The present invention relates to carrier assemblies, planarizing machines including carrier assemblies, and methods for mechanical and/or chemical-mechanical planarization of micro-device workpieces.
Mechanical and chemical-mechanical planarization processes (collectively “CMP”) remove material from the surface of micro-device workpieces in the production of microelectronic devices and other products.
The carrier head 30 has a lower surface 32 to which a micro-device workpiece 12 may be attached, or the workpiece 12 may be attached to a resilient pad 34 under the lower surface 32. The carrier head 30 may be a weighted, free-floating wafer carrier, or an actuator assembly 36 may be attached to the carrier head 30 to impart rotational motion to the micro-device workpiece 12 (indicated by arrow J) and/or reciprocate the workpiece 12 back and forth (indicated by arrow I).
The planarizing pad 40 and a planarizing solution 44 define a planarizing medium that mechanically and/or chemically-mechanically removes material from the surface of the micro-device workpiece 12. The planarizing solution 44 may be a conventional CMP slurry with abrasive particles and chemicals that etch and/or oxidize the surface of the micro-device workpiece 12, or the planarizing solution 44 may be a “clean” non-abrasive planarizing solution without abrasive particles. In most CMP applications, abrasive slurries with abrasive particles are used on non-abrasive polishing pads, and clean non-abrasive solutions without abrasive particles are used on fixed-abrasive polishing pads.
To planarize the micro-device workpiece 12 with the CMP machine 10, the carrier head 30 presses the workpiece 12 face-down against the planarizing pad 40. More specifically, the carrier head 30 generally presses the micro-device workpiece 12 against the planarizing solution 44 on a planarizing surface 42 of the planarizing pad 40, and the platen 20 and/or the carrier head 30 moves to rub the workpiece 12 against the planarizing surface 42. As the micro-device workpiece 12 rubs against the planarizing surface 42, the planarizing medium removes material from the face of the workpiece 12.
The CMP process must consistently and accurately produce a uniformly planar surface on the workpiece 12 to enable precise fabrication of circuits and photo-patterns. A nonuniform surface can result, for example, when material from certain areas of the workpiece 12 is removed more quickly than material from other areas during CMP processing. To compensate for the nonuniform removal of material, carrier heads have been developed with expandable interior and exterior bladders that exert downward forces on selected areas of the workpiece 12. These carrier heads, however, have several drawbacks. For example, the bladders typically have curved edges that make it difficult to exert a uniform downward force at the perimeter of the bladder. Additionally, the bladders cover a fairly broad area of the workpiece 12, which limits the ability to localize the downforce. Conventional bladders accordingly may not provide precise control of the localized force. For example, in some embodiments, the exterior bladders are coupled to a moveable retaining ring that slides vertically during the planarizing process. The vertical movement of the retaining ring displaces such attached bladders, which inhibits the ability of the attached bladders to provide a controlled force near the edge of the workpiece 12. Furthermore, carrier heads with multiple bladders frequently fail resulting in significant downtime for repair and/or maintenance, causing a concomitant reduction in throughput.
The present invention is directed toward carrier assemblies, planarizing machines with carrier assemblies, and methods for mechanical and/or chemical-mechanical planarization of micro-device workpieces. In one embodiment, the carrier assembly includes a head having a chamber, a magnetic field source carried by the head, and a fluid with magnetic elements in the chamber. The magnetic field source has a first member that induces a magnetic field in the head. The fluid and/or the magnetic elements move within the chamber under the influence of the magnetic field source to exert a force against a discrete portion of the micro-device workpiece. In a further aspect of this embodiment, the carrier assembly includes a flexible member in the chamber. The flexible member partially defines an enclosed cavity. The magnetic field source can be any device that induces a magnetic field, such as a permanent magnet, an electromagnet, or an electrically conductive coil. Furthermore, the magnetic field source can have various magnetic members that each individually induce magnetic fields to apply different downforces to discrete regions of the workpiece. For example, these magnetic members can be configured in various shapes, such as quadrants, annular sections, and/or sectors of a grid.
In a further aspect of the invention, the carrier assembly includes a plurality of magnets, a head carrying the plurality of magnets, and a magnetic fluid including magnetic elements within the head. Each of the magnets can selectively induce a magnetic field in the magnetic fluid. The head includes a cavity having sections proximate to each magnet. When a magnet induces a magnetic field in one of the sections, the magnetic fluid and/or the magnetic elements move toward the corresponding section of the cavity and cause a force against the micro-device workpiece. In another aspect of the invention, the carrier assembly includes a head having a cavity with a first section, a means for selectively inducing a magnetic field carried by the head, a flexible member carried by the head, and a magnetic means for exerting pressure against the flexible member in the cavity. The magnetic means moves in the cavity under the influence of the means for selectively inducing the magnetic field to exert pressure against a portion of the flexible member. The flexible member is positionable proximate to the micro-device workpiece so that the pressure against the flexible member can be applied to the workpiece.
A method for polishing a micro-device workpiece with a polishing machine having a carrier head and a polishing pad includes moving at least one of the carrier head and the polishing pad relative to the other to rub the workpiece against the polishing pad. The carrier head includes a cavity and a magnetic fluid within the cavity. The method further includes exerting a force against a backside of the workpiece by inducing a magnetic field in the carrier head that displaces a portion of the magnetic fluid within the cavity of the carrier head. In another embodiment, a method for manufacturing a carrier head for use on a planarizing machine includes coupling a magnet configured to induce magnetic fields to the carrier head and disposing a fluid with magnetic elements within a cavity in the carrier head.
The present invention is directed to carrier assemblies, planarizing apparatuses including carrier assemblies, and methods for mechanical and/or chemical-mechanical planarization of micro-device workpieces. The term “micro-device workpiece” is used throughout to include substrates in or on which micro-electronic devices, micro-mechanical devices, data storage elements, and other features are fabricated. For example, micro-device workpieces can be semi-conductor wafers, glass substrates, insulated substrates, or many other types of substrates. Furthermore, the terms “planarization” and “planarizing” mean either forming a planar surface and/or forming a smooth surface (e.g., “polishing”). Several specific details of the invention are set forth in the following description and in
In the illustrated embodiment, the carrier assembly 130 also includes a chamber 114 in the support member 134, a magnetic field source 100 in the chamber 114, and a magnetic fluid 110 in the chamber 114. The magnetic field source 100 can be a permanent magnet, an electromagnet, an electrical coil, or any other device that creates magnetic fields in the chamber 114. The magnetic field source 100 can have a single magnetic source or a plurality of magnetic sources with various configurations, such as those described below with reference to
The magnetic fluid 110 contains magnetic elements 112 disposed within the chamber 114 that can be influenced by the magnetic field(s). For example, a magnetic field can attract the magnetic elements 112 to a specific area of the chamber 114, or a magnetic field can repel the magnetic elements 112 from a specific area of the chamber 114. The concentration, properties and size of magnetic elements 112 control the magnetic properties of the magnetic fluid 110 in a manner that exerts a controlled driving force within the fluid 110. For example, if the magnetic fluid 110 has a large concentration of relatively small magnetic elements 112, the fluid 110 as a whole assumes magnetic properties. If, however, the magnetic elements 112 are relatively large, the magnetic elements 112 tend to respond as individual elements. In one embodiment, the magnetic fluid 110 can have a fluid base, such as water or kerosene, with magnetic elements 112 in suspension, such as iron oxide particles. In a further aspect of this embodiment, the magnetic elements 112 can have a polarity to further increase the attraction and/or repulsion between the magnetic elements 112 and the magnetic field source 100.
The carrier assembly 130 further includes a flexible plate 140 and a flexible member 150 coupled to the flexible plate 140. The flexible plate 140 sealably encloses the magnetic fluid 110 in the chamber 114, and thereby defines a cavity 116. The cavity 116 can have a depth of approximately 2-5 mm as measured from a first surface 102 of the magnetic field source 100 to a first surface 146 of the flexible plate 140. In other embodiments, the cavity 116 can have a depth greater than 5 mm. In the illustrated embodiment, the flexible plate 140 has a vacuum line 144 with holes 142 coupled to a vacuum source (not shown). The vacuum draws portions of the flexible member 150 into the holes 142 which creates small suction cups across the backside of the workpiece 12 that hold the workpiece 12 to the flexible member 150. In other embodiments, the flexible plate 140 may not include the vacuum line 144 and the workpiece 12 can be secured to the flexible member 150 by another device. In the illustrated embodiment, the flexible member 150 is a flexible membrane. However, in other embodiments, the flexible member 150 can be a bladder or another device that prevents planarizing solution (not shown) from entering the cavity 116. In additional embodiments, the flexible member 150 can be a thin conductor that can also induce magnetic field(s). This thin conductor can be used individually or in coordination with the magnetic field source 100 to create magnetic field(s). The flexible member 150 defines a polishing zone P in which the workpiece 12 can be planarized by moving relative to the planarizing pad 40.
In a different embodiment, a similar force can be applied to the workpiece 12 when other magnetic members 106b-d around the magnetic member 106a induce magnetic fields repelling the magnetic elements 112. In this embodiment, the magnetic elements 112 would be driven toward the section A of the cavity 116. In any of the foregoing embodiments, the magnitude of the force F is determined by the strength of the magnetic field, the concentration of magnetic elements 112, the type of magnetic elements 112, the amount of magnetic fluid 110, the viscosity of the magnetic fluid 110, and other factors. The greater the magnetic field strength, the greater the magnitude of the force F. The location of the force F and the area over which the force F is applied to the workpiece 12 is determined by the location and size of the magnetic members 106 of the magnetic field source 100. In other embodiments, such as the embodiment illustrated in
One advantage of the illustrated embodiments is the ability to apply highly localized forces to the workpiece. This highly localized force control enables the CMP process to consistently and accurately produce a uniformly planar surface on the workpiece. Moreover, the localized forces can be changed in-situ during a CMP cycle. For example, a planarizing machine having one of the illustrated carrier assemblies can monitor the planarizing rates and/or the surface of the workpiece, and accordingly, adjust the magnitude and position of the forces applied to the workpiece to produce a planar surface. Another advantage of the illustrated carrier assemblies is that they are simpler than existing systems, and consequently, reduce downtime for maintenance and/or repair and create greater throughput.
From the foregoing, it will be appreciated that specific embodiments of the invention have been described herein for purposes of illustration, but that various modifications may be made without deviating from the spirit and scope of the invention. Accordingly, the invention is not limited except as by the appended claims.
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