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Geological and environmental reference materials (RMs) play an important role in all fields of geochemical research, because they are necessary for calibration, quality control, method validation and to establish metrological traceability (Jochum and Enzweiler 2014). This annual bibliographic review gives an overview of articles in scientific journals in which analytical data of RMs and certified RMs (CRMs) were published in the year 2012. Bibliographic reviews have a long tradition in this Journal (since 1981), where Iwan Roelandts (1981–2000), Michel Valladon (2002–2006) and Klaus Peter Jochum and co-workers (since 2007) have undertaken the time-consuming literature research and the compilation of references.

The annual bibliographic review of GGR has a long tradition dating back to 1981, this being the thirty-second instalment to appear. The review contains references to articles from geochemical, geological, environmental and chemical journals in which data of reference materials (RMs) and certified RMs (CRMs) were published. The current definitions for a RM and a CRM are published in the ISO Guide 30 Amendment 1 (2008): A RM is a material, sufficiently homogeneous and stable with respect to one or more specified properties, which has been established to be fit for its intended use in a measurement process, and a CRM is a RM characterised by a metrologically valid procedure for one or more specified properties, accompanied by a certificate that provides the value of the specified property, its associated uncertainty, and a statement of metrological traceability. RMs and CRMs are necessary for quite different purposes, such as calibration, method validation, quality control and assurance, and to establish metrological traceability to measurements (Wiedenbeck et al. 2012).

This year’s review gives an overview of articles containing data for reference materials (RMs) of geological and environmental interest that were published in scientific journals in 2010. The bibliographic review in this journal has a long tradition: every year since 1979, it has identified key references from the geoanalytical literature and surveyed data on elements and isotopes published in the previous year.

The bibliographic review has a long tradition in“Geostandards Newsletter” and Geostandards andGeoanalytical Research(GGR). Successive reviewshave complied and classified articles from geochemi-cal, cosmochemical, environmental, analytical andgeological journals in which data for reference mate-rials (RMs) of geological and environmental interestwere published. As discussed in the bibliographicreview for 2006 (Jochum 2007) and in Jochum andNohl (2008), the number of geochemical publicationshas increased significantly during recent years. Thistrend continued in 2007. Figure 1 shows the numberof publications containing data for RMs, which havebeen published in the bibliographic reviews for theyears 2001-2007. The number increased slowly from220 to 340 in the five year period from 2001 to2005, then steeply to 540 in 2006 and 710 in 2007(data for 2006 in this figure were corrected becauseeighty-four papers were not considered in Jochum(2007)). The same trend can be observed for someselected RMs (Figure 1), such as the three well-knownUSGS RMs BCR-1, BCR-2 (the replacement for BCR-1)and BCR-2G (a glass made from BCR-2 and mainlyused for microanalytical purposes). Reasons for thisincrease are that the importance of RMs in analyticalwork has been recognised by geochemists (Goldsteinet al.2003, Jochum and Nohl 2008) and that geoa-nalytical laboratories are being confronted with newfields and applications, such as environmental andbiogeochemical research, “non-traditional stable iso-tope” systems and microanalysis.This review contains 710 papers from the publica-tion year 2007. Literature research was performed on

In all fields of geochemical and environmental sample analysis, reference materials play an increasingly important role. Although the provider of an analytical result must document the measurement process used to establish traceability links, most publications do not contain data of reference materials. Therefore, the focus of this paper is to clarify the role and use of reference materials and certified reference materials, to discuss the importance of reference materials for geoanalytical work and to present the GeoReM database for reference materials of geological and environmental interest. The GeoReM database contains published analytical data, compiled data and metadata for about 1800 geochemical and environmental reference materials, provides geoanalysts with details of those samples of particular relevance to applications. Preferred values and their uncertainties are also provided in this database. Although most of the GeoReM preferred values are not ISO compliant, they have a high level of confidence and are therefore useful for calibration purposes and quality control.

One of the crucial components in FET-based ICs is the thin dielectric layer which insulates the active portion of the device from the gate. Suitable silicon nitride layers are formed by thermal nitridation of Si, which due to the diffusion barrier effect is limited to a silicon nitride thickness less than 6 nm, and by plasma nitridation in dry NH3 up to a thickness of 20 nm [1], by ion implantation of nitrogen [2], plasma deposition, or nitridation of silicon oxide to form nitride oxide layers with a variable nitrogen content of up to 50 at%.

Silicon nitride is applied in integrated optics, for example, in coupling active and passive optical components, such as monolithically integrated devices, which convert electric signals into photons, and complementary ones, which convert photons into electric signals. Topics concerning optical materials, such as epitaxial growth of silicon nitride and its mechanism, were reported [1].

Semiconductor devices have to be stable and long-lasting. Electronically active parts of such devices are often thin surface layers with a thickness as low as 20 nm. p-n junctions that emerge at the surface are sensitive to mechanical damage, moisture, contamination, chemical attack, radiation, etc. Devices are protected or passivated by applying thin silicon nitride surface layers which become an integral part of the basic device and secure its specified function for a predetermined minimum period of time [1, 2]. Passivation prevents surface leakage, high diffusivity, and mobility of impurities, such as Na or K, and reduces localized near-surface states. For the determination of passivation effects, see for example [4]. The application of protective silicon nitride layers in special high-temperature processes is described in Chapter 7.1, p. 99. See also the introductory remarks of Chapter 4, p. 72.

There are two types of masks for manufacturing device structures by lithographic methods on substrates.

Silicon nitride is applied in monolithic, integrated, digital, and analog circuits composed of FETs, diodes, resistors, and thin-film capacitors on compound semiconductor substrates. Silicon nitride can be used as a mask for implanting Si to produce n-type layers and for implanting hydrogen to achieve isolation by generating radiation damage. It can also be used for encapsulating before annealing, providing recessed Mo-Au gates, and for passivation [1,2]. ICs on GaAs with a high degree of integration are fabricated by the same technique by preparing patterned multilayers consisting of a silicon nitride layer sandwiched with a silicon oxide and a PSG layer prior to annealing and preparing contacts and gate contacts [3]. Highspeed, ion-implanted GaAs ICs are annealed using a silicon nitride oxide layer for encapsulation. The silicon nitride oxide layer is deposited in a mixture of SiH4, NH3, and 02 at 923 K. The subsequent annealing is performed at 1073 K [4]. Alternatively, GaAs specimens are coated with a silicon nitride oxide layer, patterned, implanted with silicon ions, encapsulated with a silicon nitride layer, and annealed to prepare high-speed GaAs ICs [5].

The read-only memories (ROMs) are ICs where stored information is expected not to be changed during operation. Such memories have breakdown voltages much higher than the normal operating voltages. This offers the possibility to program finished ROMs after installing them in the equipment as needed applying higher voltages. Sub-classes of the general family of programmable memories, the PROMs, are the nonvolatile, electrically programmable, and UV-light erasable ROMs (EPROMs), the electrically programmable and electrically erasable ROMs (EEPROMs), to which also the so-called floating gate avalanche injection MOS (FAMOS) and electrically alterable ROMs (EAROMs) can be added.

Semiconductor devices, which utilize the interaction between photons and semiconductors, are applied as photosensors for various ranges of photon energy, photovoltaic cells, sensors in electrophotography, image sensors, etc. For CCD devices cf. Chapter 14, p. 201; for photovoltaic (solar) cells cf. Chapter 32, p. 321.

General. Patterned silicon nitride layers are used as masks for growing epitaxial compound semiconductor layers, as masks for doping by diffusion or ion implantation, and as protective dielectric layers in fabricating LEDs.

Semiconductor substrates or devices are encapsulated with high temperature-resistant silicon nitride films to protect them against damage caused by high-temperature processes. These include diffusion, electrical activation of implanted dopants, and annealing of radiation damage caused by ion implantation. Silicon nitride encapsulation prevents the decomposition of a semiconductor substrate and the diffusion or evaporation of species at elevated process temperatures. The major application of silicon nitride films as an encapsulant involves compound semiconductors and, to a minor extent, element semiconductors.

In insulating silicon nitride films, the dielectrical properties of silicon nitride are of primary importance, whereas in encapsulating and passivating silicon nitride films, the chemical barrier properties are utilized. Of course, the same film can serve more than one application. Some work on insulating silicon nitride films that is not directly related to a particular device is presented in this chapter.

Capacitors can be used for charge storage, for example, in one-transistor/one-capacitor dynamic memory cells of ICs. Silicon nitride is used as a dielectric to separate the two electrodes of the capacitor, one of them usually being the semiconductor substrate, the second one a top layer of a conductive material. Silicon nitride masks are also used to define the capacitor area during device processing

The problem to grow natural, insulating oxides with good properties on compound semiconductors such as GaAs does not favor the fabrication and application of bipolar devices and even less of MIS devices. Therefore, silicon nitride plays an important role as a masking material for diffusion, implantation, and as dielectric in the manufacture of compound semiconductor devices.

Silicon nitride is widely known for its application in integrated circuit technology as encapsulation material, as interlevel insulator for multilevel metallization, as gate dielectric for field effect transistors including memory devices, as a mask for oxidation, diffusion or ion implantation, for selective etching, and as a capping layer for compound semiconductors. Most of these applications are due to the fact that silicon nitride is an excellent diffusion barrier and a gettering and passivating agent regardless how the films are prepared, whether by atmospheric pressure (APCVD), low pressure (LPCVD), or plasma-enhanced (PECVD) chemical vapor deposition, by sputtering, or by electron-beam evaporation, only to mention a few preparation techniques [1 to 3]. PECVD silicon nitride, in the literature often also just named “plasma” silicon nitride, is in many cases just labeled “pd(PD)” silicon nitride throughout this Chapter 32.

Silicon nitride is used in the manufacture of bipolar devices, such as diodes, transistors, power transistors, and thyristors, mainly as an auxiliary means, e.g., as masking material in the different processing steps. As a basic functional constituent, silicon nitride is less used in bipolar device technology than in MISFET technology.

Devices, transistors, and ICs fabricated in thin surface layers of semiconductor wafers can have parasitic leakage currents into the bulk of the semiconductor substrate. These effects can be eliminated if the devices in thin semiconductor films are manufactured on insulating substrates, such as sapphire (SOS), spinel, or more generally on insulators (SOI), such as silicon nitride.

The principle applications of thin silicon nitride layers are for gate dielectrics and processing masks in field effect devices, such as MESFETs, JFETs, IGFETs, MISFETs, and subfamilies, such as MOSFETs, MNSFETs, MNOSFETs, etc., of which ICs are composed. The use of silicon nitride in MIS, MNS, and MNOS devices is reviewed in [1 to 3].

Charge-coupled devices (CCD) are applied to integrate circuits for signal processing, optical imaging, and computer memory. The device consists of an input element for injecting a controlled charge into the main part, an array of MIS capacitors used in the dynamic operation mode, and a sensor device registering the charge arriving at the end of the array. Charge losses must be minimized. This imposes severe requirements on the quality of the gate insulator.

Integrated circuits (ICs) based on bipolar devices may be faster than ICs based on field effect devices. However, bipolar circuits exhibit some restrictions in obtaining high integration densities due to isolation problems, parasitic capacitances, and high power consumption. Inactive regions are much larger than the active ones.

Monolithic device elements and devices have to be well-isolated from each other to avoid performance-limiting interactions or cross talk. Unwanted interactions due to electric contact or carrier tunneling are prevented by dielectric layers of silicon nitride which are thick enough to insulate. Grooves, which separate device components and devices, are etched into the silicon nitride or silicon nitride/silicon oxide layers and into the substrate. Bird’s beak has to be suppressed to obtain high integration density. The finished devices have to have a smooth surface to avoid interconnection problems.

Silicon nitride is applied in the field of high-temperature superconductors as a buffer layer between the substrate and a superconducting film, as encapsulant during annealing, and as a top layer mainly for passivating against humidity and to obtain longterm stability.

Point defects and certain types of impurities cause leakage currents and reduce the carrier lifetime. They are observed as secondary effects in high-temperature diffusion and oxidation processes. These defects and impurities can be gettered or trapped in lattice damage sites acting as sinks, thus avoiding deleterious device degradation. Gettering is performed at elevated temperatures.

Patterned or unpatterned silicon nitride films are used as masks in structured or unstructured, epitaxial or amorphous growth of semiconductor layers on single-crystal or amorphous substrates. The silicon nitride mask is stable compared to the conventionally used silicon oxide mask. Amorphous silicon nitride films are a constituent element of superlattice structures which are base materials for novel devices.

The field of sensors provides special applications for silicon nitride. Sensors are used, e.g., to monitor parameters, specifically in biochemistry and medicine, controlling processes and process conditions, and ensuring safety in manufacturing. In the following, they will be grouped into particle-sensitive or “chemical” sensors and nonparticle-sensitive or “physical” sensors.

There are applications of silicon nitride which were not covered in the preceding chapters. Some of those will be briefly mentioned here. Others to be touched upon serve to indicate the diversity of applications for silicon nitride films.

This chapter gives the results on miscellaneous magnetic materials as their fabrication involves application of silicon nitride.