Methods of restricting silicon migration

Details Methods of restricting silicon migration Methods of restricting silicon migration

2000-06-13

2002-10-22

Nelms, David (Department: 2818)

Semiconductor device manufacturing: process

Coating with electrically or thermally conductive material

To form ohmic contact to semiconductive material

C438S680000, C438S151000, C438S152000, C438S166000

Reexamination Certificate

active

06468905

ABSTRACT:

TECHNICAL FIELD
This invention relates to methods of forming refractory metal silicide components and methods of restricting silicon surface migration of an etched silicon structure relative to a surface of an underlying refractory metal layer.
BACKGROUND OF THE INVENTION
Fabrication of semiconductor devices involves forming electrical interconnections between electrical components on a wafer. Electrical components include transistors and other devices which can be fabricated on the wafer. One type of electrical interconnection comprises a conductive silicide line the advantages of which include higher conductivities and accordingly, lower resistivities.
Typically, conductive silicide components can be formed by blanket depositing a layer of refractory metal over the wafer and then blanket depositing a layer of silicon over the refractory metal layer. For example, referring to
FIG. 1
, an exemplary wafer fragment in process is shown generally at
10
and includes a substrate
12
. Exemplary materials for substrate
12
comprise suitable semiconductive substrate materials and/or other insulative materials such as SiO
2
. As used is this document, the term “semiconductive substrate” will be understood 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. A refractory metal layer
14
is formed over substrate
12
followed by formation of a layer
16
of silicon.
Referring to
FIG. 2
, layer
16
is patterned and etched to form a plurality of silicon-containing structures
17
. Silicon-containing structures
17
constitute structures from which electrical interconnects are to be formed relative to wafer
10
. The etching of the silicon-containing structures defines a silicon-containing structure dimension d
1
and a silicon-containing structure separation distance d
2
. In the illustrated example, d
1
is substantially equal to d
2
. Such relationship between d
1
and d
2
results from a desire to use as much of the wafer real estate as is available. Accordingly, the spacing between the silicon-containing structures reflects a critical dimension which is a function of the limitations defined by the photolithography technology available. The goal is to get the silicon-containing structures as close as possible to conserve wafer real estate.
Referring to
FIG. 3
, substrate
12
is exposed to suitable conditions to cause a reaction between the refractory metal layer
14
and the silicon-containing structures
17
. Typical conditions include a high temperature annealing step conducted at a temperature of about 675° C. for about 40 seconds. Subsequently, the unreacted refractory metal is stripped from the wafer. The resulting refractory metal silicide components or lines are illustrated at
18
where the resulting line dimensions d
1
′ can be seen to be larger than the silicon-containing structure dimensions d
1
(
FIG. 2
) from which each was formed. Accordingly, the relative spacing or separation between the lines is illustrated at d
2
′. With the attendant widening of the silicide components or lines, the separation distance between them is correspondingly reduced. A major cause of this widening is the diffusive nature of the silicon from which the
FIG. 2
silicon-containing structures are formed. That is, because silicon is highly diffusive in nature, the formation of the
FIG. 3
silicide components causes a surface migration of the silicon relative to the underlying substrate. In the past, when device dimensions were larger, the migration of silicon during silicide formation was not a problem. Adequate spacing between the resulting silicide lines ensured that there would be much less chance of two or more components shorting together. However, as device dimensions grow smaller, particularly at the 0.35 &mgr;m generation and beyond, there is an increased chance of shorting. This is effectively illustrated in
FIG. 4
where two refractory metal components
19
can be seen to engage one another and hence short together at
20
.
This invention grew out of concerns associated with forming silicide components. This invention also grew out of concerns associated with improving the integrity of electrical interconnections as device dimensions grow ever smaller.
SUMMARY OF THE INVENTION
Methods of forming refractory metal silicide components are described. In accordance with one implementation, a refractory metal layer is formed over a substrate. A silicon-containing structure is formed over the refractory metal layer and a silicon diffusion restricting layer is formed over at least some of the silicon-containing structure. The substrate is subsequently annealed at a temperature which is sufficient to cause a reaction between at least some of the refractory metal layer and at least some of the silicon-containing structure to at least partially form a refractory metal silicide component. In accordance with one aspect of the invention, a silicon diffusion restricting layer is formed over or within the refractory metal layer in a step which is common with the forming of the silicon diffusion restricting layer over the silicon-containing structure. In a preferred implementation, the silicon diffusion restricting layers are formed by exposing the substrate to nitridizing conditions which are sufficient to form a nitride-containing layer over the silicon-containing structure, and a refractory metal nitride compound within the refractory metal layer. A preferred refractory metal is titanium.


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