Semiconductor device manufacturing: process – Chemical etching – Vapor phase etching
Reexamination Certificate
1999-10-18
2002-03-12
Utech, Benjamin L. (Department: 1765)
Semiconductor device manufacturing: process
Chemical etching
Vapor phase etching
C438S712000, C438S719000
Reexamination Certificate
active
06355574
ABSTRACT:
This invention relates to surface treatment of semiconductors and relates to a method and a device for treating a surface of a semiconductor as well as a semiconductor. It finds applications in the field of surface cleaning, etching and nano-manufacturing.
Techniques enabling to prepare silicon wafers with perfectly passivated and extremely plane surface, made of hydrogenated silicon, whereby hydrogen forms a monoatomic layer on top of silicon, are known. Such a preparation can be made from a silicon wafer, cut according to the standard practice of the man skilled in the art and exposed to open air. We know that surrounding oxygen covers immediately the surfaces of the wafer in order to oxide silicon while forming SiO
2
molecules over a typical thickness of 5-6 atomic layers corresponding to approx. 20 Angstrom. Thus, according to a method rather well known by the specialists and produced by BELL TELEPHONIE Co., the surface-oxidised silicon wafer is dipped into two successive baths, whereas the first one contains hydrofluoric acid and the second one hydrofluoric acid as well as ammonium ions. Treated surfaces are thus etched and covered with a single hydrogen layer. The resulting wafer is kept under vacuum, protected from external contaminations.
Such techniques enable therefore to obtain extremely clean surfaces, but with an external hydrogen-passivated layer. Still, it often proves useful to have one or several external insulating layers, notably made of SiO
2
. For instance, a silicon wafer covered with an SiO
2
layer can be used for manufacturing an MOS-type transistor, by application of an additional metallic layer.
Another problem associated with surface treatment of semiconductors relates to the etching of these surfaces (lithography). Surface marking at industrial level is currently performed by a fraction of a micron, as regards the sizes of the marks as well as their positions. It has been suggested to send highly charged ions to a mica or graphite surface, in order to create permanent punctual defects using contact and highly energetic collisions. These defects build blisters of a few nanometers in size, distributed in such a way as to change the surface topography.
Major shortcomings of this etching method are that these methods only modify the surface topography.
The document E-A-0.567.985 discloses a method for manufacturing a thin film. This method comprises a first step consisting in selective irradiation of a substrate whose surface has been treated to contain hydrogen atoms so as to form an irradiated zone and a non-irradiated zone on this surface. The method comprises a second step consisting in selective formation of a thin film on the non-irradiated zone. As shown by this document, the disclosed method enables drawing up on a semiconductor substrate thin aluminium films whose thickness is liable to be as small as 100 nm.
The document patent Abstract of Japan, vol. 17, No. 649 (E 1468), JP-A-5.211.120 describes a device enabling to form a sample of thin film while adjusting the kinetic energy of an ionic beam originating from a liquid source of metallic ions and sent toward a target. The formation of the sample at the surface of a substrate is obtained by irradiating the substrate using the ionic beam.
The document Applied Physics Letters, vol. 56, No. 20 (May 14, 1990), pages 2001 to 2003, JA. DAGATA et al., mentions chemical modification of passivated silicon surfaces with hydrogen, using an STM-type tunnel effect microscope. This document mentions a 100 nm-line resolution.
This invention relates to a method for treating a surface of a silicon wafer, enabling to make this surface extremely clean and plane, and made by one or several SiO
2
monolayers.
More generally, the invention relates to a method for treating a semiconductor surface, enabling to make this surface extremely clean and well delineated, and made by an isolating compound extending over one or several molecular layers.
The aim of the invention is also to provide a method for treating a semiconductor surface, enabling to etch the said surface by approx. one nanometer.
The invention relates to such methods that can be implemented easily, enable real-time control of the surface preparation and make later control very simple as well as extremely accurate.
Another aim of the invention is a device for treating a semiconductor surface, enabling to clean this surface to make it extremely clean and well delineated, and made by an insulating compound over one or several molecular layers.
The invention also relates to a device for treating a semiconductor surface enabling to etch this surface by approx. one nanometer.
The invention relates to such treating devices that can be performed and implemented quite easily, which enable real-time control of the surface preparation and later control of the surface condition, simply as well as extremely accurately.
The invention also relates to a semiconductor with considerable information storage capacities, preferably by a factor at least equal to 10,000 times those of existing semiconductors.
In this view, the invention relates to a method for treating a semiconductor surface, whereby this surface is made by first molecules of the semiconductor with external bonds and the said bonds are saturated with hydrogen atoms.
The method comprises the steps of:
generating positive ions each having at least three positive charges, with low energy, with respect to the MeV,
sending under vacuum a beam made of these ions toward at least one zone of the surface, whereas these zones cover a determined portion of the surface;
applying to the beam a deceleration voltage close to the surface, in order to give the ions of the beam a controlled average speed, whereas the ions extract electrons of the first molecules of these zones without contacting the surface, so that these first molecules lose their hydrogen atoms and that the corresponding external bonds become pendant, and
sending toward these zones a product saturating the pendant external bonds in order to form second molecules of an insulating compound.
By ‘surface’, we mean a superficial part of the semiconductor, generally cut approximately along a crystallographic plane.
The surface is advantageously plane, in order to serve notably as a substrate for growing layers or for etching. In embodiment variations, the surface is curved.
By ‘highly charged’ positive ions, we mean ions with at least three positive charges and preferably at least fifteen positive charges. Their energy is said to be ‘low’ with respect to that of ions obtained using a particle accelerator, whereas this energy is approx. one MeV or one GeV. The low energy of the ions is thus smaller than a few tens keV.
The ‘vacuum’ under which the beam of ions is sent may correspond to relatively high pressure, for instance in the order to 10
−9
Pa. It can also be ultrahigh vacuum.
The deceleration voltage is applied in order to give very low energy to the ions, close to zero and generally smaller than a few tens eV.
An important aspect of the treatment method according to the invention is that the ions do not contact the surface. On the contrary, they attract surface electrons, then flow away in the opposite direction.
Extracting electrons from a semiconductor by using highly charged ions with low energy is explained in the article by Jean-Pierre BRIAND presented at the Fourteenth International Conference of Accelerator Applications in Research and Industry, DENTON-Texas, 6-9
th
November 1996. Diagrammatically, a highly charged ion with low energy starts to interact with the semiconducting medium at quite a long distance from the surface, that can reach a few tens Angstroms. The ion attracts and then captures conduction or valence electrons that go through Rydberg conditions. The ion thus becomes a hollow atom, i.e. an atom with internal layers, which are at least partially empty, and with external layers made by energised electrons. The number of electrons captured by the ion is considerably higher than its charge, since a portion of these electrons a
Deo Duy-Vu
Universite Pierre et Marie Curie
Utech Benjamin L.
Young & Thompson
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