Active solid-state devices (e.g. – transistors – solid-state diode – Combined with electrical contact or lead – Solder wettable contact – lead – or bond
Reexamination Certificate
2003-04-28
2004-07-06
Lam, Cathy (Department: 1775)
Active solid-state devices (e.g., transistors, solid-state diode
Combined with electrical contact or lead
Solder wettable contact, lead, or bond
C257S780000, C257S781000
Reexamination Certificate
active
06759751
ABSTRACT:
TECHNICAL FIELD
The invention pertains to methods of electroless deposition of nickel over aluminum-containing materials and copper-containing materials, and in particular embodiments pertains to methods of forming under bump metallurgy (UBM) for subsequent solder bumps.
BACKGROUND OF THE INVENTION
Conductive bumps are currently being utilized for connecting integrated circuitry associated with a semiconductor chip to other circuitry external of the integrated circuitry. Solder bumps are utilized in, for example, flip chip applications, multi-chip module applications, and chip scale packaging applications.
An exemplary solder bump construction is described with reference to FIG.
1
. Specifically,
FIG. 1
illustrates a fragment
10
of a semiconductor construction. Fragment
10
comprises a substrate
12
having a conductive layer
14
supported thereon. Substrate
12
can include a semiconductive material, such as, for example, monocrystalline silicon. To aid in interpretation of the claims that follow, the terms “semiconductive substrate” and “semiconductor substrate” are defined to mean any construction comprising semiconductive material, including, but not limited to, bulk semiconductive materials such as a semiconductive wafer (either alone or in assemblies comprising other materials thereon), and semiconductive material layers (either alone or in assemblies comprising other materials). The term “substrate” refers to any supporting structure, including, but not limited to, the semiconductive substrates described above. Additionally, the terms “material” and “layer” are to be understood to encompass pluralities of materials and layers, as well as single materials and layers, unless specifically stated otherwise.
Conductive material
14
can comprise a metallic material, such as, for example, one or more of aluminum and copper. In particular applications, conductive material
14
comprises aluminum or copper.
Substrate
12
can further include various circuit components (not shown), such as, for example, capacitors and transistors; and additionally can include insulative materials. Conductive material
14
can electrically connect with various of the circuit components associated with substrate
12
.
An adhesion layer
16
is formed over conductive material
14
. Adhesion layer
16
comprises, for example, titanium; and is utilized to improve adhesion of a masking material to the conductive material
14
. For instance, if conductive material
14
comprises aluminum, a titanium-containing adhesion layer
16
can improve adhesion of various masking materials (such as materials comprising polyamide or BCB) over the aluminum.
A masking layer
18
is formed over adhesion layer
16
. Masking layer
18
can comprise, for example, polyamide or BCB materials (with BCB materials being materials derived from bisbenzocyclobutane chemistry). Masking layer
18
can be patterned by providing photoresist (not shown) over the masking layer, using photolithographic methods to pattern the photoresist, and subsequently transferring a pattern from the photoresist to layer
18
with an appropriate etch.
The patterning of masking layer
18
forms an opening
20
extending through patterned masking layer
18
. Opening
20
is shown extending through adhesion layer
16
and to conductive material
14
. The shown opening
20
can be formed by first patterning masking layer
18
to expose a portion of adhesion layer
16
, and subsequently removing the exposed portion of adhesion layer
16
to extend the opening entirely through layer
16
and to conductive material
14
.
A nickel-containing layer
22
is formed within opening
20
and over conductive material
14
. Nickel-containing layer
22
can be formed by, for example, electroless deposition, which is also referred to as autocatalytic electrolytic deposition (AED). Prior to the electroless deposition of nickel-containing layer
22
, aluminum-containing material
14
within opening
20
is cleaned, and then subjected to activation with a zinc-containing solution. Such activation forms a thin zinc-containing material (not shown) over aluminum-containing layer
14
. Subsequently, nickel-containing layer
22
is formed on the thin zinc-containing material by reduction of nickel from a nickel salt. An exemplary chemistry for electroless deposition of zinc comprises reactions I and II.
NiSO
4
+2
e
−→Ni+SO
4
2−
I.
3H
+
+(NH
4
)
2
H
3
P
2
O
4
→2NH
4
+
+2H
3
PO
2
−
+2
e−
II.
After formation of nickel-containing layer
22
, a gold-containing layer
24
is formed over nickel-containing layer
22
. Gold-containing layer
24
can be formed by electroless deposition utilizing, for example, gold sulfide as a source of gold. The gold can be used as a wetting agent for subsequent solder formation.
It is noted that nickel-containing layer
22
can consist of, or consist essentially of, nickel; and that gold-containing layer
24
can consist of, or consist essentially of, gold.
A solder bump
26
is formed over gold-containing layer
24
. Solder bump
26
can comprise, for example, a tin and/or lead-based solder.
The methodology described above is typical of what would be utilized for forming a solder bump over a layer
14
which comprises predominantly aluminum (i.e, comprises more than 50 atomic percent aluminum), consists essentially of aluminum, or consists of aluminum. If layer
14
comprises copper, the methodology will typically be somewhat different. For instance, adhesion layer
16
will typically be eliminated, and masking layer
18
will typically comprise BCB materials. Further, a layer
14
which comprises predominantly copper, consists essentially of copper, or consists of copper, will typically be exposed to an activation solution which comprises palladium, instead of zinc, to form a thin layer of palladium (not shown) over layer
14
. Subsequently, nickel-containing layer
22
will be formed over the thin layer of palladium utilizing the electroless chemistry described previously, and gold layer
24
will be formed over nickel-containing layer
22
utilizing electroless chemistry. Finally, solder bump
26
can be formed over gold layer
24
.
It would be desirable to develop improved methods for forming electrical connections from solder bumps to conductive materials associated with semiconductor substrates.
SUMMARY OF THE INVENTION
In one aspect, the invention encompasses a method of electroless deposition of nickel over an aluminum-containing material. A mass is formed over the aluminum-containing material, with the mass predominantly comprising a metal other than aluminum. The mass is exposed to palladium, and subsequently nickel is electroless deposited over the mass.
In another aspect, the invention encompasses a method of electroless deposition of nickel over aluminum-containing materials and copper-containing materials. The aluminum-containing materials and copper-containing materials are both exposed to palladium-containing solutions prior to electroless deposition of nickel over the aluminum-containing materials and copper-containing materials.
In another aspect, the invention encompasses a method of forming a solder bump over a first material. The first material comprises one or both of aluminum and copper material. A titanium-containing material is formed over the first material, and a patterned mask is formed over the titanium-containing material. The patterned mask comprises polyamide and/or a BCB material, and has an opening extending therethrough to the titanium-containing material to expose a portion of the titanium-containing material. A palladium-containing material is formed on the exposed portion of the titanium-containing material. A nickel-containing material is electroless deposited on the palladium-containing material, and a gold-containing material is formed on the nickel-containing material. Finally, a solder bump is formed over the gold-containing material.
REFERENCES:
patent: 3599060 (1971-08-01), Triggs et al.
patent: 38253
Lam Cathy
Micro)n Technology, Inc.
Wells St. John P.S.
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