GB2176938A - Pad metallization structure - Google Patents

Pad metallization structure Download PDF

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Publication number
GB2176938A
GB2176938A GB8613511A GB8613511A GB2176938A GB 2176938 A GB2176938 A GB 2176938A GB 8613511 A GB8613511 A GB 8613511A GB 8613511 A GB8613511 A GB 8613511A GB 2176938 A GB2176938 A GB 2176938A
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Prior art keywords
layer
aluminum
copper
nickel
semiconductor device
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GB8613511A
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GB8613511D0 (en
Inventor
Hem P Takiar
Divyesh P Shah
Jagdish G Belani
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National Semiconductor Corp
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National Semiconductor Corp
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Publication of GB8613511D0 publication Critical patent/GB8613511D0/en
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Abstract

A metallization pad structure for semiconductor devices comprises layers of aluminium 20, nickel 22, and copper 24, deposited directly over a conventional aluminium metallization pad 12. The nickel layer 22 serves to inhibit the migration of copper into the underlying aluminium metallization pad, while the additional aluminium layer inhibits the migration of both nickel and copper into the device substrate. <IMAGE>

Description

SPECIFICATION Pad metallization structure The present invention relates generally to tapeautomated bonding between metallization pads on semiconductor devices and lead frames for these devices. More particularly, the invention relatestoa novel metallization pad structure which is useful for bonding to copper bumped tape and which employs a nickel barrier layerto inhibit migration of copper fromthetape into the underlying aluminum metallization.
Tape automated bonding isa methodforconnecting a plurality of metallization pads on a semiconductor device simultaneouslyto corresponding leads on the lead frame on which the device is to be mounted.
The metallization pads provide input and outputter minalsforthesemiconductordeviceandarecon- nected to individual leads on the lead frame to enable connection of the device to an external circuit such as provided by a printed circuit board. Tape automated bonding is accomplished using a metal tape, typically a thin coppertape, having short connector leads or 'beams' formed therein. By aligning the tape with the semiconductor device, the inner ends ofthe leads may be bonded to the metallization pads on thesemi- conductor device in a single compression, typically thermal compression, step.After the inner end connections are formed, the device is mounted on the lead frame, the outer bonds between the outer ends ofthe beams and the lead frames are formed, and the excess tape is excised.
In forming the inner lead bonds, it is necessary that a projection or'bump' be formed on either the tape or the metallization pad. Such a bump serves to provide the metal necessary for forming the bond, as well as for providing the necessary distance or offset between the connector beam and the semiconductor die. The present invention relates to the use of bumped tape wherein the bumps are formed atthe inner leads ofthe connector beams.
When employing bumped copper tape, it is desirable to prevent or inhibitthe migration ofcopperfrom the tape into the metallization ofthesemiconductor die. Moreover, it is necessary to provide a structure which allows the tape to bond to the metallization pad. Heretofore, copper migration into the aluminum metallization has been prevented by use of atungsten-titanium barrier layer between the copper tape and the aluminum. It would, however, be desirable to avoid deposition ofthetungsten-titanium barrier layer.
It would thus be desirable to provide alternate methods and metallization structures which would facilitate forming of inner lead bonds when using bumped coppertape. In particular, it would be desirable to provide such methods and structures which would avoid the need to utilize titanium-tungsten barriers beneath the metallization pad.
Summary of the invention In one aspect the present invention provides a novel metallization pad structure comprising three metal layers which are deposited sequentially on top of an aluminum metallization pad. Such a three layer structure allows inner lead bonding of bumped coppertapeto a semiconductordie,while simultaneous ly inhibiting the migration of the metals in the layers into the aluminum metallization pad.
The metallization pad structure may be formed by sequentially depositing layers of aluminum, nickel, and copper onto the aluminum metallization pad. The aluminum layer adheres strongly to the underlying metallization pad and may be applied to a sufficient thickness so that the overlying metal layerswillnot penetrate into the silicon substrate. The nickel layer is applied as an intermediate between the aluminum and the overlying copper layer. The nickel layerforms a stable nickel-aluminum alloy at the interface with the aluminum layer. The copper layer may then be applied directly over the nickel layer by sputter deposition, similarlyforming a stable copper nickel alloy at that interface. The nickel layer in the resulting construction acts as a barrier in inhibiting the migration of copper into the aluminum metallization.
Brief description of the drawings Figure 1 illustrates by way of example a metallization pad covered by a pair of insulating layers priorto formation of a metallization pad structure.
Figure2 illustrates the metallization pad of Figure 1 after a hole has been etched in the insulating layers to provide access to the metallization pad.
Figure 3 illustrates the exposed metallization pad of Figure 2 after aluminum, nickel and copper layers have been sequentially applied.
Figure 4 illustrates the metallization pad structure of Figure 3further including a photoresist layer formed thereover.
Figure 5 illustrates the structure of Figure 4, wherein the photoresist layer has been exposed and developed to remove all areas otherthan those overlying the metallization pad.
Figure 6 illustrates by way of example a final metallization pad structure, which has been formed by etching the copper, nickel, and aluminum layers and stripping the photoresist.
Description of the preferred embodiment The present invention provides in a preferred form an improved aluminum metallization pad structure intended for tape automated bonding to copper bumped tape. The preferred form of metallization pad structure comprises three metal layers deposited sequentially over an exposed aluminum metallization pad to define a structure suitable for directthermal compression bonding tothe copper bumped tape.
First, an aluminum layer may be applied directlyto the underlying aluminum metallization pad. The thickness ofthe aluminum layer should be sufficient to inhibit the migration of the subsequently deposited metals into the underlying silicon substrate. A nickel layer maythen be applied directly to the aluminum layer, forming a nickel-aluminum alloyatthe interface. The nickel will adhere strongly to the underlying aluminum forming a stable nickel-aluminum alloy at the interface. Finally, a copper layer may be applied directly over the nickel layer, forming a stable coppernickel alloy at the interface. The copper may be bonded directly to the copper bumped tape to form the inner lead bonds.
Referring nowto Figures 1-6, a preferred process forforming the metallization pad structures will be described in detail. Figure 1 illustrates a semiconductorsubstrate 10 having an aluminum metallization pad 12 formed on its surface. Insulating layers 14 and 16 have been formed over the metallization pad 12, in a known manner. In order to form a metallization pad structure according to the present invention, it is first desirable to provide an access hole through the insulating layers 14 and 16. This may be accomplished by ordinary photolithographictechniques, to provide the access hole 18, as illustrated in Figure 2.
Afterformation ofthe access hole 18, an aluminum layer 20 (Figure 3) may be formed directly overthe aluminum metallization pad 12, as well as covering the insulating layer 16. The thickness of the aluminum layer is not narrowly critical, but should be sufficientlythickto inhibit migration ofthe nickel and copper metals which will be applied in subsequent steps. The aluminum layerwilltypicallyhaveathicknessofat least 2,000 A, more typically being in the range from 2,000 to 6,000 A, usually being about 4,000 A. Since the aluminum layer is being applied directly overthe aluminum metallization pad 12,thealuminum layer may be applied by sputter deposition evaporation or other conventional techniques.Applying aluminum has the advantage that it is unnecessary to remove the aluminum oxide film which would be formed over the aluminum metallization pad 12.
Afterthe aluminum layer 20 is deposited, a nickel layer 22 is deposited directly overthe aluminum layer. The nickel layer may be deposited by sputter deposition, and will form a nickel-aluminum alloy at the interface between layers 20 and 22. The thickness of the nickel layer should besufficientto prevent migration of the copper into the aluminum; it may be at least about 2,000 A, preferably in the range from 2,000 to 5,000 A, and more preferably about 3,000 A.
Copper layer 24 is next deposited by sputter deposition to a thickness of at least 4,000 A, usually in the range from about 4,000 to 15,000 A, more usually about 8,000 A. The copper layer serves to bond directly to the copper bumped tape in a conventional manner.
After the application ofthethree metal layers 20,22 and 24 of the metallization pad structure, a photoresist layer 26 (Figure4) is applied overthesemicon- ductordevice. The photoresist is used to define the limits ofthe metallization pad structure. First, the photoresist is exposed and developed so that the photoresist is removed from most of the area ofthe semiconductor device, but remains overthe metallization pad 12, as illustrated in Figure 5. The copper and nickel layers 22 and 24, respectively, are then etched in a liquid etchant, such as nitric acid and hydrogen peroxide, followed by an aluminum etch in a phosphoric/acetic acid mixture.The etches run until the metal layers are substantially removed from all areas of the semiconductor device except those areas above the metallization pads 12 which are protected by the photoresist caps 26a. Photoresist caps 26a are then removed and the copper cleaned in a mild organic acid, such as citric acid for a short time, typically about 1 minute. The resulting structure is illustrated in Figure 6.
Generally, itwill be desirableto deposit a layer of gold overthe entire semiconductor device, typically using an electroless gold plating solution, such as a gold-cyanide bath for a short time, typically about 5 minutes. The gold layer will be relativelythin,typically having a thickness in the rangefrom about 200 to 1,000 A, usually about 500 A. The semiconductor device is then in a condition for being bonded to the inner leads of a copper bumped tape.

Claims (17)

1. A semiconductor device characterized by having at least one metallization pad structure comprising an aluminum metallization pad, an aluminum layer deposited overthe aluminum metallization pad, a nickel layer deposited directly over the aluminum layertoform a stable aluminum-nickel alloy at the interface and a copper layer deposited overthe nickel layerto allow bonding to copper bonding tape.
2. Asemiconductordeviceaccordingtoclaim 1, wherein the aluminum layer has a thickness in the range from about2,000Ato 6,000 A.
3. A semiconductor device according to claim 1 or claim 2 wherein the nickel layer has a thickness in the range from about2,000Ato 5,000 A.
4. A semiconductor device according to anyforegoing claim, wherein the copper layer has a thickness in the range from about 4,000 A to 15,000 A.
5. A semiconductor device according to any foregoing claim, wherein the semiconductor device is further characterized by a gold layer deposited over the metallization pad structure.
6. A semiconductor device according to claim 5, wherein the gold layer has a thickness in the range from about200Ato 1,000 A.
7. A semiconductor device substantially as hereinbefore described and as illustrated in Figure 6.
8. A method forforming a bonding structure on an aluminum metallization pad, said structure being capable of bonding to copper bumped tape, said method comprising: applying an aluminum layer overthe aluminum metallization pad; applying a nickel layer overthe aluminum layer; and applying a copper layer over the nickel layer.
9. A method according to claim 8, wherein the aluminum layer is applied to a thickness in the range from about2,000Ato 6,000 A.
10. A method according to claim 8 or claim 9, wherein the nickel layer is applied to a thickness in the range from about 2,000 Ato 5,000 A.
11. A method according to any of claims 8to 10, wherein the copper layer is applied to a thickness in the range from about 4,000 Ato 15,000 A.
12. A method according to any of claims 8 to 11, further comprising applying a gold layeroverthe semiconductor device after the copper has been deposited.
13. Amethodaccordingtoclaim 12,whereinthe gold layer is applied to a thickness in the range from about200Ato 1,000A.
14. Amethod according to claim 12 or claim 13, wherein the gold is applied by electroless plating.
15. A method according to any of claims 8 to 14, wherein the aluminum layer is applied by sputter deposition.
16. Amethod according to any of claims 8to 15, wherein the nickel layer is applied by sputter deposition.
17. A method according to anyofclaims8to 16, wherein the copper layer is applied by sputter deposi tion.
GB8613511A 1985-06-24 1986-06-04 Pad metallization structure Withdrawn GB2176938A (en)

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Application Number Priority Date Filing Date Title
US74758885A 1985-06-24 1985-06-24

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GB8613511D0 GB8613511D0 (en) 1986-07-09
GB2176938A true GB2176938A (en) 1987-01-07

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GB8613511A Withdrawn GB2176938A (en) 1985-06-24 1986-06-04 Pad metallization structure

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JP (1) JPS61296752A (en)
DE (1) DE3620405A1 (en)
FR (1) FR2583925A1 (en)
GB (1) GB2176938A (en)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0675674A1 (en) * 1994-04-01 1995-10-04 AT&T Corp. Film circuit metal system for use with bumped IC packages

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1193373A (en) * 1967-01-26 1970-05-28 Philips Electronic Associated Improvements in and relating to Electronic Devices
GB2004686A (en) * 1977-09-21 1979-04-04 Texas Instruments Inc Elevated metal bumps for microelectronic circuits

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1193373A (en) * 1967-01-26 1970-05-28 Philips Electronic Associated Improvements in and relating to Electronic Devices
GB2004686A (en) * 1977-09-21 1979-04-04 Texas Instruments Inc Elevated metal bumps for microelectronic circuits

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0675674A1 (en) * 1994-04-01 1995-10-04 AT&T Corp. Film circuit metal system for use with bumped IC packages

Also Published As

Publication number Publication date
FR2583925A1 (en) 1986-12-26
GB8613511D0 (en) 1986-07-09
JPS61296752A (en) 1986-12-27
DE3620405A1 (en) 1987-01-02

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