Electronic probe

Abstract: An electronic probe consists of a steel elongate base (10) having a conical tip (12) and a thin layer (14) of semi-conducting diamond on the tip (12). The diamond tip (16), viewed end-on, will generally have a radius of less than 3000 angstroms.

Description: This invention relates to an electronic probe. The Scanning Tunnelling Microscope (STM) is an instrument capable of mapping electronic states at the surface of a specimen with atomic scale resolution. By selectively imaging the tunnelling current from specific electronic states, both chemical and physical information may be obtained in addition to the arrangements of atoms within the surface structure. The STM uses a tunnelling junction consisting of a conducting surface and a tip electrode or probe. The Journal of Crystal Growth, vol 62, 1983, pages 642-644 discloses growing crystalline diamond on a non-diamond substrate such as a metal or silicon. Summary of the Invention According to the present invention, there is provided an electronic probe comprising a base of an electrically conductive material and a fine pointed tip of a semiconducting material which is doped diamond or doped diamond-like carbon, said tip being in electrical contact with the base. Description of the Drawings Figures 1 and 2 are sectional side views of two embodiments of an electronic STM probe of the invention. Detailed Description of the Invention The invention relates to electronic probes such as STM probes, field ion microscope probes and electronic probes for integrated circuit (IC) testing. The base is preferably an elongate object having a pointed end and the semiconducting diamond material is provided as a thin layer on the pointed end. The layer will generally have a thickness of no more than 5 µm. The tip of semiconducting diamond material will be fine, typically having a radius of less than 3000 Å. The semiconducting material may be actual diamond, preferably single- or poly-crystalline diamond or a diamond-like carbon produced by many chemical vapour deposition methods. The semiconducting diamond will preferably be boron-doped diamond. The base may be made of any suitable electrically conductive material and is preferably made of steel or boron-doped silicon. The deposition of the semiconducting diamond or diamond-like carbon on the base is achieved using chemical vapour deposition (CVD). Chemical vapour deposition is a known method of growing diamond or a diamond-like carbon on a substrate and involves creating an atmosphere of a gaseous carbon compound around the base, and subjecting the gaseous compound to suitable energy to cause the compound to decompose and to deposit carbon, as diamond, on the base. The atmosphere of gaseous carbon compound will also contain atoms such as boron, phosphorus or like atoms which will dope the deposited diamond layer producing a semiconducting diamond layer. The gaseous carbon compound may be decomposed by use of various energies including heat, radio frequency energy, microwave energy or a combination thereof. The preferred CVD method of growing the diamond tip on the base is that described and claimed in EP-A-0348026. This method includes the steps of placing the base on a nitride surface, creating around the base an atmosphere of a gaseous carbon compound and atoms of boron, phosphorus or the like, bringing the temperature of the nitride surface and the base to at least 600°C, and subjecting the gaseous carbon compound to microwave energy suitable to cause the compound to decompose and to produce carbon which deposits on the base together with atoms of boron, phosphorus or the like and forms crystalline semiconducting diamond thereon. The nitride is typically silicon nitride, aluminium nitride, titanium nitride, or the like. Generally, the nitride surface and the base will be maintained at a temperature of 600 to 1000°C during the time when the decomposition of the carbon compound and the deposition of the carbon on the base takes place. The microwave energy will be generally in the range of 200 MHz to 90 GHz. The gaseous carbon compound will generally be a hydrocarbon compound such as methane. The source of the other atoms in the atmosphere may be hydrogen, diborane and similar such atmospheres. The method of this European Patent Application allows thin layers of crystalline diamond to be produced on the base. Generally, the pointed tip of an elongate base as described above will be exposed to the diamond growth so that a thin layer of diamond is produced thereon. The attached drawing illustrates two embodiments of the invention. Referring to Figure 1, the STM probe consists of an elongate steel body 10 having a fine conical tip 12 at one end thereof. A thin layer 14 of boron-doped diamond is deposited on the tip to provide the probe with a fine diamond tip 16. The layer 14 has a thickness of about 0.1 µm and the tip 16 is rounded such that either when viewed end-on or in the direction of the arrow, or when viewed side-on, it has a radius of less than 3000 Å. Figure 2 illustrates a second embodiment in which there is again provided an elongate steel body 20. The steel body has a less sharp conical tip 22 on which is deposited a layer 24 of boron-doped diamond. The diamond layer provides the probe with a fine tip 26. The layer 24 is thicker than the layer 14 of the Figure 1 embodiment and is physiochemically etched to provide the fine point. The tip 26 has the same radius as the tip 16. The boron-doped diamond layers 14,24 may be deposited on the steel tips using the method described and claimed in the abovementioned European application. In particular, these layers may be produced by placing the elongate steel body on a silicon nitride surface, creating around the body an atmosphere of a gaseous compound such as methane, introducing boron atoms into the atmosphere, bringing the temperature of the nitride surface and the body to a temperature of the order of 700 to 800°C, subjecting the gaseous methane to microwave energy of the order of 2,45GHz and maintaining these conditions for a period of about 2 hours. The methane decomposes and produces carbon which, together with the boron atoms, deposit on the conical tip of the steel body to form crystalline boron-doped diamond thereon. If the diamond tip produced in this manner is not sufficiently fine, the diamond may be polished to produce a tip of the desired fineness.

Claims: An electronic probe comprising a base (10,20) of an electrically conductive material and a fine pointed tip (16,26), of semiconducting material, which is doped diamond or doped diamond-like carbon, said tip being in electrical contact with the base. A probe according to claim 1, wherein the base (10,20) is an elongate object having a pointed end (12,22) and the semiconducting diamond or diamond-like carbon forms a thin layer (14,24) on the pointed end (12,22). A probe according to claim 2, wherein the thin layer (14,24) has a thickness of less than 5µm. A probe according to any one of the preceding claims, wherein the tip (16,26) has a radius of less than 3000 Å. A probe according to any one of the preceding claims, wherein the semiconducting material is doped crystalline diamond. A probe according to claim 5, wherein the semiconducting material is boron-doped diamond. A probe according to any one of the preceding claims, wherein the base (10,20) is made of steel. A probe according to any one of claims 1 to 6, wherein the base (10,20) is made of boron-doped silicon.

Inventors: JONES BARBARA LYNN, JONES, BARBARA LYNN
Applicants: DE BEERS IND DIAMOND, DE BEERS INDUSTRIAL DIAMOND DIVISION (PROPRIETARY) LIMITED
Application year: 1989
Main classification: G01R1
IPC codes: G01R1, G01B7, H01L21, H01J37, G01Q70