Semiconductor device manufacturing: process – Having diamond semiconductor component
Patent
1999-02-25
2000-10-31
Monin, Jr., Donald L.
Semiconductor device manufacturing: process
Having diamond semiconductor component
438931, 257 77, 257 22, H01L 2100
Patent
active
06140148&
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
This invention relates to a method of making ohmic contacts to n-type diamond and injecting contacts to p-type diamond.
n-Type diamond can be prepared by suitable implantation-annealing sequences of the required donor atoms, for example phosphorus. This causes a massive movement in the position of the Fermi level towards the conduction band, which, in turn, makes it difficult to effect ohmic contacts to such a layer.
In the case of p-type diamond containing boron acceptors, many different methods have been devised to prepare ohmic contacts. Contacts with low resistance can be prepared by first overdoping a thin layer at the surface of the contact with boron acceptors. Such a layer allows the current or charge carriers to tunnel into the diamond thus eliminating any unwanted rectifying behaviour. A popular way to achieve the latter is to implant the surface with boron ions (typically at energies varying from 30 to 60 keV) and to a very high dose (typically larger than 1.times.10.sup.16 ions cm.sup.-2) while maintaining the diamond at temperatures between room temperature and approximately 300.degree. C. At these high ion doses, the implanted surface layer becomes amorphous. After a subsequent anneal, typically at temperatures ranging from 600 to 1400.degree. C., the layer becomes graphitic and can be etched off by using a suitable oxidising acid solution. After etching the remaining surface then contains a very high density of boron acceptors, which facilitates the preparation of ohmic contacts.
This method does not work for larger atoms like phosphorus. After following the same procedure, the etched surface does not contain a large density of phosphorus atoms. Although it is possible to dope the diamond n-type, it is more difficult to prepare an overdoped surface. It is known that highly damaged diamond, prepared, for example, by implanting carbon ions to a high does under similar conditions as the boron-ions mentioned above can act like n-type diamond by creating a p-n junction when prepared on a p-type semiconducting diamond. One would thus expect that a similar treatment of n-type diamond may lead to ohmic contacts. However, this was found not to be the case.
SUMMARY OF THE INVENTION
According to the present invention, a method of making an ohmic contact to an n-type diamond or an injecting contact to a p-type diamond includes the steps of: dose just below the amorphisation threshold of the diamond to create an implanted region below the surface and extending from the surface; the diamond in the case of an n-type diamond, and allow electrons to be injected into the diamond in the case of a p-type diamond; and implantation occurred.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1 to 4 illustrate graphically data obtained in various experiments carried out on p-type and n-type diamond.
DESCRIPTION OF EMBODIMENTS
When implanting diamond with any ion at temperatures below about 500.degree. C., there exists an upper dose threshold beyond which the implanted layer becomes amorphous, such that when the layer is annealed, this implanted layer is converted into graphite. This threshold dose depends on the ion being implanted (the larger the ion, the lower this dose) and the temperature of the diamond. At higher temperatures some self-annealing can occur which increases this threshold dose. Just below this threshold, the damage is very large and although annealing does not lead to graphite, it causes new substructures to form which may be equated to a partial or total phase change of the diamond material. It has been suggested that these phases may be a so-called amorphous diamond which maintains an sp.sup.3 bonded network structure as is found in diamond-like carbon films. Thus, in step (ii) of the method of the invention, a change in physical characteristics occurs in the implanted region such as to produce this type of structure. It is this structure combined with the dopant atoms, generally in high density, in it, which allows electrons to tunnel into the diamond for an n-type
REFERENCES:
patent: 4894255 (1990-01-01), Page et al.
patent: 5382809 (1995-01-01), Nishibayashi et al.
patent: 5609926 (1997-03-01), Prins
J.F. Prins, Diamond and Related Materials, vol. 4, Nos. 5/6, pp. 580-585, "Ion-Implanted n-Type Diamond: Electrical Evidence", May 1, 1995.
J.F. Prins, Journal of Physics D: Applied Physics, vol. 22, No. 10, pp. 1562-1564, "Preparation of Ohmic Contacts to Semiconducting Diamond", Oct. 14, 1989.
Monin, Jr. Donald L.
Pham Hoai
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