Semiconductor devices are used in a large number of electronic devices, such as computers, cell phones, and others. Semiconductor devices comprise integrated circuits that are formed on semiconductor wafers by depositing many types of thin films of material over the semiconductor wafers, and patterning the thin films of material to form the integrated circuits. Integrated circuits include field-effect transistors (FETs) such as metal oxide semiconductor (MOS) transistors.
One of the goals of the semiconductor industry is to continue shrinking the size and increasing the speed of individual FETs. To achieve these goals, fin FETs (FinFETs) or multiple gate transistors will be used in sub 32 nm transistor nodes. For example, FinFETs not only improve areal density but also improve gate control of the channel.
Bipolar junction transistors (BJTs) and FETs require different structures and hence typically are fabricated using different fabrication processes. Merely adding a BJT process sequence to an FET process sequence results in an increase in the number of process steps, many of which are redundant. Further, if some of the BJT processes are different from the FET processes, they require separate development, thus increasing the process cost. Generally, in IC fabrication, it is desirable to reduce the total number of processing steps and use existing processes to avoid independent process development. Hence, to reduce costs, BJTs and FETs may be fabricated using a common process. However, such fabrication introduces a number of process and design challenges, especially with introduction of FinFET devices.
Another goal of the semiconductor industry is to protect electronic devices and systems from electrostatic discharge (ESD), which is one of the main factors of electrical overstress (EOS). If EOS due to ESD occurs, unprotected integrated circuits (ICs) in electronic devices and systems may be permanently damaged. Any damage to the ICs in the electronic devices or systems may lead to abnormal operation of electronic products. Accordingly, a number of methods have been developed to protect semiconductor IC devices against possible ESD damage.