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The Fabrication Of Bipolar Junction Transistors By Diffusion Planar Process - Lab Report Example
Author : abraham21
Design & Technology
Pages 9 (2259 words)
The fabrication of Bipolar Junction Transistors (B.J.T.) by the Diffused Planar Process is the objective of this report. The diffused planar process is self-explanatory in itself by the name. “The diffusion method for manufacturing junction transistors, pioneered by C. A. Lee at Bell Labs, uses a vapour of the impurity atoms surrounding the semiconductor material as it is heated…
The fabrication of BJT comprises of various sub-steps like RCA (Cleaning Process), Thermal Oxidation, Photolithography, Diffusion, Metallization, Alloying Process etc. The process of fabrication starts by cleaning the substrate of impurities by the RCA procedure followed by developing a layer of SiO2 on the planar surface by the process of oxidation. The wafer is then coated with an appropriate photoresist material and developed by exposure to UV through base mask (mask #1). After sufficient time of exposure, the SiO2 is removed by etching out from the region of base-diffusion followed by cleaning away the covering of the remaining photoresist coating. The P-type base i.e. Boron is diffused into this region followed by re-oxidation to develop the layer of SiO2. Next, by the process of Photolithography, the oxide layer is stripped off from the regions of collector and emitter by mask #2 and Phosphorous (N-type) is diffused on it. The entire sample is re-oxidized and once again coated with the photoresist material and developed. The substrate is then exposed to vapors of Aluminum which are allowed to condense upon it. The excess Aluminum on the substrate i.e. at non-contact regions is removed chemically by ‘lift-off’. The final step in the process is alloying of the contacts.
Dust, SiO2, oxides and metallic contaminants are removed. Consequently, the process has three chief procedures namely the Organic Clean, the Oxide Clean and the Ionic Clean. ...