Martin Paul Lepselter

Low-power bipolar transistor memory cells

Low- and high-barrier Schottky diodes have been combined with bipolar transistors to produce planar integrated-circuit low-area memory cells that hold at 75 /spl mu/W. Low-barrier diodes formed on p-type ion-implanted silicon (10/SUP 17/ cm/SUP -3/) are used as high-resistance collector loads. High-barrier diodes formed on n-type epitaxial silicon (10/SUP 16/ cm/SUP -3/) provide low-capacitance low-leakage coupling to digit lines in a memory array. The highly reproducible rhodium silicide on silicon Schottky diodes, as well as high-quality ohmic contacts, are formed in one sequence of sputtering and high-temperature operations. The process is fully compatible with beam-lead technology. It is estimated that a 512-word memory module using these cells would operate at a 60-ns READ or WRITE cycle time.

Solid state: X-ray lithography breaks the submicrometer barrier; A new X-ray lithography system allowed Bell Labs engineers to make the smallest, fastest MOSFETs yet reported

Describes an X-ray lithography system which allowed Bell Labs. engineers to make MOSFETs with channel lengths of 0.3 to 0.4 micrometers, switching speeds of 30 to 75 picoseconds, and speed-power products of 5 femtojoules (5×10-15 Ws) to 50 femtojoules. The X-ray system is smaller, less expensive, and more reliable than previous X-ray systems, and it also has a higher throughput-potentially 75 wafers per hour. It uses an exposure power of 4.5 kW, compared to the 20 to 40 kW in other systems. The key to a short exposure time with a low power source is the use of a novel resist that is more radiation-sensitive than conventional resists. Another advantage of the system is exceptional linewidth control-better than 0.1 micrometer across the wafer.

A method of tungsten dopant deposition for dual-dielectric charge-storage cells

Electron-beam evaporation of small single-crystal ingots of tungsten has been employed as a laboratory-scale method for introducing the tungsten interfacial dopant in dual-dielectric charge-storage cells. Several other tungsten-evaporation methods, which are potentially more suitable for large-scale manufacturing operations, are evaluated. They are: 1) evaporation from resistively heated tungsten; 2) evaporation of tungsten trioxide powder from a resistively heated crucible; and 3) reactive evaporation of tungsten trioxide from resistively heated tungsten in a low-pressure ambient of oxygen. The latter method, which seemed the most attractive, was tested and was found to be a practical alternative to the electron-beam method. It possesses the advantages of low operating temperatures, control of small deposition rates to produce tungsten trioxide deposits in the submonolayer range of coverage, pure deposits, and requires a minimum of operator attention. Furthermore, sources can have a long operating life.