Kurokawa, Hiroyuki (MEMC Electronic Materials, Inc. 501 Pearl Drive P.O. Box 8 St. Peters, MO, 63376, US)
Iwamoto, Yosio (MEMC Electronic Materials, Inc. 501 Pearl Drive P.O. Box 8 St. Peters, MO, 63376, US)
Kurokawa, Hiroyuki (MEMC Electronic Materials, Inc. 501 Pearl Drive P.O. Box 8 St. Peters, MO, 63376, US)
|1.||A method of washing a wafer carrier, said carrier being adapted to hold one or more semiconductor wafers during a wafer washing process, said method comprising the steps of : immersing the carrier in a bath of deionized water; replacing at least a portion of the water in the bath while the carrier is immersed in the bath; removing the carrier from the bath after an immersion period; and airdrying the carrier in a position adjacent the bath after removing the carrier from the bath.|
|2.||The method of claim 1 wherein the step of replacing the deionized water includes renewing the water in the bath at a generally uniform renewal rate of at least about 1/100 of the water volume per minute during the immersion period.|
|3.||The method of claim 1 wherein the step of replacing the deionized water includes renewing the water in the bath at a renewal rate between approximately 1/100 and 1/10 of the water volume per minute during the immersion period.|
|4.||The method of claim 1 wherein the temperature of the water in the bath is at least about 80°C.|
|5.||The method of claim 1 further comprising the steps of automatically carrying out the immersing step at a predetermined wash interval and automatically carrying out the air drying step after the immersion period.|
|6.||The method of claim 1 wherein the step of airdrying the carrier includes blowing a dried gas upon the carrier.|
|7.||An apparatus for washing a wafer carrier, said carrier being adapted to hold one or more semiconductor wafers during a wafer washing process, said apparatus comprising: a container of deionized water into which the carrier is immersed, said container having an overflow receptacle into which the water overflows for replacing at least part of the water in the container; a robot for transporting the carrier, said robot positioning the carrier in the container to immerse the carrier in the water and removing the carrier from the container after an immersion period; and a dryer for airdrying the carrier in a position adjacent the container after the carrier is removed from the container by the robot.|
|8.||The apparatus of claim 7 wherein the container has an inlet port through which deionized water is introduced into the bath for renewing the water in the bath at a generally uniform renewal rate of at least about 1/100 of the water volume per minute during the immersion period.|
|9.||The apparatus of claim 7 wherein the container has an inlet port through which deionized water is introduced into the bath for renewing the water in the bath at a renewal rate between approximately 1/100 and 1/10 of the water volume per minute during the immersion period.|
|10.||The apparatus of claim 7 wherein the temperature of the water in the bath is at least about 80°C.|
|11.||The apparatus of claim 7 wherein the dryer blows a dried gas onto the carrier for drying the carrier.|
|12.||The apparatus of claim 7 further comprising an identification device associated with the carrier, said identification device recording information regarding the washing of the carrier.|
|13.||The apparatus of claim 7 wherein the robot is responsive to the information recorded in the identification device for transporting the carrier to automatically carry out the immersing step at a predetermined wash interval.|
|14.||The apparatus of claim 7 for use with an apparatus for washing the wafers and wherein the container is disposed adjacent the apparatus for washing the wafers.|
One conventional process for washing semiconductor wafers and the like involves immersing the wafers in a bath while subjecting the wafers to ultrasonic waves. A carrier holds the wafers in the bath. Unfortunately, the carrier is typically a fluororesin, such as TEFLONX PFA fluoropolymer resin available from E. I. du Pont de Nemours and Company, which absorbs various chemicals in the bath used for washing the wafers. For example, the bath often contains ammonium hydroxide, hydrogen fluoride, and/or hydrochloric acid. The absorbed chemicals react with each other to form a salt such as ammonium fluoride or ammonium chloride. This salt forms on the carrier and presents a risk of contaminating the wafers. Therefore, the carrier used for washing the wafers must be cleaned periodically. U. S.
Patent Nos. 5,839,460,5,816,274, and 5,327,921, for example, describe known systems for washing a plurality of wafers.
Generally, an acid absorbed in the carrier can be compulsorily reacted with an alkali to form a salt. The resulting salt deposited on a surface of the carrier can then be removed by washing out the carrier. For example, baking the carrier at about 100°C or higher for at least one hour reacts an acid absorbed in the carrier with an alkali to form a salt. After the salt is formed, deionized water is used to wash it away. Finally, the carrier is dried.
This process for washing salt from the carrier, however, usually leaves a salt residue and does not completely wash the formed salt from the carrier. Moreover, it is generally impossible to prevent an operator from touching the carrier during the conventional carrier
cleaning process. As a result, it is difficult to completely avoid contamination of the carrier due to an artificial cause.
For these reasons, an improved method and apparatus are desired for more completely cleaning the carrier used in the wafer washing process and for reducing the risk of contaminating the carrier.
SUMMARY OF THE INVENTION The invention meets the above needs and overcomes the deficiencies of the prior art by providing an improved method and apparatus for cleaning a wafer carrier used for washing semiconductor wafers. Among the several objects and features of the present invention may be noted the provision of a method and apparatus that permit more complete cleaning of the carrier; the provision of such method and apparatus that reduce the risk of contaminating the carrier by an operator handling or touching the carrier during cleaning; the provision of such method and apparatus that reduce the risk of contaminating the carrier by an artificial cause or source; and the provision of such method and apparatus that are economically feasible and commercially practical.
Briefly described, the present invention is directed to a method of washing a wafer carrier adapted to hold one or more semiconductor wafers during a wafer washing process.
The method includes the steps of immersing the carrier in a bath of deionized water and replacing at least a portion of the water in the bath while the carrier is immersed in the bath.
The method further includes removing the carrier from the bath after an immersion period and then air-drying the carrier in a position adjacent the bath after removing the carrier from the bath.
An apparatus embodying aspects of the invention is useful for washing a wafer carrier adapted to hold one or more semiconductor wafers during a wafer washing process. The apparatus includes a container of deionized water into which the carrier is immersed. The container has an overflow receptacle into which the water overflows for replacing at least part
of the water in the container. A robot transports the carrier for positioning the carrier in the container to immerse the carrier in the water and removing the carrier from the container after an immersion period. The apparatus further includes a dryer for air-drying the carrier in a position adjacent the container after the carrier is removed from the container by the robot.
Alternatively, the invention may comprise various other methods and apparatuses.
Other objects and features will be in part apparent and in part pointed out hereinafter.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a plan view of a main portion of a washing apparatus for washing semiconductor wafers and a container for cleaning a carrier used for holding the wafers during washing according to a preferred embodiment of the invention.
FIG. 2 is a front view of the washing apparatus of FIG. 1.
FIG. 3 is a sectional view of the container of FIG. 1.
Corresponding reference characters indicate corresponding parts throughout the drawings.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS Referring now to FIG. 1, a plan view schematically shows a main or principal portion of a wafer washing apparatus suitable for use in connection with the present invention.
According to the invention, a carrier 1 holds one or more semiconductor wafers (not shown) during a washing operation performed by an apparatus such as the one illustrated in FIG. 1.
A truck 2 driven by a conventional drive mechanism (not shown) conveys one or more of the carriers 1 to their respective positions for wafer washing. In a preferred embodiment, wafer carriers 3 are used to transport wafers to and from the wafer washing apparatus. A wafer
transfer apparatus 4 carries in unwashed wafers on one or more of the carriers 3 from a previous processing operation and then mounts the wafers to be washed in wafer washing carriers 1. Following the washing operation, another wafer transfer apparatus 4'preferably demounts the washed wafers from the wafer washing carriers 1 and returns the wafers to carriers 3 for transport to subsequent processing operations.
The wafer washing apparatus includes a plurality of vessels, or containers 5. Each container 5 preferably holds a bath in which wafer washing carrier 1 is immersed for washing one or more semiconductor wafers held by carrier 1. The washing apparatus also includes a drying apparatus 6 for drying the wafers after washing and a track 7. A preferred embodiment of the invention includes a carrier wash vessel, or container 11, having a sectional structure schematically as shown in FIG. 3. The carrier wash container 11 is preferably disposed in or near the washing apparatus for periodically washing carriers 1 following the wafer washing operation. According to the invention, container 11 holds a bath of very warm, deionized water in which carriers 1 are immersed for cleaning. During the wafer washing process, a robot 12 moves along the track 7 for selectively transporting wafer washing carriers 1 to and from containers 5. Preferably, the robot 12 also selectively delivers carriers 1 to wash container 11.
FIG. 2 is a front view of the wafer washing apparatus of FIG. 1. Further details of the wafer washing apparatus have been omitted from the present description for simplicity because those skilled in the art have an understanding of such details.
FIG. 3 il} « rates aspects of carrier wash container 11 according to a preferred embodiment of the invention. As shown, a dryer 13 blows a gas for drying carrier 1 in situ after it is removed from carrier wash container 11. FIG. 3 also shows an overflow vessel, or receptacle 14, extending from the main body of carrier 11. The present invention preferably pumps deionized water into container 11 at a predetermined rate. The bath of deionized water then overflows from the main body of container 11 into the overflow receptacle 14, which temporarily holds the water before it is cooled through a pipe (not shown) arranged
near receptacle 14 and discharged outside the system. In the alternative, container 11 employs a notch in a part of a partition wall of carrier wash container 11 for overflowing the deionized water at a specific rate.
In addition, container 11 includes a device (not shown) for maintaining wafer wash carrier 1 in position and a heater 15 for maintaining the temperature of the deionized water bath at a desired temperature (e. g., approximately 85°C). The heater 15 may be any suitable heater capable of maintaining the temperature of the deionized water at approximately 80°C or warmer. As such, heater 15 may be disposed inside or outside of wash container 11. In one preferred embodiment, the wafer washing apparatus is an automatic washing apparatus to which container 11 is fixed and can be used as an apparatus of the present invention. In other words, carrier wash container 11 may be disposed in a working relationship with wafer drying apparatus 6, truck 2 for conveying wafer carrier 1, wafer transfer apparatus 4, and wafer transfer apparatus 4'and, thus, the washing apparatus of FIG. 1 in combination with container 11 constitutes an apparatus for washing wafer carriers 1. It is to be understood, however, that other configurations are contemplated for the carrier washing apparatus, particularly, configurations providing for at least a portion of the bath of deionized water in container 11 to be replaced at a generally uniform rate and for air-drying carrier 1 in situ after it is lifted from the bath.
When carrier wash container 11 is incorporated in line into the wafer washing apparatus, an appropriate modification is given to each part of the apparatus as necessary.
When container 11 is disposed near the wafer washing apparatus, it is disposed at a position such that it does not disturb the wafer wash line and without remarkable fluctuations in the environment. Since container 11 holds a warm bath of deionized water, steam may be generated. For this reason, one embodiment of the invention includes a ventilator (not shown), for example, disposed near container 11 to remove the steam effectively from the periphery of the carrier wash container 11.
In a preferred embodiment of the invention, wafer carrier 1 is periodically washed according to a schedule based on, for example, the time since the last washing of the particular carrier 1 or the number of times carrier 1 has been used for washing wafers since the last washing of the particular carrier 1. During washing, carrier 1 is immersed in the bath of deionized water held by container 11 for a predetermined period of time (e. g., approximately 30 to 60 minutes).
At temperatures below about 80°C, the elution effect of the chemicals may not be exhibited sufficiently. Since heater 15 preferably keeps the bath in container 11 at least about 80°C or warmer, the deionized water is better able to desorb the various chemicals from the immersed carrier 1. In this manner, the chemicals from the wafer washing bath that are absorbed and/or adsorbed by carrier 1 during the wafer washing process are eluted.
Ultrasonic waves are employed in one embodiment of the invention to improve the washing of carrier 1. A wash container or vessel suitable for ultrasonic washing can be used as carrier wash container 11 in this embodiment.
As described above, at least a part of the deionized water in container 11 is replaced at a substantially constant, or uniform, rate while carrier 1 is immersed. In one embodiment, this is accomplished by introducing deionized water into container 11 through a conventional inlet port (not shown) situated near the bottom of container 11 and overflowing a predetermined volume of deionized water from container 11 into overflow receptacle 14. The water replacement rate during the immersion period is preferably selected to prevent the concentration of the eluted chemicals in the bath from exceeding a desired limit. For example, the carrier washing apparatus of the invention overflows about 1/100 to 1/10 of the volume of water in container 11 per minute. When the rate is less than approximately 1/100 volume per minute, eluted chemicals may not be effectively removed outside the system.
Even if the rate of overflowing water exceeds approximately 1/10 volume per minute, efficiency in removing chemicals is not improved significantly enough to justify the increased consumption of deionized water and, thus, the increased cost. It is also
contemplated that the water renewal rate may vary between about 1/10 to 1/00 volume per minute, particularly at different times during the immersion period. For example, a higher renewal rate may be desired when carrier 1 is first immersed and a lower renewal rate near the end of the immersion period.
Immersing carrier 1 in the deionized water bath for about 30 to 60 minutes is generally sufficient for cleaning carrier 1 when the water is replaced by overflowing or the like at a suitable rate. In the alternative, the length of the immersion period is selected as a function of the interval of washing or another parameter. For example, if the interval between washes for a particular carrier 1 is relatively long, a longer immersion period is generally warranted. Another embodiment of the present invention includes a specific resistance meter 17, for example, disposed in container 11 for measuring the specific resistance of the bath of deionized water. Those skilled in the art will recognize that the resistivity of the bath will vary depending on the concentration of certain chemicals in the water. As such, the specific resistance of the deionized water used to rinse carrier 1 indicates a degree or index of cleansing. Carrier 1 is then removed from container 11 when the specific resistance of the deionized water reaches a predetermined level representing a desired degree of cleansing.
The meter 17 monitors the specific resistance of the deionized water in which carrier 1 is immersed to determine whether carrier 1 is sufficiently clean. The immersion period can end when the specific resistance of the deionized water that overflowed into overflow receptacle 14 becomes greater than or equal to, for example, 18 MQcm. In other words, carrier 1 is preferably determined to be sufficiently clean when the bath of deionized water is substantially free of electrolytes. To monitor fluctuations in specific resistance of the overflowed deionized water, specific resistance meter 17 is preferably disposed in the overflow receptacle 14 of container 11 as schematically shown in FIG. 3.
Following completion of the immersion period, the carrier washing apparatus lifts carrier 1 from the water bath in container 11 for air-drying in situ. In other words, dryer 13
dries carrier 1 at a position adjacent the bath of deionized water. Advantageously, this position is also near the wafer washing apparatus, at least part of which constitutes the carrier washing apparatus in the illustrated embodiment. This beneficially reduces the risk of carrier 1 being contaminated due to touching by an operator. In the drying step, robot 12 holds carrier 1 disposed in the washing apparatus to avoid contamination due to artificial factors.
At that time, drying is preferably facilitated by blowing nitrogen gas or dry air on carrier 1 using dry-gas blowing dryer 13. Generally, dryer 13 sufficiently dries carrier 1 in a relatively short amount of time (e. g., about one to five minutes). Dryer 13 operates quickly due to the deionized water being naturally removed from the surface of carrier 1 when it is lifted from container 11. In this instance, a considerable volume of the deionized water is air dried during the carrier lifting operation because the water used for washing carrier 1 has a relatively high temperature. Moreover, the surface of carrier 1 is generally hydrophobic, which in combination with the surface tension of water, causes carrier 1 to easily shed some of the water.
For a number of reasons, including quality control, wafer manufacturers desire to track wafers as they travel facility-to-facility within a plant and to record process data on each lot of wafers sliced from a particular ingot through final packing. In this respect, one or more carriers may be used to transport a single lot of wafers. Several devices are available for automatically identifying various objects, including devices for bar-code reading and optical character recognition (e. g., photoelectric tubes or the like), for use in warehousing, distribution and manufacturing processes. Such identification devices visually identify distinctive markings on an object (e. g., a unique bar-code label) to identify it.
In a preferred embodiment of the invention, carrier 1 includes an identification device such as a transponder tag (not shown) coded to identify the particular carrier 1 and the batch of wafers that is holds. Preferably, the transponder tag also stores information relating to the past history of carrier 1, such as when carrier 1 was last washed and/or how many times carrier 1 has been used for washing wafers since the last time carrier 1 was washed. The
information record stored in the tag (i. e., the washing record of carrier 1) enables the carrier washing apparatus to automatically subject carrier 1 to the washing operation when a predetermined period of time has passed since the last washing or when washing is desired based on a past history of use (e. g., after the particular carrier 1 has been used for washing wafers three to six times). When carrier 1 is due for washing, the carrier washing apparatus preferably uses the information in the tag or other identification device to cause carrier 1 to be automatically transported to container 11 during the time normally spent waiting for wafer transfer apparatus 4 to load carrier 1 with wafers. In the alternative, the frequency at which carrier 1 is washed may be determined by other methods such as an independent washing standard or measuring a specific resistance on a surface of carrier 1 or, if circumstances warrant, after every wafer washing operation.
As an example, the tag is a multiple page read/write transponder capable of storing information relating to a unique carrier address, cassette lot number, plant order, current and next process operation, product count and other information valuable to the manufacturing process. A suitable tag is the TIRES@ multi-page read/write transponder manufactured by Texas Instruments which has 17 pages (80 bits each).
A reader (not shown) for reading the tag or other identification device on carrier 1 is preferably disposed near the carrier washing apparatus. In one embodiment, the reader and tag are part of a carrier data communication system that provides, for example, applications for operator interfaces, product work-in-process, container inventory, scheduling container moves, interlocking equipment, history and reporting as a function of data gathered by the communication system. The carrier data communication system includes data capture devices, control modules, power supplies, communication hardware and software to buffer the captured data. In this instance, the data capture devices employ radio frequency identification (RFID) tracking technology for capturing data from a passive data carrying device (i. e., the tag) attached to carrier 1. A preferred reader is the configurable data collection reader, Sircon IV Reader available from Sirit Corp.
The reader preferably transmits RF energy via an antenna (not shown) located near container 11 of the carrier washing apparatus. The relatively small FM radio transponder, or tag, mounted on carrier 1 receives the transmitted RF signal and generates a reply signal. The reader receives the reply signal via the respective antenna. In one embodiment, the RFID reader then uploads the information scanned from the tag to a cell controller (not shown) (e. g., a host computer linked to a data network at the wafer processing facility). The host computer can also write information to the tag using a similar process. By keeping track of the washing events, the host computer facilitates the regular washing of carrier 1 and prevents omission of washing due to operator error or the like. Moreover, since the present invention automatically records a washing record of each carrier 1 through the use of the identification and transmitting devices, it is possible to trace the causes of any contamination in specific wafers on the basis of the washing record.
A method for washing carrier 1 usable for washing semiconductor wafers according to the present invention is described below with reference to an example. However, the present invention is by no means limited to the example.
EXAMPLE: The apparatus for washing wafers schematically shown in FIG. 1 was used and constitutes the carrier washing apparatus. Truck 2 transported wafer carrier 1 between wafer transfer apparatus 4 for mounting wafers on carrier 1 and wafer transfer apparatus 4'for demounting wafers on carrier 1. When the information stored in the identification device indicated that carrier 1 was due for washing, robot 12 delivered carrier 1 to wash container 11. Carrier 1 was immersed in container 11 for approximately 40 minutes.
At this point in time, a specific resistance of the warm deionized water used for immersing was confirmed to be at least about 18 MQcm, based on an indicated value of specific resistance meter 17 disposed in the overflow receptacle 14 of container 11 so as to monitor fluctuations in specific resistance. Thus, it was confirmed that sufficient washing had been conducted. After the immersing operation was completed, robot 12 removed carrier 1 from
wash container 11 where dryer 13 blew a nitrogen gas on carrier 1 for about two minutes with keeping carrier 1 in the air to complete a washing operation.
Advantageously, the method of the invention provides automatically washing carrier 1 inside or near a wash apparatus. Therefore, the method not only eliminates contamination due to an artificial mistake but also is free from repeated operations of forming salt by baking, washing out the salt, and drying carrier 1. Thus, the method is very effective.
Further, an apparatus for washing carrier 1 according to the present invention can be used for the aforementioned effective wash method.
In view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results attained.
As various changes could be made in the above constructions and methods without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.
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