Patent Application
20050178402
The present invention generally relates to cleaning and drying of semiconductor wafers, and more particularly relates to mega-sonic cleaning and gas/vapor drying of semiconductor wafers.
Chemical mechanical polishing (CMP) is a technique which has been conventionally used for the planarization of semiconductor wafers. Furthermore, chemical mechanical polishing is often used in the formation of microelectronic devices to provide a substantially smooth, planar surface suitable for subsequent fabrication processes such as photoresist coating and pattern definition. A typical chemical mechanical polishing apparatus suitable for planarizing a semiconductor surface generally includes a wafer carrier configured to support, guide, and apply pressure to a wafer during the polishing process, a polishing compound such as a slurry to assist in the removal of material from the surface of the wafer, and a polishing surface such as a polishing pad.
A wafer surface is generally polished by moving the surface of the wafer to be polished relative to the polishing surface in the presence of a polishing compound. In particular, the wafer is placed in a carrier such that the surface to be polished is placed in contact with the polishing surface, and the polishing surface and the wafer are moved relative to each other while slurry is supplied to the polishing surface.
After a wafer is subjected to the CMP process, there will remain on the wafer a residue of the polishing slurry and particles of the material removed during the process. This necessitates that the wafer be cleaned and dried before further processing can take place. While the above refers to CMP processes, it should be understood that, additionally, other processes such as plasma etching, may also leave a residue on a wafer that necessitates cleaning and drying of the wafer. Any residue left on a wafer may cause defects on the wafer such that subsequent processing steps will not be properly or completely performed, resulting in reductions in yields due to inoperable devices.
The cleaning of the wafer typically involves, for example, scrubbing, spraying cleaning, musing and the like. Currently, one of the well known methods for cleaning wafers utilizes the application of mega-sonic energy created by a transducer and channeled by some mega-sonic applicator to a fluid medium where the acoustic energy travels through the medium to the wafer surface, imparting energy useful in cleaning and dislodging particles. Mega-sonic applicators can come in a variety of styles including quartz tanks for batch clean, quartz rods, coated metal plates or ceramic plates.
After a wafer has been wet cleaned, the wafer is further processed to remove water or cleaning agents so as to prevent the water and/or cleaning agent from drying and leaving a contaminating residue on the wafer surface. Spin drying is a process commonly used to remove liquid residue from the surface of a wafer. During spin drying, the cleaning liquid is applied to the center of a rapidly spinning wafer. The centrifugal force created by the spinning wafer forces the applied liquid quickly to the edge of the wafer and subsequently off the wafer.
Previously available cleaning and drying processes have proven unsatisfactory for a number of reasons. For example, the general utility of previously available cleaning and drying processes is limited depending on the properties of the surfaces that are being cleaned and dried. Liquids wet a hydrophilic surface, i.e., a thin layer of liquid spreads relatively evenly over the wafer surface and flows off the edge of the wafer upon the application of centrifugal forces as described above. As the wafer dries, only a small amount of residue is left on the wafer surface. Due to the need for faster integrated circuitry, however, there has been increased use of low dielectric constant (K) dielectrics such as carbon-doped oxides and spin-on materials (e.g., polyimide) that exhibit hydrophobic characteristics, that is, they repel liquids. Liquids bead on hydrophobic surfaces, and as the hydrophobic nature of the material increases, the contact angle of a bead of liquid on the surface increases. This beading phenomenon results in greater amounts of liquid residing on smaller defined areas of the wafer surface. While spin drying, the resulting centrifugal force on each bead of liquid causes each bead to roll toward the edge of the wafer. Unfortunately, as the bead rolls toward the edge of the wafer, it leaves droplets of water behind that dry, leaving contaminants on the surface. These contaminants can appear as radial lines or streaks corresponding to the trail of droplets left by the bead as it rolled toward the wafer's edge. The amount of contaminant left on the hydrophobic surface exceeds that left on a hydrophilic surface because of the beading and because the failure to “wet” the surface results in inferior cleaning. Accordingly, local areas of contaminants on wafers surfaces that are hydrophobic, or both hydrophilic and hydrophobic, exhibit significant reduction in yield, overload of metrology systems, and create problems in devices produced on the wafer.
Previously available cleaning and drying processes also have proven unsatisfactory because of the amount of cleaning fluids commonly required in the processes. To achieve adequate cleaning and drying, a significant amount of cleaning fluids typically are sprayed on to the wafer from a nozzle disposed above the wafer. Such significant amounts of cleaning fluids can be costly. In addition, such significant amounts of cleaning fluids may run counter to environmental regulations. Solvents, such as isopropyl alcohol liquid and vapor, acetone liquid and vapor, and the like, often are sprayed on to the wafer to reduce the surface tension of the cleaning fluids. However, the amounts of solvents used may be restricted by environmental regulations.
Moreover, such spraying of the cleaning fluids on the wafer may cause “misting,” wherein the cleaning fluids atomize upon impact with the wafer surface or surfaces of the cleaning apparatus. This mist can redeposit on the wafer after it is cleaned and dried, again resulting in particulate contamination, spotting, and corrosion.
Accordingly, it is desirable to provide a cleaning and drying process and apparatus that efficiently and quickly clean and dry wafers. In addition, it is desirable to provide a cleaning and drying process and apparatus that uses a minimum amount of cleaning fluid. It also is desirable to provide a cleaning and drying process and apparatus that minimizes the redeposition of moisture and particulates on the wafer. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.
The present invention will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and
The following detailed description of the invention is merely exemplary in nature and is not intended to limit the invention or the application and uses of the invention. Furthermore, there is no intention to be bound by any theory presented in the preceding background of the invention or the following detailed description of the invention.
For purposes of illustration only, the invention will be described as it applies to the apparatus and methods for cleaning and drying a semiconductor wafer. It is not intended, however, that the invention be limited to these illustrative embodiments; instead, the invention is applicable to a variety of processes and processing apparatus and to the processing and handling of many types of work pieces.
Referring to
Apparatus 10 further comprises a press plate 14 having a first surface 24. First surface 24 of press plate 14 may be formed of any suitable material that is not adversely affected by the cleaning and/or drying fluids used during the cleaning and drying process, as described in more detail below. Examples of suitable materials from which first surface 24 of press plate 14 may be formed include, ceramic materials, quartz, and metals and metallic alloys coated with an inert polymer, such as, for example, TEFLON®. Press plate 14 is connected to actuators 22, which raise and lower press plate 14 relative to wafer carrier 12 and wafer 20 so that a wafer can be positioned on wafer carrier 12 before the cleaning and drying processes and can be maintained a predetermined distance from first surface 24 of press plate 14 during the cleaning and drying process, as described in more detail below. Press plate 14 is disposed coaxially with wafer 20 and is approximately at least as large as wafer 20 to minimize edge effects that may occur during cleaning and drying and to minimize the amount of cleaning fluid mist and other particulates that may redeposit on surface 32 of wafer 20 during the cleaning and drying processes.
As illustrated in
At least one mega-sonic transducer 26 is disposed on a second surface 28 of press plate 14. Mega-sonic transducer 26 may comprise any suitable sonic transducer as used in the semiconductor industry. The mega-sonic transducer 26 may be the size of the entire second surface 28 of press plate 14 or may disposed proximate to only a portion of the second surface 28 of press plate 14, as illustrated in
In another exemplary embodiment of the present invention, mega-sonic transducer 26 also may be of the type that can measure the impedance from acoustic energy reflected back from first surface 32 and/or second surface 36 of wafer 20. In this manner, once the impedance is measured, the distance between first surface 24 of press plate 14 and first surface 32 of wafer 20 may be increased or decreased before or during cleaning to enhance cleaning efficiency. In addition, mega-sonic transducer 26 may measure the impedance to determine if wafer 20 is suitably positioned on wafer carrier 12, if wafer 20 is broken or damaged, if wafer 20 has fallen from wafer carrier 12, and the like.
In another exemplary embodiment of the invention, a plurality of mega-sonic transducers 26 may be disposed on second surface 28 of press plate 14. The mega-sonic transducers 26 may be independent of each other or may be connected to each other in series or parallel. The plurality of mega-sonic transducers may be configured to provide various cleaning efficiencies at different areas of first surface 24 of press plate 14. In addition, each of the mega-sonic transducers 26 may emit acoustic energy at a suitable wavelength or wavelengths so that both the first surface 32 and second surface 36 of wafer 20 are cleaned.
A cleaning and drying process using apparatus 10 will now be described with reference to
After wafer 20 is suitably situated between wafer carrier 12 and press plate 14, and preferably after wafer carrier 12 and press plate 14 are situated a predetermined distance from each other, at least one cleaning fluid 34 is dispensed through fluid port 30 of press plate 14 at a predetermined flow rate to wafer 20. Cleaning fluid 34 may be any suitable cleaning fluid known and used in the semiconductor industry, such as acids, bases, surfactants and chelating agents, and can also comprise de-ionized water. In addition, any suitable number of cleaning fluids may be used sequentially. For example, an acidic cleaning fluid may be used initially to clean the wafer surface, followed by a de-ionized water rinse. While the present invention contemplates that port 30 may be situated at any suitable location within press plate 14, preferably port 30 is situated at or sufficiently close to the center of press plate 14 so that cleaning fluid 34 flows uniformly radially from approximately the center of wafer 20 to its edges upon rotation. During or after dispensing of cleaning fluid 34, drive assembly 18 rotates wafer carrier 12 and/or wafer chucks 16 so that wafer 20 is rotated about its central axis.
During the cleaning of wafer 20, mega-sonic transducer 26 is activated. Mega-sonic transducer 26 produces acoustic energy that is transmitted by presser plate 14 to cleaning fluid 34. The acoustic energy travels through cleaning fluid 34 and causes particulates to be dislodged from first surface 32 of wafer 20. Mega-sonic transducer 26 may also produce acoustic energy that travels through wafer 20 to dislodge particulates from second surface 36 of wafer 20. In addition, mega-sonic transducer 26 may measure the impedance reflected back from first surface 32 and/or second surface 36 of wafer 20. Depending on the measured impedance, the distance between first surface 24 of press plate 14 and wafer 20 may be increased or decreased to enhance the cleaning process.
The speed of rotation of the wafer, the flow rate of cleaning fluid 34, and the distance between wafer 20 and press plate 14 are such that a layer of cleaning fluid 34 is provided, and a meniscus of cleaning fluid 34 is maintained, between first surface 32 of wafer 20 and first surface 24 of press plate 14. The wafer is rotated at a speed that is sufficient to cause cleaning fluid 34 to uniformly spread from port 30 to the edge of the wafer but is not so high that it overcomes the surface tension forces of cleaning fluid 34 and causes cleaning fluid 34 to be flung from the wafer under the influence of centrifugal forces. In one embodiment of the invention, the speed of rotation of the wafer is in the range of about 5 rpm to about 70 rpm. In another embodiment of the invention, the speed of rotation of the wafer is in the range of about 5 rpm to about 50 rpm. In a preferred embodiment of the invention, the speed of rotation of the wafer is about 20 rpm.
The minimum distance that may be maintained between first surface 24 of press plate 14 and surface 32 of wafer 20 during cleaning and drying depends, in part, on the flatness of surface 32 of wafer 20. Accordingly, first surface 24 of press plate 14 is maintained at a sufficient distance from wafer 20 so that press plate 14 does not make contact with wafer 20. The maximum distance that may be maintained between first surface 24 of press plate 14 and surface 32 of wafer 20 variously depends, in part, on the flow rate of cleaning fluid 34 and rotation of wafer 20. The maximum distance is the greatest distance that still maintains a meniscus of cleaning fluid between first surface 24 of press plate 14 and first surface 32 of wafer 20. In one exemplary embodiment of the present invention, for example, the distance between first surface 24 of press plate 14 and first surface 32 of wafer 20 may be in the range of approximately 0.1 mm to approximately 4.0 mm. In a preferred embodiment of the present invention, the distance between first surface 24 of press plate 14 and first surface 32 of wafer 20 may be in the range of approximately 0.2 mm to approximately 3.5 mm. In a more preferred embodiment of the present invention, the distance between first surface 24 of press plate 14 and first surface 32 of wafer 20 may be approximately 2.0 mm. The distance between surface 24 of press plate 14 and first surface 32 of wafer 20 also may be increased or decreased during cleaning to facilitate the cleaning process.
Referring now to
Referring again to
Drying may be terminated once cleaning fluid 34 is substantially removed from surface 32 of wafer 20 by drying fluid 60. The drying time may be calculated based on the size of wafer 20, the flow rate of drying fluid 60, and the distance between wafer 20 and press plate 14. In one embodiment of the invention, drying fluid 60 may be dispensed between first surface 32 of wafer 20 and first surface 24 of press plate 14 so that the drying process continues for at least 2 seconds. In a preferred embodiment of the invention, drying fluid 60 may be dispensed between first surface 32 of wafer 20 and first surface 24 of press plate 14 so that the drying process continues for at least 5 seconds. In a more preferred embodiment of the invention, drying fluid 60 may be dispensed between first surface 32 of wafer 20 and first surface 24 of press plate 14 for at least 10 seconds.
As will be appreciated, because press plate 14 is disposed closely to surface 34 of wafer 20 during cleaning and drying, apparatus 10 minimizes the amount of cleaning fluid required to suitably clean wafer 20, as little more than an amount sufficient to fill the volume of space between the surface 34 of wafer 20 and surface 24 of press plate 14 may be needed. In addition, apparatus 10 minimizes the amount of drying fluid required to suitably clean wafer 20, as, again, little more than an amount sufficient to fill the volume of space between the first surface 32 of wafer 20 and surface 24 of press plate 14 may be needed. Because the cleaning fluid and/or drying fluid may comprise materials that are environmentally regulated, minimizing the amount of cleaning and/or drying fluids may make the cleaning and drying processes more environmentally feasible. Moreover, because the cleaning and drying fluids cover first surface 32 of wafer 20 during the cleaning and drying processes, the apparatus of the present invention provides an anaerobic environment to which surface 34 of wafer 20 is exposed. This anaerobic environment may minimize or eliminate corrosion of the wafer due to exposure to oxygen. This configuration also may minimize photogalvonic corrosion, which otherwise may occur from photons impinging on the wafer surface 32. In addition, because press plate 14 is of a size at least as large as wafer 20, this exemplary embodiment of the invention minimizes the redeposition of moisture, such as cleaning fluid mist, and other particulates on surface 32 of wafer 20.
While the above description contemplates wafer carrier 12 moving wafer 20 relative to press plate 14, it will be appreciated that wafer 20 and press plate 14 both may be rotated, preferably in the same direction. Further, while
In another exemplary embodiment of the invention, the movement of wafer 20, press plate 14, or both, and/or the flow rate of the drying fluid may be varied during the drying process to regulate the growth of the bubble of drying fluid between wafer 20 and press plate 14. In this manner, the bubble may be permitted to grow uniformly or at varying rates so that uniform drying of surface 32 of wafer 20 may be achieved regardless of the topology of the wafer surface or the surface tension of the cleaning fluid.
In a further exemplary embodiment of the invention, first surface 24 of press plate 14 may be formed of a hydrophilic material, which may facilitate the wetting of the wafer surface by the cleaning fluid. Alternatively, first surface 24 of press plate 14 may be formed of a hydrophobic material or of a combination of hydrophobic and hydrophilic materials to facilitate or enhance the cleaning and drying processes.
In yet another exemplary embodiment of the invention, first surface 24 of press plate 14 may be substantially planar. In an alternative embodiment of the present invention, surface 24 of press plate 14 may have various topologies. For example, the press plate surface 24 may be substantially convex or substantially concave, or may be convex and concave depending on the radial distance from the center of the press plate. In addition, the press plate surface may be conical, may be thinner at its edges, may be thicker at its edges, or may have any other suitable topography or geography the facilitates cleaning and/or drying. The various topologies may compensate for various inconsistencies in the cleaning and/or drying process, such as, for example, a non-planar wafer surface or a wafer surface comprising both hydrophilic and hydrophobic materials.
Referring to
Referring to
Referring now to
Thus, processes and apparatus for efficiently cleaning and drying a work piece in a single apparatus are provided. The processes and apparatus of the invention utilize a press plate disposed a distance from the work piece during cleaning and drying forming a space between the two. During cleaning, the press plate, the work piece, or both, is set in motion and a cleaning fluid is dispensed to substantially fill the space between the press plate and the work piece. After the cleaning process, a drying fluid is dispensed between the press plate and work piece, forcing the cleaning fluid from the work piece surface and drying the work piece surface. Accordingly, cleaning and drying of work piece surfaces formed of hydrophilic materials, hydrophobic materials, or both, may be effectively cleaned and dried in one apparatus. In addition, cleaning and drying of the work piece surface is achieved with minimal use of cleaning and drying fluids.
While at least one exemplary embodiment has been presented in the foregoing detailed description of the invention, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment of the invention. It being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope of the invention as set forth in the appended claims.
