Tham khảo tài liệu '21st century manufacturing episode 2 part 1', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 194 Semiconductor Manufacturing Chap. 5 im SiOj b Figure Simplified views of the oxidation equipment and process from Semiconductor Device Fundamentals by Pierret 1996. Reprinted by permission of Prentice-Hall Inc. Upper Saddle River NJ . However dry oxygen is again preferred for growing the gate oxide s SiO2 because it gives better Si to SiO2 interface properties. Rapid thermal oxidation RTO allows short time oxidation at suitably high temperatures Campbell 1996 . Creating Photomasks The CAD flies containing the desứed cừcuit patterns are transferred to a set of photographic plates or photomasks. To do this the CAD files are first fed into a pattern generator a computer controlled exposure machine. The generator uses flash exposure to transfer the IC pattern onto a light-sensitive plate known as the mask. This step is similar to photographic developing. The generator flashes onto the plate a large series of rectangles that correspond to the circuit diagram. The plate is covered in an emulsion photoresist material which deliberately breaks down under the exposure. Then once the exposed resist is sloughed off the plate is transparent just in those areas that correspond to the circuit. Photolithography Projecting the Mask Pattern onto the Wafer Many steps follow to transfer the pattern in each photomask to the wafer. Hie wafer surface is coated with light-sensitive photoresist material. Typically photoresist liquid is poured onto the center of the round wafer which is spun at 1 000 to 5 000 rpm in order to produce a uniform thin adhesion. The thickness of the film can be controlled by altering liquid viscosity and spinning speed. The photoresist is dried in a warm nitrogen or plain air oven. Photolithography is shown in Figures through . In the early days of IC manufacture contact and proximity printing were used Wolf and Tauber 1986 . In such methods the photomask was in contact with or very close to the wafer. Moro
