Rudolf Hezel

Silicon Nitride in Magnetic Devices

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

Silicon Nitride Application as Masks

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

Specific Applications of Silicon Nitride Films

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.

Read-Only Memories (ROMs)

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.

Silicon Nitride in Compound Semiconductor Field Effect Transistors

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 as Mask and Dielectric in Field Effect Devices

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].

Silicon Nitride in Sensors

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.

Preparation and Patterning of Silicon Nitride Layers and Films

The chemistry of preparing silicon nitride and the techniques to fabricate thin layers of silicon nitride in general are covered in detail in “Silicon” Suppl. Vol. B 5a. Preparation techniques relevant to general applications of silicon nitride in microelectronics are treated briefly in Chapter 2.1, p. 5; those relevant to specific devices are included in the respective chapters of this volume.

Application of Silicon Nitride for Solar Cells

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 in Bipolar Devices (Diodes, Transistors and Thyristors)

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.