Abrading – Precision device or process - or with condition responsive... – With indicating
Reexamination Certificate
1999-11-03
2001-09-04
Banks, Derris H. (Department: 3723)
Abrading
Precision device or process - or with condition responsive...
With indicating
C451S288000, C451S287000
Reexamination Certificate
active
06283828
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a wafer polishing apparatus, and more particularly to a wafer polishing apparatus with a chemical mechanical polishing method (CMP).
2. Description of Related Art
A wafer polishing apparatus with a CMP polishes an oxidized membrane and a metal membrane, and so forth, which are formed on a wafer, and such a polishing apparatus requires a precise control of a polishing amount. Thus, as an apparatus for controlling the polishing amount, that is, as an apparatus for detecting an end of the polishing, an apparatus is suggested which determines a rotation torque of a wafer holding head and then detects the end of the polishing according to the rotation torque.
As shown in
FIG. 4
, the apparatus for detecting the end of the polishing detects, focussing on a difference in rotation resistance (processing resistance) which occurs due to different processing resistances at layers and different types of polishing liquids (slurries), the change in the processing resistance and finishes processing at an intended layer. The relationship between the each layer and the rotation resistance is “metal layer”<“membrane between layers”<“barrier metal layer”.
However, because the apparatus for determining the rotation torque of the wafer holding head according to a change in electrical resistance of a motor determines the rotation torque including the rotation resistance of a deceleration mechanism connecting an output shaft of the motor and the wafer holding head, the rotation torque of only the wafer holding head cannot be determined exclusively; thus the end of the polishing cannot be detected accurately.
A wafer polishing apparatus disclosed in Japanese Patent Application Laid-open No. 9-19863 forms a pressurized air layer between a carrier and a wafer, and presses the wafer against a platen through the pressurized air layer to polish the wafer. Moreover, according to the wafer polishing apparatus, a retainer ring is arranged at an outer periphery of the carrier; thus, the retainer ring prevents the wafer from jumping out of the carrier during polishing. In other words, the outer periphery of the wafer during polishing is contacted with an inner periphery of the retainer ring whereby preventing the wafer from jumping out of the carrier.
Directed to a case in which the retainer ring is directly fixed to the outer periphery of the carrier, an impact at contact of the wafer to the retainer ring is not absorbed to the retainer ring side, and such an impact rather becomes a counterforce applied to the wafer; as a result a wafer may be damaged.
In view of the above-described adverse effect, the wafer polishing apparatus has the retainer ring arranged with a gap with respect to the outer periphery of the carrier, so as to prevent the wafer from a damage by absorbing the impact with the gap.
Further, the wafer polishing apparatus has the retainer ring arranged with the gap with respect to the carrier; thus the wafer is polished, its position with respect to the carrier always moving.
In the wafer polishing apparatus, the wafer is polished preferably in a state that the center of the wafer is held on the central axis of the carrier in purpose of improving the polishing precision of the wafer.
However, the conventional wafer polishing apparatus has a difficulty in improving its polishing precision of the wafer since the position of the wafer always changes.
This problem can be solved by fixing the retainer ring directly to the outer periphery of the carrier and polishing the wafer without the gap, but the wafer may be damaged without the gap as described above.
SUMMARY OF THE INVENTION
The present invention has been developed in view of the above-described circumstances, and has as its object the provision of a wafer polishing apparatus with a detecting device which accurately detects the end of the polishing according to the change in a rotation resistance of the wafer during polishing.
Further object of the present invention is the provision of the wafer polishing apparatus, which can prevent damage of the wafer which occurs by the impact at contact of the wafer with a retainer ring, while improving the polishing precision by polishing the wafer in the state that the center of the wafer is held on the central axis of the carrier.
To achieve the above-mentioned object, the present invention is directed to a wafer polishing apparatus, comprising: a platen which rotates; a holding head which holds a wafer and presses the wafer against the platen to polish the wafer, the holding head comprising a head body which is rotated and arranged to face the platen, a carrier which is arranged below the head body and holds the wafer at its bottom face, a connecting member which connects the head body with the carrier and transmits a rotation force from the head body to the carrier, and a torque determining device which is provided to the connecting member and determines a rotation torque of the carrier applied from the carrier to the connecting member; and a polishing amount determining device which determines a polishing amount of the wafer according to the rotation torque determined by the torque determining device.
Moreover, to achieve the above-mentioned object, the present invention is directed to a wafer polishing apparatus, comprising: a platen which rotates; a holding head which holds a wafer and presses the wafer against the platen to polish the wafer, the holding head comprising a head body which is rotated and arranged to face the platen, a carrier which is arranged below the head body and holds the wafer at its bottom face, a connecting member which connects the head body with the carrier and transmits a rotation force from the head body to the carrier, and a friction force determining device which is provided to the connecting member and determines a friction force in a rotation direction of the platen which occurs at the wafer and the platen and is applied from the carrier to the connecting member; and a controller which controls wafer polishing according to a change in the friction force determined by the friction force determining device.
According to the present invention, the head body and the carrier constituting the holding head are connected with each other by the connecting member which comprises a torque determining device which determines only a rotation torque of the carrier; thus a polishing end can be accurately detected.
Further, according to the present invention, a strain measuring device for measuring the strain of the connecting member is applied as the torque determining device. The processor calculates the rotation torque of the carrier according to the strain measured by the strain measuring device. Therefore, the accurate rotation torque of the carrier can be obtained.
According to the present invention, a strain gage is applied as the strain measuring device of the torque determining device, so that the rotation torque of the carrier can be easily determined. In that case, the processor calculates the rotation torque of the carrier according to an electric signal outputted from the strain gage.
Still according to the present invention, the head body and the carrier of the holding head are connected with each other by the; connecting member which is provided with a friction force determining device. The friction force determining device determines the friction force in a rotation direction of the platen, which occurs by the wafer and the platen, and the controller controls wafer polishing according to the friction force.
In wafer polishing by CMP, a friction coefficient of the wafer and the platen changes when a dressing condition of the platen is poor and a polishing rate drops. The friction coefficient tends to be low when the polishing rate is high, and tends to be high when the polishing rate drops. Therefore, the present invention for detecting the change in the friction coefficient, that is, change in the friction force, stores beforehand the friction force indicating when
Banks Derris H.
Nixon & Peabody LLP
Safran David S.
Tokyo Seimitsu Co. Ltd.
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