Semiconductor device manufacturing: process – Coating with electrically or thermally conductive material – To form ohmic contact to semiconductive material
Reexamination Certificate
2001-10-24
2003-09-23
Niebling, John F. (Department: 2812)
Semiconductor device manufacturing: process
Coating with electrically or thermally conductive material
To form ohmic contact to semiconductive material
C438S679000, C438S686000, C438S687000
Reexamination Certificate
active
06624070
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to the field of seed layers for subsequent metallization. In particular, this invention relates to methods for depositing and repairing seed layers prior to metallization.
The trend toward smaller microelectronic devices, such as those with sub-micron geometries, has resulted in devices with multiple metallization layers to handle the higher densities. One common metal used for forming metal lines, also referred to as wiring, on a semiconductor wafer is aluminum. Aluminum has the advantage of being relatively inexpensive, having low resistivity, and being relatively easy to etch. Aluminum has also been used to form interconnections in vias to connect the different metal layers. However, as the size of via/contact holes shrinks to the sub-micron region, a step coverage problem appears which in turn can cause reliability problems when using aluminum to form the interconnections between the different metal layers. Such poor step coverage results in high current density and enhances electromigration.
One approach to providing improved interconnection paths in the vias is to form completely filled plugs by using metals such as tungsten while using aluminum for the metal layers. However, tungsten processes are expensive and complicated, tungsten has high resistivity, and tungsten plugs are susceptible to voids and form poor interfaces with the wiring layers.
Copper has been proposed as a replacement material for interconnect metallizations. Copper has the advantages of improved electrical properties as compared to tungsten and better electromigration property and lower resistivity than aluminum. The drawbacks to copper are that it is more difficult to etch as compared to aluminum and tungsten and it has a tendency to migrate into the dielectric layer, such as silicon dioxide. To prevent such migration, a barrier layer, such as titanium nitride, tantalum nitride and the like, must be used prior to the depositing of a copper layer.
Typical techniques for applying a metal layer, such as electrochemical deposition, are only suitable for applying copper to an electrically conductive layer. Thus, an underlying conductive seed layer, typically a metal seed layer such as copper, is generally applied to the substrate prior to electrochemically depositing copper. Such seed layers may be applied by a variety of methods, such as physical vapor deposition (“PVD”) and chemical vapor deposition (“CVD”). Typically, seed layers are thin in comparison to other metal layers, such as from 50 to 1500 angstroms thick.
Oxide on a metal seed layer, particularly a copper seed layer, interferes with subsequent copper deposition. Such oxide forms from exposure of the metal seed layer to sources of oxygen, such as air. Typically, the longer such seed layer is exposed to oxygen, the greater the amount of oxide formation. Where a copper seed layer is thin, the copper oxide may exist as copper oxide throughout the layer. In other areas of electroplating, such as in electronics finishing, copper oxide layers are typically removed by acidic etching baths. These baths dissolve the oxide layer, leaving a copper metal surface. Such etching processes are not generally applicable to copper seed layers because of the thinness of the seed layer. As the oxide is removed from the seed layer surface there is the danger that the entire seed layer may be removed in places, creating discontinuities in the seed layer.
U.S. Pat. No. 5,824,599 (Shacham-Diamand et al.) discloses a method of preventing oxide formation on the surface of a copper seed layer by conformally blanket depositing under vacuum a catalytic copper layer over a barrier layer on a wafer and then, without breaking the vacuum, depositing a protective aluminum layer over the catalytic copper layer. Such blanket deposition of a copper layer under vacuum is typical of such procedures used commercially.
PCT patent application number WO 99/47731 (Chen) discloses a method of providing a seed layer by first vapor depositing an ultra-thin seed layer followed by electrochemically enhancing the ultra-thin seed layer to form a final seed layer using an alkaline copper bath. According to this patent application, such a two step process provides a seed layer having reduced discontinuities, i.e. areas in the seed layer where coverage of the seed layer is incomplete or lacking. However, such electrolytic copper deposits are not as conformal as electroless deposits. Thus such electrolytic deposits may not provide substantial fill of discontinuities without substantial upward plating.
Physical or chemical vapor deposition methods do not provide metal layers having as low impurity deposits as that provided by non-vapor deposition processes such as electrolytic and electroless deposition. Further, PVD methods tend to deposit metal in a line of sight fashion. Electroless deposition, unlike PVD or CVD, tends to be conformal, thus providing better aperture sidewall coverage leading to a more continuous seed layer and, consequently, reduced void formation following subsequent electroplating. However, conventional colloidal palladium catalysts for electroless plating typically contain strong acids which could strip off thin copper seed layers. Such conventional catalysts also contain tin which must be stripped prior to electroless plating. If such tin is not completely removed, defects in the plated film may result.
Organic dielectric materials used in these applications typically have a lower dielectric constant than conventional dielectric materials. However, such organic dielectrics cannot suitably be used because the processing temperatures for the physical vapor deposition of barrier layers is too high.
Thus, there is a continuing need for methods of depositing substantially continuous seed layers that conform to surface geometries in electronic devices, particularly in devices having small geometries such as 0.5 micron and below. Also, there is a need for lower temperature processes for depositing barrier layers. There is a further need for non-electrolytic methods for enhancing discontinuous seed layers.
SUMMARY OF THE INVENTION
It has been surprisingly found that the present compositions are suitable for enhancing or repairing discontinuities in a seed layer, particularly a copper seed layer. Also, the present invention is suitable for depositing thin copper seed layers without the use of tin. The present electroless plating catalysts are neutral to alkaline and thus are less harmful to thin copper seed layers than conventional acidic electroless catalysts.
In one aspect, the present invention provides a composition suitable for depositing an electroless plating catalyst on a substrate having ≦1 &mgr;m apertures including one or more metal salts, one or more copper complexing agents, one or more organic binders, one or more reducing agents and base.
In a second aspect, the present invention provides a method for depositing an electroless plating catalyst on a substrate having ≦1 &mgr;m apertures including the step of contacting the substrate with a composition including one or more metal salts, one or more copper complexing agents, one or more organic binders, one or more reducing agents and base.
In a third aspect, the present invention provides a method for enhancing a discontinuous seed layer including the steps of: contacting a substrate including a discontinuous metal seed layer with a composition including one or more metal salts, one or more copper complexing agents, one or more organic binders, one or more reducing agents and base; activating the catalyst; and contacting the catalyst with an electroless plating solution.
In a fourth aspect, the present invention provides a method for depositing a metal seed layer on a substrate including the steps of: contacting a substrate with a composition including one or more metal salts, one or more copper complexing agents, one or more organic binders, one or more reducing agents and base; activating the catalyst; and contacting the catalyst with an electrol
Bains Narinder
Goosey Martin T.
Merricks David
Cairns S. Matthew
Gurley Lynne A.
Shipley Company L.L.C.
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