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

Abstract

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...

Deposition of silicon nitride film at room temperature using a SiH4-NH3-N2 plasma

“…Less than 3% of hydrogen content was reported. 5) This was also observed as SiN film was deposited by the electron cyclotron resonance (ECR) plasma 6) or ECR-enhanced magnetron sputtering. 7) Recently, the deposition of SiN films at room temperature was studied as a function of process parameters.…”

Final capping passivation layers for long-life microsensors in real fluids

“…Recently, major interest has been placed on the development of novel PECVD techniques for the deposition of high-density SiNx films at low temperature with reduced surface damages and controlled residual stress. As a result, the most effective methods to produce high-quality dielectric films at low temperatures (≤ 100°C) are the high-density plasma techniques such as electron cyclotron resonance plasma (ECR-CVD) [53][54][55][56] and inductively coupled plasma CVD (ICP-CVD) [57][58][59][60][61][62].…”

Adding functionality to microchips by wafer post-processing

“…Dielectrics with excellent insulating properties can be formed using chemical-vapor deposition (CVD) methods, like ECR-CVD [22,23], ICP-CVD or atomic layer deposition [24]. Metal oxides and perovskites are deposited using lowtemperature deposition techniques such as sputtering [25], metalorganic CVD [24], laser ablation [26] or atomic-layer deposition.…”