Manufacturing method for a thick oxide layer

Details Manufacturing method for a thick oxide layer Manufacturing method for a thick oxide layer

1999-10-22

2003-07-29

Fourson, George (Department: 2823)

Semiconductor device manufacturing: process

Formation of electrically isolated lateral semiconductive...

Grooved and refilled with deposited dielectric material

C438S425000

Reexamination Certificate

active

06599812

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a method for manufacturing a thick oxide layer on a semiconductor substrate using a trenching method.
BACKGROUND OF THE INVENTION
As is well known, a process for manufacturing a layer of thick oxide on a portion of semiconductive substrate of a wafer comprises the following steps: the formation of a thin layer of oxide; the formation of a layer of nitride, for protecting the portion of semiconductive substrate where the thick layer of oxide will not be formed; and the carrying out of a thermal treatment in wet oxidizing atmosphere (0
2
wet).
According to the prior art, in order to obtain a layer of oxide, for example, of 3 &mgr;m it is necessary to carry out a thermal treatment in a wet oxidizing atmosphere of the wafer for about 15 hours at a temperature of 1100° C. This is an example of a LOCOS (local oxidation of silicon) oxide process. Some of the problems with the LOCOS process are: formation of a “bird beak” structure, a lack of planarization of the structure, the requirement of a very high temperature, and a long oxidation time. Because of these problems, oxide layers are generally not grown more than 2-3 &mgr;m thick.
FIG. 1
shows a portion of semiconductive substrate
1
′ of wafer on which a thick layer of oxide
4
′ has been formed according to the prior art. As is evident from the drawing, after having carried out the thermal treatment, the layer of oxide
4
′ is also formed between the layer of nitride
3
′ and the substrate
1
′ connecting with the thin layer of oxide
2
′. In particular, the layer of oxide
4
′ extends itself under the layer of nitride
3
′ by an amount which is substantially about its thickness D′. This is the bird beak structure.
Furthermore, the surface of this layer of oxide
4
′ is raised, with respect to the surface of the substrate
1
, of an amount equal to half the thickness D′ of the layer itself.
Therefore, after the formation of the layer of oxide
4
′, the entire surface of the wafer is not planar.
A known technical solution for planarizing the surface of the wafer is described in the book: “SILICON PROCESSING FOR THE VLSI ERA,” VOL. II, page 42, hereby incorporated by reference.
Thermal treatment with high temperatures is also necessary in order to carry out this process of planarization.
SUMMARY OF THE INVENTION
Embodiments of the present invention are directed toward a method for manufacturing a thick layer of oxide, having such characteristics which allow the formation and subsequent planarization with a low thermal temperature that overcomes the limitations and/or the drawbacks which, at the moment limit the methods for forming thick layers of oxide according to the prior art.
Embodiments of the invention form, in the portion of substrate where the formation of a layer of thick oxide is desired, a plurality of trenches, before carrying out conventional thermal treatments.
Characteristics and advantages of the invention will be seen from the description, following herein, of an embodiment given as an indication and not limiting with reference to the drawings attached.


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Wolf S. “Silicon Processing for the VLSI-ERA: vol. 2-Process Integration”, 1990, Lattice Pr., vol. 2, pp. 51-58.

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