Active solid-state devices (e.g. – transistors – solid-state diode – Specified wide band gap semiconductor material other than... – Diamond or silicon carbide
Patent
1996-03-26
1998-12-29
Crane, Sara
Active solid-state devices (e.g., transistors, solid-state diode
Specified wide band gap semiconductor material other than...
Diamond or silicon carbide
428408, 428688, 428698, 117929, 427249, 427589, 438105, H01L 2980
Patent
active
058544950
DESCRIPTION:
BRIEF SUMMARY
This invention relates to the preparation of carbon containing films on substrates, especially single crystal substrates. Specifically, this invention relates to the formation of a thin film composed of aligned square platelets on a single crystal substrate. The invention includes a step-wise process for the production of a thin film structure of this type. The resulting films provide a template by which oriented films may be grown onto single crystal substrates.
The growth of thin film materials is an important concept used in the manufacture of electronic devices, e.g. integrated circuits and thermistors. The thin films used to form active regions of electronic devices are required to have a well defined structure and contain a low level of impurities.
Diamond films produced by microwave plasma chemical vapour deposition (CVD) can potentially be incorporated into electronic devices. However, CVD diamond suffers from the problem that it is a polycrystalline material and possess a random morphology. This results in boundaries forming between adjacent diamond grains. Non-diamond carbon deposits aggregate in these voids and interrupt the passage of electrical charge through the diamond film. Hence the material is of limited use for active electronic applications.
Our copending British patent application No. 2270326 describes a process for depositing oriented diamond films composed of aligned square crystals onto silicon substrates. This material has markedly improved characteristics as compared with random polycrystalline diamond films, including enhanced electrical properties, and consequently makes the production of active electronic devices feasible. Oriented films also show great potential in optical applications as windows and photolithography masks.
As a result of a greater insight into the structural changes occurring during the process described in our above patent application, it has been realised that a structure can be produced having a very thin carbon-containing film of aligned square platelets, which can be used as a template to form thicker layers of well defined structure.
According to one aspect of the invention there is provided a structure which comprises a substrate whose surface carries an adherent thin film of generally quadrilateral carbon-containing platelets, the structure of said film being visible by atomic force microscopy (AFM).
Semiconductor devices can be made by chemical vapour deposition (CVD) onto a suitable substrate. This technique can be used, for example, to grow a thin layer of diamond or silicon carbide onto a suitable substrate. The resultant semi-conducting layers have an oriented crystal structure with low angle grain boundaries between mutually adjacent grains. In the case of diamond, this structure reduces the aggregation of non-diamond carbon in the film and hence shows great promise in areas including active electronics, e.g. thermistors and transistors, and passive electronics, e.g. heat spreaders. For maximum effectiveness as a heat spreader, the diamond layer needs to be extremely flat in order to enhance the thermal conductance. Mechanical polishing of the diamond surface would lead to increased costs and can introduce undesirable pits into the diamond surface.
The present invention arises from the realisation that the surface characteristics of the final diamond or other semi-conducting surface are strongly influenced by preconditioning the surface prior to deposition of the semi-conducting surface by CVD. It is important to nucleate the substrate by a preconditioning step. The precise chemical changes occurring during such a step have been monitored by surface sensitive techniques, such as X-ray Photoelectron Spectroscopy (XPS). XPS analyses the energy distribution of photoelectrons emitted from a material exposed to bombardment by X-rays. Electrons are emitted from a material with energies that are characteristic of the elements which make up the material. These photoelectrons are also sensitive to the chemical state of the elements in the material. The e
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Beer Carolyn Elizabeth
Buhaenko David
Ellis Peter John
Southworth Paul
Crane Sara
Kobe Steel Europe Limited
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