High Pressure Oxidation of Silicon

Silicon oxidation has been a fundamental process of silicon device technology for a long time. However, an understanding of oxidation methods and the phenomena involved is far from com­plete. An oxidation method that has received increased attention over the last few years is a high pressure oxidation method. This method is known to offer a practical means for thermally growing silicon oxides at lower temperatures and faster rates than those grown in conventional wet (влажный) oxidation. Presently, efforts to implement low temperature processes have become a sig­nificant driving force in the evolution of silicon device fabrication technology. The lower temperature aspect of high pressure oxida­tion has its greatest potential impact in the high density world of submicron VLSI where improvements in process control preci­sion will have a significant effect on performance and yield.

Thin oxide film grown at low temperature by high pressure oxidation has excellent dielectric breakdown strength.

Developments in high pressure oxidation will become more important with progress in other low temperature processes such as ion implantation, laser annealing, and plasma enhanced tech­nology during the next few years.

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Optical lithography has indisputably been the leading in­tegrated circuit pattern defining technique for many years. It is es­sentially two steps. First, the design and fabrication of the optical mask, which is both costly and time consuming, and secondly, the exposure of the wafer, covered with a layer of light sensitive pho­toresist, to ultraviolet light shone through the mask. The method is ideal for large scale production because once the expensive mask-making process has been carried out, an unlimited number of wafers may be patterned at very low cost to the producer. On the other hand, where specific or semicustom (полузаказные) ICs are concerned this process has proved unacceptable since the cost and time involved in mask fabrication cannot be justified by the production of only a few devices which may require several it­erations for optimum results. For these reasons, electron beam direct-write lithography is proving invaluable in the field of applica­tion specific or semicustom integrated circuits. This technique al­lows fast turnaround, a high flexibility and comparatively low cost for very small batches. In addition, the short wavelength of elec­tron-beam offers very high resolution patterning and so may be essential where sub-micron features are required. Despite the possibility of low throughput, e-beam generated patterns allow either simple wafer-scale integration or devices for several cus­tomers, each possibly with a variety of trial designs to be imple­mented on a single wafer. The major advantage of the e-beam's high resolution capability will be nullified if the resist pattern can­not be very precisely reproduced onto the metallization layer. For this reason wet-etching of the metal with its inherent undercutting is particularly unsuitable and plasma-processing becomes neces­sary. Reactive ion etching is a type of plasma etching where the wafer is placed on an electrode which is capacitively coupled to an RF generator. A second electrode larger than this driven one is grounded and a plasma is generated by electronic excitation of a low pressure gas contained between them. The arrangement of the system is such that the driven electrode experiences a negative bias with respect to the plasma causing positive ions to be acceler­ated towards the wafer. This means that not only is there chemical reaction causing removal of the metallization but also ion-en­hanced chemical etching and physical sputtering to the vertical etching essential for precise replication of the resist pattern. Dry processing has the added benefits of easily handled process mate­rials, easy automation and good reproducibility.

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Molecular electronics is a new concept of electronic systems. Basically it seeks to integrate into a solid block of the material the functions performed by electronic circuits or even whole systems. Its goal is to rearrange the internal physical properties of the solid in such a way that phenomena occurring within or between do­mains of molecules will perform a function ordinarily achieved through the use of an assembly of electronic components.

Molecular electronics is the most forward-looking of several modern approaches to the development of small, reliable, efficient electronic systems. Almost all attempt to perform the required electronic functions in solid semiconductor-type materials. Molecular electronics, however, is unique in its goal of doing away with the traditional concept of circuit components. Should this goal be fully realized, or even partially so, it would extend the ca­pabilities of electronic systems well beyond that which can be achieved today. In addition to lowering size and weight, increasing reliability and reducing power requirements, molecular blocks could make possible the execution of tasks now too complex to be performed economically by conventional methods and permit the performance of electronic functions which cannot be achieved at all with lumped (отдельный) components.

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