WO2007124166A2

WO2007124166A2 - Devices and methods for drying objects using aerosols

Info

Publication number: WO2007124166A2
Application number: PCT/US2007/009896
Authority: WO
Inventors: Timothy H. Gens
Original assignee: Gens Timothy H
Priority date: 2006-04-22
Filing date: 2007-04-23
Publication date: 2007-11-01
Also published as: WO2007124166A3

Abstract

The invention provides a wafer dryer including a wafer bath vessel for supporting at least one wafer having an exposed surface to be dried. A tub has a drying liquid spray device and a non-reactive carrier gas spray device opposing the drying liquid spray device. The spray device emits a stream of pressurized drying liquid that converges with a stream of opposed pressurized non-reactive carrier gas emitted by the spray device of pressurized non-reactive gas to produce a drying liquid fog. The tub vents the drying liquid fog into the wafer bath vessel with the drying liquid fog drying the wafer. A method for drying a wafer includes emitting a stream of pressurized drying liquid and a stream of pressurized non-reactive carrier gas opposed to said drying liquid stream to produce a drying liquid fog.

Description

DEVICES AND METHODS FORDRYING OBJECTS USING AEROSOLS

Background of the Invention

1. Technical Field The invention relates to drying manufactured objects using aerosols mechanically created by a venturi aerosol maker. More particularly, objects manufactured through the use of various processing liquids such as semiconductors, flat panel displays, optics, micro-electro-mechanical devices and other electronic devices are dried by the aerosol with little or no contamination of the object.

2. Background Information

It is well-known that the ability to perform a particle-neutral and water spot-free dry during surface preparation of various manufactured objects is a technology enabler. Such capability is especially important for electronic devices with high-aspect ratio features such as vias, deep trenches, contacts, and poly-Si features where water spots form easily at hydrophilic/hydrophobic interfaces. Spots that are large enough to overlap more than one die will result in defects, high leakage currents, critical-dimension variations, and film adhesion problems, all of which also may contribute to yield loss. The International Technology Roadmapfor Semiconductors from SEMI set specifications for water spots at less than one per wafer at both the 130- and 100-nm nodes. The drying process must be implemented in a short time interval relative to other process steps and with the minimum use of energy and chemicals in an environmentally sensitive manner.

Known methods for drying integrated circuits use heated or superheated gases. For example, McConnell et al. in U.S. Pat. No. 4,911,761 et al. and Elsaway et al. in U.S. Pat. No. 6,328,809 disclose methods of drying semiconductor wafers by flowing a heated vapor past the wafers to be dried in a vessel. The preferred drying vapor is superheated isopropanol, which forms a minimum boiling azeotrope with water and is believed to displace water from the wafer surfaces. The vapor simultaneously flows in the vessel at one end and out the other end of the vessel. One of

l the drawbacks with these disclosed methods is that the drying vapor ineffectually flows out of the vessel. Accordingly, these methods use more than about half a liter of isopropanol for each standard drying cycle and this large quantity of isopropanol and other organic emissions must be captured and disposed off in an environmentally friendly manner. Another drawback is safely heating and handling the drying vapor which is flammable.

Other examples that similarly use heated or superheated gases are Bergman in U.S. Pat. No. 6,199,298Bl and Mertens et al. in U.S. Pat. No. 6,568,408 B2 which disclose methods of drying wafers by directing heated vapor to the wafer surface while rotating the wafer. Admittedly, the particle contamination performance is not equal to other known methods. Other drawbacks with these disclosed methods include the ineffectual delivery of the drying vapor, the difficulty in achieving condensation on the wafer surface, using large amounts of drying vapor, safely heating and handling a flammable drying vapor.

Another known example of drying integrated circuits is by using ultrasonically generated aerosols. Ferrell et al. in U.S. Patent No. 6,270,584, No. 5,968,285, No. 5,964,958, No. 5,685,086, and No. 5,653,045 disclose methods and apparatus cleaning and/or drying objects in a vessel by atomizing isopropanol using an ultrasonic generator and a vibrating head. The vibrating head is mounted in the vessel directly over the object. As the rinse liquid is drained, some atomized particles settle onto the exposed surfaces of the objects, and displace and remove liquid residues from the exposed surfaces of the objects by a "chemical squeegeeing" effect. One of the drawbacks of these methods is the non-uniform, scattered distribution of relatively large droplets (a mass mean aerodynamic diameter significantly greater than about 50 microns and droplet diameters in excess of about 200 microns) dissolving into the rinse water while using an ultrasonic atomizer from Lechler GmbH in Germany to generate the reported test results. Another drawback of these methods is the large amount of isopropanol used in each standard dry cycle because a mask located underneath the vibrating head catches and disposes of the majority (about > 90%) of the atomized isopropanol. Without the mask, the majority of the atomized isopropanol would uselessly dissolve into the rinse liquid or potentially carry large contamination particles onto the object. Another problem is reproducibility due to particle "spikes" caused by contamination particles collecting on the vibrating head and in the shunt leading to the vibrating head because they were not part of a loop, but instead a "dead leg". When the ultrasonic generator was turned off at the end of a duty cycle, the isopropanol evaporated, potentially leaving contamination particles on the interior of the shunt and the vibrating head. These particles could dislodge when the duty cycle started and fall onto and contaminate the object in the vessel. Another drawback is that the energy used by ultrasonic atomizer heats the atomized isopropanol with resulting organic emissions and also potentially imparts a static charge on the object which attracts contamination.

The need remains for reproducibly drying objects without contamination while requiring no energy and only environmentally friendly amounts of a drying liquid. Preferably, the drying process is performable over a wide range of temperatures and is scalable to objects of different sizes and shapes. A few of the advantages of overcoming these problems is a reproducible drying process with higher yields, less consumable usage, and a more energy-efficient manufacturing process.

Brief Summary of the Invention

Briefly, the invention provides, in one embodiment, a wafer dryer including a wafer bath vessel for supporting at least one wafer having an exposed surface to be dried A tub is mounted to the bath vessel. The tub has a drying liquid spray device and a non-reactive carrier gas spray device opposing the drying liquid spray device. The spray device emits a stream of pressurized drying liquid that converges with a stream of opposed pressurized non-reactive carrier gas emitted by the spray device of pressurized non-reactive gas to produce a drying liquid fog. The tub vents the drying liquid fog into the wafer bath vessel with the drying liquid fog drying the wafer.

A method for drying a wafer includes: emitting a stream of pressurized drying liquid; emitting a stream of pressurized non-reactive carrier gas opposed to said drying liquid stream, said streams converging to produce a drying liquid fog; venting the drying liquid fog into a wafer bath vessel having at least one wafer with an exposed surface to be dried; and drying the exposed surface to be dried with said drying liquid fog.

Brief Description of the Several Views of the Drawing These features and advantages of the invention, as well as others, will be apparent from the following description when read in conjunction with the accompanying drawings, wherein:

Figure 1 is a partial schematic view illustrating a drying liquid management system and a aerosol management system and a partial cross-sectional side view of a Venture Aerosol Maker in accordance with the invention; Figure 2A is a side view with the interior in phantom of a gas jet provided by the invention;

Figure 2B is a top perspective view of the gas jet shown in Figure 2A; Figure 3 A is a cross-sectional view of a drying liquid entrainment device along lines A-A in Figure 3B;

Figure 3B is a top perspective view of a drying liquid entrainment device of the invention; Figure 4A is a side view with the interior in phantom of a primary baffle provided by the invention;

Figure 4B is a perspective view of the primary baffle shown in Figure 4A; Figure 5 A is a cross-sectional side view of the Venturi Aerosol Maker during an aerosol creation stage; Figure 5B is a cross-sectional side view of the Venture Aerosol Maker during a self- cleaning stage;

Figure 6 A is a partially exploded perspective view of a stand alone dryer embodiment of the invention;

Figure 6B is a side view of the stand alone dryer embodiment shown in Figure 6A; Detailed Description of the Invention

Referring now to Figure 1, a self-cleaning system 20 in accordance with the invention includes a Venturi Aerosol Maker (VAM) 22, a drying liquid (DL) management system 24, and a aerosol management system 26. The DL management system 24 includes a container 28 for holding the DL 30. Preferably, a high DL level sensor 32 and a low DL level sensor 34 are positioned in the container 28 to respectively determine whether the container 28 is full or needs filling. The container 28 can be the original container from the DL supplier, connected to a DL bulk feed from the operator's facility, a freestanding container into which the DL 30 is manually filled, or other reservoir means. The illustrated container 28 attaches to a sealable DL fill port 264 and a filtered vent port 29. A DL feed line 36 extends from the container 28 to a DL pump 38 which can control the feed of the DL 30 from the container 28 to the remainder of the DL management system 24 and VAM 22.

The DL feed line 36 also passes through a filter means, generally depicted as 40, which can contain one or more individual filters or other means of removing contaminants from the DL 30. Preferably, a first filter 42 contains apertures sized to remove more coarse contaminants from the DL. A 0.1 micron diameter aperture in the first filter 42 and a second filter 44 containing apertures sized at a 0.05 micron diameter to remove more fine contaminates from the DL 30 is suitable to achieve the 100 nm particle test results recited herein. Filters with smaller apertures can be used to further improve the cleanliness of the DL 30. Preferably, the DL feed line 36 also contains a first pressure transducer 46 for monitoring the pressure of the DL 30 in the DL feed line 36 before the filter means 40 and a second transducer 48 after the filter means 40. The first 46 and second 48 transducers allow monitoring of the pressure differential across the filter means 40 to determine if the filter means 40 is no longer operating effectively and is becoming clogged as the pressure differential increases. The pressure transducers 46, 48 also provide a safety mechanism to prevent the DL feed line 36 from experiencing pressure beyond its rated capability. The DL management system 24 also includes a DL return line 50 extending from the VAM 22 to the container 28. Preferably, the DL return line 50 includes a valve 52 which can stop the flow of the DL 30 between the VAM 22 and the container 28.

The DL feed line 36 and the DL return line 50 can be made of any suitable material which is non-reactive with the DL. Preferably, Teflon tubing is used with a diameter of about 0.5 inch. The materials used in the construction of the DL pump 38, filter means 40 and the DL valve 52 should also be made of materials that are non-reactive with the DL 30 so that these components do not contribute contamination particles in the DL 30.

The VAM 22 includes a housing 54 having a bottom wall 56, a top wall 58, and side walls 60 and 62 to define a VAM chamber 64 which is sealed to prevent fluid leakage. The bottom wall 56 contains therethrough a DL feed port 66 and a DL return port 68 for the DL 30 to enter and exit the VAM chamber 64. The bottom wall 56 also includes a carrier gas feed port 70 therethrough to deliver a carrier gas 72 into the VAM chamber 64 from a carrier gas feed line 73 controlled by a carrier gas flow controller 75. Attached to the bottom wall 56 is a gas jet 74 which creates an area of low pressure with the carrier gas 72 to entrain the DL 30 to begin to form an aerosol 76.

Connected to the gas jet 74 is a liquid entrainment device 78 which partially fits over the gas jet 74. The top wall 58 includes an aerosol exit port 80 therethrough for delivery of the aerosol 76 to an object holder 82. Attached to the top wall 58 is a primary baffle 84 having an interior 86 which includes an aerosol distribution port 88. The primary baffle 84 is aligned over the top of the gas jet 74 and entrainment device 78. The aerosol 76 and carrier gas 72 exit the VAM 22 through the aerosol distribution port 88, the interior 86 of the primary baffle 84, and the aerosol exit port 80 to enter into an aerosol exit tube 90 leading to a three-way valve 92. The three-way valve 92 is also connected to an aerosol feed tube 94 that leads to the object holder 82 and a second DL return line 96 that connects to the container 28. The three-way valve 92 is part of the aerosol management system 26 and completes either a pathway from the VAM 22 to the object holder 82 or a pathway from the VAM 22 to the container 28. The gas jet 74 is shown in more detail in Figures 2 A and 2B. The gas jet 74 includes a jet body 100 having a generally cylindrical shape and with a bottom end 102 and a top end 104. The bottom end 102 is partially open to expose a fitting 106 which is adapted to accept connection to the carrier gas feed line 73. The top end 104 of the jet body 100 mounts approximately flush with the VAM chamber 64 along the bottom wall 56 of the VAM 22. A flange 108 along the perimeter of the top end 104 of the jet body 100 mounts to a reciprocal flange 110 (seen in Figure 1) integrally formed in the bottom wall 56 of the VAM 22. The gas jet 74 may be mounted to the VAM 22 in a variety a ways such as press fitting flange 108 into reciprocal flange 110, with fasteners, or by integrally forming the gas jet 74 with the VAM bottom wall 56. A rod 112 having a bottom end 114 is integrally attached to the top end 104 of the jet body 100. The rod 112 includes a top end 116 which extends into the VAM chamber 64 when the gas jet 74 is mounted to the VAM 22. The top end 104 of the jet body 100 provides a shelf 118 for mating with the entrainment device 78. The shelf 118 has a one or more notches like 120 which partially extend inward from the perimeter of the jet body 100 towards the bottom end 114 of the rod 112. The depth of the notch 120 in the surface of the shelf 118 is only an indentation and is not sufficient to create a hole through the jet body 100. The notch 120 is also defined by a plurality of shelf arms like 122 that are the portion of the shelf 118 for mating and supporting the entrainment device 78. The fitting 106 of the gas jet 74 extends along the interior of the jet body 100 to connect to a bottom end 124 of a jet chamber 126 for directing the carrier gas 72 from the fitting 106 to the jet chamber 126. The jet chamber 126 includes a top end 128 with a jet orifice 130 which directs the carrier gas 72 from the jet chamber 126 into the VAM 22. The jet chamber 126 has a diameter which is larger than the diameter of the jet orifice 130 so that the velocity of the carrier gas 72 is accelerated as the carrier gas 72 flows from the jet chamber 126 through the orifice 13.0 into the VAM 22. The relative diameter sizes of the jet chamber 126 and orifice 130 are dependent on several factors such as the feed pressure of the carrier gas 72, desired exit pressure of the carrier gas 72 through the orifice 130 and the like. Examples of suitable dimensions for the diameters of the jet chamber 126 and orifice 130 are 0.122 inch and 0.031 inch respectively. The entrainment device 78 is shown in more detail in Figures 3A and 3B. The entrainment device 78 includes an entrainment body 132 having a generally cylindrical shape for mating over the jet body 100 of the gas jet 74. The entrainment body 132 has a bottom end 134, a top end 136, and an interior wall 138. The interior wall 138 defines a cavity 140 into which mates the rod 112 (Figures 2 A and 2B) of the gas jet 74. The rod 112 is slightly smaller in diameter than the cavity 140 diameter leaving a DL feed gap 142 between the exterior surface of the rod 112 and the interior wall 138 of the cavity 140 so that DL can flow therebetween from the bottom end 134 to the top end 136 of the entrainment body 132.

The bottom end 134 includes a base 144 extending outwardly from the entrainment body 132. The base 144 has at least one DL feed port 146 extending therethrough. The base 144 has a concave shape so that only the perimeter 148 of the bottom end 134 contacts the shelf arms 122 of the gas jet 74 for support leaving a channel 150 between the bottom end 134 of the entrainment body 132 and the shelf 118 of the gas jet 74. The channel 150 extends from the DL feed port 146 to the DL feed gap 142 to form the primary DL source 152 for aerosol creation by allowing DL to flow from the VAM chamber 64 through the DL feed port 146, across the channel 150, to the DL feed gap 142, and to the top end 136 of the entrainment device 78 to a DL feed ring 154. The top end 136 of the entrainment body 132 also includes a plurality of posts like 156 is integrally formed with the top end 136 of the entrainment device 78 and is used to align the primary baffle 84 over the DL feed ring 154 and jet orifice 130. Referring to Figures 2A and 3 A, the DL feed ring 154 which is where the interior wall 138 terminates and the DL 30 of the primary DL source 152 exits the interior wall 138 of the entrainment device and is directed towards the carrier gas 72 exiting from the jet orifice 130 of the gas jet 74. The DL feed gap 142 terminates at the underside of the DL feed ring 154 and feeds the DL 30 into the carrier gas 72 flowing from the jet orifice 130 to create a venturi flow as indicated by arrow 174 comprising the DL 30 and carrier gas 72. The venturi flow 174 is created by the pressure drop of the carrier gas 72 leaving the jet orifice 130 which entrains the DL 30. The pressure drop is also responsible for drawing the DL 30 up the DL feed gap 142 from the VAM chamber 64.

Referring to Figures 2B and 3 A, a secondary DL source 158 for aerosol creation is formed by allowing DL to flow from the VAM chamber 64 along the exterior surface of the notch 120 to a back side 160 of the notch 120. A secondary DL feed gap 162 is defined between the back side 160 of the notch and the portion of the base 144 near the perimeter 148 of the bottom end 134 of the entrainment body 132. The secondary DL feed gap 160 extends from the back side 160 to the channel 150. The secondary DL source 158 then allows the DL to flow from the back side 160, through the secondary DL feed gap 162, across the channel 150, to the DL feed gap 142, and to the top end 136 of the entrainment device 78 to the DL feed ring 154.

The use of the primary DL source 152 and secondary DL source 158 provides greater control over the creation of the aerosol 76 so that a wider range of particle size, size distribution, DL concentration, and the like, can be selected for use. As an example, and not for limitation, a suitable size for the DL feed gap 142 is about 0.027 inch, for the channel 150 is about 0.027 inch, for the secondary DL feed gap 162 is about 0.020 inch, for the diameter of the DL feed ring 154 is about 0.055 inch, and for the diameter of the DL feed port 146 is about 0.075 inch.

The primary baffle 84 is shown in more detail in Figures 4A and 4B. The primary baffle 84 includes a baffle body 164 having a generally cylindrical shape tapered towards a bottom end 166 and having a top end 168. The interior 86 of the primary baffle 84 is shown in phantom in Figure 4A and is closed at the bottom end 166 by a baffle cap 170 having a baffle edge 172. The venturi flow 174 comprising the DL 30 and carrier gas 72 (shown in Figure 2A) strikes the baffle cap 170 and continues flowing to the baffle edge 172 to create the aerosol 76. Located near the bottom end 166 of the primary baffle 84 is one or more aerosol distribution ports like 88 that open to the interior 86 of the baffle body 164. The aerosol distribution port 88 is positioned to be generally perpendicular to the surface of the baffle cap 170 and to be reached after the venturi flow 174 strikes the baffle cap 170. The aerosol 76 and carrier gas 72 exit the VAM 22 through the aerosol distribution port 88, the interior 86 of the primary baffle 84 and, as shown in Figure 1, continues through the aerosol exit port 80 to enter into an aerosol exit tube 90 leading to a three-way valve 92.

The baffle body 164 includes a baffle flange 176 around its perimeter for mounting with the VAM chamber 64 along the top wall 58 of the VAM 22. The baffle flange 176 is located along the baffle body 164 allowing the baffle cap 170 and aerosol distribution port 88 to extend into the

VAM chamber 64. The primary baffle 84 may be mounted to the VAM 22 in a variety a ways such as press fitting baffle flange 176, using fasteners, or by integrally forming the primary baffle 84 with the VAM top wall 58.

The venturi flow 174 interaction with the primary baffle 170 creates an aerosol 76 having smaller diameter particles with a smaller size distribution. Those particles which are too large coalesce into the DL 30 flowing through the VAM chamber 64. On the way to the object holder 82, the aerosol 76 travels through the three-way valve 92 which acts as a secondary baffle to further refine the size and distribution of the aerosol particles. Again, a small percentage (about 1-3%) of the aerosol particles coalesce and drain down the aerosol exit port 80 back into the DL 30 in the VAM chamber 64. Particle size is usually reported as mass median aerodynamic diameter

(MMAD), which is the diameter around which the mass of the aerosol is equally divided. This characterizes the population of aerosol particles produced and since the volume of the particle is determined by the cube of the radius, most of the particles will be smaller than the MMAD. The MMAD can be measured by instruments like a phase doppler. A suitable MMAD for the aerosol 76 in the invention is about 50 microns or less. Preferably, the MMAD of the aerosol 76 used in the invention is about 10 microns or less.

It is believed that the primary factors determining aerosol particle size are carrier gas velocity and the ratio of liquid to gas flow. An increase in gas velocity decreases particle size, whereas an increase in the ratios of DL to gas flow increases particle size. Gas velocity affects the flow rates for both the gas and the DL.

Another unique feature and advantage of the invention is that the aerosol 76 is created without any energy expenditure. The aerosol is non-electrical, non-thermal, and neutral-charged. This "passive" aerosol has physical and chemical properties which provide significantly better performance than atomized DL aerosols, DL vapors, and the like. The passive aerosol is a suspension in a continuous gas phase of fine particles of liquid that have not undergone a phase transformation into a vapor. The invention prefers to create the aerosol at or near room temperature. No energy is imparted to the DL that would increase its temperature to change the DL into a vapor.

Further operation of the self-cleaning system 20 is described by referring to Figures 1, 5 A, and 5B. In Figure 5 A, the level of the DL 30 in the VAM chamber 64 is shown during the creation of the aerosol 76 by the VAM 22 or the aerosol creation stage. A VAM DL level sensing means, generally referred to as 178, controls the level of the DL 30 in the VAM chamber 64 so that there is sufficient DL 30 present to feed the primary DL source 152 and the secondary DL source 158 into the gas jet 74 and entrainment device 78. However, the DL 30 in the VAM chamber 64 should not be so high as to interfere with the DL 30 exiting from the DL feed ring 154 of the entrainment device 78 and the carrier gas 72 exiting from the jet orifice 130 of the gas jet 74. Preferably, a high VAM DL level sensor 180 and a low VAM DL level sensor 182 are positioned in the side wall 62 of the VAM to respectively determine whether the DL 30 level in the VAM chamber 60 is at the appropriate level or needs filling.

When the aerosol creation stage is to begin, the DL pump 38 stops pushing the DL 30 through the DL feed line 36 into the VAM chamber 64. The DL 30 level begins to drop as the DL 30 drains back to the container 28 through the DL return line 50. The DL valve 52 remains open as the DL 30 in the VAM chamber 64 drops to the desired level for aerosol creation to begin as indicated by the high VAM DL level sensor 180. The DL valve 52 can remain open as the DL pump 38 uses a low flow to keep the DL 30 level between the low VAM DL level sensor 182 and the high VAM Dl level sensor 180 during aerosol creation. Simultaneously, the three-way valve 92 opens the connection between the aerosol exit tube 90 and the aerosol feed tube 94 to provide a pathway for the aerosol 76 to reach the object holder 82 from the VAM 22. The connection to the secondary DL return line 96 is blocked by the three-way valve 92. The carrier gas 78 is also turned

U to high flow (between about 4 L/min to about 150 L/min) at the carrier gas feed port 70 and flows into the gas jet 74 as previously described. The DL 30 flows into the entrainment device 78 as previously described to begin the creation of the aerosol 76.

During to the aerosol creation step, the DL pump 38 runs at a low flow to advance sufficient DL 30 through the DL feed line 36 into the VAM chamber 64 to not only feed the aerosol creation but also to recirculate through the DL return line 50 to the container 28. Having the DL 30 continue to flow though the VAM chamber 64 during aerosol creation prevents any accumulation of contamination. Preferably, the VAM chamber 64 includes a turbulence wall 184 in Figure 1 integrally formed with the bottom wall 56 and upstanding perpendicularly therefrom. The turbulence wall isolates the turbulence created by the DL pump 38 adding more DL 30 to the VAM chamber 64 during the aerosol creation stage. The turbulence wall allows the addition of more DL 30 to gently cascade over its top before coming in contact with the gas jet 74 and entrainment device 78.

Other suitable embodiments of the aerosol creation stage include, but are not limited to, closing the DL valve 52 during aerosol creation and running the DL pump 38 at a lower flow or pulsing flow to keep the DL 30 at an acceptable level. Another embodiment would fix the flow rate from the DL pump 38 and control the DL30 level in the VAM chamber 64 with a proportional type valve for DL valve 52.

After the aerosol creation stage is complete, the self-cleaning system 20 can return to a cleaning stage. When the cleaning stage is to begin, the carrier gas 72 shifts to a low flow at the carrier gas feed port 70 sufficient to keep the DL 30 from entering the gas jet 72. The three-way . valve 92 opens the connection between the aerosol exit tube 90 and the secondary DL return line 96 to provide a pathway for the DL 30 to flow to the container 28. The connection to the aerosol feed tube 94 is blocked by the three-way valve 92. The DL valve 52 is closed. The DL pump 38 shifts to a high flow and pushes the DL 30 from the container 28 through the DL feed line 36 to overfill the VAM chamber 64. As shown in Figure 5B, the DL 30 level has filled the VAM chamber 64 and is proceeding up the aerosol exit tube 90 as indicated by arrow 186. As the DL pump 38 continues to a high flow feed of the DL 30 into the VAM 22, the DL 30 will fill the VAM 22, the aerosol exit tube 90, the three-way valve 92, and flow back to the container 28 through the secondary DL return line 96 for continued recirculation of the DL 30 through this loop.

Another embodiment of the cleaning stage creates a second recirculation loop by opening DL valve 52 and allowing the DL30 to also exit from the VAM chamber 64 through the DL return line 50 and DL valve 52 to the container 28 for continued recirculation of the DL 30 through this second loop. Alternately, a valve could be used at the gas jet 74 to prevent the DL 30 from entering the gas jet 72.

The invention uses a unique multi-level flow rate method and device for circulating the DL 30 providing significantly increased cleanliness. A high flow rate circulates the DL 30 through the filter means 40 repeatedly during the cleaning stage which greatly improves the removal of particles. The resulting very pure DL 30 minimizes the possibility of contamination of the object from the DL 30. Using all of the same components in the self-cleaning system 20 and shifting to a low flow rate for the DL 30 during the aerosol creation stage is also minimizes particle contamination. Avoiding the use of different components when shifting between the cleaning stage and the aerosol creation stage eliminates possible sources of contamination. Other advantages of the high speed recirculation include, but are not limited to: eliminating down-time for the tool when the DL container is replenished, having the tool always ready to perform regardless of inactive periods, and the tool can be pressed into service faster. A suitable high flow rate is about 300 ml to 600 ml per minute which will typically circulate an entire gallon of the DL 30 through the filter means 40 in about two minutes. Of course this is an example and can be adjusted to be faster or slower by sizing the components like the DL pump 38 and the filter means 40 to the desired flow rate and resulting pressure.

The invention also uses a unique method and device for eliminating contamination from having the DL 30 evaporate on surfaces leaving behind particle contamination. Generally, the surfaces of all the components in the self-cleaning system 20 remain "wetted" by the DL 30 whether in the cleaning stage or in the aerosol creation stage. The DL 30 is not allowed to dry or evaporate on any surface so the opportunity for particle accumulation is eliminated and reproducible results are achieved. Specifically, when the VAM chamber 64 is flooded during the cleaning stage, all the surfaces of the gas jet 74, entrainment device 78, primary baffle 84, aerosol exit tube 90, and three-way valve 92 that were exposed to either the DL 30 or the aerosol 76 during the aerosol creation stage are submerged in DL 30 that is circulating through the filter means 40 during the cleaning stage.

One of the device embodiments of the invention is stand alone dryer 200 shown in Figures 6A and 6B. The dryer 200 includes a front panel 202 and a side panel 204 attached to a frame 206 for supporting an object holder, specifically a process chamber 208, sized to hold one or more of the objects (not shown) to be dried. A lid 210 includes a lid seal 212 for sealing the process chamber 208 when closed. The opening and closing of the lid 210 is controlled by an air cylinder 214 which receives compressed air from a facility feedstock (not shown) through a compressed air port 216 and an air regulator 244. The lid 210 contains one or more manifolds like 218 inserted on the underside 220 of the lid facing the process chamber 208. The manifold 218 directs an inert purge gas into the process chamber 208. The lid 210 has an interior 222 shown in phantom specifically in Figure 6B which contains a purge gas filter 224 for minimizing particle contamination of the purge gas before it enters the process chamber 208.

The process chamber 208 has a top end 226 and a bottom end 228. Connected to the process chamber 208 near the bottom end 228 is a drain 230 having a drain valve 232 and a drain motor 234 which leads to a drain port 236 in the facility. The drain motor 234 variably controls the drain rate of any process liquid from the process chamber 208. The drain 230 is also connected to an air amplifier 238 and exhaust ports 240, 242. A process liquid feed port 246 and process liquid return port 248 directs one or more process liquids into and from the process chamber 208 through a process liquid valve 250. A purge gas port 252 connects to the facility feedstock and delivers the purge gas through a purge gas regulator 254 and a purge gas primary filter 256. The purge gas is then split into two pathways. A first pathway leads to a VAM mass flow controller 258 which controls the delivery of the purge gas to the carrier gas feed port 70 and the gas jet 74 wherein the purge gas is used as the carrier gas 72 (as shown in Figure 1 et al.). A second pathway leads the purge gas through a purge mass flow controller 260 into a heater 262 connecting with the filter 224 and the manifold 218 to direct the purge gas into the process chamber 208. The container 28 for storing the DL has a unique construction integrating a DL fill port 264 that protrudes from the front panel 202 to allow easy accessibility for replenishing the DL in the container 28. The DL fill port 264 has a DL fill cap 266 which reversibly seals and extends upwardly so as to present a flat filling surface 268 that is generally level to the ground to minimize spillage when the DL is being poured into the DL fill port 264. The container 28 has an elongated body 270 which extends from the front panel 202 downwardly towards a back panel 272 of the dryer. The integration of the elongated body 270 with the DL fill port 264 provides a larger capacity for storing the DL and the downward slant allows gravity to aid in filling and dispensing the DL to the self-cleaning system 20. The container 28 connects to the DL pump 38, the first filter 42, the second filter, the first transducer 46, and the second transducer 48. The self cleaning system 20 also includes the VAM 22, the three-way valve 92 and the aerosol feed tube 94 that leads into an aerosol chamber port 276 in a side wall 274 of the process chamber 208. The aerosol chamber port 276 is in a position on the side wall 274 located above the highest level maintained by the process liquid in the process chamber 208.

The dryer 200 also includes an electrical cabinet generally depicted as 278. The front panel 202 includes a touch screen 280 with a stop button 282 and a start button 284 for operator control. The DL should be inert or non-reactive with the object being dried and the other materials that the DL comes in contact with during the drying process. The DL should have a significantly lower surface tension than the process liquid or rinse liquid that is being removed. Preferably, the DL should have a surface tension of less than about 25 dynes/cm at 20 C°. Examples of suitable Drying Liquids include isopropanol, methanol, ethanol, acetone, tetrahydrofuran, perflurohexane, ether, hexane, hydrofluororether (methyl nonafluorobutyl ether or methoxy nonafluorobutane collectively referred to herein as HFE), and an ethylated hydrofluoroether commercially available from the 3M Company in Minneapolis, MN. The DL can also be a combination of these examples.

The carrier gas should also be inert or non-reactive with the object being dried and the other materials that the DL comes in contact with during the drying process. Examples of a suitable carrier gas are nitrogen or carbon dioxide.

The process liquid should have a significantly high surface tension than the DL. An example of a suitable process liquid is de-ionized water, but also can include various chemistries that are aqueous based or mixed with water.

Examples of suitable materials for the process chamber include polyvinylidene fluoride, polypropylene, quartz, Halar, or stainless steel coated with Teflon. Suitable materials for the manifold minimize contamination of the purge gas and are heat resistant should the purge gas be heated. An example of a suitable material is a linear aromatic polymer called PEEK which comprises oxy- 1 ,4-phenyleneoxy- 1 ,4-phenylene-carbonyl- 1 ,4-phenylene.

EXAMPLES

A stand alone dryer of the type described herein, was used in a semiconductor facility to dry one cassette of 25 wafers @ 200mm per each production run. These were actual production wafers that had been subjected to various semiconductor processes including a CMP polishing, megasonic cleaning, and chemical processing using SCl, SC2, and dilute HF and the like. The stand alone dryer was loaded and unloaded manually in a class 100 clean room using isopropanol as the drying liquid. A purge gas of nitrogen at about 215 C° was used for about 250 to 300 seconds after the process chamber was drained. The measurements were performed with a WIS CR-80 particle detection instrument. With over one thousand consecutive production runs, the results were particle neutral at 130 run. The size of the process chamber was about 15 inches by 12 inches and contained about 8.5 gallons of de-ionized water when filled. Typically, the VAM dispensed aerosol for less than about, four minutes at a rate of 0.5 ml/min for a total isopropanol usage of less than about 3 ml per production run. While particular embodiments and applications of the invention have been illustrated and described, it is to be understood that the invention is not limited to the precise construction disclosed herein and that various modifications, changes, and variations will be apparent to those skilled in the art may be made in the arrangement, operation, and details of construction of the invention disclosed herein without departing from the spirit and scope of the invention as defined in the appended claims.

Claims

What is claimed is:

1. A wafer dryer comprising: a wafer bath vessel having means for supporting at least one wafer having an exposed surface to be dried; and a tub mounted to the bath vessel, the tub having a drying liquid spray device and a non- reactive carrier gas spray device opposing the drying liquid spray device, the spray device emitting a stream of pressurized drying liquid that converges with a stream of opposed pressurized non- reactive carrier gas emitted by the spray device of pressurized non-reactive gas to produce a drying liquid fog, the tub also having means for venting the drying liquid fog into the wafer bath vessel, the drying liquid fog drying the wafer.

2. The apparatus of claim 1 further comprising means for retaining relatively larger sized drying liquid fog particles and wherein said means for venting include means for venting the non-retained drying liquid fog particles into the wafer bath vessel.

3. The apparatus of claim 1 wherein said means for retaining larger sized drying liquid fog particles includes a lip.

4. The apparatus of claim 1 wherein said means for venting the drying liquid fog into the wafer bath vessel includes a port disposed in said tub.

5. The apparatus of claim 1 wherein said drying liquid is isopropyl alcohol and said non-reactive carrier gas is nitrogen.

6. The apparatus of claim 1 wherein the tub includes a decreasing volume of water.

7. The apparatus of claim 1 wherein said tub further has a source of non-reactive carrier gas introducing a non-reactive carrier into said tub.

8. The apparatus of claim 1 wherein said drying liquid spray device includes a tip with a tip opening through which the pressurized drying liquid stream is emitted in a first direction and wherein the pressurized non-reactive carrier gas source includes an opening through which the pressurized drying liquid stream is emitted in a second direction opposing the first direction.

9. The apparatus of claim 8 further comprising a throat adjacent to the spray device tip, the non- reactive carrier gas source disposed in the wafer bath vessel, the throat comprising an opening, wherein the pressurized non-reactive carrier gas is emitted through the throat.

10. The apparatus of claim 9 wherein said spray device tip is disposed within the throat opening, partially blocking the opening, and wherein said drying liquid stream and said non-reactive gas stream coverage in the throat.

11. The apparatus of claim 9 wherein said spray device tip is disposed adjacent the throat opening and said non-reactive gas stream is emitted through the throat opening to converge with said drying liquid stream beneath said spray device tip and above said throat opening.

12. The apparatus of claim 9 wherein said pressurized non-reactive gas stream source emits a central stream of non-reactive gas and one or more streams of non-reactive gas through openings in a body of said source co-axial with said central stream.

13. The apparatus of claim 12 further comprising a flange disposed about a lower portion of said throat, said flange including openings receiving said one or more co-axial streams of non-reactive gas.

14. The apparatus of claim 1 wherein said drying liquid spray device is a nebulizer.

15. A method for drying a wafer comprising: emitting a stream of pressurized drying liquid; emitting a stream of pressurized non-reactive carrier gas opposed to said drying liquid stream, said streams converging to produce a drying liquid fog; venting the drying liquid fog into a wafer bath vessel having at least one wafer with an exposed surface to be dried; and drying the exposed surface to be dried with said drying liquid fog.

16. The method claim 15 further comprising providing a non-reactive carrier gas stream for moving said drying liquid fog toward said exposed surface.

17. The method of claim 15 wherein said drying liquid is isopropyl alcohol and said non-reactive carrier gas is nitrogen.

18. The method of claim 15 further comprising retaining relatively larger particles of the liquid drying fog and venting relatively smaller particles of the liquid drying fog.