JP3204503B2 - Steam cleaning method and apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to electrical materials such as semiconductor wafers and magnetic disks, optical components, electronic components, printed boards on which these are mounted, electronic devices, optical devices, and the like. The present invention relates to a steam cleaning method and apparatus for cleaning a cleaning object with steam, and more particularly to a steam cleaning method and apparatus suitable for obtaining a high cleaning effect even when an object to be cleaned has hydrophobicity.

[Prior Art] In recent years, the degree of integration of semiconductor devices such as LSIs has been remarkably improved, and mass production of 4-megabit DRAMs has started.
It has progressed to 6 megabits and 64 megabits. As described above, when the microfabrication technology advances and enters the submicron era, only the fine impurities remaining on the surface of the semiconductor wafer will result in defective LSIs using the wafer.
Therefore, the role of the cleaning technology in the LSI manufacturing process will increase considerably.

Generally, when removing contaminants adhering to the surface of a substrate such as a semiconductor wafer, a solvent (trichlene, acetone,
H ₂ O ₂ -NH ₄ OH mixed solution, etc.) to remove grease contaminants using, then acid-alkali _{(HF, H 2 O 2 -NH} 4 OH, HCl-
H ₂ O ₂ mixture) to remove the contaminant metal. The substrate from which the contaminants have been removed by using such a chemical solution is then washed with ultrapure water, and after the water droplets of the ultrapure water remaining on the surface after this cleaning are removed (dried), Sent to the process.

The purity of the ultrapure water used here is extremely high, and the specific resistance is 18M
Ω-cm, TOC 10 ppb or less, water quality of 10 particles / ml or less of 0.1 μm or more is maintained. However, even if the substrate is cleaned using such ultrapure water, the LS using this substrate is used unless the water droplets remaining on the surface after cleaning are removed properly.
I has a high rate of defective products. Therefore, it is necessary to devise a method for removing (drying) water droplets.

Conventional techniques for removing (drying) water droplets include drying by hot air (hot air drying method), rotating the substrate after washing and scattering water droplets by the centrifugal force (spin drying method), and organic solvents (for example, isopropyl alcohol, hereinafter). , IPA) by replacing residual water droplets with this organic solvent using steam and drying the organic solvent (IP
A steam drying method), which is used in the actual wafer cleaning process. In the current cleaning with ultrapure water,
Immerse the substrate in a container with overflowed ultrapure water,
A method of replacing a chemical solution attached to a substrate with ultrapure water has been adopted.

Incidentally, Japanese Patent Application Laid-Open No. 61-1749
No. 82, JP-A-61-138582, JP-A-61-138583, JP-A-61-200885, Ultra LSI Ultra Clean Technology Symposium No. 2, Proceeding of ultrapure water / high purity chemical supply system, pp399 There is.

[Problems to be Solved by the Invention] In the cleaning of a semiconductor wafer or the like, impurities (for example, fine particles contained in the solution used for cleaning or precipitates of dissolved substances) are finally present on the surface of the object to be cleaned. It is necessary not to remain. It is also desirable that the cleaning can be performed quickly and at low cost. However, in the prior art, these points are insufficient, and there is a possibility that impurities may remain on the surface of the object to be cleaned.

In the hot-air drying method, water droplets adhering to the substrate surface are evaporated by hot air, so that fine particles contained in the water droplets may remain or substances dissolved in the water droplets may precipitate on the substrate surface. In the spin dry method, not all of the water droplets adhered to the substrate surface cannot be removed. In particular, it is difficult to remove water droplets remaining in fine grooves, and fine particles and precipitates may remain. In the IPA vapor drying method, the residual water droplets are replaced with IPA and then dried, so there is no effect of the fine particles and dissolved substances in the residual water droplets, but the fine particles and dissolved substance precipitates in the replaced IPA may remain. . In addition, although IPA is inexpensive, there is a problem that the cost increases when used in large quantities.

Furthermore, in the conventional cleaning method, a large amount of ultrapure water, which is expensive to manufacture, is used in large quantities. Therefore, the cleaning cost is high, and an apparatus for producing a large amount of ultrapure water and its container are also required to be installed. There is also a problem. In addition, when the object to be cleaned has a hydrophobic property like a semiconductor wafer, there is a problem that the cleaning effect by ultrapure water is not so improved because of the property of repelling water.

Although the above-described problem has been described by taking a semiconductor wafer as an example, the same can be said for an object to be cleaned such as a lens as an optical component or another electronic device.

An object of the present invention is to provide a steam cleaning method and apparatus capable of cleaning an object to be cleaned inexpensively and quickly without leaving any impurities.

[Means for Solving the Problems] The above object is achieved by cleaning the surface of an object to be cleaned with water vapor that has passed through a hydrophobic porous membrane.

[Operation] When passing through the hydrophobic porous membrane, the mist in the vapor is removed by the hydrophobic porous membrane to become high-purity vapor, so that impurities on the surface of the object to be cleaned can be cleaned well.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a configuration diagram of a steam cleaning apparatus according to one embodiment of the present invention. The steam cleaning device of the present embodiment is a steam generator
108, a cleaning tank 101, and a cooling medium supply device 104. Water or an IPA aqueous solution 109 is supplied to a steam generator 108 and heated by a heater 114 to be turned into steam. The steam generator 108 is provided with a hydrophobic porous membrane 110 made of an organic film such as polyethylene at the steam outlet, and mist in the steam is removed by the hydrophobic porous membrane 110, and the high purity steam 111 is removed. And supplied to the cleaning tank 101 via the switching valve 112.

An object to be cleaned is installed in the cleaning tank 101, and high-purity steam 111 is provided.
Washed in. In this embodiment, a plate-shaped substrate 102 is used as an object to be cleaned, and the front and back surfaces of the substrate 102 are subjected to steam cleaning.
The cleaning tank 101 includes a support 107 on which the substrate 102 is mounted. The support 107 and the substrate 102 separate the airtight two chambers. Then, cleaning steam is supplied to one chamber to clean one surface of the substrate 102, and a cooling medium is supplied to the other chamber to directly cool the substrate 102 to be cleaned.

The cooling medium supply device 104 supplies ultrapure water or an inert gas such as nitrogen as a cooling medium to the cleaning tank 101 via a switching valve 113. The high-purity steam 111 and the cooling medium 103 are connected to the switching valve 112 and the switching valve 113, and when supplying the high-purity steam 111 to the first chamber of the cleaning tank 101, the cooling medium 103 is supplied to the second chamber. When the high-purity steam 111 is supplied to the second chamber, the cooling medium 103 is supplied to the first chamber. Then, the condensed liquid 105 (106) of the mixed vapor and the waste liquid 106 (105) of the cooling medium that are discharged at the time of cleaning are discharged from the discharge ports of the respective chambers.

Superheated steam or a high-temperature inert gas 115 is supplied to both chambers (first and second chambers) of the cleaning tank 101. After the substrate is cleaned, the substrate 1
02 is dried on both sides.

In the steam cleaning apparatus having such a configuration, the substrate 102 from which contaminants have been removed using a chemical solution in the previous step is attached to the cleaning tank 101. The mixed steam of IPA and water generated by the steam generator 108 is subjected to mist removal by the hydrophobic porous membrane 110, and the first chamber (the surface of the substrate 102 on the first chamber side of the substrate 102 is first exposed, The surface on the second chamber side is the back.) On the other hand, a cooling medium is supplied to the second chamber, and the substrate 102 is cooled by the cooling medium that directly contacts the back surface of the substrate 102.

The mixed vapor sprayed on the surface of the substrate 102
Heat is taken away and condensed. Since IPA in the mixed vapor has an OH group, which is a hydrophilic group, the condensate of the mixed vapor adheres to the surface of even a hydrophobic substrate such as a semiconductor wafer, and the condensed liquid forms on the surface of the substrate. The impurities will be washed away. In this embodiment, since the substrate 102 is directly cooled by the cooling medium, the amount of condensate condensed on the substrate surface increases, and good cleaning becomes possible.

Thereafter, the switching valves 112 and 113 are switched, and the back surface of the substrate is similarly cleaned with the mixed vapor. At this time, the substrate 102 is cooled by bringing a cooling medium into direct contact with the front side of the substrate. Finally, both surfaces of the substrate are dried by flowing superheated steam 115 or the like into both chambers. If ultrapure water is used as the cooling medium, cleaning with ultrapure water on the back side can be performed at the same time as the steam cleaning on the front side, which is efficient.

Next, the optimum concentration range of the IPA aqueous solution that enables good cleaning will be described. FIG. 2 is a vapor-liquid equilibrium diagram of the IPA aqueous solution. FIG. 3 is a graph showing the relationship between the concentration of the IPA aqueous solution and the surface tension. An object to be cleaned having hydrophobicity, for example, a bare Si wafer (a wafer whose surface SiO ₂ has been removed with fluorine) or the like has a low affinity unless the liquid has a surface tension of 30 dyne / cm or less. Therefore, the surface tension of the condensed liquid condensed on the Si wafer must be at most this value. According to FIG. 3, the IPA concentration at which the surface tension value is 30 dyne / cm must be at least about 30%. That is, the IPA concentration in the mixed vapor is adjusted to 30%. On the other hand, according to FIG. 2, it can be seen that in order to make the concentration of IPA in the gas phase state, that is, the vapor state to 30%, it is sufficient to use 3% in the liquid phase. That is, by heating a 3% IPA aqueous solution with a heater, a mixed vapor having an IPA concentration of 30% is generated. When evaporating the IPA aqueous solution, the mist accompanying the evaporation is removed by a hydrophobic porous membrane.
If the IPA concentration is too high, it becomes difficult to remove the mist. The experimental value indicating this limit is 40 dyne / cm in the surface tension value of the stock solution. That is, according to FIG. 3, the limit value is 20% density. That is, the optimal concentration of the IPA aqueous solution is
3-20%.

FIG. 4 is a view showing an effect when the cleaning steam is sprayed on the wafer by using a nozzle. When the wafer is placed in a steam atmosphere and the back surface of the wafer is cooled, FIG.
As shown in (1), water droplets of the condensate adhere to the entire surface of the wafer.
At this time, when the cleaning steam is sprayed on the wafer by using a nozzle as shown in FIG. 3C, a clean liquid film is formed at the sprayed portion as shown in FIG. There is also an effect of blowing off, and the cleaning effect is improved. To uniformly clean the entire surface of the wafer, the nozzle may be moved as shown by the arrow in FIG. It should be noted that cleaning with mixed steam is more effective. However, by using a nozzle, a certain effect can be obtained even with cleaning using only steam.

FIG. 5 is a configuration diagram of a continuous cleaning device. The object to be cleaned 504 automatically flows from right to left in the steam cleaning device 501. The object to be cleaned 504 that has entered the steam cleaning device 501 is first cleaned with a chemical solution 506. And in the next room, cooling medium 5
The object to be cleaned cooled in 02 is cleaned on one side by the mixed vapor 503. In the next room, the other side is similarly cleaned, and finally dried with a high-purity inert gas 505.

In the above-described embodiment, the mixed vapor for cleaning was generated by evaporating the IPA use liquid.
It goes without saying that a configuration in which the vapor of A is generated and the vapors are mixed with each other to form a cleaning vapor may be used. In this case, for the water vapor, a hydrophobic porous membrane for removing the mist in the water vapor may be prepared, and for the mist in the IPA vapor, a separate hydrophobic porous membrane for removing the mist may be separately prepared. After that, a configuration in which a hydrophobic porous membrane is passed through may be used.

In addition, although IPA was adopted as a substance to be mixed with water vapor, the present invention is not limited to this, and other organic substances may be used. Any substance can be used as long as the substance can be reduced.

[Effects of the Invention] According to the present invention, since the value of the surface tension of the condensate generated by cleaning is small, the affinity is high and the cleaning effect by the condensate is enhanced. Further, by cooling the object to be cleaned at the time of the steam cleaning, a large amount of condensed liquid can be generated, and the cleaning effect by the condensed liquid can be enhanced.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a steam cleaning apparatus according to an embodiment of the present invention, FIG. 2 is a vapor-liquid equilibrium diagram of an IPA aqueous solution, FIG. 3 is a graph showing a relationship between the concentration of the IPA aqueous solution and surface tension, 4 (a) and 4 (b) are explanatory views of the cleaning effect by the nozzle, FIG.
FIG. (C) shows an example of the nozzle, and FIG. 5 is a configuration diagram of the continuous cleaning device. 101 cleaning tank, 102 substrate (object to be cleaned), 103 cooling medium, 104 cooling medium supply device, 108 steam generator, 109 IPA aqueous solution, 110 hydrophobic porous Membrane, 111 ...
... high-purity mixed steam, 114 ... heater.

──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Harumi Matsuzaki 4026 Kuji-cho, Hitachi City, Ibaraki Prefecture Inside Hitachi, Ltd. Inside the laboratory (72) Inventor Mitsugu Nomura 2-6-2 Otemachi, Chiyoda-ku, Tokyo Inside Babcock Hitachi Co., Ltd. (72) Inventor Toshiki Furue 2-6-2 Otemachi, Chiyoda-ku, Tokyo Inside Babcock Hitachi, Ltd. (56) reference Patent flat 2-215127 (JP, a) JP Akira 64-76726 (JP, a) JP flat 3-127673 (JP, a) (58 ) investigated the field (Int.Cl. ⁷ , DB name) H01L 21/304 B08B 3/00

Claims (5)

(57) [Claims] In a vapor cleaning method for cleaning an object to be cleaned with steam, a mixed vapor is generated from an aqueous solution of an organic substance, the mixed vapor is passed through a hydrophobic porous membrane, and the object to be cleaned is used by using the mixed vapor. A steam cleaning method characterized by washing a steam. 2. The steam cleaning method according to claim 1, wherein the cleaning is carried out with the vapor of an aqueous solution mixed with a substance that reduces the surface tension of the condensate of the mixed vapor to 30 dyne / cm or less. 3. A steam cleaning method according to claim 1, wherein the object to be cleaned is cooled with a cooling medium at the time of cleaning. 4. The steam cleaning method according to claim 1, wherein the object to be cleaned is plate-shaped, and one surface is cleaned with mixed steam and then the other surface is also cleaned with mixed steam. 5. A steam cleaning apparatus for cleaning the surface of an object to be cleaned with water vapor, comprising: cleaning means for cleaning the vapor after passing through the hydrophobic porous membrane; and cooling means for cooling the object to be cleaned with a cooling medium during cleaning. A steam cleaning device, comprising: