Раздел 3 Третье занятие

151

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 1C design and processing. It can be applied to both MOS and bipolar integrated cir­cuits including injection logic. This technology applies to veiy 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 quick! у becomes a reality in con­junction with its one-chip memory or, alternately, a minicomputer will tend to have everything in one chip.

The utilization of submicron technology requires a completely new facility. All aspects of mask making, inspection, and other proce­dures are changed.

5. Контроль умения аннотировать и реферировать.

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Optical Lithography

Optical lithography has undisputably been the leading integrat­ed circuit pattern defining technique for many years. It has essen- tially two steps. First, the design and fabrication of the optical mask,

Микроэлектроника настоящее и будущее

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 maskmaking 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 interactions for optimum results. For these reasons, electron beam direct-write lithography is prov­ing invaluable in the field of application of 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 throughout, 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-process- ing becomes necessary. Reactive ion etching is a type of plasma etching where the wafer is placed on an electrode which is capaci- tively 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.