Abrading – Abrading process – With tool treating or forming
Reexamination Certificate
1999-12-30
2001-10-23
Eley, Timothy V. (Department: 3723)
Abrading
Abrading process
With tool treating or forming
C451S443000, C451S444000
Reexamination Certificate
active
06306019
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method and apparatus for conditioning a polishing pad. More particularly, the present invention relates to a method and apparatus for conditioning a polishing pad used in the chemical mechanical planarization of semiconductor wafers.
BACKGROUND
Semiconductor wafers are typically fabricated with multiple copies of a desired integrated circuit design that will later be separated and made into individual chips. A common technique for forming the circuitry on a semiconductor is photolithography. Part of the photolithography process requires that a special camera focus on the wafer to project an image of the circuit on the wafer. The ability of the camera to focus on the surface of the wafer is often adversely affected by inconsistencies or unevenness in the wafer surface. This sensitivity is accentuated with the current drive toward smaller, more highly integrated circuit designs. Semiconductor wafers are also commonly constructed in layers, where a portion of a circuit is created on a first level and conductive vias are made to connect up to the next level of the circuit. After each layer of the circuit is etched on the wafer, an oxide layer is put down allowing the vias to pass through but covering the rest of the previous circuit level. Each layer of the circuit can create or add unevenness to the wafer that is preferably smoothed out before generating the next circuit layer.
Chemical mechanical planarization (CMP) techniques are used to planarize the raw wafer and each layer of material added thereafter. Available CMP systems, commonly called wafer polishers, often use a rotating wafer holder that brings the wafer into contact with a polishing pad moving in the plane of the wafer surface to be planarized. A polishing fluid, such as a chemical polishing agent or slurry containing microabrasives, is applied to the polishing pad to polish the wafer. The wafer holder then presses the wafer against the rotating polishing pad and is rotated to polish and planarize the wafer.
With use, the polishing pads used on the wafer polishers become clogged with used slurry and debris from the polishing process. The accumulation of debris reduces the surface roughness and adversely affects polishing rate and uniformity. Polishing pads are typically conditioned to roughen the pad surface, provide microchannels for slurry transport, and remove debris or byproducts generated during the CMP process.
One present method for conditioning a polishing pad uses a rotary disk embedded with diamond particles to roughen the surface of the polishing pad. Typically, the disk is brought against the polishing pad and rotated about an axis perpendicular to the polishing pad while the polishing pad is rotated. The diamond coated disks produce predetermined microgrooves on the surface of the polishing pad. Because the linear velocities of the leading, center and lagging portions of the disk are different, the rate of microgrooving is different. This non-uniform microgrooving has led some pad conditioner manufacturers to add a continuous oscillation motion to the rotational movement of the rotary disk pad conditioners. This extra movement can result in part of the wafer being exposed to freshly conditioned portions of the polishing pad and another part of the wafer being exposed to a used portion of the pad.
Another apparatus and method used for conditioning a pad implements a rotatable bar on the end of an arm. The bar may have diamond grit embedded in it or high pressure nozzles disposed along its length. In operation, the arm swings the bar out over the rotating polishing pad and the bar is rotated about an axis perpendicular to the polishing pad in order to score the polishing pad, or spray pressurized water on the polishing pad, in a concentric pattern. These types of pad conditioners often do not provide uniform pad conditioning because they are only applied to a small portion of the width of the pad's surface at any given time. Thus, the pressure of the conditioner against the pad can vary.
SUMMARY
According to a first aspect of the invention, an elongated pad conditioning member comprising an abrasive substance is positioned around a shaft. The shaft has an axis substantially parallel to a plane of a polishing pad. The axis of the elongated pad conditioning member is positioned at greater than 180° to the direction or vector of travel of the polishing pad. A motor is connectable to the elongated pad conditioning member. The motor is configured to variably rotationally reciprocate the exterior circumference of the elongated pad conditioning member at varying speeds about the shaft.
In a further aspect of the invention, a roller has an axis of rotation oriented substantially parallel to a polishing plane of the polishing pad. Additionally, the axis of rotation of the elongated pad conditioning member is positioned at greater than 180° to a direction of travel of the polishing pad. A motor is attachable to the roller providing continuous powered rolling. The motor is configured to continuously roll the outer circumference of the roller at variable speeds about the axis of rotation of the roller.
According to another aspect of the present invention, a method of conditioning a polishing pad includes the steps of providing a polishing pad conditioner having a cylindrical roller with a longitudinal rotational axis, positioning the polishing pad conditioner adjacent the polishing pad so that the longitudinal rotational axis of the roller is oriented substantially parallel to the polishing pad, positioning the polishing pad conditioner so that the longitudinal rotational axis of the roller is not oriented at right angles to a vector or direction of travel of the polishing pad, and moving the roller against the polishing pad while the polishing pad is moving. A pressure is maintained against the polishing pad with the cylindrical roller. The roller is rotationally reciprocated about the longitudinal axis at variable speeds by a motor. In an alternative embodiment, the roller is continuously rotated about the longitudinal axis at variable speeds by a motor.
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Copy of International Search Report for PCT/US00/35457 dated Apr. 27, 2001.
Brinks Hofer Gilson & Lione
Eley Timothy V.
Lam Research Corporation
Nguyen Dung Van
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