Текст 3.5. Прочитайте текст и найдите ответы на поставленные вопросы:
1. What is submicron technology? 2. What is it based on? 3. Why is it not possible to use conventional optical methods to define the surface of an integrated circuit of small dimensions? 4. What are the conventional methods substituted by in submicron technology? 5. What are the advantages of submicron technology? 6. What impact will it have on production techniques? 7. Where can submicron technology be applied most effectively? 8. Does the new technology require any facility changes? Why?
Submicron Technology
Silicon is the workhorse for most integrated circuit devices. Silicon processing technologies continually change. A number of technological changes must be expected with the advent of electron beam mask-making, i.e. with the development of submicron technology to produce ultra-complex devices based upon dimensions which can no longer be fabricated with the use of visible or near visible light.
The need for submicron technology is based upon continuing pressures to improve microelectronic capabilities. The present optical methods are reaching their limits. The increasing sophistication pf electronics systems continually pushes the state-of-the-art of both memory and logic circuits. Improvements in cost, speed, density and power consumption are being sought.
Submicron technology refers to the fabrication of semiconductor devices with features having masked dimensions less than one micron. Normal IC technology uses mask dimensions of about five microns. By using electron beams, it is now possible to fabricate circuits with features less than one micron. Within the next few years submicron technology will become a major factor in the production of integrated circuits.
Because of the small dimensions required, it is no longer possible to use conventional optical methods to define the surface of an integrated circuit. Even optical inspection is limited because of the small dimensions. In place of light, X-rays and electron beams are used to pattern the surface of the semiconductor wafer.
In the same manner as the electron microscope provided superior resolution over the optical microscope, electron beam technology is about to impact the integrated circuit industry. The advantage of e-beam technology is that the wavelength of electrons is substantially less than the wavelength of light. E-beam technology is accompanied by the use of X-rays. X-rays have the advantage that they travel in a straight line. X-rays do not require vacuum as do electrons, which may simplify production techniques.
The use of submicron technology has the same effect as increasing the size of the silicon wafer. Since the devices are smaller, the number of devices per wafer is greater. Also, since the die sizes are smaller, the loss due to a die containing a material defect is smaller. The yield percentage increases. The net effect is more good dice per wafer. As is known, one of the basic measures of semiconductor performance is the number of good dice per wafer. Submicron technology can be used for standard IC design and processing. It can be applied to both MOS and bipolar integrated circuits including injection logic. This technology applies to very fast circuits and microwave structures.
The impact of submicron technology on the IC industry will be more significant than the impact of MOS on the semiconductor industry. A principal application impact of submicron technology will be in the areas of magnetic bubble and semiconductor memories. Although the first submicron production structures range about 64 kilobits, "million-bit chips" are possible. The super-LSI technology appears in new products where increased complexity can still be utilized. The one-chip medium-size computer quickly becomes a reality in conjunction with its one-chip memory or, alternately, a minicomputer will tend to have everything on one chip.
The utilization of submicron technology requires a completely new facility. All aspects of mask making, inspection, and other procedures are changed.
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Polysilicon has been the dominant interconnect material as it offered low threshold voltages and good stable coverage with uniform and economical deposition. Its high temperature characteristic aids in stability during annealing, after etching and implantation operations. Aluminum alloy films provide better control over electromigration and putting then pure aluminum and the improvement in evaporation and sputtering deposition processes give better control over the film's microstructure with better step coverage.
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3.19. Ответьте развернуто на следующие вопросы:
1. What is the physical nature of semiconductors? 2. How does semiconductor behave at lower than room temperatures? 3. Why is a crystal of pure silicon a poor conductor? 4. What is the difference between n-type silicon and p -type silicon? 5. What is the process of doping? 6. In what ways are the areas to be doped defined? 7. What are the main dopants? 8. What role do the holes play in the conduction process? 9. What particles are the carriers of electric current in a p -type semiconductor? 10. What is the simplest semiconductor device and how does it operate? 11. What technological processes are used in the fabrication of integrated circuits? 12. What is understood by the planar technology? 13. How are the problems of tighter control of impurity diffusion solved? 14. Which techniques are referred to as direct methods of film preparation and which of them as indirect? (Describe briefly each of the techniques used.) 15. What makes the automation of crystal growing equipment a necessity?
3.20. Обсудите традиционные технологические процессы и новые направления в технологии. При обсуждении используйте следующие выражения:
1. Processing a wafer is not a simple technological process; 2. Various methods are reviewed...; 3. It is pointed out that...; 4. Doping gives rise to...; 5.... have received increasing attention over the past years; 6. It is expected that this trend will continue...
3.21. Дайте определения следующих терминов. Опишите, что представляет собой:
1. insulator; 2. conductor; 3. semiconductor; 4. doping; 5. dopant; 6. hole; 7. deficiency; 8. a silicon wafer; 9. mask; 10. n -type semiconductor; 11. thermal oxidation; 12. deposition; 13. sputtering
