Semiconductor device manufacturing: process – Coating with electrically or thermally conductive material – Insulated gate formation
Reexamination Certificate
1999-10-11
2001-01-16
Elms, Richard (Department: 2824)
Semiconductor device manufacturing: process
Coating with electrically or thermally conductive material
Insulated gate formation
C438S597000, C438S622000, C438S637000, C438S687000
Reexamination Certificate
active
06174793
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention is in the field of integrated circuits, and is more specifically directed to the application of copper.
2. Description of the Prior Art
In contemporary fabrication of integrated circuits, interconnect usually is formed by metal. Available metals for interconnect must satisfy some requirements such as low resistivity, high resistance to electromigration failure effects, excellent adhesion to underlying substrate material and low film stress, etc.
Among all of the available metals, aluminum is most widely used in the contemporary manufacture of silicon integrated circuits. Advantages of aluminum include low resistivity (2.7 &mgr;&OHgr;-cm) and good adhesion to silicon dioxide and silicon.
As device dimensions continue to scale down, however, some disadvantages of aluminum such as relatively poor resistance to electromigration effects and corrosion become a bottleneck, and then it is necessary to find other metal for the interconnect.
Because copper has low resistivity (1.7 &mgr;&OHgr;-cm) and good electromigration resistance, it would thus be a processing interconnect material, especially when device dimensions approach deep-submicron sizes.
However, copper could rapidly diffuse into surrounding dielectric materials, especially into silicon dioxide, due to its nature. Thus, it is necessary to inhibit this diffusion by a diffusion barrier layer to render certainly real profile of copper connect, similar to the desired profile of copper connect. As usual, the diffusion barrier layer is provided by silicon nitride layer which is formed by a plasma enhanced chemical vapor deposition (PECVD) process.
There are, in principal, still two issues about the application of copper and silicon nitride. First, silicon nitride has poor adhesion to copper surfaces, resulting in the peeling of the silicon nitride from the copper surface. Second, copper is easy to be oxidized and then an additional process is required to remove the unwanted copper oxide layer.
Accordingly, it is necessary to overcome these issues to take advantages of the copper connect. Especially when the chemical mechanical polishing process is broadly used to remove excess copper, the lack of properly dry etching does not restrict the application of copper.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a method for enhancing adhesion ability between copper and silicon nitride.
It is another object of the invention to provide such a method that decreases the resistance between copper and conductive structure.
It is still another object of the invention to provide an efficient method to prevent copper from diffusing into surrounding dielectric layer.
It is a further object of the invention to provide a manufacturable fabrication of integrated circuit.
First embodiment is a method for enhancing adhesion ability between copper and silicon nitride. The method comprises four steps: first, provide a substrate; second, form a copper layer on the substrate; third, form an intervening copper phosphide layer on the copper layer; and finally, form a silicon nitride layer on the intervening copper phosphide layer. Moreover, the copper phosphide layer is formed by a plasma enhanced chemical vapor deposition process with PH3 plasma.
As a matter of fact, though copper is easy to react with oxygen but copper oxide also is easy to be removed by reacting with ionized hydrogen gas in PH3 plasma environment. Accordingly, the adhesion of copper phosphide and silicon nitride is essentially better than that of copper and silicon nitride. Therefore, copper phosphide layer that is formed by reaction between phosphorus ions and copper layer can enhance adhesion between copper and silicon nitride without any additional treatment to remove unwanted copper oxide. Beside, application of copper phosphide further comprises two advantages: provide low resistance and prevent copper from diffusing into surrounding dielectric layer.
The second embodiment of the invention is a method for forming a copper interconnect. The presented embodiment comprises following steps: provide a substrate that is covered by a first dielectric layer and then form a first silicon nitride layer and a second dielectric layer on the first dielectric layer in sequence. Form a gap in both second dielectric layer and first silicon nitride layer by a photolithography process and an etching process, and then cover second dielectric layer by a copper layer, wherein copper layer substantially fills the gap. Then remove the copper layer by a chemical mechanical polishing process, wherein the gap is still substantially filled by the copper layer. Sequentially, form a copper phosphide layer on the gap by a PECVD process with a PH3 plasma and then form a second silicon nitride layer on the second dielectric layer and covers the copper phosphide layer. Finally, form a third dielectric layer on the second silicon nitride layer.
As a summary, one of the main characteristics of the invention is that copper phosphide is used to connect copper and silicon nitride, and any copper oxide layer on the copper layer can be automatically replaced by the copper phosphide layer. By the way, not only the adhesion of silicon nitride to copper is improved by copper phosphide but also copper phosphide act as both a blocking layer of copper and a low resistivity interface between copper and conductive structure (such as contact).
REFERENCES:
patent: 5422289 (1995-06-01), Pierce
patent: 5756396 (1998-05-01), Lee et al.
patent: 5786273 (1998-07-01), Hibi et al.
patent: 5877076 (1999-03-01), Dai
patent: 6015747 (2000-01-01), Lopatin et al.
Liu Chih-Chien
Tsai Cheng-Yuan-Chen
Wu Juan-Yuan
Elms Richard
Harness & Dickey & Pierce P.L.C.
Lebentritt Michael S.
United Microelectronics Corp.
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