Semiconductor device manufacturing: process – Making device or circuit emissive of nonelectrical signal – Passivating of surface
Reexamination Certificate
2002-05-30
2004-04-20
Nelms, David (Department: 2818)
Semiconductor device manufacturing: process
Making device or circuit emissive of nonelectrical signal
Passivating of surface
Reexamination Certificate
active
06723578
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to improvements in the field of the fabrication of semiconductor devices made of a III-V compound semiconductor material undergo strong oxidation in the presence of oxygen, especially devices made of indium antimonide InSb (diodes used in the manufacture of infrared detectors), but also for example those made of gallium antimonide GaSb.
DESCRIPTION OF THE PRIOR ART
The process for fabricating semiconductor devices made of III-V compounds (that is to say compounds of elements from Groups III and V of the Periodic Table of Elements) exposes a work-hardened surface layer which it is necessary to remove. To remove this work-hardened layer, it is known, in the case of indium antimonide InSb, to subject the surface of the material to a chemical treatment by a mixture of various acids (nitric acid, hydrofluoric acid, acetic acid, lactic acid, bromic acid, etc.), and an insulator (for example SiO
x
) is then deposited, by evaporation or by vacuum sputtering, onto the surface of the material in order to provide protection (passivation).
However, it has been found that the chemical treatment used to remove the work-hardened surface layer of the InSb semiconductor material results in a high degree of oxidation of the surface of the material with the formation of oxides of the constituent elements (indium oxide and antimony oxide).
It has also been found that deposition of the layer of insulator (for example SiO
x
) on the surface thus treated of the semiconductor material leads to a chemical modification of the surface of the material with the formation of elemental chemical substances. Now, the presence of these compounds at the interface between the semiconductor material and the insulator layer has proved to be deleterious to obtaining semiconductor devices of good quality; in particular, the presence of elemental indium and/or antimony at the InSb/SiO
x
interface has an unfavourable effect on the performance of the diodes thus fabricated.
SUMMARY OF THE INVENTION
It therefore seems desirable to remove the oxides present on the surface after the chemical treatment to remove the work-hardened layer.
For this purpose, the invention provides a method for deoxidizing and passivating, by sulphidation, a surface of a III-V compound semiconductor material undergo strong oxidation in the presence of oxygen, which method is characterized, according to the invention, in that the surface to be passivated is immersed in a dilute aqueous solution containing sulphide ions with a concentration of between about 10
−1
M and 10
−7
M. The best results are obtained for sulphide ion concentrations of between 10
−2
M and 10
−3
M.
Admittedly, the sulphidation of semiconductor surfaces is already used in the electronics, and especially optoelectronics, industry. This treatment results in both electrical and chemical passivation of the semiconductor surface. Electrical passivation is manifested by a reduction in the density of surface states; chemical passivation allows the surface to be protected from oxidation from the action of the oxygen contained in air. This sulphidation treatment may be carried out chemically or electrochemically.
However, this known treatment employs sulphur precursors in the form of concentrated, or even pure solutions. The treatment of an InSb surface using (NH
4
)
2
S
x
as a pure solution (~3M) is described in the article “
A
(
NH
4
)
2
S
x
—treated InSb
(001)
surface studied by using X
-
ray photoelectron spectroscopy, low
-
energy electron diffraction, and inverse photoemission spectroscopy
”, by S. Ichikawa et al., in Journal of Vacuum Science and Technology A, Vacuum, Surfaces and Films, Vol. 17 No. 2, 1999, pages
421-424. This treatment causes a substantial modification to the chemical composition of the surface with, in particular, the growth of a thick film based on indium and sulphur. This surface structure may then be removed, but it does nevertheless represent a real technological problem. The invention reduces, or even eliminates, this drawback.
DETAILED DESCRIPTION OF THE INVENTION
A method for deoxidizing and passivating, by sulphidation, a surface of a III-V compound semiconductor material undergo strong oxidation in the presence of oxygen comprises, according to the invention, the step of immersing the surface to be passivated in a dilute aqueous solution containing sulphide ions with a concentration of between about 10
−1
M and 10
−7
M. The best results are obtained for sulphide ion concentrations of between 10
−2
M and 10
−3
M.
According to the invention, the sulphidation of a III-V semiconductor surface is carried out by immersing this semiconductor surface in the solution: the process is simple to employ.
Again according to the invention, the solution containing the sulphide ions which is used is a dilute, or even very dilute, solution compatible with the conditions of working in a clean room. Chemical bonds, which vary depending on the concentration of sulphide ions, may thus form between one or more of the elements of the III-V compound semiconductor material and the sulphur. Surface formation of indium oxide and antimony oxide occurs on the indium antimonide InSb whose work-hardened surface layer was removed by the chemical treatment indicated above. The sulphidation of this surface including the oxides results in an exchange between the oxygen of the oxides and the sulphur of the dilute treatment solution, thereby leading to substantial deoxidation of this surface. Controlling the sulphide ion concentration allows control:
i) of the type of sulphidation, with the formation of different chemical bonds between the sulphur and the III and V elements depending on the sulphide ion concentration;
ii) of the thickness of the sulphided surface layer, only in the case of antimonides, which appears to be critical for the desulphidation step which is then necessary in order to obtain high-performance InSb diodes.
In addition, this treatment allows the treated surface to be protected from oxidation by air, which oxidation is observed after a non-protecting treatment such as deoxidation by an acid solution.
The sulphidation solution dilution conditions recommended according to the invention allow a III-V semiconductor surface to be uniformly sulphided, while minimizing the amount of sulphur on this surface. This aspect appears to be paramount because of the fact that the presence of sulphur at the semiconductor material/insulating layer (for example SiO
x
) interface is prejudicial to obtaining high performance in the final semiconductor device (for example InSb infrared diodes). Given the fact that desulphidation (for example by vacuum sublimation or by chemical etching in an aqueous acid solution) of the semiconductor surface is necessary before the final step of fabricating the semiconductor devices (junction formation), the presence of a smaller amount of sulphur on the surface seems to be a distinct advantage in terms of simplifying, controlling and speeding up the desulphidation process. In the case of InSb diodes, the maximum temperature envisaged for desulphidation is close to 300° C. taking into account the technology used. This temperature is perfectly well suited to the use of dilute sulphur solutions for which desulphidation is obtained above 230° C., but can no longer be envisaged in the case of more concentrated solutions in which desulphidation is obtained only above 400° C. for a pure (NH
4
)
2
S
x
solution.
In addition, the use of dilute, or even very dilute, solutions containing sulphide ions allows industrial implementation of this “clean room” treatment without the need for particular safety conditions, which would be the case if more concentrated solutions were employed.
As is already apparent from the above explanations, the method of the invention is particularly effective for treating antimony-based materials, and especially indium antimonide which is very useful in the fabrication of infrared-detecting diodes. A preferred and most particul
Canava Bruno
Etcheberry Arnaud
Herlem Michel
Lorans Dominique
Vigneron Jacky
Hoang Quoc
Larson & Taylor PLC
Nelms David
Sagem SA
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