Semiconductor device manufacturing: process – Formation of electrically isolated lateral semiconductive... – Having substrate registration feature
Reexamination Certificate
1998-12-31
2001-04-10
Zarabian, Amir (Department: 2824)
Semiconductor device manufacturing: process
Formation of electrically isolated lateral semiconductive...
Having substrate registration feature
C438S410000, C438S258000, C029S516000, C029S516000
Reexamination Certificate
active
06214692
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a method for the aligned joining of disk-shaped semiconductor substrates, so-called wafers, provided with alignment marks, which are held on substrate carriers, wherein the wafers are adjusted to a parallel position of their sides facing towards each other, are aligned according to alignment marks provided on these sides, and are then joined, where for detecting the alignment marks to be brought to coincidence there are used microscope units with coaxial lenses directed towards opposite sides.
DESCRIPTION OF THE PRIOR ART
This invention also relates to an apparatus for performing this method, comprising a processing station used for joining the semiconductor substrates having alignment marks, in which processing station two substrate carriers are provided for holding one semiconductor substrate each, of which the second substrate carrier can be moved with respect to the first substrate carrier in the three coordinate directions by means of actuators and can be rotated about an axis extending normal to the supporting plane of the semiconductor substrate, measuring means and actuators for determining and adjusting the relative positions of the two substrate carriers and of the substrates held on the same, and microscope units with coaxial lenses directed towards opposite sides for monitoring the mutual alignment of the semiconductor substrates by detecting pairs of alignment marks provided on their sides to be mounted opposite each other.
Such methods and apparatuses are required to provide for a rather precise alignment of two wafers, which must be joined or which complete each other. In the microstructures commonly used in semiconductor technology, the alignment accuracy achievable by means of mechanical alignment aids, e.g. flats or notches at the edge of the wafer, is not sufficient, so that corresponding methods and apparatuses must be used for fine alignment, which mostly concerns only fractions of a millimeter, but accuracies in the &mgr;-range and below.
A method and an apparatus as described above are known from practice in such a form that in the processing station microscope units can be mounted so as to be moved in and out, where these microscope units each have two divergent, but rather coaxial lenses which form images of the alignment marks of the opposing wafers, so that—mostly by using electronic image generators at the microscopes—a mutual alignment to coincidence of the images of the alignment marks becomes possible. The alignment accuracy depends on the accuracy of the alignment of the two lenses with respect to the measuring axis. Because the microscope units are mounted and can be moved in and out between the wafers, the same must be mounted in the processing station at a large distance from each other during the adjustment and be moved with respect to each other only subsequently, where first of all the microscope units must be moved out of the area of adjustment. When the optical measuring axes of the microscope units do not precisely correspond with each other and with the axis of movement of the actuator joining the wafers, or when a clearance of the actuator provides for only minimum lateral deviations, virtually non-correctable errors occur during the joining of the wafers. The large distances of the wafers to be maintained merely for moving in and out the microscope units are not necessary as such for the normal production and lead to an unnecessary complication in the total design of the processing station and to the adjustment errors mentioned above. In other known methods there should be used wafers with alignment marks mounted on both sides so as to coincide with each other. In this case, the adjustment can be effected by means of appropriate microscopes according to the alignment marks pointing to the outside, and shorter adjusting paths or distances between the wafers are required, but here as well the processing station is loaded by the microscopes, and the adjustment accuracy depends on the accuracy with which the additional outer alignment marks are provided, for which additional processing steps must be performed.
SUMMARY OF THE INVENTION
It is the object of the invention to create a method as described above and an apparatus suitable for performing said method, by means of which method or apparatus a high alignment accuracy between the wafers can be achieved, while the design of the processing station is simplified.
In terms of a method, this object is solved in accordance with the invention in that the substrate carrier for the one semiconductor substrate is at least movable in a coordinate direction approximately parallel to the main plane of the semiconductor substrate from a processing station into a measuring station, and the other substrate carrier is movable in the three coordinate directions, is rotatable about an axis normal to the main plane of the semiconductor substrate carried by the same, and for wedge error compensation is adjusted in its tilted position with respect to the other substrate carrier, where via measuring and control means set positions of the substrate carriers are detected and reproduced, that in the measuring stations the two lenses of the microscope units are mounted at a distance from each other and facing towards each other, so that the substrate carriers with the substrates can be introduced between the same, where these substrate carriers are moved into the measuring station one after the other, and upon introduction of the first substrate carrier, the microscope units with their corresponding lenses are adjusted to the alignment marks of the semiconductor substrate held at the first substrate carrier, this first substrate carrier is then moved back, and the second substrate carrier now introduced is adjusted to the other lenses of the microscope units, even if the microscope setting remains unchanged, for aligning the alignment marks of the semiconductor substrate carried by the same, and that finally the substrate carriers are joined with the aligned semiconductor substrates outside the measuring station.
By providing the microscope units outside the processing station in a separate measuring station, a considerable simplification is achieved in terms of design and size of the processing station, and in particular the adjusting paths to be maintained for joining the wafers can be reduced to the necessary extent. Since the microscope units have lenses facing towards each other—which may in turn be connected with electronic image generators to simplify the monitoring—the microscope units are not moved between the wafers, as in the known methods, but the wafers are moved between the lenses of the microscope units, where the distance of the lenses of a lens pair should substantially only cover the thickness of a substrate carrier and the wafer lying thereon.
It is common practice to withdraw the wafers from magazines and lay the same onto the substrate carriers by means of corresponding devices, on which substrate carriers they are fixed for instance by a vacuum or also by electrostatic forces. In the magazines, the wafers are mostly aligned equal to each other and accordingly bear the respective alignment marks pointing to the same side. Accordingly, the mechanical alignment aids, i.e. the above-mentioned flats or notches, are present in both wafers to be joined in the same arrangement with respect to the alignment marks. Substantially identical conditions are obtained when the wafers are roughly aligned in a preadjusting station, mostly by using auxiliary optical means. In consideration of these facts, a simplification of the necessary adjusting and working operations is achieved in the method in accordance with the invention in that both semiconductor substrates are laid and onto the associated substrate carriers with alignment marks pointing towards the same side, and fixed, and when the associated substrate has been laid onto the one substrate carrier, the same is turned for predetermining the desired opposite position of the two substrates.
A preferred
Collard & Roe P.C.
Luu Pho
Zarabian Amir
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