Semiconductor device manufacturing: process – Coating with electrically or thermally conductive material – To form ohmic contact to semiconductive material
Reexamination Certificate
1998-09-18
2001-06-12
Faburyl, Wael (Department: 2823)
Semiconductor device manufacturing: process
Coating with electrically or thermally conductive material
To form ohmic contact to semiconductive material
C438S625000, C438S628000, C438S629000, C438S643000, C438S644000, C438S648000, C204S192100
Reexamination Certificate
active
06245668
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to semiconductor devices, and more particularly, to a method of sputtering tungsten diffusion barriers in contact and via holes in semiconductor devices having increased robustness.
2. Description of Related Art
In the manufacture of semiconductor devices, metal conductive layers are patterned for the purpose of making interconnections between different points on the device. After formation of this patterned metal conductive layer, an electrically insulative material such as silicon dioxide or silicon nitride is deposited over the metal conductive layer by conventional deposition techniques. The surface of this electrically insulative layer will routinely be uneven due to the uneven underlying contour of the patterned conductive layer. The presence of a metal interconnect path beneath the insulative layer results in a corresponding elevated path in the surface contour of the insulative layer.
Often it is necessary, especially in high density devices, to form additional patterned conductive layers on the surface of the insulative layer. In order to interconnect the metal conductive layers to each other and to the substrate, the generally followed practice is to etch holes in the insulative layer prior to deposition of a metallic layer onto the insulative layer. These holes or “vias” are located in positions where contacts are desired between conductive regions, such as previously deposited patterned metal layers, or conductive substrate layers underlying the insulative layer and metal patterns deposited on the insulative layer. Vias are best visualized as cylinders which are filled with a metal so that devices located on different metallization levels can be electrically connected.
Vias are typically formed by applying a resist mask to the insulative layer. The resist mask is patterned and etched to form openings where via holes are to be etched into the insulative layer. An etchant is then applied to the mask layer such that via holes are etched where openings occur in the etching mask. The etching mask is then removed from the surface of the insulative layer and a metal layer is deposited on the insulative layer.
Prior to deposition of the metal layer the via may be filled with another metal to form a via stud. Such techniques as chemical vapor deposition of tungsten (CVD-W) followed by planarization of the blanket tungsten film may be used to form a tungsten via stud. However, during CVD-W to fill the via, the underlying materials are often attacked by the chemicals used in the CVD process. This requires a robust diffusion barrier to be deposited into the via between the underlying metal, usually aluminum, and the CVD-W chemistry, and to act as an adhesion layer for the CVD-W. Robustness is considered in the industry as encompassing the reliability, quality, and low failure rate of the diffusion barrier. Robustness of the diffusion barrier is important since failure of the barrier films result in attack of the underlying structures and/or defects in the CVD-W stud. Despite significant improvements in the barrier film quality, failure of these barriers is still a serious problem in semiconductor manufacture.
The prior art is replete with the use of diffusion barriers comprising titanium adhesion films alone or with titanium nitride or tungsten films. These films are generally deposited by physical vapor deposition (PVD), also known as sputtering, with the use of a collimator. Sputtering techniques using collimators, or collimation, traditionally give excellent step coverage in high aspect ratio vias by focusing the spray of the sputtered material. However, it has been found that during collimation tremendous energy is created which is transferred to the silicon wafer of the semiconductor device. Temperatures exceeding 420° C. are possible leading to extrusion of the aluminum lines. It is desirable to have a process of depositing diffusion barrier films which does not employ such high temperature or result in aluminum extrusion but still provides robust barrier films and achieves the needed step coverage required in high aspect ratio vias.
Bearing in mind the problems and deficiencies of the prior art, it is therefore an object of the present invention to provide a method of sputter depositing a tungsten diffusion barrier film without employing excessively high temperatures.
It is another object of the present invention to provide a method of depositing a tungsten diffusion barrier having improved robustness.
It is a further object of the present invention to provide a method of depositing a tungsten diffusion barrier film which does not result in aluminum line extrusion.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.
SUMMARY OF THE INVENTION
The above and other objects and advantages, which will be apparent to one of skill in the art, are achieved in the present invention which is directed to, in a first aspect, a method of forming inter-level contacts between metal layers in a semiconductor device. The method comprises the steps of: (a) providing a semiconductor substrate having a surface; (b) providing at least one level of interconnect on the surface of the substrate; (c) depositing an insulator layer on the substrate; (d) opening a plurality of interconnect vias in the insulator layer to expose a portion of at least one level of interconnect; (e) placing the substrate into a sputter chamber having a tungsten target; and (f) non-collimated sputter depositing a tungsten film such that the sputtered tungsten film is in contact with at least one level of interconnect. Preferably, the non-collimated sputtered tungsten film has a thickness of about 200 Å to about 1000 Å.
The sputter chamber has a pressure of about 1 mTorr to about 10 mTorr. The inert gas flow inside the chamber, preferably nitrogen or argon, is at least 25 cm
3
/min. to about 150 cm
3
/min. Shielding inside the sputter chamber is coated with a material that promotes adhesion of tungsten to the shielding. Preferably, the material coating the shielding is aluminum oxide.
The present method may further include the step of depositing by CVD sufficient tungsten to fill all of the vias forming the via stud. The step of depositing an adhesion layer prior to depositing the tungsten film can also be included. Preferably, the adhesion layer is a titanium film having a thickness of about 0 Å to about 500 Å.
Utilizing non-collimated sputter depositing increases the target to substrate distance inside the sputter chamber than collimated sputter depositing. Non-collimated sputtering reduces the heating effect of traditional collimated sputtering reducing extrusion of metal wires. In addition, non-collimated sputtering provides lower via resistance than collimated sputtering.
In another aspect, the present invention relates to a method of fabricating an integrated circuit. The method comprises the steps of: (a) patterning a dielectric layer to form vias which expose the underlying material, the exposed underlying material comprises an electrically conducting material; (b) depositing an adhesion film into the via; and (c) non-collimated sputter depositing a tungsten film covering the adhesion film in the via.
The step of non-collimated sputter depositing the tungsten film occurs in a sputter chamber containing shielding coated with a material, preferably, aluminum oxide, that promotes adhesion of tungsten to the shielding. The chamber pressure is about 1 mTorr to about 10 mTorr with an inert gas flow of at least 25 cm
3
/min. to about 150 cm
3
/min. The adhesion film is selected from the group consisting of titanium, and titanium-tungsten alloy. Preferably, the sputter deposited tungsten film has a thickness of about 200 Å to about 1000 Å.
In yet another aspect, the present invention relates to a method of sputtering tungsten to form a diffusion barrier in inter-level vias. The method comprises the steps of: (a) providing a sub
Brodsky Stephen B.
Murphy William J.
Rutten Matthew J.
Strippe David C.
Vanslette Daniel S.
Berezny Neal
DeLio & Paterson LLC
Faburyl Wael
International Business Machines - Corporation
Peterson Peter W.
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