Patent GB-1503512-A (GB)
Title: Semiconductor devices responsive to incident radiation and to their manufacture
IPC: H01L31/0384
Filed: 1975-05-15
Abstract: 1503512 Semi-conductor devices FERRANTI Ltd 15 May 1975 [5 June 1974] 25145/74 Heading H1K A radiation responsive device is made by embedding semi-conductor particles, each having'a PN junction formed between its core and a surface layer in a layer of radiation transparent insulating potting material from one face of which they project to a first plane parallel to the face, providing on the face a metallic layer contacting and interconnecting the surface layers of the particles, mechanically removing particle material down to a second plane parallel to and between the first plane and the face, removing particle material damaged by the mechanical removal down to a third plane between the face and the second plane to expose the particle cores, applying insulating material leaving the cores exposed but covering exposed parts of the metal and surface layers and of PN junctions, and applying a second metallic layer to contact and interconnect the exposed cores, the opposite face of the structure remaining unobscured to receive incident radiation. The particles when spherical may vary in size to facilitate close packing but if of pastille form are conveniently of the same size. The PN junctions are formed by diffusion preferably in a fluidized bed. In one method the particles are initially adhered, e.g. electrostatically, to a carrier tape and then completely covered with the potting material. After mechanically stripping or dissolving the tape potting material is etched away so that the particles project, though this step may be avoided by coating the tape with a layer of water-soluble material prior to potting. The first metal coating is applied over the entire surface which is then treated to mechanically remove particle material either before or after provision of an insulating layer, and mechanical damage removed by etching, leaving the particle cores exposed. An insulating material is then applied and treated to leave only the cores exposed. This may be achieved by roller coating leaving the recessed particle surfaces uncoated followed by application of a heated platen to spread the coating over the exposed PN junction parts, or by using as insulation a positive photo resist and irradiating the opposite face of the structure uniformly or with a scanning laser beam, using the particles as lenses to cause selective removal of resist from the cores, e.g. by causing it to evaporate, bubble or crack or become soluble, enabling its removal, optionally using scanning plasma beam to remove any remaining traces. Alternatively, before insulation is applied the particle locations are determined by a differential reflectance method and the information stored in a computer subsequently used to control removal of the insulation by a scanning laser or electron beam. The second metallic layer is then formed. To facilitate connection of the devices, which are preferably of elongated strip form, in series to form a solar cell array the metallic layers as shown in Fig. 11 are extended over flexible portions of potting material to contact pads which are held in contact by an adjustable clamp or a shaped plastics clip such as 36 engaging protrusions 38 located above the pads. Reference has been directed by the Comptroller to Specification 1,421,459.