Cleaning and liquid contact with solids – Processes – Using sequentially applied treating agents
Reexamination Certificate
2000-11-28
2003-06-10
Gulakowski, Randy (Department: 1746)
Cleaning and liquid contact with solids
Processes
Using sequentially applied treating agents
C134S002000, C134S003000, C134S011000, C134S026000, C134S028000, C134S031000, C134S034000, C134S036000, C134S041000, C134S902000, C438S906000, C034S443000, C034S448000, C034S516000
Reexamination Certificate
active
06576066
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a supercritical drying method and supercritical drying apparatus for suppressing collapse of a fine pattern caused by the surface tension of a rinse solution in drying after rinse processing using water.
Recently, as MOS LSIs become larger, chips become larger, and patterns in the manufacture of LSIs become finer. At present, patterns having line widths smaller than 100 nm can be formed. The decrease in line width enables forming a pattern having a high aspect ratio (height/width). Fabricating large-scale, high-performance devices such as LSIs requires hyperfine patterns.
This hyperfine pattern includes, e.g., a resist pattern photosensitive to light, X-rays, or an electron beam that is formed through exposure, developing, and rinse processing. Further, the hyperfine pattern includes an etching pattern made of an inorganic material such as an oxide that is formed through etching, water rinsing, and rinse processing by selective etching using a resist pattern as a mask. The resist pattern can be formed by processing a photosensitive resist film of an organic material by lithography. When the photosensitive resist film is exposed, the molecular weight or molecular structure in the exposed region changes to generate a difference in solubility in a developing solution between the exposed region and an unexposed region. Developing processing using this difference can form a pattern finer than the photosensitive resist film.
If this developing processing continues development, the unexposed region also starts dissolving in the developing solution, and the pattern disappears. To prevent this, rinse processing using a rinse solution is performed to stop developing. Finally, the pattern is dried to remove the rinse solution, thereby forming the resist pattern as a processed mask on the resist film.
A serious problem in drying in forming a fine pattern is pattern collapse as shown in
FIGS. 11A
to
11
C.
A fine resist pattern having a high aspect ratio is formed through rinse cleaning and drying after development. A fine pattern having a high aspect ratio is also formed from a material other than the resist. For example, when a substrate pattern having a high aspect ratio is to be formed by etching a substrate using a resist pattern as a mask, the substrate is cleaned after etching, and a substrate pattern
1102
is dipped in and rinsed with water
1103
together with a substrate
1101
, as shown in FIG.
11
A. After that, the substrate pattern
1102
is dried.
However, as shown in
FIG. 11B
, a bending force (capillary force)
1105
acts in drying due to the pressure difference between the water
1103
left in the substrate pattern
1102
and external air
1104
. As a result, as shown in
FIG. 11C
, pattern collapse of the substrate pattern
1102
occurs on the substrate
1101
. The collapse phenomenon becomes prominent for a pattern having a higher aspect ratio. The capillary force is reported to depend on the surface tension of the rinse solution, such as water, remaining between patterns (reference: Applied Physics Letters, Vol. 66, pp. 2655-2657, 1995).
This capillary force not only collapses a resist pattern made of an organic material, but also distorts a stronger pattern made of an inorganic material such as silicon. Therefore, the problem of capillary force caused by the surface tension of the rinse solution is serious. The problem due to the capillary force can be solved by processing using a rinse solution whose surface tension is low. For example, when water is used as a rinse solution, the surface tension of water is about 72×10
−3
N/m. On the other hand, the surface tension of methanol is about 23×10
−3
N/m. Pattern collapse is, therefore, suppressed when ethanol is dried after water is substituted by ethanol, compared to direct water drying.
Pattern collapse is more effectively suppressed when perfluorocarbon having a surface tension of 20×10
−3
N/m is used, a rinse solution is substituted by a perfluorocarbon solution, and then perfluorocarbon is dried. Although generation of pattern collapse can be reduced using a rinse solution having a low surface tension, pattern collapse cannot be eliminated using a liquid because the liquid has surface tension to a certain extent. To eliminate pattern collapse, a rinse solution whose surface tension is 0 is used, or a rinse solution is substituted by a liquid whose surface tension is 0 and then the substituted liquid is dried.
An example of the liquid whose surface tension is 0 is a supercritical fluid. The supercritical fluid is a substance at a temperature and pressure exceeding the critical temperature and critical pressure. The supercritical fluid has a dissolving power almost equal to that of a liquid, but exhibits a tension and viscosity almost equal to those of a gas. The supercritical fluid can be said to be a liquid which maintains a gaseous state. Since the supercritical fluid does not form any gas-liquid interface, its surface tension is 0. Hence, drying in the supercritical state is free from any concept of surface tension, and pattern collapse does not occur.
The supercritical fluid has both diffusion of a gas and solubility (high density) of a liquid, and can change in state from a liquid to a gas without the mediacy of any equilibrium line. If the supercritical fluid is gradually discharged in a state in which the supercritical fluid is filled, no liquid-gas interface is formed, and a pattern can be dried without any surface tension acting on a hyperfine pattern to be dried.
The supercritical fluid has been used for 10 years originally as an impurity extraction means. For example, the supercritical fluid is used as a caffeine extraction medium in a plant where caffeine is extracted from coffee. Since the solubility of the supercritical fluid changes by a set pressure for obtaining the supercritical state, the pressure can be changed to easily adjust the solubility to a substance to be extracted. For this reason, the supercritical fluid is used for extraction of caffeine. Extraction using a supercritical fluid such as carbon dioxide need not discharge any solvent waste in comparison with extraction using an organic solvent, and is evaluated as an easy-to-use extraction means. At present, supercritical extraction has been studied and put into practical use.
As a supercritical fluid, carbon dioxide which is low in critical point and safe in many cases is used. When the supercritical fluid is used for drying, a rinse solution in which a substrate surface is dipped at room temperature or less is substituted by liquid carbon dioxide in a sealed vessel, and drying starts. Since carbon dioxide liquefies at room temperature at a pressure of about 6 MPa, this substitution is done by increasing the internal pressure of the vessel to about 6 MPa. After the substrate is completely covered with liquid carbon dioxide, the interior of the vessel is set to a temperature and pressure equal to or higher than the critical point of carbon dioxide (critical point of carbon dioxide; 31° C., 7.3 MPa), and liquid carbon dioxide is converted into supercritical carbon dioxide.
Finally, part of the vessel is opened to externally discharge supercritical carbon dioxide, the interior of the vessel is reduced to the atmospheric pressure, and supercritical carbon dioxide in the vessel is gasified to end drying. In pressure reduction, carbon dioxide does not liquefy but gasifies, so no gas-liquid interface on which surface tension acts is formed on the substrate. For this reason, hyperfine patterns on the substrate can be dried without any collapse.
An example of the supercritical drying apparatus is an apparatus constituted by connecting a cylinder
1203
storing liquid carbon dioxide via a valve
1204
to a reaction chamber
1202
in a sealable vessel
1201
, as shown in FIG.
12
. In this apparatus, the valve
1204
on the liquid carbon dioxide inlet side is opened to introduce liquid carbon dioxide into the reaction chamber
1202
, and a valve
1
Allen Kenneth R.
Gulakowski Randy
Kornakov M.
Nippon Telegraph and Telephone Corporation
Townsend and Townsend / and Crew LLP
LandOfFree
Supercritical drying method and supercritical drying apparatus does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Supercritical drying method and supercritical drying apparatus, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Supercritical drying method and supercritical drying apparatus will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3151562