United States Patent [I91
`Lou et al.
`
`5,729,042
`[ill Patent Number:
`~451 Date of Patent: Mar. 17, 1998
`
`[54] RAISED FUSE STRUCTURE FOR LASER
`REPAIR
`
`[75] Inventors: Yung-Song Lou, Ruey-Tung;
`C E q - C h e w Rou, Shan-Wang
`Shiang; l h g Chou, Ne-Hu;
`Chao-Ming Koh, Pao-Shan; Shin-Chi
`Lee, Chu-Tung; Chuen-Nan Chen,
`Hsin chu, all of Taiwan
`
`v3] Assignee: Vanguard International
`Semiconductor Corporation, Hsinchu,
`Taiwan
`
`[21] Appl. No.: 831,877
`Apr. 2, 1997
`
`[22] Filed:
`
`Related U.S. Application Data
`
`[63] Continuation of Ser. No. 514,800, Aug. 14, 1995, aban-
`doned.
`[5 11 Int. C1.6 ..................................................... HOlL 29/00
`1521 U.S. C1. .......................... 2571529; 4281601; 428nOO;
`4281958
`1581 Field of Search ............................. 2571529; 4381132,
`4381601,700,958
`
`1.5 61
`
`References Cited
`m
` DOCUMENTS
`U.S. P
`4,455,194 611984 Yabu et al. ............................. 2571529
`
`W1985 Takayama et al. ....................... 291578
`........................
`711986 C h a n m a r
`2571529
`.....................................
`511988 Takagi
`2571529
`....................................
`W1989 Fischer
`2571529
`311990 Kikuchi et al. ......................... 2571529
`...............................
`@I991 Billig et al.
`357151
`811993 Motonami et al. ..................... 2571529
`811995 Yoshizumi et al. ..................... 2571529
`............... .......................
`;
`711996 Chen
`2571529
`
`Primary hminer-J. Carroll
`Attornex Agent, or Finn--George 0. Saile; Stephen B.
`Ackerrnan
`
`~571
`
`ABSTRACT
`
`A novel raised polycide fusible link structure is described.
`This structure enables a highly reliable laser-cutting process
`to be used in which the fuse can be easily and totally severed
`over a wide range of laser energy levels. The primary feature
`of the structure is that the fusible link is located on apedestal
`that raises it above the surface of the main body of the
`integrated circuit, thereby providing a measure of thermal
`isolation for the fuse when it is irradiated by the laser. An
`efficient process for manufacturing the structure is also
`described.
`
`6 Claims, 2 Drawing Sheets
`
`IPR2015-01087 - Ex. 1008
`Micron Technology, Inc., et al., Petitioners
`1
`
`

`
`US. Patent
`
`Mar. 17, 1998
`
`Sheet 1 of 2
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`F I G .
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`- P r i o r A r t
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`F I G .
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`2
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`

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`US. Patent
`
`Mar. 17, 1998
`
`Sheet 2 of 2
`
`5,729,042
`
`0
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`0 . 5
`1
`1 . 5
`L a s e r E n e r g y ( u J )
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`2
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`F I G . 3
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`L o s e r E n e r g y ( u J )
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`F I G . 4
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`3
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`

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`5,729,042
`
`This is a continuation of Ser. No. 081514,800, filed on
`Aug. 14, 1995, abandoned.
`
`BACKGROUND OF THE INVENITON
`
`and ''
`
`1
`RAISED FUSE STRUCTURE FOR LASER
`REPAIR
`
`2
`No. 5,025,300 June 1991) is concerned withlaser fusedlinks
`and is similar to Takagama in that the link lies at the bottom
`of a trench. Unlike Takagama, Billig also makes use of a
`final protective layer of
`5 Monotami et al. (U.S. Pat. No. 5,241,212 August 1993)
`also place the fuse in a trench but the protective layer stops
`at the trench's top edge, thereby leaving the link itself
`exposed. The upper surface of the fusible link is level with
`(1) Field of the Invention
`the bottom of the trench. In an alternative, optional,
`The invention relates to the general field of semiconductor lo embodiment, a layer of insulation 6-8,000 Angstrom units
`thick is deposited over the fuse. The fuse is heated through
`inkgrated circuits, more particularly to circuits that may be
`laser energy, most of which passes through this optional
`personalized, repaired or modified by means of fusible links.
`layer.
`(2) Description of the Prior Art
`An example of a fusible link structure of the type found
`Semiconductor integrated circuits (ICs) that have opti-
`cannot, in general, be l5 in the prior art is shown in FIG. 1 as a schematic cross-
`mum density
`section. The fusible link (layers 3 and 4) lies on silicon
`repaired or moditied There exists, however, a large class of
`of
`dioxide layer which has been fmed On the 'IJdace
`ICs that are intended to be repairable and/or modifiable. In
`silicon substrate 1 which comprises the integrated circuit.
`certain cases, no real circuit exists until the IC has been
`The fusible link has been overcoated with passivation layers
`personalized by breaking certain connections,
`deter-
`mining how the components are to be connected to one 20
`Experiments on fusible link structures such as the one
`another.
`illustrated in FIG. 1 have shown that the range aver which
`One method for realizing circuits of this type is to arrange
`For
`the applied laser energy may vary is quite
`for some of the connections
`components to be
`example, as shown in FIG. 3, over an energy range of from
`being permanently removed ('pened) as desired 25 0 to 2 microjules, the minimum energy required to cause
`The portion of such a connection that is
`physically
`links to open up was found to be about 0.5 microjoules.
`removed is referred to as a fusible link.
`However, between 0.5 and 1 microjoule, the resistance of
`In general, the method for removing a particular
`links that had been subjected to laser pulses was found to
`link comprises heating it briefly, but with suflicient intensity
`vary over a wide range, from short to open circuits. B~~~~
`so that it vaporizes without appreciably heating other cir- 30 1 and 1.5 microjoules, links that had been subjected to laser
`c u i q in its vicinity. Delivery of the heat pulse that is
`pulses were consistently found to have open circuited, as
`required to produce the selective vaporization of any Par-
`intended. However, in the range of from 1.5 to 2
`ticular fusible link is achieved in one of two ways. An X-Y
`microjoules, a wide variation in link resistance, similar to
`addressing scheme may be used to &fiver a high current
`what was seen for the 0.5 to 1 microjoule range, was again
`pulse to the link that vaporization Occurs as a result of 35 seen. In the latter case, the cause was identified as being the
`~oule heating or a high energy beam of intense laser light
`result of heat reaching the underlying silcon substrate in
`may be directed at the surface of the fusible link for a short
`amounts sufic.ent to melt some of the silicon, which then
`time.
`contributed to the recondensed debris.
`A common problem, associated with both methods of
`should also be noted that, for laser heated links in
`vaporizing fusible links, is that some, or all, of the debris that 40
`the duration of the laser pulse will always be
`slightly longer than the mum he needed to cause the
`is a byproduct of said vaporization process recondenses on
`link to explode. his is inevitable, gven that the exact
`the surface of the IC and may cause short circuiting. This is
`commonly dealt with by coating the entire integrated circuit
`energy nee&. varies slightly from link to link. AS a
`with a layer of insulation as afinal step in the m a n u f a m g
`consequence, the underlying material on which the link
`process, thereby electrically isolatingitfroman~ conductive 45 rested prior to its explosion will be directly exposed to the
`material that may recondense on it. Said final layer of
`laser for a shod be.
`insulation also covers the fusible links, thereby increasing
`S-Y
`OF THE INVENIION
`the mass of material that must be vaporized whenever a
`It is an object of the present invention to provide a fusible
`particular link is to be blown.
`Ideally, all the heat energy that is directed at a particular 50 link structure, opened via laser irradiation, said opening
`process to have no side effects, such as occasional short
`fusible link will be used for effecting its vaporization. In
`circuiting.
`practice, some of this energy will be conducted into the
`A further object of the present invention is to provide a
`substrate, or main body of the integrated circuit, away from
`fusible link that may be opened by means of laser irradiation
`the fusible link. Thus it will not be available for the
`vaporization process and, additionally, it may have an unde 55 over a wide range of laser energies.
`sirable effect on the integrated circuit itself. This phenom-
`Yet another object of the present invention is to provide a
`enon can lead to a narrowing of the process window that is
`process for manufacturing a fusible link having these
`available for heating the link-too
`little energy and vapor-
`characteristics, said process to cost little or nothing more
`ization of the link is incomplete, too much energy and
`than the processes used to manufacture other types of fusible
`surrounding circuitry gets damaged.
`60 link.
`A number of issued patents address various aspects of
`These objects have been achieved in a structure in which
`the fusible link is located on a pedestal that raises it above
`these two problems. Takagama (U.S. Pat. No. 4,536,949
`the surface of the main body of the integrated circuit,
`August 1985) is concerned with electrical (as opposed to
`thereby providing a measure of thermal isolation for the fuse
`laser) fusing. The fusible link sits at the bottom of a deep
`trench on whose walls the products of vaporization are 65 when it is irradiated by the laser. Aprocess for manufactur-
`ing this structure is described in which the link acts as its
`expected to condense, thereby keeping them away from
`other parts of the integrated circuit. Billig et al. (U.S. Pat.
`own self-aligned mask during the forination of saidpedestal.
`
`4
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`

`
`5,729,042
`
`3
`4
`BRIEF DES(XUTION OF THE DRAWINGS
`The laser used for effecting the explosion of the fusible
`Q-switched Nd-do~ed Ythium
`links was a
`FIG. 1 is a schematic cross-section of a fusible link
`thanum Fluoride (YLE) laser. The laser energy was normally
`structure based on prior art.
`in the range between 0.8 and 1.2 microjoules with a spot
`FIG. 2 is a schematic cross-section of a fusible link
`diameter of microns and a pulse width of 35 ns. To
`structure based on the present invention.
`determine whether or not a given link had been successfully
`FIGS. 3 and 4 show the results of laser irradiation of the
`blown, an electrical continuity measurement was
`designs of EGS. 1 and 2 respectively, over a range of
`by applying a constant voltage across the blown fuse and
`incident laser energies.
`then measuring the passing current. The fuse was considered
`10 to have been blown successfully (be in an open state) if the
`DESCRIPTION OF THE PREFERRED
`measured resistance was greater than 10 megohms.
`EMBODIMENTS
`The results of the above described experiments are iUus-
`We will now describe a trpical embodiment of the present
`trated in FIGS.
`and 4- HG. 3 is for the planar @rior art)
`overcomes the deficiencies in the prior art
`invention
`structure. Four distinctregions are shown in the figure, each
`that were described above. Referring to mG. 2, we show in
`15 reflecting different explosion characteristics of the links. In
`of silicon o&e,
`schematic cross-section, a pedestal
`O to Oa5 microjoules, the resistance measure-
`the region
`resting on layer 12 of the same mat&. Layer 12 lies on the
`11, which comprises the inte- ments
`showed a shorted state, indicating that the
`surfaCe of
`incident laser energy was below the threshold level needed
`grated circuit. we
`oxide is the preferred material
`link (and the passivating layers
`for pedestal 10. the invention
`to evaporate the
`still operate
`with any similar material that has relatively low thermal 20 above it)'
`In the region of 0.5 to 1.0 microjoules, a wide range of
`conductivity. For successful operation, the thickness of the
`resistance values was 0bServed In this energy range the
`pedestal may range from about 1,000 to 9,000 Angstrom
`laser heating produced a liquid pressure high enough to
`units, about 5,000 Angstrom units being preferred. The
`fracture the passivating layers. However, due to strong
`thickness of insulating layer 12 immediately beneath the
`but any 25 optical absorption by both the silicide layer and the passi-
`pedestal is typically about 4,000 Angstrom
`vating layers, some of the ejected m material may be
`thickness in the range of about 1,000 to 10,000 Angstrom
`redeposited around the crater and lead to full or partial short
`units would be satisfactory.
`circuiting.
`The fusible link itself comprises two layers. Layer 13
`In the region of 1.0 to 1.5 microjoules. the process worked
`comprises plycrystalline silicon, heavily doped to increase 30
`as intended and an elechfcally open state was obtained for
`its conductivity. Typically, the dopant used was phosphorus
`all cases. This implies that the applied energy was su86lcient
`at an implanted dose of about 5x10~' atomslsq. cm.
`to fully vaporize the link and direct the debris away from the
`Although layer 13 could have a thickness in the general
`crater.
`range of from 100 to 2,000 Angstrom units, we have
`typically used a value of about SOOAngstrom units. Layer 14 35
`In the region of 1.5 to 2.0 microjoules, the resistance was
`comprises tungsten silicide, deposited through chemical
`again found to vary over a substantial range, similar to that
`vapor deposition, typically about 1,500 Angstrom units
`observed for the 0.5 to 1.0 microjoules region. Cross-
`thick, although any thickness in the range of about 500 to
`sectional micrographs showed that this was due to laser
`3,000 Angstrom units would be satisfactory.
`energy having caused the underlying silicon substrate to
`In order to manufacture the structure of FIG. 2, layers 2, 40 become heated to a sufficient degree for some of it to be
`3, and 4 (as shown in FIG. 1) were first deposited onto the
`evaporated and contribute to the debris.
`surface of the integrated circuit. Thereafter, the fusible link
`The above results illustrate that, with the planar design of
`(comprising layem 3 and 4 in FIG. 1) was patterned, using
`the prior art, the process window for laser energy application
`conventional photolithographic techniques, into appropriate
`is rather narrow. h contrast, consider the results illustrated
`shapes that served to connect various Parts of the integrated 45 in FIG. 4 which are for a fusible link structure based on the
`circuit that might, or might not, be severed at a later time, as
`present invention. As can be seen, once the threshold energy
`~ ~ e d e d . m e patterned fuse links were now used as self-
`of 0.5 microjoules has been exceeded, all links, after laser
`&gned masks while about 5,000 Angstrom units of layer 2
`induced explosion, were found to be fully open circuited,
`independent of the laser energy, to at least 2 microjoules.
`were etched away- This was folhwed by the deposition of
`~assivating layers 15 and 16, giving the finished Structure 50 These results confirm that the pedestal design of the present
`the appearance shown in FIG. 2.
`invention serves to confine the laser induced heat to the
`Note that (in FIG. 2) layer 15 comprises about 2,000
`immediate vicinity of the fusible link, thereby greatly mini-
`Angstrom units of boro-phosphosilicate glass. although any
`mizing the side-effects associated with the planar design.
`thickness in the range from 0 to about 7,000 Angstromunits me the invention has been particularly
`and
`would work, while layer 16 comprises about 6,500 Ang- 55 described with reference to this preferred embodiment, it
`strom units of silicon nitride (deposited by means of Plasma
`will be understood by those
`in the art that various
`~nhanced chemical Vapor ~ e p s i t i o n ) although any thick-
`changes in form and details may be made without departing
`ness in the range from 0 to about 7,000 Angstrom units
`from the spirit and scope of the invention.
`would still work.
`What is claimed is:
`In order to evaluate the invention and, particularly, to 60 1. A method for manufacturing a fusible link structure
`compare it to the prior art, a structure embodying the present
`invention (as illustrated in FIG. 2) was compared with a
`structure of the type illustrated in FIG. 1. The thicknesses of
`the various layers involved was the same in both cases. the
`principal difference being the pedestal geometry of the 65
`present invention versus the planar geometry of the prior art
`example.
`
`providing a sacon integrated circuit;
`depositing a first
`layer;
`depositing a fusible link layer;
`patterning said fusible link layer into a shape that is
`suitable for it to be part of the integrated circuit;
`
`5
`
`

`
`5,729,042
`
`5
`using said patterned fusible link layer as a mask, remov-
`ing between 4,000 and 9,000 ~ngstroms of said first
`insulating layer, thereby forming a pedestal on which
`said patterned fusible link layer lies; and
`then coating the structure with a second insulating layer.
`2. The method of claim 1 wherein said first insulating
`layer comprises silicon oxide.
`3. The method of claim 1 wherein the step of coating the
`structure with said secondinsulating layer further comprises
`depositing a layer of boro-phosphosilicate glass and then lo
`depositing a layer of silicon nitride.
`
`*
`
`6
`4. The method of claim 1 wherein said second insulating
`layer is deposited to a thickness that is between 0 and about
`14,000 Angstrom units.
`5. The method of claim 1 wherein the step of depositing
`a fusible link layer further comprises depositing a layer of
`polycrystalline silicon and then depositing a layer of brig-
`sten silicide.
`6. The method of claim 1 wherein the fusible link is
`deposited to athickness that is between about 5,00 and about
`5,000 Angstrom units.
`*
`
`*
`
`*
`
`*
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`
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`6