Abrading – Machine – Endless band tool
Reexamination Certificate
1999-08-04
2002-01-08
Morgan, Eileen P. (Department: 3723)
Abrading
Machine
Endless band tool
C451S296000, C451S307000
Reexamination Certificate
active
06336851
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the field of chemical mechanical polishing. More particularly the present invention relates to apparatus and methods for chemical mechanical polishing of substrates used in the manufacture of integrated circuits.
BACKGROUND OF THE INVENTION
Chemical mechanical polishing is a method of planarizing or polishing semiconductor and other types of substrates. At certain stages in the fabrication of devices on a substrate, it may become necessary to polish the surface of the substrate before further processing may be performed. One polishing process, which passes a conformable polishing pad over the surface of the substrate to perform the polishing, is commonly referred to as mechanical polishing. Mechanical polishing may also be performed with a chemically active abrasive slurry, which typically provides a higher material removal rate and a higher chemical selectivity between films of the semiconductor substrate than are possible with mechanical polishing. When a chemical slurry is used in combination with mechanical polishing, the process is commonly referred to as chemical mechanical polishing, or CMP.
Prior art CMP process typically include a massive rotating platen containing colloidal particles in an alkaline slurry solution. The substrate to be polished is held against the polishing platen by a polishing head or carrier which can be moved in an x-y direction over the plane of the platen from a position near its outside diameter to a position close to its center. The platen is several times larger than the substrate to be polished. The substrate is rotated independently while pressure is maintained between the substrate and the polishing pad.
The rate of material removal from the substrate in CMP is dependent on several factors including, among others, the chemicals and abrasives used in the slurry, the surface pressure at the polishing pad/substrate interface and the net motion between the substrate and the polishing pad. Generally, the higher the surface pressure and net motion at the regions of the substrate which contact the polishing pad, the greater the rate of removal of material from the substrate. It should be appreciated that equipment capable of performing this process is relatively massive and difficult to control to the precision necessary to consistently remove an equal amount of material on all areas of the substrate.
Using a large polishing pad of CMP processing creates several additional processing limitations which lead to non-uniformities in the polished substrate. Because the entire substrate is rotated against the polishing pad, the entire surface of the substrate is polished to a high degree of flatness as measured across the diameter of the substrate. However, where the substrate is warped, the portions of the substrate which project upwardly due to warpage tend to have higher material removal rates than the remainder of the substrate surface. Furthermore, as the polishing pad polishes the substrate, material removed from the substrate forms particulates which may become trapped in the pad, as the polishing slurry dries on the pad. When the pad becomes filled with particulates and the slurry dries in the pad, the polishing surface of the pad glazes and its polishing characteristics change. Unless the user constantly monitors the removal rate of the polishing pad with each substrate, or group of substrates, and adjusts the slurry, load, position, and/or rotational speed of the polishing pad to maintain the desired material removal rate, the amount of material removed by the polishing pad from each substrate consecutively processed thereon will decrease.
SUMMARY OF THE INVENTION
The present invention provides methods and apparatus for polishing substrates where the polishing pad is a flexible membrane strip or belt (preferably continuous) which moves linearly between adjacent support rollers to provide uniform polishing of the substrate in contact with the moving membrane. In one embodiment a flexible polishing membrane has a substrate holder (polishing head), holding a substrate for polishing on a first side of the linearly moving membrane and a membrane backing member on a second side of the linearly moving membrane. The substrate holder and the membrane backing member are collectively configured to provide a set of clamping forces to urge the substrate and the first side of said membrane into contact with one another for polishing.
In one embodiment the membrane backing member is a flat surface having generally equally distributed fluid holes therein. The holes face the back of the flexible polishing membrane such that when the membrane backing member is brought into close proximity to the flexible membrane and fluid (liquid or gas) is flowing out from the holes a fluid layer is formed between the surface of the backing member and the second side of the flexible membrane (belt). Clamping forces urging the belt and backing member together are generally uniformly resisted by the intervening fluid layer which provides a nearly uniform pressure between the membrane and backing member. The uniform pressure on the backside (second side) of the membrane is substantially transferred through the membrane to provide uniform mechanical abrasion over the surface of the substrate being polished by rubbing against the first side of the membrane. The set of forces urging the substrate and membrane against one another can be varied in conjunction with, or independently of, any adjustment in the speed at which the membrane moves relative to the substrate being polished.
Preferably the substrate is fixed in the substrate holder at a location generally closely adjacent to the path of the freely moving membrane (belt). The backing member is supported by an urging member whose force can be adjusted. In one example, the force supplied by the urging member on the backing member is provided by a bellows assembly having bellows whose internal pressure is controlled to maintain a pre-set force on the back of the membrane regardless of dimensional variations in the surface of the substrate and in the thickness of the membrane belt and any liquids or slurries on its surface.
Alternately, the backing member can be held fixed while the substrate holder and substrate can be urged by an adjustable urging member whose force can be adjusted. Similar to the urging member discussed above for the backing member, the force supplied by the urging member on the substrate member is provided by a bellows assembly having bellows whose internal pressure is controlled to maintain a pre-set force on the membrane regardless of dimensional variations.
As a third alternative, adjustable urging forces can be provided to both the substrate holder and to the membrane backing member. However the balancing of such forces would have to be controlled carefully to assure that nearly central alignment of the flexible membrane between its adjacent rollers (pulleys) is maintained.
Polishing of wafers as described above is done by a belt which is generally wider and longer than the size of a single substrate (wafer). Polishing contact takes place over the whole surface of the wafer at once, as the belt is generally in contact with the full width and length of the substrate's surface at one time. If the wafer were held stationary relative to the belt, then anomalies or imperfections in the polishing membrane (belt) would be transferred to the wafers surface. To avoid or reduce the possibility that any such anomalies would form the substrate is slowly rotated and is also oscillated from side to side to distribute the effect of any such anomalies over a larger area.
To avoid excess polishing at the edges of the substrate from the natural bowing of the flexible membrane when it is subjected to pressure from one side, a perimeter or fence ring is provided around the substrate. The perimeter ring, made of a highly abrasion resistant material such as Delrin or Ultra High Molecular Weight plastics, such as polyethylene, provide an artificial extension of the ed
Applied Materials Inc.
Fish & Richardson P.C.
Morgan Eileen P.
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