D. V. Tsu

Deposition of silicon dioxide and silicon nitride by remote plasma enhanced chemical vapor deposition

We have developed a low temperature process for the deposition of thin films of silicon dioxide and silicon nitride. The process consists of four steps: (a) excitation of an oxygen or nitrogen‐containing molecule in an RF plasma; (b) transport of the excited oxygen or nitrogen species out of the plasma region; (c) mixing of the transported excited species with silane (or disilane) out of the plasma region to form precursor species; and (d) a CVD reaction at a heated substrate to form the desired thin film. We call this process remote plasma enhanced CVD (RPECVD). Silicon rich oxide films have been grown at substrate temperatures (Ts) between 100 and 350 °C using an excited O2/He mixture. Two different ‘‘silicon nitrides’’ have been deposited depending on the excited gas, NH3 or an N2/He mixture, and Ts. Using either nitrogen source and Ts greater than 450 °C, we obtain near stoichiometric films of Si3N4. On the other hand, films grown from NH3 and deposited with Ts of about 50 to 100 °C are silicon diimid...

Local bonding environments of Si–OH groups in SiO2 deposited by remote plasma‐enhanced chemical vapor deposition and incorporated by postdeposition exposure to water vapor

We have deposited thin films of SiO2 by remote plasma‐enhanced chemical vapor deposition and have identified similar infrared (IR) spectroscopic signatures of Si–OH groups incorporated during either film growth, or the cooling down process in the deposition chamber. These films can also be hygroscopic and, on postdeposition exposure to atmospheric water vapor, they show changes in the IR spectra associated with the incorporation of additional Si–OH groups. These changes are (i) the development of a new symmetric feature, centered at about 3350 cm−1, within the asymmetric O–H stretching band generated during growth and/or cooling down; (ii) the development of a new spectral feature at 925 cm−1; and (iii) a shift in the Si–O bond‐stretching band to higher wavenumber. We show that the first two changes in the IR spectra are due to near‐neighbor Si–OH bonding groups that result from the reaction between water vapor and the Si–O–Si bonds of the SiO2 host network. These spatially correlated Si–OH groups have di...

Remote plasma enhanced CVD deposition of silicon nitride and oxide for gate insulators in (In, Ga)As FET devices

We have deposited silicon nitride (Si3N4) and silicon oxide (SiO2) thin films using remote plasma enhanced chemical vapor deposition (RPECVD). We have characterized the chemical composition of the films by infrared absorption (IR), x‐ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), and Rutherford backscattering (RBS), and have studied the electrical properties in metal insulator semiconductor (MIS) device configurations. We have configured the deposition system and adjusted gas flow rates in order to minimize: (a) O contamination in the Si3N4 films; and (b) OH groups in the SiO2 films. This paper describes the deposition apparatus and the process, and presents a phenomenological model for the plasma phase and surface reactions involved. We have combined both types of insulators in a trilayer dielectric that has been used as a gate insulator for (In,Ga)As insulated gate field effect transistors (IGFET’s). We have found that the electrical properties of these devices are superior to ...

Atomic structure in SiO2 thin films deposited by remote plasma‐enhanced chemical vapor deposition

We have studied selected structure‐dependent properties of thin films of SiO2 prepared by remote plasma‐enhanced chemical vapor deposition (remote PECVD) and thermal oxidation of crystalline silicon, and have identified process‐dependent differences in their local atomic structures. We have determined the frequency ν and linewidth Δν of the Si–O bond‐stretching infrared‐active vibration near 1075 cm−1, and have found that all relatively thick oxide films, t>1000 A, prepared by either of these two techniques display the same linear relationship between Δν and ν. This behavior has been interpreted in terms of a central force model that gives the average bond angle 2θ at the oxygen atom sites, and attributes the linewidth to a distribution of vibration modes associated with a ±30° spread in 2θ. We have determined that (i) in remote PECVD films deposited at temperatures (Ts ) between 200 and 350 °C, 2θ varies between 140° and 144°; (ii) in thermal oxides grown over a temperature range (Tox ) between 800 and 1...

Optical emission and mass spectroscopic studies of the gas phase during the deposition of SiO2 and a‐Si:H by remote plasma‐enhanced chemical vapor deposition

This paper will present mass spectrometric and optical emission spectroscopic studies of the deposition process of amorphous hydrogenated silicon (a‐Si:H) and silicon dioxide (SiO2) by remote plasma‐enhanced chemical vapor deposition (remote PECVD). We have established that the silane reactant, which is not directly exposed to a rf plasma in either of the deposition processes, is not fragmented or chemically combined in the gas phase. Specifically there is no evidence for the formation of disilane, Si2H6, or siloxanes or silanols in the gas phase, as in the direct PECVD process. In the case of the a‐Si:H depositions, the silane is excited in the gas phase and the excited species, SiH*4 , is the deposition precursor. In the case of the SiO2 depositions, the active species promoting deposition is an O2 metastable neutral molecule. The by‐products of the respective reactions are H2 and H2O.

Evidence for the occurrence of subcutaneous oxidation during low temperature remote plasma enhanced deposition of silicon dioxide films

Chemical vapor deposition of SiO2 is often thought of as an innocuous process by which an insulating layer can be formed without affecting the underlying substrate. Here evidence is presented which indicates that a subcutaneous oxidation process takes place during remote plasma enhanced chemical vapor deposition of SiO2 which oxidizes a few monolayers of the underlying substrate. This oxidation process is evidenced most directly by electrical measurements on metal–insulator semiconductor (MIS) structures fabricated on Ge and GaAs materials. These MIS structures utilize a thin Si interlayer between the semiconductor and the SiO2 to form relatively low interface state density structures. Electrical measurements indicate that depositing SiO2 60 nm in thickness results in consumption of the 1 to 2 nm Si layer through oxidation. The performance of Si metal–oxide semiconductor structures fabricated using deposited oxides degrades as the thickness of the oxide is increased. The presence of a poor quality, highly...

Optical and electrical properties of a-Si:H films grown by remote plasma enhanced chemical vapor deposition (RPECVD)

Abstract We have deposited a-Si:H films by RPECVD (substrate temperatures, Ts = 38 to 400°C) and have studied the IR and optical absorbance, and other electrical and optical properties. The RPECVD films differ from glow discharge (GD) and sputtered films most notably in the Ts dependence of the hydrogen bonding environments (SiH, SiH2, etc.), and the photoconductivity. RPECVD films produced with Ts = 235°C have properties comparable to ‘device grade’ GD films.

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

Abstract 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.

Spectroscopic emission studies of O2/He and N2/He plasmas in remote plasma enhanced chemical vapor deposition

We have analyzed He, O2 /He, and N2 /He plasmas of the remote plasma enhanced chemical vapor deposition of a‐Si:H, silicon oxide, and nitride deposition by emission optical spectroscopy and by mass spectrometry. We have detected species such as atomic N and O as well as metastable He. These will be discussed relative to the deposition of silicon nitrides, oxides, and amorphous silicon.

Properties of intrinsic and doped a‐Si:H deposited by remote plasma enhanced chemical vapor deposition

We have grown films of a‐Si:H by remote plasma enhanced chemical vapor deposition (RPECVD) with substrate temperatures Ts between 38 and 400 °C and studied the infrared and optical absorbance (including sub‐band‐gap absorbance), and other photoelectronic properties. The RPECVD films differ from glow discharge (GD) and sputtered films, most notably in the Ts dependence of the hydrogen bonding environments (SiH, SiH2, etc.) and the photoconductivity. RPECVD films produced with Ts=235 °C are similar to ‘‘device grade’’ GD films. Based on the differences between these films, we construct a model for the RPECVD deposition process that includes SiH3 species as precursors to the growth of high‐quality films. We also present experimental evidence of the selectability of precursor formation in the RPECVD process.