Euro Spectra SCIENTIFIC and TECHNICAL REVIEW of THE

SCIENTIFIC ÁND TECHNICAL REVIEW OF THE COMMISSION OF THE EUROPEAN COMMUNITIES SEPTEMBER 1973 VOL. XII NO. 3 58 GIANCARLO BERTOLINI, FRANCESCO CAPPELLANI, GIAMBATTISTA RESTELLI ION IMPLANTATION IN SEMICONDUCTORS 73 JAN G. SMEETS ECOLOGY AND ENVIRONMENTAL HYGIENE 84 TECHNICAL NOTES 88 RECENT PUBLICATIONS ON INDUSTRIAL CHEMICAL ANALYSIS METHODS Five editions: English, German, French, Italian and Dutch Published and edited by: Quarterly Commission of the European Commu- Scientific publication nities, Directorate-General and Technical Information and Info rma- tion Management, Rue de la Loi, 200 1973 - 3 0ùntcnt& 1040 Brussels. Tel. 350040 euro spectra Scientific and Technical Review of the Commission of the European Communities (ex-"Euratom-Review") SHOULD YOU WISH TO RE• CEIVE euro-spectra REGU• LARLY, PLEASE SEND THE ORDER FORM TO: Agence et Messageries de la Presse Rue de la petite tie, 1 1070 Brussels, Belgium (Postal account 416.69) H.M. Stationery Office P.O. Box 569 London S.E. 1 Great Britain or European Communities Information Service 2100 M Street, N.W. (Suite 707), Washington, D.C. 20037 U.S.A. Yearly subscription rate: Europe : 180 Belgian Francs Other countries: 220 Belgian Francs Single copies: Europe : 50 Belgian Francs Other countries: 60 Belgian Francs Any article published In this Review may be reproduced in whole or In part without restric• tion, provided that the source Is mentioned. On the vast construction site of the European Community, where ideally every one brings his own brick to contribute to the structure, work does not always proceed with the desired speed and organi• zation. Difficulties and problems arise both with the architects who design and supervise the building work and with the labour force which harbours a persistent nucleus of anti-Europeans. There has been no lack of noisy demonstrations of opinion from these people both recently and in the euro past. The typical anti-European, who has his own Euro-brick like everyone else, does not bring it to the common site to contribute to the construction but spectra feels only the irresistible urge to hurl it at the heads of those he thinks are responsible for the project. Scientific and The irate anti-Europeans with itchy hands flourish Technical Review equally in the newly-acceded countries of the Com• of the Commission of the European munity and in those which helped create it. The Communities former would have preferred not to have to work on (ex-"Euratom-Review") the site, being staunch upholders of the old adage that foretells endless trouble for those who abandon the old ways for the new, whilst the latter identify the success, or even more simply, the raison d'être of the Europe of the nine either with the total abolition of customs formalities and frontier control or with the levelling of potato prices down to the last halfpenny in all the tiny outlying markets in Italy, Belgium, Denmark, Holland, and so on. Like all large-scale and complicated undertakings, the Community of Europe has its convinced detrac• tors who are often in the dark as regards what has been done, what is being done, what it is proposed to do and why, and who are stubbornly determined not to know. Obviously having to help carry the bricks on The Commission of the European Commu• the site is not as easy or as pleasant as going to live nities or any persons acting on its behalf in a soundly constructed building but it is equally disclaim all liability with respect to the true that without labourers no one has ever managed completeness of the information contained to build anything. in this periodical as well as to any damage which might result from the use We should like to ask the typical anti-Europeans of information disclosed or of equipment, to devote to the construction of Europe just one tenth methods or processes described therein. of the interest and attention which they lavish on their house plans for themselves and their children. Picture credits : Cover : Gaston Bogaert, This would undoubtedly help them to proceed to a Brussels. profitable examination of their conscience. Pictures : pp. 63, 66, 67 : JRC Ispra ; pp. 73, 75, 76, 82 : Jan van de Kam, Griendtsveen ; p. 80 : Cas Oorthuys, Amsterdam. Printed in Belgium by Maison d'Edition s.c 6001 Marcinelle Ion implantation 2) The purity of the material which is introduced does not depend on the in semiconductors original material and is very closely controllable. In thermal diffusion everything depends on the degree of purity of the materials used: e.g., residual impurities in the single crystal GIANCARLO BERTOLINI, FRANCESCO CAPPELLANI, are diffused together with the doping GIAMBATTISTA RESTELLI atoms. 3) Implantation is not an "equilibrium process" like thermal diffusion and it is not bound by the physicochemical ENERGIZED IONS can be used to formation by the introduction of impu properties of the solute/solvent (ion/ change the properties of materials: rities takes place on the surface of the target) system. It follows that concen this new technique is known as "ion semiconductors and extends to only a trations in excess of the thermal solu implantation". The required atomic very small depth below the surface (of bility limits can be obtained and species ionized and accelerated in an the order of μιτι or less); secondly, the atoms with a very low diffusion electrostatic field is fired at the material alteration of the original electrical velocity or zero solubility can be which is to be treated. The ions penetrate properties is useful when extremely small introduced in depth. the target and lose their energy in colli amounts of impurities are introduced 4) Basically ion implantation is a process sions with the atoms and electrons in the (from one atom per hundred million to which takes place at much lower solid until the rest energy is reached one per hundred atoms of the semi temperatures than diffusion, avoiding (thermal energy). This, briefly, is the conductor). the difficulties caused by the use of process. In the present state of the art, the high temperatures (500-700 °C as In 1954 Shockley, who with Brattain methods which can be used for "doping" against over 1 000 °C). and Bardeen shared the Nobel prize in are, in order of importance: 5) The ions penetrate the crystal as a 1956 for invention of the transistor, - thermal diffusion; directional beam; in this way the patented the use of an accelerated ion - introduction during the growth of the doped region is defined with remark beam as a means - in conjunction with crystal or the formation of an epitaxial able precision, contrary to what traditional processes - of producing elec layer; happens in diffusion where the iso- tronic devices, outlining the potential - alloying with a metal. tropy of the process causes leakage at advantages of a technology which was the edges of the mask which delimits only effectively developed at the indus The first method is by far the most the doping zone (Fig. 1). trial level at the end of the sixties. As used and it is mainly as an alternative is known, the manufacture of solid state to this method that ion implantation has On the other hand, the main disad electronic devices involves the introduc been introduced, even in industrial vantage of ion implantation must be tion of a specified quantity of electrically production. It may seem rather extra attributed to the slowing down of the active impurities into a semiconductor ordinary that such a recent technique ions during their penetration into the (e.g., silicon). The semiconductors under should be able to replace thermal dif semiconductor. The single crystal origi go a change in their original electrical fusion, which is braked by a vast amount nally has an ordered periodic structure properties which depends on the type of of development work and technological which determines its electrical properties. impurity. This is what is meant by the research. The energized ion penetrating this term "doping", which is the key process In fact ion implantation is not a collides with the atoms of the solid, for all solid state electronics. complete alternative but is only a which may receive enough energy to be With this system, combined with the substitute technique used in the produc displaced from their lattice position so creation of insulating layers and various tion of some devices or in certain phases that the bonds are broken and as a types of connections, it is possible to of the manufacturing process. result the characteristic regularity of the produce devices ranging from simple The advantages of ion implantation structure is lost. In extreme cases, if a diodes to complex integrated circuits compared with thermal diffusion can be sufficiently large number of atoms are which incorporate many thousands of itemized as follows: displaced, the solid changes from crystal line to amorphous. Fortunately this devices. 1) The quantity of impurities introduced, disadvantage can be largely remedied by The two basic characteristics of the the depth of penetration and therefore carefully heating the bombarded sample; "doping" process are, firstly, that trans- the concentration in the crystal are this annealing restores the crystal struc parameters which can be controlled ture and makes it possible to retain the precisely and independently through typical electrical properties of the chem GIANCARLO BERTOLINI, the intensity of the ion beam and FRANCESCO CAPPELLANI, the energy of the ions. By contrast, in ical species of the introduced ions. This is GIAMBATTISTA RESTELLI- diffusion it is possible to act on the still one of the main problems, however, Electronics Division, Joint Research Centre diffusion time and the temperature, as it may raise difficulties with some of the Commission of the European Commu materials.

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