Growth Mechanism of Silicon Plasma Anodic Nitridation

Abstract

Nitridation of silicon was performed in a temperature range of 680~176 by 13.56 MHz RF oscillation in nitrogenhydrogen plasma. Growth kinetics and activation energy of nitridation were investigated. The relationship between nitridation time (t) and nitrided film thickness (xn) was found to be xn (2 -0.00695Vd~) = 0.86 x 10-% External dc voltage (V~D on plasma nitridation was effective in obtaining a high growth rate of nitrided film on silicon. Activation energy for the plasma anodic nitridation of silicon (0.25 eV) was twice as large as the value of plasma nitridation without an external dc voltage. The role of hydrogen in plasma nitridation was also studied with quadrupole mass spectroscopy. Progress in MOSVLSI densification requires a large capacitance in a small capacitor area (I). Therefore, the direct nitridation of silicon may be one of the most attractive techniques for the device fabrication process. Compared with the widely used silicon dioxide film, silicon nitride film has a higher dielectric constant. The silicon nitride film is chemically stable and is also much better as a diffusion barrier for impurities and metals. In spite of these advantages, the silicon nitride film deposited on silicon wafers by LPCVD cannot be used for the gate dielectric film of MOSFET because it was interfacial instabilities between the silicon nitride and the silicon substrafe. Many attempts at achieving direct nitridation and forming the silicon nitride film have already been made (2, 3). Ito et aL reported that uniform amorphous silicon nitride films could be obtained from the reaction of silicon in an ammonia ambient and applied to the LSI device fabrication (4). However, these films were very thin because of the slow diffusion of nitridant species through the nitrided film. To improve the low growth rate, plasma nitridation and plasma anodic nitridation were attempted. A high reaction rate was given by the plasmaexited reactive species compared with the thermal reaction. Plasma anodic nitridation was expected to give an enhanced growth rate, similar to that in the case of the anodic oxidation of silicon (5). Also, the reaction temperature could be decreased below the temperature of the thermodynamical limit beause the plasma reaction forms reactive species.In this paper, the growth mechanism of plasma anodic nitridation will be investigated. To prevent the contamination of oxygen and hydro-oxygen, we used highly purified hydrogen and nitrogen for our experiment. ExperimentalThe vacuum system, gas sources, and experimental arrangements for achieving the plasma anodic nitridation of silicon are shown in Fig. i. They are the same as those used in the earlier study (6). Nitrogen plasma was generated at a pressure range from 0.5 to 2.0 torr by an RF oscillator whose frequency was 13.56 MHz. Anodization voltage applied between the anode and the ground level was supplied by an external dc supply. The nitridation experiments were performed in a temperature range from 680 ~ to 920~ Boron-doped n-type (100)-oriented CZ silicon ...

Plasma-assisted oxidation, anodization, and nitridation of silicon

“…The growth rate obeyed a parabolic rate expression, with an effective activation energy, when an anodizing voltage of -150 V was applied to the substrate electrode, of 0.25 eV [76]. The presence of hydrogen appeared to enhance the diffusion or drift of nitrogen species [76]. MBDF for as-grown nitride layers was ~3 MV/cm [75],…”

“…For instance, an ~50-nm film was grown using an Ar plasma with small (2-8%) additions of N,, NHj, or N,/H, in an rf (400-kHz) induction system at a pressure of 80 mTorr and temperatures below 850°C [73]. With capacitively coupled systems at 13.56 MHz, the silicon wafer in contact with the rf-driven electrode, 950°C, and a pressure of 1 Torr, an NH, plasma grew 5.5 nm in one hour [74], while an N,/H, plasma at 900°C and the same conditions grew 9 nm in one hour [75,76]. Direct comparison of the results of these studies is difficult, since the potentials in the capacitively coupled systems were clearly different.…”

“…Direct comparison of the results of these studies is difficult, since the potentials in the capacitively coupled systems were clearly different. All films had oxygen contamination ranging from -2% [74] to 10-15% [73,75,76]; the origin of the oxygen was presumed to be reactor leaks and native oxide layers. By analogy with silicon anodization, the nitridation mechanism was believed to be the incorporation of nitrogen species into the growing nitride surface, followed by diffusion of the nitrogen species (probably charged as well as uncharged) to the Si/SiN^ interface [74][75][76].…”

“…All films had oxygen contamination ranging from -2% [74] to 10-15% [73,75,76]; the origin of the oxygen was presumed to be reactor leaks and native oxide layers. By analogy with silicon anodization, the nitridation mechanism was believed to be the incorporation of nitrogen species into the growing nitride surface, followed by diffusion of the nitrogen species (probably charged as well as uncharged) to the Si/SiN^ interface [74][75][76]. The growth rate obeyed a parabolic rate expression, with an effective activation energy, when an anodizing voltage of -150 V was applied to the substrate electrode, of 0.25 eV [76].…”

“…By analogy with silicon anodization, the nitridation mechanism was believed to be the incorporation of nitrogen species into the growing nitride surface, followed by diffusion of the nitrogen species (probably charged as well as uncharged) to the Si/SiN^ interface [74][75][76]. The growth rate obeyed a parabolic rate expression, with an effective activation energy, when an anodizing voltage of -150 V was applied to the substrate electrode, of 0.25 eV [76]. The presence of hydrogen appeared to enhance the diffusion or drift of nitrogen species [76].…”