Stock material or miscellaneous articles – Structurally defined web or sheet – Discontinuous or differential coating – impregnation or bond
Reexamination Certificate
2003-04-15
2004-05-25
Jones, Deborah (Department: 1775)
Stock material or miscellaneous articles
Structurally defined web or sheet
Discontinuous or differential coating, impregnation or bond
C428S210000, C428S446000, C428S701000, C428S702000
Reexamination Certificate
active
06740392
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of fabricating a barrier layer and, more particularly, to a method of fabricating a barrier layer on a top surface of metal in damascene structures utilizing ion implantation.
2. State of the Art
One of the main problems confronting the semiconductor processing industry, in the ultra large scale integration (“ULSI”) age, is that of capacitive-resistance loss in wiring levels. This has led to a large effort to reduce the resistance of, and lower the capacitive loading on, the wiring levels. Since its beginning, the industry has relied on aluminum and aluminum alloys in metallization layers. To improve conductivity in the wiring, it has been proposed that copper metallurgy be substituted for the aluminum metallurgy. However, several problems have been encountered in the development of the copper metallurgy. One of the main problems is the fast diffusion of copper through insulative materials, such as silicon and silicon dioxide (“SiO
2
”), to form an undesired copper oxide compound. In addition, copper is known to cause junction poisoning effects. These problems have led to the development of a liner to separate the copper metallurgy used in the metallization layer from the insulative material. However, copper does not adhere well to oxygen-containing dielectric materials or to itself. Therefore, the liner functions as both an adhesion layer and a barrier layer. In other words, the liner is used to provide adhesion between the copper metallurgy and the insulative material and also to prevent the diffusion of copper through the insulative material.
Liner materials that act as a barrier layer to prevent the diffusion of copper have been investigated by numerous researchers. The use of titanium (“Ti”), zirconium (“Zr”), or hafnium (“Hf”) in the barrier layer has been disclosed. Anonymous, “Improved Metallurgy for Wiring Very Large Scale Integrated Circuits,” International Technology Disclosures, v. 4 no. 9, (Sep. 25, 1986). Chemical vapor deposition (“CVD”) of titanium nitride (“TiN”) has also been proposed. C. Marcadal et al., “OMCVD Copper Process for Dual Damascene Metallization,” VMIC Conference Proceedings, p. 93-98 (1997). It is currently believed that an optimal liner material for a barrier layer is either a metal, such as tantalum (“Ta”) or tungsten (“W”), or a compound such as tantalum nitride (“TaN”) or trisilicon tetranitride (“Si
3
N
4
”). Changsup Ryu et al., “Barriers for Copper Interconnections.” Solid State Technology, p. 53-56 (1999).
Researchers have also proposed an alternate method of forming the barrier layer where the copper of the metallization layer is alloyed with a reactive element, such as aluminum or magnesium. S. P. Muraka et al., “Copper Interconnection Schemes: Elimination of the Need of Diffusion Barrier/Adhesion Promoter by the Use of Corrosion Resistant, Low Resistivity Doped Copper,” SPIE, v. 2335, p. 80-90 (1994) (hereinafter “Muraka”); Tarek Suwwan de Felipe et al., “Electrical Stability and Microstructural Evolution in Thin Films of High Conductivity Copper Alloys,” Proceedings of the 1999 International Interconnect Technology Conference, p. 293-295 (1999). Copper alloys with 0.5 atomic percent aluminum or 2 atomic percent magnesium were used. The reactive element reacted with SiO
2
to form dialuminum trioxide (“Al
2
O
3
”) or magnesium oxide (“MgO”), which acted as a barrier to the further diffusion of the copper into the Sio
2
.
Similarly, in U.S. Pat. No. 5,130,274 issued to Harper et al. (hereinafter “Harper”), an oxide layer that acts as a barrier is disclosed. To form the barrier, a copper alloy containing an alloying element, such as aluminum or chromium, is deposited as a layer. The alloying element reacts with SiO
2
or a polyimide to form an oxide that functions as a barrier compound.
Semiconductor products that incorporate some of these solutions to the problem of copper diffusion have begun to ship, on a limited basis. However, a problem of how to achieve the lowest possible resistivity in ever smaller lines still remains. As shown in Panos C. Andricacos, “Copper On-Chip Interconnections,” The Electrochemical Society Interface, p. 32-37 (Spring 1999) (hereinafter “Andricacos”), the effective resistivity obtainable by use of barrier layers was approximately 2&mgr;&OHgr;-cm with a line width greater than 0.3 &mgr;m. The effective resistivity undesirably increases for narrower lines. The alloys investigated by Muraka had similar resistivity values to those found by Andricacos. Muraka also found that the use of 0.5 atomic percent aluminum in the copper was apparently insufficient to provide complete protection from copper diffusion into the SiO
2
. However, a significant reduction in the rate of copper penetration through the SiO
2
was achieved. The maximum solubility of aluminum in copper is 9.4 weight percent or approximately 18 atomic percent and the maximum solubility of magnesium in copper is 0.61 weight percent or approximately 0.3 atomic percent. Thus, the alloys investigated in Muraka were saturated with magnesium but were far below the saturation limit when aluminum was used as the reactive element.
Other researchers have investigated the capacitive loading effect with various polymers, such as fluorinated polyimides, to determine if the polymers are possible substitutions for SiO
2
as an insulative material. Several of these polymers have dielectric constants that are considerably lower than the dielectric constant of SiO
2
. However, as in the case with SiO
2
, the polymers also exhibit incompatibility problems with copper metallurgy. It has been shown that polyimide, and many other polymers, react with copper during the curing process to form CuO
2
, which is dispersed within the polymer. D. J. Godbey, L. J. Buckley, A. P. Purdy and A. W. Snow, “Copper Diffusion in Organic Polymer Resists and Inter-level Dielectrics,” at the International Conference on Metallurgical Coatings and Thin Films, San Diego, Calif., Apr. 21-25, 1997, Abstract H2.04 p. 313 (hereinafter “Godbey”). CuO
2
is conductive, so its presence raises the effective dielectric constant of the polymer and, in many cases, also increases the conductivity of the polymer.
Andricacos notes that the use of a copper conductor along with the barrier layer provides a significant improvement in conductivity over the Ti/AlCu/Ti sandwich structure currently used in the industry. Andricacos also noted that as the line width decreases, even a thin barrier layer has a significant effect on the resistance of the composite line. The solutions proposed by Harper and Muraka attempted to address this problem by forming the barrier layer in situ by chemically reacting the insulative material and the copper alloy. The barrier layer is formed in the area that was previously the insulative material, leaving the conductor width and height unaffected. However, these processes also affect the resistivity of the conductor because the use of an aluminum alloy, even at a concentration so low as not to be completely effective, shows a measurable increase in resistance compared to that of an unalloyed copper line. While the process of Harper uses only one layer of the copper alloy, the one layer has a significantly high concentration of aluminum and, therefore, the final structure will have an increased resistivity.
As minimum dimensions shrink, the use of even a 20 Angstrom (“Å”) layer of an alloy having a high resistivity will significantly affect the total resistivity of the conductor composite. For example, a 200 Å layer on both sides of a 0.1 &mgr;m trench is 40 percent of the total trench width. Therefore, at the same time that the dimensions of the conductor element decrease, the specific resistivity increases, which provides a high resistivity at the very time a conductor having a low resistivity is desired.
It has also been shown that there is a significant difference in the amount of copper oxide formed when a polyimide is used as the insulative material if the acidity of t
Jones Deborah
Koppikar Vivek
TraskBritt
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