Patent GB-1270130-A (GB)
Title: Improvements in and relating to methods of manufacturing semiconductor devices
IPC: H01L21/00
Filed: 1969-06-18
Abstract: 1,270,130. Making semi-conductor devices. PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd. 18 June, 1969 [21 June, 1968], No. 30851/69. Heading H1K. A semi-conductor body is selectively coated with a film which (or, part of which) is doped with a dopant to be diffused into the underlying surface of the body. Undesired diffusion of the impurity from the coating into the body through an aperture in the coating is cut down by providing, as a competitive area for diffusion, a mass of a powdered semi-conductor in the diffusion furnace. The powdered semi-conductor may also act as a diffusion source for one or more dopants which enter the body through the aperture and/or through the coating itself. It is also possible for the mass of powdered semiconductor to act as the source of a particular dopant intended to enter the body through the aperture at a given concentration even though the coating is doped with a much greater concentration of the same dopant. Two methods of forming the thyristor structure of Fig. 2 are described. In the first method, aluminium is diffused into both sides of an n-type silicon wafer 27 to form p-type layers 23, 28; borosilicate coatings 21, 25 are provided and the coated body then heated in the presence of phosphorus-doped silicon powder to form p<SP>+</SP>- type layers 22, 29 (by diffusion of boron from the coating) and an n-type layer 24 by diffusion of phosphorus. In the second method, an n-type silicon wafer is provided with borosilicate coatings 21, 25 and is then heated in the presence of silicon powder which is doped with arsenic and of silicon powder bearing a deposit of aluminium; the fast-diffusing aluminium enters the body both through aperture 26 and directly through the coatings 21, 25 to form the deep p-type regions 23, 28, the slow-diffusing arsenic enters the body through the aperture 26 to form the n-type region 24, and boron diffuses from the coatings 21, 25 to form the shallow p<SP>+</SP> regions 22, 29. In both cases, contacts are subsequently provided on regions 22, 24 and 29. A transistor is formed by taking an n<SP>+</SP> (antimony-doped) silicon wafer 48, providing an n-type epitaxial layer 47, forming an apertured borosilicate glass layer 41, and by heating the coated body in the presence of silicon powder doped with both arsenic and boron. Boron diffusing through the aperture moves faster than the arsenic, p-type region 46 and n-type region 43 being formed by the double diffusion. The very high concentration of boron in the coating 41 gives rise to the deeper parts of the p-type layer limited by junction part 45. This method avoids emitter dip found in conventional double-diffused transistors. If the borosilicate glass is replaced by a phosphosilicate glass of the correct phosphorus content, a Zener diode may be formed by the same method. Other manufactures are outlined. Semi-conductors used for the body and powder (they are not necessarily of the same material) are silicon, germanium, and A<SP>III</SP>B<SP>V</SP> compounds. The coating may be doped only in selected areas (thus, for example, allowing diffusion of aluminium alone in these areas). Gallium, indium antimony, and bismuth may be used as gaseous phase dopants or as dopants in the coating.