Valves and valve actuation – Rotary valves – Ball valve
Reexamination Certificate
1999-04-30
2002-04-23
Loke, Steven (Department: 2811)
Valves and valve actuation
Rotary valves
Ball valve
C257S762000, C257S764000
Reexamination Certificate
active
06375159
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a fuse element used in integrated circuit devices, and more particularly to the structure of a fuse link to be deleted by laser radiation. The invention further relates to the method of making the fuse link.
2. Description of Related Art
Fuses are used in semiconductor chips to provide redundancy, electrical chip identification, and customization of function. For designs having three (or more) layers of wiring, the fuses are typically formed from a segment of one of the wiring layers, usually the last metal layer or the penultimate metal layer, i.e., the “last metal minus one” wiring layer.
Fusing is the deletion of a segment of metal fuse line. One standard way this can be accomplished is by exposing the segment to a short, high intensity pulse of light energy from a laser, typically having infrared wavelength. The metal line absorbs the laser light energy, melts, and ruptures, disrupting line continuity and causing high electrical resistance, i.e., an open line. A sensing circuit may be used to detect this fuse segment resistance. The technique of laser fuse deleting or trimming has been widely used both in memory and logic integrated circuit fabrication.
Fuse fabrication has taken advantage of the energy transfer from infrared laser light. Lasers allow for precise selection and illumination of integrate circuit segments. Using this technology to delete fuse links facilitates IC fabrication. For example, in U.S. Pat. No. 5,608,257 issued to Lee, et al., on Mar. 4, 1997, entitled, “FUSE ELEMENT FOR EFFECTIVE LASER BLOW IN AN INTEGRATED CIRCUIT DEVICE,” a fuse structure is taught that increases absorption of the laser energy, having a melt-away elongated fuse link joining two segments of an interconnecting line, a plurality of fins integral and coplanar to the fuse link such that each of the fins transversally extends away from the fuse link, and a reflecting plate positioned underneath the fuse link to reflect the applied laser energy. By adding structure to the fuse link (fins and reflective pad), the fuse is made more absorptive of the infrared laser energy. Thus, minimizing the incident energy required to delete the fuse.
In some circuits, such as CMOS logic circuits, the fuses are located in arrays close together. This close proximity of fuses provides technical challenges when infrared laser light is applied to blow a particular fuse. Spurious reflections of beam energy and the explosive effects of fuse blowing can adversely affect any element adjacent to the blown fuse link.
In U.S. Pat. No. 5,420,455, issued to Gilmour, et al., on May 30, 1995, entitled, “ARRAY FUSE DAMAGE PROTECTION DEVICES AND FABRICATION METHOD,” an approach to limit these reflections is taught by adding non-frangible, high melting point barriers, positioned adjacent to the fuse structures, to prevent both the beam energy and the effects of fuse blowing to reach or affect any adjacent element in the circuit. These barriers act as protective shields for adjacent structures.
Inter-element dimensions in these arrays remain an essential characteristic. However, technology advances require that these dimensions continue to get smaller.
As the reflectivity, mass, and melting temperature of the fuse link metal increases, higher laser energies and longer (or multiple) laser pulses are required to accomplish deletion of the fusible link. These higher energies and longer pulses provide sufficient energy to adjacent and underlying structures, e.g., silicon under the fuse area, to cause severe damage to the interlayer dielectric oxide and adjacent fuse wiring. Additionally, infrared laser deletion of copper fuses is more difficult due to the high reflectivity of copper, especially in the 1.0 to 1.4 &mgr;m wavelength range that is commonly available in laser fuser tools.
Bearing in mind the problems and deficiencies of the prior art, it is therefore an object of the present invention to provide a fusible link structure and method for making the same that allows for deletion of fuses having high reflective, high melting point conductors, when exposed to an infrared laser energy beam at energy levels lower than that required in the current state of the art for blowing fuse links.
It is another object of the present invention to provide a fusible link with increased absorption to infrared laser light.
A further object of the invention is to provide a fusible link that allows for close placement of fuse arrays without structural damage to adjacent structures during fuse deletion, and without the need for protective barriers between adjacent structures.
Still other advantages of the invention will in part be obvious and will in part be apparent from the specification.
SUMMARY OF THE INVENTION
The above and other objects and advantages, which will be apparent to one of skill in the art, are achieved in the present invention which is directed to, in a first aspect, a conductor having a given conductivity characteristic that can be substantially altered by radiation, comprising an electrical conductor having a first layer of a first material that is substantially insensitive to the radiation, and a second layer of a second material that is sensitive to radiation. The sensitivity of the second material is to radiation emitted from a laser in an infrared energy spectrum. The first material is a primary electrical conductor and the second material is an electrical conductor of a composition such that when combined with the primary electrical conductor provides for a high infrared energy absorbing structure.
The first material is copper and the second material is tungsten or a titanium-tungsten composition. The infrared energy spectrum comprises energy having wavelengths in the range of 1.0 to 1.4 &mgr;m. The first layer of the first material is greater than or equal to 500 angstroms in thickness, and the second layer of the second material is greater than or equal to 500 angstroms in thickness.
In a second aspect, the invention is directed to a fusible link that can be selectively opened by laser radiation at a predetermined wavelength, comprising a first conductor that is not substantially absorptive for the radiation at the predetermined wavelength, and a second conductor that is substantially absorptive for the radiation at the predetermined wavelength.
In a third aspect, the invention is directed to a fusible link having a given conductivity characteristic that can be substantially altered by infrared radiation, comprising a first layer of copper, and a second metal layer, wherein the second metal layer is tungsten or titanium-tungsten that is sensitive to the infrared radiation. The infrared radiation comprises energy in the range of 1.0 to 1.4 &mgr;m wavelengths.
In a fourth aspect, the invention is directed to a method for making a conductor on a semiconductor substrate sensitive to incident infrared radiation, comprising the steps of: a) forming a damascene copper wiring underlayer on the semiconductor substrate; b) recessing the copper underlayer to a first predetermined thickness; c) depositing a metal overlayer at a second predetermined thickness on the copper underlayer, having optical properties for absorbing the infrared radiation at an amount greater than the copper underlayer; and, d) polishing the metal overlayer to remove extraneous metal, and having the metal overlayer cover the copper underlayer in its entirety.
The method may further comprise the step of e) completing integrated circuit fabrication or other passivation sequence.
The method step (b), recessing the copper underlayer, further comprises using a blanket wet etch.
In the method step (c), the metal overlayer is tungsten or titanium-tungsten, and depositing the metal overlayer, further comprises using a chemical vapor deposition technique or a sputtering technique. The blanket wet etch comprises ammonium persulfate.
In a fifth aspect, the invention is directed to a method for making a conductor on a semiconductor substrate sensitive to incident infrared radiation,
Daubenspeck Timothy H.
Motsiff William T.
Curcio Robert
Delio & Peterson LLC
International Business Machines - Corporation
Loke Steven
Owens Douglas W.
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