Active solid-state devices (e.g. – transistors – solid-state diode – Alignment marks
Reexamination Certificate
2001-09-28
2003-03-04
Cao, Phat X. (Department: 2814)
Active solid-state devices (e.g., transistors, solid-state diode
Alignment marks
C257S798000
Reexamination Certificate
active
06528895
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention is generally related to integrated circuits and more specifically to integrated circuit processing, design, and debugging.
2. Description of the Related Art
Prior art fiducials have typically been produced with a single layer or multiple layers of metals deposited on a semiconductor substrate in a characteristic shape, such as a cross or plus-sign (‘+’) shape, or some similar but recognizable shape. By using a recognizable shape, these fiducials have been constrained to be large patterns which prove distinctive when viewed by the people who use them for navigating on a semiconductor integrated circuit. A fiducial in the prior art would often consume a square-shaped space on the integrated circuit 150 &mgr;m on a side, which could only be used for the fiducial, not for any active circuitry. As a result, valuable resources on the integrated circuit would be unavailable in that region.
FIG. 1
illustrates one prior art scheme for placement of fiducials. Package
1
10
contains integrated circuit
130
. Package
110
also have four package fiducials
120
located on the outside of package
110
, which are used by someone who needs to locate a specific portion of integrated circuit
130
. After locating and aligning to a first package fiducial
120
, a portion of the package
110
may be removed to expose integrated circuit
130
. Each of four fiducials
140
are incorporated into integrated circuit
130
. Upon aligning to a first fiducial
140
, a person may then navigate over the integrated circuit
130
by looking at a layout diagram of integrated circuit
130
which shows the location of the fiducials
140
relative to the circuitry incorporated in integrated circuit
130
.
As will be appreciated, positioning the fiducials such as fiducials
140
proves difficult due to constraints on available space on integrated circuit
130
. In the case of a fiducial consuming a square of space 150 &mgr;m on a side, four such squares must be reserved in the area available on integrated circuit
130
, and no other signals may be routed in those reserved areas. In some prior art processes, the fiducial must be deposited in every significant layer of deposition in the semiconductor fabrication process.
Furthermore, even in situations in which automated alignment equipment is used, such equipment must use an optical system for locating the fiducials. Whether human, mechanical, or some combination of human and mechanical, the optical systems are limited by their inability to resolve images below a certain size (length or area) threshold on semiconductor devices. This limitation leads to a limitation on the size of fiducials used for alignment when using optical alignment systems, thus leading to the 150 &mgr;m length of prior art fiducials. It will be appreciated that even though an optical system may be capable of resolving features much smaller than the overall size of a fiducial, that the need for a distinctive shape of the fiducial leads to a fiducial much larger than the size of the smallest feature an optical system may resolve.
SUMMARY OF THE INVENTION
In one embodiment, the invention includes a method. The method includes scanning a light source over a surface of an integrated circuit. The method also includes measuring a photo-induced current from a fiducial in the integrated circuit. The method also includes correlating the current to a position of the light source as the scanning progresses.
REFERENCES:
patent: 5497033 (1996-03-01), Fillion et al.
patent: 5940545 (1999-08-01), Kash et al.
patent: 5942805 (1999-08-01), Winer et al.
patent: 5948466 (1999-09-01), Sarashina et al.
patent: 5963781 (1999-10-01), Winer
patent: 6287876 (2001-09-01), Fujiwara
US 6,304,668, 10/2001, Evans et al. (withdrawn)
Livengood Richard
Winer Paul
Blakely , Sokoloff, Taylor & Zafman LLP
Cao Phat X.
Intel Corporation
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