Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Making electrical device
Reexamination Certificate
1999-09-03
2002-03-19
Duda, Kathleen (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Making electrical device
C430S325000
Reexamination Certificate
active
06358673
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a pattern formation method and apparatus for forming fine patterns used in the fabrication of semiconductor devices and, more particularly, to a method and apparatus for performing development and drying in forming such fine patterns by lithography.
Recently, with increasing scale of MOSLSIs, the chip sizes are increasing, and patterns in LSI fabrication are shrinking; nowadays, patterns having line widths of less than 100 nm are formed. This narrowing of lines results in the formation of patterns having high aspect ratios (height/width).
Also, the formation of fine patterns necessarily increases the aspect ratios of resist patterns as processing masks used in the etching process. These resist patterns can be formed by processing a resist film as an organic material by lithography. That is, when a resist film is exposed to light, the molecular weight or the molecular structure in the exposed region changes to produce a difference in solubility in a developer between this exposed region and the unexposed region. By using this difference patterns can be formed in the resist film by development. If this development continues, even the unexposed region starts dissolving in the developer and the patterns vanish. Therefore, rinsing is performed using a rinse solution to stop the development. Finally, the rinse solution is removed by drying to form resist patterns as processing masks in the resist film.
One major problem encountered when drying is performed in such fine pattern formation is the bending or distortion of patterns
1701
as shown in the sectional view of FIG.
17
. That is, such fine resist patterns having a high aspect ratio are formed through rinsing and drying after development. High-aspect-ratio fine patterns are not restricted to resist patterns. For example, substrate patterns with a high aspect ratio are formed through cleaning, rinsing (washing), and drying after a substrate is etched using resist patterns as masks. During the drying after the rinsing process, the patterns
1701
bend toward each other. This phenomenon becomes conspicuous as the aspect ratio of the patterns
1701
increases. As shown in
FIG. 18
, this phenomenon is caused by a bending force (capillary force)
1810
exerted by a pressure difference between a rinse solution
1802
remaining between patterns
1801
and outside air
1803
when a resist or a substrate is dried. It is reported that this capillary force
1810
depends on the surface tension produced by the liquid/gas interface between the rinse solution
1802
and the patterns
1801
(reference: Applied Physics Letters, Volume 66, pp. 2655-2657, 1995). This capillary force not only bends resist patterns made from an organic material but also has power to distort even strong patterns made from, e.g., silicon, an inorganic material. This makes the aforesaid problem of the surface tension of rinse solution very important. This capillary force problem can be solved by processing using a rinse solution with small surface tension. For example, when water is used as a rinse solution, the surface tension of water is about 72 dyn/cm. However, the surface tension of methanol is about 23 dyn/cm. Therefore, the degree of pattern bending or collapse is suppressed more when water is replaced with ethanol and the ethanol is dried, than when water is directly dried. Furthermore, pattern bending is more effectively suppressed when the rinse solution is replaced with a perfluorocarbon solution and this perfluorocarbon solution is dried. However, as long as these liquids are used, pattern bending cannot be eliminated, although it can be reduced, because all of these liquids have surface tension to some extent.
To solve this problem of pattern bending, it is necessary to use a rinse solution with a zero surface tension or to first replace a rinse solution by a liquid having a zero surface tension and then dry this liquid. A supercritical fluid is an example of the liquid with a zero surface tension. This supercritical fluid is a gas at a temperature and a pressure exceeding the critical temperature and the critical pressure, respectively, and has solubility close to that of a liquid. However, the supercritical fluid has tension and viscosity close to those of a gas and hence can be said to be a liquid keeping a gaseous state. Since this supercritical fluid dose not form any liquid/gas interface, the surface tension is zero. Accordingly, when drying is performed in this supercritical state, there is no surface tension, so no pattern bending takes place. Carbon dioxide is generally used as this supercritical fluid. Since carbon dioxide has low critical points (7.3 MPa, 31° C.) and is chemically stable, it is already used as a critical fluid in biological sample observations.
Conventionally, supercritical drying using the supercritical state of carbon dioxide is done as follows. That is, liquefied carbon dioxide is previously introduced into a predetermined processing vessel to replace a rinse solution by repeatedly discharging the solution. After that, the processing vessel is heated to a temperature and a pressure higher than the critical points, changing the liquefied carbon dioxide in the vessel into supercritical carbon dioxide. Finally, while only this supercritical carbon dioxide adheres to fine patterns, the vessel is evacuated to vaporize the supercritical carbon dioxide and thereby dry the pattern.
Supercritical drying apparatuses marketed or manufactured so far to perform the supercritical drying as described above have the structure as shown in FIG.
19
. In this supercritical drying apparatus, a carbon dioxide cylinder
1903
is connected to a reaction chamber
1901
as a processing vessel for holding a substrate
1902
to be processed. A temperature controller
1904
controls the internal temperature of the reaction chamber
1901
. In this supercritical drying apparatus, after supercritical carbon dioxide is supplied to replace a rinse solution, this supercritical carbon dioxide is exhausted at a given flow rate by a flow meter
1905
. No pressure adjustment is performed during liquefaction and supercritical carbon dioxide processing. The pressure depends upon the amount of liquefied carbon dioxide. Therefore, the pressure after heating is increased to be much higher than the critical pressure by supplying liquefied carbon dioxide as much as possible. Additionally, to supply a sufficient amount of liquefied carbon dioxide, it is necessary to cool the reaction chamber
1901
to the extent that moisture aggregates.
Conventionally, this apparatus is used in resist pattern formation, particularly drying after rinsing, as follows. This drying method will be explained below. First, the substrate
1902
to be processed is rinsed and placed in the reaction chamber
1901
. In this state, the rinse solution is still adhered on the substrate
1902
. After that, a liquid of carbon dioxide is supplied from the cylinder
1903
into the reaction chamber
1901
heated to a predetermined temperature by the temperature controller
1910
, thereby replacing the rinse solution. Next, the interior of the reaction chamber
1901
is set at a temperature and a pressure exceeding the critical points to convert the liquefied carbon dioxide in the reaction chamber
1901
into supercritical carbon dioxide. After that, this carbon dioxide as a supercritical fluid is exhausted from the reaction chamber
1901
to evacuate it, thereby vaporizing the supercritical carbon dioxide and drying resist patterns.
It is also possible to supply dry ice (solid carbon dioxide) into the reaction chamber without using a cylinder. In this method, supercritical carbon dioxide is generated in the reaction chamber by heating the dry ice in the reaction chamber.
Unfortunately, when these conventional supercritical drying apparatuses are used to dry after rinsing in resist pattern formation, resist patterns formed in a dried resist film swell and hence cannot be used as etching masks.
When drying is performed as above, in the reaction
Blakely & Sokoloff, Taylor & Zafman
Duda Kathleen
Nippon Telegraph and Telephone Corporation
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