Drying and gas or vapor contact with solids – Process – With contacting of material treated with solid or liquid agent
Reexamination Certificate
2003-08-08
2004-10-19
Rinehart, Kenneth (Department: 3749)
Drying and gas or vapor contact with solids
Process
With contacting of material treated with solid or liquid agent
C034S405000, C034S413000
Reexamination Certificate
active
06804900
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for drying a microstructure member, such as a semiconductor substrate, that has a fine irregular surface (microstructure surface) using liquid carbon dioxide or supercritical carbon dioxide. In particular, it relates to a method for drying a microstructure member without causing micro patterns to swell or collapse.
2. Description of the Related Art
In a lithographic process of a semiconductor manufacturing process, patterns formed using a photoresist material often collapse when the patterns are dried to remove a developer or a rinsing solution remaining in the pattern (concavities) after development. This problematic phenomenon of collapse of patterns is caused by the volume expansion of the developer or the rinsing solution resulting from heat applied during the drying. However, the phenomenon is also caused by a capillary force that attracts the patterns to each other during drying. The phenomenon is becoming more acute as the patterns become increasingly finer and the aspect ratio becomes increasingly larger (i.e., as the height becomes larger relative to the width).
In order to minimize the adverse affects of capillary force and volume expansion during drying, a drying method that uses a supercritical fluid has been investigated. This method can dry microstructure members such as wafers in a capillary-force-free state since a supercritical fluid having a temperature and a pressure exceeding the critical points has no gas-liquid interface.
In this supercritical drying method, carbon dioxide, which has a critical temperature and a critical pressure dramatically lower than those of water, is widely used as the supercritical fluid. Supercritical carbon dioxide is a good solvent that can dissolve highly polar solvents such as methanol, ethanol, and isopropanol as well as less polar solvents such as hexane or fluorocarbons. Thus, when any one of these solvents is used as the developer or the rinsing solution for the resist material, supercritical carbon dioxide can extract and remove the developer or the rinsing solution from inside the patterns, thereby drying the microstructure member, such as a wafer.
However, in the field of semiconductor LSI, a resist material that is developed with aqueous tetramethylammonium hydroxide (TMAH) instead of the above-described organic solvents is more commonly used. In such a case, water, i.e., ultrapure water, is used as the rinsing solution. Since water is not miscible with in supercritical carbon dioxide, water inside the patterns must be replaced with a liquid miscible with supercritical carbon dioxide in order to perform drying with supercritical carbon dioxide.
Water can be easily replaced by using a hydrophilic organic solvent such as ethanol. However, the resist material developed with an aqueous solution described above dissolves in alcohols such as ethanol. Thus, alcohols cannot be used as the liquid for replacing the water.
On the other hand, hexane and fluorocarbons are not miscible with water and thus cannot replace water. To overcome these difficulties, Japanese Unexamined Patent Application Publication No. 2001-165568 teaches a technology for completely substituting water into aliphatic hydrocarbon by emulsifying the water with aliphatic hydrocarbon, such as hexane, using a surfactant, such as a fatty acid ester. However, the publication does not disclose a specific method for emulsifying water with aliphatic hydrocarbon. Emulsification by mechanical, forced agitation may result in collapse of patterns, and thus cannot be employed in the semiconductor manufacturing process. On the other hand, a complete emulsification state cannot be achieved without agitation. When emulsification is incomplete, an interfacial tension still exists at the interface between water and aliphatic hydrocarbon and causes collapse of patterns due to the capillary force between the adjacent patterns.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide a drying method in which water inside concavities of the microstructure member, e.g., water remaining in the pattern, is substituted with a hydrophobic solvent miscible with supercritical carbon dioxide in a capillary-force-free state to prevent collapse of patterns and the like.
To achieve this object, the present invention provides a method for drying a microstructure member having a large number of micro concavities in a surface, the micro concavities containing water, the method including the steps of (1) adjusting the temperature of a liquid inside the micro concavities to a temperature in the range of the cloud point of a surfactant (A) ±1° C., and supplying a large amount of a mixture of the surfactant (A) and a hydrophobic solvent (B) adjusted to a temperature in the range of the cloud point of the surfactant (A) ±1° C. into the micro concavities to remove part or all of the water inside the micro concavities; (2) heating the liquid inside the micro concavities to a temperature exceeding the cloud point of the surfactant (A) +1° C., and supplying a large amount of the hydrophobic solvent (B) controlled to a temperature exceeding the cloud point of the surfactant (A) +1° C. into the micro concavities to replace the liquid in the concavities with the hydrophobic solvent (B); and (3) placing the microstructure member with the concavities containing the hydrophobic solvent (B) into contact with liquid carbon dioxide or supercritical carbon dioxide to replace the hydrophobic solvent (B) with the liquid carbon dioxide or the supercritical carbon dioxide. Steps (1) and (2) are performed under atmospheric pressure.
Since the surfactant (A) having a cloud point is used and the water is replaced with the hydrophobic solvent (B) at a temperature in the range of the cloud point ±1° C., the water is replaced with the hydrophobic solvent (B) in an interfacial-tension-free state to prevent collapse of the microstructure such as a pattern.
In Step (1) above, the mixture of the surfactant (A) and the hydrophobic solvent (B) may be supplied to the surface of the microstructure member while rotating the microstructure member. In this manner, the water can be readily replaced with the hydrophobic solvent (B).
In Step (1) above, prior to supplying the mixture into the micro concavities, an aqueous solution of the surfactant (A) controlled to a temperature less than or equal to the cloud point of the surfactant (A) +1° C. may be supplied into the micro concavities. In this manner, the replacement with the hydrophobic solvent (B) in an interfacial-tension-free state can be easily performed.
The surfactant (A) preferably has a cloud point in the range of 10 to 100° C. from the viewpoint of damage to a resist material, energy cost, and boiling point of water.
The present invention also includes a microstructure member dried by the method according to the method described above.
According to the present invention, water remaining on the surface of the microstructure member can be replaced with a hydrophobic solvent having a high affinity to carbon dioxide in an interfacial-tension-free state prior to liquid/supercritical carbon dioxide treatment. Thus, the patterns of the microstructure member can be prevented from collapsing.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention provides a method for drying a microstructure member. An example of the microstructure member is an article, such as a semiconductor substrate, with a fine irregular surface formed by development of a photoresist. However, the microstructure member is not limited to the semiconductor substrate. The drying method may be used to prepare articles of metal, plastic, ceramic, or the like having clean dry surfaces.
The drying method of the present invention is based on the assumption that water is contained inside the micro concavities at the surface of the microstructure member. In a typical semiconductor wafer manufacturing process, a resist pattern is developed with aqueous tet
Kawakami Nobuyuki
Kugimiya Toshiro
Kabushiki Kaisha Kobe Seiko Sho
Rinehart Kenneth
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