Semiconductor device manufacturing: process – Coating with electrically or thermally conductive material – To form ohmic contact to semiconductive material
Reexamination Certificate
2002-02-26
2003-12-09
Niebling, John F. (Department: 2812)
Semiconductor device manufacturing: process
Coating with electrically or thermally conductive material
To form ohmic contact to semiconductive material
Reexamination Certificate
active
06660633
ABSTRACT:
TECHNICAL FIELD
The present invention relates to semiconductor devices and their methods of fabrication. More particularly, the present invention relates to the processing of copper interconnect material and the resultant device utilizing the same. Even more particularly, the present invention relates to reducing electromigration in copper interconnect lines by doping their surfaces with a barrier material using wet chemical methods.
BACKGROUND ART
Currently, the semiconductor industry is demanding faster and denser devices (e.g., 0.05-&mgr;m to 0.25-&mgr;m) which implies an ongoing need for low resistance metallization. Such need has sparked research into resistance reduction through the use of barrier metals, stacks, and refractory metals. Despite aluminum's (Al) adequate resistance, other Al properties render it less desirable as a candidate for these higher density devices, especially with respect to its deposition into plug regions having a high aspect ratio cross-sectional area. Thus, research into the use of copper as an interconnect material has been revisited, copper being advantageous as a superior electrical conductor, providing better wettability, providing adequate electromigration resistance, and permitting lower depositional temperatures. The copper (Cu) interconnect material may be deposited by chemical vapor deposition (CVD), plasma-enhanced chemical vapor deposition (PECVD), sputtering, electroless plating, and electrolytic plating.
However, some disadvantages of using Cu as an interconnect material include etching problems, corrosion, and diffusion into silicon.
1
These problems have instigated further research into the formulation of barrier materials for preventing electromigration in both Al and Cu interconnect lines. In response to electromigration concerns relating to the fabrication of semiconductor devices particularly having aluminum-copper alloy interconnect lines, the industry has been investigating the use of various barrier materials such as titanium-tungsten (TiW) and titanium nitride (TiN) layers as well as refractory metals such as titanum (Ti), tungsten (W), tantalum (Ta), molybdenum (Mo), and their silicides.
2
Although the foregoing materials are adequate for Al interconnects and Al—Cu alloy interconnects, they have not been entirely effective with respect to all-Cu interconnects. Further, though CVD and PECVD have been conventionally used for depositing secondary metal(s) on a primary metal interconnect surface, neither technique provides a cost-effective method of forming a copper-zinc alloy on a Cu interconnect surface. Therefore, a need exists for a low cost and high throughput method of reducing electromigration in copper interconnect lines by decreasing the drift velocity in the copper line/via, in order to decrease the copper migration rate as well as the void formation rate, by using an interim conformal Cu-rich copper-zinc (Cu—Zn) alloy thin film electroplated on a copper (Cu) surface from a stable chemical solution, and controlling the Zn-doping thereof, which improves also interconnect reliability and corrosion resistance.
1
Peter Van Zant, Microchip Fabrication: A Practical Guide to Semiconductor Processing, 3
rd
Ed., p. 397 (1997).
2
Id., at 392.
DISCLOSURE OF INVENTION
Accordingly, the present invention provides a method of reducing electromigration in copper interconnect lines by decreasing the drift velocity in the copper line/via, thereby decreasing the copper migration rate as well as the void formation rate, by using an interim conformal Cu-rich Cu—Zn alloy thin film electroplated on a copper (Cu) surface from a stable chemical solution, and controlling the Zn-doping thereof, which improves also interconnect reliability and corrosion resistance, and a semiconductor device thereby formed. The present method involves electroplating the Cu surface, such as a blanket Cu seed layer and a partial thickness plated Cu layer, in a unique nontoxic aqueous chemical electroplating solution containing salts of zinc (Zn) and copper (Cu), their complexing agents, a pH adjuster, and surfactants, thereby forming an interim Cu—Zn alloy thin film layer having some degree of oxygen (O) concentration, wherein the Zn-doping is controllable by varying the electroplating conditions; and annealing the interim Cu—Zn alloy thin film formed on the Cu surface in an environment such as vacuum, nitrogen (N
2
), hydrogen (H
2
), formine (N
2
H
2
), or mixtures thereof for reducing the O-concentration in the alloy thin film layer, for modifying the grain structure of the Cu—Zn alloy thin film as well as of the underlying Cu surface, and for forming a mixed Cu—Zn/Cu interface; and further electroplating the alloy thin film layer with Cu for completely filling the via, thereby forming the interconnect structure. The present invention further provides a particular electroplating method which controls the parameters of Zn concentration, pH, temperature, and time in order to form a uniform reduced-oxygen Cu—Zn alloy thin film on a cathode-wafer surface such as a Cu surface for reducing electromigration in the device by decreasing the drift velocity therein which decreases the Cu migration rate in addition to decreasing the void formation rate.
More specifically, the present invention provides a method for fabricating a semiconductor device having an interim conformal Cu-rich Cu—Zn alloy thin film formed on a Cu surface by electroplating the Cu surface in the present chemical solution. The method generally comprises the steps of: (1) providing a semiconductor substrate having a Cu surface; (2) providing a chemical solution; (3) electroplating the Cu surface in the chemical solution, thereby forming an interim Cu—Zn alloy thin film on the Cu surface; (4) rinsing the interim Cu—Zn alloy thin film; (5) drying the interim Cu—Zn alloy thin film; (6) annealing the interim Cu—Zn alloy thin film; (7) filling the via with a Cu-fill on the interim Cu—Zn alloy thin film; and (8) completing fabrication of the semiconductor device.
By electroplating this Cu—Zn alloy thin film on the cathode-wafer surface such as a Cu surface using a stable chemical solution in the prescribed concentration ranges and by subsequently annealing the Cu—Zn alloy thin film electroplated on the Cu surface, the present invention improves Cu interconnect reliability, enhances electromigration resistance, improves corrosion resistance, and reduces manufacturing costs. In particular, the present invention chemical solution is advantageous in that it facilitates formation of an acceptable Cu—Zn alloy thin film over a wide range of bath compositions while the subsequent annealing step removes undesirable oxygen impurities from the formed alloy thin film. The desirable Zn concentration in the Cu—Zn alloy thin film, preferably in a range of approximately 0.2 at. % to approximately 9.0 at. % determined by X-Ray Photoelectron Spectroscopy (XPS) or Auger Electron Spectroscopy (AES), is controllable by varying the electroplating conditions and/or the bath composition. By so controlling the Zn-doping, the present method balances high electromigration performance against low resistivity requirements. Additionally, the Cu surface (e.g., seed layer), being formed by a technique such as electroless deposition, ion metal plasma (IMP), self-ionized plasma (SIP), hollow cathode magnetron (HCM), chemical vapor deposition (CVD), and atomic layer deposition (ALD), is enhanced by the Cu—Zn alloy thin film and is prevented from etching by the high pH value (i.e., basic) of the chemical solution from which the alloy thin film is formed.
Further advantages arise from the present invention's superior fill-characteristics. The present Cu—Zn electroplating solution facilitates better filling of a Cu—Zn alloy thin film on an interconnect, especially for feature sizes in a dimensional range of approximately 0.2 &mgr;m to approximately 0.05 &mgr;m, thereby lowering the resistance of the formed Cu—Zn alloy thin film (e.g., in a resistance range of approximately 2.2 &mgr;&OHgr;·cm to approximately 2.5 &mgr;&OHgr;·c
Lopatin Sergey
Nickel Alexander H.
Advanced Micro Devices , Inc.
Gurley Lynne A.
LaRiviere Grubman & Payne, LLP
Niebling John F.
LandOfFree
Method of reducing electromigration in a copper line by... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method of reducing electromigration in a copper line by..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method of reducing electromigration in a copper line by... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3161456