Patent GB-975472-A (GB)
Title: Improvements in or relating to methods of producing electrical circuits
IPC: C22F3/00
Filed: 1962-05-18
Abstract: <PICT:0975472/C6-C7/1> A process of modifying the characteristics of a surface layer of a body comprises adsorbing a photolytically decomposable vapour into the layer and decomposing the adsorbed layer by exposure to light.  The process is particularly concerned with the formation of microminiaturised electric circuits such as cryotrons and semi-conductors.  A thin film is first deposited on a substrate, e.g. by vapour deposition, and a vapour such as a methyl halide is adsorbed into the film and then decomposed by a light source which is directed on to the layer in a predetermined pattern. The decomposition of the methyl halide results in the methyl radical reacting with the film material to form a volatile compound thus removing the film material from those areas exposed to the light pattern and leaving a coating film to a predetermined pattern. The process is particularly adapted to film materials such as Pb, Sn, Sb, Zn, Bi, Cd, Te, Li, Na, K, Ca, Hg, As and Be.  Furthermore the photolysis reaction may be used for depositing metals from an adsorbed layer of a decomposable vapour of metal alkyl compounds such as those of Cd, Sn, Pb, Ge and Si.  The adsorbed vapour is selectively decomposed on a heated substrate under vacuum by exposure to a predetermined pattern of light. An insulating layer may also be formed by adsorbing on to a substrate the vapour of low molecular weight hydrocarbons such as ethylene and butadiene and exposing the film to light to form polymers.  In a further adaptation a thin magnetic film is formed on a substrate under vacuum and a long chain polymer is then selectively formed on the coating in the required pattern by the photolysis of an adsorbed hydrocarbon.  The uncovered magnetic film is then etched to remove the metal and the polymer is then dissolved to leave the required magnetic circuit pattern.  The apparatus for carrying out the process comprises a vacuum chamber 10 containing two graphite crucibles 24, 26 which contain the source material to be deposited.  Substrates 42, 44 are secured to a hinged holder 40 which can be rotated through 180 degrees.  Masks 50, 52, 54 movable by a rack and pinion are positioned between the source and the substrates.  After depositing the required film the coated substrate is rotated to a position directly below a quartz light 72 of a wavelength of 2000-3000<\>rA, the light passing through masks in holder 74.  The photolytically decomposable vapours enter via 86, are adsorbed on to the heated substrate, and decomposed by the light source.  A superconductive cryotron, Fig. 2A (not shown), is formed by vapour depositing a first coating of Pb and a second coating of SiO on a glass substrate. The vapour of (CH3)4Sn is adsorbed on the coating and photolytically decomposed to form a Sn coating according to a required pattern and then adsorbed butadiene is photolytically decomposed to form an insulating polymer coating.  The vapour of (CH3)4Pb is then decomposed to form a Pb film pattern.  Alternatively the insulating layer could be completely coated with Sn by normal vacuum deposition and then a photolytic reaction could be used to remove some of the Sn and leave a required pattern of Sn. A semi-conductor circuit, Fig. 2B (not shown), is formed by coating a substrate of glass, silicon or germanium with germanium by the photolytic decomposition of adsorbed (CH3)2Ge.  Zn and Sb are then similarly deposited using suitable masks for the light source and the substrate is then heated to form the required p-n function. Specification 862,178 is referred to.