Patent GB-993388-A (GB)
Title: Improvements in or relating to semiconductor devices
Inventor: ADAM FRITZ GUNTER
IPC: H01L21/22
Filed: 1964-02-05
Abstract: 993,388. Semi-conductor devices. STANDARD TELEPHONES & CABLES Ltd. Feb. 5, 1964, No. 4931/64. Heading H1K. In a method of manufacturing a plurality of semi-conductor devices in a slice of semi-conductor material by diffusion of impurities through a mask, the mask is provided with apertures for producing an array of discrete devices and for producing an array of areas to form an auxiliary pattern of structures separate from the devices, on which resistivity measurements are made. A plurality of highpower transistors are manufactured by oxidizing the surface of a slice of N-type silicon which is then coated with a photoresist and exposed to the pattern shown in Fig. 2. The photoresist is developed and the oxide layer is etched to produce windows corresponding to the shaded areas 3, 4 and 5. Boron is applied to the surface of the slice which is then heated to " drive-in " the impurity to form P-type base regions corresponding to areas 3 and an auxiliary pattern 4, 5 of P-type areas. The exposed surface of the slice is re-oxidized during the diffusion but this fresh layer of oxide is thinner than the remaining layer and can be seen due to the multiple interference of light reflected between the surfaces of the layer. A second exposure mask, see Fig. 5, is aligned using the T-shaped stripes visible on the slice, and corresponding windows are etched in the oxide layer. A four-point probe is applied to the diffused auxiliary layer exposed by area 11 to measure the surface resistivity of the layer. This is repeated at several places across the slice and any slices which show a variation in resistivity are discarded. If the resistivity is uniform but of an unsuitable value the slice may be reprocessed either by heating to continue the diffusion or by depositing more impurity and then heating. Phosphorus is then diffused into suitable slices to form N-type areas, the patterns 9 forming the emitter regions of the transistors. The oxide layer is again reformed, the pattern shown in Fig. 9 is aligned, again using the T-shaped stripes, and corresponding windows are etched. The four-point probe is used to measure the surface resistivity of the N-type diffused layer by applying it to the auxiliary stripes. The area 10, Fig. 5, provides a narrow N-type region 13, Fig. 15, across certain of the non-T- shaped P-type stripes 7 diffused into the slice and the four-point probe can be applied to measure the resistance of the P-type channel passing between substrate 1 and region 13 to give an indication of the base resistance of the transistors, and unsuitable slices can be discarded or reprocessed. Aluminium is vapour deposited over the surface of the slice, masked and etched, and then heated to alloy the aluminium and produce the required emitter and base contacts. The slice is then scribed along the auxiliary stripes and flexed to break it into individual transistors. The use of the invention for low and medium power transistors is also described, the differences being in the geometry of the devices and slightly different patterns of the auxiliary structures (Figs. 21 and 26, not shown).