Patent Application
20140308813
The present invention generally relates to chemical mechanical planarization (CMP) systems, and more particularly is directed to methods and apparatus for polishing a substrate edge.
Existing substrate edge polishing systems typically use a tape or film media impregnated with an abrasive that is drawn across the edge of the substrate to polish and shape the edge into a desired profile. Note that the edge of the substrate includes the outer edge formed by a bevel from the major surface of the substrate and an edge exclusion region that extends radially from the bevel toward the center of the major surface. Contact-based edge polishing systems are typically wet systems that consume the polishing tape and deionized (DI) water and/or polishing chemicals. Thus, the operating costs of conventional edge polishing systems include the cost of the consumables. Further, the edge exclusion region can be difficult to isolate based on the geometry of conventional edge polishing systems. In other words, conventional edge polishing systems may not be able to separately polish only the edge exclusion region. Additionally, the accuracy of using an abrasive tape for polishing imposes some practical limitations that may desire using different grit abrasive tapes (with different and varying removal rates) which also may necessitate several steps in a polishing process as the abrasive tapes are replaced. Thus, what is needed are methods and apparatus that enable edge polishing with reduced operating costs, improved accuracy, control, and/or isolation over the polishing process.
Inventive methods and apparatus are provided for non-contact edge polishing of substrates. In some embodiments, the present invention uses ion milling (e.g., using an Argon ion beam) to provide precise control and accuracy of removal of material from the substrate edge without risking damage to the substrate that conventional methods can introduce. A substrate to be processed is loaded into an evacuated chamber and mounted on a rotating chuck (e.g., an electrostatic or vacuum chuck). The edge of the substrate is aligned with an ion beam projected onto the edge of the substrate using a capture ring and/or one or more sensors. The substrate is rotated while the ion beam sputters off material from the substrate's edge. An optical sensor can be employed for end point detection and a shield such as a tubular mask can be employed to prevent sputtered off particles from landing on the major surface of the substrate.
In some embodiments, a system is provided that includes a rotatable chuck configured to secure a substrate; an ion milling machine configured to project an ion beam on an edge of the substrate and to sputter off matter from the substrate; and an endpoint detection sensor configured to determine if a material removal endpoint of the substrate has been reached. Numerous additional features are disclosed.
In other embodiments, a method is provided that includes loading a substrate onto a rotatable chuck so that an edge of the substrate is aligned with an ion gun of an ion milling machine; sputtering off material from the edge of the substrate as the substrate is rotated by the chuck; and determining if an endpoint of material removal has been reached using a sensor disposed over the edge of the substrate.
In some embodiments, a system is provided that includes a processor; and a memory coupled to the processor and storing processor executable instructions to control a plurality of components to load a substrate onto a rotatable chuck so that an edge of the substrate is aligned with an ion gun of an ion milling machine; sputter off material from the edge of the substrate as the substrate is rotated by the chuck; and determine if an endpoint of material removal has been reached using a sensor disposed over the edge of the substrate.
Numerous other aspects are provided. Other features and aspects of the present invention will become more fully apparent from the following detailed description, the appended claims and the accompanying drawings.
Inventive methods and apparatus are provided for non-contact edge polishing processes and systems. In some embodiments, the present invention uses ion milling (e.g., using an Argon ion beam) to provide precise control and accuracy of removal of material from the substrate edge without risking damage to the substrate that conventional methods can introduce. A substrate to be processed is loaded into an evacuated chamber and mounted on a rotating chuck (e.g., an electrostatic or vacuum chuck). The edge of the substrate is aligned with an ion beam projected onto the edge of the substrate using a capture ring and/or one or more sensors. The substrate is rotated while the ion beam sputters off material from the substrate's edge. An optical sensor can be employed for end point detection and a shield such as a tubular mask, can be employed to prevent sputtered off particles from contaminating the major surface of the substrate.
Optimizing material removal rates from the edge (e.g., up to 10 mm from the outer edge) of a substrate while polishing the substrate using conventional chemical mechanical planarization (CMP) methods presents a number of challenges since conventional removal mechanisms and techniques are dependent on many dynamic variables. The present invention provides a novel method of edge profile optimization that is separate from the CMP process and localized to the edge of the substrate. Instead of contacting the substrate edge with a polishing media, the present invention uses ion milling to polish the substrate edge. In some embodiments, the system of the present invention operates at atmosphere and in others; the system is contained in a sealable chamber and can be operated in a vacuum. The desired level of repeatability and removal rate can dictate whether a sealable chamber and/or a vacuum are used. In some embodiments, removal rate tuning can be controlled by adjusting the incident beam angle, the beam aperture, and/or the kinetic energy of the beam.
In addition, embodiments of the present invention allow for cost effective removal of any non-uniformities occurring at the edge of the substrate that can be introduced by conventional CMP processes. Embodiments of the present invention may also eliminate the cost burden of having to use consumable materials and components such as polishing tape, polishing pads, and slurry. Further, since method embodiments of the present invention do not require mechanical polishing of the substrate edge, potential damage to the substrate is avoided. This is particularly relevant to thin (e.g., less than approximately 50 μm) substrate applications such as fragile “Through Silicon Via” (TSV) substrates that are vulnerable to and easily damaged by any edge contact.
Turning to
Although not represented in the drawings for clarity sake, the system 100 can include an appropriate sized, sealable chamber suitable to house the components of the system and to accommodate the desired size substrates. The chamber can include one or more ports and robot arms for loading and unloading substrates. In addition, the system chamber can include pumps to create a vacuum within.
The substrate 102 is positioned under the beam 104 via the use of a capture ring 108. The capture ring 108 can be made of ceramic and function to both center the substrate 102 and protect the surfaces supporting the substrate 102 from the ion beam 104. In some embodiments, the capture ring 108 can be a replaceable/consumable component. As shown most clearly in the cross-section profile depiction of
In some embodiments, the ion milling machine 106 used can be a commercially available ion milling machine such as, for example, the model IM4000 Argon ion milling system manufactured by Hitachi High Technologies America, Inc., a Delaware corporation. However, other practicable ion milling systems can be used. Conventionally, such ion milling machines have been used to thin samples until they are transparent to electrons. By making a sample electron transparent, the sample can be imaged and characterized in a transmission electron microscope (TEM). Ion beam milling has also been used for cross-section preparation for use with scanning electron microscope (SEM) analysis of materials. Thus, all known prior applications of ion milling machines were limited to sample thinning for TEM imaging and preparation for SEM analysis.
A shield 110 (e.g., a tubular mask) is disposed between the edge of the substrate and the remainder of the major surface of the substrate to block particles sputtered off of the edge from reaching the center of the substrate 102. The shield can be made from roughened ceramic or ceramic coated material. In some embodiments, the shield 110 can be a replaceable/consumable component. In some embodiments, the shield 110 may be held slightly above the substrate (e.g., approximately 0.5 mm to approximately 5 mm above) or, in other embodiments, the shield may rest on the substrate 102 and rotate with the substrate 102.
A sensor 112 (e.g., an optical sensor) is used to detect the polishing end point. An example of a commercially available optical sensor suitable for use with the system of the present invention is the model SD1024GL sensor manufactured by Verity Instruments, Inc., headquartered in Texas. In some embodiments, inductive sensors may be used. Other practicable sensors may also be used. The system 100 can be operated by a controller 114 (e.g., a processor, computer, embedded controller, programmable logic array, microprocessor, discrete logic, etc.) configured, or programmed to execute software/instructions, to perform the methods of the present invention.
The substrate 102 is rotated on a chuck 202 driven by a motor 204 or any other suitable actuator. The chuck 202 can be made from, for example, a ceramic encased or coated electrode or an electrode embedded in a polymer film. In some embodiments, an aluminum nitride bonded copper electrode can be used. An example of a ceramic coated electrode is a plasma sprayed aluminum oxide on an aluminum electrode. An example an electrode embedded in a polymer film is a copper electrode embedded in polyimide film. In some embodiments, the chuck 202 can include a substrate holding mechanism such as an electrostatic device or vacuum pressure ports to maintain the substrate's position as the substrate 102 is rotated. In some embodiments, the chuck can include thermal control devices to pre-heat the substrate 102 or cool the substrate 102 during processing. Thus, the thermal control devices may include heating elements and/or channels for cooling fluids (e.g., liquids or gases). In some embodiments, helium can be dispensed between the chuck 202 and the substrate 102 for both cooling and to provide a conductive layer.
The chuck 202 may be driven by a motor 204 coupled directly or through a linkage to the lower center of the chuck 202. In some embodiments, other components and arrangements for rotating the chuck 202 may be employed such as drive wheels at the perimeter of the chuck 202. An example motor 204 that can be employed is a 0.5 HP electric motor configured to rotate the chuck 202 at approximately 1 rpm to approximately 100 rpm. Other types of, power, and speed motors can be used.
In addition to pumps for creating a vacuum in the system chamber, the system 100 of the present invention may also include a ventilation system 206. The ventilation system 206 can include a hood or intake nozzle disposed proximate to the substrate 102 near the sputtering activity of the ion beam 104 as shown in
Turning now to
In some embodiments, as indicated by Arrows A, B, and C, the position of the ion gun of the milling machine 106 can be adjusted to facilitate creating the desired material removal profile. The adjustments to the ion gun allow the position, shape, size, and energy concentration of an ion beam spot projected on the substrate edge to be precisely configured to achieve the desired material removal profile.
Arrow A indicates that the ion gun can be moved closer to, or further from, the surface of the substrate edge. This adjustment can be used to control the projected area and the amount of energy that is delivered to the substrate edge and therefore the material removal rate. Arrows B indicate that the ion gun can be moved in a direction perpendicular to the directions of double-ended Arrow A. This adjustment can be used to move the beam to and from the outer edge of the substrate 102, i.e., radially relative to the center of the substrate 102. By oscillating the ion gun at an appropriate rate in the B directions while rotating the substrate during milling, an edge area larger than the ion beam spot can be polished. Arcing Arrow C indicates the rotational angle adjustability of the ion gun that allows for adjustment of the aspect ratio of the projected area and the size (e.g., area) of the ion beam spot. While not represented in the drawings, the aperture of the ion gun can also be adjusted (e.g., dilated) in some embodiments. Adjustment of the ion gun's aperture allows control over the size of the ion beam spot which affects the energy concentration of the ion beam and thus, the material removal rate.
In some embodiments, the ion gun of the milling machine 106 can be disposed over the center of the substrate 102, pointing radially outward toward the edge of the substrate. In such embodiments, a horizontally disposed shield or mask can be held over or on the portion of the major surface of the substrate 102 to be protected. Such embodiments may reduce the amount of redepostion on the substrate. Likewise, in some embodiments, the ion gun of the milling machine 106 can be disposed so that the beam is aimed in a direction that is parallel with a line tangential to the substrate.
Once the ion gun of the milling machine 106 is adjusted to provide the desired material removal profile and the substrate 102 is being rotated by the chuck 202, the ion milling machine is activated and material is sputtered off the surface of the substrate's edge (412). Meanwhile, the ventilation system 206 evacuates the sputtered material, the shield 110 blocks the sputtered material from reaching the center of the substrate 102, and the capture ring 108 blocks the ion beam 104 from milling the chuck 202. The temperature of the substrate can be controlled via the cooling facilities in the chuck 202 to keep the substrate 102 within a desired thermal range. As the milling continues, the sensor 112 is used by the controller 114 to detect the amount of material that has been removed and whether a desired pre-defined endpoint has been reached (414). In some embodiments, the end point can include a flatness variation specification and/or a substrate thickness definition.
In some embodiments, the same substrate edge may be exposed to multiple ion beams concurrently. For example, two or more ion guns may be aimed at adjacent areas on the same surface of the substrate edge. In addition to increasing the material removal rate, having more than one ion beam can provide greater flexibility and more options in defining and implementing the desired material removal profile.
In this embodiment, the ion beam 104 is projected at a substantially zero incidence angle relative to the top and bottom surfaces of the substrate edge (e.g., substantially parallel to the surface of the substrate edges) and parallel to a line tangential to the major surfaces of the substrate. In
In some embodiments, the ion beam 104 can be collimated to project with less spread. In some embodiments, the ion gun may include a horizontal bar mask (e.g., having a thickness slightly thinner than the thickness of the substrate 102) across the aperture that prevents the ion beam from hitting most of the outer edge (and bevel) of the substrate while allowing the ion beam 104 to mill layers off of the edge surfaces of the substrate. In some embodiments, the system 500 may also include an absorption target 502 to capture parts of the ion beam 104 that do not hit the substrate 102.
Accordingly, while the present invention has been disclosed in connection with the preferred embodiments thereof, it should be understood that other embodiments may fall within the scope of the invention, as defined by the following claims.
