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Productivity and Quality Control Overview

In this chapter, we introduce the topic of production quality control in terms of yield and productivity issues, which are indispensable cost factors for LCD. At first, the historical evolution of productivity is discussed, followed by yield management and improvement. Finally, quality control systems are reviewed tracing back to the world’s first a‐Si TFT factory operated by Sharp in the 1980s. The authors’ first work on LCDs was in 1972 at Sharp. At that time, Sharp successfully started the world’s first LCD production in April 1973 for hand calculators and watches, and later for hand translators using 4‐ to 10‐digit segment type screens based on simple passive‐matrix LCD. That plant consists of simple clean booths that were far from the real cleanrooms available today. Then, the new “active‐matrix LCDs” technology burst onto the scene. Since the presentation by Le Comber, Dundee University, on a‐Si film in 1979 [1], many activities started aimed at utilizing a‐Si TFT arrays for LCD backplane. Sharp also participated in such development of active‐matrix using a‐Si TFT in a quite unqualified cleanroom. In 1983, Epson announced color TV using TFT‐LCDs [2], and many Japanese companies joined the industrialization of LCD color TVs using a‐Si TFT. Sharp completed a prototype 3.2‐inch a‐Si TFT LCD [3], followed by construction of a‐Si TFT LCD plant with the capacity of 50 k/month for 3‐inch diagonal screens and commercialization in May 1987. The initial mother glass size for those small‐size TV screens was settled at 320 mm × 300 mm owing to the substrate size capability of the photolithography exposure machine by Nikon. However, for the next target of a full page size display, it was obvious that the mother glass size should be much larger and ever since that time the remarkable plate glass size evolution commenced. The mother glass size expansion enabled reduction of the production cost, a critical barrier for the industry, with improvement in both productivity and production yield a first priority. Productivity had increased through glass size expansion as well as tact time reduction. In terms of the production yield, during the primitive stages in late 1980s most of equipment was transferred from IC industry and not dedicated to LCD production, lacking the full spectrum of instruments for inspection and quality check. Therefore, new knowledge and skills related to equipment, cleanroom structure, anti‐particle countermeasures, UPW (ultra‐pure water) preparation system, non‐stop power supply, and bulk/specialty gas supply system, were necessary throughout the LCD industry and high‐tech community. Since then, as more and more LCD plants were built, the quality control and yield improvement have been continuous challenges. 17