Cobalt tungsten phosphorus electroless deposition process...

Details Cobalt tungsten phosphorus electroless deposition process... Cobalt tungsten phosphorus electroless deposition process...

2002-06-19

2004-11-23

LaVilla, Michael (Department: 1775)

Compositions: coating or plastic

Coating or plastic compositions

Metal-depositing composition or substrate-sensitizing...

C106S001270, C205S126000, C205S187000, C427S443100

Reexamination Certificate

active

06821324

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates generally to metallic deposition materials and processes, and more specifically to materials and processes for metallic electroless deposition.
BACKGROUND OF THE INVENTION
Metallic diffusion and/or drift between different metallic layers, or metallic and semiconductor layers induce changes over time in the properties of the layer into which diffusion and/or drift has occurred. These properties include electrical, mechanical, thermal, visual, physical and chemical properties. There is great importance to many industries to produce products having both constant properties over time and high reliability. These industries include, but are not limited to semiconductor, microelectronics, electro-finishing, aeronautic, space and motor industries. Products requiring high reliability include, for example, semiconductor chips, ULSI products, jewelry, nuts and bolts, and airplane wings and car parts. Typically, the smaller the product, the more pronounced an effect of a localized change in a property of a layer.
In the semiconductor industry, the diffusion of metals into adjacent layers is well documented. For example, copper diffuses into silicon materials. To prevent such diffusion, a barrier layer between the copper and silicon may be deposited (U.S. Pat. No. 5,695,810 to Dubin et al.)
The microelectronics industry constantly aims to reduce the size of components and the distance between interconnects, yet, simultaneously, tries to increase the number of electronic features per unit area. Thus, there is an increasing requirement for more accurate and well-controlled metal deposition techniques. For example, with decreasing size of copper/SiO
2
interconnects, standard processes known in the art for metal deposition cannot typically meet the new requirements for precision. There is therefore an urgent need for better designed processes, materials and manufacturing methods for metal deposition.
One of the concerns in manufacturing and processing copper, amongst other metals, is its corrosion, before and after Chemical-Mechanical Polishing (CMP), which may induce deterioration in the electrical and mechanical properties of the copper. Another concern is the migration of copper onto the inter-level dielectric and the silicon substrate. Copper contamination in inter-level dielectrics weakens the dielectrics' mechanical properties and reduces electrical reliability. Copper is also a deep level dopant in silicon, which may lower the minority carriers lifetime and may enhance leakage currents to significant levels.
Copper has poor adhesion to most dielectrics that are used in ULSI manufacturing, such as, but not limited to, SiO
2
, SiOF, polyimide and low-K dielectrics. Therefore, the implementation of a copper encapsulation method is desirable. One possible solution is to wrap the Cu lines with special thin metallic cladding that serves as a. a corrosion resistance layer; b. a diffusion barrier; and c. adhesion promoter.
There are many materials that are known to be good barrier diffusion. Usually they are refractory metals, such as Ta, W and Mo, or refractory metal nitride thin films such as TiN, TaN, and W
x
N
y
. The layers can be deposited by conventional physical vapor deposition (PVD), chemical vapor deposition (CVD) or Atomic Layer Chemical Vapor Deposition (ALCVD).
Alternative methods for barriers are electroplating and electroless (autocatalytic) deposition of Co- or Ni-based alloys. For example, it was shown that 100 nm thick electroless Co—P functions as barrier against Cu diffusion at temperatures of up to 400° C. Addition of a refractory metal (e.g. W, Mo, or Re) ion to Co—P alloy improves its barrier properties significantly and 30 nm Co
88
W
2
P
10
holds against copper diffusion at temperatures up to 500° C.
Commonly used solutions for wet deposition of cobalt and nickel thin films contain alkali metal ions such as sodium or potassium. For example, conventional bath compositions for electroless deposition of Co(P,W) and Ni(P,W) layers include tri-sodium citrate as complexing agent, sodium tungstate as a source for W, sodium hypophosphite as a reducing agent, and sodium or potassium hydroxides to adjust the pH of the solution.
Alkali metal ions have many negative effects on the performance of CMOS integrated circuits. Sodium and potassium ions migrate rapidly under electric field in inter-level oxide, field oxide and gate oxide. The alkali metal ions degrade the dielectric strength of SiO
2
by increasing leakage current and decreasing breakdown field. The effect of alkali metal ions is also very pronounced in transistor technologies that their characteristics depend on the electric field at the Si/SiO
2
interface. Since alkali metal ions are very mobile in SiO
2
the effective charge's position in the silicon dioxide may vary under the applied electric field at normal circuit operation. This shift in the charge distribution centroid affects the internal electric field distribution and may causes long-term instabilities.
There is therefore an urgent need to develop novel materials and methods for metallic deposition which overcome the diffusion, drift and migration of metallic ions, in particular, alkali metal ions, between layers.
SUMMARY OF THE INVENTION
It is an object of some aspects of the present invention to provide improved materials and processes for providing a barrier layer for metallic layers, such as copper.
In preferred embodiments of the present invention, improved materials and processes are provided for the electroless deposition of cobalt tungsten phosphorus, substantially devoid of alkali metal ions and alkaline earth metal ions.
In other preferred embodiments of the present invention, methods and materials for activating a non-metallic surface for electroless deposition thereupon of cobalt tungsten phosphorus, substantially devoid of alkali metal ions and alkaline earth metal ions, are provided.
In further preferred embodiments of the present invention, methods and materials for activating a metallic surface for electroless deposition thereupon of cobalt tungsten phosphorus, substantially in the absence of alkali metal ions and alkaline earth metal ions, are provided.
In further preferred embodiments of the present invention, methods and materials for electroless deposition of cobalt tungsten phosphorus, substantially devoid of alkali metal ions and alkaline earth metal ions, on a single silicon crystal, on a thermal oxide on silicon, and on thin films of copper and cobalt on silicon substrates are provided.
In yet further preferred embodiments of the present invention metallic deposits of cobalt phosphorus and cobalt tungsten phosphorus are provided, wherein the deposits are substantially alkali metal free, alkaline earth metal free and oxygen free.
In still further preferred embodiments of the present invention, metallic thin films of cobalt phosphorus and cobalt tungsten phosphorus are provided, wherein the films are substantially alkali metal free, alkaline earth metal free and oxygen free.
There is thus provided in accordance with a preferred embodiment of the present invention, an aqueous composition for the electroless deposition of cobalt tungsten phosphorus, including;
at least one cobalt ion;
at least one tungsten containing ion; and
a reducing agent comprising at least one phosphorus atom; and,
wherein the composition is substantially devoid of alkali metal ions and alkaline earth metal ions.
In a preferred embodiment of the invention, the at least one cobalt ion is provided by cobalt sulfate heptahydrate (CoSC
4
.7H
2
O). Preferably, the cobalt sulfate septahydrate (CoSO
4
.7H
2
O) is present at a concentration of 10-25 g/l. Yet more preferably, the cobalt sulfate septahydrate (CoSO
4
.7H
2
O) is present at a concentration of 15-18 g/l. In another preferred embodiment of the invention, the cobalt ion is provided in the form of cobalt chloride hexahydrate (CoCl
2
.6H
2
O) in a concentration of 10-40 g/l.
In a preferred embodiment, the at least one tungsten containing ion is provided

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