The main technological processes for the production of p-n-transitions
The fusion method. This technological process consists in melting the impurity in a plate of a semiconductor of one type of conductivity, necessary for the formation of a semiconductor of a different type of conductivity. For example, an indium tablet is placed on an n-type germanium plate and heated to a melting point. In this case, the impurity melts, and the semiconductor material is partially dissolved in it, creating a p-type conductivity layer in the boundary zone. All-round pn junctions have high reliability, are operable at large reverse voltages and have a small internal resistance, providing a small direct voltage drop across them.
The diffusion method. In this technological process, p - and the n-region are produced in a semiconductor by the penetration of acceptor or donor impurities contained in the atmosphere vapor, where a plate of semiconductor heated to a high temperature is placed. Since the impurity atoms diffuse into the plate from the surface, the largest impurity concentration is observed in the near-surface region and decreases with increasing distance into the depth of the semiconductor.Method of epitaxial growth. The process of crystallization of one substance on a substrate crystal of another is called epitaxial growth. The crystal lattice of the substrate determines the lattice structure, in which the build-up layer crystallizes. Semiconductor epitaxial layers (films) can be obtained in various ways: by hermetic evaporation in a vacuum; crystallization in a molten substance containing an impurity; precipitation from the vaporous form. By varying the type of impurity and the buildup conditions, it is possible to vary the electrical properties of the epitaxial film within a wide range.
Ionic doping. The process consists in bombardment with ions of an impurity of a heated semiconductor wafer, which is in a vacuum. The ions are pre-accelerated to a certain speed and, being introduced into the semiconductor plate, play the role of donor or acceptor impurities.
Oxide masking. This process is used to ensure that impurities penetrate only to certain areas of the plate, protecting the rest of its surface from them. Silicon-based semiconductor structures use SiO2 silicon dioxide as a mask, which is a good insulator and has a significantly lower diffusion rate of impurities than pure silicon. To obtain an oxide film, the silicon wafer is heated to 900-1200 ° C. in an oxygen atmosphere. After cooling, those sections of the semiconductor that must be exposed to impurities are freed from the oxide film by etching.
Photolithography. This is the process of obtaining on the surface of the oxide film the necessary pattern of the arrangement of windows. The oxide film is covered with a photoresist (photosensitive layer) and exposed (illuminated) with ultraviolet rays through a mask on which a pattern is made in the form of transparent and opaque areas. The areas of the photoresist exposed to illumination turn out to be blocked (insoluble), and the photoresist is removed from the unlit areas by a solvent.
Etching of a silica film from areas not protected by a stuck photoresist is produced by hydrofluoric acid, resulting in the formation of windows in the oxide film through which diffusion, epitaxial build-up, or ion doping occurs.
How to ...
We made your life easier with putting together a big number of articles and guidelines on how to plan and write different types of assignments (Essay, Research Paper, Dissertation etc)