Cleaning and liquid contact with solids – Apparatus – Sequential work treating receptacles or stations with means...
Reexamination Certificate
1999-03-30
2002-01-08
Stinson, Frankie L. (Department: 1746)
Cleaning and liquid contact with solids
Apparatus
Sequential work treating receptacles or stations with means...
C134S095200, C134S102300, C134S902000
Reexamination Certificate
active
06336463
ABSTRACT:
BACKGROUND OF THE INVENTION
(a) Field of the Invention
The present invention relates to a cleaning/drying station and a semiconductor device production line having the cleaning/drying station. More particularly, the present invention relates to a cleaning/drying system in a semiconductor device production line in which two different cleaning treatments (i.e., performances of cleaning) and two different drying treatments (i.e., performances of drying) can be selected with a high degree of flexibility, as well as to a production line for semiconductor devices having such a cleaning/drying system in which the layout or arrangement of cleaning devices and drying devices is optimized.
(a) Description of the Related Art
During fabrication of semiconductor devices, a cleaning treatment for wet-cleaning a wafer and a drying treatment for drying the wafer subsequent to the cleaning treatment are conducted before and after each of various processing treatments performed on the wafer.
For example, when a wafer is dry-etched, a cleaning treatment is first performed in order to remove contaminants from a dry-etched wafer surface, and a drying treatment is performed in order to dry the cleaned wafer. Such a cleaning treatment is almost inevitably performed before and after each processing treatment; e.g., before formation of a silicon oxide film on a wafer, after ion implantation, and before epitaxal growth. That is, in many cases, a cleaning treatment is performed between two successive processing treatments. Further, a drying treatment is generally performed after the cleaning treatment. In general, the cleaning treatment includes a chemical cleaning step for cleaning a wafer by use of chemical solution, and a rinse cleaning step for removing, by use of a rinsing liquid, the chemical solution remaking on the wafer.
A typical example of combined of a chemical cleaning step and a rinse cleaning step is an RCA cleaning process. The RCA process includes: a first step in which a wafer is cleaned by use of a mixed cleaning solution containing ammonium, hydrogen peroxide and water in predetermined ratios, followed by rinsing by use of purified water; a second step in which the wafer is immersed into a diluted-HF solution, followed by rinsing by use of purified water; and a third step in which a wafer is cleaned by use of a mixed solution containing hydrochloric acid, hydrogen peroxide and water in predetermined ratios, followed by rinsing by use of purified water.
Also, there is known a specific cleaning method in which both a native oxide film and metal contaminants are removed from a wafer through use of aqueous solution of hydrofluoric acid or hydrofluoric acid-hydrogen peroxide cleaning solution containing 0.5% hydrofluoric acid and 1-10% hydrogen peroxide, followed by rinsing the wafer by use of pure water.
In this text, processing by use of such a hydrofluoric acid based chemical solution will be referred to as “cleaning by use of an HF (cleaning) solution,” and processing by use of non-hydrofluoric acid based chemical solution such as alkaline cleaning, acid cleaning, or RCA cleaning will be referred to as “cleaning by use of a non-HF (cleaning) solution.”
Conventionally, a drying treatment after cleaning has been performed by use of a spin drying device. In the spin drying device, a cleaned wafer is rotated at a high speed in order to remove water remaining on the wafer after a rinsing step, by the effect of centrifugal force and air flow. The spin drying device can dry wafers at a high throughput, but cannot remove water completely, resulting in formation of water marks and the like on a wafer. The spin drying device is a typical example of a high throughput/low performance drying device and is mainly used in a drying treatment after a cleaning treatment performed by use of a non-HF cleaning solution, wherein a high drying performance is not generally required.
Conventional spin drying devices are classified into three types; i.e., a multi-cassette dryer, a single-cassette dryer, and a single-wafer dryer. An example of the single-cassette spin dryer is of a rotation-type in which, as shown in
FIG. 1
, a single cassette “C” carrying wafers “W” is received in a drum “D”, which is rotated about an eccentric axis “E” An example of the multi-cassette spin dryer is of a revolution-type in which, as shown in
FIG. 2
, two cassettes “K” each carrying wafers “W” are received in a drum “D” to be located at diametrically opposite positions, and the drum “D” is rotated about a vertical rotational axis “F.”
With an increase in the wafer deter for the semiconductor devices, a decrease in element dimensions and employment of multi-level wiring, the surface profile of the wafer including projections and depressions on the wafer surface has become finer and the level difference in the profile has increased. Thus, the aspect ratio of via holes has increased. Therefore, it has become difficult to dry wafers to a desired drying level by a spin drying method, resulting in occurrence of problems such as generation of water marks on the wafer surface, and an increased contact resistance of a via hole stemming from incomplete drying of the bottom portion of the via hole.
In order to solve the above-described problems, an IPA vapor drying technique making use of IPA (isopropyl alcohol) has recently come into practical use. As shown in
FIG. 3
, in an IPA vapor drying device using the IPA vapor drying technique, water droplets or a water film remaining on a wafer is replaced with condensed IPA, which is then allowed to drop and evaporate eventually. Thus, the wafer is dried.
Since the IPA vapor drying device (hereinafter simply referred to as an “IPA drying device”) can almost completely replace water on a wafer with IPA and the IPA can evaporate after replacement, water marks are less likely to be generated. The IPA drying device is a typical example of a high performance/low throughput dryer and is used mainly in a drying treatment after a cleaning treatment making use of an HF cleaning solution, wherein a high drying performance is generally required Further, there has been developed a direct IPA drying method utilizing an integrated apparatus including a cleaning device and a drying device. In this method, cleaning, rinsing, and drying are performed within a closed space in order to minimize exposure of a wafer to an oxidizing atmosphere, which exposure would otherwise occur when the wafer is transported from a rinsing stage to a drying stage.
In a conventional production line for semiconductor devices, in order to secure a high throughput of a drying treatment, a high throughput/low performance drying device is provided after a cleaning treatment by use of non-HF cleaning solution, such as alkali cleaning, acid cleaning or RCA cleaning, which does not require a wafer to be dried to a high degree. On the other had, in order to secure a high quality of the drying treatment, a low throughput/high performance drying device is provided after a cleaning treatment, such as a chemical cleaning treatment making use of an HF cleaning solution.
With reference to
FIG. 4
, a conventional production line for semiconductor devices will be described. The conventional production line
90
includes a series of processing stations
92
A-
92
E each performing a predetermined processing treatment on a wafer. A wafer is transported to the processing stations
92
A-
92
E and is successively subjected to the respective processing treatments in the processing stations
92
A-
92
E. In the production line
90
, a cleaning/drying treatment must be performed for a wafer before and/or after the processing treatment at each processing station
92
.
For example, in a step for forming a gate oxide film, an oxide film is wet-etched, and then a nitride film is wet-etched. During the wet etching of the oxide film, contaminants are dissolved into rinse droplets, resulting in contamination of a wafer surface. In order to suppress such contamination, a wafer is generally cleaned by use of an HF cleaning solution, and is subjected to IPA dryin
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