Patent GB-957170-A (GB)
Title: Methods of preparing junctions in semi-conductors and semi-conductor devices obtained by these methods
IPC: H01L29/00
Filed: 1959-12-11
Abstract: 957,170. Semi-conductor devices. STANDARD TELEPHONES & CABLES Ltd. Dec. 11, 1959 [Dec. 18, 1958], No. 42206/59. Drawings to Specification. Heading H1K. Method of making semi-conductor devices, such as diodes, transistors and PNPN diodes, comprises placing into contact two plane surfaces, one surface being that of a first semiconductor body in which a rectifying junction is to be formed, the other surface being that of a second semi-conductor body of the same semiconductor material as the first body and acting as a source of impurities, and maintaining the two surfaces in contact while heating the bodies to a temperature below their fusion temperature so that impurity material diffuses across the contacting surfaces into the first semi-conductor body. The first body can be of one conductivity type and the second body of the opposite conductivity type so that a PN junction is formed in the first body. The first body can be of P-type silicon with boron as impurity, of about 10<SP>16</SP> atoms per cm.<SP>3</SP> and the second body of N-type silicon with phosphorus as impurity, of about 10<SP>20</SP> atoms per cm.<SP>3</SP>, and the heat treatment can be at 1200‹ C. to 1300‹ C. The two surfaces can be kept in contact during heating at a pressure sufficient to induce welding of the bodies at the contacting surfaces which are highly polished, the heating taking place in vacuum or in a reducing atmosphere. The heat treatment can be carried out in a neutral atmosphere. In a modification the heat treatment is carried out in an oxidizing atmosphere to produce a semi-conductor oxide layer between the two bodies which ensures that no welding of the two surfaces takes place, the semi-conductor material being one whose oxide is permeable to the impurity material which diffuses from the second body. The bodies can be plates arranged one on the other or bars arranged side-by-side and several devices can be formed in one operation. The first body can be of N-type silicon and the second body of silicon having a number of impurities of different diffusion speeds and conductivity types, e.g. boron and arsenic, those having the lower diffusion speeds being in higher concentration so that on heating more than one PN junction is formed in the first body to form, for example, the base and emitter regions of a transistor. A semiconductor diode can be formed by stacking three plane parallel plates of the same semiconductor material, the first plate containing P-type impurity, the second plate being of intrinsic conductivity and the third plate containing N-type impurity, and maintaining the plates in contact while beating them to a temperature below their fusion temperature so that P- and N-type impurities diffuse from the first and third plates respectively into opposite sides of the second plate to leave a thin layer of intrinsic semi-conductor material between the P- and N-type layers formed in the second plate to produce a diode with a high inverse voltage. Other steps in forming th diode can be as above described. Several specific examples are described including a PNPN diode in which the surface of the junctions is reduced from the outer surfaces.