WO1981001529A1 - Chemical vapour deposition process with lazer heating - Google Patents

Abstract

A chemical vapor deposition coating process that uses lazer (1) irradiation for localized heating of a wafer (6) to be coated, giving spatial control of the coating deposit and cleaner growth of the coating film. The process avoids the growth of material on surfaces where no coating is desired and undesirable diffusion processes between the deposited film and the wafer. Also avoided is the absorption of significant quantities of energy by the reactants which is also undesirable.

Description

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DESCRIPTΪVE REPORT OF INVENTION

PATENT"CHEMICALVAPOURDEPOSITIONPROCESSWITHLAZERHEATING"

The growth of films of material beginning with a chemical reaction in the vapour phase is a key process in the production of electronic comp nents such as transistors, diodes, integrated circuits, solar cells, etc.

In the following we will present a description of the state of the art taking as an exam pie the deposition of silicon films.

In the process, the silicon atoms are obtained by the vapour decomposition of a silicon compound over the surface of a silicon, saphire or quartz wafer. The hydrogen reduction of SiCl.,

SiBr. , SiHCl., and the pyrolisis of SiH,, can be cited as examples of this process.

Depending on the conditions of growth and of the wafer, the film may be polycrystaline or monocrystaline. ,

The decomposition reactions occur at high temperatures, which are obtained by heating of the wafers in graphite crucibles using the joule effect, either with direct current or by RF induction.

Due to the heating of large areas of wafer and the crucible, both the reator walls and the reagents absorb significant quantities of energy, which leads to uncontrolled and unwanted deposition of impuri¬ ties, whose effects are highly prejudicial to the elec¬ trical properties of the silicon films.

Also due to the heating of the whole wafer at high temperatures, undesirable processes of dif sion between the wafer and film occur, since it is generally desired to deposit a film with a different type of electric conductivity (P-type over N-type wafer or N-type over P-type wafer), which means, a film with a different type of impurity to the wafer's impurities.

Thus, it is difficult to produce abrupt junctions by this process, which, due to their better electrical properties, are of great interest, as for example, for improvements in the gain and switching time of transistors.

The present process is ilustrated in figure 1.

The decomposition energy of the reagents is obtained by laser irradiation (1) . The power density and consequently the temperature, are con¬ trolled by a lens system (2) , and are spatialy controlled in the XY plane by a set of movable mirrors (3,4) . The reactor is composed of a window (5) transparent to the laser irradiation, a dep sition wafer blade support (6) and a controllable system

(7) for entry/exit access by the reagents.

The type of laser is chosen so that the reagents remain transparent to the frequency of irradiation and that absorption, should occur on the wafer where the film is to be deposited. By way of example, for the deposition of Si from SiCl, on quartz or silicon wafers, one could employ a CO~ laser operating at 10,6ym.

With respect to the above exposi¬ tion and due to the localized heating, the following advantages are possible over the conventional processes: a) Resolution and spatial control of deposition; b) Growth of cleaner films due to the reduced area heated; c) Minimization of the interdiffusion of impurities over the junction; d) Limited wafer distortion; e) Production of electronic devices with completely new structures.

Claims

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1. The Film Deposition Process from the Vapour Phase is characterized by the furnishing of energy for the decomposition of reagents through la¬ ser irradiation, which allows spatial control of the deposition of metalic semiconductor films and dielectrics, without the use of photografic masks.