Abstract:
Method and apparatus for characterizing the dynamic input impedance of a test element by measuring the rise-time degradation of an input waveform. A pulse having a very fast rise-time is supplied by a pulse generator and transmitted down two branches of a balanced transmission line. One leg of the balanced transmission line is connected to a sensing means while the other leg of the balanced transmission line is connected to a test element as well as the sensing means. Thus, the sensing means would receive two identical pulses but for the rise-time degradation of the pulse connected to the test element. The test element is characterized on the basis of this rise-time degradation.
Abstract:
In the fabrication of integrated circuits, a method of forming openings through an insulative layer wherein a plurality of openings being formed through said insulative layer are subjected to two separate etching steps in order to insure that the opening is made. In the method, a layer of electrically insulative material is formed on a substrate. The layer is covered with a first photoresist mask having a plurality of openings. Then, a plurality of openings through the insulative layer coincident with the mask openings is made by applying a chemical etchant through the photoresist mask. The second photoresist mask having a plurality of openings coincident with the openings in the insulative layer is then formed on said layer; these openings in the second photoresist mask have smaller lateral dimensions than the openings in the insulative layer. Thus, the sides of the openings in the insulative layer are masked by photoresist. The chemical etchant is reapplied through the second photoresist mask. In this reapplication, any openings which may not have been fully etched through the insulative layer in the first etching step are now made. On the other hand, because the sides of completed openings are already masked by photoresist, there is no possibility of the reapplied etchant etching through the sides of such completed holes to overetch such holes.