen

Low pressure chemical vapor deposition (LPCVD) of SiO2 in a horizontal LPCVD furnace using liquid diethylsilane and oxygen has been studied. A temperature deposition window ranging from 425–500 °C was observed resulting in a maximum deposition rate of ∼275 Å/min. The pressure dependence of the deposition rate revealed a threshold of ≳950 mTorr for gas phase reactions at a deposition temperature of 450 °C. Analysis of the films by Rutherford backscattering spectroscopy has indicated that as-deposited films are stoichiometric SiO2 for deposition temperatures ≤450 °C. Best case across wafer uniformity was ±5% for a caged boat. Wet chemical and reactive ion etch rates were found to be comparable to those of thermal oxides after annealing. Cross-sectional scanning electron microscopy images of the SiO2 films deposited on 2 μm deep 1 μm wide silicon trenches revealed a conformality of ∼80%. The electrical properties of films deposited at 450 °C were studied. The electrical properties of the films were studied as-deposited and after annealing the films in a cold-wall rapid thermal annealing (RTA) system. RTAs were performed at temperatures ranging from 950 to 1100 °C in Ar, N2, or O2 ambients. Current–voltage, current–temperature, and capacitance–voltage measurements were performed for the electrical characterization. Catastrophic breakdown field measurements have shown electric field strengths of 9.5 MV/cm for as-deposited 500 Å films. A study of the leakage current conduction mechanisms has indicated that as-deposited films exhibit trap conduction mechanisms at high electric fields and temperatures. However, if deposition is followed by a RTA in Ar or O2, the leakage current follows closely the Fowler–Nordheim mechanism and yields a leakage-current electric field dependence comparable to a thermal oxide. Results have shown that values as low as 6 × 1010/cm2 for fixed charge density can be obtained if oxide deposition is followed by a RTA in Ar or N2.