Semiconductor device manufacturing: process – Coating with electrically or thermally conductive material – To form ohmic contact to semiconductive material
Reexamination Certificate
1999-11-01
2002-02-26
Nguyen, Ha Tran (Department: 2812)
Semiconductor device manufacturing: process
Coating with electrically or thermally conductive material
To form ohmic contact to semiconductive material
C438S614000, C438S627000, C438S628000, C438S644000, C438S654000, C438S685000, C438S687000, C438S688000
Reexamination Certificate
active
06350667
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
This invention relates to a method of fabrication used for semiconductor integrated circuit devices, and more specifically to the formation of aluminum pad metal structures are described which improve adhesion between the tantalum nitride pad barrier layer and the underlying copper metallurgy. It is the object of the present invention to provide a process wherein a thin adhesion layer of aluminum is placed in between the underlying copper metal and the top tantalum nitride pad barrier layer providing improved adhesion to the pad metal stack structure.
As a background to the current invention, tantalum nitride has been commonly used as the barrier material for copper metallization. The copper metallization process needs an aluminum pad to be transparent with an aluminum metal process. However, if aluminum metal is deposited on top of copper, most of the aluminum is consumed reacting with the underlying copper forming CuAl
2
. A barrier layer of tantalum nitride is necessary, inserted between the underlying copper and top aluminum pad, to prevent the reaction between these metals. A poor adhesion problem exists between the tantalum nitride barrier layer and the underlying copper because there is no compound formation between copper and tantalum. Therefore, the present invention's key process step is to insert a thin adhesion promoting layer of aluminum in between the underlying copper and the top tantalum nitride barrier layer, chemically reacting and chemically bonding to both layers.
It is a general object of the present invention to provide a novel and improved method for forming aluminum pad metal structures are described which improve adhesion between the tantalum nitride pad barrier layer and the underlying copper metallurgy.
(2) Description of Related Art
The present invention is a new and improved method for fabricating aluminum metal pad structures wherein a thin adhesion layer of aluminum is placed in between the underlying copper metal and the top tantalum nitride pad barrier layer providing improved adhesion to the pad metal stack structure. In summary, present invention teaches a method comprising of forming a copper underlayer, forming a key aluminum adhesion layer, forming the tantalum nitride barrier layer, and finally forming the aluminum pad. Related Prior Art background patents will now be described in this section.
U.S. Pat. No. 5,904,565 (Nguyen et al.) describes an interconnect process with multiple conductive and non-conductive barrier layers. A method of forming a direct, copper-to-copper, connection between levels in an IC is disclosed. A via interconnection is formed by isotropically depositing a barrier material in a via through an insulator to a lower copper level, and then anisotropically etching the via to remove the barrier material covering the lower copper level. The anisotropic etch leaves the barrier material lining the via through the insulator. The subsequently deposited upper metal level then directly contacts the lower copper level when the via is filled. A dual damascene interconnection is formed by etching an interconnection trench in an insulator and anisotropically depositing a non-conductive barrier material in the trench bottom. Then a via is formed from the trench interconnect to a lower copper level. As above, a conductive barrier material is isotropically deposited in the trench/via structure, and anisotropically etched to remove the barrier material covering the lower copper level. The insulating barrier material, lining the trench and via, remains. An IC via interconnection structure and a dual damascene interconnection structure, made in accordance with the above described methods, are also provided.
U.S. Pat. No. 5,795,796 (Kim) shows an Al interconnect with a TaN barrier layer. A method of fabricating a metal line includes the steps of preparing a semiconductor substrate, depositing a first metal on the semiconductor substrate, heat-treating the first metal to form a first metal nitride layer, depositing a second metal on the first metal nitride layer, heat treating the second metal, depositing a third metal on the second metal, and heat treating both the third metal and the second metal to form a metal insulating layer in which the second and the third metals are mixed. The method of fabricating increases the area occupied by the metal line in a contact hole, decreases contact resistance, and increases the speed of the device.
U.S. Pat. No. 5,668,411 (Hong at al.) shows a Al/TaN/Al structure with an anneal step. A diffusion barrier trilayer is comprised of a bottom layer, a seed layer and a top layer. The diffusion barrier trilayer prevents reaction of metallization layer with the top layer upon heat treatment, resulting in improved sheet resistance and device speed.
U.S. Pat. No. 5,785,236 (Cheung et al.) shows an Al pad over a Cu interconnect. A process is provided which enables electrical connection to be formed between gold and aluminum wires and copper interconnects. Conventional techniques for wire bonding are ineffective for bonding gold wires or aluminum wires to copper pads or copper interconnects. A process is provided to modify the copper pads so that conventional wire bonding techniques can be employed. In the process of the present invention an aluminum pad is formed over the copper interconnects. The metal wire is then bonded to the aluminum pad using conventional wire bonding techniques. No new hardware and/or technology is required for the metal wire bonding. No new technology is required to integrate the process of the invention into existing IC fabrication processes.
U.S. Pat. No. 5,547,901 (Kim et al.) shows a Cu wire with an Al oxide containing barrier layer. A method for forming a metal wiring of a semiconductor element, which uses an aluminum film as an oxidation prevention film to prevent oxygen from being diffused into copper contained in the metal wiring. An aluminum oxidation prevention film-layer is selectively formed on an exposed surface of the copper metal wiring layer using a selective chemical vapor deposition method. The width of the aluminum layer formed is below 100 Angstroms, and is converted into aluminum oxide with heat treating or under an atmosphere, thereby preventing the copper from oxidation. A diffusion prevention film between the substrate and the copper metal wiring layer is further included for preventing the copper from diffusing into the substrate.
U.S. Pat. No. 5,631,498 titled “Thin Film Metallization Process For Improved Metal To Substrate Adhesion” granted to Anchel, Ormond and Hayunga on May 20, 1997 describes a metallization layer formed on a substrate with improved adhesion thereto, by performing the deposition at an elevated temperature which favors the formation of chemical bonds of the metal to the substrate as well as clusters of metal embedded within the substrate and contiguous with the metallization layer. In polymer substrates the chemical bond is made to carbonyl functional groups such as ketones or aldehydes. The adhesion is enhanced by the removal of moisture from the surface of the substrate at the elevated temperatures employed. A high degree of adhesion is also obtained through the deposition of a mixture of metals including chromium and copper which initially has a high chromium to copper ratio which is decreased during the deposition process. Completion of the process is determined by the reaching of a final desired chromium to copper ratio as observed by optical emission spectroscopy. The process can be carried out on a continuous basis by the use of a multi-chamber vacuum sputtering system, cluster system or in-line system.
The present invention is directed to a novel and improved method of fabricating metal pad structures. The method of the present invention requires less processing time, has lower cost than conventional methods and produces robust metal pad structures with good adhesion properties and good conductivity.
SUMMARY OF THE INVENTION
It is a general object of the present invention
Chen Sheng-Hsiung
Yang Fan Keng
Ackerman Stephen B.
Nguyen Ha Tran
Saile George O.
Taiwan Semiconductor Manufacturing Company
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