Remote PECVD Process Research Articles

High-Rate Rpecvd of a-Si:H Films by Means of a VHF Resonant Plasma Source

AbstractHigh deposition rate (up to 5 nm/s) a-Si:H films suitable for recrystallization were deposited using a λ/4 helical resonator source. Refractive index, Tauc-gap, photo- and dark conductivities were measured for film characterization. The metastable behaviour was characterized by the light- induced degradation of the photoconductivity. Hydrogen content and bonding configuration were analyzed by IR absorption and mass separated thermal effusion transients, film microstructure was studied by intentionally incorporating carbon and oxygen. Most of the hydrogen is located on internal surfaces in the otherwise dense material. Differences between the deposition from our highly excited plasma and the conventional remote PECVD process are discussed.

The preparation of microcrystalline silicon (μc-Si) thin films by remote plasma-enhanced chemical vapor deposition

We have used remote plasma-enhanced chemical vapor deposition (remote PECVD) to deposit both intrinsic and doped μc-Si thin films at temperatures between 100 and 400 °C. Two different deposition pathways have been studied: (i) plasma excitation of He/H2 mixtures with downstream injection of silane, SiH4, and the dopant gases phosphine, PH3 or diborane, B2H6; and (ii) plasma excitation of He, with downstream injection of SiH4 and H2, as well as the dopant gases. We have observed that the second pathway, (ii) readily promotes nucleation of μc-Si on a number of different substrate materials, including crystalline Si, fused silica, and silicon dioxide, SiO2, deposited by the remote PECVD process. The other pathway, with the H2 coexcited with He, frequency results in the deposition of a thin amorphous silicon transition region between the substrate and the μc-Si film, which then nucleates within the a-Si material, rather than at the substrate itself. The properties of μc-Si films deposited by remote PECVD have been characterized by Raman spectroscopy, transmission electron microscopy (TEM), dark conductivity, and photoconductivity.

Si-N Bonding at The SiO2/Si Interfaces During Deposition of SiO2 by the Remote Pecvd Process

Thin films of SiO2 were deposited on Si substrates by remote PECVD following an in-situ cleaning/surface passivation with atomic-H. Si-N bonds were found in the immediate vicinity of the SiO2/Si interface when nitrous oxide, N2O, was used as O-atom source gas in the remote PECVD process. Si-N bonds, as well as Si-surface roughening produced by H-atom etching, contribute to the formation of high densities of midgap trapping states, Dit ∼1011 cm−2 eV−1, at the SiO2/Si interface. Eliminating the H-atom processing step, and exposing the Si surface to plasma-generated O-atoms prior to the SiO2 deposition: i) eliminated Si-N bonding at the Si/SiO2 interface; ii) reduced midgap Dit to ∼ 1–3×1010 cm−2eV−1 iii) eliminated surface roughening; and iv) improved process latitude and reproducibility.

Si-N Bonding at the SiO2/Si Interfaces During Deposition of SiO2 by the Remote Pecvd Process

Thin films of SiO2 were deposited on Si substrates by remote PECVD following an in-situ cleaning/surface passivation with atomic-H. Si-N bonds were found in the immediate vicinity of the SiO2/Si interface when nitrous oxide, N2O, was used as O-atom source gas in the remote PECVD process. Si-N bonds, as well as Si-surface roughening produced by H-atom etching, contribute to the formation of high densities of midgap trapping states, Dit ∼1011 cm−2eV−1, at the SiO2/Si interface. Eliminating the H-atom processing step, and exposing the Si surface to plasma-generated O-atoms prior to the SiO2 deposition: i) eliminated Si-N bonding at the Si/SiO2 interface; ii) reduced midgap Dit to ∼1−3×1010 cm−2eV−1; iii) eliminated surface roughening; and iv) improved process latitude and reproducibility.

Deposition of Amorphous and Microcrystalline Si,C Alloy Thin Films by a Remote Plasma-Enhanced Chemical-Vapor Deposition Process

ABSTRACTWe have extended the remote PECVD process to the deposition of intrinsic and doped, amorphous and microcrystalline silicon, carbon alloy films, a-Si,C:H and μc-Si,C, respectively. The electrical and optical properties of a-Si,C:H deposited by remote PECVD are comparable to those of films deposited by the glow discharge or GD process. The degree of crystallinity in the μc-Si,C alloys, as determined from the relative intensities of crystalline and amorphous features in the Raman spectra, is lower than that of μc-Si films deposited under comparable deposition conditions. The Raman spectra indicate that the crystallites in the μc-Si,C alloys are Si, while the infrared measurements establish that the intervening amorphous component is an a-Si,C:H alloy.

Deposition of Heavily-Doped μc-Silicon Thin Films by Remote Plasma-Enhanced Chemical-Vapor Deposition Process (remote PECVD)

ABSTRACTWe have succeeded in depositing both activated n- and p-type μc-Si, by a low temperature, 250°C, remote PECVD process in which dopant gases (PH3 or B2H6)/Silane (SiH4) mixtures are injected downstream from the exit port of a He/H2 plasma. The room temperature conductivities and activation energies for the n- and p-type μc-Si are respectively, 40 S/cm with Eaa=0.018 eV, and 5 S/cm with Ea =0.040 eV. Doped μc-Si is obtained for PH3/SiH4 ratios up to 1%, and for B2H6/SiH4 ratios to 0.1%. For B2H6/SiH4 ratios < 0.1%, the deposited p-type material is doped a-Si rather than doped μc-Si. We have shown that these heavily doped μc-Si film are a viable candidate for the gate electrode in MOS devices. The application of these doped μc-Si films in p-i-n diode devices has also been studied.

Dependence of a-Sl:H/Si 3N 4 interface properties on the deposition sequence in amorphous silicon thin film transistor produced by remote PECVD process

Two different layer deposition sequences using Remote PECVD have been investigated by in- situ Auger Electron Spectroscopy and photoconductivity. The carrier lifetime at the interface depends on the specific dielectric and on the film deposition sequence. A field effect mobility of 0.74 cm 2/Vs is measured for the inverted staggered a-Si TFT formed at 238°C using a Si 3N 4 bottom gate dielectric.

Formation of thin film dielectrics by remote plasma-enhanced chemical-vapor deposition (remote PECVD)

This paper describes the low-temperature deposition of thin films of silicon oxides, nitrides and oxynitrides by remote PECVD. The remote PECVD process differs from conventional and direct PECVD process in two ways: (a) only a subset of the process reactants and/or diluents are directly plasma excited; and (b) thin film deposition takes place on a substrate that is outside of the plasma glow region. In order to: (a) restrict the multiplicity of reaction pathways, (b) control oxide and nitride stoichiometry; and (c) minimize bonded hydrogen incorporation, the silane reactant is never directly plasma excited. In the context of the remote PECVD process, we discuss: (a) multichamber systems with in-situ process diagnostics and in-situ surface analysis; (b) different deposition protocols; (c) reaction pathways; (d) process gas-substrate reactions; (e) chemical-bonding, and the optical and vibrational properties of the deposited thin films; (e) differences between remote PECVD and thermally grown silicon oxides; and (f) remote PECVD dielectrics in device structures.

Plasma enhanced chemical vapor deposition: Differences between direct and remote plasma excitation

Films of silicon oxide, nitride, and oxynitride produced by direct plasma enhanced chemical vapor deposition (DPECVD) and utilizing silane as one of the gas phase reactants generally contain up to ten times more bonded hydrogen than films produced by remote PECVD (RPECVD) and deposited at the same substrate temperature (Ts). We attribute this difference to the way silane is utilized in the deposition process chemistry. In DPECVD, silane is plasma excited along with other reactant gases, resulting in the formation of radicals and molecular fragments, e.g., SiH3 and SiH2, which at low temperatures (200–400 °C) serve as precursors for hydrogen incorporation, and in addition promote significant departures from insulator stoichiometry: SiO2−x, Si3N4−x, etc. In contrast, in the RPECVD process active oxygen and nitrogen species (and generally rare-gas diluents) are extracted from a remote plasma region and reacted with neutral silane to form precursor species with Si–O and Si–N bonding groups. These precursor molecules take part in chemical vapor deposition reactions in which hydrogen from SiH3 groups of the precursors is eliminated from the films through replacement reactions with excess active oxygen and nitrogen species.