Semiconductor device manufacturing: process – Coating with electrically or thermally conductive material – To form ohmic contact to semiconductive material
Reexamination Certificate
2000-03-10
2001-09-25
Chaudhuri, Olik (Department: 2814)
Semiconductor device manufacturing: process
Coating with electrically or thermally conductive material
To form ohmic contact to semiconductive material
C438S658000, C438S664000, C438S683000
Reexamination Certificate
active
06294464
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates in general to a local interconnect, and, more particularly, to a low resistance local interconnect having a refractory metal silicide, and a process of making the same.
In the manufacture of integrated circuits used in the construction of dynamic random access memories (DRAMs), static random access memories (SRAMs), and the like, interconnects are required to provide the necessary electrical paths between field effect transistors and other devices fabricated on the semiconductor substrate and the external circuitry used to pass data to and from these devices. Polycide structures are commonly used to form the gate of a metal oxide semiconductor field effect transistor (MOSFET). Polycide structures are especially attractive for self-aligned gates. A polycide structure is formed by depositing a layer of doped polysilicon over the gate insulation layer. The polysilicon is then etched to define the gate electrode. A refractory metal, such as titanium, is then formed over the remaining polysilicon and silicon substrate. A metal silicide is formed by annealing the polysilicon and the refractory metal with the polysilicon supplying the source of silicon for the silicide. The unreacted refractory metal is etched, with the remaining polysilicon and metal silicide forming the polycide gate.
A local interconnect is typically used to connect the polycide gate to certain active semiconductor areas, such as the drain or source of another MOSFET. A local interconnect may also be used to connect active semiconductor areas to other active semiconductor areas which are separated by an insulating region, such as a field oxide region. Titanium silicide (TiSi
2
) is commonly used as a local interconnect for connecting desired polycide gates and active semiconductor areas. TiSi
2
may be formed through physical vapor deposition (PVD) or chemical vapor deposition (CVD). PVD entails sputtering titanium followed by a layer of silicon. The titanium and silicon are reacted to form TiSi
2
. Silicon from the underlying areas also reacts with the titanium to form TiSi
2
. CVD typically entails reacting titanium tetrachloride (TiCl
4
) and silane (SiH
4
) in the gas phase to form TiSi
2
. Silicon from the underlying areas is also consumed in the CVD reaction to form TiSi
2
.
While TiSi
2
is a relatively low resistive conductor, the titanium is susceptible to oxidation during and after its formation. The resultant titanium dioxide (TiO
2
) increases the sheet resistance of the interconnect thereby increasing power dissipation and reducing the speed of the device. As used herein, sheet resistance is an electrical quantity measured on a thin layer and has the units of ohms/square. Further, a layer of TiO
2
makes it difficult to form good electrical contacts on the TiSi
2
interconnect and poses adhesion problems when subsequent layers are deposited on top of the interconnect line. Further, TiSi
2
is susceptible to damage during subsequent contact formation as the typical contact etch also consumes TiSi
2
. Typically, the size of the interconnect must be increased in order to compensate for damage caused by the contact etch.
Accordingly, there is a need for a local interconnect having a lower resistance and one in which the effects of oxidation are reduced. Preferably, the local interconnect is smaller in width and thickness. There is also a need for a method of forming such a local interconnect. Preferably, such a method would be inexpensive, easy to implement and would not entail excess processing steps.
SUMMARY OF THE INVENTION
The present invention meets these needs by providing a local interconnect formed by a process in which a layer of metal silicide serves both as a hard mask and source of silicon for an underlying layer of metal. The metal silicide is patterned to form the boundaries of the local interconnect and then reacted with the underlying layer of metal. Silicon from the metal silicide combines with the underlying metal to form another metal silicide. An intermetallic compound comprised of metal from the underlying metal layer and metal from the-metal silicide is also formed. Unreacted metal from the underlying metal layer is removed to form the local interconnect. The metal silicide also serves as a contact etch stop during subsequent contact formation thereby allowing for a smaller local interconnect.
According to a first aspect of the present invention, a process of forming a local interconnect comprises providing at least one semiconductor layer. A layer of metal is formed over the at least one semiconductor layer. A contact etch stop is formed over the layer of metal. The layer of metal is reacted with the contact etch stop and then the unreacted metal is removed from the layer of metal to form the local interconnect. The contact etch stop may comprise a metal silicide. The process may further comprise the step of patterning the contact etch stop to form the boundaries of the local interconnect. The step of patterning the contact etch stop to form the boundaries of the local interconnect may be performed prior to the step of reacting the layer of metal with the contact etch stop.
According to another aspect of the present invention, a process of forming a local interconnect comprises providing at least one semiconductor layer. A layer of metal is formed over the at least one semiconductor layer. A layer of metal silicide is formed over the layer of metal. The layer of metal silicide is reacted with the layer of metal, and then unreacted metal remaining from the layer of metal is removed to form the local interconnect. The layer of metal may comprise a refractory metal selected from the group consisting of chromium, cobalt, molybdenum, nickel, niobium, palladium, platinum, tantalum, titanium, tungsten, and vanadium. Preferably, the refractory metal comprises titanium. The layer of metal may have a thickness in the range of about 200 Angstroms to about 600 Angstroms, and preferably, approximately 300 Angstroms. The layer of metal silicide may comprise tungsten silicide. The layer of metal silicide may have a thickness in the range of about 500 Angstroms to about 1200 Angstroms, and preferably, in the range of about 600 Angstroms to about 700 Angstroms. The step of reacting the layer of metal silicide with the layer of metal may comprise annealing the layer of metal silicide and the layer of metal at a temperature ranging from about 600° C. to about 700° C.
According to yet another aspect of the present invention, a process of forming a local interconnect comprises providing at least one semiconductor layer. A layer of metal is formed over the at least one semiconductor layer by chemical vapor deposition (CVD). A layer of metal silicide is formed over the layer of metal by CVD. The layer of metal silicide is then patterned. The metal silicide is reacted with the layer of metal and then unreacted metal remaining from the layer of metal is removed to form the local interconnect. The step of forming a layer of metal over the at least one semiconductor layer by CVD and the step of forming a layer of metal silicide over the layer of metal by CVD are preferably carried out in the same vacuum environment.
According to a further aspect of the present invention, a process of forming a local interconnect comprises providing at least one semiconductor layer. A layer of metal is formed over the at least one semiconductor layer. A layer of first metal silicide is formed over the layer of metal. The layer of first metal silicide and the layer of metal are annealed to form a composite structure. Remaining metal from the layer of metal is removed to form the local interconnect. The composite structure may comprise the first metal silicide, a second metal silicide and an intermetallic compound comprising metal from the layer of metal and metal from the first metal silicide. The layer of metal may comprise titanium and the first metal silicide may comprise tungsten silicide, such that the composite structure comprises tungsten silicide, titanium silic
Chaudhuri Olik
Kilworth, Gottman, Hagan & Schaeff, L.L.P.
Micro)n Technology, Inc.
Peralta Ginette
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