Patent GB-782863-A (GB)
Title: Methods of treating semiconductor bodies
IPC: G01R31/26
Filed: 1955-05-25
Abstract: <PICT:0782863/III/1> <PICT:0782863/III/2> <PICT:0782863/III/3> A semi-conductor silicon body is heated to between 350 DEG  and 500 DEG C. for 1 to 48 hours and then cooled, to increase the electron carrier concentration of at least a part thereof.  If a body of "normal" P-type silicon is heated to between 350 DEG  to 500 DEG  C. for from 1 to 48 hours, it is converted to N-type.  N-type silicon subjected to this heating process will have its resistivity reduced. The converted N-type material may be reconverted to P-type by heating to a higher temperature such as from 900 DEG  to 1300 DEG  C. for a short period (e.g. one minute), and the resulting P-type silicon may again be converted to N-type by the first heating process.  If the higher temperature heating process is maintained for a longer period (e.g. 15 hours) the body becomes "stable" P-type which cannot be reconverted back to N-type by the first heating process.  P-type silicon, stabilised in this way, may be used for diffusion techniques, such as those described in Specifications 734,255, [Group XXXVI], and 782,662. If stable P-type silicon is heated to, say, 1500 DEG  C., so that it fuses, and is then cooled rapidly, it reverts to "normal" P-type, so that conversion to N-type by the first heating process is possible.  The higher temperature process for producing the "normal" or "stable" P-type silicon may be applied to small regions of the semi-conductor body, and thus by selecting successive heat treatments, PN junctions and other special semi-conductor bodies may be produced.  The PN junctions have good photo-electric properties.  A crystal of "normal" P-type silicon may be produced by a crystal growing process such as that described in Specification 706,849, but if there is no rotation of the crystal or agitation of the melt during the growing process, the crystal consists of "stable" P-type material.  Fig. 5 shows a silicon crystal, the bulk consisting of N-type surrounded by a thin, discontinuous skin of P-type, produced by heating a body of "normal" P-type material to between 350 DEG  and 500 DEG  C. for from 1 to 48 hours and air cooling.  A wafer cut from this N-type crystal was placed in contact, for 30 seconds, and preferably in the presence of water vapour, with a tungsten or graphite needle 42 (Fig. 6) heated to 1000 DEG  C.  The resulting heat, converted region 44 of the wafer to P-type, to provide a PN junction.  In alternative arrangements, an oxy-hydrogen flame, or a high-frequency heating coil is used to fuse in air part of a "stable" P-type wafer which is rapidly cooled and the wafer is then heated to between 350 DEG  and 500 DEG  C. to convert the fused portion to N-type; the unfused portion remains "stable" P-type, and thus a PN junction is provided.  For small area junctions the fusing of a region of the "stable" P-type wafer may be effected by passing current pulses through a point contact.  In a further alternative, part of a bar of "stable" P-type silicon is fused, and cooled, and the whole bar then heated to the conversion temperature to convert the fused portion to N-type conductivity. Specification 700,231, [Group XXXVI], also is referred to.