Silicon nitride thin films

If we restrict our attention to one set of chemical precursors (SiH4, NH3, N2), we have available more detailed data describing the quality of PECVD silicon nitride thin films as a function of the several operating parameters.3 Experiments were carried out in a parallel-plate reactor placed in a horizontal hot tube system where the wafer was placed on the grounded electrode. 

Lustig, N. Kanicki J. (1989). Gate dielectric and contact effects in hydrogenated amorphous silicon-silicon nitride thin-film transistors, J. Appl. Phys., Vol. 65, 3951-3957, ISSN 0003-6951... 

Silicon oxynitrides (SiOxNy) are thin films that are basically a mixture of silicon oxide and silicon nitride, produced in a CVD-process by adding nitrous oxide (N20) to the gases used for silicon nitride deposition. By changing the oxide-to-ni-tride ratio, the properties of these films can be modified towards improved thermal and moisture stability and lower stress compared to pure silicon oxide or silicon nitride thin films [32]. At low oxygen concentrations (0/(0+ N) <0.3), oxynitride layers have good diffusion barrier characteristics [33] and oxidation resistance. 

Bulk-micromachined membranes are usually formed from dielectric materials like silicon oxide or silicon nitride combined with additional materials for example, in pressure sensors, silicon is used to increase the membrane thickness to the required values and in thermal sensors, platinum or other metals are needed for the sensing elements. The overall stress state of the membranes has to be controlled well to prevent buckhng (under high compressive stress) or fracture (under high tensile stress). With proper processing control, silicon oxide and silicon nitride thin films meet this requirement, making them ideal candidates for membrane-type devices. 

A summary of frequently employed CVD systems for silicon nitride thin films is given in Table 5-10. 

Numerical thermo-mechanical studies have been performed to improve the robustness of the membrane, addressing buckling and stress concentration (Puigcorb6 et al., 2003). Thermo-mechanical reliability depends on the design and materials used. In general, the membranes made of dielectric materials deposited at a higher temperature (e.g. low-pressure chemical vapor deposition - LPCVD) are more robust. The membrane is usually formed of a stress-compensated stack of thin films of silicon nitride, silicon oxynitride and/or silicon oxide. A heater embedded in between LPCVD low-stress silicon nitride thin films has proven to be robust (Demarne et al.,... 

Ronning C., Banks A. D., McCarson B. L. et al.. Structure and electronic properties of boron nitride thin films containing silicon, J. Appl. Phys., 84 (1998) pp. 5046-5051. 

Hu YZ, Yang G-R, Chow TP, Gutmann RJ. Chemical-mechanical polishing of PECVD silicon nitride. Thin Solid Films 1996 290-291 453-455. 

Silicon oxides (SiOx) are the most widely used thin films in silicon microelectronic and micromechanical devices. Similar to silicon nitride (Section 5.5.4), these amorphous films exhibit dielectric properties. Silicon oxide is often utilized as part of a dielectric membrane, as a passivation or insulating layer, or as a sacrificial layer, which can be etched with hydrofluoric acid (HF)-containing etchants. Two different approaches to forming a silicon oxide thin film are... 

Davis, R.R (1994) Deposition and characterization of diamond, silicon carbide and gallium nitride thin films. /. Cryst. Growth, 137(1-2), 161-169. 

RBS has also been used to characterize palladium and tin catalysts on polyetherimide surfaces [229], titanium nitride thin films [230], silicon oxynitride films [231], and silicon nitride films [232]. and to study the laser mixing of Cu-Au -Cu and Cu - W - Cu thin alloy films on Si3N4 substrates [233], and the annealing behavior of GaAs after implantation with selenium [234]. 

Silicon Nitride Silicon Carbonitride Thin Films From Silazane Oligomers... 

The refractive index of silicon nitride and silicon carbonitride thin films deposited at various temperatures is shown in Fig. 9. The re active index of silicon nitride has been well characterized and is generally reported to be between 1.8 and 2.1 [18]. The scatter in the reported values is largely attributed to variations in film stoichiometry and methods of deposition. The presence of impurities such as hydrogen, oxygen and firee silicon in particular, may also account for some of the r orted divergences. The measured refractive index of silicon nitride increased with deposition temperature from 1.82 to 1.95. Minor fluctuations in the atomic ratio of Si—to—N, that can be seen from the AES analysis (Kg. 7) may be responsible for the observed dependence of the refractive index on the deposition temperature. The refractive index for silicon carbonitride similarly ranged from 1.68 to 1.94. 

The market for silicon nitride is fast growing, particularly in structural and chemical resistance applications and as a thin film in semiconductor devices.P 1... 

Interconnect. Three-dimensional structures require interconnections between the various levels. This is achieved by small, high aspect-ratio holes that provide electrical contact. These holes include the contact fills which connect the semiconductor silicon area of the device to the first-level metal, and the via holes which connect the first level metal to the second and subsequent metal levels (see Fig. 13.1). The interconnect presents a major fabrication challenge since these high-aspect holes, which may be as small as 0.25 im across, must be completely filled with a diffusion barrier material (such as CVD titanium nitride) and a conductor metal such as CVD tungsten. The ability to fill the interconnects is a major factor in selecting a thin-film deposition process. 

Thin films of electrical insulators are essential elements in the design and fabrication of electronic components. The most widely used insulator materials (dielectrics) are silicon oxide (Si02) and silicon nitride (Si3N4). These materials are extensively produced by CVD. 

Electrochemical experiments have been carried out on materials deposited by PVD on silicon microfabricated arrays of Au pad electrodes [Guerin et al., 2006a]. The substrate is made up of a square silicon wafer capped with silicon nitride (31.8 mm x 31.8 mm), which has an array of 100 individually addressable Au pad electrodes. These electrodes make up a square matrix on the wafer, which can be masked when placed in a PVD chamber, allowing deposition of thin films on the Au electrodes. Figure 16.3 is a schematic drawing of the configuration. Small electrical contact pads in Au for the individual addressing of electrodes (0.8 mm x 0.8 mm) are placed on the boundaries. 

J. Sun, N. Lindvall, M.T. Cole, K.B.K. Teo, A. Yurgens, Large-area uniform graphene-like thin films grown by chemical vapor deposition directly on silicon nitride, Applied Physics Letters, 98 (2011) 252107. 

A cross-sectional schematic of a monolithic gas sensor system featuring a microhotplate is shown in Fig. 2.2. Its fabrication relies on an industrial CMOS-process with subsequent micromachining steps. Diverse thin-film layers, which can be used for electrical insulation and passivation, are available in the CMOS-process. They are denoted dielectric layers and include several silicon-oxide layers such as the thermal field oxide, the contact oxide and the intermetal oxide as well as a silicon-nitride layer that serves as passivation. All these materials exhibit a characteristically low thermal conductivity, so that a membrane, which consists of only the dielectric layers, provides excellent thermal insulation between the bulk-silicon chip and a heated area. The heated area features a resistive heater, a temperature sensor, and the electrodes that contact the deposited sensitive metal oxide. An additional temperature sensor is integrated close to the circuitry on the bulk chip to monitor the overall chip temperature. The membrane is released by etching away the silicon underneath the dielectric layers. Depending on the micromachining procedure, it is possible to leave a silicon island underneath the heated area. Such an island can serve as a heat spreader and also mechanically stabihzes the membrane. The fabrication process will be explained in more detail in Chap 4. 

The rapid developments in the microelectronics industry over the last three decades have motivated extensive studies in thin-film semiconductor materials and their implementation in electronic and optoelectronic devices. Semiconductor devices are made by depositing thin single-crystal layers of semiconductor material on the surface of single-crystal substrates. For instance, a common method of manufacturing an MOS (metal-oxide semiconductor) transistor involves the steps of forming a silicon nitride film on a central portion of a P-type silicon substrate. When the film and substrate lattice parameters differ by more than a trivial amount (1 to 2%), the mismatch can be accommodated by elastic strain in the layer as it grows. This is the basis of strained layer heteroepitaxy. 

This approach allows the deposition of thin films at low temperatures. By comparison, polymer deposition generally requires very high temperatures. For instance, the chemical vapor deposition of silicon nitride requires a temperature of about 900°C, whereas the plasma chemical deposition requires a temperature of only 350°C. 

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