Semiconductor device manufacturing: process – Chemical etching – Combined with the removal of material by nonchemical means
Reexamination Certificate
1998-04-22
2001-04-17
Wilczewski, Mary (Department: 2822)
Semiconductor device manufacturing: process
Chemical etching
Combined with the removal of material by nonchemical means
C438S959000
Reexamination Certificate
active
06218306
ABSTRACT:
BACKGROUND
The present invention relates generally to chemical mechanical polishing of substrates, and more particularly to a method of polishing a metal layer.
An integrated circuit is typically formed on a substrate by the sequential deposition of conductive, semiconductive or insulative layers on a silicon wafer. After each layer is deposited, the layer may be etched to create circuitry features. One fabrication step involves the formation of metal vias, plugs and lines to provide conductive paths between thin film circuits. Metal vias can be created by depositing a metal layer over a patterned insulative layer and then planarizing the metal layer until the insulative layer is exposed. The portions of the metal layer remaining between the raised pattern of the insulative layer form the metal vias, plugs and lines.
Chemical mechanical polishing (CMP) is one accepted method of planarization. This planarization method typically requires that the substrate be mounted on a carrier or polishing head. The exposed surface of the substrate is placed against a rotating polishing pad. The polishing pad may be either a “standard” pad or a fixed-abrasive pad. A standard pad has a durable roughened surface, whereas a fixed-abrasive pad has abrasive particles held in a containment media. The carrier head provides a controllable load, i.e., pressure, on the substrate to push it against the polishing pad. A polishing slurry, including at least one chemically-reactive agent, and abrasive particles if a standard pad is used, is supplied to the surface of the polishing pad.
An effective CMP process not only provides a high polishing rate, but also provides a substrate surface which is finished (lacks small-scale roughness) and flat (lacks large-scale topography). The polishing rate, finish and flatness are determined by the pad and slurry combination, the relative speed between the substrate and pad, and the force pressing the substrate against the pad. The polishing rate sets the time needed to polish a layer. Because inadequate flatness and finish can create defective substrates, the selection of a polishing pad and slurry combination is usually dictated by the required finish and flatness. Given these constraints, the polishing time needed to achieve the required finish and flatness sets the maximum throughput of the CMP apparatus.
A reoccurring problem in metal CMP is the so-called “microscratching” of the substrate surface. Specifically, some CMP processes create shallow grooves, e.g., on the order of 500 angstroms deep, in the substrate surface. These grooves render the substrate finish unsuitable for integrated circuit fabrication, lowering the process yield.
Another problem relates to slurry waste. In some metal polishing processes, two slurries, one acidic and one alkaline, are delivered to two polishing pads in the CMP apparatus. Since the two slurries have an opposite pH, the slurry drainage system must be designed so that the slurries do not mix when they are drained from the polishing pad.
SUMMARY
In one aspect, the invention is directed to a method of forming a patterned metal layer on a substrate. In the method, a metal layer is formed on a non-planar, non-metallic surface of the substrate, and the metal layer is chemical mechanical polished with a slurry and a first polishing pad until the metal layer is substantially planarized and a residual layer remains over the non-metallic surface. The residual layer has a thickness approximately equal to the depth of a potential microscratch. The residual layer is chemical mechanical polished with the slurry and a second polishing pad which is softer than the first polishing pad until the non-metallic surface is exposed.
Implementations of the invention may include the following. The non-metallic layer may be overpolished to assure that the entire residual layer is removed. A barrier layer may be formed between the non-metallic layer and the metal layer, and the residual layer may include a portion of the barrier layer. The non-metallic layer may be over-polished to assure that the entire barrier layer is removed. The first chemical mechanical polishing step may include polishing at a plurality of polishing stations, whereas the second chemical mechanical polishing step may include polishing at a single polishing station. The residual layer may have a thickness between about 200 and 1000 angstroms. The slurry may be acidic.
In another aspect, the invention is directed to a method of forming a patterned metal layer on a substrate in which a metal layer is formed on a non-planar, non-metallic surface of the substrate, and the metal layer is chemical mechanical polished with a slurry and a first polishing pad until the metal layer is substantially planarized and a residual layer having a thickness between about 200 and 1000 angstroms remains over the non-metallic surface. The residual layer is chemical mechanical polished with the slurry and a second polishing pad which is softer than the first polishing pad until the non-metallic surface is exposed.
Advantages of the invention may include the following. Microscratch defects are reduced or eliminated, thereby increasing process yield. The CMP process uses only one slurry, permitting the CMP apparatus to be constructed with a simpler and less expensive slurry supply and slurry drainage system. In addition, the throughput of the CMP apparatus and the finish of the resulting substrates are improved.
Other features and advantages will be apparent from the following description, including the drawings and claims.
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Fishkin Boris
Lin Ronald
Wijekoon Kapila
Applied Materials Inc.
Fish & Richardson
Wilczewski Mary
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