Abrading – Abrading process – Glass or stone abrading
Reexamination Certificate
2000-12-14
2003-10-28
Nguyen, Dung Van (Department: 3723)
Abrading
Abrading process
Glass or stone abrading
Reexamination Certificate
active
06638143
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to Chemical-mechanical polishing (CMP) and products used therefor. More particularly, the present invention relates to fabricating semiconductor devices by planarizing and/or thinning layers on a semiconductor substrate by CMP. The present invention is applicable to manufacturing high speed integrated circuits having submicron design features and high conductivity interconnect structures with high production throughput.
2. Background of the Related Art
Integrated circuits are typically formed on substrates, particularly semiconductor substrates, such as monocrystalline silicon substrates, by sequentially depositing and etching conductive, semiconductive and/or insulative layers to ultimately form a plurality of features and devices. The active devices, which are initially isolated from one another, are interconnected to form functional circuits and components through the use of well-known multilevel interconnections.
CMP is pervasively employed at strategic stages in the fabrication of semiconductor devices to remove topographical irregularities and/or reduce the thickness of a particular layer to achieve planar surfaces and/or thinner layers. CMP is performed not only on a semiconductor substrate itself, but also on various dielectric layers, barrier layers, conductive layers, or layers containing a combination of the above materials. CMP is, therefore, particularly important in the manufacture of high density multilevel semiconductor devices.
Generally, CMP involves subjecting a target surface to mechanical abrasion and chemical action, as with a polishing pad and abrasive chemical slurry, to effect removal of surface materials. In conventional CMP techniques, a semiconductor substrate in need of planarization and/or thinning is mounted on a carrier or polishing head. The exposed surface of the substrate is then placed against a rotating polishing pad which in turn is mounted on a rotating platen driven by an external driving force. The carrier provides a controllable force, i.e. pressure, urging the substrate against the rotating polishing pad. Additionally, the carrier may rotate to affect the relative velocity distribution over the surface of the substrate. A polishing slurry, typically containing an abrasive and at least one chemically-reactive agent, may be distributed over the polishing pad to provide an abrasive chemical solution at the interface between the pad and substrate.
The slurry initiates the polishing process by chemically reacting with the layer being polished. The polishing process is facilitated by the rotational movement of the pad relative to the substrate as slurry is provided to the substrate/pad interface. The dual mechanisms effect the chemical and mechanical polishing of the target layer.
Polishing is continued in this manner until the desired layer is appropriately planarized, thinned, or removed. The slurry composition is an important factor in the CMP step. Depending on the choice of the oxidizing agent, the abrasive, and other useful additives, the polishing slurry can be tailored to provide effective polishing to metal layers at desired polishing rates while minimizing surface imperfections, defects, corrosion and erosion.
Conventional polishing pads employed in abrasive slurry processing typically comprise a grooved porous polymeric surface, such as a porous polyurethane surface, and the abrasive slurry varied in accordance with the particular material undergoing CMP. Basically, the abrasive slurry is impregnated into the pores of the polymeric surface while the grooves convey the abrasive slurry to the wafer undergoing CMP.
Although conventional CMP is pervasively employed throughout the semiconductor manufacturing process with similar success and limitations, CMP of metal layers in the fabrication of interconnects for integrated circuits have proved particularly problematic. In applying conventional CMP planarization techniques to a metal layer, such as a copper (Cu) film, it is extremely difficult to achieve a high degree surface uniformity, particularly across a surface extending from a dense array of Cu features, e.g., Cu lines, bordered by an open field.
A dense array of metal (Cu) features is typically formed in an interlayer dielectric, such as a silicon oxide layer, by a damascene technique wherein trenches are initially formed. A barrier layer, such as a Ta-containing layer e.g., Ta, TaN, is then deposited lining the trenches and on the upper surface of the silicon oxide interlayer dielectric. Cu or a Cu alloy is then deposited, as by electroplating, electroless plating, physical vapor deposition (PVD) at a temperature of about 50° C. to about 150° C. or chemical vapor deposition (CVD) at a temperature under about 200° C., typically at a thickness of about 8,000 Å to about 18,000 Å. In planarizing the wafer surface after copper metallization, erosion and dishing are typically encountered, thereby decreasing the degree of surface uniformity or planarity and challenging the depth of focus limitations of conventional photolithographic techniques, particular with respect to achieving submicron dimensions, such as below about 0.18 micron.
Conventional techniques for CMP Cu and Cu alloys consequently exhibit unacceptably low polishing rates or poor polishing results. Conventional CMP slurries for Cu and Cu alloys contain abrasive particles, an oxidizer, a complexing agent, and a film forming agent. Conventional CMP operates by oxidizing the surface of the metal to a metal oxide. The complexing agent also has a propensity to oxidize the metal but is added primarily to complex and dissolve the formed metal oxide into the slurry. Abrasion by the abrasive particles completes the removal and planarization of the metal layer.
The oxidizers form an oxide film on the metal layer and typically stop etching once a thin oxide film forms. Conventional complexing agents are small organic molecules, such as a carboxylic acids, amines, their salts. The complexing agents, however, tend to attack the metal layer as well as any formed oxide film further etching the metal layer. Further, the use of small molecules tends to diffuse to the metal/oxide interface, or simply diffuses through the less dense oxide film due to their small size and affinity for the metal surface causing continued etching of the target metal. Such over-etching of metal lines results in dishing which may form capillary forces to suck the aqueous solution thereby exacerbating dishing. Currently, dishing is a significant problem in CMP of metal layers, particularly Cu and Cu alloys.
Another difficulty of polishing substrate is achieving uniform planarity of the substrate surface. Uniform planarity includes the uniform removal of material from the surface of substrates as well as removing non-uniform layers which have been deposited on the substrate. For example, the edge area, or bevel edge, of the substrate may receive an excess amount or minimal amount of deposition, typically referred to as an edge bead, during the deposition process. This edge area of the substrate is often described as the edge bead removal (EBR) area.
Excess materials, such as copper or tungsten, deposited on the beveled edge of a substrate tends to flake or peel off during chemical mechanical polishing, which particles may damage adjacent portions of the substrate and can detrimentally affect processing uniformity by the polishing pad on subsequent substrates. Material may also be deposited on the backside of the substrate which is not normally removed during a polishing process and also provides a potential source of particle during processing. Alternatively, minimal depositions of material are not planarized in many conventional polishing processes and may also result in a non-planar surface. Therefore, the copper or tungsten deposited on the bevel edge and EBR area is usually of a different level as the tungsten material deposited on the rest of the substrate surface which particles can detrimentally affe
Bajaj Rajeev
Redeker Fred C.
Tsai Stan D.
Wang Yuchun
Wijekoon Kapila
Applied Materials Inc.
Moser Patterson & Sheridan
Nguyen Dung Van
LandOfFree
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