Supported by Delco Electronics


The research proposed for 1986 was to develop the technology for fabricating, measuring, and computer modeling the polysilicon emitter bipolar transistor. Fabrication consisted of producing three types of bipolar transistors; a regular bipolar device to act as the control, a polysilicon contacted emitter transistor, and a polysilicon emitter directly on the base region with a very thin oxide at the interface. The proposed fabrication research concentrated on investigating a new method of fabricating polysilicon contacted emitter bipolar transistors. The new fabrication technique uses plasma etching of the emitter location on the base region and, without breaking vacuum, depositing amorphous silicon (a-Si) on the cleaned interface. The a-Si was then to be doped by ion-implantation and heated to 600-700 C ° to produce the polysilicon emitter contact. The controlled interface and the fine grained polysilicon should lead to more uniform and predictable betas for the polycontacted transistors. Both polysilicon contacted emitters and polysilicon emitters were to be investigated over a range of base doping. We proposed the modeling work in two directions: l) 2-D simulation so that small geometry transistors can be accurately modeled and 2) simulation of polysilicon contacted emitter transistors. Measurements on the devices described above will be used to develop a polysilicon model. The objective of this part of the project is to develop a numerical device simulator with predictive capability, i.e. one that can be used with confidence in place of actual device fabrication. The numerical device models will be provided to Delco and should find many applications in development and manufacturing. The fabrication highlights of the 1986 work were the design and fabrication of preliminary bipolar transistors and polysilicon emitters, the design and layout of the test wafer, and the fabrication and measurements on shallow arsenic doped emitter devices. There were 22 sets of fabrication runs made beyond the preliminary devices. The last results of these runs show that the shallow Arsenic emitter (0.05 /i) and the very narrow base width (0.1 y) control devices with metal emitter contact, have an average peak beta of about 75. Poly contacted emitter devices fabricated at the same time on the same wafer show a beta enhancement to 232, a factor of about 2.7 to 3.0 in the average peak beta. The polysilicon was deposited in a standard way in a LPCVD tube. We are presently fabricating polysilicon devices for studying the effects of the methods used in treating the surfaces before the poly is deposited and the way the poly is formed (amorphous PELPCYD).

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