US20020032973A1 - Method of and apparatus for drying a wafer using isopropyl alcohol - Google Patents
Method of and apparatus for drying a wafer using isopropyl alcohol Download PDFInfo
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- US20020032973A1 US20020032973A1 US09/801,636 US80163601A US2002032973A1 US 20020032973 A1 US20020032973 A1 US 20020032973A1 US 80163601 A US80163601 A US 80163601A US 2002032973 A1 US2002032973 A1 US 2002032973A1
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- isopropyl alcohol
- cleaning liquid
- liquid
- drying
- heated
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
- H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
- H01L21/04—Manufacture or treatment of semiconductor devices or of parts thereof the devices having at least one potential-jump barrier or surface barrier, e.g. PN junction, depletion layer or carrier concentration layer
- H01L21/18—Manufacture or treatment of semiconductor devices or of parts thereof the devices having at least one potential-jump barrier or surface barrier, e.g. PN junction, depletion layer or carrier concentration layer the devices having semiconductor bodies comprising elements of Group IV of the Periodic System or AIIIBV compounds with or without impurities, e.g. doping materials
- H01L21/30—Treatment of semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/26
- H01L21/302—Treatment of semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/26 to change their surface-physical characteristics or shape, e.g. etching, polishing, cutting
- H01L21/304—Mechanical treatment, e.g. grinding, polishing, cutting
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
- H01L21/67—Apparatus specially adapted for handling semiconductor or electric solid state devices during manufacture or treatment thereof; Apparatus specially adapted for handling wafers during manufacture or treatment of semiconductor or electric solid state devices or components ; Apparatus not specifically provided for elsewhere
- H01L21/67005—Apparatus not specifically provided for elsewhere
- H01L21/67011—Apparatus for manufacture or treatment
- H01L21/67017—Apparatus for fluid treatment
- H01L21/67028—Apparatus for fluid treatment for cleaning followed by drying, rinsing, stripping, blasting or the like
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
- H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
- H01L21/02041—Cleaning
- H01L21/02057—Cleaning during device manufacture
- H01L21/0206—Cleaning during device manufacture during, before or after processing of insulating layers
- H01L21/02063—Cleaning during device manufacture during, before or after processing of insulating layers the processing being the formation of vias or contact holes
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10S134/00—Cleaning and liquid contact with solids
- Y10S134/902—Semiconductor wafer
Definitions
- the present invention relates to a method of and an apparatus for drying a wafer. More particularly, the present invention relates to a method of and an apparatus for drying a wafer using isopropyl liquid after the wafer is cleaned following a semiconductor manufacturing process.
- Semiconductor devices or semiconductor chips are manufactured by processing a wafer that is usually formed of silicon.
- the wafer is typically subjected to a series of semiconductor device manufacturing processes such as photolithography, chemical or physical vapor deposition and plasma etching.
- the wafer may be washed using de-ionized water (hereinafter referred to as “DIW”). Because the DIW will eventually dissolve the silicon, the wafer must be completely dried after being washed with the DIW or else water spots will be formed.
- DIW de-ionized water
- Japanese Patent Laid-Open Publication No. Hei 8-61846 discloses a method of directly spraying liquid isopropyl alcohol over a wafer, forming a mixture of the water and the isopropyl alcohol on the surface of the wafer, and volatilizing the mixture by means of a high temperature nitrogen gas.
- U.S. Pat. No. 6,029,371 issued to Kamikawa et al. discloses a method of drying a wafer by directly spraying a washed wafer with a drying gas comprising heated isopropyl alcohol and nitrogen.
- drying apparatuses using isopropyl alcohol are disclosed in U.S. Pat. No. 5,634,978 issued to Mohindra et al., U.S. Pat. No. 5,855,077 issued to Chang-Hyun Nam et al., U.S. Pat. No. 4,633,893 issued to McConnell et al., and U.S. Pat. No. 4,911,761 also issued to McConnell et al.
- These drying apparatuses execute a method in which the isopropyl alcohol is introduced as a mist over the cleaned wafer to eliminate the water on the wafer.
- FIG. 1 shows one example of a conventional apparatus 100 that works on the Marangoni effect to dry the wafer using an isopropyl alcohol mist.
- the apparatus 100 includes a cleaning section (or a rinsing section) 110 containing a cleaning liquid (or rinsing liquid) 113 for cleaning (or rinsing) the wafer.
- the cleaning section 110 in turn includes an inner bath 112 having an upper open end, and an outer bath 116 covered with a lid 117 .
- the outer bath 116 and lid 117 enclose the inner bath 112 .
- a wafer 101 is immersed in the cleaning liquid 113 of the inner bath 112 for cleaning. Once the cleaning liquid 113 over-flows the inner bath 112 , the over-flown cleaning liquid 113 a gathers in the outer bath 116 from where it is drained from the cleaning section 110 .
- a cleaning liquid supply tube line 114 a is connected to the inner bath 112 at the bottom thereof.
- First and second cleaning liquid drain tube lines 114 b and 114 c are connected to the inner bath 112 and the outer bath 116 , respectively, at the bottoms thereof.
- the cleaning liquid supply tube line 114 a supplies the cleaning liquid 113 , such as DIW, to the inner bath 112 .
- the first cleaning liquid drain tube line 114 b drains the cleaning liquid 113 a which has over-flown the inner bath 112 into the outer bath 116 .
- the second cleaning liquid drain tube line 114 c gradually drains the cleaning liquid 113 from within the inner bath 112 .
- the apparatus 100 for drying the wafer is also equipped with an isopropyl alcohol mist supply tube line 134 for supplying the isopropyl alcohol mist from an isopropyl alcohol supply unit (not shown).
- the isopropyl alcohol supply unit makes the isopropyl alcohol bubble by using nitrogen as a carrier gas to form the isopropyl alcohol mist.
- the isopropyl alcohol mist and nitrogen are supplied to the upper portion of the outer bath 116 via the isopropyl alcohol mist supply tube line 134 .
- a diffuser 136 is furnished at the central portion of the lid 117 of the outer bath 116 for consistently diffusing the isopropyl alcohol mist and nitrogen throughout the inside of the outer bath 116 .
- a nitrogen gas supply tube line 140 is connected to the lid 117 for supplying heated nitrogen gas into the outer bath 116 during the drying process to create a drying ambient.
- the conventional apparatus 100 for drying a wafer operates as follows.
- the cleaning liquid 113 such as the DIW
- the cleaning liquid supply tube line 114 a to initiate the cleaning operation.
- the cleaning liquid is supplied into the inner bath 112 at such a rate that it overflows the inner bath 112 during the cleaning operation.
- the over-flown cleaning liquid 113 a is gathered in the outer bath 116 and drained from the bottom of the outer bath 116 via the first cleaning liquid drain tube line 114 b.
- FIGS. 2A, 2B and 2 C are schematic diagrams illustrating the drying process.
- the nitrogen gas and the isopropyl alcohol mist entrained thereby are introduced via the isopropyl supply tube line 134 and diffuser 136 into the upper portion of the outer bath 116 .
- the ambient in outer bath 116 is converted into a drying ambient.
- approximately 50 cc of the isopropyl alcohol mist is supplied.
- the heated nitrogen gas is supplied into the outer bath 116 via the nitrogen gas supply tube line 140 connected to the lid 117 .
- the cleaning liquid 113 is drained via the drain tube line 114 c while the nitrogen gas is supplied via the nitrogen gas supply tube line 140 .
- the cleaning liquid 113 is drained at a constant rate via the second drain tube line 114 c .
- the height of the cleaning liquid 113 is decreased at a rate of about 3 mm/sec.
- the water spots on the wafers 101 are eliminated by means of the Marangoni effect created by the isopropyl alcohol.
- FIG. 2C once the cleaning liquid 113 is completely drained to a level below the wafers 101 , the last of the heated nitrogen gas is introduced into the outer bath 116 via the nitrogen supplying tube line 140 , thereby completing the drying process.
- Japanese Patent Laid-Open Publication Nos. Hei 11-87305, Hei10-154689 and Hei10-22257 disclose methods of drying a wafer in which an isopropyl alcohol mist is used. In these methods, an isopropyl alcohol liquid layer is formed by the mist over a cleaning liquid, and the wafers are raised from the cleaning liquid into the isopropyl alcohol liquid layer, thereby drying the wafer.
- the mist of isopropyl alcohol is supplied to the outer bath using nitrogen as a carrier gas. Therefore, the amount of isopropyl alcohol injected into the outer bath is determined by measuring the reduction in the amount of isopropyl alcohol in the isopropyl alcohol supply unit. For this reason, the amount of isopropyl alcohol used for forming the isopropyl alcohol layer cannot be accurately determined. Furthermore, it is difficult to accurately control the amount of isopropyl alcohol being supplied.
- the isopropyl alcohol sprayed by the diffuser adheres to the side wall of the outer bath.
- the isopropyl alcohol is likely to fall as drops onto the wafer. These drops create wafer defects.
- Japanese Patent Laid-open No. Hei 9-213672 discloses a method in which an isopropyl alcohol layer is formed over a cleaning liquid in which a wafer is immersed, and the wafer is dried while ascending from the cleaning liquid.
- the isopropyl alcohol layer formed on the cleaning liquid has a thickness of about 5 mm, and the wafer is to raised gradually from the cleaning liquid.
- the above-described method requires a large quantity of isopropyl alcohol and a relatively long amount of time for forming the isopropyl alcohol liquid layer. Also, the drying effect produced by this method is so insufficient that water spots remain after the wafer is cleaned. The water spots leave too many particles on the wafer.
- the object of the present invention is to overcome the above-described drawbacks of the conventional prior art.
- a first object of the present invention is to provide a highly effective and time-efficient method of drying a wafer using the Marangoni effect.
- a second object of the present invention is to provide an apparatus for drying a wafer particularly suitable for performing such a method.
- the present invention provides a method of drying an object comprising supplying heated inert gas over a cleaning liquid in which the object is immersed, heating a liquid having a smaller surface tension than that of the cleaning liquid, and then supplying the heated liquid onto the cleaning liquid in a fluid state. This forms a liquid layer on the cleaning liquid, and an ambient over the cleaning liquid comprising the vapor of the heated liquid and the inert gas. Then, the object is removed from the cleaning liquid while the heated liquid layer is maintained. The object is dried further by supplying more of the heated inert gas into the ambient surrounding the object.
- the heated inert gas is preferably nitrogen gas
- the liquid used to form a layer on the cleaning liquid is preferably isopropyl alcohol.
- the present invention provides a cleaning apparatus comprising a cleaning section housing the cleaning liquid for cleaning the object, and an isopropyl alcohol supplying unit that supplies heated liquid isopropyl alcohol onto the cleaning liquid to form an isopropyl alcohol liquid layer and an isopropyl alcohol ambient over the cleaning liquid, and a nitrogen supply unit that supplies heated nitrogen gas above the cleaning liquid housed in the cleaning section.
- a separating unit can remove the object from the cleaning liquid while the isopropyl alcohol layer is maintained.
- the nitrogen gas is heated and supplied into the cleaning section at a location above the cleaning liquid in which the wafer is immersed, and the liquid isopropyl alcohol liquid is heated and supplied directly onto the cleaning liquid.
- the isopropyl alcohol liquid layer diffuses quickly to form a liquid layer on the cleaning liquid, the liquid isopropyl alcohol liquid supplied in the fluid state also forms an ambient with the nitrogen gas that is non-volatile above the cleaning liquid.
- the wafer is dried only by removing it from the cleaning liquid into the ambient while only the heated nitrogen gas continues to be supplied.
- FIG. 1 is a schematic diagram of a conventional apparatus for drying a wafer
- FIGS. 2A to 2 C are schematic diagrams of cleaning sections of the conventional drying apparatus, illustrating a drying process executed by the conventional apparatus
- FIG. 3 is a schematic diagram of a first embodiment of an apparatus for drying a wafer according to the present invention.
- FIG. 4 is top view of a cleaning section of the drying apparatus showing the arrangement of a nitrogen gas supply tube line and first and second isopropyl alcohol supply tube lines relative to a bath of the cleaning section;
- FIGS. 5A to 5 D are respective side views of the cleaning section, illustrating a first embodiment of a method of drying a wafer according to the present invention
- FIG. 6 is a schematic diagram showing the change in the level of cleaning liquid and an isopropyl alcohol layer, which occurs during the draining step shown in FIG. 5B;
- FIG. 7 is a flowchart of the first embodiment of the method of drying a wafer according to the present invention.
- FIG. 8 is a timing chart of the first embodiment of the method for drying the wafer according to the present invention.
- FIG. 9 is a graph plotting the change in the number of particles before and after a wafer is washed and dried in accordance with the method of the present invention.
- FIG. 10 is a graph plotting the change in the number of particles before and after a wafer is washed and dried in accordance with the method of the present invention, using the average values from FIG. 9, and in accordance with a prior art process;
- FIG. 11 is a graph plotting the number of particles before and after a wafer is washed and dried for different amounts of supplied isopropyl alcohol;
- FIG. 12 is a schematic diagram of a second embodiment of an apparatus for drying a wafer according to the present invention.
- FIG. 13 is a flowchart of the second embodiment of a method of drying a wafer according to the present invention, which method can be performed by the apparatus shown in FIG. 12.
- FIG. 3 shows a first embodiment of an apparatus 200 for drying a wafer according to the present invention.
- the drying apparatus 200 includes a cleaning section 210 containing a cleaning liquid 213 for cleaning wafers 201 .
- DIW may be used as the cleaning liquid 213 .
- the cleaning section 210 comprises an inner bath 212 in which the wafers 201 are immersed in the cleaning liquid 213 to be cleaned, and an outer bath 216 enclosing the inner bath 212 .
- the wafers 201 are loaded on a wafer guide 203 that can be seated in the cleaning bath 210 .
- the wafer guide 203 comprises two opposing guide plates 203 a , three guide rods 203 b (see FIG.
- the guide arm 203 c has a horizontally extending portion at the top thereof to facilitate the handling of the wafer guide 203 .
- the top of the inner bath 212 is open.
- the outer bath 216 is covered with a lid 217 . Any of the cleaning liquid that overflows the inner bath 21 is gathered in the outer bath 216 . From there, the over-flown cleaning liquid 213 a is drained from the cleaning section 210 .
- the lower portion of the outer bath 216 is preferably funnel-shaped to facilitate the draining of the cleaning liquid 213 a.
- Cleaning liquid lines 214 for supplying and draining the cleaning liquid 213 are connected to the bottom of the inner bath 212 .
- a cleaning water supply tube line 214 a constitutes a cleaning water supply unit that supplies the cleaning liquid to the inner bath 212 from a cleaning water supply source (not shown).
- a cleaning water draining unit 230 includes an outer bath cleaning water drain tube line 214 b and an inner bath cleaning water drain tube line 214 c .
- One end of the outer bath cleaning water drain tube line 214 b is connected to the funnel-shaped bottom of the outer bath 216 , and the other end thereof is connected to a common drain tube line 214 d .
- a first drain valve 214 V 1 is provided in-line with the outer bath cleaning water drain tube line 214 b .
- the inner bath cleaning water drain tube line 214 c extending from the bottom of the inner bath 212 branches into a first inner bath cleaning water drain tube line 214 c 1 and a second inner bath cleaning water drain tube line 214 c 2 .
- the first inner bath cleaning water drain tube line 214 c 1 and the second inner bath cleaning water drain tube line 214 c 2 are connected to the common drain tube line 214 d.
- a second drain valve 214 V 2 is provided in-line with the first inner bath cleaning water drain tube line 214 c 1
- a draining pump 214 P is provided in-line with the second inner bath cleaning water draining tube line 214 c 2 .
- the drying apparatus 200 also includes an isopropyl alcohol supply unit 220 for supplying isopropyl alcohol to the cleaning section 210 . More specifically, the isopropyl alcohol supply unit 220 supplies heated isopropyl alcohol liquid onto the cleaning liquid 213 to form an isopropyl alcohol liquid layer on the cleaning liquid 213 . Isopropyl alcohol as a liquid has a surface tension that is smaller than that of the cleaning liquid. The heated isopropyl alcohol liquid is also partially volatilized to form an isopropyl alcohol ambient at the upper portion of the outer bath 216 , i.e., over the cleaning liquid 213 .
- isopropyl alcohol supply unit 220 is preferably operated to supply the cleaning section with isopropyl alcohol vapor while the cleaning liquid 213 is being drained to thereby maintain the ambient of isopropyl alcohol in the cleaning section 210 .
- the isopropyl alcohol supply unit 220 includes an isopropyl alcohol tank 224 partially filled with liquid isopropyl alcohol 222 .
- the tank 224 is connected to an isopropyl alcohol supply tube line 232 by which the tank 224 is continuously supplied with isopropyl alcohol liquid.
- a pressurizing unit 225 is provided at the upper portion of the tank 224 for pressurizing the isopropyl alcohol liquid 222 .
- the pressurizing unit 225 may exert hydraulic pressure or pneumatic pressure on the isopropyl alcohol liquid 222 .
- the pressurizing unit 225 employs nitrogen gas to pressurize the isopropyl alcohol liquid.
- the pressurizing unit 225 includes a nitrogen gas supply tube line 226 and a nitrogen gas supply source 228 .
- the pressurizing unit 225 may employ an inert gas such as argon or helium instead of nitrogen.
- One end of the nitrogen gas supply tube line 226 is connected with a nitrogen gas supply source 228 , and the other end thereof is disposed over the isopropyl alcohol liquid 222 .
- the nitrogen gas supplied from the nitrogen gas supply source 228 via the nitrogen gas supplying tube line 226 exerts pressure on the surface of the isopropyl alcohol liquid 222 . Such pressure causes the isopropyl alcohol liquid 222 to be forced from the tank 224 .
- the isopropyl alcohol liquid 222 is supplied to the upper portion of inner bath 212 via an isopropyl alcohol supply tube line 234 .
- One end of the isopropyl alcohol supply tube line 234 is connected to the isopropyl alcohol tank 224 .
- the isopropyl alcohol supplying tube line 234 branches into a first isopropyl alcohol supply tube line 234 a and a second isopropyl alcohol supply tube line 234 b .
- the outlets of the first and second supply tube lines 234 a and 234 b are disposed over the inner bath 212 of the cleaning section 210 .
- First and second supply tube lines 234 a and 234 b are preferable in terms of their ability to supply the isopropyl alcohol efficiently to the inner bath 212 , and to form a layer of isopropyl alcohol liquid uniformly on the cleaning liquid, etc.
- the isopropyl alcohol supply tube line 234 may nonetheless extend to the upper portion of the inner bath 212 without being branched or may branch into three or more supply tube lines within the purview of the present invention.
- FIG. 3 shows the isopropyl alcohol liquid being supplied into the inner bath from the front and rear directions of the wafer guide 203 .
- the isopropyl alcohol liquid is preferably introduced into the inner bath 211 from the right and left sides of the wafer guide 203 as shown in FIG. 4.
- First and second heaters 250 a and 250 b are disposed around the outlets of the first and second supply tube lines 234 a and 234 b , i.e., adjacent locations where the first and second supply tube lines 234 a and 234 b enter the outer bath 216 .
- the first and second heaters 250 a and 250 b heat the isopropyl alcohol liquid 222 flowing through the first and second supply tube lines 234 a and 234 b so that heated isopropyl alcohol liquid 222 is supplied to the inner bath 212 .
- the temperature of the first and second heaters 250 a and 250 b is set to be higher than 50° C. and lower than the boiling point of isopropyl alcohol (approximately 83° C. at atmospheric pressure). Preferably, the temperature of the first and second heaters 250 a and 250 b is set to be about 60 ⁇ 70° C.
- the isopropyl alcohol liquid enters the cleaning section 210 at a temperature of about 40 ⁇ 70° C., preferably at about 50 ⁇ 60° C. If the temperature of the first and second heaters 250 a and 250 b were lower than 50° C., the isopropyl alcohol entering the cleaning section 210 would be unsuitable for forming the isopropyl alcohol ambient. On the other hand, if the temperature of the first and second heaters 250 a and 250 b were higher than the boiling point of isopropyl alcohol, the isopropyl alcohol would enter the cleaning section 210 while boiling.
- a flow control meter 260 is disposed in-line with the isopropyl alcohol supply tube line 234 upstream of the first and second supply tube lines 234 a and 234 b .
- the flow control meter 260 allows only a constant amount of isopropyl alcohol liquid 222 to flow for a prescribed time period through the isopropyl alcohol supply tube line 234 so that a proper amount of the isopropyl alcohol liquid 222 is supplied to the inner bath 212 .
- the isopropyl alcohol liquid layer formed on the cleaning liquid 213 should have a thickness of approximately 1 ⁇ 3 mm, preferably 1.5 ⁇ 2.5 mm, for about 4 seconds. If the thickness of the liquid layer of isopropyl alcohol is less than about 1 mm or larger than 3 mm, too many particles will remain on the wafer after the drying process. Therefore, the flow meter 260 regulates the flow of the isopropyl alcohol to such a rate that the isopropyl alcohol liquid layer formed on the cleaning liquid 213 acquires a thickness within the desired range.
- the drying apparatus 200 of the present invention also includes a nitrogen gas supply unit 240 comprising a nitrogen gas supply tube line 242 and a nitrogen gas supply source 246 .
- a nitrogen gas supply unit 240 comprising a nitrogen gas supply tube line 242 and a nitrogen gas supply source 246 .
- One end of the nitrogen gas supply tube line 242 is connected to the nitrogen gas supplying tube line 246 , and an outlet thereof is disposed at the upper portion of the outer bath 216 .
- FIG. 4 shows the arrangement of the nitrogen gas supply tube line 242 and the first and second isopropyl alcohol supply tube lines 234 a and 234 b with respect to the cleaning section 210 .
- the outlet of the nitrogen gas supply tube line 242 is disposed at a level above the outlets of the first and second isopropyl alcohol supply tube lines 234 a and 234 b relative to the outer bath 216 .
- the nitrogen gas supply tube line 242 has a plurality of holes 242 a that allow the nitrogen gas to be supplied uniformly throughout the upper portion of the outer bath 216 .
- a heater 244 for heating the nitrogen gas is provided in-line with the nitrogen gas supply tube line 242 upstream of the outer bath 216 .
- the temperature of the heater 244 is controlled so that the nitrogen gas entering the cleaning section 210 produces a suitable nitrogen gas ambient.
- the nitrogen gas should have a temperature of about 70 ⁇ 90° C., and more preferably, a temperature of about 80° C.
- the heater 244 must be regulated to have a temperature in the range of 100 ⁇ 200° C., and preferably to be about 150° C.
- the wafer guide 203 loaded with the wafers 201 is placed into the inner bath 212 in the direction of arrows A-A in FIG. 4.
- the cleaning liquid 213 such as DIW
- the cleaning liquid 213 is supplied to the inner bath 212 via the cleaning water supply tube line 214 a .
- the cleaning liquid 213 is continuously supplied from the lower portion of the inner bath 212 so that the cleaning liquid 213 overflows the inner tub 212 .
- the over-flown cleaning liquid 213 a gathers in the funnel-shaped lower portion of the outer bath 216 , and is drained therefrom via the first cleaning liquid draining tube line 214 b and the common drain tube line 214 d .
- the first drain valve 214 V 1 in the first drain tube line 214 b is obviously open.
- the wafer is washed using the DIW for about 300 seconds.
- nitrogen gas is supplied from the nitrogen gas supply source 246 into the outer bath 216 to create a nitrogen gas ambient within the outer bath 216 .
- the nitrogen gas supplied from the nitrogen gas supply source 246 passes through the nitrogen gas supply tube line 242 , whereby it is heated by heater 244 to approximately 70 ⁇ 90° C., and preferably to about 80° C.
- the heated nitrogen gas enters the upper portion of the outer bath 216 via the holes 242 a in the nitrogen gas supply tube line 242 such that the nitrogen gas ambient is uniform throughout the inside of outer bath 216 .
- FIG. 5 b nitrogen gas is supplied from the nitrogen gas supply source 246 into the outer bath 216 to create a nitrogen gas ambient within the outer bath 216 .
- the nitrogen gas supplied from the nitrogen gas supply source 246 passes through the nitrogen gas supply tube line 242 , whereby it is heated by heater 244 to approximately 70 ⁇ 90° C., and preferably to about 80° C.
- the heated nitrogen gas enters the upper portion of the outer bath 216 via the holes 242
- step S 20 Thereafter, the second drain valve 214 V 2 disposed in the first inner bath drain tube line 214 c 1 is opened for a short time period to drain some of the cleaning liquid 213 , whereby the water level of the cleaning liquid 213 in the inner bath 212 drops slightly.
- the drain pump 214 P in the second inner bath drain tube line 214 c 2 may be operated to drain the cleaning liquid 213 .
- the second drain valve 214 V 2 is closed (or the pump 214 P is turned off) before the wafers 201 are exposed.
- the difference in water level ⁇ H of the cleaning liquid 213 during this process (step S 30 ) is preferably approximately 5 mm.
- heated isopropyl alcohol liquid 222 a is supplied to the inner bath 212 (step S 40 ).
- nitrogen gas under pressure is supplied from the nitrogen gas supply source 228 to the isopropyl alcohol tank 224 via the nitrogen gas supply tube line 226 .
- the nitrogen gas exerts pressure on the surface of the isopropyl alcohol liquid 222 in the tank 224 . Accordingly, the isopropyl alcohol liquid 222 is forced from the tank and into isopropyl alcohol supply tube line 234 .
- the isopropyl alcohol liquid 222 is introduced into the cleaning bath 210 at a constant rate due to the flow control meter 260 .
- the amount of liquid isopropyl alcohol 222 a allowed to flow into the inner bath 212 is sufficient to form an isopropyl alcohol liquid layer 215 having a thickness of 1 ⁇ 3 mm, and preferably about 2.1 mm, on the cleaning liquid 213 .
- the total amount of the isopropyl alcohol 222 a admitted into the inner bath 212 depends on the surface area of the cleaning liquid 213 , i.e., the size of the inner bath 212
- the thickness of the isopropyl alcohol liquid layer 215 is independent thereof.
- only a small amount of isopropyl alcohol 222 a is introduced into the inner bath 212 . Accordingly, it takes only a few seconds (four seconds in the present embodiment) to feed the heated isopropyl alcohol into the inner bath 212 .
- the liquid isopropyl alcohol 222 having passed through the flow control meter 260 is divided into two parts by the first supplying tube line 234 a and the second supplying tube line 234 b . Then the isopropyl alcohol 222 is heated by the first and second heaters 250 a and 250 b just before being introduced into the outer bath 216 .
- the heaters 250 a and 250 b heat the isopropyl alcohol to a temperature of 50° C. or so.
- the heated isopropyl alcohol liquid 222 a spills from the outlets of the first and second receiving tube lines 234 a and 234 b onto the upper surface of the cleaning liquid 213 .
- the isopropyl alcohol liquid 222 a thus quickly forms an isopropyl alcohol liquid layer 215 on the upper surface of the cleaning liquid 213 , and is partially evaporated.
- the isopropyl alcohol vapor mixes with the nitrogen ambient in the upper portion of the outer bath 216 . Roughly 10 seconds are required for forming the isopropyl alcohol liquid layer 215 (step S 50 ).
- the heated nitrogen gas is preferably supplied intermittently to the upper portion of the outer bath 216 via the nitrogen gas supply tube line 242 .
- a separate isopropyl alcohol gas supply tube line may be connected to the upper portion of the outer bath 216 .
- isopropyl alcohol vapor is introduced directly into the upper portion of the outer bath 216 while the nitrogen gas is being supplied via the nitrogen gas supply tube line 242 .
- the line may be connected to the nitrogen gas supply tube line 242 so that isopropyl alcohol vapor is mixed with the nitrogen gas so that the isopropyl alcohol vapor is forced to fill the area between the outer bath 216 and the inner bath 212 .
- the area between the outer bath 216 and the inner bath 212 can alternatively be filled with isopropyl alcohol vapor by operating the first and second heaters 250 a and 250 b to heat the isopropyl alcohol liquid remaining in the first and second receiving tube lines 234 a and 234 b . By doing so, the heated liquid isopropyl alcohol is evaporated to produce isopropyl alcohol vapor 222 b .
- the isopropyl alcohol vapor 222 b exits the outlets of the first and second receiving tube lines 234 a and 234 b and expands into the upper portion of outer bath 216 .
- step S 60 a process of draining the cleaning liquid 213 is initiated (step S 60 ).
- the pump 214 P is turned on whereupon the cleaning liquid 213 is drawn through the second inner bath drain tube line 214 c 2 of the inner bath drain tube line 214 c and into the common drain tube line 214 d at a constant speed. If the cleaning liquid 213 were drained too fast, the isopropyl alcohol liquid layer 215 would break apart and the Marangoni effect would be lost. Draining the cleaning liquid too slowly is disadvantageous in terms of the efficiency of the cleaning process.
- the pump 214 P is operated to drain the cleaning liquid 213 at such a speed that the water level of the cleaning liquid 213 in the inner bath 216 drops by about 1.5 to 2.5 mm/sec.
- the isopropyl alcohol layer 215 is maintained so that water spots on the wafers 201 are eliminated by the Marangoni effect.
- FIG. 6 shows how the cleaning liquid 213 and the isopropyl alcohol layer 215 behave around the wafers 201 during the draining process illustrated in FIG. 5C.
- the cleaning liquid 213 is gradually drained, portions of the cleaning liquid 213 and the isopropyl alcohol layer 215 closest to the wafers 201 remain adhered to the wafers at a level above the other portions of the cleaning liquid 213 and the isopropyl alcohol layer 21 .
- the isopropyl alcohol has a surface tension that is smaller than that of the DIW, fluid flows from isopropyl alcohol layer 215 toward the cleaning liquid 213 , thereby preventing the fluid from remaining on the wafers 201 .
- the isopropyl alcohol is preferably continuously heated while the cleaning liquid 213 is being drained so that isopropyl alcohol vapor is provided at the upper portion of the outer bath 216 , i.e., over the cleaning liquid 213 and liquid isopropyl alcohol layer 215 . This process stabilizes the isopropyl alcohol layer 215 on the cleaning liquid 213 as the cleaning liquid 213 is being drained. This, of course, enhances the cleaning effect.
- the cleaning liquid 213 is drained for about 145 ⁇ 240 seconds.
- P 1 in FIG. 8 the first and second heaters 250 a and 250 b are turned off.
- the isopropyl alcohol vapor 222 b is no longer supplied into the outer bath 216 .
- the supplying of the heated nitrogen gas is also stopped.
- the second valve 214 V 2 disposed in the first inner bath drain tube line 214 c 1 may be open.
- the pump 214 P in the second inner bath drain tube line 214 c 2 remains operating to thereby completely drain the cleaning liquid 213 from the inner bath 212 .
- the heated nitrogen gas is injected into the outer bath 216 via the nitrogen gas supply tube line 242 to complete the drying process.
- the lower peripheral portions of the wafers that are the last portions to separate from the cleaning liquid
- any concave portions of the wafers such as those defining contact holes, are dried.
- the wafer guide 203 loaded with the wafers 201 is pulled out of the cleaning bath 210 and is transferred to another apparatus.
- FIG. 12 shows a second embodiment of a method of and an apparatus for drying a wafer according to the present invention.
- the apparatus 300 for drying a wafer includes an outer bath draining unit comprising an outer bath drain tube line 214 b connected to the outer bath 216 and a first drain tube valve 214 V 1 disposed in the drain tube line 214 b .
- the cleaning liquid 213 a over-flowing the inner bath 212 during the washing process gathers in the funnel-shaped lower portion of the outer bath 216 .
- the cleaning liquid 213 is then drained from the outer bath 216 via the drain tube line 214 b.
- the apparatus 300 for drying a wafer also includes an inner bath draining unit an inner bath drain tube line 214 c and a second drain valve 214 V 2 disposed in the inner bath drain tube line 214 c .
- the second drain valve 214 V 2 is opened to drain some of the cleaning liquid 213 from the inner bath. Specifically, the cleaning liquid is drained until the level thereof in the inner bath 216 drops by approximately 5 mm.
- the drying apparatus 300 further includes a wafer elevating unit 301 for raising the wafers 201 .
- the wafer elevating unit 301 comprises a support stand 350 , a piston support unit 340 , a power transfer mechanism 330 , a piston shaft 320 , and a coupling unit 310 .
- the support stand 350 is disposed to one side of the lower portion of the outer bath 216 .
- the piston support unit 340 has central through-hole and is fixed to the support stand 340 .
- the piston shaft 320 extends freely through the through-hole of the piston support unit 340 so as to be capable of reciprocating.
- the coupling unit 310 couples the upper end of the piston shaft 320 and the wafer guide arm 203 c .
- the piston shaft 320 coupled to the wafer guide arm 203 c moves the wafer guide 203 up and down to immerse the wafers 201 in the cleaning liquid 213 and to raise them out of the cleaning liquid 213 .
- the piston shaft 320 is connected to a power generating unit 332 , such as a motor, via the power transfer mechanism 330 .
- the power transfer mechanism 330 may be a gear box, or a belt and pulley system configured to transmit the rotary output of the power transferring unit 332 to the piston shaft 320 as rectilinear motion.
- the power transfer mechanism 330 thus can move the piston shaft 320 vertically in either direction.
- the wafer guide 203 loaded with the wafers 201 is placed within the inner bath 212 .
- the cleaning liquid 213 such as DIW, is fed into the inner bath 212 via the cleaning liquid supply tube line 214 a to start the washing process (step S 110 ).
- the washing process is identical to that described with respect to step S 10 of FIGS. 7 and 8.
- step S 120 in FIG. 13 nitrogen gas is supplied into the outer bath 216 for producing a drying ambient. This process is identical to that described with respect to step S 20 of FIGS. 7 and 8.
- step S 130 the second drain valve 214 V 2 is opened for a short period of time to drain the cleaning liquid 213 from the inner bath 212 and thereby reduce the level of the cleaning liquid 213 in the inner bath 212 slightly.
- step S 130 heated liquid isopropyl alcohol 222 a is supplied from the isopropyl alcohol supplying unit 220 into the inner bath 212 via the isopropyl supply tube line 234 (step S 140 ). This process is identical to that described with respect to step S 40 of FIGS. 7 and 8.
- the heated isopropyl alcohol liquid 222 a quickly forms a liquid isopropyl alcohol layer 215 on the surface of the cleaning liquid 213 , and at the same time partially evaporates to form an isopropyl alcohol ambient in the upper portion of outer bath 216 (step S 150 ). This process is identical to that described with respect to step S 50 of FIGS. 7 and 8.
- step S 160 the wafer elevating unit is preferably operated to raise the wafers at a speed of 1.5 ⁇ 2.5 mm/sec as in step S 60 .
- the wafers 201 are completely removed from the cleaning liquid 213 .
- the first and second heaters 250 a and 250 b are turned off and the supplying of the isopropyl alcohol vapor 222 b ceases.
- the supplying of the heated nitrogen ceases.
- the second drain valve 214 V 2 is opened to thoroughly drain the cleaning liquid 213 from the inner bath 212 .
- the heated nitrogen gas is introduced into the outer bath 216 via the nitrogen gas supply tube line 242 to complete the drying process (step S 170 ).
- the wafer guide 203 loaded with the wafers 201 is transferred from the outer bath 216 to another processing apparatus.
- the wafers 201 were washed for 300 seconds using DIW as the cleaning liquid.
- the heater 244 was then operated at about 150° C. to heat the nitrogen gas to about 70 ⁇ 90° C.
- the heated nitrogen gas was supplied to the upper portion of the outer bath 216 via the nitrogen gas supply tube line 242 for 60 seconds and at a pressure of 3 kg/cm 2 .
- the second drain valve 214 V 2 in the first inner bath drain tube line 214 c 1 was opened to lower the level of the cleaning liquid 213 in the inner bath 212 by as much as 5 mm.
- the second drain valve 214 V 2 was closed, and the first and second heaters 250 a and 250 b were set at 70° C.
- the isopropyl alcohol liquid layer 215 formed on the surface of the cleaning liquid 213 as a result had a thickness of about 2.1 mm.
- the heated nitrogen gas was supplied into the upper portion of the outer bath 216 while the first and second heaters 250 a and 250 b were operated to produce the isopropyl alcohol vapor 222 b .
- the cleaning liquid 213 was drained from the inner bath 212 at a rate of 2 mm/sec using the pump 214 P disposed in the second inner bath drain tube line 214 c 2 . This draining process was carried out for about 145 seconds or 240 seconds until the level of the cleaning liquid 213 in the inner bath 212 sank below the wafers 201 .
- the first and second heaters 250 a and 250 b were turned off.
- the supplying of the heated nitrogen gas was ceased, and the second drain valve 214 V 2 disposed in the second inner bath drain tube line 214 c 2 was opened to thoroughly drain the remaining cleaning liquid 213 and the isopropyl alcohol liquid layer 215 from the inner bath 212 .
- the heated nitrogen gas was supplied into the outer bath for 300 seconds to dry the wafers 201 completely.
- the number of particles having a diameter of at least 0.12 ⁇ m on the wafer prior to the washing operation was compared to that after the washing and drying operation. Three wafers were sampled from each lot of 24 wafers, one each from the front, center and rear of the lot. Ten lots of the wafers were tested in total.
- FIG. 9 shows the change in the number of particles before and after the cleaning operation for the sampled wafers of the ten lots.
- a negative ( ⁇ ) number denotes a decreased number of particles and a positive (+) number denotes an increased number of particles.
- the plot using the diamond-shaped symbol is a result from the wafers sampled at the rear of the wafer guide
- the plot using a square-shaped symbol is a result from the wafers sampled at the center portion of the wafer guide
- the plot using triangle-shaped symbol is a result from the wafers sampled at the front of the wafer guide.
- the graph plotted using the character X is the average result from the sampled wafers.
- the change in the number of particles before and after the cleaning of the wafers at the rear of the wafer guide was ⁇ 4.4 on average, that at the center of the wafer guide was 2.4 on average, and that at the rear of the wafer guide was 3.2 on average.
- the average change in the number of particles of all of the sampled wafers was 0.4.
- the isopropyl alcohol liquid was employed at room temperature instead of being heated.
- the nitrogen gas was introduced into the outer bath at room temperature instead of being heated.
- the isopropyl alcohol liquid was employed at room temperature instead of being heated, and was introduced into the outer bath at room temperature instead of being heated.
- the cleaning and drying operations were conducted in the same manner as with Experiment 1.
- the wafers were examined for changes in the number of particles having a diameter of at least 0.12 ⁇ m before and after the washing and drying operations.
- Experiment 5 was conducted to provide a comparison of the conventional wafer drying method and that according to the present invention in terms of the variation in the number of particles on the wafers.
- FIG. 10 is a graph of the results.
- the plot using the square-shaped symbol is the average result of examining lots of the wafers cleaned according to the present invention
- the plot using the diamond-shaped symbol is the average result of examining wafers cleaned using the conventional apparatus of FIG. 1.
- the isopropyl alcohol liquid layer must have a thickness of about 1 mm to 3 mm if a satisfactory limit on the particles left by water spots after the cleaning process is to be met.
- the preferred thickness of the isopropyl alcohol liquid layer is 1.5 ⁇ 2.5 mm, and more preferably at least 2 mm and no more than 2.5 mm.
- the present invention in the process of drying a wafer using the Marangoni effect, heated liquid isopropyl alcohol is supplied onto the surface of the cleaning liquid.
- the isopropyl alcohol diffuses quickly to form an isopropyl liquid layer. Therefore, as compared with the conventional method in which the isopropyl alcohol liquid layer is formed by an isopropyl alcohol mist carried in nitrogen gas, the present invention is more efficient.
Abstract
Description
- 1. Field of the Invention
- The present invention relates to a method of and an apparatus for drying a wafer. More particularly, the present invention relates to a method of and an apparatus for drying a wafer using isopropyl liquid after the wafer is cleaned following a semiconductor manufacturing process.
- 2. Description of the Related Art
- Semiconductor devices or semiconductor chips are manufactured by processing a wafer that is usually formed of silicon. The wafer is typically subjected to a series of semiconductor device manufacturing processes such as photolithography, chemical or physical vapor deposition and plasma etching.
- After executing these processes, foreign material such as chemicals or dust remains on the surface of the wafer. In order to assure the quality of the semiconductor devices, the foreign material must be removed from the surface of the wafer. The cleaning process used to remove the foreign material involves both washing and drying the wafer.
- In particular, the wafer may be washed using de-ionized water (hereinafter referred to as “DIW”). Because the DIW will eventually dissolve the silicon, the wafer must be completely dried after being washed with the DIW or else water spots will be formed.
- In addition, a method of using isopropyl alcohol to enhance the drying of a wafer has been developed. For example, Japanese Patent Laid-Open Publication No. Hei 8-61846 discloses a method of directly spraying liquid isopropyl alcohol over a wafer, forming a mixture of the water and the isopropyl alcohol on the surface of the wafer, and volatilizing the mixture by means of a high temperature nitrogen gas. In addition, U.S. Pat. No. 6,029,371 issued to Kamikawa et al. discloses a method of drying a wafer by directly spraying a washed wafer with a drying gas comprising heated isopropyl alcohol and nitrogen.
- Also, drying apparatuses using isopropyl alcohol are disclosed in U.S. Pat. No. 5,634,978 issued to Mohindra et al., U.S. Pat. No. 5,855,077 issued to Chang-Hyun Nam et al., U.S. Pat. No. 4,633,893 issued to McConnell et al., and U.S. Pat. No. 4,911,761 also issued to McConnell et al. These drying apparatuses execute a method in which the isopropyl alcohol is introduced as a mist over the cleaned wafer to eliminate the water on the wafer.
- FIG. 1 shows one example of a
conventional apparatus 100 that works on the Marangoni effect to dry the wafer using an isopropyl alcohol mist. Theapparatus 100 includes a cleaning section (or a rinsing section) 110 containing a cleaning liquid (or rinsing liquid) 113 for cleaning (or rinsing) the wafer. Thecleaning section 110 in turn includes aninner bath 112 having an upper open end, and anouter bath 116 covered with alid 117. Theouter bath 116 andlid 117 enclose theinner bath 112. Awafer 101 is immersed in the cleaningliquid 113 of theinner bath 112 for cleaning. Once the cleaningliquid 113 over-flows theinner bath 112, the over-flown cleaningliquid 113 a gathers in theouter bath 116 from where it is drained from thecleaning section 110. - A cleaning liquid
supply tube line 114 a is connected to theinner bath 112 at the bottom thereof. First and second cleaning liquiddrain tube lines inner bath 112 and theouter bath 116, respectively, at the bottoms thereof. The cleaning liquidsupply tube line 114 a supplies the cleaningliquid 113, such as DIW, to theinner bath 112. The first cleaning liquiddrain tube line 114 b drains the cleaningliquid 113 a which has over-flown theinner bath 112 into theouter bath 116. The second cleaning liquiddrain tube line 114 c gradually drains the cleaningliquid 113 from within theinner bath 112. - The
apparatus 100 for drying the wafer is also equipped with an isopropyl alcohol mistsupply tube line 134 for supplying the isopropyl alcohol mist from an isopropyl alcohol supply unit (not shown). The isopropyl alcohol supply unit makes the isopropyl alcohol bubble by using nitrogen as a carrier gas to form the isopropyl alcohol mist. Then, the isopropyl alcohol mist and nitrogen are supplied to the upper portion of theouter bath 116 via the isopropyl alcohol mistsupply tube line 134. Adiffuser 136 is furnished at the central portion of thelid 117 of theouter bath 116 for consistently diffusing the isopropyl alcohol mist and nitrogen throughout the inside of theouter bath 116. - In addition, a nitrogen gas
supply tube line 140 is connected to thelid 117 for supplying heated nitrogen gas into theouter bath 116 during the drying process to create a drying ambient. - The
conventional apparatus 100 for drying a wafer operates as follows. - Once a
wafer guide 103 loaded withwafers 101 is seated within theinner bath 112, the cleaningliquid 113, such as the DIW, is supplied to theinner bath 112 via the cleaning liquidsupply tube line 114 a to initiate the cleaning operation. The cleaning liquid is supplied into theinner bath 112 at such a rate that it overflows theinner bath 112 during the cleaning operation. The over-flown cleaningliquid 113 a is gathered in theouter bath 116 and drained from the bottom of theouter bath 116 via the first cleaning liquiddrain tube line 114 b. - Once the cleaning operation is complete, the process of drying the
wafer 101 begins. FIGS. 2A, 2B and 2C are schematic diagrams illustrating the drying process. - Referring to FIG. 2A, after the cleaning process is complete, the nitrogen gas and the isopropyl alcohol mist entrained thereby are introduced via the isopropyl
supply tube line 134 and diffuser 136 into the upper portion of theouter bath 116. Thus, the ambient inouter bath 116 is converted into a drying ambient. At this time, approximately 50 cc of the isopropyl alcohol mist is supplied. Also, at this time, the heated nitrogen gas is supplied into theouter bath 116 via the nitrogen gassupply tube line 140 connected to thelid 117. - Referring to FIG. 2B, the
cleaning liquid 113 is drained via thedrain tube line 114 c while the nitrogen gas is supplied via the nitrogen gassupply tube line 140. At this time, thecleaning liquid 113 is drained at a constant rate via the seconddrain tube line 114 c. The height of the cleaningliquid 113 is decreased at a rate of about 3 mm/sec. During the draining operation, the water spots on thewafers 101 are eliminated by means of the Marangoni effect created by the isopropyl alcohol. Referring to FIG. 2C, once the cleaningliquid 113 is completely drained to a level below thewafers 101, the last of the heated nitrogen gas is introduced into theouter bath 116 via the nitrogen supplyingtube line 140, thereby completing the drying process. - In addition to this conventional method, Japanese Patent Laid-Open Publication Nos. Hei 11-87305, Hei10-154689 and Hei10-22257 disclose methods of drying a wafer in which an isopropyl alcohol mist is used. In these methods, an isopropyl alcohol liquid layer is formed by the mist over a cleaning liquid, and the wafers are raised from the cleaning liquid into the isopropyl alcohol liquid layer, thereby drying the wafer.
- According to all of these heretofore known methods, the mist of isopropyl alcohol is supplied to the outer bath using nitrogen as a carrier gas. Therefore, the amount of isopropyl alcohol injected into the outer bath is determined by measuring the reduction in the amount of isopropyl alcohol in the isopropyl alcohol supply unit. For this reason, the amount of isopropyl alcohol used for forming the isopropyl alcohol layer cannot be accurately determined. Furthermore, it is difficult to accurately control the amount of isopropyl alcohol being supplied.
- Moreover, the isopropyl alcohol sprayed by the diffuser adheres to the side wall of the outer bath. In this case, the isopropyl alcohol is likely to fall as drops onto the wafer. These drops create wafer defects.
- Additionally, a large amount of time is required to form from the mist a sufficient layer of isopropyl alcohol above the cleaning liquid within the inner bath for producing the Marangoni effect. The overall processing time is thus significant. Moreover, such a mist is likely to be exhausted if the outer bath is not completely sealed.
- In view of these problems of the conventional art, a method has been proposed in which the isopropyl alcohol liquid is supplied directly onto the upper portion of the cleaning liquid. For example, Japanese Patent Laid-open No. Hei 9-213672 discloses a method in which an isopropyl alcohol layer is formed over a cleaning liquid in which a wafer is immersed, and the wafer is dried while ascending from the cleaning liquid. In this method, the isopropyl alcohol layer formed on the cleaning liquid has a thickness of about 5 mm, and the wafer is to raised gradually from the cleaning liquid.
- However, the above-described method requires a large quantity of isopropyl alcohol and a relatively long amount of time for forming the isopropyl alcohol liquid layer. Also, the drying effect produced by this method is so insufficient that water spots remain after the wafer is cleaned. The water spots leave too many particles on the wafer.
- Therefore, the object of the present invention is to overcome the above-described drawbacks of the conventional prior art.
- More specifically, a first object of the present invention is to provide a highly effective and time-efficient method of drying a wafer using the Marangoni effect. A second object of the present invention is to provide an apparatus for drying a wafer particularly suitable for performing such a method.
- To achieve the first object, the present invention provides a method of drying an object comprising supplying heated inert gas over a cleaning liquid in which the object is immersed, heating a liquid having a smaller surface tension than that of the cleaning liquid, and then supplying the heated liquid onto the cleaning liquid in a fluid state. This forms a liquid layer on the cleaning liquid, and an ambient over the cleaning liquid comprising the vapor of the heated liquid and the inert gas. Then, the object is removed from the cleaning liquid while the heated liquid layer is maintained. The object is dried further by supplying more of the heated inert gas into the ambient surrounding the object.
- The heated inert gas is preferably nitrogen gas, and the liquid used to form a layer on the cleaning liquid is preferably isopropyl alcohol.
- To achieve the second object, the present invention provides a cleaning apparatus comprising a cleaning section housing the cleaning liquid for cleaning the object, and an isopropyl alcohol supplying unit that supplies heated liquid isopropyl alcohol onto the cleaning liquid to form an isopropyl alcohol liquid layer and an isopropyl alcohol ambient over the cleaning liquid, and a nitrogen supply unit that supplies heated nitrogen gas above the cleaning liquid housed in the cleaning section. A separating unit can remove the object from the cleaning liquid while the isopropyl alcohol layer is maintained.
- According to the present invention, to dry the object such as a wafer, the nitrogen gas is heated and supplied into the cleaning section at a location above the cleaning liquid in which the wafer is immersed, and the liquid isopropyl alcohol liquid is heated and supplied directly onto the cleaning liquid. The isopropyl alcohol liquid layer diffuses quickly to form a liquid layer on the cleaning liquid, the liquid isopropyl alcohol liquid supplied in the fluid state also forms an ambient with the nitrogen gas that is non-volatile above the cleaning liquid. The wafer is dried only by removing it from the cleaning liquid into the ambient while only the heated nitrogen gas continues to be supplied.
- The above and other objects, features and advantages of the present invention will become more apparent by referring to the following detailed description of the preferred embodiments thereof made with reference to the attached drawings, of which:
- FIG. 1 is a schematic diagram of a conventional apparatus for drying a wafer;
- FIGS. 2A to2C are schematic diagrams of cleaning sections of the conventional drying apparatus, illustrating a drying process executed by the conventional apparatus;
- FIG. 3 is a schematic diagram of a first embodiment of an apparatus for drying a wafer according to the present invention;
- FIG. 4 is top view of a cleaning section of the drying apparatus showing the arrangement of a nitrogen gas supply tube line and first and second isopropyl alcohol supply tube lines relative to a bath of the cleaning section;
- FIGS. 5A to5D are respective side views of the cleaning section, illustrating a first embodiment of a method of drying a wafer according to the present invention;
- FIG. 6 is a schematic diagram showing the change in the level of cleaning liquid and an isopropyl alcohol layer, which occurs during the draining step shown in FIG. 5B;
- FIG. 7 is a flowchart of the first embodiment of the method of drying a wafer according to the present invention;
- FIG. 8 is a timing chart of the first embodiment of the method for drying the wafer according to the present invention;
- FIG. 9 is a graph plotting the change in the number of particles before and after a wafer is washed and dried in accordance with the method of the present invention;
- FIG. 10 is a graph plotting the change in the number of particles before and after a wafer is washed and dried in accordance with the method of the present invention, using the average values from FIG. 9, and in accordance with a prior art process;
- FIG. 11 is a graph plotting the number of particles before and after a wafer is washed and dried for different amounts of supplied isopropyl alcohol;
- FIG. 12 is a schematic diagram of a second embodiment of an apparatus for drying a wafer according to the present invention; and
- FIG. 13 is a flowchart of the second embodiment of a method of drying a wafer according to the present invention, which method can be performed by the apparatus shown in FIG. 12.
- The preferred embodiments of the present invention will be described in detail hereinafter with reference to accompanying drawings.
-
Embodiment 1 - FIG. 3 shows a first embodiment of an
apparatus 200 for drying a wafer according to the present invention. - The
drying apparatus 200 includes acleaning section 210 containing a cleaningliquid 213 for cleaningwafers 201. DIW may be used as the cleaningliquid 213. Thecleaning section 210, in turn, comprises aninner bath 212 in which thewafers 201 are immersed in the cleaning liquid 213 to be cleaned, and anouter bath 216 enclosing theinner bath 212. Thewafers 201 are loaded on awafer guide 203 that can be seated in thecleaning bath 210. Thewafer guide 203 comprises two opposingguide plates 203 a, threeguide rods 203 b (see FIG. 4) fixed between theguide plates 203 a, and aguide arm 203 c extending upwardly from one of theguide plates 203 a. Theguide arm 203 c has a horizontally extending portion at the top thereof to facilitate the handling of thewafer guide 203. - The top of the
inner bath 212 is open. Theouter bath 216 is covered with alid 217. Any of the cleaning liquid that overflows the inner bath 21 is gathered in theouter bath 216. From there, the over-flown cleaning liquid 213 a is drained from thecleaning section 210. The lower portion of theouter bath 216 is preferably funnel-shaped to facilitate the draining of the cleaning liquid 213 a. -
Cleaning liquid lines 214 for supplying and draining the cleaningliquid 213 are connected to the bottom of theinner bath 212. Of theselines 214, a cleaning watersupply tube line 214 a constitutes a cleaning water supply unit that supplies the cleaning liquid to theinner bath 212 from a cleaning water supply source (not shown). - A cleaning
water draining unit 230 includes an outer bath cleaning waterdrain tube line 214 b and an inner bath cleaning waterdrain tube line 214 c. One end of the outer bath cleaning waterdrain tube line 214 b is connected to the funnel-shaped bottom of theouter bath 216, and the other end thereof is connected to a commondrain tube line 214 d. A first drain valve 214V1 is provided in-line with the outer bath cleaning waterdrain tube line 214 b. The inner bath cleaning waterdrain tube line 214 c extending from the bottom of theinner bath 212 branches into a first inner bath cleaning waterdrain tube line 214 c 1 and a second inner bath cleaning waterdrain tube line 214c 2. The first inner bath cleaning waterdrain tube line 214 c 1 and the second inner bath cleaning waterdrain tube line 214 c 2 are connected to the commondrain tube line 214 d. - Moreover, a second drain valve214V2 is provided in-line with the first inner bath cleaning water
drain tube line 214c 1, and adraining pump 214P is provided in-line with the second inner bath cleaning water drainingtube line 214c 2. - The
drying apparatus 200 also includes an isopropylalcohol supply unit 220 for supplying isopropyl alcohol to thecleaning section 210. More specifically, the isopropylalcohol supply unit 220 supplies heated isopropyl alcohol liquid onto the cleaning liquid 213 to form an isopropyl alcohol liquid layer on the cleaningliquid 213. Isopropyl alcohol as a liquid has a surface tension that is smaller than that of the cleaning liquid. The heated isopropyl alcohol liquid is also partially volatilized to form an isopropyl alcohol ambient at the upper portion of theouter bath 216, i.e., over the cleaningliquid 213. In addition, the isopropylalcohol supply unit 220 is preferably operated to supply the cleaning section with isopropyl alcohol vapor while the cleaningliquid 213 is being drained to thereby maintain the ambient of isopropyl alcohol in thecleaning section 210. - The isopropyl
alcohol supply unit 220 includes anisopropyl alcohol tank 224 partially filled withliquid isopropyl alcohol 222. Thetank 224 is connected to an isopropyl alcoholsupply tube line 232 by which thetank 224 is continuously supplied with isopropyl alcohol liquid. - Also, a pressurizing
unit 225 is provided at the upper portion of thetank 224 for pressurizing theisopropyl alcohol liquid 222. To this end, the pressurizingunit 225 may exert hydraulic pressure or pneumatic pressure on theisopropyl alcohol liquid 222. However, in the preferred embodiment of the present invention, the pressurizingunit 225 employs nitrogen gas to pressurize the isopropyl alcohol liquid. In this case, the pressurizingunit 225 includes a nitrogen gassupply tube line 226 and a nitrogengas supply source 228. Alternatively, the pressurizingunit 225 may employ an inert gas such as argon or helium instead of nitrogen. - One end of the nitrogen gas
supply tube line 226 is connected with a nitrogengas supply source 228, and the other end thereof is disposed over theisopropyl alcohol liquid 222. The nitrogen gas supplied from the nitrogengas supply source 228 via the nitrogen gas supplyingtube line 226 exerts pressure on the surface of theisopropyl alcohol liquid 222. Such pressure causes theisopropyl alcohol liquid 222 to be forced from thetank 224. - The
isopropyl alcohol liquid 222 is supplied to the upper portion ofinner bath 212 via an isopropyl alcoholsupply tube line 234. One end of the isopropyl alcoholsupply tube line 234 is connected to theisopropyl alcohol tank 224. From there, the isopropyl alcohol supplyingtube line 234 branches into a first isopropyl alcoholsupply tube line 234 a and a second isopropyl alcoholsupply tube line 234 b. The outlets of the first and secondsupply tube lines inner bath 212 of thecleaning section 210. First and secondsupply tube lines inner bath 212, and to form a layer of isopropyl alcohol liquid uniformly on the cleaning liquid, etc. However, the isopropyl alcoholsupply tube line 234 may nonetheless extend to the upper portion of theinner bath 212 without being branched or may branch into three or more supply tube lines within the purview of the present invention. - In addition, FIG. 3 shows the isopropyl alcohol liquid being supplied into the inner bath from the front and rear directions of the
wafer guide 203. However, this is shown in the drawing for the sake of simplicity. Actually, the isopropyl alcohol liquid is preferably introduced into the inner bath 211 from the right and left sides of thewafer guide 203 as shown in FIG. 4. - First and
second heaters supply tube lines supply tube lines outer bath 216. The first andsecond heaters isopropyl alcohol liquid 222 flowing through the first and secondsupply tube lines isopropyl alcohol liquid 222 is supplied to theinner bath 212. - The temperature of the first and
second heaters second heaters cleaning section 210 at a temperature of about 40˜70° C., preferably at about 50˜60° C. If the temperature of the first andsecond heaters cleaning section 210 would be unsuitable for forming the isopropyl alcohol ambient. On the other hand, if the temperature of the first andsecond heaters cleaning section 210 while boiling. - Next, a
flow control meter 260 is disposed in-line with the isopropyl alcoholsupply tube line 234 upstream of the first and secondsupply tube lines flow control meter 260 allows only a constant amount ofisopropyl alcohol liquid 222 to flow for a prescribed time period through the isopropyl alcoholsupply tube line 234 so that a proper amount of theisopropyl alcohol liquid 222 is supplied to theinner bath 212. - For example, in order to satisfactorily dry a silicon wafer having a diameter of 300 mm, for example, the isopropyl alcohol liquid layer formed on the cleaning liquid213 should have a thickness of approximately 1˜3 mm, preferably 1.5˜2.5 mm, for about 4 seconds. If the thickness of the liquid layer of isopropyl alcohol is less than about 1 mm or larger than 3 mm, too many particles will remain on the wafer after the drying process. Therefore, the
flow meter 260 regulates the flow of the isopropyl alcohol to such a rate that the isopropyl alcohol liquid layer formed on the cleaningliquid 213 acquires a thickness within the desired range. - The
drying apparatus 200 of the present invention also includes a nitrogengas supply unit 240 comprising a nitrogen gassupply tube line 242 and a nitrogengas supply source 246. One end of the nitrogen gassupply tube line 242 is connected to the nitrogen gas supplyingtube line 246, and an outlet thereof is disposed at the upper portion of theouter bath 216. - FIG. 4 shows the arrangement of the nitrogen gas
supply tube line 242 and the first and second isopropyl alcoholsupply tube lines cleaning section 210. Note, though, the outlet of the nitrogen gassupply tube line 242 is disposed at a level above the outlets of the first and second isopropyl alcoholsupply tube lines outer bath 216. Furthermore, the nitrogen gassupply tube line 242 has a plurality ofholes 242 a that allow the nitrogen gas to be supplied uniformly throughout the upper portion of theouter bath 216. - A
heater 244 for heating the nitrogen gas is provided in-line with the nitrogen gassupply tube line 242 upstream of theouter bath 216. The temperature of theheater 244 is controlled so that the nitrogen gas entering thecleaning section 210 produces a suitable nitrogen gas ambient. To this end, the nitrogen gas should have a temperature of about 70˜90° C., and more preferably, a temperature of about 80° C. To heat the nitrogen gas to such a temperature, considering the initial temperature and flux of the nitrogen gas supplied from nitrogengas supply source 246, theheater 244 must be regulated to have a temperature in the range of 100˜200° C., and preferably to be about 150° C. - The method of cleaning the wafer according to the present invention using the above-described
apparatus 200 shown in FIG. 3 will now be described with reference to FIGS. 4, 5A-5D, 6 and 7. - Referring first to FIGS. 4 and 5A, the
wafer guide 203 loaded with thewafers 201 is placed into theinner bath 212 in the direction of arrows A-A in FIG. 4. Then, the cleaningliquid 213, such as DIW, is supplied to theinner bath 212 via the cleaning watersupply tube line 214 a. During a washing operation, the cleaningliquid 213 is continuously supplied from the lower portion of theinner bath 212 so that the cleaningliquid 213 overflows theinner tub 212. Theover-flown cleaning liquid 213 a gathers in the funnel-shaped lower portion of theouter bath 216, and is drained therefrom via the first cleaning liquid drainingtube line 214 b and the commondrain tube line 214 d. At this time, the first drain valve 214V1 in the firstdrain tube line 214 b is obviously open. As shown in FIGS. 7 and 8 (step S10), the wafer is washed using the DIW for about 300 seconds. - Once the washing process is completed, the drying process of the
wafer 201 begins. Referring to FIG. 5b, nitrogen gas is supplied from the nitrogengas supply source 246 into theouter bath 216 to create a nitrogen gas ambient within theouter bath 216. Specifically, the nitrogen gas supplied from the nitrogengas supply source 246 passes through the nitrogen gassupply tube line 242, whereby it is heated byheater 244 to approximately 70˜90° C., and preferably to about 80° C. The heated nitrogen gas enters the upper portion of theouter bath 216 via theholes 242 a in the nitrogen gassupply tube line 242 such that the nitrogen gas ambient is uniform throughout the inside ofouter bath 216. As shown in FIG. 7, the supplied nitrogen gas maintains a pressure of 2˜4 kg/cm2, and preferably 3 kg/cm2. (step S20) Thereafter, the second drain valve 214V2 disposed in the first inner bathdrain tube line 214c 1 is opened for a short time period to drain some of the cleaningliquid 213, whereby the water level of the cleaning liquid 213 in theinner bath 212 drops slightly. Alternatively, thedrain pump 214P in the second inner bathdrain tube line 214 c 2 may be operated to drain the cleaningliquid 213. Then, the second drain valve 214V2 is closed (or thepump 214P is turned off) before thewafers 201 are exposed. The difference in water level ΔH of the cleaning liquid 213 during this process (step S30) is preferably approximately 5 mm. - Thereafter, heated
isopropyl alcohol liquid 222 a is supplied to the inner bath 212 (step S40). As shown in FIG. 3, nitrogen gas under pressure is supplied from the nitrogengas supply source 228 to theisopropyl alcohol tank 224 via the nitrogen gassupply tube line 226. The nitrogen gas exerts pressure on the surface of theisopropyl alcohol liquid 222 in thetank 224. Accordingly, theisopropyl alcohol liquid 222 is forced from the tank and into isopropyl alcoholsupply tube line 234. Theisopropyl alcohol liquid 222 is introduced into the cleaningbath 210 at a constant rate due to theflow control meter 260. The amount ofliquid isopropyl alcohol 222 a allowed to flow into theinner bath 212 is sufficient to form an isopropylalcohol liquid layer 215 having a thickness of 1˜3 mm, and preferably about 2.1 mm, on the cleaningliquid 213. Although the total amount of theisopropyl alcohol 222 a admitted into theinner bath 212 depends on the surface area of the cleaningliquid 213, i.e., the size of theinner bath 212, the thickness of the isopropylalcohol liquid layer 215 is independent thereof. In the present invention, only a small amount ofisopropyl alcohol 222 a is introduced into theinner bath 212. Accordingly, it takes only a few seconds (four seconds in the present embodiment) to feed the heated isopropyl alcohol into theinner bath 212. - The
liquid isopropyl alcohol 222 having passed through theflow control meter 260 is divided into two parts by the first supplyingtube line 234 a and the second supplyingtube line 234 b. Then theisopropyl alcohol 222 is heated by the first andsecond heaters outer bath 216. - The
heaters isopropyl alcohol liquid 222 a spills from the outlets of the first and secondreceiving tube lines liquid 213. - The
isopropyl alcohol liquid 222 a thus quickly forms an isopropylalcohol liquid layer 215 on the upper surface of the cleaningliquid 213, and is partially evaporated. The isopropyl alcohol vapor mixes with the nitrogen ambient in the upper portion of theouter bath 216. Roughly 10 seconds are required for forming the isopropyl alcohol liquid layer 215 (step S50). - After the heated
liquid isopropyl alcohol 222 a is supplied to theinner bath 212, the heated nitrogen gas is preferably supplied intermittently to the upper portion of theouter bath 216 via the nitrogen gassupply tube line 242. - Also, a separate isopropyl alcohol gas supply tube line may be connected to the upper portion of the
outer bath 216. In this case, isopropyl alcohol vapor is introduced directly into the upper portion of theouter bath 216 while the nitrogen gas is being supplied via the nitrogen gassupply tube line 242. Alternatively, the line may be connected to the nitrogen gassupply tube line 242 so that isopropyl alcohol vapor is mixed with the nitrogen gas so that the isopropyl alcohol vapor is forced to fill the area between theouter bath 216 and theinner bath 212. - The area between the
outer bath 216 and theinner bath 212 can alternatively be filled with isopropyl alcohol vapor by operating the first andsecond heaters receiving tube lines isopropyl alcohol vapor 222 b. Theisopropyl alcohol vapor 222 b exits the outlets of the first and secondreceiving tube lines outer bath 216. - Thereafter (refer to FIG. 5C), a process of draining the cleaning
liquid 213 is initiated (step S60). In this process, thepump 214P is turned on whereupon the cleaningliquid 213 is drawn through the second inner bathdrain tube line 214c 2 of the inner bathdrain tube line 214 c and into the commondrain tube line 214 d at a constant speed. If the cleaningliquid 213 were drained too fast, the isopropylalcohol liquid layer 215 would break apart and the Marangoni effect would be lost. Draining the cleaning liquid too slowly is disadvantageous in terms of the efficiency of the cleaning process. Therefore, thepump 214P is operated to drain the cleaning liquid 213 at such a speed that the water level of the cleaning liquid 213 in theinner bath 216 drops by about 1.5 to 2.5 mm/sec. During the draining operation, theisopropyl alcohol layer 215 is maintained so that water spots on thewafers 201 are eliminated by the Marangoni effect. - FIG. 6 shows how the cleaning
liquid 213 and theisopropyl alcohol layer 215 behave around thewafers 201 during the draining process illustrated in FIG. 5C. As the cleaningliquid 213 is gradually drained, portions of the cleaningliquid 213 and theisopropyl alcohol layer 215 closest to thewafers 201 remain adhered to the wafers at a level above the other portions of the cleaningliquid 213 and the isopropyl alcohol layer 21. Because the isopropyl alcohol has a surface tension that is smaller than that of the DIW, fluid flows fromisopropyl alcohol layer 215 toward the cleaningliquid 213, thereby preventing the fluid from remaining on thewafers 201. Consequently, water spots will not form on thewafers 201 and hence, particles will not be left on thewafers 201 after the cleaning operation. The isopropyl alcohol is preferably continuously heated while the cleaningliquid 213 is being drained so that isopropyl alcohol vapor is provided at the upper portion of theouter bath 216, i.e., over the cleaningliquid 213 and liquidisopropyl alcohol layer 215. This process stabilizes theisopropyl alcohol layer 215 on the cleaning liquid 213 as the cleaningliquid 213 is being drained. This, of course, enhances the cleaning effect. - Referring now to FIG. 5D, the cleaning
liquid 213 is drained for about 145˜240 seconds. At some point in time (P1 in FIG. 8) in this process, when the level of the cleaning liquid 213 lies beneath thewafers 201, the first andsecond heaters isopropyl alcohol vapor 222 b is no longer supplied into theouter bath 216. Also, the supplying of the heated nitrogen gas is also stopped. Under this state, the second valve 214V2 disposed in the first inner bathdrain tube line 214 c 1 may be open. However, thepump 214P in the second inner bathdrain tube line 214 c 2 remains operating to thereby completely drain the cleaning liquid 213 from theinner bath 212. - Finally, the heated nitrogen gas is injected into the
outer bath 216 via the nitrogen gassupply tube line 242 to complete the drying process. In this way, the lower peripheral portions of the wafers (that are the last portions to separate from the cleaning liquid) and any concave portions of the wafers, such as those defining contact holes, are dried. Once the drying process is complete, thewafer guide 203 loaded with thewafers 201 is pulled out of thecleaning bath 210 and is transferred to another apparatus. -
Embodiment 2 - FIG. 12 shows a second embodiment of a method of and an apparatus for drying a wafer according to the present invention.
- This embodiment is similar to that of the first embodiment described with reference to FIGS. 3, 4 and5A to 5D, except that in this embodiment, the wafers are raised to remove them from the cleaning liquid. Accordingly, parts similar to those of the first embodiment of the drying apparatus are designated by the same reference numerals.
- Referring now to FIG. 12, the
apparatus 300 for drying a wafer includes an outer bath draining unit comprising an outer bathdrain tube line 214 b connected to theouter bath 216 and a first drain tube valve 214V1 disposed in thedrain tube line 214 b. As in the first embodiment (refer to FIG. 5A), the cleaning liquid 213 a over-flowing theinner bath 212 during the washing process gathers in the funnel-shaped lower portion of theouter bath 216. The cleaningliquid 213 is then drained from theouter bath 216 via thedrain tube line 214 b. - The
apparatus 300 for drying a wafer also includes an inner bath draining unit an inner bathdrain tube line 214 c and a second drain valve 214V2 disposed in the inner bathdrain tube line 214 c. As described with reference to FIG. 5B, after thewafers 203 have been washed and prior to introducing theheated isopropyl alcohol 222 a onto the surface of the cleaningliquid 213, the second drain valve 214V2 is opened to drain some of the cleaning liquid 213 from the inner bath. Specifically, the cleaning liquid is drained until the level thereof in theinner bath 216 drops by approximately 5 mm. - The
drying apparatus 300 further includes awafer elevating unit 301 for raising thewafers 201. Thewafer elevating unit 301 comprises asupport stand 350, apiston support unit 340, apower transfer mechanism 330, apiston shaft 320, and acoupling unit 310. Thesupport stand 350 is disposed to one side of the lower portion of theouter bath 216. Thepiston support unit 340 has central through-hole and is fixed to thesupport stand 340. Thepiston shaft 320 extends freely through the through-hole of thepiston support unit 340 so as to be capable of reciprocating. Thecoupling unit 310 couples the upper end of thepiston shaft 320 and thewafer guide arm 203 c. Thepiston shaft 320 coupled to thewafer guide arm 203 c moves thewafer guide 203 up and down to immerse thewafers 201 in the cleaningliquid 213 and to raise them out of the cleaningliquid 213. - The
piston shaft 320 is connected to apower generating unit 332, such as a motor, via thepower transfer mechanism 330. Thepower transfer mechanism 330 may be a gear box, or a belt and pulley system configured to transmit the rotary output of thepower transferring unit 332 to thepiston shaft 320 as rectilinear motion. Thepower transfer mechanism 330 thus can move thepiston shaft 320 vertically in either direction. - The method of drying the wafers will now be described with reference to FIG. 13.
- The
wafer guide 203 loaded with thewafers 201 is placed within theinner bath 212. Then, the cleaningliquid 213, such as DIW, is fed into theinner bath 212 via the cleaning liquidsupply tube line 214 a to start the washing process (step S110). The washing process is identical to that described with respect to step S10 of FIGS. 7 and 8. - Once the process of washing the
wafers 201 is complete, the process of drying thewafers 201 begins. First, nitrogen gas is supplied into theouter bath 216 for producing a drying ambient (step S120 in FIG. 13). This process is identical to that described with respect to step S20 of FIGS. 7 and 8. - Thereafter, the second drain valve214V2 is opened for a short period of time to drain the cleaning liquid 213 from the
inner bath 212 and thereby reduce the level of the cleaning liquid 213 in theinner bath 212 slightly (step S130). This process is identical to that described with respect to step S30 of FIGS. 7 and 8. Next, heatedliquid isopropyl alcohol 222 a is supplied from the isopropylalcohol supplying unit 220 into theinner bath 212 via the isopropyl supply tube line 234 (step S140). This process is identical to that described with respect to step S40 of FIGS. 7 and 8. - The heated
isopropyl alcohol liquid 222 a quickly forms a liquidisopropyl alcohol layer 215 on the surface of the cleaningliquid 213, and at the same time partially evaporates to form an isopropyl alcohol ambient in the upper portion of outer bath 216 (step S150). This process is identical to that described with respect to step S50 of FIGS. 7 and 8. - Thereafter, nitrogen gas is supplied to the upper portion of the
outer bath 216 via the nitrogen gassupply tube line 242. At the same time, thepower generating unit 332 is supplied with electric power. The output of thepower generating unit 332 is transmitted to thepiston shaft 320 as rectilinear motion via thepower transfer mechanism 330, to thereby raise thepiston shaft 320. Thewafer guide 203 loaded with thewafers 201 is thus raised until thewafers 201 are removed from the cleaning liquid 213 (step S160). At this time, the wafer elevating unit is preferably operated to raise the wafers at a speed of 1.5˜2.5 mm/sec as in step S60. - As denoted by the dashed lines of FIG. 12, the
wafers 201 are completely removed from the cleaningliquid 213. Then, the first andsecond heaters isopropyl alcohol vapor 222 b ceases. Also, the supplying of the heated nitrogen ceases. Under this state, the second drain valve 214V2 is opened to thoroughly drain the cleaning liquid 213 from theinner bath 212. Thereafter, the heated nitrogen gas is introduced into theouter bath 216 via the nitrogen gassupply tube line 242 to complete the drying process (step S170). After the drying process is completed, thewafer guide 203 loaded with thewafers 201 is transferred from theouter bath 216 to another processing apparatus. -
Experiment 1 - Ten lots of the wafers (one lot consists of 24 wafers) were dried according to the method shown in FIG. 8 using the first embodiment of the wafer drying apparatus shown in FIG. 3.
- Referring again to FIG. 8, the
wafers 201 were washed for 300 seconds using DIW as the cleaning liquid. Theheater 244 was then operated at about 150° C. to heat the nitrogen gas to about 70˜90° C. The heated nitrogen gas was supplied to the upper portion of theouter bath 216 via the nitrogen gassupply tube line 242 for 60 seconds and at a pressure of 3 kg/cm2. Thereafter, the second drain valve 214V2 in the first inner bathdrain tube line 214c 1 was opened to lower the level of the cleaning liquid 213 in theinner bath 212 by as much as 5 mm. Then, the second drain valve 214V2 was closed, and the first andsecond heaters isopropyl alcohol liquid 222 a was supplied via the first and second isopropyl alcoholsupply tube lines alcohol liquid layer 215 formed on the surface of the cleaning liquid 213 as a result had a thickness of about 2.1 mm. - Then, the heated nitrogen gas was supplied into the upper portion of the
outer bath 216 while the first andsecond heaters isopropyl alcohol vapor 222 b. After roughly 10 seconds, the cleaningliquid 213 was drained from theinner bath 212 at a rate of 2 mm/sec using thepump 214P disposed in the second inner bathdrain tube line 214c 2. This draining process was carried out for about 145 seconds or 240 seconds until the level of the cleaning liquid 213 in theinner bath 212 sank below thewafers 201. At this point in time, the first andsecond heaters drain tube line 214c 2 was opened to thoroughly drain the remainingcleaning liquid 213 and the isopropylalcohol liquid layer 215 from theinner bath 212. Finally, the heated nitrogen gas was supplied into the outer bath for 300 seconds to dry thewafers 201 completely. The number of particles having a diameter of at least 0.12 μm on the wafer prior to the washing operation was compared to that after the washing and drying operation. Three wafers were sampled from each lot of 24 wafers, one each from the front, center and rear of the lot. Ten lots of the wafers were tested in total. - FIG. 9 shows the change in the number of particles before and after the cleaning operation for the sampled wafers of the ten lots. In FIG. 9, a negative (−) number denotes a decreased number of particles and a positive (+) number denotes an increased number of particles. Also, in FIG. 9, the plot using the diamond-shaped symbol is a result from the wafers sampled at the rear of the wafer guide, the plot using a square-shaped symbol is a result from the wafers sampled at the center portion of the wafer guide, and the plot using triangle-shaped symbol is a result from the wafers sampled at the front of the wafer guide. The graph plotted using the character X is the average result from the sampled wafers. The change in the number of particles before and after the cleaning of the wafers at the rear of the wafer guide was −4.4 on average, that at the center of the wafer guide was 2.4 on average, and that at the rear of the wafer guide was 3.2 on average. The average change in the number of particles of all of the sampled wafers was 0.4.
- These results show that the drying process according the present invention hardly leaves any particles that are the result of water spots. Furthermore, there is little variation in the change in the number of particles over the different positions that the wafers occupy in the bath. Accordingly, the drying process according to the present invention is remarkably uniform and effective.
- In
Experiment 2, the isopropyl alcohol liquid was employed at room temperature instead of being heated. InExperiment 3, the nitrogen gas was introduced into the outer bath at room temperature instead of being heated. InExperiment 4, the isopropyl alcohol liquid was employed at room temperature instead of being heated, and was introduced into the outer bath at room temperature instead of being heated. Otherwise, the cleaning and drying operations were conducted in the same manner as withExperiment 1. And, as withExperiment 1, the wafers were examined for changes in the number of particles having a diameter of at least 0.12 μm before and after the washing and drying operations. - The results of these first to fourth experiments are qualified below in Table 1.
TABLE 1 Nitrogen Variation of number IPA liquid gas of particles Evaluation Experiment 1 Heated Heated Varied very little at Excellent all Experiment 2Unheated Heated Varied severely Poor Experiment 3 Heated Unheated Varied slightly Good Experiment 4 Unheated Unheated Varied highly Poor - As shown in Table 1, when the isopropyl alcohol was heated to form the isopropyl alcohol liquid layer on the cleaning liquid, as in
Experiments Experiments - Moreover, when the nitrogen gas was injected without being heated, as in
Experiment 3, not enough isopropyl alcohol vapor was produced in the ambient above the cleaning liquid. This resulted in a much greater variation in the number of particles as compared withExperiment 1 in which the heated nitrogen gas was used. - Although the isopropyl alcohol liquid was introduced at room temperature without being heated in both
Experiments Experiment 2, in which the heated nitrogen gas was used, showed a smaller variation in the number of particles thanExperiment 4 in which the unheated nitrogen gas was used. And, although the heated isopropyl alcohol liquid was used in bothExperiments Experiment 3, in which the unheated nitrogen gas was used, showed a greater variation in the number of particles thanExperiment 1 in which the heated nitrogen gas was used. From these observations, it is clear that the drying effect is improved by using the heated nitrogen gas. Apparently, the isopropyl alcohol is evaporated somewhat by the heated nitrogen gas to ensure that the isopropyl alcohol vapor is present throughout the nitrogen gas ambient formed over the upper portion of the cleaning liquid. -
Experiment 5 -
Experiment 5 was conducted to provide a comparison of the conventional wafer drying method and that according to the present invention in terms of the variation in the number of particles on the wafers. - More specifically, the conventional cleaning and drying apparatus shown in FIG. 1 was used to perform a cleaning operation, an apparatus of the present invention was used to perform the cleaning operation shown in FIG. 8, and the number of particles having a diameter of at least 0.16 μm on the wafers was checked before and after the cleaning operations. FIG. 10 is a graph of the results. In FIG. 10, the plot using the square-shaped symbol is the average result of examining lots of the wafers cleaned according to the present invention, and the plot using the diamond-shaped symbol is the average result of examining wafers cleaned using the conventional apparatus of FIG. 1.
- As can be seen from FIG. 10, when the conventional wafer drying process is executed, the variation in the number of particles before and after the process was 33 on average. This means that, on average, the process performed by the conventional apparatus left 33 particles having a diameter of at least of 0.16 μm on a wafer. On the other hand, the cleaning process performed according to the present invention left only a negligible number of particles having a diameter of at least 0.12 μm.
-
Experiment 6 -
Experiment 6 was conducted to determine how the quantity of the isopropyl alcohol liquid affects the number of particles left on the wafers. - In this experiment, tests were performed in which 20 ml, 30 ml, 50 ml and 70 ml each of the isopropyl alcohol liquid was supplied to the inner bath. Otherwise, the processes were conducted according to that shown in FIG. 8. The inner bath was 40 cm long by 35 cm wide. Thus, the isopropyl alcohol liquid layers formed on the cleaning liquid were approximately 5 mm, 3.6 mm, 2.1 mm and 1.4 mm thick, respectively. The variation in the number of particles having a diameter of at least 0.12 μm before and after the processes was measured. The results of these measurements are shown in FIG. 11.
- The number of particles increased by 140, 88.9 and 30.2 on average, when the amounts of isopropyl alcohol liquid supplied were 70 ml, 50 ml and 20 ml, respectively. However, the number of particles increased by only 0.4, on average, when 30 ml of the isopropyl alcohol was supplied to the inner bath. This experiment showed that the amount of isopropyl alcohol liquid supplied needs to be carefully regulated.
- In fact, these tests revealed that the isopropyl alcohol liquid layer must have a thickness of about 1 mm to 3 mm if a satisfactory limit on the particles left by water spots after the cleaning process is to be met. The preferred thickness of the isopropyl alcohol liquid layer is 1.5˜2.5 mm, and more preferably at least 2 mm and no more than 2.5 mm.
- According to the present invention, in the process of drying a wafer using the Marangoni effect, heated liquid isopropyl alcohol is supplied onto the surface of the cleaning liquid. The isopropyl alcohol diffuses quickly to form an isopropyl liquid layer. Therefore, as compared with the conventional method in which the isopropyl alcohol liquid layer is formed by an isopropyl alcohol mist carried in nitrogen gas, the present invention is more efficient.
- Furthermore, in the conventional process, it is difficult to regulate the amount of isopropyl alcohol being supplied because the isopropyl alcohol is supplied as a mist through the use of the carrier nitrogen gas. Thus, it is difficult to optimize the process while it is being carried out. However, in the present invention, the isopropyl alcohol is supplied in a liquid state. Therefore, the exactly quantity of isopropyl alcohol required to prevent the forming of water spots that leave too many particles on the waters can be supplied.
- Although the present invention has been shown and described with reference to particular embodiments thereof, various changes in form and details may be effected therein without departing from the true spirit and scope of the invention as defined by the appended claims.
Claims (23)
Applications Claiming Priority (2)
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KR10-2000-0044984A KR100417040B1 (en) | 2000-08-03 | 2000-08-03 | Method for drying a wafer and apparatus for performing the same |
KR2000-44984 | 2000-08-03 |
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US20020032973A1 true US20020032973A1 (en) | 2002-03-21 |
US6430840B1 US6430840B1 (en) | 2002-08-13 |
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US09/801,636 Expired - Lifetime US6430840B1 (en) | 2000-08-03 | 2001-03-09 | Method of and apparatus for drying a wafer using isopropyl alcohol |
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US (1) | US6430840B1 (en) |
JP (1) | JP2002158204A (en) |
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Also Published As
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DE10118751A1 (en) | 2002-02-21 |
KR20020011600A (en) | 2002-02-09 |
KR100417040B1 (en) | 2004-02-05 |
JP2002158204A (en) | 2002-05-31 |
US6430840B1 (en) | 2002-08-13 |
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