Marangoni dryers have been used in the past to dry semiconductor wafers that are being processed, such as by liquid baths. Marangoni drying is based on surface tension gradient forces and is an ultra-clean drying process. In this technique, a volatile organic compound with lower surface tension than water, such as isopropyl alcohol (IPA), is introduced in the vicinity of a substrate semiconductor wafer in the form of a vapor as the substrate wafer is slowly withdrawn from a bath of water. As the small quantity of alcohol vapor comes into contact with the continuously refreshed water meniscus, it is absorbed into the water and creates a surface tension gradient. The gradient causes the meniscus to partially contract and assume an apparent finite flow angle. This causes a thin water film to flow off the substrate and leave it dry. This flow also will assist. In removing non-volatile contaminants and entrained particles.
Using current processes, a lifting mechanism raises the wafer most of the way out of the bath of water, and then a knife structure pushes the wafer from below the rest of the way out of the bath of water. The reason the knife structure is used is that it minimizes contact points on the semiconductor wafer as the wafer is being moved past the water meniscus. However, the knife is in direct physical contact with a part of the wafer as it emerges from the liquid, so there remains a water mark on the wafer at this contact point. Furthermore, because the knife is used to push the wafers up and out of the water from below, there must be slots for the wafers to fit through to maintain the wafers in their vertical orientation. Such slots may scratch the sides of the wafer during this process.
Thus, a need exists for an updated apparatus and method for drying semiconductor wafers using the Marangoni process that overcomes the noted deficiencies.
The invention is directed to an apparatus and method for drying semiconductor wafers. The apparatus includes a tank that holds hold a liquid, a first lifting assembly, and a second lifting assembly. The first lifting assembly lifts and lowers a first wafer carrier and one or more semiconductor wafers supported thereon between a first lowered position in which the one or more semiconductor wafers are completely submerged in the liquid in the tank and a first raised position in which an upper portion of the one or more semiconductor wafers are not submerged in the liquid in the tank. The second lifting assembly has a second wafer carrier that engages the upper portion of the one or more semiconductor wafers and continues to lift the one or more semiconductor wafers until an entirety of the one or more semiconductor wafers are no longer submerged in the liquid in the tank.
In one embodiment, the invention can be an apparatus for drying semiconductor wafers, the apparatus comprising: a tank containing a liquid; a first lifting assembly comprising a first wafer carrier configured to hold one or more semiconductor wafers, the first lifting assembly being operable to move the first wafer carrier between a first lowered position wherein the one or more semiconductor wafers are completely submerged in the liquid in the tank and a first raised position wherein a lower portion of the one or more semiconductor wafers remain submerged in the liquid in the tank and an upper portion of the one or more semiconductor wafers is no longer submerged in the liquid in the tank; and a second lifting assembly comprising a second wafer carrier that is configured to: engage the upper portion of the one or more semiconductor wafers after the upper portion of the one for more semiconductor wafers has been removed from the liquid; and continue to raise the one or more semiconductor wafers until an entirety of the one or more semiconductor wafers is removed from the liquid in the tank.
In another embodiment, the invention can be a method of drying semiconductor wafers, the method comprising: supporting one or more semiconductor wafers with a first wafer carrier at one or more contact points, wherein the one or more semiconductor wafers and the first wafer carrier are completely submerged in a liquid; raising the first wafer carrier to begin lifting the one or more semiconductor wafers out of the liquid until an upper portion of the one or more semiconductor wafers is removed from the liquid and the one or more contact points remain submerged in the liquid; engaging at least a portion of the upper portion of the one or more semiconductor wafers that has been removed from the liquid with a second wafer carrier; and raising the second wafer carrier so that the second wafer carrier takes over support of the one or more semiconductor wafers, the second wafer carrier lifting the one or more semiconductor wafers until an entirety of the one or more semiconductor wafers is no longer submerged in the liquid.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.
The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein
The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses.
The description of illustrative embodiments according to principles of the present invention is intended to be read in connection with the accompanying drawings, which are to be considered part of the entire written description. In the description of the exemplary embodiments of the invention disclosed herein, any reference to direction or orientation is merely intended for convenience of description and is not intended in any way to limit the scope of the present invention. Relative terms such as “lower,” “upper,” “horizontal,” “vertical,” “above,” “below,” “up,” “down,” “left,” “right,” “top,” “bottom,” “front” and “rear” as well as derivatives thereof (e.g., “horizontally,” “downwardly,” “upwardly,” etc.) should be construed to refer to the orientation as then described or as shown in the drawing under discussion. These relative terms are for convenience of description only and do not require that the apparatus be constructed or operated in a particular orientation unless explicitly indicated as such. Terms such as “attached,” “affixed,” “connected,” “coupled,” “interconnected,” “secured” and similar refer to a relationship wherein structures are secured or attached to one another either directly or indirectly through intervening structures, as well as both movable or rigid attachments or relationships, unless expressly described otherwise. Moreover, the features and benefits of the invention are described by reference to the exemplary embodiments illustrated herein. Accordingly, the invention expressly should not be limited to such exemplary embodiments, even if indicated as being preferred. The discussion herein describes and illustrates some possible non-limiting combinations of features that may exist alone or in other combinations of features. The scope of the invention is defined by the claims appended hereto.
For purposes of this invention, it is to be understood that the term semiconductor wafer is intended to mean any solid substance onto which a layer of another substance is applied and that is used in the solar or semiconductor industries. This includes, without limitation, silicon wafers, glass substrates, fiber optic substrates, fused quartz, fused silica, epitaxial silicon, raw wafers, solar cells, medical devices, disks and heads, flat panel displays, microelectronic masks, and other applications requiring high purity fluids for processing. The terms substrate and wafer may be used interchangeably throughout the description herein. Furthermore, it should be understood that the invention is not limited to any particular type of substrate and the methods described herein may be used for the preparation and/or drying of any flat article.
Referring first to
The apparatus 1000 generally comprises a tank 100, a first lifting assembly 200, and a second lifting assembly 300. The tank 100 is configured to hold a liquid within which one or more semiconductor wafers are positioned. The liquid may be deionized water in some particular embodiments. The first and second lifting assemblies 200, 300 are configured to work together to remove the one or more semiconductor wafers from the liquid in the tank 100 to dry the one or more semiconductor wafers using the Marangoni drying process, which is a process that is well known by persons of ordinary skill in the art and has been described briefly above. The first and second lifting assemblies 200 may move at a slow speed such as in a range of 0.1 mm/second to 3 mm/second, and more specifically approximately 1 mm/second (with the term “approximately” including a plus/minus of 0.2 mm/second). Isopropyl alcohol (IPA) as a vapor or gas or a mixture of IPA vapor and nitrogen gas may be introduced into the tank to form an IPA vapor barrier on the uppermost surface of the liquid in the tank. The IPA vapor may continue to be dispensed into the tank as the one or more semiconductor wafers emerge from the surface of the liquid in the tank 100, although this is not required in all embodiments. Regardless, as the one or more semiconductor wafers pass through the liquid to IPA vapor interface, the one or more semiconductor wafers are quickly dried due at least in part to the creation of a surface tension gradient between the isopropyl alcohol and the liquid in the tank 100 at the surface.
Referring to
The tank 100 may also comprise a drain so that any liquid introduced into the tank 100 may be drained as desired or needed. The tank 100 may comprise the interior cavity 101 and an overflow cavity (not shown) in some embodiments so that liquid which overflows the interior cavity 101 may flow into the overflow cavity during a drying operation.
The first lifting assembly 200 comprises a first wafer carrier 210 that is configured to hold the one or more semiconductor wafers (a single semiconductor wafer 500 is illustrated being held by the first wafer carrier 210 in
The first wafer carrier 210 is configured to support one or more wafers such that each wafer is positioned between two adjacent ones of the first set of combs 213 and two adjacent ones of the second set of combs 214 that are in alignment with the two adjacent ones of the first set of combs 213. Of course, other structures for holding the one or more semiconductor wafers may be used in other embodiments. For example, the first wafer carrier 210 may comprise a cassette in some embodiments that is configured to hold the one or more wafers. Thus, the exact structural details of the first and second carrier arms 211, 212 of the first wafer carrier 210 are not limiting of the present invention in all embodiments and variations are possible within the scope of the invention claimed herein. Moreover, in some embodiments the first wafer carrier 210 may be a continuous structure with a floor such that it does not have carrier arms, but instead has lateral surfaces at the location of the carrier arms.
As seen in
The first lifting assembly 200 comprises a vertical first track structure 220, a clamp member 230 that is coupled to the vertical first track structure 220, and a first motor 240 that controls movement of the clamp member 230 along the vertical first track structure 220. The first and second carrier arms 211, 212 of the first wafer carrier 210 are coupled to the clamp member 230 by a vertical carrier arm 215, 216. The clamp member 230 is coupled to and rides along the vertical first track structure 220 along a vertical axis A-A. That is, the clamp member 230 operates as a follower member and comprises a structure that engages and rides along the vertical first track structure 220 when the motor 240 is activated. The clamp member 230 and the vertical first track structure 220 may have mating structures that maintain the coupling between the clamp member 230 and the vertical first track structure 220 while permitting the clamp member 230 to move along the first track structure 220 during operation of the apparatus 1000. When the first motor 240 is activated, the clamp structure 230 rides either upwardly or downwardly along the vertical first track structure 220 (depending on the rotational direction of the motor 240), which causes the first wafer carrier 210 and the first and second carrier arms 211, 212 that are coupled to the clamp structure 230 to move vertically upwardly and downwardly in the direction of the vertical axis A-A. When the first wafer carrier 210 is carrying one or more semiconductor wafers 500, the semiconductor wafers 500 similarly move upwardly and downwardly in the vertical direction of the vertical axis A-A along with the clamp member 230.
The first lifting assembly 200 is configured to carry the semiconductor wafers 500 positioned thereon for a distance out of the liquid bath, but not the entire way out of the liquid bath. The reason for this is that there is a desire to eliminate contact points between the lifting assemblies and the semiconductor wafers 500 as the semiconductor wafers emerge from the liquid. Specifically if a portion of the semiconductor wafer 500 emerges from the liquid while being contacted by the first lifting assembly 200, the portion of the semiconductor wafer 500 that is being contacted will be prevented from adequately drying. In particular, the effects of the IPA vapor and the tension gradient will not be imparted to those portions of the semiconductor wafer 500 that are contacted by the first lifting assembly 200 as the semiconductor wafer 500 passes through the surface of the liquid in the tank. Thus, by neglecting to raise the first lifting assembly 200, or at least portions thereof that are in contact with the semiconductor wafer 500, out of the liquid in the tank 100, this prevents water spots and helps to ensure a more thorough drying of the semiconductor wafers 500. After the semiconductor wafers 500 are partially lifted out of the liquid by the first lifting assembly 200, the semiconductor wafers 500 are transferred to the second lifting assembly 300, which then lifts the semiconductor wafers 500 the rest of the way out of the liquid. Importantly, the second lifting assembly 300 only makes contact with portions of the semiconductor wafers 500 which have already been lifted out of the liquid and dried. Portions of the second lifting assembly 300 that are intended to contact the semiconductor wafer 500 are never submerged in or otherwise put in contact with the liquid in the tank 100.
The second lifting assembly 300 comprises a second wafer carrier 310 that is configured to carry and lift the semiconductor wafers 500 out of the liquid in the tank 100 after being transferred from the first wafer carrier 210 of the first lifting assembly 300 as described herein. The second wafer carrier 310 may comprise a first carrier arm 311 and a second carrier arm 312. The first and second carrier arms 311, 312 may be oriented parallel to one another in a spaced apart manner. Moreover, the first and second carrier arms 311, 312 may be oriented parallel to the first and second carrier arms 211, 212 of the first wafer carrier 210 described above in some embodiments. As best shown in
Although not shown in the exemplified embodiment, the first and second carrier arms 311, 312 of the second wafer carrier 310 may comprise combs much like the combs 213, 214 of the first and second carrier arms 211, 212 of the first wafer carrier 210 to enable the first and second carrier arms 311, 312 to support the one or more semiconductor wafers 500 and maintain them in their upright orientation as shown. That is, there may be slots or grooves formed into the outer surface of the first and second carrier arms 311, 312 within which edge portions of the semiconductor wafers 500 may nest to facilitate the engagement between the first and second carrier arms 311, 312 and the semiconductor wafers 500. The first and second carrier arms 211, 212 may include other structures to achieve this instead of the combs, and in still other embodiments there may be no added features to that which is depicted in the drawings, so long as the first and second carrier arms 311, 312 are capable of holding, supporting, and carrying support the semiconductor wafers 500 in the upright orientation. The first and second carrier arms 311, 312 may have outer surfaces which face one another and which are angled so as to diverge from one another with increasing distance from the first wafer carrier 210 (i.e., moving in a direction from a floor of the tank 100 to a roof of the tank 100).
Moreover, while the first and second carrier arms 311, 312 are depicted as elongated bar-like rods, the invention is not to be so limited in all embodiments. In other embodiments, the first and second carrier arms 311, 312 may be arcuate plates having a concave inner surface that faces the semiconductor wafers 500. This may facilitate a better engagement between the first and second carrier arms 311, 312 and the semiconductor wafers 500 to ensure that the first and second carrier arms 311, 312 hold the semiconductor wafers 500 in the upright orientation during use.
The second lifting assembly 300 may comprise a second track structure 320. The second track structure 320 may comprise a first track 321 and a second track 322. In the exemplified embodiment, each of the first and second tracks 321, 322 is a slot forming a pathway within which follower members of the second lifting assembly 300 move. The details of the shape and orientation of the first and second tracks 321, 322 will be provided below with reference to
The second lifting assembly 300 comprises a first follower member 331 that nests within and/or otherwise and rides along the first track 321 and a second follower member 332 that nests within and/or and rides along the second track 322. The first follower member 331 is coupled to the first carrier arm 311 and the second follower member 332 is coupled to the second carrier arm 312. Thus, the movement of the first follower member 331 along the first track 321 dictates the path of movement of the first carrier arm 312 whereas the movement of the second follower member 332 along the second track 322 dictates the path of movement of the second carrier arm 312. In the exemplified embodiment, each of the first and second follower members 331, 332 comprises a protuberance that nests within the slots of the first and second tracks 321, 322, respectively. Of course, in other embodiments the follower members 331, 332 could be slots and the tracks 321, 322 could be protuberances, or some other arrangement of parts may be possible while still enabling the movement of the second lifting assembly 300 as described further herein below. In the exemplified embodiment, there is a second motor 340 distinct from the first motor 240 that controls movement of the second lifting assembly 300. However, in other embodiments the same motor may be configured to control the movement of both of the first and second lifting assemblies 200, 300.
Referring to
Referring to
Referring briefly to
As will be discussed in greater detail below, when the first and second follower members 331, 332 are in their lowermost position along the bottom end of the bottom portions 323 of the first and second tracks 321, 322, the first and second carrier arms 311, 312 are spaced apart from one another a distance D1 (specifically, a minimum distance) that is greater than a diameter D2 of the semiconductor wafers 500 (see
It should be appreciated that the apparatus 1000 may comprise a processor or controller or control unit that automatically activates the movement of the first and second lifting assemblies 200, 300 in a proper timing sequence to properly remove the semiconductor wafers 500 from the liquid in the tank 100 at a sufficiently slow rate for the Marangoni process to adequately dry the semiconductor wafers 500. In particular, the apparatus 1000 may in some embodiments comprise a processor and a memory device. The processor and memory device may be separate components, or the memory device may be integrated with the processor within the control unit. Furthermore, the control unit may include only one processor and one memory device, or it may include multiple processors and multiple memory devices. The processor of the control unit may be any computer or central processing unit (CPU), microprocessor, micro-controller, computational device, or circuit configured for executing some or all of the processes described herein, including without limitation: activation and deactivation of the first and second motors 240, 340; activation and deactivation of isopropyl alcohol injection; filling of the tank 100 with the liquid, recirculating the liquid within the tank 100, and other process steps which may be automated by such a processor.
The memory device of the control unit may include, without limitation, any suitable volatile or non-volatile memory including random access memory (RAM) and various types thereof, read-only memory (ROM) and various types thereof, USB flash memory, and magnetic or optical data storage devices (e.g. internal/external hard disks, floppy discs, magnetic tape CD-ROM, DVD-ROM, optical disk, ZIP™ drive, Blu-ray disk, and others), which may be written to and/or read by the processor which is operably connected thereto. The memory device may store algorithms and/or calculations that can be used by the processor to determine when to activate/deactivate the various motors, valves, heat sources, injectors, and the like which are described herein.
Referring to
Referring first to
Furthermore, at this point in the process the second wafer carrier 310 of the second lifting assembly 300 is located outside of the liquid 150. That is, the liquid 150 has a surface level 151, and the second wafer carrier 310 is located within the internal cavity 101 of the tank 110, but no part thereof is submerged in the liquid 150 because it is located between the surface level 151 of the liquid 150 and the roof of the tank 100. As a result, the second wafer carrier 310 is completely dry. In some embodiments, the second wafer carrier 310 may never contact the liquid 150 in the tank 100 so that the second wafer carrier 310 stays completely dry. As noted above, the diameter D2 of the semiconductor wafer 500 is less than the distance D1 between the first and second carrier arms 311, 312 of the second wafer carrier 310. This is important because it ensures that there is sufficient space for the semiconductor wafer 500 to fit between the first and second carrier arms 311, 312 of the second wafer carrier 310 as the first lifting assembly 200 lifts the semiconductor wafer 500 out of the liquid 150.
As best seen in
Referring to
In some embodiments, as the first lifting assembly 200 moves from the lowered position (
While only a single nozzle 400 is shown, there may be multiple nozzles 400 spraying the IPA (or other VOC) vapor 401 into the internal cavity 101 of the tank 100 in other embodiments or other components that achieve the introduction of the IPA vapor 401 into the tank 100. The nozzles 400 may be located along the sidewalls of the lid rather than along the roof thereof. Moreover, other methods of introducing the IPA vapor 401 into the internal cavity 101 of the tank 100 may be employed as long as the IPA vapor 401 introduces a surface tension gradient where it interfaces with the liquid 150 on the liquid surface 151 to facilitate a quick drying of the semiconductor wafer 500. Thus, as the semiconductor wafer 500 emerges through the surface level 151 of the liquid 150, the semiconductor wafer 500 becomes dry.
The IPA vapor may continue to be introduced into the tank 100 while the semiconductor wafers 500 are raised/lifted out of the liquid (see
In some embodiments, the injection of the IPA into the tank 100 may stop before the first lifting assembly 200 is activated. In other embodiments, the IPA may continue to be injected into the tank 100 even during the raising of the semiconductor wafers 500 out of the liquid 150. However, generally it is preferable to start the IPA vapor introduction prior to raising/lifting the semiconductor wafers 500 out of the liquid 150 so that the layer of the IPA vapor 700 exists on top of the surface level 151 of the liquid 150 as the semiconductor wafers 500 emerge through the surface level 151 of the liquid 150. As such, once the semiconductor wafers 500 break through the surface level 151 of the liquid 150, the semiconductor wafers 500 will quickly dry by the Marangoni effect.
When the first lifting assembly 200 reaches the raised position as shown in
Also as seen in
Referring to
The first and second carrier arms 311, 312 of the second wafer carrier 310 engage the semiconductor wafer 500 along an edge thereof. That is, the semiconductor wafers 500 have a front surface, a rear surface, and an edge extending between the front and rear surfaces. It is generally preferable to avoid contact with the front and rear surfaces of the semiconductor wafers 500 to the extent possible. Thus, the first and second carrier arms 311, 312 may engage/contact with semiconductor wafers 500 along their edges rather than along their front and/or rear surfaces.
As shown in
As shown in
As noted above, the first and second carrier arms 311, 312 are illustrated simplistically, but may have grooves, cassettes, slots, teeth, combs, or other structure for holding the semiconductor wafers 500 upright as shown in other embodiments. The first and second carrier arms 311, 312 are never submerged or otherwise put into contact with the liquid 150, and thus the first and second carrier arms 311, 312 remain completely dry and contact between the first and second carrier arms 311, 312 and the semiconductor wafer 500 will not create any wet spots on the semiconductor wafer 500.
Referring to
As shown in
Although not shown, the next step in the process is to slowly drain the liquid 150 from the tank 100 to dry the first wafer carrier 210 via the Marangoni effect and to lower the first wafer carrier 210 from the first raised position back to the first lowered position. Once the first wafer carrier 210 is dried, the second lifting assembly 300 may be lowered to place the semiconductor wafers 500 back onto the first wafer carrier 210 of the first lifting assembly 200. Alternatively, a robot or other handling device may remove the semiconductor wafers 500 from the second lifting assembly 300 for further processing.
While the invention has been described with respect to specific examples including presently preferred modes of carrying out the invention, those skilled in the art will appreciate that there are numerous variations and permutations of the above described systems and techniques. It is to be understood that other embodiments may be utilized and structural and functional modifications may be made without departing from the scope of the present invention. Thus, the spirit and scope of the invention should be construed broadly as set forth in the appended claims.
The present application claims the benefit of priority to U.S. Provisional Patent Application Ser. No. 63/209,642, filed Jun. 11, 2021, the entirety of which is incorporated herein by reference.
Number | Date | Country | |
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63209642 | Jun 2021 | US |