Optical: systems and elements – Lens – With viewed object support
Reexamination Certificate
2000-11-29
2004-05-04
Mai, Huy (Department: 2873)
Optical: systems and elements
Lens
With viewed object support
C359S808000, C359S811000, C250S492200, C430S022000
Reexamination Certificate
active
06731438
ABSTRACT:
BACKGROUND OF THE INVENTION
Alignment marks are a commonly used tool, especially in photolithographic processes. Successive masks used in the patterning of substrate or subsequent layers must be aligned with respect to each other. As a result, it is common to form alignment mark(s) in a substrate or subsequent layer, for example, and then develop that alignment mark. Subsequent lithographic processes can then be aligned to that mark.
Alignment marks can also be used during the subsequent packaging of the semiconductor device. For example, an alignment mark generated in a previous photolithographic process can be used during singulation or by a pick-and-place machine to align the semiconductor device to its package.
SUMMARY OF THE INVENTION
When manufacturing alignment marks, it is generally required that the alignment marks have some feature that can be easily identified and located with a high degree of precision. For example, cross-style alignment marks are a common configuration in which the lines of the cross are precisely formed. Each line of this cross allows the masks to be aligned in one dimension. The lines together thus allow the two dimensional alignment of the mask to the substrate to the precision to which the lines of the cross can be located.
The requirement for precise lines or “hard edges” in typical alignment mark structures is difficult to obtain in a sub-class of photolithographically-based processes in which edges are smoothed in subsequent processing. One of example of such a process is the mass transport process that is used to manufacture small optical structures. Specifically, this technique is described in U.S. Pat. Nos.: 5,807,622 or 5,618,474. The general scheme is to etch structures or mesas in a substrate using reactive ion etching. The width of the mesas is related to a desired contour line of the surface of the element to be produced in that the volume of substrate material relocated from above a predetermined desired contour line is equal to the volume to be filled below the predetermined contour line. The substrate is then baked or heat-treated to relocate substrate material, from adjacent mesas, to fill in voids in the space between mesas to produce a smooth surface on the substrate conforming to the predetermined contour of the surface of the element. These characteristics of the mass transport process make it difficult to manufacture the hard edged alignment features that are associated with common strategies.
The present invention is directed to a technique for creating an alignment feature in mass transported substrates. It yields alignment features that can be located with high degrees of accuracy. Specifically, structures are created that yield a light pattern when the part of the substrate is imaged or a plane near the substrate is imaged. This light pattern is then used to align the substrate during subsequent lithography or packaging processes.
In general, according to one aspect, the invention features a mass transported alignment mark system. This system comprises a substrate that has been subjected to a mass transport process and a lens structure formed on the substrate that yields a light pattern when the substrate or a plane near the substrate is imaged.
Generally, a light pattern above the substrate is useful when alignment is performed with a non-contact mask aligner. Typically, such aligners position the mask near the substrate, typically closer than 200-500 micrometers from the top surface of the substrate. Thus, focal lengths for the inventive lens structures will usually be less than 200-600 micrometers when the depth of the feature below the substrate surface is taken into account. Typically, the deepest point of the lens structures are depressed from the surface of the substrate by 0.25 to 25 micrometers after mass transport.
Typically, the substrate is currently gallium phosphide, although, in other embodiments, silicon substrates, for example, are used.
In the current implementation, the alignment marks are used to align a subsequent metal layer to the light pattern, and thus, the lens structure. This metal layer is used in metal, such as solder or thermo-compression, bonding processes.
In the preferred embodiment, the lens structure that is created is concave. Presently, concave cylindrical lenses are used that have been formed in the substrate. These lens structures focus light preferably near a surface of the substrate in reflection. Thus, when the substrate is viewed with an imaging system, such as a microscope system of a mask aligner, the lens shaped alignment marks appear as bright lines to the imaging system.
In general, according to another aspect, the invention features an alignment mark system that comprises a substrate and a lens structure formed in the substrate that has a focal point in the substrate or near a surface of the substrate.
The above and other features of the invention including various novel details of construction and combinations of parts, and other advantages, will now be more particularly described with reference to the accompanying drawings and pointed out in the claims. It will be understood that the particular method and device embodying the invention are shown by way of illustration and not as a limitation of the invention. The principles and features of this invention may be employed in various and numerous embodiments without departing from the scope of the invention.
REFERENCES:
patent: 4935939 (1990-06-01), Liau et al.
patent: 5674650 (1997-10-01), Dirksen et al.
patent: 5807622 (1998-09-01), Liau et al.
patent: 5933228 (1999-08-01), Taylor et al.
Liau Zong Long
Stern Margaret B.
Axsun Technologies, Inc.
Houston J. Grant
Mai Huy
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