Semiconductor device manufacturing: process – Formation of electrically isolated lateral semiconductive... – Recessed oxide by localized oxidation
Reexamination Certificate
2002-07-31
2004-01-13
Fourson, George (Department: 2823)
Semiconductor device manufacturing: process
Formation of electrically isolated lateral semiconductive...
Recessed oxide by localized oxidation
C438S466000
Reexamination Certificate
active
06677218
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to a method for fabricating an integrated semiconductor circuit, in which a recess is formed in a surface of a semiconductor substrate, a material is grown on the inner wall of the recess, an electrically insulating layer is produced on the surface of the semiconductor substrate outside the recess, and the material is grown selectively on the inner wall of the recess as a result of the semiconductor substrate, as an electrode, being brought into contact with an electrolysis liquid and electrolysis being carried out, during which the insulating layer prevents the material from growing outside the recess.
During the production of integrated semiconductor circuits, recesses, in particular, trenches, are formed and are then filled with a different material than the semiconductor substrate, generally, silicon. Often, relatively complex structures are also produced within a trench. In some cases, it is necessary for the inner wall of the trench to be covered with a thin film without the trench being completely filled. In these applications, the trenches are very deep in relation to their cross-section; they have a high aspect ratio, i.e., a high ratio of the trench depth to the trench cross-section. In the case of shallow trench isolations, the ratio may be between 2 and 8, while in the case of deep trench isolations this ratio may be up to 60.
To fill deep trenches or to cover their inner wall, the material that is to be introduced or the constituent that has to be introduced to form the material has to be guided onto the inner wall such that the trench opening is not closed up before the trench has been filled or its inner wall has been lined.
Keeping the trench opening clear during the deposition represents a considerable technical problem, in particular, in the case of deep trenches. It is often not possible to achieve complete, void-free filling of the trenches because growth closes up the trench in its upper region before it has been completely filled from below. In such a case, cavities, referred to as voids, remain in the interior of the trench.
The method that is most frequently used for partial or complete filling of a trench is chemical vapor deposition (CVD). In the CVD method, chemical compounds, such as for example, oxides or nitrides, are deposited from a vapor phase, which generally contains organometallic substances. Therefore, the deposition takes place over the entire surface of the semiconductor substrate, i.e., both within and also laterally outside or above the recesses. The deposition takes place to a thickness that corresponds to at least half the trench diameter, and, consequently, the growth closes up the trench from the sides. In the case of anisotropic deposition in a direction that is perpendicular to the substrate surface, the trench can also be filled from the bottom. During the filling of a trench with the aid of deposition, a layer that extends over the entire surface of the semiconductor substrate is deposited, the layer having to be removed again above the trench opening. Such removal requires planarization processes, such as chemical mechanical polishing (CMP). These processes entail additional outlay and, on account of topography structures of the semiconductor substrate, do not always result in complete and uniform removal of the deposited material. In some cases, oxidation processes are used to form oxide layers on regions of the surface of a semiconductor substrate. A metal that is exposed on an inner wall of a trench can also be oxidized in this way. The oxidation is carried out at high temperatures in an oxygen-containing environment. However, during the filling of trenches by oxidation processes the oxide layer also grows on the substrate surface; furthermore, the temperature of, for example, 600° C. required for the oxidation, which would have to be maintained throughout the entire duration of the conditioning step, can cause damage to semiconductor structures.
For the material that is intended to fill the trenches to be deposited only in the trenches but not on the remainder of the substrate surface, prior art methods provide for an electrically insulating layer to be produced on the surface of the semiconductor substrate outside the recess and for the material to be grown selectively on the inner wall of the recess as a result of the semiconductor substrate, as electrode, being brought into contact with an electrolysis liquid and electrolysis being carried out, during which the insulating layer prevents the material from growing outside the recess. The material that is grown by electrolysis only on the inner wall of the recess obviates the need for subsequent removal of the outer substrate surface because the electrically insulating layer that has been applied to this surface prevents electrolytic growth.
Although electrolytic conversion only at the inner wall of trenches leads to selective growth only in the interior of recesses, which are not covered with the insulating layer, in such a method, the semiconductor substrate is attacked. As a result, the original trench dimensions are changed.
However, this method has the drawback that the electrolysis changes the original trench dimensions; during the electrolytic oxidation, the oxide that is formed (silicon oxide in the case of a silicon substrate) grows not only into the trench opening but also into the surrounding substrate material because silicon is consumed during the oxidation process.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a method for filling trenches in integrated semiconductor circuits that overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices and methods of this general type and that allows a material to be grown only on the inner wall of recesses in a semiconductor substrate, i.e., avoiding growth outside the recesses, while maintaining the lateral dimensions of the recesses.
With the foregoing and other objects in view, there is provided, in accordance with the invention, a method for fabricating an integrated semiconductor circuit, including the steps of forming at least one recess in a surface of a semiconductor substrate, epitaxially depositing a reserve material on an inner wall of the recess, producing an electrically insulating layer on the surface of the substrate outside the recess, and bringing the substrate as an electrode into contact with an electrolysis liquid and carrying out electrolysis to selectively grow the material on the inner wall of the recess while the insulating layer prevents the material from growing outside the recess and to convert the reserve material into the material being grown by the electrolysis.
According to the invention, in the method, before the electrolysis is carried out, a reserve material is epitaxially deposited on the inner wall of the recess, and during the electrolysis the reserve material is converted into the material that is being grown by electrolysis.
According to the invention, electrolytically produced growth is linked to a deposition process. Although the use of a deposition process is not recommended, in particular, if the substrate is covered with an insulating layer that inhibits electrolytic growth outside the recesses, because the electrically insulating covering layer is able to prevent electrolytic growth outside the recesses but cannot prevent growth during a deposition process, according to the invention epitaxial and, therefore, selective growth, which takes place only on the inner wall of the recesses, is used, with the result that at the inner wall of the recesses a reserve material is formed on the semiconductor material and is subsequently converted by electrolysis.
According to the invention, therefore, the steps of “deposition” and “electrolysis”, which have hitherto been alternatives to one another, are combined with one another.
Before the electrolysis is carried out, a reserve material is epitaxially deposited on the inner wall of the recess, and, during the e
Kirchhoff Markus
Schrems Martin
Fourson George
Greenberg Laurence A.
Infineon - Technologies AG
Locher Ralph E.
Stemer Werner H.
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