Quang khắc (photolithography) - là tập hợp các quá trình quang hoá nhằm tạo ra các chi tiết trên bề mặt phiến silicon có kích thước và hình dạng giống như thiết kế. Để làm được điều này cần phải có những bộ mặt nạ (mask), chất cảm quang (photoresist) nguồn sáng UV và dung dịch hiện hình (developer). Mặt nạ thường là một tấm thuỷ tinh hữu cơ được phủ một màng crôm trên đó khắc hoạ những chi tiết phù hợp với thiết kế của cảm biến hoặc mạch tích hợp (IC). . | Bipolar Process The basic active devices in the bipolar process are the npn and pnp transistors. These names are descriptive since rhe devices are constructed with three layers of n- or p-type semiconductor material with the middle layer different from the other two. These layers can be fabricated either laterally or vertically. A simplified pictorial description of these transistors including the established symbols for the devices appears in Fig. . Several excellent references discuss the basic operation of the B 17 The modeling of the BIT is discussed in Chapter 3. As will be seen later the characteristics of the collector and emitter regions as well as their geometries are intentionally different and as such the designation of the collector and emitter contacts is not arbitrary. The convention that has been established for designating the collector and emitter contacts will be discussed in Chapter 3. convention npn or pnp FIGURE Bipolar transistors. 77 The components available in the bipolar process are 1. npn bipolar transistors. 2. pnp bipolar transistors. 3. Resistors. 4. Capacitors. 5. Diodes. 6. Zener diodes 7. Junction Field Effect Transistors JFETs not available in all bipolar processes. A familiarity with the process is crucial to utilizing this wide variety of components in the design of an integrated circuit. Unlike discrete component circuit design with these same devices whose characteristics can be specified over a wide range and which can be connected in any manner the basic characteristics of the devices available for bipolar integrated circuits are determined by the process and the range of practical values and parameters is severely limited. In addition the methods of interconnection are strictly limited the basic devices have characteristics that are quite temperature dependent and the passive component values arc typically somewhat dependent on the signal applied. In spite of these restrictions to be discussed later .
