Room temperature SiO 2 films deposited by multipolar ECR PECVD

et al. 2008

J. Electrochem. Soc.

As the semiconductor industry strives toward wafer postprocessing and three-dimensional integration, a demand has arisen for high-quality thin films deposited at temperatures below 400°C. In this work, we present SiO 2 films deposited at near room temperature, using a multipolar electron cyclotron resonance ͑ECR͒ plasma source, introducing the SiH 4 gas by using a highvelocity jet of silane diluted in helium. The electrical properties were studied under varying deposition parameters, such as gas flow rate, deposition pressure, and postdeposition and postmetallization annealing processes. At a low pressure, low SiH 4 flow and high helium flow, device-quality SiO 2 layers were obtained after a deposition combined with a 5 min postmetallization annealing at 400°C. These layers exhibited a refractive index of 1.46, an O/Si ratio of 2, an interface trap density in the order of 10 11 cm −2 eV −1 , an oxide charge density down to 10 10 cm −2 , and a breakdown field up to 11 MV/cm. They are thus suitable as a gate dielectric in a thin-film transistor.

Section: Methodsmentioning

confidence: 99%

Low-Temperature SiO[sub 2] Layers Deposited by Combination of ECR Plasma and Supersonic Silane/Helium Jet

Kovalgin

et al. 2008

J. Electrochem. Soc.

“…7͒, most likely due to higher oxygen concentration. Si 3 N 4 films exhibit critical fields of 4 MV/cm, 24 while SiO 2 has a higher critical field of around 6.5 MV/cm 25 due to different conduction mechanisms. Thus, the oxynitrides obtained at higher pressure exhibit larger critical fields, due to higher oxygen content ͑Fig.…”

Section: Resultsmentioning

confidence: 99%

Low Hydrogen Content Silicon Nitride Films Deposited at Room Temperature with an ECR Plasma Source

Wallinga

et al. 2004

J. Electrochem. Soc.

Silicon nitride layers with very low hydrogen content ͑less than 1 atomic percent͒ were deposited at near room temperature, from N 2 and SiH 4 , with a multipolar electron cyclotron resonance plasma. The influences of pressure and nitrogen flow rate on physical and electrical properties were studied in order to minimize the hydrogen and oxygen content in the layers. The optimized layers were characterized by a refractive index of 1.98, a dielectric constant of 7.2, and Si/N ratio values of 0.78. The layers exhibited very good dielectric strength, which was confirmed by large breakdown fields of 12 MV/cm, very high resistivities of 10 16 ⍀ cm, and maximum charges to breakdown values of 90 C/cm 2 . Increasing the deposition pressure and decreasing the N 2 flow improved the SiN/Si interface, due to increased oxygen incorporation. The dominant conduction mechanism in the layers was the PooleFrenkel effect. The critical field and the trap energy had similar dependencies on deposition pressure. Fowler-Nordheim tunneling occurred at high gate biases, for the layers deposited at the highest pressure of about 22 mTorr.Decreasing the temperature at which dielectrics are deposited without causing any deterioration of the dielectrics properties has become a priority in the thin film research area. Low-temperature deposition is needed, for example, for producing thin film transistors ͑TFTs͒ on ultrathin, plastic substrates that can withstand temperatures of up to 100°C. 1,2 Such flexible substrates may replace the glass screens in future displays due to several advantages, e.g., lower cost, lower power consumption, lower weight, and better flexibility.The standard gate dielectric nowadays for amorphous TFTs is silicon nitride (Si 3 N 4 ) deposited by radio-frequency plasma enhanced chemical vapor deposition ͑rf-PECVD͒. However, the processing temperature of rf-PECVD is 300°C, which is too high for flexible displays. Furthermore, these layers exhibit high hydrogen contents of up to 20 atomic percent ͑atom %͒ and low dielectric strength. In contrast, electron cyclotron resonance ͑ECR͒ PECVD Si 3 N 4 layers with good material and electrical properties have been successfully deposited in recent years, at much lower temperatures. 3-5 ECR plasma operates at a low pressure, has a low electron and ion energy, and a high degree of ionization. 6,7 Because of these soft and dense characteristics of the ECR plasma, 8 the deposition temperature can be lowered, while reducing the concentration of unwanted hydrogen bonds through ion bombardment.Although very good quality Si 3 N 4 films with good interfaces and high breakdown fields have been deposited at room temperature using divergent ECR plasma sources and distributed ECR plasma sources, 3,9,10 the level of hydrogen contamination could not be reduced below 5 atom %.A less known ECR discharge configuration, called multipolar ECR 11 has been shown to reduce the hydrogen content even more. This new technique has certain advantages such as a magnetic field parallel to the substrate, which mi...

“…8 Electronic pure nitrous oxide (N 2 O) and 2% silane (SiH 4 ) diluted in helium were used as the gas precursors. The base pressure in the reaction chamber was 3ϫ10 Ϫ6 Torr.…”

Section: Methodsmentioning

confidence: 99%

Conduction and trapping mechanisms in SiO2 films grown near room temperature by multipolar electron cyclotron resonance plasma enhanced chemical vapor deposition

Journal of Vacuum Science &Amp; Technology B: Microelectronics and Nanometer Structures Processing, Measurement, and Phenomena

Wallinga

et al. 2004

Silicon dioxide layers with stoichiometric composition and excellent electrical properties were deposited at a substrate temperature of 60 °C with an electron cyclotron resonance plasma source. This work is focused on determining the electrical conduction and trapping mechanisms of the deposited films. From the temperature dependence of current density–electric field characteristics, Fowler–Nordheim tunneling was found to be the dominant conduction mechanism in SiO2 films obtained with low silane flow and at low pressure. For layers deposited with higher silane flows and higher pressures, the current at low biases is highly dependent on temperature. Positive charge was measured at the Si/SiO2 interface during low electric stress, while electrons were trapped at the interface for electric fields higher than 7 MV/cm. Constant current stress measurements confirmed that low silane flow and low total pressure are suitable deposition conditions for obtaining a film comparable to thermally grown oxide from the reliability point of view.