D.J. Stephens

Fabrication and performance of thin film transistors, TFTs, incorporating doped μc-Si source and drain contacts, and boron-compensated μc-Si channel layers

PH 3 doped n + μc-Si, and lightly B 2 H 6 doped intrinsic μc-Si, iμc-Si, thin films have been integrated into bottom-gate TFTs. The use of n + μc-Si as a source/drain contact material in a-Si:H TFTs reduces the threshold voltage compared to n + a-Si:H contacts. The use of iμc-Si as the TFT channel material, combined with a post-deposition, back-channel exposure to atomic-H yielded low-temperature processed TFTs with effective channel mobilities of -6.5 cm 2 /V-s

Integrated processing of amorphous and microcrystalline Si thin film transistors by plasma-assisted chemical-vapor deposition

Abstract Thin film transistors (TFTs) have been fabricated in an ultra-high vacuum compatible integrated processing system with on-line surface analysis diagnostics - Auger electron spectroscopy (AES) and reflection high energy electron diffraction (RHEED). This paper deals with TFTs that include dual-layer oxide-nitride dielectrics, and either hydrogenated amorphous and/or microcrystalline Si thin films for the channel, and source and drain regions. The emphasis is on the integrated processing of bottom-gate device structures, and on the way the electrical performance of the TFTs are correlated with the properties of the dielectric and semiconducting films, their included internal interfaces and the external exposed surfaces.

In-situ Multilayer Film Growth Characterization by Brewster Angle Reflectance Differential Spectroscopy

Brewster Angle Reflectance Differential Spectroscopy (BARDS) has been proposed as an optical method for real-time characterization of the growth of thin films. BARDS is based on changes in the reflectivity, Rp, of parallel (p)-polarized light incident at, or near, the Brewster angle of the substrate material. Changes in R are sufficiently large to monitor layer growth, and to determine the thickness and the optical constants of the deposited film. In this paper we extend the method to multilayer film deposition. The derivative properties of R are correlated with differences in the optical constants of the two materials, and with the sharpness of their interface. We present spectra for SiO2/Si3N4/SiO2/Si, demonstrating some of these aspects of this new and effective approach to in-situ monitoring.

Low temperature plasma-assisted oxidation and thin-film deposition processes for forming device-quality SiO2/Si and composite dielectric-SiO2/Si heterostructures

In the high-temperature thermal oxidation of Si, the SiO2/Si interface is continuously regenerated as the bulk oxide grows. This paper describes an alternative low temperature, 200–300 °C, plasma-assisted process that optimizes electrical properties of SiO2/Si interfaces and bulk SiO2 layers by separately controlling interface formation and bulk oxide deposition. Composite dielectrics, oxide/nitride (ON) and oxide (ONO), have been fabricated by extending the low temperature plasma-assisted processes to include deposition of Si3N4 films. The electrical properties of SiO2/Si structures formed by the two-step, low temperature oxidation-deposition process are essentially the same as those of SiO2/Si structures formed by high temperature, 850–1050 °C, thermal oxidation. The electrical properties of devices incorporating ON and ONO composite dielectrics are degraded with respect to the SiO2/Si structures, but are similar to those of composite dielectrics formed by combinations of high temperature processing.

Quasi-Stoichiometric Silicon Nitride Thin Films Deposited by Remote Plasma-Enhanced Chemical-Vapor Deposition

Conditions for depositing quasi-stoichiometric silicon nitride films by low-temperature, remote plasma-enhanced chemical-vapor deposition, RPECVD, have been identified using on-line Auger electron spectroscopy, AES, and off-line optical and infrared, IR, spectroscopies. Quasi-stoichiometric films, by the definition propose in this paper, do not display spectroscopic evidence for Si-Si bonds, but contain bonded-H in Si-H and Si-NH arrangements. Incorporation of RPECVD nitrides into transistor devices has demonstrated that electrical performance is optimized when the films are quasi-stoichiometric with relatively low Si-NH concentrations.

Control of Process-Induced Defects in the Formation of Single and Multiple layer dielectric Structures for Si Semiconductor Devices

A low-temperature, 200–300°C, plasma-assisted oxidation-deposition process sequence has been developed for formation of SiO 2 /Si heterostructures. Adding a nitride layer to form an ON, or ONO composite dielectric, increases the density of trapping states, D it , at the SiO 2 /Si interface, unless the entire structure is subjected to a high-temperature rapid thermal anneal, e.g., 30 s at 900°C. By interrupting the nitride deposition, and using on-line Auger electron spectroscopy, AES, the increase in D it correlates with a migration of N-atoms to the SiO 2 /Si interface during the nitride deposition. There is no evidence for N-atom incorporation into the oxide layer itself. In contrast, for remote PECVD deposition of oxides onto nitrides, O-atoms react with the nitride, and form an oxy-nitride alloy interfacial region layer.