Low-stress and Long-term Stable a-SiNx:H Films Deposited by ICP-PECVD

AbstractBased on a systematic variation of the gas flow ratio of silane (SiH4) and nitrogen (N2), amorphous hydrogenated silicon nitride (a-SiNx:H) thin films are synthesized with an inductively coupled plasma enhanced chemical vapour deposition (ICP-PECVD) technique offering a low (< 50MPa) film stress in combination with a negligible drift behaviour. Most recently, two dominating regimes were identified, characterized by either high, but stable compressive stress or low stress, but with a strong drift behaviour. A rapid change in chemical composition at the transition point promotes the oxidation of the layer in the latter case causing the drift, and is confirmed by the corresponding change of the refractive index n, as well as FT-IR (Fourier-Transform Infrared Spectroscopy) and XPS (X-ray Photoelectron Spectroscopy) measurements

Fundamental properties of a-SiNx:H thin films deposited by ICP-PECVD for MEMS applications

In this study, the impact of deposition conditions on the properties of amorphous hydrogenated silicon nitride (a-SiNx:H) films using an inductively coupled plasma enhanced chemical vapor deposition technique (ICP-CVD) is evaluated. Due to the large number of experiments - even when taking only the most important synthesization parameters into account such as the total pressure in the deposition chamber, the substrate temperature, the ICP power and the flow rate ratio of N2/SiH4 - a design of experimentsbased approach is chosen. As expected, the deposition rate strongly depends on the ICP power and the N2/SiH4 flow rate ratio, respectively. Films in the field of investigation deposited with a high flow rate of N2 labeled as Type I show relatively low mechanical stress values between −50 and +200 MPa, but exhibit a strong drift behavior toward compressive stress. Layers deposited at low nitrogen flow rates (Type II), however, yield large compressive stress and are stable as a function of time. The wet etch rate in hydrofluoric acid shows a gap of over two orders of magnitude when comparing the two a-SiNx:H types, indicating strong differences in the chemical composition. Fourier-transform infrared measurements demonstrate that in Type I films the hydrogen is mainly bonded to nitrogen, in contrast to Type II films, where Si-H bonds dominate. Surface related X-ray photoelectron spectroscopy measurements show that Type II layers have higher relative silicon content, while depth profiles yield that the oxygen content Type I films is above 10 at.%. This high oxygen content is proposed to be the result of diffusion of H2O into the layer, causing oxidation, and, as a consequence, the drifting behavior of the intrinsic film stress

Mechanical and electrical properties of DC magnetron sputter deposited amorphous silicon nitride thin films

Amorphous silicon nitride SiNx thin films in a thickness range of 40 to 500 nmwere deposited onto (100) silicon wafers using DC magnetron sputtering. The biaxial stress of the films was found to be tuneable in the range of −1300 MPa (compressive) to almost 0 by varying the plasma power density and the back pressure in the deposition chamber. The films were close to stoichiometric composition with x ranging from 1.27 to 1.34. The refractive index n decreases from 2.10 to 1.97 with increasing back pressure, indicating compositional changes in the thin films. This finding, however,was not confirmed by Fourier-TransformInfrared Spectroscopymeasurements. On the other hand, lower wet chemical etch rates revealed a larger robustness of layers deposited at conditions where the mean kinetic energy of the sputtered particles is higher. Temperature dependent leakage current measurements using Au/Cr/SiNx/Si MIS (metal-insulator-semiconductor) structures between 25 and 300 °C have shown that ohmic and Poole-Frenkel conduction mechanisms dominate the leakage current behaviour at electrical fields ranging up to 0.5MV/cm. The extracted physical parameters such as the corresponding activation energies were found to be mildly affected by the deposition parameters.Amorphous silicon nitride SiNx thin films in a thickness range of 40 to 500 nmwere deposited onto (100) silicon wafers using DC magnetron sputtering. The biaxial stress of the films was found to be tuneable in the range of −1300 MPa (compressive) to almost 0 by varying the plasma power density and the back pressure in the deposition chamber. The films were close to stoichiometric composition with x ranging from 1.27 to 1.34. The refractive index n decreases from 2.10 to 1.97 with increasing back pressure, indicating compositional changes in the thin films. This finding, however,was not confirmed by Fourier-TransformInfrared Spectroscopymeasurements. On the other hand, lower wet chemical etch rates revealed a larger robustness of layers deposited at conditions where the mean kinetic energy of the sputtered particles is higher. Temperature dependent leakage current measurements using Au/Cr/SiNx/Si MIS (metal-insulator-semiconductor) structures between 25 and 300 °C have shown that ohmic and Poole-Frenkel conduction mechanisms dominate the leakage current behaviour at electrical fields ranging up to 0.5MV/cm. The extracted physical parameters such as the corresponding activation energies were found to be mildly affected by the deposition parameters

Impact of auxiliary capacitively coupled plasma on the properties of ICP-CVD deposited a-SiNx:H thin films

In this study, we report on the properties of amorphous hydrogenated silicon nitride (a-SiNx:H) thin films synthesized by inductively coupled plasma enhanced chemical vapour deposition (ICP-CVD), combined with an auxiliary capacitively coupled plasma excitation. Physical properties, such as the deposition rate, refractive index and film stress, as well as the chemical composition, microstructure and etch resistance of the samples were investigated. Depending on the capacitively coupled plasma power PRF, two regions can be distinguished which are dominated either by an increased generation of plasma radicals or by an enhanced ion bombardment. At PRF = 35 W, a maximum in the deposition rate is observed as well as an abrupt change in the chemical composition, resulting in an extremely high (>2.5 GPa) compressive stress, in comparison to the layers deposited with PRF = 0. In addition, the wet etch rate in hydrofluoric acid (HF) decreases substantially. Above, up to PRF = 150 W, ion bombardment of the growing film surface is more pronounced due to an increased self-bias of the substrate decreasing the effective deposition rate. Fourier-transform infrared spectroscopy measurements indicate that this behaviour is in close relation to the N-H bond density in the samples. Additionally, the continuous increase of the refractive index and Si-H bond density, accompanied by the redshift of the Si-N infrared absorption peak show that with higher PRF the Si content of the films increases

Mechanical and electrical properties of RF magnetron sputter deposited amorphous silicon-rich silicon nitride thin films

Amorphous silicon nitride thin films in a thickness range of 40 to 500 nmare deposited onto (100) siliconwafers using radio frequency magnetron sputter deposition. Analysis of variance techniques are used to determine which deposition parameter has a significant impact on the film properties. The biaxial stress of the layers is found to be compressive independent of the plasma chamber pressure levels and to increase with increasing plasma power. The chemical composition of the films is silicon-rich, resulting in an index of refraction (IOR) of 2.55 independent of deposition conditions. Both IOR and X-ray photoelectron spectroscopy measurements indicate a nitrogen to silicon ratio in the range of 0.71-0.85. The etch rates for HFwet chemical etching and for CF4:O2 reactive ion etching are found to be much higher compared to direct current sputter deposited silicon nitride films with only a weak dependency on the deposition conditions. Temperature dependent leakage current measurements using Au/Cr/SiNx/Si structures between 25 and 300 °C show two dominating leakage currentmechanisms: ohmic conduction dominates at lowapplied electric field values below0.1MV/cmand Poole-Frenkel type conduction above 0.3 MV/cm. The extracted electrical parameters such as the activation energy or the barrier height are found to be nearly unaffected by the deposition parameters.Amorphous silicon nitride thin films in a thickness range of 40 to 500 nmare deposited onto (100) siliconwafers using radio frequency magnetron sputter deposition. Analysis of variance techniques are used to determine which deposition parameter has a significant impact on the film properties. The biaxial stress of the layers is found to be compressive independent of the plasma chamber pressure levels and to increase with increasing plasma power. The chemical composition of the films is silicon-rich, resulting in an index of refraction (IOR) of 2.55 independent of deposition conditions. Both IOR and X-ray photoelectron spectroscopy measurements indicate a nitrogen to silicon ratio in the range of 0.71-0.85. The etch rates for HFwet chemical etching and for CF4:O2 reactive ion etching are found to be much higher compared to direct current sputter deposited silicon nitride films with only a weak dependency on the deposition conditions. Temperature dependent leakage current measurements using Au/Cr/SiNx/Si structures between 25 and 300 °C show two dominating leakage currentmechanisms: ohmic conduction dominates at lowapplied electric field values below0.1MV/cmand Poole-Frenkel type conduction above 0.3 MV/cm. The extracted electrical parameters such as the activation energy or the barrier height are found to be nearly unaffected by the deposition parameters

Human papillomavirus infections among Hungarian female sex workers

The purpose of this study was to assess the human papillomavirus (HPV) prevalence in cervical, oropharyngeal and anal samples of the high-risk population of Hungarian female sex workers (FSWs). HPV testing of swab specimens from FSWs (n = 34) using polymerase chain reaction (PCR) methodology was performed. Results were compared with control group (n = 52) matched for age. Questionnaires were used to obtain data regarding participants' sexual behaviour. Data were analysed using SPSS. HPV DNA was detected in at least one location in a great majority of FSWs (82.4%), compared with 46.2% of the general female population (P < 0.05). Both the cervical and the anal samples of sex workers showed higher infection rates than those of controls (64.7% vs. 34.6% and 50.0% vs. 15.4%, respectively, P < 0.05). High-risk HPV prevalence was also significantly higher in sex workers (55.9% vs. 25.0%, P < 0.05). A significantly higher proportion of FSWs had a history of genital warts (26.5% vs. 3.8%, P < 0.05). The results suggest that condom use may not result in adequate protection from HPV infection. The high infection rates among FSWs should be viewed as a priority group for HPV and cervical cancer prevention programmes since they are sources of HPV infection for the general population