S.S. He

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

Control of bonded-hydrogen in plasma-deposited silicon nitrides: Combined plasma-assisted deposition and rapid thermal annealing for the formation of device-quality nitride layers for applications in multilayer dielectrics☆

Abstract This paper discusses silicon nitride layers for applications in silicon device technologies, and in particular deposited nitride films for gate multi-layer dielectrics for (i) amorphous and microcrystalline silicon (a-Si and μc-Si, respectively) thin film transistors (TFTs), and (ii) crystalline silicon (c-Si) MOS capacitors and field effect transistors (FETs). A low temperature (300°C) remote plasma-enchanced chemical-vapor deposition process was used to form the silicon nitride films. A materials issue impacting on the targeted applications is the stability of bonded-hydrogen atoms in SiH and SiNH bonding groups at the respective TFT and FET processing temperatures.

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.

A Low Temperature Plasma-Assisted Deposition Process for Microcrystalline Thin Film Transistors, TFTS

The drive-current of low-temperature (∼300°C) deposited TFTs has been increased by replacing the a-Si:H channel, and source and drain materials with μc-Si. Lightly B 2 H 6 doped, near-intrinsic μc-Si has been used as the channel layer of the TFTs, and n+ μc-Si was used for the source and drain contacts. The compensation of intrinsic defects in the undoped μc-Si by boron doping increases the dark conductivity activation energy from ∼0.35 eV to 0.8 eV. TFIs were fabricated in a bottom gate structure, and required an H 2 plasma treatment to produce devices with effective channel mobilities of ∼6.8 cm 2 /V-s and threshold voltages of ∼3.7 V in the saturation region.

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.

Nitrogen: Not a Dopant in Crystalline Si (C-Si), But an N-Type Dopant in A-Si:H, Why?

We have incorporated N-atoms into hydrogenated amorphous silicon in the Si-rich alloy regime to ∼12 at.% N, and have observed a transition from n-type doping to alloying as the concentration of N-atoms is increased above about 5 at.%. By analogy with the local bonding arrangements of P-donors in n-doped a-Si:H, we attribute the doping to four-fold coordinated N-atoms with second neighbor H-atoms as in N + -Si-H linkages. The occurrence of these arrangements is supported by (i) IR studies which indicate a non-statistical association of N and H-atoms bonded to the same Si-atom, and (ii) a chemical bonding model in which the large effective electronegativies of four-fold coordinated N + atoms and neutral O-atoms promote similar bonding properties with respect to their nearest-neighbor arrangements with Si and H atoms such as N + (O) -Si-H linkages

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.

Microstructure of Si Films Deposited on Si(100) Surfaces by Remote Plasma-Enhanced Chemicalvapor Deposition, Rpecvd: Dependence on Process Pressure and Substrate Temperature

The microstructure of Si thin films, deposited on in-situ cleaned Si(100) surfaces by remote plasma-enhanced chemical-vapor deposition (RPECVD), is dependent on the process pressure, substrate temperature and H 2 flow rate. Surface characterization by on-line low energy electron diffraction, LEED, has been used to detect changes in the character of the deposited films which can either be amorphous, microcrystalline or crystalline, hereafter designated as a-Si, Sμc-Si, and c-Si, respectively. We have used these results to generate phase diagrams for the Si microstructure as a function of the process pressure and substrate temperature, including the flow rate of H 2 as an additional deposition parameter.

Minority Carrier Diffusion Lengths And Photoconductivity In a-Si,N:H Deposited By Remote Pecvd

We have deposited films of a-Si,N:H by remote PECVD from N 2 and SiH 4 for N-concentrations, [N], to about 12 atomic percent (at. %). Bonded-H concentrations were ∼7–10 at. %, Mostly in Si-H groups. The films with [N] = 9–12 at. % have eθ4 bandgaps of ∼2.0 to 2.2 eV, which makes them potentially useful as wide bandgap photo-active materials in tandem PV cells. Several properties are of special interest for PV applications. First, like many other a-Si:H-based alloys, the photoconductivity relative to a-Si:H is degraded by alloying, but less than for a-Si,C:H alloys with the same bandgaps. Second, the ambipolar diffusion lengths (Ld) obtained with the Steady State Photocarrier Grating (SSPG) technique for films with [N] = 10 at. % and eθ4 = 2.1eV, are comparable to those of a-Si:H. For lightly-nitrided films to [N] ∼5 at. %, Ld first decreases with respect to a-Si:H and then increases as [N] increases from ∼7 at.% to 10–12 at. %. These trends follow the dark conductivity activation energy, E a , which initially drops due to doping, and then increases into an alloy regime for [N] > 5 at. %. Films with [N1=10 at. % have dark conductivities and E a s comparable to those of undoped a-Si:H. Third the magnitude of the Staebler-Wronski effect, as monitored by the photo- to dark conductivity ratio after a 1000 Minute lightsoak, was about the same as in a-Si:H. Finally, we contrast the properties of these films prepared from N 2 with a-Si,N:H alloys with the same [N] and E 04 , but prepared from an ammonia N-atom source gas and attribute differences in their photoelectronic behavior such as a significantly enhanced Staebler-Wronski effect.to the presence of Si-NH bonding arrangements in the films grown from NH 3 .