Semiconductor device manufacturing: process – Formation of electrically isolated lateral semiconductive... – Having substrate registration feature
Reexamination Certificate
1999-10-19
2001-07-03
Nelms, David (Department: 2818)
Semiconductor device manufacturing: process
Formation of electrically isolated lateral semiconductive...
Having substrate registration feature
C438S462000
Reexamination Certificate
active
06255189
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a method of manufacturing a semiconductor device, in particular an integrated circuit, in a silicon body which is provided at a surface with an alignment grating for aligning the silicon body relative to masks which are used in a number of successive process steps to image patterns onto the surface of the silicon body, the alignment grating being provided in the form of a strip pattern of adjacent elevations and valleys, and the surface also being provided with a mask of a material which protects the silicon body against oxidation, which mask is provided with apertures at the location of the semiconductor device, whereafter the silicon body is provided with an oxide pattern by means of oxidation, which pattern is recessed in the silicon body over at least a part of its thickness and defines active regions in the silicon body.
A method of the type mentioned in the opening paragraph is known from U.S. Pat. No. 5,700,732. In said known method, prior to the manufacture of a semiconductor device, which is provided with an oxide pattern which is at least partly recessed in a silicon body, a surface of the silicon body is provided with an alignment grating in the form of a strip pattern of adjacent elevations and valleys, which correspond to a difference in height which is desirable for aligning. In subsequent process steps carried out to manufacture the semiconductor device, the previously provided alignment grating is used to align the silicon body relative to masks which, during these process steps, are used to image patterns onto the surface of the silicon body.
A disadvantage of the known method is that, prior to the process steps, which are relevant for the manufacture of the semiconductor device, extra process steps are necessary to provide the alignment grating. These extra process steps generally include a lithography step in which regions on the surface of the silicon body are defined for the valleys to be ultimately provided, followed by an etch step in which the valleys are formed by performing an etching operation on the silicon body over a specific distance corresponding to the difference in height necessary for aligning. The extra lithography and etch steps contribute significantly to the overall number of necessary process steps and hence to the total process costs.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a method of the type mentioned in the opening paragraph, which enables a semiconductor device with a partly recessed oxide pattern in a silicon body to be manufactured, without the necessity of extra process steps for providing an alignment grating necessary for the manufacture of the semiconductor device.
To achieve this, the inventive method mentioned in the opening paragraph is characterized in that the alignment grating and the partly recessed oxide pattern are provided simultaneously, the material which protects against oxidation being provided at the location of the alignment grating to be produced so as to comprise first wide strips, where the surface remains entirely free of recessed oxide, which alternate with second wide strips, which are each formed by a sub-pattern of relatively narrow strips of the material which protects against oxidation, which narrow strips are separated from each other by relatively narrow apertures, which are smaller than the apertures at the location of the semiconductor device, whereafter, during oxidation, each of the second wide strips is provided with a segmented, also partly recessed, oxide pattern with a profiled surface, the relatively narrow apertures having a width such that the recessed oxide pattern in the alignment grating is thinner than the simultaneously formed recessed oxide pattern in the semiconductor device. It has been established by experiment that if a silicon body, on which a mask of a material providing a shield against oxidation is provided, which mask is patterned at the location of the alignment grating to be formed, as mentioned in the measure of the invention, is subjected to oxidation, oxide is formed in the relatively narrow apertures at the location of the alignment grating, the thickness of the oxide being smaller than that of the oxide simultaneously formed in the apertures at the location of the semiconductor device. The smaller the apertures made at the location of the alignment grating, the thinner the oxide in these apertures ultimately becomes. In the method in accordance with the invention, this is used to create, at the location of the alignment grating, a difference in height necessary for aligning the silicon body, which difference in height is smaller than that which would be created if the oxide could also attain the full thickness at the location of the alignment grating, i.e. the thickness at the location of the semiconductor device. In this manner, it is possible to provide an oxide pattern which is partly recessed in the silicon body and simultaneously provide the surface of the silicon body with an alignment grating necessary for the further manufacture of the semiconductor device, without this leading to extra process steps and hence extra process costs.
An embodiment of the method in accordance with the invention is characterized in that the alignment grating is used, both in process steps preceding the provision of the opaque layer and in subsequent process steps, to align the silicon body relative to the masks used in the relevant process steps. By virtue thereof, the alignment grating can be used for aligning purposes throughout the manufacture of the semiconductor device.
An embodiment of the method in accordance with the invention is characterized in that the recessed oxide pattern in the alignment grating is provided in such a manner that at the location of the alignment grating an average optical difference in height is achieved between the first and the second wide strips, which corresponds approximately to (2n+1)&lgr;/4, where n is an integer ≧0 and &lgr; is the wavelength of the light used for aligning. In order to minimize aligning errors during aligning the silicon body relative to a mask, it is favorable to create an average optical difference in height corresponding to approximately (2n+1)&lgr;/4 at the location of the alignment grating.
An embodiment of the method in accordance with the invention is characterized in that approximately &lgr;/4 is used as the average optical difference in height. As mentioned hereinabove, it has been found that the smaller the relatively narrow apertures at the location of the alignment grating are, the thinner the oxide in these apertures eventually becomes. In view of a possible future shift to smaller pitches as a result of, for example, the steadily increasing use of higher diffraction-order signals for aligning the silicon body, an average optical difference in height of approximately &lgr;/4 has the advantage that relatively small pitches are possible.
An embodiment of the method in accordance with the invention is characterized in that the recessed oxide pattern in the alignment grating is provided so as to have an average thickness in the range from approximately 0.1 to 0.4 &mgr;m. For a usable range of wavelengths lying between 500 and 1100 nm, it has been found that, if the thickness of the recessed oxide pattern in the alignment grating lies in the range from approximately 0.1 to 0.4 &mgr;m, an average optical difference in height corresponding to approximately &lgr;/4 is achieved between the first and second wide strips of the alignment grating, thereby minimizing alignment errors.
An embodiment of the method in accordance with the invention is characterized in that the recessed oxide pattern in the semiconductor device is provided so as to have a thickness ranging from 0.5 to 1.0 &mgr;m. If the thickness of the recessed oxide pattern in the semiconductor device lies in the above-indicated range, it is possible, using the method in accordance with the invention, to create the optical difference in height, necessary for aligning,
Driessen Frank A. J. M.
Muller Christiaan J.
Biren Steven R.
Nelms David
Nhu David
U.S. Philips Corporation
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