Patent Application
20070094885
The present invention relates to apparatus and processes for drying objects, especially silicon wafer substrates, flat panel display substrates, and other types of substrates which must be cleaned, rinsed, and dried during the manufacture of a device. The invention especially relates to removing remaining amounts of liquid from silicon wafer substrates during the manufacture of integrated circuits. However, the invention can also be applied to the manufacture of raw wafers, lead frames, medical devices, disks and heads, flat panel displays, microelectronic masks, and other applications requiring high level cleanliness and/or drying during processing.
In the manufacture of semiconductors, semiconductor devices are produced on thin disk-like substrates. Generally, each substrate contains a plurality of semiconductor devices. The exact number of semiconductor devices that can be produced on any single substrate depends both on the size of the substrate and the size of the semiconductor devices being produced thereon. However, semiconductor devices have been becoming more and more miniaturized. As a result of this miniaturization, an increased number of semiconductor devices can be produced for any given area, thus, making the surface area of each substrate more and more valuable.
In producing semiconductor devices, substrates are subjected to a multitude of processing steps before a viable end product can be produced. These processing steps include: chemical-etching, wafer grinding, photoresist stripping, and masking. These steps typically occur in a process tank and often require that each substrate undergo many cycles of cleaning, rinsing, and drying during processing so that particles that may contaminate and cause devices to fail are removed from the substrates. However, these rinsing and drying steps can introduce additional problems in of themselves.
One major problem is the failure of the drying step to completely remove liquid from the substrates after rinsing (or any other processing step where the substrate is exposed to a liquid). It is well known in the art that those semiconductor devices that are produced from an area of the substrate where liquid droplets remained have a greater likelihood of failing. Thus, in order to increase the yield of properly functioning devices per substrate, it is imperative that all liquid be removed from the substrate surface as completely as possible.
Very sophisticated systems and methods have been devised to dry substrates as quickly and as completely as possible. However, due to deficiencies of prior art systems and methods of drying it is impossible to completely remove all traces of liquid from the substrate surfaces in an efficient and inexpensive manner. When substrates are placed in a tank for processing, the substrates are typically supported in an upright position by a support device which can be a carrier or an object support member that is built into the process tank itself. It is a well recognized problem in the art to quickly and effectively remove traces of water from those areas of the substrate that are in contact with the supporting device. Therefore, there is a certain very valuable portion of the substrate which is wasted due to what is known in the art as “edge exclusion,” a term referring to the portion of the substrate near the edges which cannot be completely dried and must be discarded. Because semiconductor devices are becoming more miniaturized, the “edge exclusion” areas are also becoming more valuable in that an increased number of functioning devices would be able to be produced from these areas if it were not for the water-spotting caused by the remaining amounts of liquid.
There have been many attempts to improve dryer systems and drying methods so as to eliminate the need for edge exclusion by completely drying the wafer substrate. However, none have fully solved the problem in an effective and efficient manner.
For example, Mohindra, et al., U.S. Pat. No. 5,571,337, teaches pulsing a drying fluid such as nitrogen gas at the edge of the partially completed semiconductor to remove the liquid from the edge. Application of the Mohindra process results in evaporation of the liquid at the contact points. Evaporation is undesirable because particles or non-purities that may have been present in the water are left behind, both of which decrease yields. Moreover, the equipment necessary to perform the Mohindra process can be expensive and cumbersome.
McConnell, et al., U.S. Pat. No. 4,984,597, teaches using large amounts of IPA to replace water and enhance drying. However, such a process requires special tanks and elaborate support equipment to safely handle and process the IPA. Additionally, the McConnell process is costly due to the large amounts of IPA used.
A third drying system is taught by Munakata in U.S. Pat. No. 6,125,554. Munakata teaches a system for drying substrates comprising a rack having grooves for supporting substrates in a vertical position. The substrates are contacted and supported in the grooves of the rack. Each groove has an aperture near the groove that is capable of sucking water that adheres to the substrate near the groove contact point into the aperture. This system requires additional equipment to create a vacuum force at each groove and the open apertures and cavities within the rack can present problems in a liquid filled process tank because of air bubbles and trapped particles. Additionally, the rack used in Munakata can be both expensive and difficult to manufacture.
Many other systems and methods have been proposed to try to solve the edge exclusion problem resulting from the inability to efficiently remove water residue from the contact points between the edges of substrates and the supporting devices of dryers in a clean, low cost, and timely manner, but none have completely solved the problem.
Recently, methods and systems for processing a single substrate at a time have become widely used. An example of such a system is disclosed in U.S. Pat. No. 6,295,999, Bran. Such systems and methods support a single substrate in a horizontal orientation and rotate the substrate during processing. These single-substrate apparatus and processing methods suffer from the same problems discussed above with respect to edge exclusion and inadequate drying.
It is therefore an objective of the present invention to provide a quicker method of drying high value objects, such as substrates.
A further objective of the present invention is to provide a more cost-effective method of drying high value objects.
A yet further objective of the present invention is to reduce or eliminate the problem of edge exclusion that exists at contact points between the support structure and the objects being dried.
A still further objective is to improve yields of high value integrated circuits from silicon wafers.
Yet another objective of the present invention is to reduce the need for great amounts of expensive drying chemicals.
Still another objective of the present invention is to provide and apparatus and method of drying a single substrate in accordance with the previous objects.
Additional objects and advantages of the invention will be set forth in the description that follows and will become apparent to those skilled in the art upon examination of the following or may be learned with the practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the claims.
In one aspect, the invention is an apparatus for drying at least one substrate comprising: a rotatable support comprising a fixture for supporting a substrate in a substantially horizontal orientation by contacting only a perimeter region of a substrate; the fixture comprising one or more contact surfaces that contact and support the perimeter region of the substrate; and wherein the one or more contact surfaces comprise a capillary material.
Preferably, the fixture is adapted to support the perimeter region of the substrate by contact with capillary material exclusively. Constructing the fixture so that all surfaces of contact between the perimeter region of the substrate and the fixture comprise the capillary material will help ensure that all liquid that becomes trapped between the substrate and the fixture will be drawn into the capillary material and away from the substrate, thereby improving drying and reducing edge exclusion.
In one embodiment, the fixture can be constructed entirely of capillary material. Alternatively, the fixture can comprise a channel of capillary material extending from the capillary material of the contact surfaces and through the fixture. This channel of capillary material allows liquid to be drawn outwardly away from the substrate. Rotation of the support causes centrifugal forces to pull the liquid that has been drawn into the channel outwardly through the channel.
While the capillary material can be any material that is capable of drawing in liquid through the use of capillary forces, it is preferred that the capillary material be a cellular capillary material, such as a porous flouropolymer or a porous polypropylene (“PP”).
In order to hold a substrate in place during rotation, the apparatus may comprise one or more clamps for securing the substrate to the fixture. In this embodiment, the one or more clamps will preferably have an engagement surface that contacts and secures the substrate in place during rotation. Most preferably, the engagement surfaces of the clamps will also comprise the capillary material.
In one embodiment, the fixture can comprise a flange extending from an inner surface of the fixture. In such an embodiment, the flange forms a step-like groove having a floor and a wall extending upward from the floor on an inner portion of the fixture. When a substrate is positioned on the fixture, the floor of the groove contacts a bottom surface of the perimeter region of the substrate and the vertical wall contacts an edge of the substrate. Thus, this embodiment, it is the floor and the wall of the groove that act as the contact surfaces and are formed of the capillary material.
If desired, at least one channel of the capillary material can be provided that extends from the capillary material of the wall and the floor of the groove and through the fixture. In this embodiment, the channel of the capillary material preferably terminates in an exposed surface on an outer surface of the fixture.
The fixture is preferably a generally ring-shaped fixture. The apparatus can further comprise a process chamber wherein the rotatable support is positioned in the process chamber. The apparatus can also comprise a source of a drying fluid positioned to apply a meniscus of the drying fluid to a substrate positioned on the rotatable support.
In another aspect, the invention can be an apparatus for drying at least one substrate comprising: a rotatable support comprising a fixture having a flange protruding from an inner surface, the flange forming a step-like groove in the fixture having a floor and a wall extending upward from the floor; wherein the step-like groove is sized and shaped to accommodate a substrate so that the floor of the groove contacts a bottom surface of a perimeter region of the substrate and the vertical wall contacts an edge of the substrate; and wherein all surfaces of the floor and wall that contact the perimeter region of the substrate when the substrate is supported by the fixture comprise a capillary material.
In yet another aspect, the invention can be an apparatus for drying at least one substrate comprising: a rotatable support comprising at least one fixture adapted to contact a perimeter region of a substrate and support the substrate in a substantially horizontal orientation; the perimeter region of the substrate contacting the fixture at one or more contact surfaces; and wherein the contact surfaces comprise a capillary material. In this embodiment, the fixture(s) adapted to contact and support the perimeter region of the substrate can be portions of a segmented ring or any other structure that can adequately support the substrate at its perimeter.
In still another aspect, the invention is a method of drying a substrate comprising: providing a rotatable support comprising a fixture for supporting a substrate in a substantially horizontal orientation by contacting only a perimeter region of a substrate; contacting a wet substrate on the rotatable support so that only the perimeter region of the substrate contacts the fixture, wherein all surfaces of the fixture that contact the substrate comprise a capillary material; rotating the fixture so as to remove a major portion of liquid from the substrate; and wherein remaining liquid from the substrate is drawn into the capillary material and away from the substrate.
In a further aspect, the invention can be a method of drying a substrate comprising: providing a process chamber having a rotatable support comprising a generally ring shaped fixture; supporting a wet substrate on the rotatable support so that a perimeter region of the substrate contacts the generally ring shaped fixture at one or more contact surfaces, the substrate being supported by the generally ring shaped fixture in a substantially horizontal orientation, the contact surfaces comprising a capillary material; rotating the rotatable support so as to remove a major portion of liquid from the substrate; and drawing remaining liquid from the substrate with the capillary material.
The methods can further comprise the step of applying a drying liquid to the substrate during the rotating step. The drying liquid can comprise isopropyl alcohol and the capillary material can be a porous flouropolymer or a porous PP. As with the apparatus, the inventive method is not limited to being practiced with a support having a ring shaped fixture but can be practiced with any fixture(s) adapted to contact the perimeter region of the substrate and support the substrate in a substantially horizontal orientation.
The inventive methods of the present application can be used in conjunction with a multitude of semiconductor processing steps, including etching, rinsing, and stripping. In many cases, all of these steps can be performed sequentially without moving the substrate from the apparatus of the invention.
The figures and following description describes embodiments of the present invention for purposes of illustration only. Those skilled in the art will readily recognize from the following discussion that alternative embodiments of the structures and methods illustrated herein may be employed without departing from the principles of the invention.
As the size of semiconductor wafers increases, rather than cleaning a cassette of wafers at once, it is more practical and less expensive to use a cleaning apparatus and method that cleans a single wafer at a time.
Referring to
The rotatable support 108 comprises a ring shaped fixture 108a, a plurality of spokes 108b, a hub 108c, and a shaft 110. The ring shaped fixture 108a is supported by a plurality of spokes 108b which are in turn connected to a hub 108c. The hub 108c is supported on the shaft 110. The shaft 110 extends through the bottom wall 101 of the processing chamber 104. An O-ring 113 or other seal can be added around the shaft 110 to hermetically seal the bottom wall 101 of the process chamber 104. Outside the process chamber 104, the shaft 110 is connected to a motor 112 so that the entire support 108 and the wafer 106 can be rotated as needed during processing. The mechanical/operable connection of the shaft 110 to the motor 112, and the operation of the motor 112 during wafer processing is well within the ambit of those skilled in the art.
Referring now to
Three clamps 200 are provided on the top surface 113 of the ring shaped fixture 108a for engaging and securing a wafer 106 thereto during rotating and processing. The three clamps 200 are provided on the top surface 113 of the ring shaped fixture 108a approximately 120° apart from one another.
Referring now to
The flange 127 forms a step-like groove 120 on the top inner portion of the ring shaped fixture 108a. The step-like groove 120 extends about the entire inner circumference of the ring shaped fixture 108a. The step-like groove comprises a floor 121 and a vertical wall 122 that extends upward from the floor 121. The floor 121 of groove 120 forms a ledge upon which the perimeter region of the bottom surface of a substrate 106 rests. The vertical wall 122 acts as a restraint to prohibit substantial horizontal movement of the wafer 106 during rotation. The material of construction of the ring shaped fixture 108a, which is of the main concern of the present invention, will be discussed in greater detail below.
Referring now to
Once the wafer 106 is in position on the ring shaped fixture 108a, the clamps 200 are moved into a closed position (illustrated), causing the grippers 210 of clamps 200 to be above the top surface 106c of the perimeter region of the wafer 106. The grippers 210 press down on top surface 106c of wafer 106 at three locations about the perimeter region of the wafer 106, thereby securing the wafer 106 in position for processing.
While clamps 200 are illustrated as being used to secure the wafer 106 in place, the invention is not so limited. For example, other means can be used, such as latches, a tight fit assembly, an upper ledge above the floor 121 forming a recess into which the wafer edge will slidably fit, or a suction assembly. In fact, it may not be necessary to use any means at all to hold the wafer 106 in place in some embodiments of the invention.
Referring back to
Preferably, the capillary material is a cellular capillary material. Suitable examples of cellular capillary materials that can be used in practicing the present invention are porous flouropolymers, such as polytetraflouroethylene (“PTFE”) and PVDF. Porous PP is also a suitable cellular capillary material. When porous PP is used, acceptable pore size is in the range of 125 to 170 microns. Acceptable pore volume of the porous PP ranges between 35-50%. This means that 35-50% of the volume of the porous PP is open air. While porous PP and porous PTFE are the preferred cellular capillary materials to be used in the present invention, those skilled in the art will understand that the term capillary material encompasses a much broader range of materials, including materials not yet known or discovered, so long as these materials exhibit the ability to draw liquid in through the capillary force phenomenon. Examples of suitable non-capillary materials include non porous flouropolymers, such as PP, PTFE, and PVDF.
The floor 121 and the vertical wall 122 of the step-like groove 120 are constructed of cellular capillary material 117. The cellular capillary material 117 of the ring shaped fixture 108a forms a channel 131 that extends from the floor 121 and the wall 122 and through the non-capillary material 118 of the ring shaped fixture 108a. The channel 131 terminates at the outer surface 125 of the ring shaped fixture 108a in such a manner that the capillary material is exposed on the outer surface 125.
Referring now to
By constructing the contact surfaces of the ring shaped fixture 108a, (i.e. the floor 121 and the wall 122 in this embodiment), of capillary material 117, liquids that get trapped between the wafer 106 and the contact surfaces will be drawn into the capillary material 117 and away from the wafer 106, thereby drying the wafer 106 completely and reducing and/or eliminating edge exclusion.
Providing the channel 131 of capillary material through the ring shaped fixture 108a allows the liquid that is drawn into the cellular capillary material 117 to be pulled outwardly by centrifugal forces through the channel 131 and away from wafer 106 during rotation of the support 108. This is advantageous because it performs a purging function in that particles and contaminants that become trapped in the capillary material 117 are moved away from the wafer 106. Moreover, the channel 131 allows the capillary material 117 to drain, thereby drying the capillary material so that it does not become saturated and unable to perform its capillary drying function and the contact surfaces.
In an alternative embodiment, the ring shaped fixture 108a can be constructed entirely of capillary material 117, so long as capillary material is selected that provides sufficient rigidity to support the wafer 106 during processing.
Referring now to
A method of drying according to an embodiment of the present invention will now be described. First, a wafer 106 is positioned in the support 108 as illustrated in
The process chamber 104 can be sealed during the processing and/or drying sequences by closing a lid or otherwise shielding the process chamber 104 from the external environment.
While the invention has been described and illustrated in detail, various alternatives and modifications will become readily apparent to those skilled in the art without departing from the spirit and scope of the invention. Particularly, the apparatus and method of invention are not limited to removing DI water after a rinse step but can be used to remove any liquid from the substrate.
